Micro-devices with a bi-material-cantilever (BMC) commonly suffer initial curvature due to the mismatch of residual stress. Traditional corrective methods to reduce the residual stress mismatch generally involve the development of different material deposition recipes. In this paper, a new method for reducing residual stress mismatch in a BMC is proposed based on various previously developed deposition recipes. An initial material film is deposited using two or more developed deposition recipes. This first film is designed to introduce a stepped stress gradient, which is then balanced by overlapping a second material film on the first and using appropriate deposition recipes to form a nearly stress-balanced structure. A theoretical model is proposed based on both the moment balance principle and total equal strain at the interface of two adjacent layers. Experimental results and analytical models suggest that the proposed method is effective in producing multi-layer micro cantilevers that display balanced residual stresses. The method provides a generic solution to the problem of mismatched initial stresses which universally exists in micro-electro-mechanical systems (MEMS) devices based on a BMC. Moreover, the method can be incorporated into a MEMS design automation package for efficient design of various multiple material layer devices from MEMS material library and developed deposition recipes.

We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) process. The metal interconnection of the device is fabricated by a 0.5 μm standard CMOS process on 8-inch silicon wafer. Then, a –Si low-temperature fusion bonding is developed to bond the CMOS wafer and the MEMS wafer, with the electrical connection realized by the tungsten through silicon via process. Wafer-level AlGe eutectic bonding is adopted to package the Pirani gauge in a non-hermetic cavity to protect the gauge from being damaged or contaminated in the dicing and assembling process, and to make it suitable for actual applications. To increase the accuracy of the test and restrain negative influence of temperature drift, the Wheatstone bridge structure is introduced. The test results show that before capping, the gauge has an average sensitivity of 1.04 × K· in dynamic range of 0.01–20 Torr. After capping, the sensitivity of the gauge does not decrease but increases to 1.12 × K· .

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