Radio Frequency Co-sputtering Research Articles

A Study of MgZnO Thin Film for Hydrogen Sensing Application.

This research introduces a hydrogen sensor made from a thin film of magnesium zinc oxide (MgZnO) deposited using a technique called radiofrequency co-sputtering (RF co-sputtering). Separate magnesium oxide (MgO) and zinc oxide (ZnO) targets were used to deposit the MgZnO film, experimenting with different deposition times and power levels. The sensor performed best (reaching a sensing response of 2.46) when exposed to hydrogen at a concentration of 1000 parts per million (ppm). This peak performance occurred with a MgZnO film thickness of 432 nanometers (nm) at a temperature of 300 °C. Initially, the sensor's responsiveness increased as the film thickness grew. This is because thicker films tend to have more oxygen vacancies, which are imperfections that play a role in the sensor's function. However, further increases in film thickness beyond the optimal point harmed performance. This is attributed to the growth of grains within the film, which hindered its effectiveness. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were employed to thoroughly characterize the quality of the MgZnO thin film. These techniques provided valuable insights into the film's crystal structure and morphology, crucial factors influencing its performance as a hydrogen sensor.

Stability Enhancement in Copper-Doped Iron Oxide Resistive Random Access Memory via RF Co-Sputtering

In the study, the ITO/Cu-doped Fe2O3/ITO thin film RRAM is prepared using an RF sputtering system. The XRD pattern shows that the Cu:Fe2O3 thin film has a rhombohedral structure and does not display secondary or impurity phases for copper. Results revealed that the standard deviation and average voltage of Cu:Fe2O3 thin film are −1.98 and 0.92 V for Vset, respectively, while those for Vreset are 1.31 and 0.39 V, respectively. The resistive switching cycles and data retention test times of the Cu:Fe2O3 thin film device show that the on/off ratio is 39.4 and over 104 s. These results indicated that the Cu-doped Fe2O3 thin film can improve the performance of RRAM.

Improved Resistive Switching Behaviors of Al/Ag-Doped Fe2O3 Film/ITO Devices Fabricated with a Radio-Frequency Co-Sputtering System

We fabricated Fe2O3−x and Ag-doped Fe2O3−x devices with resistive switching behavior by using a radiofrequency cosputtering system. Our results indicated that doping Ag into Fe2O3−x can effectively improve device performance, increasing the data retention test time to beyond 104 s and resulting in switching cycles of approximately ∼3 × 102 times; resistance on/off ratios of approximately ∼103; and mean setting and reset voltages of 0.94 V and −1.35 V, respectively. The improvement in performance had several possible reasons. In our case, conductive filament formation was mainly induced by oxygen vacancies and Ag atoms. X-ray photoelectron spectroscopy showed that oxygen vacancies increased significantly with Ag doping. This phenomenon can improve device performance. Ag atoms served as trap centers, allowing for the easy trapping and release of charges. This effect facilitated the formation of conductive filaments. Ag-doped Fe2O3−x has significant potential for application in resistive switching random access memory devices.

Study on the preparation and properties of (BixGa1-x)2O3 alloy semiconductor film deposited by radio frequency co-sputtering

Study on the preparation and properties of (BixGa1-x)2O3 alloy semiconductor film deposited by radio frequency co-sputtering

