V. Pendrick

Microwave properties of highly oriented YBa2Cu3O7−x thin films

We have performed intra‐ and extra‐cavity microwave frequency (1–100 GHz) measurements on high quality Y1Ba2Cu3O7−x superconducting thin films on (100) LaAlO3 substrates. The ∼0.3 μm thin films fabricated by the pulsed laser deposition technique exhibit superconducting transition temperatures >90 K, as determined by resistivity and ac susceptibility measurements, and critical current densities of 5×106 A/cm2 at 77 K. Moreover, ion beam channeling minimum yields of ∼3% were measured, indicating the extremely high crystalline quality of films grown on the LaAlO3 substrate. Microwave surface resistance values at 77 K for these films are found to be more than one to two orders of magnitude lower than for copper at 77 K for almost the entire frequency range explored. We postulate that the reason we observe such low surface resistances in these films is the virtual absence of grain and phase boundaries coupled with the high degree of crystallinity. Furthermore, we believe that the residual resistance measured b...

Low-loss substrate for microwave application of high-temperature superconductor films

We have shown that strontium lanthanum aluminate (SrLaAlO4) has considerable potential as a substrate material for high‐temperature superconductor (high Tc) microwave applications. Excellent lattice match is obtainable on a 14° tilt from the c axis. The lattice dimensions encourage ab plane epitaxial growth. The thermal expansion was found to be 7.4×10−6 °C−1. Patterned sputtered niobium resonators on SrLaAlO4 exhibit Q values at 5 K comparable to similar niobium resonators on polycrystalline alumina, (Q≳10 000 from 2 to 15 GHz). Deposited YBa2Cu3O7−x (YBCO) films on this substrate show sharp ac susceptibility transitions indicating good homogeneity and ab plane orientation.

Measurement of microwave surface resistance of patterned superconducting thin films

A simple and versatile measurement technique has been demonstrated for characterization of thin film superconductors and the substrates on which they are deposited. Unlike other state of the art measurements that characterize only the top layer of unpatterned thin films in end-plate replacement or perturbation-type cavity arrangements, we test the sample under conditions very close to those of actual microwave circuit applications. Measurements on a laser deposited, thin-film YBCO superconductor, patterned in the form of a meander line on a LaAlO3 substrate, show a microwave surface resistance one order of magnitude lower than that of copper at 79 K and 11 GHz. At 1.4 GHz and 79 K, an improvement by over two orders of magnitude is observed. This is the first demonstration of superior microwave performance of a comb filter structure using a HTS thin film.

Performance of a narrow band microwave filter implemented in thin-film YBa2Cu3O7-δ with ohmic contacts

Using in situ deposited thin‐film Y1Ba2Cu3O7−δ on LaAlO3 substrates, we have developed a pseudo‐interdigital three‐pole stripline filter with a minimum passband loss under 3.5 dB at 9.5 GHz and 77 K. The passband is very narrow, having a bandwidth of only 50 MHz (0.5%). The filter occupies a volume of less than 0.1 cm3. An equivalent copper filter produced a loss of 18.5 and 28 dB at 77 and 300 K, respectively. The input and output coupling is achieved by ex situ sputtered Au thin‐film contacts defined on the Y1Ba2Cu3O7−δ by a lift‐off technology and ultrasonically bonded to hermetic K connectors. Some of the major concerns in the realization of narrow band filters such as air gaps between high dielectric constant substrates and uniformity of the substrate’s dielectric constant are addressed.

Off‐axis sputter deposition of YBa2Cu3O7 thin films for microwave applications

Thin films of superconducting YBa2Cu3O7 were grown in situ by off‐axis sputter deposition for microwave device fabrication. These ∼1 cm2 films, which are reproducible, exhibit midpoint Tc’s of 89–90.5 K as measured by ac susceptibility, ion channeling yields of 4.7%–6%, and c‐axis rocking‐curve half‐widths of 0.5°, even with a rich microstructure as seen by scanning electron microscopy. Two films were photodefined into miniature X‐band microwave bandpass filters. These narrow‐band filters (0.5% bandwidth) exhibited 4.4‐and 4.5‐dB insertion losses at 77 K and 9.25 GHz, with little temperature dependence below 80 K.

Superconducting narrow band pass filters for advanced multiplexers

X-band microstrip filters with a 50-MHz-wide passband that provide 1.3-dB insertion loss at 77 K using copper ground planes have been built. Recent advances in double side coating of lanthanum aluminate substrates with YBa/sub 2/Cu/sub 3/O/sub 7- delta / will lower this figure to 0.6 dB. Circuit designs were evaluated for intermodulation distortion effects. An improvement over previous designs has increased the third-order output intercept point to +29 dBm. Methods of nondestructive dielectric and conductor loss testing were used to evaluate materials throughout the filter development.<<ETX>>

Microwave compatible YBa2Cu3O7−x films on ferrimagnetic garnet substrates

High quality epitaxial YBa2Cu3O7−x (YBCO) thin films have been deposited onto ferrimagnetic yttrium iron garnet (100) substrates using a double buffer layer lattice engineering scheme. The YBCO films are c‐axis oriented and show superconductive transition temperatures of 88–89 K with transition widths ≤0.5 K. The films also exhibited Jc’s of 2.7×106 A/cm2 in zero field and 1.1 ×106 A/cm2 in 2000 G at 77 K. Dielectric resonator measurements indicated unloaded Q values of 29 000 at 77 K and 24 GHz for unpatterned films. These values correspond to a surface resistance (RS) of 500 μΩ at 77 K, 10 GHz, which is the lowest obtained to date for a YBCO film on a ferrimagnetic substrate. Such films could be used for fabricating miniature‐high‐temperature superconducting microwave elements such as nonreciprocal and passive microwave devices, making possible, their integration on a single ferrimagnetic wafer.

Microwave properties and modeling of high-T/sub c/ superconducting thin film meander line

Meander lines have been utilized for characterizing laser-deposited, thin-film, high-T/sub c/ superconducting material. The dispersion characteristics of the meander line have been modeled and the power dependence of high-T/sub c/ materials as a function of frequency and temperature has been investigated. Measurements showed that magnetic fields as low as 0.1 Oe will affect the superconducting material, decreasing the Q of the meander lines. The Q deterioration is temperature and frequency dependent and the latter is less pronounced at higher frequencies.<<ETX>>

Microwave Measurements on Patterned High Temperature Superconducting Thin Film Circuits

The microwave surface resistance and dispersion of laser deposited YBaCuO films patterned in the form of a meander line have been measured from L through Ku-band at temperatures from 5 to 90K. Surface resistance values below 1 mΩ were demonstrated at 10 GHz and 79K. The results show great promise for the realization of effective high-Tc superconductive passive microwave components in the near future.

Miniature circulators for microwave superconducting systems

Ultraminiature high performance lumped element high temperature superconductor (HTS) circulators have been successfully demonstrated. Epitaxial HTS YBCO films have been deposited by pulsed laser deposition (PLD) onto buffered Yttrium Iron Garnet (YIG) substrates with measured surface resistance values (<1 m/spl Omega/ at 10 GHz @ 77 K) comparable to those of HTS films on lanthanum aluminate. The lumped element circulators occupy an area about an order of magnitude smaller in size than that of conventional disc junction circulators. Excellent low loss (<0.23 dB) and high isolation (>30 dB) over 5% bandwidth have also been demonstrated.<<ETX>>