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Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip
Department of Mechanical Engineering, National Chung Hsing University, Taichung, 402, Taiwan
* Author to whom correspondence should be addressed.
Received: 25 September 2010; in revised form: 28 October 2010 / Accepted: 28 October 2010 / Published: 10 November 2010
Abstract: This study presents the design and fabrication of a capacitive micro humidity sensor integrated with a five-stage ring oscillator circuit on chip using the complimentary metal oxide semiconductor (CMOS) process. The area of the humidity sensor chip is about 1 mm2. The humidity sensor consists of a sensing capacitor and a sensing film. The sensing capacitor is constructed from spiral interdigital electrodes that can enhance the sensitivity of the sensor. The sensing film of the sensor is polypyrrole, which is prepared by the chemical polymerization method, and the film has a porous structure. The sensor needs a post-CMOS process to coat the sensing film. The post-CMOS process uses a wet etching to etch the sacrificial layers, and then the polypyrrole is coated on the sensing capacitor. The sensor generates a change in capacitance when the sensing film absorbs or desorbs vapor. The ring oscillator circuit converts the capacitance variation of the sensor into the oscillation frequency output. Experimental results show that the sensitivity of the humidity sensor is about 99 kHz/%RH at 25 °C.
Keywords: humidity sensors; polypyrrole; CMOS-MEMS; ring oscillator circuits
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MDPI and ACS Style
Yang, M.-Z.; Dai, C.-L.; Lu, D.-H. Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip. Sensors 2010, 10, 10095-10104.
Yang M-Z, Dai C-L, Lu D-H. Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip. Sensors. 2010; 10(11):10095-10104.
Yang, Ming-Zhi; Dai, Ching-Liang; Lu, De-Hao. 2010. "Polypyrrole Porous Micro Humidity Sensor Integrated with a Ring Oscillator Circuit on Chip." Sensors 10, no. 11: 10095-10104.