This paper presents the design, fabrication, and characterization of an inductive complementary metal oxide semiconductor micro-electromechanical systems (CMOS-MEMS) accelerometer with on-chip digital output based on LC oscillators. While most MEMS accelerometers employ capacitive detection schemes, the proposed inductive detection scheme is less susceptible to the stress-induced structural curling and deformation that are commonly seen in CMOS-MEMS devices. Oscillator-based frequency readout does not need analog to digital conversion and thus can simplify the overall system design. In this paper, a high-Q CMOS inductor was connected in series with the low-Q MEMS sensing inductor to improve its quality factor. Measurement results showed the proposed device had an offset frequency of 85.5 MHz, sensitivity of 41.6 kHz/g, noise floor of 8.2 mg/√Hz, bias instability of 0.94 kHz (11 ppm) at an average time of 2.16 s, and nonlinearity of 1.5% full-scale.
Keywords: CMOS-MEMS; LC tank; accelerometer; digital output; inductive; inductor; oscillator; quality factor; sprinductor.