Cat-CVD SiN passivation films for OLEDs and packaging

A Roll-to-roll type catalytic chemical vapor deposition (Cat-CVD) apparatus was developed for the application to flexible organic light-emitting diode (OLED) displays and packaging. Silicon nitride (SiN_x) films were prepared by this roll-to-roll type apparatus at temperatures below 60 °C. It was found that these SiN_x films are highly moisture resistant, and the water vapor transmission rate (WVTR) on plastic substrates could be lowered to 0.01 g/m² day. Roll-to-roll type Cat-CVD is one of the most promising methods for the preparation of barrier films for OLED displays and packaging.     

Plastic substrate with gas barrier layer and transparent conductive oxide thin film for flexible displays

A novel plastic substrate for flexible displays was developed. The substrate consisted of a polycarbonate (PC) base film coated with a gas barrier layer and a transparent conductive thin film. PC with ultra-low intrinsic birefringence and high temperature dimensional stability was developed for the base film. The retardation of the PC base film was less than 1 nm at a wavelength of 550 nm (film thickness, 120 µm). Even at 180 °C, the elastic modulus was 2 GPa, and thermal shrinkage was less than 0.01%. The surface roughness of the PC base film was less than 0.5 nm. A silicon oxide (SiO_x) gas barrier layer was deposited on the PC base film by a roll-to-roll DC magnetron reactive sputtering method. The water vapor transmission rate of the SiO_x film was less than 0.05 g/m²/day at 40 °C and 100% relative humidity (RH), and the permeation of oxygen was less than 0.5 cc/m² day atm at 40 °C and 90% RH. As the transparent conductive thin film, amorphous indium zinc oxide was deposited on the SiO_x by sputtering. The transmittance was 87% and the resistivity was 3.5 × 10^− 4 ohm cm.     

Silicon oxide diffusion barrier coatings on polypropylene

In this study the influence of process conditions for the plasma-enhanced chemical vapor deposition of SiO_x diffusion barrier coatings on polypropylene (PP) is investigated and compared to results obtained on polyethylene terephthalate (PET). It was observed that the thermal load during deposition is much more crucial in the case of PP. If the thermal load is not the limiting factor, the composite parameter (CP) energy input per mass of precursor showed to be valuable to describe plasma conditions at constant oxygen to monomer ratio. Low oxygen transmission rates (OTRs) of 5.1 ± 3.6 and 0.3 ± 0.1 cm³/m²day/atm were achieved on PP and PET foil, respectively, for an optimal CP of 4.1 × 10⁵ J/g. Fourier transform infrared (FTIR) spectroscopy revealed that low carbon and silanol content is necessary for good barrier performance. Low RF power, necessary to reduce thermal load on PP, can be compensated by increasing the oxygen to monomer ratio.For favorable plasma conditions, the dependence of the OTR on the coating thickness follows a similar trend for both substrate materials with a critical thickness of approximately 12 nm. The residual permeation can be correlated to the defect density at each stage of film growth by means of a simple correlation. Further support for permeation through defects is found by the activated rate theory, since the apparent activation energy of oxygen permeation is below typical values of amorphous glasses and remains unchanged due to the deposition of SiO_x on both substrates.     

Development of Cat-CVD apparatus for 1-m-size large-area deposition

Thin film deposition on large-area substrates of 1-m size is demonstrated by catalytic chemical vapor deposition (Cat-CVD) apparatus equipped with a newly developed showerhead catalyzer unit. The arrangement of catalyzer wires for uniform film thickness was determined by simulation, assuming that decomposed species on catalyzers were transported by isotropic thermal diffusion without an influence of the gas flow. A film thickness uniformity of ±7.5% was successfully achieved on a substrate of 400 mm×960 mm at an average deposition rate of 32 nm/min for hydrogenated amorphous silicon (a-Si:H) film. Film thickness uniformity of ±8.6% for a-Si:H film and ±12.3% for silicon nitride film were also successfully obtained on substrates of 680 mm×880 mm size at an average deposition rate of 12.1 and 2.5 nm/min, respectively. These results suggest that Cat-CVD is a promising method for the fabrication of large-area devices such as thin-film-transistor liquid-crystal displays and solar cells.     

