special report – mems accelerometers for modern defence applications

MEMS Accelerometers for Modern Defence Applications

S P E C I A L R E P O R T

Published by Global Business Media


A Leap Forward in Sensor Technology: MEMS Accelerometers

Critical Parallel Work in the Defence Industry to Deliver Precision Targeting

The Military Helicopter Market Shows Future Market Opportunities for MEMS Accelerometers

Sponsored by

www.msinstruments.co.uk

SPECIAL REPORT: MEMS ACCELEROMETERS FOR MODERN DEFENCE APPLICATIONS


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Contents

Foreword 2Martin Richards, Editor

MEMS Accelerometers for Modern Defence Applications 3Jean-Michel Stauffer, VP Sales & Marketing, Colibrys (Switzerland) Ltd.

Introduction MEMS AccelerometersModern Defence Applications and RequirementsProduct Study: Sensor, Assembly and Packaging, ElectronicsMEMS SensorAssembly and PackagingElectronicsA Success Story: Guidance Application for Smart MunitionsConclusion

A Leap Forward in Sensor Technology: MEMS Accelerometers 7Marushka Dubova, Defence Correspondent

Early Accelerometers and Inertial Navigational DevicesAn Introduction to MEMS TechnologyThe Originator of Nano TechnologyThe Role of WestinghousePrecision Etching Moves ForwardA Revolution in Safety for the Automotive Industry

Critical Parallel Work in the Defence Industry to Deliver Precision Targeting 10Meredith LLewelyn, Lead Contributor

British Expertise Bought by Goodrich Helps Space ProgressExtensive Defense Market Penetration for MEMS Accelerometers by GoodrichThales: An Important ContributionOvercoming Critical Problems with MEMS AccelerometersDevelopmental Hurdles Ahead

The Military Helicopter Market Shows Future Market Opportunities for MEMS Accelerometers 12Don McBarnet, Staff Writer

The Military Helicopter MarketAnother View of the MarketThe Implications for MEMS Accelerometers of the Explosion in Smart Phones for the Defence Market

References 14

WWW.DEFENCEINDUSTRYREPORTS.COM | 1


S P E C I A L R E P O R T



A Leap Forward in Sensor Technology: MEMS Accelerometers

Critical Parallel Work in the Defence Industry to Deliver Precision Targeting

The Military Helicopter Market Shows Future Market Opportunities for MEMS Accelerometers

Sponsored by

Foreword

The fast changing world of MEMS accelerometers is the subject of this

issue of Special Report. This fascinating world of micromachined

silicon chips is delivering huge impact on the sensor market where

MEMS accelerometers are now able to deliver ruggedness, fl exibility and

temperature resilience to provide low cost, lightweight capabilities that

would have been a technologists dream 20 years ago.

The Report opens with an overview of the ever-increasing role of MEMS

accelerometers in high-end modern defence applications in the Mil Aerospace

market. It goes on to examine advantages of MEMS accelerometers over

conventional techniques for manufacturing processes to produce microscopic

mechanical structures and highlights their use for IMU and AHRS on aircraft,

helicopters, UAV/ULV, short range missiles and guided munitions. MEMS sensors

have been developed over many years and the Report gives an insight into their

design and manufacture, using the very latest techniques.

The next section in the Report looks at how 20th century developments in the

United States and Europe produced not only the familiar revolution in computer

technology but a drive to miniaturize the product. Once the preserve of massive

Intercontinental Ballistic Missiles they are now of suffi cient quality and relatively

low cost to have a massive range of applications in defence: for fi xed wing,

rotorcraft and land vehicles, as well as personal computers on the ground to

deliver situation awareness.

The parallel development of a burgeoning commercial market for

accelerometers and how this has had useful spin offs for defence is covered

in the third piece. The ubiquitous airbag and now the penetration of the smart

mobile phone developing at speed for the popular market allow the defence

market to benefi t from the incremental knowledge gained. The defence fi eld

will always demand special qualities for special missions, and the industry is

going a long way to meet these needs.

In the fi nal section, the future opportunities for MEMS accelerometers are

reviewed with particular emphasis on their application to the military helicopter

market. It is anticipated that the market for MEMS and MEMS sensors will

experience double-digit growth from 2009 to 2015 and that this will be

accompanied by a spin-off in the development of MEMS accelerometers, which

will feed through to the defence market.

