Dielectric properties of polyacrylamide polymer films

Summary Polyacrylamide polymer films of thickness 4.15 μm were prepared by isothermal immersion technique. The dielectric capacitance and dielectric loss of the films were studied as functions of frequency and temperature in the range 100 Hz|10 MHz and (300|450)K, respectively. Two dielectric loss peaks were observed in the dielectric loss spectra and were identified as β and α peaks. The β peak was attributed to the reorientation of dipoles and the α-peak was attributed to the deformations accompanied by large changes in the directions or locations of the dipoles.     

Preparation and properties of GaN films on Si(111) substrates

High-quality gallium nitride (GaN) films were prepared on Si(111) substrates by sputtering post-annealing-reaction technique. XRD, XPS, and SEM measurement results indicate that polycrystalline GaN with hexagonal structure was successfully prepared. Intense room- temperature photoluminescence that peaked at 354 nm of the films is observed. The bandgap of these films has a blueshift with respect to bulk GaN.     

Optical and dielectric properties of gadolinium–erbium oxide films prepared on Si(100) substrate

Samples of Er-doped Gd-oxide thin films were prepared on quartz and Si(p) substrates for optical and electrical investigations. These samples were annealed at different conditions and characterised by UV-VIS absorption spectroscopy, X-ray fluorescence, and X-ray diffraction. The constructed metal–oxide–semiconductor (MOS) devices were characterised by measuring their capacitance and ac conductance as a function of gate voltage. The ac conductance of the MOS devices was studied as a function of frequency in the range 500 Hz to 100 kHz. It was found that the corrected barrier hopping model controls experimental results and the parameters of the model were determined. PACS 77.55.+f; 72.20.-i; 78.70.En     

Dielectric properties of ultrathin films of molecular crystals

Dielectric properties of thin films (TF) of molecular crystals, including the effect of size and the boundary surfaces were analysed using Green's function method. Polarisability of molecules in various film layers and dielectric susceptibility of TF were calculated. A comparison with crystal bulk has shown that dielectric properties of TF are strongly influenced both by the sample dimensions and by the boundary conditions.The frequency dependence of the dielectric susceptibility has also been derived. One obtains the monotonous variation for the frequencies above and below exciton band. However, for the frequencies within the exciton band there appears to be complicated, non-monotonous dependence. The relationship between the dielectric susceptibility and the film width for the same frequency shows a complex, oscillatory behaviour. Furthermore, the amplitude of these oscillations increases with increasing film width, demanding the introduction of a damping factor. Finally, the thickness dependence of dielectric susceptibility was analysed in the Cole-Cole plot.     

溶胶凝胶制备氧化钒薄膜的生长机理及光电特性

采用溶胶凝胶法, 在不同的退火温度下制备了不同的氧化钒薄膜. 利用扫描电子显微镜、X射线衍射仪、高阻仪、紫外-可见分光光度计和傅里叶红外光谱仪等, 对薄膜的形貌、晶态、电学和光学特性进行了分析. 结果表明, 溶胶凝胶法获取V₂O₅薄膜的最佳退火温度为430 ℃, 低于此温度不利于使有机溶剂充分分解, 高于此温度则V–O键发生裂解、形成更多的低价态氧化钒. 本文制备的氧化钒薄膜具有较高的电阻温度系数和光吸收率, 适合应用在非制冷红外探测器中. 本文揭示了溶胶凝胶法制备氧化钒薄膜的生长机理. 关键词： 氧化钒薄膜 溶胶凝胶 光电特性 生长机理     

Li-doping effects on the electrical properties of ZnO films prepared by the chemical-bath deposition method

Zn_1−xLi_xO thin films, with x varying from 0.0 to 0.5, successfully have been deposited on glass substrates using the chemical bath deposition (CBD) technique. J–E characteristics, DC conductivity and dielectric measurements have been carried out. These measurements were done as a function of temperature, Li concentration and applied electric field intensity. The J–E characteristics are explained in terms of the Pool–Frenkel and Schottky effects. The J–E relation and DC conductivity are strongly dependent on both the Li concentration and applied electric field intensity. Dielectric hysteresis was observed between heating and cooling runs which revealed that the dielectric constant often increases slowly in the low-temperature region, then increases faster above the phase transition.     

Dielectric properties of anodic films on sputter-deposited Ti-Si porous columnar films

For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti-7 at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti-7 at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are ∼500 nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100-200 nm. When the porous Ti-7 at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to ∼35 V, while it is limited to less than 6 V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti-7 at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti-7 at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film.     