Water permeation through organic-inorganic multilayer thin films

We prepared organic (self-assembled monolayer (SAM))-inorganic (TiO₂) multilayer barrier films on polyethylene terephthalate substrate using atomic layer deposition and molecular layer deposition methods in the same deposition chamber. The water permeation was mainly blocked by the inorganic TiO₂ layer. While the lag time was proportional to the thickness of the TiO₂ layer, the steady-state permeation rate was relatively independent of the thickness. The multilayer approach was effective in extending the lag time due to both the tortuous path effect and the internal desiccant effect. Water permeation occurred sequentially in the organic-inorganic multilayer barriers by water accumulation in the organic SAM layers. The water vapor transmission rate was 7.0 × 10^− 4 g/m²·day during the lag time of 155 h at 60 °C and a relative humidity of 85% with 5-dyad barrier film.     

Comparison of a-Si TFTs fabricated by Cat-CVD and PECVD methods

We investigate the characteristics of amorphous silicon thin film transistors (a-Si TFTs) fabricated by plasma-enhanced chemical vapor deposition (PECVD) and catalytic CVD (Cat-CVD), and their stability under bias and temperature (BT) accelerated stress. The Cat-CVD a-Si TFTs have off-leak current as small as 10^− 14 A, and a smaller threshold voltage shift under the BT stress. The superiority in off-leak current and stability is observed in the Cat-CVD a-Si TFTs fabricated at both 320 °C and 180 °C. The high performance and stability of the Cat-CVD a-Si TFTs will enable to use low-cost glass substrates and result in a cost reduction of TFT fabrication.     

Aluminum oxide barrier coating on polyethersulfone substrate by atomic layer deposition for barrier property enhancement

Aluminum oxide layers were deposited on flexible polyethersulfone (PES) substrates via plasma enhanced atomic layer deposition (PEALD) process using trimethylaluminum (TMA) and oxygen as precursor and reactant materials. Several process parameters in PEALD process were investigated in terms of refractive index and layer thickness. Number of process cycle increased the thickness and refractive index of the layer to enhance the barrier properties. Non-physisorbed TMA and unreacted oxygen were purged before and after the plasma reaction, respectively. Identical purge time was applied to TMA and oxygen and it was optimized for 10 s. Thinner and denser layer was formed as substrate temperature increased. However, the PES substrate could be deformed above 120 °C. Aluminum oxide layer formed on PES at optimized conditions have 11.8 nm of thickness and reduced water vapor transmission rate and oxygen transmission rate to below 4 × 10^− 3 g/m² day and 4 × 10^− 3 cm³/m² day, respectively. Polycarbonate and polyethylene naphthalate films were also tested at optimized conditions, and they also showed quite appreciable barrier properties to be used as plastic substrates.     

Synthesis and characterization of mesoporous silica thin films as a catalyst support on a titanium substrate

Mesoporous silica films with a thickness of 500-900 nm were synthesized on a titanium substrate by the evaporation-induced self-assembly method (with 900-1200 rpm for 90 s) using cetyltrimethylammonium bromide (CTAB) as structure-directing agent and tetraethyl orthosilicate as the silica source. Prior to coating deposition, the titanium substrate was oxidized to increase the surface roughness up to 500 nm and to produce a thin titania layer. Just before the synthesis, the titania layer was made super hydrophilic by an UV treatment for 2 h to provide a better adhesion of the silica film to the substrate. Films with hexagonal and cubic mesostructures with a uniform pore size of 2.8 nm and a surface area of 1080 m²/g were obtained and characterized by different methods. An alternative approach for surfactant removal by gradual heating up to 250 °C in vacuum was applied. Complete removal of CTAB from the as-synthesized silica films was confirmed by infrared spectroscopy.     

Evaluation of thin film passivation using inorganic Mg-Zn-F heterointerface for polymer light emitting diode

In this study, we manufactured Mg-Zn-F targets using magnesium fluoride (MgF₂) and zinc (Zn). The passivation films were deposited on a poly-ethylenenaphthalate (PEN) substrate using a radio-frequency magnetron sputter. The thickness of the manufactured passivation film was 120 nm. Among the three targets tested, the 4:6 weight target of MgF₂ to Zn resulted in films with the highest Zn content that would increase the packing density of the thin film. The water vapor transmission rate of a 120 nm Mg-Zn-F film prepared from this target and inserted between two 40 nm MgF₂ interlayers on PEN was 2.9 × 10^− 2 g/(m² day) at a relative humidity of 90% and a temperature 38 °C. Its optical transmittance was approximately 80%.     

