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Most currently integrated silicon microsystems available for pressure sensing are based on preprocessing before CMOS IC technology. These microsystems are generally very sensitive to parasitism effect and not available for IC-compatible process. This limits the accuracy of the microsystem and batch-fabrication. Calibration cost is also increased. To overcome these problems, a new generation of pressure microsystems without preprocessing CMOS IC technology has been proposed. This pressure-sensing system consists of a miniature silicon capacitive sensor, fabricated with silicon-silicon bonding technique, and a detection integrated circuit. Only the standard layers of CMOS process are used to build the system and only several photolithography steps are necessary to achieve the micromachined structure in postprocessing, so a high long-term stability could be assured. The entire system converts absolute pressure changes, in the pressure range useful for barometal applications, to frequency changes. A reference capacitor is used in the system and a (delta) C model is applied to cancel out temperature dependence and to compensate non-linearity. The pressure range of the sensor is from 0.5 bar to 1.5bar and the temperature varies between -25 degree(s)C and -60 degree(s)C. A sensitivity of 50Hz/Torr could be achieved.
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