Rugged, reliable and affordable micromachines are moving into prime-time avionics applications in unmanned air vehicles and precision-guided munitions. Tiny micro electromechanical systems, or MEMS, are no longer the stuff of fiction.
The movie "Fantastic Voyage" captured our imagination in 1966. In the film scientists shrink a small submarine and its crew to microscopic size and then insert the vessel into a man's blood stream, so the crew can perform a lifesaving operation.
As fantastic as the story line was, its premise of creating microscopic tools to use in new ways and places has become reality. The enabling technology is MEMS (micro electromechanical systems).
"MEMS is the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through microfabrication technology," according to www.mems-exchange.org, a Web site sponsored by the Defense Advanced Research Projects Agency (DARPA). Manufacturers create MEMS devices by selectively adding layers to or etching layers from a silicon wafer. The electronics are manufactured using integrated circuit processes, such as CMOS, bipolar or BICMOS.
The marriage of microelectronics with micromachining technology has enabled "systems on a chip." The microelectronic integrated circuits are the systems' brains, while the individual MEMS devices are the arms and legs. The MEMS devices sense and gather information about their environment; the microelectronics processes the information and then direct microactuators to effect desired outcomes. MEMS can be manufactured reliably and inexpensively, thanks to batch fabrication techniques similar to those used for integrated circuits. The technology yields very rugged products that are a fraction of the size, power, weight and cost of a conventional device.
MEMS are being used for an ever growing number of optical, electrical, computational, thermal, mechanical, hydraulic and pneumatic tasks. Prevalent applications include read/write magnetic heads for computer hard drives, inkjet printer micronozzles, airbag accelerometers, tire pressure sensors and micromirror switches.
About 1.6 MEMS devices are already in service for every one person in the United States, whose population is about 296 million. According to a 2004 survey by the MEMS Industry Group, the major revenue streams for MEMS by 2007 will be microfluidics (27 percent), inertial sensors (22 percent), optical MEMS (22 percent), pressure sensors (11 percent), other sensors (10 percent), other actuators (5 percent) and radio frequency MEMS (3 percent).
Avionics Magazine last year reported the development of a MEMS-based atomic clock that will be used in radios, radar and secure communications (November 2004, page 30).
MEMS also are being used in navigation devices. Honeywell and Rockwell Collins in November formed a joint venture, Integrated Guidance Systems LLC, which plans to introduce a MEMS deeply integrated inertial navigation system (INS)/GPS product, with anti-jam, by mid-2006.
The INS/GPS was created for and is flying on an unmanned air vehicle (UAV) that Honeywell is developing under DARPA's Organic Air Vehicle (OAV) program. The UAV will weigh less than 112 pounds (51 kg) and have vertical takeoff/landing (VTOL) hover and cruise capabilities. The U.S. Army's smallest operational units would use OAVs for reconnaissance, surveillance and targeting.
DARPA expects OAVs to be fully autonomous and require little or no operator intervention, so the INS/GPS would play a significant role. Honeywell provides the MEMS and Collins provides the selective availability/anti-spoofing module (SAASM) GPS receiver. The overall volume of the INS/GPS is about 14.5 cubic inches.
"Our primary MEMS focus is inertial sensors like accelerometers and gyros used for navigation, and many of our MEMS sensors are used on precision-guided projectiles," says Bob Whitcraft, Honeywell's aerospace product marketing manager, Guidance & Navigation, Missiles, Munitions, and Unmanned Aircraft Systems.
In the INS/GPS system the inertial measurement unit (IMU) consists of three MEMS gyros packaged on a circuit board with supporting electronics, three MEMS accelerometers packaged on a board with supporting electronics, and one electronics microprocessor board with basic software.
Under the LLC the two companies can share their intellectual property (IP) more closely and combine their manufacturing capabilities. They will jointly own the IP, and each can independently offer the LLC's products for non-missile/munitions applications. Each will remain a merchant supplier of its own non-integrated inertial and GPS products.
Honeywell is reviewing its use of the INS/GPS for helicopter flight control augmentation, as a backup system, supplementing attitude, acceleration and position information acquired from a helicopter's primary system. Honeywell also is working on MEMS rate sensors to replace certain mechanical rate sensors used in aircraft.
Northrop Grumman's Navigation Systems division has worked with MEMS since the mid-80s, says Charles Volk, the division's vice president and chief technologist. "Our first MEMS product was a very high-performance accelerometer, and we've now produced in excess of 15,000."
"The primary benefit we are chasing is lower costs," Volk says. "We can produce 100 accelerometers on a 4-inch [10-cm] silicon wafer, so our cost is dramatically less. The next attraction is size; we can fabricate products in a much smaller form factor with MEMS than with traditional technologies.
"The third benefit is power consumption although this is not a big driver."
Northrop's premier MEMS-based product is the LN-200 IMU, which is used in missiles (for rudimentary navigation) and for other stabilization and tracking applications. The LN-200 provides inertial sensing and then outputs angular rates in three axes and linear rates in three axes. The basic unit is not integrated with GPS, but can be. A Northrop Italian unit integrates the LN-200 with GPS to create an attitude heading reference system for helicopters.
Another application for the MEMS accelerometers is the NG-2000, which is used on sensing pods to keep the platform stable. MEMS also are used in a new GPS/air data/inertial reference system for the Airbus A380.
"That product, the LTN-101E, will use a MEMS accelerometer similar to the one in the LN-200," Volk says. "Additionally, we are replacing the ring laser gyro with a fiber optic gyro. By doing all this, we've reduced the unit's cost and power consumption and improved its reliability."
Northrop also plans to mate a MEMS gyro with MEMS accelerometers to form a complete MEMS IMU. This will be used for the same purposes as the LN-200. Using MEMS gyros enables much smaller and lower-cost units. The LN-200 is 30 cubic inches, while the MEMS IMU will be 9 cubic inches.
The MEMS IMU will deliver tactical grade navigation. For higher performance, the company also is developing a MEMS gyro that uses nuclear magnetic resonance technology.
Volk foresees Northrop's MEMS accelerometer moving into more military applications, in particular high-shock, high-vibration environments. The company's MEMS gyros could replace low- and middle-performance ring laser and fiber optic gyros in the next five to 10 years.
Agilent Technologies www.home.agilent.com
BAE Systems www.baesystems.com
Concurrent Technologies Corp. www.ctc.com
Infotonics Technology Center www.infotonics.org
ITRI International www.itri.com
Innovative Micro Technology www.imtmems.com
Intel Corp www.intel.com
Meggitt Electronics www.meggitt.com
Northrop Grumman northropgrumman.com
Philips Semiconductor www.philips.com
Quantum Leap Packaging www.qlpkg.com
Texas Instruments www.ti.com
Textron Systems www.systems.textron.com