Absolute Pressure Sensing

In VTI's absolute pressure sensor a silicon wafer is locally thinned to form a pressure sensitive diaphragm. The diaphragm acts as a movable plate of the capacitive sensor. The stationary plate is a thin film metal deposited on a second, glass coated silicon wafer. The wafers are joined by anodic bonding so that a hermetically enclosed space is formed between them.

The diaphragm defletcs due to the pressure difference between the exterior of the sensor and the internal vacuum reference chamber.

The sensor has very good thermal stability, since the mechanical properties of silicon are very stable. Contrary to piezoresistive sensors, the unstable electrical properties of silicon do not affect the capacitive sensor. Silicon is only used as an electrically well conducting mechanical material