Resistance switching of heteroepitaxial Cr-doped SrZrO<Subscript>3</Subscript> thin films

Heteroepitaxial Cr-doped SrZrO₃ thin films were grown on 200 nm-thick SrRuO₃ films deposited on SrTiO₃ (100) substrates by pulsed laser deposition. The Cr-doped SrZrO₃ films on the SrRuO₃ bottom electrode exhibited an XRD peak for the (hh0/00l) planes of SrZrO₃ and SrRuO₃ thin films, showing a good epitaxial relationship. The I–V characteristics of the Au/Cr-doped SrZrO₃/SrRuO₃ MIM structures revealed resistance switching behavior with an ON/OFF resistance ratio of 20.     

Epitaxial 0.65PbMg1/3Nb2/3O3-0.35PbTiO3 (PMN-PT) thin films grown on LaNiO3/CeO2/YSZ buffered Si substrates

Ferroelectric PMN-PT thin films with a thickness of 600 nm were epitaxially grown on buffered Si (0 0 1) substrates at a substrate temperature that ranged from 550 to 700 °C using pulsed laser deposition (PLD). LaNiO₃ (LNO) electrode thin films with a resistivity of ∼1900 μΩ cm were epitaxially grown on CeO₂/YSZ buffered Si (0 0 1) substrates. The PMN-PT thin films grown at 600 °C on LNO/CeO₂/YSZ/Si substrates had a pure perovskite and epitaxial structure. The PMN-PT films exhibited a high dielectric constant of about 1818 and a low dissipation factor of 0.04 at a frequency of 10 kHz. Polarization-electric-field (P-E) hysteresis characteristics, with a remnant polarization of 11.1 μC/cm² and a coercive field of 43 kV/cm, were obtained in the epitaxial PMN-PT films.     

Characteristics of TiN thin films grown by ALD using TiCl4 and NH3

Titanium nitride thin film was deposited on a silicon wafer by the Atomic Layer Deposition (ALD) method using TiCl₄ and NH₃ as source chemicals. Nitrogen gas was used for carrying the TiCl₄ and purging the reactants. The gases were introduced into the reaction chamber in the sequence of TiCl₄?N₂?NH₃?N₂ for the saturated surface reaction on the wafer. TiN film was grown with [100] preferred orientation at 350°C, while with [111] preferred orientation at 450°C and higher temperatures. The deposition rate was constant as 0.17 Å/cycle irrespective of deposition temperature, which demonstrates TiN film was grown by the ALD growth mechanism. TiN thin films grown at a temperature higher than 450°C with thickness of 320 Å showed electrical resistivity as low as 72×10^?6 Ωcm.     

Direct deposition of CeO2 films on Ni metal substrate by chemical vapor deposition

Cerium dioxide thin films have been grown in-situ directly on cube textured Ni substrate by metal-organic chemical vapor deposition (MOCVD). At a lower deposition temperature of 400°C, an amorphous film was formed. The texture of crystalline CeO₂ film was changed from (200) orientation to (111) orientation when the deposition temperature was increased from 450°C to 550°C. The growth rate was ~40 nm/min and the rms surface roughness was 50 nm for the CeO₂ film deposited at 450°C for 10 min. Surface roughness of the film was increased with the development of (111) orientation. Deposited CeO₂ film showed a mixed texture of (100)<001> and (100)<011> orientation. Depending on the deposition condition, the transition from (100)<001> texture to (100)<011> orientation was observed.     

Influence of laser treatment on the electrical properties of plasma-enhanced-atomic-layer-deposited TiO2 thin films

TiO₂ dielectric films with 38 nm thickness were grown on Si (100) substrates at 200°C by plasma-enhancedatomic-layer deposition. Laser-irradiated TiO₂ films maintained an amorphous phase similar to as-grown films and showed an increase in permittivity and leakage current density with increasing laser powers and the number of laser shots at constant laser power. Laser-irradiation of TiO₂ films at room temperature produced oxygen vacancies at the film surface and new Ti³⁻ valences. The electrons and space charges produced through the defect chemistry increased the leakage current density and permittivity in laser-irradiated TiO₂ films, respectively. The dielectric and electrical properties of the laser-irradiated TiO₂ films were completely recovered to correspond with those of as-grown films by post-annealing at 300°C for 5 min in O₂ ambient.     

