A description is given of recent work at Berkeley on superconducting detectors and mixers for infrared and millimeter wavelengths. The first report is a review article which summarizes the status of development of superconducting components for infrared and millimeter wave receivers. Next, a report is given on measurements and theoretical modeling of the absorptivity (surface resistance) of high quality epitaxial films of the high-Tc superconductor YBCO from 750 GHz to 21 THz. The next report describes measurements of the thermal boundary resistance between YBCO films and various substrates. This resistance is much larger than expected from the acoustic impedance mismatch model and gives a thermal time constant in the nanosecond range for typical YBCO films. Reports are also included on the design and experimental performance of two different types of high-Tc bolometric detectors. One is a conventional bolometer with a gold-black absorber. The other is an antenna coupled microbolometer. The properties of a low-Tc microbolometer are also described. The last reports describe accurate measurements and also theoretical modeling of an SIS quasi-particle waveguide mixer for W-band which uses very high quality Ta junctions. The best mixer noise is only 1.3 times the quantum limit. Both the mixer gain and the noise are in quantitative agreement with the quantum theory.

High Tc superconducting thin films of YBa2Cu3O7-(delta ) (YBCO) were deposited on sapphire substrates with buffer layers of yttria-stabilized zirconia and cerium oxide by using pulsed laser deposition (PLD) technique. The epitaxial relationship between the substrate and buffer layers as well as the buffer layer and the superconducting film was established. Furthermore, using the same thin film technique, YBCO superconducting thin films were deposited on both sides of substrates of up to 5 cm in diameter. The superconducting properties of the films on both the sapphire with buffer layers and large-area substrates were comparable to the ones of the best YBCO films.

Improvement of the sensitivity in infrared detectors made of high Tc superconducting films is discussed. Usually these films are grown on a substrate which results in reduced sensitivity due to additional heat capacity of the substrate. A five-fold increase of the noise equivalent power is calculated if free-standing superconducting films are used. A new technique for preparation of thin films of YBa2Cu3Ox without a substrate is also described. The film material is deposited by pulsed laser ablation on a thin carbon film. When the film is annealed in situ in oxygen, the carbon burns off, leaving a free-standing film. The film area can be large as 10X10 mm2 and less than one-half micron thick. They have the correct stoichiometry, the orthorhombic phase and an onset temperature of about 85 K.

An anomalous optical response was observed in YBa2Cu3O7-x thin films showing percolative behavior in the superconducting transitions. Despite the fact that the temperature derivative of the resistance had increased considerably, no pronounced increase of optical response was found in the high resistivity regime of the transition. This nonbolometric response is likely related to inhomogeneities in superconducting properties of the films, but its nature is not well understood.

Low-frequency surface degradation studies of the YBa2Cu3O7-x (123) and Bi-Sr-Ca-Cu-O superconducting ceramics have been performed in N2, Ar2, O2, wet and dry air. The time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu- O bulk ceramics are measured from 100 Hz to 20 kHz at room temperatures and pressures. In humid environments the rate of degradation of 123 is dependent on the humidity and appears to be unaffected by the carrier gas. The surface impedance change due to humidity follows a power law and does not appear to saturate at a final value. In an environment without water present, the surface impedance of 123 follows an exponential curve of the form 1+e-at, where a is approximately 150 sec. This implies that the surface of the ceramic is relatively stationary and that it is losing oxygen. This oxygen loss converts the surface from a highly conductive state to an insulating state. This is supported by ESCA analysis of the exposed surface and freshly abraded or broken sample's interiors. In the ESCA spectra of the exposed surface there is a lack of Cu-O bond peaks; in the center of the same sample the Cu-O peaks are present. For the 2223 material there is an aging effect similar to the 1+e-at aging in 123 in inert and dry environments. The time constant for 2223 aging is 120-150 sec. Once again this is interpreted to imply the formation of a less conductive (nonsuperconductive) surface layer on the 2223. The precise mechanism and products of this decay are as yet unknown. In stark contrast with the results obtained on 123, there is no drastic difference between humid and dry inert environment surface impedance vs. time runs for 2223. This implies that 2223 is relatively nonreactive with respect to water.

Microwave data on epitaxial Tl2Ba2CaCu2O8 thin films grown on LaAlO3 substrates are reported. The authors fabricated and tested microstrip resonators using these films and performed measurements of the loss tangent of lanthanum aluminate substrates at 5 GHz and 77 K. Loss tangent values of 2 to 4X10-5 were measured. The authors extracted surface resistance for the superconducting thin films from unloaded Q measurements on microstrip resonators. They infer scaled surface resistance values of approximately 300 (mu) ohms at 10 GHz and 77 K from unloaded Q measurements at 5.6, 11.1, and 16.3 GHz. The measured surface resistances scale very closely with the square of the frequency.

