Highly transparent low resistance ATO/AgNWs/ATO flexible transparent conductive thin films

Indium-free flexible transparent conductive thin films (TCFs) composed of silver nanowire (AgNW) networks and Sb doped SnO₂ (ATO) layers were prepared on polyethylene terephthalate (PET) substrates. The ATO layers were deposited via radio frequency (RF) magnetron sputtering at room temperature. The AgNWs were achieved via a modified polyol reduction method and embedded between the ATO layers. The effects of AgNW networks and ATO layers on electrical and optical properties of the ATO/AgNWs/ATO flexible tri-layer thin films are investigated. The ATO layers can improve the optical transmittance and reduce the resistivity of tri-layers, and the corresponding mechanisms are proposed. Typically, an ATO/AgNWs/ATO flexible tri-layers show a high figure of merit value (30.06 × 10^-3 Ω^-1) with a low sheet resistance of 7.1 Ω/sq. and a high transmittance of 85.7%. Meanwhile, the tri-layers present excellent mechanical flexibility, and the ATO layers acted as the protecting layers improve the adhesive and environmental stability at high temperature and humidity for the ATO/AgNWs/ATO flexible tri-layers. These results indicate that ATO/AgNWs/ATO flexible tri-layer thin films can be useful for the fabrication of wearable electronic devices.     

Fabrication of high-quality flexible transparent conductive thin films with a Nb2O5/AgNWs/Nb2O5 sandwich structure

Different sandwich structures of flexible transparent conductive thin film (TCFs) composed of Nb₂O₅ layers and Ag nanowires (AgNWs) have been prepared onto flexible polyethylene terephthalate (PET) substrate at room temperature to develop an indium-free TCF. The AgNWs are synthesized by a modified polyol method and inserted into the Nb₂O₅ layers that are prepared by radio frequency magnetron sputtering. The optical and electrical properties can be modified by changing the number of spin-coating cycle of AgNW suspension. At optimized condition, we achieve a flexible Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film with a low sheet resistance of 9.61 Ω/square and a high optical transmittance of 84.3%. Meanwhile, the resistance remains nearly constant after 30 tape tests, suggesting a strong adhesion to the PET substrate. The sandwich thin films show high long-term stability to oxidation, humid heat, and chemicals compared with that of AgNW networks, which can be attributed to the effective covering of Nb₂O₅ layer on the AgNWs. In addition, the Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin films show good stability after repeated bending. This Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film can therefore serve as a high-performance transparent conductive electrode for numerous flexible electronic devices.     

Mechanical performance of ITO/Ag/ITO multilayer films deposited on glass substrate by RF and DC magnetron sputtering

ITO/Ag/ITO multilayer thin films have been a potential substitute of the conventional single-layer transparent conducting film. Nevertheless, the mechanical stability under preparation and in-service conditions still limits their applications and developments. In this paper, the influences of different structural properties as well as layer structure on both surface morphological properties and mechanical properties of the ITO/Ag/ITO multilayer thin films in comparison with commercial single-layer ITO thin film were systematically investigated. The results demonstrate that, i) the tri-layer composite has large impacts on the preferential orientation, and exhibits the decreased values of surface roughness, net lattice distortion and residual stress; ii) the increased hardness (H) and decreased Young's modulus (E) for full annealed ITO/Ag/ITO multilayer films indicate that it is possible to tailor mechanical properties of the materials by manufacturing multilayer composite; iii) the ITO/Ag/ITO multilayer thin film exhibits remarkable improvements in wear resistance with the increase of annealing temperature, which is mainly attributed to the increased ratios of H/E and H³/E².     

Ga and Ti co-doped In2O3 films for flexible amorphous transparent conducting oxides

