Magnetron Co-sputtering Method Research Articles

Threshold resistance switching in silicon-rich SiOx thin films**Project supported by the Open Project Program of Surface Physics Laboratory (National Key Laboratory) of Fudan University, China (Grant No. KF2015_02), the Open Project Program of National Laboratory for Infrared Physics, Chinese Academy of Sciences (Grant No. M201503), Zhejiang Provincial Science and Technology Key Innovation Team, China (Grant No. 2011R50012), and Zhejiang Provincial

Si-rich SiOx and amorphous Si clusters embedded in SiOx films were prepared by the radio-frequency magnetron cosputtering method and high-temperature annealing treatment. The threshold resistance switching behavior was achieved from the memory mode by continuous bias sweeping in all films, which was caused by the formation of clusters due to the local overheating under a large electric field. Besides, the I–V characteristics of the threshold switching showed a dependence on the annealing temperature and the SiOx thickness. In particular, formation and rupture of conduction paths is considered to be the switching mechanism for the 39 nm-SiOx film, while for the 78 nm-SiOx film, adjusting of the Schottky barrier height between insulator and semiconductor is more reasonable. This study demonstrates the importance of investigation of both switching modes in resistance random access memory.

Microstructure and piezoelectric properties of reactively sputtered highly C-axis ScxAl1-xN thin films on diamond-like carbon/Si substrate

We report deposition of pure AlN and ScxAl1-xN thin films with different Sc concentration on DLC/Si substrate by RF and DC reactive magnetron co-sputtering method by using Al and Sc as targets. The X-ray diffraction (XRD) results showed that the films have high c-axis-orientation. Electron probe microanalyzer (EPMA) analysis reveals the presence of scandium atoms reduce the space occupied by aluminum atoms, leading to lattice distortion during the phase transition. The SEM cross-section results showed that the ScxAl1-xN films are highly aligned along c-axis and have columnar like morphology. The top view of SEM results indicated that the new phase formation above Sc 30.33%, however no new peak appeared in the XRD pattern. The piezoelectric coefficient (d33) of ScxAl1-xN thin films are measured and the highest value (11.54 pC/N) is achieved at x=30.33% increasing 14 times, as that with AlN/DLC/Si, 0.73 pC/N. ScxAl1-xN films on DLC/Si substrate have a great potential to be applied on high frequency SAW devices in the future.

Heavily-doped ZnO:Al thin films prepared by using magnetron Co-sputtering: Optical and electrical properties

Photovoltaic applications require transparent conducting-oxide (TCO) thin films with high optical transmittance in the visible spectral region (380 − 780 nm), low resistivity, and high thermal/chemical stability. The ZnO thin film is one of the most common alternatives to the conventional indium-tin-oxide (ITO) thin film TCO. Highly transparent and conductive ZnO thin films can be prepared by doping with group III elements. Heavily-doped ZnO:Al (AZO) thin films were prepared by using the RF magnetron co-sputtering method with ZnO and Al targets to obtain better characteristics at a low cost. The RF sputtering power to each target was varied to control the doping concentration in fixed-thickness AZO thin films. The crystal structures of the AZO thin films were analyzed by using X-ray diffraction. The morphological microstructure was observed by using scanning electron microscopy. The optical transmittance and the band gap energy of the AZO thin films were examined with an UV-visible spectrophotometer in the range of 300 − 1800 nm. The resistivity and the carrier concentration were examined by using a Hall-effect measurement system. An excellent optical transmittance > 80% with an appropriate band gap energy (3.26 − 3.27 eV) and an improved resistivity (~10 −1 Ω·cm) with high carrier concentration (1017 − 1019 cm −3) were demonstrated in 350-nm-thick AZO thin films for thin-film photovoltaic applications.

Surface characterization of PZT thin films obtained at various O2 gas ratios

We fabricated PZT (Pb(Zr1-xTix)O3, PZT) thin films at various O2 gas ratios by utilizing the radio frequency (RF) magnetron co-sputtering method. Ar-ion sputtered depth profile was performed to investigate both the surface and the bulk region of the PZT thin films. The thickness of the PZT thin films was monitored through the means of a surface profiler and a decrease from 272.7 to 89.7 nm was observed after introducing O2 gas in the sputter gas. Based on the XRD study, the perovskite phase of PZT evolved after O2 gas was introduced to the system. As the O2 gas ratio increased, the portion of Pb increased while Zr and Ti decreased, in which this was confirmed by XPS. The conductivity of the PZT thin films obtained at 0 and 5% of O2 gas ratio in the sputter gas dramatically decreased from 778.6 to 75.4 S/cm, respectively.

