Indium Tin Oxide Films Research Articles

Characterization and ohmic contact properties of indium tin-oxide films prepared on p-type GaN using electron-cyclotron-resonance plasma-sputter deposition

The optical and electrical properties of indium tin oxide (ITO) films deposited using electron cyclotron resonance (ECR) plasma-sputter deposition and the ohmic contact properties between the ITO films and p-type gallium nitride (p-GaN) were evaluated. The electrical properties of the ITO films were evaluated in terms of the dependence on the tin (IV) oxide (SnO2) content of the ITO target and radio frequency (RF) power. The ohmic contact properties between the ITO films and p-GaN were also characterized by varying the top-surface Mg concentration of the p-GaN substrate. An ohmic contact was achieved without post-annealing treatment by depositing the film on a p-GaN high-dope substrate with a top-surface Mg concentration of 2.0 × 1020 cm−3 under low RF-power deposition using an ITO sputter target with 10 wt.% SnO2. The interface between the ITO films and p-GaN that achieved an ohmic contact was observed using scanning transmission electron microscopy (STEM) and was very smooth with no crystal disorder. This indicates that the crystallinity of the ITO films and p-GaN surface is a factor affecting ohmic-contact properties. The inter-diffusion between the ITO films and p-GaN surface was also evaluated using transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDS), and no inter-diffusion was observed.

ZnS:Mn electroluminescent display based on nanostructured indium tin oxide films

Thin-film electroluminescent (TFEL) displays have found applications in various industries and areas due to their unique advantages, where high brightness, a wide temperature range, and reliability are crucial. However, despite their benefits, they also face certain limitations and challenges. TFEL displays typically demand relatively high operating voltages. Total internal reflection in the multilayered structure can significantly impede light extraction from the display. In this study, we propose an optimization of the TFEL display structure to enhance light extraction efficiency and reduce operating voltage. Nanostructured indium tin oxide films, obtained by electron beam evaporation on a heated substrate, were utilized to amplify the electric field in a phosphor layer and to create a non-regular light-scattering relief that effectively breaks internal reflection conditions within the display structure. As a result, the display brightness at operating voltage increased by more than 1.5 times.

Investigation on optical and electrical properties of multilayer ITO/AZO/ITO transparent conductive oxides

This paper examines how varying the thickness of the indium tin oxide (ITO) seed layer, ranging from 8 to 20 nm, impacts the optical, electrical, and structural properties of triple-layer transparent conductive oxide ITO/aluminum doped zinc oxide (AZO)/ITO. ITO and AZO films were deposited by DC and RF magnetron sputtering, respectively. The thickness and density of each layer were measured by X-ray reflectometry (XRR). X-ray diffraction showed that as the thickness of the ITO seed layer increased, both the average size of the crystallites and the volume of the crystalline phase in the AZO film also increased. Measurements of the electrical characteristics indicated a decrease in resistivity as the thickness of the ITO seed layer increased. This reduction is attributed to enhanced charge mobility, resulting from improved crystallinity. It has been shown that a 20-nm-thick ITO seed layer is sufficient to achieve a charge mobility comparable to that of pure ITO films. The photoluminescence spectra have shown a decrease in the concentration of the oxygen vacancies with the introduction of both the cover and seed layers of ITO. The figure of merits (FOM) of the triple-layer coatings and the optical constants of the AZO and ITO films were calculated. The results of this paper indicate that the ITO20/AZO48/ITO12 triple-layer coating possesses optimal characteristics for use in high-efficiency silicon solar cells.

Exploring negative ion behaviors and their influence on properties of DC magnetron sputtered ITO films under varied power and pressure conditions

Abstract We deposited indium-tin-oxide (ITO) films on silicon and quartz substrates by magnetron sputtering technology in pure argon. Using electrostatic quadrupole plasma diagnostic technology, we investigate the effects of discharge power and discharge pressure on the ion flux and energy distribution function of incidence on the substrate surface, with special attention to the production of high-energy negative oxygen ions, and elucidate the mechanism behind its production. At the same time, the structure and properties of ITO films are systematically characterized to understand the potential effects of high energy oxygen ions on the growth of ITO films. Combining with the kinetic property analysis of sputtering damage mechanism of transparent conductive oxide (TCO) thin films, this study provides valuable physical understanding of optimization of TCO thin film deposition process.

