Infrared detection based on nonlinear oscillation of thin film resonator

An infrared detector that uses nonlinear oscillation is proposed. The torsional oscillator has bi-material structure. When the infrared is incident and absorbed at the torsional oscillator increasing the local temperature, the thermal stress due to the difference of thermal expansions of the materials bends the oscillator. This bending hardens the spring constant of torsional oscillator and results in the shift of the resonant frequency. The dynamic operation can remove DC drift and the high sensitive frequency measurement can be combined. The oscillators consist of poly-Si film (400 nm-thick, B doped) released from substrate. The torsion bars support the wider center part. This part is attracted toward the substrate by the electrostatic force generating the twisting motion. The copper black film of the light absorbing material is deposited through the stencil mask. Reflectivity of 0.2% is realized against the light with the wavelength of 650 nm. When the light is incident on the oscillator, the shifting ratio of the resonant frequency of -0.14 kHz/(kW/m²) is observed.