Microsystems Technology on the Cusp
With automotive industry driving growth, nano mechanization of sensing devices is big business
By Roger H. Grace
Only a few large volume applications of microsystems technology-based (MST) commercial solutions now exist: read/write heads (1.4 B units), inkjet print heads (900M units), airbag accelerometers (120M units), manifold absolute pressure sensors (30M units), and disposable blood pressure sensors (25M units). While the automotive market has two of these limited number of killer applications, many emerging automotive electronic system applications will probably have a large number of recently developed MST devices. Since their first introduction into vehicle electronic engine control systems in the mid 1970s, automotive MST application opportunities have grown dramatically.
More than 100 potential applications exist for these devices. Many have found their initial application in high-end vehicles (BMW 7xx and Mercedes Benz 5xx) where the cost is less important, providing performance/convenience differentiation for automakers, rather than in lower-end vehicles, where cost is a much more important issue.
Unlike other market sectors that have been adversely affected by economic downturn, such as fiber-optic communications, the automotive sector continues to be robust worldwide, with 2005 production projected at 57.2M units, and an expected 1.6% compound annual growth rate (CAGR) from 2003-2008.
This steady growth, compounded by the continuous introduction of new safety, convenience, and performance functions, is creating a market growth for MST expected to be in the 15-17% CAGR range. Consider the well-established applications. as well as the short term, just introduced, and currently-under-development opportunities:
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Manifold absolute pressure sensors: A silicon MST solution replaced a coil and magnet pressure sensor. This new approach affords the system integrator a more reliable, smaller, and (potentially) lower cost solution.
This device measures the pressure in the intake manifold and feeds the information back to a computer whose programmed algorithm determines the optimum air/fuel mixture. This minimizes uncombusted hydrocarbons and maximizes fuel economy.
Today, most vehicles have one of these devices as part of the electronic engine control system. However, alternate solutions of directly measuring the airflow currently exist, some using MST, as well as those using discrete solutions.
Airbag accelerometers: The earlier implementations of this device introduced in the mid 1980s were truly electro-mechanical in nature. One version was a ball and tube approach (Breed Automotive) where a ball bearing would roll along a machined tube and strike a contact at its end in response to a critical and watershed acceleration.
Another version was a conductive metal cylinder attached to a beryllium copper spring, which rolled up an inclined plane and made contact with a conductive terminal because of a car’s sudden deceleration. This approach was a TRW product, the Rollarmite.
Both of these devices were large, provided an on/off signal, and had a cost of approximately $20 in automotive volumes. MSTs displaced these solutions starting in the early 1990s.
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Terminology Manifold absolute pressure (MAP) sensor is an important sensor in modern internal combustion engines that use fuel injection. It connects to the intake manifold and measures the level of manifold vacuum so the engine’s electronic control unit can tune the fuel input, as well as the timing of injections and spark plug ignition. Airbag accelerometer is a device for measuring acceleration, which in the case of an airbag involves the measurement of negative acceleration, such as a sudden stop or crash. Simple micro electromechanical systems (MEMS) are transducers that convert mechanical motion into an electrical signal that is proportional to the acceleration value of the motion. Accelerometers serve along with gyroscopes in inertial guidance systems, as well as in other scientific and engineering systems. Magnetic reluctance is the resistance of a material to a magnetic field. It is the ratio of magnetomotive force to magnetic flux. Hall effect refers to the potential difference (Hall voltage) on opposite sides of a thin sheet of conducting or semiconducting material in the form of a ‘Hall bar’ or a van der Pauw element through which an electric current is flowing, created by a magnetic field applied perpendicular to the Hall element. Global Positioning System, usually called GPS (the U.S. military refers to it as NAVSTAR GPS), is a satellite navigation system used for determining one’s precise location and providing a highly accurate time reference almost anywhere on Earth or in Earth orbit. It uses a satellite constellation of at least 24 satellites. Piezoelectricity is the ability of certain crystals to generate a voltage in response to applied mechanical stress. The word comes from the Greek piezein, which means to squeeze or press. In fact, the effect is reversible. If one applies a voltage to a piezoelectric crystal, it will change shape by a small amount. |
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Not only did the new solution provide a more reliable and smaller approach, but since it operated in the analog domain, the resulting crash pulse could be measured and compared to stored crash signals to determine if in fact a crash was under way versus a gang of rambunctious teenagers banging on the vehicle bumper to set off the airbag.
