Electrode effect on resistive switching of Ti-added amorphous SiOx films

Ti-added amorphous SiO_x films were sputter-deposited into stacks of Pt/SiO_x/Pt and Cu/SiO_x/Pt. Optimally prepared Pt/SiO_x/Pt exhibits unipolar resistive switching over 10² cycles, resistance ratio ∼ 10³, yet wide voltage distribution (2 ∼ 7 V for SET, 0.5 ∼ 1.5 V for RESET). Cu/SiO_x/Pt exhibit similar endurance, resistance ratio up to 10⁷, and SET and RESET voltages reduced to 1.8 ∼ 4.2 V and 0.5 ∼ 1 V, respectively. Cu diffusion into SiO_x at the virgin state may play a role in resistive switching of Cu/SiO_x/Pt stack besides of filament conduction. Ti-added amorphous SiO_x films incorporating Cu electrode shows potential for resistive memory.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

Gasochromic switching of reactively sputtered molybdenumoxide films: A correlation between film properties and deposition pressure

Molybdenumoxide (MoO_x) thin films can change their optical properties upon exposure to hydrogen. Since the film properties strongly depend on process parameters we have studied how the films are affected by the total pressure during deposition. Stoichiometric and sub-stoichiometric MoO_x films were prepared by reactive direct current magnetron sputtering in an atmosphere of argon and oxygen. Substoichiometric films were coated with platinum as a catalyst and were colored in diluted hydrogen atmosphere and bleached in air. Optical spectroscopy, X-ray reectometry, spectroscopic ellipsometry and simulations of the measured spectra were used to characterize the films ex situ. In situ switching characteristics as revealed by optical spectroscopy and changes in stress were measured as well. We find that the total pressure during sputter deposition has a strong influence on the optical constants, the film density, and the sputter rate. The mechanical stresses and switching Preprint submitted to Elsevier Science 10 March 2006 cycles during the film coloration and bleaching also strongly depend on the total pressure. The influence of the sputter pressure on film properties is explained by the kinetics during the sputter process.     

Investigation of SiOxCy film as the encapsulation layer for full transparent OLED using hollow cathode discharge plasma at room temperature

The plasma polymer of SiO_xC_y film has attracted much attention because it could possess both the organic and inorganic properties simultaneously for wide range applications. In this work, a SiO_xC_y film with a gradient composition through tuning the N₂O/N₂O + Ar ratio from 0% to 100% was used for TOLED encapsulation using hollow cathode discharge plasma. In order to confirm whether the plasma damage was caused during the PECVD process, a ZnO buffer layer prepared using RF sputtering was deposited before encapsulation. Furthermore, the reference samples with glass lid encapsulation were also used for comparison. The results showed that the SiO_xC_y film with a gradient composition cooperated with the sputtering ZnO buffer layer was a simple and effective method for TOLED encapsulation.     

Mechanical and environmental properties of Ge1−xCx thin film

Ge_1−xC_x thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ as precursors and its mechanical and environmental properties were investigated. The samples were measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum, FT-IR spectrometer, WS-92 testing apparatus of adhesion and FY-03E testing apparatus of salt and fog. The results show that the infrared refractive index of Ge_1−xC_x thin film varies from 2 to 4 with different x values. The adhesion increases with increasing gas flow ratio of GeH₄/CH₄ and decreases with increasing film thickness. The nanoindentation hardness number decreases with increasing germanium content. Three series films exhibit the best anti-corrosion property when the RF power is about 80 W, or substrate temperature is about 150 °C, or DC bias is about −100 V. Furthermore, increasing the gas flow ratio of GeH₄/CH₄ improves the anti-corrosion property of these films.     

Regulate the content of magnesium in MgxZn1−xO films by vacuum anneal

Mg_xZn_1−xO thin films were grown on c-sapphire substrates by metal-organic chemical vapor deposition (MOCVD), followed by annealing in vacuum at different temperatures for 1 h. The UV emission peak was blue shifted in the photoluminescence (PL) spectra and a dramatic shift of (0 0 2) diffraction peak to higher angle was observed in X-ray diffraction (XRD) pattern with increasing anneal temperature. This suggested the band gap and the lattice parameter of Mg_xZn_1−xO had been affected by annealing in vacuum. Furthermore, the structure of the film became sparser due to annealing in vacuum. From the X-ray photoelectron spectroscopy (XPS) and ICP of the Mg_xZn_1−xO film, we can find that the anneal temperature have an effect on the content of each element in Mg_xZn_1−xO quantitatively. In addition, the value of x in Mg_xZn_1−xO varied slightly as the annealing temperature increased. The above phenomena indicated that annealing in vacuum could slightly adjust the percentage of Mg indirectly in Mg_xZn_1−xO film and offer a good idea in Mg_xZn_1−xO devices facture.     

