Micromachining of CVD Diamond for MEMS Applications

Takayuki Shibata

Electronics and Information Engineering,

Graduate School of Engineering, Hokkaido University

Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan

Abstract

The excellent mechanical, electrical, thermal, and chemical properties of diamond make it a candidate material for microsensors and microstructures to be used in microelectromechanical systems (MEMS). There is, therefore, a growing interest in utilizing chemical-vapor-deposited diamond thin film as a material in MEMS, and a variety of micromachining techniques for diamond thin film have been developed. This paper reviews these micromachining techniques and their suitability for the fabrication of diamond MEMS devices. They include the patterning of diamond thin film by selective deposition or dry etching, sacrificial layer etching for the fabrication of movable microstructures to be released from a substrate, a silicon (Si) mold technique for the fabrication of three-dimensional microstructures, and bonding techniques for assembly. In addition, a number of examples of diamond MEMS devices such as a diamond microgripper driven by an electrostatic comb actuator, a semiconductive diamond tip for a scanning tunneling microscope (STM) as well as a machining tool, and a diamond probe for an atomic force microscope (AFM) are also demonstrated. The microgripper was fabricated by patterning boron-doped p-type semiconductive diamond thin film onto a sacrificial SiO₂ layer by selective deposition and releasing the movable parts by sacrificial layer etching. The semiconductive diamond tip was fabricated using a pyramidal pit formed on the surface of a (001) Si substrate by anisotropic etching with a KOH solution. Using the fabricated pyramidal diamond microstructure, the machining of polished Si to form nanoscale grooves, and then in situ STM measurements of the machined structures were carried out. A batch fabrication process for constructing AFM probes with a diamond cantilever integrated with a diamond tip was also developed using our newly developed anodic bonding technique for diamond film to glass together with micromachining techniques, such as the Si mold technique for producing sharp diamond tips and the selective deposition for patterning diamond cantilevers. Applying the fabricated diamond probes to measurements on a commercial AFM system, it was demonstrated that they were capable of obtaining AFM images.

Keywords: CVD diamond, micromachining, MEMS, microstructures, microsensors

Takayuki Shibata

Electronics and Information Engineering,

Graduate School of Engineering,

Hokkaido University,

Kita 13 Nishi 8, Kita-ku,

Sapporo 060-8628, Japan

E-mail: shibata@nano.eng.hokudai.ac.jp

Fax: +81-11-707-6581

Tel: +81-11-706-6441