Antenna-coupled uncooled THz microbolometer based on micromachined GaAs and LSMO thin film

We report on preliminary results on antenna-coupled microbolometer designed for frequency range 1.4-11.3 THz. Thin film of a composition of La_0.67Sr_0.33MnO₃ (LSMO) was selected as a proper material, since it provides high TCR values due to its phase transition. The microbolometer consists of LSMO disk (~8 mum in diameter) placed in a feed point of gold thin-film log-periodic antenna. These main parts are fabricated on 2 mum thick suspended GaAs island thermally isolated from the rest of the micromachined GaAs substrate by four microbridges. MgO buffer layer was used to ensure epitaxial growth of LSMO film on GaAs substrate. Though our LSMO films deposited by magnetron sputtering on single-crystalline MgO substrates show TCR = 0.03 K^-1 at 300 K [11], the epitaxial films sputtered on MgO-buffered GaAs substrates have peculiar temperature dependence of the optical response (OR). The shape of OR(T) differs from that of differentiated R(T), which implies that the OR is not of pure bolometric origin. At the same time, thorough structural analyses reveal high-quality epitaxial growth of both the layers - MgO buffer and LSMO. Therefore, the switch to pulsed laser deposition technique is necessary in order to achieve the goal - fabrication of THz detector working at room temperature.