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CMOS micromachining technology allows the integration of micromachined structures defined by the fine-line geometry of the CMOS interconnect with circuits on the same chip. The mechanical structure is composed of the metal and oxide layers of the CMOS interconnect. One important consideration in design is the control of residual stress difference in the various layers that produce internal bending moments that cause structures to curl in and out of the substrate plane. A temperature stabilization scheme utilizing integrated polysilicon heaters embedded within the micromachined sensor structure to maintain the sensor at a constant temperature has been described. The temperature is maintained higher than the maximum operating temperature of the device. The heated structure is thermally isolated from the substrate to minimize power. This technique has been demonstrated on an out-of-plane accelerometer with a non-linear temperature coefficient of sensitivity. The dc bias stability of the accelerometer improved from 1.7 G °C−1, to 42 mG °C−1, and the sensitivity variation reduced from 60% to 18% of the nominal value over a temperature range of 70 °C after temperature control.
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