Properties Of Tantalum Oxide Films Research Articles

Effect of Laser Fluence on the Structural and Optical Properties of Tantalum Oxide Films Ablated by Pulsed Laser

The influence of laser fluence on the properties of thin films of tantalum oxide is studied in this paper, varying the laser fluence from 5.7 to 8.3 J/cm2. Thin films of tantalum oxide were deposited on glass substrates using pulsed-laser ablation technique. X-ray diffraction studies confirm the amorphous/nanocrystalline nature of all the films irrespective of the laser fluence. The Tauc plot analysis suggests that tantalum oxide is an indirect band gap material, whose band gap decreases with increase in laser fluence. The refractive index of the films is found to decrease with increase in laser fluence but the extinction coefficient of the films increases with increase in laser fluence. Fourier transform infrared studies suggest the use of tantalum oxide thin films as oxygen sensors. Micro-Raman analysis reveals the sensitiveness of Ta-O-Ta and Ta-O vibration modes to laser fluence. Among all the films, the film deposited at a laser fluence of 7 J/cm2 is found to be superior in quality.

The effect of substrate material on the properties of tantalum oxide films

The effect of substrate material on the electrical characteristics of Ta x O y films produced by high-frequency magnetron sputtering of a tantalum oxide target is studied. The effect of oxygen plasma on leakage currents, dielectric permittivity, and dielectric dissipation factor of thin (300–400 nm) Ta x O y layers is found. It is proposed to process tantalum oxide films in oxygen plasma to control their electrical and dielectric properties.

Effect of oxygen plasma on the properties of tantalum oxide films

The effect of oxygen plasma on the leakage current, permittivity, and the dielectric loss tangent of Ta2O5 thin layers (300–400 nm) is studied. It is suggested to treat tantalum oxide films in oxygen plasma to control their electrical and dielectric characteristics.

Effects of the post-annealing ambience on the microstructure and optical properties of tantalum oxide films prepared by pulsed laser deposition

Tantalum oxide films were synthesized by pulsed laser deposition (PLD). The influences of annealing temperatures and oxygen pressures on the crystalline, morphological and optical properties were investigated. Experimental results indicate that annealed film became crystallized in orthorhombic structure at 700 °C. The root-mean-square (RMS) roughness of the film became higher with the increase of annealing temperature. The transmittance and the optical band gap of the film increased with the increase of annealing temperature and the increase of annealing oxygen pressure. In addition and interestingly, crystallinity led to a decrease of transparency due to the increase of scattering losses, which resulted from the polycrystalline structure and the increase of RMS roughness. At the optimized ambience of 600 °C and 20 Pa, the transmittance of the annealed film achieved about 93% (the transmittance of bare substrate) at its peak values. And its optical band gap was 4.18 eV, which was close to the theoretical value of 4.2 eV.

Electrical and dielectrical properties of tantalum oxide films grown by Nd:YAG laser assisted oxidation

Tantalum pentoxide (Ta 2O 5) thin films (20 to 44 nm) have been grown by 1064 nm Nd:YAG laser oxidation of Ta deposited films with various thickness on Si. Fourier Transform Infrared (FTIR) spectrum, thickness distribution, dielectric and electrical properties of laser grown oxide layers have been studied. The effect of the sputtered Ta film thickness, laser beam energy density and the substrate temperature on the final Ta 2O 5 film structure has been determined. It is shown that the oxide layers obtained for the laser beam energy density in the range from 3.26 to 3.31 J/cm 2 and the substrate temperature around 350 °C have superior properties. FTIR measurement demonstrates that the Ta 2O 5 layers are obtained with the laser assisted oxidation technique. Metal Oxide Semiconductor capacitors fabricated on the grown oxide layers exhibits typical Capacitance–Voltage, Conductance–Voltage and Current–Voltage characteristics. However, the density of oxide charges is found to be slightly higher than the typical values of thermally grown oxides. The conduction mechanism studied by Current–Voltage measurements of the capacitors indicated that the current flow through the oxide layer is modified Poole–Frenkel type. It is concluded that the Ta 2O 5 films formed by the technique of Nd:YAG laser-enhanced oxidation at relatively low substrate temperatures are potentially useful for device applications and their properties can be further improved by post oxidation annealing processes.

