The microfabrication technology for MEMS was adopted from microelectronic fabrication technology and has been extended to include other technologies. In this chapter we describe essentials of the microfabrication that are needed to design and fabricate MEMS. If readers need in-depth knowledge of microfabrication technology, they may consult a professional in the field of microfabrication or refer to microfabrication-related articles or books (e.g., Petersen, 1982; Jaeger, 1988; Kovacs, 1998).
2.1 BULK AND SURFACE MICROMACHINING
The terms bulk micromachining and surface micromachining may be used to refer to how to construct both MEMS structures and electronic devices. Readers not familiar with the microfabrication of electronic devices may have difficulty understanding micromachining. For easy understanding of bulk and surface micromachining, we shall use analogies or similar cases from macroscale systems. We begin by considering architectures from ancient cultures. Shown in Fig. 2.1 is a channel built by our ancestors to connect a reservoir to a river and an arched bridge over the channel. The channel shown was made simply by digging the earth. However, building the bridge was is much more difficult. To build the bridge, our ancestors developed the technology shown in Fig. 2.2. Sand and stones (Fig. 2.2b) that would serve as temporary or sacrificial layers were first deposited over the channel, and stones was arranged to make the arch (Fig. 2.2c) that ...