Masahiko Hiratani

Rutile-type TiO2 thin film for high-k gate insulator

Abstract We investigated rutile-type titanium dioxide (TiO2) films for possible use as a high-k gate insulator. The TiO2 thin films were directly deposited on Si substrates using a RF magnetron sputtering method with a sintered oxide target. A single phase of rutile-type TiO2 whose dielectric constant of approximately 75 was obtained when the film was deposited in an inert gas atmosphere and annealed at 800 °C in an oxidizing gas atmosphere. The oxygen ions were deficient in the as-deposited film, and consequently, a sufficient oxygen supply was needed to crystallize the film to a single phase of rutile during the post-annealing. However, the interfacial SiO2 layer between the TiO2 and the Si substrate simultaneously grew thicker than 2 nm. As the interfacial SiO2 grew, the leakage current was decreased and the equivalent oxide thickness was increased, in the Au/rutile-type TiO2/Si capacitor. Therefore, we concluded that the growth of the interfacial SiO2 layer thicker than 2 nm is inevitable to form the single phase of rutile-type TiO2 and to decrease the leakage.

Remote-charge-scattering limited mobility in field-effect transistors with SiO2 and Al2O3∕SiO2 gate stacks

We examined, both experimentally and theoretically, the mobility reduction in metal-insulator-semiconductor field-effect transistors (MISFETs) limited by remote charge scattering. The accuracy of the mobility calculations was confirmed by agreement with experiments on MISFETs with pure SiO2 gate dielectrics, in which mobility is reduced due to scattering from the depletion charges in the polycrystalline silicon gate. In MISFETs with Al2O3∕SiO2 gate stacks, we could not identify the contributions from the remote phonon scattering by using low-temperature measurements of the mobility. The experimental mobility reduction is explained by a model in which both negative and positive charges are located at the Al2O3∕SiO2 interface. According to this model, the mobility increases with the interfacial SiO2 thickness. We confirmed this by fabricating MISFETs with various interfacial SiO2 thicknesses.

Effective Electron Mobility Reduced by Remote Charge Scattering in High-κ Gate Stacks

The mobility reduction in high-κ gate stacks is discussed in terms of remote charge scattering. The mobility is recovered by growing an additional layer of SiO2 at the interface between the high-κ dielectric and the silicon substrate. A good explanation for this finding is that the Coulomb potential which is induced by the fixed charge at the dielectric/SiO2 interface is responsible for the scattering of electrons.

SrRuO3 Thin Films Grown under Reduced Oxygen Pressure

SrRuO3 thin films are grown under reduced oxygen pressures between 10-6 Torr and 100 mTorr by pulsed laser deposition. The thin films grown at temperatures above 640° C and at a pressure of 10-6 Torr are characterized in terms of the lattice shrinkage due to oxygen deficiency. The resistivity increases and the temperature dependence changes to semiconductive from metallic as the oxygen pressure during growth is decreased. The Hall coefficient of the film grown at 740° C and at a pressure of 10-6 Torr is thirty times higher at low temperatures than at room temperature. The transport properties of the film are thought to result from the high carrier concentration but the low mobility due to the oxygen deficiency.

High-capacitance Cu/Ta 2 O 5 /Cu MIM structure for SoC applications featuring a single-mask add-on process

This paper presents a metal-insulator-metal capacitor for SoC applications which has the highest capacitance density (up to 12 fF//spl mu/m/sup 2/) ever reported for a device in this field. The simple MIM structure allowed development of the process as a single-mask add-on to conventional Cu BEOL processing.

