【作者】 刘欢；

【导师】 龚树萍； 周东祥；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2008， 博士

【摘要】 半导体陶瓷是一类具有半导体特性的无机非金属多晶材料,其敏感元件在微电子、光电、激光等高技术领域获得了广泛的应用。随着微电子技术的飞速发展,半导体陶瓷的微纳化已成为近年来最为活跃的研究热点之一。本文尝试从半导体陶瓷粉体的纳米化技术出发,系统地研究微纳半导体陶瓷及其敏感元件的关键制备技术,探讨微纳尺度多晶半导体陶瓷的导电机理,以期为相关新型敏感元件的研制提供理论与实践基础。论文首先研究了纳米半导体陶瓷粉体的可控生长技术。在分析和探讨溶胶—凝胶法、聚合物网络法及水热法等液相合成方法的工艺原理及特点的基础上,通过大量实验研究和工艺参数优化,成功制备出颗粒均匀、团聚程度低、热稳定性好的纳米氧化锡(可低至4.1 nm)及纳米钛酸钡(小于40 nm)粉体,可较好满足半导体陶瓷微纳化发展的要求。采用所获得的纳米氧化锡粉体,通过浆料配制、电极制作、丝网印刷、干燥及烧成等制备工艺研究,发展出对硫化氢气体具有良好气敏特性的纳米氧化锡半导体陶瓷厚膜元件。结果表明,纳米氧化锡半导体陶瓷气敏元件不仅具有较高的灵敏度和较低的工作温度(约150℃),而且有着良好的选择性和响应—恢复特性,灵敏度与气体浓度的关系遵循幂定律。采用聚合物网络法合成的纳米粉体制作的厚膜元件在保持较小的晶粒尺寸的同时,具有更为疏松、多孔和均匀的微观结构,表现出最优的气敏性能。基于钛酸钡材料的特点及其半导化原理,探讨了制备微晶热敏半导体陶瓷的技术途径。以溶胶—凝胶法合成的纳米钛酸钡粉体为原料,选用钇和锰分别作为施、受主杂质元素并适当提高二者的掺杂量,采用水基流延绿色成型工艺,通过适当提高预烧温度、降低烧结温度的烧成方式实现施、受主的二次掺杂,抑制晶粒生长,成功获得具有较为理想微晶结构的钛酸钡半导体陶瓷片式热敏元件。1280℃烧结所得典型样品的晶粒尺寸约3.0μm,室温电阻率为360Ω·cm,升阻比达10~4。论文还从理论上研究了晶粒尺寸对钛酸钡半导体陶瓷导电特性的影响。分析了钛酸钡半导体陶瓷的微观结构及导电模型,采用十四面体晶粒模型计算出其电阻与晶粒尺寸存在反比关系,进而讨论了微晶钛酸钡半导体陶瓷的晶界特性。研究认为,微晶钛酸钡半导体陶瓷晶界钡缺位向晶粒体内的扩散形成的势垒层很薄,因而存在壁垒效应使得材料晶粒电阻率上升;同时,量子隧穿效应引起的隧穿电流易导致元件升阻比及耐电压性能的降低。更多还原

【Abstract】 Semiconductive ceramics are generally inorganic non-metal polycrystalline materials with semindonductive properties.Their sensitive components have found applications in many high-tech fields such as microelectronic,photoelectronic and laser technology. Recently,the rapid development of microelectronic technology has registered increasing research interests in micro/nano semincounductive ceramics.This disseration was to develop micro/nano seminconductive ceramics and their sensitive components by using nanophase semiconductive ceramic powders,where the key fabrication technics were systematically investigated.The conduction mechanism of micro/nano semiconductinve ceramics was also discussed in order to provide both experimental and theoretical basis for the development of novel sensitive components.Firstly,attempts were made to synthesizing seminconductive ceramic nanopowders controllablly.The basic principle and characteristics of wet-chemcial methods such as sol-gel method,polymer network method and hydrothermal synthesis were briefly reviewed.A lot of experiments were conducted to optimize the synthesis process,resulting in uniform tin oxide nanopowders(even low as 4.1 nm) and barium titanate nanopowders (below 40 nm) with slight agglormerization and good thermal stablility,which were much desirable for micro/nano semincoundutive ceramics.After a careful study of the fabrication techniques such as slurry preparing, screen-printing,drying and sintering processes,we prepared nanocrystalline tin oxide thick-film sensors based on the as-synthesized nanopowders,the sensing performances of which toward hydrogen sulfide gas were much better considering the sensitivity,selectivity, response properties and operation temperature(around 150℃).A power law between the sensitivity and the partial pressure of hydrogen sulfide has been obtained.At same time, most favorable sensing behaviors were observed for the sensor samples based on tin oxide nanopowders synthesized by polymer network mehod,which might be attributed to the loose and porous microstructure with good uniformity.Meanwhile,the technical approaches to the realization of fine-grained mircostrucure were explored by studying the semincounctive characteristics and conduction mechanism of barium titanate ceramics.After optimizing the material composition and fabrication conditions in the water-based tape casting and sintering process,chip thermistors with fine-grained microstructre were developed based on barium titanate nanopowders synthesized by the sol-gel method,where adequate concentrations of yttrium element was introduced in the presintering process as the donor,while manganese element was introcueced in the sintering process as the acceptor,separately.Results indicated that twice doping was more appropriate for the inhibition of grain growth and the enhancement of electrical properties.Also,increasing the presintering temperature properly was helpful to to the reliazation of fine-grained microstucture when sintered at relatively tow temperature. The typical samples sinterd at 1280℃have smaller grain size of about 3.0μm,with room-temperature resistivity of about 360Ω·cm and the resistance jump of above 10~4.Finally,theoretical analysis was presented concerning the influence of grain size on the conduction properties of fine-grained barium titanate seminconductive ceramics.After the discussion of the microstructue and conduction model of polycrystalline barium titanate ceramics,an inverse relation between the resistance and the grain size of barium titante ceramics was calculated by using a tetrakaidecahedron model.Then.the properties of grain boundaries were discussed as far as the fine-grained barium titanate ceramics were concerned.With the decrease of the grain size,the barrier layer induced by the diffusion of Ba-vacancies from the boundary into the bulk of the grain becomes so narrow.As a result, the barrier effect may lead to the increase of the resitivity of the grains.Besides,the tunneling current caused by the quantum tunneling effect may lead to the decrease of the reistance jump and withstand voltage.更多还原