Fabrication and measurement of high Tc superconducting microbolometers

The authors fabricated and measured the performance of antenna-coupled microbolometers based on the resistive transition of a high-T_c superconducting film for use as detectors of far-infrared and millimeter waves. A planar lithographed antenna (log-periodic or log-spiral) is used to couple the radiation to a thin YBCO film with dimensions (≈6×13 μm²) which are smaller than the wavelength to be measured. This film acts both as the resistor to thermalize the RF currents and as a transition edge thermometer to measure the resulting temperature rise. Because of its small size, both the thermal conductance from the film into the bulk of the substrate and the heat capacity of the thermally active region are small. Consequently, the microbolometer has low noise, fast response, and a high voltage responsivity. A phonon-limited electrical NEP of 4.5×10^-12 WHz^-1/2 at a 10-kHz modulation frequency and a responsivity of 478 V/W at a bias of 550 μA were measured. Measurements of the optical efficiency are discussed