Ferroelectric properties of dysprosium-doped Bi4Ti3O12 thin films crystallized in various atmospheres

Dysprosium-doped Bi4Ti3O12 （Bi3.4Dy0.6Ti3O12, BDT） ferroelectric thin films were deposited on Pt（111）/Ti/SiO2/Si（111） substrates by chemical solution deposition （CSD） and crystallized in nitrogen, air and oxygen atmospheres, respectively. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. The results show that the crystallization atmosphere has significant effect on determining the crystallization and ferroelectric properties of the BDT films. The film crystallized in nitrogen at a relatively low temperature of 650 ℃, exhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2Pr = 24.9 ℃/cm^2 and a coercive field of 144.5 kV/cm. While the films annealed in air and oxygen at 650 ℃ do not show good crystallinity and ferroelectricity until they are annealed at 700 ℃. The structure evolution and ferroelectric properties of BDT thin films annealed under different temperatures （600-750 ℃） were also investigated. The crystallinity of the BDT films is improved and the average grain size increases when the annealing temperature increases from 600 ℃ to 750 ℃ at an interval of 50 ℃. However, the polarization of the films is not monotonous function of the annealing temperature.     

Properties of multilayer gallium and aluminum doped ZnO(GZO/AZO) transparent thin films deposited by pulsed laser deposition process

Multilayer gallium and aluminum doped ZnO (GZO/AZO) films were fabricated by alternative deposition of Ga-doped zinc oxide(GZO) and Al-doped zinc oxide(AZO) thin film by using pulsed laser deposition(PLD) process. The electrical and optical properties of these GZO/AZO thin films were investigated and compared with those of GZO and AZO thin films. The GZO/AZO (1:1) thin film deposited at 400 °C shows the electrical resistivity of 4.18×10^?4 ωcm, an electron concentration of 7.5×10²⁰/cm³, and carrier mobility of 25.4 cm²/(V·s). The optical transmittances of GZO/AZO thin films are over 85%. The optical band gap energy of GZO/AZO thin films linearly decreases with increasing the Al ratio.     

Nano-indentation fracture test of Pb(Zr0.52Ti0.48)O3 ferroelectric thin films

In this paper, we propose an elastic groundsill beam model with piezoelectric effect considered to assess the interfacial adhesion of ferroelectrics thin films, complemented and validated by nano-indentation fracture test on Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films. It was observed that the hardness and elastic modulus of thin films depend on the indentation depth. It was also observed from the load-indentation depth curves and atomic force microscopy (AFM) images that the fracture failure of PZT thin films induced by nano-indentations can be divided into three typical stages: no damage, bulging and spallation. The delamination of thin film systems was modeled as an interfacial crack propagation problem, with the energy release rate determined from the elastic groundsill beam model. Good agreement was observed between the indentation load and the radius of the largest imprint. For PZT thin films deposited on single Si substrate with thickness of 350 nm and 450 nm, the energy release rates per unit new crack area are in the range of 3.4~52.4 J/m² and the phase angles are constant of 13.4°. The corresponding mode I and mode II stress intensity factors are in the range of K_I=0.4–1.6MPa·m^1/2 and K_II=0.6–2.2MPa·m^1/2.     

Effects of atomic layer deposition temperatures on structural and electrical properties of ZnO films and its thin film transistors

Organic-inorganic thin film transistors (OITFTs) with Al/ZnO/PVP structure on Si substrate were fabricated and studied as to their structural and electrical properties. PVP (poly-4-vinylphenol) organic gate insulator was coated on Si substrate by spin coating method. The ZnO was deposited as an active layer by using the atomic layer deposition (ALD) method on PVP/Si substrate at various temperatures ranging from 80 to 140 °C. The structural and electrical properties of ZnO thin films were analyzed by X-ray diffraction and by hall-effect measurement system for optimum process of the OITFT. The grain size and carrier concentration of ZnO films increased, and the resistivity decreased as the deposition temperature increased from 80 to 140 °C. The field effect mobility, on/off current ratio and threshold voltage of OITFTs with ZnO active layer deposited at 100 °C were found to be 0.37 cm²/V·s, 5×10² and 5 V, respectively.     

