Sputtered Indium Tin Oxide Films Research Articles

Quantitative study of the thickness-dependent stress in indium tin oxide thin films

A quantitative analysis of stress in indium tin oxide (ITO) films with varying thicknesses was conducted using high-precision stylus profilometry. The experimental results revealed a transition of the stress type from tensile to compressive as the ITO film thickness increased. Further investigation of the surface morphology of the ITO films indicated that the tensile stress originated from the impingement and coalescence of newly deposited equiaxed grains, while the observed compressive stress was attributed to the incorporation of excess material in the boundaries of columnar grains. The ability to monitor stress evolution in sputtered ITO films on glass substrates provides valuable insights for process control in ITO device manufacturing.

Impact of oxygen partial pressure during Indium Tin Oxide sputtering on the performance of silicon heterojunction solar cells

TCO has multiple functions in SHJ solar cell design, including the lateral transport of the photogenerated current and also providing high transparency and anti-reflective behavior. While superior performance lies behind concurrently addressing its multi-functions. Hence the balance between the optical and electronic properties of TCOs need careful engineering. In this study, RF sputtered Indium Tin Oxide films are analyzed in terms of their optical and electrical properties. The variations in the resistivity, mobility, carrier concentration, and specific contact resistivity of the film concerning oxygen partial pressure are discussed. Specific contact resistivity value for screen-printed low-temperature Ag contacts is decreased down to 0.4mΩ.cm2. The total increment on short-circuit current density is 0.6 mA/cm2 by reactive ITO sputtering. The photoconversion efficiency values of SHJ cells fabricated on 170 cm2 area with reactive sputtering is 20.56%, and optical loss analysis is carried out for the SHJ solar cells to quantify the performance of solar cells.

Out-of-Plane Thermal Expansion Coefficient and Biaxial Young’s Modulus of Sputtered ITO Thin Films

This paper proposes a measuring apparatus and method for simultaneous determination of the thermal expansion coefficient and biaxial Young’s modulus of indium tin oxide (ITO) thin films. ITO thin films simultaneously coated on N-BK7 and S-TIM35 glass substrates were prepared by direct current (DC) magnetron sputtering deposition. The thermo-mechanical parameters of ITO thin films were investigated experimentally. Thermal stress in sputtered ITO films was evaluated by an improved Twyman–Green interferometer associated with wavelet transform at different temperatures. When the heating temperature increased from 30 °C to 100 °C, the tensile thermal stress of ITO thin films increased. The increase in substrate temperature led to the decrease of total residual stress deposited on two glass substrates. A linear relationship between the thermal stress and substrate heating temperature was found. The thermal expansion coefficient and biaxial Young’s modulus of the films were measured by the double substrate method. The results show that the out of plane thermal expansion coefficient and biaxial Young’s modulus of the ITO film were 5.81 × 10−6 °C−1 and 475 GPa.

Evaluation of electrical resistivity, residual stress and surface roughness of sputtering indium tin oxide films with different thicknesses

This paper investigates the influence of film thickness on the electrical and mechanical properties of transparent indium tin oxide (ITO) thin films. Two groups of ITO thin films deposited on unheated substrates were prepared by the radio-frequency magnetron sputtering technique. The biaxial residual stress and surface roughness for two groups of ITO thin films were measured by a Twyman–Green interferometer and a Linnik microscopic interferometer, respectively. The electrical resistivity of the ITO films was measured by a four-point probe apparatus, the thickness was determined mechanically with a profilometer. The measurement results show that the average resistivity of ITO thin films decreases with increasing the deposited thickness. The compressive residual stress in the ITO thin films decreases with increasing the deposited thickness. We also find that an anisotropic stress in the two groups of ITO films is more compressive in a certain direction. The RMS surface roughness in the two groups of ITO films is less than 1 nm.

