Cu2O thin films deposited by reactive direct current magnetron sputtering

The Cu₂O thin films were prepared on quartz substrate by reactive direct current magnetron sputtering. The influences of oxygen partial pressure and gas flow rate on the structures and properties of deposited films were investigated. Varying oxygen partial pressure leads to the synthesis of Cu₂O, Cu₄O₃ and CuO with different microstructures. At a constant oxygen partial pressure of 6.6 × 10^− 2 Pa, the single Cu₂O films can be obtained when the gas flow rate is below 80 sccm. The as-deposited Cu₂O thin films have a very high absorption in the visible region resulting in the visible-light induced photocatalytic activity.     

Overview of optical properties of Al2O3 films prepared by various techniques

We study optical properties of Al₂O₃ films prepared by various techniques using spectroscopic ellipsometry. The film preparation techniques include conventional pulsed magnetron sputtering in various gas mixtures, high power impulse magnetron sputtering, annealing of as-deposited Al₂O₃ in an inert atmosphere and annealing of as-deposited Al in air. We focus on the effect of the preparation technique, deposition parameters and annealing temperature on the refractive index, n, and extinction coefficient, k, of stoichiometric Al₂O₃. At a wavelength of 550 nm we find n of 1.50-1.67 for amorphous deposited Al₂O₃, 1.65-1.67 for amorphous Al₂O₃ obtained by Al annealing, 1.46-1.69 for γ-Al₂O₃ and decreasing n for Al₂O₃ annealing temperature increasing up to 890 °C. The results facilitate correct interpretation of optical characterization of Al₂O₃, as well as selection of a preparation technique corresponding to a required Al₂O₃ structure and properties.     

Formation process of Al2O3 thin film by reactive sputtering

Al and Al₂O₃ films were deposited by RF magnetron sputtering using a mixed gas of Ar and O₂. The surface of the Al target was changed from the metallic mode to the oxide mode at a critical O₂ flow ratio of 8%. The atomic ratio of sputtered Al atoms to supplied oxygen atoms was found to be approximately 2:3 at the critical O₂ flow ratio. The oxide layer thickness formed on the Al target was estimated to be 5-7 nm at an O₂ flow ratio of 100% by ellipsometry.     

Low resistivity transparent conducting CdO thin films deposited by DC reactive magnetron sputtering at room temperature

Transparent conducting cadmium oxide (CdO) films were deposited on PET (polyethylene terephthalate) substrate by DC reactive magnetron sputtering at room temperature. All the films deposited at room temperature were polycrystalline in rock-salt structure. Dependences of the physical properties of the CdO films on the oxygen partial pressure were systematically studied. The films deposited at low oxygen flow rate were (200) oriented, while the films deposited at an oxygen flow rate greater than 20 sccm were (111) oriented. The average grain size of the CdO films decreased as the oxygen flow rate increases as determined by XRD and SEM. The Hall effect measurement showed that CdO films have high concentration, low resistivity, and high mobility. Both the mobility and the concentration of the carrier decreased with the increase of the oxygen flow rate. A minimum sheet resistance of 36.1 Ω/□, or a lowest resistivity of 5.44 × 10^− 4 Ω cm (6.21 × 10²⁰/cm³, μ = 19.2 cm²/Vs) was obtained for films deposited at an oxygen flow rate of 10 sccm.     

Electrical properties of AlNxOy thin films prepared by reactive magnetron sputtering

