Transparent Conductive Thin Films Research Articles

Fabrication of Atomic Layer Deposited Zinc Oxide Thin Film Transistors with Organic Gate Insulator on Flexible Substrate

In the fabrication of transparent conductive oxide thin film transistor (TFT), an atomic layer deposited (ALD) zinc oxide (ZnO) and a cross-linked poly-vinyl-alcohol (c-PVA) were each used as active layer and gate insulating layer on poly-ethylene (PET) substrate respectively. Considering the transmittance and the deposition rate of the ALD ZnO at a low temperature without any damage on PET substrate, the ZnO layer was deposited at a temperature of 120°C on a spin-coated c-PVA layer. From the atomic force microscope (AFM) images, it was possible to conclude that the surface morphologies of ZnO deposited on a c-PVA layer was not inferior to those of ZnO deposited on bare-Si and that the c-PVA can be used as a gate insulator at 120°C. The fabricated ZnO TFT showed good electrical characteristics such as the mobility of 0.1 cm2/V · s, on-off current ratio of 4.5 × 104.

Influence of single layer thickness on the performance of undoped and Mg-doped CuCrO2 thin films by sol–gel processing

Transparent conductive thin films of copper chromium oxide were processed on borosilicate glass by sol–gel technique. The resistivity of the films was decreased by lowering the single layer thickness of multi-layer stacks deposited by dip-coating, as well as by doping with magnesium. The additional effort of increasing the number of coating cycles from four to fifteen and sintering after each coating resulted in denser films with increased crystallite size. But whereas conductivity was improved by this procedure, the transmittance of the thin films simultaneously dropped by more than 10%. The optimum values obtained for an Mg-doped sample were ρ = 0.38Ω cm at T = 26.8%.

Transparent conductive CuI thin films prepared by pulsed laser deposition

AbstractCuprous iodide (CuI) thin films were prepared by a pulsed laser deposition (PLD) technique, and the effects of the laser energy and substrate temperature on the structure and optical–electrical properties were investigated by X‐ray diffraction (XRD), scanning electronic microscopy (SEM), transmittance spectra, and resistivity measurements. At a substrate temperature of room temperature (RT), thin films include highly crystallized and (111)‐orientation preferred γ‐CuI and trace I2O5 phases, and have resistivity of the order of 10−1 Ω cm, average transmittance of about 80% at 410–1000 nm, and the bandgap (Eg) of 3.01 eV at different laser energies. At the same laser energy of 250 mJ/pulse, phase structure, and Eg of the films are uniform as substrate temperature increases to 350 °C, but the resistivity increases to the order of 1 Ω cm and the average transmittance decreases to 60%; the structure and properties of the films completely change as substrate temperature increases to 500 °C. The XRD and transmittance spectra analysis indicate that rudimental oxygen is introduced into CuI thin films, which results in obviously lower resistivity than that of the previously reported value (103 Ω cm). These results imply that the prepared CuI films exhibit excellent transparent conductive properties and can be used in solar cells.

Optical and Electrical Properties of Large Area SnO<sub>2</sub>: F Thin Films by Spray Pyrolysis

SnO2:F transparent conductive thin films with the area of 500×500mm2 were deposited on glass substrates by spray pyrolysis using SnCl4•5H2O and HF as the starting material and dopant respectively in methanol. The effects of HF concentration on the crystallized status, microstructures, transmittance, conductivity and low emissivity performances of the films have been studied. The results indicated that when HF content was excessive the solution presented strong acidity and it was difficult to obtain the uniform and dense films. However, when HF content was less, the conductivity of the film was poor. In this paper, The optimal mount of dopant HF was investigated and the molar ratio of Sn to F is 1:0.5. And also the uniform and dense SnO2:F transparent conductive oxide thin films can be obtained, whose resistivity reached 6.36×10-4Ω•cm, and the average transmittance in visible region was 80%.The low emissivity of this film was 0.25, which could be used as the Low-E glass.

