Reactive RF Magnetron Sputtering Research Articles

Frequency dependence of wake-up and fatigue characteristics in ferroelectric Al0.93B0.07N thin films

B-doped AlN ferroelectric thin films are promising candidates for non-volatile memory device applications, due to their relatively low deposition temperatures, large remanent polarizations (up to 120 μC/cm2), and outstanding polarization retention properties. In this research, the polarization switching fatigue characteristics in epitaxial B-doped AlN thin films were investigated. Films were deposited via reactive RF magnetron sputtering onto W-coated c-plane sapphire substrates. Polarization switching fatigue measurements were conducted with triangular waveforms for frequencies between 50 and 1000 Hz from room temperature to 200°C. On repeated cycling, the films undergo wake-up; the wake-up process was characterized by an activation energy of 0.15 ± 0.05 eV. After a period of normal switching, the film leakage current increased with additional cycling, and finally the films underwent dielectric breakdown. Unpatterned Al0.93B0.07N films with 100 nm thick Pt top electrodes survived ∼104 bipolar cycles, whereas films with 1000 nm W top electrodes survived ∼105 cycles before dielectric breakdown. Modeling was used to design a field plate, which improved the performance to ∼106 fatigue cycles. It was found that dielectric failure during fatigue was not due to surface flashover but was associated with hard breakdown events in the dielectric. Failure for 100 Hz cycling was not associated with device self-heating but was exacerbated by field concentrations; at higher frequencies, the instantaneous temperature rise during the switching becomes prominent. Based on the fatigue process under 100 Hz under various ambient temperatures, the activation energy of the polarization switching fatigue of B-doped AlN thin films was found to be Ea = 0.10 ± 0.03 eV.

Effect of parametric variation on the surface composition, structure, and tribological properties of zirconium nitride/oxynitride thin films

This paper evaluates the effect of parametric variation on the structure, surface composition and tribological properties of reactive RF-magnetron sputter deposited ZrN/ Zr2ON2 thin films. The properties of the films were investigated with respect to Ar: N2 flow rate, and power coupled to the plasma. X-ray photoelectron spectroscopy (XPS) revealed the presence of both the Zr2ON2 and ZrO2 stoichiometric components on the surface. Also, coupled power beyond 100 W promotes the formation of Zr2ON2 on the film surface. That’s why samples having thickness as low as 101–106 nm exhibit lower COF values 0.42–0.46 owing to the dominant presence of lubricating ZrO2 phase in the surface layer. Grazing angle X-ray (GIXRD) diffractogram exhibit that in the bulk, c-ZrN (311) and c-Zr2ON2 (440) phases are dominant. With increased power beyond 100 W, the (222) orientation of the Zr2ON2 phase also becomes significant, owing to enhanced reaction rate between the sputtered Zr and reactive gas atoms. Tribological studies show that the sample with the lowest surface roughness (S5) (∼114 nm) has the highest specific wear rate (∼1.26 ×10−3 mm3/ Nm). Colour of the films changed with applied power from grey at 50 W, to brownish yellow at 100 W, blue at 150 W, and golden yellow at 200 W. The films exhibited long term stability after 18 months of deposition, in terms of adhesion and colour, upon exposure to ambient condition.

Growth mechanism and field emission of B doped AlN films

This paper highlights the effect of boron dopant on the field emission and growth mechanism of AlN films. The films have been grown by reactive RF magnetron sputtering method. For undoped films, columnar AlN structure was obtained. In the case of boron doped AlN films, the structure growth proceeded gradually through four layers of different thicknesses and structures. It was found that boron favors the formation of an amorphous layer within which oxygen and boron based precipitates develops, retarding the growth of columnar morphology. Depth profiling X-ray photoelectron spectroscopy analyses confirm the presence of B-O, B-N, Al-B and Al-O groups.The study on the field emission (FE) properties of undoped and B doped AlN films on Si substrates indicates that the addition of boron allow to improve FE properties with low turn on field of 2.6 V/μm and low threshold filed of 3.07 V/μm. Such good field emission properties can be attributed to the formation of densely nanograined surface and the appearance of boron based groups.

