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IEEE Transactions on Applied Superconductivity

Conversion gain and noise of YBa/sub 2/Cu/sub 3/O/sub 7/ weak-link mixers

Donald P. Butler, Jiaqi Wang, Anil Bhandari, Z. Celik-Butler

Published Mar 1, 1993• 5 citations
Publisher

Abstract

Microwave mixing and parametric conversion in YBa/sub 2/Cu/sub 3/O/sub 7/ microbridges were investigated. The devices have been operated as down-converters, converting a 20-GHz radio frequency to a 1.5-GHz intermediate frequency under the action of an 18.5-GHz local oscillator. The microbridges were fabricated both as granular films on MgO substrates possessing grain boundary weak links and as epitaxial films deposited over substrate steps in LaAlO/sub 3/ substrates. The authors have measured conversion gains as high as -8+or-4 dB when mixing on the nonlinear resistive (superconducting-normal) transition and as high as -30 to -40 dB when parametrically converting via the nonlinear inductance of the bridge at bias currents less than the critical current. Output referred noise powers as low as -206 dB/Hz (3*10/sup -21/ W/Hz) have been measured. In some samples, noise switching events were observed.>

DOI
10.1109/77.233551

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Dec 22, 1998•1 citation
Microwave mixing and parametric conversion in YBa/sub 2/Cu/sub 3/O/sub 7/ microbridges were investigated. The devices have been operated as down-converters, converting a 20-GHz radio frequency to a 1.5-GHz intermediate frequency under the action of an 18.5-GHz local oscillator. The microbridges were fabricated both as granular films on MgO substrates possessing grain boundary weak links and as epitaxial films deposited over substrate steps in LaAlO/sub 3/ substrates. The authors have measured conversion gains as high as -8+or-4 dB when mixing on the nonlinear resistive (superconducting-normal) transition and as high as -30 to -40 dB when parametrically converting via the nonlinear inductance of the bridge at bias currents less than the critical current. Output referred noise powers as low as -206 dB/Hz (3*10/sup -21/ W/Hz) have been measured. In some samples, noise switching events were observed.>
A YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) step-edge microbridge JJ (Josephson junction), two 12-GHz YBCO microstrip bandpass filters, a 1-GHz YBCO filter, and current bias and voltage monitor circuits were successfully combined on a 20-mm*20-mm MgO substrate and integrated into a frequency downconverter for receiving DBS (direct broadcast satellite) signals. The YBCO downconverter and the GaAs low-noise IF (intermediate frequency) amplifier were combined in a microwave cryostat. The dependence of mixing signals on temperature and LO (local oscillator) input power was measured. The conversion gain and the noise figure corresponding to the YBCO downconverter package were -14.5 dB and 12.2 dB, respectively, at 15 K and low LO power (-25 dBm). The first demonstration of the HTS (high-temperature superconductive) subsystem, i.e. the monolithic YBCO downconverter, shows potential for applications in mobile radio communications and satellite broadcasting.>
A microwave mixer was patterned on a microstrip transmission line of superconducting YBCO (YBa/sub 2/Cu/sub 3/O/sub 7-x/). The YBCO film was epitaxially laser deposited on a SrTiO/sub 3/ bicrystal substrate. A weak link was constructed by patterning a microbridge in the microstrip at the bicrystal boundary. Microwave signals at 9.000 GHz and 9.941 GHz were applied at the input of the microstrip line. An output intermediate frequency signal was observed at 941 MHz and was detected as the transmitted signal. The microbridge junction, which behaved as a resistively shunted Josephson junction (RSJ), was current biased slightly above the critical current I/sub c/. The mixer conversion loss was measured at the input and output ports of the device package. The mixing efficiency was determined at the device junction. This efficiency was compared with the calculated efficiency determined by numerical solution of the Josephson equation for the weak link junction.>
A microstrip transmission line was patterned from a superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ film which was laser deposited on a SrTiO/sub 3/ bicrystal substrate. A microbridge in the microstrip was then patterned at the bicrystal interface to fabricate a superconducting grain boundary junction. Microwave mixing was observed with an input local oscillator frequency of 9.000 GHz, and an input signal frequency of 9.941 GHz. The output signal at 941 MHz was detected as a transmitted signal. The junction was current biased slightly above the critical current I/sub c/. The measured conversion loss was compared to the calculated value based upon a numerical solution of the equation for a superconducting weak link junction.>
We fabricated weak link rings using YBCO thin films deposited on the single crystal MgO substrate by laser ablation. The dimensions of the microbridges in the rings were between 0.5–1 μ in length and 500 Å–0.5 μ in width which were made by focused ion beam milling. We biased the ring by Faraday induction voltage while monitoring the voltage across the microbridge. The frequency of the input signal was varied between 10 kHz and 5 MHz. When we superimposed a microwave signal (2–18 GHz) to the ring, below the superconducting transition temperature (Tc), we observed strong nonlinearities in the voltage measured across the microbridge. The microwave frequency was chosen to be close to the ring natural electromagnetic resonance.
Microbridge-type Josephson junctions made of granular bulk YBCO superconductors were experimentally studied at microwave frequencies. Although the bridge included many grain boundaries, clear Shapiro steps were induced at every hf/2e voltage for microwave frequencies, and step height dependence for microwave power similar to that of a single weak link bridge was observed. A heterodyne mixing experiment of microwaves at about 20 GHz was also performed using the detector. The IF signal showed peak amplitudes corresponding to the peak dynamic resistance due to nonlinearity resulting from the Josephson effect. It was confirmed that the detector operates stably for the Josephson-effect heterodyne mixer at 60 K or below. The detector has potential for high sensitivity and good impedance matching due to its large dynamic resistance and high normal state resistance, respectively.
Small volume high-Tc super-conducting YBa2Cu3O7 (YBCO) thin films are used as low power, very wide bandwidth mixers in the frequency range of 75 GHz to 2.5 THz. The YBCO films are patterned into lattice-cooled hot-electron bolometers (HEB) coupled to an integrated Au thin-film antenna and transmission line. Near 77 K, these mixers have responsivity as high as 780 V/W using only 8 nW of local oscillator (LO) power at 585 GHz. The responsivity can be shown to be truly bolometric. Direct heterodyne and homodyne down-conversion mixing using local-oscillator frequencies of 75 GHz and 585 GHz show overall conversion gains of -35 dB, which includes a -18 dB coupling loss, using only approximately 1 (mu) W of LO power. The gain bandwidth shows a simple Lorentzian roll-off with -3 dB point of 5 to 8 GHz. The large gain bandwidth and small power requirements make these high-Tc superconducting mixers an attractive alternative to existing Schottky diode and conventional superconducting receiver technologies.