We describe the requirements and status of high-T superconductor (HTS) films for the development of electronic applications with an emphasis on passive microwave devices. One of the most general requirements, a low rf surface resistance relative to Cu, has been achieved in films of several different HTS compounds. However the best films, made of YBa2Cu3O7 (YBCO) by any one of several techniques, have in common a residual surface resistance that is much greater than predicted by conventional superconductivity theory. Improvement in films is also limited by the current size and selection of single-crystal substrate materials. Other issues that must be resolved to develop a full integrated circuit technology for HTS are substrate heating during film deposition, deposited epitaxial insulators, and determination of which interfaces in a multilevel circuit must be formed in 8ztu.

Rapid isothermal processing and microwave-excited gases (N2O + O2 + He) have been used to deposit YBCO films on YSZ substrates. The thermal cycle represents the lowest thermal budget used by any other researcher. A Tc of 75 K was observed. These results coupled with the capability of depositing YBCO on BaF2/Si substrate indicate the usefulness of MOCVD for the practical realization of superconductor/semiconductor hybrid devices.

Thin films of Y-Ba-Cu-O have been deposited on barrier layers of SrTiO3 and ZrO2 by laser ablation or RF planar magnetron sputter deposition. The barrier layers are required to prevent interactions of the deposited superconducator with the underlying semiconductor and at the same time enhance the texture in the superconductor to increase the critical current density. The ability of various processing steps to enhance these properties and simultaneously allow scale-up to coat larger areas successfully are discussed.

Pulsed laser deposition is a technique commonly used to deposit high quality thin films of high temperature superconductors. This paper discusses the results obtained when this technique is applied to the deposition of Tl-Ca-Ba-Cu-O thin films using a frequency doubled Nd:YAG laser operating at 532 nm and an excimer laser operating at 248 nm. Films with onset temperatures of 125 K and zero resistance temperatures of 110 K deposited on (100) oriented MgO from a composite Tl2Ca2Ba2Cu3Ox target were obtained at both wavelengths upon appropriate post deposition annealing. Films deposited at 532 nm exhibit a rough surface, while those deposited at 248 nm are smooth and homogeneous. Upon annealing, films deposited at both wavelengths are single phase Tl2Ca2Ba2Cu3Ox.

Interdiffusion and reaction at the interface between an YBaCuO film and a Si substrate degrade the superconductivity of the film. Using a buffer layer, the film-substrate interaction can be reduced. Thus, a superconducting thin film is formed on a silicon substrate. A new method of patterning superconducting thin films based on the Si-YBaCuO intermixing has been developed. On a silicon substrate, a thin layer of noble metal was first evaporated and patterned using photolithography. An YBaCuO film was then deposited by e-beam evaporation and annealed in a rapid thermal processing system. After a high temperature annealing, the patterned feature became superconducting separated by Si-YBaCuO intermixed areas. Superconducting micron-sized the structures with Tc of 73 K have been demonstrated. This patterning technique may be useful for making high-Tc superconducting interconnects and devices on a Si wafer.

Interpretations of IR and millimeter wave measurements in superconductors are generally carried out in terms of the Mattis-Bardeen calculations, which apply either to the anomalous skin effect regime or to the dirty limit regime. In high temperature superconductors neither limit applies. Reflectance measurements on high quality, epitaxially-grown, laser-deposited films indicate that these samples are in the clean-limit, normal skin effect regime. Features that have been previously identified as the gap appear in both the superconducting and the normal-state spectra, although obscured by the free carrier absorption above Tc. Below Tc these features become more evident as the free carrier contribution condenses into a delta function at zero frequency.

The development by NASA JPL of high-temperature superconductors (HTSs) for use in microwave circuit elements is discussed. The synthesis of HTS films and characterization of their microwave absorption are reviewed. Applications to cryogenic low-noise receivers, spacecraft microwave systems, and low-noise oscillators are considered.

Epitaxial YBa2Cu3O7 films were grown on several microwave substrates. Surface resistance and penetration depth measurements were performed to determine the quality of these films. Here, the properties of these films on key microwave substrates are described. The fabrication and characterization of a microwave ring resonator circuit to determine transmission line losses are presented. Lower losses than those observed in gold resonator circuits were observed at temperatures lower than critical transition temperature. Based on these results, potential applications of microwave superconducting circuits such as filters, resonators, oscillators, phase shifters, and antenna elements in space communication systems are identified.