Growth, microstructure and electrical properties of sputter-deposited hafnium oxide (HfO2) thin films grown using a HfO2 ceramic target

Hafnium oxide (HfO₂) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(1 0 0) substrates under varying growth temperature (T_s). HfO₂ ceramic target has been employed for sputtering while varying the T_s from room temperature to 500 °C during deposition. The effect of T_s on the growth and microstructure of deposited HfO₂ films has been studied using grazing incidence X-ray diffraction (GIXRD), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive X-ray spectrometry (EDS). The results indicate that the effect of T_s is significant on the growth, surface and interface structure, morphology and chemical composition of the HfO₂ films. Structural characterization indicates that the HfO₂ films grown at T_s < 200 °C are amorphous while films grown at T_s > 200 °C are nanocrystalline. An amorphous-to-crystalline transition occurs at T_s = 200 °C. Nanocrystalline HfO₂ films crystallized in a monoclinic structure with a (−1 1 1) orientation. An interface layer (IL) formation occurs due to reaction at the HfO₂-Si interface for HfO₂ films deposited at T_s > 200 °C. The thickness of IL increases with increasing T_s. EDS at the HfO₂-Si cross-section indicate that the IL is a (Hf, Si)-O compound. The electrical characterization using capacitance-voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing T_s. The current-voltage characteristics indicate that the leakage current increases significantly with increasing T_s due to increased ILs.     

Some properties of indium-tin oxide films

Thin films of indium-tin oxide have been deposited by DC diode sputtering from an indium-tin alloy target in an argon, hydrogen and oxygen atmosphere. Films with sheet resistance of 11 ohms/square and 80% light transmission have been obtained. The effect of cathode composition and gas mixture on sheet resistance and optical transmission properties of the films have been studied.     

Orientation-dependent dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films prepared by sol-gel method

The orientation-dependent dielectric properties of barium stannate titanate (Ba(Sn_0.15Ti_0.85)O₃, BTS) thin films grown on (1 0 0) LaAlO₃ single-crystal substrates through sol-gel process were investigated. The nonlinear dielectric properties of the BTS films were measured using an inter-digital capacitor (IDC). The results show that the in-plane dielectric properties of BTS films exhibited a strong sensitivity to orientation. The upward shift of Curie temperature (T_c) of the highly (1 0 0)-oriented BTS thin films is believed to be attributing to a tensile stress along the in-plane direction inside the film. A high tunability of 47.03% was obtained for the highly (1 0 0)-oriented BTS films, which is about three times larger than that of the BTS films with random orientation, measured at a frequency of 1 MHz and an applied electric field of 80 kV/cm. This work clearly reveals the highly promising potential of BTS films for application in tunable microwave devices.     

Dielectric and leakage current properties of Li doped (Ba,Sr)TiO3 thick film interdigital capacitors on the alumina substrates

Li doped (Ba,Sr)TiO₃ thick films were fabricated by employing the screen printing method on the alumina (Al₂O₃) substrates. Interdigital capacitor patterns with seven fingers of 200 μm gap, 250 μm length were designed and screen printed on the alumina substrates. Ba_0.5Sr_0.5TiO₃ materials, paraelectric state at the room temperature, have been chosen for the microwave devices due to high dielectric permittivity and low loss tangent, however, the sintering temperature of (Ba,Sr)TiO₃ is over 1350 °C. In order to lower the sintering temperature, Li (3 wt%) was added to the (Ba,Sr)TiO₃ materials. Li doped (Ba,Sr)TiO₃ thick films screen printed on the alumina (Al₂O₃) substrates were sintered at 900 °C for 1.5 h. The structural feature was analyzed with X-ray diffraction method. Temperature dependent dielectric properties were characterized from 303 to 403 K at 1 MHz. Within the ±100 V of bias voltage, current-voltage characteristics of Li doped (Ba,Sr)TiO₃ films were investigated from 303 to 403 K. Through the current-voltage characteristics, the resistivity of Li doped (Ba,Sr)TiO₃ films were calculated.In this paper, the significant negative temperature coefficient of resistance (NTCR) of Li doped (Ba,Sr)TiO₃ films will be presented through the activation energy fitting. Measured activation energy is approximately 0.366 eV.     

