Infrared imaging of an integratable, robust thermal flow sensor with a thick silicon dioxide membrane and through-going silicon heat conductors

A silicon based gas flow sensor have been designed, manufactured and investigated. The sensor, with an integrated channel, is designed to be robust, integratable and to be capable of high pressure applications. To realize a thick pressure-withstanding membrane with low thermal conductivity, trenches are formed through deep reactive ion etch (DRIE), and then refilled through thermal oxidation. Silicon vias are used to conduct heat from heaters placed on top of the membrane to the gas in the channel. Silicon vias separated by 60 μm of the silicon oxide membrane show to have a temperature difference of 116°C when one is heated 154°C above room temperature. Characterization of the device was performed using both direct electric measurement on the sensor and thermal imaging (with an infrared camera). The sensor signal that has been recorded at flows from 0 to 650 sccm agrees with data obtained with infrared imaging.