Low-Concentration Ammonia Gas Sensors Manufactured Using the CMOS–MEMS Technique

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

A Review of Gas Measurement Set-Ups

“…By contrast, in the dynamic mode of measuring sensor properties, changes in the measured quantity, most often resistance, are recorded over time [ 50 , 71 , 77 , 94 ]. Dynamic measurement, as the name suggests, progresses continuously—recording the dynamics of the sensor while feeding gas to the measuring chamber after stopping the gas dosing.…”

“…Despite the fact that there are many publications on gas sensors, there is no review on measurement methods and measuring set-ups, which makes it impossible to directly compare the obtained results. Usually, in the papers describing the tests of the properties of gas sensors, the test set-up is only briefly described [ 50 , 51 , 52 ] or often not at all [ 53 , 54 , 55 ]. Therefore, it is reasonable to prepare an overview of gas-sensor measuring set-ups and to try to characterise their properties and parameters.…”

Manufacturing and Characterization of Three-Axis Magnetic Sensors Using the Standard 180 nm CMOS Technology

“…The CMOS technology is adopted to make micro elements [19,20], micro actuators [21][22][23][24] and micro sensors [25][26][27][28][29][30]. The benefits of MSs that are made using the CMOS technology have low noise, high performance and easy mass-production.…”

VOCs Sensing by Metal Oxides, Conductive Polymers, and Carbon-Based Materials

“…Most studies of gas/vapor sensitive materials are focused on the detection of low concentrations of CO, NO 2 , O 3 , H 2 , NH 3 , or H 2 S due to their toxicity, their relation with atmospheric composition, or the fact that these gases can be found at high levels in certain environments [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. However, in recent years, the application of gas/vapor sensitive materials has been extended to the detection of volatile organic compounds (VOCs), not only because their presence is significant in the industry and domestic sector, but also because of their relevance as markers for (indoor/outdoor) air [ 19 ] and food quality [ 20 ], and early diagnosis of several diseases [ 21 ].…”