Effect of sputtering power and annealing temperature on the properties of indium tin oxide thin films prepared from radio frequency sputtering using powder target

Indium tin oxide (ITO) thin films were deposited on quartz substrates by radio frequency (RF) sputtering with different RF power (100–250 W) using the powder target at room temperature. The effect of sputtering power on their structural, electrical and optical properties was systematically investigated. The intensity of (400) orientation clearly increases with the sputtering power increases, although the films have (222) preferred orientation. Increasing sputtering power is benefit for lower resistivity and transmittance. The films were annealed at different temperature (500–800 °C), then we explored the relationship between their electro-optical and structural properties and temperature. It has been observed that the annealed films tend to have (400) orientation and then show the lower resistivity and transmittance. The ITO thin film prepared by RF sputtering using powder target at 700 °C annealing temperature and 200 W sputtering power has the resistivity of 2.08 × 10^?4 Ω cm and the transmittance of 83.2 %, which specializes for the transparent conductive layers.     

Correlation between microstructure and electrical,optical properties of thermal annealed ITO thin films

Indium tin oxide (ITO) thin films with the thickness of 300 nm were deposited on quartz substrates via electron beam evaporation. Five samples were post-annealed in air atmosphere for 10 min at five selected temperature points from 200 to 600 °C, respectively. X-ray diffractometer, Hall measurement system and UV–Vis spectrophotometer were adopted to characterize the ITO thin films. Influence of thermal annealing in air atmosphere on microstructure was investigated. Furthermore, the correlation between microstructure and electrical, optical properties of ITO thin films was discussed in detail. All of the ITO thin films had a polycrystalline structure and a preferred orientation of (222), no matter annealed or not. The intensity ratio of I₍₂₂₂₎/I₍₄₄₀₎ initially increased and then decreased, it reached the maximum of 7.37 after annealed at 400 °C for 10 min. The lattice expansion evidently reduced after annealed at 300 °C or even higher temperature. The variation of mean grain size was minor during thermal annealing process regardless of annealing temperature. The carrier concentration is predominant in electrical conductivity, and it is dependent on the activation of donors and the density of oxygen vacancies. Hall mobility is strongly dependent on the mean grain size, lattice distortion and defect density. The optical transmittance is influenced by the density of oxygen vacancies and the consistency of grain orientations.     

Effect of annealing time on the structural,optical and electrical characteristics of DC sputtered ITO thin films

Using an Indium tin oxide (ITO) ceramic target (In₂O₃:SnO₂, 90:10 wt%), ITO thin films were deposited by conventional direct current magnetron sputtering technique onto glass substrates at room temperature. The obtained ITO films were annealed at 400 °C for different annealing times (1, 2, 5, 7, and 9 h). The effect of annealing time on their structural, optical and electrical properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM), ultra violet–visible (UV–Vis) spectrometer, and temperature dependence Hall measurements. XRD data of obtained ITO films reveal that the films were polycrystalline with cubic structure and exhibit (222), (400) and (440) crystallographic planes of In₂O₃. AFM and Scanning Electron Microscopy SEM have been used to probe the surface roughness and the morphology of the films. The refractive index (n), thickness and porosity (%) of the films were evaluated from transmittance spectra obtained in the range 350–700 nm by UV–Vis. The optical band gap of ITO film was found to be varying from 3.35 to 3.47 eV with the annealing time. The annealing time dependence of resistivity, carrier concentration, carrier mobility, sheet resistance, and figure of merit values of the films at room temperature were discussed. The carrier concentration of the films increased from 1.21 × 10²⁰ to 1.90 × 10²⁰ cm^?3, the Hall mobility increased from 11.38 to 18 cm² V^?1 s^?1 and electrical resistivity decreased from 3.97 × 10^?3 to 2.13 × 10^?3 Ω cm with the increase of annealing time from 1 to 9 h. Additionally, the temperature dependence of the carrier concentration, and carrier mobility for the as-deposited and 400 °C annealed ITO films for 2 and 9 h were analysed in the temperature range of 80–350 K.     

