Co-sputtering Deposition Technique Research Articles

Development of Sb phase change thin films with high thermal stability and low resistance drift by alloying with Se

A single Sb phase demonstrates potential for use in phase change memory devices. However, the rapid crystallization of Sb at room temperature imposes limitations on its practical application. To overcome this issue, Sb is alloyed with Se using a reactive co-sputtering deposition technique, employing both Sb and Sb2Se3 sputter targets. This process results in the formation of Sb-rich Se thin films with varying compositions. Compared to pure Sb, the Sb-rich Se thin films exhibit enhanced thermal stability due to the formation of Sb–Se bonds and reduced resistance drift. In particular, the Sb86.6Se13.4 thin film demonstrates an exceptionally low resistance drift coefficient (0.004), a high crystallization temperature (Tc = 195 °C), a high 10-year data retention temperature (116.3 °C), and a large crystallization activation energy (3.29 eV). Microstructural analysis of the Sb86.6Se13.4 reveals the formation of a trigonal Sb phase with (012) texture at 250 °C, while Sb18Se and Sb2Se3 phases form at 300 °C. Conversely, the Sb98.3Se1.7 thin film shows the formation of the single Sb phase with (001) texture, a Tc of 145 °C, and a low resistance drift coefficient (0.011). Overall, this study demonstrates that the alloying strategy is a viable approach for enhancing thermal stability and reducing resistance drift in Sb-based phase-change materials.

Highly Reliable Selection Behavior With Controlled Ag Doping of Nano-Polycrystalline ZnO Layer for 3D X-Point Framework

In this letter, a threshold switching (TS) selector with Ag doping-based nano-polycrystalline ZnO switching layer (SL) having (002) preferred orientation has been manifested, without incorporating an active Ag metal layer, using a facile co-sputtering deposition technique. The TS selectors with extremely controlled doping of ~0.14 at. % Ag concentration showed remarkable electroforming (EF)-free selection behavior such as gigantic selectivity (~1011), extreme-low off-current (~10 fA), high on-current density (~1.6 MA/cm2), ultra-steep switching slope (~0.8 mV/decade), satisfactory endurance (>106), fast switch-on speed (~38 ns) and relaxation speed (~64 ns), and high device yield (~90%). Furthermore, selector devices showed reproducible selection behavior with stable threshold voltage (Vth) having merely 8% variances.

Layered structure enhances the hardness of Cu-48at.%Cr film prepared by co-sputtering deposition technique

The Cu-48at.%Cr film was prepared by magnetron co-sputtering deposition technique with working pressure from 0.2 Pa to 1.5 Pa. The microstructure and nanoindentation hardness were investigated. When the working pressure decreased to 0.2 Pa, the consecutive layered structure formed. The formation of layered structure was attributed to the diffusion barrier ability of Cr element and the uphill diffusion of Cu atoms. While at higher working pressure, the sputtering particles energy near the substrate was not enough to promote the Cu diffusion. Therefore, the layered structure became indistinct as the working pressure increased. Owing to the interface strengthen, this layered structure made the nanoindentation hardness increase markedly from 4.2 GPa to 9.3 GPa as the working pressure decreased from 1.5 Pa to 0.2 Pa. This study could provide a good basis for preparing the film with specific microstructure in Cu–Cr system, even in other immiscible systems.

Thermal stability of co-sputtered TaCu amorphous nano-multilayers

Comprehensive knowledge of the thermal stability of films is essential from the perspective of design and application. In this case, TaCu amorphous nano-multilayers with a Ta nominal content of 68 at.% were prepared by magnetron co-sputtering deposition technique. Nano-multilayers with a modulation period of 12.8 nm are constituted of equal-thickness sublayers both exhibiting pronounced Ta-rich amorphous phase. The Ta content presents an obviously sinusoidal fluctuation along the growth direction. The relatively intuitive processes of phase separation and layered structure destruction were obtained through isothermal annealing in the temperature range of 450–700 ℃ for 1 h. The high interfacial energy produced by co-sputtering deposition drives the thermally-activated Cu atoms to diffuse uphill, leading to the amorphous sublayers with the higher Cu content crystallizing initially at 450 ℃. Upon annealing at 480 ℃ for 1 h, the formation of the thermal groove between adjacent Cu grains and the diffusion of Ta atoms along the Cu grain boundaries synergistically induce the sublayers to fracture. Nanoindentation experiments showed that the hardness of the annealed films increases due to the clearer interface by uphill diffusion, but the enhancement only remains until the layered structure disappears. This study provides a good basis for the design and application of TaCu amorphous nano-multilayers, even in other immiscible systems.

