Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N20: Dielectrics |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Fred Walker, Yale University Room: Colorado Convention Center 105 |
Wednesday, March 7, 2007 8:00AM - 8:12AM |
N20.00001: The mechanism of Fermi level pinning/unpinning at high k Oxide/GaAs interface M.L. Huang, W.C. Lee, P. Chang, T.D. Lin, Y.J. Lee, M. Hong, J. Kwo Unpinning of Fermi level at oxide/GaAs interface is the one of the key issues of realizing GaAs-based III-V metal-oxide-semiconductor field-effect-transistors (MOSFETs) for high-speed and high power applications due to inherent advantages of high electron mobility, semi-insulating substrates, and high breakdown fields. In this study several important high dielectric constant materials, Al$_{2}$O$_{3}$, HfO$_{2}$, Ga$_{2}$O$_{3}$(Gd$_{2}$O$_{3})$ and Y$_{2}$O$_{3}$, were \textit{in-situ} deposited on GaAs(001), and exhibited the different Fermi level pinning/unpinning behavior of current-capacitance (C-V) characteristics. In order to correlate the relationship between the oxide/GaAs interfacial structure and their electrical behavior,\textit{ in-situ} XPS analysis was conducted shortly after nano high $\kappa $ oxides were deposited on GaAs. Our studies suggest that Fermi level unpinning in the oxide/GaAs hetero-structure is attributed to the exclusion of the As-As and the As-O bonding during the initial interfacial formation. [Preview Abstract] |
Wednesday, March 7, 2007 8:12AM - 8:24AM |
N20.00002: MOS Ge Diodes Based on High $\kappa $ Gate Dielectrics Grown by MBE and ALD Kun Yu Lee, W.C. Lee, T.D. Lin, C.S. Lee, Y.C. Chang, Y.J. Lee, M.L. Huang, Y.D. Wu, M. Hong, J. Kwo Germanium-based CMOS technology is gaining importance due to its high carrier mobility. In this work high $\kappa $ gate-dielectrics, Al$_{2}$O$_{3}$, HfO$_{2}$, Y$_{2}$O$_{3}$ and Ga$_{2}$O$_{3}$(Gd$_{2}$O$_{3})$ grown by MBE and ALD were investigated as passivation layers on n type Ge(100). Thermal stability of the MOS diodes was examined after various anneals. Prior to dielectric depositions surface pretreatments were applied to reduce the unwanted GeO$_{x}$ interfacial layer, and to improve electrical properties. Frequency dispersion of C-V curves was reduced by using a 350$^{o}$C preclean process, compared to the sample without precleaning. The leakage current density of ALD grown HfO$_{2}$ (6.8nm) is 4.6×10$^{-6 }$A/cm$^{2}$ with $\kappa $ of 10.5. The improved CV curve was attributed to less GeO$_{x}$ formed at substrate and oxide interface, as confirmed by XPS analysis. However, with higher cleaning temperature over 400$^{o}$C, the CV curves showed additional inversion capacitance, possibly due to minority carriers from defect states near the interface. [Preview Abstract] |
Wednesday, March 7, 2007 8:24AM - 8:36AM |
N20.00003: Inelastic Electron Tunneling Spectroscopy of Silicon Based MOS Diode with High Permittivity Gate Dielectrics Syuanlong You Inelastic electron tunneling spectroscopy (IETS) has been known as a powerful technique for detecting the molecular vibrations in the spectra. This technique was also applied to the study of the silicon MOS to reveal the information of electrode phonons, dielectric phonons, chemical bonding, and trap states in MOS structure. In this work IET spectra of silicon MOS diode with SiO$_2$, high $\kappa$ \quad HfO$_2$, and YDH (HfO$_2$ doped with Y$_2$O$_3$) as gate dielectrics were investigated. The gate bias dependence of the IET spectrum enables us to ascribe the vibration mode adjacent to the metal gate interface, or to the silicon substrate interface. We show variations of the IET spectrum with respect to Y$_2$O$_3$ doping and annealing conditions of the dielectrics, and compare with reported data of infrared, Raman, and XPS. We also present the changes in IET spectra as induced by electrical stress that eventually leads to soft-breakdown in the dielectrics. [Preview Abstract] |
Wednesday, March 7, 2007 8:36AM - 8:48AM |
