Implementation of a Monolithic Single Proof-Mass Tri-Axis Accelerometer Using CMOS-MEMS Technique

Abstract

This paper presents a novel single proof-mass tri-axis capacitive type complementary metal oxide semiconductormicroelectromechanical system accelerometer to reduce the footprint of the chip. A serpentine out-of-plane (Z-axis) spring is designed to reduce cross-axis sensitivity. The tri-axis accelerometer has been successfully implemented using the TSMC 2P4M process and in-house postprocessing. The die size of this accelerometer chip containing the MEMS structure and sensing circuits is 1.78 × 1.38 mm, a reduction of nearly 50% in chip size. Within the measurement range of 0.8 ∼ 6G, the tri-axis accelerometer sensitivities (nonlinearity) of each direction are 0.53 mV/G (2.64%) for the X-axis, 0.28 mV/G (3.15%) for the Y-axis, and 0.2 mV/G (3.36%) for the Z-axis, respectively. In addition, the cross-axis sensitivities of these three axes range from 1% to 8.3% for the same measurement range. The noise floors in each direction are 120 mG/rtHz for the X-axis, 271 mG/rtHz for the Y-axis, and 357 mG/rtHz for the Z-axis. Index Terms-Complementary metal oxide semiconductor (CMOS)-MEMS, tri-axis accelerometer. I. INTRODUCTIONS MALL SIZE, low cost, multifunction, low power consumption, and easy integration with consumer electronics are some of the primary design issues for commercial microelectromechanical system (MEMS) applications such as inertia sensors and microphones. Various approaches have been reported to meet the related design requirements. The fabrication of micromechanical components using existing IC foundries provides a promising option to realize MEMS sensors. MEMS sensors can be fabricated by means of a complementary metal oxide semiconductor (CMOS) process together with post-CMOS processing, named the CMOS-MEMS process [1].

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