Rf Sputter Deposition Research Articles

Low-stress diamond-like carbon films containing carbon nanoparticles fabricated by combining rf sputtering and plasma chemical vapor deposition

Carbon nanoparticles (CNPs) incorporated diamond-like carbon (DLC) films have been fabricated by a combination of rf sputtering and plasma chemical vapor deposition. Spherical CNPs with a mean size of 21.2 nm are sandwiched between DLC layers with a mass density of 1.7 g cm−3. The film stress is decreased to 119 MPa, by depositing the CNPs over the base DLC layer at a surface coverage of 10.7%. This reduction is approximately half of that without CNPs. Raman spectroscopy indicates the insertion of CNPs barely alters the bonding structure of the upper DLC layer.

In situ X-ray measurements over large Q-space to study the evolution of oxide thin films prepared by RF sputter deposition

Sputter deposition is a versatile and industrially important deposition technique for thin films, with increasing demand for matching the characteristics of thin film materials to specific requirements. The actual film properties are largely determined by sputtering parameters such as pressure conditions, temperature and power settings. By means of various X-ray diffraction and scattering techniques, it is shown that the characterization of film formation and growth is feasible in real time at synchrotron sources, thus adding an important dimension to the fundamental understanding of the evolution of thin film microstructure. In particular, grazing incidence small-angle X-ray scattering, grazing incidence X-ray powder diffraction and X-ray reflectometry are used in a complementary manner to study the influence of deposition temperature and substrate choice on the crystallization kinetics and growth of polycrystalline BaTiO $$_3$$ films.

Study of humidity sensing properties and ion beam induced modifications in SnO2-TiO2 nanocomposite thin films

Swift heavy ion beam induced dense electronic excitation in the nanocomposite thin film is a unique way to introduce various modifications such as track formation, atomic transport and phase transformation. Therefore, this work based on the modification in the properties of Titanium dioxide and Tin oxide nanocomposite thin films prepared by RF sputtering deposition technique in the mol% 50:50 on ITO coated glass and silicon substrates. The prepared nanocomposite thin films annealed at 500 °C and irradiated with SHI of 150 MeV Fe11+ ion beam with varied ion fluences ranging from 5 × 1012to 5 × 1013 ions.cm−2. The SRIM simulation was confirmed the electronic energy loss (Se) as 1.038 × 102 eV/nm, nuclear energy loss (Sn) as 1.33 × 10−1 eV/nm and the projectile depth of the iron ion inside the thin films was founded to be 17.18 um. Structural analyses of pristine and irradiated thin films were analyzed by X-ray diffraction technique. Changes observed in the peak intensity were confirmed by the significant variations in crystallite size, which was calculated by the Debye Scherrer equation. The crystallite size of all samples was found to be improved from 59 nm to 141 nm. The influence of ion irradiation on surface topography of nanocomposite thin films was analyzed by Atomic Force Microscopy (AFM). The sectional analysis of AFM images reveals that the grain size depends on the ion irradiation fluences. The grain size was increased from 52 nm to 129 nm. The optical properties were studied using UV–Visible spectroscopy and Photoluminescence (PL) spectroscopy. Tauc's method was used to calculate the optical energy band gap of the samples. The direct band gap was decreased as ion fluence increases may be due to creation of metastable energy states in between the valance and conduction band. The recombination and separation of photo generated charge carriers were studied by the photoluminescence spectroscopy. Rutherford Backscattering Spectrometry (RBS) was performed on all samples to ensure depth profiling, elemental composition and absence of impurities in titanium dioxide and tin oxide nanocomposite thin films. The response time, recovery time, repeatability and ageing effect after (one, two and three) weeks of nanocomposite thin films were obtained during humidity sensing measurements.

Low-Current-Density Magnetic Tunnel Junctions for STT-RAM Application Using MgO$_{{x}}$ N$_{\text{1}-{x}}\,\,({x}=\text{0.57}$ ) Tunnel Barrier

