Analysis of full and cross-shaped boss membranes with piezoresistors in transversal strain configuration

A 3D force sensor is developed using bulk silicon micromachining for measuring force in the sub-muN range. It is intended for use in high precision coordinate measuring machines. Full and cross-shaped boss membranes are fabricated, where the total chip size is 6.5 X 6.5 mm2. The full membrane is 3000 X 3000 mum2 and the beams of the cross-shaped membrane are 900 X 700 mum2 with 16 p-diffused piezoresistors in transversal strain configuration. The strains detected by the piezoresistors are measures of the three orthogonal components of the force applied at the tip of the stylus, which is glued on the center of the boss. When a vertical load is applied to the stylus, higher sensitivity is obtained for the cross-shaped membrane than for the full membrane.