Martin Richards

Editor


2 | WWW.DEFENCEINDUSTRYREPORTS.COM



MEMS Accelerometers for Modern Defence ApplicationsJean-Michel Stauffer, VP Sales & Marketing, Colibrys (Switzerland) Ltd.

1. IntroductionMicro Electro Mechanical Systems (MEMS) also known as ‘microsystems’ in Europe describe both a manufacturing process, generally based on Silicon (Si) wafers, and sensor elements, which can be accelerometers, vibration, seismic or tilt sensors but also gyro, pressure, flow or gas sensors etc.

MEMS manufacturing processes provide an alternative to conventional macro-scale machining and assembly techniques. This technology derives from the microelectronics industry and combines the conventional techniques developed for integrated circuit (IC) processing with specific MEMS processes, to produce microscopic mechanical structures. Thin layers of materials are deposited onto a Silicon wafer and used as mask to selectively etch away the material, revealing microscopic 3D structures such as beams, diaphragms, membranes, levers or springs. This process, also known as bulk micromachining, was developed during the early 1980s and has been largely improved during the years with the introduction of innovative etching techniques such as DRIE (Deep Reactive Ion Etching) and new micromachining concepts and techniques such as Silicon Wafer Bonding and Wafer Level Packaging.

MEMS devices incorporate miniaturized mechanical structures, with minimum dimensions typically ranging from 1 to 50µm (equal or smaller than a human hair), with electronic components in a package.

2. MEMS AccelerometersThe success of MEMS accelerometers started in the early 90s with the acceptance of the product by the automotive industry. Today, the adoption of MEMS motion sensors is continuously growing with the generalized use of accelerometers

and gyroscopes in consumer electronics. While, in the beginning, MEMS accelerometers replaced existing devices, they have become real enablers for new functionalities, previously not possible, such as camera stabilization, human body control, cell phones and gaming. The key success factors in these applications are extremely low cost, reliability and low power for moderate performance (4 to 12 bit resolution). The market for automotive and consumer motion sensors is increasing tremendously with an estimated growth of 23% in 2011 and by 2014 is expected to surpass the current leading MEMS applications, which are inkjet printing and projector devices.

Within the last few years, a similar process has started for high-end MEMS accelerometers. High performance MEMS products are already successfully used and of increasing interest in various applications in the Mil/Aerospace, Industrial and Instrumentation, Testing and Energy markets.

To conquer new high-end applications, one of the fi rst barriers is technical, relating mainly to the stability (1 to 100 ppm of the full scale) and the resolution requirements (16 to 24 bits). The other success factors for MEMS accelerometers are lower cost, excellent general performance –

AbstractMEMS accelerometers penetrate more and more high-end and modern defence applications in the Mil Aerospace market, replacing the well established, expensive and fragile electromechanical devices. The driving forces for this revolution are the need for devices offering the same or even better performance, at lower cost, lower power and smaller size and that can be signifi cantly more robust.

Figure 1. The market of accelerometers



The Military and

Aerospace markets

for motion sensors

cover a wide range of

applications generally

characterized by long

qualifi cation cycle times

and strict requirements

in terms of continuity

of supply, stability of

design and lifetime

technology sustainability.

sometimes even surpassing those of traditional electro-mechanical devices – robustness, power and size.

To address these market requirements, attempts have been made to use upgraded versions of automotive or consumer sensors but with relatively little success. It turns out that the basic technologies developed for automotive and consumer applications, mainly driven by cost requirements, are not adequate to reach the required performance levels. This limitation is generally characterised by a different business model, by the volume and qualifi cation requirements or by the long term commitments that are radically different for automotive/consumer compared to modern defence applications.

In the world of motion sensors, Colibrys has a very clear and unique position and focuses fully on the high-end markets with an appropriate business model and with technologies specifi cally designed for performance.

3. Modern Defence Applications and RequirementsThe Military and Aerospace markets for motion sensors cover a wide range of applications generally characterized by long qualification cycle times and strict requirements in terms of continuity of supply, stability of design and lifetime technology sustainability. This market continuously drives innovation and increasingly complex multidisciplinary technology integration. For several years, the various families of Colibrys accelerometers have gained worldwide acceptance, and modern defence applications are extensively taking advantage of inertial accelerometers for IMU and AHRS on aircrafts, helicopters, UAV/ULV, short range missiles and guided munitions. An accelerometer can also be used for vibration measurements in applications such as fl ight testing, wind tunnel testing of new structures, transportation monitoring or vibration monitoring systems on fi xed wings and helicopters for HUMS and preventive maintenance. As tilt sensors, they are used for camera, radar and any other platform stabilization, automatic guns, as well as range fi nding and north fi nding. Finally, as seismic sensing they offer solutions for homeland security, border or perimeter security, unattended ground sensors and buried sensors.

