RF Reactive Sputtering Research Articles

Control of spin‐reorientation transition in (0001) oriented α‐Fe2O3 thin film by external magnetic field and temperature

A pure‐phase, unstrained and epitaxial α‐Fe2O3 film of thickness 250 nm has been fabricated by reactive rf sputtering over c‐Al2O3 substrate with nominal average surface roughness of 0.71 nm. Field induced spin‐reorientation temperature (TSR) and temperature dependent spin‐reorientation field (HSR) have been investigated. A linear relationship in the result has been found with ∂TSR/∂HSR equal to −0.92 ± 0.05 K kOe−1 and −0.89 ± 0.175 K kOe−1 by both methods, respectively. The field induced entropy change is argued to be the possible cause for the shift in the spin‐reorientation temperature with applied field. The entropy change associated with the first‐order phase transition is calculated on the basis of Clausius–Clapeyron equation and found to be 0.029 J kg−1 K−1.

Electrical properties of RF-sputtered Zn-doped GaN films and p-Zn-GaN/n-Si hetero junction diode with low leakage current of 10−9 A and a high rectification ratio above 105

Zn-doped GaN films have been deposited on Si (100), SiO2/Si (100), and glass substrates by RF reactive sputtering at 100–400°C with single cermet targets. The Zn-GaN films deposited with a 10% Zn cermet target showed the good electrical properties, wurtzite structure, and the p-type behavior without a thermal annealing process. At room temperature (RT), the 400°C-deposited film with mobility (μ) of 17.7cm2/V·s had the highest hole concentration (np) of 6.1×1017cm−3 and electrical conductivity of 1.72S·cm−1. The values of band gap (Eg) for Zn-GaN films were found in the range of 2.83–3.01eV. Furthermore, to prove the p-type behavior of Zn-doped GaN, the p-GaN/n-Si hetero junction diode was also made by RF reactive sputtering. At room temperature, the device showed the leakage current of 1.65×10−9A at −5V, the turn-on voltage of ∼2.3V, and the breakdown voltage above −20V. The high rectification (on/off) ratio of the diode was calculated to be ∼1.08×105 at bias of ±5V and ∼2.3×105 at the bias of ±20V. The electrical characteristics of the diode were also tested at the temperature range of 25–150°C. By using equations based on the standard thermionic-emission (TE) mode and the Cheungs’ method, the barrier height, ideality factor, and series resistance of the diode were also determined.

Synthesis of Nanoparticles Using Low Temperature Plasmas and Its Application to Solar Cells and Tracers in Living Body

Three applications of nanoparticles synthesized using plasmas has been demonstrated such as third generation solar cells and biotechnology. We produced Si, Ge and In nanoparticles by reactive plasmas, rf sputtering and plasma in water, respectively. We have confirmed multiple exciton generation in cells using Si and Ge nanoparticles. Using In nanoparticles, we have realized high sensitive tracers for understanding nanoparticle kinetics in living body.

Transparent SnOx thin films fabricated by radio frequency reactive sputtering with a SnO/Sn composite target

SnOx thin films are potentially excellent conductive material with large hole mobility and have attracted ever-increasing attention for next generation electronic applications. In this study, SnOx thin films were deposited on a borosilicate glass substrate by radio frequency (rf) reactive sputtering using a SnO/Sn (9:1mol% ratio) composite target. The composite target was used to produce a chemically stable composition of SnOx thin film while controlling structural defects by chemical reaction between tin and oxygen. The effects of oxygen contents and annealing on various properties of SnOx thin films were studied. The structural analysis was carried out using X-ray photoelectron spectroscopy and X-ray diffraction. The electrical and optical analyses were performed by the Van der Pauw Hall effect measurement and UV/VIS spectrometer, respectively. SnOx thin films at PO2=0% (annealed) and 3% (as deposited) exhibited a p-type conductivity of 0.09–0.11Ω−1cm−1, a hole mobility of 0.2–1.2cm2V−1s−1, and a hole concentration of ~1018cm−3. Also, these thin films showed the transmittance of about 70% and an optical bandgap of 2.75–3.01eV.

