【作者】 万帅；

【导师】 吕文中；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2010， 博士

【摘要】 鉴于片式压敏电阻向低压化、低温烧结及“绿色”制造等方向发展,本文以低电压梯度ZnO-Bi2O3-TiO2-Co2O3-MnCO3(ZBTCM)压敏陶瓷为研究对象,探讨了该压敏陶瓷材料体系的掺杂改性和低温烧结,并利用水基流延工艺制备出了低温共烧型片式压敏电阻器。首先研究了烧结温度和升温速率对ZnO-Bi2O3-TiO2-Co2O3-MnCO3(ZBTCM)压敏陶瓷致密度、物相组成、微观结构和电性能的影响。结果表明：当升温速率为60℃／h,烧结温度为1100℃时,其致密度和综合电性能最佳：密度ρ=5.42g/cm3、电压梯度E1mA=35.6V/mm、非线性系数α=33.3、漏电流密度JL=0.31μA/cm2、8/20μs脉冲电流冲击后压敏电压的变化率ΔV1mA=15.4%。该材料体系虽然具有低电压梯度和高非线性特性,但其耐8／20μs脉冲电流冲击能力较差,而且相对较高的烧结温度使其无法实现与Ag电极的叠层共烧。接下来,探讨了过渡金属氧化物W03对ZBTCM压敏陶瓷致密度、物相组成、微观结构和电性能的影响规律。研究表明：当W03含量x≤0.3mol%时,W03与Bi2O3反应生成Bi2WiO3(1+i)(i=1／7,2／7)低熔化合物,促进了ZBTCM压敏陶瓷的烧结,使其致密化温度下降了100℃,并且增加了界面态密度和晶界势垒高度,提高了非线性特性和耐8／20μs脉冲电流冲击能力。但是,当x>0.3mol%时,片状低电阻率Bi2WO6相的生成阻碍了ZBTCM压敏陶瓷的烧结,并且引起晶界势垒高度急剧降低,非线性特性严重恶化。当WO3含量为0.3mol%时,ZBTCM压敏陶瓷在1000℃烧结时其综合电性能最佳：E1mA=54.2V/mm,α=36,JL=0.6μA/cm2,ΔV1mA=8.9%。进一步研究了与WO3同族的过渡金属氧化物Cr2O3对ZBTCM压敏陶瓷致密度、物相组成、微观结构和电性能的影响。Cr2O3溶入ZnO晶粒和Bi2O3晶界相中,促进了ZBTCM压敏陶瓷的烧结,使其致密化温度降低至1000℃,同时增加了界面态密度和晶界势垒高度。当Cr2O3添加量y=0.3mol%时,其E1mA和α值取得各自最大值90.8V／mm和46。此外,随着y值的增加,△V1mA值呈现逐渐减小的变化趋势,当y≥0.3mol%时,其ΔV1mA值降低至10%以下。该结果表明Cr2O3能够大幅提高ZBTCM压敏陶瓷的非线性特性和耐8／20μs脉冲电流冲击能力,但美中不足的是其电压梯度也随之迅速增大。研究了ZnO-B2O3玻璃对ZBTCM压敏陶瓷致密度、物相组成、微观结构和电性能的影响。结果表明：ZnO-B2O3玻璃可以促进ZBTCM压敏陶瓷的烧结,但降温作用有限,仅使其致密化温度降低了约50℃。当烧结温度T<1050℃时,ZnO-B2O3玻璃掺杂ZBTCM压敏陶瓷的晶粒生长动力学指数nZ≈4.54,激活能Qz≈316.5kJ/mol,此时未全部熔化的ZnO-B2O3玻璃析晶相对ZnO颗粒边界迁移起阻滞作用,阻碍了ZnO晶粒的生长；而当烧结温度T≥1050℃时,其动力学指数nZ≈2.92,激活能Qz≈187kJ/mol,此时完全熔化的ZnO-B2O3玻璃析晶相提高了液相烧结作用,促进了ZBTCM压敏陶瓷的晶粒生长。ZnO-B2O3玻璃析晶相ZnB2O4分布在ZBTCM压敏陶瓷晶界处形成晶界俘获态,提高了界面态密度和晶界势垒高度。当ZnO-B2O3玻璃含量为0.1wt%时,ZBTCM压敏陶瓷在1050℃烧结时其综合电性能最佳：E1mA=36.7V/mm,α=35.4, JL=0.35μA/cm2,ΔV1mA=12.1%,该ΔV1mA值略高于合格标准10%。研究了Bi2O3-B2O3玻璃对ZBTCM压敏陶瓷致密度、物相组成、微观结构和电性能的影响。与ZnO-B2O3玻璃相比,Bi2O3-B2O3玻璃对ZBTCM压敏陶瓷促烧作用更明显,使其致密化温度降低至900℃。Bi2O3-B2O3玻璃掺杂ZBTCM压敏陶瓷的晶粒生长动力学指数和激活能为nB≈2.15、QB≈146.2 kJ/mol,该值明显降低。Bi203-B203玻璃析晶相Bi2B4O9分布在ZBTCM压敏陶瓷晶界处形成晶界俘获态,增加了界面态密度,提高了晶界势垒高度。当Bi2O3-B2O3玻璃含量为2wt%时,ZBTCM压敏陶瓷在900℃烧结时其综合电性能最佳：E1mA=124.9V/mm,α=46.2, JL= 0.2μA/cm2,ΔV1mA=8.3%。研究了Bi2O3-B2O3玻璃掺杂ZBTCM压敏陶瓷粉体的水基流延工艺,通过对流延浆料固相含量、粘结剂、分散剂、增塑剂、表面活性剂及消泡剂的优化,成功制备出了厚度为40μm左右且性能良好的水基流延膜。水基流延浆料的最佳配方为：固相含量为50wt%,去离子水含量为41.4wt%, PVA为3wt%, PAA-NH4为0.5wt%,丙三醇含量为2.7wt%,Span-20为1.5wt%,正丁醇为0.9wt%。该水基流延膜在900℃烧结时,其电性能为：E1mA=112.4V/mm,α=34.6,JL=0.5μA/cm2。最后研究了等静压压力对片式压敏电阻微观结构的影响,以及水基流延膜与Ag电极的低温共烧特性。当等静压压力为60MPa时,水基流延膜间及流延膜与Ag电极的界面结合非常紧密,在900℃共烧时,没有出现明显的开裂和分层现象,而且在共烧界面处并未发现有界面反应和金属离子扩散现象。该水基流延片式压敏电阻在900℃烧结时获得了良好的电性能：V1mA=6.1V,α=28.1,IL=0.15μA。更多还原

