Abstract
This study investigates the fabrication and characterization of an acetone microsensor with a ring oscillator circuit using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The acetone microsensor contains a sensitive material, interdigitated electrodes and a polysilicon heater. The sensitive material is α-Fe2O3 synthesized by the hydrothermal method. The sensor requires a post-process to remove the sacrificial oxide layer between the interdigitated electrodes and to coat the α-Fe2O3 on the electrodes. When the sensitive material adsorbs acetone vapor, the sensor produces a change in capacitance. The ring oscillator circuit converts the capacitance of the sensor into the oscillation frequency output. The experimental results show that the output frequency of the acetone sensor changes from 128 to 100 MHz as the acetone concentration increases 1 to 70 ppm.
Highlights
Gas sensors are important devices for several industrial, environmental, foodstuff and biomedical applications, etc
The LCR meter was adopted to measure the capacitance of the acetone sensor, and the spectrum analyzer was used to record the output frequency of the oscillator circuit
The results revealed that the output frequency of the acetone sensor was
Summary
Gas sensors are important devices for several industrial, environmental, foodstuff and biomedical applications, etc. Liu et al [7] reported a gas microsensor for detecting acetone, and the sensor was fabricated using micromachining technology. The sensitive film of the sensor was SnO2-TiO2 doped with Ag prepared by the sol-gel method, and the film was coated onto the interdigitated electrodes on an alumina substrate using screen printing. Srivastava et al [8] utilized MEMS technology to develop a gas sensor for sensing acetone, methanol and propanol. The acetone sensor without circuits on chip, developed by Srivastava et al [8], had a smallest sensing concentration of 500 ppm. Presented an acetone sensor without circuits on chip, and its smallest sensing concentration was 50 ppm. We employ the same process to develop a capacitive acetone microsensor with a ring oscillator circuit on-a-chip. The post-process consists of removing the sacrificial oxide layer and coating the α-Fe2O3 film
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