A study on experimental demonstration of CMOS–MEMS PiezoMOS force sensors integrated with current-mirror readout circuitry

Purpose This study aims to experimentally validate and characterize PMOS and NMOS current-mirror-integrated cantilever-and bridge-based force sensors. Design/methodology/approach Four sensor configurations were fabricated and characterized, consisting of PMOS- and NMOS-based current-mirror readouts integrated on both cantilever and bridge structures on 2-inch <100> silicon wafers. In each device, the reference MOSFET is placed on the substrate and remains unaffected by applied load, while the output MOSFET, embedded at the fixed edge, converts mechanically induced stress into drain voltage variations via the piezoresistive effect of the MOSFET. Device characterization was performed under controlled and repeatable loading conditions using a nanoindenter. Findings All four sensors showed reproducible voltage responses to the applied force. The sensor sensitivities ranged from 0.010 to 0.95 mV/mN, with the NMOS cantilever sensor showing the highest sensitivity. The NMOS sensors showed approximately an order of magnitude higher sensitivity than PMOS sensors, consistent with the larger piezoresistive coefficients of N-type silicon for the <100> orientation. Furthermore, cantilever sensors showed higher sensitivity than bridge sensors due to their greater mechanical deflection under equivalent loading conditions. Repeated trials and measurements performed on multiple devices showed comparable behavior across the tested samples. Originality/value This work experimentally validates current-mirror-integrated cantilever- and bridge-based force sensors. The proposed approach converts mechanically induced stress directly into an output voltage through a current-mirror circuit, eliminating the need for ΔR/R measurements while maintaining complementary metal-oxide-semiconductor compatibility and reducing readout circuit complexity. The results provide a basis for realizing monolithically integrated piezoMOS force sensing systems, with potential applications in tactile sensing, robotics and biomedical instrumentation.