Resistivity Indium Tin Oxide Research Articles

Clear transparency all-solid-state switchable mirror with Mg–Ti thin film on polymer sheet

We applied magnesium–titanium (Mg–Ti) thin film as the optical switching layer to all-solid-state switchable mirror on plastic sheet (polyethylene terephthalate, PET) in the viewpoint of clear transparency at the transparent state. For the switching speed from the reflective to the transparent states, the PET-device showed a little slower switching speed than the glass-device, and it depended on the sheet resistance of indium tin oxide (ITO). When Mg–Ti thin film was applied to the PET-device, absorption at the visible ray was reduced, resulting in near-colorless state at the transparent state. The PET-device with Mg–Ti thin film showed chromaticity coordinates of x=0.341 and y=0.339 and a luminous transmittance of 42.4% at the transparent state. However, the PET-device had lower durability than that of the glass-device. It seemed to be related with the degradation mechanism of the optical switching layer. When Mg–Ti thin film after the durability test was analyzed by XPS, though the glass-device had much oxidized state of magnesium, the PET-device had mixture states of oxide and hydroxide in the optical switching layer. We suggest that the hydroxide in the layer will be formed by including water in the PET sheet, and the hydroxide might significantly affect the rapid degradation of the PET-device.

Enhancement of current-voltage characteristics of multilayer organic light emitting diodes by using nanostructured composite films

With the aim of improving the photonic efficiency of an organic light emitting diode (OLED) and its display duration, both the hole transport layer (HTL) and the emitting layer (EL) were prepared as nanostructured thin films. For the HTL, nanocomposite films were prepared by spin-coating a homogeneous solution of low molecular weight poly(4-styrenesulfonate) (PEDOT-PSS) and surfactant-capped TiO2 nanocrystals onto low resistivity indium tin oxide (ITO) substrates; for the EL, nancrystalline titatium oxide (nc-TiO2)-embedded Poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV+nc-TiO2) conjugate polymers were spin-coated onto the HTL. Also, for a shallow contact of Al/LiF/MEH-PPV instead of Al/MEH-PPV a super LiF thin film was deposited onto the EL by vacuum evaporation. The resulting multilayer OLED had the following structure of Al/LiF/MEH-PPV+nc-TiO2/PEDOT-PSS+nc-TiO2/ITO. Characterization of the nanocomposite films showed that both the current-voltage (I-V) characteristics and the photoluminescent properties of the nanocomposite materials were significantly enhanced in comparison with the standard polymers. OLEDs made from these layers would exhibit a large photonic efficiency.

Modification of optical and electrical properties of ITO using a thin Al capping layer

In this study, the work function, transmittance, and resistivity of indium tin oxide (ITO) thin films were successfully modified by depositing an Al capping layer on top of ITO with subsequent thermal annealing. The 5 nm thick Al layer was deposited by a conventional dc magnetron sputtering method and the layer was converted into an aluminum oxinitride by subjecting the sample to rapid thermal annealing (RTA) under a nitrogen atmosphere. The films exhibited a high transmittance of 86% on average within the visible wavelength region with an average resistivity value of 7.9 × 10 − 4 Ω cm. Heat-treating the Al/ITO films via RTA resulted in the decrease of the optical band gap from that of bare ITO. In addition, the films showed red-shift phenomena due to their decreased band gaps when the heat-treatment temperature was increased. The resultant electrical and optical characteristics can be explained by the formation of aluminum oxinitride on the surface of the ITO films. The work function of the heat-treated films increased by up to 0.26 eV from that of a bare ITO film. The increase of the work function predicts the reduction of the hole-injection barrier in organic light-emitting diode (OLED) devices and the eventual use of these films could provide much improved efficiency of devices.

Reflectivity and Abnormal Absorption at ITO/Al Interface

The electrical and optical thermal stability of indium tin oxide (ITO)/Al bilayers are investigated in this study. The electrical resistivity of ITO and ITO/Al multilayers, both about 1 × 10 −3 Ω cm after annealing at 300°C for 1 min, are measured by the four-probe measurement method. In addition to the electrical measurements, we also observe the rapid initial diffusion of Al atoms into the ITO thin films. When the diffusing elemental Al atoms occupy interstitial sites they tend to form defects, causing a serious decrease in the reflectance of the a-ITO/Al bilayer in the wavelength region from 400 nm to 600 nm.

