Micro gap effect on dilute H2S sensing properties of SnO2 thin film microsensors

The micro gap effect has been investigated on dilute H2S sensing using SnO2 thin film microsensors equipped with Au or Pt micro gap electrode. The micro gap electrode was fabricated by means of MEMS techniques (photolithography and FIB) and the gap size was varied in the range of 0.1–1 μm. For the SnO2 sensors equipped with Au micro gap electrode, the sensor response to dilute H2S was slightly increased with decreasing gap size, suggesting the small micro gap effect. The sensor response was divided into that at oxide–electrode interface (Si) and at oxide grain boundary (Sgb). It was found that the small Sgb/Si ratio was responsible for the small micro gap effect and that the high sensor response at grain boundary was characteristic in SnO2–H2S system. On the other hand, the SnO2 sensors with Pt micro gap electrode, the clear and large micro gap effect was obtained on dilute H2S sensing. In the Pt electrode sensor, the large Sgb/Si value induced the large micro gap effect. It was found that the Pt/SnO2 interface showed much higher sensor response than the Au/SnO2 interface. The electrode material strongly affected the sensing properties of semiconductor gas sensor with micro gap electrode.