Highly Sensitive Sputtered ZnO:Ga Thin Films Integrated by a Simple Stencil Mask Process on Microsensor Platforms for Sub-ppm Acetaldehyde Detection

Abstract

The integration of a 50-nm-thick layer of an innovative sensitive material on microsensors has been developed based on silicon micro-hotplates. In this study, integration of ZnO:Ga via radio-frequency (RF) sputtering has been successfully combined with a low cost and reliable stencil mask technique to obtain repeatable sensing layers on top of interdigitated electrodes. The variation of the resistance of this n-type Ga-doped ZnO has been measured under sub-ppm traces (500 ppb) of acetaldehyde (C2H4O). Thanks to the microheater designed into a thin membrane, the generation of very rapid temperature variations (from room temperature to 550° C in 25 ms) is possible, and a rapid cycled pulsed-temperature operating mode can be applied to the sensor. This approach reveals a strong improvement of sensing performances with a huge sensitivity between 10 and 1000, depending on the working pulsed-temperature level.