High dielectric constant polymer-ceramic (Epoxy varnish-barium titanate) nanocomposites at moderate filler loadings for embedded capacitors

Polymer-ceramic nanocomposites are the major candidate dielectrics for embedded capacitors. Due to the poor adhesion and poor thermal stress reliability at high filler loadings, commercially available polymer-ceramic composites can only achieve a maximum dielectric constant of ∼30. However, a high dielectric constant of ∼50–200 is required to make the layout area small enough for embedding applications. In this work, we systematically studied the material formulations in order to obtain a high dielectric constant (κ>50) at the lowest ceramic filler loading. It was found that material design and processing were critical. By modifying the epoxy matrix with a chelating agent and using bimodal fillers and a proper amount of dispersing agent, dielectric constants ∼50 were obtained at moderate filler loadings.     

Cyanoethylated pullulan as a high-k solution processable polymer gate dielectric for SWCNT TFTs

Cyanoethylated pullulan (CEP), a high-k solution processable polymer gate dielectric, is used to fabricate bottom gated single wall carbon nanotube (SWCNT) network thin film transistors (TFTs). Both aqueous and organic dispersions of highly semiconducting enriched SWCNTs are used as the channel material. Use of CEP as the dielectric enables fabrication of devices operating at low voltage (<3 V) with high on-state currents, good on/off ratios (∼10⁵), low subthreshold swings (∼200 mV/decade) and minimal hysteresis (<1 V). However, despite high apparent mobilities extracted from gate voltage sweeps, driving these devices at even modest frequencies (>1 Hz) is found to significantly decrease the transconductance. This is shown to be related to a significant frequency dependence of the capacitance associated with a slow polarization response of the dielectric. Despite this limitation, CEP could be a useful dielectric in SWCNT TFTs for applications such as sensors and low frequency amplifiers.     

Polymerization conditions influence on the thermomechanical and dielectric properties of unsaturated polyester-styrene-copolymers

The influence of different polymerization conditions like curing agent (MEKP) amount and styrene content on the glass transition temperature, the relative dielectric constant as well as loss factors of unsaturated polyester-styrene-polymer systems after solidification was investigated in depth. With respect to a high average molecular mass and Vickers hardness a curing agent content of 3 wt% is recommendable. Increasing MEKP-concentrations cause a slight elevation of the polymers relative dielectric constant as well as of the loss factor. Regarding an easy film formation using tape casting a.o. higher styrene amounts lower the viscosity of the resin significantly, the relative dielectric constant and the loss factor decrease also. As an average value a relative dielectric constant of 3 under ambient conditions can be obtained.     

外延CeO2高k栅介质层的结构及介电性能

利用脉冲激光沉积两步生长法在Si(111)衬底上制备了厚度为10～40nm的外延CeO<,2>薄膜,构建了Pt/CeO<,2>/Si MOS结构.研究了CeO<,2>薄膜的界面及介电性能,实验发现,界面处存在的电荷对MOS结构C-V特性的测量有较大影响,采用两步生长法制备的外延CeO<,2>薄膜在保持较大介电常数的同时...     

A study on the temperature dependence of epoxy/BaTiO<Subscript>3</Subscript> composite embedded capacitor films

In this study, the temperature dependence of capacitance, one of the most important properties of embedded capacitor films (ECFs), was investigated. The temperature dependence of the capacitance of ECFs was determined by the temperature dependence of the dielectric constant and thickness, and among these, the main factor was the dielectric constant of ECFs. The dielectric constant of ECFs was determined by that of epoxy and BaTiO₃ powders. Below 130°C, the dielectric constant of ECFs increased as temperature increased, and was mainly affected by an epoxy matrix. However, above 130°C (the Curie temperature of BaTiO₃), the increased rate of the dielectric constant of ECFs started decreasing. This was due to the fact that BaTiO₃ powder undergoes a phase transition from a tetragonal to a cubic structure, and its dielectric constant decreases at 130°C. The dielectric constant of BaTiO₃ powder was obtained from measured dielectric constants of ECF and application of the Lichtenecker logarithmic rule.     

Tuning the dielectric constant of polymers using organic dopants

Four different electron-rich organic dopants were added to an unsaturated polyester resin to determine the influence on the rheological properties as well as on the softening and dielectric properties after solidification. While the viscosity is slightly reduced with increasing dopant concentration, which simplifies thin-film formation for the integration in a printed circuit board, as unwished side effect the glass transition temperature of the solid polymer drops also. The aspired increase in the relative constant could be realized, starting with an initial value around 3 the addition of 20 wt% of phenanthrene enabled a value for ε_rel of 5.5 (20 °C, 100 kHz). A rise of the dielectric loss could be observed also.     

