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Electronics and Communications in Japan (Part I Communications)

Millimeter wave video detection using pb thin film microbridge josephson junction

Shigeru Yoshimori, Mitsuo Kawamura

Published Jan 1, 1982• 2 citations
Publisher

Abstract

Abstract An experiment in video signal detection at 70 GHz was conducted with a Pb micro‐bridge prepared by electron‐beam exposure and the lift‐off method. It was found that for the dc Josephson effect the external noise is dominant over the internal noise of the specimen and that the equivalent noise becomes large near the critical temperature. The response to 100 kHz amplitude‐modulated signals was found to be ten times more rapid than that of the superconductor bolometer. Theoretically the maximum responsivity is obtained near the first Shapiro step, which, however, does not give a stable bias; maximum responsivity was actually observed near the zeroth Shapiro step, where it exceeded 6.3 × 104 V/W. The responsivity was found to increase with increasing IcRn.

DOI
10.1002/ecja.4410650813

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Applied Physics Letters•Aug 29, 1988•24 citations
Abstract An experiment in video signal detection at 70 GHz was conducted with a Pb micro‐bridge prepared by electron‐beam exposure and the lift‐off method. It was found that for the dc Josephson effect the external noise is dominant over the internal noise of the specimen and that the equivalent noise becomes large near the critical temperature. The response to 100 kHz amplitude‐modulated signals was found to be ten times more rapid than that of the superconductor bolometer. Theoretically the maximum responsivity is obtained near the first Shapiro step, which, however, does not give a stable bias; maximum responsivity was actually observed near the zeroth Shapiro step, where it exceeded 6.3 × 104 V/W. The responsivity was found to increase with increasing IcRn.
Millimeter-wave detection was investigated using a step-edge microbridge Josephson junction fabricated by a YBaCuO thin film for both the video detection and harmonic mixing detection. Current–voltage (I–V) characteristics, which could be described by the resistively shunted junction (RSJ) model, were obtained up to 70 K with the IcR product of 150 μV at 70 K. The responsivity and noise equivalent input power were calculated as 2400 W/V and 4.4×10−14 W/√Hz, respectively, in the video detection assuming the RSJ model approximation. Clear dependence of the intermediate frequency output on the applied dc bias voltage was observed in the harmonic mixing detection with the harmonic numbers of 5–16, reflecting the change of dynamic resistance at the constant voltage steps induced by the local oscillation signal on the I–V curve. A minimum detection power of −59.4 dB m and a conversion efficiency (η) of −49.6 dB were obtained for the harmonic number (N) of 5 at 60 K. The relationship between the η and N was expressed as η∝N−2.2.
Millimeter-wave detection was investigated using a step-edge microbridge Josephson junction (SEJJ) fabricated by a sputter-deposited DyBaCuO thin film. The SEJJ exhibited a clear response to 110-GHz millimeter-wave irradiation, and Shapiro steps could be observed up to the seventh step. Harmonic mixing detection was successfully achieved using microwaves of 6 approximately 22 GHz as a local oscillation signal. The dependence of conversion efficiency ( eta ) on the harmonic number was expressed as eta varies as N/sup -3.3/. The detector was operative at temperatures up to 65 K, although the efficiency rapidly decreased above 50 K.>
For Josephson bicrystal YBaCuO junctions 3–1.5 µm in size, the response to an external signal with a frequency of 165 GHz was measured. Receivers with similar ICRN values at helium temperatures and different RN values were chosen for the study. The amplitudes of the Shapiro steps were measured for various external signal powers and sample temperatures. The dependence of the output voltage noise on the operating point, temperature, and external signal power was measured. It is shown that fluctuations of the critical current have the greatest influence on the output noise of the receiver. The volt-watt responsivity and noise-equivalent power were evaluated for a 165 GHz external signal. The experimental results are compared with numerical calculations based on the model of a resistive-capacitive shunted Josephson junction. Optimal temperature operating ranges for the use of each structure were shown.
We present a superconducting noise bolometer for terahertz radiation, which is suitable for large-format arrays. It is based on an antenna-coupled superconducting micro-bridge embedded in a high-quality factor superconducting resonator for a microwave bias and readout with frequency-division multiplexing in the GHz range. The micro-bridge is kept below its critical temperature and biased with a microwave current of slightly lower amplitude than the critical current of the micro-bridge. The response of the detector is the rate of superconducting fluctuations, which depends exponentially on the concentration of quasiparticles in the micro-bridge. Excess quasiparticles are generated by an incident THz signal. Since the quasiparticle lifetime increases exponentially at lower operation temperature, the noise equivalent power rapidly decreases. This approach allows for large arrays of noise bolometers operating above 1 K with sensitivity, limited by 300-K background noise. Moreover, the response of the bolometer always dominates the noise of the readout due to relatively large amplitude of the bias current. We performed a feasibility study on a proof-of-concept device with a 1.0 × 0.5 μm2 micro-bridge from a 9-nm thin Nb film on a sapphire substrate. Having a critical temperature of 5.8 K, it operates at 4.2 K and is biased at the frequency 5.6 GHz. For the quasioptical input at 0.65 THz, we measured the noise equivalent power ≈3 × 10−12 W/Hz1/2, which is close to expectations for this particular device in the noise-response regime.
Microwave properties of an Y-Ba-Cu-O microstrip detector have been studied at 24 GHz frequency band at the liquid-nitrogen temperature. The amplitude of the video detection signal was found to be proportional to the incident microwave power. Direct mixing action was also demonstrated, setting the upper limit for the film response time as short as 40 ps. Occurrence of microwave mixing in the absence of dc current bias was observed, suggesting the presence of the inverse Josephson effect. Physical properties of the detector response were very similar to the enhanced mode of detection, characteristic for granular superconducting films.