Introduction to Major Flat Panel Display

Technologies

1. Liquid crystal displaysLiquid crystal displays ( LCD s) are the most common type of flat

panel displays ( FPD s) and has been widely used since the early 1970's. All LCD s utilize the fact that certain organic molecules (liquid crystals, LC ) can be reoriented by an electric field. As these materials are optically active, their natural twisted structure can be used to turn the polarization of light by, for example, 90 degrees. Two crossed polarizers normally do not transmit any light but if a 90º-twisted LC is inserted in between, light will be transmitted as shown to the left in See Principle of a passive-matrix twisted nematic liquid crystal display.. . On the other hand, applying an electric field will unwind the helical structure and the LC therfore loses its polarization-rotating characterisics. As a result, the display turns dark as shown to the right in See Principle of a passive-matrix twisted nematic liquid crystal display.. . An LCD consists of an array of picture element ("pixels") which can be individually addressed according to the princple below.

Direct-view LCD s can largely be categorized into reflective and transmissive displays which utilize ambient light and light from a fluorescent backlight tube, respectively.

 

Figure 1. Princple of a passive-matrix twisted nematic liquid crystal display.

The twisted nematic ( TN ) type of LC s shown in See Princple of a passive-matrix twisted nematic liquid crystal display.. are in the passive matrix configuration (i.e. simple electrodes for applying the electric field) primarily used in products such as wrist-watches, handheld calculators, pagers, pocket games, and other inexpensive devices requiring low power consumption and a small form factor. Its response speed is, however, insufficiently fast for high resolution and/or high frame-rate displays.

In the late 1980's, this problem was solved by the introduction of super twisted nematic ( STN ) LC s which are twisted 270º instead of 90º. With a response speed of around 200 ms, STN enabled screen sizes of 8-10 inch with VGA resolution (640x480 pixels). It is no exaggeration to say that STN was the enabling technology for notebook computers.

Despite this progress, though, the response speed is still not high enough for displaying fast moving images such as mouse movements or video. Moreover, increased screen-size and pixel counts negatively affects STN parameters such as contrast, grey scale capability, and

noise because of a large capacitance and limited conductivity of the electrodes.

To solve this, a sample-and-hold circuit can be attached to each pixel which maintains the voltage during one frame scan. Such a circuit was practically realized by the advent of thin-film transistors ( TFT s). At first, TFT s were extremely expensive to manufacture and the price of a notebook with STN and TFTLCD s could differ more than $1,000. Today, however, production technology has caught up and TFTLCD s are now the mainstream technology for notebook displays. The structure of a TFTLCD is shown in See Structure of a thin-film transistor liquid crystal display. .

 

Figure 2. Structure of a thin-film transistor liquid crystal displayThe first TFT s were made from cadmium selenide (CdSe) in 1972

but an investment momentum in the solar cell industry convinced the Japanese to move towards amorphous silicon (a-Si) although CdSe both has higher electron mobility and handles higher current densities.

The electron mobility is a crucial parameter increasing the frame rates and/or pixel count. It is also important when downsizing TFT

devices for fine-pitch displays such as 120 ppi (pixels per inch) or

more. Polycrystalline silicon (p-Si), with a higher mobility than a-Si, is expected to play an important role in this context. Indeed, projection displays using tiny TFTLCD shutters (typically 2-inch diagonal) often employ p-Si because of a pixel pitch of only a few tens of micrometers. Whereas these devices are grown at high temperatures on expensive quartz substrates, direct-view displays require low-temperature processes which are compatible with conventional glass. Low temperature processing of p-Si is therefore attracting extremely much attention at the moment.

In 1998, Sharp Corp. and the Semiconductor Energy Laboratory announced a new technology called continuous grain silicon ( CGS ) which could potentially revolutionize TFTLCD s. With a mobility close to crystalline silicon, a 2.6-inch projection display device for high-definition TV , was successfully demonstrated. In addition to enabling higher resolutions, the CGS and p-Si technologies allow driver circuitry - and eventually complete LSIs and CPUs - to be integrated monolithically.

Apart from being employed in notebook computers and, recently, in desktop monitors with diagonal sizes up to 30 inch, TFTLCD s are used in reflective displays for mobile terminal applications requiring video speed.

2. Displays for portable devicesThe strong customer demand for portable gadgets in Japan has

triggered research on alternatives to the mainstream liquid crystal modes TN and STN , which, because of low transmittance and thus high power consumption, are more suitable for backlit displays for desktop monitors.

With the goal of bringing reflective display quality close to paper print, brightness, contrast, and color saturation must be improved. Since polarizers effectively cut off 50% and color filters 66% of the incoming ambient light energy, several new modes without color filter or polarizers have been developed. One such mode is guest-host in which an anisotropic dye (guest) is incorporated in a LC (host). The applied electric field reorients both the LC and the dye molecules, which due to its anisotropic absorption will switch between

transparent and opaque states. Displays employing the guest-host mode are bright, have wide viewing angle, but slow response. It is therefore mainly used in watches and portable digital assistants ( PDA

s)Another way to switch light is by controlling the amount of

scattering in a mixture of polymers and LC droplets. Whereas the polymer matrix is fixed, the LC droplets can be reoriented as usual by an electric field. For certain directions, the refractive indices of the droplets and polymer are matched and light therefore goes through without scattering. On the other hand, orienting the droplets in such a way that the indices are mismatched causes increased scattering and therefore a lower brightness. Displays based on this principle still needs color filters but the brightness is greatly improved over the two-polarizer conventional TN display. Applicatons include projectors and large-size shutters for window glass.

Another type of reflective displays utilize light control via diffraction by changing the LC phase electrically. Cholesteric LC s, for example, have a periodic structure that either selectively backscatters light of a certain wavelength or transmit the remaining ones. Applying an electric field will change the cholesteric phase to focal conic which efficiently scatters incoming light and the display will appear dark. In the reflective mode, the helical pitch determines the wavelength of the diffracted light so cholesteric LCD s appear colored.

The electrically induced phase change is reversible but has a hysteresis with built-in bistability. Therefore, display contents will be maintained even after the power has been switched off. Moreover, Ch LCD s do not require active matrix driving because of the bistability and displays with extremely high resolutions (300+ ppi) are therefore within the reach. There are still, however, several problems that have to be solved prior to commercialization. Switching is slow (typically hundreds of ms) and requires high voltages (typically 40 V) incompatible with battery power. Because of the bistability, means to achieve full color are also an issue.

Ferroelectric LC s ( FLC s) play a special role in LCD s becuase of an intrinsic fast response in the microsecond range. The surface

stabilized FLC ( SSFLC ) mode is bistable and does not require any active matrix driving. With the bistability, however, grey scale (or color) must be simulated by spatial dithering. Manufacturing SSFLC devices is very challenging since it requires a laterally homogeneous inter-substrate spacing of less than 2 micrometers. Canon has, nevertheless, commercialized a 15-inch SXGA (1280x1024) display using the SSFLC technology. Meanwhile, Toshiba is working on an active-matrix anti - FLC which does not suffer from bistability and, consequently, not from any lack of grey scale capability. Similarly, Denso has developed prototypes of a passive-matrix AFLC using a partial phase-change mode. Although FLCD s look promising from a matieral point of view, unreliable production, limited operating temperature range, and lower contrast are still issues.

3. Field Emission DisplaysField emission displays ( FED s) have many similarities with

conventional cathode ray tubes ( CRT , See Cathode Ray Tubes. ). In fact, one company calls its FED product "flat CRT ". As for the CRT , electrons are accelerated in vaccuum towards phosphors which then glow. The main difference is that the electrons are generated by field emission rather than thermal emission so the device consumes much less power and can be turned on instantly. Instead of one single electron gun, each pixel comprises several thousands sub-micrometer tips from which electrons are emitted.

To achieve a low operating voltage, the tips are made of a low-work function matieral such as molybdenium and is shaped into very sharp tips so that the local field strengths become high enough for even a moderately low gate voltage. The state-of-the-art FED s can operate at gate voltages as low as 12 V. Sucked out of the tips, the electrons are accelerated towards the phosphor screen by either a low or high voltage. A low voltage simplifies the device design but disables the use of highly efficient and mature CRT phosphors. The design problems are rapidly being overcome and the mainstream FED

is therefore of the high-voltage type.Since it is difficult to control the current of each individual tip, the

display operates in a saturated mode with each pixel turned either on

or off. Thanks to the fast response of the device (ns range), grey scale can be obtained by pulse-code modulation ( PCM ).

Much of the FED research is still focused on suitable emitter matierals which can lower the driving voltage. One of the most exciting ones is diamond which enables field emission at voltages as low as 1-2 V. Manufacturing such tips, however, is a hurdle and the commercial FED s are therefore still using metal tips.

Since the FED is a vaccuum device, atmospheric pressure becomes a severe problem for large-area panels. In particular, internal support posts which prevent the device from imploding, must be thin enough to fit into space between pixels. This together with lifetime issues and bringing down the driving voltage are the main challenges ahead for FED developers.

Figure 3. Field emission displayTypical FED applications include portable ruggedized instruments,

pocket video players, mobile videophones, aircraft video displays, and, eventually, laptop computers. Compared to TFTLCD s, FED s are far

superior with a wider viewing angle, faster response, higher color saturation, and lower power consumption. Despite this, however, manufacturing and liftime problems have prevented a full-scale commercialization of FED s as have furious investment in the TFTLCD

production capacity, resulting in unhealthy price drops.Surface conduction emitter display ( SED ) is a new FED -type display

type pursued by Canon. The emitter consists of a thin film of ultrasmall palladium oxide (PdO) particles which is patterned into narrow gaps (10 nm) where the film has been removed. As electrons are driven in the surface film, they tunnel through the gap, are multiply scattered against the other edge and finally accelerated by the anode voltage. SED devices are not new but emission of previous materials (mainly metals) have proven unstable and thus unsuitable for display applications. SED prototypes have promisingly demonstrated luminances more than twice of that of PDP s ( See Plasma Display Panels. ) at a lower power consumption so Canon is aiming at introducing the technology in consumer products.