Investigation of AlGaZnO pH Sensors Fabricated by Using Cosputtering System

In this study, the extended gate field-effect transistor (EGFET) pH sensors with the aluminum–gallium–zinc-oxide (AGZO) sensing film were fabricated by the radio frequency (RF) cosputtering method at various aluminum–gallium-oxide (AGO):zinc-oxide (ZnO) power ratios. The transfer characteristic curve was measured by the constant voltage mode and the constant current mode at various pH values of 2–12. The pristine AGO sensing film exhibited 23.00 mV/pH and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12.00~\mu \text{A}$ </tex-math></inline-formula> /pH of the pH voltage sensitivity and pH current sensitivity, respectively. The pH sensitivity increased with the increased AGO:ZnO power ratio and achieved the highest value at AGO:ZnO of 80 W:50 W. At this condition, the pH voltage sensitivity and the pH current sensitivity were improved to 30.01 mV/pH and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$31.06~\mu \text{A}$ </tex-math></inline-formula> /pH, respectively, and both with the great linearity around 0.99. This was attributed to both the carrier transport improved by the ZnO and the increased surface roughness. From the surface morphology analysis, it was observed that the AGO:ZnO power ratio of 80 W:50 W demonstrated the highest surface roughness of 1.08 nm, related to more surface contact area and more binding sites than other conditions, resulting in the highest pH sensitivity. Therefore, cosputtering AGO and ZnO to form the AGZO sensing film can improve the carrier transport, increase the surface roughness, lead to higher surface reactivity, and enhance the pH voltage sensitivity and the pH current sensitivity.

Low power Ti-doped NbO2-based selector device with high selectivity and low OFF current

The crossbar array-based resistive memory is considered a potential architecture for high-density nonvolatile memory applications. However, the sneak current path problem associated with the crossbar array structure limits its use in practical applications. This limitation can be removed by employing a selector device in the crossbar array structure. Therefore, we propose NbO2 as a selector device as it operates at a rapid speed during the insulator-metal transition (IMT). Herein, we fabricated a Ti-doped NbO2 selector device and demonstrated a very low OFF current (5 × 10-11 A). The effect of Ti doping in the NbO2 device was studied by varying the Ti concentration during a radio frequency co-sputtering process. We intentionally prevented the formation of Nb2O5, and a high-quality NbO2 layer was deposited with an appropriate Ti concentration. Furthermore, we modulated the IMT characteristics of the NbO2 device by varying the Ti concentration. The fabricated Ti-doped NbO2 selector device showed an ION/IOFF ratio greater than 5 × 104. Additionally, a drift-free fast switching operation (<20 ns) was achieved for the optimized selector device. These results suggest the high suitability of IMT-based NbO2 devices in selector applications.

Switching Properties Improvement of Tungsten-Doped Indium Oxide Phototransistor

High-performance and transparent tungsten-doped indium oxide (InWO) thin-film transistors (TFTs) with aluminum or indium oxide (In2O3) source and drain (S/D) electrodes were fabricated using the radiofrequency (RF) co-sputtering method. Due to the lower electron barrier height of the In2O3/InWO interface, the device with a homojunction structure exhibited better performance (μ eff = 20.1 cm2 V−1 ·s−1 and S.S. = 0.17 V dec−1) than the one with a heterojunction structure. Moreover, due to the high transparency of the S/D electrode, the light-sensing area was magnified. Thus, the responsivity of the phototransistor was significantly improved from 23.68 A W−1 to 89.47 A W−1. This result improved the properties of the interface between the S/D electrode and the channel layer and simplified the manufacturing process for InWO TFTs.

Multifunctional stratified composite coatings by electrophoretic deposition and RF co-sputtering for orthopaedic implants

In this study, multifunctional stratified antibacterial and bioactive coatings were deposited and characterised. Initially, PEEK/bioactive glass (BG)/ mesoporous bioactive glass nanoparticle (MBGN) layers with a thickness of 110–120 μm were deposited on stainless steel substrates using electrophoretic deposition (EPD). Thin silver nanocluster-silica composite layers with a thickness of 70–155 nm were then deposited by radio frequency (RF) co-sputtering on the previously deposited EPD coatings. The deposition was carried for two different sputtering times (20 min and 40 min), which led to different layer thicknesses. PEEK/BG/MBGNs coatings were also deposited via single-step EPD. A comparison between the physicomechanical and biological characteristics of single layer PEEK/BG/MBGNs composite coating and bilayer Ag-PEEK/BG/MBGNs is presented. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) indicated that silver nanoclusters were homogeneously distributed in the multilayered EPD/RF coatings. An apatite-like structure was formed on the surface of the coatings upon immersion in simulated body fluid (SBF) after 1 day. Silver nanoclusters embedded in the silica matrix as a top layer provided controlled release of silver ions which led to a potent antibacterial effect against E. coli and S. carnosus. Single layer coatings exhibited a burst release of Ag ions, which led to antibacterial effects but were toxic to osteoblast cells. Finally, the results of WST-8 assays confirmed that the multi-structured coatings allow osteoblast-like cells to proliferate and attach strongly on the surface of the coatings.

