Micro-machined accelerometer

Abstract

The transducer is fabricated using micro-machining techniques of a silicon wafer. The transducer includes E-shaped leaf springs of silicon dioxide suspending a mass from a support. The transducer is formed by chemical etching through openings of opposite faces of a silicon wafer on which etch stop layer patterns are diffused. Sense and force conductive patterns are diffused onto the opposite faces of the suspended mass. The spring-mass-support structure is then sandwiched between opposite plates having corresponding sense and force conductive patterns which face such patterns on the suspended mass. Circuitry is provided by which a sense voltage and a force voltage are applied between opposite sense and force conductive patterns of the opposite plates creating a sense electric field and a force electric field across the sense and force patterns of the mass. A feedback circuit arrangement is provided to maintain the mass at a predetermined reference position between the support plates. Forward circuitry of the feedback arrangement produces a displacement signal in response to a voltage induced on the sense area of the mass as it moves in response to acceleration applied to the support structure. The feedback arrangement produces an amount of charge in response to the displacement signal which is applied to the force conducting area of the mass. The force on the mass is proportional to the product of that charge and the force electric field intensity which causes the mass to remain close to a reference position between the plates.