seminar report

SEMINAR REPORT

ON

GRATING LIGHT VALVE TECHNOLOGY

Submitted by

Amit kumar

In partial fulfillment of the award of the degree of

Bachelor of Technology in

ELECTRONICS AND COMMUNICATION ENGINEERINGOf

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

SEPTEMBER 2010

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

Toc H INSTITUTE OF SCIENCE & TECHNOLOGY

Arakkunnam P.O, Ernakulam District, KERALA- 682 313

Toc H INSTITUTE OF SCIENCE & TECHNOLOGY

Arakkunnam P.O, Ernakulam District, Kerala – 682 313.

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

CERTIFICATE

This is to certify that the seminar entitled “Grating Light Valve Technology” submitted by “Amit

Kumar” of semester VII is a bonafide account of the work done by him under our supervision

during the academic year 2010-2011

Seminar Guide Head of the Department

Head of the Institution

.

ACKNOWLEDGEMENT

The satisfaction and euphoria that successful completion of any task would be incomplete sans

the mention of the people who made it possible, whose constant guidance and encouragement

crowd our effort with success.

First and foremost we would like to express our whole hearted thanks to the invisible, the

indomitable god for his blessings showered upon us in enabling us to successfully present the

seminar.

We would like to extend our heartiest thanks to the management of our college, who provided us

with necessities for the completion of the seminar. We feel highly privileged in making a mention

of Prof.(Dr.) V. Job Kuruvilla (Principal, TIST) for his co-operation and help.

We would also like to extend our heartfelt thanks to Asst. Prof. Deepa Elizabeth George

(H.O.D., ECE) for the inspiration inculcated in us and for the apt guidance.

It would be a grave error if we forget to take a mention of our guides Ms. Sangeetha C.P and

Ms.Soumya.K.S whose constant persistence and support helped us in the completion of our

seminar.

We also stand grateful to all teaching and non-teaching staff and fellow students for their constant

help and support.

ABSTRACT

The Grating Light Valve™ (GLV™) technology is a micromechanical phase

grating. . Operation is based on electrically controlling the mechanical

positions of grating elements to modulate diffraction efficiency. Thus by providing

controlled diffraction of incident light, a GLV device will produce bright or dark pixels

in a display system .With pulse width modulation, a GLV device will produce precise

gray-scale or color variations. Built using micro electromechanical system (MEMS)

technology, and designed to be manufactured using mainstream IC fabrication

technology, the GLV device can be made both small and inexpensively. A variety of

display systems can be built using GLV technology each benefiting from the high

contrast ratio, fill ratio, and brightness of this technology. In addition, GLV technology

can provide high resolution, low power consumption, and digital gray-scale and color

reproduction

TABLE OF CONTENTS

CHAPTER TITLE PAGE NO.

1 INTRODUCTION 01

2 FUNDAMENTAL CONCEPTS 02

3 OPTICS OF GLV

3.1 DIFFRACTION GRATING ANALYSIS 04

3.2 BASIC OPTICAL SYSTEM 06

4 BUILDING THE GLV DEVICE 09

5 CONTROLLING THE GLV 12

6 APPLYING THE GLV TECHNOLOGY

6.1- APPLYING THE GLV TECHNOLOGY 15

6.2- COLOR PRODUCTION 15

6.2.1- METHOD 1 16

6.2.1- METHOD 2 17

6.2.3- METHOD 3 18

6.2.4- METHOD 4 18

7 COMPARING THE GLV 20

8 CONCLUSION 21

FUTURE SCOPE 22

REFERENCES 23

CHAPTER 1INTRODUCTION

Semester: VIIBranch :Electronics &

CommunicationEngineering

Seminar Title: Grating light valve technology

1.1 INTRODUCTION

The Grating Light Valve (hereafter GLV) is a micromechanical light valve intended for

display applications.. The body of the device is a collection of ten beams stretched across a

frame. This frame is attached by a spacer to the substrate, leaving the beams suspended in air.

By moving the beams electrostatically it is possible to modulate the diffraction efficiency of light

incident on the structure.

As a light valve for display, the GLV has a number of interesting properties. GLV fabrication is

fairly simple, requiring only one mask step for basic devices and only three or four for complete

array fabrication. This should translate into low production cost. The GLV is capable of either

black-and-white (BW) or color operation with white light illumination. The pixels of the GLV are

extremely fast, switching in under 25 ns. Furthermore, the pixels are bistable with applied

voltage: it may be possible to operate the GLV and achieve active matrix performance with only

a passive matrix. The combination of speed and bistability may be used for spatial light

modulator applications as well as for simplifying the design of drivers (fast pixels can be

addressed by a passive matrix, while slow pixels require the increased complexity of an active

matrix structure).

