Conductive Indium Tin Oxide Films Research Articles

Tri-band transparent conductive coating of indium tin oxide.

A tri-band transparent conductive indium tin oxide (In2O3:Sn, ITO) film for the visible, near-infrared (NIR) and mid-infrared (MIR) was deposited on a sapphire substrate by radio frequency (RF) magnetron sputtering. Deposition parameters, including RF power, substrate temperature, and oxygen flow rate, were optimized to improve the optical property without reducing the conductivity of the film by maximizing the Hall mobility and minimizing the carrier concentration. Films deposited at optimized conditions exhibit a Hall mobility of ∼20 cm2 V-1 s-1, a carrier concentration of ∼4.99×1020 cm-3, and a sheet resistance of 61.2 Ω/sq. Average transmissions of these films are 81.40% in the 0.4-1.6 μm region and 60.81% in the 3.0-5.0 μm region. An index-matching stack of MgF2 was developed, improving the transmittance to 90.55% and 73.20% in the regions above, respectively. These results make ITO film a promising alternative material to conventional metal mesh for missile domes shielding electromagnetic waves.

Highly conductive and transparent ITO films deposited at low temperatures by pulsed DC magnetron sputtering from ceramic and metallic rotary targets

The fabrication of complex device structures often requires deposition of Indium tin oxide (ITO) thin films on temperature sensitive substrates. For example, substrates containing electronic components or organic materials used in displays, touch panels, and electroluminescent devices often restrict process temperatures to below 100°C. Currently the best ITO quality is attained for films deposited with magnetron sputtering using ceramic targets at substrate temperatures above 200°C. In the present study, ITO layers with thicknesses ranging from 25nm to 200nm were deposited on glass substrates by pulsed DC magnetron sputtering using rotary ceramic ITO targets and reactive sputtering from rotary indium-tin targets. Optical and electrical properties were measured and compared for both types of ITO layers. The as-deposited layers were treated post-growth to enhance electrical conductivity and optical transmission. A standard thermal treatment is compared to flash lamp annealing (FLA) with the goal of keeping substrate temperature below 100°C. The enhancement of both electrical and optical properties has been determined by sheet resistance measurements and optical spectroscopy. ITO coatings with optical transmissions higher than 87% and resistivity lower than 2.5×10−4Ωcm could be achieved. A strong influence of the oxygen flow during deposition has been observed for the electrical and optical properties after post-treatment.

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 °C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl(-) anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136±39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

Total Internal Reflection-Based Free Space Optical Communication System

We present a free space optical communication system that uses electrostatically modulated microelectromechanical systems (MEMS) structures coupled with a glass total internal reflection-type corner cube retroreflector (CCR) as a nonemitting data transmitter. MEMS structures consists of an array of light scattering membranes fabricated on silicon-on-insulator wafer. The MEMS structures are bonded to a glass lid with a transparent conductive indium tin oxide film using flip chip bonding. The chip is aligned and bonded to a passive glass CCR using an ultraviolet (UV) epoxy with an accuracy of 20–30 arc-s. The MEMS structures can be modulated either toward or away from the bonded glass, thus disrupting evanescent energy delivered from a probing laser beam. Retroreflective optical communication over 300 m was achieved using an interrogating 635-nm laser. [2014-0301]

Influence of discharge power and annealing temperature on the properties of indium tin oxide thin films prepared by pulsed-DC magnetron sputtering

Indium tin oxide (ITO) films, prepared by a pulsed direct current magnetron sputtering system, are investigated at powers from 0.4 to 2.0 kW (power density in the range 0.8–4.1 W/cm2). It is found that the carrier concentration and crystallinity of the ITO films increase with increasing discharge power, while the electron mobility decreases from 49.2 cm2/Vs at 0.4 kW to 30.3 cm2/Vs at 2.0 kW. X-ray photoelectron spectroscopy measurements demonstrate that the ITO films prepared at high powers have more oxygen deficient and Sn4+ bonding states. These two types of bonding states are most relevant to the oxygen vacancies and substitutional tin atoms, which are the dominant electron donors in ITO. This observation explains why highly conductive ITO films are achieved at high deposition powers. Besides the investigation of the as-deposited ITO properties, annealing induced changes are explored in air ambient. The ITO properties are maintained for most of the samples when annealed at 150 °C, while degraded ITO properties are observed when annealed at 200 °C, especially for films grown at low powers. The annealing induced changes are most probably related to changes of the film crystallinity. A clear improvement of the crystallinity is observed for low power deposited ITO films after annealing at 200 °C for 240 min.