We designed Ga and Ti co-doped In₂O₃ (IGTO) films to use as a flexible and transparent amorphous conducting oxide electrode in thin film heaters (TFHs) and flexible touch screen panels (FTSPs) for automobiles. The properties of the IGTO electrodes deposited on cyclic olefin copolymer (COP) at room temperature were investigated as a function of the O₂/(Ar + O₂) flow ratio, to confirm the best sputtering condition for transparent and flexible electrode. Depending on the oxygen flow ratio, the IGTO/COP electrodes showed sheet resistance of (39.3 – 1.57) × 10⁴ Ohm/sq, an average transmittance of (84.90 – 87.12) % at visible wavelength area, and a surface roughness of (0.95 – 3.23) nm. In addition, IGTO/COP samples exhibited good mechanical flexibility with critical bending radius of 3 mm, which is enough to be used as FTSPs. From the previously mentioned results, we found the amorphous IGTO/COP to be a promising flexible and transparent electrode for curved TFHs and FTSPs. The flexible IGTO/COP TFHs demonstrated a saturated temperature of 78.6 °C when applied with low operating direct current (DC) of 8 V, due to its low sheet resistance. In addition, the IGTO/COP FTSPs showed very stable touch sensitivity, even at a bent state. We found that the optimized IGTO/COP is a promising flexible and transparent electrode for next-generation automobiles.     

Fabrication and thermo stability of the SnO2/Ag/SnO2 tri-layer transparent conductor deposited by magnetic sputtering

Using the magnetic sputtering technique, the SnO₂/Ag/SnO₂ tri-layer transparent films were fabricated on float glasses successfully. Compared with the commercial FTO (F-doped SnO₂) film, the SnO₂/Ag/SnO₂ tri-layer films have higher visible-light transmittance and better conductivity. The total thickness of the SnO₂/Ag/SnO₂ films is one third of the commercial FTO film leading to the high visible-light transmittance. The high carrier concentration of the SnO₂/Ag/SnO₂ films contributes to the tri-layer films’ low resistivity. In addition, to further improve the performance of the SnO₂/Ag/SnO₂ tri-layer films, samples were annealed under different temperatures. The results illustrate that the lowest sheet resistance (5.92 Ω/sq) and the highest visible-light transmittance (87.0%) were obtained after annealing at 200 °C. Furthermore, the thermal stability of the films could be enhanced by a multi-step annealing process due to the recrystallization effect.     

High performance of carbon nanotubes/silver nanowires-PET hybrid flexible transparent conductive films via facile pressing-transfer technique

To obtain low sheet resistance, high optical transmittance, small open spaces in conductive networks, and enhanced adhesion of flexible transparent conductive films, a carbon nanotube (CNT)/silver nanowire (AgNW)-PET hybrid film was fabricated by mechanical pressing-transfer process at room temperature. The morphology and structure were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), the optical transmittance and sheet resistance were tested by ultraviolet-visible spectroscopy (UV-vis) spectrophotometer and four-point probe technique, and the adhesion was also measured by 3M sticky tape. The results indicate that in this hybrid nanostructure, AgNWs form the main conductive networks and CNTs as assistant conductive networks are filled in the open spaces of AgNWs networks. The sheet resistance of the hybrid films can reach approximately 20.9 to 53.9 Ω/□ with the optical transmittance of approximately 84% to 91%. The second mechanical pressing step can greatly reduce the surface roughness of the hybrid film and enhance the adhesion force between CNTs, AgNWs, and PET substrate. This process is hopeful for large-scale production of high-end flexible transparent conductive films.     

ZnMgBeO/Ag/ZnMgBeO transparent multilayer films with UV energy bandgap and very low resistance

The ZnMgBeO/Ag/ZnMgBeO multilayer structures were sputter grown and their electrical and optical properties have been investigated in detail. Results indicated that the ZnMgBeO(30 nm)/Ag(10 nm)/ZnMgBeO(30 nm) optimum structure shows energy bandgap of ~4.5 eV, electrical resistivity of ~6.5×10⁻⁵ Ωcm, and optical transmittance of 78–90% over the visible wavelength range and 74–90% over 300–400 nm range, representing a significant improvement over the previously reported transparent conducting films. High resistivity (~0.12 MΩcm) of the ZnMgBeO layer did not critically affect the conductivity of the multilayer, because the Ag films act as the conducting path. It was also observed that the properties were substantially deteriorated at the Ag thickness of 5 nm, as the Ag film is only partly continuous, resulting in very rough interfaces and surfaces.     