High switching speed, endurance, and low-current-based perpendicular magnetic tunnel junction (p-MTJ) memory is attracting wide interest as a key promising candidate for next-generation spintronic memory technology. p-MTJ-based spin-transfer torque RAM (STT-RAM) has been extensively investigated, and despite the promise, there is concern about the high switching current density and low stability with regard to scaling. In this work, the current controllability of p-MTJ in iron (Fe)-enriched Co20Fe60B20 with a newly designed MgO x N1– x tunnel layer is systematically investigated, with the expectation that the introduction of N minimizes the oxidation of Fe to improve the performance of the device. A facile, plasma-based oxynitridation (MgO x = 0.57N1– x =0.43) of MgO through RF-sputter deposition serves as a reliable procedure to establish a tunnel barrier for an MTJ structure fabricated with ~300-nm diameter and pinned with synthetic antiferromagnetic (SAF) [Co/Pt] ${_{n}}$ multilayer stack. Current-controlled tunneling magnetoresistance (TMR) up to ~65% was observed at room temperature (RT) with ultralow switching current density ( ${J}_{c}$ ) of 136 ± 17 kA/cm2. TMR along with tunnel conductance ( ${g}$ ( ${V}$ )) was measured to be highly stable in the read-bias regime (−200 to +200 mV) for MgO x N1– x as compared to the reported MgO barrier. The analogous MgO x N1– x -based MTJ structures were modeled using the nonequilibrium Green’s function (NEGF) with appropriate tunnel barrier parameters and incorporating modulated barrier height as compared with the MgO barrier. The current–voltage characteristics of the modeled device showed close agreement with experimental data indicating high spin current. Based on the field-induced magnetization analysis, the macro-magnetic reversal analysis suggests the free-layer switching duration of ~3 ns. These observations show the strong candidature of MgO x N1– x ( ${x} = {0.57}$ ) MTJs for STT-RAM device application.

Fabrication and characterization of nitrogen selective thin-film metallic glass/polyacrylonitrile composite membrane for gas separation

Zr-based (Zr55Cu29Al11Ni5.0) thin-film metallic glass (TFMG) is a new material for gas separation membrane. In this study, we fabricated Zr-based TFMG/polyacrylonitrile (PAN) composite membranes via RF sputtering deposition. The surface morphology, crystallinity, and thermal stability of uncoated and TFMG-coated membranes were then characterized. Variable monoenergy slow positron beam analysis revealed a strong correlation between the pore size and thickness of the TFMG active layers. The resulting membranes were more permeable to N2 than to CO2 or O2 due to weaker interactions with the pore walls and faster diffusion. The best N2 performance was 4288 GPU with ideal selectivity of 1.81 for N2/O2 and 1.95 for N2/CO2. Overall, we demonstrated the considerable potential of TFMG/PAN composite as a membrane for nitrogen selective applications.

Annealing effect on phase transition and thermochromic properties of VO2 thin films

Abstract Vanadium dioxide (VO2) is one kind of desired thermochromic material for many smart devices because of its notable temperature-responsive infrared modulation and metal−insulator transition with underlying structural phase transition (SPT). Understanding on the tuning of these properties in an anticipated manner is essential to accomplish device realization. Here, we report the annealing time induced modifications in SPT and the thermochromic properties of VO2 thin films. Using RF sputtering deposition, VO2 thin films were grown at room temperature and their ex-situ annealing was carried out at 600 °C for different time from 2 min to 60 min. Structural, electronic and thermochromic properties of these films were investigated. VO2 thin films samples annealed for longer time exhibit larger crystallite size, higher surface roughness and SPT temperature, and the reduced hysteresis width of SPT during heating and cooling cycle. X-ray absorption spectroscopy results indicate that the variation in the annealing time do not alter the electronic structure significantly. Nevertheless, VO2 thin film samples with prolonged annealing display higher IR transmittance modulation across the SPT.

Phase transformation by the irradiation with swift heavy ions on vanadium oxide thin films

ABSTRACTIn this work, the thin films of vanadium oxide on Si substrate were deposited by RF sputtering and pulsed laser deposition method. The as-deposited samples were annealed in argon atmosphere at 500°C for 1 h and cooled at natural rate in argon atmosphere. The as-deposited and annealed samples were irradiated with 100 MeV Ag ions at different fluences. Structural characterizations were done by grazing incidence X-ray diffraction (GIXRD) and Raman spectroscopy at room temperature. GIXRD and Raman spectra revealed that phase transformation took place after swift heavy ions irradiation and the ratio of oxygen/vanadium concentration of the films decreased. The phase transformation and change in concentration may be due to transiently molten cylindrical zone created by the passage of swift heavy ions in the material.

