Off-axis Magnetron Sputtering Research Articles

The effects of crystal orientation on the ferroelectric and optoelectronic properties of Pt/Na0.5Bi0.5TiO3/La0.5Sr0.5CoO3 heterostructures

Due to their excellent ferroelectric, semiconducting, and optoelectronic properties, perovskite ferroelectric thin films have attracted increasing attention in the photovoltaic field. Using La0.5Sr0.5CoO3 (LSCO) as the bottom electrode, flake, strip and pyramidal Na0.5Bi0.5TiO3 (NBT) films were prepared on (001), (110) and (111) SrTiO3 (STO) substrates by off-axis magnetron sputtering and pulsed laser deposition, respectively. XRD and Phi scan results show that both LSCO and NBT are perovskite structures and satisfy the epitaxial growth along the substrate STO. NBT orientation has a significant effect on the ferroelectric properties of Pt/NBT/LSCO heterostructures. The remnant polarization 2Pr values for NBT(111), NBT(110) and NBT(001) are 87.5, 62.6 and 28.5 μC/cm2, respectively, and thus 2Pr(111)>2Pr(110)>2Pr(001). NBT(111) shows the best ferroelectric properties (Pr=41.3 μC/cm2), excellent fatigue-resisting (up to 1010 cycles) and retention performance (duration 104s). The 2Pr-T association 2 Pr=41.72+16.05*T0.35 for NBT(111) was obtained according to the curve fitting, it is found that the NBT orientation has a significant effect on the PV effect for PT/NBT/LSCO photovoltaics and the open-circuit voltage ∆Voc. The short-circuit current ∆Jsc of polarization regulate intensity follows the laws of ∆Voc-111>∆Voc-110>∆Voc-001 and ∆Jsc-111>∆Jsc-110>∆Jsc-001, the Jsc for Pt/NBT(111)/LSCO heterostructures increases linearly with the illumination Ip increasing, while the Voc decreases linearly. The ferroelectro-polarized modulation PV mechanism was investigated by analyzing band structure of the Pt/NBT/LSCO heterostructures, which is attributed to the coupling effect of the ferroelectric depolarization field and the interfacial Schottky barrier.

Structural and resistive properties of Pt/BiFeO3/La0.5Sr0.5CoO3 heterostructure for storage application

BiFeO3 has promissing application in non-volatile ferroelectric memory, but the dominant mechanism has not been unified. Here, Pt/BiFeO3 (100 nm)/La0.5Sr0.5CoO3 (Pt/BFO/LSCO) heterostructures have been fabricated on (001) SrTiO3 (STO) single crystal substrates by off-axis magnetron sputtering. Both XRD and TEM analyses confirm that the (001) oriented BFO/LSCO heterostructures have been epitaxially grown on STO. In addition, XRD, TEM along with XPS analyses further indicate that the BFO film (001) presents epitaxial perovskite structure. On the basis of electric field regulation of Pt/BFO and BFO/LSCO interface barrier, the switching interface state is controlled by charge filling and trapping in interface potential well, which is responsible for I–V resistance and G-V hysteretic curve. Based on the fitting results of the conduction mechanism of I–V characteristic curve, it proves that the space charges limiting current play a dominant role, and the filling and trapping of interface traps are considered as the main resistance mechanisms. Moreover, ultraviolet irradiation can modulate the I–V resistance curve but does not change its conduction mechanism. This work provides experimental data for the practical application of integrated BFO resistive memories.