Erbium-ytterbium co-doped aluminum oxide thin films: Co-sputtering deposition, photoluminescence, luminescent lifetime, energy transfer and quenching fraction

Abstract Erbium-ytterbium co-doped aluminium oxide (Al2O3:Er3+:Yb3+) thin films were deposited on thermally oxidized silicon wafers using reactive radio frequency co-sputtering deposition. The effects of deposition parameters (including oxygen flow rate, substrate temperature and substrate bias) were investigated to obtain low loss Al2O3 films (~0.15 dB/cm at 1550 nm). A set of singly- and co-doped Al2O3 films (surface roughness: ~144.8 p.m.) with various Er3+ concentrations (1.4, 2.0 and 2.5 × 1020 cm−3) and/or Yb3+ concentrations (1.3, 2.1, 3.2, 4.3 and 5.8 × 1020 cm−3) were deposited and investigated. The Er3+ photoluminescence (PL) spectrum around 1550 nm exhibits a pump power-independent full width at half maximum (FWHM) of ~40 nm with and without the presence of Yb3+ as a sensitizer. The luminescent lifetime of Er3+ (4I13/2, 6.52–7.14 m s) exhibits a power-dependent characteristic, while that of Yb3+ (2I5/2, 0.514–0.716 m s) is power-independent. A power-dependent role of energy transfer upconversion is concluded from both the power-dependent Er3+ PL intensity trend and its power-dependent PL decay rate. Yb3+-Er3+ ion energy transfer also exhibits power-dependent characteristics. The energy transfer coefficient (up to ~3.2 × 10−17 cm3s−1) and energy transfer efficiency (up to ~80%) depend on the Yb3+ and Er3+ concentrations. The PL intensity trend and power-dependent absorption of Er3+ and Er3+-Yb3+ under 1469-nm excitation can be well described by using a three-energy-level model. The derived Er3+ quenching fraction based on the fittings of the measured absorption and PL intensity, decreases with the presence of Yb3+ ions. In addition, the Yb3+ quenching fraction was derived based on a two-energy-level model for 973-nm absorption. This work provides parametric references and insights regarding deposition, characterization, and design of the evolving rare-earth-doped Al2O3 platform for on-chip near-infrared applications.

Study on the structure and properties of Ag/Cu nanocomposite film deposited on the surface of polyester substrates

In order to study the influence of substrates on the structure and properties of deposited functional nanocomposite film, polyester fabrics with different structures were used as substrates, metal silver (Ag) and copper (Cu) were used as targets, and nanocomposite films were deposited by DC(direct current) and RF(radio frequency) co-sputtering. Surface morphology and structure of samples were analyzed, and anti-ultraviolet, electromagnetic shielding, and water repellency properties of samples were measured. The experimental results show that Ag/Cu nanocomposite film on the surface of the nonwoven fabric is uniform and continuous, the diameter of nanoparticles on the surface of woven fabric is small, and particle distribution on the surface of knitted fabric is continuous, with some island-like clusters. Cu (111), Cu (200), Ag (111) and Ag (200) diffraction peaks of nanocomposite film on the surface of the sample are not obvious due to low crystallinity. XPS (X-ray photoelectron spectrometer) image shows that nanoscale film is not oxidized but exists in elemental form. The anti-ultraviolet and anti-electromagnetic shielding properties of nanocomposite film with non-woven fabric as substrates are the highest, whereas the knitted fabric lowest. The contact angle results suggest that Ag/Cu nanocomposite film deposited on polyester fabrics provides excellent hydrophobicity.

