Reduced Residual Stress Curvature and Branched Comb Fingers Increase Sensitivity of MEMS Acoustic Sensor

We present an enhanced in-plane capacitive readout for sensing out-of-plane displacement in a MEMS acoustic sensor. The sensor is fabricated in a multi-user silicon-on-insulator process, using a thicker device layer to reduce misalignment between moving and fixed comb fingers. This misalignment is found to reduce the sensitivity and render the response nonlinear. In addition, incorporation of a branched comb design doubles the readout capacitor surface area for a given sensor size, to further increase the sensitivity. These two modifications restore linearity to the readout and increase its sensitivity to displacement by an order of magnitude.