Effect of thermal annealing on sensing properties of optical fiber sensors coated with indium tin oxide nano-overlays

In this work we discuss an effect of thermal annealing on optical and electrical properties of indium tin oxide (ITO) thin films deposited on a short section of multimode polymer-clad silica (PCS) optical fiber core. ITO films were deposited using different configuration of high power impulse magnetron sputtering (HiPIMS) and radio frequency magnetron sputtering (RF MS) cathodes. Due to tuned ITO film thickness it was possible to observe for these structures a lossy-mode resonance (LMR) and trace changes in properties of the films. Electrical resistance of the ITO overlays was also measured. Both optical and electrical measurements were repeated after annealing at 200°C in a tube furnace and nitrogen atmosphere. The measurements have shown that thermal annealing changes optical response to external refractive index (RI) of the fiber sensor and also changes the ITO layer resistivity. As an effect of thermal annealing we observed a shift of the LMR towards longer wavelengths. In addition as a result of annealing, the resistivity of the ITO layer was reduced. Full Text: PDF ReferencesM. Sobaszek et al., "Optical monitoring of thin film electro-polymerization on surface of ITO-coated lossy-mode resonance sensor", Proc. SPIE, vol. 10323, pp. 103234W, 2017. CrossRef I. Del Villar et al., " Generation of lossy mode resonances by deposition of high-refractive-index coatings on uncladded multimode optical fibers", J. Opt., vol. 12, no. 9, pp. 95503, 2010. CrossRef M. Śmietana et al., "Simultaneous optical and electrochemical label-free biosensing with ITO-coated lossy-mode resonance sensor", Biosensors and Bioelectronics, vol. 154, pp. 112050, 2020. CrossRef P. Niedziałkowski et al., " Electrochemical performance of indium-tin-oxide-coated lossy-mode resonance optical fiber sensor", Sensors and Actuators B: Chemical, vol. 301, no. 12, pp. 1-10, 2019. CrossRef V. Stranak et al., "Effect of mid-frequency discharge assistance on dual-high power impulse magnetron sputtering", Surface & Coatings Technology, vol. 206, no. 11-12. pp. 2801-2809, 2012. CrossRef I. Del Villar et al., "Design rules for lossy mode resonance based sensors", Appl. Opt., vol. 51, no. 19, pp. 4298-4307, 2012. CrossRef W. F. Wu and B. S. Chiou, "Effect of annealing on electrical and optical properties of RF magnetron sputtered indium tin oxide films", Appl. Surf. Sci., vol. 68, no. 4, pp. 497-504, 1993. CrossRef M. Smietana et al., "Optical Monitoring of Electrochemical Processes With ITO-Based Lossy-Mode Resonance Optical Fiber Sensor Applied as an Electrode", J. Light. Technol., vol. 36, no. 4, pp. 954-960, 2018. CrossRef M. Śmietana et al., "Study on Combined Optical and Electrochemical Analysis Using Indium‐tin‐oxide‐coated Optical Fiber Sensor", Electroanalysis, vol. 31, no.2, pp. 398-404, 2019. CrossRef

Stage-by-stage formation of superficial nanostructures in ITO films reduced by H2-GD at low temperature (100 °C) for applications on plastic substrates

The formation of superficial nanostructures (SNs) in reduced indium tin oxide (ITO) thin films by H2-Glow discharge (GD) at a low reduction temperature (Tr = 100 °C) was investigated. Sputtered ITO films deposited at low (Td = 100 °C) and high (Td = 300 °C) temperatures were reduced using this low-temperature process. Scanning electron and atomic force microscopy were applied to study the evolution of the nanostructural features and three stages were identified: emerging/densification, coalescence, and depletion stages. The structural characteristics of the SNs were characterized by grazing incidence and conventional θ/2θ x-ray diffractions showing that at Tr = 100 °C, the reduction process was limited to the surface region in which the ion bombardment had influence. The mean diameter, <D>, of the SNs in ITO deposited on the glass substrate was controlled from ∼10–90 nm and the SN densities, d, were obtained from ∼109–1011 SNs cm−2. Finally, the superficial nanostructures were successfully formed in ITO films deposited on flexible polyethylene naphthalate (PEN) substrates. It was demonstrated that, on these substrates, is possible to obtain a uniform distribution in the size and density of the SNs, with <D> = 9.5–20.7 nm and d = 2.66 × 1011–4.20 × 1010 SNs cm−2.