Junctionless Structure Indium-Tin Oxide Thin-Film Transistors Enabling Enhanced Mechanical and Contact Stability.

In recent years, considerable attention has focused on high-performance and flexible crystalline metal oxide thin-film transistors (TFTs). However, achieving both high performance and flexibility in semiconductor devices is challenging due to the inherently conductive and brittle nature of crystalline metal oxide. In this study, we propose a facile way to overcome this limitation by employing a junctionless (JL) TFT structure via oxygen plasma treatment of the crystalline indium-tin oxide (ITO) films. The oxygen plasma treatment significantly reduced oxygen vacancies in the ITO films, contributing to the significant reduction in the carrier concentration from 4.67 × 1020 to 1.39 × 1016. Importantly, this reduction was achieved without inducing any noticeable structural changes in the ITO, enabling the successful realization of ITO JL TFTs with an adjustable threshold voltage. Furthermore, the ITO JL TFTs demonstrate good stability and reliability under various bias stress conditions, aging in the air atmosphere, and high-temperature processes. In addition, the ITO JL TFTs exhibit low light sensitivity due to the wide bandgap of ITO and further suppression of Vo defects, making them suitable for applications requiring stable performance under light exposure. To compare and analyze the flexibility of the JL structure and conventional structure with additional source/drain (S/D) junction in ITO TFTs with nonencapsulation, we utilized mechanical simulations and transmission line method (TLM). By employing the JL structure in ITO TFT through carefully optimized oxygen plasma treatment, we successfully mitigated stress concentration at the S/D-channel interface. This resulted in a JL ITO TFT that exhibited a change in contact resistance of less than 20% even after 20,000 bending cycles. Consequently, a stable and flexible ITO TFT with field-effect mobility (μFE) of 12.74 cm2/(V s) was realized, outperforming conventionally structured ITO TFTs with additional S/D junction, where the contact resistance nearly tripled.

Optical constants and thickness gradients for light intensities in glass substrate layers and for complex electric fields in indium tin oxide (ITO) transparent conductor thin film layer, using Bode and Nyquist wavelength-dependent diagrams

Abstract The optical constants of a thin film layer of transparent conductive indium tin oxide (ITO), deposited on a thick glass substrate (G), were obtained for an ITO-G sample using a multilayer matrix method by fitting the regular transmittance and specular reflectance measurements to the collimated equations of the four-flux model, once the optical constants of the glass substrate layer had previously been obtained from a G sample of a single glass substrate layer. The accuracy of the results was validated using a feedback system called the three-extinction matching requirement, that is, obtaining the same extinction coefficients from the optical constants and from the forward and backward collimated differential equations of the four-flux model. To calculate the extinction coefficients of the glass from optical constants, the compression of the wavelength of the incident light in the glass substrate and in the thin ITO film layer was demonstrated, with a thickness less than the wavelength of incident light. The thickness gradients of the forward and backward collimated light intensities, on the glass substrate of the ITOG sample, were compared with those obtained for the single-layer G sample. Then, the thickness gradients for the complex forward and backward electric fields of the ITO thin film layer were obtained and plotted using spectral magnitude and phase Bode plots and new Nyquist plots, i.e. imaginary versus real parts, dependent on wavelength.

A Spoof Surface Plasmon Polaritons Filter with Controllable Negative Slope Equalization Based on Surface Resistance

This paper presents a novel spoof surface plasmon polariton (SSPP) filter integrated with controllable negative slope equalization. Different from traditional microwave filters, two microwave functions - amplitude compensation and interference suppression - are integrated into one device by depositing a lossy indium tin oxide (ITO) film on the rectangular corrugated stub of the SSPP unit. The key point of negative slope equalization benefits from the surface resistance of the ITO film, and the circuit model and behavior are analyzed in detail. Based on the principle, a prototype of a SSPP filter operating from S to C band is designed and fabricated. The measurement results show that the attenuation in the passband increases almost linearly from 3.5 GHz (−4.8 dB) to 6.9 GHz (−15.4 dB), indicating that −10.6 dB equalization is achieved. The improved S21 is attributed to the good impedance matching by sputtering the ITO film on the rectangular metal strip rather than the central strip. Due to the natural low-pass property of SSPPs, the high-order parasitic band is suppressed above the cut-off frequency of 8.5 GHz. The analyses, simulations and measurements show that the proposed SSPP filter is provided with an additional ability to compensate for positive amplitude fluctuation in wideband antennas.

