Structure Of Oxide Thin Films Research Articles

A light-stimulated synaptic transistor with synaptic plasticity and memory functions based on InGaZnOx–Al2O3 thin film structure

In this work, a synaptic transistor based on the indium gallium zinc oxide (IGZO)–aluminum oxide (Al2O3) thin film structure, which uses ultraviolet (UV) light pulses as the pre-synaptic stimulus, has been demonstrated. The synaptic transistor exhibits the behavior of synaptic plasticity like the paired-pulse facilitation. In addition, it also shows the brain's memory behaviors including the transition from short-term memory to long-term memory and the Ebbinghaus forgetting curve. The synapse-like behavior and memory behaviors of the transistor are due to the trapping and detrapping processes of the holes, which are generated by the UV pulses, at the IGZO/Al2O3 interface and/or in the Al2O3 layer.

Characteristic of Bismuth-Doped Tin Oxide Thin-Film Transistors

The influences of bismuth doping contents on the structure, morphology and electrical properties of amorphous bismuth-doped tin oxide (a-TBO) thin films have been investigated. With the increase of Bi content, the resistivity of TBO films monotonously increases due to the decreased oxygen vacancies. The thin-film transistors (TFTs) with a-TBO films as channel layers have been prepared on SiO2–Si substrate. Through the comparison of the transfer characteristic curves of the TFTs with different Bi contents, it is observed that Bi doping is useful to suppress the excess carrier concentration and improve the performances. TBO-TFTs with Bi content 2.7 at.% show the optimum performances, with a field effect mobility of 4.7 cm $^{2}\text{V}^{-1}\text{s}^{-1}$ , a threshold voltage of −3.9 V, a subthreshold swing value of 1.3 V/decade, and an ON–OFF current ratio of $2.3 \,\, \times \,\, 10^{6}$ . In addition, the bias stress stabilities of intrinsic SnO2 TFTs and a-TBO TFTs were compared and analyzed.

Effect of oxygen deficiency on electronic properties and local structure of amorphous tantalum oxide thin films

The dependence of electronic properties and local structure of tantalum oxide thin film on oxygen deficiency have been investigated by means of X-ray photoelectron spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS), and X-ray absorption spectroscopy (XAS). The XPS results showed that the oxygen flow rate change results in the appearance of features in the Ta 4f at the binding energies of 23.2eV, 24.4eV, 25.8, and 27.3eV whose peaks are attributed to Ta1+, Ta2+, Ta3+/Ta4+, and Ta5+, respectively. The presence of nonstoichiometric state from tantalum oxide (TaOx) thin films could be generated by the oxygen vacancies. In addition, XAS spectra manifested both the increase of coordination number of the first Ta-O shell and a considerable reduction of the Ta-O bond distance with the decrease of oxygen deficiency.

Electrical characterization of ZnO/4H‐SiC n–p heterojunction diode

The structure and electrical properties of zinc oxide (ZnO) thin films fabricated by atomic layer deposition (ALD) as well as electrical properties of ZnO/4H‐SiC n–p heterojunction diodes were investigated. Hall measurements of ZnO films show their n‐type high intrinsic conductivity. Structural characterization of the ZnO layers performed using X‐ray diffraction show their polycrystalline morphology. Aluminum (Al) ohmic contacts fabricated to n‐ZnO demonstrate linear characteristics and low resistivities. The I–V measurements of ZnO/4H‐SiC n–p heterojunction showed strong diode‐like behavior with the low leakage current, turn‐on voltage of around 1.7 V, ideality factor of 1.17, and high rectification ratio. Extracting the built‐in potential (1.71 V) from the C–V measurements allowed to determine band offsets and thus the flat‐band energy diagram of produced heterostructure.