Coplanar transmission lines made from high-Tc superconducting thin films are investigated theoretically. A full wave analysis is performed for the coplanar waveguide structure by a partial wave synthesis. For modeling the superconducting behavior the two- fluids model and the London theory are applied. The authors use two ways of analysis. The first is to calculate the electromagnetic field for the structure assuming ideal conductors and to introduce the conductor losses afterwards by using the surface impedance matrix. The surface impedance matrix takes into consideration the coupling of the tangential magnetic fields on both surface planes of a thin superconducting film. Thus the thickness of the film may be in any range compared with the London penetration depth. This method is compared with the accurate solution obtained by calculating the electromagnetic field also within the conductor. Transmission line structures are analyzed. The behavior of measured and published coplanar waveguide (lambda) /2 resonators made of high-Tc superconducting thin films is discussed. Micrometer structures are considered in the frequency range up to 100 GHz. Such transmission line structures are of special interest for low loss, low dispersion chip-to-chip interconnections. The results obtained with superconductors are compared to the results obtained for the same geometry with normal conductors.

The high T sub c superconducting microstrip line and coplanar waveguide are compared in terms of the loss characteristics and the design aspects. The quality factor Q values for each structure are compared in respect to the same characteristic impedance with the comparable dimensions of the center conductor of the coplanar waveguide and the strip of the microstrip line. Also, the advantages and disadvantages for each structure are discussed in respect to passive microwave circuit applications.

Microwave stripline resonator measurements are presented of Rs on large-area YBCO (Y1Ba2Cu3O7-x) films sputter deposited on cleaved MgO substrates. Dependence of Rs on temperature, frequency, and applied input power was determined. The films exhibited excellent dc properties with typical Tcs equals approx. 85 K, and Jcs equals 1 MA/cm2 at 77 K. At 1.2 GHz the inferred microwave Rs equals approx. 100 (mu) (Omega) at 4.2 K and Rs equals approx. 2 m(Omega) at 78 K for these same films. Losses in the patterned YBCO center strips showed large changes over an 80 dBm range for input power. These patterned center strips exhibited a much stronger dependence on input power than did unpatterned ground planes. This may be related to peak currents and high Hrf fields inside the stripline near the edges of the patterned center strip. Film degradation due to environmental effects has also been observed, with films stored for over 6 months degrading by a factor of two in Rs when retested. With respect to frequency, Rs approximates an f2 dependence when higher harmonics of the resonator are measured on these YBCO films.

Addressed are various antenna-system components such as filters, radiating elements, and delay lines. The importance of film growth on both sides of a large area substrate is stressed, as are packaging issues in connection with the demonstration of integrated subsystems in the near future. The discussion is focused only on the components cited because they are good examples (but not the only ones) of devices that can be used as vehicles for high-temperature superconducting (HTS) insertion into microwave systems.

The performance of semiconductor and high critical temperature superconductor switches is compared as they are used in delay-line-type microwave and millimeter-wave phase shifters. Such factors as their ratios of the off-to-on resistances, parasitic reactances, power consumption, speed, input-to-output isolation, ease of fabrication, and physical dimensions are compared. Owing to their almost infinite off-to-on resistance ratio and excellent input-to-output isolation, bolometric superconducting switches appear to be quite suitable for use in microwave phase shifters; their only drawbacks are their speed and size. The SUPERFET, a novel device whose operation is based on the electric field effect in high critical temperature ceramic superconductors is also discussed. Preliminary results indicate that the SUPERFET is fast and that it can be scaled; therefore, it can be fabricated with dimensions comparable to semiconductor field-effect transistors.

Thin film low-pass microwave filters have been made with laser-ablated YBa2Cu3O(7-delta) (YBCO) deposited on LaAlO3 substrates, using a coplanar waveguide structure. The coplanar waveguide sections had dimensions suited for integrated circuits. Measured losses in liquid nitrogen were superior to the loss in a similar thin-film copper filter throughout the 0 to 9.5 GHz pass-band. A simple transmission-line model is adequate for filter design using YBCO films with repeatable characteristics. The measured filters demonstrate the performance of fully patterned YBCO after sealing in space-qualifiable hermetic packages. Five packaged filters of this design were delivered to the Naval Research Laboratory as candidates for space flight in the High Temperature Superconductivity Space Experiment.

The U.S. Army's technical progress and technology strategy for microwave applications of high temperature superconducting (HTSC) thin films for system applications is described. Data is presented on an X-band oscillator, filters, and resonators. Information on film fabrication and preparation is included. The research is continual, and some of the results presented in this work are of a preliminary nature. A theoretical analysis on the effect of temperature variation on Schottky barrier diodes is also included.

