A Novel Micromachining Process Using DRIE, Thermal Oxidation, Electroplating, and Planarization to Create High Aspect Ratio Coplanar Waveguides

• Published in: Journal of microelectromechanical systems 2010-02, Vol.19 (1), p.55-63
• Main Authors: Todd, S.T., Huang, X.T., Bowers, J.E., MacDonald, N.C.
• Format: Article
• Language: English
• Subjects: Applied sciences; Circuit properties; Conductors; Coplanar waveguides; Coplanar waveguides (CPWs); Electric power lines; Electric, optical and optoelectronic circuits; Electronics; electroplating; Exact sciences and technology; Gold; High aspect ratio; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Mesas; Microelectronic fabrication (materials and surfaces technology); Micromachining; Micromechanical devices and systems; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Oxidation; Physics; Planar transmission lines; Planar waveguides; Planarization; Precision engineering, watch making; RF MEMS; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Solids; Surface impedance; thermal oxidation; Transmission lines
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2009.2036745

A micromachining process has been developed to create high aspect ratio coplanar waveguides (HARCs). The process creates tall Si mesas using deep reactive-ion etching and converts them into solid SiO 2 mesas using thermal oxidation. Tall Au conductors are deposited using electroplating and planarized using lapping and chemical-mechanical planarization. The solid SiO 2 mesas form the dielectric gap between the tall Au conductors, resulting in HARCs with a planar surface. The tall conductor sidewalls created from the high aspect ratio process reduce the transmission line resistance, which allows the lines to have lower loss at low impedances compared to conventional transmission lines. Transmission lines with characteristic impedances of 16-21 ¿ have been fabricated on high-resistivity Si. Transmission line characteristics were measured from 1 to 50 GHz and showed an attenuation of 1.0-1.4 dB/cm at 10 GHz. Measurements were compared to HFSS simulations and showed reasonable agreement over the frequency range.