Thermal stability of oxidized noble metal Schottky contacts to ZnO

Thermally stable oxidized palladium (PdOx, x=1.4) and oxidized iridium (IrOx, x=1.9) Schottky contacts (SCs) that showed strong rectification at 180°C were fabricated on the Zn-polar (0001) face of hydrothermally-grown single crystal ZnO wafers, using reactive rf sputtering and reactive eclipse pulsed laser deposition, respectively. These PdOx and IrOx SCs were highly rectifying with effective barrier heights of 1.25eV and 1.02eV, respectively, more than 12 orders of magnitude of room-temperature current rectification (at biases of ±2.0V), and were almost ‘ideal’ with ideality factors of 1.03 and 1.02, respectively, that were very close to the image-force-controlled limit for laterally homogeneous contacts. The strong rectifying performance of these SCs was maintained at 180°C, with current rectification in excess of 7 and 6 orders of magnitude for the PdOx and IrOx SCs, respectively, indicating their suitability for high temperature applications. Current-voltage characteristics over the temperature range 20–180°C were used to extract Richardson constant values of 39±15 Acm−2K−2 and 9±1 Acm−2K−2 for the PdOx and IrOx SCs, respectively, close to the theoretical value of 32 Acm−2K−2.

Fabrication of amorphous silicon nitride thin films by radio-frequency sputtering assisted by an inductively coupled plasma

We have investigated the preparation of amorphous silicon nitride (a-Si1-xNx:H) thin films by reactive RF sputtering assisted by inductively coupled plasma (ICP) with argon (Ar), hydrogen (H2) and nitrogen (N2). The ICP assist system gives the high density ICP mode plasma near the substrate with relatively low plasma potential and electron temperature by applying >50W to the ICP antenna coil. The E04 band gap is successfully controlled from 2.2eV to 3.3eV by changing the RF power to the antenna coil. The ICP mode plasma significantly enhances the formation of Si-N bonds in a-Si1-xNx:H films, due to the effective generation of N radicals near the substrate. The ICP mode plasma also gives the high deposition rate for wide band gap a-Si1-xNx:H films. A small N2 gas ratio (<1%) is enough to produce wide band gap a-Si1-xNx:H films, therefore, a sufficient Ar gas ratio can be maintained for the Si sputtering. This method gives a simple and effective process to produce wide band gap a-Si1-xNx:H films with a relatively high deposition rate.

Structural, morphological, and optical properties of Bi2O3 thin films grown by reactive sputtering

Bi2O3 thin films were grown using reactive RF sputtering from a metallic Bi target. The influence of various deposition parameters (substrate temperature, applied power on target and oxygen content in the working gas) on the morphology, structure and optical properties of films was investigated. Depending on the O2/(Ar+O2) ratio of the working gas, bismuth, δ-Bi2O3, α-Bi2O3 or a mixture of these phases can be deposited, with a narrow window for growth of [111]-oriented δ-Bi2O3 thin films. The δ-Bi2O3 phase is stable from room temperature up to 350°C (in air), where an irreversible transition to α-Bi2O3 occurs. This phase transformation is also shown to occur during TEM sample preparation, because of the inherent heating from the ion-milling process, unless liquid-nitrogen cooling is used.

Comparative Analysis of SnOx Thin Films Deposited by RF Reactive Sputtering with Different SnO/Sn Target Compositions

A p-type oxide is a key element for transparent thin-film transistor applications. Among the various p-type oxides currently available, SnOx deposited by sputtering is the subject of interest in this study for high-performance and reliable thin films. A tin target or a tin oxide target is typically used to fabricate p-type SnOx during sputtering. A metallic target provides easy control of various film properties and chemical compositions, while a ceramic target offers structural stability and better control of stoichiometry. To use the advantages of both metallic and ceramic targets, a composite target of Sn and SnO was devised, which may provide reliable p-type SnOx and better control of structural defects. We evaluated four different composition ratios of Sn+SnO targets: a 100 mol% metallic Sn target, a composite target with 50 mol% Sn powder + 50 mol% SnO powder, a composite target with 20% Sn powder + 80 mol% SnO powder, and a 100 mol% ceramic SnO target. SnOx films were deposited under various sputtering conditions and analyzed structurally, electrically and optically. The composite target with 20 mol% Sn was found to be a promising candidate for p-type SnOx films, showing >75% transmittance and high mobility up to 9.07 cm2V−1s−1.

