A Capacitive Micro Gas Flow Sensor based on Slip Flow

Abstract

This paper presents a capacitive pressure-based micro gas flow sensor with slip flow analyses considering velocity slip at the wall. The sensor consists of a pair of capacitors for measuring pressure difference between the inlet and outlet and absolute pressure at the outlet, inlet/outlet reservoirs, and the main microchannel causing pressure difference. The main microchannel is 128.0 μm wide, 4.64 μm deep, and 5680 μm long, where the outlet Knudsen number is 0.0137. The sensor was fabricated using wet etching, ultrasonic drilling, Deep Reactive Ion Etching (RIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet to outlet pressure ratio increased up to 1.24. With the increasing pressure difference, the capacitance change of the differential pressure sensor and flow rates through the main microchannel increases. The sensitivity of the sensor will also be discussed.