Papers

ICMCTF2007 Session H1: Novel Film Synthesis Strategies for the Next Generation of Devices

Wednesday, April 25, 2007 8:00 AM in Room Tiki Pavilion

Wednesday Morning

Start	Invited?	Item
8:00 AM		H1-1 Piezoelectric Quantum Structures for Full Spectrum Light Emitters C. Wetzel (Rensselaer Polytechnic Institute) Group-III nitride semiconductors are the prime contender for energy efficient solid-state lighting by means of high power light-emitting diodes. Within a single alloy system, a very wide range of optical bandgap energies can be achieved for a rich variety of electronic bandgap engineering. Yet, these uniaxial materials are also highly piezoelectric leading to internal electric fields of the order of a few MV/cm. At such large field strengths, piezoelectric polarization provides an additional design parameter for electronic state control and device design. In this talk I will report on the implementation of such a system for the development of green an deep green (500 - 580 nm) light-emitting diodes. I will analyze the current status and a future pathway for the achievement of higher performance device that soon could replace all incandescent lighting with far more energy efficient solid-state solutions.
8:40 AM		H1-3 Synthesis and Characterization of Ferroelectric Properties of Ce₂Ti₂O₇ Thin Film W.S. Kim, J.-K. Yang, C.-K. Lee, H.-H. Park (Yonsei University, Korea) Ferroelectric materials with a pseudo-pyrochlore structure of the general formula A₂B₂O₇, such as Sr₂Nb₂O₇ (SNO), La₂Ti₂O₇ (LTO), and Nd₂Ti₂O₇ (NTO), exhibit a high coercive field, good thermal stability, and a low dielectric constant. In addition, compared with conventional ferroelectric materials, such as PZT (lead zirconium titanate) or SBT (strontium bismuth tantalate), these materials show superior insulating properties that arise from their low defect densities due to the absence of a highly volatile element. In this work, ferroelectric Ce₂Ti₂O₇ films were grown with a pseudo-pyrochlore structure on an Y₂O₃/Si substrate by low-vacuum (50 mTorr) anneal at 800°C. The crystallinity of CTO and the oxidation state of cerium were characterized by synchrotron X-ray diffraction and X-ray absorption-near-edge-structure spectra using the 8C1 beam line of the Pohang Light Source facility in Korea. The dielectric constant at 1 MHz and dielectric loss of the film in the Pt/Ce₂Ti₂ O₇/Pt structure were measured as 48.7 and 0.013, respectively. A relatively large memory window of 1.24 V was measured with a Pt/Ce₂Ti₂O₇/Y₂O₃/Si capacitor structure at an applied voltage of 6 V. The capacitance-voltage hysteresis was symmetrical without shift from the origin due to an effective suppression of the interfacial SiO₂ formation under low-vacuum annealing conditions.
9:00 AM		H1-4 Physical Properties and Preparation of SrBi₂Ta₂O₉ Ferroelectric Films by Pyrolysis and Thermal Annealing H.K. Ku (National Cheng-Kung University, Taiwan); H.S. Koo (Ming-Hsin University, Taiwan) Strontium-bismuth-tantalate - SrBi₂Ta₂O₉ ferroelectric thin films on Pt/Ti/SiO₂/Si substrates have been fabricated by the processing of spray pyrolysis and post-annealing treatment. The as-prepared films were annealed in the atmosphere of inert and oxygen at the different temperatures and duration. Thermal characteristics and crystal structure of the as-prepared films were observed by DTA/TGA and XRD. The resultant film, which was annealed at 800C for 30min, shows optimal characteristics of dielectric constant to be 220, remanent polarization to be 4.0C/cm², saturation polarization to be 8.8C/cm² and coercive field to be 63kV/cm. Leakage current of the resultant film annealed at 800°C for 30min can achieve 10-6A/cm², while leakage characteristics of the films will be the remarkable improvement of the films which are post-annealed at temperature 700°C for 10min and Ar atmosphere.
