Magnetron Sputtered Indium Tin Oxide Research Articles

Influence of oxygen on the optical and electrical properties of magnetron-sputtered indium tin oxide thin films at ambient temperature

Indium Tin Oxide (ITO) thin films are commonly used as transparent conductive layers in the production of solar cells. ITO films are typically heat-treated at temperatures exceeding 200 °C after magnetron sputtering to optimize the physical, optical, and electrical characteristics for photovoltaic devices. This high temperature heating procedure greatly limits the use of potential substrates, particularly those comprised of low-temperature-rated polymers. Herein, we examine the physical, optical, and electrical transport effects of oxygen:argon plasmas during radio frequency magnetron sputtering of ITO on glass and flexible polymer surfaces without subsequent heat treatment. ITO thin films were characterized via sheet resistance testing, UV–Vis spectroscopy, X-ray diffraction, and scanning electron microscopy imaging. Sheet resistance measurements revealed an increase in surface resistance with increasing oxygen concentration during sputtering. UV–Vis optical transmittance measurements demonstrated an improvement in optical transmittance with an increase in oxygen concentration reaching a maximum transmittance at an oxygen concentration of 1-2%. Most importantly, it was discovered that producing bilayers of ITO with pure argon sputtered plasmas followed by oxygen:argon plasmas produced ITO thin films with suitable resistance and transmittance without the need for high temperature post annealing. These results highlight a methodology for the deposition of ITO thin films on temperature sensitive substrates for flexible photovoltaics and low-cost module production.

Tunable optical nonlinearity of indium tin oxide for optical switching in epsilon-near-zero region

Abstract The propagation of light in the epsilon-near-zero (ENZ) region of materials exhibits intriguing linear and nonlinear optical phenomenon that have been extensively exploited for a plethora of applications. Here, we show that the optical properties as well as the ENZ wavelength of magnetron-sputtered indium tin oxide (ITO) thin films could be judiciously engineered. The measurement of nonlinear optical properties reveals that the control of deposition conditions allows for the tuning of absorptive optical nonlinearity between saturable absorption and reverse saturable absorption. The ENZ wavelength for the ITO film is deduced as around 1553 nm. We obtain the highest third-order nonlinear absorption coefficient and imaginary part of third-order nonlinear susceptibility for the ITO thin film through Z-scan method as −50.56 cm/GW and ∼38 × 10−14 e.s.u. at 1050 nm, and −64.50 cm/GW and ∼45 × 10−14 e.s.u. at 1550 nm, respectively. We demonstrate further that the strong saturable absorption of the ITO thin film enables Q-switched pulse laser generation in ∼1050 and ∼1550 nm regions with tunable repetition rates and pulse energies. The present results suggest the great application potential of the ITO thin film in the field of nonlinear optical devices.

Effect of nitrogen partial pressure on the TCR of magnetron sputtered indium tin oxide thin films at high temperatures

Indium tin oxide (ITO) is a promising sensitive material for ultra-high temperature thin-film sensors (UTTSs) applied in thermal and mechanical parameters test in hot section parts. However, the instability of the temperature coefficient of resistance (TCR) in the ITO film is still one of the major limiting factors in accuracy improvement of the UTTSs. In this work, different ITO thin film samples were prepared by RF magnetron sputtering with various N2/Ar ratios changing from 10%–40%, and the effect of nitrogen partial pressure (NPP) on the TCR of ITO films in elevated temperature from 500 °C to 1200 °C was studied. The micromorphology, crystallographic structures and electrical performances of ITO films were examined by scanning electron microscope (SEM), X-ray diffraction (XRD) and Hall effect measurement, respectively. Results show that lower crystallinity and smaller grain of ITO films can be observed with the increase of NPP. In addition, we found that the recrystallization is one of the main factors affecting the TCR repeatability in the thermal cycle test. The grain growth rate (GGR) is only 27.0% in the 20%N2 ITO film after the thermal cycle test from 500 °C to 1200 °C, far lower than that of the 40%N2 ITO film (309.6%). Consequently, the 20%N2 ITO film showed the lowest TCR volatility rates (TVR) after the thermal cycle test, which were respectively recorded as only about 0.5% and 2.1% at 800 °C and 1200 °C. The high TCR stability in the 20%N2 ITO film can be attributed to the formation of the stable phase structure during the thermal cycle test. Furthermore, the 20%N2 ITO film also has the smallest TCR compared with other ITO films.

