Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N14: Focus Session: Multifunctional Oxides II |
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Sponsoring Units: FIAP DMP Chair: Jean Fompeyrine, Jane Chang, IBM Room: LACC 403B |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N14.00001: Molecular beam epitaxy for advanced gate stack materials and processes Invited Speaker: The material requirements for future CMOS generations - as given by the ITRS roadmap - are very challenging. This includes a high K dielectric without a low K interfacial layer, a high mobility channel and the appropriate metal gate. With the help of two projects INVEST and ET4US, we are building up a molecular beam epitaxy (MBE) infrastructure to grow this material set on large area wafers that can be further processed into small scale devices. In the INVEST project, we have developed an MBE system for the growth of complex oxides on semiconductors. The system follows the overall design of a production tool and is equipped with an RF atomic oxygen source, effusion cells, e-beam evaporators and a differential pumping stage. The oxide growth process starts with desorbing the initial surface oxide on the Si wafers in ultra-high vacuum and high temperature to create a clean reconstructed 2x1 surface. Using the atomic oxygen it is possible to oxidize the surface in a well controlled manner at low temperature and to grow very thin and dense SiO$_{x}$ layers, followed by the growth of 2-6 nm amorphous high K dielectrics. The process parameters permit to tune the interface layer from a SiO$_{x}$ rich to a silicide rich interface with a significant impact on the capacitance and the leakage. Initial focus is on developing an optimized growth recipe for high quality amorphous HfO$_{2}$ and LaHfO$_{3.5}$ films. This recipe was subsequently used to make wafers for a transistor batch that gave us the first N short channel MBE MOSFET's (100 nm) using an etched gate process flow. Some highlights of the first batch for 3nm HfO$_{2}$ MOSFET are a high mobility ($>$ 270 cm$^{2}$/Vs) with a corresponding low leakage current of 2 mA/cm$^{2})$. While there were some process issues for LaHfO$_{3.5}$, the 3 nm MOSFET showed very low leakage currents below 10$^{-6}$ A/cm$^{2}$. Interestingly all the LaHFO$_{3.5}$ MOSFETs showed very low threshold voltage instabilities. In collaboration with C. Marchiori, M. Sousa, A.Guiller, H. Siegwart, D. Caimi, J. Fompeyrine, D. J Webb, C. Rossel, R. Germann of IBM Research GmbH Zurich Switzerland; L. Pantisano, M. Claes, T. Conard, M. Demand, W. Deweerd, S. DeGendt, M. Heyns, M. Houssa, M. Aoulaiche, G. Lujan, L. Ragnarsson, E. Rohr, T. Schram of IMEC Leuven Belgium; J. Hooker, Z.M Rittersma, Y. Furukawa of Philips Research Leuven Belgium and J. W. Seo of EPFL Lausanne Switzerland. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 8:48AM |
N14.00002: Interface Electrostatics and the Schottky Barrier for Alkaline Earth Oxides on Silicon Rodney McKee, Fred Walker, Curt Billman In our recent work relating to Schottky Barrier Height measurements for alkaline earth oxides on silicon we reported on Coulomb Buffer effects for oxide/semiconductor junctions. The Coulomb Buffer effects arise from both interface chemistry and dielectric phenomena associated with ionic polarizability in an interface phase. In this talk we will address the latter of these issues with both XPS and capacitance measurements of the electronic structure of alkaline earth oxide/silicon heterostructures. We find systematic variations of the barrier height that are unique to a crystalline/crystalline interface in a MOS capacitor. This observation suggests a coupling between the dielectric constant of the oxide and the charge density that is localized around the silicon atoms in the interface phase. [Preview Abstract] |
Wednesday, March 23, 2005 8:48AM - 9:00AM |
N14.00003: Magnetoelectric interactions in single crystal ferrite-piezoelectric bilayers G. Srinivasan, C. P. DeVreugd, C. S. Flattery, V. M. Petrov, M. I. Bichurin, A. A. Ivanov, J. Zhai, S. Dong, D. Viehland The nature of low-frequency (10$^{-2}$ - 10$^{4}$ Hz) magnetoelectric (ME) coupling has been investigated in bilayers of single crystal Ni-Zn ferrites and polycrystalline lead zirconate titanate or single crystal lead magnesium niobate-lead titanate. Important observations are as follows. (i) The ME coupling in the bilayers is found to be stronger than in polycrystalline multilayers [1]. (ii) Zn substitution in ferrite is found to enhance the strength of ME interactions. (iii) ME voltage coefficients show significant variation with the orientation of the bias magnetic field. (iv) Data analysis using our model reveals that superior magneto-mechanical coupling in the ferrites is the cause of strong ME interactions [2]. 1. G. Srinivasan, E. T. Rasmussen, and R. Hayes \textit{Phys. Rev. B}. \textbf{67}, 014418 (2003). 2. M. I. Bichurin, V. M. Petrov and G. Srinivasan$.$ \textit{Phys. Rev. B}. \textbf{68}, 054402 (2003). - supported by grants from the the National Science Foundation (DMR-0302254), Russian Ministry of Education (Å02-3.4-278), and the Universities of Russia Foundation (UNR 01.01.026). [Preview Abstract] |
