Laser direct write patterning technique of indium tin oxide film

The circuit patterns of transparent conductive oxide films (TCO films) have widely formed using the traditional photolithography method. The indium tin oxide (ITO) films of flat panel displays are one of the TCO films and usually ablated using the wet etching, which is widely adopted in the semiconductor processing. However, the chemical wet etching techniques usually appear with more disadvantages in the procedure, including the chemical pollution, the under-cut effect, the swelling and the costly. Therefore, the dry etching would be replaced the photolithography procedures. The laser directing method is one of the dry etching techniques and could form the circuit pattern on the ITO glasses. Moreover, the laser directing techniques could flexibility make the circuit pattern in the TCO film and the substrate would be not eroded by the laser ablation. The investigation is interested in circuit patterning of glass substrate using the laser direct writing techniques to ablate the ITO films by a UV laser materials processing system. The UV laser is a third-harmonic Nd: YAG laser with a 355 nm of wavelength and the power is 1.0 W. In this paper, the ITO films are ablated by the UV laser materials processing system which used the different repetition rate and the feeding speeds of tables. The results of laser pattering of ITO films are measured using the optical microscope (OM) and the scanning electron microscope (SEM), and it indicates the repetition rate of laser would affect the width of line.     

High-quality parallel patterning of carbon nanotube thin films by a pulsed laser beam

Single-walled carbon nanotube thin films solution-deposited on the glass substrate were directly patterned by a spatially-modulated pulsed laser beam (wavelength = 355 nm, pulse width = 5 ns) incident from the backside of the substrate. This method utilizes a ultrashort pulse-induced strong thermo-elastic force exerting on the film which plays a role to detach it from the substrate. The threshold energy density required for patterning was as low as 90 mJ/cm², making it possible to pattern over a few square centimeters by a single pulse with maximum energy of 180 mJ. The irradiated regions of the film were clearly photoetched without leaving any residual nanotubes. High-fidelity patterns could be fabricated with a feature size of 35 μm.     

Femtosecond laser induced micropatterning of graphene film

Micropatterning of CVD synthesized large area graphene film is demonstrated with femtosecond laser cutting process. Homogenous microribbon or other patterned structure can be fabricated without using any resist or other material containing the graphene surface within a very short duration. Once the suitable laser beam doses are determined, sharp edge profile and clean etching are obtained. Scanning electron microscopic study shows that the patterned microribbon is having 5 μm width and mm in length. The width of the patterned microribbon can be controlled with control of laser energy and preprogramming of laser ablation process. Raman study at the edge of the microribbon shows increase in D peak and appearance of D + G mode, signifying edge defects. The defect can be explained from the breaking of sp² carbon hybridization with oxidation due to laser etching. The Raman study shows no amorphous carbon formation with laser cutting of the graphene film. The presented process shows a simple way to make patterned microribbon on large area graphene sheet which can be extremely necessary for microelectronics fabrication.     

Fabrication of TiO2 nanotube film by well-aligned ZnO nanorod array film and sol-gel process

High density TiO₂ nanotube film with hexagonal shape and narrow size distribution was fabricated by templating ZnO nanorod array film and sol-gel process. Well-aligned ZnO nanorod array films obtained by aqueous solution method were used as template to synthesize ZnO/TiO₂ core-shell structure through sol-gel process. Subsequently, TiO₂ nanotube array films survived by removing the ZnO nanorod cores using wet-chemical etching. Polycrystalline anatase TiO₂ nanotube films were ∼ 1.5 μm long and ∼ 100 nm in inter diameter with a wall thickness of ∼ 10 nm.     

Highly conductive, transparent flexible films based on open rings of multi-walled carbon nanotubes

Open rings of multi-walled carbon nanotubes were stacked to form porous networks on a poly(ethylene terephthalate) substrate to form a flexible conducting film (MWCNT-PET) with good electrical conductivity and transparency by a combination of ultrasonic atomization and spin-coating technique. To enhance the electric flexibility, we spin-coated a cast film of poly(vinyl alcohol) onto the MWCNT-PET substrate, which then underwent a thermo-compression process. Field-emission scanning electron microscopy of the cross-sectional morphology illustrates that the film has a robust network with a thickness of ~ 175 nm, and it remarkably exhibits a sheet resistance of approximately 370 Ω/sq with ~ 77% transmittance at 550 nm even after 500 bending cycles. This electrical conductivity is much superior to that of other MWCNT-based transparent flexible films.     