PVP a binder for the manufacture of ultrathin ITO/polymer nanocomposite films with improved electrical conductivity

This paper presents the manufacture of ultrathin (<1 µm) transparent conductive indium tin oxide (ITO) films based on nanoparticulate ITO slurries by the profile rod technique using the binder polyvinyl pyrrolidone (PVP) as an organic additive. The influence of the slurry composition on the film thickness and the specific electrical resistance as well as the transmission of the dried films is evaluated. The organic solvent ethanol and different types of the PVP binder were tested for slurry preparation and layer performance. ITO green films with low specific electrical resistance of 3 Ω cm, 87 % inline transmission, and layer thicknesses of only 250 nm could be manufactured. Furthermore, the influence of heat treatments up to 400 °C on the electrical properties of the ITO films was evaluated.

Indium-tin oxide thin films deposited at room temperature on glass and PET substrates: Optical and electrical properties variation with the H2–Ar sputtering gas mixture

The optical and electrical properties of indium tin oxide (ITO) films deposited at room temperature on glass and polyethylene terephthalate (PET) substrates were investigated. A clear evolution of optical transparency and sheet resistance with the content of H2 in the gas mixture of H2 and Ar during magnetron sputtering deposition is observed. An optimized performance of the transparent conductive properties ITO films on PET was achieved for samples prepared using H2/(Ar+H2) ratio in the range of 0.3–0.6%. Moreover, flexible ITO-PET samples show a better transparent conductive figure of merit, ΦTC=T10/RS, than their glass counterparts. These results provide valuable insight into the room temperature fabrication and development of transparent conductive ITO-based flexible devices.

Transparent conductor-Si pillars heterojunction photodetector

We report a high-performing heterojunction photodetector by enhanced surface effects. Periodically, patterned Si substrates were used to enlarge the photo-reactive regions and yield proportionally improved photo-responses. An optically transparent indium-tin-oxide (ITO) was deposited on a Si substrate and spontaneously formed an ITO/Si heterojunction. Due to an electrical conductive ITO film, ITO/Si heterojunction device can be operated at zero-bias, which effectively suppresses the dark current, resulting in better performances than those by a positive or a negative bias operation. This zero-bias operating heterojunction device exhibits a short response time (∼ 22.5 ms) due to the physical reaction to the incident light. We revealed that the location of the space charge region (SCR) is crucial for a specific photon-wavelength response. The SCR space has the highest collection efficiency of the photo-generated carriers. The photo-response can be maximized when we design the photodetector by superposing the SCR space over a corresponding photon-absorption length. The surface enhanced Si pillar devices significantly improved the photo-responses ratios from that of a planar Si device. According to this design scheme, a high photo-response ratio of 5560% was achieved at a wavelength of 600 nm. This surfaced-enhanced heterojunction design scheme would be a promising approach for various photoelectric applications.

Radio frequency-H2O plasma treatment on indium tin oxide films produced by electron beam and radio frequency magnetron sputtering methods

Electron beam and radio frequency (RF: 13.56MHz) magnetron sputtering methods were used to obtain a highly transparent and conductive indium tin oxide (ITO) films. The coated thin films were treated by RF-H2O plasma in order to improve optical and electrical properties. RF-H2O plasma characteristics were investigated by optical emission spectroscopy during surface treatments. X-ray photoelectron spectroscopy results on O 1s core levels indicated the activated oxygen species in both amorphous and crystalline ITO structures. The structural, electrical and optical properties of ITO film were characterized by scanning electron microscopy, X-ray diffraction, and four-probe techniques. After the RF-H2O plasma treatment, the ITO films exhibited lower resistivity and better transparency due to the formation of radical species.

Adhesion enhancement of indium tin oxide (ITO) coated quartz optical fibers

Abstract Transparent conductive indium tin oxide (ITO) film was prepared on optical fiber through a multi-step sol–gel process. The influence of annealing temperature on the adhesion of ITO coated optical fibers was studied. Different surface treatments were applied to improve the adhesion between ITO film and quartz optical fiber. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction analysis (XRD), UV–vis spectrophotometer and Avometer were used to characterize the morphology, crystal structure and photo-electric properties. A thermal shock test was used to evaluate the adhesion. The result shows that the adhesion between ITO film and quartz optical fiber can be strongly influenced by the annealing process, and optimal adhesion can be acquired when annealing temperature is 500 °C. Surface treatments of ultrasonic cleaning and the application of surface-active agent have effectively enhanced the adhesion and photo-electric properties of indium tin oxide film coated quartz optical fiber.