Role of RF Magnetron Sputtering Power on Optical and Electrical Properties of ITO Films on Soda-Lime Glass Substrates

The optical and electrical properties of indium tin oxide (ITO) thin films grown on soda-lime glass substrates using a radio frequency (RF) magnetron sputtering technique were studied as a function of the sputtering RF power. Fixed 100 nm thickness of ITO films were deposited on the soda-lime glass substrates at 300 °C, using RF powers ranging between 50 to 150 W. The optical and electrical properties of the sputtered ITO films were characterized by Ultraviolet–Visible Spectroscopy (UV-Vis), Hall Effect Measurement and Atomic Force Microscope (AFM). Varying the substrate temperature and RF sputtering power affected surface roughness to decrease from 5.80, 4.59 and 3.46 nm while the resistivity also decreased from 18.73 x 10−4, 6.484 x 10−4 and 2.421 x 10−4 Ω.cm. Deposition of ITO thin films on soda-lime glass substrates by RF magnetron sputtering at 300 °C substrate temperature contributed to 74 to 79 % of optical transmittance in the 450 nm region. Results of this study suggested that a better performance of both optical transparency and electrical conductivity of ITO films can be achieved by operating at high temperature substrate and high level of sputtering power.

Chemical sensing properties of indium-tin-oxide (ITO) printed films fabricated on biodegradable plastics

A chemical sensor was fabricated using indium-tin-oxide (ITO) films printed on biodegradable plastic substrates. The ITO layers were printed on polylactic acid (PLA) films. To optimize the printing procedure, the thermal properties of the PLA substrate were investigated using the differential scanning calorimetry method. The structural and electrical properties of the fabricated ITO films (P-ITO) were compared with commercial sputtered ITO films (S-ITO). X-ray diffraction and Hall effect measurements were used to estimate the grain size and the carrier transportation mechanism of the ITO films. The small grain size of P-ITO was attributed to its scattering mechanism. Grain boundary scattering was shown to be dominant in the P-ITO. The chemical sensing properties were also evaluated using a droplet of methanol (20 µl), indicating that the response rate of the P-ITO film was considerably higher (650%) than that of the S-ITO film. These results were attributed to the large surface area of the P-ITO film.

Sputtered indium tin oxide as a recombination layer formed on the tunnel oxide/poly-Si passivating contact enabling the potential of efficient monolithic perovskite/Si tandem solar cells

We focus on utilizing sputtered indium tin oxide (ITO) as a recombination layer, having low junction damage to an n-type silicon solar cell with a front-side tunnel oxide passivating electron contact, thereby enabling the development of a high efficiency monolithic perovskite/Si tandem device. High transparency and low resistivity ITO films are deposited via low power DC magnetron sputtering at room temperature onto a front-side thin SiOx/n+ poly-Si contact in a complete Cz n-Si cell with a back-side Al2O3/SiNx passivating boron-diffused p+-emitter on a random pyramid textured surface. We report the cell characteristics before and after ITO sputtering, and we find a cure at 250 °C in air is highly effective at mitigating any sputtering induced damage. Our ITO coated sample resulted in an implied open-circuit voltage (iVoc) of 684.7 ± 11.3 mV with the total saturation current density of 49.2 ± 14.8 fA/cm2, an implied fill factor (iFF) of 81.9 ± 0.8%, and a contact resistivity in the range of 60 mΩ-cm2 to 90 mΩ-cm2. After formation of a local Ag contact to the rear emitter and sputtered ITO film as the front-side contact without grid fingers, the pseudo-efficiency of 20.2 ± 0.5% was obtained with the Voc of 670.4 ± 7 mV and pseudo FF of 77.3 ± 1.3% under simulated one sun with the calculated short-circuit current density of 30.9 mA/cm2 from the measured external quantum efficiency. Our modelling result shows that efficiency exceeding 25% under one sun is practically achievable in perovskite/Si tandem configuration using the ITO recombination layer connecting a perovskite top cell and a poly-Si bottom cell.