Low energy Kr5+ ion beam engineering in the optical, structural, surface morphological and electrical properties of RF sputtered TiO2 thin films

Titanium dioxide (TiO2) thin films were grown on Silicon and glass substrates at room temperature by RF sputtering deposition technique. All deposited thin films were irradiated by 800 keV Kr5+ low energy ion beam with varying ion fluence from 1E15 ions/cm2 to 1E17 ions/cm2. The decreases in crystallite size from 42.09 nm to 27.36 nm (by Scherrer's formula) with increased in ion fluence were observedusing X-ray Diffraction (XRD) technique. The orientation of the different planes was observed but the plane (112) confirmed the preferred orientation as determined by the texture coefficient using XRD patterns. The surface morphology of the samples was studied by Atomic Force Microscopy (AFM) technique in the tapping mode and the Root Mean Square (RMS) roughness (Rq) was found to be increased from 0.739 nm to 3.20 nm with increases the ion fluence. The energy bandgap was found to be increased from 4.06 eV to 4.30 eV by increased in ion fluence due to electron confinement at nano-scale and also observed Urbach energy and optical conductivity by UV–Visible spectroscopy. The Urbach energy of thin films was observed to increased with increasing the ion fluence. The photoluminescence (PL) spectra confirmed the enhancement in the recombination of electron hole pair with increases the oxygen vacancies by increases the ion fluence. The peak at 382 nm was observed at higher fluence of 7E15 ions/cm2, 3E16 ions/cm2 and 1E17 ions/cm2. In the Raman studies, all six Raman modes at their positions for anatase phase of TiO2 thin films were successfully observed. The thickness of thin films was observed 268 nm and elemental composition of titanium and oxygen in all thin films were confirmed in the ratio of 1:2 by using Rutherford Backscattering Spectrometry (RBS). The electrical properties were studied by measuring the variation of current (I) with respect to the applied potential (V) at room temperature and the conductivity of the irradiated thin films was decreased with increases of ion fluence.

Band-alignment dominated retention behaviors in high-k composite charge-trapping memory devices

A nonvolatile memory structure with a high-k composite of ZnO-TiO2 as a charge-trapping dielectric was fabricated by using rf-sputtering and atomic layer deposition techniques, in which the potential of the conduction-band minimum of the composite was designed to be lower than that of Si by the use of the special energy-band offsets among Si, ZnO, and TiO2. Compared to the conduction-band minimum of Si, a relatively negative potential of the high-k composite leads to a continuous rise in the shift of the flat-band potential of the memory device except a drop at the beginning part of the time-dependent retention curve after a programming operation. The drop was attributed to the escape of trapped charges at the Si/Al2O3 interface. After extracting the contribution to the deterioration of the retention curve from the traps at the Si/Al2O3 interface, it was identified that the band alignment in a charge-trapping memory device dominated its retention behaviors.

Sputter deposited GeSn alloy: A candidate material for temperature sensing layers in uncooled microbolometers

In this paper, we study the resistance versus temperature characteristics of Ge1-xSnx thin film alloys to assess the possibility of using them for temperature sensing layers in microbolometers. Ge1-xSnx thin films, with 200 nm thicknesses, are deposited at room temperature using simultaneous RF and DC sputter deposition from Ge and Sn targets. Accordingly, Ge1-xSnx thin films with different Sn concentrations were prepared. Atmoic force microspcopy (AFM) analysis is performed showing rms surface roughnesses less than 0.56 nm for all the prepared Ge1-xSnx thin films. Sheet resistance versus temperature measurements are made revealing temperature coefficients of resistances (TCRs) of −3.96, −3.63 and −3.29%/K at resistivity values of 164.6, 69.14, and 45.46 Ω∙cm for Sn concentrations of 17%, 22% and 25% respectively. This study shows that the Ge1-xSnx material can be considered as a potential candidate towards high performance low cost uncooled microbolometers.

Influence of 120 MeV S9+ ion irradiation on structural, optical and morphological properties of zirconium oxide thin films deposited by RF sputtering

The calibrated and controlled swift heavy ions (SHI) beam irradiation generate defects which can cause modifications in various properties of the materials such as structural, optical, magnetic, morphological, and chemical etc. The passage of ion through the target material causes the nuclear energy losses (Sn) and electronic energy losses (Se). The Se dominates over Sn in SHI irradiation. In the present study, ZrO2 thin films were grown on silicon and glass substrate by using RF sputtering deposition technique. For the purpose of modifications induced by swift heavy ions, these films were irradiated by a 120 MeV S9+ ion beam of 1 pnA current, with varying ion fluences from 5E12 to 1E13 ions/cm2, using the tandem accelerator at the Inter University Accelerator Center (IUAC), New Delhi, India. The X-ray diffraction (XRD) patterns confirmed the formation of monoclinic and tetragonal phases and it was observed that XRD peaks intensity increased up to the fluence of 5E12 ions/cm2 followed by opposite behavior at higher fluences. Atomic force microscope (AFM) study revealed the increased surface roughness after SHI irradiation. In addition to it, the formation of electronic transition states in optical band gap region and enhancement of absorption edge was observed from UV-visible spectroscopy (UV-Vis) results due to which direct band gap energy value decreased from those of un-irradiated samples. Photoluminescence (PL) broad emission spectra were determined using the excitation wavelength at 290 nm with the prominent peak at 415 nm which can be ascribed to Zr vacancies due to band edge emission as a result of free-exciton recombination. Rutherford backscattering spectrometry (RBS) technique was used for depth profiling and elemental composition in zirconia thin films. The expected role of electronic energy loss during ion irradiation is to modify the properties of the material has been discussed.

