Mitsuo Suga

Oxygen Diffusion in Pt Bottom Electrodes of Ferroelectric Capacitors

Oxygen diffusion through the grain boundaries of Pt films during the crystallization annealing of Pb(Zr, Ti)O3 (PZT) was investigated for the stacked structure of PZT/Pt/TiN. If the Pt film was sputtered on the TiN film by an in-vacuum process, then columnar (111)-oriented grains were grown with continuous grain boundaries normal to the substrate. On the other hand, a Pt film deposited on a TiN film exposed to air after the TiN deposition consisted of granular grains with a random orientation, because the Pt film was grown on the native oxide surface of the TiN film. The degree of oxygen diffusion in the Pt film deposited on the exposed TiN film was lower than that on the nonexposed TiN film after the PZT was crystallized at 650° C in O2. Differences in the grain boundary structure, such as the diffusion length, are considered to determine the oxygen diffusion rate.

Non-superconductivity of La2−xBaxCaCu2O6

Abstract Oxygen defect intergrowths copper perovskite, La 2−x Ba x CaCu 2 O 6 , was prepared by rapid heating and quenching, and subsequently by high O 2 - pressure annealing. The oxygen ion site between two-dimensional Cu-O planes is thought to be completely vacant. Although copper valency is +2.15, high enough to produce superconductivity, superconductivity cannot be observed. In the electrical property, carrier localization was still observed at low temperatures, as seen in the same type of compounds with low copper valency (+2.05). The temperature dependence of magnetic susceptibility was characterized by Curie-like behavior, and neither a 2D- nor 3D-antiferromagnetic correlation was observed.

QUANTUM TRANSPORT IN POLYCRYSTALLINE SILICON SLIT NANO WIRE

Electrical conduction characteristics of polycrystalline silicon (poly‐Si) ‘‘slit nano wire’’ between room temperature and 2 K are reported. The slit nano wire is fabricated by the self‐aligned confinement of a 100‐nm‐wide and 100‐nm‐deep trench formed in silicon substrate; the wire is 5–8 nm wide, 10–20 nm high and has grain length of around 100 nm. The resistance increases with the reduction of temperature, which might be due to the quasi‐one‐dimensional structure of the slit nano wire. The conductance exhibits a dip of about 30 mV below 10 K, which is attributed to a barrier height of about 1 meV at the grain boundary of the poly‐Si layer.

Tunneling study on copper oxide N-S bi-layer system

Abstract A tunneling study is performed on the surface of the normal-conducting copper oxide La 1.5 Ba 1.5 Cu 3 O 7- y (LBCO) in the N (LBCO)-S (HoBa 2 Cu 3 O 7- y (HBCO)) bi-layer system. The measured tunneling d I /d V curve has a gap-like structure which is similar to those of high- T c superconductors. The peak-to-peak voltage 2Δ in the tunneling d I /d V curve exponentially decreases with increasing LBCO layer thickness. These facts suggest that superconductivity is induced in the LBCO layer. The characteristic decay length ξ of Δ is 260±50 nm , which is two orders larger than the value expected from the conventional theory of the proximity effect.

Superconducting energy gap in copper oxide SN system

Abstract A tunneling study is performed on the surface of a normal-conducting copper oxide La 1.5 Ba 1.5 Cu 3 O 7−y (LBCO) in S(HoBa 2 Cu 3 O 7−y (HBCO))-N(LBCO) bi-layer system. Measured tunneling dI/dV curve has a gap-like structure. The peak-to-peak voltage 2Δ in the tunneling dI/dV curve exponentially decreases with increasing LBCO layer thickness. These facts suggest that a superconductivity is induced in the LBCO layer. The characteristic decay length ξ of Δ is 260±50 nm, which is two orders larger than the value expected from the conventional theory of the proximity effect.

Highly Accurate Composition Analysis of (Pb,Zr)TiO3 Using a Scanning Electron Microscope/Energy Dispersive X-Ray Spectrometer

A highly accurate composition analysis method for (Pb,Zr)TiO3 (PZT) thin films was developed that uses a scanning electron microscope/energy dispersive X-ray spectrometer (SEM/EDX). This method, highly accurate (HA)-SEM/EDX, consists of two measurements with different electron beam acceleration voltages to control the signal generation depth. The measurement time is sufficiently elongated to reduce the statistical noise. Measurement accuracy of the PZT composition is ±1%, which is sufficient to predict the electrical characteristics of PZT capacitors. We applied HA-SEM/EDX to the failure analysis of PZT capacitors, and found that composition variation was the cause of failure in both failed samples we examined. The composition variations of PZT within a Si wafer were also measured. The composition variation of a PZT film fabricated by the sol-gel method was over ±2%, which was much larger than that of PZT deposited by ozone jet evaporation method (±1%).

Quasi-One Dimensional Conduction in Polycrystalline Silicon Nano Wire

Electrical conduction characteristics of polycrystalline silicon (poly-Si) nano wire between temperature of 300 K and 2 K are reported. The nano wire, 5-8 nm wide, L0-20 nm high and grain length of around 100 nm is fabricated by the self-aligned confinement of a 100 nm wide and 100 nm deep trench formed in silicon substrate. The resistance increases with the reduction of temperature, which might be attributed to the weak localization phenomena due to the quasione dimensional structure of the nano wire. The conductance exhibits a gap of about 30 mV below 1.0K, which is attributed to a barrier height of about 1 meV at the grain boundary of the poly-Si layer. A-4-2

Magnetic Properties of Pr1+xBa2-xCu3O7-y (0<x<0.5)

Magnetic susceptibility of Pr1+xBa2-xCu3O7-y (0 < x < 0.5) is measured. Antiferromagnetic ordering is observed for all nonstoichiometric compounds investigated here. Neel temperature decreases both with increasing Pr content and with decreasing oxygen content. This is considered to be a consequence of reduced hybridization between Pr 4f electrons and O 2p electrons due to decreased hole concentration in two-dimensional Cu-O2 planes.

Interaction Between Superconductivity and the Magnetic Transition in (Pr,Y)Ba2Cu3Oy

Interaction between superconductivity and the anti-ferromagnetic (AFM) transition of Pr ions in PrxY1−xBa2Cu3Oy ((Pr,Y)123) is investigated. Samples for which the AFM transition temperature (TM) of Prions is within the superconducting transition temperature width (ΔTC) are prepared, and the temperature dependence of their resistivity is measured in magnetic fields up to 5T. In high magnetic fields, the ρ-T curves show inflection points around TM within ΔTC, and T C zero converges to 2K. The AFM transition is thought to affect the transport property of carriers, causing these inflections at TM.

Electrical Characteristics of All-Oxide S-N-S Junctions

Electrical characteristics are measured of all-oxide superconductor-normal conductor-superconductor(S-N-S) junctions in which the normal conductor and superconductor are PrBa2Cu3O7−x and HoBa2Cu3O7−y, respectively. The normal transport property qualitatively changes from insulating to metallic depending on junction length and temperature. When the junction length is sufficiently long, the normal resistance of the junctions show almost the insulating property of PrBa2Cu3O7−x itself. Junctions shorter than 1 µm, on the other hand, show a resistance lower than the value expected from the resistivity of PrBa2Cu3O7−x, and junctions as short as 0.1 µm shows metallic transport. A model of carrier transport at the junction is discussed.