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In this paper, a contamination-insensitive differential capacitive pressure sensor with a sealed gap is presented. This device is made of three polysilicon layers including a stationary middle plate and the top and bottom plates that are rigidly coupled together by a series of posts hence deflecting in tandem by a change in differential or gauge pressure. Because of the posts, however, the device is insensitive to common-mode pressure. As the differential pressure is changed from -70 to 70 kPa, the capacitance between the bottom and middle plates changes by 73 fF (sensitivity of approximately 0.5 fF/kPa), yet there is only a 2-fF change in output when the common-mode pressure is changed from 30 to 200 kPa. The devices have a linearity error on the order of -15% FSS and a temperature coefficient of offset of 170 ppm//spl deg/C.