Fabrication of mems devices – a scanning micro mirror case study

Abstract

This paper presents the working principle, design, and fabrication of a silicon-based scanning micromirror with a new type of action mechanism as an example of MEMS (Micro-Electro-Mechanical Systems). Micromirrors can be found in barcode readers as well as micro-projectors, optical coherence tomography, or spectrometers’ adjustable filters. The fabrication process of the device prompted us to describe and discuss the problems related to the manufacture of MEMS. The article starts with some terminology and a brief introduction to the field of microsystems. Afterwards, the concept of a new scanning micromirror is explained. The device is operated by two pairs of thermal bimorphs. A special design enables to maintain a constant distance from the center of the mirror to the light source during the scanning process. The device was implemented in a one degree-of-freedom micromirror and a two degree-of-freedom micromirror. The fabrication process of both types is described. For each case, a different type of substrate was used. The first type of substrate was a standard silicon wafer; the second one, SOI (Silicon-On-Insulator). The process with the first one was complicated and caused many problems. Replacing this substrate with SOI solved some of the issues, but did not prevent new ones from arising. Nevertheless, the SOI substrate produces much better results and it is preferable to manufacture this type of MEMS devices.