Preparation of polyacenic semiconductive thin films by excimer laser ablation

Polyacenic semiconductive thin films (PAS-TFs) were prepared onto a quartz or a KBr substrate by excimer laser ablation at 308 nm of a bulk phenol-formaldehyde (PF) resin and the bulk of a PAS material which was obtained by heat treatment of the PF resin at 535 °C (pyrolytic PAS (535 °C)). These were homogeneous brown and/or dark brown thin films consisting of fine particles. The electric conductivities of the films thus prepared from PF resin and pyrolytic PAS(535 °C) were about 10⁻⁸ and 10⁻⁵ S cm⁻¹ at room temperature, respectively. Remarkable increase of electric conductivities was achieved on increasing the substrate temperature during the deposition process. In particular, the conductivity of the film from pyrolytic PAS (535 °C) reached more than 10 ⁻² S cm⁻¹, which is comparable to that of bulk PAS material prepared by pyrolytic treatment at 775 °C, when deposited on a substrate at 300 °C.     

Effect of annealing temperature on ferroelectric properties of （Bi, Nd）4（Ti, V）3O12 thin films

Thin films of Nd^3＋/V^5＋-cosubstituted bismuth titanate, （Bi3.sNd0.5）（ Ti2.96V0.04）O12 （BNTV）, were fabricated on the Pt（111）/Ti/SiO2/Si（100） substrates by a chemical solution deposition technique and annealed at different temperatures of 650, 700, 750 and 800 ℃. The surface morphology and ferroelectric properties of the samples were studied in detail. The result shows that the film annealed at 800 ℃ indicates excellent ferroelectricity with a remanent polarization of 2Pr=40.9 i.tC/cm^2, a coercive field （Ec） of 114 kV/cm at an applied electrical field of 375 kV/cm. The substitution of Ti-site ion by V^5＋ ions could improve the upper limit of the optimal annealing temperature by decreasing the space charge density in BNT thin film. Additionally, the mechanism concerning the dependence of ferroelectric properties of BNTV thin films on the annealing temperature was discussed.     

Structural,microstructural and magnetic investigations on the epitaxially grown Ni2MnGa(010) films on MgO(100) substrate

We report the epitaxial growth of Ni₂MnGa thin films on MgO(100) substrate deposited at elevated temperature using direct current magnetron sputtering. The structural and texture analysis of as-deposited film reveal the (010) crystallographic orientation with seven modulated martensite phase and an epitaxial relationship of Ni₂MnGa(010){101} || MgO(001){110} between the film and the substrate. The crystal quality of the films was analysed by performing symmetric and asymmetric rocking curve measurements and dislocation density for screw and edge dislocations is determined to be 6 × 10⁹ cm⁻² and 3.45 × 10¹⁰ cm⁻², respectively. The presence of micro-twins at an angle of 45° with respect to growth direction and seven modulated nano-twins formed by adaptive modulation has been observed with transmission electron microscopy investigations. The magnetic measurements indicates magnetic field induced reorientation of martensitic variants, strong magneto-crystalline anisotropy and a very high saturation magnetization (I_S) of 61 emu g⁻¹ in the film.     

BiFeO3 thin films of (1 1 1)-orientation deposited on SrRuO3 buffered Pt/TiO2/SiO2/Si(1 0 0) substrates

