Abstract
A zinc oxide nanorod ammonia microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process was investigated. The structure of the ammonia sensor is composed of a sensitive film and polysilicon electrodes. The ammonia sensor requires a post-process to etch the sacrificial layer, and to coat the sensitive film on the polysilicon electrodes. The sensitive film that is prepared by a hydrothermal method is made of zinc oxide. The sensor resistance changes when the sensitive film adsorbs or desorbs ammonia gas. The readout circuit is used to convert the sensor resistance into the voltage output. Experiments show that the ammonia sensor has a sensitivity of about 1.5 mV/ppm at room temperature.
Highlights
Ammonia sensors are important devices that can be applied in agriculture, biomedicine and industry
The ammonia sensor chip without readout circuit was set in the test chamber, and its resistance variation under different ammonia concentrations was recorded by the LCR meter
A zinc oxide nanorod ammonia microsensor integrated with a readout circuit manufactured by the complementary metal oxide semiconductor (CMOS)-microelectromechanical system (MEMS) technique was successfully implemented
Summary
Ammonia sensors are important devices that can be applied in agriculture, biomedicine and industry. Briand et al [6] employed anisotropic bulk silicon micromachining to fabricate a low-power consumption metal-oxide-semiconductor field-effect transistor (MOSFET) array gas sensor. Fabrication of MEMS devices using the commercial CMOS process is called the CMOS-MEMS technique [7,8,9,10] Microdevices manufactured by this technique can be integrated with circuits as a system -on-a-chip (SOC) due to their compatibility with the CMOS process. In this study we utilize the CMOS-MEMS technique to develop an ammonia sensor with a readout circuit-on-a-chip. The post-process includes etching the sacrificial oxide layer and coating the sensitive film. The ammonia sensor produces a change in resistance as the sensitive film absorbs or desorbs ammonia, and the readout circuit converts the resistance variation of the sensor into the output voltage
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