Nanofabrication of Planar High Temperature Superconducting Josephson Junctions Using Focused Ion Beam Technology
- PDF / 3,364,610 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 4 Downloads / 168 Views
Nanofabrication of Planar High Temperature Superconducting Josephson Junctions Using Focused Ion Beam Technology Hong-Ying Zhai1, Quark Y. Chen, Jiarui Liu, and Wei-Kan Chu Department of Physics and Texas Center for Superconductivity, University of Houston, 3201 Cullen Blvd., Houston, TX 77204. 1 Now in Solid State Division, Oak Ridge National Laboratory, P. O. Box 2008, Bldg. 3150 Oak Ridge, TN 37831-6056 ABSTRACT Superconductor-normal metal-superconductor (SNS) high-Tc Josephson junctions have been fabricated on c-oriented YBa2Cu3O7-δ (YBCO) films. Focused ion beam (FIB) nano-structure modification (cutting of the film and local deposition of a metal) was used to form the junction with tungsten barrier. The junctions exhibit resistively shunted junction (RSJ) -like I-V characteristics. INTRODUCTION Fabrication of Josephson junctions made of high temperature superconductors (HTS) is more difficult than that of Josephson junctions of traditional low temperature superconductors. A wellknown source of difficulty is extremely short coherence length ξ of several angstroms in a-b plane for YBCO. In addition to grain boundary weak links [1-3], a solution for this problem is proximity-coupled, superconductor-normal layer-superconductor (SNS) junctions [4-6]. In this paper, we present high-Tc SNS Josephson junctions fabricated by nano-modification of coriented YBCO thin films using Focused Ion Beam (FIB) techniques. Such junctions are formed with planar device structure and have no limitations regarding the substrate. Accordingly, the integration of Josephson junctions arrays can be made easily, moreover, the expected Josephson junctions’ positions can be independent of the grain-boundary, or step-edge prefabricated on the substrate and thus make the fabrication flexible. EXPERIMENTAL YBCO films are deposited on (100) SrTiO3 (STO) using a 4cm hollow cylindrical magnetron sputtering device. The sputtering gun is operated in the d.c. mode with a current of 0.3 A and a voltage of 135 V in an argon-oxygen mixture with partial pressures of 0.45 torr and 0.2 torr respectively. After deposition on the substrate at 780 °C, the YBCO films are annealed in situ in ultra-high purity O2. The measured superconducting transition temperature (Tc) is over 91 K, with a critical superconducting current larger than 2×106 A/cm2 for 120 nm YBCO films at 77K [7]. Crystalline quality is confirmed by x-ray diffraction (XRD). The minimum yield of Rutherford Backscattering Spectrometry (RBS)/ channeling is ~4%. A standard photolithography process and a 300 eV Ar+ ion milling are used to produce 3 µm by 10 µm YBCO micro-bridges. A 50 keV Ga+ focused ion beam is used to cut the micro-bridge to form a trench of less than 100 nm width across the bridge. Tungsten metal is filled in situ into the trench using local micro-chemical vapor deposition from tungsten carbonyl source material. D5.8.1
As a result, the two neighboring superconductors are connected by a normal metal tungsten. Transport measurements were performed on those junctions at 77 K. RESULTS
Data Loading...
