Breakdown behavior of oil-impregnated polypropylene as dielectricin film capacitors

The dielectric breakdown behavior of thin metalized PP films for use in HV capacitors was studied as function of temperature with and without rape-seed oil as impregnation medium. The impregnating oil penetrates into the amorphous regions of the dielectric. With oil impregnation, the dielectric breakdown strength of the PP film is increased by >25%. A correlation between the breakdown strength and the degree of impregnation was found. With increasing temperature the breakdown strength of PP films decreases. Moreover, the measurements showed abrupt changes of slope in the breakdown strength at defined temperatures. From these results a correlation was established between the dielectric breakdown strength of PP films and temperature induced structure changes. It was shown that the abrupt changes of slope in the breakdown strength occurring at defined temperatures are due to the additives contained in the PP capacitor films used. Finally, guidelines for further development of impregnated PP films as dielectrics for high power capacitor applications are presented     

Investigation of dielectric properties of polymer laminates withpolyvinylidene fluoride

The breakdown field strength of polymer laminates consisting of polymer base films coated with a thin layer of polyvinylidene fluoride (PVDF) was investigated. The spin coating technique was used to make a layer of PVDF film. It was found that the dc breakdown field strength could be increased by as much as 18% by applying a very thin coating. The breakdown field strength was insensitive to the thickness of the polymer base films and the thickness of the PVDF coating within the thickness range used in the experiment. The effect of the coating on the permittivity and dissipation factor of polymer films over a wide frequency range was determined. Possible mechanisms for the enhancement of breakdown field strength have been discussed     

Characterization of dielectric and acoustic properties of CSD PZT thin films at high frequencies

In this study, the microwave dielectric and the acoustic properties of Pb(Zr _x ,Ti_1-x )O₃ (PZT) thin films deposited using chemical solution deposition (CSD) were investigated using the same measurement setup. High dielectric constants in the range of ~280–540 and loss tangents less than 0.1 at 4 GHz were measured, where the value depends on the thickness of the PZT film. The voltage tunability of the 340 nm and 440 nm thick PZT thin films was ~34% and 5% for the 140 nm thick PZT film at 120 kV/cm and 4 GHz. The acoustic parameters of the PZT thin films under DC bias voltages were determined using a one-dimensional acoustic wave resonator model. For the PZT films of thicknesses 340 nm and 440 nm, the acoustic resonance frequency shift was about 15 MHz and the electromechanical coupling coefficient was ~10% at an electric field of 160 kV/cm. The large dielectric constant and high tunability suggest that the characterized PZT thin films may be suitable for radio frequency (RF) applications such as high-density RF MIM capacitors and other tunable devices.     

Effects of thickness of the thermal insulation layer on the properties of PbTiO3 thin films

A multilayer pyroelectric thin film structure (MPTFS) is one of promising candidates for applications on uncooled IR focal plane array detectors. In the MLPTFS, a porous silica film is used as a thermal insulation layer, and the thermal insulation is improved with increasing thickness of a porous silica film. On the other hand, the effects of thickness of the porous silica films on the electrical properties of pyroelectric thin films need to be addressed. The research results have shown: the thickness of the porous silica films can not be increase unboundedly. With increasing thickness of porous silica films, the coercive field increase, the dielectric constant and the breakdown field decrease respectively. When the thickness of the porous silica films is lower than 3 μm, the effects of the porous silica films on the properties of PT thin films are acceptable. The optimized thickness of the porous silica films is determined according to the results of the electrical properties.     

Thickness dependent ferroelectric properties of BSTO thin films deposited by RF magnetron sputtering

The thickness dependence of ferroelectric permittivity of (Ba, Sr)TiO₃ has been investigated. The BST films could be obtained to have a simple cubic perovskite structure, space group Pm3m, and practically c-axis epitaxial structure deposited at 800^∘C. Through post-annealing process, we have improved the dielectric properties; dielectric permittivity, dielectric loss, and tunability. The change in dielectric properties before and after annealing is attributed to the change in film strain and the contraction in film lattice. As the thickness of BST films increases from 55 nm to 350 nm, the dielectric constant of BST films increases from about 100 to above 670 due to the reduction of interfacial dead layers with low dielectric constant between films and top electrodes. The dielectric loss of BST thin films decreased as the thickness increases. The existence of interfacial dead layers in a thinner film had a larger effect on the effective dielectric constant than tensile strain between the BST films and MgO substrate.     

