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Experimental investigation of a twin-bridges superconducting switch

BK Tan, G. Yassin, F Boussahay, C Chaumonty

Published Jan 1, 2017• 0 citations
OpenAlex

Abstract

We present the design and some preliminary measured results of a planar superconducting on/off switch comprising two niobium nitride (NbN) bridges deposited across the slotline section of a unilateral finline. The two bridges are separated by a distance of λ/4, such that the superconducting impedance of the bridges could be cancelled out at the resonance frequency. Both the NbN bridges were switched from the superconducting state to the normal state via a bias current exceeding the critical current of the NbN film. A millimetre wave source calibrated with a terahertz power meter is used to illuminate the switch, and the response of the switch in each state was measured using a superconductor-insulator-superconductor (SIS) chip as a direct detector. Preliminary measured results agreed generally well with our simulations, especially when the multiple wave reflection effect is included in our model.

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URSI General Assembly and Scientific Symposium•Aug 1, 2014•0 citations
We present the design and some preliminary measured results of a planar superconducting on/off switch comprising two niobium nitride (NbN) bridges deposited across the slotline section of a unilateral finline. The two bridges are separated by a distance of λ/4, such that the superconducting impedance of the bridges could be cancelled out at the resonance frequency. Both the NbN bridges were switched from the superconducting state to the normal state via a bias current exceeding the critical current of the NbN film. A millimetre wave source calibrated with a terahertz power meter is used to illuminate the switch, and the response of the switch in each state was measured using a superconductor-insulator-superconductor (SIS) chip as a direct detector. Preliminary measured results agreed generally well with our simulations, especially when the multiple wave reflection effect is included in our model.
We present preliminary measured responses of a planar superconducting on/off switch centred at the 220 GHz. The superconducting switch, comprising three niobium nitride (NbN) bridges, deposited across the slotline section of a back-to-back unilateral linline, made of a similar superconducting material. The transmission characteristics of the superconducting switch illuminated by a sub-millimetre source were measured using a superconductor-insulator-superconductor (SIS) chip as direct detector. The NbN bridges were switched from the super-conducting state to the normal state by a bias current exceeding the critical current of the bridges. With this arrangement, we have measured a switching dynamic range of ∼ 13 dB at 245 GHz, demonstrating the successful operation of the multiple NbN bridges planar superconducting on/off switch.
We present preliminary measured responses of a planar superconducting on/off switch operating at millimeter wavelengths. The superconducting switch, comprising three niobium nitride (NbN) bridges, is deposited across the slotline section of a back-to-back unilateral finline. The transmission characteristics of the superconducting switch illuminated by a millimeter source was measured using a superconductor-insulator-superconductor (SIS) tunnel junction as direct detector. The NbN bridges were switched from the superconducting state to the normal state by passing current through the bridges with magnitude that exceeds its critical current value. With this arrangement, we have measured a typical switching dynamic range of approximately 10 dB across the 205-240 GHz band, with the highest dynamic range of ~ 20 dB at 230 GHz. This demonstrated the successful operation of the multiple NbN bridges as a planar superconducting on/off switch.
We present the design of planar superconducting on/off switch comprising a number of high normal resistance nano-bridges deposited across a the slot of a unilateral finline. We have simulated the performance of this device and have shown that it has a much larger dynamic range than a single nano-bridge fabricated from the same material (Niobium Nitride, NbN). The response of a single bridge device was measured either directly using a terahertz power meter or by using superconductor-insulator-superconductor (SIS) device as direct detector. In either method, we have demonstrated good agreement between simulations and measurements, and therefore confirmed the integrity of our analysis of the device performance. We have recently designed and fabricated multiple nano-bridges superconducting switches using 50m thick NbN film. The measurement of these devices is currently in progress and we expect to report the results in the forthcoming ISSTT conference in March.
In this paper, we describe the design of a planar superconducting on/off switch comprising a high normal resistance nano-bridge deposited across a slotline transmission line. We present preliminary experimental results measured at 220 GHz range, and we discuss in detail the various parameters that affect the performance of the planar on/off switch, including the optimum thickness required for the nano-bridge to achieve high dynamic range and low transmission loss. The analysis is done by combining the accurate superconducting surface impedance description with rigorous electromagnetic simulations, and comparing the simulated results with the measured performance of a previously fabricated on/off switch fed by a backto- back unilateral finline taper. Finally, we propose an improved method to further increase the dynamic range of the switch, by introducing a multi-bridge design to tune out the residual inductance of the nano-bridges.
We investigate a new concept, where a single superconductor-insulator-superconductor (SIS) based mixer chip is switched between two RF frequency bands. A single broadband antenna is used to couple the RF/LO signal to two SIS mixers via a power splitter and two superconducting on/off switches, forming a switching circuit. The planar on/off switches comprise a superconducting microstrip bridging two transmission lines used to alternate the RF/LO signal between the two branches of the power splitter circuit by switching the impedance of the microstrip from the superconducting to normal state, and vice versa. An important application of this dual-band design is to enable combination of adjacent observing astronomical windows into a single receiver cartridge, freeing valuable space in the receiver cabin.
In this paper, we report on the terahertz (THz) direct detection performance of two superconducting niobium nitride (NbN) hot-electron bolometers (HEBs) of different micro-bridge sizes. At the optimum bias point, the two HEB devices show similar thermal conductance (~80nW/K). The measured responsivity coincides well with the electrical responsivity calculated from the measured current-voltage (IV) curves at different bath temperatures. The noise equivalent power (NEP) of the two HEB devices is found to be about 10-12W/√Hz.