Indium Tin Oxide Film Thickness Research Articles

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.

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.

Annealing-free fabrication of high-quality indium tin oxide films for free-carrier-based hybrid metal–semiconductor nanophotonics

Recent discoveries have revealed that indium tin oxide (ITO), due to the presence of an epsilon-near-zero (ENZ) point and suitable carrier concentration and mobility, can be used to modulate the refractive index, confine fields in the nanoscale, enhance nonlinear effects, achieve ultrafast light switching or to construct so-called time-varying media. While this potential positions ITO as a key material for future nanophotonic devices, producing ITO films with precisely engineered properties remains a significant challenge. Especially when the device’s complex geometry or incorporated materials require the fabrication process to be conducted at substrate temperatures below 100 °C and without any post-annealing treatment. Here we present a comprehensive study on the low-temperature deposition of 70 nm thick ITO films using an e-beam PVD system. The nanolayers evaporated under different conditions were characterized by SEM and AFM microscopy, Hall effect measurement system as well as spectroscopic ellipsometry. We discuss the factors influencing the optical, electrical, and morphological properties of ITO films. We show that smooth nanolayers of similar quality to annealed samples can be obtained at 80 °C by controlling the oxygen plasma parameters, and the ENZ wavelength can be tuned throughout the NIR spectral range. Finally, we show that using the proposed methodology, we fabricated ITO films with resistivity as low as 5.2 × 10–4 Ω cm, smooth surface with RMS < 1 nm, high carrier concentration reaching 1.2 × 1021 cm−3 and high transmittance (85%) in the Vis/NIR spectrum.

Simple Fabrication Method for Solution-gated One-piece Transistors for Biosensing Applications

INTRODUCTIONSolution-gated field-effect transistors (FETs) with silicon or other semiconductive materials as channels can specifically and selectively detect ions and biomolecules related to biological functions by chemically modifying the gate electrode surface, and these are known as biologically coupled FETs (Bio-FETs) [1]. Since Bio-FETs can directly detect the charges of ions and biomolecules, they do not require to label fluorescent dyes and to induce redox reactions based on enzymes. Therefore, Bio-FETs are expected to be used as in vitro diagnostic devices for a label-free monitoring of health conditions in daily life.Recently, indium tin oxide (ITO) has been widely used as an electrode material for flat panel displays owing to its transparency and conductivity. Our laboratory previously reported that solution-gate FETs fabricated by one-step sputtering provided a steep subthreshold slope (SS) owing to the absence of the interfaces among source/channel/drain electrodes and the large electric double-layer capacitance caused by direct contact between electrolyte solutions and the channel surface [2]. While this technique was simple, it utilized the diffusion of atoms during sputtering between a modified mask and substrates and was also dependent on the mask size, which limited the miniaturization of the transistor. On the other hand, the conventional fabrication methods of solution-gated FETs facilitate the miniaturization and the precise control of device structure by use of photolithography, but such methods inevitably produce impurities at the source/channel/drain electrode interfaces and may cause the degradation of device performances.In this study, we propose a new method to fabricate solution-gated ITO thin-film channel FETs without interfaces among the source/channel/drain electrodes, which facilitates to miniaturize and control the device structure. A conductive ITO thin film with a thickness of about 100 nm is deposited on a glass substrate by sputtering. Then, the ITO film is protected by photoresist and then the channel area is exposed by photolithography. The exposed area is etched to 20 nm or less thickness, which induces semiconductive characteristics. This method enables the fabrication of the desired solution-gated ITO thin-film channel FET. Furthermore, we evaluate its electrical characteristics and examines its potential for biosensor applications.EXPERIMENTALFirst, photoresist was patterned on a glass substrate by photolithography. ITO thin film (100 nm thickness) was deposited on the patterned area by sputtering, and the photoresist was removed using a solvent. Next, photolithography was used again to deposit the resist film so that the channel area was exposed. Etching was performed by dropping 0.1 M hydrochloric acid on the exposed channel area (Figure). Etching time was controlled by applying a voltage between the source and drain electrodes and measuring the change in current over time. A semiconductor parameter analyzer was used to measure the current during etching, the gate voltage (VG)-drain current (ID) transfer characteristics, and the pH responsivity of the fabricated devices. The film thickness was measured by a white interferometer-equipped laser microscope (Keyence).RESULTS and DISCUSSIONBy controlling the current during etching, the current value was decreased rapidly at the end of the etching. This may be because the thickness of ITO film was thinner and reached about 20 nm, which resulted in the semiconductive characteristics. Then, the etching was stopped to obtain the solution-gated ITO thin-film channel FET. The fundamental electrical characteristics such as VG-ID transfer curves were investigated, and the fabricated device was found to operate as the solution-gated FET. It was also found that the devices showed the Nernst response for the change in pH and a steep subthreshold slope of approximately 90 mV/decade (pH 7.41). Furthermore, the ITO channel thickness was measured by laser microscopy; as a result, it was about 10–20 nm.CONCLUSIONS In this study, we proposed the new method to fabricate the solution-gated ITO thin-film channel FET. The device actually worked as a transistor, and it showed good sensitivity to potential. This method enabled the solution-gated FETs to be produced by the simple method. Thus, the solution-gated ITO thin-film channel FET is applied to biosensors, which is highly sensitive and affordable to detect biomolecules in the future.REFERENCES[1] Sakata, T. ACS Omega, 4, 11852 (2019).[2] Sakata, T.; Nishitani, S.; Saito, A.; Fukasawa, Y. ACS Appl. Mater. Interfaces, 13, 38569 (2021). Figure 1

