Papers

ICMCTF2006 Session H2-2: Thin Films for Next Generation Devices

Wednesday, May 3, 2006 1:30 PM in Room Terrace Pavilion

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		H2-2-1 Effect of Various Substrates on Electrical Resistance and Thermo-Electric Power of Physical Vapor Deposited Tellurium Thin Film S.K. Rawal, H.N. Shah (Charotar Institute of Technology-Changa, India); B.R. Rehani (Faculty of Technology & Engineering-Vadodara, India); N.C. Chourasik (Charotar Institute of Technology-Changa, India) The materials because of their Nanocrystallite size exhibits entirely different properties than bulk specially when they are prepared by PVD technique in different thickness of nano sizes on various substrates. The type & surface characteristics of substrate also play vital role on properties apart from other preparation parameters. Tellurium thin films being semi-conducting in nature have applications in Thermopiles, Sensors, Infrared detectors, etc. In the present work Tellurium thin films (99.9% pure) of various thickness ranges (500 to 5000nm) were deposited onto well cleaved/cleaned substrates like Glass slides, Cover slips, Mica, Mylar and Commercial Formica by PVD technique at an air residual pressure of 10^-4 Pa with deposition rate of 1.0-1.5nm/sec.The thickness and rate of deposition were monitored by Quartz Crystal Monitor. All the thickness on various substrates are polycrystalline (confirmed by X-ray diffraction) & show P-type of conductivity. Before Tellurium film deposition, silver contacts of thickness greater than 1000nm were prepared on various substrates at 10^-3Pa pressure in vacuum. The TEP & resistance variation studies were carried out on as deposited & annealed films. The films were vacuum annealed at a temperature of 50^oC for half an hour at a pressure of 10^-1Pa. It was observed that TEP & resistance of as deposited and annealed films were thickness and substrate dependent. The annealed film shows lower values than as deposited ones because of the fact that defects incorporated during deposition are annealed out & leads to recrystallization. However in some cases the decrease in resistance & TEP is observed and may be due to substrate surface nature or oscillating thickness dependent nature of material. In lower thickness ranges the oscillating behavior exists which decays when thickness is increased. Depending on the substrate material there is one critical thickness at which TEP is Maximum.
1:50 PM		H2-2-3 Effect of Mechanical Strain on the Performance of P-Channel Poly-Silicon TFT Fabricated on Metal Foil Substrate M.-C. Wang (National Tsing Hua University, Taiwan); T.-C. Chang (National Sun Yat- Sen University, Taiwan); P.-T. Liu (National Chiao Tung University, Taiwan); J.-R. Chen (National Tsing Hua University, Taiwan); S.-W. Tsao (National Sun Yat-Sen University, Taiwan) The P-type poly-Si TFTs were successfully fabricated at temperatures of 200°C. After treated by 450°C furnace activation , the average hole mobility of TFT fabricated at 200°C could be34.2 cm² /V-s. The P-type poly-Si TFTs were mechanically strained to investigate electrical characteristics, using inward (compression) or outward (tension) cylindrical bending method. The effect of mechanical strain on the performance of P-type poly-Si TFTs was studied under uniaxial compressive and tensile strain with orientation parallel to the TFT source-drain current path. The mobility, and channel conductance had a notable change under the mechanical strain, originated from the change in the material characteristic under bending strain.
2:10 PM		H2-2-4 Fabrication of Copper Gate Electrode by Selective Electrodeposition Through Mask for Thin-Film Transistors S.-N. Jenq, C.-C. Wan, Y.-Y. Wang (Tsing-Hua University, Taiwan); H.-W. Li, P.-T. Liu (National Chiao Tung University, Taiwan); J.-H. Chen (Quanta Display Inc.) Copper metallization has been used extensively for the fabrication of electronic parts and devices owing to its good electric conductivity being only second to silver. Recently, owing to the successful experience of copper metallizations in fabricating ULSI circuits, copper metallization with electrodeposition also has attracted a great deal of attention for the future demand of AM-LCDs. However, most studies focus on subtractive process including panel deposition on copper seed and etching of copper. This work developed additive process consisting of Cu deposition through mask and etching of conductive layer. The conventional conductive layer used in Cu electrodeposition for ULSI circuits is copper seed. It is difficult to selectively etch copper seed without etching deposited copper. Therefore, it is convenient for selectively etching to replace copper seed by a conductive barrier layer. Nickel with good electric conductivity has been used widely as a barrier layer that prevents Cu diffusing into Au for PCB. In this study, Cu electrodeposition through mask on a nickel barrier layer was developed. It was found that Cu deposit on a nickel barrier layer is black copper oxide without suitable pretreatment prior to electrodeposition. After activation pretreatment in acid sulfate solution, the Cu deposit has a bright color and good adhesion on a nickel barrier layer. Moreover, the influence of individual organic additive (PEG, SPS) on the sidewall shape of Cu pattern was identified during electrodeposition on a nickle barrier. A synergy-effect shows up when both PEG and SPS are present owing to the competition of the two behavior of organic additive in the formation of the pattern shape. Furthermore, the copper gate electrode for TFTs was fabricated after selectively etching of nickel barrier. The electric property of Cu gate was also investigated.