Dielectric and ferroelectric photovoltaic properties of epitaxial BiFeO3 film with La0.5Sr0.5CoO3 bottom electrode

In order to deeply investigate the dielectric and ferroelectric photovoltaic properties of BiFeO3 (BFO) thin films, the Pt/BFO/La[Formula: see text]Sr[Formula: see text]CoO3 (LSCO) heterostructure ferroelectric capacitor grown on (001) SrTiO3 (STO) substrate is successfully fabricated by off-axis magnetron sputtering. The X-ray diffraction (XRD) and Phi scanning results show that the STO-based BFO and LSCO films are both (001) epitaxial structure. Although the BFO ferroelectric film exhibits an obvious dielectric dispersion phenomenon, a remarkable ferroelectric photovoltaic performance is obtained with open circuit voltage ([Formula: see text]) of 0.38[Formula: see text]V and short-circuit current ([Formula: see text]) of 0.23[Formula: see text]mA/cm2, respectively. With increasing test temperatures, [Formula: see text] decreases slowly and then rapidly, while [Formula: see text] increases rapidly and then decreases. At a critical temperature of 80∘C, the BFO ferroelectric film exhibits a faster photovoltaic response, in which the values of [Formula: see text] and [Formula: see text] are about 0.19[Formula: see text]V and 0.28[Formula: see text]mA/cm2, respectively. Moreover, the energy band analysis indicates that a large work function difference ([Formula: see text][Formula: see text]eV) between LSCO and Pt leads to a strong built-in electric field in the BFO film, which is beneficial to separate the photo-generated carriers and improve ferroelectric photovoltaic effect. In all, this study not only shows that BFO is an excellent and environmentally friendly photovoltaic candidate material, but also provides a practical strategy for improving the performance of BFO ferroelectric photovoltaic devices.

Wide range tunability of surface plasmon resonance of nanostructured Ag deposited by off-axis magnetron sputtering

In this work, nanostructured Ag showing size distribution dependent tunable surface plasmon resonance (SPR) are grown on glass substrate using off-axis DC magnetron sputtering at a sputtering power of 74 W. Argon gas pressure is set at 8.0 Pa and the deposition time is varied in the range 5–300 s. The structural, morphological, and optical properties are examined by using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), and UV–Visible spectrophotometer. XRD patterns of all samples reveal characteristic (111) and (200) peaks of fcc Ag. Broad XRD peaks suggest formation of nanosized Ag crystallites with mean crystallite size of 3 nm. FESEM images depict near spherical Ag grains up to 120 s deposition time and elongated grains with greater substrate coverage with extended deposition time of 300 s. SPR features are well distinct in the optical absorption spectra which are highly sensitive to the deposition time. Within a short deposition time of 5–60 s, nanostructured Ag demonstrates wide range SPR tunability from 438 nm to 530 nm. It is observed that the variations in the size distribution as estimated from FESEM images are crucial to observe systematic red shift of SPR with increasing deposition time. Nanosized Ag produced by off-axis magnetron sputtering may be used as a vital component in plasmonic devices and sensors.

Ferromagnetic insulating epitaxially strained La2NiMnO6 thin films grown by sputter deposition

The field of oxide spintronics can strongly benefit from the establishment of ferromagnetic insulators with near room-temperature Curie temperature. Here, we investigate the structural, electronic, and magnetic properties of epitaxially strained thin films of the double perovskite La2NiMnO6 (LNMO) grown by off-axis radio-frequency magnetron sputtering. We find that the films retain insulating behavior and a bulk-like Curie temperature in the order of 280 K independently of the epitaxial strain conditions. These results suggest a prospective implementation of LNMO films in multi-layer device architectures where a high-temperature ferromagnetic insulating state is a prerequisite.

Improved thin film growth using Slow Kinetics Intermittent Sputtering

Radio-frequency off-axis magnetron sputtering is a well established technique to produce high quality epitaxial thin films of complex oxides. It has been successfully used for over two decades to grow thin films, superlattices and even solid solutions. The main drawback is the common lack of in situ monitoring of the growth, which can significantly slow down the optimisation of the many growth parameters. However, once the optimal parameters are found, they are usually very stable in time, leading to consistently high quality thin films. One of the main growth parameters is the growth temperature, with typical optimal ranges as narrow as 20 °C. Here, using the prototypical ferroelectric PbTiO3 as a model system, we show that by periodically interrupting the deposition process to allow the deposited material to relax, we can significantly increase the temperature range over which we obtain atomically flat surfaces to more than 50 °C. Moreover, the overall crystalline quality is greatly improved, as shown by X-ray diffraction. Finally, we demonstrate the applicability of this method to other materials.