9:20 AM		H1-5 Stable Resistive Switching Behaviors of Sputter Deposited V-doped SrZrO₃ Thin Films C.-C. Lin, J.-S. Yu, C.-C. Lin (National Chiao Tung University, Taiwan); C.-H. Lin (Winbond Electronics Corporation, Taiwan); T.-Y. Tseng (National Chiao Tung University, Taiwan) Stable resistive switching behaviors of V-doped SrZrO₃ (SZO) thin films have attracted broad attention due to their potential application for nonvolatile memory. In this study, highly preferred orientation V-doped SZO thin films were deposited on LaNiO₃ (LNO) bottom electrodes by using an rf-magnetron sputtering system. The thicknesses and surface morphologies, crystal structures, and chemical bonding configurations of these thin films were investigated by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, respectively. Stable resistive switching properties are observed in the SZO thin films sputtered at various temperatures. The 0.3 mol% V-doped SZO thin films have the best resistive switching properties among various concentration V-doped films. The improvement of conductivity of LNO bottom electrode can effectively reduce the resistive switching voltage. However, the resistive switching voltage is less dependent on the thickness of the SZO thin film. The data retention time longer than 10⁵ s can also be obtained at 85°C for the SZO thin film. Based on our experimental results, the V-doped SZO thin film is very suitable for nonvolatile memory application.
9:40 AM		H1-6 Optimization of the Geometry of the MEMS Electrothermal Actuator to Maximize In-Plane Tip Deflection E.S. Kolesar, B. Least, J. Tippey, T. Htun (Texas Christian University) Several microactuator technologies have been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion represent the most common modes of microactuator operation. This investigation optimized the geometry of the asymmetrical electrothermal actuator to maximize its in-plane deflection characteristics. The motivation was to present a unified description of the behavior of the electrothermal actuator so that it can be adapted to a variety of microsensor and microactuator applications. The MEMS polysilicon surface micromachined electrothermal actuator uses resistive (Joule) heating to generate differential thermal expansion and movement. In the traditional asymmetrical electrothermal actuator design, the single-hot arm is narrower than the cold arm, and thus, the electrical resistance of the hot arm is greater. When an electrical current passes through the device (both the hot and cold arms), the hot arm is heated to a higher temperature than the cold arm. This temperature differential causes the hot arm to expand along its length, thus forcing the tip of the device to rotate about its flexure. In this investigation, a 3D model of the electrothermal actuator was been designed, and its geometry was optimized using the finite-element analysis (FEA) capabilities of the ANSYS computer program. The electrothermal actuator's geometry was systematically varied to establish optimum values of several critical geometrical ratios that maximize tip deflection. The value of the ratio of the length of the flexure component relative to the length of the hot arm was discovered to be the most sensitive geometrical parameter ratio that maximizes tip deflection.
10:00 AM		H1-7 Novel Strategies for Low Temperature CVD of Advanced Materials J.R. Abelson (Frederick Seitz Materials Research Laboratory and University of Illinois Urbana Champaign) In low-temperature chemical vapor deposition, we have employed growth promoters and growth suppressors, in combination with well-designed precursor molecules, to control the film growth rate and morphology. This is a new approach to the CVD process which affords many of the control parameters that have been exploited in electrochemical deposition. We have obtained remarkable results: films of metallic HfB₂ and of insulating MgO have been deposited at substrate temperatures with perfect conformal coverage on cylindrical vias with 30:1 aspect ratio, including 100% filling; films of HfB₂ and CrB₂ have been deposited superconformally in deep trenches, i.e. from the bottom up; and the rate of film nucleation has been controlled, from extremely rapid and dense in the case of TiB₂ on SiO₂ substrates, to zero in the case of HfB₂ on SiO₂ substrates, which provides the basis for selective growth. We have also developed the low temperature CVD of Ru films using a new organoruthenium precursor. Conformal growth occurs when the net surface reaction probability for an incident molecule is extremely low, i.e. < 10-4 for depth:width ratios of > 20:1. Such low values are obtained by site blocking according to the Langmuir mechanism, where the surface is largely passivated by adsorbed precursor molecules, dissociated ligands, or by adsorbed suppressor species. However, growth can still proceed at a technologically useful rate because the layer of adsorbed precursor continuously reacts to form film. For example, HfB₂ can be deposited conformally at a rate of 200 nm/min on features with 3:1 aspect ratio. We analyze the reaction kinetics using line-of-sight mass spectroscopy, spectroscopic ellipsometry, and modeling of trench coverage profiles. Our results demonstrate that the control of surface chemistry using growth suppressors and promoters provides a practical means to achieve conformal coatings on very high aspect ratio features using steady-state CVD.