Thermoelectric Properties of β-Zn<sub>4</sub>Sb<sub>3</sub> Thin Films Deposited on Polyimide Flexible Substrate

Due to the high-performance in the medium temperature application, β-Zn4Sb3 thermoelectric material has been received much attention. It is found that low dimensional thin film can improve the thermoelectric properties of materials by quantum local area effect and interface effect in recent years. In this paper, the β-Zn4Sb3 thin film was prepared on polyimide flexible substrate by DC magnetron co-sputtering method. The results showed that the thin film exhibited predominately ZnSb phases when the thin film was prepared by DC magnetron sputtering using Zn4Sb3 alloy target. It is suggested that the element Zn has high saturated vapor pressure and the thin film is lack of Zn due to the evaporation during the heat treatment process. We further adopted co-deposition Zn and Zn4Sb3 by DC magnetron co-sputtering to supplement the content of Zn. The sputtering power of Zn4Sb3 is fixed and Zn is set to 21W, 27W and 34W, respectively. The results indicated that the thin films transformed from ZnSb phase into β-Zn4Sb3 phase after Zn added. EDS analysis demonstrated that the atomic ratio of Zn:Sb was approach 4:3, and a slightly surplus of Zn. The thermoelectric properties of thin films with β-Zn4Sb3 phase were improved obviously.

Influence of the surface properties on bactericidal and fungicidal activity of magnetron sputtered Ti–Ag and Nb–Ag thin films

In this study the comparative investigations of structural, surface and bactericidal properties of Ti–Ag and Nb–Ag thin films have been carried out. Ti–Ag and Nb–Ag coatings were deposited on silicon and fused silica substrates by magnetron co-sputtering method using innovative multi-target apparatus. The physicochemical properties of prepared thin films were examined with the aid of X-ray diffraction, grazing incidence X-ray diffraction, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy methods. Moreover, the wettability of the surface was determined. It was found that both, Ti–Ag and Nb–Ag thin films were nanocrystalline. In the case of Ag–Ti film presence of AgTi3 and Ag phases was identified, while in the structure of Nb–Ag only silver occurred in a crystal form. In both cases the average size of crystallites was ca. 11nm. Moreover, according to scanning electron microscopy and atomic force microscopy investigations the surface of Nb–Ag thin films was covered with Ag-agglomerates, while Ti–Ag surface was smooth and devoid of silver particles. Studies of biological activity of deposited coatings in contact with Bacillus subtilis, Pseudomonas aeruginosa, Enterococcus hirae, Klebisiella pneumoniae, Escherichia coli, Staphylococcus aureus and Candida albicans were performed. It was found that prepared coatings were bactericidal and fungicidal even in a short term-contact, i.e. after 2h.

Phase evolution of binary immiscible Al–Sn film

Binary immiscible Al–Sn alloy is a very important potential anode material for lithium ion batteries. The phase stability and separation process of Al–Sn film, fabricated by magnetron co-sputtering method, was investigated by X-ray diffractometer (XRD), differential scanning calorimetry (DSC) and in situ transmission electron microscopy (TEM) and explained by Miedema theoretical model. Thermodynamic analysis reveals that the as-deposited Al–Sn film will decompose spontaneously into Al-riched areas and Sn-riched areas because of the positive mixing enthalpy. The crystallization process takes place when the Al content in the Al-riched area or Sn content in the Sn-riched area increases. Experimental results show that Al–Sn thin film is composed of an amorphous matrix and well-dispersed composite nanoparticles. Every particle contains an Al-riched area and a Sn-riched area. The Sn-riched area crystallizes and swallows up the Al-riched area gradually during heating through uphill diffusion of the Sn atoms. Based on the theoretical analysis and experimental results, an empirical model to explain the phase evolution process in the Al–Sn film was proposed.

Influence of Content of Al2O3 on Structure and Properties of Nanocomposite Nb-B-Al-O films.

