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.
Highlights
In 1988, Demarne et al [1] patented the first metal-oxide semiconductor (MOS) gas sensors based on a micromachined silicon substrate
We explore the use of fully compatible micromachining technologies to elaborate microheaters and deposit sensitive layers to obtain sensors at the micron scale
Because the microheater was designed for use on a thin membrane, it was possible for us to generate very fast temperature variations, and a rapid temperature cycled mode could be applied
Summary
In 1988, Demarne et al [1] patented the first metal-oxide semiconductor (MOS) gas sensors based on a micromachined silicon substrate. It has been shown that the well-defined pore structure of metal-organic frameworks was able to provide molecular sieving at the surface of ZnO nanowires [5] Another common method to enhance selectivity is to use sensor arrays based on two or more sensing elements in order to detect gas with data of higher dimensions [6]. Llobet et al [9] showed that the transient response of thermally cycled metal oxide sensors decreases the influence of humidity on sensor response and the drift in the resistance of the gas sensitive layer In this approach, it has been shown that, with very short temperature pulses, transient sensor responses are strongly dependent on the ambient mixture of gases, so this approach can enhance sensor selectivity [10]. The microsensors were tested with variable thermal sequences under a low-level concentration (0.5 ppm) of acetaldehyde
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