Surface Dielectric Properties Research Articles

Crystalline nanostructure and morphology of TriF-IF-dione for high-performance stable n-type field-effect transistors

The device performance and stability of n-type organic field-effect transistors (OFETs) based on 1,2,3,7,8,9-hexafluoro-indeno[1,2-b]fluorene-6,12-dione (TriF-IF-dione) were investigated. The electrical characteristics of TriF-IF-dione FETs were optimized by systematically controlling the dielectric surface properties via insertion of organic interlayers, such as self-assembled monolayers (NH2–, CH3–, and CF3–) or polymeric layers (polystyrene, PS) at the semiconductor–SiO2 dielectric interfaces. In particular, a thin PS buffer layer on the SiO2 surface provided a device that performed well, with a field-effect mobility of 0.18 cm2 V−1 s−1 and an on–off current ratio of 4.4 × 106. The improvements in the performance of TriF-IF-dione OFET conveyed by the PS interlayers were examined in terms of the crystalline nanostructure and the charge modulation effects in the channel. These properties were strongly correlated with, respectively, the hydrophobicity and the electron-donating characteristics of the dielectric surface. The TriF-IF-dione FETs with a PS interlayer showed excellent electrical stability attributed to high activation energies for charge trap creation. A complementary inverter comprising both p-type pentacene and n-type TriF-IF-dione was also successfully demonstrated.

Influence of Stoichiometric Ratio and Mn-Doping on the Surface Morphology and Dielectric Properties of Perovskite (La,Sr)FeO3 Films

Lanthanum strontium ferrite (La1−xSrxFeO3, x = 0.1, 0.3, 0.5, 0.7) (LSF) films were prepared on platinized/silica/silicon (Pt/SiO2/Si) substrates by a sol–gel method. The crystallization, surface morphology and dielectric properties of the LSF films have been studied. Among the samples, La0.5Sr0.5FeO3 thin film have the most homogeneous, smooth surface and the best dielectric properties (er = 2881.58, tanδ = 1.20) at the frequency of 1 kHz. Mn-doping (y) in La0.5Sr0.5FeO3 further improves the dielectric properties (er = 2922.91, tanδ = 1.11) of the film. Both er and tanδ values of the Mn-doped (y = 0.02) La0.5Sr0.5FeO3 films decreases with increasing the frequency. The biggest er value is 3238.18 at the frequence of 0.02 kHz.

Diffuse Phase Transition and Pyroelectric Behavior of Cerium Doped Ba(Zr0.52Ti0.48)O3

Surface morphology, dielectric and pyroelectric properties of cerium (Ce) doped Ba(Zr0.52Ti0.48)O3 ceramics processed by solid state reaction are reported here. Surface morphology and microstructures of the dielectric ceramics were examined by atomic force microscope. Dielectric properties of these ceramics with two different concentrations were investigated as a function of temperature. The dielectric constant as a function of temperature exhibited diffuse phase transition behavior accompanied with higher value of dielectric constant for Ce-doped ceramics. The dielectric constant decreases with increasing concentration of Ce from 0.0 to 0.1, while it increased with further increase in Ce concentration from 0.1 to 0.2. The pyroelectric current measured as a function of temperature revealed an existence of both primary effect at lower temperatures whereas secondary effect at higher temperatures. The influence of Ce concentration on grain size plays an important role in maintaining the dielectric constant, which are suitable for tunable dielectric device applications.

Preparation of uniform titania microspheres with good electrorheological performance and their size effect

Titania is a potential high-performance electrorheological (ER) material due to its relatively high dielectric constant and polarization ability. The size and shape of titania particles are critical factors influencing ER activity. In this paper, we have developed an acetic acid (AA) assisted sol–gel strategy for the synthesis of uniform titania microspheres with good ER effect. The diameter of the titania microspheres (from 420 to 240 nm) can be tuned by changing the amount of AA added. The facile route has the great potential in bulk synthesis of the titania based ER materials. Results from surface area, rheological, conductivity and dielectric properties measurements indicate that the enhanced ER performance is due to the combined effect of the increased polar molecules content and reduced particle size.

