ICMCTF2008 Session C2-1: Optical Thin Films for Active Devices and Microsystems

Tuesday, April 29, 2008 8:00 AM in Room Royal Palm 1-3

Tuesday Morning

Start	Invited?	Item
8:00 AM	Invited	C2-1-1 Recent Advances on Amorphous Oxide Based Thin Film Transistors E. Fortunato, P. Barquinha, L. Pereira, G. Gonçalves, R. Martins (CENIMAT/I3N, Portugal) Amorphous oxide semiconductors are nowadays playing an important scientific and technological role for the next generation of optoelectronic devices. The recent applications using these new semiconductor materials, besides covering both p and n-type semiconductor properties present a high electronic mobility being the structure amorphous. This specific characteristic contrast to conventional amorphous semiconductors like a-Si:H, where carrier transport is limited by the disorder of the amorphous phase, ie band tail limited. In this paper we will present some of the recent achievements already obtained with special attention to thin film transistors.
8:40 AM		C2-1-3 High Performance Transparent Conducting Oxide for Application of Flexible Organic Solar Cell J.-W. Kang, D.-G. Kim, J.-K. Kim (Korea Institute of Materials Science (KIMS), Korea); H.-K. Kim (Kumoh National Institute of Technology, Korea); J. Kim (Korea University, Korea) Optical and mechanical properties of transparent conduction oxide (TCO) such as indium tin oxide (ITO) and indium zinc oxide (IZO) coated on flexible substrate were described. High-performance TCO were deposited on flexible substrate such as polyethersulfone (PES) and polyethylene terephthalate (PET), and applied to fabrication of flexible organic solar cells. The performance of TCO materials was observed with four-point probe, hall-effect measurement, UV-Vis-NIR spectrophotometer, and XRD. We have demonstrated their use as flexible TCO for efficient polythiophene-fullerene bulk-heterojunction solar cell with an efficiency of ~2 % under an AM1.5 simulated solar intensity of 100 mW/cm².
9:00 AM		C2-1-4 Bacterial Cellulose Membranes as Flexible Substrate for Organic Light Emitting Devices C. Legnani, W.G. Quirino (Inmetro - National Institute of Metrology, Standardization and Industrial Quality, Brazil); M. Cremona (PUC-Rio, Brazil); C. Vilani (Inmetro - National Institute of Metrology, Standardization and Industrial Quality, Brazil); H. Barud (IQ-UNESP, Brazil); C.A. Achete (Universidade Federal do Rio de Janeiro, Brazil); S.J.L. Ribeiro (IQ-UNESP, Brazil); V.L. Calil (PUC-Rio, Brazil) The developing of new kind of flexible optoelectronic devices is increasing as the number of applications, from electronic paper (e-paper) to medical sensors. Indium tin oxide (ITO) is a very attractive material for optoelectronic applications due to its useful properties such as high transmittance in the visible and the high electrical conductivity. In this work we investigate the possibility to deposit ITO films onto a particular bacterial cellulose membrane in order to be able to produce a flexible Organic Light Emitting Diode (OLED). Cellulose produced by acetobacter xylinum bacteria is markedly different from plant cellulose. It is produced as highly hydrated pure cellulose membrane displaying a nanometric network of nanowires allowing application from biomedical to optoelectronics. In the work, ITO films were deposited at room temperature onto the membrane using rf magnetron sputtering with a rf power of 30 W and at pressure of 8 mPa in Ar atmosphere. In order to decrease the membrane surface roughness and to improve the O₂ and H₂O impermeability a SiO₂ interlayer was introduced between the membrane and the ITO film. The average roughness obtained was 244 nm. The resistivity, the mobility and the carrier concentration were 4,90x10^-4 Ω cm, 8,08 cm²/V-s and -1,5x10²¹ cm^-3, respectively. Finally, three different OLED devices were fabricated using: common glass substrate; cellulose membrane with SiO₂ and without SiO₂.The relation between the total OLED luminance was 1 to 0,5 to 0,25. The results show the viability of using this particular membrane as flexible substrates in organic optoelectronic devices.
