We report, for the first time, a MEMS fabrication process for building atomically smooth, symmetric 3-D wineglass and spherical shell structures, using low internal loss materials, namely fused quartz and ultra low expansion titania silicate glass (ULE TSG). The approach consists of three major steps: (1) a deep fused quartz cavity etch, (2) plasma activated bonding of fused quartz to fused quartz or TSG and (3) a high temperature (up to 1700 • C) micro-glassblowing process. An in-house process capability of 1800 • C glassblowing with a rapid cooling rate of 500 • C/min was developed. Feasibility of the process has been demonstrated by fabrication of fused quartz and TSG micro-glassblown structures. Spherical and inverted-wineglass shells with self-aligned stem structures were fabricated using this process. The approach may enable new classes of TSG and fused quartz MEMS devices with extremely low surface roughness (0.23 nm surface average), intrinsically low thermoelastic dissipation (QTED > 5E+10), and highly symmetric structures (radial error < 500 ppm).

We present a long-term bias drift compensation algorithm for high quality factor (Q-factor) MEMS rate gyroscopes using real-time temperature self-sensing. This approach takes advantage of linear temperature dependence of the drive-mode resonant frequency for self-compensation of temperature-induced output drifts. The approach was validated using a vacuum packaged silicon Quadruple Mass Gyroscope (QMG), with signal-to-noise ratio (SNR) enhanced by isotopic Q-factors of 1.2 million. Owing to the high Q-factors, measured frequency resolution of 0.01 ppm provided a temperature self-sensing precision of 0.0004 • C, on par with the state-of-the-art MEMS resonant thermometers. The real-time self-compensation yielded a total bias error of 2 • /h and a scale-factor error of 700 ppm over temperature range of 25-55 • C. The presented approach enabled repeatable long-term rate measurements required for MEMS gyrocompassing applications with a milliradian azimuth precision.

Automotive applications are known to impose quite harsh environmental conditions such as vibration, shock, temperature, and thermal cycling on inertial sensors. Micromachined gyroscopes are known to be especially challenging to develop and commercialize due to high sensitivity of their dynamic response to fabrication and environmental variations. Meeting performance specifications in the demanding automotive environment with low-cost and high-yield devices requires a very robust microelectromechanical systems (MEMS) sensing element. This paper reviews the design trend in structural implementations that provides inherent robustness against structural and environmental parameter variations at the sensing element level. The fundamental approach is based on obtaining a gain and phase stable region in the frequency response of the sense-mode dynamical system in order to achieve overall system robustness. Operating in the stable sense frequency region provides improved bias stability, temperature stability, and immunity to environmental and fabrication variations.

No abstract

No abstract