How to invent (or not invent) the first silicon MEMS gyroscope

Draper designed and constructed traditional mechanical gyroscopes for Apollo and for strategic guidance systems. In 1984, Draper started the double gimbal gyro, which led to the silicon-on-glass tuning fork gyroscope that reported the first useful performance of a silicon MEMS gyroscope in 1992. This work became the basis for the successful Honeywell MEMS inertial measurement units and the starting point for other MEMS angular rate sensors. This paper will discuss considerations that were factored into the first tuning fork. These known factors included the thin, available proof masses, efficient mass use, quadrature stiffness, fluid gas “surf boarding”, noise sources, frequency variation, and modal response. Unconsidered phenomena, such as glass charging, stiffness non-linearity, comb drive cross-coupling and electrical feed through, were designed around on the fly. Other fortuitous events such as material and parameter selection which avoided thermoelastic damping, which was not understood in MEMS until 2003, the limits of quadrature trimming, and the addition of key personnel, will be covered. In summary, demonstrating the first silicon MEMS gyroscope required wellapplied engineering and a bit of serendipity.