【Abstract】 Based on the development of low-voltage, low-temperature sintering and "green" manufacturing of multilayer varistors, ZnO-Bi2O3-TiO2-Co2O3-MnCO3 (ZBTCM) varistor ceramics are chosen as the research objective. In this dissertation, the nonlinear electrical properties and low-temperature sintering of ZBTCM varistor ceramic, and the multilayer varistors fabricated by aqueous tape casting were investigated.The effects of sintering temperature and heating rate on the densification, phase transformation, microstructure and electrical properties of ZBTCM varistor ceramic were investigated. When ZBTCM varistor ceramic is sintered at 1100℃with a heating rate of 60℃/h, the optimal density and electrical properties are determined as follows:densityρ=5.42g/cm3, voltage gradient E1mA=35.6V/mm, nonlinear coefficientα=33.3, leakage current density JL=0.31μA/cm2, the variation of V1mAunder 8/20μs pulseΔV1mA=15.4%. The varistor ceramic has a low E1mA and largeαvalue, but the 8/20μs surge current withstand capacity is poor. And the high sintering temperature could not meet the demand for using Ag as inner electrode for MLV.Thereafter, the effects of WO3 additive on the densification, phase transformation, microstructure and electrical properties of ZBTCM varistor ceramic are investigated. Bi2WiO3(1+i) (i=1/7,2/7) are formed when WO3 content x≤0.3mol%, which reduce the sintering temperature to 1000℃, increase the density of interface states and the barrier height, and improve the nonlinearity and 8/20μs surge current withstand capacity of ZBTCM varistor ceramic. However for x≥0.3mol%, the present of plate-like low resistivity Bi2WO6 inhibits the grain growth of ZnO and impairs the nonlinearity of ZBTCM varistor ceramic. The varistor ceramics with 0.3mol% WO3 sintered at 1000℃exhibit the best performance:E1mA=54.2V/mm,α=36, JL=0.6μA/cm2,ΔV1mA=8.9%.The influences of Cr2O3 additive on the densification, phase transformation, microstructure and electrical properties of ZBTCM varistor ceramic were studied. The sintering temperature could be reduced to 1000℃and the potential barrier height is increased, which is attributed to the solid solution of Cr2O3 into ZnO and Bi2O3 crystal lattice. When Cr2O3 content y value is equal to 0.3mol%, the E1mA and a reach the maximum of 90.8V/mm and 46. WhileΔV1mA was decreased to 10% for y≥0.3mol%. The results show that the nonlinearity and 8/20μs surge current withstand capacity of ZBTCM varistor ceramic was improved as the increasing Cr2O3 content, but the E1mA value was also obviously increased.The effects of ZnO-B2O3 frit on the densification, phase transformation, microstructure and electrical properties of ZBTCM varistor ceramic were investigated. When ZnO-B2O3 frit is added to ZBTCM system, the sintering temperature only lowers 50℃. The grain growth kinetic exponent nZ and apparent activation energy