Micro-hotplate concept and technologies

Silicon micromachining has been used to generate thermally insulated heating elements suspended on a dielectric membrane. By patterning metallic 

The operation of a metal-oxide gas sensor relies on the change in resistance of an n- or p-type semiconducting layer - mainly Sn02 - when exposed to reducing or oxidizing gases. 

A diagram of a typical cross-sectional view of a silicon micromachined metal-oxide (MOX) sensor is presented in Fig. 6.2. Their development has evolved towards silicon substrates to produce devices suitable for commercialization due to their low-cost, low-power consumption and high reliability. To lower the resistivity of the gas sensitive film, as well as to improve the kinetics of the chemical reactions, the metal-oxide layer is heated with a micro-heater. The heated area is usually embedded in a thin dielectric membrane to improve the thermal insulation and to reduce the power consumption of the device, which is typically in the order of a few tens of milliwatts at 300°C, and its thermal time constant (few to tens of milliseconds). Thermal programming allows kinetically controlled selectivity. 

2 Cross-sectional diagram of a micromachined metal-oxide gas sensor. 

3 Heat losses in a micro-heating device conduction, convection and radiation. 

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