Nobuo Kamehara

The Effect of Ca2PbO4 Addition on Superconductivity in a Bi-Sr-Cu-O System

We examined the effect of Ca2PbO4 addition on superconductivity in a Bi-Sr-Cu-O system. We determined that Ca2PbO4 is formed in Bi-Pb-Sr-Ca-Cu-O at temperatures lower than 750°C on the basis of powder X-ray diffraction and micro-Raman scattering. A high-Tc phase was synthesized by adding Ca2PbO4 to the Bi-Sr-Cu-O system which has a single CuO layer. It seems that the synthesis process of the high-Tc phase is based on a reaction between the low-Tc structure and Ca2+ in the liquid phase which is caused by decomposition of Ca2PbO4 at 822°C.

Piezoelectric Properties of PbNi1/3Nb2/3O3–PbTiO3–PbZrO3 Ceramics

The longitudinal electromechanical coupling factor (k33) was investigated as a function of PbNi1/3Nb2/3O3– PbTiO3–PbZrO3 (PNN-PT-PZ) piezoelectric ceramic compositions close to the morphotropic phase boundary (MPB). The k33 was influenced by the grain size of PNN-PT-PZ ceramics. The composition of the MPB determined by k33 is slightly different from that of the free permittivity. The maximum value of k33 in PNN-PT-PZ system attained to 0.8 on the composition of 0.5PNN-0.345PT-0.155PZ.

Investigation of the importance of interface and bulk limited transport mechanisms on the leakage current of high dielectric constant thin film capacitors

The importance of interface and bulk transport mechanisms on the leakage current of high dielectric constant thin film capacitors is examined by deriving an equation for the J–VA characteristic of a capacitor that includes the transport mechanisms of thermionic emission (TE), thermionic field emission (TFE), and carrier drift–diffusion (DD). The current is controlled by the slowest of three effective velocity parameters v1md, vD, and ṽ2dm characterizing electron injection into the dielectric at the cathode by TE and TFE, carrier DD in the film bulk, and electron ejection from the dielectric at the anode by TE and TFE, respectively. The effective velocity parameters are evaluated for a Pt/BST/Pt thin film capacitor that has been exposed to forming gas and it is shown that the dominant transport mechanism is interface limited TFE from the cathode with negligible influence of carrier transport by DD in the film bulk. Implications of these results on existing transport calculations for high dielectric constan...

Composition dependence of high Tc phase formation in Pb‐doped Bi‐Sr‐Ca‐Cu‐O thin films

We studied the composition dependence of high Tc phase Bi2Sr2Ca2Cu3Ox formation in Pb‐doped Bi system thin films. Films were prepared by rf magnetron sputtering using three targets and post‐annealed to synthesize superconducting films. In addition to a Bi‐Sr‐Ca‐Cu‐O target, PbO and CuO targets were used to dope sufficient Pb into the films and to optimize the Cu content. Although heavily Pb‐doped thin films form the high Tc phase rapidly, they are multiphased and have poor morphology. The Cu content decreases slightly during sintering. Minimizing the amount of doped Pb needed for the high Tc phase formation improves morphology, and slightly Cu‐rich composition is effective in forming the high Tc phase. Nearly single‐phase high Tc films were obtained from the as‐deposited compositions of Bi:Pb:Sr:Ca:Cu=1.02:0.80:1.00:0.99:1.64 after only one hour of sintering in air at 851 °C. The single‐phase high Tc film forms in a very narrow sintering temperature range.

Preparation and magnetic properties of Bi‐Pb‐Sr‐Ca‐Cu‐O superconducting ceramics

A high Tc phase (Tc ≂110 K) in Bi‐Pb‐Sr‐Ca‐Cu‐O systems was synthesized by adding Ca2PbOx to the mixture of a low Tc phase (Tc ≂80 K) and a Bi‐Sr‐Cu‐O (Tc ≂10 K). X‐ray powder diffraction measurement suggests that the sintered bulk mainly consists of the high Tc phase. The volume fraction of the high Tc phase was 74% from the measurement of magnetization. The lower critical field Hc1 was 10 Oe at 77.3 K. The critical current density Jc of 3.0×102 A/cm2 was obtained for a repressed sample with a highly oriented microstructure.

A study of current transport in (BaxSr1−x)Ti1+yO3+z thin-film capacitors containing a voltage-dependent interface state charge distribution

J–V–T characteristics, measured over a very wide temperature (50–441 K) range, are analyzed simultaneously with C–V measurements to investigate conduction mechanisms and the state of charge of Pt/BaxSr1−xTi1+yO3+z(BST)/Pt thin-film capacitors during an applied voltage or current stress. A time- and voltage-dependent state of charge of the Pt/BST/Pt capacitors is inferred from stress-induced voltage shifts in the C–V curves. The voltage and temperature dependence of the C–V curve shifts is shown to be consistent with a voltage-dependent charge in interface states resulting from a change in potential across interfacial dipole layers. An intimate contact Schottky barrier model incorporating a voltage-dependent charge in interface states at both cathode and anode contacts is used to investigate conduction mechanisms in Pt/BST/Pt thin-film capacitors. The basic transport mechanisms of drift-diffusion, thermionic field emission, and Fowler–Nordeim tunneling are shown to dominate leakage in limiting voltage and ...