Page No.1Toc H Institute of Science & Technology

Arakkunnam – 682 313

CHAPTER 2FUNDAMENTAL CONCEPTS

Semester: VII Branch :Electronics & CommunicationEngineering


2.1 FUNDAMENTAL CONCEPTS

A Grating Light Valve (GLV) device consists of parallel rows of reflective ribbons. Alternate rows

of ribbons can be pulled down approximately one-quarter wavelength to create diffraction effects

on incident light (see figure below).

( Figure 1:showing dark and bright state)

When all the ribbons are in the same plane, incident light is reflected from their surfaces. By

blocking light that returns along the same path as the incident light, this state of the ribbons

produces a dark spot in a viewing system. When the (alternate) movable ribbons are pulled

down, however, diffraction produces light at an angle that is different from that of the incident

light. Unblocked, this light produces a bright spot in a viewing system.

Page No.2Toc H Institute of Science & TechnologyArakkunnam – 682 313



.

If an array of such GLV elements is built, and subdivided into separately controllable

picture elements, or pixels, then a white-light source can be selectively diffracted to

produce an image of monochrome bright and dark pixels.

By making the ribbons small enough, pixels can be built with multiple ribbons producing

greater image brightness. If the up and down ribbon switching state can be made fast

enough, then modulation of the diffraction can produce many gradations of gray and/or

colors. There are several means for displaying color images using GLV devices. These

include color filters with multiple light valves, field sequential color, and sub-pixel color

using "tuned" diffraction gratings.

Page No.3Toc H Institute of Science & Technology

Arakkunnam – 682 313

CHAPTER 3OPTICS OF GLV

Semester: VI Branch :Electronics & CommunicationEngineering


3.1 Diffraction Grating Analysis

A diffraction grating is a periodic structure that affects either the amplitude or phase of incident

light. Typically the period is several times the wavelength of light. A detailed analysis of

diffraction gratings [Born 1980] shows that incident light is diffracted by the grating into several

directions which conform to the Bragg condition. Amplitude gratings are formed by alternating

stripes of absorbing and transmitting material. Phase gratings modulate the phase rather than

the amplitude of light.

The GLV is a micro-electromechanical phase diffraction grating. The amplitudes of the diffracted

modes of a 2.00 ~.tm period phase grating with rectangular grooves constructed from aluminum

as a function of groove depth are shown in Figure 2.1. The specular mode has a peak

reflectivity of 92% when no grooves are present (92% is the reflectivity of aluminum). This value

decreases as the light is diffracted rather than reflected. However, when the grooves are ?J2

deep, the reflectivity is again maximum. Shadowing effects (caused by reflections from the

sidewalls of the grating elements) limit this maximum reflectivity to 82%. The light that is not

reflected into the specular mode is diffracted. For small grating depths there is little diffraction.

As the round-trip depth approaches X/4 in phase, the diffraction peaks, with 41% of the light in

each of the first order diffraction modes.

The second module is the robot consisting of a microcontroller, a wireless camera and a

zigbee module. The microcontroller provides control to the movement of the robot and camera

and manipulates on the received data. The wireless camera takes the live video of the desired

area and transmits to the server wirelessly. The zigbee module transmits data collected from

the sensors.

Page No.4



Toc H Institute of Science & TechnologyArakkunnam – 682 313

(Figure 2:showing diffraction patterns)

Page No.5



Toc H Institute of Science & TechnologyArakkunnam – 682 313

3.2 Basic Optical Systems

Optical systems can be constructed to view either the reflected or diffracted light. The latter has

two clear advantages. Since the non-diffraction grating portions of the device, including bond

pads and other large areas, remain equally reflecting in both the “up” and “down” positions,

there will be a problem generating adequate contrast without the use of masking films or spatial

filters to remove the unmodulated light

The basis of BW operation was shown in Figure 2. When the beams are “up,” the device is

reflective, and the normally incident light is reflected back to the source. If the beams are

brought into the “down” position, then the pixel diffracts 82% of the incident light into the ±1

diffraction modes. Additional light is diffracted into higher order modes (about 10% of the

incident), but the optics used had too small an aperture to collect this light.