Influence of sputtering conditions and annealing parameters on structure and morphology of NiTiO3 ilmenite thin films

Nickel titanate (NiTiO3) is well known for its interesting functional properties such as photocatalysis, high-K materials or magnetoelectric coupling. Some of these properties are strongly dependent on crystallographic orientation and morphological characteristics. Deposition as thin films through adapted processes enables to control such feature during NiTiO3 growth. In this context, NiTiO3 thin films were obtained by a two-step process: i) room temperature radio-Frequency co-sputtering of metallic Ni and Ti targets, ii) ex situ annealing in air. Influences of the deposition and annealing parameters on the morphological and structural features of NiTiO3 thin films were systematically studied. First, in situ X-ray diffraction as a function of temperature (from 30°C to 1200°C) was carried out in air on a NiTi thin film to identify suitable annealing temperatures for NiTiO3 oxide formation. Then, effects of annealing duration and temperature on morphology and orientation were investigated. Annealing temperature was found to influence grain size, while increasing the annealing time was found to bring (006) crystallographic orientation. Finally, an increase of the deposition pressure from 0.5 Pa to 5 Pa promoted the growth of (104) oriented films with a Lotgering factor LF104=0.44. This approach enables to independently tune preferential orientation and grain size of NiTiO3 thin films, by tailored deposition and annealing conditions.

Columnar structure growth of Mn-doped ZnO (MZO) thin films by radio frequency co-sputtering and studies on films properties

ABSTRACT The present investigation deals with the columnar structured growth of Mn doped ZnO (MZO) thin films by radio frequency sputtering technique. The X-ray diffraction and the processed electron diffraction pattern confirmed the hexagonal wurtzite structure and the film growth direction along (101) plane. The structure of grown film was compared with the pristine ZnO film and the JCPDS card No. 00-36-1451. The microstructures of the pristine ZnO and MZO films were studied by scanning electron microscopy and atomic force microscopy. The columnar structure growth of MZO was confirmed by transmission electron microscopy using TEM cross-section sample. The presence of constituent elements and their concentrations in the films were recorded by energy dispersive X-ray diffraction spectroscopy. The optical transmittance, absorption edge and band gap of the material were studied by UV-Visible transmission spectroscopy. The field dependent magnetization at room-temperature was analysed by using vibrating sample magnetometer and magneto-optic Kerr effect.

Mobility improvement of Zn1-xMgxO:Al prepared under room temperature by co-sputtering through optimizations of Al and Mg contents

ZnO:Al (AZO) and (Zn,Mg)O:Al (AZMO) films with several Al and Mg contents were deposited by radio frequency co-sputtering process under a room temperature (25 °C). The effects of Al and Mg contents on optical and electrical properties of the AZO and AZMO films were investigated for the suitability of the transparent conductive oxide (TCO) application in optoelectronic devices, requiring low resistivity and high transparency through the enhanced mobility. It is determined that Hall mobility of the AZO is increased, and its carrier concentration is decreased with an almost constant resistivity under the decreased Al content from about 1.7 to 0.3 at.%. The AZO film with the decreased Al content to about 0.6 at.% possesses the enhanced Hall mobility to 32.1 cm2/Vs and the reduced free-carrier absorption, which is suitable for the TCO application with its low resistivity of 5.6 × 10−4 Ω cm. It is also noted that optical bandgap energy (Eg) of the AZO films is increased with the increased Al content due to a Burstein-Moss shift. Moreover, the Mg addition into the AZMO films yields the increase in their Eg and the decrease in the free-carrier absorption under the same Al content. The resistivity of about 2.5 × 10−3 Ω cm by enhancing Hall mobility is consequently obtained in the AZMO films with the Mg content range of 0.06–0.10 with the decreased free-carrier absorption for the TCO application.