N20.00004: MBE and ALD grown High k Dielectrics Gate Stacks on GaN Y.C. Chang, K.Y. Lee, W.C. Lee, T.D. Lin, Y.J. Lee, M.L. Huang, M. Hong, J. Kwo, Y.H. Wang III-nitride compound semiconductors are attractive for high-temperature and high-power MOSFET applications due to their intrinsic properties of wide band gap, high breakdown field, and high saturation velocity under high fields. In this work GaN-based high k MOS diodes were fabricated using MBE-grown Ga$_{2}$O$_{3}$(Gd$_{2}$O$_{3})$, MBE-grown HfO$_{2}$ and ALD-grown HfO$_{2}$ as the gate dielectrics with dielectric constants of 14.7, 17.4 and 16.5, respectively. All MOS diodes exhibited low leakage ($<$10$^{-6}$ A/cm$^{2}$ at V$_{fb}$+1) and well behaved capacitance-voltage curves with a low interfacial density of states of $\sim $10$^{11}$ cm$^{-2}$eV$^{-1}$. Energy-band diagrams of the MOS structures have been determined by extracting valance-band offset ($\Delta $E$_{V})$ from HR-XPS and with the bandgaps of the oxides. For example, the ALD-grown HfO$_{2}$-GaN at the interfaces gave approximately $\Delta $E$_{C}$ and $\Delta $E$_{V}$ of 1.2 eV and 1.1 eV, respectively. [Preview Abstract] |
Wednesday, March 7, 2007 8:48AM - 9:00AM |
N20.00005: Spectroscopic Study of Band Alignment in Alternative High-k MOS Dielectric Stacks E. Bersch, S. Rangan, E. Garfunkel, R.A. Bartynski The study of high-k dielectrics and metal gate electrodes is critical to next generation MOSFETs. We have measured the band offsets of alternative MOS stacks using photoemission and inverse photoemission in the same chamber as well as synchrotron photoemission. At Rutgers, we have measured the valence and conduction band densities of states (DOS) and edges with UV photoemission and inverse photoemission, respectively, in situ. Using synchrotron photoemission we have measured the core level positions as well as the valence band DOS of clean and metallized dielectric/Si systems. The measurement of the chemical shifts of the core levels upon metallization enables us to evaluate the conduction band offset at the metal/dielectric interface. For Hf(x)Si(1-x)O(2), we find the conduction band offset (CBO) does not change as x is varied from 1 to 0.8, but the valence band offset increases by 0.4 eV. Titanium, aluminum and ruthenium were chosen as gate metals because of their prospective use as low and high workfunction metals in dual metal gate CMOS devices. We measured the CBO for the Ti, Al and Ru/Hf(x)Si(1-x)O(2) interfaces and found barriers involving Ti and Ru to be in good agreement with the interface gap state model, whereas the barrier involving Al deviated substantially from it due to the formation of an AlO(X) layer at the interface. [Preview Abstract] |
Wednesday, March 7, 2007 9:00AM - 9:12AM |
N20.00006: First-principles study of direct electron tunneling through ultra-thin SiO$_{2}$ layers Joongoo Kang, K.J. Chang, Y.-H. Kim As the size of metal-oxide-semiconductor devices is scaled down to the sub-10-nm regime, the thickness of SiO$_{2}$ insulating layers reaches the range of 1-2 nm. Then, gate leakage current is unavoidable due to direct tunneling of electrons. In this work, we study the electron tunneling current through thin gate oxide layers for various Si(100)/SiO$_{2}$ interface models, which have different oxide thicknesses and crystal phases. We use a combined approach of the local-density-functional approximation and the matrix Green's function method. We test oxide layers in the $\alpha $-quartz, tridymite, and amorphous structures, which are sandwiched between two Si(100) electrodes. We find that Si induced gap states result from a decay of the silicon valence (conduction) band wave functions into the oxide region. The gate leakage current between two p+ Si electrodes is exponentially reduced as the oxide thickness increases, with the almost same decay rate of -1 decade/0.2 nm, regardless of the structure of oxide layers. We also find that the gate leakage current is affected by introducing interface roughness and oxygen vacancies in the oxide. [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:24AM |
N20.00007: Search for Sub lattice Disorder in CaCu$_{3}$Ti$_{4}$O$_{12}$ Kevin Stone, Jae-Hyuk Her, Peter Stephens, Jonathan Hanson, Haiding Mo, Christie Nelson, Lijun Wu, Yimei Zhu One of the proposed mechanisms for the Internal Barrier Dielectric Capacitance believed to be responsible for the giant dielectric response of the perovskite material CaCu$_{3}$Ti$_{4}$O$_{12}$ is that of sub lattice disorder on the Ca and Cu sites.~ Such disorder should have measurable affects on both the intensity and shape of the Bragg peaks of different symmetries.~ We investigate the possible existence of such disorder through high resolution charge density maps, based on a large dataset of x-ray and electron diffraction integrated intensity measurements, and, separately, peak shape measurements on a restricted set of reflections. Supported by the U.S. Department of Energy. [Preview Abstract] |
Wednesday, March 7, 2007 9:24AM - 9:36AM |
