Transition edge YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} microbolometers for infrared staring arrays

High-temperature superconducting staring arrays are potentially important for both space and terrestrial applications which require the combination of high sensitivity over a broad wavelength range and relatively high temperature operation. In many such array applications sensitivity is more important than speed of response. Thus, it is desirable to design low-thermal-mass pixels that are thermally isolated from the substrate. To this end, Johnson, et al. at Honeywell have fabricated meander lines of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) sandwiched between layers of silicon nitride on silicon substrates. The silicon was etched out from under each YBCO meander line to form low-thermal-mass, thermally isolated microbolometers. These 125 {micro}m {times} 125 {micro}m devices are estimated to have a noise equivalent power of 1.1 {times} 10{sup {minus}12} W/Hz{sup 1/2} near 5 Hz with a 5 {micro}A bias (neglecting contact noise). A drawback of this original Honeywell design is that the YBCO is grown on an amorphous silicon nitride underlayer, which precludes the possibility of epitaxial YBCO growth. The YBCO therefore has a broad resistive transition, which limits the bolometer response, and the grain boundaries lead to excess noise. The authors discuss the potential performance improvement that could be achieved by using epitaxial YBCO films grownmore » on epitaxial yttria-stabilized zirconia buffer layers on silicon. This analysis shows a significant signal to noise improvement at all frequencies in devices incorporating epitaxial YBCO films. Progress toward fabricating such devices is discussed.« less