Micromachining technology began to develop rapidly over fifteen years ago, using materials and processes developed for the integrated circuit industry to form miniature structures in silicon and related materials for purposes other than electronic devices. The fabrication of miniature solid state sensors has long been the main thrust of micromachining technology. Much of what is today termed "MEMS" is in some ways only an evolution and expansion of this technology. Improvements possible with MEMS technology involve the expanded range of materials and processes that can be employed, the precise dimensional scale and mechanical complexity that can be achieved in devices, and expanded capabilities for electronic integration. For commercial products, sensors are still the major near-term application thrust of MEMS both in the United States and Japan.
As the term "microelectromechanical systems" suggests, MEMS technology relates most directly and has the greatest impact on sensors for mechanical variables. In contrast, most of the solid state sensor developments for magnetic sensors, chemical sensors, gas sensors, and biosensors do not use significant microstructures or electronic integration, and so do not fall within the definitions of MEMS concepts and technology. These developments were not covered in the selection of Japanese laboratories visited or in this study, and are not discussed in detail here. Additionally, there is a vast array of sensor technology outside the realm of miniature, solid-state devices that is not addressed by this study.
This chapter examines specific MEMS-based sensor technology developments in Japan, both in industry and universities. These are then compared with sensor developments in the United States.