Q. Y. Ma

Dielectric relaxation of Ba0.7Sr0.3TiO3 thin films from 1 mHz to 20 GHz

The dielectric relaxation of Ba0.7Sr0.3TiO3 thin films was investigated up to K band (20 GHz) using time domain and frequency domain measurements. Our results show that from 1 mHz to 20 GHz, the dielectric relaxation of the complex capacitance of Ba0.7Sr0.3TiO3 thin films can be understood in terms of a power law dependence known as the Curie–von Schweidler law. The small dispersion (less than 7% decrease in capacitance from 1 mHz to 20 GHz) and low loss (loss angle less than 0.006 at 20 GHz) measured in Ba0.7Sr0.3TiO3 thin films indicate that these films are applicable to device application up to at least K band.

Hydrogen induced tunnel emission in Pt/(BaxSr1−x)Ti1+yO3+z/Pt thin film capacitors

The leakage current density–applied field (J−EA) characteristics of (BaxSr1−x)Ti1+yO3+z (BSTO) thin film capacitors with Pt electrodes that have been annealed in forming gas (95% Ar 5% H2 or D2) were investigated over the temperature range from −60 to +60 °C. Forming gas annealing significantly increased the leakage current density. The J–EA characteristics exhibited features that could not be fully explained by either a simple thermionic emission or tunneling (Fowler–Nordeim) formalism. Using the general charge transport theory of Murphy and Good, we show that the J–EA characteristics can be successfully interpreted in terms of tunneling of electrons through the interfacial Schottky barrier with the peak in energy distribution of the incident carriers strongly dependent on applied field. At high applied fields the energy distribution of incident carriers is peaked near the Fermi level in the electron injecting metal electrode at all temperatures considered in this study, leading to almost temperature ind...

Novel method of patterning YBaCuO superconducting thin films

A unique method of patterning YBaCuO thin films based on the inhibition of superconductivity by Si‐YBaCuO intermixing has been developed. In the experiment, a thin Si film was first evaporated on a MgO substrate and subsequently patterned using laser direct‐write etching. Multilayered YBaCuO thin films were then deposited by e‐beam evaporation and annealed in a rapid thermal annealing system for 30–90 s at 980 °C. The YBaCuO film deposited on the silicon regions became insulating. Auger depth profiling measurements indicate that Si‐YBaCuO intermixing had occurred in these areas. Between the insulating regions, narrow YBaCuO superconducting lines were formed. For both 10‐μm‐wide, 1‐mm‐long and 2.5‐μm‐wide, 80‐μm‐long lines, the Tc was observed above 76 K. The critical current density of the lines was measured to be 300 A/cm2 at 75 K. This patterning technique may be useful for fabrication of high Tc superconducting interconnects and devices.

Rapid thermal annealing of YBaCuO thin films deposited on SiO2 substrates

Ag/Cu/BaO/Y2O3/Ag layered structures have been formed using electron‐beam evaporation on SiO2 substrates, and post‐annealed by rapid thermal annealing at different temperatures. After a 960 °C 15‐s anneal, the film showed a superconducting onset temperature of 93 K and a zero resistance at 79 K. With a lower‐temperature anneal, the film exhibited metallic behavior. On the other hand, for a higher‐temperature anneal, silicon was found to diffuse into the film as observed by Auger depth profiling. The Si out‐diffusion degraded the superconducting properties of the film.

Effect of Schottky barrier height on EL2 measurement by deep-level transient spectroscopy

A systematic study of EL2 midgap trap in GaAs using deep‐level transient spectroscopy (DLTS) is reported for contacts having a large range of Schottky barrier height. The results show that the DLTS signal of EL2 increases as the barrier height rises from 0.62 eV and saturates for barrier height above 0.83 eV. It is found, for the first time, that for Schottky barrier height lower than 0.62 eV the EL2 signal disappears. A model for calculation of the quasi‐Fermi level in the depletion region is used to explain the variation and disappearance of the EL2 signal. This model may also apply to other electron traps near midgap.

High Tc superconducting thin films by rapid thermal annealing of Cu/BaO/Y2O3 layered structures

Superconducting thin films of YBaCuO have been formed using rapid thermal annealing of Cu/BaO/Y2 O3 layered structures, which were deposited on MgO substrates by electron beam evaporation. The best film has an onset temperature of 94 K and zero resistance at 84 K. The dependence of the film characteristics and superconducting transition temperature on the annealing conditions has been studied. Auger depth profiling was used to examine the interdiffusion between the film and the MgO substrate.

Planar microwave devices fabricated by ion‐implantation patterning of high‐temperature superconductors

We have applied ion‐implantation inhibit patterning as a new method of fabricating low‐loss microwave transmission lines in high‐temperature superconductor thin films. To determine the effectiveness of this technique, we fabricated coplanar waveguide transmission lines in YBa2Cu3O7−δ thin films that had been deposited on LaAlO3 substrates using pulsed laser deposition. Microwave characterizations of these lines are compared to a reference line fabricated with conventional ion milling. At 76 K and 12 GHz, the attenuation constants of the ion‐implanted transmission lines are approximated 0.02 dB/mm, and the overall loss response is indistinguishable from that of the ion‐milled device.

Inhibition of superconductivity in YBaCuO films by aluminum ion implantation

We have studied the inhibition of superconductivity in high‐temperature superconductors oxide films by aluminum ion implantation. Aluminum ions, with doses ranging from 1×1015–1×1016/cm2, were implanted into epitaxial YBa2Cu3O7−x (YBCO) films with an injection energy of 100 keV. Doses of 1×1016/cm2 completely suppressed the diamagnetism of the YBCO film without the need for annealing. Lower doses of 1×1015/cm2 inhibited the superconductivity after low‐temperature annealing. The results of the aluminum implantation are compared with previous silicon and boron implantations.

Observation of anomalous resistive transition around 160–200 K in Y5Ba6Cu11Ox thin films

A large resistive transition between 160–200 K has been observed in Y5Ba6Cu11Ox thin films. The films were deposited on MgO substrates by electron‐beam evaporation and annealed through rapid thermal annealing. With 960–980 °C, 30–60 s RTA, the films showed a resistance drop about one order of magnitude around 160–200 K. This resistive transition was measured reproducibly over many samples. The preparations and measurements of the Y5Ba6Cu11Ox films were similar to those of the YBa2Cu3O7−x films. The x‐ray diffraction pattern indicated that the films mainly contain the YBa2Cu3O7−x phase. The films were polycrystalline with grain sizes of a few μm and an average thickness of 0.4 μm.

Chemical etching of pure and implanted superconducting oxide films

Chemical etching of high-temperature superconducting films was studied. A new method of rapid etching which combines ion implantation and chemical etching is presented. Using phosphoric acid with concentration higher than , it is found that the etching rate in an ion implanted film is much faster than that in a pure film. Below the threshold concentration of , the acid has no etching affect on a pure film while it still etches an implanted film. This result is utilized in a selective etching process for patterning of superconducting oxide films.