Electrical and structural characteristics of tin-doped GaN thin films and its hetero-junction diode made all by RF reactive sputtering

Tin (Sn) doping in gallium nitride (GaN) has been mainly reported from the theoretical view only. Based upon the availability of Sn precursor and commercialization, Sn-GaN film has not been deposited magnetron sputtering until this work. By using the cheap and safe reactive sputtering technique, here we present Sn-GaN thin films with single cermet targets at the Sn/(Sn+Ga) molar ratios of x=0, 0.03, 0.07, and 0.1 to form Sn-x-GaN films under the atmosphere of the mixture of Ar and N2. The Sn-GaN films had the wurtzite structure. Sn can be added to GaN to form SnGaN alloy with a maximal amount of ~10%. The structural, electrical, and optical properties had changed with the Sn content until the oversaturation of Sn in Sn-0.1-GaN. The Sn doping led to the lattice expansion, worsened crystallinity, n-type GaN, increased electrical concentration, decreased the electrical mobility etc. Moreover, n-Sn-x-GaN/p-Si diodes were successfully made and their performance was evaluated in terms of the barrier height, ideality factor, and series resistance. This work has opened the door for studying the different kinds of dopants on the important III nitrides.

Metal-based bacterial cellulose of sandwich nanomaterials for anti-oxidation electromagnetic interference shielding

In this work, bacterial cellulose was successively functionalized by magnetron sputtering and RF reactive sputtering with copper (Cu) and Al2O3 to endow it with unique anti-oxidation electromagnetic shielding properties while concomitantly improving hydrophobic, mechanical, and thermal properties. The surface topographies and chemical properties of BC/Cu/Al2O3 nanocomposites were examined by different analysis instruments to conclusively testify that metal-based nanoparticles were evenly deposited on the surfaces. This sandwich structure of the nanocomposites enhanced their thermal stability, hydrophobicity, mechanical properties, and electromagnetic interference (EMI) shielding effectiveness (SE). EMI effects of these nanocomposites were also investigated by the four-point probe, uniaxial testing machine and a vector network analyzer (VNA). The results indicated that the sandwich nanoscale materials showed good mechanical properties (41.3Mpa) and excellent EMI shielding (65.3dB).

Optical and electrical properties of synthesized reactive rf sputter deposited boron-rich and boron-doped diamond-like carbon thin films

Boron-doped diamond-like carbon (B-DLC) and boron-rich DLC thin films have been deposited on n-type silicon and quartz substrates by reactive rf magnetron sputtering process. Boron carbide (B4C) target was used in the deposition. Reducing the boron/carbon ratio was achieved by either using hydrogen gas or by introducing a proper flow rate of methane. Another approach of producing B-DLC thin films was achieved by using low methane\argon ratio (5/40) while sputtering atoms from non-saturated target-surface under various sputtering rf powers. The maximum film graphitization and lowest band gap energy was achieved by applying 100 W power. The Auger electron spectroscopy and Raman shifts were used to investigate the composition of the films. The optical properties were investigated using spectroscopic ellipsometry and spectrophotometer. Furthermore, p-type B-DLC/n-type Si(100) heterojunction diode was fabricated and the I–V characteristics were investigated against the flow rates of methane or the rf power.

Investigation of structural and electrical properties of Zirconium dioxide thin films deposited by reactive RF sputtering technique

ABSTRACTZrO2 thin films with different thicknesses (400 nm, 500 nm, 600 nm) were deposited by reactive RF magnetron sputtering technique, on n-type Silicon (100) substrate at 200°C applying 125 W power ratin`g. The micro structural properties of thin films were obtained by Scanning Electron Microscope and it was observed that the films were grown successfully in the form of big grains formed by the accumulation of small particles. It was seen that the size of grains changed with the increase of film thickness. Energy-dispersive X-Ray spectroscopy was used to determine the chemical compositions of samples. The crystal structures of ZrO2 samples were analyzed by X-ray diffraction technique. In addition, the Current-Voltage and Capacitance-Voltage measurements were completed to investigate the electrical properties of samples.

