High-temperature superconductive devices on sapphire

The low-loss and uniform dielectric properties of sapphire make it attractive for high-performance microwave devices using high-temperature superconductors. YBa₂Cu₃O_7-δ films have been deposited on oxide-buffered 5-cm-diameter wafers and demonstrated a surface resistance of 0.5 mΩ at 10 GHz and 77 K. Long (9-ns) stripline delay lines have for the first time been produced on these substrates and have a measured insertion loss of 1.5 dB at 6 GHz and 77 K. Design techniques appropriate for the dielectric anisotropy of sapphire are discussed     

High-temperature superconductor resonators and phase shifters

High-T_c resonators and hybrid digital phase shifters have been designed, fabricated, and tested. The YBa₂Cu₃O_7-δ (YBCO) films used were off-axis sputtered onto 0.5-mm-thick [100] LaAlO₃ substrates and have surface impedances at 10 GHz as low as 20 μΩ at 4.2 K and 300 μΩ at 77 K. The dielectric constant of the LaAlO₃ substrates was measured using straight-line and ring resonator techniques. The superconductor straight-line resonator, which uses silver as its ground plane, has a moderately high Q factor and has an electromagnetic feedthrough level below -65 dB up to 10 GHz. The authors also report the first demonstration of a semiconductor/superconductor microwave digital phase shifter. YBCO film was used to form the circuit, with semiconductor p-i-n diodes serving as switches. A 4-b superconductor phase-shifter design is also presented along with simulation results that indicate maximum total insertion loss (which occurs with all bits forward-biased) at 77 K to be 1.1 dB at 10 GHz     

An HTS narrow bandwidth coplanar shunt inductively coupledmicrowave bandpass filter on LaAlO3

Coplanar waveguide bandpass filters with shunt inductively coupled resonators using high-temperature superconductors (HTS's) on LaAlO₃ substrates were developed for high packing density, narrow bandwidth, and low power applications. The computer-aided design and measurements on resonators to test weak end-coupling are described in this paper. A coplanar three-pole Chebychev bandpass filter with 1.8% 3-dB bandwidth at 10 GHz and 1.3-dB insertion loss at 77 K was fabricated and measured. The maximum superconducting current density of the filter is evaluated     

Adjustable multilayer HTS filters

An adjustable multilayer high-temperature superconductor (HTS) bandpass filter has been fabricated. Taped comb-line filters with multilayer structures were designed, YBa₂Cu₃O_7-δ (YBCO) thin films deposited on LaAlO₃ were used to construct the packaged multilayer HTS filter. The electrical length of the resonators in the filter was smaller than a quarter-wave length. The frequency responses of the filter were measured at liquid nitrogen temperature 77 K. The insertion loss of the packaged filter was determined to be less than 0.5 dB. By mechanically adjusting the multilayer structure, the center frequencies of the filter changed from 1.78 to 1.92 GHz, and the variations of the bandwidth from 60 to 150 MHz were also obtained     

Comparison of radio-frequency and microwave superconductingproperties of YBaCuO dedicated to magnetic resonance imaging

Properties of YBaCuO thin films are evaluated in two distinct frequency ranges using different patterns made during the same process on LaAlO₃ substrate. Microwave superconducting properties in the range 1-45 GHz are determined by S-parameters measurement of a superconducting coplanar waveguide in the range 53-95 K. We obtain a surface resistance of 0.4 mΩ at 10.8 GHz and 77 K. Radio-frequency properties are obtained by measuring the Q-factor of a superconducting resonator (YBCO multiturn transmission lines separated by a sapphire sheet) dedicated to surface magnetic resonance imaging. At 52 MHz and 77 K we measure a Q-factor of 33180. The extraction of the radio-frequency surface resistance from Q-factor measurements in the 64-95 K range takes into account external loss mechanisms and nonuniform normal current distribution and leads to a 0.0093-μΩ surface resistance at 52 MHz and 77 K, in good agreement with the value extrapolated from microwave measurements assuming an ω² frequency dependence. The evaluation of λ₀ is carried out by using several models for X_L(t). Least squares fits to data in the microwave and radio-frequency domain are performed using the Gorter-Casimir expression for X_L(t) and give the same λ₀ value for both devices     

