A Servo-controlled Capacitive Pressure Sensor with a Three-mask Fabrication Sequence

A Si micromachined servo-controlled capacitive pressure sensor is described. The use of a cappedcylinder shape with pick-off electrodes external to a sealed cavity permits this device to be fabricated in only three masking steps. Device behavior is evaluated experimentally and by finite element analysis. A fabricated device with 2 mm diameter, 9.7 μm structural thickness and 10 μm cavity height provides a measured sensitivity of 0.516 V/kPa over a dynamic range of 20100 kPa gauge pressure, with a non-linearity of <3.22% of full scale. The open-loop sensitivity of this device averaged over a dynamic range of 0-250 kPa is –408 ppm/kPa. A voltage bias applied to the servo-electrode can be used to tune both the open-loop and closed-loop sensitivity by more than 30%.