Papers

ICMCTF1998 Session C1-2: Recent Advances in Optical Coated Materials (2)

Monday, April 27, 1998 1:30 PM in Sunset Room

Monday Afternoon

Start	Invited?	Item
1:30 PM		C1-2-1 Preparation of Low-Reflective Black Thin Films of Copper Oxide for Color Filter of Multi-colored Liquid Crystal Display O. Takai, H. Matsuda, Y. Inoue (Nagoya University, Japan) A low-reflective black film with large absorbance is used for a color filter of multi-colored liquid crystal display (LCD). The black film is important for the color filter as a black matrix to separate red, green and blue areas clearly and increase the contrast. Now chromium and chromium oxide films are used as metallic black films for this purpose. Recently the chromium-related materials have been avoided because of their environment conscious problems. The development of a new black material, therefore, is required in the LCD industry instead of the chromium-related materials. This paper reports on the preparation of low-reflective black thin films of copper oxide with graded composition by dc reactive ion plating. We evaporated metallic copper by resistant heating in the dc argon-oxygen plasma and obtained copper oxide films on glass substrates. The film composition was controlled by changing the dc power. The film thickness was fixed at about 150 nm. We measured the optical density and the reflectance of the deposited films by double-beam spectroscopy. We determined the film structure by X-ray diffraction and the film composition by X-ray photoelectron spectroscopy. The copper oxide film with graded composition, 150 nm thick, showed the optical density over about 3 and the reflectance at the glass surface below about about 10% in the visible region. This film also showed the good adhesion. The graded copper oxide film can be used as a black matrix material.
1:50 PM		C1-2-2 Laser Induced Chemical Vapor Deposition of Optical Thin Films on Curved Surfaces S. Tamir, S. Berger (Technion, Israel Institute of Technology, Israel); K. Rabinovitch (Electro-optic Industries, Ltd., Israel) Laser induced chemical vapor deposition (LPCVD) of silicon nitride and silicon dioxide single and double layers have been investigated using Excimer laser operating at a wavelength of 193 nm. The composition of silicon nitride which was formed in SiH ₄/NH₃ gas mixture was nearly stochiometric having a refractive index of 1.8-1.9 and contained a small amount of hydrogen. Deposition of silicon dioxide was investigated using SiH₄ / N₂O. Using this gas mixture the films composition depended strongly upon the SiH₄ / N₂O ratio. At high ratio the film formed was silicon oxynitride, which contained both Si-N and Si-O bonds. The film also contained small amounts of Si-H bonds. Decreasing SiH₄ / N ₂O ratio led to the formation of pure silicon dioxide with a refractive index of 1.45. A double layer coating of both silicon nitride and silicon dioxide resulted in the formation of antireflection coating with a reflectivity of about 0.5% at 750 nm.
