A High-Tc Superconductor Bolometer for Remote Sensing of Atmospheric OH

The technological feasibility is being investigated of a high-Tc superconductor transition edge bolometer for far-infrared detection, which can meet the requirements of a Fabry-Perot based satellite instrument designed for remote sensing of atmospheric OH. These include a time constant τ<0.3 s, an operating temperature above 35 K, a diameter of 1.1 mm, and a noise equivalent power (NEP) smaller than about 4.0·10-12 W Hz-1/2 for radiation with λ approximately equals 85 μm. Presently, no other sensor can meet these requirements. A NEP value of 3·10-11 W/Hz1/2 and τ approximately equals 0.4 ms has been realized with high-Tc bolometers on Si membranes with a receiving area of 0.85×0.85 mm2. By replacing the Si by Si3N4 we expect that the thermal conductance G can be reduced by more than a factor 20. This should result in a NEP less than 4·10-12 W/Hz-1/2 and a time constant <0.1 s. A bond-and-etch-back technique is used to prepare a mono crystalline silicon top layer on the Si3N4 membrane, which is necessary for the epitaxial growth of the superconductor. An absorption layer will be added to the detector to enhance the efficiency. Promising candidates for use as an absorption layer are metal black films with an efficiency η around 80% at 85 μm wavelength.