Electronic technologies can provide a tactical edge in critical military systems, such as communications, electronic countermeasures, electronic-warfare (EW), and radar systems. The fundamental techniques used in some platforms, such as communications systems, undergo gradual, evolutionary progress in terms of better receiver noise figures, more robust solid-state transmitters, and more efficient modulation formats. But the changes being made in other systems are more dramatic with the infusion of relatively new technologies such as directed-energy weapons, frequencyselective materials, and microelectromechanical- systems (MEMS) devices.
One of the leading prime contractors, Raytheon (www.raytheon.com), is involved with the development of several directed-energy weapons, including the millimeter-wave-based Active Denial system. The non-lethal protection system is designed to repel individuals without causing injury. The system transmits a focused beam of millimeter-wave energy that produces an intolerable feeling of heat in the impacted individual, causing a target to flee to escape from the uncomfortable heating effects. Once the individual leaves the beam the heating sensation immediately ceases. The company has already delivered three Active Denial systems to a US Air Force customer. The firm has also built a smaller version of the system (about one-third the size and the power), known as the Silent Guardian. Raytheon also has developed the Laser Area Defense System (LADS) that combines the capabilities of the 20-m Phalanx weapon system with lasers used for rapid and accurate search, track, and engage functions for directing laser energy to target and destroy mortars and other munitions in flight. For more on laser-based and energy-guided weapons developments, see the news story beginning on page 45 of this issue.
Numerous market studies in the last few years have trumpeted the sure growth of MEMS technology in both commercial and military applications. MEMS devices are already well established in automotive electronics, for example, as part of the triggering electronics in safety airbags. And the cellular handset market is viewed as another area of sure growth. One of the major suppliers of devices to the airbag market, Analog Devices (www.analog.com), has also developed MEMS-based devices that can serve military applications, including the new ADIS16350/ADIS16355 iSensor, a complete triple-axis gyroscope and tripleaxis accelerometer inertial sensing system. The sensor includes an SPI connection for easy access to data and configuration controls. The SPI port provides access to x-, y-, and z-axis angular rates, x-, y-, and z-axis linear acceleration, internal temperature, power supply, and auxiliary analog input. The inertial sensors are precision-aligned across axes and are calibrated for offset and sensitivity. An embedded controller dynamically compensates for all major influences on the MEMS sensors, thus maintaining highly accurate sensor outputs without further testing, circuitry, or user intervention.
The sensor module provides 14-b resolution for both the gyroscope and accelerometer. It measures just 23 x 23 x 23 mm and is well suited for applications in guidance and control, platform control and stabilization, motion control and analysis, and inertial-measurement systems, as well as for guidance in robotics and unmanned aerial vehicles (UAVs). The accelerometer features a 10 g's measurement range and can survive 200 g's shock. In support of gyroscope applications, the company offers application note AN-942, "Optimizing MEMS Gyroscope Performance with Digital Control," for free download on its web site at www.analog.com.
Diamond in those MEMS
In support of further applications of MEMS technology in military systems, the Defense Advanced Research Projects Agency (DARPA, www.darpa.mil) recently announced a Phase III research project valued at $1.4 million to a team led by the US Department of Energy's (DOE) Argonne National Laboratory (www.anl.gov) to develop high-performance integrated diamond MEMS and CMOS devices for advanced radar and communications applications. The project is centered on the patented, Argonne-developed Ultrananocrystalline Diamond (UNCD) film technology. Partners on the MEMS development project include Advanced Diamond Technologies, Inc. (ADT, www.thindiamond.com), Innovative Micro Technology (IMT, www.imtmems.com),
MEMtronics Corp. (www.memtronics.com), Peregrine Semiconductor (www.peregrine-semi.com), the University of Pennsylvania, and Lehigh University.
The UNCD thin films fabricated by ADT are comprised of diamond grains that are only 3 to 5 nm in diameter. The films offer superior as-deposited smoothness compared to traditional diamond films, and can be deposited at temperatures compatible with those used in traditional semiconductor manufacturing processes.
The principal investigator and project manager for the diamond MEMS project is Derrick Mancini, associate division director for Facilities and Technology for Nanoscale Materials (CNM) at Argonne. DARPA's interest in the diamond MEMS is for their use in communications systems as well as in advanced phased-array radars. It is hoped that integration of capacitive RF MEMS and CMOS devices will enable rapid electronic steering of radar beams for improved phased-array radar tuning speed and accuracy. For commercial applications, the use of the diamond MEMS technology in monolithic devices will lead to multifunction modules suitable for a variety of wireless products.
Another US government facility exploring the possibilities of MEMS technology is Sandia Laboratories (www.mems.sandia.gov). Members of the research laboratory have developed an aluminum-nitride (AlN) process for fabricating RF MEMS resonators at frequencies from 1 MHz to 3 GHz. Employing equipment similar to that used for fabicating film-bulk-acoustic-resonator (FBAR) filters and resonators, the researchers have produced a variety of different MEMS-based RF component, including filters, switches, and oscillators.
Sandia's AlN resonator process (Fig. 1) incorporates the laboratory's molded tungsten (W) capabilities for improved performance. The use of W with AlN eliminates the need for resonators that are suspended above the substrate by quarterwave beams. The combination of materials has allowed scaling of MEMS resonators to 3 GHz without spurious modes and with relative high quality-factor (Q) performance (with Q's approaching 5000 at high frequencies).