Investigation into Micro-Polishing Photonic Crystal Fibers for Surface Plasmon Resonance Sensing

In this work, we propose and demonstrate a micro-polishing-fiber (MPF)-based surface plasmon resonance (SPR) sensor. The structure of the sensor is simple and consists of three layers of regular air holes and two small air holes. The sensitivity seldom depends on the sizes of the air holes, which leads to a sensor with high structure tolerance. A tiny polishing depth ensures the mechanical strength of the polished fiber. There are three decisive factors for mass production and application of the sensor. A thin layer of indium tin oxide (ITO) film is applied to the polished surface to excite plasmonic interactions and facilitate refractive index (RI) detection. The SPR sensor is designed and analyzed by the finite element method (FEM), and optimized in terms of the air holes’ diameter, the ITO film thickness, and the core-to-surface interval. In the wide detection range between 1.32 and 1.39, the wavelength sensitivity can reach up to 11,600 nm/RIU. The MPF–SPR sensor exhibits great potential in the fields of optics, biomedicine, and chemistry.

Regular Periodic Surface Structures on Indium Tin Oxide Film Efficiently Fabricated by Femtosecond Laser Direct Writing with a Cylindrical Lens.

Regular laser-induced periodic surface structures (LIPSS) were efficiently fabricated on indium tin oxide (ITO) films by femtosecond laser direct writing with a cylindrical lens. It was found that randomly distributed nanoparticles and high spatial frequency LIPSSs (HSFL) formed on the surface after a small number of cumulative incident laser pulses per spot, and regular low spatial frequency LIPSSs (LSFL) appeared when more laser pulses accumulated. The mechanism of the transition was studied by real-time absorptance measurement and theoretical simulation. Results show that the interference between incident laser and surface plasmon polaritons (SPPs) excited by random surface scatterers facilitates the formation of prototype LSFLs, which in turn enhances light absorption and SPP excitation following laser pulses. The effects of scanning velocity and laser fluence on LSFL quality were discussed in detail. Moreover, large-area extremely regular LSFL with a diameter of 30 mm were efficiently fabricated on an ITO film by femtosecond laser direct writing with the cylindrical lens. The fabricated LSFLs on the ITO film demonstrate vivid structural color. During LSFL processing, the decrease of ITO film thickness leads to the increase of near-infrared optical transmittance.