Influence of Post-Deposition Annealing on Structure and Optical Characteristics of Niobium Oxide Thin Films

In this work, niobium oxide thin films were deposited on silicon wafer (100) and glass slide substrate by reactive magnetron sputtering. The niobium oxide films were further annealed and effect of post annealing on the crystallinity, microstructure and optical properties was studies. In order to identify the crystalline structure and microstructure, X-ray diffraction (XRD) and scanning electron microscope (SEM) measurement carried out. The optical property was determined by UV-Vis spectrophotometer. It has been observed that with increase in annealing temperature films become microcrystalline films. In particularly, the optical property of niobium oxide thin film also improves with annealing temperature.

Correlation between Microstructure of Copper Oxide Thin Films and its Gas Sensing Performance at Room Temperature

Radio-frequency magnetron sputtering using a Cu target was used to deposit cuprous oxide and cupric oxide thin films on silicon wafer. The substrate bias voltage and the O2 flow ratio were varied during the deposition. The deposited thin films were characterized using scanning electron microscope. We found that the spherical and pyramid shapes structure of copper oxide thin films were deposited at critical O2 flow ratio between 7 and 14%. The influence of substrate bias voltage was small and negligible. The deposited thin films were used for sensing characterization using ethanol vapor. Experimental results reveal that the pyramid shape of copper oxide thin film contribute to high respond rate when exposed to ethanol vapor. The respond and recovery rates which were measured at room temperature were very fast. This work had successfully demonstrated the formation of optimized copper oxide thin films and their usage for gas sensing application.

Resistive Switching Characteristics of Tantalum Oxide Thin Film and Titanium Oxide Nanoparticles Hybrid Structure.

The fabrication of hybrid structure with TiO2 nanoparticle assembly and Ta2O5 thin film layer was demonstrated. The close-packed nanoparticles could influence the resistive switching behaviors due to the huge numbers of interface states and vacancies in the nanoparticle assembly. The device with hybrid structure presented the typical bipolar resistive switching characteristics in the structure of Ti/TiO2/Ta2O5/Au on SiO2/Si substrate. The set voltage was observed at -0.7 V, and the reset voltage occurred at (-)-0.7 V, which was smaller than that of Ta2O5 layer only. The electrical conduction mechanisms were the ohmic conduction at low resistance state (LRS) and the space charge limited conduction at high resistance state (HRS), respectively. The devices showed stable current ratio of LRS to HRS. The temperature dependent properties of the devices were also investigated. The device with nanoparticle assembly showed better electrical characteristics with low HRS current level and stable LRS current level with respect to the temperature.

Effect of negative bias on the composition and structure of the tungsten oxide thin films deposited by magnetron sputtering

Tungsten oxide thin films were deposited at room temperature under different negative bias voltages (Vb, 0 to −500V) by DC reactive magnetron sputtering, and then the as-deposited films were annealed at 500°C in air atmosphere. The crystal structure, surface morphology, chemical composition and transmittance of the tungsten oxide thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV–vis spectrophotometer. The XRD analysis reveals that the tungsten oxide films deposited at different negative bias voltages present a partly crystallized amorphous structure. All the films transfer from amorphous to crystalline (monoclinic+hexagonal) after annealing 3h at 500°C. Furthermore, the crystallized tungsten oxide films show different preferred orientation. The morphology of the tungsten oxide films deposited at different negative bias voltages is consisted of fine nanoscale grains. The grains grow up and conjunct with each other after annealing. The tungsten oxide films deposited at higher negative bias voltages after annealing show non-uniform special morphology. Substoichiometric tungsten oxide films were formed as evidenced by XPS spectra of W4f and O1s. As a result, semi-transparent films were obtained in the visible range for all films deposited at different negative bias voltages.