Structural characterization and frequency response of sol–gel derived Bi3/2MgNb3/2O7 thin films

The Bi_3/2MgNb_3/2O₇ (BMN) thin films were prepared via a modified sol–gel process on glass substrates at various post-annealing temperatures. The crystalline structure, morphology and frequency response have been investigated systematically. The X-ray diffraction results indicated that the BMN thin films had different orientations depending on post-annealing temperature. Thin films annealed above 650 °C presented well crystallized cubic pyrochlore structure with (222) orientation, and (400) preferentially oriented were observed when they were annealed below 600 °C. The surface morphology images of the BMN thin films revealed different grain size and grain size distribution, and the average grain size increased from 28.3 to 37.0 nm as the post-annealing temperature increasing. The low frequency dielectric properties of the BMN thin films were closely correlated with the (222) orientation, which was favorable to enhanced dielectric constant and tunability. The high-frequency optical measurements revealed an average transmittance (T _av ) varying between 76.6 and 82.2 % and band gap energy (E _g ) ranging from 3.40 to 3.44 as a function of the temperature and the crystallite size. Thin film annealed at 700 °C possessed the best crystallinity and highest (222) orientation, and showed the best electrical properties, with a dielectric constant of 105 at 1 MHz, dielectric tunability of 25.8 %, and an average optical transmittance of 82.2 % in the visible range (400–800 nm), making it promising for optical/electronic tunable devices applications.     

High performance humidity sensing properties of indium tin oxide (ITO) thin films by sol–gel spin coating method

The tin doped indium oxide (ITO) thin films prepared by sol–gel spin coating method with In(NO₃)3H₂O and SnCl₄·5H₂O as indium and tin sources respectively is presented. The as deposited samples were annealed at 500 °C for 2 h in order to improve the crystallinity. The structural, morphological and optical properties of the films were analysed by using X-ray diffraction, scanning electron microscope (SEM), UV–Vis transmission spectra and photoluminescence, spectra analysis. The SEM images ensure the uniform and smooth surface of the as prepared and annealed film. The optical transmittance of more than 85 % has been observed in the UV–Vis region with a band gap of 3.91 and 3.73 eV for the as prepared and annealed films of ITO respectively. The PL spectra reveal that the optical properties were significantly improved due to the annealing effect. The annealed film shows high sensitivity for humidity approximately two order changes in the resistance and the sensitivity increases for different relative humidity from 10 to 90 % due to the physisorption between the water molecules and the surface of the thin films.     

Effect of annealing temperature on structural,optical and humidity sensing properties of indium tin oxide (ITO) thin films

Tin doped indium oxide (ITO) thin films were prepared by sol–gel spin coating method with In (NO₃)·3H₂O and SnCl₄·5H₂O as indium and tin sources, respectively. The as deposited samples were annealed at various temperature such as, 300, 400, 500 and 600?°C for 2 h in ambient atmosphere. The grown ITO thin films are polycrystalline in nature with cubic structure of In₂O₃ with the space group La3 and the results are in good agreement with the standard JCPDS data (card no#06-0416). In addition crystalline size increases with increasing annealing temperature from 25 to 55 nm. Polycrystalline with uniform smooth surface was observed by SEM micrographs. The optical band gap energy was found to be decreased from 3.85 to 3.23 eV as the annealing temperature is increased from 300 to 600?°C. The humidity sensing performance (high sensitivity and fast response time) was significantly improved for 600?°C thin films samples, which is probably due to smaller energy band gap and physisorption between the water molecules and the surface of the thin films. The films were further characterized by PL and EDS analysis. The effect of temperature on humidity sensing mechanism of ITO thin films is also discussed.     

Effects of annealing temperature on the structural,morphology, optical properties and resistivity of sputtered CCTO thin film

CaCu₃Ti₄O₁₂ (CCTO) thin films with a thickness of 200 nm were deposited on ITO substrates by RF magnetron sputtering using a pure CCTO target. After the deposition, thin films were annealed at 400, 450, 500 and 550?°C, respectively, for 1 h. The effects of annealing temperature on the structural, surface morphology, optical properties and resistivity of (CCTO) thin films were investigated. The X-ray diffractometer results show that the thin films are polycrystalline in nature and are assigned to body-centered cubic perovskite configuration with a space group of Im-3. The intensity of the peaks and crystallinity gradually increased with the increase in annealing temperature. Microstructural investigation through FESEM showed that the grain size increased with increase in annealing temperature from 32 to 85 nm. The root mean square and roughness (Ra) were also enhanced with higher annealing temperatures, from 3.8 to 6.2 nm and from 4.7 to 7.7 nm, respectively, as confirmed by AFM. Increase in annealing temperature also affected the optical transmittance values which decreased to almost 60% at the visible range (550–850), as well as the optical energy band gap which decreased from 3.86 to 3.39 eV. The relevance between resistance behaviors and film microstructure is discussed. Therefore, it can be concluded that the desirable crystallinity, surface roughness, energy band gap and resistivity for 200 nm thick CCTO thin films deposited by RF magnetron sputtering can be achieved through the annealing process.     