Sandia has also developed a polysilicon MEMS resonator process for high-Q reference oscillators and intermediate-frequency (IF) filters. The process achieves electrodeto- resonator gaps of less than 100 nm to reduce the impedance of capacitively transduced devices. The process is best suited for resonators below 200 MHz but with Q's of greater than 60,000 with low frequency drift and low vibration sensitivity. In addition to its innovative device developments,Sandia has also performed slews of tests to DARPA standards in its studies of MEMS device reliability. Sandia has evaluated MEMS switches through 10 GHz at temperatures from -15 to +75C, working with customers to better understand the electrical and mechanical operation of these devices, including finding contamination issues that can lead to early failures. Sandia has also explored the performance and reliability of MEMS RF sensors, and brings extensive two-dimensional (2D) and three-dimensional (3D) modeling tools to the analysis for modeling purposes in addition to a full complement of test equipment.
BAE Systems (www.baesystems.com) entered into an agreement with fabless MEMS developer Micromem Applied Sensor Technologies, Inc. (www.micromem.com) to leverage both companies' expertise in military, commercial, and homeland security markets to find MEMS-based solutions for those markets. BAE's Microelectronics Center (Nashua, NH) will work closely with Micromem as the MEMS's developer's foundry to further advance Micromem's magnetic-random-accessmemory (MRAM) products for military applications. Micromem's patented nanosensors, which are based on the MRAM technology, can also be used as highly accurate magnetometers to measure the strength and direction of magnetic fields for use in threat detection.
Another goal of the teaming of the two organizations is also to further develop radiation-hardened GaAs nanosensors for deep-space and hostile environments. According to Gino Manzo, foundry director at BAE Systems in Nashua, "Foundry facilities are very expensive, and develop-on new products is highly capital-intensive. This arrangement will advance technology and design maturity for products developed by Micromem by giving both companies the means to produce devices for a wide range of commercial and military uses."
Silicon Designs (www.silicondesigns.com) serves a variety of industries in addition to military and aerospace customers with its non-silicon MEMS sensors for accelerometers. The firm's current sensor technology supports accelerometers with full-scale sensitivity from 2 g's to more than 20,000 g's. Military applications include launch and impact testing, flight control, inertial navigation, safe-and-arm functionality, attitude sensing, and impact detection. The company's basic design is based on capacitance change due to acceleration force as the sensed parameter. The relative insensitivity to temperature of the capacitive sensors allows their use over the wide temperature extremes experienced by military applications. The basic Silicon Designs' accelerometer unit is a 20-pin LCC package with a sensing element or chip and an ASIC. The chips kage is solder sealed to provide a simple, rugged, fully hermetic device. Built with one of two ASIC chips to provide either an analog or digital output, this basic accelerometer can be easily surface mounted to a printed-circuit board (PCB).
As far as the suitability of MEMS technology for military applications, last year, one of the most "seasoned" companies in the MEMS marketplace, Discera (www.discera.com), announced that Tyco Electronics, M/A-COM (www.macom.com) had qualified Discera's MEMS-based MOS1 series oscillators for use in M/ACOM's telemetry transmitters. The MEMS oscillators were qualified as an alternative to traditional quartz-crystal oscillators as timing devices. The test results indicated that the silicon-based MEMS oscillators and resonators were ready for use in a wide range of electronics products, including those designed for military use.
The MEMS oscillators successfully withstood shock levels to 100,000 g's, surviving 14,999 g's shock with no degradation in performance. The MEMS oscillators consist of a silicon MEMS resonator and an application- specific integrated circuit (ASIC) housed in a standard QFN or ceramic package. The oscillators are available for frequencies from 1 to 125 MHz with excellent stability over temperature.
A company with a somewhat longer track record in supplying precision oscillators, Vectron International (www.vectron.com), has also developed a military clock oscillator based on MEMS technology. The company's model VMEM5Q oscillator (Fig. 2) is designed for high shock and vibration environments using a MEMS resonator. The oscillator, which is designed to withstand shock levels to 100,000 g's, was recently put to the test, with qualification testing of a 125-MHz oscillator showed no degradation in performance to the capability of the test set, 30,000 g's in each axis. According to Mario Saucedo, director of Product Development at the company's Hudson, NH facility, "We believe the small size and rugged reliability that MEMS oscillators can offer are an important part of the future of the frequency control market. As a result, we are working to advance this next generation technology with our existing core competencies, to help customers evolve their platforms to meet and exceed market requirements and establish competitive differentiation. Our latest breakthrough, the VMEM5Q, clearly demonstrates our commitment to bring leadingedge technology to our customers who are manufacturing guidance systems for small munitions, projectile electronics, missiles, and high-shock vibration applications." Greg Smolka, vice president of Vectron's Industrial Military and Space Business unit, adds: "This MEMS-based oscillator addresses a strong need for high-shock resistant timing components in the Precision Guided Munitions (PGM) market." The Vectron oscillator makes use of a PureSilicon MEMS resonator from Discera. The VMEM5Q can be specified for frequencies from 1 to 130 MHz with 50 and 100 PPM stabilities at temperatures from -40 to +85C. It is supplied in a 5.0 x 3.2 mm QFN package.