Enhanced electrical properties of In-Ga-Sn-O thin films at low-temperature annealing

Electrical and optical properties of In-Ga-Sn-O (IGTO) thin films deposited by radio-frequency magnetron sputtering were investigated according to annealing temperatures. While IGTO films remained an amorphous phase even after a heat treatment at temperature up to 500 °C, Hall measurements showed that annealing temperature had a significant impact on electrical properties of IGTO thin films. After investigating a wide range of annealing temperatures for samples from as-deposited state to 500 °C, IGTO film annealed at 200 °C exhibited the best electrical performance with a conductivity of 229.31 Ω^?1cm^?1, a Hall mobility of 36.89 cm²V^?1s^?1, and a carrier concentration of 3.85 × 10¹⁹ cm^?3. Changes in proportions of oxygen-related defects and percentages of Sn²⁺ and Sn⁴⁺ ions within IGTO films according to annealing temperatures were analyzed with X-ray photoelectron spectroscopy to determine the cause of the superb performance of IGTO at a low temperature. In IGTO films annealed at 200 °C, Sn⁴⁺ ions acting as donor defects accounted for a high percentage, whereas hydroxyl groups working as electron traps showed a significantly reduced percentage compared to the as-deposited film. Optical band gaps of IGTO films obtained from UV–visible spectrum were 3.38–3.47 eV. The largest band gap value of 3.47 eV for the IGTO film annealed at 200 °C could be attributed to an increase in Fermi-level due to an increase of carrier concentration in the conduction band. These spectroscopic results well matched with electrical properties of IGTO films according to annealing temperatures. Excellent electrical properties of IGTO thin films annealed at 200 °C could be largely due to Sn donors besides oxygen vacancies, resulting in a significant increase in free carriers despite a low annealing. temperature.     

Structural and optoelectronic properties of transparent conductive c-axis-oriented ZnO based multilayer thin films with Ru interlayer

ZnO and Ru multilayer thin films are deposited using the sputtering deposition technique at room temperature. The effects of the Ru interlayer thickness and annealing temperature on the properties of multilayer thin films have been studied. An X-ray diffraction study reveals that ZnO layers are highly c-axis-oriented. The use of an Ru interlayer improves the crystalline quality of the subsequently deposited ZnO layers. Moreover, the crystalline quality of the entire structure is further enhanced through thermal annealing in a vacuum. Atomic force microscopy images show that the surface roughness of the multilayer thin films increases with a Ru interlayer thickness greater than 6 nm. The roughness of the film surface increases in correlation with annealing temperatures. This accounts for the decreased optical transmittance of the multilayer thin films annealed at temperatures higher than 450 °C. The electrical resistivity of multilayer thin films decreases with an increase in the metallic interlayer thickness. Thermal annealing at 450 °C causes low resistivity in multilayer thin films. The lowest resistivity reached ～5.4 × 10^?4 Ω cm for multilayer films with a 10-nm-thick Ru interlayer annealed at 450 °C.     

Low-temperature conducting performance of transparent indium tin oxide/antimony tin oxide electrodes

We fabricated transparent indium tin oxide (ITO)/antimony tin oxide (ATO) electrodes using a combined process of spin-coating of hybrid ITO nanoinks, electrospraying of ATO, and hydrogen (H₂) activation carried out at a low annealing temperature of 200 °C. The produced ITO electrode exhibited an enhanced surface densification and phase conversion of In(OH)₃ to ITO. As a result, the H₂-activated ITO/ATO electrodes exhibited excellent transparent conducting performances with a superior sheet resistance of ~47.5 Ω/□ and a good transmittance of ~85.3% as compared to the ITO and ITO/ATO electrodes. Despite the use of the low annealing temperature, the achieved improvement in the conducting performance could be attributed to the synergistic effect of the enhanced carrier concentration and the Hall mobility related to the improved surface densification achieved with the electrosprayed ATO thin film and reduction of the residual In(OH)₃ phase by H₂ activation. Therefore, our method can be used as a novel strategy for obtaining high-performance solution-processed transparent conducting oxides at a low annealing temperature of 200 °C for use in various optoelectronic applications.     

