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Hafnium oxides and hafnium silicate films were investigated as a possible replacement for the SiO2 gate dielectric. Hafnium oxide films were formed by reactive sputtering from a single Hf oxide target in a predominantly Ar atmosphere containing small additions of oxygen. Hafnium silicates were made by adding a He-diluted silane gas for Si incorporation. By changing the silane gas flow, different Si atomic concentrations were incorporated into the Hf oxide films. Depositions were performed with the substrate held at temperatures of 22 °C and 500 °C. The chemical composition of the films was determined with nuclear techniques. Optical reflectivity was used to measure the optical band gap. The film morphology was investigated by transmission electron microscopy (TEM) and the electrical properties were measured with capacitance–voltage and current–voltage measurements using aluminum gate capacitors. TEM and electrical measurement showed that a SiO2 interfacial layer of about 3 nm formed at the Si interface due to the oxidizing sputter ambient. This precluded the growth of Hf based high-K films with small equivalent thickness. After correction for the interfacial oxide layer, the dielectric constant was found to decrease from about 21 for Hf oxide to about 4–5 for the Hafnium silicates with low Hf content (3 at. % Hf and 32 at. % Si). The optical band gap was found to increase from 5.8 eV for Hf oxide to about 7 eV for the silicate films. After annealing at 1000 °C followed by a 300 °C postmetallization anneal, negligible flat band voltage shift were measured on hafnium silicate films and good interface passivation was observed. However, leakage currents increased due to the high temperature processing.

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We report on physical and electrical characterization of ultrathin (3–10nm) high-κHfO2 gate stacks deposited on Ge(100) by atomic-layer deposition. It is observed that uniform films of HfO2 can be deposited on Ge without significant interfacial growth. The lack of an interlayer enables quasiepitaxial growth of HfO2 on the Ge surface after wet chemical treatment whereas a nitrided interface (grown by thermal oxynitridation in ammonia) results in an amorphous HfO2. The stacks exhibit surprisingly good thermal stability, up to temperatures only 150°C below the melting point of Ge. In terms of electrical properties, HfO2 on Ge shows significantly reduced (up to 4 decades) gate leakage currents in the ultrathin regime of equivalent electrical thickness down to ∼1.4nm due to the high-dielectric constant of ∼23. Nitrided interface is observed to be important for good insulating properties of the stack.

The crystal structure of Ca2−xSrxRuO4 with 0.2 < x < 1.0 has been studied by diffraction techniques and by high resolution capacitance dilatometry as a function of temperature and magnetic field. Upon cooling in zero magnetic field below about 25 K the structure shrinks along the c-direction and elongates in the a, b planes (0.2 < x < 1.0), whereas the opposite occurs upon cooling at highfield (x = 0.2 and 0.5). These findings indicate an orbital rearrangement driven by temperature and magnetic field, which accompanies the metamagnetic transition in these compounds.The phase diagram of Ca 2−x Sr x RuO 4 possesses quite different end members with the spin-triplet superconductor Sr 2 RuO 4 on the one side [1] and the antiferromagnetically ordered Mott insulator Ca 2 RuO 4 on the other side [2,3]. Since Sr and Ca are both divalent, one has to attribute the different physical behavior [4,5] entirely to the difference in the ionic radii. For small Ca content the octahedra present a c axis rotation and for higher Ca content (x < 0.5) a tilt of the octahedra around an in-plane axis occurs [6]. These distortions, through reduction of the hybridization, imply smaller band widths, which together with a constant Hubbard type interaction, enhance the correlation effects [7]. For Sr content lower than 0.2, finally Mott localization occurs in a material [4,5] which exhibits a strong rotation and a strong tilt deformation [6].Outstanding physical properties are found in compounds in the metallic regime but close to localization, 0.2 < x < 0.5. At T ∼ 2 K samples with x ∼ 0.5 exhibit a magnetic susceptibility a factor of 200 higher than that of pure Sr 2 RuO 4 [8]. In addition, the linear coefficient in the specific heat is exceptionally high, of the order of C/T ∼ 250 mJ mole K 2 [8,9], well in the range of typical heavy fermion compounds. Inelastic neutron scattering has revealed strongly enhanced magnetic fluctuations of incommensurate character [10], very different from those in pure Sr 2 RuO 4 [11,12].For Sr concentrations lower than 0.5, but still in the metallic phase, the tilt distortion occurs and strongly modifies the physical properties. The magnetic susceptibility at 2 K, measured in a low field, decreases with decreasing Sr content and increasing tilt; for 0.2 < x < 0.5 there is a maximum in the temperature dependence of the susceptibility [5]. In this concentration range the low-temperature low-field magnetization is, hence, small compared with the extrapolation both from high temperature and from high Sr concentration. A metamagnetic transition occurs in these compounds at low temperature yielding a high-field magnetization for x = 0.2 which actually exceeds that for x = 0.5 [8]. A similar metamagnetic transition has been reported for Sr 3 Ru 2 O 7 [13], where the related quantum critical end point has been proposed to cause outstanding transport properties.Single crystals of Ca 2−x Sr x RuO 4 were grown by a floating zone technique in image furnaces at Kyoto University (x = 0.2, 0.62 and 1.0) and at Université P...