Scaling Effect on the Dielectric Constant in Ba(Ti x Zr1−x )O3 Thin Films

Recent work on PZT and BST thin films reveal a thickness dependence of the dielectric constant for a film thickness below 100 nm. This effect is commonly attributed to an interfacial layer between the electrode and the dielectric film (dead layer). In this contribution we report on the influence of the film thickness on the dielectric constant of Ba(Ti_xZr_{1 – x})O₃ thin films with different Zr-contents (x = 0–30 at.%). The films were prepared by chemical solution deposition (CSD) with thickness between 30 and 350 nm.The electrical characterization was performed in a temperature range between 25 and 200C. Results were interpreted with respect to the formation of a serial dead layer capacitance.     

Interface potential barrier height and leakage current behavior of Pt/(Ba,Sr)TiO3/Pt capacitors fabricated by sputtering process

Abstract

Variations of the leakage current behaviors and interface potential barrier height (φ _B ) of rf-sputter deposited (Ba, Sr)TiO₃ (BST) thin films, with thickness ranging from 20nm to 150 nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. φ _B critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under N₂ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the φ _B from about 2.4 eV to 1.6eV due to the oxidation. φ _B is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20nm thick film shows tunneling current, 30 and 40 nm thick films show Schottky emission current and the thicker films show a mixed characteristics and bulk and interface limited currents although the mechanism is not clearly understood at this moment.     

AC breakdown strength of aromatic polymers under partial dischargereducing conditions

Partial discharge occurring at HV in AC electric breakdown field measurements on insulating polymeric films strongly reduces the breakdown field strength of the material and conceals the intrinsic breakdown process. By performing AC electric breakdown field measurements on polymer films in phthalic diesters, it was possible to suppress partial discharge and obtain breakdown field data of more intrinsic character. This is valuable for the evaluation of the influence of the structure and the properties of polymers on their insulating behavior. The AC electric breakdown field strength of five aromatic polymers at different film thicknesses was measured in dibutyl phthalate. The results from these measurements showed about a twofold increase in the breakdown field strength at sample thicknesses >50 μm, compared to data obtained in transformer oil. The breakdown field strength for thick samples showed a linear decrease with increasing sample thickness for all polymers except PEEK, which showed a constant breakdown field strength in the thickness range investigated. The breakdown field strength of thin samples was independent of the polymer structure. Measurements of the breakdown field strength of the polymers under dc conditions show no obvious correlation between chemical structure or polymer property and the breakdown field strength     

厚度对磁控溅射CoPt永磁薄膜磁性能的影响

CoPt永磁薄膜有较高的剩磁和矫顽力,通常用作磁传感器中的磁偏置或者微机电系统(MEMS)中的磁制动部件。CoPt薄膜多采用磁控溅射或离子束沉积工艺制备。采用磁控溅射制备了不同厚度CoPt/Cr薄膜。结果显示,CoPt薄膜矫顽力随薄膜厚度增加而降低;薄膜较厚时(大于400?),剩磁随薄膜的厚度增加而降低。这主要是因为CoPt薄膜具有密集六方结构,其自然生长为(002)面,具有垂直各向异性。由于Cr缓冲层存在,CoPt薄膜较薄时沿(1010)面生长,从而具有面内各向异性;但随薄膜厚度的增加,薄膜会沿(002)生长从而具有垂直各向异性,导致薄膜磁性能降低。     

PZT thick films on different ceramic substrates; piezoelectric measurements

The piezoelectric, microstructural and electrical characteristics of thick PZT films on relatively inert alumina substrates and on two LTCC tapes, i.e., Du Pont 951 and Electro Science Labs 41020 were studied. A thick-film paste was prepared from the pre-reacted PZT powder (PbZr_0.53Ti_0.47O₃) and printed and fired on LTCC tapes and on alumina substrates, respectively. Dielectric permittivities, dielectric losses, remnant polarizations and coercive fields were measured. The dielectric constants (100–150) of thick films fired on LTCC substrates are low. The piezoelectric coefficients d ₃₃ were measured by different methods, i.e. Berlincourt piezometer, interferometry and piezoresponse force microscope (PFM). The d ₃₃ values on LTCC substrates are low (30–70 pm/V) as compared with values obtained on alumina substrates (around 120 pm/V). Lower dielectric constants and piezoelectric coefficients d ₃₃ of films on LTCC substrates are attributed to the formation of phases with a low permittivity due to the diffusion of silica from LTCC substrates into PZT films. The d ₃₃ constants of samples with different thicknesses of PZT layers (from 20 to 160 μm) at first increase with the increasing thickness of PZT layers and then decrease for thicker films. As the cracks in the structure were not observed the reason for the decreasing d ₃₃ values for thicker films is still unclear.     