Qz are calculated as 4.54 and 316.5 kJ/mol at the temperature below 1050℃due to the non-melting ZnO-B2O3 frit pining at ZnO grain boundaries, which inhibits the grain growth of ZBTCM varistor ceramic. However, nz and Qz are 2.92 and 187 kJ/mol at the temperature higher than 1050℃due to the melting ZnO-B2O3 frit wetting the ZnO grain boundaries, which accelerates the grain growth of ZBTCM varistor ceramic. The ZnB2O4 phase, crystallized from ZnO-B2O3 frit, plays an important role in increasing the density of interface states and the barrier height. When ZnO-B2O3 frit content is equal to 0.1 wt%, the varistor ceramics sintered at 1050℃exhibit the best performance:E1mA=36.7V/mm, a=35.4, JL=0.35μA/cm2,ΔV1mA=12.1%, Whereas theΔV1mA value is a little larger than 10%.The effects of Bi2O3-B2O3 frit on the densification, phase transformation, microstructure and electrical properties of ZBTCM varistor ceramic were investigated. When Bi2O3-B2O3 frit is added, the densification temperature could be reduces to 900℃. The grain growth kinetic exponent nB and apparent activation energy QB are 2.15 and 146.2 kJ/mol, which are much lower than that of ZnO-B2O3 frit doped varistor. It indicates that Bi2O3-B2O3 frit was more effective in improving the sintering properties of ZBTCM varistor ceramic than ZnO-B2O3 frit. The Bi4B2O9 phase, crystallized from Bi2O3-B2O3 frit, plays an important role in increasing the barrier height and nonlinearity of ZBTCM varistor ceramic. When Bi2O3-B2O3 frit content is equal to 2wt%, the varistor ceramics sintered at 900℃exhibit the best performance:E1mA=124.9V/mm,α=46.2, JL=0.2μA/cm2,ΔV1mA=8.3％.The aqueous tape casting for ZBTCM varistor with 2wt% Bi2O3-B2O3 frit was researched. By optimizing the slurry composition, including binder, dispersant, plasticizer, surfactant and defoamer, the excellent green tape with a thickness of 40μm are successfully developed. The optimal recipe for the aqueous slurry is 50wt% solid loading,41.4wt% deionized water,3wt% PVA,0.5wt% PAA-NH4,2.7wt% glycerin,1.5wt% Span-20, 0.9wt%。When the green tape is sintered at 900℃, the electrical properties are determined as follows:E1mA=112.4V/mm,α=34.6, JL=0.5μA/cm2.Finally, the effects of isostatic pressures on the microstructure of green MLV, and the cofiring properties of the varistor ceramic tape with Ag were also studied. The result shows that the tapes and Ag pastes contact with each other compactly under 60Mpa. There is no chemical reaction and interfacial diffusion happed at the interface of MLV when sintered at 900℃, and the excellent electrical properties are determined as follows:V1mA=6.1V,α=28.1, IL=0.15μA.更多还原