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.
Highlights
Humidity sensors are widely used in industrial, electronic, and biomedical equipment
A spectrum analyzer, a test chamber (HRMB-80, Taichy Technology Ltd., New Taipei, Taiwan) and an LCR meter were employed to test the characteristics of the integrated humidity sensor
The output frequency of the humidity sensor was recorded by the spectrum analyzer
Summary
Humidity sensors are widely used in industrial, electronic, and biomedical equipment. Wang et al [2] proposed a resistive humidity sensor fabricated using the MEMS technology. Kim et al [3] used MEMS technology to manufacture a humidity microsensor that consisted of a top electrode with branch structure, a bottom electrode and a sensing layer. Many studies have utilized zinc oxide as the sensitive material of humidity microsensors. Kiasari et al [9] proposed a resistive humidity microsensor, and its sensitive material was zinc oxide nanowires deposited by chemical vapor deposition (CVD). The humidity microsensor with a readout circuit on-a-chip proposed by Hu et al [13], was fabricated using the commercial 0.18 μm CMOS process. The sensor requires a post-process [14] to coat the sensitive ZnO material This post-process includes etching the sacrificial oxide layer and depositing the ZnO film
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