Electrical, optical, and structural properties of ITO co-sputtered IZO films by dual target magnetron sputtering

We have investigated electrical, optical, and structural properties of indium tin oxide (ITO) co-sputtered indium zinc oxide (IZO) film prepared by a dual target direct current (DC) magnetron sputtering at room temperature in pure Ar ambient. It was shown that the resistivity and sheet resistance of ITO co-sputtered IZO films monotonically increased with increasing DC power of ITO target at constant DC power of IZO target. Synchrotron X-ray scattering and scanning electron microscope examination results show that addition of ITO in the IZO film lead to crystallization of IZTO film due to low transition temperature of the ITO from amorphous to crystalline. However, ITO co-sputtered IZO film (ITO/IZO power = 100 W:100 W) exhibit higher work function than those of pure IZO and ITO film. It was found that the work function as well as the electrical, optical, and surface properties of the IZTO film could be controlled by varying the DC power of IZO and ITO targets, respectively.

The effect of electro-annealing on the electrical properties of ITO film on colorless polyimide substrate

The effect of different annealing methods on the sheet resistance of indium tin oxide (ITO) on polyimide (PI) substrate has been investigated. ITO thin films were prepared by RF magnetron sputtering in pure Ar gas and electro-annealing, this was carried out in the flow of an electric current at several temperatures between 100 and 180 °C in air. Electro- and thermal annealing were compared in order to confirm differences between the electrical, optical and microstructural properties of the ITO thin films. As electro-annealing induced the predominant growth of crystallites of ITO thin films along (4 0 0) plane, the sheet resistance of ITO films that were electro-annealed for 2 mA at 180 °C considerably decreased from 50 to 28 Ω/cm 2.

Electromagnetic Wave Shielding Properties of ITO/PET Thin Film by Film Thickness

The thin films of indium tin oxide (ITO) are used for a variety of electronic devices such as solar cells, touch panels, liquid crystal displays (LCDs). However, these electronic devices are not strong enough against heavy impact since their ITO thin films are deposited on glass substrates. Therefore, ITO thin films were prepared by the inclination opposite target type DC magnetron sputtering equipment onto the Polyethylene Terephthalate (PET) substrate at room temperature using oxidized ITO with In2O3 and SnO2 in a weight ratio of 9:1. In this study, the transmittance, resistivity and electromagnetic wave shielding effectiveness of the ITO thin films prepared at various sputtering time (20~80min namely film thickness; 130~500nm) are measured. The results show that transmittance of the ITO thin films could show about 70% in the range of a visible ray by the variation of film thickness. It also can be seen that a minimum exists in the resistivity of ITO thin films for the variation of film thickness. Electromagnetic wave shielding effectiveness was increased as film thickness increased.

Effects of inductively coupled plasma treatment using O 2, CF 4, and CH 4 on the characteristics of organic light emitting diodes

In this study, the effects of indium tin oxide (ITO) surface treatment by various inductively coupled plasmas using O 2, CF 4, and CH 4 on the device characteristics of the organic light emitting diodes (OLEDs) consisted of ITO glass/2-TNATA/α-NPD/Alq 3/LiF/Al were investigated. Among the various plasma treatments, the treatment by the CF 4 plasma showed the best OLED device characteristics while the treatment by the CH 4 plasma showed the worst OLED characteristics. The best OLED device characteristics obtained with the CF 4 plasma treatment was believed to be related to the decrease of hole injection barrier by the formation of a thin CF x buffer layer between the ITO and OLED material in the OLED device. Also, it was believed to be related to the decrease of hole injection property by the increase of work function and the decrease of resistance of ITO with the increase of the (O + F)/(In + Sn) ratio and the decrease of the Sn 4+/In ratio on the ITO surface after the CF 4 plasma treatment. The OLED device obtained after the ITO surface treatment by the CF 4 plasma decreased the turn-on voltage from 4.8 to 3.0 V, increased the highest power efficiency from ∼ 0.58 to 1.35 lm/W, and increased the highest luminescence from 29,000 to 50,000 cd/m 2.

Study on the O2 Plasma Treatment of Indium Tin Oxide for Organic Light Emitting Diodes Using Inductively Coupled Plasma

In this study, the effect of O2 inductively coupled plasma (ICP) conditions for the indium tin oxide (ITO) surface treatment on the organic light emitting diode (OLED) device performances were investigated. By the O2 plasma treatment of ITO glass, better OLED device performances such as a lower turn-on voltage, a higher luminescence, and a higher power efficiency could be obtained and the use of lower oxygen pressure and higher ICP power improved the device properties further. DC-biasing of the ITO glass substrate degraded the device properties. The use of lower oxygen pressure and higher ICP power increased the densities of O2+ and O* in the plasma, and the plasma-treated ITO surface showed a lower carbon, a higher O/(Sn+In), and a higher Sn4+/In for the condition of lower oxygen pressure and higher ICP power. The improved OLED device properties with the ITO treated at the higher ICP power and the lower pressure appear to be from the increased hole injection to the OLED materials by decreasing the resistance of ITO and by increasing the work function of the ITO.

