Physics of high j/sub c/ Nb/AlO/sub x//Nb Josephson junctions and prospects of their applications

At critical current density of the order of 100 kA/cm/sup 2/, tunnel Josephson junctions become overdamped and may be used in RSFQ circuits without external shunting, dramatically increasing circuit density. However, the physics of electron transport in such high-j/sub c/ junctions differs from the usual direct tunneling and until recently remained unclear. We have found that the observed dc I-V curves of niobium-trilayer junctions with j/sub c/=210 kA/cm/sup 2/ can be explained quantitatively by resonant tunneling through strongly disordered barriers. According to this interpretation, random spread of critical current in high-j/sub c/ junctions may be rather small (below 1% r.m.s.) even in deep-submicron junctions, making VLSI RSFQ circuits, with density above 10 MJJ/cm/sup 2/, feasible.

[1]  Dmitry Zinoviev,et al.  FLUX chip: design of a 20-GHz 16-bit ultrapipelined RSFQ processor prototype based on 1.75-/spl mu/m LTS technology , 2001 .

[2]  I. O. Kulik,et al.  Josephson effect in superconducting bridges - Microscopic theory , 1978 .

[3]  K. Likharev,et al.  RSFQ TECHNOLOGY: PHYSICS AND DEVICES , 2001 .

[4]  J. Lukens,et al.  Self-shunted Nb/AlO/sub x//Nb Josephson junctions , 1999, IEEE Transactions on Applied Superconductivity.

[5]  C. Beenakker,et al.  Josephson current through a superconducting quantum point contact shorter than the coherence length. , 1991, Physical review letters.

[6]  Y. Naveh,et al.  Universal distribution of transparencies in highly conductive Nb/AlO(x)/Nb junctions. , 2000, Physical review letters.

[7]  V. Shumeiko,et al.  Theory of subharmonic gap structure in superconducting mesoscopic tunnel contacts. , 1995, Physical review letters.

[8]  H. Huggins,et al.  High quality refractory Josephson tunnel junctions utilizing thin aluminum layers , 1983 .

[9]  V. Semenov,et al.  RSFQ logic/memory family: a new Josephson-junction technology for sub-terahertz-clock-frequency digital systems , 1991, IEEE Transactions on Applied Superconductivity.

[10]  Peters,et al.  Subgap structure as function of the barrier in atom-size superconducting tunnel junctions. , 1994, Physical review letters.

[11]  G. Blonder,et al.  Explanation of subharmonic energy gap structure in superconducting contacts , 1982 .

[12]  C. Beenakker.  Random-matrix theory of quantum transport , 1996, cond-mat/9612179.

[13]  G. Arnold.  Superconducting tunneling without the tunneling Hamiltonian , 1985 .

[14]  G. Bauer,et al.  Universality of Transport through Dirty Interfaces , 1997 .

[15]  Juan Carlos Cuevas,et al.  The signature of chemical valence in the electrical conduction through a single-atom contact , 1998, Nature.

[16]  W. H. Mallison,et al.  Niobium trilayer Josephson tunnel junctions with ultrahigh critical current densities , 1993 .

[17]  O. N. Dorokhov.  Transmission coefficient and the localization length of an electron in N bound disordered chains , 1982 .

[18]  Takeshi Imamura,et al.  Recent advances in Josephson junction devices , 1988 .

[19]  Siyuan Ran,et al.  Fabrication of high quality, deep-submicron Nb/AlO/sub x//Nb Josephson junctions using chemical mechanical polishing , 1995, IEEE Transactions on Applied Superconductivity.

[20]  William J. Gallagher,et al.  Sub‐μm, planarized, Nb‐AlOx‐Nb Josephson process for 125 mm wafers developed in partnership with Si technology , 1991 .

[21]  M. Tsukada,et al.  A unified theory of clean Josephson junctions , 1990 .

[22]  M. Leung,et al.  Manufacturability of superconductor electronics for a petaflops-scale computer , 1999, IEEE Transactions on Applied Superconductivity.

[23]  Transport through dirty interfaces , 1997 .

[24]  Michel Devoret,et al.  Conduction Channel Transmissions of Atomic-Size Aluminum Contacts , 1997 .

[25]  C. Beenakker,et al.  Reflectionless tunneling through a double-barrier NS junction , 1994, cond-mat/9406034.

[26]  Vinay Ambegaokar,et al.  Tunneling between superconductors , 1963 .

[27]  N. R. Werthamer,et al.  Nonlinear self-coupling of Josephson radiation in superconducting tunnel junctions , 1966 .

[28]  P. Kes,et al.  Thermal conductivity of niobium in the purely superconducting and normal states , 1974 .

[29]  Konstantin K. Likharev,et al.  Superconducting weak links , 1979 .

[30]  Arnold,et al.  Observation of multiple Andreev reflections in superconducting tunnel junctions. , 1994, Physical review letters.

[31]  U. Kawabe,et al.  Niobium-based integrated circuit technologies , 1989 .

[32]  Averin,et al.  ac Josephson Effect in a Single Quantum Channel. , 1995, Physical review letters.