2:30 PM		H2-2-5 Development of a New Magnetoelastic Thin Film Gas Sensors for Humid Environment R. Zhang, I. Tejedor-Tejedor, M. Anderson (University of Wisconsin-Madison) A new magnetoelastic thin film gas sensors was developed for humid environment. Nano particles of Pt-TiO₂ was used as coating materials on the magnetoelastic foils. Impact of elasticity of coating layer on magnetoelastic Pt-TiO₂ thin-film sensors was investigated. Various direct current at peak voltage and at base frequency for the magnetic fields were used to detect change of resonant frequency in a change of adsorbed mass. An elasticity model was developed to detect the adsorbed mass by removing the impact of elasticity of sensor. The model considers two foils with different lengths, but with same material of bare foil, sputter layer, and coating layer under identical laboratory condition and procedure to provide equal elasticity and density. The adsorbed mass on the two foils can be solved under assumption of the ratio of adsorbed mass on the two foils equal to the length ratio of them, by using lengths, initial mass, and initial resonant frequency of the two foils and resonant frequency after adsorption. The calculated mass changes in two foils are in general agreement with the measured mass change on the sensors. After remove the elasticity impact on the frequency, adsorbed mass can be determined from the change of frequency. The elasticity model eliminates the necessary to simultaneously detect elasticity and adsorbed mass, which makes the thin-film sensor in gas measurement with consideration of humidity practicable.
2:50 PM		H2-2-6 Amorphous Germanium Thin Films for Negative Electrode in Lithium-ion Microbatteries B. Laforge (CEA/DRT/DTEN/STN/LTME, France); A. Billard (Ecole des Mines, France); R. Salot (CEA-Grenoble/DRT/DTEN/STN/LTME, France) Since ten years, there exists a considerable need for thin-film solid state microbatteries as power sources for small electronic devices such as MEMS. The lithium metal has been usually used for the negative electrode in thin-film microbatteries. However its low melting point (181°C) and strong reactivity with air and moisture limit its industrial applications. Therefore its substitution by an alternative material with a better chemical and thermal stability permits to overstep the today limitations. The binary lithium alloys have been extensively studied and a good candidate is Li-Si witch has a theoretical capacity of 4200 mAh/g. Its major drawback is its poor cyclability caused by mechanical cracking due to the volume expansion during the insertion of lithium. But its results in thin film are more promising. Although the Li-Ge system has only 40% of the theoretical capacity per gram of Li-Si, it can accommodate as many lithium atoms as the silicon (Li_4.4Ge). Moreover the diffusivity of lithium in germanium (2.14 x 10^-7 cm²/s) is very greater than in silicon (1.47 x 10^-8 cm²/s) at 360°C. In these conditions germanium seems to be a promising candidate as anode material. During this study the germanium thin-films were prepared by radio-frequency magnetron sputtering in argon atmosphere at room temperature. The structure and morphology of theses films were analysed by X-ray diffraction and FEG-SEM. Germanium electrodes were tested by cycling in coin cell with liquid electrolyte and also in a solid state stack. A design of experiment was realised to determine the best conditions of Ar pressure and rf power in a view of electrochemical performances. Finally their capacities, cyclabilities and power capabilities, measured using lithium as counter electrode, are discussed and related to the sputtering parameters and the structure of the films.
3:10 PM		H2-2-7 Fabricating Highly Active Mixed Phase TiO₂ Photocatalysts by Reactive DC Magnetron Sputter Deposition L. Chen (Northwestern Univeristy); K.A. Gray, M.E. Graham (Northwestern University) A study of the role of solid phase interfaces in the photocatalytic behavior of TiO₂ has been undertaken utilizing reactive magnetron sputtering to create multilayer and mixed phase coatings consisting of the anatase and rutile phases. We show that sputter deposition provides excellent control of phase and interface formation for this study. We have explored the range of phase synthesis that is controlled through the process parameters of pressure, oxygen partial pressure, target power, substrate bias (rf), deposition incidence angle, and post annealing treatment. We have successfully made multilayer anatase/rutile coatings and mixed phase coatings. These coatings have been characterized with AFM, SEM, TEM, and XRD to determine surface morphology, phase distribution and phase content. The performance as photocatalytic surfaces was measured and compared (normalized for surface area) to other materials, including Degussa P25 powder, pure sputtered anatase, and sol-gel deposited anatase. The sputtered mixed phase materials were shown to be far superior to the commercial standard and sol-gel anatase in the gas phase degradation of air pollutant acetaldehyde under UV illumination. The mechanism of charge separation and transfer has been shown to depend strongly on the anatase-rutile interface through EPR measurements in our laboratory. The nature of these interfaces is under investigation. The work continues as we explore other interface effects by depositing on carbon nanotubes. These performance results will also be presented.