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Polypyrrole porous micro humidity sensor integrated with a ring oscillator circuit on chip
Ming-Zhi Yang1, Ching-Liang Dai, De-Hao Lu
1Department of Mechanical Engineering, National Chung Hsing University, Taichung 402, Taiwan. g9761312@mail.nchu.edu.tw
Sensors (Basel, Switzerland)
|December 14, 2011
Summary
This study developed a micro humidity sensor using complementary metal-oxide-semiconductor (CMOS) technology. The sensor, featuring a polypyrrole film, achieves a high sensitivity of 99 kHz/%RH for accurate humidity monitoring.
Area of Science:
- Materials Science
- Electrical Engineering
- Sensor Technology
Background:
- Accurate humidity sensing is crucial for various applications.
- Integrated micro-sensors offer miniaturization and enhanced performance.
- Conventional humidity sensors often lack sensitivity or require complex fabrication.
Purpose of the Study:
- To design and fabricate an on-chip capacitive micro humidity sensor.
- To integrate the sensor with a five-stage ring oscillator circuit for frequency output.
- To utilize polypyrrole as a sensing film for enhanced performance.
Main Methods:
- Complementary metal-oxide-semiconductor (CMOS) process for chip fabrication.
- Spiral interdigital electrodes to increase sensing capacitance and sensitivity.
- Post-CMOS processing involving wet etching and polypyrrole film coating.
- Ring oscillator circuit to convert capacitance variations into frequency output.
Main Results:
- Fabrication of a compact humidity sensor chip (approx. 1 mm²).
- Polypyrrole sensing film with a porous structure prepared via chemical polymerization.
- Demonstrated capacitance change upon water vapor absorption/desorption.
- Achieved a high sensitivity of approximately 99 kHz/%RH at 25 °C.
Conclusions:
- Successful integration of a capacitive micro humidity sensor with a ring oscillator on a single chip.
- The developed sensor exhibits high sensitivity and potential for miniaturized humidity monitoring systems.
- The use of polypyrrole and CMOS technology offers a promising approach for advanced humidity sensing applications.