4. Product Study: Sensor, Assembly and Packaging, ElectronicsThe three key ingredients needed to make a high performance accelerometer are; a highly stable MEMS sensor; a good and very stable assembly and packaging technology; and a high-quality electronic. The advantage of

this technology over the traditional electro-mechanical solutions comes mainly from the lower manufacturing cost of MEMS devices and the volume scalability. Performance such as stability relies on the excellent quality of the raw material (silicon wafers) and capability of the design to meet the performance with manageable manufacturing tolerances and manufacturing processes, avoiding lengthy and expensive burn-in and selection procedures. High-end MEMS accelerometers need minutes to hours for testing whereas electromechanical devices can sit on test benches for days.

4.1 MEMS SensorThe latest Colibrys MEMS sensors are based on the proven out-of-plane capacitive technology. This concept has been compared to the in-plane SOI approach and clearly shows technical and performance advantages for high-end applications. Out of plane design has a larger gain provided by a larger capacitive change per mass displacement, thanks to small gaps and large capacitor areas. Furthermore out of plane design has lower Brownian noise due to the large mass.

The concept shown in Figure 2 has been used for many years on MS8000 and MS9000 products. This technology gives excellent performance and is currently used in many aerospace, defence, industrial and instrumentation applications. In order to increase the performance even further, a new generation of MEMS silicon sensors is currently under development to address mainly two issues that limit performance. The first aspect is linked to the die-attach stress that induces mechanical deformations and leads to bias shift, which is a signifi cant contributor to the temperature coeffi cient and long term stability. The second aspect is the squeezed fi lm damping

Figure 2. Cross section of the-out-of plane MEMS accelerometer and view of the three wafers ready to be assembled by SFB (Silicon Fusion Bonding)



that generates a strong peak beyond the device bandwidth, with the consequence, potentially, to generate a meaningful contribution to the rectifi cation error.

The current design under development is based on the well-established bulk silicon micromachining process, using three wafers assembled by low pressure silicon fusion bonding. It combines also wet and dry (DRIE) etching steps, providing a better control of the squeeze film damping and allowing the integration of more complex structures.

The stability of the MEMS device is determined by measuring the MEMS with the open loop electronics. It is characterized by the shift of the proof mass at 0 g after harsh treatments such as temperature cycling [-55°C to 125°C], harass testing, vibration and shocks. The movement in the proof mass after such an accelerated lifting is down to sub nanometers, which represent a bias variation of less than a milli-g.

This MEMS technology has been adopted as the basis for all new generations of Colibrys high performance accelerometers.

4.2 Assembly and PackagingThe sensor assembly is extremely critical for high precision measurements under harsh environments. Colibrys has chosen a multi chip module (MCM) approach combining the MEMS device and electronics in a hermetically sealed ceramic package. The MEMS die is attached with a propriety low stress process assuring that the intrinsically good performances of the MEMS are not degraded by the assembly process. The package has also to protect the sensor and the related electronics from external perturbations such as humidity. The MCM modules are produced to MIL standards ensuring long term stability and reliability. This contrasts with a plastic packaging approach, non-hermetic by defi nition and commonly used in automotive/consumer

devices, when the required performances, and especially the long term stability, cannot be demonstrated and qualifi ed.

4.3 ElectronicsThe electronics associated with the MEMS sensor is crucial to obtain high performance. There are two ways to operate a capacitive MEMS sensor. For the open loop approach, the mechanical plate defl ection is determined by the associated capacitance change. This concept gives excellent results and is small and low power. However it has limitations in terms of the ultimate noise and linearity. Typically, open loop sensors are good where 16 to 20 bit resolution is needed. For closed loop (or servo) accelerometers, the proof mass is maintained in a fi xed position and the inertia is compensated by electrostatic forces. With this concept the ultimate limits of MEMS sensors can be pushed further in terms of stability, noise and linearity. Closed loop sensors cover the resolution range from 20 to 24 bits and are likely to go even beyond in the future.

For its open loop sensors, Colibrys uses a patented self-balancing bridge concept implemented in an ASIC. This electronic provides very stable, low noise and highly linear analogue output with low power consumption (~ 1 mW).

