A New Silicon Tuning Fork Gyroscope for Aerospace Applications

For several years THALES Aerospace has been developing a silicon micro-machined tuning fork gyroscope for military and civil applications. The targeted performance is: bias and scale factor errors of 10 degrees/h and 500ppm for a range of 1000 degrees/s. The technology is based on Deep Reactive Ion Etching (DRIE) on a SOI wafer. Associated with an in-plane design for the drive and sense modes, this technology leads to a high geometric precision and allows the realization of the sense and the drive mechanical resonators, and trimming elements within a single active layer. Good bias stability is achieved by cancelling the quadrature bias with electrostatic trimming. The signal processing of the gyro is primarily digital and consists of two main closed loops, for controlling the drive and sense modes, and an auxiliary loop for cancelling the quadrature bias. The typical results obtained on a demonstrator of a third generation device are the following: random walk=0.01 degrees/root h, bias instability<0.1 degrees/h, noise of 0.005 degrees/s over 0-50Hz, with a 1000 degrees/s range (adjustable by the electronics), bias and scale factor errors of 8 degrees/h and 28 ppm in the temperature range -25 degrees C, 70 degrees C, linearity error<0.1 degrees/s over 1000 degrees/s. A high g shock test of 20000g has been carried out on a hardened prototype without any observable performance degradation.