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

Tuning electro-optical properties of pulsed dc magnetron sputtered indium tin oxide thin films: effects of pulsing frequency and annealing

We report on effects of pulsing frequency and annealing temperature on structural and electro-optical properties of thin indium-tin-oxide (ITO) films prepared by pulsed dc magnetron sputtering technique. Phase analysis shows that as-deposited ITO films belong to crystalline bixbyite structure with (400) preferred orientation. Optical transmittance of greater than 87 % is obtained in the visible range. This is followed by a clear shift in the absorption edge towards higher energy region which is indicative of a lower defect density near the band edge. The lowest resistivity value of 4.47 × 10−4 Ω-cm and the highest carrier concentration of 1 × 1021 cm−3 are achieved by annealing the films at 523 K in air. Variations in the energy band gap and resistivity of ITO films may be attributed to Sn doping and oxygen vacancies, which act as donors. The correlation between the deposition parameters and the film properties are discussed.

Nanomechanical investigation of thin-film electroceramic/metal-organic framework multilayers

Thin-film multilayer stacks of mechanically hard magnetron sputtered indium tin oxide (ITO) and mechanically soft highly porous surface anchored metal-organic framework (SURMOF) HKUST-1 were studied using nanoindentation. Crystalline, continuous, and monolithic surface anchored MOF thin films were fabricated using a liquid-phase epitaxial growth method. Control over respective fabrication processes allowed for tuning of the thickness of the thin film systems with a high degree of precision. It was found that the mechanical indentation of such thin films is significantly affected by the substrate properties; however, elastic parameters were able to be decoupled for constituent thin-film materials (EITO ≈ 96.7 GPa, EHKUST−1 ≈ 22.0 GPa). For indentation of multilayer stacks, it was found that as the layer thicknesses were increased, while holding the relative thickness of ITO and HKUST-1 constant, the resistance to deformation was significantly altered. Such an observation is likely due to small, albeit significant, changes in film texture, interfacial roughness, size effects, and controlling deformation mechanism as a result of increasing material deposition during processing. Such effects may have consequences regarding the rational mechanical design and utilization of MOF-based hybrid thin-film devices.

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 low resistivity and high work function ITO films prepared by oxygen flow rates and N2O plasma treatment for amorphous/crystalline silicon heterojunction solar cells.

Pulsed DC magnetron sputtered indium tin oxide (ITO) films deposited on glass substrates with lowest resistivity of 2.62 x 10(-4) Ω x cm and high transmittance of about 89% in the visible wavelength region. We report the enhancement of ITO work function (Φ(ITO)) by the variation of oxygen (O2) flow rate and N2O surface plasma treatment. The Φ(ITO) increased from 4.43 to 4.56 eV with the increase in O2 flow rate from 0 to 4 sccm while surface treatment of N2O plasma further enhanced the ITO work function to 4.65 eV. The crystallinity of the ITO films improved with increasing O2 flow rate, as revealed by XRD analysis. The ITO work function was increased by the interfacial dipole resulting from the surface rich in O- ions and by the dipole moment formed at the ITO surface during N2O plasma treatment. The ITO films with high work functions can be used to modify the front barrier height in heterojunction with intrinsic thin layer (HIT) solar cells.

Highly transparent RF magnetron-sputtered indium tin oxide films for a-Si:H/c-Si heterojunction solar cells amorphous/crystalline silicon

We prepared highly transparent magnetron-sputtered indium tin oxide (ITO) films deposited at various RF powers for a-Si:H(p)/c-Si heterojunction solar cell applications. The surface morphology of ITO films improved in terms of an increase in grain size as the RF power increased. Rapid growth of the (400) plane was observed with increasing RF power, while the (222) plane remain unchanged. The ITO film deposited at 100W showed the lowest resistivity of 3.8×10−4Ωcm and highest visible transmittance of 90.19%. The deposition rate and optical bandgap of ITO films were varied from 20 to 100nm/min and from 3.68 to 3.77eV for RF power from 50 to 250W, respectively. Highly transparent ITO films were utilized as the front anti-reflection layer in heterojunctions with intrinsic thin-layer (HIT) solar cells showed the efficiency of 16.3% for RF power of 100W. The HIT solar cells deposited at RF power of 100W also exhibited higher carrier lifetime and implied voltage.