In-situ and ex-situ investigations of pulsed laser ablation of Y target

High purity yttrium was ablated by using frequency quadrupled ultra-violet pulses of a Nd:YAG laser (λ = 266 nm, τ_FWHM = 7 ns) with power density of about 1 GW/cm². Laser ablation process was studied using in-situ mass spectrometry of the ablated species in combination with ex-situ analyses of both target surface and deposited films. An increase on the Y ablation rate was found at the beginning, followed by a significant drop with increasing of the number of laser pulses per site until it reaches a constant value after 40 pulses per site. Initial topographic changes on the target surface, observed by scanning electron microscope investigations, and plasma shielding effect could be the origin of these changes on the ablation rate. Careful time-integrated and -resolved mass spectrometric studies of the laser ablated material indicate evident hydridation and oxidation processes in gas phase of ablated yttrium. These results clearly suggest that high purity metallic thin films can be deposited only after a deep and prolonged laser cleaning treatment of the target surface. The present parametric studies are aimed and tailored to prepare photocathodes based on Y thin films to be used in RF photoinjectors.     

Durable transparent carbon nanotube films for flexible device components

This paper describes a durable carbon nanotube (CNT) film for flexible devices and its mechanical properties. Films as thin as 10 nm thick have properties approaching those of existing electrodes based on indium tin oxide (ITO) but with significantly improved mechanical properties. In uniaxial tension, strains as high as 25% are required for permanent damage and at lower strains resistance changes are slight and consistent with elastic deformation of the individual CNTs. A simple model confirms that changes in electrical resistance are described by a Poisson's ratio of 0.22. These films are also durable to cyclic loading, and even at peak strains of 10% no significant damage occurs after 250 cycles. The scratch resistance is also high as measured by nanoscratch, and for a 50 μm tip a load of 140 mN is required to cause initial failure. This is more than 5 times higher than is required to cause cracking in ITO. The robustness of the transparent conductive coating leads to significant improvement in device performance. In touch screen devices fabricated using CNT no failure occurs after a million actuations while for devices based on ITO electrodes 400,000 cycles are needed to cause failure.These durable electrodes hold the key to developing robust, large-area, lightweight, optoelectronic devices such as lighting, displays, electronic-paper, and printable solar cells. Such devices could hold the key to producing inexpensive green energy, providing reliable solid-state lighting, and significantly reducing our dependence on paper.     

Ellipsometric study of nanostructured carbon films deposited by pulsed laser deposition

When depositing carbon films by plasma processes the resulting structure and bonding nature strongly depends on the plasma energy and background gas pressure. To produce different energy plasma, glassy carbon targets were ablated by laser pulses of different excimer lasers: KrF (248 nm) and ArF (193 nm). To modify plume characteristics argon atmosphere was applied. The laser plume was directed onto Si substrates, where the films were grown. To evaluate ellipsometric measurements first a combination of the Tauc-Lorentz oscillator and the Sellmeier formula (TL/S) was applied. Effective Medium Approximation models were also used to investigate film properties. Applying argon pressures above 10 Pa the deposits became nanostructured as indicated by high resolution scanning electron microscopy. Above ~ 100 and ~ 20 Pa films could not be deposited by KrF and ArF laser, respectively. Our ellipsometric investigations showed, that with increasing pressure the maximal refractive index of both series decreased, while the optical band gap starts with a decrease, but shows a non monotonous course. Correlation between the size of the nanostructures, bonding structure, which was followed by Raman spectroscopy and optical properties were also investigated.     

Synthesis of indium oxide cubic crystals by modified hydrothermal route for application in room temperature flexible ethanol sensors

Indium oxide cubic crystals were prepared by using hexamethylenetetramine and indium chloride without the addition of any structure directing agents. The chemical route followed in the present work was a modified hydrothermal synthesis. The average crystallite size of the prepared cubes was found to be 40 nm. A blue emission at 418 nm was observed at room temperature when the sample was excited with a 380 nm Xenon lamp. This emission due to oxygen vacancies made the material suitable for gas sensing applications. The synthesized material was made as a composite film with polyvinyl alcohol which was more flexible than the films prepared on glass substrates. This flexible film was used as a sensing element and tested with ethanol vapours at room temperature. The film showed fast response as well as recovery to ethanol vapours with a sensor response of about 1.4 for 100 ppm of the gas.     