High temperature AlN thin film ultrasonic transducers with dual mode wave excitation

AlN thin film ultrasonic transducers with dual mode wave (transverse and longitudinal) excitation were deposited by reactive RF magnetron sputtering technique. The transducers deposited at radial distances of 0 and 50 mm in the sample plane exhibited well-developed straight and inclined columnar structures with dominating (002) and (103) X-ray diffraction peaks, respectively. The transducers deposited at radial distances of 0, 30, and 50 mm demonstrated excitation of longitudinal, transverse, and longitudinal-transverse waves, respectively. Short term heat treatment was conducted in air within a temperature range of 20–900 °C to investigate the high temperature ultrasonic response. Temperature dependencies of the time-of-flight and pulse-echo amplitude were analyzed. Long term heat treatment in air at 700 °C for 192 h revealed a degradation of ultrasonic response due to the oxidation of the AlN layer.

Plasmonic Titanium Nitride Nanohole Arrays for Refractometric Sensing.

Group IVB metal nitrides have attracted great interest as alternative plasmonic materials. Among them, titanium nitride (TiN) stands out due to the ease of deposition and relative abundance of Ti compared to those of Zr and Hf metals. Even though they do not have Au or Ag-like plasmonic characteristics, they offer many advantages, from high mechanical stability to refractory behavior and complementary metal oxide semiconductor-compatible fabrication to tunable electrical/optical properties. In this study, we utilized reactive RF magnetron sputtering to deposit plasmonic TiN thin films. The flow rate and ratio of Ar/N2 and oxygen scavenging methods were optimized to improve the plasmonic performance of TiN thin films. The stoichiometry and structure of the TiN thin films were thoroughly investigated to assess the viability of the optimized operation procedures. To assess the plasmonic performance of TiN thin films, periodic nanohole arrays were perforated on TiN thin films by using electron beam lithography and reactive ion etching methods. The resulting TiN periodic nanohole array with varying periods was investigated by using a custom microspectroscopy setup for both reflection and transmission characteristics in various media to underline the efficacy of TiN for refractometric sensing.

Phase-controlled molybdenum dioxide electrodes by RF reactive magnetron sputtering for achieving high-k rutile TiO2 dielectric

Molybdenum dioxide (MoO2) has recently garnered attention as a promising oxide electrode for next-generation dynamic random-access memory capacitors owing to its high work function, low resistivity, and good thermal stability. The formation of pure, reliable MoO2 films is a significant challenge because of their higher formation energy than that of non-conductive orthorhombic molybdenum trioxide (MoO3). Herein, we investigated the controlled growth of MoO2 films by manipulating the process pressure and oxygen-to-argon (O2/Ar) ratio using radio frequency reactive magnetron sputtering. By increasing the O2/Ar ratio at a fixed process pressure (pp), sputtered MoOx films were fabricated as metallic Mo, monoclinic MoO2, and orthorhombic MoO3. The MoO2 film with Mo/O atomic ratio of 0.5 was achieved in the narrow process window of O2/Ar ratio of 0.22 and pp = 3 mtorr. The MoO2 films exhibited a smooth surface morphology with a root mean square roughness of 0.34–0.68 nm. The resistivity of MoO2 film was 972 μΩ cm, which was decreased to 374–524 μΩ cm by rapid thermal annealing in N2 at 600 °C-800 °C. The phase-controlled MoO2 electrode led to the in-situ crystallization of high-k rutile TiO2 with a dielectric constant of 93 via local epitaxial growth. This might be attributed to the excellent coherence in the atomic arrangement and low lattice mismatch between the distorted rutile MoO2 (011) and rutile TiO2 (110) planes.

