In-situ calibration Of MEMS inertial sensors for long-term reliability

Abstract

Inertial sensors are pervasive in handheld electronics, UAVs, ioTs, and wearable electronics, as they enable motion awareness. MEMS inertial sensors have been successful at the SWAP corresponding to a few mm3 volumes and a few milliwatts. However, the scale factor, the conversion factor between the measured rate and the output voltage, and the bias, the output voltage at zero rate, drift over time. This aging behavior prevents them from replacing more expensive and higher SWAP inertial sensors. In order to remedy the aging, an in-package calibration approach has been explored in our group. A piezoelectric multi-modal mechanical (X, Y, θ z ) stimuli stage capable of ≈ 100ppm precision, in-situ calibration of MEMS inertial sensors packaged on the stage is demonstrated. The calibration system is capable of extracting instantaneous scale factor, bias drifts and cross axis sensitivities of MEMS Coriolis force gyroscopes. The bulk PZT calibration stage is capable of generating non-resonant sinusoidal angular rates of 0 — 300deg/s for scale factor and bias measurements and X-Y in-plane acceleration stimulus of 0 — 90m/s2 to extract the gyroscope in-plane acceleration sensitivities at 100V P , 0–250Hz drive voltage and frequencies. To achieve a long term stable calibration stage, an optical metrology system is used to calibrate the motion stage. The optical metrology system can ensure 10ppm stable stage metrology, to enable long term stable gyroscope calibration. The optical system uses an atomically stable laser source and a CMOS imager that can be potentially integrated in the same package as the calibration system, for closed loop control of the calibration stage.