Fabrication of sensitive high Tc bolometers

The rapid change of resistance with temperature of high quality films of high T sub c superconductors can be used to make resistance thermometers with very low temperature noise. Measurements on c-axis yttrium barium copper oxide (YBCO) films have given a spectral intensity of temperature noise less than 4 times 10(exp -8) K/Hz(exp 1/2) at 10 Hz. Consequently, the opportunity exists to make useful bolometric infrared detectors that operate near 90 K which can be cooled with liquid nitrogen. The fabrication and measurement of two bolometer architectures are discussed. The first is a conventional bolometer which consists of a 3000 A thick YBCO film deposited in situ by laser ablation on top of a 500 A thick SrTiO3 thickness and diced into 1x1 mm(exp 2) bolometer chips. Gold black smoke was used as the radiation absorber. The voltage noise was less than the amplifier noise when the film was current biased. Optical measurements gave an NEP of 5 times 10(exp -11) W/Hz(exp 1/2) at 10 Hz. The second architecture is that of an antenna-coupled microbolometer which consists of a small (5x10 cubic microns) YBCO film deposited directly on a bulk substrate with a low thermal conductance (YSZ) and an impedance matched planar lithographed spiral or log-periodic antenna. This structure is produced by standard photolithographic techniques. Measurements gave an electrical NEP of 4.7 times 10(exp -12) W/Hz(exp 1/2) at 10 kHz. Measurements of the optical efficiency are in progress. The measured performance of both bolometers will be compared to other detectors operating at or above liquid nitrogen temperatures so as to identify potential applications.