4. Cathode Ray TubesInvented in 1897, the cathode ray tube ( CRT ) is still the most

common display type today. The picture is rasterized by rapidly scanning an electron beam in a vacuum tube whose inner front surface is covered by red, green, and blue phosphors. Electrons generated by a heated electron gun are accelerated towards the phosphors by a static high-voltage field and deflected by magnetic fields which, together with the electron beam current, is controlled by a video signal. As the electrons impact on the screen, phosphors are excited and emit colored light ( See Principle of a cathode ray tube.. )

The CRT is a very simple and matured device and the production costs have been trimmed. It features advantages such as high response speed suitable for high-frame rate, high-resolution video, wide viewing angle, saturated colors, high peak luminance, and high contrast.

However, due to the high-voltage field, oscillating magnietic field, and Bremsstrahlung (X-rays) generated by electrons hitting the screen, the CRT has been regarded as hazardous for long-term use.

During the last decade, though, several of these problem have successfully been solved and modern computer monitors are today being designed according to strict environmental standards such as TCO -95.

 

Figure 4. Principle of a cathode ray tube.Another common cause of eye fatigue is flickering which occurs

from the short emission life time of the phosphors. An NTSC TV signal with a 30 Hz frame frequency is therefore interlaced at 60 Hz to reduce flicker. Because of the higher resolution of computer monitors, the limited reponse speed of the video electronics makes it difficult to increase the frame frequency of non-interlaced signals (standard computer output). Recent state-of-the-art video electronics can handle SXGA (1280x1024) at 75 Hz or more, though.

In addition to its size, weight, and high power consumption, traditional CRT s with cylindrically or spherically curved surfaces have suffered from geometrical distrortion, particularly at the edges. Recently, however, flat-surface CRT s have been introduced by companies such as Sony, Sharp, and Matsushita (Panasonic) which eliminate such distortion.

Although several of the drawbacks above have been removed by new technologies, CRT s will eventually face problems with high-

resolution displays requiring finer pixel pitches. Rather than thinness, lower power consumption and weight, it is for this reason TFTLCD s ( See Liquid crystal displays. ) will be a serious competitor to CRT s.

 

Figure 5. Principle of vaccuum fluorescent displays

5. Vaccum fluorescent displaysVaccum fluorescent displays ( VFD s) is another display that utilizes

thermal emission (640ºC filament) of electrons and phosphor excitation to generate color. In contrast to a CRT , however, the electrons are accelerated by a much lower voltage and the pixels are switched on/off by changing the sign of the electric potential at the target anode. A positively charged target will attract electrons wheras a negatively charge target will repell them. Attracted electrons excite

the phosphors which thereby emit light. Contrary to a CRT , the phosphors can be patterned in any shape and VFD s are therefore suitable for displaying icons in consumer electronics. Due to their ruggedness and high luminance, they are also employed in automobile dashboard- and headup displays. The two major companies in Japan pursuing VFD s are Ise Electronics and Futaba.

In prinicple, VFD s could be used in larger displays for monitor applications but since it is a vacuum device, the mechanical construction could be a problem. An advatnage over FED s, though, is that no spaces are needed between the pixels.

6. Plasma Display PanelsA plasma display panel ( PDP ) is essentially a matrix of tiny

fluorescent tubes which are controlled in a sohpisticated fashion. There are two main types, DC - and AC of which the latter has become mainstream because of simpler structure and longer lifetime. This section treats the AC -type.

A plasma discharge is first induced by the positive period of an AC

field (see See Principle of an AC PDP. ) and a layer of carriers is shortly thereafter formed on top of the dielectic medium. This causes the discharge to stop but is induced again when the voltage changes polarity. In this way, a sustained discharge is achieved. The AC voltage is tuned just below the discharge threshold so the process can be switched on/off by adding a relatively low voltage at the address electrode.

 

Figure 6. Principle of an AC PDPThe discharge creates a plasma of ions and electrons which gain

kinetic energy by the electric field. These particles collide at high speed with neon and xenon atoms, which thereby are brought to higher-energy states. After a while, the excited atoms return to their original state and energy is dissipated in the form of ultraviolet radiation. This radiation, in turn, excite the phosphors which glow in red, green, and blue ( RGB ) colors, respectively. Since each discharge cell can be individually addressed, it is possible to switch on and off picture elements (pixels).

To generate color shades, the perceived intensity of each RGB color must be controlled independently. While this is done in CRT s by modulating the electron beam current, and therefore also the emitted light intensities, PDP s accomplish shading by pulse code modulation ( PCM ). Dividing one field into eight sub-fields, each with pulseweighted according to the bits in an 8-bit word, makes it possible to adjust the widths of the addressing pulses in 256 steps. Since the eye is much slower than the PCM , it will intregrate the intensity over time. Modulating the pulse widths will therefore

translate into 256 different intensities of each color. The number of color combinations is therefore 256 x 256 x 256 = 16,777,216.

At first, PDP s had problems with disturbances caused by intereference between the PCM and fast moving pictures. By fine-tuning the PCM scheme, however, this problem has been elliminated.

While PDP s are relatively light weight and can be manufactured at a thickness of 3-4 inches, they still consume prohibitively much power. The luminous efficiency, i.e. the amount of light for a given amount of supplied electric power, is still at approximately 1 lm/W, about 10% of some other FPD technologies. Also, the discharge process causes sputtering of the cells which inevitably reduces life time. With a new protective dielectric layer of MgO, however, this problem has largely been solved.

Despite these problems, PDP s are promising because of their modest requirements on manufacturing technology. Compared to TFTLCD s, which use photolithographic and high-temperature processes in clean rooms, PDP s can be manufactured in less clean factories using low-temperature and inexpensive direct printing processes. Also, PDP s feature wide viewing angles, no susceptibility to magnetic fields, and are easy to scale up for wall-hanging TV applications.

7. Other FPD technologiesThis report will be updated shortly and information added on the

following technologies.1. Thin film electroluminescent displays ( TFEL ) 2. Light emitting diode arrays ( LED ) 3. Electrochromic displays ( ECD ) 4. Thermochromic displays ( TCD ) 5. Organic luminescent displays ( OELD ) 6. Plasma addressed liquid crystal displays ( PALC ) 7. Microdisplays on CMOS backplanes 8. Micro-Optical Electromechanical Systems ( MOEMS )

 

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Last modified Wed Oct 21 03:34:16 1998

 

Last Updated - 16Jul00

With a 100-year head start over competing screen technologies, the CRT is still a formidable technology. It’s based on universally understood principles and employs commonly available materials. The result is cheap-to-make monitors capable of excellent performance, producing stable images in true colour at high display resolutions.

However, no matter how good it is, the CRT’s most obvious shortcomings are well known:

it sucks up too much electricity

its single electron beam design is prone to misfocus

misconvergence and colour variations across the screen

its clunky high-voltage electric circuits and strong magnetic fields create harmful

electromagnetic radiation

it’s simply too big

With even those with the biggest vested interest in CRTs spending vast sums on research and development, it is inevitable that one of the several flat panel

display technologies will win out in the long run. However, this is taking longer than was once thought, and current estimates suggest that flat panels are unlikely to account for greater than 50% of the market before the year 2004.

Liquid crystal displaysLiquid crystals were first discovered in the late 19th century by the Austrian botanist, Friedrich Reinitzer, and the term ‘liquid crystal’ itself was coined shortly afterwards by German physicist, Otto Lehmann.

Liquid crystals are almost transparent substances, exhibiting the properties of both solid and liquid matter. Light passing through liquid crystals follows the alignment of the molecules that make them up - a property of solid matter. In the 1960s it was discovered that charging liquid crystals with electricity changed their molecular alignment, and consequently the way light passed through them; a property of liquids.

Since its advent in 1971 as a display medium, liquid crystal displays have moved into a variety of fields, including miniature televisions, digital still and video cameras and monitors and today many believe that the LCD is the most likely technology to replace the CRT monitor. The technology involved has been developed considerably since its inception, to the point where today's products no longer resemble the clumsy, monochrome devices of old. It has a head start over other flat screen technologies and an apparently unassailable position in notebook and handheld PCs where it is available in two forms:

low-cost, dual-scan twisted nematic (DSTN)

high image quality thin film transistor (TFT).

PrinciplesMost liquid crystals are organic compounds consisting of long rod-like molecules which, in their natural state, arrange themselves with their long axes roughly parallel. It is possible to precisely control the alignment of these molecules by flowing the liquid crystal along a finely grooved surface. The alignment of the molecules follows the grooves, so if the grooves are exactly parallel, then the alignment of the molecules also becomes exactly parallel.

The first principle of an LCD consists of sandwiching liquid crystals between two finely grooved surfaces, where the grooves on one surface are perpendicular (at 90 degrees) to the grooves on the other. If the molecules at one surface are aligned north to south, and the molecules on the other are aligned east to west, then those in-between are forced into a twisted state of 90 degrees. Light follows the alignment of the molecules, and therefore is also twisted through 90 degrees as it passes through the liquid crystals. However, following RCA America’s discovery, when a voltage is applied to the liquid crystal, the molecules rearrange themselves vertically, allowing light to pass through untwisted.