Nb-B-Al-O nanocomposite films with different power of Al2O3 were successfully deposited on the Si substrate via multi-target magnetron co-sputtering method. The influences of Al2O3’s content on structure and properties of obtained nanocomposite films through controlling Al2O3’s power were investigated. Increasing the power of Al2O3 can influence the bombarding energy and cause the momentum transfer of NbB2. This can lead to the decreasing content of Al2O3. Furthermore, the whole films showed monocrystalline NbB2’s (100) phase, and Al2O3 shaded from amorphous to weak cubic-crystalline when decreasing content of Al2O3. This structure and content changes were proof by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). When NbB2 grains were far from each other in lower power of Al2O3, the whole films showed a typical nanocomposite microstructure with crystalline NbB2 grains embedded in a matrix of an amorphous Al2O3 phase. Continuing increasing the power of Al2O3, the less content of Al2O3 tended to cause crystalline of cubic-Al2O3 between the close distances of different crystalline NbB2 grains. The appearance of cubic-crystallization Al2O3 can help to raise the nanocomposite films’ mechanical properties to some extent. The maximum hardness and elastic modulus were up to 21.60 and 332.78 GPa, which were higher than the NbB2 and amorphous Al2O3 monolithic films. Furthermore, this structure change made the chemistry bond of O atom change from the existence of O-Nb, O-B, and O-Al bonds to single O-Al bond and increased the specific value of Al and O. It also influenced the hardness in higher temperature, which made the hardness variation of different Al2O3 content reduced. These results revealed that it can enhance the films’ oxidation resistance properties and keep the mechanical properties at high temperature. The study highlighted the importance of controlling the Al2O3’s content to prepare well-defined films with high mechanical properties and thermal stability.

Deposition of n-Type Bi2Te3 Thin Films on Polyimide by Using RF Magnetron Co-Sputtering Method

Bi2Te3 thermoelectric thin films were deposited on the flexible polyimide substrates by RF magnetron co-sputtering of a Bi and a Te targets. The influence of the substrate temperature and RF power on the microstructure, chemical composition, and the thermoelectric properties of the sputtered films was investigated by using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and in-plane resistivity/Seebeck coefficient measurement. It was shown that the thermoelectric properties of the films depend sensitively on the Bi/Te chemical composition ratio and the substrate temperature, and the layered structure was clearly observed from the cross section of the (00L)-oriented, nearly stoichiometric Bi2Te3 films when the substrate temperature is higher than 250 °C. As-deposited Bi2Te3 films deposited at 300 °C show the highest power factor of 0.97 mW/K(2)m and the Seebeck coefficient of -193 μV/K at 32 °C, which also have (00L) preferred orientation and the layered structure. The durability of the Bi2Te3 films on polyimide against repeated bending was also tested by monitoring the film resistance, and it was concluded that the Bi2Te3 films are applicable reliably on the curved surfaces with the radius of curvature larger than 5 mm.

Nanostructured perovskite CdTiO3 films for methane sensing

Cadmium titanate (CdTiO3) thin films with different concentrations of titanium dioxide (TiO2) were synthesized by magnetron co-sputtering method on to glass substrates. X-ray diffraction (XRD) patterns confirmed the formation of perovskite orthorhombic crystal structure at relatively low deposition temperature. The crystallinity of the films decreased with increase in TiO2 concentration due to structural deformation caused by differences in the ionic radii of the Cd2+ and Ti4+ atoms. The grain size value was found to decrease from 80 to 30nm and a blue shift of the optical band edge was observed. The CdTiO3 films with lower concentrations of TiO2 exhibited better methane (CH4) sensing properties (100ppm) at an operating temperature of 250°C with fast response and recovery time.

Investigation of microstructure, micro-mechanical and optical properties of HfTiO4 thin films prepared by magnetron co-sputtering

Titania (TiO2) and hafnium oxide (HfO2) thin films are in the focus of interest to the microelectronics community from a dozen years. Because of their outstanding properties like, among the others, high stability, high refractive index, high electric permittivity, they found applications in many optical and electronics domains. In this work discussion on the hardness, microstructure and optical properties of as-deposited and annealed HfTiO4 thin films has been presented. Deposited films were prepared using magnetron co-sputtering method. Performed investigations revealed that as-deposited coatings were nanocrystalline with HfTiO4 structure. Deposited films were built from crystallites of ca. 4–12nm in size and after additional annealing an increase in crystallites size up to 16nm was observed. Micro-mechanical properties, i.e., hardness and elastic modulus were determined using conventional load-controlled nanoindentation testing. the annealed films had 3-times lower hardness as-compared to as-deposited ones (∼9GPa). Based on optical investigations real and imaginary components of refractive index were calculated, both for as-deposited and annealed thin films. The real refractive index component increased after annealing from 2.03 to 2.16, while extinction coefficient increased by an order from 10−4 to 10−3. Structure modification was analyzed together with optical energy band-gap, Urbach energy and using Wemple–DiDomenico model.