(Invited) Sputter Beam Epitaxy for Atomic Ordering in Complex Epitaxial Thin Films

Innovation is driven by the materials mankind has mastered to advance society. Our information age traces back to wartime invention of methods to fabricate silicon and germanium crystals with defects lower than 1 part in 100, a threshold at which the intrinsic properties could then be applied. Today, complex materials (>2 elements with atomic ordering) are at a similar inflection point. Unfortunately, improvement beyond 1 defect in 4 has proven challenging: energetic defects abound and many elements are not compatible with current low-defect growth techniques. Despite significant external funding for the materials themselves, a lack of funding for new synthetic technologies has left us with methods unable to reach the inflection point. Our goal is to transform materials discovery by developing a complex material thin film system that can attain 99% atomic ordering in today’s “too-complex” materials. This talk will highlight our progress in thin film growth via Sputter Beam Epitaxy, an approach combining the fabrication strengths of off-axis magnetron sputtering and molecular beam epitaxy.

Orientation dependent leakage current behaviors and ferroelectric polarizations of off-axis sputtered BiFeO3 thin films

Epitaxial BiFeO3 thin films with (100), (110) and (111) orientations were grown on the SrRuO3-buffered SrTiO3 substrates by using an off-axis magnetron sputtering. Unlike the BiFeO3(110) and BiFeO3(111) thin films that exhibited a single rhombohedral phase structure, a dominant rhombohedral phase accompanying with a small amount of tetragonal phase was identified in the BiFeO3(100) thin film. In particular, the leakage currents and ferroelectric polarizations of sputtered BiFeO3 thin films were focused on and these films showed utterly different current density-electric field (J-E) behaviors whether in the positive or negative electric field. Among the three films, the ferroelectric polarization of the BiFeO3(100) thin film presented a good frequency stability and had the maximum remnant polarization of Pr ∼ 78 μC/cm2 @ 10 kHz, which could be further demonstrated by pulsed polarizations of films. The distinct differences in electrical properties of orientation-engineered BiFeO3 thin films in present case can be attributed to their different crystallographic orientations and microstructures.

Lattice dynamics of mixed-phase BiFeO3 films: Insights from micro-Raman scattering

We report an investigation of Raman spectroscopy of the mixed-phase ${\mathrm{BiFeO}}_{3}$ film grown onto ${\mathrm{LaAlO}}_{3}$(001) by ${90}^{\ensuremath{\circ}}$ off-axis magnetron sputtering. The polarized Raman spectra unveil different sets of phonon vibrations, which can be assigned to the modes of the tetragonal($T$)-like polymorph, the rhombohedral($R$)-like polymorph, and the bridging phase (${S}_{\mathrm{tilt}}^{\ensuremath{'}}$ and ${T}_{\mathrm{tilt}}^{\ensuremath{'}}$) in between. Furthermore, the unpolarized Raman scattering as function of temperature unravels multiple anomalies in the phonon behavior of the $T$-like phase not only at its multiferroic transition ($\ensuremath{\sim}370\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) but also at the Polomska transition ($\ensuremath{\sim}450\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and the antiferromagnetic transition of the $R$-like phase ($\ensuremath{\sim}640\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). The unusual phonon behavior indicates the presence of spin-phonon coupling and also long-ranged strain coupling between the $T$-like and $R$-like polymorphs, which provides new insights into hybrid systems at the morphotropic phase boundaries.