The effect of air plasma on barrier dielectric surface in dielectric barrier discharge

Barrier dielectric is an important part of atmospheric pressure dielectric barrier discharge (AP-DBD), which partly affects discharge characteristics. Conversely, discharge plasma also has influence on dielectric surface properties. To investigate this influence, some experiments were carried out on a home-built AP-DBD system with glass plate as barrier dielectric. Surface wettability was evaluated by water contact angles on a drop shape analysis system. The morphologies and chemical compositions of the glass sample surfaces were observed by field-emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS) attached to FESEM. The results show that water contact angles decrease as discharge energy increases, micro-discharge etching zones are formed into glass surface and different from the control glass in surface micro-structure and chemical compositions.

Effect of copper-oxide segregation on the dielectric properties of CaCu 3Ti 4O 12 thin films fabricated by pulsed-laser deposition

We investigated the effects of post-deposition cooling conditions on the surface morphologies and dielectric properties of CaCu 3Ti 4O 12 (CCTO) thin films grown by pulsed-laser deposition on Pt/TiO 2/SiO 2/Si substrates. CCTO thin films cooled under the typical cooling parameters, i.e., slow cooling (3 °C/min) at high oxygen pressure (66 kPa) showed a severe segregation of nanoparticles near the grain boundaries, which was identified to be copper oxide from electron probe micro analyzer mapping. On the other hand, we could not observe any segregation on the film surface when the samples were cooled fast (∼ 20 °C/min) at relatively low oxygen pressure (100 Pa). The dielectric constant, ε r, of CCTO thin films deposited at 750 °C with severe surface segregation ( ε r ∼ 750 at 10 kHz) was found to be much lower than that ( ε r ∼ 2000 at 10 kHz) of CCTO thin films with smooth surface. As the copper-oxide segregation becomes more serious, which preferentially occurs at relatively high ambient oxygen pressure and temperature, the degradation in the dielectric properties of CCTO films becomes larger. The variation of dielectric constant of CCTO films with no copper-oxide segregation could be related to the presence of an impurity phase at grain boundaries.

Surface modification of BaTiO 3 particles by silane coupling agents in different solvents and their effect on dielectric properties of BaTiO 3/epoxy composites

The surface of BaTiO 3 particles was modified by 3-glycidoxypropyltrimethoxysilane (GPTMS) to attach epoxy groups on them and to improve their compatibility with epoxy resin. First, in order to analyze the effect of solvents on the degree of surface modification of BaTiO 3 particles, the surfaces of BaTiO 3 particles were modified with GPTMS in water, ethanol, and xylene at 80 °C. FT- nIR analysis showed that due to the ring-opening reaction, the epoxy group on BaTiO 3 particles was reduced after surface modification in ethanol and disappeared after surface modification in water. In contrast, when BaTiO 3 particles were modified in xylene, the epoxy groups remained. Then, the relationships among these surface structure differences, viscosity of BaTiO 3/epoxy/N-methyl-2-pyrrolidinon (NMP) suspensions, the surface morphologies of BaTiO 3/epoxy composites, and the dielectric properties of BaTiO 3/epoxy composites were investigated. While there was no relationship between the suspension viscosity and the dielectric properties of BaTiO 3/epoxy composites, a BaTiO 3/epoxy composite with a smooth surface and high dielectric properties was obtained when the BaTiO 3 surface was modified in xylene and the epoxy groups were effectively retained on the surface.

Scale-Dependent Surface Roughness Behavior and Its Impact on Empirical Models for Radar Backscatter