Investigation of the effects of AR layers on the structure and properties of transparent conductive oxide thin films

Abstract Antireflective (AR) layers, i.e., a SiO2 overcoat and an Al2O3 undercoat were added to an ITO film to improve its visible transmittance. The microstructure and optical, electrical, and mechanical properties of the ITO films with and without AR coatings were systematically investigated. It is found that: 1) while the SiO2 overcoat has little impact on the microstructure of the ITO layer, the Al2O3 undercoat decreases the lattice parameter and grain size of the ITO layer; 2) while the carrier mobility for the ITO films with and without AR coatings is quite similar, the carrier concentration for the ITO film is little affected by the SiO2 overcoat, and it is increased by 31% with the Al2O3 undercoat; 3) the ITO film with AR layers shows significant improvement in scratch resistance, which is attributable mainly to the increased value of H/E and H3/E2 (where H and E are the hardness and elastic modulus respectively) and decreased residual stress; 4) the increased ratio H/E for the ITO film sandwiched structure over the ITO single layer indicates that there is a possibility to tailor the mechanical properties of a material by making multilayer composite.

High Sensitivity <inline-formula> <tex-math notation="LaTeX">$17~\mu \text{m}$ </tex-math></inline-formula> Pixel Pitch <inline-formula> <tex-math notation="LaTeX">$640\times 512$ </tex-math></inline-formula> Uncooled Infrared Focal Plane Arrays Based on Amorphous Vanadium Oxide Thin Films

This letter presents a 17 μm pixel pitch 640 × 512 uncooled infrared focal plane arrays based on the double sacrificial layer microbolometer technology incorporating amorphous vanadium oxide thin film and frequency selective structure. The amorphous vanadium oxide thin-film features low-noise and high-thermal coefficient of resistance characteristics, which help to improve the radiometric performance of the microbolometer. By incorporating a frequency selective second platform, the responsivity of the microbolometer was improved by nearly 30% over 8~14 μm spectra band. Noise equivalent temperature difference of less than 35 mK was obtained at 300 K ambient temperature with f/1.0 optics.

Evolution of microstructural and electrical properties of sputtered HfO2 ceramic thin films with RF power and substrate temperature

Hafnium oxide (HfO2) ceramic thin films were deposited on p-type silicon substrate by radio frequency magnetron sputtering at various RF powers and substrate temperatures. The morphological and electrical properties of the sputtered films were investigated and a correlation between the surface and interface properties of the HfO2 films was established with the variation of sputtering parameters. The evolution of monoclinic structure of the hafnium oxide thin films was observed by XRD studies. The surface of the HfO2 ceramic thin films became smooth with the decrease in grain size for higher power and growth temperature. The characteristic FTIR absorption peaks in the range from 550cm−1 to 900cm−1 depicted the formation of Hf–O bond for all the samples. The oxide charge density and leakage current density was found to be increased with the increase in RF power and substrate temperature, which was mainly due to the evolution of smaller grains. HfO2 thin films, grown at room temperature with a RF power of 150W, have shown better electrical properties.

Thickness dependence of dispersion parameters of the MoOx thin films prepared using the vacuum evaporation technique

The optical behaviors of molybdenum oxide thin films are highly important due to their widespread applications. In the present paper, the effect of thickness on the structure, morphology and optical properties of molybdenum oxide (MoOx) thin films prepared on Corning glass substrates using thermal evaporation technique was studied. The structure and morphology of films were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, while their optical properties were investigated by UV-VIS-NIR spectrophotometry in the spectral range from 300 to 2500 nm. It was observed that whole films have amorphous structure and also they showed rather high transmittance values reached nearly up to 90%. Absorption analysis showed two types of electronic transitions; both direct and indirect interband transition energy values of films decrease from 4.47 to 3.45 eV and from 3.00 to 2.75 eV, respectively, with increasing the film thickness, while the width of the localized states tail increases with thickness. This decrease in the band gap value can be attributed to the rising oxygen-ion vacancy densities with the thickness. The refractive indices of films were calculated from Sellmeier coefficients determined by nonlinear curve fitting method based on the measured transmittance spectral data. The dispersion of the refractive index was discussed in terms of the Wemple-DiDomenico single-oscillator model. The dispersion parameters such as average oscillator energy, Eo, the dispersion energy, Ed, and static refractive index no were evaluated and they found to vary significantly with the film thickness.