Synthesis and optical properties of tantalum oxide films prepared by ionized plasma-assisted pulsed laser deposition

In this work, tantalum oxide (TaO x ) films were deposited on quartz glass substrates by pulsed laser deposition (PLD) and ionized plasma-assisted pulsed laser deposition (IPA-PLD). The effects of oxygen pressures and ionized oxygen plasma-assistance (IOPA) on the optical properties of deposited films have been studied. Ultraviolet–visible–near infrared (UV–VIS–NIR) scanning spectrophotometry was used to measure the transmittance of deposited films and to determine the optical band gap and absorption coefficient. Results show that the transmittance, absorption coefficient, band gap and chemical composition of deposited films reveal a strong dependence on the oxygen pressures and IOPA. Under optimum condition of IOPA, the refractive index of the synthesized film was 2.22 (at 633 nm wavelength), while an optical band gap of 4.18 eV was obtained. These two values compare very favorably with films produced by other methods.

Effect of post-deposition annealing on the structural and electrical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide thin films were formed on silicon (111) substrates kept at room temperature (303 K) by reactive sputtering of tantalum target in the presence of the mixture of oxygen and argon gases. The as-deposited films were annealed in air for an hour in the temperature range 573 - 873 K. The effect of annealing on the chemical binding configuration, structure and electrical properties of tantalum oxide films was systematically studied.

Structural and electrical properties of tantalum oxide films grown by photo-assisted pulsed laser deposition

We describe the growth of thin films of Ta 2O 5 on quartz and silicon (1 0 0) substrates by an in situ photo-assisted pulsed laser deposition (photo-PLD) using radiation from a Nd:YAG laser (wavelength, λ=532 nm ) to stimulate the ablation, and from an excimer lamp to excite additional photochemistry. The layers grown were investigated by Fourier transform infrared (FT-IR) spectroscopy, UV spectrophotometry, atomic force microscopy (AFM), ellipsometry and electrical measurements. We have found that they exhibit a significant improvement in microstructure, and optical and electrical properties compared with conventional PLD films prepared under, otherwise, identical conditions. For example, FT-IR results showed that the suboxide content in the as-grown films deposited by the photo-PLD process is less, while the leakage current density was an order of magnitude less at around 10 −6 A/cm 2 at a bias of 1 V. These results indicate that this photo-PLD process approach can be advantageous for dielectric and optical oxide film growth.

Effects of Additive Elements on Electrical Properties of Tantalum Oxide Films.

AbstractTa2O5-based composite films prepared by magnetron sputtering have been investigated with respect to their dielectric properties. As additive third oxides, Y2O3 and WO3 were found to be effective in improving insulating properties without decreasing their dielectric constant. Furthermore, electrical properties of Ta2O5-Y2O3 films were investigated by measuring the current-voltage characteristics in the temperature range from 100 to 330 K. Measurement of temperature dependence of the leakage current revealed that the conduction mechanism at RT changed from the Poole-Frenkel type to the Fowler-Nordheim tunneling type by adding Y2O3 into Ta2O5. Based on the detailed analysis of the results, it is concluded that the addition of Y2O3 into the Ta2O5 film is effective in the reduction of defect density without high-temperature annealing and the alteration of electrical conduction mechanisms of the films.

Effects of additive elements on electrical properties of tantalum oxide films

Ta2O5-based composite films prepared by magnetron sputtering have been investigated with respect to their dielectric properties. As additive third oxides, Y2O3 and WO3 were found to be effective materials for improving insulating properties. In these composite films, the dielectric constant remained unchanged. The maximum storage charge of the composite films was twice that of Ta2O5 films. The main reason for improving the insulating properties could be explained by the charge compensation of excess oxygen by these additive oxides.

Preparation and properties of tantalum oxide films by sol‐gel method

AbstractThe preparation of tantalum oxide thin film by the sol‐gel method is discussed. The conditions of the film growth are investigated carefully to avoid pinholes and cracks. In particular, the effect of hydrochloric acid added to the sol solution is clarified.The spectral and electrical properties of the thin film are investigated. The as‐grown film was amorphous and became crystallized at 720°C. The relative dielectric constant increases with an increase of the heat‐treatment temperature and the breakdown voltage decreased rapidly when the heat‐treatment temperature exceeded 600°. The optimum heat‐treatment temperature to achieve both high relative dielectric constant and high breakdown voltage was 400°C.It was found by TEM observation that the rapid degradation of the breakdown voltage was due to pinholes created during crystallization process.

