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Sensors 2014, 14(11), 20360-20371; doi:10.3390/s141120360

Sol-Gel Zinc Oxide Humidity Sensors Integrated with a Ring Oscillator Circuit On-a-Chip

1
Department of Mechanical Engineering, National Chung Hsing University, Taichung 402, Taiwan
2
Department of Mechanical and Electro-Mechanical Engineering, Tamkang University, Tamsui 251, Taiwan
*
Author to whom correspondence should be addressed.
Received: 18 August 2014 / Revised: 10 October 2014 / Accepted: 22 October 2014 / Published: 28 October 2014
(This article belongs to the Section Chemical Sensors)
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Abstract

The study develops an integrated humidity microsensor fabricated using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The integrated humidity sensor consists of a humidity sensor and a ring oscillator circuit on-a-chip. The humidity sensor is composed of a sensitive film and branch interdigitated electrodes. The sensitive film is zinc oxide prepared by sol-gel method. After completion of the CMOS process, the sensor requires a post-process to remove the sacrificial oxide layer and to coat the zinc oxide film on the interdigitated electrodes. The capacitance of the sensor changes when the sensitive film adsorbs water vapor. The circuit is used to convert the capacitance of the humidity sensor into the oscillation frequency output. Experimental results show that the output frequency of the sensor changes from 84.3 to 73.4 MHz at 30 °C as the humidity increases 40 to 90%RH. View Full-Text
Keywords: humidity sensor; ring oscillator circuit; zinc oxide nanowire humidity sensor; ring oscillator circuit; zinc oxide nanowire
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Yang, M.-Z.; Dai, C.-L.; Wu, C.-C. Sol-Gel Zinc Oxide Humidity Sensors Integrated with a Ring Oscillator Circuit On-a-Chip. Sensors 2014, 14, 20360-20371.

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