Hydrogen Permeability of TiN x Membrane Based on Bulk Mixed Hydride Ion and Electron Conductivity

Hydrogen is an ideal fuel resource, because it can be generated by water electrolysis by using renewable electricity from solar, window and water power generation. Hydrogen permeable metals such as Pd and group V meals (V, Nb, Ta) are promising as a hydrogen membrane to separate pure hydrogen from other process gases. Pd is most famous hydrogen membrane material, but it’s fiercely expensive and the resource is limited. Group V metals reveal excellent permeability, but they are ductile due to the fierce hydrogen embrittlement. Therefore, it is the motivation to develop the Pd-free hydrogen membranes which can work without hydrogen embrittlement. Recently, mixed proton and electron conductor (MPEC) oxides have attracted as new materials to use as hydrogen permeation membrane, and they have found applications in energy devices such as fuel cells and batteries. On the other hand, the conduction of hydride ions, H–, is also attractive. Recently, Verbraeken et al. reported barium hydride BaH2 exhibits fast H- ion conduction. Charge density on hydride ion is 105 times smaller than protons due to the difference of ionic radii so that bipolar diffusion of H- could be easier than H+. Unfortunately, the materials to show both hydride ion and electronic conduction are not reported. In this work, we demonstrate the highly-nonstoichiometric TiN x membrane reveal efficient hydrogen permeability because of mixed H- ion electron conduction. Highly-nonstoichiometric TiN x membranes (x = 0.71-1.02) were fabricated on a porous alumina support by RF reactive sputtering. The deposition was performed at the ubstrate temperatures of 500 oC by using Ti target (purity: 99.9%) under various nitrogen partial pressures. The morphologies and compositions of the membranes were analyzed by XRD, WDX and TEM. The hydrogen gas permeability was examined in the temperature range of 25 to 500 oC by using a homemade gas permeation test system equipped with a gas chromatography. Highly-nonstoichiometric TiN x films (x = 0.71 -1.02) were successfully fabricated by reactive RF sputtering processes by adjusting the nitrogen partial pressure. From TEM image, densely-packed TiN x films with 600 nm thickness are uniformly formed over a wide area of the porous alumina support and apparent cracks and pinholes were not formed. TiN x membranes clearly revealed the selective permeation of hydrogen. Hydrogen fluxes of the membrane exhibit Arrhenius-type temperature dependence and these are at least two orders of magnitude higher than the nitrogen fluxes due to the leakage from gas sealing. Highly-N deficient TiN0.71 show larger hydrogen flux than TiN0.95. This result discloses that N-vacancy sites make an important role for hydrogen transport in TiN x . In situ FT-IR spectra of TiN0.71 membranes exposed to hydrogen and deuterium atmosphere were measured in order to clarify the mobile hydrogen species. In H2 atmosphere, O-H, Ti-N and Ti-H stretching mode appeared. As switched from H2 to D2 atmosphere at 500°C a new sharp peak spontaneously develops at around 1200 cm-1, which is attributed to Ti-D stretching mode. These strongly suggest that H atoms bound to Ti atoms are diffusive in TiN x films so as to enable exchanging Ti-H bonding by Ti-D bonding while the H bound to oxygen are not mobile. Accordingly, it is concluded that the hydrogen permeability of TiN x film was caused by bulk conduction of mixed hydride ion and electron.

Anisotropy and interaction effects of strongly strained SrIrO3 thin films

Magneto-transport properties of SrIrO3 thin films epitaxially grown on SrTiO3, using reactive RF sputtering, are investigated. A large anisotropy between the in-plane and the out-of-plane resistivities is found, as well as a signature of the substrate cubic to tetragonal transition. Both observations result from the structural distortion associated to the epitaxial strain. The low-temperature and field dependences of the Hall number are interpreted as due to the contribution of Coulomb interactions to weak localization, evidencing the strong correlations in this material. The introduction of a contribution from magnetic scatters, in the analysis of magnetoconductance in the weakly localized regime, is proposed as an alternative to an anomalously large temperature dependence of the Landé coefficient.

Highly Stable Zinc Oxynitride Thin-Film Transistors with Field-Effect Mobility Exceeding 100 cm2/Vs

A recent work on a relatively new type of semiconductor, namely zinc oxynitride (ZnON) as a promising candidate for the next-generation display applications, will be presented.(1) High mobility ZnON thin films were deposited by RF sputtering. In order to enhance the mobility and stability of ZnON TFTs, thickness and annealing conditions of ZnON thin films were optimized. Using ZnON films grown using the optimum conditions, the fabrication of high performance devices with field effect mobility exceeding 120 cm2/Vs is demonstrated, based on simple reactive RF sputtering methods.