Comparative study of magneto-transport and lattice-vibrational properties of La2/3Ca1/3MnO3 thin films grown on SrTiO3 and LaAlO3 substrates

Epitaxial La[Formula: see text]Ca[Formula: see text]MnO3 (LCMO) thin films of 60 nm are deposited on (001)-oriented SrTiO3 (STO) and LaAlO3 (LAO) substrate by modified off-axis magnetron sputtering method. The strain state of the films have been studied by high resolution X-ray diffraction. The magneto-transport properties were found to be strongly dependent on the substrate used. Compared with LCMO/LAO film (compressive strain), LCMO/STO film with tensile strain exhibits lower metal-insulator transition temperature, suppressed Curie temperature, higher resistivity and more localization of electron. The evolution of the Raman modes has also been investigated. The vibrational mode of LCMO/LAO is comparable to the bulk, while the signature of vibration mode at about 610 cm[Formula: see text] induced by strain-related distortion has been observed only in tensile strained LCMO/STO case. The controversial 660 cm[Formula: see text] peak is not observed in our films, which precludes the possible existence of Mn3O4 precipitates in the films.

Resistive Switching Effect and Dielectric Property of Epitaxial BiFeO3 Thin Films by Off-axis Magnetron Sputtering

Resistive Switching Effect and Dielectric Property of Epitaxial BiFeO₃ Thin Films by Off-axis Magnetron Sputtering

Ferroelectric domains in epitaxial PbxSr1−xTiO3 thin films investigated using X-ray diffraction and piezoresponse force microscopy

We present a detailed study of compressively strained PbxSr1−xTiO3 thin films grown by off-axis radio frequency magnetron sputtering on (001)-oriented Nb-doped SrTiO3 substrates. Film tetragonality and the ferroelectric critical temperatures are measured for samples of different composition and thickness and compared with a phenomenological Landau-Devonshire model. 180∘ ferroelectric domains are observed using both X-ray diffraction and piezoresponse force microscopy and domain sizes obtained by the two techniques are compared and discussed.

On the Crystal Structural Control of Sputtered TiO2 Thin Films.

In this study, we focused on the origin on the selective deposition of rutile and anatase TiO2 thin films during the sputtering process. The observation on microstructural evolution of the TiO2 films by transmission electron microscopy revealed the coexistence of rutile and anatase TiO2 phases in the initial stage under the preferential growth conditions for the anatase TiO2; the observations further revealed that the anatase phase gradually dominated the crystal structure with increasing film thickness. These results suggest that the bombardment during the sputtering deposition did not obviously affect the TiO2 crystal structure, and this was also confirmed by off-axis magnetron sputtering experiments. We also investigated the mechanism of the effect of Sn impurity doping on the crystal structure using first-principles calculations. It is found that the formation energy of Sn-doped rutile TiO2 is lower than that of Sn-doped anatase TiO2; this suggests that the Sn-doped TiO2 favours the rutile phase. These results offer a guideline for the utilization of selective deposition of rutile and anatase TiO2 thin films in various industrial applications.

Characterization of Al-Doped ZnO Transparent Conducting Thin Film Prepared by Off-Axis Magnetron Sputtering

The off-axis sputtering technique was used to deposit Al-doped ZnO (AZO) films on glass substrates at room temperature. For the illustration of the sample position in the sputtering chamber, the value ofR/ris introduced. Here,ris the radius of AZO target and R is the distance between the sample and the center of substrate holder. A systematic study for the effect of deposition parameters on structural, optical, and electrical properties of AZO films has been investigated in detail. As the sample position ofR/ris fixed at 1.8, it is found that the as-deposited AZO film has relatively low resistivity of 2.67 × 10−3 Ω-cm and high transmittance above 80% in the visible region. Additionally, after rapid thermal annealing (RTA) at 600°C with N2atmosphere, the resistivity of this AZO film can be further reduced to 1.19 × 10−3 Ω-cm. This indicates the AZO films prepared by off-axis magnetron sputtering and treated via the appropriate RTA process have great potential in optoelectronic applications.

In situ X-ray diffraction and the evolution of polarization during the growth of ferroelectric superlattices.

