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• Chen, W
• Zhao, Z
• Liu, X
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• Suo, C
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• Zhao, Z
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• Zhang, Z
• Suo, C

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Sensors 2009, 9(9), 7431-7444; doi:10.3390/s90907431

Article

A Capacitive Humidity Sensor Based on Multi-Wall Carbon Nanotubes (MWCNTs)

Wei-Ping Chen^1,2 , Zhen-Gang Zhao^1,* , Xiao-Wei Liu^1,2 , Zhong-Xin Zhang¹  and Chun-Guang Suo¹

¹ Department of Microelectronics, Harbin Institute of Technology, Harbin, Heilongjiang, China ² Key Laboratory of Micro-Systems and Micro-Structures Manufacturing, Ministry of Education, China

* Author to whom correspondence should be addressed.

Received: 29 June 2009; in revised form: 11 August 2009 / Accepted: 24 August 2009 / Published: 16 September 2009

Download PDF Full-Text [485 KB, uploaded 16 September 2009 09:59 CEST]

Abstract: A new type of capacitive humidity sensor is introduced in this paper. The sensor consists of two plate electrodes coated with MWCNT films and four pieces of isolating medium at the four corners of the sensor. According to capillary condensation, the capacitance signal of the sensor is sensitive to relative humidity (RH), which could be transformed to voltage signal by a capacitance to voltage converter circuit. The sensor is tested using different saturated saline solutions at the ambient temperature of 25 °C, which yielded approximately 11% to 97% RH, respectively. The function of the MWCNT films, the effect of electrode distance, the temperature character and the repeatability of the sensor are discussed in this paper.

Keywords: capacitive sensor; humidity sensor; carbon nanotubes (CNTs); capillary condensation

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