A photodetector with high responsivity has been fabricated with a high quality Y1Ba2Cu3O7−δ film on a regular SrTiO3 (100) substrate that has no thinning or etching. The film exhibits a precipitation-free morphology and has an extremely smooth surface having a rms roughness smaller than 5 nm. The film was patterned into a 25×650 μm2 long microbridge by a conventional photolithography technique. The Tco of the microbridge can be tuned by applying different bias currents, which results in a tunable operation temperature of the photodetector at 77.35±1 K. This makes it operationally more practical and economical. The noise voltage at 10 mA bias current is less than the resolution of our setup, 15 nV  Hz−0.5. A high responsivity of 2.3×103 V/W was obtained when a bias current of 8 mA and a low power density He–Ne laser of 0.08 J/cm2 s chopped at 2 Hz were applied on the microbridge at 77.35 K. Under the same condition, the noise equivalent power (NEP) and detectivity (D*) have been measured to be 4.34×10−12 W Hz−0.5 and 3×109 cm Hz0.5 W−1, respectively.

Three Y1Ba2Cu3O7−δ superconducting thin films with 20%, 60%, and 100% coverage of precipitates were fabricated into microbridges of 25×650 μm2 by a conventional photolithography method. These microbridges exhibit a Tco(R=0) from 83.6 to 87.2 K and a transition width of about 1.8 K. These also have (dR/dt)max values of about 71–78 Ω/K. We find that the fewer the precipitates on the film, the better the thermal conduction, and a larger responsivity (S) can be achieved. The best responsivity of 783 V/W measured at Ib=8 mA, Top=86.8 K, and f=2 Hz for various wavelengths of light sources is obtained from the film with 20% precipitation. The photoresponse signals decay exponentially with the precipitation coverages, which indicates that these precipitates behave as thermal resistance layers that smooth out the ac incident signal, suppress the rise in microbridge temperature, and result in a smaller photoresponse signal for the bolometer.