Abstract
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.
Highlights
Micro-electromechanical systems (MEMS) accelerometers have been widely used in consumer electronic devices and automobiles
To alleviate the effect of residual stress on the sensor structure and its performance in the presence of structural deformation, this paper presents an inductive complementary metal oxide semiconductor (CMOS)-MEMS accelerometer employing on-chip planar variable inductors as sensing elements
This paper presents a new circuit design where a high-Q CMOS inductor is connected in series with the MEMS sensing inductor to improve the overall quality factor and, the sensor performance
Summary
Micro-electromechanical systems (MEMS) accelerometers have been widely used in consumer electronic devices and automobiles. The capacitive accelerometers have been attracting the most focus in both industry and academia due to their high sensitivity, insensitivity to temperature, and compatibility to the MEMS and complementary metal oxide semiconductor (CMOS) fabrication processes Due to their miniature dimensions and, their small signal levels, it is desirable to place the readout circuits close to the sensors to reduce the adverse effects of parasitics and noise. In a monolithically integrated CMOS-MEMS capacitive accelerometer, the sensing capacitor is composed of a movable and a fixed electrode Both electrodes are typically realized by stacking multiple metal and oxide layers of the backend CMOS processes [1,2,3,4]. To alleviate the effect of residual stress on the sensor structure and its performance in the presence of structural deformation, this paper presents an inductive CMOS-MEMS accelerometer employing on-chip planar variable inductors as sensing elements. The operation principle of the inductive accelerometer, the analysis of the effects of residual stress on the MEMS structures, the MEMS structure and CMOS circuit design, the CMOS-MEMS fabrication, and the sensor characterization are discussed
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