For the traditional closed loop accelerometers, Colibrys uses a servo concept based on analogue voltage force feed-back. This concept is used in the Colibrys SiFlex seismic sensors family.

Ultimate performance can be achieved by placing the MEMS sensor in a Sigma Delta servo loop and applying electrostatic force pulses to rebalance the proof mass position. This concept was initially developed for sensors used in seismic imaging. Currently Colibrys in Switzerland is adapting this concept to navigation grade accelerometers.

Figure 3. Open view of a Colibrys MS9000 accelerometer



The current design under

development is based on

the well-established bulk

silicon micromachining

process, using three

wafers assembled by

low pressure silicon

fusion bonding.

Figure 4: The ASIC must be mounted as close as possible to the sensor

The Sigma delta servo loop allows not only exceptional performances in terms of bias stability, noise (i.e. 20 to 24 bit resolution) and linearity but provides directly a digital output signal. This concept is implemented in a small front-end ASIC and combined with digital signal processing in an FPGA. This concept uses somewhat more power than the open loop sensors but still four times less than comparable traditional electromechanical devices.

5. A Success Story: Guidance Application for Smart MunitionsMEMS accelerometers are precise even under harsh environment. One of the best examples of utilization of the MEMS sensor technology in a very rugged defence environment is the M982 Excalibur, a 155mm extended range guided artillery shell, developed by United States based Raytheon Missile Systems and BAE Systems Bofors, a Swedish defence company and a subsidiary of BAE Systems Land and Armaments. This product includes an inertial control system with the goal to increase accuracy, minimize collateral damage and improve efficiency when complex terrain limits the effectiveness of conventional projectiles and makes it diffi cult in terms of logistics and supply. A major challenge for the control system is the inertial sensor that

has to operate at full accuracy even after the extremely harsh launch environment.

This smart munition, integrating Colibrys MEMS accelerometers, is capable, after an initial launch characterized by a gun hard shock of about 20,000g, to be guided by an inertial unit to the target within a precision of a few meters or less at a distance of approximately fi fty kilometers.

6. ConclusionThis actual example is a perfect illustration of how MEMS accelerometers are found in more and more high-end applications in the defence and aerospace market, replacing well-established, expensive and fragile electromechanical devices. It demonstrates, also, that the technology is being employed in new applications due to its technical and economic advantages. Many other applications in various Mil aerospace and civilian domains are using this technology and contribute to the success of MEMS.

Figure 5: Schematic of the sigma – delta close loop electronic from Colibrys



A Leap Forward in Sensor Technology: MEMS AccelerometersMarushka Dubova, Defence Correspondent

THE EXTREMELY rapid development in capability in MEMS accelerometers

in the last fi ve years is revolutionizing how armed forces can deliver precision in munitions, missiles and aerospace. Such is the pace in development of the technology spurred on by developments in the mobile phone and automotive sector that the military market alone is estimated to stand at $1.55Bn dominated by defense and aerospace applications, according to a 2009-2115 Yole Développement, market prediction.2 Yole sees this market growing at a 9% annual growth rate, to reach $2.60Bn in 2015. They see industrial, commercial, naval and offshore applications as the most dynamic with 16.5% yearly growth, where the aerospace and defense markets will be limited to a 5.5% and 6.8% annual growth.

What are the origins of this signifi cant change in sensor technology?

Early Accelerometers and Inertial Navigational DevicesGyroscopes and accelerometers provided the necessary signals for navigation for missiles during World War Two. Gyroscopes measure rotation, accelerometers give speed, integrating speed gives direction travelled, and therefore the essential ingredients for “dead reckoning” are known. Using gyros and accelerometers is called inertial navigation.3 The first inertial navigators according to Lawrence were used in the German V1 and V2 weapons. After the war a group of German scientists under Werner Von Braun developed this technology at Redstone Arsenal in Huntsville, Alabama for ICBMs and spacecraft. In the 1960s the Apollo program took

“For many navigation applications, improved accuracy/performance is not necessarily the most important issue, but meeting performance at reduced cost and size is. In particular, small navigation sensor size allows the introduction of guidance, navigation, and control into applications previously considered out of reach (e.g., artillery shells, guided bullets). Three major technologies have enabled advances in military and commercial capabilities: Ring Laser Gyros, Fiber Optic Gyros, and Micro-Electro-Mechanical Systems (MEMS) gyros and accelerometers”1 Neil M. Barbour, Charles Stark Draper Laboratory, Cambridge, USA for NATO



In a key development that

advanced etching in 1986,

IBM developed a micro

device called the atomic

force microscope (AFM).

inertial guidance into space and now according to Lawrence they are used in “smart munitions”.

