Polycrystalline silicon-carbide surface-micromachined vertical resonators-part II: electrical testing and material property extraction

Abstract

This manuscript is the second of a two part series describing the fabrication and testing of megahertz frequency, polycrystalline silicon-carbide (poly-SiC) micromechanical resonators made from films deposited by atmospheric pressure chemical vapor deposition. In Part I, the development of deposition and patterning techniques suitable for the fabrication of vertically actuated, clamped-clamped beam resonant structures was detailed (see Wiser, Chung, Mehregan, and Zorman, Polycrystalline Silicon-Carbide Surface-Micromachined Vertical Resonators-Part I: Growth Study and Device Fabrication, J. Microelectromech. Syst., vol. 14, no. 3, Jun. 2005). This paper describes the testing procedures used to determine the nominal resonant frequencies and quality factors for these resonators, as well as the methods used to calculate the Young's modulus and residual stress of the poly-SiC films from the resonant frequency data. Poly-SiC devices with a resonant frequency ranging from 1 to 4 MHz and quality factors of around 2500 were successfully tested. The quality factors were lower than expected for devices of this design. Modeling and experimental results indicate that the low values are likely due to insufficient doping in the poly-SiC films. Both the Young's modulus and residual stress values calculated for the poly-SiC films (436 GPa and 121 MPa, respectively) compare favorably with values reported in the literature.