RF magnetron sputtered indium tin oxide films with high transmittance and work function for a-Si:H/c-Si heterojunction solar cells

The RF magnetron sputtered indium tin oxide (ITO) films were deposited on glass substrates with low resistivity, high transmittance and work function for various oxygen (O2) flow rates. The addition of small O2 contents during the sputtering process increased the Hall mobility of ITO films while carrier concentration was decreased. The work function of ITO films was enhanced from 4.31 to 4.81 eV through the growth of (222) plane having relatively low surface energy. The highly transparent ITO films were employed as front anti-reflection layer in heterojunction with intrinsic thin layer (HIT) solar cells and the best photo-voltage parameters were found to be; Voc = 665 mV, Jsc = 35.1 mA/cm2, FF = 73.2% and η = 17.1% for the O2 flow rate of 0.1 sccm. The high work function ITO films play an important role for barrier height modification in HIT solar cell.

Elemental distribution and oxygen deficiency of magnetron sputtered indium tin oxide films

The atomic structure and composition of noninterfacial ITO and ITO-Si interfaces were studied with transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). The films were deposited by dc magnetron sputtering on monocrystalline p-type (100) Si wafers. Both as deposited and heat treated films consisted of crystalline ITO. The ITO/Si interface showed a more complicated composition. A thin layer of SiOx was found at the ITO/Si interface together with In and Sn nanoclusters, as well as highly oxygen deficient regions, as observed by XPS. High energy electron exposure of this area crystallized the In nanoclusters and at the same time increased the SiOx interface layer thickness.

Properties of RF magnetron sputtered indium tin oxide thin films on externally unheated glass substrate

Indium tin oxide (ITO) thin films were deposited by radio frequency (RF) magnetron sputtering onto glass substrates. The transparent and conducting ITO thin films were obtained on externally unheated glass substrate, without any post-heat treatment, and by varying the deposition process parameters such as the working pressure and the RF Power. The effect of the variation of the above deposition parameters on the structural, surface morphology, electrical, and optical properties of the thin films have been studied. A minimum resistivity of 2.36 × 10−4 Ω cm and 80% transmittance with a figure of merit 37.2 × 10−3 Ω−1 is achieved for the thin films grown on externally unheated substrate with 75 W RF power and 0.5 mTorr working pressure.

Micro-pressure sensors made of indium tin oxide thin films

The microstructure, electrical resistivity and piezoresistive property of magnetron sputtered indium tin oxide (ITO) films were investigated as functions of preparation and post-annealing conditions. Annealing at 400 °C for 30 min resulted in low electrical resistivity ≤6.0 × 10 −3 Ω cm and observable piezoresistive coefficient ranging from −4.3 × 10 −11 to −7.1 × 10 −11 Pa −1. Prototypes of pressure sensors with an annealed ITO film deposited on a 25 μm thick silicon diaphragm were fabricated. With a bias voltage of 1 V, the device gave a voltage response of 12.6 mV when the differential pressure across the diaphragm varied from −6 × 10 4 to 6 × 10 4 Pa.

Properties of dc magnetron sputtered indium tin oxide films on polymeric substrates at room temperature

Indium tin oxide (ITO) thin films were deposited on polymeric substrates at room temperature by dc reactive magnetron sputtering from an In–Sn (90–10 wt%) alloy target. The electrical, optical, and mechanical properties of ITO films on various substrates such as polycarbonate, acrylic, polyethylene terephthalate, and glass are influenced sensitively by sputtering parameters. Therefore, the dependence of these properties on dc power, working pressure, and partial oxygen content has been systematically investigated. Low dc power was applied to avoid the deformation of polymeric substrates. The electrical resistivity of as-deposited ITO films decreases initially and then increases as oxygen partial pressure (PO2) increases. The optical transmittance at visible wavelength of 550 nm was as much as 85%. The friction force of as-deposited ITO films on various substrates is increased with an increase of dc power, and behaves similarly to the optimum curve of resistivity with increasing PO2.