Preparation, characterization and electrochromic properties of amorphous Gd-doped TiO2 films

Titanium oxide has been widely studied in the field of electrochromism due to its unique color-changing behavior induced by ion insertion. In this paper, amorphous Gd-doped TiO2 films were synthesized via the RF magnetron reactive sputtering. The effects of Gd doping on the electrochromic performance of TiO2 films were explored in detail. The improved coloration efficiency of ∼60% at 540 nm for low Gd-doped TiO2 film (0.61%) is due to the formation of monoclinic Gd2O3 island nanostructure on the surface of TiO2, which enhances the reaction kinetics and charge capacity of the film. The wide optical modulation (73% at 650 nm), large coloration efficiency (59.7 cm2 C−1 at 650 nm) and short response time (coloring time is 16.9 s, bleaching time is 9.1 s) were obtained for the moderately Gd-doped TiO2 film (0.83%). However, for the high Gd-doped TiO2 films (≥1.0%), the coloration efficiency reduced, which is due to the excessive Gd2O3 hindered the electrolyte penetration into the TiO2 active material. By studying the effects of Gd doping on the electrochemical performance of TiO2, it can provide a valuable reference for determining the appropriate doping element and content for electrochromic materials.

Surface and interface properties of TiO2/CuO thin film bilayers deposited by rf reactive magnetron sputtering

Thin film bilayers of TiO2/CuO with intentionally varied thickness of the top layer of TiO2(25–150 nm) were grown by means of sequential rf magnetron reactive sputtering from Cu and Ti metallic targets in a flow rate-controlled Ar + O2 gas mixture. XRD diffraction in GID configuration, SEM top and cross-sectional images, EDS combined with SEM, XRR profiles, UV–VIS-NIR spectrophotometry and synchrotron soft radiation XAS in TEY mode were used to characterize crystal structure, morphology, the mode of growth, chemical composition, density and roughness as well as the optical and electronic properties of the synthesized thin film bilayers. CuO bottom layer turned out to crystallize in a monoclinic structure while TiO2 top layer remained amorphous. Film roughness of CuO decreased from about 12 nm with the increasing thickness of TiO2 thin film to about 1–2 nm. X-ray absorption spectroscopy demonstrated a presence of Cu+ and Cu2+ in TiO2 top layer of TiO2/CuO heterostructure. The photoelectrochemical measurements revealed that thin film bilayers of TiO2/CuO behaved as photocathodes in the process of water splitting. The photocurrent density was found to be an increasing function of the top TiO2 layer thickness.

Tunable Electrical Properties of Ti-B-N Thin Films Sputter-Deposited by the Reactive Gas Pulsing Process

Titanium-boron-nitrogen (Ti-B-N) thin films were deposited by RF reactive magnetron sputtering using a titanium diboride (TiB2) target in an argon + nitrogen mixture. The argon mass flow rate was kept constant, whereas that of nitrogen was pulsed during the deposition. A constant pulsing period of P = 10 s was used, and the introduction time of the nitrogen gas (duty cycle (dc)) was systematically varied from dc = 0 to 100% of the pulsing period. This reactive gas pulsing process allowed the deposition of Ti-B-N thin films with various boron and nitrogen concentrations. Such adjustable concentrations in the films also led to changes in their electronic transport properties. Boron and nitrogen contents exhibited a reverse evolution as a function of the nitrogen duty cycle, which was correlated with the transition from a metallic to semiconducting-like behavior. A percolation model was applied to the electrical conductivity as a function of the nitrogen pulsing parameters, assuming some correlations with the evolution of the Ti-B-N thin film nanostructure.

Light Trapping in Conformal CuO/Si Pyramids Heterojunction for Self-Powered Broadband Photodetection

In this letter, we report a conformal CuO/Si micropyramids heterojunction photodetector fabricated by RF reactive magnetron sputtering CuO nanofilm onto the dense and random Si micropyramids. The device presents a prominent photovoltaic effect over the broad wavelength range (300-1300 nm), which enables efficient self-powered broadband photodetection, giving a peak responsivity of 279 mA/W and specific detectivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.18\times10$ </tex-math></inline-formula> 11 Jones at zero bias upon 810 nm illumination at light intensity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.9~\mu \text{W}$ </tex-math></inline-formula> /cm2. Compared to its planar Si counterpart, the conformal CuO/Si pyramids heterojunction photodetector shows a significantly enhanced photoresponse over the broadband region. According to the theoretical simulation of photon absorption in Si pyramid structures, this should be ascribed to the pronounced light trapping effect of the pyramid structures. The light-matter interaction in the heterojunction was accordingly enhanced, leading to the improved photoresponse. This work is well compatible with the current complementary metal-oxide semiconductor (CMOS) technology and provides a facile and effective strategy for the on-chip high performance photodetection.