The second principle of an LCD relies on the properties of polarising filters and light itself. Natural light waves are orientated at random angles. A polarising filter is simply a set of incredibly fine parallel lines. These lines act like a net, blocking all light waves apart from those (coincidentally) orientated parallel to the lines. A second polarising filter with lines arranged perpendicular (at 90 degrees) to the first would therefore totally block this already polarised light. Light would only pass through the second polariser if its lines were exactly parallel with the first, or if the light itself had been twisted to match the second polariser.

An LCD consists of two polarising filters with their lines arranged perpendicular (at 90 degrees) to each other, which, as described above, would block all light trying to pass through. But in-between these polarisers are the twisted liquid crystals. Therefore light is polarised by the first filter, twisted through 90 degrees by the liquid crystals, finally allowing it to completely pass through the second polarising filter. However, when an electrical voltage is applied across the liquid crystal, the molecules realign vertically, allowing the light to pass through untwisted but to be blocked by the second polariser. Consequently, no voltage equals light passing through, while applied voltage equals no light emerging at the other end.

The crystals in an LCD could be alternatively arranged so that light passed when there was a voltage, and not passed when there was no voltage. However, since computer screens with graphical interfaces are almost always lit

up, power is saved by arranging the crystals in the no-voltage-equals-light-passing configuration.

RulesLCDs follow a different set of rules than CRT displays offering advantages in terms of bulk, power consumption and flicker, as well as ‘perfect’ geometry. They have the disadvantage of a much higher price, a poorer viewing angle and less accurate colour performance.

While CRTs are capable are displaying a range of resolutions and scaling them to fit the screen, an LCD panel has a fixed number of liquid crystal cells and can display only one resolution at full-screen size using one cell per pixel. Lower resolutions can be displayed by using only a proportion of the screen. For example, a 1024 x 768 panel can display at resolution of 640 x 480 by using only 66% of the screen. Most LCDs are capable of rescaling lower-resolution images to fill the screen through a process known as rathiomatic expansion. However, this works better for continuous-tone images like photographs than it does for text and images with fine detail, where it can result in badly aliased objects as jagged artefacts appear to fill in the extra pixels. The best results are achieved by LCDs that resample the screen when scaling it up, thereby anti-aliasing the image when filling in the extra pixels. Not all LCDs can do this, however.

Unlike CRT monitors, the diagonal measurement of an LCD is the same as its the viewable area, so there’s no loss of the traditional inch or so behind the monitor's faceplate or bezel. The combination makes any LCD a match for a CRT 2 to 3 inches larger:

Flat Panel size CRT size Typical resolution

13.5in 15in 800 x 600

14.5in to 15in 17in 1024 x 768

18in 21in1280 x 1024  or

1600 x 1200

By early 1999 a number of leading manufacturers had 18.1in TFT models on the market capable of a native resolution of 1280x1024.

A CRT has three electron guns whose streams must converge faultlessly in order to create a sharp image. There are no convergence problems with an LCD panel, because each cell is switched on and off individually. This is one reason why text looks so crisp on an LCD monitor. There’s no need to worry about refresh rates and flicker with an LCD panel - the LCD cells are either on or off, so an image displayed at a refresh rate as low as between 40-60Hz should not produce any more flicker than one at a 75Hz refresh rate.

Conversely, it's possible for one or more cells on the LCD panel to be flawed. On a 1024 x 768 monitor, there are three cells for each pixel - one each for red, green, and blue - which amounts to nearly 2.4 million cells (1024 x 768 x 3 = 2,359,296). There's only a slim chance that all of these will be perfect; more likely, some will be stuck on (creating a ‘bright’ defect) or off (resulting in a ‘dark’ defect). Some buyers may think that the premium cost of an LCD display entitles them to perfect screens - unfortunately, this is not the case.

LCD monitors have other elements that you don't find in CRT displays. The panels are lit by fluorescent tubes that snake through the back of the unit; sometimes, a display will exhibit brighter lines in some parts of the screen than in others. It may also be possible to see ghosting or streaking, where a particularly light or dark image can affect adjacent portions of the screen. And fine patterns such as dithered images may create Viewing angle problems on LCDs occur because the technology is a transmissive system which works by modulating the light that passes through the display, while CRTs are emissive. With emissive displays, there’s a material that emits light at the front of the display, which is easily viewed from greater angles. In an LCD, as well as passing through the intended pixel, obliquely emitted light passes through adjacent pixels, causing colour distortion.

Currently, most LCD monitors plug into a computer's familiar 15-pin analogue VGA port and use an analogue-to-digital converter to convert the signal into a form the panel can use. However, the VESA is working on a specification for a digital video port that is expected to have been approved as an industry

standard by early 1998. It is reasonable to expect LCD monitors to incorporate both analogue and digital inputs once the standard has been approved. As LCD monitors become more popular, digital-output ports on PCs and graphics

cards should follow.

DSTN displaysA normal passive matrix LCD comprises a number of layers. The first is a sheet of glass coated with a transparent metal oxide. This operates as a grid of row and column electrodes which passes the current needed to activate the screen elements. On top of this, a polymer is applied that has a series of parallel grooves running across it to align the liquid crystal molecules in the appropriate direction, and to provide a base on which the molecules are attached. This is known as the alignment layer and is repeated on another glass plate that also carries a number of spacer beads, which maintain a uniform distance between the two sheets of glass when they're placed together. The edges are then sealed with an epoxy, but with a gap left in one corner. This allows liquid-crystal material to be injected between the sheets (in a vacuum) before the plates are sealed completely. In early models, this process was prone to faults, resulting in stuck or lost pixels where the liquid crystal material had failed to reach all parts of the screen.

Next, polarising layers are applied to the outer-most surfaces of each glass sheet to match the orientation of the alignment layers. With DSTN, or dual scan screens, the orientation of alignment layers varies between 90 degrees and 270 degrees, depending on the total rotation of the liquid crystals between them. A backlight is added, typically in the form of cold-cathode fluorescent tubes mounted along the top and bottom edges of the panel, the light from these being distributed across the panel using a plastic light guide or prism.

The image which appears on the screen is created by this light as it passes through the layers of the panel. With no power applied across the LCD panel, light from the backlight is vertically polarised by the rear filter and refracted by the molecular chains in the liquid crystal so that it emerges from the horizontally polarised filter at the front. Applying a voltage realigns the crystals so that light can't pass, producing a dark pixel. Colour LCD displays simply use additional red, green and blue coloured filters over three separate LCD elements to create a single multi-coloured pixel.

However, the LCD response itself is very slow with the passive matrix driving scheme. With rapidly changing screen content such as video or fast mouse movements, smearing often occurs because the display can’t keep up with the changes of content. In addition, passive matrix driving causes ghosting, an effect whereby an area of ‘on’ pixels causes a shadow on ‘off’ pixels in the same rows and columns.

The problem of ghosting can be reduced considerably by splitting the screen in two and refreshing the halves independently and other improvements are likely to result from several other independent developments coming together to improve passive-matrix screens.

New signal-processing algorithms being used in LCD panels analyse incoming video signals and correct for the distortion that causes streaking - the ghost lines that continue across the screen after a real line stops. Sharp, which claims 30 to 40 percent of the desktop and notebook LCD market, calls its version of this feature Sharp Addressing, and says that most new dual-scan panels incorporate some variation on this technique.

Other evolutionary developments are simultaneously increasing dual-scan displays' speed and contrast. Most conventional DSTN displays use materials that have a response time of around 300ms, almost a third of a second. This sluggish response and the accompanying decay rate is largely responsible for the ghosting or image trails that have made dual-scan notebooks unacceptable for full-motion video applications. Other LCD materials offer response times as quick as 150ms, but simply using a faster material without making other changes causes flickering.

Creating colourIn order to create the shades required for a full-colour display, there have to be some intermediate levels of brightness between all-light and no-light passing through. The varying levels of brightness required to create a full-colour display is achieved by changing the strength of the voltage applied to the crystals. The liquid crystals in fact untwist at a speed directly proportional to the strength of the voltage, thereby allowing the amount of light passing through to be controlled. In practice, though, the voltage variation of today’s LCDs can only offer 64 different shades per element (6-bit) as opposed to full-colour CRT displays which can create 256 shades (8-bit). Using three elements per pixel, this results in colour LCDs delivering a maximum of 262,144 colours (18-bit), compared to true-colour CRT monitors supplying 16,777,216 colours (24-bit).

As multimedia applications become more widespread, the lack of true 24-bit colour on LCD panels is becoming an issue. Whilst 18-bit is fine for most applications, it is insufficient for photographic or video work. Some LCD designs manage to extend the colour depth to 24-bit by displaying alternate shades on successive frame refreshes, a technique known as Frame Rate Control (FRC). However, if the difference is too great, flicker is perceived.

Hitachi has developed a technique, whereby the voltage applied to adjacent cells to create patterns changes very slightly across a sequence of three or four frames. With it, Hitachi can simulate not quite 256 greyscales, but still a highly respectable 253 greyscales, which translates into over 16 million colours - virtually indistinguishable from 24-bit true colour.

TFT displaysMany companies have adopted Thin Film Transistor (TFT) technology to improve colour screens. In a TFT screen, also known as active matrix, an extra matrix of transistors is connected to the LCD panel - one transistor for each colour (RGB) of each pixel. These transistors drive the pixels, eliminating at a stroke the problems of ghosting and slow response speed that afflict non-TFT LCDs. The result is screen response times of the order of 25ms and contrast ratios of around 140:1.

TFT screens can be made much thinner than LCDs, making them lighter, and refresh rates now approach those of CRTs as the current runs about ten times faster than on a DSTN screen. VGA screens need 921,000 transistors (640 x 480 x 3), while a resolution of 1024 x 768 needs 2,359,296 and each has to be perfect. If one of them fails, its pixel will be permanently on or off.