10:40 AM		H1-9 Joining using Self Propagating High Temperature Synthesis (SHS) of Multilayered Ni/Ti Thin Film Ribbons M. Bai (Colorado School of Mines); D.P. Adams (Sandia National Labs) The production of thin film NiTi alloy from multilayered elemental metal (Ni-Ti) using Self Propagating High Temperature Synthesis (SHS) was studied. SHS is a process in which the exothermic heat released during a propagating combustion reaction is transferred to the adjacent reactants creating a self-sustaining reaction. The process is a good candidate for joining heat sensitive materials due to the rapid heating and cooling of the exothermic reaction. The multilayered Ni-Ti thin films are produced using sputter deposition technique. The total thickness is kept constant while the bilayer thickness and the number of bilayers are varied. Results showed that the properties of SHS reaction and the reacted products are governed by the design of the multilayered films. Previous studies have shown that compact powder assemblies of elemental Ni and Ti requires preheating in order to self propagate, while multilayered thin films are able to sustain the reaction at room temperature due to improvements in reaction kinetics. However, the thin film ribbons can not propagate when in contact with a bulk material due to the heat loss from the surface, thereby requiring preheating and/or dopant materials to increase the adiabatic temperature of the combustion reaction.
11:00 AM		H1-10 Chemical Vapour Deposition Routes to Gold / Semiconductor Nanocomposite Thin Films R.G. Palgrave, I.P. Parkin (University College London, United Kingdom) Thin films of gold nanoparticles and gold / semiconductor nanocomposites have been deposited in a single step CVD process. Aerosol Assisted CVD (AACVD) was used to deposit the films from two novel precursors: pre-formed gold nanoparticles and HAuCl₄. These precursors are unsuitable for conventional CVD as they are involatile, but have successfully been used in AACVD. Gold films and composite films were deposited from pre-formed nanoparticle solutions in toluene. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)₆], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O i-Pr)₄]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. A second set of gold films were deposited from HAuCl₄, which was combined with various conventional precursors resulting in nanocomposite films. Composite films showed metal-like reflection spectra and plasmon absorption. XPS and EDX analysis confirmed the presence of metallic gold and SEM imaging showed individual Au nanoparticles embedded in the films. These CVD techniques can be readily extended to produce other nanocomposite films by varying the precursors used.
11:20 AM		H1-11 Hydrogen Sensing Characteristics of Electrodeposited WO₃ Thin Film Gasochromic Sensor Activated by Pt Catalyst W.-J. Shiu, C.-C. Chan, J.-S. Peng, C.-C. Chang (Feng Chia University, Taiwan) The hydrogen gas sensing performance of platinum (Pt) catalyst activated WO₃ thin films were investigated. The behavior of tungsten trioxide (WO₃) thin films exhibited a gasochromic effect; i.e., a reversibly change in color from transparency when in air to blue when in H₂. The all processes proceeded rapidly at room temperature. The films were prepared by the electrodeposition method at room temperature. A layer of platinum (Pt) was then evaporated onto the surface of WO₃ film. The cycling of the coloration was obtained from UV-Vis spectra and the mechanism deduced from both visible and Fourier transform infrared (FTIR) spectra. The hydrogen (H₂) was dissociated firstly into H atoms by the Pt catalyst, and then diffused into the WO₃ thin film, which transformed to H_xW_1-xO₃ from WO₃ and changed the color of the WO₃ thin film. Therefore, we could detect the existence of H₂ by the coloration of WO₃ thin film. Sensor properties of WO₃(Pt) films were investigated at room temperature in H₂ and N₂ mixtures containing 50000 to 500000 ppm of H₂. The results show that the transmittance change(T) of the WO₃ hydrogen sensor was 2% when the concentration of H₂ was 50000 ppm, and 20% when the concentration of H₂ was 500000 ppm.