Fabrication and study of a shallow-gap Pirani vacuum sensor with a linearly measurable atmospheric pressure range

Abstract

A Pirani vacuum sensor with a shallow gap between its heated element and its surrounding substrate heat-sink was fabricated using polysilicon as a sacrificial layer. The polysilicon was post-etched by TMAH solution, and an anti-stiction method was used in several steps of the process including a crucial freeze-drying one. The smallest spacing in this device is 0.3 mu m, and via this narrow gap, the heat conductance from the gas-molecule-collisions from the hot element to the heat sink is greatly enhanced in the atmospheric pressure regime. Therefore, this Pirani vacuum sensor is capable of detecting gas pressure linearly up to around 7 bars. As for the low-pressure regime, a partial dummy compensation method reduces the ambient temperature drift effectively and pressure lower than 10(-3) Torr was measurable. Moreover, device packaging was also studied to protect the tiny sensor from any contamination including dust and particles.