Papers

ICMCTF2002 Session H4-2: Novel Materials and Processes

Thursday, April 25, 2002 1:30 PM in Room Royal Palm 4-6

Thursday Afternoon

Start	Invited?	Item
1:30 PM		H4-2-1 Integrated TiC Coatings for Moving MEMS G. Radhakrishnan, R. Robertson, R. Cole, P.M. Adams (The Aerospace Corporation) The technology for MEMS is fairly well advanced as evidenced by the large number of MEMS devices now being fabricated. However, MEMS designs that require sliding contact can be subject to rapid wear, which makes these devices unsuitable for long term operation. While "moving" MEMS devices such as microgears, micromotors, switches, and actively aligned optical devices can be fabricated with the current technology, their reliability and performance remain an open question. The number of MEMS applications would be significantly increased if there were reliable methods to prevent degradation by wear and friction effects that are responsible for the short functional life of sliding surfaces in contact. The application of wear-resistant coatings to MEMS devices offers the potential of addressing the reliability of moving MEMS devices. However, coating non line-of-sight concealed surfaces in fully released 3D-MEMS structures, especially those behind micron-sized apertures is a difficult problem to overcome with most deposition techniques. A practical and viable solution to this problem is the direct integration of wear-resistant into the MEMS fabrication process. Using this approach we have inserted pulsed laser deposited (PLD) titanium carbide (TiC) coatings between critical poly-Si interfaces during fabrication of a MEMS device. This paper will describe Aerospace's MEMS fabrication process (AIMMOS) and the details of inserting TiC coatings into the fabrication sequence to protect key sliding Si surfaces in MEMS motors. The hybrid PLD-AIMMOS technology is an effective way of inserting wear-resistant coatings such as TiC into the MEMS fabrication scheme.
2:10 PM		H4-2-3 Uniformity and Efficiency of Coatings Applied to Cylindrical Fibers Via Electron Beam Directed Vapor Deposition Y. Marciano (The Nuclear Research Center-Negev, Israel); D.D. Hass, H.N.G. Wadley (University of Virginia) High rate, highly efficient vapor deposition processes are desired for the application of films onto small diameter (<500 µm) fiber substrates. Here, a low vacuum Direct Vapor Deposition (DVD) approach is explored. In DVD, material is efficiently evaporated using an electron beam and then directed towards a substrate using a carrier gas. By altering the chamber pressure and the carrier gas speed, the vapor flux distribution can be controlled. These process parameters can then be tailored to yield a focused vapor leading to high localized vapor densities and a short mean free path resulting in significant non-line-of-sight coating. These attributes result in a high rate coating process and allows for uniform deposition profiles without rotation of the fiber. The effect of the chamber pressure, carrier gas speed and material type are presented. Multi-scale direct simulation Monte Carlo (DSMC) simulations are used to determine the fundamental role of the process parameters on the coating uniformity. By employing high chamber pressures (0.13 mbar) and low carrier gas speeds (< 100 m/s), uniform coating of aluminum onto stainless steel fibers have been achieved.
2:30 PM		H4-2-4 Ion Beam Induced Enhanced Adhesion of Films Deposited on PTFE L.A. Guzman, B.Y. Man, A. Miotello, M. Adami (University of Trento, Italy); P.M. Ossi (Polytechnic of Milan, Italy) Considerable efforts have been made to improve the physical-chemical properties of a large of number of polymers by using ion beam implantation, and the enhancement of various properties has been attributed to various mechanisms like chain scission, cross-linking and carbonization. It was observed that ion implantation can also improve the properties of polytetrafluoroethylene (PTFE) but the mechanisms for such enhancement are not completely clear yet. In this work we have studied the adhesion of Au thin films on PTFE. The substrates were implanted with 160 KeV energetic N⁺ ions to a dose range between 1x10¹⁵ and 4x10¹⁶ ions/cm². The implanted samples were examined by visible (514,5 nm) Laser micro-Raman and FT infrared (1064 nm) Raman spectroscopy. Our experimental results show that ion implantation on PTFE leads to the splitting of weaker C-C bonds and double bonds C=C are produced at higher doses. Some aspects of the basic mechanisms underlying the large change in wettability induced in this material by ion bombardment are discussed. After this pretreatment, the specimens were further coated (using a sputtering machine) with 150 nm thick, Au films. Adhesion properties of the films were examined using a scratch-tester in conjunction with scanning electron microscopy. It was observed that without the pretreatment, the coatings are poorly adherent. On the contrary a strong adhesion enhancement is observed in the pre-treated samples.