Improved luminescence properties of nanocrystalline silicon based electroluminescent device by annealing

We report an annealing effect on electrical and luminescence properties of a red electroluminescent device consisting of nanocrystalline silicon (nc-Si). The red luminescence was generated by flowing the forward current into the device at a low threshold direct current (DC) forward voltage with a rise of annealing temperature up to 500 °C. Moreover, the luminescence of the device annealed at 500 °C was more intense than that of the device annealed at 200 °C or less under the same forward current density, because of the injection of a large quantity of carriers to the radiative recombination centers at the nc-Si surface vicinity. These were attained by a low resistivity of indium tin oxide (ITO) electrode and good contact at the ITO electrode/luminous layer interface region by the annealing treatment. The above results indicated that the annealing treatment of the device is effective for the realization of high luminance due to the improvement in the injection efficiency of carriers to the radiative recombination centers.

Electromechanical Properties of Transparent Conducting Substrates for Flexible Electronic Displays

As opto-electronic devices become flexible, the designing of reliable devices becomes more challenging. In this paper, we focus on the degradation of flexible transparent anodes by mechanical and thermal stresses. Indium tin oxide (ITO)-coated polyethyleneterephthalate (PET) is susceptible to cracking at low strains (<2%), but has excellent electrical and optical characteristics. Conducting polymers, such as polyethylene dioxythiophene doped with polystyrene sulfonate (PEDOT:PSS), have good mechanical properties, but are severely degraded by temperature, and have inferior optical and electronic properties. We have developed a mandrel-bending automated test system to evaluate the degradation of flexible anodes in service, and find that even when the strain is below the virgin cracking threshold, there are measurable changes in ITO resistance. Cyclic loading of ITO-coated PET shows three regimes of resistance increase: 1) an increase in resistance, due to changes in sample dimension until equilibrium width is obtained (50-100 cycles); 2) a gradual linear increase in resistance, possibly due to cracking of ITO; and 3) a catastrophic failure after 50 000 cycles due to severe cracking. For PEDOT:PSS-coated PET, the resistance does not increase significantly with increasing tensile strain, and it is also less susceptible to damage from repeated bending.

ITO properties on anisotropic flexible transparent cellulosic substrates under different stress conditions

Cellulose derivatives have been actively investigated as flexible transparent substrates for liquid crystal display (LCD) technology. Working electronic devices deposited on flexible substrates are subject to deformation and external stress. Hydroxypropylcellulose (HPC) solid films (20–60 μm) obtained from aqueous liquid crystalline solutions present tunable topography. Substrates with anisotropic topography were obtained by casting and shearing a 65% (w/w) HPC aqueous solution (HPC-65). Two types of periodicity were observed by atomic force microscopy (AFM). A primary set of large bands, perpendicular to the shear direction (1.8–2.1 μm periodicity and 74–87 nm average peak-to-valley height) was found. A secondary smoother band texture (0.35–0.40 μm periodicity and 2.9–4.4 nm average peak-to-valley height) lies under the large bands. The resistivity of indium tin oxide (ITO), deposited on these flexible anisotropic substrates (HPC-65/ITO) under different stress conditions, was studied. These stress conditions were originated by folding the films around tubes with decreasing diameter (45–5 mm). The folding was performed along two directions. One direction was chosen with the tube axis along the shear direction (FB1). Another direction was chosen with the tube axis perpendicular to the shear direction (FB2). The resistivity of ITO films submitted to FB1 folding does not change significantly with the tube diameter, nor after release neither after overnight relaxation. The resistivity of ITO films submitted to FB2 folding increases strongly and the films become insulating for tubes with diameter lower than 10 mm. AFM measurements show that this anisotropic behavior is induced by cracks in the ITO coatings. These cracks appeared mainly along the secondary set of bands found in anisotropic substrates.

