AVS 51st International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM-MoP

Paper EM-MoP1
Oxidation of Epitaxial Al/Si(111) for Improved Josephson Tunnel Junctions

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: D.A. Hite, NIST
Authors: D.A. Hite, NIST
R. McDermott, NIST
R.W. Simmonds, NIST
K.B. Cooper, NIST
M. Steffen, NIST
S. Oh, NIST
S. Nam, NIST
J.M. Martinis, NIST
D.P. Pappas, NIST
Correspondent: Click to Email
One of the most promising candidates for a physical quantum bit (qubit) is the current biased Josephson junction. Quantized energy levels in the Josephson potential form the basis for the qubit and are manipulated by the application of currents at microwave frequencies. Recently, qubit spectroscopy (level spacing vs. dc bias current) has identified spurious resonances that have been shown to be a major source of qubit decoherence. Currently, all experimental evidence and modeling point to two-level fluctuators in the material system of the tunnel barrier as the origin of these spurious microwave resonances. In the present technology, tunnel junctions are grown as a trilayer by magnetron sputter deposition of Al with subsequent thermal oxidation for the tunnel barrier. In this talk, we will detail our efforts to identify and eliminate the spurious resonators by engineering epitaxial Josephson junctions with varying degrees of crystalline qualities and impurity concentrations. In particular, we will discuss the oxidation of ultra smooth Al films epitaxially grown on Si(111) as the base electrode of the tunnel junction. During each step in the Al/AlOx/Al trilayer growth, the structure has been investigated in situ by AES, AED and LEED. While tunnel junctions fabricated with these epitaxial base electrodes prove to be of non-uniform oxide thickness and too thin, I-V characteristics have shown a lowering of subgap currents by an order of magnitude. Transport measurements will be correlated with morphological structure for a number of devices fabricated with various degrees of crystalline quality.