Structural, Wetting and Magnetic Properties of Sputtered Fe70Pd30 Thin Film with Nanostructured Surface Induced by Dealloying Process

FePd alloys in the thin film form represent a multipurpose and versatile material with relevant chemical and physical properties studied in different research fields. Moreover, the ability to manipulate and fine-tune the film surface with nanometric scale precision represents a degree of freedom useful to adapt these thin film properties to the demands of different desired applications. In this manuscript, Fe70Pd30 (at. %) thin films are prepared with a thickness of 50 and 200 nm by means of the widely used co-sputtering deposition technique. Subsequently, selective removal of the iron element from the alloy and the consequent surface diffusion of the palladium was induced by a dealloying treatment under free corrosion conditions in hydrochloric acid. The size and shape of the grains of the as-deposited thin films determine the dissolution rate of the iron element with a direct consequence not only on the surface morphology and the stoichiometry of the alloy but also on the wetting and magnetic properties of the sample. X-ray diffraction, Scanning Electron Microscopy (SEM) images, contact angle and magnetic measurements have been performed to provide a thorough characterisation of the fundamental properties of these nanostructured bimetallic thin films.

Photo-induced structural changes in Ge-Sb-Se films

Amorphous Ge-Sb-Se thin films have been prepared by the radio-frequency (RF) magnetron co-sputtering deposition technique, and their intrinsic photosensitivity and photo-induced structural changes have been investigated. The results show a crossover from photodarkening (PD) to photobleaching (PB) in the films when the film compositions change from Se-deficient to rich. Further Raman analysis on these as-prepared thin films irradiated with a laser of wavelength 655nm in every five minutes provides direct evidence of photo-induced structure rearrangements.

Characteristics of sputter deposited Pt/Al2O3 thin films

Pt/Al2O3 thin films were prepared using a reactive co-sputtering deposition technique. Two types of power controls were used. In one type, both the DC (for the Pt target) and RF power (for the Al2O3 target) were on for the entire deposition period. In the second type, the RF power was always on while the DC power was pulsed. The resulting materials were analyzed using glazing incident X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The optical performance of the obtained films was examined using UV–vis–NIR spectrophotometry and Fourier transform infrared spectrometry. We show that the films obtained using the second type power control results in desired microstructures, leading to a total optical absorptance of 0.80.

Structural, Morphological and Electrical Properties of In-Doped Zinc Oxide Nanostructure Thin Films Grown on p-Type Gallium Nitride by Simultaneous Radio-Frequency Direct-Current Magnetron Co-Sputtering**Supported by the RU Top-Down under Grant No 1001/CSS/870019.

Zinc oxide (ZnO) is one of the most promising and frequently used semiconductor materials. In-doped nanostructure ZnO thin films are grown on p-type gallium nitride substrates by employing the simultaneous rf and dc magnetron co-sputtering technique. The effect of In-doping on structural, morphological and electrical properties is studied. The different dopant concentrations are accomplished by varying the direct current power of the In target while keeping the fixed radio frequency power of the ZnO target through the co-sputtering deposition technique by using argon as the sputtering gas at ambient temperature. The structural analysis confirms that all the grown thin films preferentially orientate along the c-axis with the wurtzite hexagonal crystal structure without having any kind of In oxide phases. The presenting Zn, O and In elements' chemical compositions are identified with EDX mapping analysis of the deposited thin films and the calculated M ratio has been found to decrease with the increasing In power. The surface topographies of the grown thin films are examined with the atomic force microscope technique. The obtained results reveal that the grown film roughness increases with the In power. The Hall measurements ascertain that all the grown films have n-type conductivity and also the other electrical parameters such as resistivity, mobility and carrier concentration are analyzed.

The influence of Bi doping in the thermoelectric properties of co-sputtering deposited bismuth antimony telluride thin films

Bismuth antimony telluride thin films were fabricated by a tri-target co-sputtering deposition technique on soda-lime glass. Direct current magnetron sputtering and radio frequency magnetron sputtering were both utilized. A substrate temperature of 250°C was used for the synthesis of BixSb2−xTe3. Thin films of different compositions were synthesized by changing the sputtering power of Bi. The influence of Bi doping on the structure, surface morphology and thermoelectric properties of the thin films were studied. The results indicated that the thin films changed from p-type semiconductor to n-type semiconductor with the increase in Bi content. In p-type semiconductor samples, Bi0.5Sb1.5Te3 thin film had the maximum power factor of 1.81×10−3Wm−1K−2. The Seebeck coefficient of the thin film was 159μV/K. Bi1.5Sb0.5Te3 thin film had the highest power factor of 7.06×10−4Wm−1K−2 in n-type semiconductor samples, with the Seebeck coefficient of −148μV/K.