PREPARATION AND CHARACTERIZATION OF ITO THIN FILMS ON GLASS BY A SOL–GEL PROCESS USING METAL SALTS

Indium-tin-oxide (ITO) thin film is one of the indispensable materials for advanced optoelectric technologies. In this work, uniform and transparent ITO films were deposited onto glass substrates using a sol–gel method. The initial sols were prepared from anhydrous ethanol solutions of indium nitrate ( In ( NO 3)3·1 H 2 O ) and tin chloride ( SnCl 4), with different In:Sn ratios. The sols were dip-coated on the substrates and were subjected to annealing at different temperatures. Depending on compositions, the electrical resistivity of ITO coating varied from 1.4×103Ω/□ to 3.5×103Ω/□, and the minimum value for the electric resistivity was observed for the films containing 8% Sn by weight. Increasing heat treatment-temperatures from 400 to 600°C led to increase in conductivity by one order of magnitude. The optical transmittance of 550°C-annealed ITO films was more than 90% in the visible region. The morphology of the ITO films was examined by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The rms-roughness of 350 nm thick ITO film was 1.5 nm. Increasing film thickness resulted in decrease in both, surface roughness and electrical resistivity. The correlations among the film properties and the film preparation conditions are discussed in detail.

High-brightness GaN-based light-emitting diode with indium tin oxide based transparent ohmic contact

We have fabricated GaN-based light-emitting diodes (LEDs) using Ni/Au with indium tin oxide (ITO) overlayer as a p-electrode. A Ni (20 Å)/Au (30 Å)/ITO (600 Å) contact with pre-annealing at 500 °C under an O2 ambient before ITO deposition (O-annealed contact) showed lower contact resistivity compared to the contact with pre-annealing under a N2 ambient (N-annealed contact) and without the pre-annealing (nonannealed contact). The pre-annealing under the O2 ambient produced NiO, which acted as the diffusion barrier for out-diffusion of N and Ga atoms and in-diffusion of In during the subsequent postannealing. Thus, the formation of a Au–In solid solution was effectively suppressed, resulting in the decrease of contact resistivity and enhancement in thermal stability. The LED with the O-annealed contact as a p-electrode showed lower operation voltage at 20 mA, better thermal stability, and enhanced light output than the LED with the N-annealed or nonannealed contact. The low operation voltage and better thermal stability originated from the low contact resistivity and low sheet resistance of ITO. The refractive index of ITO is between GaN and air, reducing the total reflection at the interface of GaN, thus enhancing the light output.

High brightness ingan green leds with an ito on n/sup ++/ -sps upper contact

Indium tin oxide (ITO) (260 nm) and Ni (5 nm)/Au (10 nm) films were deposited onto glass substrates, p-GaN layers, n/sup +/-InGaN/GaN short-period-superlattice (SPS), n/sup ++/-SPS and nitride-based green light-emitting diodes (LEDs). It was found that ITO could provide us an extremely high transparency (i.e., 95% at 520 nm). It was also found that the 1.03/spl times/10/sup -3/ /spl Omega/cm/sup 2/ specific contact resistance of ITO on n/sup ++/-SPS was reasonably small. Although the forward voltage of the LED with ITO on n/sup ++/-SPS upper contacts was slightly higher than that of the LED with Ni/Au on n/sup ++/-SPS upper contacts, the 20 mA output power and external quantum efficiency of the former could reach 4.98 mW and 8.2%, respectively, which were much larger than the values observed from the latter. The reliability of ITO on n/sup ++/-SPS upper contacts was also found to be reasonably good.

High rate deposition of insulating TiO2 and conducting ITO films for optical and display applications

An innovative reactive pulse magnetron sputtering (PMS-) system allowing to change the pulse mode (unipolar, bipolar or pulse packet) and the pulse parameters (duty cycle, frequency) of the discharge has been used to deposit different materials at high deposition rates. The new pulse packet mode combines the two fundamental pulse modes of unipolar and bipolar by applying ‘packets’ of unidirectional pulses between the two targets and changing the polarity of the discharge after each packet. As a new pulse parameter, the number of pulses of each packet can be varied. The advantages of the PMS-system were demonstrated by the reactive deposition of insulating titanium oxide (TiO 2 ) and conducting indium tin oxide (ITO) films. The TiO 2 layers sputtered on unheated substrates at deposition rates of up to 50 nm*m/min exhibited amorphous, mixed anatase/rutile or rutile structure in dependence of the pulse mode and the pulse parameters that were applied. Hardness, Young's modulus, roughness and refractive index varied in dependence of the structure of the layers. Although the sputtering from ceramic target is the most common coating technique for ITO, another economical way is the use of metallic InSn-targets. The effect of various pulse modes on the optical and electrical properties of reactively sputtered ITO layers on float glass was investigated. The specific resistivity of ITO was minimized by process parameter optimisation.

