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IEEE Transactions on Applied Superconductivity

HTS mixers based on the Josephson effect and on the hot-electron bolometric effect

Oliver Harnack, S. Beuven, Marian Darula, H. Kohlstedt, Michael A. Tarasov, E. Stephansov, Z. G. Ivanov

Published Jun 1, 1999• 15 citations
Publisher

Abstract

We report on our experimental studies of high-T/sub c/ Josephson mixers and high-T/sub c/ hot-electron bolometric (HEB) effect mixers. Mixers based on high-T/sub c/ bicrystal Josephson junctions have been fabricated, and noise, conversion efficiency, and receiver bandwidth measurements have been performed in the frequency range between 90 and 550 GHz. The dependence of the mixer performance on the operation temperature has been studied. High-T/sub c/ HEB mixers have been fabricated on MgO and sapphire substrates. We successfully sized the dimensions of the effective device volume down and managed to fabricate 50-60 nm long devices. In such short structures phonon diffusion into the normal metal electrodes should significantly improve the mixer performance.

DOI
10.1109/77.783847

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We report on our experimental studies of high-T/sub c/ Josephson mixers and high-T/sub c/ hot-electron bolometric (HEB) effect mixers. Mixers based on high-T/sub c/ bicrystal Josephson junctions have been fabricated, and noise, conversion efficiency, and receiver bandwidth measurements have been performed in the frequency range between 90 and 550 GHz. The dependence of the mixer performance on the operation temperature has been studied. High-T/sub c/ HEB mixers have been fabricated on MgO and sapphire substrates. We successfully sized the dimensions of the effective device volume down and managed to fabricate 50-60 nm long devices. In such short structures phonon diffusion into the normal metal electrodes should significantly improve the mixer performance.
We have measured the device length and temperature dependence of the intermediate frequency (IF) bandwidth and noise of hot-electron bolometer (HEB) mixers made from a high- T c superconductor. Mixer devices with lengths (L) between 50 nm and 1 µm were fabricated from 25-35 nm thick YBCO films on MgO and sapphire substrates. Bandwidth measurements were made using signal and local oscillator (LO) frequencies in the range 1-20 GHz. At low operation temperatures the IF bandwidths were about 100 MHz and several hundred MHz for devices on MgO and sapphire, respectively. At higher operation temperatures, where self-heating disappeared and flux-flow effects define the shape of the I - V characteristic, the measured IF bandwidth increased significantly. The temperature and IF dependence of absolute conversion efficiencies determined from noise measurements are in good agreement with the bandwidth data. At 2.7 GHz LO frequency the single-side-band mixer noise temperature of a 50 nm long HEB on MgO was about 8000 K.
We report on our experimental studies of noise properties and conversion efficiency of high-T/sub c/ Josephson mixers and high-T/sub c/ hot-electron bolometric (HEB) effect mixers at frequencies between 90 GHz and 550 GHz. Noise measurements using a Josephson mixer at 90 GHz gave noise temperatures of 2900 K at 20 K. Measurements in a quasi-optical setup at 430 GHz and 546 GHz showed mixer noise temperatures of 1200 K and 1100 K at 4.2 K, respectively. Heterodyne mixing experiments using high-T/sub c/ HEB mixers have been performed at temperatures around 78 K and at frequencies between 78 GHz and 119 GHz. The uncorrected conversion efficiency at an intermediate frequency of 3 GHz was measured to be -30 dB.
Superconducting hot-electron bolometers (HEB) represent a promising candidate for heterodyne mixing at frequencies exceeding 1 THz. Nb HEB mixers offer performance competitive with tunnel junctions without the frequency limit imposed by the superconducting energy gap. Although the performance of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// HEB mixers is not projected to be superior to that of Nb devices, which operate at low temperatures, they introduce the possibility of sensitive, low power heterodyne detectors operating at temperatures approaching 90 K for applications requiring portability and closed-cycle refrigeration. We report on the fabrication and characterization, both DC and RF, of high-T/sub c/ mixers based on ultra-thin (/spl les/20 nm) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films patterned to micrometer dimensions and incorporated into 2.5 THz planar mixer circuits.
We report on experimental studies of the noise performance and conversion efficiency of high-Te Josephson mixers at frequencies between 90 GHz and 550 GHz. The heterodyne mixing experiments have been performed by using YBa2Cu307_8 step-edge junctions and bicrystal junctions on MgO (E--9.6) substrates. We studied the Josephson mixer performance for the case of internal pumping (selfpumping) and external pumping. Receiver noise measurements in a waveg,uide setup for the case of external pumping at 90-94 GHz gave formally calculated double-side-band (DSB) mixer noise temperatures (Tm) of about 2000 K at physical temperatures of 10 K. Similar measurements in a quasioptical setup at 4.2 K and at operation frequencies of 430 GHz and 546 GHz yielded mixer noise temperatures of 1200 K and 1100 K, respectively. Using the internal pumped mode, i.e. mixing without external local oscillator signal, we also obtained clear IF response in hot/cold-measurements. The formally calculated Tm were between 580 K and 2300 K.
We report the experimental evaluation of a high-temperature superconducting (HTS) Josephson mixer. The mixer is fabricated from a HTS step-edge junction on MgO substrate. The mixer device operates as a lower side-band down-converter from a radio frequency between 6 and 10 GHz to a 1-2 GHz intermediate frequency under the action of a local oscillator. The experimental results of the current-voltage characteristics, optimal bias conditions, dynamic range, linearity, conversion gain, and the temperature dependence of the mixer are presented.
Superconductive hot-electron bolometer (HEB) mixers have been built and tested in the frequency range 1.1-2.5 THz. The mixer device is a 0.15-03 /spl mu/m microbridge made from a 10 nm thick Nb film. This device employs diffusion as a cooling mechanism for hot electrons. The double sideband noise temperature was measured to be /spl les/3000 K at 2.5 THz and the mixer IF bandwidth is /spl ap/9-10 GHz for a 0.1 /spl mu/m long device. The local oscillator (LO) power dissipated in the HEB microbridge was 20-100 nW. Further improvement of the mixer characteristics can be potentially achieved by using Al microbridges. The advantages and parameters of such devices are evaluated The HEB mixer Is a primary candidate for ground based, airborne and spaceborne heterodyne instruments at THz frequencies. HEB receivers are planned for use on the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA) and the ESA Far Infrared and Submillimeter Space Telescope (FIRST). The prospects of a submicron-size YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) HEB are also discussed. The expected LO power of 1-10 /spl mu/W and SSB noise temperature of /spl ap/2000 K may make this mixer attractive for various remote sensing applications.