担当区分：筆頭著者   記述言語：英語   出版者・発行元：Integrated Ferroelectrics  

Stoichiometric SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> (SBT)-Pt contact exhibits a Schottky contact with a barrier height of 0.9 eV, but small amounts of excess Bi produce ohmic contacts at low voltages, followed by perfectly quadratic space-charge limited current-voltage dependences (SCLC). Attempts to fit Schottky models to the temperature dependence of leakage currents in Bi-rich SBT films yield unphysical results, including a negative barrier height. We have generalized the SCLC theory of Rose to incorporate the temperature dependence of the dielectric constant. This theory has a single parameter T* which is a measure of trap energy distribution. A single T* value fits our data at all temperatures and all voltages. These macroscopic leakage current data are correlated with X-ray photoelectron spectroscopy (XPS) depth profiles that show how excess Bi has diffused into the electrode-ferroelectric interface region.

担当区分：筆頭著者   出版者・発行元：Journal of the Electrochemical Society  

High Pr(20 μC/cm²) Pb(Zr, Ti)O<inf>3</inf>/RuO<inf>2</inf> multilayer thin films were fabricated on (100) Si substrates by a spin-on technique. The grain structure and the resistivities of the RuO<inf>2</inf> films were found to be related to each other, with both properties being controlled by the firing schedules of the films. The crystallinity of the Pb(Zr, Ti)O<inf>3</inf> films were seriously influenced by the surface morphology of the RuO<inf>2</inf>/Si substrates. The best crystalline Pb(Zr, Ti)O<inf>3</inf> films occurred when the substrate was RuO<inf>2</inf> with root mean square roughness of 8 nm. An optimized Pb(Zr, Ti)O<inf>3</inf> capacitor with an RuO<inf>2</inf> film as a bottom electrode showed good fatigue property.

DOI： 10.1149/1.1837140

Scopus

担当区分：筆頭著者   出版者・発行元：Materials Research Bulletin  

The perovskite SrRuO<inf>3</inf> thin films were deposited on Si(100) substrates using pulsed laser deposition. These thin films had columnar structures and exhibited good surface morphology and good barrier characteristics for Si. The films exhibited metallic conductivities, with a room temperature resistivity of 529 μΩ·cm. These thin films can be useful in many applications, such as electrodes for ferroelectric and electro-optic devices.

DOI： 10.1016/S0025-5408(96)00165-1

Scopus

出版者・発行元：Ferroelectrics  

We have used x-ray photoelectron spectroscopy (XPS) and ultraviolet absorption measurements to determine unambiguous values of the electron affinities and band structure alignments for the three most popular ferroelectric memory materials (strontium bismuth tantalate SBT, lead zirconate-titanate PZT, and barium strontium titanate BST) on platinum electrodes. The PZT/Pt results and model disagree quantitatively and qualitatively with the earlier work of Wouters, Willems, and Maes [Microelectron. Eng. 29, 249 (1995)], who inferred an electron affinity of 2.6 eV, compared with our value of 3.5 eV. Nano-electrode fabrication is discussed for such memories, and nano-electrode interface models of SBT/Bi are included.

DOI： 10.1080/00150199908009114

Scopus

出版者・発行元：Ferroelectrics Letters Section  

The intermediate phase involved in the production of ferroelectric material SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> has a fluorite structure. If the structure of the intermediate phase were ideal, all the metal ions would have identical cubic oxygen environments. However, the tantalum ions are much smaller than the strontium and bismuth ions which could result in local deviations from the original structure. We present results of X-ray absorption spectroscopy studies which indicate the local tantalum atomic environments for the intermediate fluorite phase and the ferroelectric final Aurivillius phase material, a layer-structure perovskite. For both phases NEXAFS studies indicated very similar electronic structures at the tantalum sites. The EXAFS analysis revealed local structural information and indicated that the intermediate phase has a defect fluorite structure with the oxygen environment for the tantalum being related to that of the TaO<inf>6</inf> octahedra of the final phase material. © 1997 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint.