Evaluation of structural and mechanical properties of CrAlN single layer coating deposited by reactive magnetron sputtering

The objective of this study is to evaluate the structural and mechanical properties of CrAlN coating obtained by reactive RF magnetron sputtering with (Cr0.5Al0.5) alloy targets in a mixed atmosphere of Argon–Nitrogen (Ar:N2). During deposition, the RF power and substrate temperature were fixed at 120 W and 300 °C, respectively. The Ar: N2 contents were varied at different ratios like 20:2, 20:4, 20:6, 20:8 and 20:10. Grazing Incidence X-ray Diffraction (GIXRD) study was performed to identify the phases present in the coating. The surface morphology and mechanical properties were studied using Field Emission Scanning Electron Microscopy (FESEM) and Nanoindentation, respectively. GIXRD shows the presence of a dominant Face Centered Cubic (FCC) CrN phase. Plane view and cross-sectional FESEM micrographs presented the different Ar:N2 ratios-dependent changes in the microstructures. The CrAlN coating deposited at Ar:N2 contents of 20:6 shows maximum elastic modulus and hardness value compared to other coatings. In our studies, the maximum hardness (H), elastic modulus (Er), elastic recovery (We), and resistance to plastic deformation (H3/E2) were obtained to be 22.96 GPa, 225.79 GPa, 74.81%, and 273 MPa respectively for 20:6 CrAlN deposited coating. This study also shows that different Ar:N2 ratio strongly affects the crystalline microstructure and mechanical properties of the deposited coatings.

Investigation of dielectric and electric behavior of MgTiO3 and Ba0.5Sr0.5TiO3 bilayer films by RF sputtering method

The structural, microstructural, electrical, and dielectric properties of MgTiO3 (MTO)/ Ba0.5Sr0.5TiO3 (BST) bi-layer structures grown by reactive RF magnetron sputtering have been reported. The films exhibited polycrystalline nature and the stacking of BST on MTO (BST/MTO) exhibited better crystallinity than that of MTO stacking on BST(MTO/BST). The RMS roughness for BST/MTO and MTO/BST is found to be 1.82 nm and 49.2 nm, respectively. The dielectric constant (εr, ∼27.3) and loss tangent (tanδ, ∼10−2) at 100 kHz for BST/MTO are found to be intermediate to BST and MTO monolayer responses. The anomaly observed in dielectric response (εr, ∼323.2 and tanδ, ∼10−2) for MTO/BST can be attributed to the generation of charge carriers in the interfaces of individual layers. The relation between electrically active regions with the observed electrical response is studied by impedance spectroscopy. The leakage in MTO/BST (10−2 A/cm2 at 100 kV/cm) bilayer is higher than that of BST/MTO (10−4A/cm2 at 100 kV/cm) bilayer and Schottky emission along with Space-charge limited current contribute to the leakage current. Both MTO/BST and BST/MTO films exhibited tunable dielectric responses. These findings of this report provide prospective insight into the design of multilayer structured smart materials.11MTO and BST bilayer films

