Papers

ICMCTF2005 Session H3: Thin Films for Next Generation Devices

Wednesday, May 4, 2005 8:30 AM in Room Royal Palm 4-6

Wednesday Morning

Start	Invited?	Item
8:30 AM		H3-1 Macroscopic Hierarchical Nanowire Thin Films and Devices Y. Lu (Tulane University) Nanoscale components, ranging from 0-dimensional (quantum dots, nanoparticles), one-dimensional (1D) nanostructure (rods, wires, belts and tubes), to two- or three-dimensional nanostructure, have been received much interest as a result of their peculiar and fascinating properties. Device applications require integration of molecular and nanoscale components into high order structures and translation of nanoscale properties into micro/macroscopic dimensions. Here we will present synthesis, characterization, and application of macroscopic hierarchical nanowire networks. Nanowire networks were synthesized by mesoporous silica templated electrodeposition. In the research, mesoporous silica film was coated on conductive substrates firstly. Then metal or semiconductor (Pt, Pd, CdSe, etc.) was electrodeposited within the pores followed by removal of silica template resulting in robust nanowire networks. Nanowire network structure was controlled by mesostructure of the template. For example, 2D nanowires were obtained from 2D hexagonal arranged mesoporous silica, while 3D nanowires were achieved from replication of 3D bicontinuous cubic template. Nanowire diameter in the network was controlled by pore diameter of the template. As-synthesized 2D nanowires aggregate to bundles while 3D nanowires self support to form networks with high electrochemical active surface areas. Device applications of these nanowire thin films in solar cells, membranes, sensors, and other areas will be also discussed.
9:10 AM		H3-3 Hetero-Epitaxy Growth of B₁₂P₂ on Various Substrates by MOCVD D. Zhong, J.J. Moore (Colorado School of Mines); T.L Aselage (Sandia National Laboratories); H. Kleebe (Colorado School of Mines); A. Madan (MV Systems Inc. and Colorado School of Mines); A.O. Kunrath, B. Mishra (Colorado School of Mines) Icosahedral boron phosphide, B₁₂P₂, is a refractory solid and a wide bandgap semiconductor. Its self-healing of radiation damage has been demonstrated. Consequently, it could be a promising material to be used as a novel radiation tolerant, high temperature semiconductor to construct solid-state devices such as detectors, sensors and beta-cells -- direct nuclear-to-electric energy conversion devices for beta sources. We have recently developed an inductively heated MOCVD process to synthesize high-quality B₁₂P₂ from B₂H₆-PH₃-H₂ precursor systems. The growth rate is of approximately 30-40 nm/min. This paper presents the growth of B₁₂P₂ on various substrates, including <100> Si wafer, quartz, and different types of single crystal SiC wafers made by CREE, Inc. The composition, crystallographic orientation, surface morphology, and microstructure of B₁₂P₂ films were characterized by AES, XRD, Roman Spectroscopy, SEM, and TEM. This paper will demonstrate that B₁₂P₂ has been successfully synthesized, its hetero-epitaxy growth was of high quality on both Si nd SiC substrates, and the orientation of the film on SiC was strongly dependent on the degree of substrate's off-axis.
9:30 AM		H3-4 Electrolytic Deposition of Titania Films as Interference Coatings on Biomedical Implants: Microstructure, Chemistry and Nanomechanical Properties P. Kern (Swiss Federal Institute for Materials Testing and Research (EMPA), Switzerland); L. Philippe (Swiss Federal Institute of Materials Testing and Research (EMPA), Switzerland); J. Michler (Swiss Federal Laboratories for Materials Testing and Research (EMPA), Switzerland) Electrolytic deposition is an important, cost-effective tool in the formation of metallic, ceramic and organic films, including nanostructured materials and monolayers. Recently, great interest has emerged in electrolytic deposition of oxide films such as TiO₂, Nb₂O₅, ZrO₂ and Al₂O₃.¹ These films have promising applications as biocompatible and tribological coatings on orthopedic implants. Furthermore, aforementioned oxides are interesting in catalytic and electronic applications as well as for decorative purpose owing to their interference color. We electrolytically deposit TiO₂, Nb₂O₅ and ZrO₂ onto steel, TiAlV, CoCrMo and Si substrates via hydrolysis of peroxocomplexes by electrognerated base. Electrolyte formulation and deposition parameters and their impact on solution stability and deposit properties have been investigated. Films up to 100-200 nm could be deposited crack-free within minutes; longer deposition resulted in cracking and delamination due to internal stress. The as-deposited peroxocompounds are amorphous and crystallize during post heat treatment, as shown by differential thermal analysis (DTA) and Micro-Raman. Film morphologies were investigated with secondary electron microscopy (SEM), focused ion-beam (FIB) and transmission electron microscopy (TEM), showing uniform, dense and smooth films. Glow discharge optical emission spectroscopy (GDOES) depth profiling of TiO₂ films revealed very pure coatings with less contamination (e.g. sulfur, phosphor) compared to anodically grown TiO₂ films. Nano-indentation and scratch-tests characterizing film hardness and adhesion will be presented and compared to results from anodically grown films on valve metals. Main advantages of electrolytic deposition, like uniformity of film formation on complexly shaped devices, parallel processing capabilities and low equipment cost, will be discussed. ¹ I. Zhitomirsky, J. of the Europ. Ceram. Soc., 19, 2581, (1999).
