Transparent Indium Tin Oxide Films Research Articles

Preparation of ITO Thin Films by Sol-Gel Process and Their Characterizations

Indium-tin-oxide (ITO) has attracted intense interest due to some of its unique characteristics; it has high optical transmittance in the visible region, low electric resistivity, and chemical stability. Therefore, ITO thin films have been found to play an important role in opto-electronic applications. In this work, uniform and transparent ITO films were deposited onto glass substrates using a sol-gel process. The initial sols were prepared by mixing solutions of indium nitrate prepared in anhydrous ethanol with tin chloride and mechanically stirring the resultant mixture until a clear and sticky coating sol was obtained. The glass substrates were dip-coated and annealed at 550 °C. Because annealing conditions affect the microstructures, the properties of the resultant ITO films can be controlled. Depending on annealing time and film thickness, the electrical resistivity of the ITO coating varied from 27000 to 1400 Ω /□ for 8% by wt. Sn-content The optical transmittance of 200 nm thick ITO film was more than 80% in the visible region. The surface morphology examined by SEM appears to be uniform over large surface areas. Possible correlations among the film properties and film preparation conditions are discussed.

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.

Transparent Conducting ITO Films Reactively Sputtered on Polyethylene Terephtalate Substrates Without Heat Treatment

Indium tin oxide (ITO) films have been deposited on PET and glass substrates by DC reactive magnetron sputtering without post-deposition thermal treatment. High quality films have been deposited by optimizing the sputtering parameters. The influence of the working gas pressure, DC power, and oxygen partial pressure has been investigated. The lowest resistivity of ITO films deposited on PET substrates was 6×10-4Ωcm. It has been obtained at a working pressure of 3 mTorr and DC power of 30 W. The sheet resistance and optical transmittance of these films were 22 Ω/square and 84%, respectively. The best values of figures of merit for the electrical and optical chardcteristics such as T / R sh and T 10/ R sh are approximately 38.1 and 7.95 (×10-3 Ω-1), respectively.

Highly conducting transparent indium tin oxide films prepared by pulsed laser deposition

In2O3 doped with 5 wt.% SnO2 [indium-tin oxide (ITO) (5 wt.%)] films were deposited on glass substrates by pulsed laser deposition using an ArF laser (λ=193 nm). In all experiments, repetition rates of 1∼50 Hz, an energy density of 6 J/cm2, and an ablation time of 30–900 s were used. A lowest resistivity of 8.45×10−5 Ω cm and an optical transmittance of more than 80% in the visible range of the spectrum were obtained for ITO (5 wt.%) films of approximately 300-nm-thickness fabricated at a substrate temperature of 400 °C and oxygen pressure of 10 Pa. Smooth surfaces with an average surface roughness of 1.26 nm were observed by field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM).

Deposition of indium–tin-oxide films on polymer substrates for application in plastic-based flat panel displays

Indium–tin-oxide (ITO) films (1000±100 Å) were deposited on glass and polymer (polyethersulfone) substrates by RF-magnetron sputtering for plastic-based flat-panel displays. A novel device and a stepped heating process were used both to eliminate the tensile force and to diminish the thermal expansion of the polymer substrates. Therefore, we succeeded in sputtering ITO films without any cracking or shrinkage of the polymer substrates. The oxygen partial pressure and post-deposition annealing conditions were varied to observe the dependence of the optical, electrical and etching properties of ITO films on the process parameters. The substrate material was polyethersulfone with a gas barrier layer. Moreover, in order to investigate the influences of the process parameters, X-ray diffractometer observations and measurement of transmission, sheet resistance and residual resistance after etching process were performed. We found that oxygen content in the polymer matrix resulted from the gas absorption of polymer substrates cause different dependence of polymer substrates on oxygen partial pressure compare with glass substrates. Consequently, we could obtain high conductive ( 20–25 Ω □ −1) and transparent (above 80%) ITO films deposited on polymer substrates using the condition of 0.2% oxygen partial pressure and vacuum annealing at the temperature of 180°C.

