Fabrication technology for single-material MEMS using polycrystalline diamond

Diamond, due to its large band gap of 5.5 eV, offers the possibility of making MEMS structures out of a single material by varying the doping level to achieve the semiconducting, metallic and insulating (undoped) properties needed in a typical MEMS structure. Polycrystalline diamond (poly-C) is inexpensive and retains many of the unique properties of single-crystal diamond. However, the development of diamond-based single-material MEMS (SMM) technology faces two major challenges; (a) producing highly-insulating and highly-conducting poly-C films in a multilayer structure and (b) developing dry-etching technology to produce multilayer structures made of poly-C. Furthermore, poly-C can be layered to perform a number of functions, whereas a complex stack of materials would otherwise be required. Consequently, due to poly-C's high selectivity as a masking material, the SMM fabrication process developed in the current work allows the reduction of the number of fabrication masks by a factor of 1.5–2 as compared to that used in a conventional MEMS process. A number of complex poly-C SMM structures were fabricated using SiO2 as a sacrificial layer to address the SMM related issues in a single paper.