Deposition Pressure Dependent Electric Properties of (Hf, Zr)O2 Thin Films Made by RF Sputtering Deposition Method

To study the applications for ferroelectric non-volatile memory and ferroelectric memristor, etc., deposition pressure dependent electric the properties of (Hf, Zr)O2 thin films by RF sputtering deposition method were investigated. The bottom electrode was TiN thin film to produce stress effect on the formation of orthorhombic phase and top electrode was Pt thin film by DC sputtering deposition. Deposition pressure was varied along with the same other deposition conditions, for example, sputtering power, target to substrate distance, post-annealing temperature, annealing gas, annealing time, etc. The structural and electric properties of the above thin films were investigated. As a result, it is confirmed that the electric properties of the (Hf, Zr)O2 thin films depend on the deposition pressure which affects structural properties of the thin films, such as, structural phase, ratio of the constituents, etc.

A brief overview of RF sputtering deposition of boron carbon nitride (BCN) thin films

A great part of interest has been paid for fabricating new materials with novel mechanical, optical, and electrical properties. Boron carbon nitride (BCN) ternary system was applied for variable bandgap semiconductors and systems with extreme hardness. The purpose of this literature review is to provide a brief historical overview of B4C and BN, to review recent research trends in the BCN synthesizes, and to summarize the fabrication of BCN thin films by plasma sputtering technique from B4C and BN targets in different gas atmospheres. Pre-set criteria are used to discuss the processing parameters affecting BCN performance which includes the gasses flow ratio and effect of temperature. Moreover, many characterization studies such as mechanical, etching, optical, photoluminescence, XPS, and corrosion studies of the RF sputtered BCN thin films are also covered. We further mentioned the application of BCN thin films to enhance the electrical properties of metal-insulator-metal (MIM) devices according to a previous report of Prakash et al. (Opt. Lett. 41, 4249, 2016).

Construction of self-assembled vertical nanoflakes on CZTSSe thin films

Cu2ZnSn(S, Se)4 (CZTSSe) is a promising alternative absorber material to achieve high power conversion efficiencies, besides its property of involving low-cost and earth-abundant elements when compared to Cu(In, Ga)Se2 (CIGS) and cadmium telluride (CdTe), to be used in solar cell technology. In this study, a novel fabrication technique was developed by utilizing RF sputtering deposition of CZTSSe thin films having a surface decorated with self-assembled nanoflakes. The formation of nanoflakes was investigated by detailed spectroscopic method of analysis in the effect of each stacked layer deposition in an optimized sequence and the size of nanoflakes by an accurate control of sputtering process including film thickness. Moreover, the effects of substrate temperature on the formation of nanoflakes on the film surface were discussed at a fixed deposition route. One of the main advantages arising from the film surface with self-assembled nanoflakes is the efficient light trapping which decreases the surface reflectance. As a result of the detailed production and characterization studies, it was observed that there was a possibility of repeatable and controllable fabrication sequence for the preparation of CZTSSe thin films with self-textured surfaces yielding low surface reflectance.

In-situ XPS Study of Core-levels of ZnO Thin Films at the Interface with Graphene/Cu

We have investigated core-levels of ZnO thin films at the interface with the graphene on Cu foil using in-situ X-ray Photoelectron Spectroscopy (XPS). Spectral evolution of C 1s, Zn 2p, and O 1s are observed in real time during RF sputtering deposition. We found binding energy (BE) shifts of Zn 2p and ‘Zn−O’ state of O 1s depending on ZnO film thickness. Core-levels BE shifts of ZnO will be discussed on the basis of electron transfer at the interface and it may have an important role in the electronic transport property of the ZnO/graphene-based electronic device.