9:20 AM		C2-1-6 Electrochromically Switched, Gas-Reservoir Metal Hydride Devices with Application to Energy-Efficient Windows A. Anders, J.L. Slack, T.J. Richardson (Lawrence Berkeley National Laboratory) The application of electrochromic devices based on tungsten oxide has spread from the common use in rear-view mirrors to electrochromic windows for vehicles and buildings. Some alternative electrochromic materials have the promise of greater energy savings then those conventional systems mainly because they rely on the reflection of solar energy in the low-transmitting state, rather than absorption. In this contribution, we report about the development of a device system comprised of a MgNiMn alloy as the switchable layer and a solid, hydrogen-conducting electrolyte, both sandwiched between transparent conducting oxides (TCOs). The gas-facing TCO layer, also labeled as the counter electrode, contains small amounts Pd as a catalyst. The gap between glass panes of a dual-pane insulated glass unit is used as the hydrogen storage. This is safe because about 95% of the gas mixture is argon. The electrochromic and optical performance of the devices are investigated and conclusions are drawn on the potential for energy savings using such systems for commercial and residential buildings. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
9:40 AM		C2-1-7 PL and EL Characteristics in Various Bi-Activated Niobate-Based Oxide Phosphor Thin Films H. Fukada, S. Mtsui, K. Sahara, T. Miyata, T. Minami (Kanazawa Institute of Technology, Japan) This paper describes the photoluminescent (PL) and electroluminescent (EL) characteristics obtained in thin films of various Bi-activated niobate-based oxide phosphors using ternary compounds such as GdNbO₄ and YNbO₄ as well as multicomponent oxides composed of two ternary compounds as the host material. The phosphor thin films were prepared by either conventional or combinatorial r.f. magnetron sputtering deposition (r.f.-MSD). For example, GdNbO₄:Bi thin films were prepared on thick BaTiO₃ ceramic sheet substrates by conventional r.f.-MSD using a mixture of Gd₂O₃, Nb₂O₅ and Bi₂O₃ powders calcined at 1000°C in air as the powder target. The sputter depositions were carried out under the following conditions: atmosphere, pure Ar, Ar+O₂(2%) or Ar+H₂(5%); pressure, 6 Pa; and substrate temperature, 350°C. After deposition, the thin films were annealed in either an air, a pure Ar or an Ar+H₂(5%) gas atmosphere at 500-1000°C. The thin films postannealed at a temperature above approximately 800°C were identified as GdNbO₄, as evidenced from x-ray diffraction analyses. The obtainable PL and EL characteristics in GdNbO₄:Bi phosphor thin films were significantly affected by the deposition and postannealing conditions. For example, a blue emission (peaking at around 445 nm) in PL was observed from GdNbO₄:Bi thin films postannealed at a temperature above approximately 900°C in an Ar gas atmosphere. In particular, an intense blue emission in PL was obtained in a GdNbO₄:Bi thin film prepared in an Ar sputter gas atmosphere and postannealed at 1000°C in a pure Ar gas atmosphere. In addition, a bluish-green EL emission, corresponding to the CIE color coordinates of (x=0.29, y=0.44), was obtained in thin-film EL devices fabricated using GdNbO₄:Bi phosphor thin films postannealed under optimized conditions and driven by an ac sinusoidal wave voltage.
10:00 AM		C2-1-8 Electrical and Optical Behaviors of Cu₂O-Ag-Cu₂O Multilayered Thin Films P.W. Kuo (National Chung Hsing University, Taiwan); J.H. Hsieh (Mingchi University of Technology, Taiwan); W. Wu (National Chung Hsing University, Taiwan) Ag-Cu₂O (AC) and Cu₂O-Ag-Cu₂O (CAC) multilayers and Cu₂O single layer were prepared using DC-magnetron sputtering. For CAC, the thickness of Ag layer was controlled at 3, 5, 10 nm respectively. After deposition, some of these films were annealed using a rapid thermal annealing (RTA) system at 650°C for 3 minutes. A UV-VIS-NIR photometer and a Hall measurement system were used to characterize these films with and without RTA. The results show that, without annealing, the optical transmission is decreased with the increasing thickness of Ag layer, while the resistivity is decreased. After annealing both the transmission and resisvity are increased, possibly due to the clustering of Ag layers. From the absorption spectra, an additional absorption band in the visible light region is observed for all the annealed CAC films. A red-shift is observed with the decrease of Ag thickness.