Chemical cyanide treatment of polycrystalline p-Cu2O/n-ZnO solar cell

Cuprous oxide (Cu2O) and zinc oxide (ZnO) hold a very crucial position in the field of materials research because of their immense potential in many acoustic, electronic and optical applications. Cu2O is a direct-gap semiconducting material with forbidden energy gap around 2.0 eV. It has been considered as one of the most promising materials for photovoltaic applications, especially for use at the top in a cascade cell structure. The enchantment of Cu2O and ZnO as photovoltaic materials is due to fact that their constituent materials are nontoxic, abundantly available and of relatively low cost. In this work, Cu2O thin films in polycrystalline form were prepared in radio-frequency (rf) reactive magnetron sputtering route on glass substrates at different substrate temperatures. After the samples were prepared, these were taken through a crown-ether cyanide (CN) treatment. Presence of oxygen in excess compared to stoichiometry is the major active impurity in Cu2O and consequently holes are the majority charge carriers in it. With the aid of crown-ether cyanide treatment of the prepared samples, hole-mobility was found to increase and resistivity was found to decrease considerably. Finally, polycrystalline p-Cu2O/n-ZnO heterojunctions were fabricated for use in solar cells. Results of Hall measurement strongly support the observations made from DLTS studies and photocurrent measurements. Thus, our present study confirms the improvement of device performance of the p-Cu2O /n-ZnO heterojunctions on chemical cyanide treatment.

Reset First Resistive Switching in Ni1−xO Thin Films as Charge Transfer Insulator Deposited by Reactive RF Magnetron Sputtering

Reset-first resistive random access memory (RRAM) devices were demonstrated for off-stoichiometric Ni1−xO thin films deposited using reactive sputtering with a high oxygen partial pressure. The Ni1−xO based RRAM devices exhibited both unipolar and bipolar resistive switching characteristics without an electroforming step. Auger electron spectroscopy showed nickel deficiency in the Ni1−xO films, and X-ray photoemission spectroscopy showed that the Ni3+ valence state in the Ni1−xO films increased with increasing oxygen partial pressure. Conductive atomic force microscopy showed that the conductivity of the Ni1−xO films increased with increasing oxygen partial pressure during deposition, possibly contributing to the reset-first switching of the Ni1−xO films.

Influence of magnetron sputtering process parameters on low-temperature electrical transport characteristics of zirconium oxynitride thin films

In order to determine the influence of process parameters including nitrogen and oxygen flow rate on the structure and electrical transport characteristics of zirconium oxynitride(ZrOxNy) thin films, the ZrOxNy films were prepared on sapphire substrates by RF reactive magnetron sputtering deposition technology. The crystal orientation and morphology of ZrOxNy films prepared at different nitrogen and oxygen flow rate were characterized by XRD and SEM, respectively. The electric transport behavior of ZrOxNy films at 300K to 3K was measured by PPMS. The results show that the insulativity of ZrN films is enhanced with the increase of nitrogen flow rate in sputtering atmosphere. With the increase of oxygen flow rate in sputtering atmosphere, the insulativity of ZrOxNy film is enhanced.

Natural preparation of rice husk-derived silica and eggshell-derived calcium carbonate composite as a coating material for dental implant

Background: The world is in front of two emerging problems being scarceness of virgin re-sources for bioactive materials and the gathering of waste production. Employment of the surplus waste in the mainstream production can resolve these problems. The current study aimed to prepare and characterize a natural composite CaO-SiO2 based bioactive material derived from naturally sustained raw materials. Then deposit this innovative novel bioactive coating composite materials overlying Yttria-stabilized tetragonal zirconia substrate. Mate-rials and method; Hen eggshell-derived calcium carbonate and rice husk-derived silica were extracted from natural resources to prepare the composite coating material. The manufac-tured powder was characterized via Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), X-ray fluorescence (XRF), X-ray diffraction (XRD) and particle size analyzer. The bioactive composite was deposited through radiofre-quency (Rf) reactive magnetron sputtering overlying disc-shaped samples with a dimension of 10 mm diameter were prepared from partially sintered Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). Results: The particle size of the rice husk-derived ranged between (480.4 – 606.1) nm with a mean particle diameter of 541 nm. The eggshell derived calcium carbonate powder presented a particle size between (266.4-336) nm and a mean particle diameter of 299.9 nm. The XRD data revealed the crystalline nature and phase composition of the natural prepared calcium carbonate powder and demonstrate the monocrystalline nature of natural SiO2. FTIR spectrometer showed the emergence of novel spectra separated from the two innovative components. XRF analysis revealed that 99.4% of the rice husk is SiO2 while eggshell-derived powder is mainly composed of calcium oxide. Fe-SEM images of the coated zirconia exhibited average thickness of the natural CaCO3/SiO2 coat layer may reach to12.84 µ. Conclusion: The prepared composite derived from natural resource waste is suitable to be utilized as a coating material for ceramic dental implants with promising biological and mechanical properties.