Improving thermal conductivity of polymer composites in embedded LEDs systems

Polymer embedding of LEDs increases safety and waterproof levels in LED based lighting systems. The embedding allows for mechanical flexibility of these systems. The increase of polymer thermal conductivity has been a research challenge for decades. Here, we suggest materials for enhancing thermal conductivity in polymer embedded LED systems. We demonstrate that thermally conductive fillers into the polymer matrix to form a composite improved heat transfer from the LEDs to the environment. Non metallic boron nitride with a high intrinsic thermal conductivity is a good candidate. Thermal conductivity of basic polymer PDMS with various filler size and polymer ratios is reported here. Here, an in situ measurement tool to fast evaluate the quality of the composites in LED applications is demonstrated. Future work will focus on further increasing the thermal conductivity of the composites by using different mixtures.     

Investigation of strontium tantalate thin films for high-k gate dielectric applications

Strontium tantalate (STO) films were grown by liquid-delivery (LD) metalorganic chemical vapor deposition (MOCVD) using Sr[Ta(OEt)₅(OC₂H₄OMe)]₂ as precursor. The deposition of the films was investigated in dependence on process conditions, such as substrate temperature, pressure, and concentration of the precursor. The growth rate varied from 4 to 300 nm/h and the highest rates were observed at the higher process temperature, pressure, and concentration of the precursor. The films were annealed at temperatures ranging from 600 to 1000 °C. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and ellipsometry indicated that the as-deposited and the annealed films were uniform and amorphous and a thin (>2 nm) SiO₂ interlayer was found. Crystallization took place at temperatures of about 1000 °C. Annealing at moderate temperatures was found to improve the electrical characteristics despite different film thickness (effective dielectric constant up to 40, the leakage current up to 6×10⁻⁸ A/cm², and lowest midgap density value of 8×10¹⁰ eV⁻¹ cm⁻²) and did not change the uniformity of the STO films, while annealing at higher temperatures (1000 °C) created voids in the film and enhanced the SiO₂ interlayer thickness, which made the electrical properties worse. Thus, annealing temperatures of about 800 °C resulted in an optimum of the electrical properties of the STO films for gate dielectric applications.     

Mg2+和Mn2+掺杂对BaTiO3-金属复合系介电性能的影响

在钛酸钡基料中加入碱式碳酸镁、碳酸锰、金属氧化物及其它添加剂,经过球磨、预烧、造粒等工艺, 在Mg2 和Mn2 的综合作用下,系统得以在中温(低于1 150 ℃)下烧成.陶瓷的介电性能得到有效改善,εr达到2 587, tan δ小于1.2×10-2,在-55～ 170 ℃的宽广温区内,ΔC/C为± 15 %.     

共聚尼龙/PZT复合材料的压电和介电性能研究

以共聚尼龙为基体,采用简单的热压工艺制备了0-3型共聚尼龙/PZT压电复合材料,研究了所制复合材料的介电和压电性能.结果表明:以共聚尼龙为聚合物基体可以制备出具有优良介电和压电性能的新型聚合物/PZT复合材料;在共聚尼龙的体积分数为0.20时,复合材料的压电常数和相对介电常数都达到最大值,分别为55 pC/N和155.     

新型BNT系高温陶瓷电容器材料的研究

采用固相合成工艺,制备了(Bi0.5Na0.5)(1–x)CaxTiO3(BNCT)陶瓷(x=0.01～0.14)。研究了Ca含量对BNCT陶瓷介电性能的影响。结果表明,所有BNCT陶瓷样品中都存在第二相TiO2;随着Ca含量的增加,BNCT陶瓷的介电峰向低温方向移动,介温曲线越来越平坦,剩余极化急剧减小,介质损耗逐渐减小。往x=0.12的BNCT陶瓷里掺入质量分数为1.5%的MnCO3,所得陶瓷样品的室温tanδ小于1%、绝缘电阻率达到1011?.cm,并满足–55～+250℃下,?C/C25℃≤±15%的高温MLCC的要求。     

PA-Cap聚合物电容器在模拟CPU电源中的应用

在计算机CPU的电源电路中,采用电解电容器作为电源的去耦电容。研究了CPU的负载高速变化时,三种类型电容器提供瞬时电流以稳定电源电压的情况。结果显示:PA-Cap聚合物片式叠层铝电解电容器(56μF)的Res为23mΩ,△V为–90mV,而220μF钽电容Res为73mΩ,△V为–172mV,1000μF液体铝电解电容Res为56mΩ,△V为–232mV。因此,PA-Cap聚合物电容器用在开关电源和数字电路中应用前景广阔。     

Fabrication of radial ZnO nanowire clusters and radial ZnO/PVDF composites with enhanced dielectric properties

Using an improved microemulsion process novel ZnO nanostructures can be prepared on a large scale. These radial ZnO nanowires grow on hexagonal prism tips and form nanowire clusters. A detailed study of variations in dielectric properties dependent on frequency and temperature shows that composites of radial ZnO and PVDF have significantly higher dielectric constants and exhibit better thermal stability than bulk ZnO/PVDF composites as well as showing a low percolation threshold. Already a low content of radial ZnO increases the dielectric constant of the polymer matrix significantly to a value above 100.     