N20.00008: Extrinsic Mechanisms for the Giant Dielectric Constant in CaCu$_{3}$Ti$_{4}$O$_{12}$: A Low-Temperature Specific-Heat Study C.P. Sun, H.D. Yang, Jianjun Liu, W.N. Mei, J.-Y. Lin, Chun-gang Duan Low-temperature specific-heat study has been performed on the insulating giant dielectric constant material CaCu$_{3}$Ti$_{4}$O$_{12}$. Analyzing the specific heat data in the very low-temperature range (0.6 to 1.5 K) and moderately low-temperature range (1.5 to 5 K), we noticed significant contributions originated from the linear and Einstein terms, we attributed as the low-lying elementary excitations due to lattice vibrations occurred at the grain boundaries and induced by local defects. These findings correlate well with the core-shell model deduced from the earlier experiments, and offer explanation to the extrinsic mechanisms of the giant dielectric constants at both low (DC to 10$^{5}$ Hz) and high frequency (10$^{6}$ to 10$^{9 }$Hz) regions. [Preview Abstract] |
Wednesday, March 7, 2007 9:36AM - 9:48AM |
N20.00009: Fabrication and properties of TiO$_{2}$ cluster films Xiaohui Wei, Y.F Xu, Z Sun, Ralph Skomski, D.J Sellmyer Recently much interest has been directed toward nanostructured pure and doped semiconductors for their interesting dielectric, optical and magnetic properties and potential applications in spintronic devices. In this study a gas-condensation cluster-deposition system was used to make cluster-assembled films. Ti and TiO$_{2 }$targets were used to prepare Ti and TiO$_{2}$ cluster assembled films. The Ti and TiO$_{2 }$clusters were examined by TEM to determine their size and size distribution. Films were scanned by AFM to see their surface morphology and examined by XRD to see their structural evolution with annealing temperature and annealing time. TEM revealed that the sizes of the Ti and TiO$_{2}$ clusters are 9 and 20 nm respectively. After annealing at 400 $^{o}$C for an hour in oxygen, the Ti cluster films transform into pure polycrystalline rutile, which has a high dielectric constant, whereas the TiO$_{2 }$cluster films remain a mixture of anatase and some rutile even after 900$^{ o}$C annealing. The optical, magnetic and dielectric properties of the films will also be discussed. This work is sponsored by NSF-MRSEC,ONR and NCMN. [Preview Abstract] |
Wednesday, March 7, 2007 9:48AM - 10:00AM |
N20.00010: Second-harmonic generation measurements of porous low-k dielectric materials Joanna Atkin, Daohua Song, Robert Laibowitz, Eduard Cartier, Thomas Shaw, Robert Rosenberg, Tony F. Heinz Low-k dielectric materials based on porous carbon-doped oxides, with relative dielectric constants as low as 2.1, are widely used in the microelectronics industry. Knowledge of these materials' basic electronic properties, such as energy gaps, barrier heights, and trap states, is essential for developing an understanding of their electrical leakage and stability characteristics. In this paper, we present the results of measurements of optical second-harmonic generation (SHG) from thin films of the low-k material deposited on silicon. SHG measurements at low laser fluence probe the nature of interfacial trap states. At higher fluence, multiphoton charge injection is produced by the femtosecond laser pulses and yields a time dependence of the SHG signal. Analysis of these measurements provides information about barrier heights. The results of these non-contact optical measurements will be compared with C-V characterization of the dielectric films. [Preview Abstract] |
Wednesday, March 7, 2007 10:00AM - 10:12AM |
N20.00011: First-principles calculations for the elastic properties of superhard TiN/Si$_{3}$N$_{4}$ superlattices Sanwu Wang, Y.G. Shen, S.T. Pantelides We report first-principles density-functional calculations for the atomic structures, the electronic properties, and the elastic properties of superlattices containing nano-scale crystalline TiN and thin layer of silicon nitride. We found that the elastic properties (bulk modulus, shear modulus, and elastic constacts) are strongly dependent on the size of the components. Superlattices with TiN thickness smaller than 2.5 nm have far smaller values of bulk and shear moduli than bulk crystalline TiN, while $\sim $3 nm TiN can make the superlattice have the elastic properties close to those of crystalline TiN. The results are helpful for optimization of the component size to achieve high values of both elastic properties and hardness. [Preview Abstract] |
Wednesday, March 7, 2007 10:12AM - 10:24AM |
N20.00012: ABSTRACT WITHDRAWN |
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