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IEEE Transactions on Applied Superconductivity

Design and Performance of a 3-Junction Series Distributed SIS Mixer for Wide IF Applications

Edward Tong, Paul Grimes, A. Barbier, Karl-Friedrich Schuster, Ming-Jye Wang

Published Dec 20, 2012• 12 citations
Publisher

Abstract

Series distributed superconductor-insulator-superconductor mixers have been used to provide very wide instantaneous bandwidth of operation. In this paper, we explore a design based on a 3-junction array in which the junctions themselves form part of the RF tuning network of the mixer. We have developed mixers based on these designs for use in the 200 and 300 GHz bands. Receivers incorporating these wideband mixers demonstrate very low noise temperature. At a local oscillator frequency of 300 GHz, the lowest measured intermediate frequency noise temperature is about 42 K and the usable intermediate frequency bandwidth extends from 6 to 16.5 GHz. Both the design theory and experimental results are presented.

DOI
10.1109/tasc.2012.2235517

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Series distributed superconductor-insulator-superconductor mixers have been used to provide very wide instantaneous bandwidth of operation. In this paper, we explore a design based on a 3-junction array in which the junctions themselves form part of the RF tuning network of the mixer. We have developed mixers based on these designs for use in the 200 and 300 GHz bands. Receivers incorporating these wideband mixers demonstrate very low noise temperature. At a local oscillator frequency of 300 GHz, the lowest measured intermediate frequency noise temperature is about 42 K and the usable intermediate frequency bandwidth extends from 6 to 16.5 GHz. Both the design theory and experimental results are presented.
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Abstract The wide intermediate frequency (IF) bandwidth is a core performance metric for terahertz heterodyne receivers, and a wide-IF superconductor–insulator–superconductor (SIS) mixer is key to achieving this. This paper presents the simulation-based design, optimization, and performance analysis of a 345 GHz superconducting SIS mixer developed for wide-IF applications. The mixer employs a parallel-connected twin-junction tuning structure and integrates a dedicated IF impedance matching circuit, achieving wideband impedance matching between the mixer output port and low-noise amplifier. The design is based on two tunnel junction technologies, AlO x and AlN, with critical current densities of 1 kA·cm −2 and 25 kA·cm −2 , respectively. We systematically studied the effects of different junction materials and junction areas on the RF and IF bandwidth performance of the SIS mixer. It is found that for AlN-barrier junctions with diameters of 0.6 μ m and 0.8 μ m, the receiver’s IF noise temperature slowly decreased as the IF frequency increased at a high local oscillator frequency. Furthermore, we incorporated the calculated IF output port impedance into the mixer model for correction and introduced an integrated IF circuit approach, overcoming the original IF bandwidth limitation. Simulations show that the newly designed mixer achieves the stringent sensitivity and bandwidth requirements across the 320–370 GHz range, delivering an IF bandwidth of 4–22 GHz and a receiver noise temperature of 39–73 K. Notably, the −3 dB IF bandwidth is improved by more than 1.5 times compared to conventional AlO x -based designs. These findings provide new design guidelines and quantitative criteria for next-generation wide-IF receivers and other high-frequency applications requiring a wide IF bandwidth.
We present the design and the performance of a fixed-tuned, all niobium (Nb) Superconductor-Insulator-Superconductor (SIS) mixer covering RF frequencies from 163 to 211 GHz with 4-8 GHz IF bandwidth. The mixer uses two Nb/Al-AlOx/Nb junctions of size 3 μm2each with theRnAproduct of 30 Ω·μm2, in a twin junction configuration. An local oscillator (LO) directional coupler made of superconducting lines with slots in the ground plane is integrated on the SIS mixer chip. The isolated port of the LO coupler is terminated using a wide-band resistive load with a sheet resistance of 12 Ω/□. The SIS tuning circuitry is optimized to achieve best power match between the twin junctions and the embedding circuitry. The measurement of the double sideband mixer noise at 171 GHz shows that the receiver noise temperature is approximately 17 K, which is just 2hf/k. The estimated noise contribution from the RF loss and the IF chain at 176 GHz LO frequency is 8 K and 7.5 K respectively, resulting in a SIS mixer noise ofhf/2k. The mixer noise performance across the entire RF band varies between 19 to 25 K. This is to our knowledge the best reported noise temperature at these frequencies till now.
This paper presents design and performance data for a 100-GHz waveguide superconductor-insulator-superconductor (SIS) mixer, which is incorporated with a twin-junction device (i.e., two identical junctions connected in parallel through a tuning inductance) and a fixed-tuned broad-band waveguide mixer mount. The 100-GHz mixer is actually developed as a prototype of the 500-GHz one. The constructed 100-GHz SIS receiver results in an overall receiver noise temperature (DSB) of less than 40 K over the frequency range from 80-120 GHz, with a minimum value of just 20 K that is four times as large as the quantum limit (i.e., 4/spl planck//spl omega//k). Such a performance is comparable or even superior to those of the best mechanically tunable waveguide SIS receivers at the same frequency band. In addition, some interesting mixing behaviors related to this two-junction device are described in detail.
A 220 GHz mixer chip based on a 3-junction series distributed superconducting mixer has been developed. This mixer employs a design, which minimizes the output capacitances, such that it can offer a wide instantaneous bandwidth of up to 12 GHz. We have incorporated this mixer into a receiver package and a dedicated automatic test bench has been developed to characterize its performance. The receiver demonstrates ultra low noise temperature, as low as 32 K, or 3 hν/k. The measured noise temperature remains below 50 K beyond 10 GHz IF.
A 230 GHz Superconductor-Insulator-Superconductor (SIS) mixer is designed focusing on a good performance in the IF frequency range of 4–16 GHz over the RF band from 211 to 275 GHz. A transition from a full-height waveguide to a probe is designed using HFSS. The mixer chips containing SIS junctions are designed and optimized to have low total capacitance of circuits to ensure wide IF bandwidth. The chip fabrication was done in Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), where the masks were conducted by TSMC. A lab test was conducted on a superconducting mixer with a cryogenic dewar. The gap voltage in the I-V curve of the mixer is approximately 8 mV, and there is a clear nonlinearity around a current of 110 μA, which matches well with the simulation. The receiver noise temperature is approximately 60 K including optical losses and the noise from the RF input.