Wednesday, March 23, 2005 9:00AM - 9:12AM |
N14.00004: Properties of a ferromagnetic semiconductor: epitaxial Co-doped SnO2 films James Burst, Matthias Batzill, Ulrike Diebold Room-temperature ferromagnetic semiconductors are sought for future spintronic applications. Co-doped SnO2 has been shown to be a dilute ferromagnetic material that exhibits a giant magnetic moment at room temperature [1]. Here we characterize thin Co-doped SnO2 films, epitaxially grown on r-cut alpha alumina by oxygen plasma assisted molecular beam epitaxy [2]. The films exhibit the rutile structure of the SnO2 host material with a (101) orientation with the Co dopants in a Co2+ high spin state. XPD establishes that these dopants occupy Sn sites and are not forming a secondary phase in the SnO2 matrix. Angle-resolved UPS has been employed to characterize the valance band of Co-doped and pure SnO2. Further physical and magnetic properties will also be discussed. [1] S.B. Ogale, et al, Phys. Rev. Let., 91, 7, 077205 (2003). [2] M. Batzill, et al, submitted to Thin Solid Films. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N14.00005: Probing Enhanced Ferroelectricity in Strained SrTiO3 and BaTiO3 Epitaxial Films using optical Second Harmonic Generation Alok Sharan, Aravind Vasudeva Rao, Venkatraman Gopalan, Mike Biegalski, Darrell G. Schlom, Yulan L. Li, Long-Qing Chen, Kyoung Jin Choi, Chang Beom Eom This talk will present real-time second harmonic generation (SHG) experiments used for \textit{in-situ} probing of ferroelectric domain reversal and phase transitions in \textit{strained} SrTiO$_{3}$ and BaTiO$_{3}$ epitaxial thin films grown commensurately on scandate substrates such as GdScO$_{3}$ and DyScO$_{3}$. The Curie temperature, T$_{c}$ shifts by hundred of degrees because of the compressive strains (up to -1.5{\%}) imparted to these films. Using SHG we find that Tc shifts to $\sim $27C in SrTiO$_{3}$ (which normally is not ferroelectric at any temperature) and to $\sim $650C for BaTiO$_ {3}$ thin films on DyScO$_{3}$ as compared to T$_{c}$ of 120C in bulk crystals. Studies on real-time dynamics of domain reversal under external fields in these strained films beyond their normal Curie temperatures where domains are not expected at all would also be presented. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N14.00006: Anisotropic epitaxial strain effect on the charge-order phase of Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ Masao Nakamura, Yasushi Ogimoto, Hiroharu Tamaru, Makoto Izumi, Kenjiro Miyano Strain effect in charge and orbital ordered state has been investigated for Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin films deposited on (100), (110), and (111)-oriented SrTiO$_{3}$ (STO) substrates. Films on STO (001) and (111) substrates have monotonous temperature dependence for magnetic and transport properties showing no first-order phase transition. On the other hand, films on STO (110) show a clear ferromagnetic-antiferromagnetic and metal-insulator transition due to the onset of the charge and orbital order. Optical transmission spectra for the films on STO (110) show anisotry between the in-plane two axes. From the result, the orbital order plane of the film on STO (110) is deduced to be (100) or (010) plane, which lies out of the film surface. The reason for the difference in the magnetic and transport properties among the films on different substrate orientations, and why the clear metal-insulator transition occurs only on (110) substrates will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N14.00007: Magnetoelectric effect in nanostructured multiferroic ferrite-ferroelectric composite films S.C. Chae, H.J. Ryu, D.H. Kim, T.W. Noh, C.J. Bae, J. G. Park, Y.S. Oh, K.H. Kim Recently the multiferroic coupling of self assembled pillars of nanostructured CoFe$_{2}$O$_{4}$(CFO) embedded in BaTiO$_{3}$(BTO) matrix on SrRuO$_{3}$(SRO)/SrTiO$_{3}$(STO) substrate are reported. Thus, if the BTO-CFO nanocomposites can have a strong coupling between the order parameters, such composite structures will work as a new paradigm for the multiferroic research. The magnetoelectic effects are the coupling behaviors of two ferroic properties. The composite films of BTO-CFO and Pb(Zr$_{0.52}$Ti$_{0.48})$O$_{3}$-NiFe$_{2}$O$_{4 }$on SRO/STO and Nb-STO substrates were fabricated using pulsed laser deposition technique. The simultaneous growths of ferroelectric and ferrite phases were confirmed by the x-ray diffraction measurements. The ferroelectric and ferromagnetic properties are measured by TF analyzer and SQUID magnetometer, respectively. We will study the temperature dependence of dielectric properties varying external magnetic fields. We will also measure the transverse, $\alpha _{31}$, and longitudinal, $\alpha _{33}$, magnetoelectric voltage coefficient. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N14.00008: SrTiO3 single crystal field-effect transistor with an amorphous CaHfO3 gate insulator Keisuke Shibuya, Tsuyoshi Ohnishi, Takayuki Uozumi, Mikk Lippmaa, Hideomi Koinuma It becomes more and more important to understand the electronic properties of interfaces in transition-metal oxides from a viewpoint of utilizing such materials in devices; tunneling magnetoresistance (TMR) junctions, resistance random access memory (RRAM), or field-effect transistors (FET). SrTiO$_{3}$ is a wide-gap semiconductor and a good model system for studying the electronic structure of various oxides with similar crystal structures. We have fabricated a field-effect transistor composed of SrTiO$_{3}$ (100) single crystal as a channel and an amorphous CaHfO$_{3}$ layer as a gate insulator. The amorphous CaHfO$_{3}$ gate insulator layer, grown by pulsed laser deposition, was atomically flat and had an average breakdown field of 5 MV/cm. All electrode and channel patterning was done with simple contact masks. The device showed prominent n-type transistor operation, a field-effect mobility of 0.4 to 0.5~cm$^{2}$ / V s, and an on-to-off channel current ratio of $\sim $ 10$^{5}$ at room temperature. However, an improvement of these transistor properties was not observed at low temperatures. The device performance was limited by the electric structure of the interface. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N14.00009: Hydrogen-induced defect generation in amorphous SiO$_{2}$ Masayasu Miyata, Adri C.T. van Duin, Jamil Tahir-Kheli, William A. Goddard III Dielectric breakdown of thin silicon oxides (SiO$_{2})$ of metal-oxide semiconductor field-effect transistors is a long-standing problem. The breakdown is generally recognized to be due to the accumulation of defects in the oxide. An amorphous SiO$_{2}$ (a-SiO$_{2})$ has been known to have very few defects, thanks to its strong and flexible network of Si-O bonds. Then, why are defects created in this good insulator? The hydrogen related chemistry model has the potential to explain dielectric breakdown, but it is still unclear how hydrogen could generate the energy required to break Si-O bonds. Using the quartz structure, molecular dynamics simulations have been executed with Reax Force Field (ReaxFF) method that is fitted to give first principle energy profiles. In these simulations we found that at elevated temperatures a meta-stable structure of hydrogen attached to Si- O bond is formed, which we will refer to as the Attached Radical (Att{\_} Rad). Att{\_}Rad has a degenerated half-filled electronic level, so will be good candidate for breakdown precursor. We will discuss its structure and energetics, comparing to the state with hydrogen at interstitial site. Using ReaxFF, we also managed to obtain a defectless a-SiO$_{2}$ structure and found that the Att{\_}Rad state is significantly more stable in a-SiO$_{2}$ compared to quartz, indicating that this state might initiate dielectric breakdown in Si/a-SiO$_{2}$ interfaces. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N14.00010: High temperature oxidation studies of filtered arc deposited CrAlN nanolayered coatings on steel plates A. Kayani, C.V. Ramana, R.J. Smith, V.I. Gorokhovsky, V. Shutthanandan The requirements of low cost and high-temperature corrosion resistance for interconnect plates in solid oxide fuel cell stacks has directed attention to the use of metal plates with oxidation resistant coatings. We have investigated the performance of steel plates with nanolayered coatings consisting of CrAlN. The coatings were deposited using large area filtered arc deposition technology,[1] and annealed for up to 25 hours in air at 800 $^{\circ}$C. The composition, structure and morphology of the coated plates were characterized using RBS, NRA, and AFM techniques. The oxidation rate was reduced by a factor of about 40 relative to the uncoated steel plates. [1] Vladimir I. Gorokhovsky, Rabi Bhattacharya and Deepak G. Bhat, Surface and Coating Technology, \textbf{140} (2) 2001, pp. 82-92. [Preview Abstract] |
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