基于新型介电弹性体平行板电容器的研究

为了研究具有传感功能的可变电容器,采用新型介电弹性体材料制成平行板电容器。研究了该电容器充放电前后的外形变化及影响电容大小的因素。结果表明:在高压充放电前后,电容器的极板面积和两电极板间距离都发生了明显的变化;电容随着外加电压的增大而增大;在外加电压为6 000 V的条件下,电容随着材料预拉伸的增大出现一极大值,随后又减小,即在变化过程中存在拐点;另外,电容器的电极材料用石墨粉时要比用导电胶时电容大。     

An overview of laminate materials with enhanced dielectric properties

This report focuses on laminate materials (resins and reinforcements) having potential applications in the manufacture of multi-layer printed wiring boards (PWBs) that are required to efficiently transmit high-speed digital pulses. It is intended to be a primer and a reference for selection of candidate materials for such high-performance PWBs. Included are dielectric and physical properties, and where available chemical composition and/or structure, commercial availability, compatibility with typical PWB processing schemes and approximate relative cost. Recommendations are made as to the most viable candidate materials for this type of PWB application, based on a comparison of electrical and physical properties together with processing and cost considerations. The cyanate ester resin system appears promising. Such a resin may be reinforced with regular E-glass, or the more newly available S-glass, to produce a laminate useful for intermediate performance applications. For more demanding applications the E-glass will have to be replaced by a material of much lower relative permittivity. The expanded-PTFE reinforced laminates fromW. L. Gore appear to be a good choice for these applications. The processing of theGore materials can be expected to deviate from that used with FR-4 type materials, but is likely to be less problematic than laminates comprised of a fluorinated resin. Processing is a key obstacle to the implementation of any of the new materials herein. If implementation is to be successful, programs must be established to develop and optimize processing procedures. Cost will remain an important issue. However, the higher cost of the new materials may be justified in high-end products by the performance they deliver.     

两种蚀刻法制作埋嵌电容PCB的对比研究

蚀刻法是埋嵌电容技术中研究与应用较多的方法。文章研究了双面蚀刻一次层压与单面蚀刻两次层压这两种工艺方法,并指出了两种方法加工埋嵌电容PCB工艺过程的关键点。通过电容值测量及回流焊测试,对比分析了不同工艺方法对埋嵌电容PCB的容值精确度及耐热性能的影响,明确了这两种工艺方法的优缺点。     

复合陶瓷BaTiO_3/Ni_(0.5)Zn_(0.5)Fe_2O_4的常温巨介电特性研究

采用传统的固相反应法和氧化物陶瓷工艺制备了无铅磁电复合陶瓷(1–x)BaTiO3/x Ni0.5Zn0.5Fe2O4(质量配比,x=0,0.2,0.5,0.8)(BTO/NZF),研究了NZF含量对复合陶瓷的物相组成、微观形貌、致密度和介电性能的影响。结果表明:当NZF含量较低(x=0,0.2,0.5)时,NZF对复合陶瓷有介电稀释效应;当NZF含量较高(x=0.8)时,复合陶瓷晶粒尺寸、致密度及两相间接触面积增大,其NZF含量达到复合陶瓷渗流阈值,产生Maxwell-Wagner(M-W)表面极化效应,使得复合陶瓷在低频(f=40 Hz)下具有高的巨介电常数(ε′=312 238)和较低的介电损耗(tanθ=0.40)。     

Capacitance-voltage analysis of a high-k dielectric on silicon

正Device characteristics of TiO_2 gate dielectrics deposited by a sol-gel method and DC sputtering method on a P-type silicon wafer are reported.Metal-oxide-semiconductor capacitors with Al as the top electrode were fabricated to study the electrical properties of TiO_2 films.The films were physically characterized by using X-ray diffraction,a capacitor voltage measurement,scanning electron microscopy,and by spectroscopy ellipsometry.The XRD and DST-TG indicate the presence of an anatase TiO_2 phase in the film.Films deposited at higher temperatures showed better crystallinity.The dielectric constant calculated using the capacitance voltage measurement was found to be 18 and 73 for sputtering and sol-gel samples respectively.The refractive indices of the films were found to be 2.16 for sputtering and 2.42 for sol-gel samples.     

高温有机电容器的设计

简要介绍了干式高温有机电容器材料和结构的选择要点,阐述了制造高温电容器关键工艺的原理和方法,分析了聚酯(PET)、聚丙烯(PP)、聚碳酸酯(PC)、聚苯硫醚(PPS)介质耐高温电容器的电性能     

介质埋藏平面蝶形天线的设计

采用了介质埋藏的形式将平面蝶形天线埋藏于介质中,并设计了渐变的平面微带巴伦给平面蝶形天线馈电,实现了不平衡到平衡的转换;还设计了三角形微带巴伦和微带传输线一起的结构形式,进行阻抗匹配。使用电磁仿真软件Ansoft HFSS对该天线进行了优化设计和仿真实验,与制作的实物天线性能进行对比。仿真和实测结果表明,该天线S11≤-10 dB仿真的相对带宽达到88.7%而实测的相对带宽为79.3%,具有超宽带特性;在工作频率处,仿真增益为6.9 dB,实测增益为5.8 dB。该天线满足某工程项目的需要,可作为探地雷达系统的收发天线。