10:20 AM		C2-1-9 Spray Pyrolysis Deposition and Electrochemical Properties of WO₃-Based Films K. Teshima, M. Fujisawa (Shinshu University, Japan); Y. Inoue (Nagoya University, Japan); T. Suzuki (Shinshu University, Japan); O. Takai (Nagoya University, Japan); S. Oishi (Shinshu University, Japan) Tungsten oxide (WO₃) and related materials are widely used in a variety of industrial fields because of their excellent properties. One important application of WO₃-based materials is the use as electrochromic films for window, display, sensor and optical switch. In those cases, the optical property allows them to be reversibly changed in their colors by applying a burst of charges. Electrochromic properties are greatly dependent on their structures of WO₃-based films. In this study, we report on the deposition of WO₃-based films via spray pyrolysis. Furthermore, WO₃-based film growth processes were studied by means of various microscopic techniques. WO₃-based films were deposited using an ultrasonic spray system. A variety of aqueous solutions including WO₃ was used as starting material for WO₃-based film deposition. Fluorine doped tin oxide (FTO) glass was used as substrate. The deposition temperatures were varied from 400 to 500°C. Micro- and nanotextured tungsten oxide-based films were successfully deposited on FTO glasses. The film structures obviously depended on the deposition conditions such as solution composition, solution concentration, deposition temperature and deposition time. Furthermore, the micro and nanotextured WO₃-based films showed good electrochromic properties.
10:40 AM		C2-1-10 Application of Low Resistivity Ga-Doped ZnO Films to 1-3 GHz Electromagnetic Interference Shielding T. Yamada, A. Miyake, H. Makino, N. Yamamoto, T. Yamamoto (Kochi University of Technology, Japan) Low resistivity Ga-doped ZnO (GZO) thin films have been studied for its application to an electromagnetic interference (EMI) shielding. GZO films were deposited on alkali-free glass substrate by ion plating using a direct current arc discharge technique, where the deposition condition is optimized at a substrate temperature of 473 K. The film thickness was varied in the range from 300 to 1500 nm. The shielding effectiveness (SE) of the as-deposited films was measured at a frequency range of 1-3 GHz in microwave region. All the films were well-aligned polycrystalline film with a preferential c-axis orientation perpendicular to the substrate. With increasing film thickness, the sheet resistance decreased from 6.6 to 0.8 Ω/sq. This reduction resulted from not only the increase in the film thickness but also the decrease in resistivity ( a minimum resistivity of 1.6 × 10^-4 Ωcm ) due to the improvement of Hall mobility. In relationship between the sheet resistance and SE, an increase in the SE from 34 to 46 dB at a frequency of 2.45 GHz was observed with decreasing the sheet resistance. In the film with the highest SE of 46 dB, optical transmittance was more than 70 % at a wavelength of 550 nm in the visible range. These data provide evidence that GZO films are useful as EMI shielding material.
11:00 AM		C2-1-11 Self Assembled Pb_1-xFe_xSe Nanoparticle / Si Heterojunctions A. Bhardwaj, P. Srivastava, H.K. Sehgal (India Institute of Technology Delhi, India) PbSe based ternary nanoparticles find application in optoelectronic devices. This invigorates synthesis of new PbSe based ternary materials. Pb_1-xFe_xSe (0.00 ≤ x ≤0.02) nanoparticle thin films have been deposited on quartz and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with 0.00≤x≤0.02 have been studied. Pb_1-xFe_xSe nanoparticle/Si heterojunctions have been investigated. The films grow as single-phase ternary alloy of the type Pb_1-xFe_xSe with rocksalt structure. Average grain size in the films grown at a fixed bath temperature (T_b= 85°C) is observed to decrease from 72 nm to 22 nm with increase in Fe concentration from x = 0.00 to x = 0.02. Lattice parameter is observed to increase from 6.12 Å to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.02. Pb_1-xFe_xSe nanocrystalline films show direct optical band gaps (E_g) that increase with decrease in grain size and have values larger than 0.28 eV of bulk PbSe. The observed blue shift in the films originates from quantum confinement in the nanograins. Excitonic absorption is observed in the Pb_1-xFe_xSe films.@Pb_1-xFe_xSe nanoparticle / Si heterojunctions show a rectifying behavior. On illumination with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light could be due to carrier multiplication by Auger electron emission, direct generation of multiexcitons and impact ionization.