Inversion of reflection ellipsometric data

The dielectric constant of an isotropic homogeneous layer on an isotropic substrate is shown to satisfy a quintic equation, with the coefficients determined by |ρ|(2) and Re(ρ), where ρ = r(p)/r(s) is found ellipsometrically. This algebraic equation eliminates many (but not all) of the nonphysical roots in the inversion of ellipsometric data. A simple form is obtained if the angle of incidence is equal to the Brewster angle of the substrate. The problem of inversion for thin films is also discussed.     

具有多层结构的聚合物复合薄膜的介电和磁性能

采用旋涂法制备了 Fe3 O4/聚偏氟乙烯(PVDF)复合薄膜(A)、多壁碳纳米管(MWCNT)/PVDF复合薄膜(B)以及纯PVDF薄膜(P)。利用热压法制备具有3层结构的AAA、ABA及APA 复合薄膜。为了探究层状结构对复合薄膜介电和磁性能的影响,制备了单层膜A作为对比(厚度与AAA复合薄膜相同)。分别研究了薄膜的介电和磁性能。结果表明：由于界面效应,同等厚度的AAA复合薄膜较A膜而言具有较高的介电常数;以B和P薄膜替代AAA结构中间层薄膜后,其中ABA复合薄膜的介电常数高于AAA及APA复合薄膜,同时保持较低的介电损耗。对于磁性能,层状结构对复合薄膜的饱和磁化强度及矫顽力均无明显的影响,而ABA复合薄膜的饱和磁化强度高于AAA及APA复合薄膜,且ABA和APA复合薄膜的矫顽力增加。层状结构设计不仅能够调节复合材料的介电性能和磁性能,而且有利于不同纳米填料的分散,为制备多功能聚合物复合材料提供了一定的借鉴作用。     

Adhesive-free transfer of gold patterns to PDMS-based nanocomposite dielectric for printed high-performance organic thin-film transistors

Low-cost, adhesive-free direct transfer of gold patterns onto PDMS-based nanocomposite dielectric layer was investigated to significantly improve contact resistance at electrode-semiconductor interface in organic thin-film transistors (OTFTs). In particular, the nanocomposite film made from PDMS and solution-processable titanium dioxide nanoparticles was applied as dielectric layer in OTFTs, while transfer of gold patterns with a resolution lower than 3 μm is realized without use of any adhesive but through increased adhesion between gold and nanocomposite film of higher thickness and dielectric constant formed by in situ PDMS cross-linking process. Dielectric constant of the nanocomposite shows a dependence on the ratio of titanium dioxide nanoparticles to PDMS and the dielectric thickness was optimized for the best transfer efficiency. The organic transistors fabricated by this process demonstrate a high mobility of 0.038 cm(2)/(V s) and on/off ratio of 1 × 10(4) to 1 × 10(5). The electrode-semiconductor interface is evaluated by transmission line model to have width-normalized contact resistance of ～100 kΩ cm while the inert property of dielectric-semiconductor interface gives low hysteresis (ΔV(th) = 1.2 V) and low threshold voltage (V(th) = -1.3 V) in the devices. This process can be readily adapted into a low-cost mass manufacturing process for printed organic electronics.     

Optical and electronic characterization of transition layer in thin film Au-GaAs Schottky barrier

The possibility of determination of optical parameters and thickness of interfacial oxide (IO) layer by multiple-angle-of-incidence (MAI) ellipsometry has been studied for Au-IO-GaAs structures with different oxide thickness. The films parameters have been calculated by the original program of inverse ellipsometric problem solution. Parameters of oxide layer have been determined both for free GaAs surface and for that covered by Au film. Gold film was prepared by vacuum evaporation on the heated n-n+GaAs substrate. Its parameters have been determined by MAI ellipsometry and transparency measurements of Au-quartz satellite system. The investigation showed the change of optical parameters of GaAs oxide layer after the Au evaporation. In the assumption of invariable thickness of IO layer its optical parameters are : n = 1.0±0.1, k = 0.4 ÷ 0.6. The mechanism of current transport and electrical parameters of Au-IO-GaAs structures have been determined from I-V and C-V characteristics of Schottky diodes. The results of the determination of transition layer thickness to its dielectric constant ratio (d\_i)) from electrical characteristics of barrier also indicate its difference from initial parameters of oxide layer probably due to interdiffusion of Au, Ga, and As.     

