Low Power CMOS-MEMS nN Force Sensor using Force-Enabled Resistive Load Inverter (FERI)

This paper presents an N-bit nano-Newton (nN) MEMS force sensor that delivers a digital output, enabling direct integration with digital processors without needing an analog front-end. This design significantly reduces the power consumption of the sensor and its associated read-out circuitry in modern smart devices. The sensor has an array of Parylene-C cantilever-based Force-Enabled Resistive Inverters (FERIs), with a Force-Enabled Field-Effect Transistor (FE-FET) acting as the driver transistor. Each cantilever is designed to detect a specific force, with a metal strip attached to the cantilever tip. The cantilever is placed above a resistive load inverter, where the drain of the FE-FET and the load resistor (R_L) are not connected through permanent contact, resulting in a logic ‘1’ output (V_Oi = V_DD). With an external stimulus such as force, the cantilever deforms and the drain of FE-FET connected to a resistor through the cantilever tip, pulling the output voltage to logic ‘0’ (V_Oi = 0, i is the switch number). The sensor is designed to detect forces in the range of 0 to 1 μN with a resolution of 100nN (F₁). In the absence of an input force, the status of S₁-S₁₀ is 1111111111, which changes to 0000000000 with a 1 μN force. The FE-FET in FERI exhibits low leakage current, achieving an on/off current ratio of approximately 10¹⁰ between input force F_i ≥ iF₁ (on) and F_i < iF₁ (off). This ensures a strong logic ‘1’ at the output with negligible leakage current when the switch is not operating thereby eliminating the reduced logic ‘1’ problem inherent to resistive-load inverters.The sensor achieves an average DC power dissipation (P_DC) of 0.4 mW. The simulations were performed using COMSOL Multiphysics, Sentaurus TCAD, and Cadence Virtuoso, incorporating a Verilog-A–based look-up-table (LUT) methodology to accurately capture process variations and device behavior. A feasible fabrication process integration is demonstrated to realize CMOS-MEMS nN-FERI-based force sensor.