Electronic phase transition in CrN thin films grown by reactive RF magnetron sputtering

Chromium nitride thin films were prepared by reactive radio frequency magnetron sputtering on glass and Si(001) substrates. Thin films were grown at different nitrogen to argon flow rate ratio and their effect on the film composition, band gap and electronic phase transition was studied by different experimental technique. X-ray diffraction analyses establish that CrN films predominantly grow in [111]CrN and [002]CrN directions irrespective of the substrates used for the growths. The band gap was found to vary with the composition of the films. All films are semiconducting at room temperature and show discontinuity in their resistivity versus temperature curve indicating electronic transition. But the low temperature electronic phase depends on the growth conditions and composition of the films.

Microstructure and properties of the AlCrMoZrTi/(AlCrMoZrTi)N multilayer high-entropy nitride ceramics films deposited by reactive RF sputtering

The AlCrMoZrTi/(AlCrMoZrTi)N multilayer high-entropy nitride ceramic films (HENCFs) fabricated by reactive RF magnetron sputtering presented (200) preferentially oriented FCC crystal structures. With the increase in the modulation period, the nitrogen content and surface roughness of the multilayer films gradually increased, the template effect between the nanocrystalline and amorphous forms was weakened, and the multilayer interface structure decreased. The S4 film with a modulation period of 1500 nm had the highest hardness and modulus (16.6 and 225.7 GPa, respectively) and the highest H/E* and H3/E*2 values. The results of friction experiments showed that the S1 film with the smallest modulation period had a stable friction coefficient and small wear rate on both Si and Cu substrates, and it exhibited the best friction and wear performance due to its low surface roughness, high toughness and compressive yield resistance, and dense multilayer structure. The friction mechanisms of the HECNFs on Si and Cu substrates were mainly adhesive wear, abrasive wear, and a small amount of oxidative wear.

Reactive RF magnetron sputtering epitaxy of NiO thin films on (0001) sapphire and (100) MgO substrates

Epitaxial growths of NiO thin films were realized on (0001) sapphire and (100) MgO substrates by using a reactive RF magnetron sputtering method. The NiO epilayers grown on a (0001) sapphire exhibited the (111)-oriented double-domain structure, which comprised of a triangular and its inverted triangular grains. Meanwhile, the NiO epilayers on a (100) MgO exhibited the (100)-oriented single-domain structure, which comprised of quadrangular grains. The observed grain structures most likely reflect the growth planes of respective NiO epilayers, and, mixed crystals of NiO and MgO were present near the interface. Therefore, a (100) MgO substrate is suitable for obtaining a single-domain NiO epilayer, whereas a (0001) sapphire substrate is suitable for obtaining a NiO epilayer without interdiffusion between NiO and sapphire. These NiO epilayers will be expected for applying the physical properties evaluation using photoluminescence or Hall measurements, and the fabrication of electrical or optical devices.

Microstructures, mechanical properties and corrosion resistance of TiN/AlN multilayer films

TiN/AlN multilayer films with different modulation periods (Λ) were prepared by RF-reactive magnetron sputtering. The microstructures, mechanical property and corrosion resistance of TiN/AlN multilayer films were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), nanoindentation and electrochemical comprehensive tester. The results show that the TiN/AlN multilayer films are composed of face centered cubic (fcc) TiN and tightly packed hexagonal (hcp) AlN. The multilayer films are coherent epitaxial growth as Λ increases from 2 to 12 nm. The hardness and the corrosion resistance increase with Λ increases from 2 to 12 nm. The optimum hardness is 29.27 GPa and the strongest corrosion resistance displays with Λ = 12 nm. The coherent interface could be destroyed, and the alternating stress field as well as the hardness decreases sharply during the modulation period of 26 nm–36nm. The self-corrosion potential decreases and the self-corrosion current density increases. The corrosion resistance of the film decreases with Λ increase from 26 nm to 36 nm.