Amorphous Indium Tin Oxide Research Articles

Study of the morphological change of amorphous ITO films after temperature–humidity treatment

Amorphous indium tin oxide (ITO) thin films have been deposited on silicon and Corning 7059 glass substrates at room temperature (RT) and at 75 °C by direct-current magnetron sputtering method. After exposure of the two kinds of samples to the temperature–humidity (T–H) test, we find that there are two different types of circular structures are formed. RT ITO films are composed of granules, and 75 °C ITO films are composed of several different parts which have different Sn and In concentrations. Metallic ion concentration corrosion cells are used to explain the phenomena.

Highly Conductive and Transparent Poly(3,4-ethylenedioxythiophene):p-Toluene Sulfonate Films as a Flexible Organic Electrode

Highly transparent and conductive poly(3,4-ethylenedioxythiophene):p-toluene sulfonate (PEDOT:PTS) films were prepared by gas-phase polymerization using the chemical vapor deposition (CVD) technique for flexible organic electrodes. These conductive PEDOT:PTS films have a high transparency (up to 80%), and possess a very low sheet resistance of a 100 Ω/□ (up to 2500 S cm-1) at 150 nm thickness. Their sheet resistance attained 27 Ω/□ at 350 nm thickness with O2 plasma doping. The 1–3 mm pitched pattern can also be easily formed by plasma etching and/or the selective exposure technique of O2 plasma. This electrode film has a higher transmittance than an amorphous indium–tin oxide (a-ITO) electrode film with thickness under 120 nm, and their conductivities were comparable with the a-ITO layer. We report on the fabrication and characterization of a flexible organic light-emitting diode (OELD) using PEDOT:PTS for the electrodes. The device is demonstrated to exhibit light emission and a brightness level up to 1800 cd/m2 at 25 V.

Thermal crystallization kinetics and crystallite size distribution of amorphous ITO film deposited in the presence or absence of water vapor

The isothermal crystallization process of amorphous indium tin oxide films was investigated by examining the peak intensity, obtained through high-temperature X-ray diffraction analysis. The introduction of water vapor (5 × 10 − 5 Torr) during sputtering-deposition significantly reduced the rate of crystallization. This can be attributed to the presence of chemically bonded hydrogen. Classical kinetic analysis based on the Kolmogorov–Johnson–Mehl–Avrami equation indicated three distinct changes caused by the introduction of water vapor: it reduced the kinetic exponent ( n) from approximately 5/2 (2.59 ± 0.12) to 3/2 (1.53 ± 0.10), increased the activation energy ( E a ) from 79.9 to 116 kJ/mol, and increased the average crystallite size from 54 to 93 nm. Site-saturated and continuous nucleation models are tentatively proposed, to account for the crystallization of amorphous ITO films deposited in the presence and absence of water vapor, respectively.

Low-Temperature Solution-Processed Amorphous Indium Tin Oxide Field-Effect Transistors

Amorphous indium tin oxide (ITO)-based thin-film transistors (TFTs) were fabricated on various dielectrics [SiO(2) and self-assembled nanodielectrics (SANDs)] by spin-coating an ITO film precursor solution consisting of InCl(3) and SnCl(4) as the sources of In(3+) and Sn(4+), respectively, methoxyethanol (solvent), and ethanolamine (base). These films can be annealed at temperatures T(a) < or = 250 degrees C and afford devices with excellent electrical characteristics. The optimized [In(3+)]/[In(3+) + Sn(4+)] molar ratio (0.7) and annealing temperature (T(a) = 250 degrees C) afford TFTs exhibiting electron mobilities of approximately 2 and approximately 10-20 cm(2) V(-1) s(-1) with SiO(2) and SAND, respectively, as the gate dielectric. Remarkably, ITO TFTs processed at 220 degrees C still exhibit electron mobilities of >0.2 cm(2) V(-1) s(-1), which is encouraging for processing on plastic substrates.