In a normal LCD display when one end of the crystal is fixed and a voltage applied, the crystal untwists, changing the angle of polarisation of the transmitted light. Hitachi, Hosiden and NEC have developed products based on a technique called in-plane switching (IPS) which improves the viewing angle of LCD displays. With IPS, the crystals are horizontal rather than vertical, and the electrical field is applied between each end of the crystal. This improves the viewing angles considerably, but means that two transistors are needed for every pixel, instead of the one needed for a standard TFT display. Using two transistors means that more of the transparent area of the display is blocked from light transmission, so brighter backlights must be used, increasing power consumption and making the displays unsuitable for notebooks.

In late 1996, Fujitsu unveiled an LCD that uses a new type of LC material that is naturally horizontal and has the same effect as IPS, but without the need for the extra transistors. Fujitsu used this material (which was developed by Merck of Germany) for its displays from mid-1997 onwards. As well as an excellent viewing angle of 140 degrees all round, the new material offers improved response times and a contrast ratio of 300:1 with no power penalty.

By mid-1997 Sharp had upped the ante at the high end of TFT technology by bolting together two 29in LCD panels to form a monster 40in prototype LCD. These units remain proof-of-concept exercises and are not commercially available. At around the same time NEC launched a single-piece 20in LCD based on conventional TFT technology. The LCD2000 is capable of displaying 1280 x 768 pixels in 24-bit colour and provides an illustration of how improving production technology and increasing market competition impact on price trends. Whilst the LCD2000 carried a hefty price tag it replaced an earlier 15in model which sold at the same price. That represents an increase in screen area of 75% with no price increase.

There’s a significant handicap for bigger active matrix screens, however. As resolutions rise, so does one of the largest cost elements: the external driver technology. The matrix of a 1024 x 768 pixel display is driven by two sets of connections: 1024 columns and 768 rows. That means there are almost 2000 connectors that must run to the display from another set of electronics that provides the drive from the input signal. Long-term plans are to integrate the drive electronics with the TFT electronics to reduce costs and improve manufacturability.

New LCD typesA number of companies are trying to bridge the gap between DSTN and TFT LCDs. HPD (hybrid passive display) LCDs, codeveloped by Toshiba and Sharp, use a different formulation of the liquid crystal material, to provide an incremental, though significant, improvement in display quality at little increased cost. A lower viscosity liquid crystal means that the material can switch between states more quickly. Combined with an increased number of drive pulses applied to each line of pixels, this improvement means that the HPD LCD can outperform DSTN and get closer to active matrix LCD performance. For example, DSTN cells have a response time of 300ms, compared to an HPD cell’s 150ms and a TFT’s 25ms. Contrast is improved from the previous typical 40:1 ratio to closer to 50:1 and crosstalk has also been improved.

Another approach is a technique called multiline addressing, which analyses the incoming video signal and switches the panel as quickly as the specific image allows. Sharp offers a proprietary version of this technique called Sharp Addressing, now showing up under other names in monitors and notebooks from Sharp's customers. This new-generation panel all but eliminates ghosting, and generally delivers video quality and viewing angles that put them at least in the same ballpark as TFT screens, if still not quite in the same league.  Hitachi's version is called High Performance Addressing (HPA).

Canon has successfully produced a form of LCD using ferroelectric crystals. Where traditional DSTN LCDs have a response time of around 300 milliseconds, ferroelectric LCDs are around 1,000 times faster. Another unique property of the ferroelectric LCD is that it’s bi-stable; in other words, a pixel doesn’t require a continuous power supply to stay on or off - power is only

required for changes between states. This potentially helps cut down power consumption. However, production and manufacturability have proven trickier than with normal LCDs.

Recently a number of Japanese companies have also taken a fresh look at reflective LCDs. At first, that may sound a little retro: it was the poor acceptance of early reflective monochrome LCDs that forced the development of backlit and active matrix types. The new thinking though, is that combining a passive matrix technology with a backlight defeats the whole purpose. LCDs without backlights will be thinner, lighter and less power hungry, which is potentially important for palmtop and sub-notebook computers.

Specific goals have been set for the new initiative on reflective LCDs: increasing battery life and matching the reflectivity of newsprint in quality. The target for reflectance is 60%, and developers expect that a 5:1 contrast ratio will approach newspaper quality.

Polyisilicon panelsThe thin-film transistors which drive the individual cells in the overlying liquid crystal layer in traditional active-matrix displays are formed from amorphous silicon (a-Si) deposited on a glass substrate. The advantage of using amorphous silicon is that it doesn't require high temperatures, so fairly inexpensive glass can be used as a substrate. A disadvantage is that the non-crystalline structure is a barrier to rapid electron movement, necessitating powerful driver circuitry.

It was recognised early on in flat-panel display research that a crystalline or polycrystalline (an intermediate crystalline stage comprising many small interlocked crystals - analogous to a layer of sugar) of silicon would be a much more desirable substance to use. Unfortunately, this could only be created at very high temperatures (over 1,000oC), requiring the use of quartz or special glass as a substrate. However, in the late 1990s manufacturing advances allowed the development of low-temperature polysilicon (p-Si) TFT displays, formed at temperatures around 450oC. Initially, these were used extensively in devices which required only small displays, such as projectors and digital cameras.

One of the largest cost elements in a standard TFT panel is the external driver circuitry, requiring a large number of external

connections from the glass panel, because each pixel has its own connection to the driver circuitry. This requires discrete logic chips arranged on PCBs around the periphery of the display, limiting the size of the surrounding casing. A major attraction of p-Si technology is that the increased efficiency of the transistors allows the driver circuitry and peripheral electronics to be made an integral part of the display. This considerably reduces the number of components for an individual display - Toshiba estimates 40% fewer components and only 5% as many interconnects as in a conventional panel. The technology will yield thinner, brighter panels with better contrast ratios, and allow larger panels to be fitted into existing casings. Since screens using p-Si are also reportedly tougher than a-Si panels, it's possible that the technology may allow the cheaper plastic casings used in the past - but superseded by much more expensive magnesium alloy casings - to stage a comeback.

By 1999, the technology was moving into the mainstream PC world, with Toshiba's announcement of the world's first commercial production of 8.4in and 10.4 in low-temperature p-Si (LTPS) displays suitable for use in notebook PCs. The next major advance is expected to see LTPS TFTs deposited on a flexible plastic substrate - offering the prospect of a roll-up notebook display!

CRT feature comparisonThe table below provides a feature comparison between a 13.5in passive matrix LCD (PMLCD) and active matrix LCD (AMLCD) and a 15in CRT monitor:

Displa

y Type

Viewin

g

Angle

Contra

st Ratio

Respons

e Speed

Brightnes

s

Power

Consumpti

on

Life

PMLC

D

49-100

degree

40:1 300ms 70 - 90 45 watts 60K

hour

s s

AMLC

D

> 140

degree

s

140:1 25ms 70 - 90 50 watts

60K

hour

s

CRT

> 190

degree

s

300:1 n/a 220 - 270 180 wattsYear

s

Contrast ratio is a measure of how much brighter a pure white output is compared to a pure black output. The higher the contrast the sharper the image and the more pure the white will be. When compared with LCDs, CRTs offer by far the greatest contrast ratio.

Response time is measured in milliseconds and refers to the time it takes each pixel to respond to the command it receives from the panel controller. Response time is used exclusively when discussing LCDs, because of the way they send their signal. An AMLCD has a much better response time than a PMLCD. Conversely, response time doesn't apply to CRTs because of the way they handle the display of information (an electron beam exciting phosphors).

There are many different ways to measure brightness. The higher the level of brightness (represented in the table as a higher number), the brighter the white displays. When it comes to the life span of an LCD, the figure is referenced as the mean time between failures for the flat panel. This means that if it is runs continuously it will have an average life of 60,000 hours before the light burns out. This would be equal to about 6.8 years. On the face of it, CRTs can last much longer than that. However, while LCDs simply burn out, CRT's get dimmer as they age, and in practice don't have the ability to produce an ISO compliant luminance after around 40,000 hours of use.

 

'Panel Displays'  Previous  

Digital panelsAn important difference between CRT monitors and LCD panels is that the former require an analogue signal to produce a picture and the latter require a digital signal. This fact makes the setup of an LCD panel's position, clock and phase controls critical to obtain the best possible display quality and creates difficulties for panels that do not possess automatic setup features and require these adjustments to be made manually.

The problem occurs because most panels are designed for use with current graphics cards, which have analogue outputs. In this situation the graphics signal is generated digitally inside the PC, converted by the graphics card to an analogue signal, then fed to the LCD panel where it has to be converted back to into a digital signal. For the whole process to work properly, the two converters must be adjusted so that their conversion clocks are running in the same frequency and phase. This usually requires that the clock and phase for the converter in the LCD panel be adjusted to match that of the graphics card.

A simpler and more efficient way to drive an LCD panel would be to cut out the two-step conversion process and drive the panel directly with a digital signal. The LCD panel market is growing from month to month, and with it the pressure on graphics adaptor manufacturers to produce products which allow this.

Efforts to define and standardise a digital interface for video monitors, projectors and display support systems were begun in earnest in 1996. But the process moved rather slowly in ensuing years, causing concern among manufacturers desperate for a standard. Finally, the Digital Display Working Group (DDWG) came together at the Intel Developer Forum in September 1998 with the intent to put the digital display interface standard effort back on the fast track.

With an ambitious goal of clearing through the confusion of digital interface standards efforts to date, the DDWG set out to develop a universally acceptable specification. The group’s initial members included computer industry leaders

Intel, Compaq, Fujitsu, Hewlett-Packard, IBM, NEC and Silicon Image. In April 1999 the DDWG approved a draft Digital Visual Interface (DVI) specification, and in so doing, brought the prospect of an elegant, high-speed all-digital display solution - albeit at a fairly significant price premium - close to realisation.