The optical systems were used in device testing. The illumination source was either a 250 W

metal halide arc lamp with an integrated reflector or a 40 Wtungsten-halogen lamp with

dielectric reflector. The light was condensed with ff2.4 optics and imaged without magnification

at an intermediate point. At the intermediate point the image was spatially filtered to insure

adequate collimation. Since collimation within the plane is essential for good contrast, the arc or

filament of the lamp is shown perpendicular to this plane. The source image was then collimated

and directed by a turning mirror onto




the face of the device. The specular reflection was returned to the lamp, while the

diffracted orders were collected by a projection lens placed just over a focal length away.

The distance between the device and the projection lens was adjusted to focus the image

on a distant screen. In this system the projection lens is used both for projection to the




screen as well as spatial filtering of the diffracted light. A telecentric stop was placed at a

distance of one focal length from the projection lens. At this plane, all rays from the

device plane with the same angle all pass though the same point, i.e., all the +1

diffraction order rays focus at one point while all the -1 rays focus at another. By placing

a stop with slits in it at those two points, all non-diffracted light is blocked from the

screen.


CHAPTER 4BUILDING THE GLV DEVICE

4.1 Building the GLV device

The following describes the materials, dimensions and packaging of a GLV device capable of

implementing a high-resolution display. The entire GLV device is designed to be built using

mainstream IC fabrication technology (e.g. photolithographic masking, deposition, etching,

metalization, etc.) to create the micro electromechanical systems (MEMS) that make up the

GLV device. The GLV ribbons are built using silicon nitride, then coated with a very thin layer of

aluminum (see figure 2). By making the aluminum layer very thin, one avoids some of the

surface roughness that otherwise scatters the light reducing the contrast ratio.

(Figure 3: Build using IC fabrication technology)




In one implementation which Silicon Light Machines has built, the ribbon lengths are 20 μm, and

the ribbon pitch is 5 μm. The pull-down distance is approximately 1300 Angstroms, or

approximately onequarter wavelength of green light. With these dimensions, a set of four

ribbons (two fixed and two movable) produces a 20 μm square pixel (see figure 3).

( Figure 4: A single pixel consists of a pair of fixed and a pair of movable ribbons.)

The "up" position of the ribbons is maintained by the tensile stress of the silicon nitride material.

With no other forces applied, the ribbons will naturally "snap back" into an upward position. By

integrating.




electrodes below the ribbons, and applying different voltages to the ribbons and the bottom

electrodes, an electrostatic attraction force will pull the movable ribbons downward. The

deflection distance is determined during manufacture. The basic GLV pixel is defined using a

simple, 2-mask IC process. Silicon Light Machines has built devices using only 7 masks. In

general, the more masks needed to manufacture an IC, the higher the initial cost. And, each

additional masking step has a negative impact on yield (i.e. the percentage of good versus faulty

components). Thus, the simple GLV design should provide lower initial costs and higher yields

compared with light-valve technologies that require more complex manufacturing. When the

GLV device is finished and tested, a clear glass lid is fixed above the ribbons area sealing in a

dry nitrogen environment for pressure equalization and to prevent oxidation.

As shown in figure 4, additional electronic driver and control logic is built into a complete,

lightvalve, multi-chip module.

(Figure-5:shows packaging)


CHAPTER 5CONTROLLING THE GLV DEVICE



5.1 Controlling the GLV device

To control a GLV-based device, one simply directs the up and down ribbon movement of this

two-state technology. As mentioned previously, the ribbons will naturally assume the up state.

To pull them down, one must apply a voltage difference (e.g. the switch-down voltage, V2)

between the movable ribbons and bottom electrodes. Interestingly, the ribbons maintain their

down state even as the voltage differential is reduced. Thus, one can pull the ribbon down with a

switch-down voltage (V2), and maintain that state with bias voltage, Vb, such that V1<Vb<V2

volts (see figure 5), where V1 is the switch-up voltage at which the ribbon returns to its up state.

We’ve built GLV devices such that V2/V1 is approximately 2.

(Figure 6:shows ribbon hysteresis)




This ribbon hysteresis permits one to maintain present pixel states with a bias voltage, without

drawing current. In other words, a static pixel configuration can be maintained with practically

zero power consumption. Other display technologies require significantly more complex control

circuits to maintain pixel states.

.

This ribbon hysteresis offers mechanical memory and zero-power pixel-state retention.

