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International Conference on Microwave and Millimeter Wave Technology (ICMMT)

Direct detection of terahertz signals at 493GHz using Nb superconducting tunnel junctions

Zheng Wang, Dong Liu, Jing Li, Sheng‐Cai Shi

Published May 1, 2012• 1 citation
Publisher

Abstract

Superconducting tunnel junctions are good candidates for the direct detection of terahertz signals. In this paper, the direct detection behavior of Nb-based superconducting tunnel junctions at 493GHz is demonstrated. The performance of the detector is evaluated in several aspects, including noise characteristics, current response and frequency response.

DOI
10.1109/icmmt.2012.6230046

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Superconducting tunnel junctions are good candidates for the direct detection of terahertz signals. In this paper, the direct detection behavior of Nb-based superconducting tunnel junctions at 493GHz is demonstrated. The performance of the detector is evaluated in several aspects, including noise characteristics, current response and frequency response.
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Terahertz direct detectors based on superconducting tunnel junctions (STJs) have the merits of short response time, large dynamic range and relatively high operating temperature, providing a good choice for terahertz detection. Compared with commonly used niobium STJs, niobium nitride (NbN) ones have a high transition temperature close to 16K. Hence they might be useful for terahertz detection operating at temperatures well above the LHe temperature of 4.2K. In this paper, we investigate the properties of NbN STJ detectors at different bath temperatures. Detailed experiment results are given.
We are developing a broadband THz detectors using Nb-based superconducting tunnel junctions. We found two components in a current signal for 1-2 THz pulse input. From the comparison of results obtained for the signals, the frequency response for the different size of STJs and the STJs fabricated on different substrate materials, we demonstrate that they correspond to photons absorbed with the superconductor electrode (referred as 'direct' component) and phonons generated by photons absorbed with the substrate (refered as 'phonon-mediated' component).
Superconducting SIS (Superconductor-Insulator-Superconductor) tunnel junctions are promising application prospect in the incoherent detection of astronomy observation. In this paper, the direct detection performances of Nb and NbN based superconducting SIS junctions, which cover about 250 GHz and 140 GHz centered at 600 GHz respectively, are characterized at a bath temperature of 4.2 K. The experiments show that Nb and NbN based SIS junctions have a current shot noise of 2.5×10-12and 3.1×10-12A/radicHz, a current responsivity of 303 and 187 A/W (corresponding to the quantum efficiency of 0.67 and 0.43) respectively. Thus their respective NEPs are 8.4×10-15and 1.7×10-14W/√Hz.
Terahertz detection with twin superconductor–insulator–superconductor (SIS) tunnel junctions, which are connected in parallel via an inductive thin-film superconducting microstrip line, is mainly studied. Firstly, we investigate the direct-detection response of a superconducting twin-junction device by means of a Fourier transform spectrometer. Secondly, we construct a direct-detection model of twin SIS tunnel junctions. The superconducting twin-junction device is then simulated in terms of the constructed model. The simulation result is found to be in good agreement with the measured one. In addition, we observe that the direct-detection response of the device is consistent with the noise temperature behaviour.