Improvement in crystallinity of ZnO and Zn2SiO4 phases by rf sputter deposition; effect of substrate bias

We report on enhancement in crystallinity of wurtzite ZnO and rhombohedral Zn2SiO4 phase using rf sputtering deposition with substrate bias. Substrates were kept at floating potential and subjected to a bias upto −60 V for shallow implantation of Zn and O ions in SiO on Si and local energy deposition. Crystalline Zn2SiO4 phase improved upto −20 V applied bias above which it deteriorated. Wurtzite ZnO phase formed on rhombohedral Zn2SiO4 phase and showed opposite trend and a decrease in strain. The improvement in crystallinity of ZnO phase resulted in decrease in defects identified from a decrease of visible light absorption and dark current. The mechanisms identified to be responsible for the improvement in ZnO phase and formation of zinc silicate phase is transfer of energy through elastic collisions from the plasma species to the deposited atoms on the growing film and shallow implantation of Zn and O ions into SiO/Si.

Effect of low energy (keV) ion irradiation on structural, optical and morphological properties of SnO2–TiO2 nanocomposite thin films

RF Sputtering deposition technique was used to deposit the thin films of nanocomposite oxides as SnO2–TiO2 on Si and ITO coated glass substrate. As a target, SnO2–TiO2 was taken according to their molecular weight percent ratio of 3:1. Material modification has been induced by low energy ion beam with varying ion fluence from 5E13 to 5E16 ions/cm2. Glancing Angle X-ray Diffraction technique was used to study crystallite size, phase transformation and stability of different planes of pristine and irradiated thin films. The important peaks observed in XRD pattern were at angles 26.95°, 34.27°, 37.60°, 50.88° and 52.46°. The grain size distribution and surface morphology were studied by Atomic Force Microscopy technique in tapping mode. The results show that the grain size varies with ion fluence. Raman analysis revealed that the sharp peak at the frequency of 520 cm−1 ascribed to the T2g mode was observed for the pristine and lowest fluence irradiated film deposited on Si substrate. With increasing ion fluence, an opposite trend in SnO2 B2g peak was observed at nearly 775 cm−1 and the also peak bump was observed as a function of ion beam fluence. The optical band gap decreases from 3.90 to 3.63 eV due to the generation of ions and free radicals in valance band by varying ion fluence which was observed by UV/Visible Spectroscopy. The film thickness was determined to be 220 nm using Rutherford Backscattering Spectrometry. It also confirmed the absence of any impurities in the pristine and irradiated thin films. The material properties were mainly modified by the point defects and grain size growth arising due to nuclear energy loss.

Electrical properties of ZnO:H films fabricated by RF sputtering deposition and fabrication of p-NiO/n-ZnO heterojunction devices

A high-transparency ZnO thin film of high carrier concentration was grown by conventional RF sputtering, where the carrier concentration was continuously varied from 1016 to 1019 cm−3 by controlling the amounts of O2 and H2 sputtering gases. To prevent the formation of a Schottky junction at the contact with In–Zn–O, and to improve the fill factor of a visible-light-transparent solar cell, a Ag-paste/NiO/ZnO/ZnO:H/IZO p–n diode structure with the carrier concentration of the ZnO:H layer of 1019 cm−3 was fabricated. It is possible to reduce the depletion width and inverse the rectification action around ZnO/IZO by controlling the carrier concentration of the ZnO layer while maintaining the high transparency.

Investigation of electrochemical properties of bio-inspired SiOx/PI multilayered thin film anode for lithium ion batteries

The organic-inorganic multilayer thin film composed of SiOx (nonstoichiometric silicon suboxides) and PI (polyimide) has been synthesized by a hybrid sputtering system combining reactive RF sputtering and pulsed laser deposition. SiOx/PI thin films were deposited on a copper foil to investigate its electrochemical properties. The chemical composition of as-deposited SiOx/PI coatings was measured by a FE-EPMA. The overall multilayered structure was observed by a Scanning Electron Microscopy. The SiOx/PI multilayer thin film anode with proper architecture control exhibits higher columbic efficiency during 1st charge/discharge cycle and better capacity retention as compared to pure SiOx thin film anode. The fracture toughness of SiOx/PI multilayer thin film anode is measured via nanoindentation and be compared to the pure SiOx thin film anode. The results show that the multilayer structure reveals a higher fracture toughness, which leads to a better structure stability during the charge/discharge cycling.

(Invited) Fabrication and Characterization of β-Ga2O3 Heterojunction Rectifiers

Copper Oxide and Nickel Oxide were deposited and investigated for their electrical and optical properties as a wide bandgap p-type oxide semiconductor. Heterojunctions of CuxOy/β-Ga2O3 were fabricated with a rectification ratio of 2.5x104 at ±2 V. NiO films were deposited using both RF sputtering and atomic layer deposition methods, resulting in rectifying heterojunctions in both cases. A 3.6 eV bandgap was measured upon a 500 °C post-deposition anneal for the sputtered films.