This study designs and implements a stress isolation guard-ring structure to improve the performances of the existing single proof-mass three-axis piezoresistive accelerometer. Thus, the environment disturbances, such as temperature variation and force/deflection transmittance, for a packaged three-axis piezoresistive accelerometer are significantly reduced. In application, the three-axis piezoresistive accelerometer has been fabricated using the bulk micromachining process on the SOI wafer. Experimental results show that the out-of-plane deformation of the suspended spring mass on the packaged accelerometer is reduced from 0.72 to 0.10 µm at a 150 °C temperature elevation. The temperature coefficient of zero-g offset for the presented sensor is reduced, and the temperature-induced sensitivity variation is minimized as well. Measurements also demonstrate that the guard-ring design successfully reduces the false signals induced by the force and displacement transmittance disturbances for one order of magnitude. Moreover, the three-axis acceleration sensing for the presented accelerometer with guard ring has also been demonstrated with sensitivities of 0.12–0.17 mV V−1 g−1 and nonlinearity < 1.02%.

This study presents a novel double-side CMOS (complementary metal-oxide-semiconductor) post-process to monolithically integrate various capacitance-type CMOS MEMS sensors on a single chip. The CMOS post-process consists of three steps: (1) front-side bulk silicon etching, (2) backside bulk silicon etching and (3) sacrificial surface metal layers etching. Using a TSMC 2P4M CMOS process and the present double-side post-process this study has successfully integrated several types of capacitive transducers and their sensing circuits on a single chip. Monolithic integration of pressure sensors of different sensing ranges and sensitivities, three-axes accelerometers, and a pressure sensor and accelerometer are demonstrated. The measurement results of the pressure sensors show sensitivities ranging from 0.14 mV kPa −1 to 7.87 mV kPa −1. The three-axes accelerometers have a sensitivity of 3.9 mV G −1 in the in-plane direction and 0.9 mV G −1 in the out-of-plane direction; and the accelerated measurement ranges from 0.3 G to 6 G.

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