Transparent indium tin oxide films prepared by ion-assisted deposition with a single-layer overcoat

Transparent indium tin oxide (ITO) films have many applications as electrodes in Liquid Crystal displays and EMI/RFI shielding. We have compared two processes for obtaining ITO thin films with low resistivity (below 15B/sq) and high transmittance (above 90%) in the visible region. The first process was deposition using electron beam gun evaporation. The second process was using Ion Assisted Deposition (lAD) of low energy oxygen ions from an end-Hall ion source. In both cases the conductive layer was overcoated with 50-250 nm thickness of a MgF2 layer to enhance the transmittance. When ITO produced by IAD was overcoated with a MgF2 layer, the surface was found to be conductive. The surface was analyzed using the Auger Electron and Second Ion Mass Spectroscopy methods. Traces of indium were found on the MgF2 layer. We speculate that indium that diffused through the overcoat layer gives assistance to the conductivity and enables the measurement of the resistivity from the top surface of the coating. This effect occurred only when the ITO was deposited using IAD. This is an advantage in manufacturing of optical conductive windows. Otherwise there is a need to leave exposed areas of ITO for conductive contacts. The diffusion process was not observed with oxide layers. Atomic Force Microscopy scans show that the IAD process decreased the average roughness of the surface.

Low pressure and temperature deposition of transparent conductive indium tin oxide (ITO) films by the face target sputtering (FTS) process

Conductive and transparent indium tin oxide films were prepared by the face target sputtering process in pure argon gas. During deposition low pressures (0.1–10 mTorr) (0.0133–1.33 Pa) and temperatures (23–300 °C) are used. The total pressure, rather than the substrate temperature, is the dominant factor in determining the crystallinity, surface morphology, resistivity, carrier concentration and mobility of the films. Films with ϱ<500 μω cm, sheet resistance <40 ω/□, >4×10 20 cm -3, μ<50 cm 2 V -1 s -1 and optical transmittance > 85% are prepared. The optical and transport properties are largely independent of the crystallinity, texturing and thickness of the films.

Visible electroluminescence from porous silicon np heterojunction diodes

We report the preparation of silicon-based visible light-emitting diodes, configured as heterojunctions between porous silicon (formed by electrochemical etching of p-type silicon wafers), and n-type indium tin oxide (ITO). The transparent ITO film allows light emission through the top surface of the device, under a forward electrical bias of several volts across the junction. Photogenerated currents are observed under reverse biases. A tentative model for this electroluminescence is presented, based on injection of minority carriers through a narrow interphase region into the porous silicon structure, where radiative recombination occurs.

Conducting transparent indium-tin oxide films by post-deposition annealing in different humidity environments

Indium-tin oxide (ITO) films were grown by the flash evaporation method without oxygen gas flow during deposition. The minimum electrical resistivity and the maximum average optical transmittance were found at the optimized substrate temperature of about 673 K. Further improvements in the electrical conductivity and the optical transmittance of ITO films were made by post-deposition annealing under different conditions of humidity. The effects of post-deposition annealing in the presence of the different conditions of humidity on the electrical as well as the optical properties of ITO films were studied. The values of the intrinsic bandgap and effective mass were calculated. The implications are discussed.

Reaction kinetics of the formation of indium tin oxide films grown by spray pyrolysis

The electrical and optical properties of sprayed indium tin oxide (ITO) films have been reported as a function of tin concentration, substrate temperature T s and the substrate-nozzle distance D sn · D sn and T s seem to be interrelated for the optimization of good quality ITO films. Highly conduction (3 × 10 5 ohm −1m −1) and transparent (90% in visible region) ITO films were obtained when D sn = 0.3 m, T s = 693 K with 5% by weight of SnCl 4 in the starting material. These data are discussed in the light of reaction kinetics.

Methods and applications of plasmatron high rate sputtering in microelectronics, hybrid microelectronics and electronics

High rate sputtering with plasmatron sources gives high deposition rates and covers a wide assortment of metals, alloys and compounds that can be sputtered. It further offers unique possibilities for the control of substrate temperature and for ion-assisted deposition. We describe the present state of the art for the metallization of components in microelectronics. Other applications in this field are the deposition of stable resistor networks for digital-to-analogue or analogue-to-digital converters units and of conductive transparent indium tin oxide films for displays. The applicability and flexibility of high rate sputtering in thin film hybrid techniques is exemplified by a complete four-layer system. In addition, this technique proves to be of advantage for the metallization of electronic components made of quartz, oxide ceramics or piezoceramic materials.