High-T/sub c/ transition-edge bolometer for detecting guided millimeter waves

Long meanders of the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ were investigated for their suitability as transition-edge bolometers for determining the absolute power of guided millimeter waves. The devices were made of 200-300-nm-thick YBaCuO films sputtered by an inverted cylinder magnetron onto yttria-stabilized zirconia (YSZ) substrates. These films were structured by photolithographic methods to meanders 30 mm in length and 30- mu m wide. The devices structured in this way show resistances of around 30 k Omega at the midpoint of the transition to superconductivity. Measurements were performed at frequencies of 35, 70, and 94 GHz. The working temperature was at the midpoint of the transition to superconductivity, about 90 K. The responsitivity of the device measured in waveguides is 4000 V/W at 35 GHz and 2600 V/W at 70 and 94 GHz. It exceeds the value of 1000 V/W typical of semiconductor diodes in the range below 100 GHz.<>