Integrated thermal-conductivity vacuum sensor

Abstract

A thermal-conductivity vacuum sensor with a novel on-chip control system is presented. The sensing structure is a small circuit suspended over a cavity etched in the (100)-oriented silicon substrate. An integrated control system maintains a constant temperature difference between this thermally isolated sensor and the substrate. The control loop allows for a digitally adjustable operating temperature of the sensor. The sensitive range of the prototype vacuum sensor extends from 0.8 Pa (6 mtorr) to approximately 9.2 × 104 Pa (690 torr). The system has been fabricated in a completely unmodified foundry CMOS process, provides a current output, dissipates only 5 mW of power, and occupies an area of approximately 0.3 mm2.