Extraction of material parameters in NbN multilayer technology for RSFQ circuits

NbN/MgO/NbN Josephson tunnel junctions and multilayers have been achieved o n 3 inch. Si and SOI substrates in order to develop high-speed RSFQ logic g ates with terahertz cut-off frequency junctions and high operating temperat ure (10 K). Small area junctions (similar to 1 mu m(2)) with 20 kA/cm(2) J( C) and low sub-gap leakage current (V-m > 15 mV) at 4.2 K (and J(C) similar to 10 kA/cm(2) at 12 K) are reproducibly obtained from multilayers post-an nealed at 250 degrees C. Deposition of a thin MgO buffer layer underneath t he NbN base electrode is critical to insure lower NbN surface resistance va lues (R-S = 7 mu Omega at 10 GHz and 5 K) and lower London penetration dept h lambda(0) (similar to 270 nm). NbN penetration depth and intrinsic capaci tance of NbN/MgO/NbN junctions have been investigated by measuring resonant Fiske steps in the I-V curves of junctions coupled to an integrated resona nt stub. The extension of our present NbN technology for fabricating highly integrated planarized RSFQ circuits, based on self-shunted 0.5 mu m(2) are a, 20 kA/cm(2) junctions is now made possible on large area substrates (up to 8 inch). (C) 1999 Elsevier Science B.V. All rights reserved.