Manganese-doped transparent conductive magnetic indium oxide films integrated on flexible mica substrates with high mechanical durability

Recent advances in flexible electronic devices have stimulated demands for the fabrication of multifunctional materials on highly flexible substrates. However, flexible diluted magnetic semiconductor films have been inadequately reported thus far. In this study, I grew polycrystalline manganese (Mn)-doped indium oxide (In₂O₃) films on flexible mica substrates at three deposition temperatures (T_d) using the pulsed laser deposition method. All the investigated Mn-doped In₂O₃ films exhibited high optical transparency, high electrical conductivity, room-temperature ferromagnetism, and excellent mechanical durability. The present experimental results demonstrate that T_d considerably influences the optical, electrical, and magnetic properties as well as the mechanical durability of the flexible Mn-doped In₂O₃ films. Based on the robustness of inorganic mica at high deposition temperatures, this detailed investigation provides a strategy for fabricating flexible diluted magnetic semiconductor films, the properties of which could be carefully optimized by widely varying the T_d.     

Electrochemical properties of boron-carbon-nitride films formed by magnetron sputtering

The electrochemical behavior of B_1.0C_2.4N_1.0 thin film was investigated in acidic, neutral and alkaline solutions. The anodic polarization curve of the film in 1 M NaOH showed the anodic dissolution of the film. The curve of the film in 1 M HCl showed no anodic dissolution. The cathodic polarization curve in 1 M NaCl showed shift to a negative potential side, but the anodic polarization curve was the same as that of Pt. The anodic dissolution in 1 M NaOH depended on potentials, that is, no anodic dissolution was recognized in a potential range of −0.2 to 0.1 V but the dissolution rate increased with increasing potential in a range of 0.1-0.6 V. The anodic current density of the film is directly proportional to the dissolution rate at potentials higher than 0.1 V. The dissolution rate of the film was increased with increasing solution pH.     

Deposition and characterization of AZO thin films on flexible glass substrates using DC magnetron sputtering technique

Al-doped zinc oxide (AZO) thin films were deposited onto flexible ultra-thin glass substrates by using a direct current (DC) magnetron sputtering process. The effects of sputtering power, working pressure and substrate temperature on the morphology and optoelectronic performances of AZO films were investigated. The optimal sputtering power, working pressure and substrate temperature for AZO film were determined to be 100 W, 0.9 Pa and 150 ℃, respectively. Further increasing or decreasing the sputtering power, working pressure and substrate temperature degrades the quality of AZO films. XRD patterns show all as-sputtered AZO thin films are preferred to grow along <0002> direction. Moreover, the largest grain size, which depicts the best microstructure of AZO films, matches with the smallest stress value. It can be seen from SEM images that the surface is smooth and dense. The smallest value of the resistivity is 1.784×10⁻³ Ω cm and the average transmittance of all AZO films in the visible range is about 80%. The X-ray photoelectron spectroscopy spectra show that the amount of Al element in the AZO film is very small.     

Spray-grown highly oriented antimony-doped tin dioxide transparent conducting films

Undoped and Sb-doped tin dioxide films of varying thickness with a remarkable crystallographic orientation in the [200] direction were grown by spray-pyrolysis from tin(II) chloride solutions. Films grown on silica-coated glass substrates were completely crystalline and showed a higher degree of orientation with respect to films that were grown on uncoated glass. The presence of the silica barrier was seen to have increased the degree of orientation and to have enhanced the resulting electrical properties. Transmission electron microscopy revealed that the silica layer may have played the crucial role of a nucleation layer. Moreover, the developed microstructures were correlated with the optical and electrical behaviour of the films. Dense conducting films with thicknesses between 280–450 nm and visible transmittances of 80-70 % showed resistivities of about 10⁻³ Ωcm.     

Measurement-based optimization and analysis of α-IGZO/Ag/α-IGZO transparent conducting electrodes fabricated using DC magnetron sputter deposition