Switching time is approximately 20 nanoseconds. The up and down ribbon switching occurs

very quickly. The GLV device described here switches in 20 nanoseconds. That is roughly a

million times faster than conventional LCD display devices, and about 1000 times faster than

another light-valve technology (i.e. Texas Instruments DMD micro-mirror technology).

The reasons for the high speed are the small size and mass, and small excursion, of the GLV

ribbons. This high-speed switching offers several benefits. At these speeds, it is easier to

streamline drive electronics and to simplify the memory requirements. There is no need to

provide buffers or delay functions to complement the mismatch in speeds between electronic

devices and this MEMS device. Another speed advantage is the ability to modulate, over a wide

range, the time ratio of up-to-down states (or dark and bright states) which produces the effect

of shades of gray or color variations. GLV switching speeds make it easy to implement an 8-bit

or greater gray scale, and are fast enough to support colors and grays over a 1000-to-1 dynamic

range. This is much broader gray and color accuracy than is produced using LCD technology,

for example. The combination of speed and mechanical memory (e.g. ribbon hysteresis) make

controlling the GLV device very simple.




An elegantly simple row and column addressing scheme can be used, and passive matrix

(rather than the more complex active matrix) pixel control is all that is required. This eliminates

the need for any transistors in the GLV array itself, greatly simplifying the manufacturing

process. The GLV device thus lends itself to an easy interface to other display system

electronics.

Contrast ratios, fill ratios and optical efficiencies are important metrics for distinguishing among

various display technologies. High contrast ratios provide crisper images. A GLV system that is

built using relatively inexpensive optics exhibits a contrast ratio of better than 200-to-1. Fill ratios

— the ratio of optically active area to total pixel area — is already better than typical LCDs. In a

prototype GLV array built using mature 1.25 micron design rules, fill ratios of 67.5 percent was

achieved compared with 60 percent for LCDs. Using more modern, smaller, design rules, fill

ratios of 80 percent are expected.

Finally, optical efficiency for reflective devices is naturally higher than that for transmissive

devices. In a typical GLV prototype, where the optical system collects +/- 1 order of diffraction,

about 81 percent of the incident light can be collected in the bright state. This makes for brighter

images compared with other technologies when operated at comparable power consumption

levels.


CHAPTER 6APPLYING THE GLV TECHNOLOGY



6.1 Applying the GLV technology

In general, the GLV device can be used to build a relatively simple display system (see figure 6.)

Video input is format converted and then input to a digital driver. The latter interfaces directly

with the GLV device. Light is diffracted by the GLV device into an eyepiece for virtual display, or

into an optical system for image projection onto a screen.

(Figure 7:shows a simple interface to upstream electronics)

6.2 COLOUR PRODUCTION

There are several ways in which coloured images can be produced. Some of the methods are

described below




6.2.1 METHOD 1

One way of reproducing color images is by using different ribbon pitch to create a red-green-

blue pixel "triad" instead of the monochrome pixel described earlier (see figure 7). In such a

system, white light is introduced at an angle slightly off-axis to the GLV device. In essence, the

red area, having the widest pitch, refracts red light normal to the GLV plane while green and

blue light is refracted at other angles. The green and blue areas, having narrower pitch, do the

same for green and blue light, respectively. Color is produced by reducing the slit width to allow

only a limited bandwidth about each of the primary colors to be selected.

(Figure 8: color production by using different spacing between ribbons.)




6.2.2 METHOD 2

In a frame-sequential projection system (figure 8) a white light source is filtered sequentially (by

a spinning red-green-blue filter disk, for instance). By synchronizing the image data stream’s

red, green and blue pixel data with the appropriate filtered source light, combinations of red,

green and blue diffracted light is directed to the projector lens. In this system, as shown, a

turning mirror is used both to direct light onto the GLV device, and as an optical stop blocking

reflected light.

(Figure 9: color display can be built using a single light source, single GLV, and rotating RGB

filter disk.)




6.2.3 METHOD 3

An even simpler, handheld, color display device (see figure 9) uses three LED sources (red,

green and blue). A single GLV device diffracts the appropriate incident primary -color light to

reproduce the color pixel information sent to the controller board.

(Figure 10: An even simpler color display can be built with 3 LEDs (RGB) and a single GLV)

6.2.4 METHOD 4

A more elaborate and accurate color projection system can be build using three GLV devices.

