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International Conference on Information and Communication Technology Convergence (ICTC)

Wide If 230-GHz Superconductor-Insulator-Superconductor Mixer

Naeun Shin, Jung‐Won Lee, Ming-Jye Wang

Published Oct 16, 2024• 1 citation
Publisher

Abstract

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.

DOI
10.1109/ictc62082.2024.10827305

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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.
Superconductor-Insulator-Superconductor (SIS) tunnel junction mixers are now commonly used in as- tronomical receivers at (sub)millimeter wavelengths because of their superb sensitivity, high dynamic range and stability of operation. Niobium SIS mixers operating at frequencies well below the super- conducting gap (∼680 GHz) have already achieved quantum limited sensitivity. Therefore to further enhance the receiver sensitivity, increasing the Intermediate Frequency (IF) bandwidth of SIS mixers has became crucial. This thesis focuses on the theoretical modeling, design and experimental verifi- cation of Nb SIS mixers operating around 230 GHz with a wide IF bandwidth of 1–15 GHz. These mixers were designed for a single baseline heterodyne interferometer (GUBBINS), which is being built to observe the Sunyaev-Zel’dovich effect in the Cosmic Microwave Background. The combination of wide IF bandwidth SIS mixers and complex analogue correlators will allow GUBBINS to feature high surface brightness sensitivity, that helps to distinguish the weak SZ effect from the background noise. The SIS mixer detector system was assembled inside the GUBBINS cryostat together with the IF electronics and RF/LO optical systems. Low noise temperatures of around 71 K were then measured in the GUBBINS system. The Nb SIS mixer we have developed uses a unilateral finline and fully integrated planar circuits deposited on a silicon substrate, to couple the electromagnetic radiation from the waveguide into the SIS junction. The finline mixer allows a broad-band RF coupling, an easy integration of the on-chip planar circuits and an easy-to-fabricate mixer block. To achieve a wide IF bandwidth, the output impedance of the SIS mixer was well matched to the input impedance of the amplifier by a multi-stage microstrip circuit. Additionally, the planar circuit of the SIS mixer was also designed to have a small lumped inductance and capacitance. The SIS mixer chip was extensively simulated by rigorous electromagnetic software (HFSS) and the S-parameter was exported to a quantum mixing package SuperMix to produce a full-wave model of the mixer. Experimental testing yielded a best noise temperature of 50 K with an average noise temperature of 75 K over an RF bandwidth of 160 GHz– 260 GHz. We have performed thorough experimental and computational investigation of the IF system in particular the constraints on the bandwidth caused by the lumped element capacitance of the mixer chip and the matching of the output impedance of the mixer to the IF amplifier. Our conclusion is that a bandwidth of 1–15 GHz could be achieved using our mixer design, subject to the performance of the amplifier. Finally, a variable temperature load system was successfully developed and tested inside the cryostat, to avoid the losses from the room-temperature optics. We have showed that the noise temperature of the SIS detector could be reduced by as much as 15 K by testing the mixer using a variable temperature load inside the cryostat.
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.
We describe the design and fabrication of a 220 GHz superconductor-insulator-superconductor (SIS) mixer with ultrawide IF bandwidth. The mixer is fabricated on a 100 µm thick quartz substrate, with planar circuit on-chip integration. The RF power is coupled to the tunnel junction via a unilateral finline taper and a slotline-to-microstrip transition. We used a double-stub tuning network to tune out the junction’s parasitic capacitance at a broad RF bandwidth, and matched the output impedance of the mixer to the input impedance of the IF amplifier (50 Ω) from 4–18 GHz using a 6-stage IF impedance-transformer. We have fabricated these devices and have measured good DC current-voltage (IV) characteristic curves. The heterodyne mixing performance of these devices is currently being measured, and we expect to present the results in the forthcoming ISSTT conference in March.
This paper reports the simulation, performance, and detailed characterization of a low-noise heterodyne module with very wide intermediate frequency (IF) bandwidth in the 385-500-GHz radio frequency (RF) range. The module integrates a superconductor-insulator-superconductor (SIS) mixer with a 3- 21-GHz cryogenic low-noise preamplifier (CLNA). The utilization of high current density SIS junctions offers wide RF bandwidth and facilitates better matching between SIS junctions and the CLNA. Based on an equivalent circuit of the SIS mixer chip, we calculate the IF output impedance and simulate how different matching conditions affect the performance of the CLNA. Simulations predict that low-noise module performance can be obtained over a 3-18GHz IF range, limited mainly by parasitic elements in theSIS mixer chip. The measurement results of the heterodyne module demonstrate flat gain and a typical noise temperature of 70-80 K over the 3-18-GHz IF range, at local oscillator frequencies of 400-480 GHz. Mixer chip output impedance and CLNA input impedance have been directly measured by recording S-parameters at cryogenic temperatures. The results enabled us to quantify the contribution of various parasitic elements in the mixer IF circuitry. Calculations based on our model are in good agreement with measurements.
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.
A fixed-tuned SIS(Superconductor-Insulator-Superconductor) mixer across 120∼180 GHz band has been developed. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-AlO/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. In order to prevent the IF signal loss, the If output impedance of the SIS mixer was matched to the 50 input impedance of the IF chain. Measured double sideband noise temperatures of a receiver using the SIS mixer are 32∼131 K over 120∼180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14 m radio telescope.