Phymca C 207 (1993) 381-390 North-Holland PHYSICA YBa2Cu3OT_s-based, edge-geometry SNS Josephson junctions with low-resistivity PrBa2Cu3OT_ barriers J.B. Barner, B D. Hunt, M.C. Foote, W.T P~ke and R.P. Vasquez Center for Space Mtcroelectronws Technology, Jet Propulston Laboratory, Cahfornta Instttute of TechnologT, 4800 Oak Grove Drtve, Pasadena, CA 91109-8099, USA Received 13 January 1993 We investigatedthe properties of all-high-To edge-geometry Josephson weak hnks using superconducting YBa2Cu30~_,~(YBCO) electrodes and PrBa2Cu307_6 (PBCO) normal-metal layers The fabrication of the weak links mvolved first lon-mflhngthe base YBCO film using a MgO mask to form the edge and then deposmng PBCO and YBCO layers m SltUby pulsed-laserdeposlUon The optimum PBCO films had reslsUvltmS of 2 to 4 mf~ cm at room temperature and ~ 30 mf~ cm at 4 2 K Current-versus- voltage (I-V) characteristics were quahtatlvely conmstent with the reslstlvely-shunted-juncnon (RSJ) model Strong Shaptro steps were present in the 1-V characteristics of junctions under microwave irradiation and the critical current of the devines modulated with a Fraunhofer-hke dependence as a function of magnettc field The dewce parameters exhibited good scalingwith area and PBCO thickness The critical-current density vaned exponentmlly with PBCO thickness, yieldinga normal-metalcoher- ence length of 9 nm for the PBCO 1. Introduction The future ofhlgh-transmon-temperature (To) su- perconductive electronics depends on finding solu- tions to many technological Issues in thin-film growth and device fabrication At the heart of these prob- lems is the lack of rehabfllty and reproducibility in the fabrication of Josephson junctions To date, there has not been a method of fabricating all-high-T¢ su- perconductor/insulator/superconductor (SIS) structures Therefore, the majority of work has fo- cused on the fabrication of superconductor/normal metal/superconductor (SNS) Josephson junctions, or weak links with electrical performance consistent with the reslstlvely-shunted-junctmn (RSJ) model [1] The methods of fabricating SNS-hke devices fall into two bamc categories The first category stems from the fact that suppression of the superconduct- ing order parameter occurs m or near gram bound- aries m the high- T~ oxides and this acts to &srupt the superconducting properhes near the gram boundary on the scale of the coherence length Thus, a weak- link Josephson junction can be fabricated by ~solat- mg small areas of the electrodes near the grain boundary Such approaches include the use of nat- urally occurnng grain boundaries [2,3], gram boundaries formed on a step edge [4] and grain boundaries formed on bl-crystal interface [ 5 ] or bl- epltaxlal interfaces [ 6 ] Although the use of grain boundaries has pro- duced some of the best hlgh-T¢ Josephson devices to date, this method does not generally afford flexibil- ity, reliability and control of the device parameters The control of the device parameters is of particular interest to circuit design and fabrication, where con- trol of the devtce resistance and critical current is necessary, often over a wide range To th~s end, many groups have focused on the fabrication of SNS de- vices using superconductive oxide electrodes and de- posited normal-metal layers of varying thicknesses to control the device parameters The work in this area has Involved the use of noble metals [ 7-10 ] and a variety of oxides The latter include PrBa2Cu307_~ (PBCO) [ 1 I-15 ], normal YBa2Cu307_~, [ 16], Nb-doped [ 17] and undoped SrTIO3 [ 18 ], Lal 5Bal 5Cu3OT_y [ 19 ], Lao 7Cao 3MnOz [20], B12Sr2 (Ca,Bl,Sr, Dy)._ l- 0921-4534/93/$06 00 © 1993 Elsevier SciencePubhshers B V All rights reserved