The properties of transparent semiconductor Zn1 − xTixO thin films prepared by the sol-gel method

Transparent semiconductor thin films of Zn_1 − xTi_xO (0 ≦ x ≦ 0.12) were deposited on alkali-free glass substrates by the sol-gel method. The effects of Ti addition on the crystallization, microstructure, optical properties and resistivity of ZnO thin films were investigated. The as-coated films were preheated at 300 °C, and then annealed at 500 °C in air ambiance. X-ray diffraction results showed all polycrystalline Zn_1 − xTi_xO thin films with preferred orientation along the (002) plane. Ti incorporated within the ZnO thin films not only decreased surface roughness but also increased optical transmittance and electrical resistivity. In the present study, the Zn_0.88Ti_0.12O film exhibited the best properties, namely an average transmittance of 91.0% (an increase of ~ 12% over the pure ZnO film) and an RMS roughness value of 1.04 nm.     

Influences of post-annealing on structural and electrical properties of Bi1.5Zn1.0Nb1.5O7 thin films prepared by pulsed laser deposition

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si(100) substrates at 650 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The crystallinity, microstructure and electrical properties of BZN thin films were investigated to verify the influences of post-annealing thermal process on them. The X-ray diffractometer (XRD) results indicate that all Bi_1.5Zn_1.0Nb_1.5O₇ thin films without post-annealing process or with post-annealing in situ vacuum chamber and in oxygen ambient exhibit a cubic pyrochlore structure. The improved crystallinity of BZN thin films through post-annealing was confirmed by XRD and scanning electron microscope (SEM) analysis. Dielectric constant and loss tangent of the as-deposited BZN thin films are 160 and 0.002 at 10 kHz, respectively. After annealing, dielectric properties of thin films are significantly improved. Dielectric constant and loss tangent of the in situ annealed films are 181 and 0.0005 at 10 kHz, respectively. But the films post-annealed in O₂ oven show the largest dielectric constant of 202 and the lowest loss tangent of 0.0002, which may attribute to the increase in grain size and the elimination of oxygen vacancies. Compared with the as-deposited BZN thin films, the post-annealed films also show the larger dielectric tunability and the lower leakage current density.     

Structure and tribological property of MoSx-CrTiAlN film by unbalanced magnetron sputtering

MoS_x-CrTiAlN film was deposited on Mg alloy substrates using unbalanced magnetron sputtering. First of all, the CrTiAlN layer was synthesized in a gas mixture of Ar + N₂, and then the MoS_x layer on CrTiAlN were deposited by a single MoS_x target. The composition, structure and tribological property of MoS_x-CrTiAlN film were characterized by X-ray photoelectron spectrometry, X-ray diffraction, transmission electron microscopy and ball-on-disc tester. The experimental results show that crystallography structure of CrTiAlN layer is FCC whilst the MoS_x layer has a mixed microstructure with hexagonal and amorphous state. The coefficient of friction of MoS_x-CrTiAlN film is a function of load and shows a steady decreasing with the increasing in applied load.     

Preparation of inorganic solid state thin film for electrochromic application

All oxide solid state ITO (indium tin oxide)/Li_yWO_3−x/Li_1−zMn₂O₄/ITO stacked structure was deposited on a silica glass substrate by pulsed laser deposition for its electrochromic application. The Li doped amorphous tungsten trioxide Li_yWO_3−x thin film prepared at room temperature and in oxygen pressure of 7 Pa got the color of blue due to the mixture valence state of tungsten. We found that the amorphous Li_1−zMn₂O₄ thin film was suitable for the electrochromic application in spite of the low ion conductivity along in-plane direction. The ITO electrode thin film deposited at room temperature showed the relatively high transmittance and the usable conductivity. The transmittance at a wavelength of 750 nm for the ITO/Li_yWO_3−x/Li_1−zMn₂O₄/ITO stacked film changed from 50% to 80% by the applied voltage, while the transmittance at around 450 nm did not change. The blue-colored electrochromic property could be observed for the all oxide solid state film.     