2:50 PM		H4-2-5 Characteristics of Ultra Water-repellent Films Prepared by Plasma-enhanced CVD Using Trimethylmethoxysilane O. Takai (Nagoya University, Japan); Y.Y. Wu (Aichi Science & Technology Foundation and Nagoya University, Japan); Y. Inoue, H. Sugimura (Nagoya University, Japan) High water repellency is required for glass, plastics and metals in many industrial applications. When the contact angle of a water drop is more than about 150 degrees, we can say that this state is ultra water repellency or super water repellency. This paper reports on the characteristics of ultra water-repellent thin films prepared at low substrate temperatures by microwave plasma-enhanced CVD using mixtures of trimethylmethoxysilane (TMMMOS) and Ar as source gases. The evaluation of water repellency, optical transmittance, surface morphology, chemical composition and mechanical properties of the deposited films is studied. The contact angle increased with the total pressure and the maximum angle was about 160 degrees. The optical transmittance of the deposited films was more than 80 % in the visible region for coated glass and plastics. We measured the surface roughness by AFM and FESEM and the states of water drops on water-repellent films by ESEM. We discuss the surface morphology of the deposited films in connection with ultra water-repellency and transparency.
3:30 PM		H4-2-7 Resonant Infrared Pulsed Laser Deposition of Polymer Thin Films D.M. Bubb (Seton Hall University); J.S. Horwitz (US Naval Research Laboratory); M.R. Papantonakis, R.F. Haglund, Jr. (Vanderbilt University) Resonant picosecond-pulse, mid-infrared laser irradiation has been shown to ablate glassy and crystalline solids with high efficiency and low collateral damage. We have extended this concept to show that resonant infrared (IR) pulsed-laser deposition (PLD) is an effective method for depositing polymer films with physical and chemical structure as well as optical properties virtually identical to those of the bulk starting material . This contrasts sharply with PLD at ultraviolet (UV) wavelengths, where deposited polymer material can be significantly degraded. In our experiments, the output of a pulsed infrared, free electron laser with microsecond bursts of picosecond micropulses was tuned into resonance with various vibrational modes in the organic starting material and the vapor was collected on a room-temperature substrate. For polyethylene glycol (PEG, MW 1450) the laser was tuned to either C-H or O-H stretching modes at 2.9 and 3.4 µm, respectively. The properties of the deposited film were determined using infrared absorption spectroscopy and mass spectrometry. When the infrared laser was detuned from resonance, the structure and optical properties of the deposited PEG film were significantly altered, showing that the off-resonance ablation process thermally damages the polymer. In the deposition of PEG, the fluence dependence of the deposition rate for 2.9, 3.45 and 8.96 µm irradiation (O-H, C-H and C-O bands respectively) are significantly different, demonstrating mode specific behavior in the vaporization mechanism. In this system, it is most efficient to excite the weak, terminal O-H absorption band to deposit the maximum amount of material indicating the importance of intermolecular bonding in the vaporization process. RIR-PLD films of polystyrene (PS) and Teflon are functionally identical to the target material, with some fractional changes in the polymer molecular weight of the film compared to the target material. RIRPLD represents a fundamentally new approach to the growth of polymer thin films. The mechanism of ablation appears to be explosive vaporization by rapid vibrational excitation. Because of the macropulse structure of the free-electron laser, the number of vibrational quanta deposited per macropulse is extremely high. Some evidence for nonlinear absorption has already been observed as weak, visible emission can be observed in the RIR-PLD of some polymer materials. In contrast to the photochemical mechanism typical of UV ablation, the majority of the evaporated material seems to remain in the ground electronic state. The technique appears promising particularly for biomedical and electronic applications of polymeric and organic thin films. ¹D. R. Ermer, M. R. Papantonakis, M. Baltz-Knorr, D. Nakazawa and R. F. Haglund, Jr., Appl. Phys. A 70, 633-635 (2000). ² D.M. Bubb, J.S. Horwitz, R.A. McGill, D.B. Chrisey, M.R. Papantonakis, R.F. Haglund Jr. and B. Toftmann Applied Physics Letters 79, 2847-2849. (2001) ³ D. M. Bubb, M. R. Papantonakis, J. S. Horwitz, R. F. Haglund, Jr., B. Toftmann, R.A. McGill, and D. B. Chrisey, accepted for publication Chemical Physics Letters.