In epitaxially strained ferroelectric thin films and superlattices, the ferroelectric transition temperature can lie above the growth temperature. Ferroelectric polarization and domains should then evolve during the growth of a sample, and electrostatic boundary conditions may play an important role. In this work, ferroelectric domains, surface termination, average lattice parameter and bilayer thickness are simultaneously monitored using in situ synchrotron X-ray diffraction during the growth of BaTiO3/SrTiO3 superlattices on SrTiO3 substrates by off-axis radio frequency magnetron sputtering. The technique used allows for scan times substantially faster than the growth of a single layer of material. Effects of electric boundary conditions are investigated by growing the same superlattice alternatively on SrTiO3 substrates and 20 nm SrRuO3 thin films on SrTiO3 substrates. These experiments provide important insights into the formation and evolution of ferroelectric domains when the sample is ferroelectric during the growth process.

Transparent conductive Al and Ga doped ZnO films deposited using off-axis sputtering

Al and Ga doped ZnO (AZO and GZO) films were deposited using an off-axis dc magnetron sputtering method. At the off-axis positions, both the mobility and carrier density increased, resulting in enhanced conductivity of both the AZO and GZO films due to an increase in the crystallinity. The lowest resistivities of the AZO and GZO films deposited at room temperature were 1.1×10−3Ωcm and 6.5×10−4Ωcm, respectively. Increasing the substrate temperature up to 130°C led to a decrease in the lowest resistivity to 6.1×10−4Ωcm for the AZO films. The transmittance of all films was above 80% in the visible region. These results suggest that off-axis magnetron sputtering might be a potentially effective deposition method with the reduced bombardments from high-energy particles.

Converse magnetoelectric coupling in NiFe/Pb(Mg1/3Nb2/3)O3–PbTiO3 nanocomposite thin films grown on Si substrates

Multiferroic NiFe (∼30 nm)/Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT, ∼220 nm) bilayered thin films were grown on common Pt/Ti/SiO2/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMN–PT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMN–PT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMN–PT nanocomposite thin films.

Orientation-dependent piezoelectric properties in lead-free epitaxial 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 thin films

Orientation-engineered 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) thin films were deposited on La0.7Sr0.3MnO3-coated SrTiO3 single-crystalline (001), (110), and (111) substrates by off-axis radio-frequency magnetron sputtering. X-ray diffraction confirmed a highly epitaxial growth of all the as-deposited films. It is believed the strong orientation dependence of ferroelectric and piezoelectric properties on the films is attributed to the relative alignment of crystallites and spontaneous polarization vector. The optimal ferroelectric response lies in the [001] direction, whereas a comparatively large effective piezoelectric coefficient d33,eff of 100.1 ± 5 pm/V was attained in [111] BZT-BCT thin film, suggesting its potential application for high-performance lead-free piezoelectric devices.

Dramatic Reduction of FMR Linewidth in Epitaxial Pb(ZrTi)O $_{3}$-NiFe$_{2}$O$_{4}$ Nanocomposite Films

Self-assembled nanocomposite Pb(Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -NiFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> films have been grown on the (001)-oriented MgAl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> substrate by a 90° off-axis magnetron sputtering method. X-ray diffraction shows that both Pb(ZrTi)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and NiFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> phases are epitaxial with a 1-3 dimensional embedding composite structure. The vertical lattice mismatch between the Pb(ZrTi)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and NiFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> phase is only 0.65%, indicating almost perfect matching of both phases and low defect concentration. Magnetization measurement shows that the coercive field is 274 Oe and linear extrapolation of the in-plane magnetization yields a uniaxial anisotropy field of ~1.3 kOe for a 1200 nm-thickness sample. The peak-to-peak ferromagnetic resonance (FMR) linewidth of the film is about 271 Oe, therefore, suitable for nonreciprocal RF/microwave devices.

유연성 기판 위에 증착된 ITO 박막의 공정 온도에 따른 전기적·광학적 특성 평가

In this study, off-axis magnetron sputtering was used for the crystallized ITO thin films at a low temperature of about instead of the conventional RF sputtering because the off-axis sputtering can avoid the damage for the plasma as well as fabrication of thin films with a high quality. The ITO thin films grown on PET substrate at were crystallized with a (222) preferred orientation. 58-nm thick ITO films showed a resistivity of about and a transmittance of about 75% at a wavelength of 550 nm. The transmittance of the ITO thin films by an insertion of SiO2 thin films on ITO films was improved.