Investigation of the effect of oxygen flow modulation on ITO film properties to improve the performance of SHJ solar cells

Photovoltaics offer a sustainable solution for the growing energy needs of the world, while reducing environmental impact. Transparent Conductive Oxides (TCOs), which are essential in photovoltaic technology, offer high light transmittance and effective charge carrier extraction. This research focuses on the impact of oxygen (O2) flow rates in the deposition of indium tin oxide (ITO) films on n-type crystalline silicon (c-Si) substrates by DC magnetron sputtering. The structural, optical, and electrical properties were analyzed. Based on the results, the optimal O2 ratio was determined and used in the fabrication of SHJ solar cells, achieving an efficiency of 18.6%.

Impact of Temperature Optimization of ITO Thin Film on Tandem Solar Cell Efficiency.

This study examined the impact of temperature optimization on indium tin oxide (ITO) films in monolithic HJT/perovskite tandem solar cells. ITO films were deposited using magnetron sputtering at temperatures ranging from room temperature (25 °C) to 250 °C. The sputtering target was ITO, with a mass ratio of In2O3 to SnO2 of 90% to 10%. The effects of temperature on the ITO film were analyzed using X-ray diffraction (XRD), spectroscopic ellipsometry, and sheet resistance measurements. Results showed that all ITO films exhibited a polycrystalline morphology, with diffraction peaks corresponding to planes (211), (222), (400), (440), and (622), indicating a cubic bixbyite crystal structure. The light transmittance exceeded 80%, and the sheet resistance was 75.1 Ω/sq for ITO deposited at 200 °C. The optical bandgap of deposited ITO films ranged between 3.90 eV and 3.93 eV. Structural and morphological characterization of the perovskite solar cell was performed using XRD and FE-SEM. Tandem solar cell performance was evaluated by analyzing current density-voltage characteristics under simulated sunlight. By optimizing the ITO deposition temperature, the tandem cell achieved a power conversion efficiency (PCE) of 16.74%, resulting in enhanced tandem cell efficiency.

Absorptive metasurface with optical transparency for broadband RCS reduction.

Here, we introduce an optically transparent and flexible metasurface designed for effective absorption within the microwave spectrum. Indium tin oxide (ITO) films with varying square resistances fabricate a metasurface ground layer and a lossy pattern layers. Polydimethylsiloxane (PDMS) with a low refractive index, high transparency, and high flexibility is chosen as the dielectric layer. The proposed structure exhibits a reflection band of less than -10 dB with a fractional bandwidth of 167% in the range of 3.0-33.8 GHz under vertical incident electromagnetic waves. The metasurface designed based on this unit allows for the attainment of a radar cross section (RCS) reduction bandwidth of 8.75-31.1 GHz with a 10 dB reduction and a fractional bandwidth of 112%. The metasurface can maintain a broadband RCS reduction over a range of 45° incidence angles. In addition, due to the flexibility of the structure, we analyzed its RCS reduction capability when non-planar by wrapping the structure around a cylinder. The integration of simulation and testing has demonstrated that the structure exhibits excellent performance in the field of electromagnetic stealth. It has potential practical applications in electromagnetic shielding windows and the windows or domes of airplanes or satellites.