An Introduction to MEMS TechnologyThe Southwest Center for Microsystems Education and The Regents of University of New Mexico4 describe the diverse origins of the technology and its uses. They assert that the starting point was the 1947 Invention of the Point Contact Transistor. This uses electrical current or a small amount of voltage to control a larger change in current or voltage. Transistors are the building blocks of computers, cellular phones, and all other modern electronics. In 1947, William Shockley, John Bardeen, and Walter Brattain of Bell Laboratories built the fi rst point-contact transistor. The fi rst transistor used germanium, a semi-conductive chemical. Taking it further in 1954, C.S. Smith discovered that the piezoresistive effect of a semiconductor could be several magnitudes larger than that of metals. This discovery showed that silicon and germanium could sense air or water pressure better than metal – a critical development. Many MEMS devices such as strain gauges, pressure sensors, and accelerometers utilize the piezoresistive effect in silicon. Strain gauges began to be developed commercially in 1958. The Kulite Corporation was founded in New Jersey in 1959 as the fi rst commercial source of silicon strain gages. Prior to the invention of the IC (Integrated Circuit) there were limits on the size of transistors. They had to be connected to wires and other electronics. An IC includes the transistors, resistors, capacitors, and wires in one unit. So if a circuit could be made altogether on one substrate, then the whole device could be made smaller. In 1958, Jack Kilby from Texas Instruments built a “Solid Circuit“ on one germanium chip:

1 transistor, 3 resistors, and 1 capacitor. Shortly after, Robert Noyce from Fairchild Semiconductor made the fi rst “Unitary Circuit“ on a silicon chip and was awarded the fi rst patent.

The Originator of Nano TechnologyIt was from this background that Richard Feynman sparked the idea of micro and nano technology in 1959 with a presentation at a meeting of the American Physical Society in 1959. Feynman introduced the possibility of manipulating matter on an atomic scale. He was interested in denser computer circuitry and microscopes, which could see things much smaller than is possible with scanning electron microscopes.

The Role of Westinghouse In 1964, Harvey Nathanson from Westinghouse produced the first batch fabricated MEMS device. This device joined a mechanical component with electronic elements and was called a resonant gate transistor (RGT). The RGT was a gold resonating MOS (metal oxide semiconductor) gate structure. It was approximately one millimeter long and it responded to a very narrow range of electrical input signals. It served as a frequency fi lter for ICs. The RGT was the earliest demonstration of micro electrostatic actuators. It was also the fi rst demonstration of surface micromachining techniques. In 1971, Intel publicly introduced the world’s fi rst single chip microprocessor, the Intel 4004. It powered the Busicom calculator. This invention paved the way for the personal computer. “Electrochemically Controlled Thinning of Silicon” by H. A. Waggener illustrated anisotropic etching of silicon (removes silicon selectivity). This technique is the basis of the bulk micromachining process. Bulk micromachining etches away the bulk of the



silicon substrate leaving behind the desired geometries. Fabricating these micromechanical elements requires selective etching techniques such as bulk etching.

In the 1970’s, Kurt Peterson from IBM research laboratory developed a micromachined pressure sensor using a silicon diaphragm. In another development, MEMS technology was used to manufacture the nozzles for Hewlett Packard’s development of Thermal Inkjet Technology (TIJ). In the early 1980s Karlsruhe Nuclear Research Center in Germany developed LIGA. LIGA is a German acronym for X-ray lithography (X-ray Lithographie), Electroplating (Galvanoformung), and Molding (Abformung). It allows for manufacturing of high aspect ratio microstructures. LIGA structures have precise dimensions and good surface roughness.

Precision Etching Moves ForwardIn a key development that advanced etching in 1986, IBM developed a micro device called the atomic force microscope (AFM). The AFM maps the surface of an atomic structure by measuring the force acting on the tip (or probe) of a microscale cantilever. The cantilever is usually silicon or silicon nitride. This very high-resolution type of scanning probe microscope offers a resolution to fractions of an Angstrom. The eighties were to prove a critical decade when the first rotary electrostatic side drive motors were made at University of California at Berkeley. In follow-on developments in 1993, the Microelectronics Center of North Carolina (MCNC) created MUMPS a (Multiuser MEMS Process) – a foundry meant to make microsystems processing highly accessible and cost effective for a large variety of users by a three-layer polysilicon surface micromachining process. In 1998, Sandia National Labs developed SUMMiT IV (Sandia Ultra-planar, Multi-level MEMS Technology 5). This process later evolved into the SUMMiT V, a fi ve-layer polycrystalline silicon surface micromachining process.

