Coated Polymer Substrates Research Articles

Deposition of silicon oxide coatings by atmospheric pressure plasma jet for oxygen diffusion barrier applications

Silicon oxide thin-film coated polymer substrates have great applications in the packaging industry for food and medical products, because these types of treated substrates show excellent barrier properties toward oxygen and moisture diffusion. In this work, silicon oxide coatings were fabricated on polyethylene terephthalate and polyimide (PI) substrates by an atmospheric pressure jet. The deposited coatings have been carefully characterized by Fourier transform infrared spectroscopy, scanning electron microscope and atomic force microscope for chemical structures and morphology. The influence of the hexamethyldisiloxane concentration in feed gas and the distance from plasma nozzle to PI substrate is also carefully investigated. With optimized deposition conditions, the obtained silicon oxide coated PI substrates show a satisfactorily low oxygen transmission rate of 0.7ml/m2/day (at 25°C, dry oxygen).

Room Temperate Bonding of Al2O3 Layers by Atomic Layer Deposition on Polyimide Substrates

Atomic layer deposition (ALD) gas barrier layer coatings on polymer substrates have been studied to address the problem of short-lifetime of polymer devices. ALD Al2O3 layers deposited with trimethylaluminium (TMA) and H2O vapor precursors are relatively dense and conformal, so ALD Al2O3 layers are good candidates for effective gas barriers against water vapor and oxygen permeation. In order to seal such ALD Al2O3 coated polymer substrates without organic adhesives, the bonding technique of choice has to satisfy low temperature bonding requirements. Utilizing a high temperature bonding process would damage thermally sensitive polymer substrates during thermal compression bonding. Furthermore the gas barrier property of organic adhesives would be too low for effective sealing. The polymer substrates used in this study are polyimide (PI) sheets from XENOMAX® from Toyobo Co., Ltd that are widely used as substrates for flexible electronics. These polyimide sheets have extremely smooth surfaces (RMS ~1 nm), which are conducive for bonding, because good large contact areas can be obtained. These polyimide substrate sheets of 35 μm thickness were coated with Al2O3 films of 250 ALD cycles using different process temperatures ranging from 80 ºC, 150 ºC and 250 ºC, while 100 ALD cycles were used at 250 ºC. The warpage of the polyimide sheets, the surface morphology, and the results of bonding for these ALD Al2O3 coated polyimide samples were investigated as a function of different ALD deposition temperatures. The polyimide sample processed at the higher ALD Al2O3 temperature of 250 ºC exhibited much larger warpage, which is detrimental for bonding. We prepared PI sheets whose size was 10 cm x 10 cm. The ALD Al2O3 on polyimide samples deposited at 80, 150, and 250 ºC display warpage, and these edges lifted up to 1 mm, 3 mm, and 5 mm from a horizontal plane, respectively. This warpage is attributed to the difference of thermal expansion coefficients between the polyimide sheet and the deposited ALD Al2O3 layer. The surface morphology of the ALD layer was studied using atomic force microscopy (AFM) surface profiling. The sample deposited at a lower ALD temperature has smoother surface morphologies. Our ALD Al2O3 films synthesized at 80 ºC exhibited a very smooth surface morphology indicative of amorphous material, while the Al2O3 film synthesized at 250 ºC was observed to possess a granular structure demonstrating recrystallization into a polycrystalline film. The rough grain structure of ALD Al2O3 films deposited at 250 ºC exceeds the critical surface roughness and as a consequence prevents surfaces from bonding. For the bonding experiment, all PI samples coated by ALD Al2O3 were bonded using a modified method of Surface Activated Bonding (SAB) employing a nano-adhesion layer. First, ALD Al2O3 layers of about 25 nm are deposited on the surface of the polyimide substrates using trimethylaluminium (TMA) and water as precursors. Next, the Al2O3-coated surfaces are moved inside a high vacuum bonding machine and cleaned using Ar-ion beam bombardment. After the surface cleaning process step, Si nano-adhesive layers are deposited via ion-beam sputtering. Subsequently, the surface of the nano-adhesion layers are activated using the Ar-ion beam SAB method. Finally, surfaces were brought into close contact and bonded under compression in ultra-high vacuum. The structure of the bond interface was PI/Al2O3/Si/Si/Al2O3/PI. Here the thickness of each ALD Al2O3 layer and Si layer are 25 nm and 10 nm, respectively. We compared the results of the bonding of PI films coated at different ALD process temperatures. All bonding processes were performed at room temperature in ultra high vacuum. While the ALD Al2O3 samples deposited at 150 ºC suffered various non-bonded areas due to warpage and surface roughness, the ALD films deposited at 80 ºC revealed near perfect bonding without any voids, which is desirable for tight sealing of gas barrier layers. Room temperature bonding of ALD Al2O3 films on Si and polyimide substrates was successfully performed. Due to high temperature gradient induced warpage of the polymer substrate and elevated surface roughness of the ALD layer, a lower process temperature of 80 ºC for ALD synthesis of Al2O3 provided optimum gas barrier conditions. The results of our bonding experiments demonstrate that larger bonded areas were achieved when the ALD synthesis of Al2O3 gas barrier layers was performed at 80 ºC. This bonding method is expected to be used for future microelectronics packaging and gas barrier sealing for polymer substrate.