One goal of radar remote sensing is the extraction of terrain statistics and surface dielectric properties from backscatter data for some range of wavelengths, incidence angles, and polarizations. This paper addresses empirical approaches used to estimate terrain properties from radar data over a wider range of roughness than permitted by analytical models. Many empirical models assume, at least implicitly, that roughness parameters like rms height or correlation length are independent of the horizontal length scale over which they are measured, in contrast to recent surveys of natural terrain, which show that self-affine, or power-law scaling, between horizontal scale and roughness statistics is very common. The rms slope at the horizontal scale of the illuminating wavelength s(lambda) is directly related to the variogram or structure function of a self-affine surface, can be readily obtained from field-measured topography, and, when used in an empirical model, avoids the need for arbitrary wavelength-dependent terms. To facilitate comparison with earlier approaches, an expression that links the rms height at some profile length with the rms (Allan) deviation at an equivalent horizontal sampling interval is obtained from numerical simulations. An empirical model for polarimetric scattering as a function of s(lambda) at 35deg-60deg incidence from smooth to rugged lava surfaces is derived and compared with earlier models for backscatter from modestly rough soil surfaces. The asymptotic behavior of polarization ratios for the lava flows suggests that the depolarization of linear-polarized illuminating signals occurs as a first-order process, likely through single scattering by rock edges or other discontinuities, rather than as the solely multiple-scattering effect predicted by some analytical models. Efforts to fully understand radar scattering from geological surfaces need to incorporate wavelength-scale roughness, perhaps through computational simulations.

RF 스퍼터링법에 의한 SBN 박막의 표면형상 및 유전특성

The <TEX>$Sr_{0.7}Bi_{2.3}Nb_2O_9$</TEX>(SBN) thin films are deposited on Pt-coated electrode(Pt/Ti/<TEX>$SiO_2$</TEX>/Si) using RF sputtering method at various deposition conditions. We investigated the effect of deposition condition on the surface morphology and dielectric properties of SBN thin films. The optimum of the rougness showed about 4.33 nm in 70/30 of Ar/<TEX>$O_2$</TEX> ratio. The crystallinity and rougness of SBN thin films were increased with the increase of rf power. Also, Deposition rate of SBN thin films was about 4.17 nm/min in 70 W of rf power. The capacitance of SBN thin films were increased with the increase of Ar/<TEX>$O_2$</TEX> ratio, rf power and deposition temperature respectively.

Dielectric properties of Fe-doped Ba 0.65Sr 0.35TiO 3 thin films fabricated by the sol–gel method

Fe-doped Ba 0.65Sr 0.35TiO 3 (BST) thin films have been fabricated on Pt/Ti/SiO 2/Si substrate using the sol–gel method. The structural and surface morphology, dielectric, and leakage current properties of undoped and 1 mol% and 2 mol% Fe-doped BST thin films have been studied in detail. The results demonstrate that the Fe-doped BST films exhibit improved dielectric loss, tunability, and leakage current characteristics as compared to the undoped BST thin films. The improved figure of merit (FOM) of Fe-doped BST thin film suggests a strong potential for utilization in microwave tunable devices.

Surface Structures and Dielectric Properties of Yttrium-doped Barium Strontium Titanate Films by Improved Sol-Gel method

Normal Sol-Gel method was improved by adding polyvinyl pyrrolidone to sol and forming seed layer on Pt electrode.Undoped and Yttrium(Y)-doped Ba0.6Sr0.4TiO3(BST) films were prepared on Pt/Ti/SiO2/Si by the improved Sol-Gel method.The surface structures and dielectric tunable properties of the as-prepared BST films were investigated.X-ray photoelectron spectrum(XPS) shows that Ba3d,Sr3d,Ti2p or O1s on the surfaces of BST films displays two or three chemical states,and these chemical states correspond to perovskited structure and non-perovskited structure.Y doping has significant effect on the chemical states of Ba3d,Sr3d and O1s except those of Ti2p,and makes the contents of Ba,Sr and O atoms in non-perovskited structure decrease from 41% to 26%,from 33% to 29% and from 51% to 40%,respectively,thus results in large decrease of non-perovskited structure.Meanwhile,scanning electron microscope(SEM) and atomic force microscope(AFM) demonstrate that Y-doped BST films show prominent improvement in morphologies with smooth and compact surface with no crack or shrinkage cavity.Such morphologies visibly decrease the adsorption of gases and hydrocarbon contaminations and their diffusion passes,which is the probable reason for non-perovskited structure to be formed.Also,voltage-capacitance curves obtained at 40V and 100kHz illustrate that Y-doped BST films exhibit improved dielectric tunable properties with tunability of more than 43%,dielectric loss of 0.0216 and merit factor value of 20.Additionally,the improved mechanism of Y doping is discussed.

