Micromechanical IR thermal detector using torsional oscillation: Improvement of resonator profile for high sensitivity

Abstract

An infrared (IR) thermal detector, which used the torsional oscillation of a micromechanical resonator, was developed to achieve a high sensitivity. The detector has a bimaterial structure consisting of a tense Si film (oscillating body) and a metal film (IR absorber). Owing to the difference in thermal expansion between the two materials, the resonator is bent by light incidence. Because the axis of torsion is bent from the initial flat state, the spring for torsional oscillation hardens and resonant frequency shifts. To enhance bending, an Al film with a large coefficient of thermal expansion was used. In addition, the tension in the polycrystalline Si film was enhanced by metal-induced lateral crystallization using biomineralized Ni nanoparticles. The fabricated detector was flat under initial conditions and showed a bending response to the light incidence and heating. The present IR detector achieved a thermal coefficient of frequency of 1000 ppm/K, which was one order larger than that of the conventional micromechanical IR sensors.