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19 th International Symposium on Space Terahertz Technology Low noise 1.4 THz SIS mixer for SOFIA 3-1 A. Karpov, D. Miller, J. A. Stern*, B. Bumble*, H. G. LeDuc*, J. Zmuidzinas California Institute of Technology, Pasadena, CA 91125, USA * Jet Propulsion Laboratory, Pasadena, CA 91109, USA We report on the development of a 1.4 THz SIS mixer. The mixer uses SIS junctions made off Nb/Al-AlN/NbTiN. The junction area is 0.24 μm 2 and the R N A= 6 Ohm μm 2 . The junctions are diamond-like shaped in order to optimize the suppression of the Josephson DC currents. We are using a double slot planar antenna to couple the mixer chip with the telescope beam. The matching microcircuit is made of Nb and gold. The on-chip coupling prediction is plotted below in the Fig. 1. The mixer is expected to provide a low noise operation in a 1.3 – 1.5 THz receiver. The mixer IF circuit is designed to cover 4 - 8 GHz band. The 1.3-1.5 THz SIS mixer is aimed for the 1.4 Terahertz channel of the Caltech Airborne Submillimeter Interstellar Medium Investigations Receiver (CASIMIR). It is a far-infrared and submillimeter heterodyne spectrometer, designed for the Stratospheric Observatory For Infrared Astronomy, (SOFIA). The goal of this work is to provide a low noise spectrometer particularly for the studies of the H 2 D + 1 01 - 0 00 line around 1370 GHz. The mixer test with a limited LO power allows us to make an estimation of very good receiver performance with a higher LO levels (fig.2). The mixer test with a more powerful LO source is under way and will be presented. 0.7 0.6 0.5 Model prediction 1.4 THz mixer design Coupling 0.4 0.3 0.2 0.1 Fig. 1 0 0 500 1000 1500 2000 LO Frequency (GHz) Fig. 2. Receiver noise (K) 6000 5000 4000 3000 2000 1000 0 Expected receiver performance and measured conversion gain (a.u.) SIS mixer gain (a.u.) 0 10 20 30 40 LO Induced Current (uA) 30
19 th International Symposium on Space Terahertz Technology Development of an All-NbN Waveguide SIS Mixer for 0.5 THz Jing Li 1,3 , Masanori Takeda 2 , Zhen Wang 2 , and Sheng-Cai Shi 1 1. Purple Mountain Observatory, NAOC, CAS, China 2. Kobe Advanced ICT Research Center, NiCT, Japan 3. Graduate School of Chinese Academy of Science, CAS, China 2 West Beijing Road, Nanjing Jiangsu 210008, China Tel: +86-25-8333-2229; Fax: +86-25-8333-2206 E-mail: lijing@mail.pmo.ac.cn, scshi@mail.pmo.ac.cn 3-2 With a gap frequency double that of Nb-based SIS junctions (~0.7 THz), NbN SIS junctions [1] are of particular interest for the development of heterodyne mixers at frequencies beyond 1 THz. To demonstrate the feasibility of NbN SIS mixers for real astronomical applications, we firstly develop an all-NbN waveguide SIS mixer at a relatively low frequency of 0.5 THz. In this paper, we will focus mainly on the introduction of the mixer design, NbN junction fabrication and mixer performance. In addition, its LO-power requirement, IF bandwidth, and IF-output-power stability will be compared with another 0.5-THz SIS mixer adopting Nb twin junctions. This all-NbN SIS mixer has been already installed on the POST submillimeter-wave telescope [2] for the observations of two selected spectrum lines, namely, the CO (J=4-3) molecular line at 0.46 THz and the neutral carbon line at 0.49 THz. Some testing observation results will be presented. [1] Z. Wang, A. Kawakami, Y. Uzawa, and B. Komiyama, “NbN/AlN/NbN tunnel junctions fabricated at ambient substrate temperature”, IEEE Trans. Appl. Supercond., vol. 5, no. 2, pp. 2322~2325, 1995. [2] S.P. Huang, J. Li, A.Q. Cao, S.H. Chen, X.F. Shen, Z.H. Lin, S.C. Shi, and J. Yang, “Development of a Compact 500-GHz SIS Receiver,” Proc. of AP-RASC04, pp. 412-413, 2004. 31
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