Temperature sensing of π-PSFBG with ITO film coated by PLD method

In this article the temperature sensing properties of π–phase-shifted fiber Bragg grating (π-PSFBG) were investigated. Surface coating is one of the commonly used modification methods for fiber gratings, which can improve its sensing performance and even enable it to sense more physical quantities. In this article, we aim to study the effect of coating on the temperature sensing performance of π-PSFBG. Indium tin oxide (ITO) films are widely used in the optoelectronics industry due to their unique combination of electrical conduction and optical transparency. In this paper, the ITO film was coated on the surface of π-PSFBG by pulsed laser deposition (PLD) method to improve its sensing performance. In the practical application of fiber optic sensors, multiple sensors are often used simultaneously, which leads to the mutual interference superposition between the spectra. In this case, the stable extraction of the sensing signal is a problem worth considering. The sensing stability of several interference optical paths and cascaded optical paths before and after π-PSFBG coating is investigated and compared. After the surface is coated with a layer of 0.19 µm thick ITO film, the temperature sensing sensitivity of π-PSFBG is increased by about 15%. It was found that the coating of ITO film enhanced the stability of π-PSFBG in various optical paths.

Polarization-Independent, tunable, broadband perfect absorber based on semi-sphere patterned Epsilon-Near-Zero films

Epsilon-near-zero (ENZ) optical materials, whose real part of the dielectric constant crosses zero, have been demonstrated to enhance linear and nonlinear optical responses in the ENZ region. Here, a new broadband light absorption design concept based on the coupling of ENZ and localized surface plasmon resonance (LSPR) modes is proposed. It is verified by a single-layer semi-sphere patterned indium tin oxide (ITO) film based on large-area and low-cost self-assembly technology. Simulation and experimental results show that the 91 nm thick ITO film on the two-dimensional microsphere array can simultaneously excite the ENZ and LSPR modes without complex coupling structures, which enable >98% light absorption in the range of 1435–1680 nm. The perfect absorber based on a corrugated ITO film has typical polarization-independent, large-angular-spectrum, adjustable-absorption-bandwidth, and field-enhanced resonance absorption characteristics. These findings provide a new design solution for low-cost broadband perfect absorbers based on ENZ materials, which have wide prospects for application in near-infrared sensors, photoelectric detection, and ENZ photonics.

Optimization of optoelectronic performance of ITO/AG/ITO electrodes by using taguchi method and spectroscopic ellipsometry technique

In this study, a sandwich-structured electrode composed of indium tin oxide (ITO)/metal silver layer/ITO was prepared by the radio frequency magnetron sputtering method. We used the Taguchi method and spectroscopic ellipsometry (SE) analysis to optimize the geometrical structures of the electrodes and the sputtering power for the silver layer. While the Taguchi method allows us to rapidly optimize the manufacturing parameters, SE analysis enables us to precisely evaluate the thickness of each layer of the electrodes, so that the whole optimization process is more precise and effective. When the silver layers of different samples are sputtered under the same conditions, the difference in their thickness is often [Formula: see text] nm. Thus, it is difficult to understand the influences of the manufacturing parameters on the optoelectronic performance of the electrodes. Experimental results show that the thickness of the silver layer was the main factor affecting the transmittance and sheet resistance of the electrodes. However, the decisive factors for the Haacke index in the visible light range were the thickness of the bottom ITO film. Nonetheless, the signal-to-noise (S/N) ratios of some factors are quite close. Thus, further analyses are needed to understand this phenomenon. After optimization, the Haacke index is [Formula: see text], which is better than the 19.45 of the best sample, suggesting that this experiment has improved the optoelectronic properties of the electrode.