Direct current magnetron sputtering was used to produce AlN_xO_y thin films, using an aluminum target, argon and a mixture of N₂ + O₂ (17:3) as reactive gases. The partial pressure of the reactive gas mixture was increased, maintaining the discharge current constant. Within the two identified regimes of the target (metallic and compound), four different tendencies for the deposition rate were found and a morphological evolution from columnar towards cauliflower-type, ending up as dense and featureless-type films. The structure was found to be Al-type (face centered cubic) and the structural characterization carried out by X-ray diffraction and transmission electron microscopy suggested the formation of an aluminum-based polycrystalline phase dispersed in an amorphous aluminum oxide/nitride (or oxynitride) matrix. This type of structure, composition, morphology and grain size, were found to be strongly correlated with the electrical response of the films, which showed a gradual transition between metallic-like responses towards semiconducting and even insulating-type behaviors. A group of films with high aluminum content revealed a sharp decrease of the temperature coefficient of resistance (TCR) as the concentration ratio of non-metallic/aluminum atomic ratio increased. Another group of samples, where the non-metallic content became more important, revealed a smooth transition between positive and negative values of TCR. In order to test whether the oxynitride films have a unique behavior or simply a transition between the typical responses of aluminum and of those of the correspondent nitride and oxide, the electrical properties of the ternary oxynitride system were compared with AlN_x and AlO_y systems, prepared in similar conditions.     

Structural, optical and electrical properties of reactively sputtered Ag2Cu2O3 films

Ag₂Cu₂O₃ thin films were deposited on glass substrates by RF magnetron sputtering of an equiatomic silver-copper target (Ag_0.5Cu_0.5) in reactive Ar-O₂ mixtures. The reactive sputtering was done at varying power, oxygen flow rate and deposition temperature to study the influence of these parameters on the deposition of Ag₂Cu₂O₃ films. The film structure was determined by X-ray diffraction, while the optical properties were examined by spectrophotometry (UV-vis-NIR) and photoluminescence. Furthermore, the film thickness and resistivity were measured by tactile profilometry and 4-point probe, respectively. Additional mobility, resistivity and charge carrier density Hall effect measurements were done on a few selected samples. The best films in terms of stoichiometry and crystallography were achieved with a sputtering power of 100 W, oxygen and argon flow rates of 20 sccm (giving a deposition pressure of 1.21 Pa) and a deposition temperature of 250 °C. The optical transmittance and photoluminescence spectra of films deposited with these parameters indicate several band gaps, most prominently, a direct one of around 2.2 eV. Electrical characterization reveals charge carrier concentrations and mobilities in the range of 10²¹-10²² cm^− 3 and 0.01-0.1 cm²/Vs, respectively.     

Impact of substrate temperature on the microstructure, electrical and optical properties of sputtered nanoparticle V2O5 thin films

Applying reactive direct current (DC) magnetron sputtering method, nanoparticle vanadium pentoxide thin films were deposited onto glass slides and KBr substrates at different substrate temperatures. The films were characterized by X-ray photoelectron spectroscopy and atomic force microscope. Infrared spectra were recorded with a Fourier transform infrared spectrophotometer. It was found that, excepting the compositions, the film growth and vanadium oxygen bonds were strongly affected by the substrate temperature. Electrical measurements indicated that the square resistances of films showed an exponential decrease from 46 MΩ/□ to 33 kΩ/□ with substrate temperature increasing from 433 K to 593 K, and that the square resistance-temperature curves of films exhibited typical semiconducting behavior. Optical investigations were carried out in the near infrared and ultraviolet-visible range. Transmittance varied from about 95 to 55% in near-infrared range when the substrate temperature was elevated. In ultraviolet-visible range, optical band gaps and refractive indexes of films were deduced according to the transmission and reflection spectra.     

Structural properties of RF-magnetron sputtered Cu2O thin films

Cuprous oxide thin films were produced on soda-lime glass substrates using reactive RF-magnetron sputtering. The influence of deposition parameters and temperature on composition and structural properties of the single layers was extensively studied using X-ray diffraction. The control over microstructure and residual stresses is possible by changing reactive gas pressure and deposition temperature. Fiber textured Cu2O films showing a [100] preferred orientation and a fraction of untextured domains can be obtained: suitable modeling taking this microstructure into account shows the presence of a strong compressive stress decreasing with the temperature. Highly reproducible films can be obtained, whose microstructure is preserved when sputtering on tungsten and zinc oxide substrates.     