Diamond-like carbon,a barrier coating for polymers used in packaging applications

Water and oxygen permeability measurements on two polymers, poly(ethylene terephthalate) and polypropylene, are presented as a function of diamond-like carbon coating thickness. Results show that reliable and reproducible coatings can be achieved on poly(ethylene terephthalate) such that levels of permeability are about 1 cc/m²/day for oxygen and 1.5 g/m²/day for water vapour, comparable to the levels for silicon oxides and aluminium coatings used in the packaging industry. The advantages conferred by diamond-like carbon over aluminium is primarily that of retaining optical transparency in the thickness of films used in this work (20 nm). The advantages of diamond-like carbon over silicon oxides is related to its intrinsic flexibility. Other advantages over other barrier films (e.g. polyvinylidine chloride) and coating technologies is the ability to recycle the used product. The permeability of diamond-like carbon-coated polypropylene to oxygen is in the range of 200 cc/m²/day, again comparable to results obtained with the other coatings. The optimum film thickness for poly(ethylene terephthalate) to minimize permeability was 20 nm. Atomic force microscopy revealed agglomerated structures (possibly graphitic) with the underlying substrate appearing smoother than the starting material. In comparison, polypropylene exhibited increased surface roughness under the same coating conditions.     

Highly conformal SiO2/Al2O3 nanolaminate gas-diffusion barriers for large-area flexible electronics applications

The present study demonstrates a flexible gas-diffusion barrier film, containing an SiO(2)/Al(2)O(3) nanolaminate on a plastic substrate. Highly uniform and conformal coatings can be made by alternating the exposure of a flexible polyethersulfone surface to vapors of SiO(2) and Al(2)O(3), at nanoscale thickness cycles via RF-magnetron sputtering deposition. The calcium degradation test indicates that 24 cycles of a 10/10 nm inorganic bilayer, top-coated by UV-cured resin, greatly enhance the barrier performance, with a permeation rate of 3.79 × 10(-5) g m(-2) day(-1) based on the change in the ohmic behavior of the calcium sensor at 20?°C and 50% relative humidity. Also, the permeation rate for 30 cycles of an 8/8 nm inorganic bilayer coated with UV resin was beyond the limited measurable range of the Ca test at 60?°C and 95% relative humidity. It has been found that such laminate films can effectively suppress the void defects of a single inorganic layer, and are significantly less sensitive against moisture permeation. This nanostructure, fabricated by an RF-sputtering process at room temperature, is verified as being useful for highly water-sensitive organic electronics fabricated on plastic substrates.     

Characterization of the silicon oxide thin films deposited on polyethylene terephthalate substrates by radio frequency reactive magnetron sputtering

Transparent silicon oxide films were deposited on polyethylene terephthalate substrates by means of reactive magnetron sputtering with a mixture of argon and oxygen gases. The influences of process parameters, including the oxygen flow ratio, work pressure, radio frequency (RF) power density and deposition time, on the film properties, such as: deposition rate, morphology, surface roughness, water vapor/oxygen transmission rate and flexibility, were investigated. The experimental results show that the SiO_x films deposited at RF power density of 4.9 W/cm², work pressure of 0.27 Pa and oxygen flow ratio of 40% have better performance in preventing the permeation of water vapor and oxygen. Cracks are produced in the SiO_x films after the flexion of more than 100 cycles. The minimum transmission rates of water vapor and oxygen were found to be 2.6 g/m² day atm and 15.4 cc/m² day atm, respectively.     

High performance encapsulation structures utilizing Russian Doll architectures

A Russian Doll encapsulation architecture utilizing pairs of free-standing barrier films and epoxy seals separated by nitrogen spacers is presented, enabling the use of low-cost epoxy to attach two or more free-standing barrier films to a substrate with improved barrier performance. The performance of various Russian Doll encapsulations was evaluated with the calcium thin film optical transmission test, showing improved performance of the Russian doll configuration relative to a non-nested barrier/spacer architecture, and demonstrating that water vapor transmission rates (WVTR) of 0.00021 g/(m², day) or below can be achieved with low-cost materials in this architecture. This WVTR correlates to a predicted lifetime of more than 10 years for bulk heterojunction solar cell modules fabricated and tested by Konarka Technologies (Lowell, MA, USA).     