Silicon Image's PanelLink  technology - which has also been adopted as VESA's Digital Flat Panel (DFP) Standard - provides the technical basis for the digital signal protocol used in the working group's proposed interface specification. PanelLink uses Transition Minimised Differential Signaling (TMDS), a technique that produces a transition-controlled DC balanced series of characters from an input sequence of data bytes, selectively inverting long strings of 1's or 0's in order to keep the DC voltage level of the signal centred around a threshold that determines whether the received data bit is a 1 voltage level or a 0 voltage level.

Plasma displaysLike LCDs, Plasma Display Panels (PDPs) use an X and Y grid of electrodes to address individual picture elements. They work on the principle that passing a high voltage through a low-pressure gas generates light. PDPs are emissive and use phosphor - like CRTs - and so have an excellent viewing angle and colour performance. They work like fluorescent lamps, with each pixel the equivalent of a tiny coloured bulb. Gas, such as Xenon, in a small cell is converted to plasma form by an electrical charge applied across it. The charged gas releases ultraviolet light which then strikes and excites red, green and blue phosphors. As these phosphors return to their natural state they emit visible light.

Conventional plasma screens have traditionally suffered from low contrast. This is caused by the need to ‘prime’ the cells, applying a constant low voltage to each

pixel. Without this priming, plasma cells would suffer the same poor response time of household fluorescent tubes, making them impractical. The knock-on effect, however, is that pixels which should be switched off still emit some light, reducing contrast. Fijitsu has solved this problem with new driver technology which has improved contrast ratios from 70:1 to 400:1.

Manufacturing is simpler than for LCDs and costs are similar to CRTs at the same volume. However, with display lifetimes of around 10,000 hours, a factor not usually considered with PC displays comes into play: cost per hour. For boardroom presentation use this isn’t a problem, but for hundreds of general-purpose desktop PCs in a large company it’s a different matter.

However, the ultimate limitation of the plasma screen has proved to be pixel size. At present manufacturers can’t see how to get pixels sizes below 0.3mm, even in the long term. For these reasons PDPs are unlikely to play a part in the mainstream desktop PC market. For the medium term they are likely to remain best suited to TV and multi-viewer presentation applications employing large screens, from 25in up to 70in.

ALiSFujitsu is developing a new plasma display type that'll overcome the low-resolution restrictions of conventional PDPs. Called alternate lighting of surfaces (ALiS), the technique uses interlaced rather than progressive scans. The biggest drive for this is the introduction of digital television. If plasma is to compete in in this new and potentially lucrative market, it needs to support the level of definition that this technology demands (around 960 lines on the screen).

ALiS has the advantage of requiring only half the number of drivers of its predecessor. Also, the black stripes between screen elements on a standard PDP aren't present, so the image is that much brighter.

PALCDA peculiar hybrid of PDP and LCD is the plasma addressed liquid crystal display (PALCD). Sony is currently working, in conjunction with Tektronix, on making a

viable PALCD product for consumer and professional markets.

Rather than use the ionisation effect of the contained gas for the production of an image, PALCD replaces the active matrix design of TFT LCDs with a grid of anodes and cathodes that use the plasma discharge to activate LCD screen elements. The rest of the panel then relies on exactly the same technology as a standard LCD to produce an image. Again, this won't be targeted at the desktop monitor market, but at 42in and larger presentation displays and televisions. The lack of semiconductor controls in the design allow this product to be constructed in low-grade clean rooms, reducing manufacturing costs. It's claimed to be brighter, and retains the 'thin' aspect of a typical plasma or LCD panel.

Field Emission DisplaysSome believe FED (field emission display) technology will be the biggest threat to LCD’s dominance in the panel display arena. FEDs capitalise on the well-established cathode-anode-phosphor technology built into full-sized CRTs using this in combination with the dot matrix cellular construction of LCDs. Instead of using a single bulky tube, FEDs use tiny ‘mini tubes’ for each pixel, and the display can be built in approximately the same size as an LCD screen.

Each red, green and blue sub-pixel is effectively a miniature vacuum tube. Where the CRT uses a single gun for all pixels, a FED pixel cell has thousands of sharp cathode points, or nanocones, at its rear. These are made from material such as molybdenum, from which electrons can be pulled very easily by a voltage difference, to strike red, green and blue phosphors at the front of the cell. Colour is displayed by ‘field sequential colour’. The display will show all the green information first, then redraw the screen with red followed by blue.

In a number of areas, FEDs look to have LCDs beaten. Since FEDs produce light only from the ‘on’ pixels, power consumption is dependent on the display content. This is an improvement over LCDs, where all light is created by a backlight which is always on, regardless of the actual image on the screen. The LCD’s backlight itself is a problem the FED doesn’t have. Light from the backlight of an LCD passes through to the front of the display, through the liquid crystal matrix. It’s transmissive, and the distance of the backlight to the front contributes to the narrow viewing angle. In contrast, an FED generates light from the front of the pixel, so the viewing angle is excellent - 160 degrees both vertically and horizontally.

FEDs also have redundancy built into their design, most designs using thousands of electron emitters for each pixel. Whereas one failed transistor can cause a permanently on or off pixel on an LCD, FED manufacturers claim that FEDs suffer no loss of brightness even if 20% of the emitters fail.

These factors, coupled with faster than TFT LCD response times and colour reproduction equal to the CRT, make FEDs look a very promising option. The downside is that they may prove hard to mass produce. While a CRT has just one vacuum tube, a SVGA FED needs 480,000 of them. To withstand the differences between the vacuum and external air pressure, a FED must be mechanically strong and very well sealed.

ThinCRTsUS-based Candescent Technologies calls its implementation of FED technology 'ThinCRTs'. The technology works on the same principles as standard picture tubes used by desktop computers and televisions. Beams of electrons are fired from negatively-charged electrodes ('cathodes') through an evacuated glass tube. The electrons strike phosphors at the front of the tube, causing them to glow and create a high-resolution picture.

Candescent has replaced the electron guns, deflection yoke and shadow mask of a conventional CRT with a perforated conductive sheet through which conical cold cathode emitters - known as Spindt Cathodes - protrude. Passing a current through the conductive sheet causes the cathodes to emit a stream of electrons, which causes phosphor to glow in the same manner as a typical tube.

While conventional CRTs consist of a large bell-shaped tube, a ThinCRT uses a flat tube a mere 3.5 millimetres thin. This consists of two sheets of glass separated by

a 1-millimetre gap. The internal display supports are very thin walls (e.g. 0.05mm) made of a proprietary ceramic material. These are strong enough to handle 14 lbs. per square inch external atmospheric pressure - making them  sufficiently durable to withstand mechanical handling during production - yet thin enough to be hidden between pixels without affecting the electron beamlets. The face plate is coated with conventional CRT aluminised colour phosphors.

In place of the conventional CRT's single large cathode, are millions of microscopic electron emitters formed on a baseplate using thin film processing technology similar to that used in LCD panel fabrication. The cathodes are very small - only 200nm each - and it takes several to activate individual pixels onscreen, allowing a relatively high failure rate (Candescent claims 20%) before degradation is visible. This makes ThinCRT significantly more viable in terms of manufacture than LCD and - with an entire display of the order of 8mm thick - a fraction of the depth of a conventional CRT.

The technology is called 'cold cathode' because electrons are generated at room temperature without the heating necessary in conventional CRTs. The emitters consume only a small fraction of the power used by the traditional CRT's hot cathode. This results in a very power-efficient display. Further power efficiency is gained because of the absence of the shadow mask used in conventional CRTs, which can waste up to 80% of the power.

Candescent claims that almost 80% of the tools, equipment and processes used in the manufacturing process will be derived from existing CRT, LCD and semiconductor manufacturing industries, significantly cutting the cost of equipping production lines. In late 1998 an alliance with Sony was announced

aimed at bringing 14.1in displays to the market early in year 2000 at a price comparable with TFT.

Light-Emitting PolymersOf all the display technologies

emerging from the labs, none appears to have as widespread importance as LEP (light-emitting polymer) displays. Conjugated polymers had already found favour as conductors in battery electrodes, transparent conductive coatings, capacitor electrolytes and through-hole plating for double-sided circuitboards. When its developer and patent holder, Cambridge Display Technology (CDT), discovered that certain conjugated polymers can be made to emit light in addition to carrying electric current, the idea soon followed that a display device could be created using these properties.

The LEP is most closely related to the humble LED (light-emitting diode), but where the LED’s light producer is a traditional semiconductor material, LEP uses special polymers to achieve the same effect. In simple terms, conjugated polymers - such as polyprolle (which has been in existence for over 100 years) and polyaniline - are plastic materials with physical properties that confer conductive properties. As a current is passed through a cell made of this, the polymer's molecular structure is excited, creating light emission. The output efficiency of this process has improved dramatically in recent years, to the point where light emission through the spectrum from blue almost up to infrared have been recorded.

In terms of manufacture, the polymers are extremely simple to produce, and the circuitry doesn't need to be any more complex than that already used in LCDs. Indeed, the technology has many potential advantages over LCD: only one sheet of plastic is required instead of two sheets of glass, LEPs don’t need backlights, so they consume less power, and since it’s the surface of the LEP which emits light, wide viewing angles are possible. Furthermore, not only can it be applied to very large surfaces but, since they use flexible substrates, LEP displays can be curved, and possibly even made flexible.

On the strength of these advantages CDT claims that LEP screens will replace LCDs within the next few years. However, in terms of real products, it’s still early days for LEP, but the promise is an incredibly wide-ranging class of display products. So far, CDT have only produced monochrome proof-of-concept prototypes and notebook-size screens aren’t expected until 2004 at the earliest. However, the early LEP displays have been sufficiently impressive to have tempted Intel to invest in the technology.

