An ASIC for readout of post-processed thin-film MEMS resonators by employing capacitive interfacing and active parasitic cancellation

Thin-film MEMS bridges as micro-resonators have proven attractive for various sensing applications (acceleration, mass, chemical, pressure, etc.) by using frequency shift as a basis for sensing [1]. Low-temperature processing of amorphous-silicon (a-Si:H) enables low-cost fabrication of high-Q MEMS bridges having excellent compatibility with CMOS post processing. However, the a-Si:H bridges have weak motional conductances [2]. Parasitic feed-through capacitances, both due to the device structure and routing, can easily drown out the resonant behavior. This paper proposes a non-contact MEMS interfacing and readout system in standard CMOS which enables robust integration while substantially rejecting the effects of parasitic feed-through capacitance.