Pretreatment of polyethylene terephthalate substrate for the growth of Ga-doped ZnO thin film

The effect of the pretreatment of polyethylene terephthalate (PET) substrate on the growth of transparent conducting Ga-doped ZnO (GZO) thin film was investigated. Because of its high gas and moisture absorption and easy gas permeation, PET substrate was annealed at 100 degrees C in a vacuum chamber prior to the sputtering growth of GZO thin film for the outgassing of impurity gases. GZO thin film was deposited on the pretreated PET substrate by rf-magnetron sputtering and significantly improved electrical properties of GZO thin film was achieved. Electrical and structural characterizations of the GZO thin films were carried out by 4-point probe, Hall measurement, and scanning electron microscopy, and the effects of the pretreatment on the improved properties of GZO thin films were discussed. This result is not only useful to PET substrate, but also could be applicable to other plastic substrates which inevitably containing the moisture and impurity gases.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

基于PECVD方法制备的透明硅氧烷（SiOxCyHz）阻隔薄膜特性研究

柔性、透明的高阻隔性薄膜在有机太阳能薄膜电池、柔性有机发光二极管、电子纸和真空绝热板等领域都有需求。采用对电极辊结构的等离子体增强化学气相沉积方法,卷对卷的方式在聚酯(PET)基膜上,以硅醚(HMDSO)为单体,氧气(O₂)为反应气体,制备了柔性硅氧烷(SiOxCyHz)薄膜。研究了膜厚,氧气/单体比例、压力等参数对透水率(WVTR)的影响规律、测试了膜层的组分、透射光谱、应力等特性。研究结果表明,透水率随硅氧烷薄膜厚度增大而减小,随氧气/单体比例增大而减小,随压力减小而增大。500 nm厚的硅氧烷薄膜透水率低于5×10^-3g/(m²·day),可见光谱段(380-760 nm)透光率达到88.6%,表面粗糙度为1.8 nm,薄膜应力随薄膜厚度增加显著增大。     

Thickness dependent properties of nickel oxide thin films deposited by dc reactive magnetron sputtering

Nickel oxide thin films of various thicknesses were grown on glass substrates by dc reactive magnetron sputtering technique in a pure oxygen atmosphere with sputtering power of 150 W and substrate temperature of 523 K. Crystalline properties of NiO films as a function of film thickness were investigated using X-ray diffraction. XRD analysis revealed that (200) is the preferred orientation and the orientation of the films changed from (200) to (220) at film thickness of 350 nm. The maximum optical transmittance of 60% and band gap of 3.82 eV was observed at the film thickness of 350 nm. The lowest electrical resistivity of 5.1 Ω cm was observed at a film thickness of 350 nm, thereafter resistivity increases with film thickness.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

The effect of substrate temperature on the oxidation behavior of erbium thick films

The effect of substrate temperature on the oxidation behavior of erbium thick films, fabricated by electron-beam vapor deposition (EBVD), was investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The erbium thick film is black when it is deposited at substrate temperature below 450 °C and turns gray at higher substrate temperature in a vacuum pressure of approximately 1.5 × 10⁻⁶ Torr, which indicates that the thickness of erbium oxide layer formed on the surface of erbium films increases with the decreasing substrate temperature. XPS depth profile results demonstrate that the thickness of the surface erbium oxide layer of erbium film deposited at substrate temperature of 550 and 350 °C are about 50 and 75 nm, respectively. The thicker oxide layer at lower substrate temperatures may be attributed to grain size and the dynamic vacuum condition around the substrates. Other possible factors involved in the oxidation behavior are also discussed.     

Material characteristics of sputter-deposited Zr-doped In2O3/ZnO heterostructures on sapphire (0001) substrates

5 wt.% Zr-doped In₂O₃ (Zr-In₂O₃) films with thicknesses from 95 to 220 nm were grown on 90 nm-thick ZnO-buffered sapphire (0001) substrates by radio-frequency magnetron sputtering in an oxygen-deficient atmosphere. The dependence on thickness of the structural information and electrical properties of the Zr-In₂O₃ films on the ZnO-fuffered sapphire substrates was studied. The X-ray diffraction patterns show that the (002)-textured ZnO buffer-layer is a good template for the growth of the highly (222)-textured In₂O₃ films on the sapphire substrate. The surface of the Zr-In₂O₃ film becomes rougher as the film thickness increases, perhaps because of the formation of larger mounds on the film surface as the thickness of Zr-In₂O₃ increases. The carrier concentration increased markedly from 5.8 × 10²⁰ to 1.83 × 10²¹ cm^− 3 with film thickness from 95 to 220 nm, because more growth-induced defects are formed in the thick Zr-In₂O₃ film. The large increase in the number of charge carriers and the improvement in the crystalline quality in the film reduce the resistivity of the thicker Zr-In₂O₃ film.