Transparent conducting electrodes have been systematically developed for optoelectronic devices and applications in industry through materials exploration and manufacturing process optimization. The nanostructural, optical and electrical properties were correlated with the embedded Ag interlayer thickness for the first time, for α-IGZO/Ag/α-IGZO trilayer electrodes fabricated using DC magnetron sputter deposition. Optimizing the Ag interlayer thickness at 14?nm achieves a maximum Haacke figure of merit (FOM) of 7.3?×?10^?3 Ω^?1, at least two orders of magnitude greater than that of the single IGZO film, with X-ray diffraction patterns indicating a crystalline phase that is also retained for thicker layers. Electrical and surface topography measurements confirm a uniform, continuous Ag interlayer film with bulk metallic behavior and resistivity as low as 6?×?10^?5 Ω?cm. Experimentally-calibrated finite-element modeling and ray tracing simulations unravel in the multilayer films, backscattering and transmission effects from random surface roughness, as well as phonon- or ionized impurity-scattering mediated free carrier absorption plus surface/interface scattering and interference effects. Moreover, film thickness-sensitive tuning of the optical bandgap between 2.98 and 3.14?eV was demonstrated, yielding a maximum bandgap and Haacke FOM at the optimized Ag interlayer thickness, and with many-body interactions outcompeting the Burstein-Moss effect above this thickness.     

Realization of high transparent conductive vanadium-doped zinc oxide thin films onto flexible PEN substrates by RF-magnetron sputtering using nanopowders targets

RF-magnetron sputtering has been carried out at room temperature to deposit vanadium-doped zinc oxide (VZO) nanostructured thin films onto flexible PEN substrates. The sputtering targets of compacted VZO nanopowder have been prepared using a rapid and inexpensive Sol-Gel synthesis followed by a supercritical drying process. Structural and morphological study of VZO particles in the targets has been carried out via X-ray diffraction and Transmission Electron Microscopy (TEM). The nanostructured thin films have been characterized to analyze the structural, morphological, electrical and optical properties as a function of vanadium content from 0 to 4 at.%. Structural characterization of VZO thin films revealed that the deposited thin films have been grown preferentially along (002) and exhibit the hexagonal wurtzite structure. The cross-sectional and microstructural analysis performed by Scanning Electron Microscopy (SEM) confirms the columnar growth of nanostructures. The deposited thin films exhibit transparent behavior with transmission >70% in the visible region. It has been observed that nanostructured thin films with vanadium content of 2% have demonstrated the lowest resistivity (6.71 × 10^?4 Ω cm) with Hall mobility of 10.62 cm² V^?1 s^?1. The deposited vanadium doped nanostructured thin films would have potential applications in electronic and optoelectronic devices.     

Structure and high-temperature tribological properties of Pb-Cr-O composite films prepared by reactive magnetron sputtering

The formation of ternary composite oxides in a high-temperature environment has laid the foundation for the design of high-temperature wear-resistant self-lubricating film. A series of Pb-Cr-O films with different Cr contents were prepared by incorporating different ratios of Pb-Cr into a target in the reactive magnetron sputtering system. The results showed that the hardness of the Pb-Cr-O films is greatly improved compared to the pure Pb-O film. In addition, the Pb₂₉Cr₄O₆₇ film with the highest Cr content forms an amorphous structure due to the accumulation of Cr⁶⁺ at the grain boundary, which improves the H/E and H³/E² of the film. At 600 °C, in contrast with the single PbO lubricating phase formed by pure Pb₃₃O₆₇ film, the Pb₂₉Cr₄O₆₇ film forms a composite lubricating phase of Pb₅CrO₈ and PbO. This leads to a decreased wear rate as low as 7.2 × 10^?6 mm³N^?1m^?1 while maintaining low coefficient of friction comparable to pure Pb₃₃O₆₇ film. At higher temperature of 700 °C, Cr element in Inconel 718 matrix diffuses into the Pb-based oxide film and forms Pb₅CrO₈ phase similar to Pb₂₉Cr₄O₆₇ film, which improves the wear resistance of the Pb₃₃O₆₇ film while maintaining low friction coefficient of 0.15.     

Ga-doped IZO films obtained by magnetron sputtering as transparent conductors for visible and solar applications

C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In₂O₃ target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?10³ Ω^?1 cm^?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films.     