Influence of anode roughness and buffer layer nature on organic solar cells performance

Fluorine doped transparent conductive tin oxide thin films (FTO) of different surface roughness have been deposited by chemical vapor deposition (FTO SOL), classical chemical spray pyrolysis (FTO CSP), and spray pyrolysis onto heated substrates using infra red irradiation (FTO IRSP); the three deposition methods inducing different surface roughness. It was found that the different FTOs presented similar electrical properties while their structural, morphological and optical properties were related to surface properties. These FTO films have been used as anode in multilayer organic solar cells, based on coupled donor/acceptor–copper phthalocyanine/fullerene. To improve solar cell performance, buffer layers of different natures have been tried at the anode/organic material interface. Deposition of a thin molybdenum oxide film onto FTO smooth films afforded reproducible devices with performance similar to those obtained with indium tin oxide anodes. However, cell efficiency decreased as FTO surface roughness increased. The degree of degradation depended on the nature of the buffer layer. We show that it is necessary to use buffer layer material that allows consistency and completeness of the electrode coverage.

Ga doped ZnO thin films prepared by RF plasma assisted DC magnetron sputtering under reductive atmosphere without heating substrates

AbstractGa doped ZnO (GZO) transparent conductive thin films have been prepared by RF plasma assisted DC magnetron sputtering under a reductive atmosphere without intentionally heating substrate. The resistivity of the GZO film facing the erosion area in the source target falls to about a 1/1000 value by providing the RF plasma, resulting in a uniform distribution of the sheet resistance. Currently obtained values of resistivity, Hall mobility, and carrier concentration are 1 x 10‐2 Ω‐cm, 4 cm2/Vs, and 3 x 1020 cm‐3, respectively. It has been also found that the crystallization of GZO films is also enhanced by the RF plasma. After the accelerated aging test (60 °C ‐ 95%RH) for 250 hrs, the sheet resistance maintains almost the same as the initial value for the GZO film prepared with RF plasma, though that increases by 15 times for the film prepared without RF plasma. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influences in high quality zinc oxide films and their photoelectrochemical performance

Transparent conductive zinc oxide thin films have been synthesized by spray pyrolytic decomposition of aqueous solution of zinc acetate onto the corning glasses with different pre-heating temperatures. The influence of pre-heating temperature on the structural, morphological, optoelectronic and electrical properties is investigated. The X-ray diffraction patterns revealed the polycrystalline nature with hexagonal (wurtzite) crystal structure. Films show preferred c-axis orientated with (0 0 2) growth. Films deposited at various deposition temperatures exhibit different surface morphologies. It is observed that the temperature plays an important role in modifying surface morphology and size of crystallites. Compact hexagonal platelets like structure is observed for lower temperature samples. The films exhibit nanoparticles of size 60–100 nm for 250–500 °C temperatures. Films are highly transparent and conducting, we achieved 95% transmittance at 550 nm with electrical resistivity 0.062 Ω cm and figure of merit 7.88 × 10 −4 □/Ω. Moreover samples are photoelectrochemically active and exhibit the highest photocurrent of 212 μA, a photovoltage of 353 mV and 0.32 fill factor for the 450 °C films.

Synthesis of c-axis preferred orientation ZnO:Al transparent conductive thin films using a novel solvent method

Transparent aluminum doped zinc oxide (ZnO:Al, AZO) conducting thin films with a high-preferential c-axis orientation were synthesized using a new sol–gel formula. The films were deposited using a spin-coating route onto borosilicate glass substrates. We used propylene glycol methyl ether (PGME) as the solvent in place of ethylene glycol monomethyl ether (EGME), which is commonly used because it is easier to deposit onto the substrates. PGME is also superior in terms of health and safety. PGME solvent does not need to settle for several days before use and can be spin-coated as soon as the raw material and solvent are mixed. The effects of this novel solvent on the structural, morphological, electrical and optical properties are discussed using XRD, SEM, a four-point probe and UV–VIS spectrophotometry. It was found that the films produced with PGME showed a high-preferential c-axis orientation and compact microstructure in comparison films produced using EGME. The electrical resistivity of AZO thin films produced with PGME solvent was lowered to 3.474 × 10 − 3 Ω cm after annealing in 95 N 2/5H 2 atmosphere. In addition, the optical transmittances of AZO thin films on glass plates were higher than 90% in the visible wavelength region.

Properties of Nb-doped ZnO transparent conductive thin films deposited by rf magnetron sputtering using a high quality ceramic target

Nb-doped ZnO films with (002) orientation have been grown on glass substrates by rf magnetron sputtering followed by vacuum annealing at 400°C for 3 h. The microstructures and surface figures of the Nbdoped ZnO films were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. And its optical and electrical properties were measured at room temperature using a four-point probe technique and 756-type spectrophotometer, respectively. X-ray diffraction (XRD) revealed that the films are highly textured along the c axis and perpendicular to the surface of the substrate. After annealing at 400°C for 180 min under vacuum, transmittance of about 90% in visible region for Nb doped ZnO films was confirmed by the optical transmission spectra, and the low resistivity of 5·47 × 10−3 Ω·cm was obtained.

