Nikkei BP reported on January 26, 2006 that the Department of Mechanical and Electrical Engineering of Tamkang University in Taiwan successfully developed a small pressure sensor chip with a size of 50μm × 50μm, which was published at the "MEMS 2006" conference held recently. :MP28). The miniaturization is achieved by improving the film forming method of the pressure sensor portion. The sensor portion is also encapsulated using gelatin. This pressure sensor can be used in biologically relevant fields.
The process developed this time uses a SiO2 layer in the film of the sensor portion, a metal layer is used in the sacrificial layer supporting the film during production, and polysilicon is used in the piezoelectric resistor for detecting the pressure. All can be formed by a CMOS process of TSMC double-layer polysilicon four-layer metal. Holes are cut in a portion of the SiO2 layer and vias are formed, and then the sacrificial layer and via metal can be removed using a subsequent etching process. After the sacrificial layer is removed, the silicon substrate underlying the sacrificial layer is also etched to allow the piezoresistive portion to change in addition to pressure. The metal and silicon substrate are etched using a common etch material.
The process of closing the apertured film uses a different process than CMOS. Specifically, protein gelatin is filled from the cut holes to fill the lower space of the film. Simply apply liquid gelatin by spin coating. By filling gelatin, it is possible to eliminate interference from the external environment. The pressure sensitivity is 8.56 ± 0.13mv / V / psi, higher than the past piezoresistive pressure sensor.
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