Temperature-compensated surface micromachined angular rate sensor

Abstract

A motion sensor having a micromachine sensing element and electrodes formed on a silicon chip. The sensing element includes a ring supported above a substrate so as to have an axis of rotation normal to the substrate. Surrounding the ring is at least one pair of diametrically-opposed electrode structures. The sensing ring and electrode structures are configured to include interdigitized members whose relative placement to each other enables at least partial cancellation of the effect of differential thermal expansion of the ring and electrodes. As a result, the performance of the motion sensor is, to first order, insensitive to temperature variation. The sensor further includes circuitry for creating and detecting an electrostatic force between the interdigitized members of the sensing ring and electrode structures. The circuitry operates to sum the electrostatic forces such that, on the occurrence of a temperature change, a corresponding decrease in the electrostatic force between one pair of interdigitized members will at least partially cancel a corresponding increase in electrostatic force between a second pair of interdigitized members. Accordingly, the net effect is that a temperature change will have a reduced effect on the sensing performance of the sensor, because the effects of thermal expansion will be at least partially canceled.