Reflection characterization of anisotropic ultrathin dielectric films on absorbing isotropic substrates

The reflection of linearly polarized light from an ultrathin anisotropic dielectric film on isotropic absorbing substrate is investigated analytically in the long-wavelength limit. All analytical results are correlated with the numerical solution of the anisotropic reflection problem on the basis of rigorous electromagnetic theory. Simple analytical approach developed in this work not only gives a physical insight into the reflection problem but also provides a way of estimating the necessary experimental accuracy for optical diagnostics by reflection characteristics. It is shown that obtained expressions are of immediate interest for determining the parameters of anisotropic surface layers. Innovative possibilities for optical diagnostics of anisotropic properties of ultrathin dielectric layers upon absorbing materials are discussed.     

Effect of annealing temperature on K-shell X-ray fluorescence parameters of zinc oxide thin films prepared by the sol-gel method

Zinc oxide thin films were grown on a glass substrate by a sol-gel process using a spin-coating technique. The obtained thin films were annealed between 350?°C and 550?°C in 50?°C steps and were then characterized using X-ray diffraction, scanning electron microscopy, and X-ray fluorescence techniques. The samples were stimulated by 59.5?keV gamma rays emitted from an Americium-241 annular radioisotope source. K X-rays emitted by samples were counted using an ultra-low energy germanium detector with a resolution of 150?eV at 5.96?keV. It was found that there was generally a decrease in both the Kβ/Kα X-ray intensity ratios and the K X-ray fluorescence cross sections for zinc oxide between 350?°C and 500?°C, but not at 550?°C. In addition, the X-ray diffraction patterns of the films showed that the transition phase from an amorphous to a polycrystalline hexagonal wurtzite structure was complete at an annealing temperature of 500?°C. The results show that variations in these parameters can be explained by the reorganization of atoms and the charge transfer process due to the effect of the annealing temperature on the elements forming the compounds.     

Evaluation of copper Chemical-Vapor-Deposition films on glass and Si(100) substrates

Thin films of pure copper have been deposited on glass and Si(100) substrates using copper acetylacetonate [Cu(acac)₂] and copper HexaFluoroAcetylacetonate [Cu(HFA)₂] sources. A thermal, cold-wall, reduced pressure (3325–5985 Pa) Metal-Organic Chemical Vapor Deposition (MOCVD) process was employed. The effect of H₂O vapor on the grain size, deposition rate, and resistivity was examined. Electrical resistivities of 2.4 cm for copper films deposited on Si(100) and 3.44 cm for copper films deposited on glass at substrate temperatures of 265° C and a [Cu(acac)₂] source temperature of 147° C with the use of H₂O vapor were measured. When [Cu(HFA)₂] was used, the substrate temperature was 385° C and the source temperature was 85° C. An activation energy for the copper film deposition process was calculated to be 22.2 kJ/mol in the case of the [Cu(acac)₂] source. A deposition rate of 11 nm/min was obtained with Cu(acac)₂ as the source and the rate was 44.4 nm/min with the Cu(HFA)₂ source; both were obtained with the use of H₂O vapor. No selectivity was observed with either source for either substrate. The deposited films were fully characterized using XRD, LVSEM, SAXPS, and RBS.     

外加磁场对射频磁控溅射制备铝掺杂氧化锌薄膜影响的研究

利用射频磁控溅射法制备了铝掺杂氧化锌(AZO)透明导电薄膜,在传统的磁控溅射系统中引入外加磁场,研究了外加磁场对AZO薄膜沉积速率、形貌结构及光电特性的影响.研究结果表明,外加磁场后薄膜的沉积速率从不加磁场的13.04 nm/min提高到了19.93 nm/min;外加磁场后薄膜表面平整致密、颗粒大小均匀,结晶质量较高,而不加磁场薄膜表面形貌呈蠕虫状,薄膜质量较差.溅射时间为90 min时,外加磁场前后AZO薄膜方阻分别为30.74?/和12.88?/.外加磁场对薄膜可见光透过率影响不大,但使薄膜的吸收边蓝移现象更明显.运用ansys软件对磁控溅射二维磁场分布模拟后发现,外加磁场提高了靶上方横向磁场强度,改善了磁场分布的均匀性,加强了磁场对电子的磁控作用,提高了靶电流,是AZO薄膜的溅射速率、光电性能和形貌结构得到提高和优化的原因.     

Effect of RF power on the properties of transparent conducting zirconium-doped zinc oxide films prepared by RF magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films with high transparency and relatively low resistivity have been successfully prepared by radio frequency (RF) magnetron sputtering at room temperature. The RF power is varied from 75 to 150W. At first the crystallinity and conductivity of the film are improved and then both of them show deterioration with the increase of the RF power. The lowest resistivity achieved is 2.07×10^-3\Omegacm at an RF power of 100W with a Hall mobility of 16cm²V^-1s^-1 and a carrier concentration of 1.95×10²⁰cm^-3. The films obtained are polycrystalline with a hexagonal structure and a preferred orientation along the c-axis. All the films have a high transmittance of approximately 92% in the visible range. The optical band gap is about 3.33eV for the films deposited at different RF powers.     