A Revolution in Safety for the Automotive IndustryIn 1993, Analog Devices were the fi rst to produce a surface micromachined accelerometer in high volume. The automotive industry used this accelerometer in automobiles for airbag deployment sensing. This meant that, in the event of a crash or sudden harsh braking, the change in pressure on the accelerometer would trigger the airbag to save the passengers from impact and whiplash. It was sold for $5 – a reduction in price from $20. It was highly reliable, very small, and very inexpensive. It was sold in record-breaking numbers, which increased the availability of airbags in automobiles.



Because of their use

in operational areas, in

aircraft, in vehicles and in

the fi eld during confl ict,

MEMS accelerometers

have to be especially

rugged and resilient.

Critical Parallel Work in the Defence Industry to Deliver Precision TargetingMeredith LLewelyn, Lead Contributor

THE RELATIVE fall in the price of MEMS accelerometers in the commercial

market had significant implications in the defence field. The defence industry was able to develop widespread and important uses for accelerometers in aerospace, munitions and land vehicles. For example, BAE SYSTEMS produced inertial sensors and systems, including silicon-MEMS inertial based products for automotive, commercial and military markets. They developed a miniature MEMS inertial measurement unit (IMU). They claim their SiIMU02™ is capable of surviving and performing after the massive shock and vibration of a guided projectile gun-launch event, and is small enough to fit into next generation small caliber guided rockets and missiles. The robust structure of the gyro permits it to survive and operate after a 23,000g gun-launch shock.5 They also partnered Swiss producers of MEMS accelerometers for UK army next generation light anti-tank weapon (NLAW) missile guidance contracts. The aim was to move beyond the older technology of expensive and fragile ‘vibrating quartz’.

British Expertise Bought by Goodrich Helps Space ProgressOn the other side of the Atlantic, Goodrich

Corporation gyroscopes have successfully passed in orbit testing on the European Space Agency’s (ESA) Earth Explorer CryoSat-2 satellite during a mission to detect shifts in global ice cover. The Goodrich Micro Electro-Mechanical System (MEMS) gyros were the smallest ever fl own by ESA and were used to monitor the satellite’s rate of spin. They were integrated into the SiREUS rate sensor to form Europe’s fi rst MEMS-based device to be used for space vehicle navigation. At the heart of the SiREUS rate sensor are three 1-square-centimeter (0.155-square-inch) MEMS gyros from Plymouth, UK-based Atlantic Inertial Systems (AIS), which was acquired by Goodrich in December 2009.6

Extensive Defense Market Penetration for MEMS Accelerometers by GoodrichThe penetration of accelerometers and sensors systems into the defence market is remarkable. They have multiple applications across the rotary blade and fi xed wing military air lift capability performing a multitude of complex tasks: angle of attack and stall warning systems, electric brake control and actuation systems, electronic flight bags, electro-mechanical actuation systems, engine sensors, fuel measurement and management systems, ice detection and protection systems, rate gyros and inertial sensors, temperature sensors, vehicle health



management systems data recorders / servers / players to name a few.7 Such is the success of the Goodrich enterprise that in 2010/11 they are expanding their production in Minnesota with a 57,000 square foot facility for its Sensors and Integrated Systems (SIS) division in Burnsville.

Thales: An Important ContributionBut Goodrich is not alone. Thales, another prime contractor, has produced considerable research and development in its avionics division in Valence, France. THALES Avionics has twenty years of experience in quartz and silicon MEMS design and manufacturing and is recognized as a leader by the French Ministry of Defence (MOD) in this fi eld. MEMS pressure sensors and accelerometers are manufactured in large volume and used for safety-critical applications. Thales technology policy focused on planar architecture, die vacuum packaging, and deep reactive ion etching (DRIE), allowing good characteristics for sensors in development. Development was carried out on a Silicon Vibrating Beam Accelerometer single chip. Its operating principle is described as two resonators in push-pull configuration. A tuning fork planar rate gyro was also developed with exactly the same technology for industrial effi ciency. They are also working on gyro-compassing grade inertial sensors to be available during the next decade allowing low-cost, high-grade navigators using simultaneously GNSS receivers and inertial MEMS navigators.8