High performance self-aligned top-gate ZnO thin film transistors using sputtered Al2O3 gate dielectric

High performance self-aligned top-gate zinc oxide (ZnO) thin film transistors (TFTs) utilizing high-k Al₂O₃ thin film as gate dielectric are developed in this paper. Good quality Al₂O₃ thin film was deposited by reactive DC magnetron sputtering technique using aluminum target in a mixed argon and oxygen ambient at room temperature. The resulting transistor exhibits a field effect mobility of 27 cm²/V s, a threshold voltage of − 0.5 V, a subthreshold swing of 0.12 V/decade and an on/off current ratio of 9 × 10⁶. The proposed top-gate ZnO TFTs in this paper can act as driving devices in the next generation flat panel displays.     

Morphology of TiN thin films grown on SiO2 by reactive high power impulse magnetron sputtering

Thin TiN films were grown on SiO₂ by reactive high power impulse magnetron sputtering (HiPIMS) at a range of temperatures from 45 to 600 °C. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces denser films at lower growth temperature than does dcMS. Furthermore, the surface is much smoother for films grown by the HiPIMS process. The [200] grain size increases monotonically with increased growth temperature, whereas the size of the [111] oriented grains decreases to a minimum for a growth temperature of 400 °C after which it starts to increase with growth temperature. The [200] crystallites are smaller than the [111] crystallites for all growth temperatures. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films.     

Charge trapping characteristics of Al2O3/Al-rich Al2O3/SiO2 stacked films fabricated by radio-frequency magnetron co-sputtering

A thin-film structure comprising Al₂O₃/Al-rich Al₂O₃/SiO₂ was fabricated on Si substrate. We used radio-frequency magnetron co-sputtering with Al metal plates set on an Al₂O₃ target to fabricate the Al-rich Al₂O₃ thin film, which is used as a charge storage layer for nonvolatile Al₂O₃ memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance-voltage (C-V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al-O capacitor structure, we clarified experimentally that the maximum capacitance in the C-V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al₂O₃ is increased, a large charge trap density is obtained. When the Al content in the Al-O is changed from 40 to 58%, the charge trap density increases from 0 to 18 × 10¹⁸ cm^− 3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory.     

Polycrystalline ZnO-In2O3 thin films as gas sensors

Polycrystalline ZnO-In₂O₃ thin films were prepared by thermal oxidation in air of metallic Zn-In films deposited onto glass substrates by thermal evaporation under vacuum. Different oxidation conditions (oxidation temperature, oxidation time, heating rate) were used in order to prepare homogeneous films that can be used as gas sensors. Polycrystalline structure of the as-obtained films was confirmed by X-ray and electron diffraction investigations. The electrical conductivity of various thin film samples ranged between 0.84 and 6.44 (Ω cm)^− 1.Gas sensitivity to six different gasses (ammonia, methane, LPG, acetone, ethanol and formaldehyde) was evaluated and it was found that the highest sensitivity was obtained for ammonia.     

Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films

The effects of residual water on the phase formation, composition, and microstructure evolution of magnetron sputter deposited crystalline alumina thin films have been investigated. To mimic different vacuum conditions, depositions have been carried out with varying partial pressures of H₂O. Films have been grown both with and without chromia nucleation layers. It is shown that films deposited onto chromia nucleation layers at relatively low temperatures (500 °C) consist of crystalline α-alumina if deposited at a low enough total pressure under ultra high vacuum (UHV) conditions. However, as water was introduced a gradual increase of the γ phase content in the film with increasing film thickness was observed. At the same time, the microstructure changed drastically from a dense columnar structure to a structure with small, equiaxed grains. Based on mass spectrometry measurements and previous ab initio calculations, we suggest that either bombardment of energetic negative (or later neutralized) species being accelerated over the target sheath voltage, adsorbed hydrogen on growth surfaces, or a combination of these effects, is responsible for the change in structure. For films containing the metastable γ phase under UHV conditions, no influence of residual water on the phase content was observed. The amounts of hydrogen incorporated into the films, as determined by elastic recoil detection analysis, were shown to be low. Overall, the results demonstrate that residual water present during film growth drastically affects film properties, also in cases where the hydrogen incorporation is found to be low.     