Ti缓冲层及退火处理对Si(111)基片上生长的ZnO薄膜结构和发光特性的影响

采用反应磁控溅射法在Si（111）基片上制备了带有Ti缓冲层的高c轴取向ZnO薄膜.通过X射线衍射分析和光致荧光光谱测量,研究了Ti缓冲层厚度和退火处理对ZnO薄膜结晶质量和光致荧光特性的影响.研究结果表明,Ti缓冲层的引入可以有效改善Si基片上ZnO薄膜的发光性能,但缓冲层存在一个最佳的厚度.薄膜应力是影响ZnO薄膜紫外荧光发射性能的重要因素,较小的残余应力对ZnO薄膜的紫外荧光发射是有利的,残余应力的存在可以改变ZnO薄膜紫外荧光发射能量.随着退火温度的增加,薄膜中的张应力增大,导致带隙宽度减小以及激子复合跃迁峰逐渐向低能方向移动. 关键词： ZnO薄膜 缓冲层 退火处理 应力分析     

PEALD-deposited crystalline GaN films on Si(100) substrates with sharp interfaces

Polycrystalline gallium nitride(GaN) thin films were deposited on Si(100) substrates via plasma-enhanced atomic layer deposition(PEALD) under optimal deposition parameters. In this work, we focus on the research of the GaN/Si(100)interfacial properties. The x-ray reflectivity measurements show the clearly-resolved fringes for all the as-grown GaN films, which reveals a perfectly smooth interface between the GaN film and Si(100), and this feature of sharp interface is further confirmed by high resolution transmission electron microscopy(HRTEM). However, an amorphous interfacial layer(~ 2 nm) can be observed from the HRTEM images, and is determined to be mixture of Ga_xO_y and GaN by xray photoelectron spectroscopy. To investigate the effect of this interlayer on the GaN growth, an AlN buffer layer was employed for GaN deposition. No interlayer is observed between GaN and AlN, and GaN shows better crystallization and lower oxygen impurity during the initial growth stage than the GaN with an interlayer.     

A study of the optical properties of titanium oxide films prepared by dc reactive magnetron sputtering

TiO₂ thin films were deposited on the glass substrates by dc reactive magnetron sputtering technique at different sputtering pressures (2 × 10⁻³ to 2 × 10⁻² mbar). The films prepared at low pressures have an anatase phase, and the films prepared at high pressures have an amorphous phase. The optical properties were studied by measuring the transmittance and the ellipsometric spectra. The optical constants of the films in the visible range were obtained by fitting the transmittance combined with the ellipsometry measurements using the classical model with one oscillator. The refractive index of the films decreases from 2.5 until 2.1 as the sputtering pressure increases from 2 × 10⁻³ to 2 × 10⁻² mbar. The films prepared at the pressure higher than 6 × 10⁻³ mbar show a volume inhomogeneity. This volume inhomogeneity has been calculated by fitting the transmittance and the ellipsometric spectra. The volume inhomogeneity of the film prepared at the highest sputtering pressure is about 10%. Although the films prepared at high pressures show a large volume inhomogeneity, they have low extinction coefficients. It is suggested that the anatase phase results in more light scattering than amorphous phase does, and then a high extinction coefficient.     

Influence of the deposition pressure on the properties of transparent conducting zirconium-doped zinc oxide films prepared by RF magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films with high transparency and relatively low resistivity have been successfully prepared by RF magnetron sputtering at room temperature. The deposition pressure was varied from 0.6 to 2.5 Pa. A transformation from a relatively compact structure to individual grains was observed with the increase of deposition pressure. As the deposition pressure increases, the resistivity increases sharply due to both, the decrease of hall mobility and carrier concentration. The lowest resistivity achieved was 2.07 × 10⁻³ Ω cm at a deposition pressure of 0.6 Pa with a hall mobility of 16 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.95 × 10²⁰ cm⁻³. The films are polycrystalline with a hexagonal structure and a preferred orientation along the c-axis. All the films present a high transmittance of above 90% in the visible range. The optical band gap decreases from 3.35 to 3.20 eV as the deposition pressure increases from 0.6 to 2.5 Pa.