Inductively Coupled Plasma Reactive Ion Etching of Lead Zirconate Titanate Thin Films for MEMS Application

Piezoelectric lead zirconate titanate (PZT) thin film has been widely studied in microelectromechanical systems (MEMS) as an electromechanical conversion material. However, the application of the piezoelectric MEMS devices is still delayed by PZT integration difficulties, especially in PZT etching process. In this study, PZT thin film was etched using Ar/SF6 mixed gas in a conventional ICP-RIE system. The etch rate, etch selectivity and profile of the PZT film as well as platinum bottom electrode and photoresist were investigated as a function of the Ar concentration (Ar %) in Ar/SF6 mixture. The surface roughness, ferroelectric properties and dielectric properties of the PZT film were evaluated to indentify the effects of various etching receipts. It was found that high Ar % resulted in better PZT surface morphology. The largest PZT etch rate was achieved at 66.7 % of Ar. Reactive-physical mixed etching was preferred for great efficiency, but at the cost of bad surface roughness and low etch selectivity. Moreover, the ferroelectric properties and the dielectric properties of the PZT film were found not degraded by the proposed process. Fine PZT-electrode stack with the feature size of 15 μm and the PZT thickness of 1 μm was successfully obtained in this paper for piezoelectric MEMS application.

Influence of atmospheric fluorine plasma treatment on thermal and dielectric properties of polyimide film

Plasma treatment of polyimide surfaces not only causes structural modification during the plasma exposure, but also leaves active sites on the surfaces that are subject to post-reaction. In this work, the effects of atmospheric fluorine plasma treatment on the surface properties and dielectric properties of polyimide thin film were investigated by using X-ray photoelectron spectroscopy (XPS), Fourier transform-IR (FT-IR) spectroscopy, and contact angle measurement. The results indicated that plasma treatment successfully introduced fluorine functional groups on the polyimide surfaces. The polyimides also exhibited good thermal stability and a lower dielectric constant. It appears that the replacement of fluorine led to the decrease of the local electronic polarizability of polyimide. Consequently, it was found that the atmospheric fluorine plasma-treated polyimides possessed lower dielectric characteristics than the untreated polyimides.

RELAXOR BEHAVIOR OF BaZr0.2Ti0.8O3 CERAMICS WITH DIFFERENT GRAINS

ABSTRACT The surface morphology and dielectric properties of BaZr0.2Ti0.8O3 ceramics sintered at 1350°C for 0.5 h, 4 h and 8 h in air atmosphere were investigated. As the sintering time increased, the average grain size of the BZT ceramics increased. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the decreased grain size.

Influence of oxygen partial pressure on the structural and dielectric properties of Ba(Zr 0.3Ti 0.7)O 3 thin films grown on (LaAlO 3) 0.3(Sr 2AlTaO 6) 0.35 (001) using pulsed laser deposition

Epitaxial Ba(Zr 0.3Ti 0.7)O 3 thin films were grown on (LaAlO 3) 0.3(Sr 2AlTaO 6) 0.35 (001) single-crystal substrates by pulsed laser deposition at 700 °C in different oxygen partial pressures ranging from 6.7 Pa to 40.0 Pa. A strong correlation is observed between the structure and dielectric properties for the Ba(Zr 0.3Ti 0.7)O 3 thin films. The tetragonal distortion (ratio of in-plane and out-of-plane lattice parameter, a / c ) of the films depends on the oxygen partial pressures. a / c varies from 0.989 at 6.7 Pa to 1.010 at 40.0 Pa, indicating the in-plain strain changes from compressive to tensile. The in-plain strain (either compressive or tensile) shifts the Curie temperature of the Ba(Zr 0.3Ti 0.7)O 3 thin films dramatically. Surface morphology and dielectric properties of Ba(Zr 0.3Ti 0.7)O 3 thin films have a strong dependence of the oxygen partial pressure. The film grown 26.7 Pa, which corresponds to a moderate in-plain tensile strain and a Curie temperature of ~ 30 °C, shows the largest relative permittivity, tunability and the best figure of merit in a broad frequency range (1 kHz–500 MHz), which may be a promising candidate for room-temperature microwave device applications.