Digital Light ProcessorsTexas Instruments’ DLP - also called the mirror chip - is one of the most exciting innovations in display technology, as it has been successfully exploited commercially. Fundamentally, the mirror chip is a standard static memory design. Memory bits are stored in silicon as electrical charge in cells. An insulating layer with a mirror finish above the cells is put added and is then etched out to form individual hinged flat squares. When a memory bit is set, the charge in the cell attracts one corner of the square. This changes the angle of the mirrored surface and by bouncing light off this, pictures can be formed.

Complicated optics are needed to convert a picture the size of a postage stamp into a projectable display. Heat is unavoidable, since to make the final image bright enough, a lot of light is focused on the chip. A large amount of ventilation is required to cool it, which is noisy, although the latest projectors have a chip in a soundproof enclosure.

Colour is also a complication, since the mirror chip is basically a monochromatic device. To solve this three separate devices can be used, each illuminated with a primary colour, or alternatively, one device can be placed behind a rotating colour wheel with the chip displaying red, green and blue components sequentially. The chip is fast enough to do this and the resulting picture looks fine on colour stills but has problems handling moving images.

Development of the DLP is continuing and current problems are likely to be solved in the future. While the mirror chip is currently only available in projectors, it’s likely that they will appear in a back-projecting desktop display eventually.

HAD technologyAll of the displays discussed hitherto - whether they're made of liquid crystal, phosphors or plastic - have one thing in common; they're two-dimensional.

However, British start up Reality Vision is in discussion with a number of foreign companies about the further development of its HAD (holographic autostereoscopic display) technology, and expects to bring true 3D holographic screens to the consumer market by 2005.

HAD is a simple conversion of LCD technology, replacing the LCD's backlight with an HOE (holographic optical element). This is divided into two sets of horizontal bands that correspond with each eye. The result is that the left eye sees one image and the right eye sees another, thereby achieving a 3D effect.

Since its major application will be to games playing, HAD has been designed to easily facilitate switching between 2D and 3D modes simply by removing or reinstating one of the bands, so that both eyes see the same image. Its principal limitation is that the image can distort if the viewer shifts position. To combat this, Reality Vision has incorporated a system that rotates the screen in sync with the viewer's head movements when the user wears a small tracking device.

New Panel Technologies Challenge LCD Supremacy

FED and EL displays are thinner than LCD panels and offer lower power consumption, wider viewing angles and faster response

time. Production of FED has started at PixTech in the US, and EL is being

manufactured by Pioneer Electronic in Japan.

Two new flat panel displaysfield emission displays (FED) and organic electroluminescent displays (EL)are ramping up for volume production in 1996. The new displays may offer performance beyond that of LCD, because they improve its three major drawbacks: the viewing angle, response speed and power consumption.

The FED offers a light emission efficiency superior to that of the LCD, with color panels already developed in the 10

to 15 lm/W range, roughly double the four to six lm/W range of existing thin-film transistor (TFT) LCD. As a result, power consumption is roughly halved. The light emission efficiency of organic EL displays is about the same as that of LCD, but while the LCD requires a constant backlight, the organic EL display generates its own light. Only the necessary pixels are lit, lowering actual power consumption. PixTech, Inc of the US has begun FED production, while Pioneer Electronic Corp of Japan will begin production of EL displays (Fig 1) later in 1996. Although the price is still unknown, both displays plan to use these technical advantages (Fig 2) to cut a slice of the flat panel display market now monopolized by LCDs.

Growing Interest in FED

Research and development of FED is taking place primarily in Europe and the US. The Laboratorie d'Electronique de Technologie et d'Instrumentation (LETI) of France, a leading developer of FED, attracted the worldwide attention of display engineers when it announced the world's first color FED panel at the Fourth International Vacuum Microelectronics Conference (IVMC '91).

With an eye toward volume manufacturing, LETI investigated cooperative development opportunities with the world's leading electrical equipment manufacturers. They sold the technology to PixTech, Inc, which joined forces with a number of US and European manufacturers who had missed the LCD investment boat.

Manufacturers in Korea and Taiwan have also begun to show interest. At the 1995 Asian Symposium on Information Displays sponsored by the Institute of Television Engineers in October 1995, the Korea Institute of Science and Technology (KIST), the Electronics and

Telecommunications Research Institute (ETRI) of Korea, and the National Taiwan Institute of Technology all announced FED technologies. In Japan, the only firm to start full-scale development is Futaba Corp, which had no investment in LCD.

FED is emerging as a potential threat to TFT-LCD and Japanese manufacturers can no longer ignore the technology. If FED manufacturers can provide displays with better performance and a lower price, it will represent a tremendous blow to the Japanese TFT-LCD manufacturers who are currently suffering from low profitability.

With the improvement of the manufacturing process in recent years, a number of small-scale FED lines have been constructed (Table 1). Development leader PixTech began limited production of a few hundred panels a month, in January 1996. They plan to expand the production scale to a rate of 70,000 panels a year in 1997. PixTech is also launching a research and development effort to develop 10-inch panels in the third quarter of 1995 (Fig 3) , and 40-inch panels during the first quarter of 1996.

Table 1 Prototyped Panels

Other manufacturers are also constructing pilot lines for prototyping small panels. Silicon Video Corp of San Jose, California, has constructed a pilot line using 4-inch diameter circular glass substrates and is prototyping 2.4-inch color FED panels. The firm plans to demonstrate the prototyped panels in February 1996. SI Diamond Technology, Inc (SIDT) of Austin, Texas, has constructed a 5-inch monochrome FED panel pilot line. Plans exist to construct a 10-inch 800 x 600-pixel color FED panel line in the third quarter of 1996, and a 17-inch 1,120 x 768-pixel color FED in the third quarter of 1997.

Volume Production in 1997

Though PixTech, Silicon Video, and SIDT have installed pilot lines, the investment for full-scale FED production, expected to start in 1997 or 1998 (Fig 4) , will come from other manufacturers. PixTech has licensed the technology to the "FED Alliance": Texas Instruments Inc (TI), Raytheon Co, and Motorola Inc, all of the US, and Futaba of Japan. "We handle the research and development and small-scale production. The volume production we leave up to the major companies, like TI or Motorola," explains PixTech Executive vice president Francis G Courreges. Thomas D Petrovich of TI's Semiconductor Group Flat Display Products Development, amplifies, "PixTech makes the recipe for FED, and we handle volume production based on that." TI has already begun prototype production of a 2.1-inch color FED.

PixTech's pilot line is located inside IBM Corp's fab in Montpelier, France. Borrowing unused IBM space, the firm invested about US$2 million to construct the line, which can produce up to 12-inch class FED panels.

Silicon Video is receiving development capital from Hewlett-Packard

Co (HP) of the US, with three development objectives; superior image quality, lower power consumption and price. If Silicon Video can achieve these goals, then HP plans to use the new displays in its OmniBook notebook personal computers and workstations. Silicon Video plans to begin volume production at the end of 1997, starting with 10 to 12-inch color FED panels.

SIDT has received US$10 million development capital over the last two years, from Philips Electronics NV of the Netherlands. The two firms plan to establish a joint venture to begin volume production in the second quarter of 1997.

Beating TFT-LCD Performance

FED manufacturers plan to challenge the color TFT-LCD market monopoly head-on with 6-inch color panels for use in car navigation systems and similar applications, and 10-inch and larger panels for notebook PCs and desktop monitors.

FED performance has the potential to beat TFT-LCDs (Table 2), because it totally eliminates the major problems of narrow viewing angles and the slow response speed now faced by color TFT-LCDs. The viewing angle of an FED is 160° in both up-down and left-right directions, and the response time is fast enough (several µs) to handle motion video images. Another advantage is the wider operating temperature range. Because the FED is completely solid state, it will operate across a temperature range from -45°C to +85°C.

Table 2 FED vs Color TFT-LCD

Price Trends Affect Production

The remaining question is whether or not the prices can be brought down to the level of color TFT-LCD. "As far as the manufacturing process alone is concerned, the cost will be lower than color TFT-LCD," agree FED engineers. The price of color TFT-LCD, however, is decreasing more rapidly than the FED firms expect.

Regardless of higher prices, military and automtive applications will benefit from FED's superior performance, and the new products are likely to penetrate the market through these fields first. FED manufacturers don't plan to stop there, however. "By the year 2000, 15% to 20% of the flat panel display market will be supplied by FED," hopes Jean-Luc Grand-Clement, chairman and chief executive officer (CEO) of PixTech. Howard K Schmidt, SIDT's president, CEO and senior technical staff member, also predicts FEDs will hold 5% of the flat panel display by 2002.

Manufacturers involved in FED R&D believe that prices can be dropped under TFT-LCD. Even if the price of a 10.4-inch color video graphics array (VGA) LCD drops to US$300 from $350 in 1998, FED "should be able to drop under $300," says Nalin Kumar, senior technical staff member and technology and IP director of SIDT.

TI and Motorola, however, who are actually handling the capital investment for volume production, are being very cautious about when to invest. TI's Petrovich comments, "The key point in ramping up FED volume production is whether or not it can be profitable. We want to make our decision based on the color TFT-LCD status at the time of the investment." Motorola's Peter Shinyeda, vice president and general manager of the Automotive, Energy and Controls Group, Flat Panel Display Division, also expresses concern: "Motorola will be a flat panel manufacturer in the future, and FED is the best choice at the moment. But we are a little concerned at the speed with which LCD manufacturers are improving the price and performance of color TFT-LCD."

Cold Cathode, Phosphors

The basic principles of light emission are the same for the FED and the cathode ray tube (CRT). Electrons are emitted from the cathode, and collide with phosphors coated onto the anode to generate light.

