PLANAR COILS WITH FERROMAGNETIC YOKE FOR A MICROMACHINED TORQUE SENSOR

A process is described for fabrication of planar coils with ferromagne tic yoke as parts of a micromachined torque sensor. These parts are lo cated on the rear side of a silicon wafer where cues sensor devices an d circuitry had been already formed on the front side [1]. Only 'cold' process steps are necessary, such as metal evaporation, electroplatin g, wet etching, sputtering and low-temperature CVD. The wires of the c oils are realized by electroplated gold. To avoid tearing off of furth er layers over the gold edges, a special etch process was developed. T his process provides the possibility of adjusting the gradient of the gold wire slopes. The yoke legs are formed by KOH etched pits and elec troplated NiFe.