High-aligned carbon nanotube film with netlike bulges

High-aligned carbon nanotubes film with netlike bulges made of catalyst particles has been synthesized on a silica wafer by pyrolyzing ferrocene/melamine mixtures. The structure and composition of carbon nanotubes are investigated by scanning electron microscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). It is found that these nanotubes have uniform outer diameters of about 25 nm and lengths of about 40 μm. High-resolution TEM images show that each carbon nanotube is composed of graphite-like layers arranged in a stacked-cup-like structure. XPS spectrum shows that the crust covering the tops of the aligned carbon nanotube film consists of carbon, iron and ferric oxide. The EELS spectrum shows that these nanotubes are pure-carbon tubes. The formation mechanism of the netlike bulges has been provided.     

Optimization of ZnO:Al/Ag/ZnO:Al structures for ultra-thin high-performance transparent conductive electrodes

Al-doped ZnO (AZO)/Ag/AZO multilayer coatings (50-70 nm thick) were grown at room temperature on glass substrates with different silver layer thickness, from 3 to 19 nm, by using radio frequency magnetron sputtering. Thermal stability of the compositional, optical and electrical properties of the AZO/Ag/AZO structures were investigated up to 400 °C and as a function of Ag film thickness. An AZO film as thin as 20 nm is an excellent barrier to Ag diffusion. The inclusion of 9.5 nm thin silver layer within the transparent conductive oxide (TCO) material leads to a maximum enhancement of the electro-optical characteristics. The excellent measured properties of low resistance, high transmittance in the visible spectral range and thermal stability allow these ultra-thin AZO/Ag/AZO structures to compete with the 1 μm thick TCO layer currently used in thin film solar cells.     

Nanosecond UV laser graphitization and delamination of thin tetrahedral amorphous carbon films with different sp/sp content

We have produced hydrogen-free tetrahedral amorphous carbon films with different densities and Young's modulus by coating silicon with a filtered vacuum arc under different angles. The films were modified with a pulsed laser (wavelength 355 nm) into sp² rich amorphous carbon and nano crystalline carbon films. The graphitization threshold of the films depends on the film thickness as well as on the carbon density. Simulations of the optical absorption of the different carbon films permitted to confirm the experimental results. On the other side, the delamination threshold of carbon films increases with the film thickness and was found to be controlled by thermal properties of the film. The thin film graphitization and delamination is investigated by optical microscopy, atomic force microscopy, scanning electron microscopy and Raman spectroscopy.     

Zinc cadmium oxide thin film transistors fabricated at room temperature

Zinc cadmium oxide (ZnCdO) transparent thin film transistors (TFTs) have been fabricated with a back-gate structure using highly p-type Si (001) substrate. For the active channel, 30 nm, 50 nm, and 100 nm thick ZnCdO thin films were grown by pulsed laser deposition. The ZnCdO thin films were wurtzite hexagonal structure with preferred growth along the (002) direction. All the samples were found to be highly transparent with an average transmission of about 80%~ in the visible range. We have investigated the change of the performance of ZnCdO TFTs as the thickness of the active layer is increased. The carrier concentration of ZnCdO thin films has been confirmed to be increased from 10¹⁶ to 10¹⁹ cm⁻³ as the film thickness increased from 30 to 100 nm. Base on this result, the ZnCdO TFTs show a thickness-dependent performance which is ascribed to the carrier concentration in the active layer. The ZnCdO TFT with 30 nm active layer showed good off-current characteristic of below ~ 10¹¹, threshold voltage of 4.69 V, a subthreshold swing of 4.2 V/decade, mobility of 0.17 cm²/V s, and on-to-off current ratios of 3.37 × 10⁴.     

High-rate reactive deposition of transparent SiO2 films containing low amount of Zr from molten magnetron target

The paper reports on a reactive deposition of transparent SiO₂ films with a low amount (≤ 3 at.%) of Zr prepared from the molten target using the AC pulsed dual magnetron. It is shown that the deposition rate a_D of the transparent oxide film strongly increases at the critical target power density (W_t)_cr when the solid target starts to melt and the magnetron operates with a molten target. In this case, the evaporation of target material plays a dominant role in the reactive deposition of thin films. This process is called the ionized magnetron evaporation. Oxide films reactively deposited from the molten target are well transparent and highly elastic. The maximum deposition rate of the transparent oxide film achieved in our experiments is 814 nm/min.     

