Papers

ICMCTF2007 Session B1-2: Sputtering Coatings and Technologies

Wednesday, April 25, 2007 8:00 AM in Room Golden West

Wednesday Morning

Start	Invited?	Item
8:00 AM		B1-2-1 Pulsed DC Titanium Nitride Coatings for Improved Tribological Performance and Tool Life P.J. Kelly (Manchester Metropolitan University, United Kingdom); T. Vom Braucke (Swinburne University of Technology, Australia); Z. Liu (Manchester Metropolitan University, United Kingdom); R.D. Arnell (University of Central Lancashire, United Kingdom); E.D. Doyle (Swinburne University of Technology, Australia) Titanium nitride has long been used as a hard, wear resistant coating material, but it has never been regarded as a low friction material. Recent results though, suggest that TiN coatings deposited by pulsed magnetron sputtering (PMS) can have significantly enhanced tribological properties, in particular, significantly lower coefficients of friction, in comparison with films deposited by continuous DC processing. This paper, therefore, reports the results to date from a detailed study of the tribological properties of TiN coatings produced by PMS. Coatings were deposited under varying conditions of pulse frequency and substrate bias (DC and pulsed). The structural properties of the coatings were investigated by SEM and XRD, whilst the physical and tribological properties were determined using scratch adhesion testing, thrust washer wear testing and hardness testing. In addition, batches of 6.35mm diameter HSS twist drills were also coated by PMS and continuous DC processing. The performance of these drills was assessed in tool life tests, in which holes were repeatedly cut in M200 steel. Failure was adjudged to have occurred when the outer corner flank wear land extended to the full margin width and the tool emitted an audible screech. The results confirm that TiN coatings produced by pulsed processing consistently outperform those produced by continuous processing, in terms of tribological properties and tool life.
8:20 AM		B1-2-2 Mechanical Characterization of CrN and WN Coatings Prepared by Pulsed DC Magnatron Sputtering Y.Z. Tsai, J.G. Duh (National Tsing-Hua University, Taiwan) Chromium nitride and tungsten nitride coatings were grown on the silicon (100) and stainless steel substrate by pulsed DC magnetron sputtering. The pulsed frequency of CrN and WN coatings was controlled in the range between 0.2 to 20 kHz. The substrate bias was applied with a DC bias unit during deposition from 0 to 600V. The cross-sectional microstructure of these coatings was investigated by scanning electron microscopy (SEM). The nano-scratch tester was employed to evaluate the adhesion and crack behavior of CrN and WN coatings with different substrate bias. The mechanical performance of the coatings deposited with higher pulsed frequency was superior than that with lower pulsed frequency in microhardness and scratch test. In addition, the crack mechanism of both CrN and WN coatings evaluated by nano-scratch tester was proposed and discussed.
8:40 AM		B1-2-3 High-Performance Ceramics Based on Cr-Al-Si-O Compounds by High Ionization Pulsed Sputtering Technique (H.I.P.®) R. Cremer, S. Kyrsta, M. Alunovic (CemeCon AG, Germany) High Ionization Pulsed Sputtering Technique (h.i.p.®) are the foundation of economical, high-quality coatings - whether for tools or components. In this study will be shown a new type high-performance ceramics in the systems Si-O, Cr-O and Al-O combined the advantages of smooth layers, high gas ionization and high metal ionization. The work is carried out exactly as required by the application: extremely smooth, droplet-free and with the lowest possible residual stresses measured by means of x-ray diffraction, scanning electron microscopy and energy dispersive x-ray analysis as well as nanoindenter, Vickers, Rockwell and roughness measurements.
9:00 AM		B1-2-5 The Influence of Nitrogen Additions on the Nanostructure and Properties of Sputtered Ti-Al-B Films C. Rebholz (University of Cyprus); MA Monclus (National Physics Laboratory, United Kingdom); M.A. Baker (University of Surrey, United Kingdom); P.N. Gibson (Joint Research Centre, Italy); P.H. Mayrhofer (Montanuniversität Leoben, Austria); A. Leyland, A. Matthews (University of Sheffield, United Kingdom) Nanocomposite Ti-Al-B and Ti-Al-B-N films (with ~10 at.% nitrogen), containing ~30 at.% of titanium with different B/Al ratios, were synthesized by co-sputtering from TiAl and TiB₂ targets onto Si (100), AISI316 and glass substrates at 150°C. The film stoichiometry, relative phase composition, nanostructure and mechanical properties were determined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM), in combination with nanoindentation measurements. XRD and TEM studies revealed amorphous and nanocrystalline structures, respectively, for films with low (TiAl-rich) and high (TiB₂-rich) B/Al ratios; the incorporation of nitrogen was found to decrease the crystallinity and TiB₂ grain size from ~3-4 nm to ~2-3 nm. TiB₂ and Al bonds were observed in Ti-Al-B films, while nitrogen additions resulted in the formation of additional Al-N and Ti-N bonds. Hardness and elastic modulus increased from 12 to 35 GPa and 185 to 340 GPa, respectively, with increasing TiB₂ phase fraction for Ti-Al-B films. Additions of nitrogen led to tougher (more resilient) films, resulting in reduced film and counterface wear in reciprocating sliding wear experiments. Thermo-gravimetric analysis (TGA) revealed the on-set of oxidation to occur at temperatures between ~650 and ~800°C for TiB₂- and TiAl-rich Ti-Al-B films, respectively; these values increased to ~750 and ~850°C for Ti-Al-B-N films.