The effect of post-annealing under CdCl<Subscript>2</Subscript> atmosphere on the properties of ITO thin films deposited by DC magnetron sputtering

Indium tin oxide (ITO) films deposited by DC magnetron sputtering were annealed under CdCl₂ atmosphere at different temperatures. The effects of CdCl₂ heat-treatment on the structural, electrical and optical properties of the films were investigated. The X-ray diffraction measurement proves the annealing results in a change of preferred orientation from (400) to (222). It is found the resistivity increases from 1.49 × 10⁻⁴ Ω cm of the as-deposited film to 6.82 × 10⁻⁴ Ω cm of the film annealed at 420 °C. The optical energy gap for the film varies from 3.97 to 3.89 eV. It is also found that the CdCl₂ heat-treatment results in narrowing the energy gap of ITO film.     

Formation and properties of cadmium sulfide buffer layer for CIGS solar cells grown using hot plate bath deposition

In the present study, cadmium sulfide (CdS) thin films were deposited on different substrates [soda glass, fluoride doped tin oxide, and tin doped indium oxide (ITO) coated glass] by a hot plate method. To control the thickness and the reproducibility of the sample production, the thin films were coated at different temperatures and deposition times. The CdS thin films were heated at 400 °C in air and forming gas (FG) atmosphere to investigate the effect of the annealing temperatures. The thickness of the samples, measured by ellipsometry, could be controlled by the deposition time and temperature of the hot plate. The phase formation and structural properties of CdS thin films were studied by X-ray diffraction and scanning electron microscopy, whereas the optical properties were obtained by UV–vis spectroscopy. A hexagonal crystal structure was observed for CdS thin films and the crystallinity improved upon annealing. The structural and optical properties of CdS thin films were also enhanced by annealing at 400 °C in FG atmosphere (95 % N₂, 5 % H₂). The optical band gap was changed from 2.25 to 2.40 eV at different annealing temperatures and gas atmospheres. A higher electrical conductivity, for the sample annealed at FG, was noticed. The samples deposited on ITO and annealed in FG atmosphere showed the best structural and electrical properties compared to the other samples. CdS thin films can be widely used for application as a buffer layer for copper–indium–gallium–selenide solar cells.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.     

Enhanced photocatalytic activity of Mg0.05Zn0.95O thin films prepared by sol–gel method through a cycle

Mg_0.05Zn_0.95O thin films were prepared on silicon substrates by a sol–gel dip-coating technique. Microstructure, surface topography and optical properties of the thin films were characterized by X-ray diffraction, atom force microscopy, Fourier transform infrared spectrophotometer and fluorescence spectrometer. The results show that the thin film annealed at 700 °C has the largest average grain size and exhibits the best c-axis preferred orientation. As annealing temperature increases to 800 °C, the grain along c-axis has been suppressed. Roughness factor and average particle size increase with the increase of annealing temperature. The IR absorption peak appearing at about 416 cm^?1 is assigned to hexagonal wurtzite ZnO. The thin film annealed at 700 °C has the maximum oxygen vacancy, which can be inferred from the green emission intensity. Photocatalytic results show that the thin film annealed at 700 °C exhibits remarkable photocatalytic activity, which may be attributed to the larger grain size, roughness factor and concentration of oxygen vacancy. Enhanced photocatalytic activity of Mg_0.05Zn_0.95O thin films after a cycle may be attributed to the increase of surface oxygen vacancy and photocorrosion of amorphous MgO on the surface of thin film under UV irradiation.     

Inkjet-printing of indium tin oxide (ITO) films for transparent conducting electrodes

Indium-tin-oxide (ITO) films have been prepared by inkjet-printing using ITO nanoparticle inks. The electrical and optical properties of the ITO films were investigated in order to understand the effects of annealing temperatures under microwave. The decrease in the sheet resistance and resistivity of the inkjet-printed ITO films was observed as the annealing temperature increases. The film annealed at 400 °C showed the sheet resistance of 517 Ω/sq with the film thickness of ∼580 nm. The optical transmittance of the films remained constant regardless of their annealing temperatures. In order to further reduce the sheet resistance of the films, Ag-grid was printed in between two layers of inkjet-printed ITO. With 3 mm Ag-grid line-to-line pitch, the Ag-grid inserted ITO film has the sheet resistance of 3.4 Ω/sq and the transmittance of 84% after annealing at 200 °C under microwave.     