Oxygen ion drifted bipolar resistive switching behaviors in TiO2-Al electrode interfaces

The rutile TiO₂ thin film involving two different top electrodes (Pt and Al) clearly shows the unipolar and bipolar resistive switching transitions which are dependent on the degree of redox properties at TiO₂ layer-electrode interfaces. Detailed current level analysis coupled with Auger electron spectroscopy measurements of the Pt/TiO₂/Pt and Al/TiO₂/Pt structures in the on/off switching states revealed the implication of oxygen ion migration induced chemical reaction at the Al-TiO₂ interfaces. Therefore, it is expected that the bipolar transition nature of resistive switching with an Al electrode is the resulting formation of a thin AlO_x layer due to redox reaction at Al-TiO₂ layer interfaces.     

Perpendicular L10-FePt/Fe and L10-FePt/Ru/Fe graded media obtained by post-annealing

L1₀-FePt/Fe and L1₀-FePt/Ru/Fe films with perpendicular orientations were fabricated by magnetron sputtering and post-annealing. In comparison to films with sharp interfaces, the graded L1₀-FePt/Fe interface was more favorable for coercivity reduction. Inserting a ruthenium (Ru) interlayer between the hard L1₀-FePt and the soft iron (Fe) layers yielded a continuous L1₀-FePt/Fe graded film, which contributed to a large reduction in coercivity. The coercivity of L1₀-FePt/Ru/Fe films can be manipulated via the Ru thickness when the soft Fe layer is thin and via the Fe thickness when the soft Fe layer is thick.     

Effect of the oxygen fraction on the structure and optical properties of HfOxNy thin films

The main purpose of this work was to prepare hafnium oxynitride (HfO_xN_y) thin films. HfO_xN_y thin films were deposited by radio frequency reactive magnetron sputtering from a pure Hf target onto Quartz and ZnS substrates at room temperature. The depositions were carried out under an oxygen-nitrogen-argon atmosphere by varying the flow rate of the reactive gases (oxygen/nitrogen ratio). The variation of the flow rate of the reactive gases changed the structure and properties of the films. Glancing incidence X-ray diffraction (GIXRD) was used to study the structural changes of as-deposited films; a new crystalline hafnium oxynitride phase was formed in a region of oxygen/nitrogen ratio. Cross-section of the films observed by SEM revealed that the films grew with a columnar-type structure, and surface observation with AFM showed values of surface roughness changed with the flow rate of the reactive gases, higher oxygen fraction had lower surface roughness than lower oxygen fraction. Visible spectra, infrared spectra, refractive index, absorption coefficient also changed with the variation of the oxygen fraction.     

Interfacial layer growth of ZrO2 films on silicon

In this work, the interfacial layer growth for both as-deposited and annealed ZrO₂ thin films on silicon is analyzed in detail by the high-resolution cross-sectional transmission electron microscope and spectroscopic ellipsometry. For as-deposited ZrO₂/SiO₂/Si, the thickness of a SiO₂-like layer at the silicon interface was found to depend on the oxygen partial pressure during deposition. At oxygen partial pressure ratio of above 50% the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO₂ film and silicon consumption at the interface. At oxygen partial pressure ratio in the range 7-50%, the visible growth of interfacial silicon oxide layer was not present. The interfacial layer for ZrO₂/Si with optimal partial pressure (15%) during annealing at 600 °C was found to be the two-layer structure composed of the ZrSi_xO_y overlayer and the SiO_x downlayer. The formation of the interfacial layer is well accounted for diffusion mechanisms involving Si indiffusion and grain-boundary diffusion.     