9:20 AM		B1-2-6 Development of Reactively Sputtered AlN Thin Films for High Temperature Online Stress Monitoring S. Bhattacharyya, J.J. Moore (Colorado School of Mines); S.S.N. Bharadwaja, S. Trolier-McKinstry (Pennsylvania State University) In this article we report the growth and characterisation of AlN thin films grown by dc and pulsed dc reactive sputtering with a view to embed them in an engineered surface for real-time stress sensing. The piezoelectric material was deposited at low temperature, with a preferred orientation along the polar c-axis. We studied the effect of various processing parameters on the electrical and piezoelectric properties. With increasing film thickness, the leakage current decreased rapidly, and we have tried to relate this to the surface effects, mainly the surface topography, which could introduce a large inhomogeneity in the electric field. Also, the bottom electrode and the post deposition annealing temperature was found to have a pronounced effect on the crystallinity (and surface texture) of the AlN over layer. The effect of pulsing the target was found to alter the growth direction completely, thereby introducing a high residual stress. The possibility of tuning this residual stress was explored by varying the pulsing parameters. The transverse piezoelectric properties were studied by subjecting the film deposited on a flexible substrate to pseudo static and dynamic mechanical loading and measuring the out-of-plane voltage. The surface and the bulk composition of the film exhibited very interesting features, which we believe have a close correlation with the resulting electrical properties. This research program is concerned with developing a generic processing route to optimise the deposition of AlN thin films with the best out of plane electromechanical response.
9:40 AM		B1-2-7 Effects of Sputtering Conditions on Mo Bottom-Electrode Layer and Its Influence on the Subsequently Sputtered AlN Piezoelectric Thin Film J.S. Cherng, T.Y. Chen, C.M. Lin (Mingchi University of Technology, Taiwan) Various sputtering conditions were employed to explore the feasibility of depositing a suitable layer of Mo film, as a bottom electrode of an FBAR, onto a (100)-oriented Si substrate. A highly (110)-textured Mo film, with its FWHM of rocking curve as small as 1.14°, could be made when a 200 Å thick primer layer of (0002)-textured AlN film was pre-deposited between Si and Mo. In turn, the degree of (0002) texture of a subsequently deposited AlN piezoelectric film, about 1 µm in thickness, was found to be largely decided by the degree of (110) texture of the Mo film beneath it. The variation of residual stress of these films was also examined and discussed accordingly.
10:00 AM		B1-2-8 Electrical Characterisation of AlCuMo Thin Films Prepared by DC Magnetron Sputtering M. Birkett, J. Brooker (TT Electronics Welwyn Components Limited, United Kingdom); R. Penlington, A. Wilson, K. Tan (Northumbria University, United Kingdom) AlCuMo films were prepared on Al₂O₃ substrates at room temperature as a function of Mo concentration by DC magnetron sputtering and were then annealed at various temperatures in air and N₂ atmospheres. The effect of annealing temperature on the structural and electrical properties of the films was systematically investigated. Decrease in Mo content produced an increase in temperature co-efficient of resistance (TCR), a decrease in resistivity (Ï) and an improvement in long term stability (â^?Î©/Î©) of the films. SEM studies of the structures revealed that crystalinity was significantly improved as annealing temperature increased. TCR varied from negative to positive and further improvements in resistance stability of the films were also achieved through increasing annealing temperature in both air and N₂ atmospheres. A temperature region is proposed where ~near zeroâ?T TCR ( ±5ppm/°C) and long term stability of better than 0.2% can be realised.