By passing the source’s white light through dichroic filters, red, blue and green light are incident

on three separate GLV devices. Diffracted light is collected and directed through the optical

system to a viewing screen




This represents a much smaller and lower-cost solution, say, to the three-tube projection

systems now used for large-screen projection of PC images and videos. An implementation

scheme (see figure 10), shows the light source, optical components, and three-GLV module.

(Figure 11: A three-GLV color display solution is shown for a large-screen projector.)


CHAPTER 7COMPARING THE GLV



COMPARING TO OTHER DISPLAY TECHNOLOGIES

To succeed as an alternative to existing display technologies, GLV technology must

demonstrate some compelling benefits, and it does. Compared to its closest alternative —

micro-mirror light valve technology — the GLV device is much simpler to fabricate, requiring

only 7 mask steps. GLV devices use smaller, lighter, mechanical structures that move through

smaller excursions than alternative light-valve technologies. Hence, it is faster, requires less

external memory and no transistors in the MEMS array.

Several orders of magnitude faster than conventional LCDs and other light-valve technologies,

GLV technology matches much more closely the speeds of its electronic interface components.

As a result, the interface is simpler. GLV speeds also provide for higher gray scale and color

variation accuracy. For example, a GLV device can be used to build a 10-bit -per-pixel, high-

resolution display, compared with 8- bit-per-pixel, LCD displays.

Because GLV devices are built using mainstream IC fabrication technology, ribbon dimensions

are easily scaled allowing the production of smaller, lower-cost, devices with higher resolution

and fill ratios.

The GLV technology’s MEMS architecture is exhibiting very encouraging reliability. Early

experiments have shown no ribbon fatigue after 210 billion ribbon switching cycles. This is

equivalent to a television display system running non-stop, without failure , for 15 years.




With their higher optical efficiencies, GLV systems can deliver higher levels of brightness per

watt of power consumed. Their small size makes it practical to build over a million pixels in a 1.3

inch diagonal. Coupled with their mass producibility, this makes the GLV a candidate for building

high-resolution, low cost displays. And their inherent zero-power pixel-state retention make them

ideal for use in small, battery powered devices.

In essence, the GLV technology promises to revolutionize display system design by making

them smaller, cheaper, brighter, less power consuming, and with higher resolution.


CHAPTER 8CONCLUSION



CONCLUSION

The grating light valve is a relatively new display technology. It is based on reflection

phase gratings of electrically controllable depth. When the beams are suspended “up”

from the substrate the device has a minimum of diffraction, and normally incident light is

reflected.

If a potential is applied to bring the beams into contact with the substrate, then the device

diffracts 80% of the light into the first order diffraction modes, which are then collected by

a Schlieren optical system.

The contrast ratio was measured to be 20:1 for black-and-white displays. A contrast of

80:1 can be achieved with improved processing techniques. . Improved lamp collimation

should improve the saturation of the colors. Contrast ratios for optimized color devices

should exceed 200.

Pixels as small as 6x20 ~Lmare possible.

The position of the beams is bistable for intermediate voltages. For a qualitative

understanding, the beams can be modelled as strings under tension. To get better

quantitative results, a full integration of the fourth order beam equation can be used.

Switching voltages between 5 and 10 V can be used.

The device operation is not much affected by temperatures in excess of 200 °C.




FUTURE SCOPE

The aging characteristic of micromechanical displays are not well understood.

It is not clear what sort of packaging is necessary to ensure long life of the device.

Using conductive beams can help reduce the gap b/w the top and bottom electrodes.

This increase in capacitance would cause a substantial decrease in the first instability

voltage. So a research is in progress to determine its effect.

It is yet to determine the effect of surface roughness on contrast ratio.

With additional work in the above mentioned areas it is possible that the GLV will

someday be commercially produced.




REFERENCES

1. Hitoshi Tamada, Ayumu Taguchi, Kazunao Oniki, Kunihiko Saruta* and Yasuyuki Ito ©2006 IEEE

2. G. Abla, G.Wallace, D. Schissel, and et al. Shared display wall based collaboration environment in the control room of the DIII-D national fusion facility. In WACE, 2005.

3. .

4. Proceedings of the IEEE Virtual Reality Conference (VR’06) 1087-8270/06 $20.00 © 2006 IEEE

5. R. Apte, F. Sandejas, W. Banyai and D. Bloom, " Grating Light Valves for High Resolution Displays, "Solid State Sensors and Actuators Workshop, June 1994.

6. M. Born and E. Wolfe, Principles of Optics, Pergamon Press, New York, 1959.


Semester: VI Branch :Electronics & CommunicationEngineering

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