Area minimization of a three-axis separate mass capacitive accelerometer using the ThELMA process

Abstract

This paper presents a comparison between two designs of capacitive accelerometers implemented using the Thick Epitaxial Layer for Micro-actuators and Accelerometers (ThELMA) process. The design methodology aims to reduce the total device area whilst using a separate mass approach for the three different axes. The designs use a folded spring topology and serpentine spring topology for the in-plane sensors and torsional springs for the out-of-plane (Z-axis) sensor. The sensors have a resonant frequency of about 1.7 kHz, a maximum acceleration of 13g, a sensitivity of around 8 fF/g and a mechanical cross-axis sensitivity of less than 1%. A reduction of 23% in device area was achieved between these two designs, without a reduction in performance.