[14p-B2-1~19] 3.9 Terahertz technologies

▲ [14p-B2-12] Enhanced thermal sensitivity of a microelectromechanical bolometer by introducing preloaded strain in the beam structure

〇(PC)Ya Zhang¹, Suguru Hosono¹, Naomi Nagai¹, Kazuhiko Hirakawa^1,2 (1.IIS, University of Tokyo, 2.INQIE, University of Tokyo)

Keywords:terahertz detector, bolometer, MEMS resonator

Previously, we reported a room temperature, sensitive terahertz (THz) bolometer using a doubly clamped microelectromechanical (MEMS) resonator, which detects a shift in the resonance frequency caused by heating due to radiation. For bolometer applications, it is highly desirable to increase the thermal sensitivity of the device. When a heating power is applied to a NiCr film placed on the MEMS beam surface, we observed a reduction in the resonance frequency when the heating power was smaller than 1 mW. However, as the heating power was further increased, the resonance frequency started to increase, which is because of the buckling of the beam when the internal stress exceeds the critical load. We found that the positive slope is 2~3 times steeper than the negative slope, suggesting that an enhanced thermal sensitivity is obtained when a small buckling is introduced in the MEMS beam.
Therefore, we have introduced a preloaded compressive strain in the beam by using the lattice mismatch between In_xGa_1-xAs (x = 0.0013) and GaAs. Two devices of the same dimensions (120L*30W*1.2H μm³) have been fabricated with In_xGa_1-xAs and GaAs beam structures, respectively. The GaAs device shows a frequency responsivity of 120 W^-1, whereas the In_xGa_1-xAs device shows an enhanced frequency responsivity of nearly 300 W^-1, demonstrating that the introduction of buckling is useful for achieving higher thermal sensitivity for MEMS detectors.