Monolithic Low Noise and Low Zero-g Offset CMOS/MEMS Accelerometer Readout Scheme

Foundry Service of CMOS MEMS Processes and the Case Study of the Flow Sensor

The complementary metal-oxide-semiconductor (CMOS) process is the main stream to fabricate integrated circuits (ICs) in the semiconductor industry. Microelectromechanical systems (MEMS), when combined with CMOS electronics to form the CMOS MEMS process, have the merits of small features, low power consumption, on-chip circuitry, and high sensitivity to develop microsensors and micro actuators. Firstly, the authors review the educational CMOS MEMS foundry service provided by the Taiwan Semiconductor Research Institute (TSRI) allied with the United Microelectronics Corporation (UMC) and the Taiwan Semiconductor Manufacturing Company (TSMC). Taiwan’s foundry service of ICs is leading in the world. Secondly, the authors show the new flow sensor integrated with an instrumentation amplifier (IA) fabricated by the latest UMC 0.18 µm CMOS MEMS process as the case study. The new flow sensor adopted the self-heating resistive-thermal-detector (RTD) to sense the flow speed. This self-heating RTD half-bridge alone gives a normalized output sensitivity of 138 µV/V/(m/s)/mW only. After being integrated with an on-chip amplifier gain of 20 dB, the overall sensitivity of the flow sensor was measured and substantially improved to 1388 µV/V/(m/s)/mW for the flow speed range of 0–5 m/s. Finally, the advantages of the CMOS MEMS flow sensors are justified and discussed by the testing results.

Research on Decomposition of Offset in MEMS Capacitive Accelerometer

In a MEMS capacitive accelerometer, there is an offset due to mechanical and electrical factors, and the offset would deteriorate the performance of the accelerometer. Reducing the offset from mechanism would benefit the improvement in performance. Yet, the compositions of the offset are complex and mix together, so it is difficult to decompose the offset to provide guidance for the reduction. In this work, a decomposition method of offset in a MEMS capacitive accelerometer was proposed. The compositions of the offset were first analyzed quantitatively, and methods of measuring key parameters were developed. Based on our proposed decomposition method, the experiment of offset decomposition with a closed-loop MEMS capacitive accelerometer was carried out. The results showed that the offset successfully decomposed, and the major source was from the fabricated gap mismatch in the MEMS sensor. This work provides a new way for analyzing the offset in a MEMS capacitive accelerometer, and it is helpful for purposefully taking steps to reduce the offset and improve accelerometer performance.

Implementation of a CMOS/MEMS Accelerometer with ASIC Processes

This paper presents the design, simulation and mechanical characterization of a newly proposed complementary metal-oxide semiconductor (CMOS)/micro-electromechanical system (MEMS) accelerometer. The monolithic CMOS/MEMS accelerometer was fabricated using the 0.18 μm application-specific integrated circuit (ASIC)-compatible CMOS/MEMS process. An approximate analytical model for the spring design is presented. The experiments showed that the resonant frequency of the proposed tri-axis accelerometer was around 5.35 kHz for out-plane vibration. The tri-axis accelerometer had an area of 1096 μm × 1256 μm.