Study of scattering parameters of RFMEMS shunt switch with high-K dielectrics

This paper discussed about the effect of using high-k materials on scattering parameters of RFMEMS shunt switch. The effect of variation of dielectric constant (k: 3–70) of the dielectric layer of thickness 0.16 µm was studied first. In the upstate, no noticeable change is observed in insertion loss and return loss due to the variation of dielectric constants. In the down-state, both the isolation and return loss are found to be strongly dependent on the dielectric constants of the dielectric layer. Resonant frequency of the switch is decreasing exponentially with the increasing dielectric constant. In order to get resonant frequency of 35 GHz, optimum dielectric layer thicknesses for each dielectric constant are found by parametric analysis of the switch structure. With the optimum dielectric layer thicknesses, all the isolation and return loss behavior are found to be almost identical. However, now the up-state characteristics of the switch are found to be affected. Thus for Ka band applications, the insulating layer with dielectric constant 20–30, with corresponding layer thickness 0.4–0.6 μm, may be suitable for the RFMEMS switch applications. This will lead to return loss 相似文献   

Calibration and measurement of dielectric properties of finitethickness composite sheets with open-ended coaxial sensors

The application of open-ended coaxial sensors for dielectric measurement of finite thickness composite sheets is studied. Expressions for calculation of the complex aperture admittance for two geometries are presented. These expressions are used to calculate the dielectric constant of infinite half-space as well as finite thickness slabs. A more efficient method of such calculations, using a personal computer, for low to medium loss dielectrics is demonstrated. The question of when a dielectric layer may be considered as infinitely thick is also addressed, and examples are presented. A different calibration technique (compared to the conventional ones) is described and successfully implemented. This calibration technique utilizes a dielectric sheet with known dielectric properties and thickness. Measurements for different airgaps between the open-ended coaxial line and the dielectric sheet are used to perform and enhance the calibration. The results of this calibration technique and several subsequent measurements are presented and discussed     

微波多层板基材的性能要求

介绍了微波多层板所用基材的性能参数,重点阐述了材料的介电常数、介质损耗、热胀系数、特性阻抗对多层板性能的影响。通过对微带线特性阻抗公式的理论计算,得出了带线的线宽W、导体层的厚度t、介质的厚度h以及介电常数ε1的精度对特性阻抗Z。的影响程度。这4个因素中,介质的厚度h和带线的线宽W对特性阻抗Z。的精度影响最大。总结了国内外微波介质材料的研究情况,优选了适合于制造微波多层板的材料。     

Dielectric properties of sol-gel derived barium-strontium-titanate (Ba(0.4)Sr(0.6)TiO(3)) thin films

The structural and dielectric properties of sol-gel derived barium-strontium-titanate (Ba(0.4)Sr(0.6)TiO(3 )) thin films have been investigated. The as-fired films are found to be amorphous, and films crystallize to a cubic phase after a post deposition annealing at 700 degrees C for one hour in air. The variation of dielectric constant with temperature and field was investigated as a function of film thickness. These films display a nonlinear dielectric response that can be described in terms of a power series expansion of the free energy in polarization as in Landau-Ginzburg-Devonshire approach. The measured room temperature dielectric constant (epsilon') of the film was about 320. The dielectric constant did not show any significant frequency dependence up to 100 kHz. The temperature dependence of dielectric constant exhibited a diffused ferroelectric to paraelectric phase transition at -60 degrees C. The room temperature dielectric constant and magnitude of the dielectric peak at the Curie point was dependent on the thickness of the film. The obtained dielectric data on sol-gel barium strontium titanate thin films on platinized substrates were analyzed in the light of a barrier layer model.     

Enhancement of Omnidirectional Photonic Bandgaps in One-Dimensional Superconductor–Dielectric Photonic Crystals with a Staggered Structure

In this paper, the properties of the omnidirectional photonic bandgap (OBG) realized by one-dimensional (1D) photonic crystals with a staggered structure which is composed of superconductor and isotropic dielectric have been theoretically investigated by the transfer matrix method (TMM). From the numerical results, it has been shown that such OBG is insensitive to the incident angle and the polarization of electromagnetic wave (EM wave), and the frequency range and central frequency of OBG can be tuned by the ambient temperature of system, the average thickness of superconductor layer, the average thickness of dielectric layer, and staggered parameters, respectively. The bandwidth of OBG can be notably enlarged with increasing average thickness and staggered parameter of superconductor layer. Moreover, the frequency range of OBG can be narrowed with increasing the average thickness, staggered parameter of dielectric layer, and ambient temperature, respectively. The damping coefficient of superconductor layer has no effect on the bandwidth of OBG under low-temperature conditions. It is shown that 1D superconductor–dielectric photonic crystals (SDPCs) have a superior feature in the enhancement of frequency range of OBG. This kind of OBG has potential applications in filters, microcavities, and fibers, etc.     