Adjusting indium-tin-oxide film thickness to improve electrochemical corrosion resistance of gate driver on array

Common narrow-bezel display suffers from the abnormal display in the high-temperature and high-humidity environments, resulting in an early device failure. Improving electrochemical corrosion resistance of gate driver on array (GOA) may overcome the drawback of the display. Adjusting film thickness of indium tin oxide (ITO) on GOA through-hole is proposed to in situ improve the electrochemical corrosion resistance. Nano-ITO film with four different thicknesses were deposited in a direct-current magnetron sputter system. A systematic investigation was conducted on their microstructure and photoelectric performances, and a high-temperature and high-humidity display test was employed for field test. The 80.1-nm film exhibited superior surface smoothness and photoelectric performance, and the assembled GOA unit presented the best electrochemical corrosion resistance. We demonstrated that adjusting ITO film thickness may prevent the intrusion from water vapor and reduce the generation of resistance heat.

Solution-Gated Ultrathin Channel Indium Tin Oxide-Based Field-Effect Transistor Fabricated by a One-Step Procedure that Enables High-Performance Ion Sensing and Biosensing.

In this paper, we propose a one-step procedure for fabricating a solution-gated ultrathin channel indium tin oxide (ITO)-based field-effect transistor (FET) biosensor, thus providing an ″all-by-ITO″ technology. A thin-film sheet was placed on both ends of a metal shadow mask, which were contacted with a glass substrate. That is, the bottom of the metal shadow mask corresponding to the channel was slightly raised from the substrate, resulting in the creeping of some particles into the gap during sputtering. Owing to this modified metal shadow mask, a thin ITO channel (<30-40 nm) and thick ITO source/drain electrodes (ca. 100 nm) were simultaneously fabricated during the one-step sputtering. The thickness of ITO films was critical for them to be semiconductive, depending on the maximum depletion width (∼30-40 nm for the ITO channel), similarly to 2D materials. The ultrathin ITO channel worked as an ion-sensitive membrane as well owing to the intrinsic oxidated surface directly contacting with an electrolyte solution. The solution-gated 20-nm-thick channel ITO-based FET, with a steep subthreshold slope (SS) of 55 mV/dec (pH 7.41) attributable to the electric double-layer capacitance at the electrolyte solution/channel interface and the absence of interfacial traps among electrodes formed in one step, demonstrated an ideal pH responsivity (∼56 mV/pH), resulting in the real-time monitoring of cellular respiration and the long-term stability of electrical properties for 1 month. Moreover, the chemical modification of the ITO channel surface is expected to contribute to biomolecular recognition with ultrahigh sensitivity owing to the remarkably steep SS, which provided the exponential pH sensitivity in the subthreshold regime. Our new device produced in this one-step manner has a great future potential in bioelectronics.

Fabrication of highly efficient blue top-emission organic light-emitting diodes on different reflective electrodes

The performances of top-emission organic light-emitting diodes (TEOLEDs) with various P-dopant (PD) contents in the injection layer were studied by thinning or removing an indium tin oxide (ITO) film sputtered on the anode. On adjusting the thickness of the active TBPDA (N4,N4,N4′,N4′-tetra ([1,1′-biphenyl]-4-yl)-[1,1′-biphenyl]-4,4′-diamine) film used as hole transport layer, the International Commission on Illumination (CIE) coordinates of blue TEOLEDs did not change and the same CIE coordinates (0.14, 0.04) were maintained. The blue index of device I (PD of 3%) without an indium tin oxide (ITO) layer was 139.9 cd/A/CIEy at a current density of 10 mA/cm2. This value was 28% higher than that of the device B (PD of 2%), which had a 15-nm thick ITO film, and 19% higher than that of device E (PD of 2%), which had a 7-nm thick ITO film. Devices B, E, and I achieved similar voltages of approximately 3.9 V. Thus, in the optimized TEOLEDs with suitable PD contents, efficiency was improved by silver without the use of ITO as an anode.