Measured performance at 77 K of superconducting microstripresonators and filters

Results on three types of passive microwave devices fabricated and tested using epitaxial thin films of Tl₂CaBa₂Cu ₂O₈ grown on LaAlO₃ are reported. A microstrip ring resonator with unloaded Q of 2740 at 77 K and 33 GHz is described. A superconducting 4.6 GHz band-reject filter with unloaded Q greater than 15000 when operated at 77 K is reported. In addition, results on a multiple microstrip bandpass filter are presented     

高温超导膜微波滤波器

我们用氧化锆单晶衬底GBCO高温超膜研制了超导膜悬微波低通滤波器。在77K测试获得:通带插损在0—2GHz,0—4GHz和0—6GHz通带内,分别为0.326dB,0.507dB和1.393dB。文中阐明悬置微带电路用于研制高介电常数衬底的高温超导微波无源器件是适宜的。     

Low- and high-temperature superconducting microwave filters

Stripline and microstrip filters at X-band were designed and fabricated using low- and high-temperature superconductors in quarter-wave, parallel-coupled section configurations. Low-temperature superconducting niobium thin films, deposited on single-crystal sapphire, were used to build to six-pole stripline filters with adjacent passbands and approximately 3 dB crossovers and 1.2% bandwidth. Four- and six-pole microstrip filters were made with in situ epitaxial YBa₂Cu₃O₇ (YBCO) films on LaAlO₃ substrates. All the YBCO filters showed 77 K passbands with clean skirts and high out-of-band rejection. The six-pole filters had adjacent passbands with -28 dB crossovers and 1.5% bandwidth     

A Superconducting Microstrip Ultra-Wideband (UWB) Bandpass Filter at VHF-Band

A compact superconducting ultra-wideband filter with a passband from 125 to 260 MHz is demonstrated. The filter consists of ten shunt short-circuited stubs separated by connecting lines. The short-circuited stubs are grounded via a grounding strip that is attached to the box wall by a number of SiAl bonding wires. The filter is realized on two 2 in YBCO/LaAlO₃ substrates, which are connected by two bonding wires. The measured results demonstrate an insertion loss of less than 0.08 dB and a return loss of better than 21 dB without tuning. Furthermore, the experimental results of the filter are in good agreement with the simulated ones.     

Wide-band superconducting coplanar delay lines

Two 25-ns high-temperature superconductor delay lines with novel double-spiral meander line structures were fabricated and measured, one based on the conventional coplanar waveguide (CPW) and the other based on the conductor-backed CPW. Compared with other published studies, the performance of the Conductor-backed CPW delay line is among the best in terms of the widest resonance-free band (2-18 GHz), low insertion loss (0.06 dB/ns at 60 K and 10 GHz), small ripple (<1 dB up until 16 GHz), and small dispersion (<2 ns in the variation of group delay between 2-18 GHz). This is also the first coplanar delay line successfully demonstrated without using wire bonding. The reflecting elements in the delay lines were identified through time-domain measurements. Full-wave simulations were performed to compare the double-spiral meander-line structure with conventional double-spiral line, and to identify the geometric factors restricting the bandwidth of the double-spiral meander line.     

Quasi-optical millimeter-wave band-pass filters using high-Tc superconductors

Quasioptical millimeter-wave band-pass filters using YBa₂ Cu₃O₇ high-T_c superconducting films were fabricated on MgO and LaAlO₃ substrates. Transmitted power through the filter was investigated in the 75 GHz to 110 GHz frequency range at temperatures ranging from 15 to 300 K. At 15 K the measured center frequency and the bandwidth of the superconducting filter were 92 GHz and 0.85 GHz, respectively. Measurements of YBa₂Cu₃O₇ filters were compared with similar filters fabricated using gold. At 15 K and 92 GHz, an improvement of 75% in the quality factor of the superconducting filter was obtained compared with a similar gold filter     