Effect of substrate temperature on properties of Cu(In,Ga, Al)Se<Subscript>2</Subscript> films grown by magnetron sputtering

Cu(In, Ga, Al)Se₂ (CIGAS) thin films were deposited by magnetron sputtering on Si(100) and soda-lime glass substrates at different substrate temperatures, followed by post-deposition annealing at 350 or 520 °C for 5 h in vacuum. Electron probe micro-analysis and secondary ion mass spectroscopy were used to determine the composition of the films and the distribution of Al across the film thickness, respectively. X-ray diffraction analysis showed that the (112) peak of CIGAS films shifts to higher 2θ values with increasing substrate temperature but remains unchanged when the films were annealed at 520 °C for 5 h. Scanning electron microscopy and atomic force microscopy images revealed dense and well-defined grains for both as-deposited and annealed films. However, notable increase in grain size and roughness was observed for films deposited at 500 °C. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as the substrate temperature was increased.     

Effects of heat treatment on properties of ITO films prepared by rf magnetron sputtering

Indium tin oxide (ITO) films were deposited on glass substrates by rf magnetron sputtering using a ceramic target (In₂O₃-SnO₂, 90-10 wt%) without extra heating. The post annealing was done in air and in vacuum, respectively. The effects of annealing on the structure, surface morphology, optical and electrical properties of the ITO films were studied. The results show that the increase of the annealing temperature improves the crystallinity of the films, increases the surface roughness, and improves the optical and electrical properties. The transmittance of the films in visible region is increased over 90% after the annealing process in air or in vacuum. The resistivity of the films deposited is about 8.125×10⁻⁴ Ω cm and falls down to 2.34×10⁻⁴ Ω cm as the annealing temperature is increased to 500°C in vacuum. Compared with the results of the ITO films annealed in air, the properties of the films annealed in vacuum is better.     

Thermal stability of indium tin oxide thin films co-sputtered with zinc oxide

The thermal stability of indium tin oxide (ITO) films and ITO co-sputtered with zinc oxide (ZnO) films at different zinc atomic ratios in various atmospheres are investigated. The resistivity of the annealed ITO films decreased with increased annealing temperatures. The improved electrical properties were attributed mainly to the increase in carrier concentration originating from the significant formation of oxygen vacancies in the ITO films. In contrast, due to the lower oxidation potential of zinc ions, the resistivity of the annealed co-sputtered films showed no significant reduction and an increase with annealing temperatures. The film decomposition due to the high degree outdiffusion of oxygen atoms and aggregation of In atoms observed from the metal-like In phase in the diffraction patterns was responsible for the drastic thermal degradation in the electrical and optical properties of the samples annealed at elevated temperatures in reducing gas atmosphere. In contrast, the superior thermal stability of the co-sputtered films, at an atomic ratio of 60% annealed in reducing gas atmospheres, was ascribed to the stable Zn₃In₂O₆ crystalline structure that appeared in the diffraction pattern. The absorption edge observed from the optical transmittance of these annealed films also showed evidence of carrier concentration evolution in various annealing atmospheres. The lower oxidation potential of the zinc atoms introduced into the ITO films was concluded to be efficient in compensating for the formation of oxygen vacancies resulting in the alleviated decomposition behavior during thermal annealing.     

Optical characterization of ZnO thin films deposited by Sol-gel method

In this paper, ZnO thin film is deposited on Pt/TiO₂/SiO₂/Si substrate using the sol-gel method and the effect of annealing temperature on the structural morphology and optical properties of ZnO thin films is investigated. The ZnO thin films are crystallized by the heat treatment at over 400°C. The ZnO thin film annealed at 600°C exhibits the greatest c-axis orientation and the Full-Width-Half-Maximum (FWHM) of X-ray peak is 0.4360°. A dense ZnO thin film is deposited by the growth of uniform grains with the increase of annealing temperature but when the annealing temperature increases to 700°C, the surface morphology of ZnO thin film becomes worse by the aggregation of ZnO particles. In the results of surface morphology of ZnO thin film using atomic force microscope (AFM), the surface roughness of ZnO thin film annealed at 600°C is smallest, that is, approximately 1.048 nm. For the PL characteristics of ZnO thin film, it is observed that ZnO thin film annealed at 600°C exhibits the greatest UV (ultraviolet) exciton emission at approximately 378 nm, and the smallest visible emission at approximately 510 nm among ZnO thin films annealed at various temperatures. It is deduced that ZnO thin film annealed at 600°C is formed most stoichiometrically, since the visible emission at approximately 510 nm comes from either oxygen vacancies or impurities.     

