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Journal of Applied Physics

mm-wave mixer with Nb-Te-Nb Josephson junction

Koichi Nagata, Hideaki Takayanagi, Shingo Uehara

Published Jul 1, 1981• 1 citation
Publisher

Abstract

A mm-wave Josephson integrated mixing circuit has been fabricated. In the circuit, an Nb-Te-Nb sandwich Josephson junction was used as the active element. Both RF and IF circuitries were made in the form of superconducting microstriplines using Si wafer as the dielectric layer. The signal and local powers were fed through tapered ridge waveguides, which were coupled into the stripline with small loss. The circuit was tested at 50-GHz signal frequency and the conversion efficiency was measured at −7.4 dB, for a junction with 0.4-mV ICRN product. The measured efficiency showed good agreement with the theoretical prediction.

DOI
10.1063/1.329326

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IEEE Transactions on Applied Superconductivity•Mar 1, 1993•67 citations
A mm-wave Josephson integrated mixing circuit has been fabricated. In the circuit, an Nb-Te-Nb sandwich Josephson junction was used as the active element. Both RF and IF circuitries were made in the form of superconducting microstriplines using Si wafer as the dielectric layer. The signal and local powers were fed through tapered ridge waveguides, which were coupled into the stripline with small loss. The circuit was tested at 50-GHz signal frequency and the conversion efficiency was measured at −7.4 dB, for a junction with 0.4-mV ICRN product. The measured efficiency showed good agreement with the theoretical prediction.
An mm-wave mixing integrated circuit with a Josephson junction has been fabricated. An Nb–Te–Nb sandwich-type Josephson junction with no hysteresis on its I-V curve was used as the active element. Both RF and IF circuits were constructed in the form of superconducting microstriplines using an Si wafer as the dielectric layer. The circuit was tested at a signal frequency of 50 GHz, and the conversion efficiency η was measured at -7.44 dB, for a junction with a 0.42 mV I C R N product. The measured efficiency showed good ageement with the theoretical one calculated using the RSJ model and taking the impedance of the RF source into account.
Microwave superconducting mixers operating at 10–13 GHz utilizing Josephson junctions have been investigated analytically and experimentally. Measurements on mixer sensitivity were carried out at 13 GHz using waveguide-mounted experimental point-contact Josephson junctions at 4.2 K. Results showed sensitivities of −90 dBm/MHz (10−18 W/Hz) which included mismatch losses encountered in the waveguide structure. The Josephson junction mixing mechanism was analyzed on the basis of small-signal modulation of the staircase like dc I-V characteristics. It was shown that a small-signal microwave excitation results in an ac lateral shift of the regions between steps, such that: (a) Optimum Josephson mixing occurs halfway between steps. (b) Mixing occurs between all steps with maximum conversion efficiency between the zero and first step. (c) Predicted low conversion loss and possibly internal gain for a matched mixer. The analytical model was simulated by a digital computer and the behavior of the Josephson mixer predicted for various conditions of excitation. The model chosen for the analysis and the computer simulation is based on the simplest assumptions concerning bulk-formed Josephson junctions. In the laboratory an external local oscillator set 60 MHz below the signal frequency was used to induce the well-known step structure in the dc I-V characteristic of the point-contact Josephson junction. Mixing of the Lo and signal was found to occur between constant voltage steps in agreement with both analysis and computer simulation. The correctness of the model is demonstrated by the agreement between the theory and experiment.
By using an integrated superconducting sub-mm wave receiver, the composite linewidth of two Josephson flux- flow oscillators (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 R microstripline was about 0.5 pW, and could be adjusted by changing the current bias of the oscillator junction. The receiver consists of two identical FFO's and an SIS (superconductor- insulator-superconductor) mixer. The composite linewidth of the oscillators was determined by mixing the two signals in the SIS mixer to a lower intermediate frequency (if). The FFO's are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev microstriplie transformer and a fairly large inter- digital capacitor, while the second FFO has about 15-20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub, resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as rf chokes for the if-line (4 GHz). The FFO's and the SIS element are made of NbNb-oxidelPbBi tunnel junctions. The receiver circuit was optimized by careful CAD modeling (HP Microwave Design System). and gives rise to the emission of a pulse of electromagnetic energy when it hits the ends of the junction. If the arrival of solitons at one end of the junction is periodic, rf radiation is emitted. The propagation mode of the fluxon in a LJJ depends on the junction quality factor QJ, which is related to the junction losses as (3) QJ = ((wo/uJ)2P -t a)-'.
The Commonwealth Scientific and Industrial Research Organization has developed superconducting microwave monolithic integrated circuit (MMIC) mixers using step-edge Josephson junctions and on-chip filters, made from YBaCuO on MgO substrates. Integration into an MMIC results in a compact and efficiently coupled structure. These have been shown to have outstanding conversion efficiency, dynamic range, and linearity. We report here a range of simulations of this type of mixer. We have mainly used Josephson simulators and analyze the data in both the time and frequency domains. More recently, we have also used microwave simulators incorporating a novel Verilog-A Josephson junction model that we have developed. We have looked at the interactions of junction bias current, local oscillator power, and radio-frequency input power with conversion efficiency, dynamic range, and linearity. Good agreement is found overall with measurements.
A sandwich-type high- Josephson junction coupled with a coplanar-type transmission line was fabricated and heterodyne mixing characteristics were investigated. The junction was fabricated from a stacked film structure of (BSCCO/BSNCO/BSCCO) and the transmission line was made of sputter-deposited Pt film. The junction had a rectangular shape of . Current - voltage (I - V) curves of the junction showed weak-link-type characteristics. Two microwave sources of a frequency synthesizer and a sweep oscillator were used as a local oscillator (LO: 20 GHz) and a radio frequency signal source (RF: 19 GHz) for heterodyne mixing experiments. Intermediate signal (IF: 1 GHz) was transmitted through the transmission line and detected by a power meter. The conversion efficiency of -44 dB was estimated for an LO oscillator level of -23 dB m at 5.7 K when the junction was biased at the point below the first Shapiro step.
All-refractory material superconducting millimeter-wave oscillators have been designed and investigated experimentally with different superconductor-insulator-superconductor (SIS) mixers integrated on the same chip. Tested structures include a flux-flow oscillator (FFO) based on a long Josephson junction, a coupling section, and an SIS detector with tuned out junction capacitance. Coupling sections were designed as multistep microstrip quarter-wave impedance transformers. All junctions have been fabricated on the basis of a high-quality trilayer Nb-AlO/sub x/-Nb process. Microwave oscillations in the frequency range 75-500 GHz have been detected experimentally. The level of delivered power was estimated from the pumped I-V curve of the strongly coupled single junction detector. Coupled power levels higher than 0.1 mu W at 256 GHz were achieved. A spectral linewidth of the FFO of less than 1 MHz has been estimated experimentally. The first attempt to create an integrated receiver based on an FFO and an SIS array mixer integrated on the same chip was made in the 2-mm wavelength band.>