High rate deposition of insulating TiO 2 and conducting ITO films for optical and display applications

An innovative reactive pulse magnetron sputtering (PMS-) system allowing to change the pulse mode (unipolar, bipolar or pulse packet) and the pulse parameters (duty cycle, frequency) of the discharge has been used to deposit different materials at high deposition rates. The new pulse packet mode combines the two fundamental pulse modes of unipolar and bipolar by applying ‘packets’ of unidirectional pulses between the two targets and changing the polarity of the discharge after each packet. As a new pulse parameter, the number of pulses of each packet can be varied. The advantages of the PMS-system were demonstrated by the reactive deposition of insulating titanium oxide (TiO 2) and conducting indium tin oxide (ITO) films. The TiO 2 layers sputtered on unheated substrates at deposition rates of up to 50 nm*m/min exhibited amorphous, mixed anatase/rutile or rutile structure in dependence of the pulse mode and the pulse parameters that were applied. Hardness, Young's modulus, roughness and refractive index varied in dependence of the structure of the layers. Although the sputtering from ceramic target is the most common coating technique for ITO, another economical way is the use of metallic InSn-targets. The effect of various pulse modes on the optical and electrical properties of reactively sputtered ITO layers on float glass was investigated. The specific resistivity of ITO was minimized by process parameter optimisation.

An in situ sheet resistance study of oxidative-treated indium tin oxide substrates for organic light emitting display applications

Indium tin oxide (ITO) substrates are subjected to oxygen plasma and UV ozone treatments. It is observed that the treatments produced a surface layer rich in oxygen, as investigated by X-ray photoelectron spectroscopy (XPS), and this is correlated with the sheet resistance of ITO measured by a four-point probe. A method has been devised to measure the change in the sheet resistance more prominently and this measurement is carried out under purified nitrogen atmosphere after the ITO is being treated. With an oxygen-rich ITO surface layer formed on ITO after the oxidative treatments, the resistance of ITO is considered to be that of a parallel-resistor combination and the thickness of the surface layer is being estimated based on this approach.

Low resisitivity transparent electrodes for displays on polymer substrates

One of the main difficulties for manufacturing displays on polymer substrates is the deposition of low resistivity indium tin oxide (ITO). Most polymer materials do not withstand substrate temperatures above 200°C, which are required for conventional high quality ITO process on glass substrates. This is the reason why a solution is proposed which includes the substitution of a single ITO layer by a three layer system consisting of ITO/Ag/ITO. A sheet resistance below 16 Ω/□ at a transmittance over 80% at a 550-nm wavelength could be achieved. Additionally, the overall indium content in the coating is reduced. This will lead to a reduction of target costs during production.

Etching, smoothing, and deposition with gas-cluster ion beam technology

Gas cluster ion beam (GCIB) processing has recently been introduced as a commercial tool for processing ‘rough’ surfaces, such as polished substrates or thin films. The physical interaction of a gas cluster ion beam with a surface is strikingly different from that of better-known ‘monomer’ ion beams. Clusters are formed by the adiabatic expansion of gas through a nozzle, ionization by electron impact, acceleration, and then impingement upon the surface to be processed. The physics of the surface interaction of the cluster beam strongly depends upon gas composition, cluster size, cluster size distribution, and beam energy. Typical argon GCIBs are composed of clusters ranging from several hundred to several thousand atoms in size. It has been previously shown that Ar clusters can be used to smooth surfaces at a sub-nanometer level. Argon cluster beam smoothing typically occurs in the energy range between 15 and ∼30 keV. As such, the average energy per atom is of the order of 10 eV/atom upon cluster impact with the surface and subsequent dissociation. Ion cluster beams formed with reactive gases such as oxygen and nitrogen can also be formed, but at somewhat lower current densities than those obtainable with argon. Upon impact, reactive gas clusters undergo strong chemical reactions at the substrate surface. An extension of this chemical interaction is to utilize reactive clusters in an ion beam-assisted, thin-film physical vapor deposition process. This has been demonstrated with relatively low energy (E<∼10 keV) oxygen clusters in an electron-beam evaporator to form extremely low resistivity indium–tin oxide films on room-temperature substrates. This paper will describe the basics of GCIB formation and application to atomic scale smoothing of technologically interesting substrates and thin films, as well as reactive GCIB assisted deposition technology. The results presented demonstrate some of the unique physics and materials science that can be achieved with an emerging GCIB technology.