Mechanical and Electrical Stability Indium-Tin-Oxide Coated Polymer Substrates under Continuous Bending Stress Condition

AbstractIn this study, we investigated the changes of electrical resistance of indium-tin-oxide (ITO) film. To find the relationship between the physical properties of base substrate materials and mechanical stability, the mechanical and electrical stability of various ITO coated polymer substrates have been investigated. From intensive study on the mechanical and electrical stability of ITO coated polymer substrates, it was found that the physical property of base polymer material such as Young's modulus had a great influence of mechanical and electrical stability of polymer substrate under continuous bending stress condition and polymer substrate with lower Young's modulus showed better stability against compressive and tensile stresses.

The adhesion of SiN x thin layers on silica–acrylate coated polymer substrates

Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to grow 200, 300 and 400 nm thick silicon nitride layers (SiN x ) on a high temperature aromatic polyester substrate spin coated with a silica–acrylate hybrid coating (hard coat). Layers deposited without oxygen plasma treatment remained attached to the substrate, while spontaneous buckle delamination of the layer deposited with oxygen plasma treatment was observed directly after layer deposition. This effect was investigated using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). SIMS analyses showed a considerable increase of silicon oxide by exposing the substrate to oxygen plasma treatment, while AFM showed an increased roughness. Bright-field transmission electron micrographs show the presence of a particulate SiO 2 layer. The oxygen plasma treatment thus removes the acrylate from the hard coat layer leaving behind the SiO 2 particles leading to lower adhesion and thus to spontaneous buckle delamination.

Development and evaluation of bend-testing techniques for flexible-display applications

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19.3: Electrical Studies of Mechanically Deformed Indium Tin Oxide Coated Polymer Substrates

AbstractWe report on the reliability of an ITO coated polymer substrate for flexible display applications. The resistance of the ITO layer increases with strain. The increase depends on ITO thickness, substrate material and additional polymer coatings. We present data for cyclic loading of the ITO coated polymer and the increase in resistance with temperature.

The effect of refractive index on the friction coefficient of DLC coated polymer substrates

Abstract This paper describes the enhanced mechanical performance that can be achieved by the application of diamond-like carbon (DLC) coatings to polymer substrates. The polymers coated are silicone and polyethylene, and the effect on the friction coefficient is studied. Film adhesion is found to depend on the DLC film refractive index ( n ), whereas the friction is largely independent of n in the range studied. Films were deposited from a He/C 2 H 2 mixture at 20 Pa (0.15 Torr) on to the polymer substrates placed on a 10-cm-diameter electrode driven at 13.56 MHz. Film growth was monitored by in-situ ellipsometry (at 675 nm), which was performed on a glass slide placed near the polymer substrate. Friction measurements were obtained using a pin-on-disk tribometer, and measurements were carried out using a stainless-steel pin at a linear speed of 6 cm s −1 . Film adhesion was evaluated using a pull-adhesion tester. It was found that DLC coatings adhere well to the polymer substrates and can significantly reduce the friction coefficient of polymers such as silicone. Higher refractive index films (which are harder and have a higher mechanical strength) were found to have a poorer adhesion and provide a slightly increased friction on the polymer surface when compared to lower-index films. This study indicates that DLC may be used to enhance the tribological properties of polymers with potential applications in the biomaterials and light-engineering industries.

Wet-Chemical Synthesis of Thin-Film Solar Cells

AbstractWe have been working on the development of wet-chemical processing methods that can be used to create thin film photovoltaic solar cells. Electrochemically deposition methods have been used to produce copper indium diselenide (CIS) thin films on molybdenum coated polymer substrates. CIS has an extremely high optical absorption coefficient, excellent radiation resistance, and good electrical conductivity and thus has proved to be an ideal absorber material for thin film solar cells. A series of compositionally different p-type CIS films were produced by using different electrochemical deposition potentials. Cadmium sulfide (CdS) window layers were deposited directly on these CIS films using a chemical bath process. CdS is a naturally ntype wide-bandgap semiconductor which has good transparency and is well lattice-matched to CIS. Zinc oxide thin films were grown by electrochemical deposition directly on the CdS films. ZnO is a transparent and conductive thin film that serves as the top contact of the cells. The structural and elemental properties of the individual ZnO, CdS and CIS films were characterized by x-ray diffraction and energy dispersive spectroscopy. The electrical behavior of the CdS on CIS junctions was determined using current versus voltage measurements. We will discuss the performance of these devices based on the physical properties of the component films and the processing methods employed in their fabrication.

The interfacial chemistry of metallized, oxide coated, and nanocomposite coated polymer films

Aluminium, aluminium oxide, and aluminium/aluminium oxide nanocomposite coated polymer substrates have been characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, argon ion sputter depth profiling, and gas permeation measurements. A comparison of the similarities and differences between these coatings has provided a detailed insight into the physicochemical origins of gas barrier associated with metallized plastics.