Electrical mechanism analysis of Al2O3 doped zinc oxide thin films deposited by rotating cylindrical DC magnetron sputtering

Cost efficient and large area deposition of superior quality Al₂O₃ doped zinc oxide (AZO) films is instrumental in many of its applications, including solar cell fabrication due to its numerous advantages over indium tin oxide (ITO) films. In this study, AZO films were prepared by a highly efficient rotating cylindrical direct current (DC) magnetron sputtering system using an AZO target, which has a target material utilization above 80%, on glass substrates in argon (Ar) ambient. A detailed analysis on the electrical, optical, and structural characteristics of AZO thin films was performed for the solar cell, as well as display applications. The properties of films were found to critically depend on deposition parameters, such as sputtering power, substrate temperature, working pressure, and film thickness. A low resistivity of ~ 5.5 × 10^− 4 Ω cm was obtained for films deposited at 2 kW, keeping the pressure, substrate temperature and thickness constant at 3 mTorr, 230 °C and ~ 1000 nm respectively. This was due to an increase in carrier mobility and large grain size. Mobility is found to be controlled by ionized impurity scattering within the grains, since the mean free path of carriers is much smaller than the grain size of the films. The AZO films showed a high transparency of ~ 90% in the long wavelength region. Our results offer a cost-efficient AZO film deposition method that can fabricate films with significant low resistivity and high transmittance that can be applied in thin-film solar cells, as well as thin film transistor (TFT) and non-volatile memory (NVM).     

磁控溅射CrNx薄膜的制备与力学性能

采用反应磁控溅射法在不同的氮分压下制备了一系列CrNx薄膜，并利用EDS和XRD表征了薄膜的成分和相组成，采用力学探针测量了薄膜的硬度和弹性模量。研究了氮分压对薄膜成分，相组成和力学性能的影响。结果表明，随氮分压的升高，薄膜的沉积速率明显降低，薄膜中的氮含量量增加，相应地，相组成从Cr Cr2N过渡到单相Cr2N,再逐步经Cr2N CrN过渡到单相CrN,并在Cr:N原子比为1：2和1：1时，薄膜的硬度出现极值（HV27．1GPa和HV26.8GPa),而薄膜的弹性模量则在Cr2N时呈现350GPa的最高值。     

Structural,electrical and photoluminescence properties of ZnO:Al network films grown on nanochannel Al2O3 substrates by direct current magnetron sputtering with an oblique target

ZnO:Al network films were grown on nanochannel Al₂O₃ substrates at 300 K by direct current magnetron sputtering with an oblique target. The film thicknesses are 60 nm, 160 nm and 190 nm. The holes of the network films diminish with increasing film thickness. For the 60-nm thick film, the network is formed by connecting grains. For the 160-nm and 190-nm thick films, however, the network is formed by connecting granules. The granules consist of many small grains. All the network films have a wurtzite structure. The 60-nm and 160-nm thick network films mainly have a [1 0 1] orientation in the film growth direction while the 190-nm thick network film grows with a random crystallographic orientation. A temperature dependence of the resistance within 160–300 K reveals that the network films exhibit a semiconducting behavior and their carrier transport mechanism is thermally activated band conduction. Room temperature photoluminescence spectra for wavelengths between 300 nm and 700 nm reveal a violet emission centered at 405 nm for the 60-nm thick network film and a blue emission centered at 470 nm for both the 160-nm and the 190-nm thick network films. Annealing decreases the resistivity of the network film.     