Conductor-loss limited stripline resonator and filters

We report on stripline resonators on thin dielectric membranes that show dispersion-free, conductor-loss limited performance at 13.5 GHz, 27.3 GHz, and 39.6 GHz. The unloaded-Q (Q_u) of the resonators increases as √f with frequency and is measured to be 386 at 27 GHz. The measured results agree well with a new conformal mapping analysis. The stripline resonators are used in a micromachined state-of-the-art planar interdigitated bandpass filter at K-band frequencies. Excellent agreement has been achieved between the microwave model at 850 MHz and the 20 GHz filter. The micromachined filter exhibits a passband return loss better than -15 dB and a conductor-loss limited 1.7 dB port-to-port insertion loss (including input/output CPW line loss) at 20.3 GHz     

Circularly polarized 20-GHz high-temperature superconductingmicrostrip antenna array

A four-element array of circularly polarized 20-GHz YBa₂Cu₃O_x microstrip antennas has been fabricated on LaAlO₃ and characterized. The array produced good circular polarization, and the gain of the array at 77 K, relative to a copper array of the same design at 77 K, was approximately 0.75 and 1.3 dB for the two gain measurement methods presented. The relative gain increased to approximately 2.2 dB at 30 K. The results demonstrate that high-temperature superconductors, when used in microstrip antenna arrays, improve the efficiency of the array, and that circularly polarized microstrip arrays can be fabricated on LaAlO₃     

A 12-Pole Narrowband Highly Selective High-Temperature Superconducting Filter for the Application in the Third-Generation Wireless Communications

An ultra-selective high-temperature superconducting bandpass filter was designed and fabricated to satisfy the demands of the third-generation wireless communications. This filter was designed to have 12-pole quasi-elliptic response with 4.68-MHz bandwidth in the third-generation communications band (a fractional bandwidth of 0.0023). Full-wave simulations were conducted by using Sonnet software. A novel, compact, and low radiation resonator with a high-quality (Q) factor value was developed to reduce the parasitical coupling. In order to satisfy the demand of high band-edge steepness, three pairs of transmission zeros at finite frequencies were introduced in the cascaded quadruplet coupling structure. The filter was fabricated on a 2-in-diameter 0.43-mm-thick sapphire wafer with double-sided YBCO films. The measurements showed that the passband center frequency (f₀) of the filter is 2.038 GHz at 67 K with a midband insertion loss of 0.67 dB and the return loss better than 15 dB. The measured response of the filter also exhibited ultra-high band-edge steepness of 140-220 dB/MHz. Better than 60 dB of out-of-band rejections for frequencies very close to the band edge (|f-f₀|>2.7 MHz), better than 90 dB at frequencies 7.5 MHz away from the center frequency and up to 100 dB of wideband rejections were achieved     

Scattering parameter and bit error rate characterization of hightemperature superconducting coplanar transmission lines

We report the gigahertz experimental results of time and frequency performance on YBCO high temperature superconductor (HTS) and gold coplanar transmission lines. An on-wafer direct probing measurement system was used to collect data at cryogenic temperatures on both YBCO and gold coplanar lines. The insertion loss of the 6-cm lines at a frequency of 3.0 GHz was measured to be -0.12 dB for the superconducting line compared to -10.7 dB for the gold line at 80 K. Error rate and eye-diagram measurements were performed on the packaged lines and show the correlation between the insertion loss of the line and the attenuation of a Pseudo Random Bit Sequence (PBRS). The superconducting line measured at 77 K had a BER rate of less than 10^-11 at a data rate of 3 Gb/s. The measured eye height was 350 mV for the YBCO compared to 100 mV for a gold line at 3 Gb/s and a temperature of 77 K for the packaged 6-cm lines     

High Tc superconducting three-pole parallel-coupled bandpass filters made from laser ablated YBa2Cu3O7 − δ thin films

We have investigated three-pole parallel-coupled bandpass filters with fractional bandwidths of about 6% and 3% at a center frequency of 10.5 GHz utilizing high T_c superconducting YBa₂Cu₃O_{7 − δ} thin films. The films were deposited on LaAlO₃ substrates by pulsed laser ablation. Microwave responses of the filters were measured as a function of temperature and input power. The performance of the 3% bandwidth filter exhibits low insertion losses of about 0.48 dB and 0.79 dB at 20 K and 77 K, respectively. The insertion loss in the 6% bandwidth filter was 0.96 dB at 77 K. Both filters showed return losses better than 15 dB. High T_c superconducting bandpass filters showed good reproducibility. They were also compared with equivalent gold filters which showed insertion losses of more than 8 dB at 77 K.     

