A CMOS-MEMS nano-Newton force sensor for biomedical applications

This paper reports the design and microfabrication of a CMOS-MEMS capacitive force sensor capable of nano-Newton out-of-plane force measurement. Sidewall and fringe capacitance formed by the multiple CMOS metal layers were utilized and fully differential sensing was enabled by common-centroid wiring of the sensing capacitors. Single-crystal silicon (SCS) is incorporated in the entire sensing element for robust structures and reliable sensor deployment in force measurement. A sensitivity of 0.02 fF/nN in a measurable force range 2 pN to 1 mN is predicted. The minimum detection force is 2.8 pN. The CMOS-MEMS force sensor features easy post-CMOS microfabrication in which directional SiO₂ reactive ion etching (RIE) and silicon deep reactive ion etching (DRIE) are employed.