Proceedings Article | 23 September 1996
Marc Weinberg, Jonathan Bernstein, Jeffrey Borenstein, J. Campbell, J. Cousens, Robert Cunningham, R. Fields, Paul Greiff, Brenda Hugh, Les Niles, Jerome Sohn
KEYWORDS: Silicon, Gyroscopes, Sensors, Semiconducting wafers, Glasses, Micromachining, Etching, Reactive ion etching, Electronics, Scanning electron microscopy
Draper Laboratory, using silicon microfabrication techniques to achieve high yields by batch processing, has been developing miniature microelectromechanical instruments for over 10 years. During this time, considerable progress has been made in the development and fabrication of micromechanical gyroscopes, accelerometers, and acoustic sensors. Inertial instruments have become a worldwide research and commercial topic. Draper gyroscopes and accelerometers have been fabricated with measurement ranges from 50 to 500 deg/s and 10 to 100,000 g, respectively. In gyroscopes, stabilities are 20 deg/h in room temperature tests and 4.4 deg/h applying 0.3 degrees C thermal control. For accelerometers, less than 1 mg has been demonstrated in room temperature tests. These units have performed successfully across a temperature range of -40 to 85 degrees C, and have survived 80,000- to 120,000-g shock tests along all axes. Continuing development activities are expected to yield over an order of magnitude in performance enhancement. These micromechanical instruments are built using a silicon wafer process that results in crystal silicon structures that are anodically bonded on a Pyrex substrate that contains sensing and control electrodes. This silicon-on-glass configuration has low stray capacitance, and is ideally suited for hybrid or flip-chip bonding technology. Draper's inertial sensors incorporate excellent fabrication, however, building the silicon and Pyrex sensor chip is only one of many important contributions in a complete sensor system. Other equally important steps include: 1) electronics and application-specific integrated circuits (ASICs) 2) packaging, 3) test, and 4) modeling and analysis. This presentation focuses on sensor fabrication. Draper's accelerometers and gyroscopes and the dissolved wafer fabrication process are described. The evolution of gyro design, fabrication, and performance is summarized. Garnered through experience in both conventional and micromachined inertial sensors, rules of thumb that have guided Draper's micromachining efforts are discussed.
