Chapter 2 ElectroThermal-Mechanical Modeling of Gas Sensor Hotplates

Before the application of semiconducting materials and the discovery of gas sensors, canaries were taken into mines as an alarm for the presence of harmful gases, such as methane, carbon dioxide, and carbon monoxide. A canary is considered to be a songful bird, but it stops singing when exposed to these types of gases, signaling to the miners to exit the mine immediately. By the middle of the previous century, it was demonstrated for the first time that certain semiconducting materials show changing conductivity when exposed to some gas molecules, especially when heated to an elevated temperature [1]. Electrical properties of these materials change when the chemical composition of its ambient gas changes. In the early 1960s, Seyama proposed a gas-sensing device based on a thin ZnO film [2]. With a simple electronic circuit, along with a thin film-sensitive layer operating at 485◦C, it was demonstrated that the detection of a variety of gases such as propane, benzene, and hydrogen was possible. In 1967, Shaver described a new method to improve the sensing properties of some semiconducting metal oxide (SMO) materials towards reducing gases by an addition of small amounts of noble metals, namely, platinum, rhodium, iridium, gold, and