Philip Pang

5 GHz high-temperature-superconductor resonators with high Q and low power dependence up to 90 K

The authors have fabricated high-temperature superconducting films made of TlBaCaCuO (2212) and YBaCuO

High T/sub c/ superconductor and III-V solid state microwave hybrid circuits

Several high-temperature superconductor (HTS)/III-V solid-state hybrid microwave circuits were designed, fabricated, and tested. The I-V curves, S-parameters, and noise behavior for several solid-state devices at cryogenic temperatures were measured. Several high-electron-mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) C-band low-noise amplifiers were fabricated and tested at cryogenic temperatures with an additional gain of 3 dB when compared to their room-temperature gain. These amplifiers were also used in low-phase-noise oscillators stabilized by a HTS lambda /2 microstrip line resonator with a loaded Q-value of 3*10/sup 3/ or a sapphire-HTS resonator with a loaded Q-value of 1.2*10/sup 6/, both measured at 80 K. Preliminary measurement at 70 K indicates that the phase noise of an oscillator stabilized with a sapphire-HTS resonator was below -125 dBc/Hz at 10-kHz offset and limited by the test setup.<<ETX>>

High-power HTS planar filters with novel back-side coupling

Novel back-side coupling was used to produce high-power high temperature superconducting (HTS) filters. Several 2.88 GHz, 0.7% equal-ripple bandwidth, 2-pole TE/sub 01/ mode filters were fabricated using Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ HTS thin films on 20-mil LaAlO/sub 3/ substrates. The calibrated, measured performance of the filter at 77 K was <0.1 dB in-band insertion loss and 0.2 dB ripple up to 8 W. The uncalibrated measured performance of the filter was unchanged up to 21 W. This represents a significant advance in the power handling of planar HTS filters. These high-power, high-performance, compact HTS filters were designed to be used in transmitters for satellite communications.

High T/sub c/ superconductor-sapphire microwave resonator with extremely high Q-values up to 90 K

Several high-temperature-superconductor-sapphire TE/sub 011/ mode resonators were designed, fabricated, and tested. At 5.552 GHz, Q/sub 0/ reached 2*10/sup 6/ at 90 K, 3*10/sup 6/ at 80 K, and 1.4*10/sup 7/ at 4.2 K with circulating power up to 500 kW. Formulas for calculating the resonant frequency and Q-value were derived. These theoretical results showed good agreement with the experimental measurements. Applications such as frequency-stabilized oscillators and filters, and the characterizations of high-temperature superconductor films are discussed.<<ETX>>

High T/sub c/ superconducting coplanar delay line with long delay and low insertion loss

Coplanar delay lines have been fabricated from TlBaCuCuO (2212) and YBaCuO

Picosecond superconductor opening switches

Picosecond opening switches using high-T/sub c/ superconductor devices made of TlPbSrCaCuO, TlBaCaCuO, and YBCO films have been successfully demonstrated. The switches were controlled by picosecond laser pulses. A switching risetime of 78 picoseconds and a switching efficiency of 80% have been achieved. The switches were used in an inductive energy storage pulsed power system. Nanosecond electrical pulses with a peak power gain of 22 were obtained.<<ETX>>

Picosecond optical response of Tl2Ba2CaCu2O8 and Tl0.5Pb0.5Sr2(Ca0.8Y0.2)Cu2O7 high Tc superconductor films

We have investigated the optical response of 700 nm optically thick Tl2Ba2CaCu2O8 and Tl0.5Pb0.5Sr2(Ca0.8Y0.2)Cu2O7 high Tc superconductor films activated by a few mJ/cm2 laser pulses. We have systematically studied the dependence of optical response on temperature and laser intensity. Fast and slow components can be clearly identified. A 70 ps electric transient has been obtained when activated by a 3.3 mJ/cm2 laser at 80 K or by a 10 mJ/cm2 laser at 50 K.

Raman microprobe analysis of patterned Tl-2212 thin films

We have used MicroRaman spectroscopy to evaluate the effects of ion-milling on the exposed edges of patterned Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (Tl-2212) lines. Raman microprobe has previously been used to evaluate oxygen loss at the edges of patterned YBCO lines. The results indicated that appreciable oxygen loss was caused by ion-milling under certain conditions. oxygen loss at the edges will decrease non-uniformly the effective width of the superconducting line. This can, in turn, impact the electrical characteristics of patterned devices. Using the 633 nm lined of a HeNe laser, we have measured the Raman spectrum scanning across patterned and unpatterned regions of several Tl-2212 films with a mapping stage. It is well known that the Raman peak at /spl ap/497 cm/sup -1/ corresponds to the Cu-O(2) stretching mode and is correlated with the superconducting transition temperature of the material. No appreciable variation in the center frequency of the Cu-O(2) peak was observed indicating thallium cuprate films are not degraded by our patterning process, even at the edges. Variations in the power handling of Tl-2212 co-planar lines, as determined by measurement of the Third Order Intercept, were not correlated with the Raman results.

Hybrid HTS and III-V Microwave Oscillators

Low-noise oscillators operating as pure microwave frequency sources have many critical real world uses in modern radar, communications, and information processing applications. One such application would be as a local oscillator in an advanced microwave front-end receiver. Hybrid oscillators consisting of III-V FETs and high temperature superconducting (HTS) passive microwave devices have been fabricated and tested at cryogenic temperatures at Du Pont. Initial devices operating in the C-band at 4.7 GHz have utilized commercially available High Electron Mobility Transistor (HEMT) unpackaged chips. Wide band amplifiers with bandwidth from 2 to 8 GHz were fabricated and tested at 77 K show 17 dB gain. This is 3 dB higher than amplifiers operating at room temperature. Hybrid oscillators were fabricated using these wide-band amplifiers with feed back provided by a Tl2Ba2CaCu2O8 microstrip resonators. Resonators were fabricated from two-side coated HTS films on LaAlO3 substrates and had loaded Qs of 5000 with insertion loss of -6 dB. Oscillators show phase noise of less than -106 dBc (1 Hz) at 10 KHz offset from operating frequency of 4.7 GHz.

S-Parameter, I-V Curve and Noise Figure Measurements of III-V Devices at Cryogenic Temperatures

We have measured the electrical operating parameters for several three-terminal semiconductor III-V devices at both room temperature and liquid nitrogen temperature, 80 K. The fundamental performance parameters, I-V curve, S-parameters and noise figure, change quite dramatically upon cooling. It is necessary to know these parameters if an optimal cryogenic device, e.g. high-temperature superconducting/III-V hybrid, is to be designed and fabricated. The electrical operating parameters for a Fujitsu GaAs high electron mobility field effect transistor, HEMT, and a Litton GaAs metal semiconductor field effect transistor, MESFET, were measured at room temperature and at 80 K. The data collected on these devices were used to design a III-V C-band amplifier with optimum operation at 80 K. This amplifier was used to construct a high-temperature superconducting/III-V hybrid oscillator, a major step towards the high degree of circuit integration required for a useful HTS/III-V hybrid subsystem or system.