面向配电网不停电作业装置的高性能电力电容器介质材料制备

随着配电网高可靠性作业的发展,不停电作业装置是配电网运检的必备工具之一.电力电容器是配电网不停电作业装置中配电单元、AC/DC电源变换单元等的能源储存核心单元,其高性能化、轻型化和小型化是其发展的一个关键.为制备新型高储能密度的电力电容器用介质材料,利用磁控溅射技术在Pt/Ti/SiO2/Si基底上制备Ba(Sn0.3...     

嵌入屏障的绝缘介质中电树生长模型

利用WZ模型将绝缘介质离散化,使用分形理论讨论了绝缘介质中电树发展的随机性和确定性。在原有WZ模型的基础上引入了分布耐电强度的概念,建立了新的模型。通过此二维模型仿真了在绝缘介质中嵌入了耐电强度高于原介质的屏障后的电树生长情况。在针板电极结构下用模型仿真了在绝缘介质中所嵌入屏障耐电强度的不同对电树发展造成的不同影响,并比较了不同情况下的平均击穿距离。通过比较得出,当嵌入耐电强度远大于原介质的屏障后,电树发展过程中需要绕过屏障进行生长,从而等效于增加了原有介质的厚度,使得整个介质的绝缘性能有一定程度的提高。     

不同组分对PI／Al2O3复合薄膜的击穿性能和微观形貌的影响

为研究纳米填加剂(Al2O3)对PI复合薄膜击穿性能和微观形貌的影响,对0、5%、10%和20%4种不同质量分数的纳米Al2O3的PI/Al2O3复合薄膜击穿特性进行了测试,并借助扫描电镜对PI/Al2O3复合薄膜击穿孔区形貌进行特征分析,进一步利用积分法计算得到了击穿孔区的有效面积.结果表明:掺杂5%含量的Al2O3的PI复合薄膜击穿场强达到最佳.得出不同组分Al2O3的PI复合薄膜击穿孔有效面积的大小关系是:S20%＜S5%＜S10%＜S0.可见,引入纳米Al2O3颗粒可以使复合薄膜击穿孔的有效面积减小,说明掺杂纳米Al2O3对复合薄膜的击穿孔的有效面积大小是有显著影响的.     

不同场强下新型绝缘聚合物的变色特性及其介电特性

为了依靠绝缘材料在电场下的颜色变化判断电力设备带电状态,制备了等规/无规聚（3-己基噻吩）（poly(3-hexylthiophene),P3HT）共混薄膜。研究发现,等规P3HT纳米微晶在共混薄膜顶部均匀分布。随无规P3HT含量的上升,共混薄膜沿厚度方向表现出更好的绝缘性能。在无规P3HT含量为95%时,共混薄膜的工频介电常数为5.86,电阻率为3.2 T Ω·cm,直流击穿场强达到113 kV/mm。通过空间电荷积累光谱发现,当电场强度大于40 kV/mm时,电荷主要积累在绝缘的无规P3HT中,且共混薄膜吸收光谱450 nm处峰强度随电场强度的增加而升高,实现了空间电荷驱动的绝缘体系电致变色,为电力设备绝缘带电状态检测提供了新方法。     

纳米二氧化硅/聚酰亚胺耐电晕薄膜的研究

通过超声机械混合方法制备纳米二氧化硅／聚酰亚胺复合耐电晕薄膜，并对其耐电晕性进行测量。用红外光谱(IR)和原子力显微镜(AFM)观察无机纳米粒子的分散情况及其电晕前后变化。结果表明：纳米二氧化硅／聚酰亚胺复合薄膜耐电晕性比普通的聚酰亚胺薄膜高。     

Epitaxy and interfacial phase in thin films of lead scandium tantalate deposited by reactive sputtering on a platinum interlayer

Abstract

Lead scandium tantalate (PST) films with a lead-rich composition were deposited at 500°C by RF sputtering on sapphire substrates coated with Pt and were investigated by cross-sectional transmission electron microscopy. The films consisted almost entirely of the perovskite phase. The grains of perovskite PST had a crystallographic orientation almost parallel to that of the underlying Pt. Some elongated voids were observed. The presence of an interfacial phase, with interplanar spacings consistent with a pyrochlore phase, was demonstrated by electron diffraction and dark-field imaging. The crystallographic orientation of this phase is also nearly parallel to that of the Pt. Energy-dispersive X-ray microanalysis showed that the interfacial phase is lead-deficient. The interfacial phase is irregular in thickness. A reduction in the Pb content of the film leads to a thicker interfacial layer. The implications for the mechanism of growth of PST on Pt and for improvement of the film quality are discussed.     