Influence of base pressure on property of sputtering deposited ITO film

To systematically investigate the effect of base pressure on photoelectric properties of indium tin oxide (ITO) films, ITO films were prepared on glass substrates by RF magnetron sputtering with base pressures varying from 0.42 × 10−6 to 10 × 10−6 Torr in this work. Microstructure and photoelectric properties of ITO films were characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Hall-effect measurements and UV–vis transmission spectroscopy. It concluded that base pressure has an important influence on the properties of sputtering ITO films. As base pressure decreased, In2O3 was more easily decomposed into free oxygen and In2O3−x, the adhesion coefficient of oxygen reduced, and the oxygen vacancy content in ITO films increased. Therefore, with the decrease of the base pressure, the carrier concentration of ITO films increased, the resistivity of ITO films decreased, and the figure of merit of ITO films improved.

Roll-to-Roll fabrication of ITO thin film for flexible optoelectronics applications: The role of post-annealing

We have developed and examined new and cost effective methods for fabrication indium tin oxide (ITO) film on flexible substrate. The ITO film is deposited to polyethylene terephthalate film using roll-to-roll (RTR) sputtering advanced technology. The film's properties are evaluated before and after heat treatment. Effect of post annealing time on the electrical, optical, structural and surface properties of RTR sputtered ITO films is estimated. In addition, mechanical flexibility of as-sputtered amorphous ITO and annealed crystalline ITO films are compared. It is estimated that post-annealing at 150 °C reduces sheet resistance and increase the optical transmittance of the ITO films. The best results are observed when annealing time is 60 min. In this case the sheet resistance of ITO is measured to be 125 Ω/sq. and optical transmittance is 87.3% at wavelength range from 380 nm to 780 nm. It is demonstrated successful operation of touch screen panels fabricated on annealed ITO film. It is estimated that post-annealing significantly improves ITO performance as compare of that as-deposited film. Based on Hall measurement and transmittance electron microscopy examinations, possible mechanism to explain the effect of post-annealing time on RTR sputtered ITO films is manifested.

Role of sputtering power on the microstructural and electro‐optical properties of ITO thin films deposited using DC sputtering technique

The effects of sputtering power on the deposition rate as well as the microstructural, electrical, and optical properties of indium tin oxide (ITO) thin films are investigated in this paper. ITO thin films were deposited on glass substrates using direct current (DC) magnetron sputtering of different DC powers, ranging from 60 to 140 W, onto externally unheated glass substrates. All samples were grown at the minimum sustainable plasma pressure to reduce the destructive role of pressure. The microstructural, electrical, and optical properties of the sputtered ITO films were systematically characterized by X‐ray diffraction (XRD), atomic force microscopy (AFM), four‐probe electrical conductivity, and optical spectroscopy. XRD studies confirmed the cubic bixbyite ITO structure, and the main preferred orientations of the prepared thin films were (222), (400), (440), and (622). AFM analysis showed a minimum surface roughness of 1.37 nm for the films deposited at 140 W, while the average size of the grains was 65 ± 5 nm. The deposition time was fixed at 10 min for all samples, and the AFM characterization of the films showed 170, 230, and 250 nm thickness for the samples deposited at 60, 100 and 140 W, respectively. From the variations of the sheet resistance and the XRD patterns of the ITO thin films, it was concluded that, as the ratio I222/I400 of a sample approaches unity, the sheet resistance of the layer reduces. A minimum sheet resistance 16 Ω/square, transmittance 85% with the thickness of 230 nm, and optical bandgap 4.09 eV were found for the thin film grown on the externally unheated substrates at 100 W DC power and 32 mTorr working pressure. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Sol–gel versus sputtering indium tin oxide films as transparent conducting oxide materials