The effect of Ni content on gas-sensing behaviors of ZnO–NiO p–n composite thin films grown through radio-frequency cosputtering of ceramic ZnO and NiO targets

In this study, dual phase ZnO–NiO p–n composite thin films were grown through radio-frequency cosputtering of ceramic ZnO and NiO targets.

Annealing dependence of structural and optical properties of Zr-doped ZnO films deposited by radio frequency magnetron co-sputtering

To examine the effects of annealing temperatures, Zr-doped ZnO (Zn1-xZrxO1+δ; ZZO) thin films with x = ~0.067 were deposited at room temperature by radio frequency co-sputtering on quartz substrates and annealed in air at 300 °C, 400 °C, 500 °C, respectively. Annealing dependence of ZZO films was investigated by using X-ray diffraction, atomic force microscope X-ray absorption fine structure (XAFS), ultraviolet-visible (UV–Vis) spectroscopy, and resistivity. The results show that ZZO films maintain a strong preferred orientation toward c-axis, but the size of crystallites increased and the surfaces of the ZZO films were roughened with increasing annealing temperature. The Zn atoms were in divalent state and slightly affected by annealing, but Zr atoms were tetravalent and the spectra were slightly different from that of ZrO2. The variance of the Zn-O distance distribution, probed by polarization-dependent K-edge XAFS, in the ab-plane was stronger than that of the c-axis. The optical transmission spectra at 200 ≤ λ ≤ 900 nm showed high transparency of ≥90%, decrease of optical band gap, and red-shift as temperature increased. The resistivity decreased with enormously with increasing temperature. These results are ascribed to the increase of grain size.

The influence of Li2O incorporation on the electrochemical properties of Li4Ti5O12 thin film electrodes

High quality Li4Ti5O12 anode films were deposited by radio-frequency co-sputtering Li4Ti5O12 and Li2O targets on Pt-coated stainless steel substrates. The use of an additional Li2O target not only compensated the lithium content in the resulting layers but also decreased the impurity content. Consequently, the electrochemical properties of the Li4Ti5O12 anode exhibited better electrochemical properties than an identical film prepared using a single Li4Ti5O12 target. Upon annealing, the co-sputtering Li4Ti5O12 showed a relatively high discharge capacity of 618 mAh/cm3 (theoretical specific capacity of 598.5 mAh/cm3) at a current density of 0.1 C. Also, superior high rate capability with a discharge capacity of 309 mAh/cm3 at 20 C was observed, accompanied by an excellent cycling stability, with a capacity retention ratio exceeding 94% after 500 cycles at 1 C. The co-sputtering using Li2O target is most likely to have enhanced the electrochemical properties of the pure Li4Ti5O12 anode.

Antibacterial nanostructured composite coating on high performance Vectran™ fabric for aerospace structures

Excellent mechanical, thermal and chemical properties make Vectran™ fibres an attractive material to be used in high end applications. Its aerospace applications, as in inflatable light weight habitat module, require functional coating to provide antibacterial protection to ensure safe environment for the astronauts. In this study, woven Vectran™ fabric was coated with an antibacterial silver nanoclusters/silica composite coating by means of radio frequency co-sputtering technique. The successful deposition of the silver nanoclusters embedded in the silica matrix of the composite coating was confirmed by morphological, compositional and structural analysis. The coating sustained 10 washing cycles with partial dissolution of the coating during washing. Silver leaching test verified the gradual and progressive release of ionic silver in aqueous media in the range 0.03 ppm–0.43 ppm within 72 h of immersion in water. Antibacterial properties of the coated Vectran™ fabric were confirmed in inhibition halo test against Staphylococcus aureus and Escherichia coli on as deposited as well as aged samples. An inhibition halo of up to 2 mm was observed for as deposited samples while after UV exposure, the samples formed inhibition halo of 4 mm. The percutaneous absorption test demonstrated a very low release of silver into epidermis and dermis. The effect of the coating on mechanical properties of the as deposited Vectran fabric was assessed through mechanical characterizations including tensile, tear and abrasion test.