Influence of thermal annealing on optical properties and structure of aluminium oxide thin films by filtered cathodic vacuum arc

Optical and structural properties of aluminium oxide thin films are investigated in the annealing temperature range of 200–900 °C. The changes in optical properties and film structure show the great dependence on the temperature. For the film annealed at low temperatures (from 200 °C to 600 °C), the film optical properties, such as transmittance and optical constants, could be improved by thermal annealing with amorphous structure and smooth surface. However, for the film annealed at higher temperature (e.g. 900 °C), the poor performance of optical properties indicates undesirable application for precise use in optics due to significant changes in both structure and surface roughness. At optimum annealing temperature of 600 °C, the transmittance could reach as high as that of substrate and the film possesses better optical constants (refractive index was 1.73 and extinction coefficient was ∼10⁻⁴ at 550 nm) with remaining amorphous structure and smooth surface.     

Enhanced visible light response of ZnO porous thin film by post-annealing treatment

ZnO thin films were synthesized by a facile electrodeposition method in the aqueous solution. Porous ZnO thin films with wurtzite structure could be achieved by mean of annealing treatment. The growth mechanism of the porous ZnO thin film was discussed. The intensity of the E ₂ mode in the ZnO thin film, which represents crystalline quality of the thin film increases with the increasing of annealing temperature. Optical properties indicate that annealing temperature has strong effect on the optical band gap value and defect concentrations. Both the green and yellow emissions corresponding to respective oxygen vacancies and oxygen interstitials can be identified. The results show that ZnO annealed at 400 °C exhibits a significant photocurrent density enhancement which is about 18 times larger than that of the as-deposited ZnO thin films. The mechanism of the enhanced photoresponse for the ZnO thin film has been discussed in detail.     

Characterization of nanocrystalline indium tin oxide thin films prepared by ion beam sputter deposition method

Indium tin oxide (ITO) thin films were deposited on glass substrates by ion beam sputter deposition method in three different deposition conditions [(i) oxygen (O₂) flow rate varied from 0.05 to 0.20 sccm at a fixed argon (1.65 sccm) flow rate, (ii) Ar flow rate changed from 1.00 to 1.65 sccm at a fixed O₂ (0.05 sccm) flow rate, and (iii) the variable parameter was the deposition time at fixed Ar (1.65 sccm) and O₂ (0.05 sccm) flow rates]. (i) The X-ray diffraction (XRD) patterns show that the ITO films have a preferred orientation along (400) plane; the orientation of ITO film changes from (400) to (222) direction as the O₂ flow rate is increased from 0.05 to 0.20 sccm. The optical transmittance in the visible region increases with increasing O₂ flow rate. The sheet resistance (R_s) of ITO films also increases with increasing O₂ flow rate; it is attributed to the decrease of oxygen vacancies in the ITO film. (ii) The XRD patterns show that the ITO film has a strong preferred orientation along (222) direction. The optical transmittance in the visible spectral region increases with an increase in Ar flow rate. The R_s of ITO films increases with increasing Ar flow rate; it is attributed to the decrease of grain size in the films. (iii) A change in the preferred orientations of ITO films from (400) to (222) was observed with increasing film thickness from 314 to 661 nm. The optical transmittance in the visible spectral region increases after annealing at 200 °C. The R_s of ITO film decreases with the increase of film thickness.     

Structural,electrical, optical properties and reliability of ultra-thin tin doped indium oxide films for touch panels

Ultra-thin ITO films with thickness of 4–56 nm were deposited on glass by dc magnetron sputtering using 5 wt% SnO₂ doped ITO target. The effect of film thickness on the structural, electrical, optical properties and reliability was investigated for its application to touch panels. The 4 nm thick ITO film shows amorphous structure and other films present polycrystalline structure and the (222) preferred orientation. The ultra-thin ITO films show smooth surface with low Ra surface roughness smaller than 1 nm. The sheet resistance and visible transmittance of the ITO films decrease with the increase in film thickness. The 4 nm thick ITO film shows the highest resistivity (3.08 × 10^?3 Ω cm) with low carrier density and Hall mobility, and other films have excellent conductivity (<4.0 × 10^?4 Ω cm). The ITO films show high transmittance (>85 %) in visible light range and do not generate interference ripples between film and substrate interface. The ITO films with thickness of 18–56 nm show stable reliability under high temperature, high temperature & high humidity and alkaline environmental conditions. The only electrical degradation corresponds to the increase of sheet resistance in the ITO films with thickness of 4–12 nm.