Surface property controllable multilayered gate dielectric for low voltage organic thin film transistors

We report the effects of dielectric surface properties on the device performance of organic thin film transistors (OTFTs) using polymer/high-k oxide multilayered gate dielectrics. We systematically controlled the surface energy of the gate dielectric from very hydrophobic to very hydrophilic. The modified dielectric surface strongly affected the initial growth mechanism of pentacene and subsequently the performance of the OTFTs. The performance of the OTFTs with a higher surface energy was superior to that of the OTFTs with a lower surface energy.

A hybrid KA‐MoM algorithm for computation of scattering from a 3‐D PEC target above a dielectric rough surface

A new hybrid analytical‐numerical iterative algorithm, which combines the Kirchhoff approximation (KA) and the Method of Moment (MoM), is developed for computing the electromagnetic scattering from a three‐dimensional (3‐D) perfect electric conducting (PEC) target above a 2‐D infinite randomly rough dielectric surface. The equations of difference scattering due to the target presence above the rough surface are derived. The induced difference fields on the rough surface due to the interactions between the target and the rough surface are calculated by using the KA method. The excitation term on the right‐hand‐side (RHS) of target's surface integral equation (SIE), which contains the difference scattering of the rough surface, is then updated for calculating new target currents with the Conjugate Gradient (CG) procedure. Then the target currents are used to compute the difference field induced on the rough surface with the KA method. Multiple iterations take account of the multiorder interactions between the target and the underlying rough surface. Numerical quadrature upon the rough surface is performed only once to compute the coupling scattering field from the rough surface to the target, and it takes N steps (N is the discretized mesh number of rough surface). By using this hybrid KA‐MoM algorithm, the requirements of memory and CPU time can be reduced significantly. Moreover, the validity conditions and the convergence performance of this hybrid algorithm are also discussed. With Monte‐Carlo generations of randomly rough surfaces, bistatic scattering from different‐shaped targets above a Gaussian rough surface is numerically simulated. Finally, dependence of bistatic scattering pattern on the surface dielectric property and the target geometry is discussed.

Growth related properties of pentacene thin film transistors with different gate dielectrics

We report a study on the influence of dielectric surface properties on the growth, the morphology and ordering of pentacene layers and associated consequences on the performance of organic field effect transistors (OFETs). This work mainly aims at disentangling the respective influences of surface roughness and surface energy on pentacene growth. A range of inorganic high-k oxides as well as polymer dielectrics were compared: Ta2O5 deposited by e-beam evaporation or grown by anodic oxidation, polymethylmethacrylate (PMMA) single layer or PMMA/Ta2O5 bi-layer. Some complementary results on anodic HfO2 were also added. Atomic force microscopy, X-ray diffraction and infrared absorption evidenced that hydrophobicity and surface roughness drastically influence pentacene growth mechanisms. Transistors realized with the different dielectrics show characteristics well correlated to pentacene structural properties. In particularly, we point out the relationship between the grain size and the field effect mobility with the surface energy of the dielectric substrate. The general trend is that the bigger the grains, the higher the mobility but that best electrical performances of OFETs are obtained with a dielectric surface energy close to that of pentacene. This work also bears out our former results on the benefit of a polymer/high-k oxide bilayer dielectric configuration to improve the field effect mobility while keeping a low operating voltage.

Effect of Wall Surface Properties at Different Drying Kinetics on the Deposition Problem in Spray Drying

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.

A study of atmospheric-pressure CHF 3/Ar plasma treatment on dielectric characteristics of polyimide films

In this work, the influence of atmospheric-pressure CHF 3/Ar plasma treatment on surface dielectric properties of polyimide films was investigated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements. The dielectric characteristics of the films were studied using a dielectric spectrometer. From the results, it was found that the plasma treatment introduced fluorine functional groups onto the polyimide surfaces. F 1s/C 1s ratios of the polyimides were enhanced with the increase of plasma treatment time. Consequently, the fluorine groups led to a decrease of the surface free energy and dielectric constant of the polyimide films, which can largely be attributed to the decrease of the deformation polarizability or London dispersive component of surface free energy of the solid surface studied.