Tailorable ITO thin films for tunable microwave photonic applications

Tunability is a fundamental prerequisite for functional devices and forms the backbone of reconfigurable microwave photonic (MWP) signal processors. In this paper, we explore the use of indium tin oxide (ITO) thin films, notable for their combination of optical transparency and electrical conductivity, to provide tunability for integrated MWP devices. We study the impacts of post-thermal annealing on the structural, electrical, and optical properties of ITO films. The annealed ITO microheater maintains a low total insertion loss of just 0.1 dB while facilitating the tunability of the microring across the entire free spectral range (FSR) using less than half the voltage required by its non-annealed counterpart. Furthermore, the post-annealed ITO film exhibits a 30% improvement in response time, enhancing its performance as an active voltage-controlled microheater. Leveraging this advantage, we employed the post-annealed device to demonstrate continuous tunable radio frequency (RF) phase shifts from 0–330° across a frequency range spanning 15 GHz to 40 GHz with only 5.58 mW of power. The flexibility in modifying the ITO thin film properties effectively bridges the gap between achieving low-loss and high-speed thermo-optic based microheaters.

Numerical ellipsometry: Artificial intelligence for rapid analysis of indium tin oxide films on silicon

Ellipsometry is a well-known material analytical method widely used to measure thickness and optical properties of thin films and surfaces across a wide range of industrial and research applications including critical dimensions in chipmaking. The method employs the fact that light undergoes a change in polarization state upon reflection from or transmission through a material. The desired properties of the surface structure are related to measurements by the electromagnetic models expressed by Maxwell’s equations as well as models of material properties. The work here demonstrates the use of artificial intelligence in the form of a multilayer perceptron artificial neural network to apply the electromagnetic model. The reflecting surface examined here is composed of indium tin oxide (ITO) films approximately 400 nm in thickness deposited on silicon substrates. Solutions are provided by 299 artificial neural networks, one per wavelength from 210 to 1700 nm across which ITO exhibits transparent as well as absorbing characteristics. Thus, it serves as a proxy for a wide range of other materials. To train the network, simulated measurements are computed at two thicknesses which differ randomly by 1–6 nm and at three different incidence angles of 55°, 65°, and 75°. Following training, results are obtained in less than one second on a conventional desktop computer.

Comparative study of RF sputtered Fe2O3- and Fe3O4-doped indium saving indium tin oxide thin films

In present work the properties of iron-doped indium tin oxide (ITO) films with reduced to 50 mass% indium oxide content prepared by co-sputtering of ITO and Fe2O3 targets and ITO and Fe3O4 targets in mixed argon–oxygen atmosphere were studied by various methods. The influence of different working gas flow rates, RF power of iron oxide targets, type of doping oxide and heat treatment temperatures on the electrical, optical, structural, and morphological properties of the films was characterized by means of four-point probe method, ultraviolet–visible (UV–Vis) spectroscopy, X-ray diffraction and atomic force microscopy.

Electrochromic Thin‐Film Nickel‐Oxide Coatings for Systems with Adjustable Light Transmission

In this study, results on the effect of technological parameters of the nickel(II)‐oxide thin‐film deposition process, obtained through chemical vapor deposition in an argon–oxygen environment using bis‐(ethylcyclopentadienyl)‐nickel (EtCp)2Ni, on their electrochromic properties, are presented. It is shown that the films lose ability to electrochromic coloring in alkaline environments as their thickness increases up to 170 nm. The introduction of small ozone additions of 0.1 vol% O3 into the gas phase leads to a decrease in the NiO films deposition rate, the formation of a rougher layer with an average grain size up to 71.4 nm, capable of coloring in light brown. Additional cathodic treatment of NiO films at a potential of −0.8 V for 30 s in alkaline environments containing fullerene C60(OH)24 leads to the modification of the surface layer and the formation of NiO–C carbon‐containing nanocomposite coatings with enhanced contrast and the ability to retain the colored state after polarization is turned off, i.e., possessing optical memory properties. Using NiO–C nanocomposite and indium–tin–oxide films, which have opposite coloring mechanisms, in the structure of an electrochromic device allows for an increase in the grade of glass darkening, significantly reducing energy consumption, improving operational characteristics, and life span.

Identifying Current Collectors that Enable Light-Battery Interactions.