Investigations on the crystallisation properties of RF magnetron sputtered indium tin oxide thin films

X-Ray diffraction and X-ray texture analysis have been carried out on RF magnetron sputtered ITO (indium tin oxide) thin films on glass substrates in order to understand their crystal growth behaviour. Films deposited at various deposition rates and gas compositions were subjected to investigation. X-Ray diffraction analysis revealed the polycrystalline structure of the films with a difference in crystallographic orientation without any change in the BCC (Body Centred Cubic) structure. Both the increase in deposition rate and gas composition reflects the change in crystallographic orientation. X-Ray texture analysis on the grown films revealed also a difference in film texturization following the change in crystallographic orientation. Strong orientation of crystallites perpendicular to the substrate were observed for films grown with (400) preferential plane.

Internal Stress and Adhesive Strength of Reactive Magnetron Sputtered Indium Tin Oxide Films on Acrylics.

Indium tin oxide (ITO) films were deposited on acrylics by low temperature reactive magnetron sputtering. The effects of oxygen flow and film thickness on the internal stress and adhesion of ITO films on acrylics were evaluated. Results from the measurement of lattice parameters suggested that the internal compressive stress parallel to the film surface increased with increasing oxygen flow rate. This was possibly due to the peening effects of bombarding particles and the decrease in oxygen vacancies at relatively high oxygen flow. Observation of scratched surface after adhesion test showed that tensile bending moments occur within the coating as it was pushed down underneath the adhesion test indenter. The critical scratching load of ITO films invariably increased with oxygen flow and decreased with increasing thickness.

Influences of Sputtering Power and Substrate Temperature on the Properties of RF Magnetron Sputtered Indium Tin Oxide Thin Films

Indium tin oxide thin films have been deposited on glass substrates using rf magnetron sputtering at different power densities (0.27–0.80 W/cm2) and at different substrate temperatures (RT-250) °C. Film structure, crystallite size and orientation, optical absorption and bandgap have been studied to characterize the films. Carrier concentration and Hall mobility have been determined by Hall effect. X-ray diffraction (XRD) analysis of room temperature (RT) deposited samples reveals a structural change from amorphous to mixed amorphous/polycrystalline structure with <100> preferred orientation with increasing rf power density. The increase in substrate temperature results in a similar structural evolution from amorphous to a mixed phase followed, at temperatures higher than 200°C, by a polycrystalline phase with <111> orientation. The study clearly indicates that ITO films dominated by oxygen vacancies prefer to grow with <100> oriented crystallites whereas the <111> oriented films are characterized by a more effective doping by tin.

Antireflective coating for ITO films deposited on glass substrate

The refractive index n of radio-frequency (r.f.) magnetron sputtered indium tin oxide (ITO) films varies with sputtering parameters, such as sputtering power and oxygen percentage in the sputtering ambient. In this study, the feasibility to fabricate multilayer antireflective (AR) coating with a single ITO target by controlling the sputtering conditions is explored. Reduction in the reflectance can be achieved by using a one-quarter-wavelength inner layer ITO with a refractive index n = 1.87 and a one-quarter-wavelength outer layer ITO with n = 2.17. Hence, a single ITO target suffices in the preparation of multilayer AR coating. This simplifies the deposition processes and equipment for the fabrication of AR coating. Surface corrugation, another approach to the reduction of reflectance, is also discussed.

Mechanical properties of r.f. magnetron sputtered indium tin oxide films

In this study, the mechanical behavior of r.f. magnetron sputtered indium tin oxide (ITO) films with glass and polycarbonate as substrates was investigated. The microhardness, pull-off strength and scratch adhesion strength were measured to assess the film properties. The ITO coating improves the hardness of the polycarbonate substrate. Incorporation of oxygen in the sputtering ambient enhances the crystallization of the film; consequently, the film hardness of coated polycarbonate and the scratch adhesion strength of coated glass are improved. The thermal expansion mismatch between ITO and polycarbonate results in poor adhesion when polycarbonate is employed as the substrate.

Effect of oxygen concentration in the sputtering ambient on the microstructure, electrical and optical properties of radio-frequency magnetron-sputtered indium tin oxide films

Indium tin oxide (ITO) films have been prepared by radio-frequency (rf) magnetron sputtering. The effect of oxygen concentration in the sputtering ambient on the structure and properties of ITO films are investigated. The films have a preferred orientation in the (440) plane. The presence of oxygen during sputtering enhances the crystallization of the film. Film grain size increases as more oxygen is added. According to the XPS measurements, the addition of oxygen reduces the oxygen-deficient region of the film. Hence the optical transmittance of the film is improved while film conductivity decreases.