| AVS 63rd International Symposium & Exhibition | |
| MEMS and NEMS | Wednesday Sessions |
| Session MN-WeM |
| Session: | Multiscale Phenomena & Emerging Technologies in Micro- and Nano-Systems |
| Presenter: | Christian Zorman, Case Western Reserve University |
| Authors: | A.C. Barnes, Case Western Reserve University C.A. Zorman, Case Western Reserve University |
| Correspondent: | Click to Email |
This paper presents an investigation into the resonant frequency behavior of large area diaphragms made from silicon carbide thin films and the development of a plate-under-tension model to determine the Young’s modulus and residual stress from resonant frequency data. Test specimens consisted of single crystalline (100) 3C-SiC, polycrystalline (111) 3C-SiC and amorphous SiC thin films that were fabricated into nominally 1 x 1 mm2 diaphragms by silicon bulk micromachining. Single crystalline diaphragms ranged in thickness from ~1.5 µm to 125 nm while the polycrystalline and amorphous diaphragms were held in the 1.5 µm thickness range. A thin (~50 nm) Si3N4 diaphragm was also included in the study. Test specimens were excited into resonance using a PZT crystal and interferometry was used to detect the vibrational modes. Testing was performed in vacuum to eliminate damping.
Initial testing involved measurement of resonant frequencies between 50 kHz and 2 MHz at various drive amplitudes. Each diaphragm exhibited at least 50 resonant peaks in this range, with at least one diaphragm having 250 peaks. Every diaphragm exhibited at least 5 peaks with quality factors (Q) > 10,000. The highest quality factor, as well as the largest number of high Q peaks, was observed in the diaphragm with the highest residual stress.
A method to determine the Young’s modulus and residual stress of a diaphragm from the resonant frequency data using a plate-under-tension model was proposed and developed. This method, which relies on the identification of numerous high order modes, was shown to be effective for the thicker films in the study (> 1 µm); however, the technique was only able to determine the residual stress for the submicron-thick films. Based on these observations, an equation that relates the Young’s modulus and residual stress to diaphragm thickness, side lengths and mode number was derived to identify diaphragm parameters that are well suited for this method.