Hydrogen gas sensors based on electrostatically spray deposited nickel oxide thin film structures

A simple, low-cost, and home-built electrostatic spray deposition (ESD) system with the stable cone-jet mode was used to deposit nickel oxide (NiO) thin films on glass substrates kept at temperature of 400 ℃ as the primary precursor solution of 0.1 M concentration hydrated nickel chloride was dissolved in isopropyl alcohol. Electrical measurements showed that these films were of n-type conductivity while their resistance response to hydrogen flow in air ambient was varied by 2.81% with the rise and recovery time of 48 s and 40 s, respectively.

Surface and interface studies of RF sputtered HfO2 thin films with working pressure and gas flow ratio

In this work, hafnium oxide (HfO2) thin films were deposited on p-type silicon substrate by radio frequency magnetron sputtering at various working pressure ranging from 4 × 10−3 to 1 × 10−2 mbar and Ar/O2 flow ratio from 1:4 to 4:1. The morphological and electrical properties of the sputtered films were investigated and a correlation between the surface and electrical properties of the HfO2 films was established with the variation of sputtering parameters. The evolution of monoclinic structure of the hafnium oxide thin films was observed by XRD studies. The surface of the HfO2 films became rough with the increase in grain size at the sputter pressure of 8 × 10−3 mbar and Ar/O2 gas flow ratio of 1:4. The formation of HfO2 bond was seen from FTIR spectra. The oxide charge density has a lower value for the sputter pressure of 8 × 10−3 mbar and Ar/O2 gas flow ratio of 1:4 due to the evolution of larger grains. The interface charge density was found to be minimum at a sputter pressure of 8 × 10−3 mbar.

退火时间对AZO薄膜结构及光学性质的影响

退火时间对AZO薄膜结构及光学性质的影响

Structure and optical properties of nanocrystalline hafnium oxide thin films

Hafnium oxide (HfO2) films were grown by sputter-deposition by varying deposition temperature (Ts) in a wide range of 25–700°C. The deposited HfO2 films were characterized by studying their growth behavior, microstructure, and optical properties. Characterization of the films employing a wide range of analytical techniques indicate a clear functional relationship between processing conditions, structure, morphology, and optical properties. HfO2 films were amorphous at Ts⩽200°C, at which point a structural transformation occurs. HfO2 films grown at Ts⩾200°C were nanocrystalline, stabilized in a monoclinic structure. The nanocrystalline HfO2 films exhibit a strong (1¯11) texturing. The average crystallite size of HfO2 films increased from ∼10nm to ∼20nm with increasing Ts. Electron and atomic force microscopy measurements also correlated with the crystalline behavior, as well as an evenly distributed network of spherical shaped crystallites for the nanocrystalline HfO2 films. Density (ρ) of HfO2 films probed using X-ray reflectivity and ellipsometry data analysis indicate that the ρ values are strongly dependent on Ts; ρ varied in the range of 7.36–9.14g/cm3. The higher end of ρ values were noted only for HfO2 films grown at relatively higher Ts indicating the crystalline nature accounts for the ρ improvement. The band gap values of the films varied in the range of 5.78–6.17(±0.03)eV for Ts=25–700°C. Index of refraction at 550nm increased from 1.80 to 2.09, which also correlates with the characteristic feature of improved structural order, packing density of HfO2 films with increasing Ts. Based on the observed results, a correlation between growth conditions, microstructure and optical constants is established.

The effect of varying temperature and O2 flow rate in ex situ annealed tin-doped indium for fabrication of commercial grade indium tin oxide

In this work, tin-doped indium was deposited on a glass substrate via the electron beam evaporation tech- nique. Then, the as-grown thin films were baked in the presence of oxygen at different O2 flow rates and tempera- tures inside a furnace to obtain transparent conducting oxide thin film structures. The electrical and optical properties of the layers were investigated, the thickness of all samples was kept at 500 nm and the rate of deposition was set at 0.1 nm min -1 . The best optical and electrical properties were obtained at O2 flow rate of 1.5 Nl min -1 and temper- atures of 500 C where above 90 % optical transparency and B4 9 10 -3 ohm cm -1 electrical resistivity were achieved.