2:10 PM		C1-2-3 Electrochromic Coatings - Applications and Manufacturing Issues N. O'Brien, B.P. Hichwa (Optical Coating Laboratories, Inc.) Electrochromic (EC) coatings, thin films that change their optical absorptance or reflectance as a function of injected ions (typically H⁺ or Li⁺ species), are an area of research and development that has received considerable attention from academia, industry and government laboratories. OCLI has been actively involved in the development of transmissive proton-based electrochromic devices for several commercial applications. In this paper, we focus on two applications: architectural glazings and ophthalmic eyewear. Each provides its own set of challenges, ranging from coating on large area glass to small area curved plastic. We review the benefits of electrochromics for those applications and report on the technological and manufacturing challenges involved. Furthermore, we show OCLI's recent advances in producing low temperature all-sputtered EC devices. The latter is necessary for 1) Coating EC devices on temperature sensitive substrates and 2) Transferring the process into a high volume in-line sputtering platform
2:50 PM		C1-2-5 Optical and IR Transmission of Micromachined Single Crystal 3C Silicon Carbide Thin Films for Micro-optomechanical Applications J.F. Klemic (Case Western Reserve University); J.M. Sirota (University of Maryland Baltimore County); C.A. Zorman, M. Mehregany (Case Western Reserve University) Silicon carbide is a well established material for harsh chemical, high wear and high temperature industrial applications. In addition, SiC is a semiconductor with developing utility for high power, high temperature and radiation resistant electronics.¹ Research is on-going to develop SiC for micro-electromechanical systems (MEMS). Measurements of mechanical properties of micromachined SiC thin films have been reported.² This paper reports optical and IR transmission measurements of micromachined 3C-SiC thin films. Thin films of single crystal 3C-SiC have been grown on 4 inch silicon wafers via an epitaxial APCVD process. ³ Films range in thickness from 1 to 2.5 microns. Wafers have been micromachined, resulting in free-standing, single crystal SiC diaphragms of large area, ranging from 1 mm² to over 140 mm². Transmission measurements were taken using a double beam spectrophotometer and an FTIR over UV, visible and IR wavelengths ranging from 200 nm to 20 microns. These SiC thin films show transmitivity ranging from 50% to 75% for wavelengths from 600 nm to 1.1 microns, and from 75% to over 90% for wavelengths from 1.1 to 10 microns. Micromachined SiC thin films exhibit excellent properties for micro-optomechanical applications such as visible through mid IR transmissive optics. Application areas include optical packaging for harsh chemical environments, and active and adaptive optical devices. Fabrication results, transmission measurements and comparison to accepted values⁴ will be presented. ¹W. J. Choyke, G. Pensl, MRS Bulletin, 22 (3) (1997) p. 25. ²K. Chandra, C. A. Zorman, M. Mehregany, presented at the Intl. Conf. on SiC, III-nitrides and Related Materials - 1997, Stockholm. ³C. A. Zorman, A. J. Fleischman, A. Dewa, M. Mehregany, C. Jacob, and P. Pirouz, J. Appl. Phys. 78 (1995) p. 5136. ⁴S. A. Alterovitz, and J. A. Woollam, in Handbook of Optical Constants of Solids II, edited by E. Palik, Academic Press 1991, p. 705.
3:10 PM		C1-2-6 Break
3:30 PM		C1-2-7 Low-Pressure Plasma Deposition of Au/Dielectric Composite Films for Non-Linear Optical Applications. D. Dalacu, D. Rats, A.P. Brown, L. Martinu, M.R. Wertheimer, S.I. Najafi (École Polytechnique, Canada); M.P. Andrews (McGill University, Canada) Low -pressure plasma techniques offer an attractive method for the deposition of thin films for non-linear optical (NLO) applications. Two approaches using a hybrid technique for the deposition of dielectric/metal composite films are being assessed in this work: (i) magnetron sputtering of Au and plasma enhanced chemical vapor deposition (PECVD) of amorphous hydrogenated SiO_xN_y; and (ii) magnetron sputtering or evaporation of Au and plasma polymerization of fluorocarbons. In the first series of experiments the optical properties of the composite films were characterized by spectroscopic ellipsometry and by spectrophotometry. Using an effective medium approach, the relationship between the optical constants (nλ, kλ)) and the microstructural characteristics (filling factor, size and shape of Au particles) was inferred, and the influence of the fabrication conditions (growth rates of individual components, substrate temperature) on the microstructural characteristics was determined. In the second series of experiments, the third-order NLO properties were investigated using an electro-optic set-up based on Mach-Zehnder interferometer. The relationship between the third-order NLO coefficients, χ⁽³⁾, and the film's structural charactristics have been determined.