Reviews theoretical and experimental studies of superconductor-light interactions with the emphasis on the electrical response of high critical temperature superconductors to optical radiation, especially in the visible light and infrared wavelength range.

A theoretical model to predict the 1/f noise characteristics of high temperature superconductors to infrared excitations is proposed. Noise mechanisms are attributed to the effects of temperature variations on the quasiparticle fluctuations and kinetic characteristics of the superconductor. In the transition region the thermodynamic fluctuations modulate the conductivity of the sample, causing voltage variations in the presence of a bias current contributing to the 1/f noise spectral power. The predictions of the model are compared to recent experimental measurements on YBaCuO epitaxial and single crystal thin films. The theoretical predictions in both cases are in general smaller than the measured values. The authors attribute the discrepancy to the effects of noise sources associated with the flux hopping process and thermally activated flux creep in the lattice structure which are not addressed in the current theory.

The authors have recently proposed a new nonbolometric mechanism for detection of infrared photons in superconducting thin films, in which a photon nucleates the formation of a vortex- antivortex pair. This model predicts a limiting voltage responsivity of 1/(2ef), where f is the frequency of the radiation. Measurements on ultrathin NbN films at 4 K are reported which provide further evidence for this 'photofluxonic effect.' For approximately equals 0.1 (mu) W of red light (0.6 micrometers ), a responsivity of 6000 V/W of absorbed light has been measured, in agreement with the predictions. This response continues out to frequencies greater than 100 kHz, and is 1000 times greater than expected for a bolometric response. Preliminary measurements with 20 micrometers infrared radiation also agree with this picture. Voltage noise in the absence of light was less than 1 nV/(root)Hz, and was consistent with single-fluxon shot noise. Similar performance should also be possible using high-temperature superconductors. Some considerations for a fast, sensitive infrared detector based on these principles are presented.

A simple polishing technique was developed for thinning the LaAlO3 substrates for high-quality Tc bolometer films, and thus reducing their heat capacity. A 150-ms bolometer was made on a LaAlO3 substrate with a 5-Hz D* value of 1.5 x 10 exp 8. It is shown that passive temperature stabilization is adequate for operation at the transition. There remained excess noise at the transition, but this noise appears to be of nonbolometric origin.

Superconductive electronics is well known to offer substantial performance advantages over conventional technologies with respect to high-speed, low-power dissipation and high- frequency operation. Before the discovery of high-temperature superconductivity, these benefits could only be obtained at liquid helium temperature. Devices and circuits based on HTS materials offer the promise of operation at temperatures as high as 77 K. The key element of most superconductive circuits is the Josephson junction, and developing a useful and reliable junction made from high-temperature superconductors (HTS) remains a central issue for the superconductive electronics community. The current status of HTS Josephson devices as they are being developed by a number of laboratories is reviewed. Recent progress by several groups has greatly enhanced the prospects for developing a circuit process based on HTS Josephson devices.

We describe the fabrication and characterization of superconductor/normal metal/superconductor (SNS) devices made with the high-temperature superconductor (HTS) YBa2Cu3O(7-x). Structures of YBa2Cu3O(7-x)/Au/Nb on c-axis-oriented YBa2Cu3O(7-x) were made in both sandwich and edge geometries in order to sample the HTS material both along and perpendicular to the conducting a-b planes. These devices display fairly ideal Josephson properties at 4.2 K. In addition, devices consisting of YBa2Cu3O(7-x)/YBa2Cu3O(y)/YBa2Cu3O(7-x), with a 'normal metal' layer of reduced transition temperature YBa2Cu3O(7-x) were fabricated and show a great deal of promise for applications near 77 K. Current-voltage characteristics like those of the Resistively-Shunted Junction model are observed, with strong response to 10 GHz radiation above 60 K.

Investigation of sandwich-type Josephson junctions using a Bi2Sr2CaCu2Ox/Bi2Sr2CuOy/Bi2Sr2CaCu2Oz (BSCCO/BSCO/BSCCO) structure. The barrier layer (BSCO) has crystalline structure similar to that of superconducting electrodes (BSCCO). Moreover, the BSCO film was conductive even at 4.2 K. The junctions exhibited S/N/S type I-V characteristics. The clear Shapiro steps appeared

Deliberate grain boundaries have been fabricated in epitaxial films of Tl2CaBa2Cu2O8 by growing the films on substrates with localized surface damage and on substrates with surface steps produced with an anisotropic etching process. Bowtie antennas were fabricated to couple millimeter wave radiation into the weak link junctions, which were used as the nonlinear elements. Heterodyne mixing of signals at 55 GHz and 94 GHz was observed in the integrated antenna/detector structures at temperatures below 101 K in the Tl-based films. In addition, observations were made at 55 GHz, using these structures as subharmonic mixers. We have designed an integrated microwave package to measure the noise and conversion efficiency of the grain-boundary junctions at frequencies between 9 GHz and 20 GHz.

