Fabrication and manufacturing technology for optical MEMS

To the uninitiated, the phrase "optical microelectromechanical systems"or optical MEMS must appear to refer to a field of incredible specialization. Ironically, the number of disciplines involved, optics, mechanics, and electronics, make the field most accessible to scientists of great technical breadth. This is especially true when optical MEMS is used in chemical and biological applications-the theme of this text. Underlying all of them is the technology of microfabrication. One chapter could not possibly cover all of the techniques developed over the decades for very-large-scale integration (VLSI) and general MEMS systems. Indeed there are entire textbooks devoted specifically to both types. In this chapter then, we present the characteristics of fabrication and design that are specific to bring optics into the system. In particular, there are a number of materials and fabrication techniques that are specific to optical MEMS systems. When dealing with light, one may have to handle visible, ultraviolet, or infrared portions of the spectrum, each of which has its own special set of optimal substances. Since one often has to emit light or detect it in special wavelength regions, semiconductors other than silicon often must be incorporated, each with their own set of wet and dry chemical etching techniques and their own set of mechanical properties. Standard mechanical characteristics that play no role in "normal"MEMS systems may prove problematic in optical MEMS. For example small size may lead to diffraction, typical surface roughness may limit optical cavity resolution, and mechanical or motion may deform mirrors to limit the number of resolvable spots. Even thermal noise may place limits on optical design. Each of these topics is covered in the pages that follow. For the reader who is interested in further exploring many of these areas, we recommend the text by Solgaard.