Parametric Studies of Pulsed Laser Deposition of Indium Tin Oxide and Ultra-thin Diamond-like Carbon for Organic Light-emitting Devices

Device quality indium tin oxide (ITO) films are deposited on glass substrates and ultra-thin diamond-like carbon films are deposited as a buffer layer on ITO by a pulsed Nd:YAG laser at 355 nm and 532 nm wavelength. ITO films deposited at room temperature are largely amorphous although their optical transmittances in the visible range are > 90%. The resistivity of their amorphous ITO films is too high to enable an efficient organic light-emitting device (OLED), in contrast to that deposited by a KrF laser. Substrate heating at $200^{\circ}C$ with laser wavelength of 355 nm, the ITO film resistivity decreases by almost an order of magnitude to $2{\times}10^{-4}\;{\Omega}\;cm$ while its optical transmittance is maintained at > 90%. The thermally induced crystallization of ITO has a preferred directional orientation texture which largely accounts for the lowering of film resistivity. The background gas and deposition distance, that between the ITO target and the glass substrate, influence the thin-film microstructures. The optical and electrical properties are compared to published results using other nanosecond lasers and other fluence, as well as the use of ultra fast lasers. Molecularly doped, single-layer OLEDs of ITO/(PVK+TPD+ $Alq_3$ )/Al which are fabricated using pulsed-laser deposited ITO samples are compared to those fabricated using the commercial ITO. Effects such as surface texture and roughness of ITO and the insertion of DLC as a buffer layer into ITO/DLC/(PVK+TPD+ $Alq_3$ )/Al devices are investigated. The effects of DLC-on-ITO on OLED improvement such as better turn-on voltage and brightness are explained by a possible reduction of energy barrier to the hole injection from ITO into the light-emitting layer.

Amorphous indium tin oxide electrodes for piezoelectric and light-emitting device deposited by vacuum roll to roll process

The amorphous indium tin oxides (ITOs) and the transparent conducting oxides (TCOs) electrode on the flexible polymer substrate, polyvinylidene difluoride (PVDF), and their application to the suggested combinational device system were studied. The lower range ordered crystalline structure of the ITOs enable the reduction of micro-cracks or defect grains under flexible conditions. With the piezoelectric function of substrate polymer, which is added to the display function with OLED (Organic light emitting diodes), the pattern design with the separated electrodes for two devices for emitting light and vibration was considered. From these results, the concept of a combinational flexible electronic device system with a functional polymer substrate could be suggested.

On the structure and surface chemical composition of indium–tin oxide films prepared by long-throw magnetron sputtering

Structures and surface chemical composition of indium tin oxide (ITO) thin films prepared by long-throw radio-frequency magnetron sputtering technique have been investigated. The ITO films were deposited on glass substrates using a 20 cm target-to-substrate distance in a pure argon sputtering environment. X-ray diffraction results showed that an increase in substrate temperature resulted in ITO structure evolution from amorphous to polycrystalline. Field-emission scanning electron microscopy micrographs suggested that the ITO films were free of bombardment of energetic particles since the microstructures of the films exhibited a smaller grain size and no sub-grain boundary could be observed. The surface composition of the ITO films was characterized by X-ray photoelectron spectroscopy (XPS). Oxygen atoms in both amorphous and crystalline ITO structures were observed from O 1 s XPS spectra. However, the peak of the oxygen atoms in amorphous ITO phase could only be found in samples prepared at low substrate temperatures. Its relative peak area decreased drastically when substrate temperatures were larger than 200 °C. In addition, a composition analysis from the XPS results revealed that the films deposited at low substrate temperatures contained high concentration of oxygen at the film surfaces. The oxygen-rich surfaces can be attributed to hydrolysis reactions of indium oxides, especially when large amount of the amorphous ITO were developed near the film surfaces.