Development of Piezoelectric Dynamic Deformation Transducers Based on Hot Polarization of Lead Zirconate-Titanate Ferroelectric Films

A technique of hot periodic sawtooth polarization of lead zirconate-titanate ferroelectric thin films is described. The films are deposited by reactive RF sputtering on a metal foil. Work on the development of oscillator-type piezoelectric dynamic deformation sensors is discussed.

Effects of oxygen partial pressure and annealing temperature on the residual stress of hafnium oxide thin-films on silicon using synchrotron-based grazing incidence X-ray diffraction

Synchrotron radiation-based grazing incidence X-ray diffraction (GI-XRD) technique is employed here to estimate the residual stress of < 10nm thin hafnium oxide film deposited on Si (100) substrate at different argon/oxygen ratios using reactive rf sputtering. A decrease in residual stress, tensile in nature, is observed at higher annealing temperature for the samples deposited with increasing argon ratio in the Ar/O2 plasma. The residual stress of the films deposited at higher pAr (Ar:O2=4:1) is also found to be decreased with increasing annealing temperature. But the stress is more or less constant with annealing temperature for the films deposited at lower Ar/O2 (1:4) ratio. All the above phenomena can be explained on the basis of swelling of the interfacial layer and enhanced structural relaxation in the presence of excess Hf in hafnium oxide film during deposition.

V2O5 thin films for gas sensor applications

V2O5 thin films were deposited onto fused silica, alumina and conductometric sensor supports by means of rf reactive sputtering from a metallic vanadium target. Film thickness was varied between 200 and 600nm. Argon-oxygen gas mixtures of different compositions controlled by the flow rate were used for sputtering. Temperature of the film substrate was kept constant at 560K. Structural properties and phase composition of as-sputtered thin films were studied by X-ray diffraction at glancing incidence, GIXD, and Raman scattering while Scanning Electronic Microscopy (SEM) was used to investigate film morphology. Electrical properties were determined by means of impedance spectroscopy (0.1–1MHz) over the temperatures range extending from RT to 620K. Thin films of V2O5 exhibited good response towards hydrogen (5–300ppm), methane and propane (50–3000ppm).

A study on the electron transport properties of ZnON semiconductors with respect to the relative anion content.

High-mobility zinc oxynitride (ZnON) semiconductors were grown by RF sputtering using a Zn metal target in a plasma mixture of Ar, N2, and O2 gas. The RF power and the O2 to N2 gas flow rates were systematically adjusted to prepare a set of ZnON films with different relative anion contents. The carrier density was found to be greatly affected by the anion composition, while the electron mobility is determined by a fairly complex mechanism. First-principles calculations indicate that excess vacant nitrogen sites (VN) in N-rich ZnON disrupt the local electron conduction paths, which may be restored by having oxygen anions inserted therein. The latter are anticipated to enhance the electron mobility, and the exact process parameters that induce such a phenomenon can only be found experimentally. Contour plots of the Hall mobility and carrier density with respect to the RF power and O2 to N2 gas flow rate ratio indicate the existence of an optimum region where maximum electron mobility is obtained. Using ZnON films grown under the optimum conditions, the fabrication of high-performance devices with field-effect mobility values exceeding 120 cm2/Vs is demonstrated based on simple reactive RF sputtering methods.

Application of sputtered TiO2 thin films as HRT buffer layer for high efficiency CdS/CdTe solar cells

In this work titanium dioxide (TiO2) thin films were developed for application as high resistance transparent (HRT) buffer layer (BL) in high efficiency CdS/CdTe solar cells. The TiO2 HRT-BLs where deposited by the reactive RF-Sputtering technique. The solar cells had the superstrate configuration and the CdTe absorber was deposited by conventional Close Space Sublimation (CSS). Solar cells with optimized TiO2 HRT-BL had improved photoresponse in the blue wavelength region. A 15nm TiO2 film avoids migration of chemical species from the ITO front contact toward the CdS/CdTe photovoltaic heterojunction. Solar cells with the TiO2 HRT-BL have improved temperature coefficient of efficiency. A photoconversion efficiency of 12.0% was obtained by employing a 15nm TiO2 HRT-BL.