Nanoporous cluster-assembled WOx films prepared by radio-frequency assisted laser ablation

The influence of substrate temperature and ambient gas pressure-composition on the characteristics of WO_x films synthesized by radio-frequency assisted pulsed laser deposition (RF-PLD) are studied with the aim to obtain nanostructured films with large surface area that appear promising for gas sensing applications. A tungsten target was ablated both in chemically reactive molecular oxygen at 5 Pa and in a mixed oxygen-helium atmosphere at 700 Pa. Corning glass was used as the substrate, at 473, 673 and 873 K. Other deposition parameters such as laser fluence (4.5 J/cm²), laser wavelength (355 nm), radio-frequency power (150 W), and target to substrate distance (4 cm) were kept fixed. The sensitivity on the deposition parameters of roughness, morphology, nanostructure and bond coordination of the deposited films were analysed by atomic force microscopy, scanning electron microscopy, transmission electron microscopy and micro-Raman spectroscopy. The role of the investigated process parameters to nanoparticle formation and to the development of an extended nanostructure is discussed.     

Laser-induced damage threshold at different wavelengths of Ta2O5 films annealed over a wide temperature range

The laser-induced damage of Ta₂O₅ films annealed at a wide range of temperature (473-1273 K) at the laser wavelengths of 1064 and 355 nm was investigated. The relations between microstructure, optical properties, chemical composition, absorption and laser-induced damage threshold (LIDT) were studied. The dependence of a damage mechanism on laser wavelengths was discussed. It was found that the LIDT either at 1064 or 355 nm first increased and then decreased with increase of annealing temperature. The LIDT at 1064 nm was influenced by the substoichiometric defects, structural defects and thermal diffusion, whereas at 355 nm it was affected mainly by the intrinsic absorption and structural defects. Both the maximum LIDT at the two wavelengths were obtained at the annealing temperature of 873 K, which could be attributed to the lowest defect density in films.     

Surface modification by laser etching using a surface-adsorbed layer

The high-precision, low-damage patterning by laser-induced back side etching techniques is still of interest, particularly for ultra-precision engineering, although the mechanism is not yet clear. The drastically altered optical properties of fused silica etched with LESAL (laser etching at a surface-absorbed layer) give evidence for the etching mechanism. Depth-resolved UV/Vis spectroscopic measurements show that the modified layer is limited to a depth of ~ 60 nm. This is correlated with a very high calculated absorption coefficient of ~ 4 × 10⁷ m^− 1 of the modified surface layer. With Rutherford backscattering spectrometry (RBS) measurements on LESAL-modified surfaces, it was demonstrated that in dependence on the laser fluence used, an amorphized layer with a thickness of a few nanometers was generated. The RBS measurements show that carbon is incorporated into the LESAL-modified surface.     

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.     

Carbon films deposited by MCECR plasma sputtering

The mirror-confinement-type electron cyclotron resonance (MCECR) plasma source has high plasma density and high electron temperature, and it is quite useful in many plasma processing, and has been used for etching and thin-film deposition. In this paper, the carbon films about 50 nm thickness were deposited on Si (1 0 0) by MCECR plasma sputtering the sintered carbon target with the argon plasma, and its properties were studied. The bonding structure of the film was analyzed by using the X-ray photoelectron spectropscopy (XPS) and the nanostructure was evaluated with the high-resolution transmission electron microscopy (HRTEM). The tribological properties (friction coefficient, wear rate, and wear life) of the film was investigated by using the pin-on-disk tribometer under the conditions that the normal load is 1 N and the sliding velocity is 0.05 m/s. The nanohardness of the films was measured by using the nanoindenter under conditions that the maximum displacement is 30 nm and the maximum load is 500 μN. The optical properties were measured by using the ellipsometer. The residual stress was measured with a surface profilometer. The surface morphology was studied by using the atomic force microscope (AFM).     

ITO thin films deposited by advanced pulsed laser deposition

Indium tin oxide thin films were deposited by computer assisted advanced PLD method in order to obtain transparent, conductive and homogeneous films on a large area. The films were deposited on glass substrates. We studied the influence of the temperature (room temperature (RT)-180 °C), pressure (1-6 × 10^− 2 Torr), laser fluence (1-4 J/cm²) and wavelength (266-355 nm) on the film properties. The deposition rate, roughness, film structure, optical transmission, electrical conductivity measurements were done. We deposited uniform ITO thin films (thickness 100-600 nm, roughness 5-10 nm) between RT and 180 °C on a large area (5 × 5 cm²). The films have electrical resistivity of 8 × 10^− 4 Ω cm at RT, 5 × 10^− 4 Ω cm at 180 °C and an optical transmission in the visible range, around 89%.