In addition, initial designs only required one of these devices, located in a module in the passenger compartment (single point sensing), at a cost of $5. Their introduction into safety systems significantly reduced system part cost as well as the weight, cost, and labor associated with installing cable systems to connect the up to five accelerometers that were required to effectively sense a crash.
Today, virtually all vehicles are equipped with at least one of these devices, with some vehicles using as many as eight to monitor frontal as well as broadside and rear crash scenarios.
Under development
Many new systems are currently under development or have recently deployed in limited production applications.
Wheel speed sensors: Currently, variable reluctance (VR) sensors operate in the wheels of many vehicles to sense their rotation/speed for antilock braking systems.
These discrete wire wound and magnet solutions are seeing encroachment and replacement by Hall Effect sensors and anisotropic magnet resistive ratio solutions, which embody MST. These new solutions provide higher performance and are more reliable; however, they are currently slightly more expensive than their VR predecessors are.
Tire pressure sensors: Tire under inflation poses a major problem in vehicle safety. Currently, two solutions are vying for domination of this U.S. federally mandated measurement.
Tire under inflation causes excessive heat and wear, increasing the likelihood of a blowout. A number of companies have offered solutions to this problem by proposing to directly measure tire internal pressure using MST.
These silicon devices are not new to the market; they have been available for over 30 years in various forms. This solution has a challenger in the non-direct method of measuring tire rotation of using wheel speed sensors that measure differential wheel speed as a function of tire inflation. An onboard computer runs the algorithm for this method.
Although the U.S. National Traffic Highway Safety Administration has not yet selected a specific approach to solving the under inflation problems, it has dictated an introduction schedule whereby all new vehicles that will operate on U.S. roads must be fitted with one of these systems no later than 2006.
This certainly constitutes a killer application with an average of 4.2 tires, and therefore sensors, per vehicle with over 17 million vehicles sold in the U.S. yearly.
In addition, non-U.S. applications are significant due to the federal highway safety organizations of many countries dictating similar procedures. The enhanced accuracy of the direct pressure measurement system is less desirable because of its excessive systems solution cost of $65-80 per vehicle, versus that of the wheel speed based solution.
Target price for the module consisting of a pressure sensor, conditioning electronics, and a wireless transmitter package is $12-15 per wheel with a high-volume price target of $5 per wheel by 2007.
Rate and yaw sensors: These sensors measure the rate of rotation about a central axis, which is important in determining vehicle location when used in conjunction with a Global Positioning System or to determine vehicle orientation as it begins to roll over or go into an uncontrolled skid.
Early yaw rate sensors found their first application in the mid 1990s on the Mercedes Benz S500. The devices, designed and manufactured by British Aerospace, were developed from designs previously attributed to avionics guidance systems, cost approximately $80-100, and used piezoelectric sensing elements.
The current implementation of this collaboration of BA and Sumitomo uses a MST approach. The first quartz resonator MST rate gyro (gyro chip) came to the automotive market in a high-end Cadillac platform for vehicle dynamic control applications in the mid 1990s.
These devices currently sell in the $20-25 range and are in many U.S. and European vehicles. These devices will gain favor in vehicles with high centers of gravity, especially as the number of SUVs increases.
About the author
Roger H. Grace (rgrace@rgrace.com) is president of Roger Grace Associates, a consultancy specializing in Microsystems Strategic Marketing activities and located in Naples, Fla. He is also the past president and cofounder of the Micro and Nanotechnology Commercialization Foundation (MANCEF) and has degrees in electrical engineering and business.
