Abstract
This paper reports a low-cost, high-sensitivity CMOS-MEMS piezoresistive accelerometer with large proof mass. In the device fabricated using ON Semiconductor 0.5 μm CMOS technology, an inherent CMOS polysilicon thin film is utilized as the piezoresistive sensing material. A full Wheatstone bridge was constructed through easy wiring allowed by the three metal layers in the 0.5 μm CMOS technology. The device fabrication process consisted of a standard CMOS process for sensor configuration, and a deep reactive ion etching (DRIE) based post-CMOS microfabrication for MEMS structure release. A bulk single-crystal silicon (SCS) substrate is included in the proof mass to increase sensor sensitivity. In device design and analysis, the self heating of the polysilicon piezoresistors and its effect to the sensor performance is also discussed. With a low operating power of 1.5 mW, the accelerometer demonstrates a sensitivity of 0.077 mV/g prior to any amplification. Dynamic tests have been conducted with a high-end commercial calibrating accelerometer as reference.
Highlights
The piezoresistive effect is one of the most exploited physical effects in sensors
CMOS-MEMS technology provides a viable means for monolithic integration of MEMS elements with mainstream CMOS electronics, for an overall improved device performance and possible lower cost [8]
Compared to the reported devices, higher sensor sensitivity and larger process tolerance are achieved by using a maskless bulk deep reactive ion etching (DRIE) CMOS-MEMS microfabrication to include single-crystal silicon (SCS)
Summary
The piezoresistive effect is one of the most exploited physical effects in sensors. Since the discovery of the excellent mechanical properties and late on the manufacturability of silicon and other semiconductors, a large array of MEMS piezoresistive sensors have been developed [1,2,3]. According to the topological configurations of the sensing elements, the reported piezoresistive accelerometers can be classified into the following four thing listed categories [5]:. (2) Double-clamped beams, where the seismic mass is suspended by two (or more) beams and the mechanical stress is mainly concentrated in four areas in each beam;. Far most of the reported CMOS-MEMS piezoresistive accelerometers use thin film structures as proof mass [10,11]. Compared with the wet process for SCS proof mass manufacturing [14,15], the DRIE method is more effective and environmentally-friendly. A low cost, high sensitivity CMOS-MEMS piezoresistive accelerometer is designed, fabricated and tested. Compared to the reported devices, higher sensor sensitivity and larger process tolerance are achieved by using a maskless bulk DRIE CMOS-MEMS microfabrication to include SCS as proof mass. Using multiple CMOS metal layers, the four poly resistors are conveniently wired to form a full sensing Wheatstone bridge for even higher sensitivity
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