Plasma-assisted deposition of indium tin oxide thin films by sublimation using an anodic vacuum arc discharge

With the anodic vacuum arc discharge as a method of physical vapor deposition (PVD) excellent properties of thin transparent conductive oxide films can be achieved, but the relations between the process parameters and the coating properties have been insufficiently described in the literature. This paper is intended to narrow this gap by investigations on indium tin oxide (ITO) thin films deposited on borosilicate glass sheets by sublimation of indium tin oxide (90:10) using an anodic vacuum arc. The arc discharge is based on a hot hollow cathode electron source and a special evaporator connected as anode. The concentration of the discharge onto the sublimating material is achieved by combining the magnetic fields of an axially symmetrical permanent magnet system and a solenoid coil. Coating rates of about 15 nm/s were achieved with an arc current of 60 A. Measurements with a planar Langmuir probe have shown that the vapor is highly ionized (about 95%). The discharge voltages are relatively low (< 60 V), so it can be assumed that the particle energies are correspondingly low. Substrate temperature (30–300 °C), oxygen gas flow (0–100 sccm) and gas pressure (0.04–0.4 Pa) were varied to study their influence on the thin film properties. Specific electrical conductivity, density and mobility of charge carriers, as well as optical properties were determined and compared with those of other PVD processes. Low specific electrical resistance of 1.8–2.0 x 10–4 Ω cm was reached at a substrate temperature of 200–300 °C independently of the pressure. The mean optical transmission (in the spectral range between 400 nm and 1100 nm) of 100 nm thick ITO films deposited at a temperature of 200 °C and at an optimized oxygen flow was determined to 84%. The roughness of the layers determined by atomic force microscopy is significantly lower than typically for magnetron sputtered films. At a pressure of 0.04 Pa, the crystalline bixbyite phase can already be detected at a coating temperature of approx. 30 °C, whereby the layer growth begins with the formation of an amorphous structure and changes to the crystalline phase with increasing layer thickness. At a temperature above 100 °C and low coating pressure the layers are completely crystalline. At a higher pressure the transition from amorphous to crystalline phase is shifted towards higher temperature. For lower oxygen flows the crystallites exhibit mainly a preferred (211) orientation. For higher oxygen flows the texture of crystallites is changed and the intensity of (440) and (622) is increased. The formation of these special crystallographic textures can probably explain the very low roughness values of the ITO layers measured by atomic force microscopy. The investigations have shown how the film properties can be adjusted by the process parameters and that the ITO sublimation using an anodic vacuum arc is suited very well for plasma assisted ITO thin film deposition.

Surface Passivation of ITO on Heterojunction Solar Cells with Enhanced Cell Performance and Module Reliability

The indium tin oxide (ITO) thin film plays an important role in the silicon heterojunction (SHJ) solar cells, which acts as not only a carrier transport layer in vertical and lateral directions but an anti-reflection layer as well. Thickness reduction of the expensive ITO is an efficient strategy to reduce the cost of SHJ solar cells. In this work, the simulated antireflection effects of several dielectric capping layers demonstrate that Al2O3 and SiO2 are the suitable candidates for both of the SHJ solar cell and module. Hall effect measurements show that the SiO2 layer is able to passivate the ITO surface and improve the mobility and conductivity of the ITO film, which is beneficial to further reduce the thickness of ITO films. It is also found that the SiO2 capping layer can significantly enhance the adhesion strength between the solar cell and the encapsulating polymer film by 26% in the SHJ module. The improved adhesion strength is attributed to the higher surface energy of SiO2 than ITO, according to the liquid-solid contact angle measurements. These results show that the SiO2 capping layer can not only reduce the consumption of ITO thin films, but also increase the reliability of SHJ module.