DOI： 10.1080/07315179708204787

Scopus

出版者・発行元：Applied Physics A Materials Science and Processing  

Metallic ruthenium and ruthenium oxides, such as SrRuO<inf>3</inf> and RuO<inf>2</inf>, are potential electrode materials for ferroelectric capacitors. The electrical properties (e.g. leakage currents) of such thin film devices are dependent on the electronic properties of the electrode/ferroelectric junctions and therefore also on the electrode work functions. During growth and processing of film-electrode layer structures the formation of sub-oxides within the electrode is possible, with their work functions being unknown. In order to obtain information for predicting device properties, we have systematically analysed the valence bands and work functions of RuO<inf>x</inf> and SrRuO<inf>y</inf> thin films with different oxidation states by using photoelectron spectroscopy techniques. The results suggest that Ru⁰ and Ru⁴⁺ ions are present in co-existence at the surfaces of oxygen-deficient polycrystalline films (inhomogeneous oxidation). For both oxygen-deficient materials the work function coincides with that of metallic ruthenium (4.6 ± 0.1 eV). Only for fully oxidised ruthenium oxide and strontium ruthenate films (no Ru⁰ present at the surface) is the work function increased to 5.0 or 4.9 eV, respectively. As an example of importance for new dynamic random access memory applications, the junctions of Ba<inf>1-x</inf>Sr<inf>x</inf>TiO<inf>3</inf> with SrRuO<inf>y</inf> and RuO<inf>x</inf> are discussed.

DOI： 10.1007/s003390050041

Scopus

出版者・発行元：Materials Research Bulletin  

The path of crystal growth from the precursor to SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> (SBT) crystal was investigated in order to obtain a better method of fabricating SBT films. A phase diagram of the Sr-Bi-Ta-O system with a constituent element ratio similar to that of SBT was determined. Thin film samples were prepared by the metal-organic decomposition method. In the case of a Bi-rich nominal composition (compared with SBT crystal), a fluorite-like structure appeared at the early stage of the crystal growth, after which the SBT phase was finally stabilized. The lower limit of annealing temperature for synthesis of SBT thin films with thicknesses less than 100 nm was about 650°C. © 1998 Elsevier Science Ltd.

DOI： 10.1016/S0025-5408(98)00017-8

Scopus

出版者・発行元：Journal of the Korean Physical Society  

The path of the crystal growth from the precursor to SBT crystal has been investigated for obtaining the better way to fabricate SBT films. The phase diagrams of the Sr-Bi-Ta-O system with the constituent element ratio close to SBT crystal have been constructed. The thin film samples were prepared by metallo-organic decomposition method. The coated films were annealed in oxygen. The annealing temperature and the annealing period were varied as the parameters for the phase diagrams. In the case with Bi-rich nominal composition (compared with SBT crystal), a fluorite-like structure appears at early stage of the crystal growth, then, SBT phase is finally stabilized.

Scopus

出版者・発行元：Integrated Ferroelectrics  

SBT is a candidate as the ferroelectric material for large scale FeRAMs with the great advantages of less fatigue and better squareness in its P-E hysteresis curves, while SBT has the disadvantages of higher crystallization temperature that results in difficulties realizing a stacked structure cell and greater damage to its ferroelectric properties from forming gas annealing. This paper presents new top and bottom electrodes to eliminate these disadvantages for SBT. The remanent polarization decreases only slightly after forming gas annealing with the top electrodes of partially oxidized Ru. Ru-O top electrodes show no bubbles or peeling after forming gas. In order to achieve the stacked structure cell for SBT capacitors, a new diffusion barrier was developed. This new diffusion barrier withstands the high temperature annealing that is required to crystallize SBT films. With the new diffusion barrier hysteresis curves could be obtained with electrical connections through Si substrates.

DOI： 10.1080/10584589708013018

Scopus

出版者・発行元：Integrated Ferroelectrics  

A chemical vapor deposition process for the ferroelectric SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> has been developed utilizing a liquid delivery and flash vaporization technique. Uniform layered perovskite of SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> was formed over 4 inch wafers by the chemical vapor deposition followed by annealing at 800°C in oxygen ambient. The SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> thin film capacitors showed well saturated hysteresis loops with remanent polarization (2Pr) and coercive field (Ec) of up to 21.3 (μC/cm²) and 47.2 (kV/cm), respectively. The SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> capacitors with platinum electrodes showed fatigue free characteristics after switching of 1×10¹⁰ cycles. The chemical vapor deposition technique demonstrated excellent conformal coating of SrBi<inf>2</inf>Ta<inf>2</inf>O<inf>9</inf> film on 0.5 μm line-and-space patterns. These performances will meet the requirements for high-density nonvolatile memory devices.