Linear and nonlinear optical properties of Sb-doped GeSe2 thin films**Project supported by the National Key Basic Research Program of China (Grant No. 2012CB722703), the National Natural Science Foundation of China (Grant No. 61377061), the Young Leaders of Academic Climbing Project of the Education Department of Zhejiang Province, China (Grant No. pd2013092), the Program for Innovative Research Team of Ningbo City,

Sb-doped GeSe2 chalcogenide thin films are prepared by the magnetron co-sputtering method. The linear optical properties of as-deposited films are derived by analyzing transmission spectra. The refractive index rises and the optical band gap decreases from 2.08 eV to 1.41 eV with increasing the Sb content. X-ray photoelectron spectra further confirm the formation of a covalent Sb–Se bond. The third-order nonlinear optical properties of thin films are investigated under femtosecond laser excitation at 800 nm. The results show that the third-order nonlinear optical properties are enhanced with increasing the concentration of Sb. The nonlinear refraction indices of these thin films are measured to be on the order of 10−18 m2/W with a positive sign and the nonlinear absorption coefficients are obtained to be on the order of 10−10 m/W. These excellent properties indicate that Sb-doped Ge–Se films have a good prospect in the applications of nonlinear optical devices.

Controllable substrate bias voltages effectively tailoring nanocomposite Nb–B–Al–O film properties

The nanocomposite Nb–B–Al–O films based on NbB2 and Al2O3 were successfully deposited on Si substrate via multi-target magnetron co-sputtering method. The influences of substrate bias on microstructure, mechanical, thermostability and oxidation resistance properties of the films were investigated in detail. TransmissionElectronMicroscopy (TEM), X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were performed to study the structural properties such as crystallinity, binding energy and chemical composition of as-prepared films. The combination of monocrystalline NbB2 (100) texture and Al2O3 (113) crystal plane affected the mechanical properties of the films at different bias voltages. The best crystallization appeared at −160V. The maximum hardness (23.4GPa) and elastic modulus (274.5GPa) of the films were obtained at optimal substrate bias of −160V. The hardest film at −160V also showed the better thermostability and oxidation resistance properties at 300°C. This work also demonstrated that the decreased crystallinity induced at higher via voltage led to the decreasing in the mechanical properties.

Effect of Al content, substrate temperature and nitrogen flow on the reactive magnetron co-sputtered nanostructure in TiAlN thin films intended for use as barrier material in DRAMs

TiAlN thin films were deposited by using the reactive magnetron co-sputtering method whit individual Ti and Al targets, where the Ti and the Al targets were simultaneously powered by using DC and RF sources, respectively. the electrical resistivity and the structural and microstructural properties of the deposited TiAlN thin films and the effects of Al content, substrate temperature and nitrogen gas flow rate on those properties were investigated. At a low flow rate of nitrogen gas (0.51 sccm), the electrical resistivity of the films was found to increase with increasing AC power, but at a high flow rate of nitrogen gas, it was found to decrease. The structural and microstructural analyses performed by using X-ray diffraction and scanning electron microscopy (SEM) showed that with increasing substrate temperature from room temperature to 400 ℃, the films prepared at 400 ℃ have a crystalline structure while those prepared at room temperature had an amorphous nature. Also, the SEM analysis revealed that with decreasing AC power and increasing nitrogen flow rate, the size of the grains in the prepared films become larger.

Post-annealing effect on the a-SiCx passivation layer synthesized with the radio frequency magnetron co-sputtering method

The amorphous silicon carbide (a-SiC) film has been considered a good candidate for the rear passivation layer of the high-efficiency silicon solar cell. We describe the results of the post-annealing of an amorphous silicon carbide (a-SiC) film deposited using the radio frequency magnetron sputtering method. The post-annealing was performed with rapid thermal annealing process in three different chamber environments: nitrogen (N2), oxygen (O2), and hydrogen (H2). After the annealing process, the characteristic properties of the films were investigated in several categories. The transmittance of the film was measured with Scinco s-3100 at the 400–800nm wavelength. The average transmittance increased after the annealing treatment, and the highest transmittance was achieved with the H2 ambient. Using a silicon wafer lifetime tester, we measured the carrier lifetime of the films. We found that the carrier lifetime was highest in the N2 ambient annealing process. Also, the refractive index was determined using an ellipsometer. The measurement indicated that the refractive index of the film decreased in the annealing process, unlike that of the as-deposited film.

