Resonant MEMS based on cubic GaN layers

Abstract

AbstractIn this work, we report the fabrication of GaN microelectromechanical structures (MEMS) based on cubic GaN grown by molecular beam epitaxy on 3C‐SiC(100)/Si(100) pseudosubstrates. Free‐standing beam resonators with a width of 5 μm and lengths from 250 to 1000 μm were patterned and characterized. Magnetomotively and electrostatically actuated resonators were analyzed under ambient and vacuum conditions resulting in quality factors of up to 250 under ambient conditions up to 40.000 under vacuum (1.9x10‐5 mbar) and resonant frequencies from 97 to 406 kHz for the fundamental resonant mode. These results allow for the determination of the Young's modulus and the residual strain of the free standing structures. The measured GaN resonators exhibited Young's moduli from 235 to 260 GPa and high residual axial strains from 1.0x10‐3 to 1.25x10‐3. For the cubic GaN layers from which the resonators were fabricated, residual strains between 3.3x10‐3 and 5.8x10‐3 have been extracted from XRD measurements. These values are on the same order of magnitude but a definite factor higher compared to the measurement results obtained for the fabricated GaN‐beams, which indicates a partial layer relaxation caused by the influences of the MEMS fabrication processes. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)