Zhi-Yuan Shen

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

Surface resistance of large-area Tl2Ba2CaCu2O8 thin films at microwave and millimeter wave frequencies measured by three noncavity techniques

The surface resistanceRs of Tl2Ba2CaCu2O8 films fabricated on LaAlO3 wafers up to 3 inches (7.6 cm) in diameter through a post-deposition anneal process was measured over the frequency range 5.55–94.1 GHz by the following techniques: 5.55 and 27.5 GHz high-temperature superconductor (HTS)-sapphire resonators, 10 GHz parallel plate resonator, and 94.1 GHz scanning confocal resonator.Rswas found to exhibit a quadratic dependence on frequencyf at 77 K:Rs∝f2.0±0.1. The highest-quality films yieldRs=145±15μΩ at 10 GHz and 77 K. Scanning confocal resonator mapping ofRsacross a 2-inch (5.1 cm) diameter wafer yielded a base value forRsof 16±1 mΩ at 77 K and 94.1 GHz (equivalent to 180±10μΩ at 10 GHz) and good uniformity inRsacross the wafer. HTS-sapphire resonator measurements ofRsfor fifteen 1.2 cm square parts cut from a 3-inch diameter wafer yieldedRsvalues scaled to 10 GHz of 196±10μΩ at 80 K. Similar values were measured for Tl2Ba2CaCu2O8 films prepared on both sides of a 2-inch diameter wafer.Rs values at 10 GHz and 80 K of 147−214μΩ were maintained over the course of 40 independent and successive deposition runs and corresponding anneals under nominally identical film fabrication conditions. Surface resistance at 5.55 GHz remained below 80μΩ for maximum rf magnetic fields up to 85 Oe at 4.2 K and 7 Oe at 80 K, respectively. Results are compared with predictions of the two-fluid model. The relative advantages and disadvantages of the different techniques for measuring surface resistance are discussed.

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.

Power Handling Capability of Large Area HTS Thin Films at Microwave Frequencies

Measurements of the surface resistance Rs of Tl2Ba2CaCu2O8, (Tl,Pb)Sr2CaCu2O7, and YBa2Cu3O7 thin films prepared on 5 cm (2 inch) diameter LaAlO3 substrates show that these films maintain low surface resistance at microwave frequencies even while carrying high power. A 5.55 GHz TE011 mode resonator has been designed for measurement of Rs at high power. Superconductor films are placed on both sides of a sapphire cylinder and microwave power is coupled into and out of the resonator. The Q-value and S-parameters are measured, from which Rs is calculated. By controlling the temperature and changing the input power, Rs can be determined as a function of both temperature and maximum rf magnetic field amplitude Hmax. For Tl2Ba2CaCu2O8 films at 4.2 K and Hmax = 85 Oe, Rs at 5.55 GHz was 72µΩ YBa2Cu3O7 and (Tl,Pb)Sr2CaCu2O7 films exhibited similarly low Rs at 4.2 K for maximum magnetic fields up to about 20 Oe. At 90 K, the surface resistance for the Tl2Ba2CaCu2O8 films remained below 100µΩ for maximum magnetic fields up to 6 Oe. The results demonstrate the potential for superconducting films for use in high power applications at microwave frequencies.

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.