Comparative study of physical properties of vapor chopped and nonchopped Al2O3 thin films

Aluminium oxide being environmentally stable and having high transmittance is an interesting material for optoelectronics devices. Aluminium oxide thin films have been successfully deposited by hot water oxidation of vacuum evaporated aluminium thin films. The surface morphology, surface roughness, optical transmission, band gap, refractive index and intrinsic stress of Al₂O₃ thin films were studied. The cost effective vapor chopping technique was used. It was observed that, optical transmittance of vapor chopped Al₂O₃ thin film showed higher transmittance than the nonchopped film. The optical band gap of vapor chopped thin film was higher than the nonchopped Al₂O₃, whereas surface roughness and refractive index were lower due to vapor chopping.     

Effect of process parameters and post deposition annealing on the optical, structural and microwave dielectric properties of RF magnetron sputtered (Ba0.5,Sr0.5)TiO3 thin films

Thin films of (Ba_0.5,Sr_0.5)TiO₃ (BST5) in the thickness range 400-800 nm have been deposited by RF magnetron sputtering on to quartz substrates at ambient temperature. All the properties investigated, i.e. structure, microstructure, optical and microwave dielectric, show a critical dependence on the processing and post processing parameters. The surface morphology as studied by atomic force microscopy reveals ultra fine grains in the case of as deposited films and coarse grain morphology on annealing. The as-deposited films are X-ray amorphous and exhibit refractive index in the range 1.9-2.04 with an optical absorption edge value between 3.8 and 4.2 eV and a maximum dielectric constant of 35 at 12 GHz. The dispersion in refractive index fits into the single effective oscillator model while the variation in the optical parameters with oxygen percentage in the sputtering gas can be explained on the basis of packing fraction changes. On annealing the films at 900 °C they crystallize in to the perovskite structure accompanied by a decrease in optical band gap, increase in refractive index and increase in the microwave dielectric constant. At 12 GHz the highest dielectric constant achieved in the annealed films is 175. It is demonstrated that with increasing oxygen-mixing percentage in the sputtering gas, the microwave dielectric loss decreases while the dielectric constant increases.     

Comparison of hydrophilic properties of TiO2 thin films prepared by sol-gel method and reactive magnetron sputtering system

This article reports on preparation, characterization and comparison of TiO₂ films prepared by sol-gel method using the titanium isopropoxide sol (TiO₂ coating sol 3%) as solvent precursor and reactive magnetron sputtering from substoichiometric TiO_2 − x targets of 50 mm in diameter. Dual magnetron supplied by dc bipolar pulsed power source was used for reactive magnetron sputtering. Depositions were performed on unheated glass substrates. Comparison of photocatalytic properties was based on measurements of hydrophilicity, i.e. evaluation of water contact angle on the film surface after UV irradiation. It is shown, that TiO₂ films prepared by the sol-gel method exhibited higher hydrophilicity in the as-deposited state but has significant deterioration of hydrophilicity during aging, compared to TiO₂ films prepared by magnetron sputtering. To explain this effect AFM, SEM and high resolution XPS measurements were performed. It is shown that the deterioration of hydrophilicity of sol-gel TiO₂ films can be suppressed if as-deposited films are exposed to the plasma of microwave oxygen discharge.     

Property variations of direct-current reactive magnetron sputtered copper oxide thin films deposited at different oxygen partial pressures

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were deposited on glass substrates at different oxygen partial pressures by direct-current reactive magnetron sputtering of pure copper target in a mixture of argon and oxygen gases. Oxygen partial pressure was found to be a crucial parameter in controlling the phases and, thus, the physical properties of the deposited copper oxide thin films. Single-phase Cu₂O thin films with cubic structure were obtained at low oxygen partial pressure between 0.147 Pa and 0.200 Pa while higher oxygen partial pressure promoted the formation of CuO thin films with base-centered monoclinic structure. Polycrystalline Cu₂O thin films deposited with oxygen partial pressure at 0.147 Pa possessed the lowest p-type resistivity of 1.76 Ω cm as well as an optical band gap of 2.01 eV. On the other hand, polycrystalline CuO thin films deposited with oxygen partial pressure at 0.320 Pa were also single phase but showed a n-type resistivity of 0.19 Ω cm along with an optical band gap of 1.58 eV.