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO2 layer at the Ta2O5/Si interface is observed by annealing in dry O2 or N2 and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta2O5 films decreases as the annealing temperature increases when annealed in dry O2 or N2. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta2O5. The effect is larger in thicker Ta2O5 films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO2 layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO2. The electrical properties of Ta2O5 as a function of annealing conditions do not depend on the fabrication method of Ta2O5 but strongly depend on the thickness of Ta2O5 layer.

Synthesis and properties of tantalum oxide films prepared by the sol-gel method using photo-irradiation

Recently, interest in the sol-gel method has been increasing, especially in preparing dielectric thin films with high dielectric constant. Tantalum oxide (Ta 2O 5) films are good candidates for insulators in LSI devices, electroluminescent devices and film capacitors because of their large dielectric constant. In the present paper, the preparation method and properties of Ta 2O 5 films, fabricated by a new process consisting of sol-gel process together with the photo-irradiation process, is reported. In this method, it became possible to fabricate Ta 2O 5 films at low temperature. Electric characteristics of these Ta 2O 5 films were almost the same as those Ta 2O 5 films prepared by sputtering and chemical vapor deposition.

Effects of oxidation conditions on the properties of tantalum oxide films on silicon substrates

Tantalum oxides have been prepared by thermal oxidation of sputtered tantalum films on silicon and silicon dioxide substrates at temperature between 450°C and 700°C. The composition of such oxide is tantalum pentoxide (Ta 2O 5) and the amount of silicon diffused into the tantalum oxide from the silicon substrate increases as the oxidation temperature increases. The temperature dependence of the dielectric constant of Ta 2O 5 on silicon can be explained in terms of its silicon concentration. CV curves of Al/Ta 2O 5/Si capacitors reveal the presence of donor-type interface states whose density decreases as the oxidation temperature increases. The flat band voltage of Al/Ta 2O 5/SiO 2/Si capacitors become more negative as the oxidation or annealing temperature increases regardless of the annealing ambient.

Effects of oxygen content on the optical properties of tantalum oxide films deposited by ion-beam sputtering

Ion-beam sputter deposition of tantalum oxide films was investigated for possible optical coating applications. Optical properties of such films were found to be a sensitive function of oxygen-to-argon ratio in the ion beam. Refractive index and absorption coefficient were determined in the 250–2000-nm wavelength range by spectrophotometric transmissivity. The different bonding states of the tantalum atoms were revealed by x-ray photoelectron spectroscopy. The visible wavelength refractive index was found to be 2.18 and optical band gap 4.3 eV, so long as the films did not contain inclusions of metallic tantalum. Films with an admixture of oxygen deficient suboxide components had a low-energy tail of increasing magnitude in the absorption spectrum.

Optical Properties of Tantalum Oxide Films on Silicon

Tantalum oxide films on silicon were prepared by thermal oxidation of vacuum‐deposited Ta films. The optical absorption of these noncrystalline films resembles closely that of crystalline , indicating a strong similarity in their short‐range order structures. For given oxidation conditions, the refractive index of the oxide films increases from ∼1.93 to 2.34 as the thickness increases from 12.5 to 111.7 nm. For a given tantalum film thickness, higher oxidation temperatures result in thicker oxides of lower refractive index. Additional oxide growth occurs during postoxidation heat‐treatment in oxygen while the refractive index decreases. The refractive index of a given oxide film increases from the Si/oxide interface toward the outer surface, e.g., from 2.08 to about 2.4. These phenomena are attributed to the incorporation of silicon into the Ta oxide during its growth. However, the estimated amount of silicon in the oxide is not sufficient to explain the observed values if it is assumed that the lowering of the refractive index is due simply to mixing with . Thus, it is concluded that the structure of noncrystalline has a great flexibility which is further enhanced by incorporating silicon; the polarizability of the Ta‒O bond is then strongly affected by silicon. This oxide has been applied as antireflection film in recently developed shallow junction silicon solar cells of increased conversion efficiency.

The mechanical properties of anodic tantalum oxide films

The mechanical properties of tantalum oxide films formed by anodizing were determined using a bulge test. The correlations between electrolytic breakdown and microstructure and between the microstructure and the observed mechanical properties are discussed. It is concluded that a direct relation exists between the incidence of crystalline film effects and the reduction in mechanical properties above a critical film thickness. The mechanical properties were found to be sensitive to the holding time at maximum cell voltage (anodic annealing time).