We have grown superconducting NbN films using a pulsed KrF laser for potential use as superconducting electrodes in SNS Josephson junctions being developed for nonlatching logic applications. The NbN films show a superconducting transition of 16 K using an Nb target in background N2 gas. The Tc dependence on N2 pressure in the range of 50-80 mTorr was investigated at a growth temperature of 600 °C. The NbN films were grown on MgO(100) and amorphous SiNx/Si substrates. In the latter case, the films had a lower Tc, and appeared amorphous from xray diffraction measurements, while those on the MgO(100) substrates were strongly textured. AFM measurements reveal RMS surface roughness as low as 1 nm, over a 5 µm × 5 µm area, indicating that these films appear suitable for SNS junctions.
We describe a Josephson amplifier fabricated in a high-J, process, which is operational to speeds of at least 10 GHz, the highest reported for a voltage-state amplifier. The amplifier converts -200 pV digital signals to -5 mV at 10 GHz and could be used as an interface between two superconducting systems. The bit-error-rate of the circuit was -5 x at 5 GHz, the lowest reported; bit-error-rate measurements at 10 GHz were not possible. A high-J, process which was used to fabricate the amplifier was developed at UC Berkeley with extremely low I, spreads; at -9.4 kA/cm2 (r as low as 0.6% was observed. At -10 kA/cm2, the typical junction linear dimensions are 1.5 -2 pm, sues for which it is not possible -with available tools -to make reliable vias that are smaller than the junction. We use a nonplanarized junction process, where the via for contact of a wiring layer to a junction can be larger than the junction.
Absh-act-We have developed a new Nb/Al-AlOx/Nb IC process with very small critical current spread. Lowtemperature and low-stress ECR (Electron Cyclotron Resonance) P E C W (Plasma Enhanced Chemical Vapor Deposition) silicon oxide films have been used in the Nb IC process for all dielectric insulating layers to replace e-beam evaporated silicon monooxide films and RF reactive sputtered silicon oxide. Since ECR PECVD silicon oxide films have superiority in quality over e-beam evaporated silicon monooxide films and extremely low damage to underlayers compared to sputtered films, our Nb/Al-AlOx/Nb IC quality and yield have been improved greatly. The critical current spreads (maximum to minimum) are less than 1% (0 < 0.2%) on chip and lessthan 4% (0 < 0.7%) cross a four-inch wafer for 5 pm X 5 pm junctions. Even for high critical current density (-10 kA/cm2) small junctions (1.5 pm X 1.5 pn) the on-chip spead is only about 4% (0 < 0.7%). High quality Nb/Al-AlOx/Nb ICs have been fabricated and demonstrated.
Indium tin oxide is the most basic transparent electrode material for all flat panel displays. Commercial ITO glass is manufactured mostly by sputtering. Here, we report the use of pulsed laser deposition to produce ITO thin films on glass at room temperature. Several interesting properties of such films were observed. (1) It was found that the resistivity of 0.5mΩ-cm compared very well with the best published values produced at high deposition temperatures. Room temperature deposition affords the possibility of using plastics and other flexible substrates for displays. (2) The microstructure of these ITO films were quite different from those of commercial ITO glasses. (3) By passing a strong current through the film, a large thermally induced Δnl could be observed. This change was due to lateral stress and could be as large as 1μ m for a 1-μm thick film. An electro-optic shutter can easily be designed with such films. Applications of this electronically controlled Δnl to display technology are discussed.
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