Next up: NanotechnologyMicrosystem technology is growing, no doubt, but the next big wave in manufacturing will be nanotechnology. While nanotechnology is not yet mainstream, researchers are on the prowl for new developments. Nanotechnology, or molecular manufacturing, refers to the ability to build things one atom at a time. The following are just some projects using nanotechnology: Computers are a key target for nanotechnology. Researchers found by placing carbon nanotubes inside a strong magnetic field, they are getting new insights into optical properties of semi-conducting nanotubes, which may lead to faster, more powerful, energy efficient computers. “Single-walled carbon nanotubes offer engineers the intriguing possibility of building chips where electrical inputs can be converted into light and moved about the chip as optical signals rather than electrical signals,” said Junichiro Kono, associate professor of electrical and computer engineering at Rice University in Houston. Meanwhile, researchers have come up with a polymer coating made of silica nanoparticles that can create surfaces that never fog. The transparent coating can go on car windows, eyeglasses, camera lenses, ski goggles, and bathroom mirrors among others, said researchers at MIT. “Our coatings have the potential to provide the first permanent solution to the fogging problem,” said co-study leader Michael Rubner, the TDK Professor of Materials Science and Engineering. The coatings consist of alternating layers of silica nanoparticles, which are tiny particles of glass, and a polymer called polyallylamine hydrochloride, both of which are relatively cheap to manufacture, Rubner said. Speaking of automobiles, Rutgers scientists are using nanotechnology in chemical reactions that could provide hydrogen for tomorrow’s fuel-cell powered clean energy vehicles. Researchers can now make a finely textured surface of the metal iridium that can extract hydrogen from ammonia, capture it, and feed it to a fuel cell. The metal’s surface consists of millions of pyramids with facets as tiny as five nanometers (five billionths of a meter) across, onto which ammonia molecules can nestle like matching puzzle pieces. This sets up the molecules to undergo complete and efficient decomposition. “The nanostructured surfaces we’re examining are model catalysts,” said Ted Madey, State of New Jersey professor of surface science in the physics department at Rutgers. “They also have the potential to catalyze chemical reactions for the chemical and pharmaceutical industries.” A major obstacle to establishing the “hydrogen economy” is the safe and cost-effective storage and transport of hydrogen fuel. The newly discovered process could contribute to the solution of this problem. Handling hydrogen in its native form, as a light and highly flammable gas, poses daunting engineering challenges and would require building a new fuel distribution infrastructure from scratch. By using established processes to bind hydrogen with atmospheric nitrogen into ammonia molecules, which are one atom of nitrogen and three atoms of hydrogen, the resulting liquid could be handled much like today’s gasoline and diesel fuel. Then using nanostructured catalysts, pure hydrogen could come about on demand, as needed by the fuel cell, and the remaining nitrogen harmlessly released back into the atmosphere. The carbon-free nature of ammonia would also make the fuel cell catalyst less susceptible to deactivation. Solar energy also has nano connections. What if you could paint the roof of your plant with a nano type of plastic that would create enough alternative energy to heat and cool the facility? That idea may soon become a reality because of a breakthrough in solar research by a team of scientists from Wake Forest University and New Mexico State University. While traditional solar panels are made of silicon, which is expensive, brittle, and shatters like glass, the team’s organic solar cells consist of plastic that is a relatively inexpensive, flexible material that can wrap around structures or can even be applied like paint, said physicist Seamus Curran, head of the nanotechnology laboratory at New Mexico State. |
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RESOURCES “Magnetostriction positions the ride: Chassis, transmission shifting, and steering controls leaving rotary transducers.” www.isa.org/intech/magnetostriction “Take a Lickin’, Keep on Tickin’!” Fault-resilient electric motors in critical path applications such as automotive systems require designing for continuous operation and performance. www.isa.org/intech/ElectricMotors “IR is HOT For Monitoring Process Temperature: Automated infrared imaging technology gains inroads in niche temperature-sensitive segments.” www.isa.org/intech/IR ISA Directory—Car and automobile sensors and technology www.isa.org/rd.cfm?id=6947
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