Study of Cu-based Al-doped ZnO multilayer thin films with different annealing conditions

AZO/Cu/AZO multilayer thin films produced under different annealing conditions are studied in this paper, to examine the effects of atmosphere and annealing temperature on their optical and electrical properties. The multilayer thin films are prepared by simultaneous RF magnetron sputtering (for AZO) and DC magnetron sputtering (for Cu). The thin films were annealed in a vacuum or an atmosphere of oxygen at temperatures ranging from 100 to 400 °C in steps of 100 °C for 3 min. High-quality multilayer films (at Cu layer thickness of 15 nm) with resistivity of 1.99×10⁻⁵ Ω-cm and maximum optical transmittance of 76.23% were obtained at 400 °C annealing temperature in a vacuum. These results show the films to be good candidates for use as high quality electrodes in various displays applications.     

A leaf-like structured ITO conductive transparent thin film from visible to near-infrared region with enhanced stability

ITO thin films as the optical and electrical windows to transform photons and charges have been applied in many areas. Here, a leaf-like structured particle is composed of small particles growing along three different orientations leading to low thermal stress accompanied by well transmittance (85%) in a wide wavelength range from visible to near-infrared region and a narrowed band gap 3.07 eV. The evolution of structure and electronic performance was studied to obtain the low resistivity (12 μΩ m) and enhanced stability of the film (1000 °C). The leaf-like structure can be maintained under 600 ℃ and the electrical properties can be modified in He and N₂ atmosphere, owing to the reduced defects, increased concentration of Sn and carrier mobility. Although the structure has changed after being annealed at 1000 °C in N₂, the thin film performs excellent electrical properties (?3.44 × 10²⁰ cm^?3 and 28 cm² V^?1 s^?1).     

Optical and electrical properties of ITO film on flexible fluorphlogopite substrate

Indium Tin Oxide (ITO) films were prepared, at room temperature, on a fluorphlogopite substrate using magnetron sputtering technology. At various temperatures of 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, the samples were (had) annealed for 2 h (a 2-h duration). The results showed improvement in the crystalline performance of ITO film at selected annealing temperatures, with a significant reduction in resistivity at 800 °C. The lowest resistivity is 4.08 × 10^?4 Ω-cm, which is nearly an order of magnitude lower than the unannealed sample. All samples have an average light transmittance above 85% in the visible light range (400–800 nm), and with increasing annealing temperature, the average light transmittance tends to decrease. Besides, at the sensitive wavelength of 550 nm, the light transmittance is as high as 93.74%. The sheet resistance testing of the sample was through the number of bending times, which revealed that with the increase of the number of bending, the sheet resistance increases. However, after 1200 bending times, the change rate of the sheet resistance remains below 5%. Thus, the ITO film prepared on the flexible fluorphlogopite substrate revealed excellent optical and electrical properties, good flexibility, and improved stability after high-temperature annealing, which guarantees successful application in flexible electronic devices.     

Effect of different post-annealing durations on electromagnetic properties of La0.67Ca0.33MnO3:Ag0.2 thin films prepared by pulsed laser deposition

La_0.67Ca_0.33MnO₃:Ag_0.2 thin films were obtained by pulsed laser deposition followed by post-annealing at 1200 °C for varied durations. Surface morphologies, structures, and electrical and magnetic properties of films prepared with different annealing durations were significantly different. X-ray diffraction results showed that annealed films exhibited stronger diffraction peaks and C-axis preferred growth. Regarding their electrical properties, metal-insulator transition temperature (T_MI) and temperature coefficient of resistance (TCR) increased first and then decreased with the increase in annealing duration. In terms of their magnetic properties, thin films displayed ferromagnetic-paramagnetic transition. With the increase in annealing duration, Curie temperature increased first and then decreased. Specifically, the film annealed for 3 h showed excellent electromagnetic properties, with relatively high TCR of 20.3%·K^-1 and near room temperature T_MI of 285.7 °C. Owing to these excellent properties, as-prepared thin films have application potential in infrared detectors.     

Dielectric properties and electrical behaviors of tunable Bi1.5MgNb1.5O7 thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on Au-coated Si substrates by rf magnetron sputtering. We systematically investigated the structure, dielectric properties and voltage tunable property of the films with different annealing temperatures. The relationships of leakage current and breakdown bias field with annealing temperature were firstly studied and a possible explanation was proposed. The deposited BMN thin films had a cubic pyrochlore phase when annealed at 550 °C or higher. With the increasing of annealing temperature, the dielectric constant and tunability also went up. BMN thin films annealed at 750 °C exhibited moderate dielectric constant of 106 and low dielectric loss of 0.003–0.007 between 10 kHz and 10 MHz. The maximum tunability of 50% was achieved at a bias field of 2 MV/cm. However, thin films annealed at 750 °C had lower breakdown bias field and higher leakage current density than films annealed below 750 °C. The excellent physical and electrical properties make BMN thin films promising for potential tunable capacitor applications.     