THE EFFECTIVE DIELECTRIC CONSTANT OF DUST LAYERS

The electrical breakdown of a dust layer usually occurs at average electric fields which appear to be too small to initiate the breakdown. This suggests that the local electric field where breakdown occurs is somehow enhanced over that of the average field across the layer. AC dielectric measurements performed on the dust layer can be used to determine an effective static dielectric constant at a given temperature. The use of this dielectric constant in an expression for the local electric field, which combines the effects of dielectric polarization and space charge in the layer, results in predicted values of the local electric field which can be more than an order of magnitude larger than the applied field. In studies involving 11 different dust species, the dielectric constant was found to depend on temperature and layer thickness, as well as the concentration of alkali and alkaline earth metals in the dust.     

Direct numerical inversion method for kinetic ellipsometric data. I. Presentation of the method and numerical evaluation

A direct numerical inversion method for the determination of the refractive index and the thickness of the outermost layer of a thin transparent film on top of a multilayer has been developed. This method is based on a second-order Taylor decomposition of the coefficients of the Abelès matrices of the newly grown layer. The variations of the real-time spectroscopic ellipsometry data are expressed as polynomial fuctions depending on the dielectric constant and the thickness of the newly grown layer. The method is fast, capable of single-wavelength and multiwavelength inversion of continuous as well as discontinuous-index profiles, and can be adapted to many different polarimetric instruments.     

差分表面等离激元共振传感仿真研究

从薄膜光学理论出发,对不同金属膜厚度、不同实折射率和不同复介电常数的环境介质的表面等离激元共振(SPR,Surface Plasmon Resonance)信号进行了分析,给出了最佳金属膜厚度,并且,折射率与共振角呈线性关系(R=0.999 4).分析了采用差分处理时,随环境介质的复介电常数变化的光反射率曲线.结果表明,同组两个探测器信号的和随环境介电常数的虚部变化,与实部无关,其信号差则相反,因此,能够同时测量环境介质的介电常数的实部和虚部.     

Microwave moisture measurement of grains

A two-parameter transmission technique is described for online, in situ measurement of the bulk moisture content of grains using microwaves. This noncontacting 4.9-GHz system is configured so that a well-collimated TEM beam is transmitted through a layer of grain, e.g., moving on a conveyer or flowing in a chute. The changes in attenuation and phase serve as two independent measurement parameters from which the wet and dry basis weights (grams per square centimeter) and moisture can be found using a linear model, independent of the layer thickness. If the layer thickness is also known, the wet and dry densities (grams per cubic centimeter) and complex dielectric constant can be found     

Effect of the dielectric layer with photo-controllable surface relief on liquid crystal devices

We present experimental results for the dielectric layer effect on the electro-optical properties of liquid crystal (LC) devices together with numerical simulations. The photo-controllable polymer is used as a dielectric material on which the alignment agent of the LC is prepared. The surface relief structure can be induced on the dielectric polymer layer by photo-irradiation for fabricating LC microlens arrays or wide-viewing LC displays. It is found that the operation voltage of the LC device decreases with increasing the dielectric constant or with decreasing the layer thickness of the polymer. The experimental data agree well with theoretical results predicted from a simple dielectric model in the continuum theory.     

Investigation of Ti layer thickness dependent structural, magnetic, and photoemission study of nanometer range Ti/Ni multilayer structures

Structural, magnetic, and electronic properties of Ti/Ni multilayer (ML) samples as a function of Ti layer thickness are studied and reported in this paper. For this purpose [Ti (t nm)/Ni (5 nm)] x 10 ML samples, where t = 3, 5, and 7 nm have been deposited by using electron beam evaporation technique under UHV conditions at room temperature. Structure of ML samples were determined by using XRD (X-ray diffraction) technique and observed that Titanium is deposited mainly in amorphous nature with FCC structure at lower Ti layer thickness of 3 nm, which transform to crystalline HCP structures above than this Ti layer thickness. Corresponding fitted GIXRR (grazing incidence X-ray reflectivity) patterns shows asymmetric nature of Ti-Ni and Ni-Ti interfaces because of heavy intermixing and interdiffusion of Ni and Ti atoms at Ti-Ni interfaces at lower Ti layer thickness. The depth profiling core level and valence band measurements carried out by using XPS (X-ray photoelectron spectroscopy) technique confirms the interdiffusion and intermixing leading to Ti-Ni alloy phase formation at interfaces during deposition, particularly at lower Ti layer thickness of 3 nm. The corresponding magnetization behavior of ML samples has been investigated using Magneto-Optical Kerr Effect (MOKE) technique and observed that, coercitivity decreases while saturation magnetization increases with Ti layer thickness variations. These results are interpreted and discussed in terms of observed micro-structural changes due to Ti layer thickness vitiations in Ti/Ni multilayer samples.     