What is different is the cathode itself. The CRT uses a point electron source, while the FED has an array of fine electron sources. In the CRT the electrons emitted from the source are deflected and scanned across the screen to produce the image, while in the FED several hundred cathodes are used for lighting each pixel. There is no scanning. Electrons from the cathodes sited directly below the phosphors of a pixel create the image, and as a result the panel thickness can be reduced to several millimeters.

Further, while the CRT is a hot cathode devicethat is, it heats the cathod to produce electronsthe FED uses a cold cathode, generating electrons with a high voltage instead.

Spindt Cathode Used

PixTech uses a Spindt-type structure, where the tips of the cold cathodes are conical (Fig 5) (Fig 6). Cathodes are made of Mo, and are about 1.2µm tall. There are about 200 Spindt cold cathodes for a single pixel composed of red, green and blue elements.

First, +350V is applied to the anode. Then +80V is applied to the gate to control the electron flow from the cold cathode. The electrons are accelerated by the voltage of the anode, and emit light when they strike the phosphor coated on the anode. Gray scale is controlled by applying a voltage from 0V to 30V at the cathode, depending on the image data.

The drive IC and pixel electrode are connected through a 25µm via the glass substrate, and the drive IC itself is flip-chip mounted on the rear of the substrate. This makes it possible to reduce the area of the screen frame.

The phosphors are an improvement from CRT materials. In the CRT, the phosphors emit light at the collision of electrons accelerated by several kV, but PixTech uses a phosphor which emits light at only around 50V. "The basic material is the same as used in the CRT," explains PixTech's Courreges, "but we modified it for use in FED so that it emits even at low voltages." A monochrome FED panel prototyped by Futaba of Japan, after it joined the FED Alliance, uses the same ZnO:Zn phosphor used in florescent tubes.

Anode Switching Technique

PixTech's product has the above-mentioned basic structure, with two additional improvements. One is the formation of an amorphous Si resistor film between the Spindt cold cathode and the cathode terminal electrode. This film serves to prevent short-circuits between

the gates and the cold cathodes, because manufacturing variations makes a cold cathode unusually close to a gate, causing high currents to concentrate in the cold cathode and possibly leading to a short circuit. This current crowding is prevented with the resistance film.

The second is the method used for color display, which is called anode switching. Because the response speed of the FED is so fast, a single frame (1/60s) is split into three phases, and voltage sequentially applied to the three anodes (transparent electrodes) coated with the red, green and blue phosphors separately. The voltage is about +350V. Commercially-available power transistors are used for anode switching.

TI has already started manufacturing a drive IC for 6-inch color FED panels, an anode switching IC and a dedicated DC-DC converter IC, and is shipping them to PixTech and Raytheon. Development of the drive IC for a 10-inch color FED panel is completed.

Development of Organic EL

Organic EL displays also have the potential to surpass LCD performance. Development of new materials for organic EL displays has made enormous advances in the past few years, at last attaining practical application levels. The major obstacle to putting EL displays into use has been service life, but new materials offer 5,000 hours or more. While production will begin with small-size panels, the target for the future includes large-size wall-mounted televisions.

Pioneer Electronic begins volume production of small-size panels during the second half of 1996. By the end of 1996 the firm plans to use the new panels in its audio-visual (AV) equipment. Other firms like TDK Corp and Idemitsu Kosan Co, Ltd, both of Japan, are also considering entering the business.

The prototype demonstrated by Pioneer Electronic (Fig 1b) is green, with a 256 x 64-pixel format, using a simple matrix drive with a 1/64 duty cycle. The service life defined with a half brightness time has been increased to over 10,000 hours with a 200cd/m2 initial brightness, and light emission efficiency is 6.2lm/W with a 16V drive. For screen dimensions 94.7mm x 21.1mm, the power consumption is about 0.2W.

"We were able to attain the high efficiency and longer service life thanks to rapid development in emission layer and other materials," says Teruo Toma, deputy general manager of the Corporate Research and Development Laboratory at Pioneer Electronic's Research & Development Group. The firm developed a material consisting of 8-hydroxyquinoline aluminum (ALQ3) doped with a quinacridone derivative. It prototyped an organic EL display using a green phosphor, with a layer structure consisting of transparent electrode (indium tin oxide), hole transport layer, organic emission layer and Mg-Ag electrode layer, attaining a peak brightness of about 100 kcd/m2. The peak emission wavelength is 540nm.

This light emission layer is sandwiched between organic thin films consisting of the electron transport layer and hole transport layer, and then the thin films are sandwiched between electrodes (Fig 7) . The anode uses Al-Li alloy, which easily releases electrons, and the cathode is transparent indium tin oxide (ITO). Neither the structure nor the manufacturing method is unique to Pioneer Electronic, and a number of other firms have also developed organic EL displays with the same structure.

EL Service Life Increased

Service life has been improved for both blue- and green-light emitting material. Idemitsu Kosan uses a distyryl-

arylene derivative in the emission layer to achieve the service life of over 5,000 hours with an initial brightness of 100cd/m2. The emission efficiency is 5 lm/W, and the drive voltage 5V (Fig 8) .

The panel structure has a cathode, electron transport layer, emission layer, hole transport layer and anode, the same as the Pioneer Electronic design, except that it uses Mg-Al for the cathode. Idemitsu has confirmed that the structure allows the response time to be improved to 80µs, and a peak pulse emission brightness of 10 kcd/m2 at a drive voltage of under 20V. The firm has concluded that this structure and material can be used with a simple matrix drive to construct displays with up to 1,000 scan lines.

Material development for the red-light emission layer is a bit farther behind. According to Pioneer Electronic, the service life is only several thousand hours. Pioneer's Toma comments, "The panel structure is pretty much settled, and the only really major issue left is the material for the emission layer. Red is especially difficult, because the longer the wavelength the higher the drive voltage, and the shorter the service life. I'm confident we'll find a way to solve it, and hope to achieve a practical service life for red within a year."

by Katsumi Yamashita and Tomohiro Nakamori

SOCIETY FOR INFORMATION DISPLAYUK & IRELAND CHAPTER

NEWSLETTER 

Number 27 September 1997

CONTENTSEID '97  Meeting Report Flat Panel Emissives    Thanks to Host Companies   Best Paper Award   The Year 2000 And All That...    

Electronic Materials for Displays       Use of Members Names & Addresses   SID on the WWW   Honours & Awards Electronic Form   Press Releases

EID '97Following on from the huge success of last year's

joint venture with Eurodisplay, this years Electronic

Information Display Exhibition and Conference will

be held at the Sandown Park exhibition and

conference centre on the 18th, 19th and 20th of

November.

This years show will feature many new names in the

exhibition, with several suppliers now being

represented by new companies. This premier

exhibition for the displays community is more

important than ever for those engineers and scientists

who need to remain aware and involved with

commercial and technical developments in the

displays supply field. 

The conference will be opened with a day

celebrating 100 years of the CRT, focusing on the

history and future for this most prevalent of

technologies. 

Days two and three contain a wide range of papers

covering new developments in current flat panel

be plenty of time to raise questions with the authors

of the papers being presented. 

In addition, a number of lunchtime "workshop"

events are being held, where commercial suppliers

will offer short presentations on particular aspects

of their new products and technologies. These

events are a new addition to EID, and are being

offered to give advice and guidance to users who

may have interest in the products under discussion.

Entrance to these events will be free for conference

attendees, and if they prove to be successful, they

will become a permanent feature of future EID

conferences. 

Delegates feedback on both the conference and

workshops is essential to allow the SID committee,

and the exhibition organisers, to ensure that the

correct blend of papers on new and old technology

together with technical theory and practical

application is developed and maintained. 

The SID UK and Ireland Chapter exists only to

technologies, such as passive and active matrix LCD,

as well as a number of update papers on the new

display technologies that are being spearheaded here

in the UK. The SIDsponsored EID97 conference is

THE place to be if you want to hear questions asked,

and answers given, about all the key aspects of

displays technology, both new and old, and to review

whether Europe can be a mass production base for

flat panel displays. 

This year, significant discounts are being given for

conference attendees who wish to visit for two or

three consecutive days. Conference proceedings will

be available for attendees, and there will 

serve its members. Please tell us if the topics you

want to hear about have not been included in this

years EID, and we will seek to address your

(reasonable) requests, either in a normal day

seminar, or in EID98. 

We hope to see you at EID97 in November. 

SID EID97 subcommittee  John Raines (Chairman), Chris Williams, Neville

Milward

FLAT PANEL EMISSIVESReport by T D Wilkinson, University of Cambridge

The oneday meeting and AGM for the UK&Ireland

Chapter held at Clare College, Cambridge, was

hailed as a success by all those who attended. The

programme was the AGM followed by five invited

technical talks on the topic of flat panel emissives.

The AGM was chaired by the leaving chapter chair,

Paul Emmerson, and saw the voting of the new

chapter chair Barbara Needham for the year. The

AGM then handed over to Barbara to chair the

technical papers. The meeting was well attended by

over 85 delegates from across the displays

spectrum. 

The technical session started with Chris King from

Planar who presented the latest results on their work

into electroluminescent displays. The large format

display produced included an ROB high contrast

device and work is progressing on a full RGB

system. The talk also presented Planar's miniature

Both were demonstrated over lunch. Bill Crossland

presented the next paper from Cambridge

University Engineering Department and Screen

Technology Limited on the new technology of

liquid crystal photoluminescent displays (PLLCDs).

The PLLCD combines the use of photoluminescent

phosphors with LCD technology switching a back

illumination in the far UV spectrum. The aim is to

produce a high brightness, wide viewing angle

display that capitalises on the high efficiency of

photoluminescent phosphors and LCD modulation.

Progress so far has produced a simple three colour

demonstrator based on a 365nm W. LCD system. 