Si diffusion induced adhesion and corrosion resistance in annealed RF sputtered SiC films on graphite substrate

Silicon carbide (SiC) is one of the promising candidates for graphite protection in different applications involving high temperatures and a highly corrosive environment. An ideal Silicon carbide coating should withstand a corrosive environment without compromising its adhesion. Herein, RF magnetron sputtered silicon-rich SiC thin films were deposited on a graphite substrate followed by annealing at 1000 °C, 1200 °C, and 1400 °C in an inert atmosphere. The impact of annealing temperature on microstructure, adhesion and chemical stability of SiC thin films was demonstrated. Different analytical techniques like Scanning electron microscopy (SEM), X-Ray Diffraction (XRD), Fourier's Transform Infrared (FTIR) spectroscopy and nano-indentation were used to study microstructural evaluation and mechanical characteristics. Moreover, the electrochemical analysis (Tafel and Electrochemical impedance spectroscopy) was performed in 3.5% NaCl solution. The microstructural analysis revealed that the amorphous SiC thin film turned into a crystalline and dense film upon annealing. Scanning electron micrographs showed that silicon-rich regions at SiC film surface started to disappear as Si diffuses into graphite matrix at elevated temperatures. Both these factors contributed to improvement in the adhesion of SiC coating with graphite substrate as annealing temperature increased. In addition, the nano-indentation hardness of 5.2 GPa was obtained for as grown sample, which decreased at 1000 °C, and then increased at 1200 °C and 1400 °C. Furthermore, the electrochemical analysis confirmed the enhancement in corrosion resistance upon annealing at a temperature of 1200 °C and 1400 °C due to Si diffusion and film compactness in these samples.     

Effects of annealing temperature on the microstructure,optical, ferroelectric and photovoltaic properties of BiFeO3 thin films prepared by sol–gel method

Bismuth ferrite thin films were prepared via sol–gel spin-coating method and the effects of annealing temperature on microstructure, optical, ferroelectric and photovoltaic properties have been investigated. The results show that the bismuth ferrite thin films annealed at 550 °C is single phase and the grain size increases with the rise of annealing temperature. The band gap of bismuth ferrite thin films annealed at 550–650 °C is between 2.306 eV and 2.453 eV. With the rise of the annealing temperature, the remnant polarization gradually decreases and the coercive electric field increases. The short circuit photocurrent density decreases with the rise of annealing temperature, and the open circuit photovoltage and the power conversion efficiency of bismuth ferrite thin films annealed at 550 °C are higher than the thin films annealed at higher temperature.     

Effects of element chemical states and grain orientation growth of ITO targets on photoelectric properties of the film

A study was carried out to compare element chemical states and grain orientation growth between two ITO targets, which were respectively sintered at 1560 °C (target A#) and 1600 °C (target B#). The lower sintering temperature can be beneficial to increase mass content ratio of In₂O₃ to SnO₂, reduce the production of Sn²⁺ ions and the component of O-In as well as increase oxygen holes, and can also promote grain orientation growth of In₂O₃ and In₄Sn₃O₁₂ phase. Three groups of ITO films were deposited at 230 °C using these targets to investigate the effects of sputtering parameters on the photoelectric properties of ITO films. Under different sputtering pressures, the sheet resistance for target A# has higher sensitivity to low O₂ flow, while target B# displays higher sensitivity to high O₂ flow. In the case of sputtering pressure of 0.5 Pa, ITO films for target A# displays the highest visible transmittance. In addition, annealing process could decrease the sheet resistance and improve the transmittance of ITO films because of its effect on the crystallinity and surface morphology of ITO films.     