Energy band calculation of amorphous indium tin oxide films on polyethylene terephthalate substrate with indirect transition

Amorphous indium tin oxide films were grown on a polyethylene terephthalate substrate by RF-magnetron sputtering. The energy band, which contained not only the width of the optical band but also detailed information about the Fermi level (Ef) and mobility edge , was calculated according to the theory of amorphous semiconductors with the experimental parameters of transmittance and electrical conductivity. Furthermore, the calculated energy band can be used to effectively explain both the variation of electrical conductivity and the weak absorption at the wavelength range of 750–800 nm in our experiment. An indirect transition was also clearly observed in our samples during the calculation of the optical energy band.

Electrical transport properties in indium tin oxide films prepared by electron-beam evaporation

Amorphous and polycrystalline indium tin oxide films have been prepared by electron-beam evaporation method. The amorphous films exhibit semiconductor behavior, while metallic conductivity is observed in the polycrystalline samples. The magnetoconductivities of the polycrystalline films are positive at low temperatures and can be well described by the theory of three-dimensional weak-localization effect. In addition, the electron phase-breaking rate is proportional to T3/2. Comparing the experimental results with theory, we find that the electron-electron scattering is the dominant destroyer of the constructive interference in the films. In addition, the Coulomb interaction is the main contribution to the nontrivial corrections for the electrical conductivity at low temperatures.

Excimer laser beam/ITO interaction: from laser processing to surface reaction

AbstractWe investigated interactions between UV light and Indium Tin Oxide (ITO) thin films sputtered at room temperature. Owing to their photon energy, higher than the band gap of In2O3 (3.5–4.0 eV), KrF (5.0 eV) or XeCl (4.0 eV) lasers proved useful, at high fluences (1‐3 J/cm2) for minute laser shaping, at low fluences (100 mJ/cm2) for laser annealing, or even at very low fluences for gases desorption. Sputtered ITO becomes totally amorphous when an oxygen flow is mixed in the process argon and adjusted for the lowest resistivity. As non optimised layers behave like gas sensors, amorphous ITO is immune to atmospheric agents. The band structure of indium oxide and exposures to UV light at selected wavelengths helped to a better understanding of the gas sensing mechanisms on oxygen rich and oxygen poor layers. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effect of oxygen partial pressure on optical and electrical properties of co‐sputtered amorphous zinc indium tin oxide thin films

AbstractTransparent thin films of amorphous zinc indium tin oxide were prepared at room temperature by co‐sputtering of zinc oxide and indium tin oxide. Effect of oxygen partial pressure on the optical and electrical properties of amorphous zinc indium tin oxide thin films were investigated. Conductivity, carrier concentration and Hall mobility showed strong dependence on the oxygen partial pressure and these parameters decreased with the increase of oxygen pressure. The effect of subgap states caused a sharp difference in measured optical band gap values between the films deposited with and without oxygen partial pressure. Carrier transport studies were carried out by temperature dependent conductivity measurements. At low electron density, the conductivity showed thermally activated behaviour and at higher carrier concentrations it changed to almost degenerate band conduction. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optical and Carrier Transport Properties of Cosputtered Zn–In–Sn–O Films and Their Applications to TFTs

The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO) thin films and the characteristics of the thin-film transistors (TFTs) were examined as a function of chemical composition. The as-deposited films were very conductive and showed clear free carrier absorption (FCA). The analysis of the FCA gave the effective mass value of and a momentum relaxation time of 3.9 fs for an film with . TFTs with the as-deposited channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at decreased the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages when Zn contents were or larger. shifted to larger negative values, and subthreshold voltage swing increased with decreasing the Zn content, while large on–off current ratios were kept for all the Zn contents. The field effect mobilities ranged from 12.4 to for the TFTs with Zn contents varying from 5 to . The role of Zn content is also discussed in relation to the carrier transport properties and amorphous structures.