Optical properties of amorphous In-doped GeSe2 films for all-optical applications

In-doped GeSe2 films were prepared by magnetron co-sputtering method. Amorphous behavior of as-deposited films was confirmed by the X-ray diffraction. The linear optical properties of the films have been derived by analyzing transmission spectra. The experimental results show that linear refractive index rises and optical band gap reduces from 2.04eV to 1.66eV with increasing In content. The proper In content of 13.18 at.% is obtained by optimizing the composition of the films. The nonlinear optical properties of the films were studied at 800nm by using femto-second Z-scan measurement. Experimental results show that the third-order nonlinear refractive index and nonlinear susceptibility of In13.18(GeSe2)86.82 film are up to 8.50×10−16m2/W and 1.41×10−9esu, respectively, almost two orders larger than those of the GeSe2 film. These excellent properties indicate that In-doped GeSe2 films are perspective in the aspect of all-optical applications.

Preparation of Cr2O3-Ta2O5 Composites Using RF Magnetron Sputtering

We prepared Cr2O3-Ta2O5 composite films using our RF magnetron co-sputtering method for the first time. X-ray diffraction (XRD) patterns and photoluminescence (PL) spectra of the films annealed at 700℃, 800℃, 900℃, and 1000℃ were evaluated. From their XRD patterns, the Cr2O3-Ta2O5 film annealed at 700℃ seemed to be almost amorphous, and the one annealed at 800℃ seemed to be hexagonal Ta2O5 doped with Cr. In addition, the Cr2O3-Ta2O5 films annealed at 900℃ and 1000℃ seemed to include tetragonal CrTaO4 phases. Furthermore, it seems that almost no defect exists in our Cr2O3-Ta2O5 composite films annealed at 700℃ - 1000℃ because their PL spectra have no defect-related peak. We thus find that good-quality Cr2O3-Ta2O5 composite films including CrTaO4 can be obtained using our very simple co-sputtering method and subsequent annealing above 900℃.

Influence of Cu on Transport Properties of Thermoelectric Thin Film Fabricated via Magnetron Co-sputtering Method

A simple magnetron co-sputtering method was used to fabricate Cu dispersed Bi0.5 Sb1.5 Te3 thin films, and the co-sputtering method was beneficial to the preferential growth of Bi0.5 Sb1.5 Te3 thin films along c-axis. Cu atoms were well-dispersed in the nano-structured materials. The electrical conductivity sharply increased with the increasing content of Cu due to the effect of Cu on transport property. For Cu target sputtering power of 20 W, a maximum power factor of 20 μW/(cm·K2) with an electrical conductivity of 15 × 104 S/m at 355 K were achieved.

Preparation and characterization of self-assembled percolative BaTiO3–CoFe2O4 nanocomposites via magnetron co-sputtering

BaTiO3–CoFe2O4 composite films were prepared on (100) SrTiO3 substrates by using a radio-frequency magnetron co-sputtering method at 750 °C. These films contained highly (001)-oriented crystalline phases of perovskite BaTiO3 and spinel CoFe2O4, which can form a self-assembled nanostructure with BaTiO3 well-dispersed into CoFe2O4 under optimized sputtering conditions. A prominent dielectric percolation behavior was observed in the self-assembled nanocomposite. Compared with pure BaTiO3 films sputtered under similar conditions, the nanocomposite film showed higher dielectric constants and lower dielectric losses together with a dramatically suppressed frequency dispersion. This dielectric percolation phenomenon can be explained by the ‘micro-capacitor’ model, which was supported by measurement results of the electric polarization and leakage current.

Enhancement of thermoelectric properties induced by oriented nanolayer in Bi2Te2.7Se0.3 columnar films

In this paper, it was found that layered and columnar structure can favorably influence the carrier and phonon transport properties of films. The n-Bi2Te2.7Se0.3 columnar film with layered structure was successfully achieved by simple magnetron co-sputtering method at 400 °C deposition temperature, due to the more sufficient growth along the in-plane direction induced by the enhanced mobility of deposited atoms. The layered nanostructure is clear with each layer <25 nm in the columnar film. The properties of the Bi2Te2.7Se0.3 columnar film with layered structure were greatly enhanced in comparison with those of the columnar and the ordinary films synthesized respectively at 350 °C and 250 °C deposition temperature. The layered Bi2Te2.7Se0.3 columnar film with a thermoelectric dimensionless figure-of-merit ZT = 1.27 was obtained at room temperature. The layered column structure was the main reason for the properties enhancement observed in the Bi2Te2.7Se0.3 film. Introduction of such uniquely layered and columnar structure into thermoelectric films is therefore a very promising approach.