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. [1030]

Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part II: Beam Resonators for MEMS Above IC

“…14 shows the transfer function of a typical c-c device. The 8.51-MHz device has a Q-factor of 1100, which is among the highest Q-factors reported to date for an SiC flexural-mode beam-type resonant structure through transmission measurements, e.g., [42]. The parallel resonance due to the feedthrough capacitance can be seen but is far enough from the resonant peak to not significantly alter the measurements.…”

Grain size control of (111) polycrystalline 3C-SiC films by doping used as folded-beam MEMS resonators for energy dissipation

“…In an oscillating flexural beam resonator, the relaxation rate of the bending beams affects TED (Feng et al 2006). Using the known material parameters for 3C-SiC (Wiser et al 2005;Fu et al 2005;Trevino et al 2005;Mitchell 2001) and the device dimensions as measured from various SEM micrographs, an estimate of the minimal energy dissipation caused by TED was calculated using Eqs. 2 and 3 (Roszhart 1990).…”

“…This approach has the distinct advantage over the other methods in that it evaluates the performance of a resonator using Si-based circuit elements, holding the potential for on-chip integration should the resonator technology prove to be suitable for applications that would benefit from MEMS technology such as RF communications. However, two previous publications attributed low quality factors in poly-SiC resonators to high electrical resistivities in the structural films (Gao et al 2003;Wiser et al 2005). One of the studies measured the quality factor of kHz frequency, folded-beam poly-SiC resonators to be about 690 (Wiser et al 2005).…”

“…However, two previous publications attributed low quality factors in poly-SiC resonators to high electrical resistivities in the structural films (Gao et al 2003;Wiser et al 2005). One of the studies measured the quality factor of kHz frequency, folded-beam poly-SiC resonators to be about 690 (Wiser et al 2005). The other measured the quality factor of vertically actuated, MHz frequency polySiC resonators obtaining a quality factor of 128.…”

Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part I: Process Development and Characterization

“…Therefore, etching using aqueous solutions must be performed at temperatures greater than 600 • C [43], which makes wet etching impractical for CMOS-compatible processes. As a result, dry etching techniques such as RIE or liftoff methods [44] are commonly employed for patterning SiC. The versatility of RIE, combined with the ability to achieve vertical sidewalls, made it the technique of choice for the process presented here.…”