BiFeO₃ (BFO) thin films of varying degrees of (1 1 1) orientation were successfully grown on SrRuO₃-buffered Pt/TiO₂/SiO₂/Si(1 0 0) substrates by off-axis radio-frequency magnetron sputtering. They demonstrate much enhanced ferroelectric behavior, including a much enhanced remnant polarization (2P_r ～ 197.1 μC cm^?2 at 1 kHz) measured by positive-up negative-down (PUND), at an optimized deposition temperature of 590 °C. The effects of film deposition temperature on the degree of (1 1 1) orientation, film texture, ferroelectric behavior, leakage current and fatigue endurance of the BFO thin films were systematically investigated. While the degree of (1 1 1) orientation is optimized at 590 °C, the defect concentration in the film increases steadily with increasing deposition temperature, as demonstrated by the dependence of leakage behavior on the deposition temperature. The polarization behavior is shown to strongly depend on the degree of (1 1 1) orientation for the BFO thin film. Oxygen vacancies are shown to involve in the conduction and dielectric relaxation of the BFO thin films deposited at different temperatures, as demonstrated by their dielectric and conduction behavior as a function of both temperature (in the range 294–514 K) and frequency (in the range 10^?1–10⁶ Hz).     

High-repetition rate pulsed laser deposition of ZrC thin films

ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that the films were crystalline. Films deposited under residual vacuum or 2 × 10^− 3 Pa of CH₄ atmosphere exhibited a (200)-axis texture, while those deposited under 2 × 10^− 2 Pa of CH₄ atmosphere were found to be equiaxed. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES), showed the usual high oxygen contamination of carbides. Once the topmost − 3-5 nm region was removed, the oxygen concentration rapidly decreased, being around 3-4% only in bulk. Scanning electron microscopy (SEM) investigations showed a smooth, featureless surface morphology, corroborating the roughness values below 1 nm (rms) obtained from simulations of the X-ray reflectivity (XRR) curves. From the same simulations we also estimated films mass density values of around 6.32-6.57 g/cm³ and thicknesses that correspond to a deposition rate of around 8.25 nm/min. Nanoindentation results showed a hardness of 27.6 GPa and a reduced modulus of 228 GPa for the best quality ZrC films deposited under an atmosphere of 2 × 10^− 3 Pa CH₄.     

Annealing time dependent structural,morphological, optical and electrical properties of RF sputtered p-type transparent conducting SnO2/Al/SnO2 thin films

Transparent p-type conducting SnO₂/Al/SnO₂ multilayer films were fabricated on quartz substrates by radio frequency (RF) sputtering using SnO₂ and Al targets. The deposited films were annealed at a fix temperature of 500 °C for different time durations (1–8 h). The effect of annealing time on the structural, morphological, optical and electrical performances of SnO₂/Al/SnO₂ multilayer films was studied. X-ray diffraction (XRD) results show that all the p-type conducting films possess polycrystalline SnO₂ with tetragonal rutile structure. Hall-effect results indicate that 500 °C for 1 h is the optimum annealing condition for p-type SnO₂/Al/SnO₂ multilayer films, resulting in a hole concentration of 1.14×10¹⁸ cm^–3 and a low resistivity of 1.38 Ω·cm, respectively. The optical transmittance of the p-type SnO₂/Al/SnO₂ multilayer films is above 80% within annealing time range of 1–8 h, showing maximum for the films annealed for 1 h.     

Kinetics of formation and growth of epitaxial SrTiO<Subscript>3</Subscript> films of single-crystal (001) SrTiO<Subscript>3</Subscript> supports

The aim of this study was to quantitatively estimate the kinetics of the formation and growth of oxide SrTiO₃ (STO) films using the method of the in situ reflection high-energy electron diffraction (RHEED) and compare the obtained results with the known growth models and theoretical estimates. The kinetics of the relaxation and crystallization of particles is studied under pulsed laser deposition (PLD) from oxide targets onto (001) STO supports or onto the surface of STO film growth at 650–800°C. Deposition frequencies of 0.1–10 Hz typical of PLD were used. The surface morphology and film structure was studied ex situ using the methods of AFM and X-ray-structural analysis. It was found that the time of relaxation of deposited particles is within the range of 2–20 s, which greatly exceeds or is comparable to the relative pulse duration. It was experimentally shown that structural distortions in epitaxial films for temperatures of ≤900°C are mainly due to the high rate of deposition and limited surface mobility of particles. The effect of structural relaxation in films is observed after the end of deposition; the time constant of bulk structural relaxation is ∼10 − ∼10² s or more. The obtained kinetic parameters of the formation of an oxide structure may be useful for the development of crystallization theory, as well as to optimize the conditions of epitaxial oxide film growth.     