Overcoming Critical Problems with MEMS AccelerometersBecause of their use in operational areas, in aircraft, in vehicles and in the fi eld during conflict, MEMS accelerometers have to be especially rugged and resilient. Their tiny size can make this a challenging hurdle to surmount. Thales has been working on developing new products. An accelerometer combines an inertial measurement unit and a GNSS (Global Navigation Satellite Systems) or GPS (Global Positioning Systems) capability. However, GPS are subject in warfare to jamming, multipath due to atmospheric conditions and signal outages. Thales has been working on a possible solution for compensating navigation errors by using strategies resulting from the theory of neural networks (NN) or fuzzy logic.9

But Thales has not been working alone – many other centres are working on related problems. As Neil M. Barbour of Charles Stark Draper Laboratory notes:

“MEMS is probably the most exciting new inertial sensor technology ever and development

is a worldwide effort. Apart from size reduction, MEMS technology offers many benefits such as batch production and cost reduction, power (voltage) reduction, ruggedization, and design flexibility, within limits. However, the reduction in size of the sensing elements creates challenges for attaining good performance. In general, as size decreases, then sensitivity (scale factor) decreases, noise increases, and driving force decreases. Also, the change in Young’s Modulus of silicon is ~100 ppm/°C, which leads to thermal sensitivity concerns. At present, the performance of MEMS IMUs continues to be limited by gyro performance which is now at around 10 - 30 deg/h, rather than by accelerometer performance, which has demonstrated tens of micro g or better. One of the most recently developed MEMS IMUs is by Northrop Grumman/Litef with performance announced at better than 5 deg/h and 3 milli g.”10

He highlights, also, the still key limitation of an accelerometer dependent on GPS or GNSS technology:

“The vulnerability of GPS (e.g. to jamming, or in applications where GPS is unavailable (such as indoors or in tunnels and caves), or cannot be acquired quickly enough (such as very short-time-of-fl ight munitions)) means that other navigation sensors will always be required. The key driver for which system architecture to use is cost for mission performance, where cost includes not only purchase but also life cycle cost.”

Developmental Hurdles AheadThe extent to which MEMS accelerometers are now used in diverse applications in missiles and rotor and fixed wing aircraft cannot be underestimated. They deliver data at low cost for little added weight and represent a major step forward in providing the war fighter with improved situational awareness and control over his aircraft or land vehicle. However, there are areas of doubt. Temperature resilience is one, as is dependence on GPS signals. There have also been attempts to produce a “gun hard” MEMS accelerometer that can deliver at very high levels of G. Some manufacturers feel they are close to having achieved this.



For some soldiers with

a good GPS signal, the

modern Apple iphone

4 or competing smart

phones with an MEMS

accelerometer can

offer better situational

awareness than many

of the latest military

personal computers.

The Military Helicopter Market Shows Future Market Opportunities for MEMS AccelerometersDon McBarnet , Staff Writer

IN THEIR survey of the short term global market for IMUs (inertial measurement unit)

Yole Développement of France delivers a strong forecast.11

“The high-performance IMU market was a $1.55B market in 2009. This market is expected to reach $2.60B in 2015. In volume, this is a 190k units market in 2009, growing to 650k units in 2015! Defense and aerospace applications dominate the market, while industrial applications are significant and are expected to be the most growing markets until 2015. Most of the volume is expected to come from industrial applications but with lower cost sensors. The defense market is doing some interesting volume with ammunition applications mainly. Aerospace market is mostly low volume high added value.”

The Military Helicopter MarketThe military helicopter market is for the purpose of this analysis subdivided into two areas –military helicopters at 500 units per year, and helicopters dedicated to special missions for

example, offshore applications or fi re services, which have as high a level of specifi cation as defence helicopters. Special mission rotorcraft are about 200 units per annum. Yole see the military rotorcraft in total market growing at a constant rate. The major manufacturers are Boeing, Sikorsky, Lockheed Martin in the USA and Eurocopter and AgustaWestland in Europe. They each use a multiplicity of MEMS accelerometers and other MEMS devices. These helicopters are frequently supplied with two inertial systems, one for redundancy. Increased quantities of MEMS IMU’s are used because lower accuracy is required, for example on the Eurocopter NHI NH90.

