Abstract
This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked aluminum layers that are made using the CMOS process. The sensing material; polypyrrole/reduced graphene oxide (PPy/RGO), is synthesized using the oxidation–reduction method; and the material is characterized using an electron spectroscope for chemical analysis (ESCA), a scanning electron microscope (SEM), and high-resolution X-ray diffraction (XRD). After the CMOS process; the AGS needs post-processing to etch an oxide layer and to deposit the sensing material. The resistance of the AGS changes when it is exposed to ammonia. A non-inverting amplifier circuit converts the resistance of the AGS into a voltage signal. The AGS operates at room temperature. Experiments show that the AGS response is 4.5% at a concentration of 1 ppm NH3; and it exhibits good repeatability. The lowest concentration that the AGS can detect is 0.1 ppm NH3
Highlights
Gas sensors are used to detect harmful gases and avoid the danger of harmful gases being inhaled
Nitrogenous waste is released via the respiratory system, so NH3 concentration in the patients’ breath is higher than that of healthy subjects
Prajesh [11] used a microfabrication process to make an ammonia gas sensor (AGS), which consisted of a sensing film, a micro-heater, and interdigitated electrodes (IDEs)
Summary
Gas sensors are used to detect harmful gases and avoid the danger of harmful gases being inhaled. Peng [9] used the MEMS process to produce an ammonia gas sensor (AGS) with a micro-hotplate that consumed less power. Prajesh [11] used a microfabrication process to make an AGS, which consisted of a sensing film, a micro-heater, and interdigitated electrodes (IDEs). The sensing film for the AGS consisted of tungsten trioxide powders with a Ru sol mixture that was synthesized using the sol–gel process This was coated onto a MEMS membrane with electrodes and a heater. The sensing material was graphene metal oxide, and this was deposited on the micro-hotplate using an inkjet printing process. A non-inverting amplifier circuit converts the change in the resistance of the AGS to a voltage output.
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