Automatic breakdown voltage measurement of polymer films

Determining the breakdown strength of dielectric films is tedious, as the breakdown strength at 1% breakdown probability is more relevant to system insulation design than the Weibull characteristic breakdown strength, and obtaining reasonable confidence limits at 1% breakdown probability requires very large numbers of breakdowns. An automatic system for DC ramp breakdown strength measurements has been reported [1]. This system comprises a HV-probe and a movable arm equipped with an electrode holder that scans over the sample surface. One problem with this approach is that the metal electrodes are damaged by the breakdowns which, based on the author's experience, results in occasional low breakdowns that can distort the statistical distribution. To avoid this problem, a breakdown tester that can carry out breakdown strength measurements automatically utilizing metalized film electrodes has been developed. In this system, metalized films are used as electrodes and renewed after each breakdown. This is accomplished using a mechanical assembly under computer control through a LabView interface. By utilizing metalized films and renewing them after each breakdown, the system does not suffer from breakdown-induced electrode damage. To evaluate the system, we carried out 100 breakdowns with three active areas varying from 2 cm2 to 20 cm2. The breakdown data were analyzed using a Weibull distribution, agreed well with previous data obtained manually, and scaled properly as a function of area based on a Weibull distribution [2]. We have carried out over 600 breakdowns automatically, which is sufficient to provide very good data at low probability of breakdown. The development of the automatic breakdown strength tester provides a means to evaluate polymer films at low breakdown probability which is relevant to insulation design.     

厚度对M型钡铁氧体薄膜结构及磁性能的影响

采用射频(RF)磁控溅射法在蓝宝石基片上制备M型钡铁氧体(Ba M)薄膜,研究了薄膜厚度对Ba M铁氧体薄膜的结构及磁性能影响。结果显示,样品的衍射峰全部为Ba M薄膜的(00l)衍射峰,表明样品都具有良好的c轴取向性。显微结构分析结果表明,在膜厚为40~90nm范围内,薄膜样品表面主要为c轴取向的片状晶粒,未出现c轴随机取向的针状晶粒;当样品厚度增加至140nm时,出现了较明显的针状晶粒;随着薄膜厚度进一步增加到190nm时,样品表面出现了大量c轴随机取向的针状晶粒,且部分针状晶粒长度达到了μm级。磁性能测试结果显示,随着薄膜厚度的增加,薄膜样品饱和磁化强度降低,垂直膜面方向矫顽力和剩磁比减小,膜厚40~90nm范围的薄膜在垂直膜面方向获得了最大剩磁比和矫顽力,表现出较好的磁晶各向异性。     

Characterization of Polyurethane Foam Dielectric Strength

Internal flashovers in hollow insulation systems can produce serious damage. Frequently, SF₆ or N₂ is used to eliminate this problem, but possible gas leakage may endanger the insulation. This paper proposes the use of polyurethane foams to fill the hollow spaces in insulation systems. Thus far, few publications deal with the dielectric properties of foams. This paper demonstrates the dielectric strength of three different foams which are investigated using ac and lightning impulse voltages under different humidity and temperature conditions. The results show that polyurethane foams have 2-3 times better dielectric strength than air. The breakdown strength decreases with the thickness of the foam; temperature and humidity have negligible effects on the breakdown voltage. The major parameter is the size of the voids in the foam. Reducing the size of the voids increases the breakdown strength. This can be achieved by improving the manufacturing technology.     

Nanoscale phenomena of gallium-doped ZnO thin films on sapphire substrates

Gallium-doped ZnO (1.2 at. %) thin films with various thicknesses were deposited on sapphire (001) substrates at 500^∘C using a pulsed laser deposition (PLD) technique. The thin films with different thicknesses (20, 40, 100, 200, 400, and 600 nm, respectively) were obtained by changing the deposition time. An x-ray diffractometer (XRD) was used to investigate the structural properties of the thin films. All of the thin films had a preferred (002) orientation. However, the thin films with 20 and 40 nm thicknesses were of low crystallinity. With increasing thickness the (002) peak increased greatly, and the full width at half maximum (FWHM) values were calculated by using omega scans. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to investigate the nanoscale phenomena and the surface morphologies of the thin films. The surface roughness increased as the thickness increased. The thin film with 20 nm thickness was very smooth, and no nucleation center could be observed. However, the thin film with thickness over 100 nm showed nucleation. The nucleation center varied with increasing thickness. A spectrometer was used to investigate the luminescent properties of the thin films. It was found that all of the thin films showed near band edge emissions and no deep-level emissions were observed. A blueshift was also observed due to the Burstein-Moss effect.