Enhanced conductivity of solution-processed indium tin oxide nanoparticle films by oxygen partial pressure controlled annealing

A highly conductive and transparent indium tin oxide (ITO) film was developed using a nanoparticle-based solution process through the control of oxygen partial pressure during annealing. At an oxygen partial pressure of 2.1 × 10−3 Torr, a maximum conductivity of 313 Ω−1 cm−1 was obtained: a great improvement over the conductivity of conventional ITO nanoparticle films (at this conductivity, the sheet resistance decreased to 30 Ω sq−1, and the transmittance reached 90%). By analyzing the electron concentration and mobility using Hall measurements, we determined that the main factor contributing to the enhanced conductivity is the increase in electron concentration that occurs due to the formation of oxygen vacancies under low oxygen partial pressures. However, if the oxygen partial pressure is too low, the removal of the organic ligands covering the ITO nanoparticles is incomplete, and the electron mobility is reduced. Microstructure control is also necessary for further improvement of the mobility.

Flexibility and electrical stability of polyester-based device electrodes under monotonic and cyclic buckling conditions

The flexibility and electrical stability of highly conductive and transparent amorphous indium tin oxide (a-ITO) films coated on polyethylene terephthalate and polyethylene naphthalate substrates were investigated by buckling tests with in situ monitoring of the electrical resistance. Monotonic and cyclic loading tests of the ITO/polymer systems were conducted. The results show that monotonic buckling in tension is more critical for electromechanical stability of ITO films than in compression (an increase in electrical resistance was observed at a critical radius of curvature, of ~3 and ~1mm, respectively for both cases investigated). In contrast, cyclic loading tests show that the compression mode is more critical than the tensile mode which may be a result of the residual stress present in the film structure. Failure of the ITO film was caused by buckling-driven delamination observed using scanning electron microscopy after the tests. The presence of residual stress could mean that buckling-driven delamination is the dominant failure mode for ITO/polymer systems under repeated flexing. In general, comparable electromechanical stability was observed in both cases. Investigating the electromechanical response of such material systems is important for polymer substrate selection and life-time prediction of flexible polyester-based electronic devices.

Poly-crystallinity of indium-tin-oxide films improved by using simultaneous ion beam and heat treatment of the plastic substrate

The combined treatment effects of an ion beam with directionality and heat of a low temperature on a plastic substrate was investigated as a method to increase the electrical conductivity of indiumtin-oxide (ITO) films deposited on plastic substrate surfaces at low temperatures. Polyethylene terephthalate (PET) surface treatment by using an ion beam at low temperature (120 °C), which can be applied to plastic substrates, improves the conductivity of ITO films. X-ray diffraction indicates that ITO films deposited on PET surfaces treated simultaneously by using an ion beam and heat of a low temperature have an almost polycrystalline structure even though they have small amorphous party on. As a supplementary measurement, the contact angle showed that the polycrystalline structure was due to a self-assembly effect at the PET surfaces. Consequently, the electrical conductivity of an ITO film deposited by using the proposed technique is three times higher than that of an ITO film treated only with heat of low temperature due to the improved polycrystalline structure.

AlGaInN-based light emitting diodes with a transparent p-contact based on thin ITO films

A method for obtaining transparent conductive ITO (indium-tin oxide) films aimed for use in light emitting diodes of the blue spectral range is developed. The peak external quantum efficiency of light-emitting diodes with a p-contact based on the obtained films reaches 25%, while for similar light-emitting diodes with a standard semitransparent metal contact, it is <10%. An observed increase in the direct voltage drop from 3.15 to 3.37 V does not significantly affect the possibility of applying these films in light-emitting diodes since the optical power of light-emitting diodes with a transparent p-contact based on ITO films exceeds that of chips with metal semitransparent p-contacts with a working current of 20 mA by a factor of almost 2.5. Light-emitting diodes with p-contacts based on ITO films successfully withstand a pumping current that exceeds their calculated working current by a factor of 5 without the appearance of any signs of degradation.

Transparent Polyimides and their ITO Flexible Conductive Film

The preparation and properties of indium tin oxide (ITO) coated transparent polyimide substrates were reported in the paper. The transparent polyimide films were prepared through thermal imidization of poly(amic acid) films. Transparent conducting ITO films were prepared on polyimide substrates by magnetron-sputtering technique at room temperature. The optical and electrical properties of the obtained films have been investigated. Polycrystalline ITO films were deposited with resistivity as low as 10-4 Ω.cm on polyimide substrates. The average transmittance exceeded 78% in the visible spectrum for 200nm thick films deposited on polyimide.

Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method

Indium tin oxide (ITO) thin films with well-controlled layer thickness were produced by dip-coating method. The ITO was synthesized by a sol–gel technique involving the use of aqueous InCl 3, SnCl 4 and NH 3 solutions. To obtain stable sols for thin film preparation, as-prepared Sn-doped indium hydroxide was dialyzed, aged, and dispersed in ethanol. Polyvinylpyrrolidone (PVP) was applied to enhance the stability of the resulting ethanolic sols. The transparent, conductive ITO films on glass substrates were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The ITO layer thickness increased linearly during the dipping cycles, which permits excellent controllability of the film thickness in the range ~ 40–1160 nm. After calcination at 550 °C, the initial indium tin hydroxide films were transformed completely to nanocrystalline ITO with cubic and rhombohedral structure. The effects of PVP on the optical, morphological and electrical properties of ITO are discussed.

Electrochemically Assisted Deposition as a New Route to Transparent Conductive Indium Tin Oxide Films

Tin-doped indium oxide (ITO) films with Sn/In atomic ratios in the range 0−0.1 were synthesized by electrochemically assisted deposition (EAD). The process involves a fast one-step cathodic deposition of a highly crystalline In−Sn hydroxide (InSnOH) film followed by thermal conversion into ITO at 300 °C. The cathodic precipitation of InSnOH is preceded by formation of an In−Sn complex in solution. The films were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, UV−visible spectroscopy, and electrical measurements. In the Sn/In atomic ratio range 0−0.1, InSnOH and ITO films adopt the morphologies and cubic crystal structures of In(OH)3 and In2O3, respectively. The atomic environment of Sn and O atoms in the ITO films was shown to resemble that of films deposited by other techniques and commercial ITO samples made by chemical vapor deposition. Separate tin oxide/hydroxide phases were not observed by any of the characterization methods. The mor...

Properties of the ITO layer in a novel red light-emitting diode

An optically transparent electrode, indium tin oxide (ITO) film is fabricated by vacuum E-beam evaporation. The thermal annealing effects on the ITO/GaP contact have been investigated by means of the transmission line model method. Under 435 °C, with rapid thermal annealing for 40 s in N2 ambient, the ITO contact resistance reaches the minimized value of 4.3 × 10−3 Ω · cm2. The results from Hall testing and Auger spectra analysis indicate that the main reasons for the change of the contact resistance are the difference in the concentration of carriers and the diffusion of In, Ga, O. Furthermore, the reliability of AlGaInP LEDs with a 300-nm thickness transparent conducting ITO film is studied. The increase of LED chip voltage results from the degradation of ITO film. Moreover the difference between the thermal expansion coefficient of GaP and ITO results in the invalidation of the LED chip.

Patterning of nanoparticulate transparent conductive ITO films using UV light irradiation and UV laser beam writing

Indium tin oxide (ITO) thin film is one of the most widely used as transparent conductive electrodes in all forms of flat panel display (FPD) and microelectronic devices. Suspension of already crystalline conductive ITO nanoparticles fully dispersed in alcohol was spun, after modifying with coupling agent, on glass substrates. The low cost, simple and versatile traditional photolithography process without complication of the photoresist layer was used for patterning ITO films. Using of UV light irradiation through mask and direct UV laser beam writing resulted in an accurate linear, sharp edge and very smooth patterns. Irradiated ITO film showed a high transparency (∼85%) in the visible region. The electrical sheet resistance decrease with increasing time of exposure to UV light and UV laser. Only 5 min UV light irradiation is enough to decrease the electrical sheet resistance down to 5 kΩ□.

Ferromagnetism in transparent Mn(II)-doped indium tin oxide films prepared by sol–gel coating

We observe remarkably strong room temperature ferromagnetism [∼1.5 μ B/Mn(II)] in optically transparent Mn(II)-doped indium tin oxide (ITO) films. The nanocrystalline films with average grain size 10–22 nm and thickness 150–350 nm are prepared by sol–gel coating technique on soda lime silica glass substrate. The ferromagnetic property is, of course, weak for films deposited on pure silica glass substrate. The structural parameters of the films appear to be governing the magnetic property strongly which vary appreciably depending on the substrate. The observation of room temperature ferromagnetism in transparent conducting ITO films may find a plethora of applications in the area of magneto-optics.