Abstract
An oxygen gas microsensor based on nanostructured sol-gel TiO2 thin films with a buried Pd layer was developed on a silicon substrate. The nanostructured titania thin films for O2 sensors were prepared by the sol-gel process and became anatase after heat treatment. A sandwich TiO2 square board with an area of 350 μm × 350 μm was defined by both wet etching and dry etching processes and the wet one was applied in the final process due to its advantages of easy control for the final structure. A pair of 150 nm Pt micro interdigitated electrodes with 50 nm Ti buffer layer was fabricated on the board by a lift-off process. The sensor chip was tested in a furnace with changing the O2 concentration from 1.0% to 20% by monitoring its electrical resistance. Results showed that after several testing cycles the sensor's output becomes stable, and its sensitivity is 0.054 with deviation 2.65 × 10−4 and hysteresis is 8.5%. Due to its simple fabrication process, the sensor has potential for application in environmental monitoring, where lower power consumption and small size are required.
Highlights
Traditional semiconductor gas sensors for relevant gases like CO, H2, NOx and O2 based on metal oxides have been thoroughly investigated due to their good sensitivity, excellent chemical stability and reversible operation [1]
Titanium dioxide (TiO2) has attracted much attention of researchers since it is a typical metal oxide material which can work in harsh environments such as toxic atmospheres and bad temperature conditions
We describe them in detail
Summary
Traditional semiconductor gas sensors for relevant gases like CO, H2, NOx and O2 based on metal oxides have been thoroughly investigated due to their good sensitivity, excellent chemical stability and reversible operation [1]. Thin-film metal oxide semiconductor sensors can be integrated with MEMS (Micro-Electro-Mechanical System) micro-hotplates, which results in lower power consumption compared to traditional ones based on thick-film processes. The preparation of TiO2 thin films with good response properties is a precondition for developing a gas microsensor using such a kind of material. Dry etching tends to change the properties of the deposited TiO2 films, with negative effects on the sol-gel films. A micro O2 sensor which consists of a nano sol-gel TiO2 thin-film board and a pair of interdigitated electrodes was investigated. A wet etching process was applied to define the TiO2 thin-film pattern, and after comparing the quality of the etched board with that fabricated by the dry etching process, wet etching was applied in the micro gas sensor fabrication. Since the sensor was fabricated on a silicon wafer by the standard micromachining process, it could become an individual device with low power consumption which can be integrated with a micro hotplate in the future and play a useful role in environmental monitoring
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