Optical properties of amorphous, erbium-doped yttrium alumino-borate thin films

In this paper, we report on the optical characterizations of erbium-doped yttrium alumino-borate glassy thin films prepared by the polymeric precursor and sol-gel routes and the spin-coating technique. High quality planar waveguides were produced by a multilayer processing of Y_1−xEr_xAl₃(BO₃)₄ compositions with x = 0.02, 0.05, 0.10, 0.30, and 0.50. Their optical properties were investigated using transmission, photoluminescence, and m-lines spectroscopy, whereas high resolution scanning electron microscopy (HR-SEM) was applied to check film thickness and surface homogeneity. The refractive indices determined from transmission and m-lines spectroscopy are in good agreement just like the film thickness measured by HR-SEM and transmission spectroscopy. We observed low propagation losses, together with efficient photoluminescence emission for polymeric precursor thin films, involving low cost and environment friendly reactants.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Characterization of the chemical bath deposited In(OH)xSy films: Effect of the growth conditions

The In(OH)_xS_y thin films were deposited by chemical bath deposition (CBD) using three different deposition procedures: ‘hot’: starting the deposition at 70 °C, ‘cold’: starting the deposition at room temperature and pre-treatment with In³⁺ ions prior the ‘hot’ deposition. The analysis of the deposited In(OH)_xS_y layers on glass revealed that modifications in the chemical bath deposition procedure provoked significant changes in the nucleation process, the growth rate, the layer elemental composition and the layer morphology. With an additional In³⁺ pre-treatment or starting from a cold solution, the formation of a dense bottom layer has been observed, resulting in In(OH)_xS_y films with more compact structure with refractive index values of 2.6. The comparison of the measured In/S ratio with a thicker layer suggests, that the In(OH)_xS_y deposition starts with an OH-rich layer. Assuming the indirect allowed band gap transition type, an E_g of 2.2 eV was found independent of the procedure type or deposition time.     

Determination of optical constants of Cd1−xZnxTe thin films by spectroscopic ellipsometry

The optical response of vacuum-evaporated Cd_1−xZn_xTe thin films in the 1.5-5.6 eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The films of Cd_1−xZn_xTe (x=0.04) were deposited at room temperature onto well-cleaned glass substrates of film thickness 450 nm. The measured dielectric-function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points corresponding to the interband transitions. Dielectric related optical constants such as complex refractive index, the absorption coefficients and the normal incidence reflectivity, are presented. Results are in satisfactory agreement with the calculations over the entire range of the photon energies.     

Plasma deposition of n-SiOx nanocrystalline thin film for enhancing the performance of silicon thin film solar cells

In this paper, we firstly optimized the properties of n-SiO_x nanocrystalline thin film through tuning deposition parameters by plasma enhanced chemical vapor deposition, so that we can actively control the properties of materials obtained. Secondly, we proposed using n-SiO_x/Al as back reflector for amorphous silicon (a-Si:H) solar cells. Compared to Al single-layer as back reflector, adding an n-SiO_x layer into the back reflector could improve the solar cell performance, which not only enhances the short circuit current density by an improvement of spectral response in the wavelength range of 550-750 nm, but also improves the open circuit voltage. With an optimized n-SiO_x/Al back reflector, a-Si:H solar cells with an intrinsic layer thickness of 270 nm show 13.1% enhancement in efficiency. In addition, a-Si:H/μc-Si:H tandem solar cells with n-SiO_x as intermediate reflector were also researched. As a result, it evidently balanced the current matching between top and bottom cell.     

Influence of underlayers on the c-axis distribution in Co80Pt20 thin films

A series of approximately 40 nm thick Co₈₀Pt₂₀ thin films have been sputter-deposited onto a combination of Ta, Pt and Ru underlayers grown at different layer thicknesses. The addition of a Ta seed layer to the Pt and Ru underlayers caused the {0002} hexagonal close packed (hcp) Co₈₀Pt₂₀'s c-axis dispersion's full width at half maximum to narrow from approximately 12° to approximately 2°. In-situ stress measurements taken during deposition showed that the Ta seed layer reduced the growth stresses for the Pt and an initial 1 nm of growth for the Ru underlayers. The Ru layer thickness controlled the c/a ratio of the hcp Co₈₀Pt₂₀ film which regulated the degree of magnetic easy-axis alignment in the Co₈₀Pt₂₀ film. The optimal underlayer material stack for Co₈₀Pt₂₀ with a narrow c-axis dispersion and a high degree of magnetic easy-axis alignment was 5 nm Ta/10 nm Pt/5 nm Ru.