Stabilisation features and condition monitoring use inertial sensors but do not require an IMU. Twenty to thirty accelerometers are installed for vibration and acceleration monitoring for the different parts for maintenance purposes. The following parts are also monitored – gear box, main rotor, cockpit, nose and blades. They conclude that most of the market for IMU is for INS (Inertial navigation systems), AHRS



(Attitude Heading Reference System) systems use lower price IMUs ($15-$20k compared to $50-$55k for navigation), giving a smaller market opportunity. Yole highlight, also, the fact that retrofi t for sensors is also a large portion of the market.

Another View of the MarketS Jean-Michel, from Colibrys in Switzerland saw the market from a different angle. In a paper on Inertial Sensing in 2004: “The worldwide accelerometer business is split in two distinctive markets: The “movement monitoring and event detection” is largely driven by the automotive and low cost consumer business and the and the “measurement and control” world on the other hand, mainly driven by the aerospace and inertial navigation business and historically served principally by conventional relative high cost micro mechanical products.” He emphasizes, also, that Colibrys have overcome some of the hurdles to the design of high specification products for the defence market – high performances MEMS capacitive accelerometers, offering the required long-term stability and vibration rectif ication error characteristics are produced to serve inertial guidance and navigation for aeronautic and defence applications. Furthermore, these products are offering advanced functionalit ies

and are performing extremely well without degradation of specifications in rugged environments such as gun hard shocks with amplitudes higher than 20,000g.

The Implications for MEMS Accelerometers of the Explosion in Smart Phones for the Defence MarketFor some soldiers with a good GPS signal, the modern Apple iphone 4 or competing smart phones with an MEMS accelerometer can offer better situational awareness than many of the latest military personal computers. Indeed MEMS accelerometers are established as the “must-have” feature for many smart phones. The commercial mobile phone is highly competitive and changing very quickly. As Yole Développement put it “We are at a turning point for MEMS and MEMS sensors for handsets” and they anticipate the market will experience double-digit growth from 2009-2015. This will be accompanied by a spin-off in development of MEMS accelerometers, which will feed through to the defence market.



References:1 T Inertial Navigation Sensors Neil M. Barbour

Charles Stark Draper Laboratory (P-4994) Cambridge, MA 02139 USA

email: [email protected] NATO

2 http://www.i-micronews.com/upload/Rapports/Yole_IMU&High_Performance_Inertial_MEMS_Report_sample.pdf -

YOLE 2009-2115 MARKET PREDICTION

3 Modern inertial technology: navigation, guidance, and control By Anthony Lawrence

4 N Pleil: Southwest Center for Microsystems Education and The Regents of University of New Mexico. Southwest Center

for Microsystems Education (SCME) www.scme-nm.org

5 Press release COLIBRYS SIGNS PARTNERSHIP AGREEMENT WITH BAE SYSTEMS

Neuchâtel – May 24, 2005.

6 Press release Goodrich November 2010

7 Goodrich sensors and integrated systems, Aerospace and Defense Business Overview January 2010

8 Aerospace and Electronic Systems Magazine, IEEE Issue Date: 2007 Volume: 22 Issue:10 On page(s): 31 - 36 ISSN:

0885-8985 INSPEC Accession Number: 9631479 Digital Object Identifi er: 10.1109/MAES.2007.4385708

Date of Current Version: 19 November 2007

9 17th European Signal Processing Conference (EUSIPCO 2009)Glasgow, Scotland, August 24-28, 2009

OUTAGE MITIGATION FOR GNSS/MEMS NAVIGATION USING NEURAL NETWORKS

J.-R. De Boer(1), V. Calmettes(2), J.-Y. Tourneret(1), and B. Lesot(3)

(1) Universite de Toulouse ENSEEIHT, IRIT 2 rue Charles Camichel B.P. 7122 31071 Toulouse Cedex 7, France www.irit.fr

(2) Universite de Toulouse ISAE, DEOS, TESA 10 av. Edouard Belin B.P. 54032 31055 Toulouse Cedex 4, France www.isae.fr

(3) Thales Avionics 25 rue Jules Vedrines 26000 Valence, France www.thalesgroup.com

email: [email protected], [email protected], [email protected] and

[email protected]

10 Inertial Navigation Sensors Neil M. Barbour Charles Stark Draper Laboratory (P-4994) Cambridge, MA 02139 USA

11 http://www.i-micronews.com/upload/Rapports/Yole_IMU&High_Performance_Inertial_MEMS_Report_sample.pdf by

Laurent Robin and Mike Perlmutter

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