Dynamics of a thick-walled dielectric elastomer spherical shell

The nonlinear vibration response of a thick-walled spherical shell subjected to the mechanical pressure and electric field is studied in this paper. When subject to an electric field through the thickness of the spherical shell, the material expands in plane and contracts in thickness. The dielectric elastomer is assumed to be isotropic and neo-Hookean. Based on simple geometrical and spherical capacitor assumptions, we deduce an explicit analytical equation of motion of the dielectric elastomer spherical shell. The dynamic behaviors of the spherical shell under a constant electric loading and periodic electric loading are analyzed. In addition, the critical voltage is calculated in terms of various loading.     

Thickness and erbium doping effects on the electrical properties of lead zirconate titanate thin films

Thin films of erbium doped lead zirconate titanate (PZT) of different thickness were deposited by sol–gel technique on Pt/TiO₂/SiO₂/Si substrates. Capacitance–voltage measurements show that the dielectric constant continuously increases with the thickness. This is interpreted in terms of effects due to a low permittivity interfacial layer in series with the ferroelectric bulk. The linear fit of the reciprocal of capacitance vs. thickness leads to a true dielectric constant of the ferroelectric of 774 and interfacial capacitance of 14.6 nF. The leakage current properties also depend on thickness and temperature. The calculated interfacial potential barrier height amounts to 0.81 and 0.74 eV, respectively for erbium doped and pure PZT thin films.     

Modeling and Optimization of a Microscale Capacitive Humidity Sensor for HVAC Applications

This paper presents a comprehensive numerical study of the performance of a capacitive humidity sensor for heating, ventilation, and air conditioning (HVAC) applications. The proposed sensor comprises a sensing layer sandwiched between an array of top and bottom electrodes. A combination of both parallel plate and interdigitated electrode arrangements is considered to achieve their distinctive advantages. Polyimide is used as the humidity sensing material due to good sensing characteristics and aluminum is used as the electrode material because of the ease of fabrication. A layer of polyimide covers the top electrodes to provide protection from atmospheric contamination thus improving durability. The influence of relative humidity on the dielectric constant of the sensing layer is determined theoretically using the models of Looyenga and Shibata The model is validated by comparing model predictions with experimentally measured data for a previously reported capacitive humidity sensor. The model is then used to simulate and predict the performance of the proposed humidity sensor. The effects of design configuration, sensing layer thickness, electrode polarity, electrode width and thickness, and electrode gap are studied. The influence of operating conditions including relative humidity, temperature and voltage is investigated. Based on the simulation results, the optimum design configuration is identified.     

Preparation and characterization of (Ba1−xSrx)TiO3 films by sol–gel processing

Barium strontium titanate ((Ba, Sr)TiO3) thin films were prepared on Pt/Ti/Si substrates by the sol–gel method using metal alkoxides. The dependence of the dielectric constant for the films on the film compositions and on the film thickness were investigated. The dielectric constant of the film of thickness 180 nm had the highest value of 230 at composition ratios of [Ba+Sr]/[Ti]=1.04 and [Sr]/[Ba+Sr]=0.6. The dielectric constant of the films with this composition decreased from 390 to 160 with a decrease in the film thickness from 440 to 100 nm. The decrease in the dielectric constant with increasing film thickness is attributed to the existence of a low-dielectric-constant interface layer adjacent to the electrodes. © 1998 Kluwer Academic Publishers     

Three-dimensional electrostatic effects of carbon nanotube transistors

We explore the three-dimensional (3-D) electrostatics of planar-gate carbon nanotube field-effect transistors (CNTFETs) using a self-consistent solution to the Poisson equation with equilibrium carrier statistics. We examine the effects of the gate insulator thickness and dielectric constant and the source/drain contact geometry on the electrostatics of bottom-gated (BG) and top-gated (TG) devices. We find that the electrostatic scaling length is mostly determined by the gate oxide thickness, not by the oxide dielectric constant. We also find that a high-k gate insulator does not necessarily improve short-channel immunity because it increases the coupling of both the gate and the source/drain contact to the channel. It also increases the parasitic coupling of the source/drain to the gate. Although both the width and the height of the source and drain contacts are important, we find that for the BG device, reducing the width of the 3-D contacts is more effective for improving short channel immunity than reducing the height. The TG device, however, is sensitive to both the width and height of the contact. We find that one-dimensional source and drain contacts promise the best short channel immunity. We also show that an optimized TG device with a thin gate oxide can provide near ideal subthreshold behavior. The results of this paper should provide useful guidance for designing high-performance CNTFETs.