Various designs for high temperature superconductor (HTS) filters are reviewed. A hybrid approach utilizing HTS and very loss dielectric resonator is shown. Narrow band microstrip filter configurations, including elliptic designs required to meet satellite transponder requirements, are discussed. Tradeoff analysis is performed and recommendations for the best design are given.

The use of superconductors to increase antenna radiation efficiency and gain is examined. Although the gain of all normal-metal antennas can be increased through the use of superconductors, some structures have greater potential for practical improvement than others. Some structures suffer a great degradation in bandwidth when replaced with superconductors, while for others the improvement in efficiency is trivial due to the minimal contribution of the conductor loss mechanism to the total losses, or the already high efficiency of the structure. The following antennas and related structures are discussed: electrically small antennas, impedance matching of antennas, microstrip antennas, microwave and millimeter-wave antenna arrays, and superdirective arrays. The greatest potential practical improvements occur for large microwave and millimeter-wave arrays and the impedance matching of antennas.

Infrared detectors based upon high transition temperature ('high Tc') superconductors include superconducting transition edge microbolometers, nonequilibrium photoeffect detectors and photon-assisted tunneling detectors. Superconducting transition edge microbolometers offer moderate performance as individual detectors; a potential application is for large two-dimensional staring focal plane arrays. Experimental search for the nonequilibrium photoeffect in high Tc superconductors reveals unwanted bolometric signals. Photon-assisted tunneling in theory provides very high performance, but no experimental data are available.

A thin-film high-Tc superconducting multielement optical detector made of Y-Ba-Cu-O has been designed and evaluated using optical pulses from a diode laser (830 nm) and a Q-switched CO2-laser (10.6 microns). Different thin films have been tested. A laser deposited film showed the strongest response amplitude for short pulses and responded to an ultrafast, 50 ps wide pulse. Comparisons between dR/dT and response as a function of temperature indicated, however, a bolometric response.

Y-Ba-Cu-O thin film infrared detectors were fabricated and studied with various lasers. Operation of the detector in both the bolometric and nonbolometric modes was investigated at 10 microns with a CO2 laser. In the bolometric mode, the detectivity of the detector at 90 K was 2.1 x 10 to the 8th cm sq rt Hz/W with a response time of 15 microsec, corresponding to a bandwidth of 70 KHz. The speed of the detector in the nonbolometric mode was much faster and was beyond the instrument resolution. With a picosecond N2 laser, the output showed an instrument limited duration of 2 ns. The detectivity could not be determined in the nonbolometric mode due to the extremely low noise. The superconducting film quality is critical to the performance of these detectors.

A sensitive high-Tc superconducting bolometer has been fabricated with a YBCO thin film thermometer on a 20 microns thick sapphire substrate. Electrical measurements showed no noticeable film degradation after bolometer fabrication. Optical measurements gave a noise equivalent power of 5 x 10 to the -11th W/sq rt Hz at 10 Hz and a responsivity of 22 V/W. This performance is comparable to that of the very best pyroelectric detectors. Significant improvement appears possible.

The effects of thermal fluctuation noise in thermal detectors can be lessened by reducing heat capacity and thermal conductance. An attempt to accomplish this with the YBa2Cu3O(7-x) (YBCO) bolometer by making YBCO resistors on thermally isolated membranes is reported. The spectral power of the electrical noise of YBCO films on SrTiO3, bulk silicon with a buffer layer, and in thin dielectric membranes is measured. It is found that 1/f noise predominates in polycrystalline YBCO films on silicon-based substrates. Films on SrTiO3 with good electrical properties are dominated by thermal fluctuation noise, just as in the case of low-temperature superconductors. The implications of these findings for bolometer are addressed. The specific detectivity of a bolometric pixel made on bulk SrTiO3 is reported.

The TREMBOL (transition-edge microbolometer) and the composite TREMBOL are introduced as detectors for FIR imaging arrays. The TREMBOL uses a superconductor's sharp change in resistance at the normal conduction to superconduction transition. The structure of the composite TREMBOL enables heating of the individual detectors in an array up to their transition temperature, and can thus be used in multiplexing, which would be very advantageous for two-dimensional arrays.