9:50 AM		H3-5 Structure-Electrical Properties Relationship of Sodium Superionic Conductor Sputter-Deposited Coatings D. Horwat (Laboratoire de Science et Génie des Surfaces, France); E. Siebert (LEPMI, France); A. Billard (École des Mines Parc de Saurupt, France) Sodium (Na) superionic conductors (Nasicon) are interesting candidates for applications where fast ionic conductivity is required. Indeed, bulk Nasicon of Na₃Zr₂Si₂PO₁₂ stoichiometry allows Na⁺ conductivity around 10^-3 S.cm^-1 comparable to that of the best polymeric gels [1]. Their synthesis as thin films increases their interest for applications in the field of sensors. Few attempts were made to synthesise Nasicon coatings by pulsed laser deposition [2] and radiofrequency magnetron sputtering [3], but the resulting composition was rather different than that of the initial target. In a previous paper, we showed that the deposition of Nasicon coatings by co-sputtering of two targets was possible with a composition close to the targeted Na₃Zr₂Si₂PO₁₂ stoichiometry [4]. In this paper, we present recent results about Nasicon thin films obtained by co-sputtering of two targets. After a short description of the deposition procedure, the evolution of the composition of the films is discussed in relation with the deposition conditions. The structural evolution of the amorphous as-deposited coatings, determined by X-ray diffraction and Raman spectroscopy measurements, is then presented for different compositions as a function of their annealing temperature. Hence, the electrical properties of the films, assessed by complex impedance spectroscopy, are finally investigated in relation with their structure. [1] J.P.Boilot, G.Collin, Ph.Colomban, J.Sol.State Chem., 73(1988), 160 [2] M.Meunier, R.Izquierdo, L.Hasnaoui, E.Quenneville, D.Ivanov, F.Girard, F.Morin, A.Yelon, M.Paleologou, Appl.Surf.Science, 127-129(1998), 466 [3] Th.Lang, M.Caron, R.Izquierdo, D.Ivanov, J.F.Currie, A.Yelon, Sensors and Actuators, B31(1996), 9 [4] D.Horwat, A.Billard, presented at Patras Conference on Solid State Ionics Transport Properties(2004), Submitted to Ionics(2004).
10:10 AM		H3-6 Parameterized Approach to MEMS Mechanical Gear Design E.S. Kolesar, C.A. Edwards (Texas Christian University) The need for mechanical gears in Microelectromechanical Systems (MEMS) technology presents the problem of accurately and efficiently designing gears of the required types and sizes in a short amount of time. Currently, all gears must be hand drawn in commercial MEMS CAD programs, with each new gear requiring the customization of each of its features. Despite this difficulty, mechanical gear design has currently been accomplished to some extent, but the process is time consuming, it is difficult to render precise gears, and, as a result, their use has been limited. To facilitate rapid and accurate mechanical gear design, a new parameterized approach to Microelectromechanical Systems (MEMS) gear de-sign has been developed. To facilitate the expeditious design of a complicated gear mechanism, a parameterized mathematical design process has been developed. This parameterized approach to gear design facilitates the creation of gears with any practical inner radius, outer radius, tooth number, tooth size, number of spokes, dimples, and other features, simply by specifying the desired attributes. After the MEMS designer specifies these parameters, they are entered into a script file, in this case, a .cif file, which can then be imported into the desired commercial MEMS CAD program. The result is the creation of a customized gear design within minutes.
10:30 AM		H3-7 Deposition of TaN Thin Films by DC-Magnetron Sputtering of Ceramic TaN Sputtering Targets A. Schintlmeister, P. Wilhartitz (Plansee AG, Austria); B. Sartory (University of Innsbruck, Austria) TaN is a promising material for nanoscale diffusion barriers in copper metallization. However, the deposition of uniform and chemically homogeneous thin films is difficult to achieve by conventional PVD processing. The deposition of TaN thin films with nm thickness using reactive sputtering of metallic Ta targets is mainly limited by total cycle time and target poisoning. In this study, an advanced PVD process was applied for the deposition of TaN thin films by non reactive (0%N2), quasi reactive (<20%N2) and fully reactive (up to 50% N2) DC-magnetron sputtering of ceramic TaN sputtering targets. The targets were fully compacted (porefree), with fine and homogeneous microstructure. The deposition process turned out to be very stable and no poisoning effects have been observed. Thin film properties (ie homogeneity, stochiometry, stress and electrical conductivity) versus deposition parameters will be discussed.