Transparent conductive tungsten-doped tin oxide thin films synthesized by sol–gel technique on quartz glass substrates

Transparent conductive tungsten-doped tin oxide (SnO2:W) thin films were synthesized on quartz glass substrates by sol–gel dip-coating method. It was found that the films were highly transparent and the average optical transmission was about 90% in the visible and near infrared region from 400 to 2,500 nm. The optical band gap is about 4.1 eV. The lowest resistivity of 5.8 × 10−3 ohm cm was obtained, with the carrier mobility of 14.2 cm2 V−1 s−1 and carrier concentration of 7.6 × 1019 cm−3 in 3 at.% W-doping films annealed at 850 °C in air. The structural properties, surface morphology and chemical states for the films were investigated.

Study of Boron-Doped ZnO Transparent Conductive Thin Films

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Effect of Ga Doping Concentration on Electrical and Optical Properties of Nano-ZnO:Ga Transparent Conductive Films

Transparent conductive nano ZnO thin films with different Ga doping concentrations (1, 3, 5, 7 at.%) were prepared on glass substrate by RF magnetron sputtering. The influence of Ga doping concentration on the structural, electrical and optical properties of ZnO:Ga films was investigated by XRD, SEM, Hall measurement and optical-transmission spectroscopy. It shows that the nano ZnO:Ga films are dense and flat, and have polycrystalline structure with preferential (002) and weak (101) orientation. The grain sizes, carrier concentration and Hall mobility changes non-linearly with the increase of Ga-content. The lowest resistivity of 1.44×10−3 Ωcm appears at 3 at.% Ga doping concentration. The average transmittance of the films is about 80∼90% in the visible range. The optical band gap obtained for these films is larger than for pure ZnO (∼3.37 eV).

Effect of Substrate Temperature on the Properties of Nano-ZnO: In Transparent Conductive Films

High quality transparent conductive In-doped nano-ZnO thin films with In content of 2 at% were prepared by RF magnetron sputtering. The effect of substrate temperature on the structure, electrical and optical properties of nano-ZnO thin films was investigated by XRD, Hall measurement and optical transmittance spectroscopy. It shows that all the films are polycrystalline with hexagonal wurtzite structure and c-axis is perpendicular to the substrate. The grain size of the films changed from 22.4 to 28.7 nm with different substrate temperatures. The lowest resistivity of the films obtained is 3.18×10−3 Ω⋅cm as the growth temperature is 100 °C. The transmittance of all the films is about 85% in the visible region, and the optical band gap is in the range of 3.40∼3.45 eV.

311 スパッタ法により形成させた透明導電薄膜の圧抵抗特性評価(機械材料・材料加工II)

311 スパッタ法により形成させた透明導電薄膜の圧抵抗特性評価(機械材料・材料加工II)

Electrical and optical properties of molybdenum-doped ZnO transparent conductive thin films prepared by dc reactive magnetron sputtering

Molybdenum-doped ZnO (ZMO) transparent conductive thin films were prepared by dc reactive magnetron sputtering on glass substrates from metallic targets. The structure, surface morphology, chemical state, optical and electrical properties of ZMO films were studied. The XRD pattern confirmed that ZMO thin films were polycrystalline with the hexagonal crystal structure, and the surface morphology measured by AFM demonstrated that the surface was smooth and compact. Chemical state analysis revealed that molybdenum atoms existed mainly in Mo6+ and Mo5+ ions but not in only single oxidation states. The minimum resistivity of 7.9 × 10−4 Ω cm is obtained with a carrier mobility of 27.3 cm2 V−1 s−1 and a carrier concentration of 3.1 × 1020 cm−3, and the average transmittance is more than 85% in the visible light region. The refractive index and extinction coefficient at the wavelength of 550 nm are 1.853 and 7.0 × 10−3, respectively. The energy bands increase from 3.37 eV to 3.8 eV with the increase in carrier concentrations and the carrier effective mass m* is 0.33 times the electron mass.