Optical and electrical properties of co-sputtered amorphous transparent conducting zinc indium tin oxide thin films

Highly conductive and transparent thin films of amorphous zinc indium tin oxide are prepared at room temperature by co-sputtering of zinc oxide and indium tin oxide. Cationic contents in the films are varied by adjusting the power to the sputtering targets. Optical transmission study of films showed an average transmission greater than 85% across the visible region. Maximum conductivity of 6 × 10 2 S cm − 1 is obtained for Zn/In/Sn atomic ratio 0.4/0.4/0.2 in the film. Hall mobility strongly depends on carrier concentration and maximum mobility obtained is 18 cm 2 V − 1 s − 1 at a carrier concentration of 2.1 × 10 20 cm − 3 . Optical band gap of films varied from 3.44 eV to 3 eV with the increase of zinc content in the film while the refractive index of the films at 600 nm is about 2.0.

Electrical and optical study of ITO films on glass and polymer substrates prepared by DC magnetron sputtering type negative metal ion beam deposition

Transparent, conducting indium tin oxide (ITO) films were deposited without intentional substrate heating on glass and polyethersulfone (PES) substrates by a magnetron sputter type negative metal ion source (MSNIS). The effect of substrate type on optical transmittance, electrical resistivity, surface morphology and roughness of the ITO film was analyzed. ITO/glass substrates show a higher optical transmittance (89%) and lower resistivity (4 × 10 −4 Ω cm) than ITO/PES (78%, 6 × 10 −4 Ω cm). X-ray diffraction (XRD) spectra indicate polycrystalline ITO films deposited on glass and amorphous ITO films on PES. Atomic force microscopy (AFM) images also indicate that ITO/glass has a lower surface roughness than ITO/PES. The values of figure of merit ( T 10/ R sh) for ITO/glass ( ϕ TC = 7.7 × 10 −3 Ω −1) are higher than ITO/PES ( ϕ TC = 1.3 × 10 −3 Ω −1), indicating that ITO/glass achieved the best performance in this study.

Thermal change of amorphous indium tin oxide films sputter-deposited in water vapor atmosphere

Amorphous ITO thin films were deposited on silicon wafers at room temperature by RF + DC magnetron sputtering at water vapor partial pressures between 0 and 6 × 10 − 5 Torr. The O/(In + Sn) ratio was determined by Rutherford backscattering spectroscopy. The effect of water vapor on the thermal crystallization process was monitored by high-temperature X-ray diffraction (XRD) analysis. We found a simple dependence between the crystallization temperature and the water vapor partial pressure. After the high-temperature XRD, the films deposited at low water vapor pressures (2 × 10 − 5 Torr or lower) exhibited <100> preferred orientation, whereas those deposited at high water vapor pressures (3 × 10 − 5 Torr or higher) exhibited <111> preferred orientation. Introduction of water vapor during the deposition decreased carrier concentration and increased mobility. The carrier concentration after thermal crystallization was dependent on the water vapor partial pressure.

Thermally induced changes in amorphous indium-tin-oxide thin films

Amorphous indium-tin-oxide (ITO) transparent conducting film (15 at% Sn; thickness, 150–190 nm) was deposited on silicon wafer at room temperature by RF magnetron sputtering for temperature programmed desorption (TPD) in vacuum. The thermal crystallization was accompanied by evolution of water vapor (the main gas), argon and carbon dioxide. The total amount of evolved water vapor (H2O [mol]/(In [mol]+Sn [mol])>0.2) was one or two orders of magnitude more than that from the nanocrystalline ITO films reported in our previous papers. The thermal change of amorphous ITO film was remarkably affected by the position of the substrate. An abrupt gas evolution was characteristic of the amorphous ITO films deposited on the position near the target center. The evolution temperature (548–563 K) was higher than the gas evolution temperature from the crystalline films. The far from center positioned films crystallized at higher temperature with relatively slower evolution of the gases.