Superconducting tunnel diodes (SISs) are investigated for both the generation and detection of submillimeter wavelengths. For detection, heterodyne receivers using SISs are investigated. Josephson currents are found to have a large effect on SIS mixers in the submillimeter, even though their effect is less at lower frequencies. At 492 GHz, fixer conversion gain increased by 4 dB when Josephson currents are not suppressed by a magnetic field. A much higher noise is seen in this gain mode, but further investigation of this recently discovered phenomenon is warranted. For submillimeter generation, a two-dimensional array of SISs is investigated. The ac Josephson effect in the SIS is expected to deliver submillimeter power into a free-space radiation mode traveling perpendicular to the array. No experimental devices have been developed yet, but the authors show computer simulations and microwave scale model measurements of array structures.

Accurate measurements have been made of the noise and gain of superconducting-insulating- superconducting (SIS) mixers employing small-area (1 micrometers 2) Ta/Ta2O5/Pb0.9Bi0.1 tunnel junctions. The authors have measured an added mixer noise of 0.61 +/- 0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta. A detailed comparison is made between theoretical predictions of the quantum theory of mixing and experimentally measured noise and gain. The authors used the shapes of I-V curves pumped at the upper and lower sideband frequencies to deduce values of the embedding admittances at these frequencies. Using these admittances, the mixer noise and gain predicted by quantum theory are in excellent agreement with experiment.

Identifies a high-Tc temperature-transition edge, nonbolometric detector response in microstrip line device structures fabricated from thin films of Y1Ba2Cu3O7-x deposited on MgO single crystal substrates. Such detectors have an intrinsically fast response and in principle are capable of operating up to frequencies represented by the superconducting energy gap (terahertz region), if such an energy gap concept is applicable to these unique materials. The detector output, a dc output voltage across the device, is function of bias current and temperature, with an optimum temperature in the vicinity of the point at which zero resistance is reached (To). The mechanism for the detector action is believed to be related to the switching of the superconductor from its superconducting state to its normal state, driven by the input radiation, while the superconductor is held at a suitable current bias point and temperature. Both films made by the laser ablation process and chemical spray pyrolysis form detector elements. However, the films formed by these two techniques are vastly different morphologically. The extent to which film morphology influences detector performance has been examined in an effort to examine the so-called weak-link question. The Noise Equivalent Power (NEP) of a laser ablated detector has been estimated to be below -80 dbm for an operating condition of 70 K, frequency of 8 GHz and modulation of 60 KHz. The measurement limitation is extrinsic noise, and it is believed that these devices are extremely low noise, far better than possible with conventional Schottky diodes/p-n junctions, or Josephson-like SIS structures for that matter. Various other performance characteristics are presented, along with a suggested NSN model for electrical conduction.

Optical response measurements are presented for granular, predominantly c-axis oriented crystalline YBaCuO films prepared by electron beam multi-layer evaporation to infrared radiation. The results appear to indicate that both bolometric and nonbolometric components contribute to the optical responses. For a typical patterned film of area 100 X 40 micrometers , the responsivity is above 103 v/w, the NEP is 10-11 w, and D* is 103 cm(Hz)1/2 /w to wavelength range of 8-14 micrometers , chopped at a frequency of 80 Hz.

Results of measurements of the optical response of high Tc superconducting infrared detectors fabricated from YBaCuO thin films for wavelengths of 3-5 micrometers and 8-14 micrometers at an operating temperature above liquid nitrogen. The measurements of a meander line detector yield a noise equivalent power (NEP) of 2 X 10-9 w Hz-1/2 and a detectivity (D*) of 1.5 X 108 cmHz1/2W-1 for radiation of 8-14 micrometers at a chopping frequency of 50 Hz. The response for 3-5 micrometers radiation is lower than that for 8-14 micrometers for the same detector. The authors have investigated the dependence of the optical response of these detectors on several parameters, including bias current, chopping frequency, substrate material, and film quality (associated with different fabricating methods). In addition, the device design and methods to improve the sensitivity have been discussed.

The influence of technological parameters at laser deposition on YBa2Cu3O7_5 films properties, including parameters of a laser beam, oxygen pressure, substrate temperature, target-substrate distance are discussed. The relationship between optimal values of these parameters and the relationship of microstructure and transport properties of the films are shown. The importance of the initial growth stage epitaxial YBa2Cu3O7_5 films on sapphire substrate with jc(78K) < 106A/cm2 is discussed. The influence of dynamics of laser plasma expansion on film growth is demonstrated.