【作者】 王志伟；

【导师】 李雷； 王剑；

【作者基本信息】 浙江大学 ， 材料工程， 2015， 硕士

【摘要】 聚合物基介电复合材料由于能综合传统介电陶瓷和介电聚合物的优点,使其成为最有潜力应用于微电子领域的新型介电材料,主要包括介电陶瓷／聚合物型和导电颗粒／聚合物型两大类,但均存在高介电常数与低介电损耗难以协调的问题。本论文以具有半导特性的本征巨介电常数材料Ln1.5Sr0.5NiO4 (Ln=La、Nd)为填充物,研究了Ln1.5Sr0.5NiO4/聚偏氟乙烯(PVDF)复合材料的介电特性及其机理,并获得了高介电常数与低介电损耗的协调。采用热压法制备了(NSNO)/PVDF复合材料,并研究其在温度213～403 K和频率1-107Hz范围内的介电性能。当NSNO体积分数(fNSNO)增大到0.25以上时,复合材料的交流电导率和介电常数随着fNSNO的增加而急剧增大,表现出典型的渗流现象,拟合得到其渗流阈值为0.276,此现象源于NSNO陶瓷颗粒的半导性。同时,在fNSNO低于渗流阈值时,复合材料表现出起源于PVDF中β相变的介电弛豫现象；在fNSNO高于渗流阈值时,复合材料表现出截然不同的介电弛豫,此弛豫来源于NSNO填料的热激活小极化子跃迁。得益于NSNO本征巨介电效应,当fNSNO高于渗流阈值时,复合材料得到了巨介电常数和低介电损耗的协调,并且具有良好的温度稳定性,表现出与其他聚合物基介电复合材料迥异的介电行为。当fNSNO=0.35时,在1 kHz和250～400 K温度范围内,其介电常数稳定在9300～12000范围内,介电损耗维持在较低值0.33～0.41之间。如此优良的综合介电性能说明NSNO/PVDF复合材料具有应用于微电子领域嵌入式电容的巨大潜力。为了研究聚合物基介电复合材料的微波介电性能,发展了评价高损耗材料微波介电性能的改进型金属谐振腔法。这种方法采用小尺寸待测试样,并引入大尺寸低损耗参考试样,从而有效降低了谐振系统的损耗,实现了高损耗材料的测试。与已知方法相比,这种方法具有测试精度高、试样易制备的优点。同时,将这种方法应用于CaCu3Ti4012、Ba(Fe1/2Nb1/2)O3和Sr(Fe1/2Nb1/2)O3等巨介电陶瓷的测试,研究了烧结温度和热处理气氛对其微波介电性能的影响。三种陶瓷的介电常数具有很弱的频率依赖性,且对制备条件不敏感；而介电损耗则表现出很强的频率依赖性,且对制备条件敏感。对于CaCu3Ti4O12陶瓷,随着烧结温度提高其微波介电损耗明显增大；而对于Ba(Fe1/2Nb1/2)O3和Sr(Fe1/2Nb1/2)O3陶瓷,热处理气氛对其介电损耗具有更明显的影响。这是表明对这三种材料来说,在微波下存在不同的非本征极化机制。进一步的工作中,采用热压法制备了La1.5Sr0.5NiO4 (LSNO)/PVDF复合材料,并研究了其在室温下直至微波频段的介电性能及极化机制.LSNO/PVDF复合材料在1～107Hz下的介电行为与NSNO/PVDF复合材料相类似,其在1 kHz下的介电常数随着LSNO含量的增加先平缓增大,随后急剧增大,表现出典型的渗流特性,其渗流阈值约为0.306。但随着频率的升高直至微波频段,渗流阈值附近介电常数的变化变缓,更符合有效介质理论模型而非渗流模型。这表明界面极化对介电性能的贡献随着频率的升高而减弱,较高频率下介电性能主要由LSNO的本征介电性能决定,而较低频率下则由本征介电性能及界面极化共同决定。更多还原

【Abstract】 Polymer-based dielectric composites can combine the advantages of traditional dielectric ceramic and dielectric polymer, indicating the great potential as novel dielectric materials in microelectronics. Insulate polymer is used as the matrix in polymer-based dielectric composites, and the filler can be dielectric ceramic or conductive material, while the combination of high permittivity and low dielectric loss is a key problem. In this thesis, semi conductive Ln1.5Sr0.5MO4 (Ln=La、Nd) ceramic particles with intrinsic giant permittivity were used as fillers, and the dielectric characteristics and mechanisms of Ln1.sSr0.5NiO4/polyvinylidene fluoride (PVDF) composites were investigated, in which the combination of high permittivity and low dielectric loss was obtained.Nd1.5Sr0.5NiO4 (NSNO)/PVDF dielectric composites were prepared by hot pressing and the dielectric properties were characterized at 213-403 K and 1～107 Hz. The composites showed typical percolative behaviors due to the semiconductivity of Ndi.5Sro.5Ni04 filler, for which the AC conductivity and permittivity increased rapidly with the filler volume fraction near to the percolation threshold (0.276). Different dielectric relaxations were observed when the filler volume fraction was below and above the percolation threshold, and they were attributed to the β relaxation of PVDF matrix and thermal-activated small polaronic hopping of Nd1.5Sr0.5NiO4 filler, respectively. Different from other polymer-based dielectric composites, the present composites exhibited both temperature-stable giant dielectric constant and relatively low dielectric loss above the percolation threshold, which benefited from the intrinsic giant permittivity of Nd1.5Sr0.5MO4 filler. When the filler volume fraction was 0.35, the optimal dielectric properties with permittivity of 9,300-12,000 and dielectric loss of 0.33-0.41 at 1 kHz were obtained in the temperature range of 250-350 K, indicating the great potential of the present composites as embedded capacitors.In order to investigate the microwave dielectric properties of polymer-based dielectric composites, the modified metal cavity method was developed to evaluate the microwave dielectric properties of high loss materials. In this method, small-size sample under test and large-size low-loss reference ceramic were used to reduce the overall loss of the resonant system, so that the measurement for high-loss sample could be conducted. Compared to other methods, this method has the advantages of high accuracy and easy preparation of samples. This method was used to measure the microwave dielectric properties of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3 and Sr(Fe1/2Nb1/2)O3 giant permittivity ceramics, and the effects of sintering temperature and annealing atmosphere were focused. Their dielectric constant showed slight frequency dependence, and was insensitive to the preparing conditions, while strong frequency dependence and sensitivity to preparing conditions were observed for dielectric loss. Microwave dielectric loss increased significantly with sintering temperature for CaCu3Ti4O12, while the annealing atmosphere had more notable effect on the dielectric loss of Ba(Fe1/2Nb1/2)O3 and Sr(Fe1/2Nb1/2)O3, indicating the different extrinsic polarization mechanisms at microwave frequencies for the three ceramics.In the further work, La1.5Sr0.5NiO4 (LSNO)/PVDF composites were prepared by hot pressing, and the dielectric properties were characterized up to microwave frequencies at room temperature. The dielectric properties of LSNO/PVDF composites were similar to NSNO/PVDF composites, and the permittivity increased rapidly with the filler volume fraction near to the percolation threshold (0.305) at 1 kHz. However, the permittivity near to the percolation threshold increased more slowly with the filler volume fraction for higher frequency, and it fitted the effective medium theory better rather than percolation theory, indicating that the contribution of interfacial polarization to permittivity was weakened with the increase of frequency. The dielectric properties were dominated by intrinsic mechanisms of LSNO at higher frequencies, while by both interfacial polarization and intrinsic mechanisms at lower frequencies.更多还原