Influence of defects and processing parameters on the properties of indium tin oxide films on polyethylene napthalate substrate

Indium tin oxide (ITO) thin films were deposited on polyethylene napthalate (PEN) by rf sputtering using different rf powers (60 and 120W) and at different substrate temperatures (room temperature and 100°C). Selected PEN substrates were pretreated using an Ar plasma before ITO sputter deposition. Rutherford backscattering spectrometry was used to determine the oxygen content in the films. Hall effect measurements were used to evaluate the electrical properties. In this paper the influence of defect structure, sputtering conditions, and the effect of annealing on the electrical and optical properties of ITO on PEN have been investigated. Electrical properties such as carrier concentration, mobility, and resistivity of the ITO films varied with rf power and substrate temperature. The electrical and optical properties of the films changed after annealing in air. This study also describes how the as-deposited amorphous ITO changes from amorphous to crystalline as a result of heat treatment, and investigates the effects of Sn defect clustering on electrical and optical properties of the ITO films.

Heavy Phosphate Adsorption on Amorphous ITO Film Electrodes: Nano-Barrier Effect for Highly Selective Exclusion of Anionic Species

We prepared an amorphous indium tin oxide (ITO) film and studied it with respect to its surface characterization and the effect of phosphate adsorption on its electrochemical properties. The film was deposited using RF sputtering under ambient low-oxygen conditions at room temperature. The XPS results revealed that the amount of phosphate adsorbed on the amorphous ITO film was more than 4.6 times greater than that adsorbed on commercially available polycrystalline ITO film in spite of the smaller microscopic surface area of the former. Electrochemical responses for anionic species such as L-ascorbic acid (AA) and 3,4-dihydroxyphenylacetic acid (DOPAC) on the phosphate-adsorbed ITO film electrodes were more effectively suppressed at the amorphous ITO film electrode than at the polycrystalline ITO film electrode when a phosphate-containing electrolyte was used. Such suppression could be attributed to the electrostatic repulsion between the anionic species and more heavily adsorbed phosphate on our amorphous ITO film electrode surface. This effect is made more pronounced by increasing the phosphate concentration to 1 mM. With 1 mM phosphate, the amorphous ITO film electrode showed the highest selectivity for dopamine (DA) against the anionic species, namely, 880 for DA/AA and 330 for DA/DOPAC, respectively. In contrast, the selectivity was 120 for DA/AA and 20 for DA/DOPAC with the polycrystalline ITO film electrode.

Room temperature crystallization of indium tin oxide films on glass and polyethylene terephthalate substrates using rf plasma

The crystallization of amorphous indium tin oxide (ITO) films was achieved by rf (13.56MHz) plasma treatment. Although the films were crystallized after 2min, the sample temperature was lower than 90°C without compulsory cooling even after 10min of treatment and polyethylene terephthalate (PET) substrates had no damage. Plasma-crystallized sputtered ITO films have a bixbite structure and the resistivity reached to 1.6×10−4Ω∙cm. ITO thin films have almost the same resistivity in both cases of PET and glass substrates used and plasma-treated PET ITO films have a bit higher resistivity than that of glass ITO films, while mass spectroscopy measurements indicated that ITO films deposited on PET substrates are expected to include no apparent gas species ejected from PET substrate. It was found that the plasma gas pressure is the key parameter for the effective crystallization and the appropriate gas pressure depends on the plasma gas species.

Thin-film transistors with transparent amorphous zinc indium tin oxide channel layer

Thin-film transistors (TFTs) with transparent amorphous zinc indium tin oxide (ZITO) channel layer are demonstrated. Optical transmission of the channel layer is approximately 85% in the visible portion of the electromagnetic spectrum. The channel layer is formed via rf magnetron sputter deposition and then furnace annealed in air. Peak incremental mobilities of 5–19 cm2 V−1 s−1 and turn-on voltages of −4 to −17 V are obtained for devices annealed post-deposition at 100–300 °C, respectively. Current–voltage measurements indicate n-channel, depletion-mode transistor operation with excellent drain current saturation and a drain current on-to-off ratio greater than 106. ZITO is one example of an emerging class of high performance TFT channel materials involving transparent amorphous multicomponent oxides composed of heavy-metal cations with (n − 1)d10ns0 (n ⩾ 4) electronic configuration.