A novel infrared detector using highly nonlinear twisting vibration

Abstract

A new resonant infrared (IR) detector is proposed. The twisting motion of the thin film torsion bar is first used. The resonant frequency gives the information of the temperature change of the moving element caused by IR absorption. The dynamic sensing using the electrostatic force can remove the drift without the heat generation. The large nonlinearity of the thin film torsion bar combined with the frequency measurement increases the advantage of the high sensitivity. The IR detector is fabricated by the surface micromachining using sub-μm thick poly-Si film. Its structure consists of two parts. One is the thin film torsion bars and another is the bending center part. They can be basically designed separately. The center part has bi-layer structure to induce bending against the temperature increase caused by the IR absorption. One fabricated IR detector has the resonant frequency of about 35kHz and shows the sensitivity of 30Hz/K and the shifting ratio of 830ppm/K. This sensitivity is larger than the previously reported Si detectors. The shifting ratio is larger than devices including the high-frequency quartz and ZnO detectors.