The penultimate presentation was from Peter

Wilshaw from Oxford University on the topic of

field emission displays. In his talk, he outlined the

current trends in this technology based on

sharpened tip emission devices. Both high and low

displays for helmet mounted systems. On show was

the VGA format, with an XGA format device out

soon, also the future will see a full colour miniature

display. The second talk, on light emitting polymers,

was presented by Paul May of Cambridge Display

Technology. He reported progress on the

development of high brightness polymer based

displays and stressed the need for high purity to

guarantee efficiency. The majority of their work is

currently on improving the lifetime of the devices,

with devices being tested for over 1500 hours

(green) and 2000 hours (red). Work is also

progressing to develop a multiplexed display. 

The post lunch session was led by Paul Childerhouse

from Delphi Information Systems who presented

Fujitsu's plasma displays. In the talk, he outlined the

functionality and features of two plasma displays

that Fujitsu are launching onto the market. The first

was a VGA, 21" colour display that is only 3" thick

which is currently available in the marketplace. The

second was an impressive 42.", 852x480 colour

plasma display, 6" thick, which will be available

shortly.

voltage systems were presented, with the accent on

the quest for a low voltage, high efficiency blue

phosphor. Devices are being promised by both

Pixtech and Raytheon in the near future. The final

talk of the day was given by Aaron Vecht from

Greenwich University on the topic of Flat

Emissives Promise or Exasperation. In this

entertaining presentation he outlined some of the

problems and setbacks in the development of

emissive displays. The emphasis was to return to

one's roots and answer the fundamental questions,

which have been left unanswered by the rapid

progress of technology. 

Overall the standard of the presentations was high,

with a variety of current UK related topics in the

field of flat emissive displays. It was also good to

see several working display units on show during

the day. Thanks must go to Adrian Travis who

organised the venue and ensured a smooth running

day at Clare College.

Thanks to our Host Companies                             The Alfred Woodhead Best Paper Award

We should like to acknowledge the generous

support of several companies who give us the use

of their premises, free of charge, for our oneday

meetings. Without this, not only would the

meetings cost far more to attend, they would not

have the friendly, informal atmosphere which helps

contribute to their success. Our last four meetings

have been hosted by De Montfort University,

Leicester, Clare College, Cambridge University,

British Aerospace Sowerby Research Centre at

The winner of this award at the meeting reported

above on "Flat Panel Emissives" held at Blare

College, Cambridge on 17th April was Bill

Crossland of Cambridge University for his

contribution on "Liquid Crystal Photoluminescent

Displays (PLLCDs)". The marking was very close,

with only 0.5 (out of 10) separating the average

scores of the top five speakers.     

Filton and GEC Marconi Research Centre at Great

Baddow. If your company has the facilities and

would like to host one of our meetings, please

contact a member of the committee.

 

The Year 2000 And All That....I will have the pleasure of being Chairman for the

SID UK and Ireland Chapter during the forthcoming

Millenium celebrations. 

As a professional engineer, not a scientist, I have a

natural tendency to want to celebrate the Millenium

with visits to various Rugby Football grounds and

licensed hostelries, followed by ingestion of

quantities of Chinese or Italian foods. 

I know many of my professional engineering

colleagues within the Display Industry win be in

close accord with me (indeed several will be with

me on the visits!!), but being aware of the wide

range of appetites and social types within the

academic, scientific and industrial communities that

are involved with SID, I feel that it would be

sensible to seek YOUR input on the range of

activities you would like us to present in order for

you to get the maximum enjoyment from your SID

membership during the Millenium period. 

We can be sensible and politically correct, and stay

with a balanced programme of one-day technical

seminars and threeday EID conference/exhibition,

or we can...... 

If you have ideas on how we might stage one or

more celebrations to enjoy the technologies we

work with, and enjoy ourselves at the same time,

please send your ideas to me. Those that are

repeatable will be discussed at SID committee and

presented to all members through future editions of

the newsletter. 

Chris Williams  ViceChairman  Contact via fax: 01635 299214 or phone 01635

298395   

Electronic Materials for Displays ProgrammeEPSRC Announces 1997/8 Call for Proposals

At the beginning of September EPSRC invited proposals

for the fourth tranche of funding for Electronic Materials

for Displays (EMD), with a closing date for

applications of 14 November 1997. The Materials

Programme is able to commit up to £1M to promote

innovative materials research for the development of

advanced display technologies. For the coming year, the

Research Objectives of EMD have been refocussed in the

Applications should be made on the standard

EPS(RP) form, but an industrial relevance

form (available from Tanya) also needs to be

completed. 

The first stage in the application procedure is

to contact the programme Co-ordinator, Roger

Heckingbottom, phone 01768 773732, fax

light of the advice received following the recent

Workshop held by the Programme and, following

comments from the assessors, the Panel is keen to see the

links with industry receiving more emphasis. 

A full copy of the new Call can be obtained from Ms

Tanya Withers at EPSRC, phone 01793 444345, fax

01793 444470, email: tanya.withers@epsrc.ac.uk.

01768 774902, email

roger.heckingbottom@btsys.bt.co.uk, who is

also the contact point for any technical

queries. 

Any general enquiries should be made to the

Associate Programme Manager, Mrs Glenys

France, phone 01793 444319, fax 01793

444470, email glenys. france@epsrc. act uk. 

Decisions on funding for new grants will be

made by the end of February 1998.

Use of Members Names and AddressesFollowing the receipt of comments from members, the UK &

Ireland Chapter Committee wish to inform all members that

the Chapter members database is not sold on for commercial

purposes. We are registered with the Data Protection Agency

and the only access allowed to our database is for

organizations closely related to Display technology matters,

such as related conference and exhibition organisers. Insert

material is included in the Chapter Newsletter or Notice of

Meetings if the Committee supports the objectives of the

material and feel that it is relevant to the displays industry.

We believe that our actions meet the

Corporate Objectives of SID in maintaining

our members awareness of the latest

developments in the technology, and we

trust that our members accept that we are

acting in their best interests.  Chris Williams  Vice Chairman

SID on the World Wide WebYou can access the SID pages at the following address http://www.res.cms.dmu.ac.uk/sid. An account of

our last meeting "3D Displays A Technology Update. can be accessed from this page and by the time you

receive this newsletter, there should be a link from this to the SID site in the USA.

Honours and Awards Electronic Nomination FormAn electronic Honours and Awards Nomination Form

is now available for use by all members of the SID.

The new form is located on the home page of the SID

at http:www.sid.org and is currently listed under

What's New. Just click on the "nomination form" and

it will appear on your screen. It is requested that from

now on, honours and awards nominations are to be

Once the form is filled out, then by clicking

Submit Form rectangle at the end of the form, the

nominator will be able to automatically send the

completed nomination to the committee.

Nominations will still be accepted in hard copy

form, but there is a strong preference that, if at all

possible, nominations should be sent to the

submitted to the SID Honors and Awards Committee

using this electronic form.

committee via the Internet using this electronic

form.

Press ReleasesEuropean Union "Esprit" Project No 22615 "PHOSPAP"

(Development of UV Phosphors for Large Colour Plasma Display Panels)

Five European organisations have joined forces in

ESPRIT'S project PHOSPAP to develop new

phosphors required for large, flat, colour plasma

displays envisioned for consumer TV. The

consortium members include Phosphor

Technology Ltd in the UK, Thomson Tubes

Electroniques and Thomson CSF LCR in France,

Philips Research Laboratories in Germany and the

Technical University of Delft in The Netherlands. 

The project aims to develop improved phosphors

with characteristics optimised for large size flat

Plasma Display Panels (PDPs) for future consumer

TV and professional applications. One of the key

points of the project is to ensure European

availability of improved PDP phosphors and display

devices containing them.

Role of Phosphor Technology Ltd: Working

closely with the other consortium members, PTL

will be involved in the development and scaleup of

improved red, green and blue phosphors. Major

innovations are expected in the development of new

materials and manufacturing processes for the

improved phosphors. On successful completion of

the project, PTL aims to maintain large scale

production of the developed phosphors and

consolidate its position as a major supplier for these

improved materials. 

For more information, contact Phosphor Technology

by fax at  +44 (0)1992 893729.

NEW PAL Video to SuperVGA LCD Scan Converter Announced

Imagine Graphics Ltd., the specialist display

technology company, announces the VIDEOMATE

3, a scan converter card that enables PAL video to be

digitised and displayed on the latest SuperVGA

(800x600) LCD flat panel displays. Applications for

the card include medical computing, professional

broadcast engineering, image processing, security,

industrial computing and defence. The price of the

card is just £450 + VAT (£528.75 incl. VAT). 

The VIDEOMATE 3 scan converter card allows

either composite (CVBS) or Y/C (SVHS) PAL

video to be displayed pixelforpixel on an 800x600

conversion process including the direct connections

to the X,Y matrix of the LCD panel thereby

eliminating noise and providing the best possible

display quality. All the latest SuperVGA TFT panels

from manufacturers such as Sharp, Toshiba, Hitachi,

LG etc. are supported. Other converter cards on the

market convert PAL video to VGA resolution for

LCD panels at 640x480 and therefore display

information is lost and the quality is lower. No

interlace or interfield motion (combing) artefacts

are seen when using the VIDEOMATE 3 to display

full motion video. Additionally, an analogue RGB

SuperVGA LCD panel at 262,000 colours. The card

differs from other video to LCD conversion

interfaces in that the PAL video is digitised, DE-

INTERLACED and scan converted using the unique

DICE chip from Genesis. All signal paths remain

digital throughout the

output is provided which enables deinterlaced video

to be displayed on a standard SuperVGA computer

monitor. 

For more details contact:  Norman Garland, Imagine Graphics Ltd.  Tel +44 (0)1727 844 744, Fax +44 (0)1727 811 660