Investigation of semiconducting YBaCuO thin films: A new room temperature bolometer

We explore the application of the semiconducting phases of YBaCuO thin films as a bolometer for uncooled infrared detection. For this study, four different structures were built with different types of buffer layers: YBaCuO on a Si substrate with and without a MgO buffer layer, and on an oxidized Si substrate with and without a MgO buffer layer. These films were all amorphous without a detectable long range order. For comparison, crystalline tetragonal YBa2Cu3O6.5 and YBa2Cu3O6.3 thin films on a LaAlO3 substrate were included into the study. All six films exhibited semiconducting resistance versus temperature characteristics. The bolometer figures of merit, responsivity, and detectivity were calculated from the measured temperature coefficient of resistance ~TCR! and the inherent noise characteristics of the temperature sensing element. The room temperature TCRs for all four amorphous films were greater than 2.5% K. The highest TCR of 4.02% K was observed on the amorphous YBaCuO thin film deposited on MgO/Si without a SiO2 layer. The TCR of the tetragonal films, on the other hand, remained 2% K 21 or less in the same temperature range. Noise measurements performed in the 1–100 Hz frequency range revealed a quadratic dependence on the bias current as would be expected from ohmic electrical characteristics. The Johnson and 1/f regions were clearly identified in the noise spectrum. From TCR and noise measurements, we estimated the amorphous semiconducting YBaCuO bolometers would have a responsivity as high as 3.8310 V/W and a detectivity as high as 1.6310 cm Hz/W for 1 mA bias current and frame frequency of 30 Hz if integrated with a typical air-gap thermal isolation structure. © 1996 American Institute of Physics. @S0021-8979~96!02924-6#