Past and present planetary exploration is briefly reviewed, and the planned 1996 Cassini mission to Saturn and Titan is examined. The CIRS experiment aboard Cassini, which will retrieve information on the atmospheres of Titan and Saturn, is discussed. Ongoing efforts to build a high-sensitivity, high-Tc bolometer that would greatly improve detection in Titan's atmosphere are addressed.

The response is reported of thin films of YBa2Cu3O(7-delta) with either a very grainy or a smooth epitaxial morphology to visible radiation. SrTiO3 substrates were employed for both types of films. The grainy films were formed by sequential multi-layer electron beam evaporation while the epitaxial films were formed by laser ablation. Both films were patterned into H shaped detectors via a negative photolithographic process employing a Br/ethanol etchant. The bridge region of the H was 50 microns wide. The patterned films formed by laser ablation and sequential evaporation had critical temperatures of 74 K and 72 K respectively. The bridge was current biased and illuminated with chopped He-Ne laser radiation and the voltage developed in response to the illumination was measured. A signal was detected only above the critical temperature and the peak of the response coincided with the resistive transition for both types of films although the correspondence was less exact for the grainy film. The details of the responses and their analysis are presented.

The response to short infrared pulses of some epitaxial YBCO films prepared by sputter deposition and by electron-beam evaporation is reported. The response is found to be essentially bolometric on the ns timescale, with some indirect hints of nonequilibrium electron transport on the ps scale. Fast switching could be obtained either by biasing the switch close to the critical current or by cooling the film below about 20 K. These results are encouraging for potential application to a high-current optically-triggered opening switch.

We report studies of a thin high-Ta film operating as a fast bolometric detector of infrared radiation. The film has a response of several mV when exposed to a 1 W, 1 ns duration broadband infrared pulse. The decay after the pulse was about 4 ns. The temperature dependence of the response accurately tracked dR/dT. A thermal model, in which the film's temperature varies relative to the substrate, provides a good description of the response. We find no evidence for other (non-bolometric) response mechanisms for temperatures near or well below T.

High temperature superconducting Tl-Ca-Ba-Cu-0 thin films were sputter deposited from a single composite powder target on SrTiO3 and LaAlO3 substrates, in an rf magnetron sputtering system. The as-deposited thin films were sintered and annealed in an excess Tl partial pressure to obtain superconductivity. The superconducting films were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD) and resistance vs temperature (R vs T) measurements. Fine line features as small as 25 jim were obtained in as-deposited thin films using standard photolithography and wet chemical etching in a weak acid. From the XRD and SEM results, the annealed thin films were found to be highly c-axis oriented, with smooth platelets of 2-10 pm in size. The R vs T measurements showed zero resistance at temepratures as high as 107 K on SrTiO3 and 103 K on LaA1O3.

The phenomenon of kinetic inductance, exhibited by superconducting transmission lines in which the conductor separation and thickness are on the order of a magnetic field penetration depth , can be exploited both for device applications and for the measurement of fundamental superconductor properties. Penetration depths in the high-Ta materials (thousands of angstroms) are typically an order of magnitude or more larger than the penetration depths of the low temperature superconductors (hundreds of angstroms). With regard to geometric tolerances, fabrication restrictions for high-Ta micmelectronic devices utilizing kinetic inductance are therefore much less severe than for their low-Ta counterparts. Microwave S-parameter measurements on microstrip resonators made from very thin conductors, separated by a thin, lowloss dielectric, can be used to determine the absolute value of the penetration depth, th applicability of kinetic inductance effects in the superconductors, and the surfa,e resistivities of the superconductors. This paper describes the fabricatioti of high-Ta superconducting thin films of BiCaSrCuO, and the patterning of these films into integrated microstrip transmission line resonators designed to exhibit the effects of kinetic inductance. Of particular interest are techniques we have developed to fabricate very thin, low-loss dielectric layers on BiCaSrCuO. We report on microwave S-parameter measurements on these resonators, and on the functional dependence of transmission line phase velocity and characteristic impedance with temperature and microwave power density, especially at temperatures just below T. These results are then used to infer high frequency penetration depths and surface resistivities in BiCaSiCuO. Applications are also suggested.