Micromachined semiconductor gas sensors

Abstract This chapter reviews micromachined semiconductor gas sensors. First, the chapter briefly discusses the history of this technology. 

It then addresses the micro-hotplates concept that has led to the development of different types of micromachined gas sensor devices. The different reahzations of micromachined semiconductor gas sensors are presented thin- and thick-film metal-oxide, field effect, and those using complementary metal-oxide semiconductors (CMOSs) and silicon-on-insulator (SOI) technologies. Finally, recent developments based on gas sensitive nanostructures, polymers, printing and foil-based technologies are highlighted. 

Key words silicon micromachining, micro-hotplates, semiconductor, metal-oxide, field-effect, gas sensors, CMOS and SOI, nanowires, printing, polymeric, plastic. 

This chapter therefore focuses on silicon micromachined semiconductor gas sensors. After a brief history of silicon hotplates and metal-oxide 

1 Diagram of the MGS 1100 sensor from Motorola. Micromachined sensor element is illustrated on the left, and the sensor housing on the right. The sensitive films were obtained by rheotaxial growth and thermal oxidation of tin layers (RGTO) deposited on the silicon oxide-nitride membrane. From Simon etal. (2001). 

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Silicon micromachined semiconductor gas sensors are mainly packaged using standard metallic transistor outline (TO) headers as support, and wire bonding is used for their electrical connection. Typically, a metallic cap with a grid is fixed to the TO header with a hydrophobic gas permeable membrane on top of it. A filtering agent can be also included in the package. 

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