DOI： 10.1080/10584589708019981

Scopus

記述言語：英語   出版者・発行元：Materials Research Society Symposium Proceedings  

Ferroelectric Bi <inf>2</inf>SrTa <inf>2</inf>O <inf>9</inf> thin films were successfully prepared by liquid delivery MOCVD, and structural and electrical properties were investigated. As-deposited films showed sharp distinct peaks, which were indexed assuming a fluorite-type structure. These precursors were transformed to bismuth-layered structures by annealing at 800 °C in flowing oxygen. Reasonable ferroelectric properties were observed in a film with 170 nm-thickness. Remanent polarization and coercive field were estimated to be 5.2 μC/cm ² and 52 kV/cm, respectively, at 5V.

Scopus

記述言語：英語   出版者・発行元：Journal of the American Ceramic Society  

Smooth, fine-grained RuO<inf>2</inf> thin films have been synthesized and deposited onto 〈100〉 silicon substrates via a solution chemistry technique. Ruthenium(III) chloride n-hydrate dissolved in ethanol was used as the precursor solution. Thin films from a 0.38M solution were spun at 4000 rpm for 20 s onto the substrates and fired at temperatures between 400° and 800°C. XRD analysis shows that RuO<inf>2</inf> forms over this entire temperature range. Using an appropriate firing schedule, the grain growth can be controlled and reproduced to provide for a uniform grain size distribution consisting of equiaxed, submicrometer diameter grains. The electrical resistance of the films has been measured at 300 K using the conventional four-point probe technique. The resistivity values range from 1.8 μΩ·m for the films with an average grain size of 250 nm to 3.1 μΩ·m for the films with 30 nm grains. The presence of residual carbon and hydrogen is not believed to have a significant effect on the resistivity.

DOI： 10.1111/j.1151-2916.1996.tb08159.x

Scopus

出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers  

The effect of plasma treatment and a dielectric diffusion barrier on electromigration (EM) performance was examined. The characteristics and adhesion properties at the interface between copper (Cu) and the dielectric diffusion barrier were also investigated by scanning transmission electron microscopy-electron energy loss spectrometry (STEM-EELS). The existence of oxygen at the interface after hydrogen (H<inf>2</inf>) plasma treatment, which has a large pre-exponential factor, causes a large EM drift velocity. Ammonium (NH<inf>3</inf>) plasma treatment can reduce the Cu oxide completely, resulting in an improvement in EM performance. On the other hand, the dielectric diffusion barrier of SiC<inf>x</inf>N<inf>y</inf>, which has a better adhesion property then SiC<inf>x</inf>, reduces EM drift velocity and provides a larger activation energy. The reduction of CuO<inf>x</inf> completely by plasma treatment is essential and the selection of dielectric diffusion barrier is important to improve the EM performance of Cu damascene interconnects. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.1570

Scopus

出版者・発行元：Annual Proceedings Reliability Physics Symposium  

Electromigration testing pattern to identify the dominant diffusion path of Copper (Cu) damascene interconnects is proposed. It is confirmed that dominant diffusion path is the interface between Cu and barrier dielectrics using the proposed testing pattern. After identification of the dominant path, the effects of the plasma treatment and barrier dielectric SiCxNy and SiCx on the EM performance is investigated. Failure analysis reveals that Cu oxide at the interface of SiCx samples with H <inf>2</inf> plasma treatment accelerates the Cu EM diffusion, resulting in lower activation energy and shorter lifetime. In addition, it is also found that nitrogen at the interface retards Cu diffusion drastically.

Scopus

出版者・発行元：IEEE International Reliability Physics Symposium Proceedings  

Electromigration testing pattern to identify the dominant diffusion path of Copper (Cu) damascene interconnects is proposed. It is confirmed that dominant diffusion path is the interface between Cu and barrier dielectrics using the proposed testing pattern. After identification of the dominant path, the effects of the plasma treatment and barrier dielectric SiCxNy and SiCx on the EM performance is investigated. Failure analysis reveals that Cu oxide at the interface of SiCx samples with H<inf>2</inf> plasma treatment accelerates the Cu EM diffusion, resulting in lower activation energy and shorter lifetime. In addition, it is also found that nitrogen at the interface retards Cu diffusion drastically.

DOI： 10.1109/RELPHY.2004.1315331

Scopus