Micropatterned epitaxial (Pb,La)(Zr,Ti)O3 thin films on Nb-doped SrTiO3 substrates by a chemical solution deposition processwith resist molds

Arrays of lead lanthanum zirconate titanate pillars were fabricated on niobium-doped (001) strontium titanate substrates using a chemical solution deposition method with resist molds. Periodic arrays of submicron ferroelectric pillars with high crystallinity are required to produce high-quality tunable photonic-crystal devices. The relationship between the crystallinity and width of the pillars was investigated. The highest crystallinity was obtained at a width of 0.67μm. All the pillars exhibited ferroelectric strain. Since this width is in the order of that of optical wavelengths, this process and the periodic structures produced have potential applications in fabricating two-dimensional tunable photonic crystals.

Dielectric constant dispersion of yttrium-doped (Ba,Sr)TiO3 films in the high-frequency (10kHz–67GHz) domain

The frequency dispersion of the dielectric constant of yttrium (Y)-doped (Ba,Sr)TiO3 thin films (Y-BST) in the high-frequency domain (10kHz–67GHz) was investigated. In order to remove the substantial parasitic capacitances, inductances, and resistances from the measured impedance data, test samples, short-circuit standard, and open-circuit standard structures were fabricated and their frequency response was measured. Before removing parasitic components, the measured dielectric response showed a rolloff at approximately 4GHz. However, after circuit calibration, the dielectric constant was almost constant up to 40GHz where another rolloff was observed. However, this rolloff was due to the uncompensated small parasitic components. Therefore, the dielectric constant of the Y-BST films (170 with a film thickness of 30nm) showed small frequency dispersion corresponding to the Curie–von Schweidler dispersion, of which the exponent is −0.0131, up to 40GHz. Furthermore, the decrease of the capacitance was 17% in ...

Oxygen tracer diffusion in Pb(Zr,Ti)O3 thin film enhanced by catalytic platinum

The self-diffusion of O18 into Pb(Zr,Ti)O3 [PZT] thin films on Pt∕TiO2 coated Si wafers from an ambient of 99% O218 gas tracer was investigated by secondary ion mass spectroscopy (SIMS) when annealed at 450°C, 550°C, and 650°C for up to 30min. The results show that the O18 profile in PZT changed significantly with anneal temperature and the highest concentration of exchanged oxygen was at the PZT/Pt interface when annealed at 650°C. Modeling of the oxygen tracer diffusion profiles from the 450°C and 550°C data yielded an activation energy of 0.83eV when assuming 1D diffusion. Simulation of the 650°C SIMS data indicated that the oxygen was dissociating on the catalytic Pt film underneath the PZT and then back diffusing into the PZT causing a higher concentration of oxygen at the PZT/Pt interface than at the surface.The self-diffusion of O18 into Pb(Zr,Ti)O3 [PZT] thin films on Pt∕TiO2 coated Si wafers from an ambient of 99% O218 gas tracer was investigated by secondary ion mass spectroscopy (SIMS) when annealed at 450°C, 550°C, and 650°C for up to 30min. The results show that the O18 profile in PZT changed significantly with anneal temperature and the highest concentration of exchanged oxygen was at the PZT/Pt interface when annealed at 650°C. Modeling of the oxygen tracer diffusion profiles from the 450°C and 550°C data yielded an activation energy of 0.83eV when assuming 1D diffusion. Simulation of the 650°C SIMS data indicated that the oxygen was dissociating on the catalytic Pt film underneath the PZT and then back diffusing into the PZT causing a higher concentration of oxygen at the PZT/Pt interface than at the surface.

Low inductance thin film capacitors for decoupling applications

Low inductance and high capacitance density thin film capacitors using barium strontium titanate (BST) based thin films have been developed for use in decoupling applications for GHz LSI operations. Increasing clock frequency and integration density of high performance logic LSI such as CPU requires very low power line impedance over wide frequency ranges up to GHz order. Decoupling capacitors for GHz LSI are required having both high capacitance and low inductance. BST thin film capacitors are promising for GHz LSI applications due to excellent electrical properties such as low leakage current, high capacitance, and high temperature stability. Fundamental electrical properties of Pt/BST/Pt thin film capacitor structures were investigated. BST thin films deposited by RF magnetron sputtering achieved C/A = 4000 nF/cm2 and leakage current density < 10-9 A/cm 2. The fabricated thin film chip capacitors show low equivalent series inductance (ESL) lower than 20 pH. Developed high capacitance low inductance capacitors are fabricated on Si wafers, therefore, it is very easy to integrate to system packaging