Diffusion and reaction kinetics governing surface blistering in radio frequency sputtered hydrogenated a-SixGe1-x (0 ≤ x ≤ 1) thin films

The preparation of blister free layers of hydrogenated a-SixGe1-x (0 ≤ x ≤ 1) is a primary requisite for their technological applications. In RF (Radio Frequency) sputtered layers the formation of blisters is temperature dependent, as also shown here. This dependence is used to propose a theoretical model aimed at a better understanding of the mechanisms determining the blistering. Beside the reaction kinetics responsible for the release of H atoms from SiH and/or GeH complexes the model takes into particular account the contribution of the diffusion of H. The activation energy for blistering also enters in the model. The validation of the theoretical frame of the model is confirmed by the fact that it predicts a blistering threshold temperature in reasonable agreement with the experiment. The amorphous hydrogenated thin layers were deposited on polished silicon by RF co-sputtering. They were annealed between 150 and 350 °C. The structural changes of the surface of the SiGe films have been explored systematically by light beam reflection, scanning electron microscopy while the depth distribution of hydrogen was measured by secondary neutral mass spectrometry.

Effect of heating cycle on cobalt-antimonide-based thin films for high-temperature thermoelectric energy conversion applications

In this study, a comparative analysis of the structural and thermoelectric properties of all possible Co-Sb-based phases in thin-film form for high-temperature applications is presented and discussed. A series of thin-film samples were prepared via radiofrequency co-sputtering on an oxidized silicon substrate. For improved crystallinity, the thin-film samples were subjected to heat treatment in the form of a high-temperature heating cycle where the temperature was slowly ramped up to about 760 K. The films were characterized using X-ray diffraction for phase identification and crystalline quality. Energy-dispersive spectroscopy was performed to determine the stoichiometric composition and homogeneity, whereas the surface morphology and microstructure were examined using scanning electron microscopy and atomic force microscopy. To investigate film performance at high temperatures, the electrical resistivity and Seebeck coefficient were measured at regular temperature intervals, and results were correlated with identified phases, composition, and crystalline quality. The CoSb phase was observed to have metallic features, the CoSb2 phase had doped semiconductor characteristics, whereas the CoSb3-phase thin films showed typical semiconductor behavior. The CoSb2 and CoSb3 samples shows a transition of the Seebeck coefficient from positive to negative at a temperature range of 500–550 K and 550–600 K respectively. The thermoelectric power factor was evaluated from the measured parameters and maximum values of 3.2, 7.8, and 3.8 mWm−1·K−2 for the CoSb, CoSb2, and CoSb3 thin films, respectively, are reported. We observed a wide range of structural and thermoelectric properties in the series of samples, demonstrating a route to tailoring and improving properties for maximal performance.

Crystal phase content-dependent functionality of dual phase SnO2-WO3 nanocomposite films via cosputtering crystal growth.

In this study, crystalline SnO2–WO3 nanocomposite thin films were grown through radio-frequency cosputtering of metallic Sn and ceramic WO3 targets. The W content in the SnO2 matrix was varied from 5.4 at% to 12.3 at% by changing the WO3 sputtering power during thin-film growth. Structural analyses showed that increased WO3 phase content in the nanocomposite films reduced the degree of crystallization of the SnO2 matrix. Moreover, the size of the composite films' surface crystallites increased with WO3 phase content, and the large surface crystallites were composed of numerous nanograins. Addition of WO3 crystals to the SnO2 matrix to form a composite film improved its light harvesting ability. The SnO2–WO3 nanocomposite films exhibited improved photodegradation ability for Rhodamine B dyes compared with their individual constituents (i.e., SnO2 and WO3 thin films), which is attributable to the suitable type II band alignment between the SnO2 and WO3. Moreover, an optimal WO3 phase content (W content: 5.4 at%) in the SnO2 matrix substantially enhanced the ethanol gas-sensing response of the SnO2 thin film. This suggested that the heterojunctions at the SnO2/WO3 interface regions in the nanocomposite film considerably affected its ethanol gas-sensing behavior.