Shape, Morphology, and Phase Transitions during Co Oxide Growth on Au(111)

The surface structure and morphology of cobalt oxide thin films grown on Au(111) were studied using scanning tunneling microscopy (STM) and ultraviolet and X-ray photoelectron spectroscopies. Initial growth in O2 led to 2-D CoO clusters exhibiting a superstructure in STM images characteristic of the lattice mismatch between the rocksalt (111) surface and the substrate. The superstructure governed the CoO cluster shape; as a result, the shapes of clusters containing up to thousands of Co atoms were modulated by the most efficient packing of spheres. Continued growth led to a transition to 3-D, fully oxidized, spinel phase Co3O4 clusters. These Co3O4 clusters were embedded with characteristic “Y” shaped grain boundaries that result from high reactivity toward oxygen at specific edges of the CoO clusters, and the doubling of the periodicity when CoO is oxidized to Co3O4. Exposure of the Co3O4 films to O atoms induced oxidation toward Co2O3, which roughened the surface. Reducing these overoxidized films produ...

Bipolar Switching Properties of the Manganese Oxide Thin Film RRAM Devices

Up to now, the various non-volatile memory devices such as, ferroelectric random access memory (FeRAM), magnetron random access memory (MRAM), and resistance random access memory (RRAM) were widely discussed and investigated. For these nonvolatile memory devices, the resistance random access memory (RRAM) devices will play an important role because of its non-destructive readout, low operation voltage, high operation speed, long retention time, and simple structure. The resistance random access memory (RRAM) devices were only consisting of one resistor and one corresponding transistor. The subject of this work was to study the characteristics of manganese oxide (MnO) thin films deposited on transparent conductive thin film using the rf magnetron sputtering method. The optimal sputtering conditions of as-deposited manganese oxide (MnO) thin films were the rf power of 80 W, chamber pressure of 20 mTorr, substrate temperature of 580°C, and an oxygen concentration of 40%. The basic mechanisms for the bistable resistance switching were observed. In which, the non-volatile memory and switching properties of the manganese oxide (MnO) thin film structures were reported and the relationship between the memory windows and electrical properties was investigated.

Structure and properties of uranium oxide thin films deposited by pulsed dc magnetron sputtering

Crystalline uranium oxide thin films were deposited in an unbalanced magnetron sputtering system by sputtering from a depleted uranium target in an Ar+O2 mixture using middle frequency pulsed dc magnetron sputtering. The substrate temperature was constantly maintained at 500°C. Different uranium oxide phases (including UO2−x, UO2, U3O7 and U3O8) were obtained by controlling the percentage of the O2 flow rate to the total gas flow rate (fO2) in the chamber. The crystal structure of the films was characterized using X-ray diffraction and the microstructure of the films was studied using transmission electron microscopy and atom probe tomography. When the fO2 was below 10%, the film contains a mixture of metallic uranium and UO2−x phases. As the fO2 was controlled in the range of 10–13%, UO2 films with a (220) preferential orientation were obtained. The oxide phase rapidly changed to a mixture of U3O7 and U3O8 as the fO2 was increased to the range of 15–18%. Further increasing the fO2 to 20% and above, polycrystalline U3O8 thin films with a (001) preferential orientation were formed. The hardness and Young's modulus of the uranium oxide films were evaluated using nanoindentation. The film containing a single UO2 phase exhibited the maximum hardness of 14.3GPa and a Young's modulus of 195GPa. The UO2 thin film also exhibited good thermal stability in that no phase change was observed after annealing at 600°C in vacuum for 104h.