Development of Novel Josephson Tunnel Junctions for Quantum Computing

1. Statement of Work Investigators at Arizona State University will provide the appropriate professional labor, facilities, and support services and exert their best efforts within time and funding constraints to carry out the tasks detailed in this proposal and summarized below. This effort will largely focus on choosing, synthesizing and processing low-noise dielectrics for Josephson tunnel barriers and for junction isolation and wiring insulation in the microfabrication process. Assuming the research described here is successful, the dominant source of noise and decoherence in superconducting QUBITS will be reduced markedly, and attention will then be given to optimizing the device and circuit design and manufacture. Success will benefit all those involved in the pursuit of information processors to be built using superconducting QUBITS. Task 1. Develop device fabrication methods for novel Josephson Junction electrodes and insulating dielectrics with an emphasis on developing processing methods and materials that minimize the sources of noise and decoherence in Josepshon Junction technologies. (ASU, NG) Subtask 1.1 Use conventional photolithography, RIE and ion mill dry etching, SiO2 PE-CVD, physical vapor and sputter metal deposition and other standard techniques to produce trilayer junction devices Subtask 1.2 Investigate low loss alternative dielectrics, including low loss nitrides and oxides of tantalates and titanates. to replace the SiO2,, SiNx, used in conventional superconductor technology fabrication lines. Many of the materials we will explore are used extensively in low loss microwave technology. If thermally stable junctions are produced (see Subtask 2.3b), higher processing temperatures will be used to produce improved dielectrics with lower loss and lower noise for device isolation and wiring insulation a. chemical property characterization to determine purity, nature of contaminants in dielectrics (RBS, SIMS, XPS, AES, analytical TEM, EELS) b. structural property characterization to determine microstructure (XRD, AFM, imaging TEM) c. electrical, optical and magnetic measurements to determine properties of deposited materials: chemical stoichiometry, microstructure and point defect characteristics (concentration, energy levels) (I-V, C-V, DLTS, X-ray diffraction, TEM, UV/VIS/IR absorption, magnetic susceptibility, XPS, AES) d. microwave measurements using our recently-developed self-resonant techniques to accurately characterize the loss in the dielectric films. Our method excites a self-resonant modes in the film and substrate to quantitatively determine the loss tangent as a function of temperature and magnetic field. The observation of electron paramagnetic resonances during the magnetic field sweeps allows for the identification of the nature and concentration of point defects and complexes Subtask 1.3 Systematically investigate the influence of microfabrication techniques on the junction properties, including the subgap leakage and noise. Compare the results using dry etching techniques to those defined by shadow masks and/or wet etching. Task 2: Synthesize Josephson tunnel junctions, using a wide range of electrodes and barrier materials- replace amorphous AlOx by other insulating oxides, particularly oxides of transition metals with high oxygen affinity, which will be (preferably) grown by thermal oxidation of films with Tc>1K. These films will represent a much larger variety of superconducting electrodes and insulators than have been studied in the past. Subtask 2.1 Choose suitable substrate& deposit alternative metal Josephson Junction electrodes including Transition Metal (TM) films (ASU, NG) a. Consider elements, bilayers and alloys of Ta, Zr, Hf, Mo, Zr/Ta, Hf/Ta, Sn, In Subtask 2.2 Explore oxides and nitrides of Hf, Ta, Zr, Mg, Ta/Ti, Ta/Zr for barriers (ASU, NG) Subtask 2.3 Alter growth conditions and substrates used to vary materials microstructure a. Deposit electrodes and barriers at 300 K to produce conventional polycrystalline e