3:50 PM		C1-2-8 Measurement and Control of Interface Strength V. Gupta (University of California, Los Angeles) A laser spallation technique to measure the tensile strength of planar thin film interfaces will be presented. In this experiment, a laser-produced compressive stress pulse in the substrate upon reflection into a tensile pulse from the coating's free surface, pries off the coating. The critical interface stress is calculated by recording the coating=92s free-surface velocity by using a Doppler interferometer.=20 Because interface separation is accomplished at a relatively high strain rate, all inelastic deformations during the coating decohesion process are essentially suppressed, and the measured value approaches the intrinsic strength of a flaw-free interface. Thus, the strength value so obtained can be related directly to the atomic structure and chemistry of the interfacial region. This latter feature distinguishes this technique from many others in the literature, which essentially give an overall background strength value, inclusive of all extrinsic effects arising from material plasticity and interface roughness. The talk will review all measurements done to date for the microelectronic device, tribology, paint, jet aircraft, biomedical and composite industries, and follow it up with the fundamental strength-structure-chemistry relationship results obtained for Nb/sapphire interfaces, with and without the intervening layers of Cr and Nb. We show how the microstructure in the interfacial region can be modified by depositing 1 to 40 Å-thick interlayers of Cr and Sb, and related one-on-one to the tensile strengths obtained from the laser spallation experiment. The atomic structure in the interfacial region is obtained using a high resolution transmission electron microscope. A controlled delamination technique to measure the intrinsic toughness of interfaces will also be presented. These values relate fairly well to the tensile strengths obtained from the laser technique and thus confirm the fundamental nature of these measurements.
4:30 PM		C1-2-10 Mechanical Properties of Plasma-deposited Inhomogeneous Optical Coatings D. Rats, D. Poitras, L. Martinu (École Polytechnique, Canada) The importance of multifunctional coatings is steadily increasing: such coatings simultaneously combine optimized optical, electrical, mechanical and permeation barrier characteristics. Improved mechanical properties (such as adhesion and wear-resistance) are required particularly for optical films and coatings, used as optical filters, antireflective systems and optical waveguides. In this context, using appropriate design and fabrication steps, graded index and graded hardness films provide an attractive way to improve the optical performance and, simultaneously, to reduce the mechanical stress at the interface. This, in turn, can lead to enhanced adhesion and to better protection of the substrate. In the present study, we use a dual mode microwave/radio frequency (MW/RF) plasma approach to deposit single layer, multilayer and graded-layer structures of amorphous hydrogenated silicon nitride, oxide, and oxynitrides on polycarbonate and silicon substrates. The coatings are characterized both optically, using spectrophotometry and spectroscopic ellipsometry, and mechanically, with scratch-testing and depth-sensing indentation. A comparison is made between the properties of multilayer and inhomogeneous coatings with the corresponding optical performance. Deposition parameters (gas composition, ion bombardment energy) are optimized in order to obtain strongly-adherent optical filters on polymeric substrates.
4:50 PM		C1-2-11 Adhesion Enhancement of Optical Coatings on Plastic Substrate via Ion Treatment A. Rizzo (Pastis-CNRSM, Italy); M. Alvisi (INFM - Università di Lecce, Italy); F. Sarto (ENEA, CRE-Cassacia, Italy); S. Scaglione (ENEA, CRE-Casaccia, Italy); E. Melissano (Pastis-CNRSM, Italy); L. Vasanelli (INFM-Università di Lecce, Italy) The main limitation in using plastics for optical components is the softness of their surface, which is responsible for low impact and abrasion resistance and for weak adhesion between the film and the substrate. The impact resistance of polymeric lenses can be increased protecting the substrate by a hard film. However, deposition of thin film on plastic chemically cleaned substrates resulted in fast delamination of the coating. This paper discusses the problems associated with coated plastics, presents the ion assistance as one of the solutions and identifies the relevant ion source parameters. A hard oxide layer with additional ion pre-treatment is proposed as protection for plastic optics. Fourier Transform Spectroscopy has been used to analyze the effect of different substrate pretreatments. The adhesion between the film and the substrate has been evaluated by scratch-test and the hardness has been calculated performing several indentations at a fixed load with a Knoop diamond tip. (This work has been financially supported by INFM (Genova, Italy) in the framework of P.O. Ricerca e Svilupo Tecnologico ed Alta Formazione 94-99-FESR.)