10:50 AM		H3-8 Memory Effect of Sol-Gel Derived V-doped SrZrO₃ Thin Films C.-Y. Liu, C.-C. Chuang, J.-S. Chen (National Chiao-Tung University, Taiwan); A. Wang, W.-Y. Yang, J.-C. Young, K.-Y. Chiu (Winbond Electronics Corp., Taiwan); T.-Y. Tseng (National Chiao-Tung University, Taiwan) V-doped SrZrO₃ (SZO) thin films on LaNiO₃/SiO₂/Si substrate are synthesized by sol-gel method to form metal-insulator-metal (MIM) sandwich structure. The physical and electrical properties of the MIM device are studied. The microstructure and surface morphology of the SZO films are also characterized by X-ray diffraction and scanning electron microscopy to correlate with their electrical properties. Such a device has the bistable switching properties of current-voltage characteristics. The resistive switching between the high and low leakage-states can also be operated with voltage pulses. The device with the properties of long retention time and non-destructive read is suitable for nonvolatile memory application.
11:10 AM		H3-9 Protein Immobilization on Thin ZnO Films Grown on (100) p-Si for Biosensor Applications S Krishnamoorthy (University of Maryland); T. Bei (National Institute of Health); A. Iliadis (University of Maryland) Thin ZnO films are excellent materials for gas sensing, piezoelectric and UV optical detectors. The characteristics of the surface in conjunction with the thin film properties also provide this system with a high potential for sensitive biosensors. One of the critical steps in the development of biosensors is the controlled immobilization of minimal amounts of specific proteins onto the surface of thin film sensors. In the present study thin ZnO films were deposited on Si (100) substrates by pulsed laser deposition in order to examine Bovine Serum Albumin (BSA) and InterLeukin-6 (IL-6) protein immobilization processes. The ZnO films are grown on Si at 250°C and an oxygen pressure of 1e-4 Torr and examined by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy for crystalline quality. Thin (200nm) SiO₂ films thermally grown on (100)Si were also used for immobilization and comparison. We demonstrate for the first time by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques as well as ELISA quantitative biochemical assays that these proteins can be effectively and controllably immobilized on the ZnO film surface. Furthermore, following the same methodology, the proteins were immobilized on the SiO₂ surface, although the amount bound on ZnO was at least one order of magnitude higher than that on SiO₂, thus allowing substantially lower amounts of protein immobilization to be achieved controllably on the ZnO surface. Support from NSF grant ECS0302494 is acknowledged.
11:30 AM		H3-10 Deposition and Characterization of a Novel Integrated ZnO Nanorod/ZnO Thin Film Structure on Glass T.L. Chou, J.-M. Ting (National Cheng Kung University, Taiwan) Zinc oxide (ZnO) is an excellent material for use in optoelectronic applications due to its wide direct band gap of 3.33eV. Among its various forms, ZnO nanorod has become an important one as a result of the advance of nanotechnology. In previous papers@super 1,2@ we have reported a new route for ZnO nanorod synthesis using a sputter deposition technique. It was found that the formation of ZnO nanorods critically depends on a decisive layer of copper. The copper layer allows an initial formation of ZnO thin film and subsequent formation of ZnO nanorods without changing any conditions during the synthesis. Recently we have found ZnO nanorod/ZnO thin film structure a potential application in solar cells as an integrated current collector/electrode. For such an application, it is essential to understand the characteristics of ZnO nanorod/ZnO thin film structures. As a result, we report in this paper our investigation on the morphology, microstructure, electrical properties, and optical properties of ZnO nanorod/ZnO thin film structures. ZnO nanorod/ZnO thin film structures were deposited using a magnetron sputter deposition technique. Both Si and glass were used as the substrates. Prior to the deposition of ZnO nanorod/ZnO thin film structures, the substrates were pre-coated with Cu using an electroless plating technique. During the sputter deposition process, ZnO thin film was first obtained on Cu pre-coated substrate and followed by the formation of ZnO nanorods. ZnO nanorod/ ZnO thin film structures were deposited under different deposition times, O₂/Ar ratios, and substrate temperatures. The resulting ZnO nanorod/ZnO thin film structures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry, and micro-cathodoluminescence (CL). It was found that the ZnO nanorod/ZnO thin film structures obtained exhibit different physical dimensions, degree of crystallinity, oxygen contents, electrical resistance, optical band gaps, and optical transmittances. Correlation between the results of characterizations and the deposition parameters is discussed. super 1@ Y.S. Chang and Jyh-Ming Ting, "Growth of ZnO Thin Films and Whiskers," Thin Solid Films, 398-399 (2001) 29-34. ² Jyh-Ming Ting, Wen-Ting Chiou, Wan-Yu Wu, "Growth of Single Crystal ZnO Nanowires Using Sputter Deposition," Diamond and Related Materials 12 (2003) 1841-1844.