Annealing-temperature-modulated optical,electrical properties,and leakage current transport mechanism of sol–gel-processed high-k HfAlOx gate dielectrics

Deposition of HfAlO_x gate dielectric films on n-type Si and quartz substrates by sol-gel technique has been performed and the optical, electrical characteristics of the as-deposited HfAlO_x thin films as a function of annealing temperature have been investigated. The optical properties of HfAlO_x thin films related to annealing temperature are investigated by ultraviolet-visible spectroscopy (UV–vis) and spectroscopy ellipsometry (SE). By measurement of UV–vis, average transmission of all the HfAlO_x samples are about 85% owing to their uniform composition. And the increase in band gap has been observed with the increase of annealing temperature. Moreover, the increase of refractive index (n) and density with the increase of annealing temperature are obtained by SE measurements. Additionally, the electrical properties based on Al/Si/HfAlO_x/Al capacitor are analyzed by means of the high frequency capacitance-voltage (C-V) and the leakage current density-voltage (J-V) characteristics. Results have shown that 400 °C-annealed sample demonstrates good electrical performance, including larger dielectric constant of 12.93 and lower leakage current density of 3.75×10⁻⁷ A/cm² at the gate voltage of 1 V. Additionally, the leakage current conduction mechanisms as functions of annealing temperatures are also discussed systematically.     

Transparent and conductive indium tin oxide/polyimide films prepared by high‐temperature radio‐frequency magnetron sputtering

A highly transparent and thermally stable polyimide (PI) substrate was prepared and used for the fabrication of indium tin oxide (ITO)/PI films via radio‐frequency magnetron sputtering at an elevated substrate temperature. The effect of the deposition conditions, that is, the oxygen flow rate, substrate temperature, sputtering power, and working pressure, on the optical and electrical properties of the ITO/PI films were investigated from the microstructural aspects. The results indicate that the optical and electrical properties of ITO were sensitive to the oxygen. Moreover, it was beneficial to the improvement of the ITO conductivity through the adoption of a high substrate temperature and sputtering power and a low working pressure in the deposition process. A two‐step deposition method was developed in which a thick bulk ITO layer was overlapped by deposition on a thin seed ITO layer with a dense surface to prepare the highly transparent and conductive ITO/PI films. The ITO/PI film after annealing at 240°C gave a transmittance of 83% and a sheet resistance of 19.7 Ω/square. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42753.     

Effect of annealing and room temperature sputtering power on optoelectronic properties of pure and Al-doped ZnO thin films

Transparent ZnO and Al-doped ZnO (AZO) thin films have been prepared by radio frequency sputtering deposition at room temperature. The optical, electrical, and structural characteristics of the obtained films have been extensively investigated as a function of sputtering and annealing parameters. Spectrophotometry, X-ray diffraction (XRD), atomic force microscopy (AFM), four-point probe and Hall-effect measurements were employed. The ZnO films generally exhibited excellent crystalline properties, while providing a UV cut-off in the absorption spectrum for optical filtration. AZO thin films exhibited an average transparency (larger than 85%) over the visible region of the spectrum, and resistivity of the order of 10^?3 Ω cm was obtained. The carrier concentration and electron mobility values proved to be dependent on the deposition parameters and annealing temperature. The obtained results showed that annealing temperatures higher than 400 °C were not necessary and potentially degraded the electronic properties of the AZO thin films.     

Temperature Stable Dielectric Behavior of Sol–Gel Derived Compositionally Graded SrTiO3/Na0.5Bi0.5TiO3/SrTiO3 Thin Films

Polycrystalline sol–gel‐derived SrTiO₃/Na_0.5Bi_0.5TiO₃/SrTiO₃ (ST/NBT/ST) thin films were designed to achieve the electrical isolation of the NBT, and to mediate the temperature dependency of the dielectric properties. Proper thermal annealing of particulate phase enabled us to achieve compositionally graded elemental profiles between individual ST and NBT layers. The dielectric and ferroelectric properties were investigated with respect to the electrical behavior of the monophasic ST and NBT thin films. The dielectric characteristics of the multilayer thin film were marked by a temperature stable behavior (temperature coefficient of dielectric constant of 780 ppm/°C) in the measured ?50°C to 200°C range, frequency‐independent response at room temperature and improved dielectric loss characteristics compared with the NBT; however, on the expense of decreased permittivity and a reduced ferroelectric stability. Nevertheless, stable dielectric properties were achieved and properties of multilayer may well be exploited in functional devices that demand insensitive operation over wide temperature and frequency ranges.     

