High Sensitivity Photo-activated Nanostructure and Atmospheric Pressure Plasma Jet Treated Zinc Oxide Gas Sensor at Room Temperature
Date Issued
2015
Date
2015
Author(s)
Luo, Jie-Chun
Abstract
Volatile organic compounds (VOCs) monitoring is one of key indices for environmental monitoring. Long exposure of VOCs at a specific concentration could lead to nervous system suppressing, cancers, and potentially an explosion disaster. It is important nowadays that governance was used to regulate the VOCs emission. Traditional gas sensors utilizing metal oxide as the sensing material were typically equipped with a heater. Although the sensitivity was increased by incorporating a heater, one more photo-mask and additional processing were required to define the heater. With the high temperature heating, it’s not desirable to integrate with CMOS-based circuits and use in explosive environment. In this work, we developed a semiconductor-based gas senor which can detect toluene with high sensitivity at room temperature. Two main topics were conducted in this research work. The first topic is to develop a high sensitivity gas sensor using micro-electromechanical systems (MEMs) technologies. The seed sensing film was deposited by a sputter and nanostructures were fabricated by a hydrothermal method with a special Zinc-nitrate/HMTA ratio. The second topic is to develop an atmospheric pressure plasma Jet (APPJ) treated ZnO sensing film for thin film gas sensor at room temperature. In our ZnO gas sensor using a hydrothermal method to form nanostructures, we found an optimized fabricating time of 5 minutes to provide the maximum sensitivity of the sensor, the nanostructures are coral-like shape. Comparing to a thin film gas sensor with 100nm thickness ZnO without surface treatment, the sensitivity increased approximately 10 times when using a nanostructured ZnO gas sensor. The linearity of our gas sensor for toluene is in the range of 100-5000 ppm, the detection limit is 50 ppm, the rising time is ~10.17 seconds and recovery time is ~5.17 seconds. Comparison with the sensor operated at dark condition, we found the photo-activated sensor with 2 μw/cm2 UV exposure can increase the sensitivity approximately 17%. In APPJ treated gas sensors, we fixed the gas concentration in the range of 500-5000 ppm to compare the heating time and the heating temperature between APPJ and calcination approach. The best parameter for calcination is 200℃ for 3 hours, the resulted sensor rising time is ~3 seconds and recovery time is ~3.5 seconds. Comparison with gas sensors without annealing, gas sensors with annealing provided a better sensitivity of 2.80 ppm/ppm (~9.03% increase than ZnO thin film sensors). The best parameter for APPJ is 1 minute, the resulted sensor rising time is ~10 seconds and recovery time is ~5.75 seconds. Comparison with gas sensors without annealing, gas sensors using APPJ treatment provided a better sensitivity of 2.71 ppm/ppm ( ~5.68% increase than ZnO thin film sensors ). The sensor performance using calcining for 3hr at 200℃ is similar to the sensor performance with APPJ treatment for 1min.
Subjects
gas sensor
UV
room temperature
ZnO
nanostructure
atmospheric pressure plasma jet treatment
SDGs
Type
thesis
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