Thin film YBCO infrared detector design and characterization

The IR‐response of YBCO bolometers, fabricated from thin films that have room temperature resistivity of 500 μΩ‐cm, dρ/dT=130 μΩ‐cm/K at the middle of the transition, and linear metallic behavior in the R vs T with zero intercept at T=0, has been studied. Films with 150 to 550 nm thickness on single crystal MgO and LaAlO substrates were deposited using the in situ planar magnetron sputtering technique. The films were patterned by conventional photolithography (spin on photoresist and acid etch) into different serpentine designs. The IR‐response vs. modulation frequency, temperature, and bias current of the above bolometers were measured.The governing mechanisms in the responsivity for very low to high modulation frequency range (0.5 Hz–100 KHz) were investigated using existing models. We have observed a response, two order of magnitude higher than the values predicted by the existing models in the middle frequency range of a few 100 Hz to about 10 KHz, which has potential for use in IR‐imaging. A model of the bolometer response is presented involving the responsivity as a function of bias current, and the stability of the bias point (operating temperature of the bolometer) due to power dissipation by the current, as well as the distribution of the incident radiation. High detectivity, D*, in the HTSC bolometers are shown to be obtainable based upon the measurement on the designed bolometers. The NEP attainable and D* are discussed. Values of the specific heat of LaAlO are deduced from our studies.