Effect of crystallization temperature on microstructure and ferroelectric property of Bi3.25 Eu0.75 Ti3O12 thin films prepared by MOD method

1 Introduction Many researches have been done on candidates in ferroelectric material for non-volatile random access memories applications. Among them, lead zirconate titanate(PZT) thin films have been widely studied because they have many advantages such…     

Substrate heterostructure effects on interface composition,microstructure development and functional properties of PZT thin films

Platinum- and (La_0.8,Sr_0.2)MnO₃ (LSMO)-terminated silicon substrates were used for the liquid-phase deposition of Pb(Zr_0.52,Ti_0.48)O₃ (PZT) thin films. Different layer thicknesses ranging from 100 to 600 nm were processed by sequential coating. Characterization of the films involved X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy (XPS) combined with depth profiling to probe the interface composition. The films deposited on Pt exhibit an intermetallic layer, Pt_xPb, after annealing at 500 °C in air. This film has been used to establish the XPS signature of the intermetallic phase which consists of a negative shift of the peak position of Pt(4f) due the electron transfer from Pb to Pt. In all cases pure phase perovskite thin films were obtained after short annealing at 700 °C. XPS depth profiling shows unambiguously the existence of an intermetallic layer, Pt_xPb, of approximately 10 nm at the interface between Pt and PZT, while an interdiffusion layer of ～30 nm was observed between LSMO and PZT. The impacts of interfacial layers on microstructure development and functional properties translate in the formation of specific textures, i.e. a pronounced (1 1 1)-texture on Pt due to lattice matching between (1 1 1)-PZT and (1 1 1)-Pt_xPb, and a random film orientation on LSMO, and a substantial thickness dependence of the dielectric and ferroelectric properties, though specific behaviors were observed for the two different substrate heterostructures.     

Growth and characterization of epitaxial Ba(Zn1/3Ta2/3)O3 (1 0 0) thin films

We have synthesized and characterized epitaxial and stoichiometric Ba(Zn_1/3Ta_2/3)O₃ (1 0 0) dielectric thin films grown on MgO (1 0 0) substrates by pulsed laser deposition. Advanced electronic structure calculations were used to guide the interpretation of the experimental data. Zn-enriched targets and high oxygen pressures were used to compensate for Zn loss during film growth. The Ba(Zn_1/3Ta_2/3)O₃ films had an indirect optical band gap of ～3.0 eV and a refractive index of 1.91 in the visible spectral range. Zn–Ta B-site ordering was not observed in the Ba(Zn_1/3Ta_2/3)O₃ thin film X-ray diffraction data. A dielectric constant of 25 and dissipation factor of 0.0025 at 100 kHz were measured using the interdigital capacitor method. The Ba(Zn_1/3Ta_2/3)O₃ films exhibited a small thermally activated ohmic leakage current at high fields (<250 kV cm^–1) and high temperatures (<200 °C) with an activation energy of 0.85 eV.     

Characterization of rapid thermally processed LiMn204 thin films derived from solution deposition

Cathode material LiMn₂O₄ thin films were prepared through solution deposition followed by rapid thermal annealing. The phase identification and surface morphology were studied by X-ray diffraction and scanning electron microscopy. Electrical and electrochemical properties were examined by four-probe method, cyclic voltammetry and galvanostatic charge-discharge experiments. The results show that the film prepared by this method is homogeneous, dense and crack-free. As the annealing temperature and annealing time increase, the electronic resistivity decreases, while the capacity of the films increases generally. For the thin films annealed at different temperatures for 2 min, the thin film annealed at 800 °C has the best cycling behavior with the capacity loss of 0.021% per cycle. While for the thin films annealed at 750 °C for different times, the film annealed for 4 min possesses the best cycling performance with a capacity loss of 0.025% per cycle. For the lithium diffusion coefficient in LiMn₂O₄ thin film, its magnitude order is 10⁻¹¹ cm²·s⁻¹.