Zn-doped CuAlS2 transparent p-type conductive thin films deposited by pulsed plasma deposition

CuAl0.90Zn0.10S2 thin films were deposited by pulsed plasma deposition. The dependence of structural, surface morphology, electrical, and optical properties of the films on substrate temperature was investigated. X-ray diffraction patterns reveal that the film be amorphous structure. The electrical properties are sensitive to the substrate temperature. A typical sample with conductivity of 50.9 S cm−1, carrier mobility of 3.13 cm2 V−1 s−1, carrier concentration of 1.41×1019 cm−3, and average transmission of 74% in visible range of 400–700 nm was obtained. A transparent p-CuAlS2:Zn/n-In2O3:W heterogeneous diode was also fabricated and exhibits rectifying current-voltage characteristics. The ratio of forward current to the reverse current exceeds 80 within the range of applied voltages of −3.0–+3.0 V and the turn-on voltage is approximately 0.5–0.8 V.

Electrical properties of transparent conducting carbon nanotube films

Single walled-carbon nanotube (SWCNT) thin film is one of the candidates for the next-generation flexible and transparent conductive thin film, which is a crucial component in various applications such as electrodes of flat-panel displays, solar cells, light emitting diodes, and touch panels. An intensive research work is underway to develop thin and flexible SWCNT films. The most important requirement of an SWCNT thin film is that it should show a low sheet resistance coupled with a high transparency. In this work, thin films of SWCNTs are prepared by vacuum filtration. The electrical properties of the as-prepared, annealed and HNO3-treated SWCNT films have been investigated. It is found that the square resistance can be significantly changed upon anneal and HNO3-treatment. A room-temperature ethanol alcohol sensor based on the SWCNT film has also been demonstrated.

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/m 2/day at 40 °C and 100% relative humidity (RH), and the permeation of oxygen was less than 0.5 cc/m 2 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.

Optical and electrical properties of SnO 2:Sb thin films deposited by oblique angle deposition

The antimony doped tin oxide (SnO 2:Sb) (ATO) thin films were prepared by oblique angle electron beam evaporation technique. X-ray diffraction, field emission scanning electron microscopy, UV–vis–NIR spectrophotometer and four-point probe resistor were employed to characterize the structure, morphology, optical and electrical properties. The results show that oblique angle deposition ATO thin films with tilted columns structure are anisotropic. The in-plane birefringence of optical anisotropy is up to 0.035 at α = 70°, which means that it is suitable as wave plate and polarizer. The electrical anisotropy of sheet resistance shows that the sheet resistance parallel to the deposition plane is larger than that perpendicular to the deposition plane and it can be changed from 900 Ω/□ to 3500 Ω/□ for deposition angle from 40° to 85°, which means that the sheet resistance can be effectively tuned by changing the deposition angle. Additionally, the sandwich structure of SiO 2 buffer layer plus normal ATO films and oblique angle deposition ATO films can reduce the resistance, which can balance the optical and electrical anisotropy. It is suggested that oblique angle deposition ATO thin films can be used as transparent conductive thin films in solar cell, anti-foggy windows and multifunctional carrier in liquid crystal display.

Analysis of thermal effect on transparent conductive oxide thin films ablated by UV laser

Transparent conductive oxide thin films are applied to many computer, communication and consumer electronics products including thin film transistor liquid crystal displays, organic light emitting diodes, solar cells, mobile phones, and digital cameras. The laser direct write patterning of the indium tin oxide (ITO) thin film processing technique produces a heat affected zone that has an enormous effect on the electro-optical efficiency of transparent conductive oxide films. This is because direct laser writing patterning in thermal machining process can create debris and micro-cracks in the substrate. Therefore, this study establishes the ultraviolet (UV) laser ablation of temperature model on the polycarbonate and soda-lime glass substrates using the finite element analysis software ANSYS, and measures the temperature field based on the laser micro-patterning process. The meshing model determines the structure of the pre-processors and parameters were set with ANSYS parameter design language. This study also simulates the Gaussian distribution laser irradiation on the pre-processor structure. A UV laser processing system made micro-patterning on ITO thin films to analyze which conditions damaged the substrates. Comparing the simulation and experiment results reveals the minimum laser ablation threshold of the ITO thin films with the melting and vaporization temperatures. Simulation results show that the temperature distribution on PC and soda-lime glass substrates after laser irradiation of 1.05 μs with a laser output power of 0.07 W produces temperatures of approximately 52 °C, 54 °C and 345°Cand 205 °C at the laser output power of 0.46 W. The experiment results show that the patterning region is similar to the simulation results, and the lower laser power does not damage the substrates.