An integrated air-gap-capacitor pressure sensor and digital readout with sub-100 attofarad resolution

The fabrication and characterization of an integrated air-gap-capacitor pressure sensor are presented. The capacitor fabrication process uses standard IC processing to create NMOS circuits, and an added polysilicon layer to create poly-to-n/sup +/ capacitors with a 0.6- mu m-thick dielectric using deposited oxide. Subsequent processing is used to produce deformable, parallel-plate, air-gap capacitors on the front side alongside MOS circuits. Sensor chips are fabricated using 100- mu m*100- mu m, 100-fF air-gap capacitors with on-chip circuitry. The sensor chip is a part of a capacitive measurement system that uses a charge-redistribution sense technique to achieve very high capacitance resolution. The behavior of the pressure sensor chips was studied as a function of applied pressure in the 0-240-kPa (0-35-psi) range. Measurements indicate a sensitivity of 0.93 mV/kPa (6.40 mV/psi) with a deflection of 10 nm/kPa (70 nm/psi) at 0-69 kPa (0-10 psi). Standard deviations indicate a static pressure resolution of 0.54 kPa (0.078 psi), which translates to 30 attofarads at a sampling frequency of 11 kHz. >

[1]  Roger T. Howe,et al.  Process Integration for active polysilicon resonant microstructures , 1989 .

[2]  Hae-Seung Lee,et al.  An integrated air-gap-capacitor process for sensor applications , 1991, TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers.

[3]  Joseph Tze-Shew Kung.  Integrated capacitive sensors using charge-redistribution sense techniques , 1992 .

[4]  D. W. Burns,et al.  Processing conditions for polysilicon films with tensile strain for large aspect ratio microstructures , 1988, IEEE Technical Digest on Solid-State Sensor and Actuator Workshop.

[5]  A. Heuberger,et al.  Anisotropic Etching of Crystalline Silicon in Alkaline Solutions I . Orientation Dependence and Behavior of Passivation Layers , 1990 .

[6]  Michael A. Huff,et al.  A threshold pressure switch utilizing plastic deformation of silicon , 1991, TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers.

[7]  K.D. Wise,et al.  Scaling limits in batch-fabricated silicon pressure sensors , 1987, IEEE Transactions on Electron Devices.

[8]  Hae-Seung Lee,et al.  A compact, inexpensive apparatus for one-sided etching in KOH and HF , 1991 .

[9]  K. Wise,et al.  Pressure sensitivity in anisotropically etched thin-diaphragm pressure sensors , 1979, IEEE Transactions on Electron Devices.

[10]  P. W. Barth,et al.  A theoretical study of transducer noise in piezoresistive and capacitive silicon pressure sensors , 1988 .

[11]  R. Howe,et al.  A digital readout technique for capacitive sensor applications , 1988 .