Nanostructural and Functional Properties of Ag-TiO2 Coatings Prepared by Co-Sputtering Deposition Technique

Ag-TiO2 nanocomposite coatings with varying Ag content were prepared by co-sputtering from two separate sputter sources. This technique allows to prepare coatings not only with a large variation of Ag content and different gradient but also allows much better control of nanocomposite thickness and nanostructure compared with mostly used techniques based on wet chemical approaches. Various thicknesses of nanocomposite layers with different deposition parameters were studied to obtain a better understanding on the growth of Ag nanostructures in the TiO2 films. The metal-volume-fraction was varied between 15% and 47%. Structural and microstructural investigations of the nanocomposite films were carried out by transmission electron microscopy. Special attention was paid to surface segregation of Ag and its suppression. The observed segregation on TiO2 contrasts sharply with the well known embedding tendency of Ag clusters on polymers. Functionality of the Ag-TiO2 nanocomposites was demonstrated via UV-Vis spectroscopy and antibacterial tests. It was shown that a thin layer of TiO2 can be used as an effective barrier to tailor the release behaviour of Ag ions.

Au–Cu nanoparticles in silica glass as composite material for photonic applications

In the framework of metal nanocluster composite glasses for photonic application, (gold + copper)-containing silica films were synthesized by radiofrequency co-sputtering deposition technique by varying the Au/Cu ratio. To obtain the formation of metallic (alloy) nanoclusters, the deposited samples were annealed in reducing atmosphere at 900 °C. The linear and nonlinear optical properties of the composite glasses were investigated. In particular, the nonlinear ultrafast optical response was measured by means of the Z-scan technique at a wavelength of 527 nm with single 6 ps pulse configuration. Significant refractive and absorptive effects were observed in all the annealed samples. The two main figures of merit related to the performance of materials for optical switching device application were evaluated for all samples, showing interesting values for the Cu-rich composites.

RF magnetron co-sputtering deposition of Cu-based nanocomposite silica films for optical applications

The size, the size distribution, the structure and the concentration of the metallic particles embedded in a host dielectric matrix determine the linear and non-linear optical properties of this kind of composite glasses. In this work, copper-containing silica films about 0.5μm thick were prepared by radio frequency magnetron co-sputtering deposition technique, and then heat-treated in oxidizing and/or reducing atmospheres. The characterization of the samples was performed by optical absorption spectroscopy, Rutherford backscattering spectrometry and transmission electron microscopy. The investigated preparation protocols actually allow to control the final composite structure. Preliminary results indicate that some nanocomposite films have non-linear optical properties in the ps regime.

Structural and physical properties of cobalt nanocluster composite glasses

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres.

Radiofrequency magnetron co-sputtering deposition synthesis of Co-based nanocomposite glasses for optical and magnetic applications

Transition element nanoclusters embedded in dielectric matrix are important for their optical and magnetic properties. In this work, composite silica films with cobalt atomic concentration up to 10% were synthesized by radiofrequency (rf) magnetron co-sputtering deposition technique. The composite systems structure could be triggered by varying the deposition parameters and by using a subsequent thermal treatment to promote the nanocluster formation. Magnetic measurements showed that the embedded cobalt nanoparticles act as superparamagnets, with coercive field and blocking temperature related to their size and structure (hcp or fcc).

Structural and optical properties of Cu:silica nanocomposite films prepared by co-sputtering deposition

Copper-containing silica films were synthesized by radiofrequency (rf) co-sputtering deposition technique, and then heat-treated in different annealing atmospheres, i.e. either oxidizing or reducing, with the aim to develop suitable preparation methodologies for controlling the composite structure. Characterization of the samples along the various preparation steps was performed by Rutherford backscattering spectrometry (RBS), transmission electron microscopy and optical absorption spectroscopy. The nonlinear optical coefficient n2 of the nanocomposite films was estimated by the Z-scan technique. Experimental observations showed that copper migration and aggregation depend critically on the annealing conditions, giving rise to quite different stable structures. In particular, for samples heat-treated first in air and then in a H2–Ar gas mixture, the oxidizing atmosphere drives copper towards the surface while the reducing one promotes the subsequent clusterization in a well defined region.

Characteristics of thin films of hexagonal boron nitride mixed with copper controlled by a magnetron co-sputtering deposition technique

Thin film properties, such as surface morphology, internal stress and surface energy, of hexagonal boron nitride/copper mixtures, produced by a magnetron co-sputtering deposition technique, were investigated. Techniques included scanning electron microscopy, film deflection and contact angle measurements. It was possible to fabricate nano-scale islands on the surface of the film and to control the size of the islands by adjusting the sputter discharge conditions. The internal stress and surface energy can be significantly modified depending on these conditions indicating that they are dependent variables. This technique of co-sputtering deposition is a promising candidate for the control of nano-structures on a surface and for controlling internal stress and surface energy.

Thermal stability and hardness of metastable Co–C composite alloy films

Co–C alloy films containing metastable cobalt carbides have been prepared by a new type of co-sputtering deposition technique and their thermal stability was examined and discussed in terms of the concept of the formation enthalpy. Dynamic hardness and magnetic properties, such as saturation magnetization, were also evaluated for the Co–C alloy films. Both hardness and magnetization of the films were found to decrease almost linearly with increasing fraction of carbon content in the film, suggesting that the measurement of hardness can serve as a monitor of film qualities. It is also shown that the hardness of metastable cobalt carbides is greater than that of the Co–C alloy film.