Optoelectronic Properties of Ultrathin Indium Tin Oxide Films: A First-Principle Study

First-principle density functional theory simulations have been performed to predict the electronic structures and optoelectronic properties of ultrathin indium tin oxide (ITO) films, having different thicknesses and temperatures. Our results and analysis led us to predict that the physical properties of ultrathin films of ITO have a direct relation with film thickness rather than temperature. Moreover, we found that a thin film of ITO (1 nm thickness) has a larger absorption coefficient, lower reflectivity, and higher transmittance in the visible light region compared with that of 2 and 3 nm thick ITO films. We suggest that this might be due to the stronger surface strain effect in 1 nm thick ITO film. On the other hand, all three thin films produce similar optical spectra. Finally, excellent agreement was found between the calculated electrical resistivities of the ultrathin film of ITO and that of its experimental data. It is concluded that the electrical resistivities reduce along with the increase in film thickness of ITO because of the short strain length and limited bandgap distributions.

Promising near-infrared plasmonic biosensor employed for specific detection of SARS-CoV-2 and its spike glycoprotein

Timely and accurately identification of the novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can greatly contribute to monitoring and controlling the global pandemic. This study gained theoretical insight into a novel phase-modulation plasmonic biosensor working in the near-infrared (NIR) regime, which can be employed for sensitive detection of SARS-CoV-2 and its spike (S) glycoprotein. The proposed plasmonic biosensor was created by integrating two-dimensional (2D) Van der Waals heterostructures, including tellurene and carboxyl-functionalized molybdenum disulfide (MoS2) layers, with transparent indium tin oxide (ITO) film. Excellent biosensing performance can be achieved under the excitation of 1550 nm by optimizing the thickness of ITO film and tellurene-MoS2 heterostructures. For a sensing interface refractive index change as low as 0.0012 RIU (RIU, refractive index unit), the optimized plasmonic configuration of 121 nm ITO film/three-layer tellurene/ten-layer MoS2-COOH can produce the highest detection sensitivity of 8.4069 × 104 degree/RIU. More importantly, MoS2–COOH layer can capture angiotensin-converting enzyme II, which is an ideal adsorption site for specifically binding SARS-CoV-2 S glycoprotein. Then, an excellent linear detection range for S glycoprotein and SARS-CoV-2 specimens is ∼0–301.67 nM and ∼0–67.8762 nM, respectively. This study thus offers an alternative strategy for rapidly performing novel coronavirus diagnosis in clinical applications.

Ultra-narrowband light absorption enhancement of monolayer graphene from waveguide mode.

Greatly improving the light absorption efficiency of graphene and simultaneously manipulating the corresponding absorption bandwidth (broadband or narrowband) is practically important to design graphene-based optoelectronic devices. In this work, we will theoretically show how to largely enhance the absorption in graphene and efficiently control the absorption bandwidth in the visible region, by the excitation of the waveguide mode for the graphene monolayer to be sandwiched between the gold sphere array and dielectric waveguide structure composed of indium tin oxide (ITO) film on a quartz substrate. It is found that the maximum absorption efficiency can reach as high as about 45% and the full-width at half-maximum (FWHM) of the absorption peak can be tuned from about 1 to 10 nanometers, when the array period of gold spheres or the thickness of ITO film is changed.

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 &amp; 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

Study of indium tin oxide films deposited on colorless polyimide film by magnetron sputtering

Polyimide attracted most interest for its high performance as a flexible substrate of touch panels. Experimental models were built to evaluate production feasibility. The solution with monomer was coated on a glass substrate, cured at 250 °C to form a solid colorless polyimide (CPI) film. Then, a supporting layer with silicon oxide and a conducting layer with indium tin oxide (ITO) were deposited on the CPI film by magnetron sputtering. Composite with a CPI substrate and ITO patterns were prepared via a series of procedures. Test results indicated ITO film thickness and sheet resistance could be controlled by adjusting sputtering power, and the film showed smooth curves on the contour line chart. The transmittance of CPI/ITO film composite was up to 80%. The bending durability of the film was evaluated by two-point bending method, and it could be significantly improved by shielding the ITO pattern with ultraviolet cured resin as an external buffer layer. Samples with buffer layers passed 64,000 cycles bend test, and the minimum fracture radius reached 4 mm. The increase of ITO film thickness had no significant negative impact on the performance of flexible devices.

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.