EE Seminar: On-Chip Compensation of Stress, Temperature, and Nonlinea...

Speaker: Erdinç Tatar

Title: On-Chip Compensation of Stress, Temperature, and Nonlinearity in a MEMS Gyroscope

Date/Time: December 29, 2017  /  13:40-14:30

Place: FENS G032

Abstract: In this talk I will mainly focus on my PhD research in Carnegie Mellon University, and the summary is provided below. I will conclude my talk with my future research interests based on my MS/PhD work and industry experience. The first MEMS gyroscope was introduced by the Draper Laboratory in the early 90’s. Over the past three decades, micro-gyroscope performance has improved as a result of extensive research, and advancements in fabrication technologies and readout electronics. Today MEMS inertial sensors are widely used in various fields such as consumer electronics, car safety, stabilization, and navigation. My PhD thesis proposes stress, temperature, and nonlinearity compensation techniques for high performance MEMS gyroscopes to further improve the performance. The performance of the micro-gyroscopes is limited with the long term drift. Temperature has been found to be one of the important sources of long term drift but constant temperature testing of one of the state of the art gyroscopes still exhibits long term drift. The main motivation of my thesis is solving the long term gyroscope drift problem by measuring the stress on the mechanical structure with on-chip stress sensors. Towards that end, a simulation methodology that couples finite element analysis and circuit solver has been developed to understand the stress zero rate output (ZRO) relation and stress tests have been performed on an in-house fabricated and vacuum packaged SOI-MEMS gyroscope. Through ovenization my research successfully demonstrates that stress compensation significantly suppresses long-term drift resulting in 9°/hr angle random walk and 1°/hr bias instability at 10,000 s (around 3 hr) averaging time, which is seven times improvement over the uncompensated gyroscope output. High drive displacement improves the signal to noise ratio of a gyroscope but also leads to a nonlinear force displacement behavior that is observable as a hysteresis in the frequency-phase and frequency-amplitude relations. These nonlinearities lead to Amplitude-frequency effect where resonance frequency depends on the displacement. My thesis proposes a cubically shaped nonlinearity tuning comb finger design that cancels the inherent softening nonlinearity of the gyroscope by introducing a DC voltage controlled hardening nonlinearity. The functionality of the fingers is demonstrated and cancelling drive nonlinearities leads to a better bias instability compared to the high displacement with nonlinear characteristics.

Contact: Murat Kaya Yapıcı