Fatty acids based transparent polyurethane films and coatings

Renewable resources used in the preparation of polymers are falling in the class of biomaterials which are rich in hydrocarbons and most of the times obtained from parts of profusely available agriculture feedstock. Use of non-edible vegetable oils and their fatty acids are currently the raw materials focused in synthesizing polymeric materials as renewable sources due to increasing economic and environmental concerns of petroleums. The current oil based polymers are prepared by consuming petroleum based anhydrides and dicarboxylic acids. With this investigation, we tried to substitute almost all components of petroleum feed stock by renewable sources in preparation of polyol. Initially palmitic acid was used as a renewable source to prepare palmitamide by amidation reaction. Further amide was converted into the polyesteramide resin (PEPAD) by reacting it with another renewable resource, i.e. dimer fatty acid which is the dimerized product of unsaturated fatty acids of vegetable oils. Structure of the prepared resin was confirmed by spectroscopic techniques and resin was also characterized by end group analysis like hydroxyl and acid values. The molecular weight of PEPAD was ranged between 2590 and 2760 g mol⁻¹. Palmitic acid based polyesteramide was used to prepare polyurethanes by varying amount of diisocyanate. The transparent polyurethane films and coatings were obtained and examined for water absorption, contact angle, hardness, coating properties, solvent, acid and alkali resistances. The thermal properties of the polyurethane films were estimated by TGA and discussed. It was found that change in NCO content affected on transparency as well flexibility of the prepared films. It also noticed that thermal stability was shifted toward higher range by increasing mole (NCO/OH) ratios due to formation of urea linkages.     

Mechanical characterization of ultra-thin fluorocarbon films deposited by R.F. magnetron sputtering

Fluorocarbon films were deposited on silicon substrate by R.F. magnetron sputtering using a polytetrafluoroethylene (PTFE) target. Structure of the deposited films was studied by X-ray photoelectron spectroscopy (XPS). Hardness, elastic modulus and scratch resistance were measured using a nanoindenter with scratch capability. -CF_x (x = 1, 2, 3) and C-C units were found in the deposited fluorocarbon films. The hardness and elastic modulus of the films are strongly dependent on the R.F. power and deposition pressure. The film hardness is in the range from 0.8 GPa to 1.3 GPa while the film elastic modulus is in the range from 8 GPa to 18 GPa. Harder films exhibit higher scratch resistance. Differences in nanoindentation behavior between the deposited fluorocarbon films, diamond-like carbon (DLC) films and PTFE were discussed. The fluorocarbon films should find more applications in the magnetic storage and micro/nanoelectromechanical systems.     

Effect of sputtering pressure on structural and dielectric tunable properties of BaSn0.15Ti0.85O3 thin films grown by magnetron sputtering

Lead?free ferroelectric BaSn_0.15Ti_0.85O₃ (BTS) thin films are grown on Pt-coated Si substrates by magnetron sputtering at 650?°C, the effect of sputtering pressure on the microstructural, surface morphological, dielectric properties and leakage characteristic is systematically investigated. XRD analysis shows the crystallinity of BTS thin films with perovskite structure can be improved by appropriate control of the sputtering pressure. The surface morphology analyses reveal that grain size and roughness can be affected by sputtering pressure. The BTS thin films prepared at sputtering pressure of 3.0?Pa exhibit a low dispersion parameter of 0.006, a medium dielectric constant of ~357, a high dielectric tunability of 65.7%@?400?kV/cm and a low loss tangent of 0.0084?@?400?kV/cm. Calculation of figure of merit (FOM) displays a high value of 84.1, and the measurement of leak current shows a very low value of 4.39?×?10^–7 A/cm² at 400?kV/cm. The results indicate that BTS thin film deposited sputtering pressure of 3.0?Pa is an excellent candidate for electrically steerable applications     

Microstructure,hardness and toughness of boron carbide thin films deposited by pulse dc magnetron sputtering

Boron carbide thin films were deposited on (100) silicon substrates at ambient temperature via. pulse dc magnetron sputtering. Various frequency and duty cycles were applied to the hot-pressed B₄C target in order to understand their influence on the structure and mechanical properties of the B₄C films. X-ray Energy dispersive spectrum, Raman spectroscopy and Transmission electronic microscopy were used to characterize the composition and microstructure of the films. Nanoindenter was employed to measure the hardness and modulus. The film toughness was evaluated by a microindentation method. The results show that both pulse frequency and duty cycle significantly affect the B/C atomic ratio and then hardness and modulus in the boron carbide films. However, the amorphous structure of the films was maintained when the frequency and duty cycle changed. The maximum hardness of 29 GPa and modulus of 247 GPa combined with relative high toughness (3.3 MPa m^1/2) were achieved under 50 kHz frequency and 30% duty cycle. In addition, there was no evidence to prove that the graphite phase existed in the B₄C films although exceeded C concentration was detected.