Monolithic CMOS-MEMS Tactile Force/Proximity Sensors with Full Wheatstone Bridge and Shielding Electrode

This study demonstrates a tactile sensor design by monolithic integration of capacitive proximity and piezo-resistive sensing units. The vertically integrated sensors with distinct sensing mechanisms reduce device footprint and avoid cross-talk of sensors. The structural configuration induces opposing stress under normal loading, enabling full Wheatstone bridge-based normal force detection, which significantly enhances sensitivity and reduces thermal drift. Additionally, the incorporation of a shielding electrode improves the performance of the proximity sensing unit. The proposed design is leveraged by the TSMC $0.35\mu \mathrm{m}$ 2P4M standard CMOS process and in-house post-CMOS release. Measurement results demonstrate that the full Wheatstone bridge configuration enhances normal force detection sensitivity by 1.93-fold and reduces thermal drift by 4.3-fold. Furthermore, the incorporation of a shielding electrode improves proximity sensing sensitivity by 2.4-fold.