In recent years, there has been an increased focus on studying light-battery interactions in the context of operando optical studies and integrated photoelectrochemical energy harvesting. However, there has been little insight into identifying suitable "light-accepting" current collectors for this class of batteries. In this study, fluorine-doped tin oxide, indium-tin oxide, and silver nanowire-graphene films are analyzed along with carbon paper, carbon nanotube paper, and stainless-steel mesh as current collectors for optical batteries. They are categorized into two classes - transmissive and non-transmissive, based on the orientation of the light-electrode interaction. Various methods to prepare the electrode are highlighted, including drop casting and the fabrication of free-standing electrodes. The optical and electrical properties of these current collectors as well as their electrochemical stability are measured using linear sweep voltammetry against zinc and lithium anodes. Finally, the rate performance and long-term cycling stability of lithium manganese oxide (LiMn2O4) cathodes are measured against lithium anodes with these current collectors and their performance is compared. These results show which current collector to choose depends on the application and cell chemistry. These guidelines will assist in the design of future optical cells for in-situ measurements and photoelectrochemical energy storage.

Overall aspect for designing magnetron sputtering plasma sources and their applications in the deposition of ITO films

This work reports a systematic review of the studies of magnetron sputtering (MS) discharges and their utilities for the deposition of transparent coating oxide thin films like indium tin oxides (ITOs). It collates the overall information of plasma science, diagnostics, and chemistry and their usefulness in controlling the plasma process, film growth, and properties. It discusses studies on various MS systems and their capabilities and reports scientific aspects like the formation of instability and plasma flares to understand the various discharge phenomena. The study also discusses various issues, progress, and challenges in ITO films for industrial applications. In addition, this work highlights the importance of plasma parameters and energy flux on thin film growth and film properties.

Probing Intercalated Indium-Tin Oxide Films by Non-Local Resistance Measurements

Probing Intercalated Indium-Tin Oxide Films by Non-Local Resistance Measurements

Optimization of p-type contact for electrical injection and light extraction for 365 nm UV-A LEDs

This paper demonstrates low-resistance and high-transparency p-type contact materials for ultraviolet (UV) micro-light-emitting diodes (LEDs) at 365 nm. As a commonly used p-type LED contact, indium tin oxide (ITO) and nickel/ITO (Ni/ITO) contacts were studied before and after rapid thermal annealing (RTA) treatments. The transmittance at 365 nm wavelength of 200 nm thick ITO films increased from approximately 57%–90% after RTA at a temperature exceeding 400 °C, while the Ni/ITO film had a transmittance of about 73% after annealing. Micron-sized UV-LEDs with Ni/ITO p-contact were fabricated. Electrical characterization shows that Ni/ITO films annealed at 600 °C demonstrated good ohmic contact behavior and the highest on-wafer external quantum efficiency, despite slightly lower transmittance. This paper shows the potential of annealed Ni/ITO films as promising p-contact materials for high-performance 365 nm UV-LEDs.

Wafer-Scale Characterization of 1692-Pixel-Per-Inch Blue Micro-LED Arrays with an Optimized ITO Layer.

Wafer-scale blue micro-light-emitting diode (micro-LED) arrays were fabricated with a pixel size of 12 μm, a pixel pitch of 15 μm, and a pixel density of 1692 pixels per inch, achieved by optimizing the properties of e-beam-deposited and sputter-deposited indium tin oxide (ITO). Although the sputter-deposited ITO (S-ITO) films exhibited a densely packed morphology and lower resistivity compared to the e-beam-deposited ITO (E-ITO) films, the forward voltage (VF) values of a micro-LED with the S-ITO films were higher than those with the E-ITO films. The VF values for a single pixel and for four pixels with E-ITO films were 2.82 V and 2.83 V, respectively, while the corresponding values for S-ITO films were 3.50 V and 3.52 V. This was attributed to ion bombardment damage and nitrogen vacancies in the p-GaN layer. Surprisingly, the VF variations of a single pixel and of four pixels with the optimized E-ITO spreading layer from five different regions were only 0.09 V and 0.10 V, respectively. This extremely uniform VF variation is suitable for creating micro-LED displays to be used in AR and VR applications, circumventing the bottleneck in the development of long-lifespan and high-brightness organic LED devices for industrial mass production.

Effect of Sheet Resistance of Indium Tin Oxide Films on Thermal Management in Optoelectronic Devices

Effect of Sheet Resistance of Indium Tin Oxide Films on Thermal Management in Optoelectronic Devices