Superconducting characteristics of a planar‐type HoBa2Cu3O7−x −La1.5Ba1.5Cu3O7−y−HoBa2Cu3O7−x junction

A planar‐type junction of HoBa2Cu3O7−x−La1.5Ba1.5Cu3O7−y −HoBa2Cu3O7−x having an electrode spacing as small as 0.1 μm is fabricated and its electrical characteristics are measured. Supercurrent through the La1.5Ba1.5Cu3O7−y layer is detected up to the temperature of 69 K. A superconducting region extends from the YBa2Cu3O7−x electrodes into a normal La1.5Ba1.5Cu3O7−y layer with a submicrometer scale. The superconducting decay length is 65 nm, which is two orders of magnitude larger than the value calculated from the conventional proximity theory.

Improved theory for remote-charge-scattering-limited mobility in metal–oxide–semiconductor transistors

Transport theory is extended to include the remote-charge-scattering-limited electron mobility of metal–oxide–semiconductor field-effect transistors. We evaluated remote-charge-scattering from the depletion charge in the polycrystalline silicon gate. We obtained an analytical expression for the scattering potential, by taking image charge, screening, and quantization effects into account. The potential increases with decreasing gate-oxide thickness, which results in a mobility degradation at lower vertical electric fields. The calculated mobility agrees well with recent measurements.

Hexagonal tungsten trioxide obtained from peroxo-polytungstate and reversible lithium electro-intercalation into its framework

A hexagonal form of WO{sub 3} (a = 7.3244(6), c = 7.6628(5) {angstrom}, z = 6) was synthesized by the low temperature sintering of an ammonium peroxo-polytungstate precursor. This compound, the N/W ratio of which is 0.015 at most, is not identical to reported hexagonal WO{sub 3} from WO{sub 3}{center dot}1/3 H{sub 2}O because its c-axis is significantly shorter than that of the latter (7.798 {angstrom}). Powder XRD profile refinements were performed in the space group P6{sub 3}/mcm. The authors found two kinds of structural models that showed reasonably good profile agreement (R {approx} 0.07). Both models are built up of remarkably distorted WO{sub 6} octahedra, in which part of the O-O distances are very short (2.32 {approximately} 2.42 {angstrom}). Electrochemical intercalation of lithium into the present WO{sub 3} framework work was investigated using a Li{vert bar}LiPF{sub 6}{vert bar}WO{sub 3} cell. It was found that Li was intercalated reversibly up to the composition Li{sub 1.0}WO{sub 3}.

Hexagonal polymorph of tantalum–pentoxide with enhanced dielectric constant

A tantalum–pentoxide dielectric with an enhanced permittivity of over 50 was found to be crystallized in a hexagonal symmetry with a=0.628 nm and c=0.389 nm. The incommensurate epitaxy of tantalum pentoxide on hcp-ruthenium metal stabilizes the hexagonal phase with √3-time periodicity in plane, as compared with that of the known hexagonal δ phase. The crystallographic assumption, which is based on one-dimensional Ta–O–Ta chain along the c axis, can explain large polarizability caused by delocalized electrons on the one-dimensional chain.

Post-annealing effects on antireduction characteristics of IrO2/Pb(ZrxTi1−x)O3/Pt ferroelectric capacitors

Antireduction characteristics of IrO2/Pb(ZrxTi1−x)O3(PZT)/Pt ferroelectric capacitors are improved by post annealing. When an as-processed capacitor receives a 3% hydrogen annealing at 300 °C (a process condition for fabricating the interlayer dielectric), capacitor characteristics are heavily degraded. This is because Ir that is produced by IrO2 reduction plays a catalytic role in PZT reduction. By contrast, if the IrO2/PZT/Pt capacitor is post annealed in O2 atmosphere at 600 °C for 1 h, the capacitor characteristics can be maintained even if it undergoes the hydrogen annealing. The O2 annealing improves the crystallinity of the IrO2 top electrode and excess PbOx in sol-gel derived PZT diffuses into the IrO2 film. As a result, antireduction characteristics of the IrO2 top electrode itself are drastically improved and the PZT film becomes stoichiometric at the same time. Exclusion of excess PbOx in PZT results in an increase in spontaneous polarization of the IrO2/PZT/Pt ferroelectric capacitor. Furtherm...