High-temperature thin film lithium niobium oxide transducers for bolts

In the present work, we studied structure, surface morphology, and ultrasonic response of thin film Lithium Niobium Oxide (LNO) transducers deposited on Inconel bolts, stainless steel and silicon substrates by radio frequency magnetron sputtering. The deposited transducer material was a mixture of LiNbO₃/LiNb₃O₈ phases, having a well-developed columnar structure. Further, the in-situ high-temperature ultrasonic response was studied in the temperature range of 18–800 °C in ambient air during short-term annealing. It was observed that long-term annealing (at 700 °C for 160 h and 800 °C for 40 h) deteriorated the ultrasonic response, owing to the irreversible change from the initial columnar structure to the porous granular structure. Dielectric and piezoelectric properties of the thin film LNO transducers were also studied. The thin film LNO ultrasonic transducers have potential applications in bolts and screws up to 700 °C.     

Synthesis and characterisation of chemical bath deposited TiO2 thin-films

A series of titania thin films was prepared by chemical bath deposition (CBD) of TiCl₃ on indium tin oxside (ITO) glass at room temperature, followed by calcinations at 500 °C for 4 h. The effect of cyclic deposition on phase composition, microstructure and electrical resistivity of TiO₂ thin films was characterised using X-ray diffraction, scanning electron microscopy and four-point probe respectively. Results showed that TiO₂ films produced by single deposition cycle were amorphous. In contrast, those produced by 5 and 6 deposition cycles were partly amorphous and partly crystalline with the formation of rutile. Both the film thickness and electrical resistivity increased with an increase in the number of deposition cycles.     

Improved photoluminescence emission and gas sensor properties of ZnO thin films

In this article, we report a comparative study of the influence of pressure-assisted (1.72 MPa) versus ambient pressure thermal annealing on both ZnO thin films treated at 330 °C for 32 h. The effects of pressure on the structural, morphological, optical, and gas sensor properties of these thin films were investigated. The results show that partial preferential orientation of the wurtzite-structure ZnO thin films in the [002] or [101] planes is induced based on the thermal annealing conditions used (i.e., pressure assisted or ambient pressure). UV–vis absorption measurements revealed a negligible variation in the optical -band gap values for the both ZnO thin films. Consequently, it is deduced that the ZnO thin films exhibit different distortions of the tetrahedral [ZnO₄] clusters, corresponding to different concentrations of deep and shallow level defects in both samples. This difference induced a variation of the interface/bulk-surface, which might be responsible for the enhanced optical and gas sensor properties of the pressure-assisted thermally annealed film. Additionally, pressure-assisted thermal annealing of the ZnO films improved the H₂ sensitivity by a factor of two.     

The ultraviolet emission mechanism of ZnO thin film fabricated by sol–gel technology

ZnO thin films were successfully deposited on SiO₂/Si substrate by sol–gel technology. The as-grown ZnO thin films were annealed under an ambient atmosphere from 600 to 900 °C by rapid thermal annealing (RTA) process. X-ray diffraction and scanning electron microscopy analyses reveal the physical structures of ZnO thin films. From PL measurement, two ultraviolet (UV) luminescence bands were obtained at 375 and 380 nm, and the intensity became stronger when the annealing temperature was increased. The strongest UV light emission appeared at annealing temperature of 900 °C. The chemical bonding state in ZnO films was investigated by using X-ray photoelectron spectrum. The mechanism of UV emission was also discussed.     

Spectroscopic characterization of thin SiC films

The electrical, structural and optical properties of thin SiC films were investigated. A new approach based on high temperature annealing of layered carbon–silicon structures was used for the formation of the films. The SiC films were prepared by deposition of 30 nm thick carbon films on crystalline silicon (c-Si) and on porous silicon layers grown on c-Si. The layers were annealed to temperatures between 800 and 1400°C for different annealing times ranging between 15 and 180 s. The structure of the resulting SiC films was analyzed by Raman spectroscopy. The Raman spectra of as-deposited films consist of two broad bands at 1350 and 1580 cm⁻¹ characteristic of the presence of amorphous carbon. These bands were shifted to lower frequencies in the spectra of annealed layers and were assigned to the hexagonal and cubic SiC phases. The photoluminescence spectra of the studied layers show a broad band at 550 nm. The most intense photoluminescence was observed from non-annealed porous silicon layers covered with thin carbon films. A degradation of the luminescence and a simultaneous increase of the conductivity of the layers with increasing annealing temperature and/or duration of annealing was observed. This behavior strongly suggests the creation of defect states which determine the conductivity of the layers and at the same time act as non-radiative centers. The increase of defect states was explained as originating from the dehydrogenation of the silicon carbide layers by annealing.