Interface-engineered Josephson junctions optimized for high JC

High-temperature superconducting interface-engineered junctions were fabricated using YBa₂Cu₃O_7-δ on LaAlO₃ (LAO) and sapphire substrates. We report on the improvements in the electrical characteristics by junction narrowing. Originally, the 2-μm-wide junctions had high critical current densities of 1.2 × 10⁶ A/cm at 4.0 K and showed wide junction effects. Narrowing the junctions to below a micrometer reduced the wide junction effect over a large range of temperatures and the junctions had characteristic voltages of 5.16 mV at 4.0 K. The magnetic-field modulation of the critical current was also more ideal after narrowing. Furthermore, we show that interface engineered junctions on sapphire substrates have similar characteristics to those on LAO     

Miniaturized high-temperature superconductor microstrip patchantenna

Experimental as well as computational results are presented for 2.4 GHz microstrip antennas which are miniaturized (total length, 6 mm) by both a new, stepped impedance patch shape and a relatively high substrate permittivity. The antennas investigated were fabricated from YBa₂Cu₃O_7-δ thin films epitaxially grown on single-crystalline LaAlO₃ substrates by pulsed excimer laser ablation or by high-pressure oxygen DC sputtering and, for comparison, from copper on the same substrate material. It is shown that the radiation efficiency of this antenna structure is only about 1% to 6% for copper at 77 K but is increased to values between 35% and 65% for HTS films. From experimental investigations of the power dependence of the antenna gain at 77 K, nonlinearities, especially a sharp drop at a current density of about 2×10⁶ A/cm², were observed     

Microwave dielectric properties of DNA based polymers between 10 and 30 GHz

Deoxyribonucleic acid (DNA) based polymer thin-films were characterized at microwave frequencies for the first time. The dielectric properties of the film were extracted from comparison of the propagation constants of the co-planar waveguide (CPW) lines on bare MgO substrates and the DNA based films on MgO substrates. The insertion loss introduced by the DNA film is only 0.1 dB at 10 GHz and 0.5 dB at 30 GHz. The relative dielectric constant of the DNA based film averages to four at microwave frequencies, and the loss-tangent was below 0.1 up to 30 GHz.     

Hybrid high temperature superconductor/GaAs 10 GHz microwaveoscillator: temperature and bias effects

Hybrid YBa₂Cu₃O_7-x superconductor/GaAs microwave oscillators have been designed, fabricated and characterized. The planar oscillators were built on a single 10 mm×10 mm LaAlO₃ substrate. The active elements in the hybrid oscillators were GaAs MESFETs. A ring resonator was used to select and stabilize the frequency. A superconducting ring resonator had a loaded Q at 77 Kg which was 8 times larger than the loaded Q of a ring resonator fabricated out of copper. S-parameters of the GaAs FET were measured at cryogenic temperatures and used to design the oscillator which had a reflection mode configuration. The transmission lines, RF chokes and bias lines were all fabricated from YBa₂Cu₃ O_7-x superconducting thin films. The performance of the oscillators was measured as a function of temperature. The rate of change of the frequency as a function of temperature was smaller for an oscillator patterned from a pulsed laser deposited film than for an oscillator patterned from a sputtered film. As a function of bias at 77 K, the best circuit had an output power of 11.5 dBm and a maximum efficiency of 11.7% The power of the second harmonic was 25 dB to 35 dB below that of the fundamental, for every circuit. At 77 K, the best phase noise of the superconducting oscillators was 68 dBc/Hz at an offset frequency of 10 kHz and less than -93 dBc/Hz at an offset frequency of 100 kHz. At an offset frequency of 10 kHz, the superconducting oscillator had 12 dB less phase noise than the copper oscillator at 77 K