The aim of this paper is the replacing of the expensive sputtering method with the low cost sol–gel one in TCO applications. To this end two sets of indium tin oxide (ITO) thin films are compared and discussed in this paper: one obtained by r.f. sputtering and one by the sol–gel technique and dip-coating. For each of these sets of samples, a series of deposition parameters have been varied in an effort to obtain the most promising optical and electrical properties. Comparative structural, morphological and opto-electrical characterization of sol–gel and sputtered ITO-based films was performed by X-ray diffraction, Scanning electron microscopy, Atomic force microscopy, Spectroellipsometry, UV–VIS Spectroscopy and Hall Effect measurements in order to establish whether the chemical deposition method could lead to thin films with competitive properties as those obtained through the physical method. Comparable, high transmittance (85–90 %) in the VIS–NIR range (250–1050 nm) and carrier concentration values (1020–1021 cm−3) were obtained between sputtered and sol–gel ITO films. The sputtered ITO film in 75 % N2, annealed at 500 °C and the sol–gel 0.1 M ITO film with 10 layers deposited on SiO2/glass exhibit degenerate semiconductor behavior.

Effect of ambient combinations of argon, oxygen, and hydrogen on the properties of DC magnetron sputtered indium tin oxide films

Sputtering has been well-developed industrially with singular ambient gases including neutral argon (Ar), oxygen (O2), hydrogen (H2) and nitrogen (N2) to enhance the electrical and optical performances of indium tin oxide (ITO) films. Recent preliminary investigation into the use of combined ambient gases such as an Ar+O2+H2 ambient mixture, which was suitable for producing high-quality (low sheet resistance and high optical transmittance) of ITO films. To build on this promising preliminary work and develop deeper insight into the effect of ambient atmospheres on ITO film growth, this study provides a more detailed investigation of the effects of ambient combinations of Ar, O2, H2 on sputtered ITO films. Thin films of ITO were deposited on glass substrates by DC magnetron sputtering using three different ambient combinations: Ar, Ar+O2 and Ar+O2+H2. The structural, electrical and optical properties of the three ambient sputtered ITO films were systematically characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, four probe electrical conductivity and optical spectroscopy. The XRD and Raman studies confirmed the cubic indium oxide structure, which is polycrystalline at room temperature for all the samples. AFM shows the minimum surface roughness of 2.7 nm for Ar+O2+H2 sputtered thin film material. The thickness of the films was determined by the cross sectional SEM analysis and its thickness was varied from 920 to 817 nm. The columnar growth of ITO films was also discussed here. The electrical and optical measurements of Ar+O2+H2 ambient combinations shows a decreased sheet resistance (5.06 ohm/□) and increased optical transmittance (69%) than other samples. The refractive index and packing density of the films were projected using optical transmission spectrum. From the observed results the Ar+O2+H2 ambient is a good choice to enhance the total optoelectronic properties of the ITO films. The improved electrical and optical properties of ITO films with respect to the Ar+O2+H2 ambient sample were discussed in detail. In addition, the physical properties were also discussed with the influence of this ambient combination with respect to Ar, Ar+O2 and Ar+O2+H2.

Study of quartz crystal microbalance NO2 sensor coated with sputtered indium tin oxide film

A study of NO2 gas sorption ability of thin indium tin oxide (ITO) deposited on 16 MHz quartz crystal microbalance (QCM) is presented. ITO films are grown by RF sputtering of indium/tin target with weight proportion 95:5 in oxygen environment. The ITO films have been characterized by X-ray photoelectron spectroscopy measurements. The ITO surface composition in atomic % is defined to be: In-40.6%, Sn-4.3% and O-55%. The thickness and refractive index of the films are determined by ellipsometric method. The frequency shift of QCM-ITO is measured at different NO2 concentrations. The QCM-ITO system becomes sensitive at NO2 concentration ≥ 500 ppm. The sorbed mass for each concentration is calculated according the Sauerbrey equation. The results indicated that the 1.09 ng of the gas is sorbed into 150 nm thick ITO film at 500 ppm NO2 concentration. When the NO2 concentration increases 10 times the calculated loaded mass is 5.46 ng. The sorption process of the gas molecules is defined as reversible. The velocity of sorbtion /desorption processes are studied, too. The QCM coated with thin ITO films can be successfully used as gas sensors for detecting NO2 in the air at room temperature.