10:20 AM		B1-2-9 Investigation of Electrochromic Properties of Tungsten Oxide Films Prepared by Reactive Magnetron Sputtering H.-H. Lu (National Chin-Yi Institute of Technology, Taiwan) The electrochromism have been extensively investigated due to their potential applications such as smart window of architecture and automobile glazing to save energy and modulate the transmittance of light and solar radiation. The objective of this study is to investigate the effects of sputtering conditions on the composition, microstructure, and electrochromic properties of tungsten oxide films prepared by d.c. reactive magnetron sputtering. Experimental results showed that the oxygen contents of the films increased with the oxygen flow rate. In addition, the films showed good reversibility at high oxygen flow rate. The transmission change between colored and bleached states at a wavelength of 550 nm was 61.4% as the oxygen flow rate was 30 sccm. The film obtained high optical density, and coloration efficiency was 7.79cm²/C. It was also found that the crystallinity of films was obtained at the substrate temperature larger than 300°C. As the substrate temperature increasing from room temperature to 350°C, the optical band gap changed from 3.64 to 3.08eV due to the existence of oxygen vacancies or larger grain size. The crystalline tungsten oxide films showed high reflectance in the near IR region. The transmittance of colored and bleached was reproducible after 100 cycles. It means the tungsten oxide films deposited by d.c. reactive magnetron sputtering had good quality stability.
10:40 AM		B1-2-10 Thermal Stability of Sputtered W-Si-N Coatings K. Fadenberger, C. Rebholz (University of Cyprus); M.A. Baker (University of Surrey, United Kingdom); R. Daniel (University of Leoben, Austria); J. Musil (University of West Bohemia, Czech Republic); P.H. Mayrhofer, C. Mitterer (University of Leoben, Austria) Increasing requirements on hard coatings in high performance machining processes, such as high-speed and dry cutting, demand the further development of already well established coatings, resulting in a search for new materials to be employed as protective coatings on tools. Thermal stability is a key parameter for coatings in this field. The aim of this work was therefore to investigate the thermal stability of high silicon containing W-Si-N coatings. Coatings were deposited onto various substrate materials from a powder metallurgically produced WSi₂ target (99.95 % purity) by unbalanced D.C. magnetron sputtering in Ar/N₂ mixtures at 490°C. Different structures were observed by varying the partial nitrogen pressure. The total pressure was kept constant, while the N₂ fraction was varied between 0 and 0.57. For characterization of thermally activated processes, a combination of differential scanning calorimetry (DSC) and biaxial stress temperature measurement (BSTM) was used. Additionally X-ray diffraction (XRD) and Martens hardness (HM) measurements were employed to characterize the coatings in the as-deposited state and after different annealing treatments under vacuum from 800°C to 1100°C. The chemical composition was evaluated by X-ray photo electron spectroscopy (XPS), and scanning and transmission electron microscopy (SEM, TEM) studies were employed to characterize morphological changes of the coatings caused by the different annealing treatments. The thermal stability was found to be dependent on the coating structure, and values between ~700°C and ~ 1000°C were observed, before decomposition in N₂, WSi₂, W₅Si₃ and WSiNi (Ni diffusing from substrate) occurred. The obtained results demonstrate how the thermal stability of W-Si-N hard coatings can be further improved.
11:00 AM		B1-2-11 Sheet Resistance Effect of the Flexible ITO/PET Substrate on the Electrochromic Performance of Deposited WO₃ Layer Y.L. Yan, P.C. Chen, Y.F. Lan, J.L. He (Feng Chia University, Taiwan) Flexible electrochromic device has been drawn great interest due to its versatile applications for smart windows, displays and reflectance controllable mirrors. Flexible transparent conducting substrate such as ITO/PET is usually considered as the electrode, with however very little attention been paid to its effect on the electrochromic performance, sheet resistance in particular. This study is to reveal the electrochromic behavior of tungsten oxide layer, coated on flexible ITO/PET substrate via reactive magnetron sputter deposition. Flexible ITO/PET substrate, with a sheet resistance of 100 Ω/square, 250 Ω/square, 350 Ω/square and 500 Ω/square, and ITO glass for comparison, with a sheet resistance of 3 Ω/square and 100 Ω/square, respectively were chosen as substrates. The relationship between electrochromic performance such as initial current of coloring J_ic (J_ib for bleaching), optical transmission difference ΔT as well as response time τ (τ_coloring and τ_bleaching) of the deposited tungsten oxide and the sheet resistance of the ITO layer were investigated. Experimental results show that as the sheet resistance changes from 500 Ω/square to 3 Ω/square, the J_ic increases from 1.7 mA to 34.8 mA and the J_ic increases from 3.2 mA to 57 mA. This corresponds to an increasing ΔT from 5.1 % to 28.8 %. Meanwhile, τ_coloring decreases from 43 s to 25 s and τ_bleaching reduces from 26 s to 6 s. the significant influence of the ITO sheet resistance is ascribed to the carrier mobility of the electron, where high electron mobility in the low sheet resistance ITO film enables fast charge exchange between tungsten oxide layer and ITO layer.