Optimisation of chemical solution deposition of indium tin oxide thin films

An environmentally friendly aqueous sol–gel process has been optimised to deposit indium tin oxide (ITO) thin films, aiming to improve the film properties and reduce the deposition costs. It was demonstrated how parameters such as cation concentration and viscosity could be applied to modify the physical properties of the sol and thereby reduce the need for multiple coatings to yield films with sufficient conductivity. The conductivity of the thin films was enhanced by adjusting the heat treatment temperature and atmosphere. Both increasing the heat treatment temperature of the films from 530 to 800°C and annealing in reducing atmosphere significantly improved the electrical conductivity, and conductivities close to the state of the art sputtered ITO films were obtained. A pronounced decreased conductivity was observed after exposing the thin films to air and the thermal reduction and ageing of the film was studied by in situ conductivity measurements.

Highly conducting, transparent, and flexible indium oxide thin film prepared by atomic layer deposition using a new liquid precursor Et2InN(SiMe3)2.

Highly conductive indium oxide films, electrically more conductive than commercial sputtered indium tin oxide films films, were deposited using a new liquid precursor Et2InN(SiMe3)2 and H2O by atomic layer deposition (ALD) at 225-250 °C. Film resistivity can be as low as 2.3 × 10(-4)-5.16 × 10(-5) Ω·cm (when deposited at 225-250 °C). Optical transparency of >80% at wavelengths of 400-700 nm was obtained for all the deposited films. A self-limiting ALD growth mode was found 0.7 Å/cycle at 175-250 °C. X-ray photoelectron spectroscopy depth profile analysis showed pure indium oxide thin film without carbon or any other impurity. The physical and chemical properties were systematically analyzed by transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, optical spectrometer, and hall measurement; it was found that the enhanced electrical conductivity is attributed to the oxygen deficient InOx phases.

Preliminary Study on Resistance of Non-Treated and Treated ITO Films

A study on the resistance of directly sputtered films and treated films of Indium Tin Oxide (ITO) is done to initiate an extensive study on the material. This study involves variation in terms of number of layers and duration of deposition. Treated films are produced by undergoing annealing process which is carried out using Split Type Tube Furnace. Resistance measurements were carried out using Semiconductor Parametric Analyzer (SPA). Results show that the directly sputtered ITO films produced lower resistance compared to the treated ITO films.

Reflectance Analysis of Sputtered Indium Tin Oxide(ITO) Using UV Lambda

Preliminary analysis has been done on the reflectance of sputtered Indium Tin Oxide (ITO) layers. The analysis is done for two different types of layers which is the directly sputtered ITO films and the treated ITO films. In both type of the film it is divided into the thickness of the layer and deposition time. Analysis is done using Perkin Elmer Lambda 950 UV/Vis/NIR Spectrophotometer. The working spectral range is from 250 nm to 800 nm (for transmittance), covering the ultra-violet (UV) and visible spectrum. Results shows thatthe directly deposited thin ITO films had lower reflectance compared to the thick films. The reflectance of the thick films with three and four layers was high (95%) compared to the rest of the films. The treated films produce very low reflectance.

Control of preferred (222) crystalline orientation of sputtered indium tin oxide thin films

We report a two-step growth process for the fabrication of (222)-plane textured indium tin oxide (ITO) films. A thin ITO seed layer was grown in mixed Argon+Oxygen gases, followed by a thick ITO deposited in Argon gas. X-Ray diffraction shows that the sputtered ITO films exhibit strongly preferred (222) crystalline orientation. The (222)-plane textured ITO films have high transmittance above 80% in the visible range and carrier concentration, mobility and resistivity in the range of 1021cm−3, 40cm2/Vs and 10−4Ω·cm, respectively. The surface roughness of our (222) textured ITO films is 1.4nm, which is one of the smallest value obtained from sputtered ITO thin films.