【作者】 王鹏飞；

【导师】 李志宏；

【作者基本信息】 天津大学 ， 材料学， 2010， 博士

【摘要】 立方氮化硼(cBN)具有禁带宽度大、热导率高、介电常数小等优良的功能特性,cBN基多晶材料作为陶瓷基板、热沉材料、微波窗口材料等的潜在应用亟待研究与开发。本文在高温高压条件下烧结制备cBN基多晶材料,研究了其微观结构形貌和电、热、光学等功能属性,分析了晶粒、晶界相等对多晶材料的烧结及功能特性的影响,并初步探讨了与cBN基多晶材料形成欧姆接触的银电极制备方法及其表面金属化用低熔玻璃料的一些性质。本论文的主要研究结果如下:1.高温高压条件下由cBN微粉快速烧结可制备具有近紫外发光特性的cBN基多晶材料。Si含量增多,Si-cBN多晶材料的发光强度增大。热处理对纯cBN多晶烧结材料的发光性质影响不大,但显著提高了Si-cBN多晶材料的近紫外发光强度。cBN多晶材料的短波长光发射和光谱振动结构均与cBN晶体的声子作用直接相关。Si在高温高压烧结过程中直接实现了对cBN多晶材料的n型浅掺杂。2. Mg对提高cBN多晶材料的相对密度效果明显,Mg-cBN多晶材料具有低电阻率(处于半导体电阻率范围)和近紫外发光特性。热处理对Mg-cBN多晶材料的表面形貌影响较大,对调整试样内部cBN晶粒形态作用较小;热处理生成的MgO晶体的声子与试样中hBN的声子作用产生声子伴线结构。3. Al与cBN反应生成晶界相AlN和AlB12,能够显著促进Al-cBN多晶材料的烧结,对热导率和光吸收性能影响显著。Al添加量增大,Al-cBN多晶材料的致密度增大,热导率增大,其吸收特性逐渐体现为AlN的吸收特性;晶界相的存在使Al-cBN多晶材料的热导率数值整体较小,使其禁带宽度变窄。4. Al-cBN多晶材料在高电压、高频下具有优良的电学和介电性能。Al-cBN多晶材料具有较高的体积电阻率和良好的高压电阻稳定性,具有与生长-烧结型cBN多晶接近的介电性质及较高的高频介电稳定性。研究得出了Al-cBN多晶材料的I-V之间具有低电压下的二次非线性和高电压下的e指数递增变化规律,Al-cBN多晶材料的介电常数及其与介电损耗之积和气孔率之间都存在e指数递减关系。5.使用导电银胶在cBN多晶烧结试样表面获得较好的欧姆接触;随着cBN基多晶材料中Si含量的增多,其电极接触的欧姆特性逐渐减弱。更多还原

【Abstract】 Cubic boron nitride (cBN) has fascinating functional properties, such as wide band gap, high thermal conductivity, and relatively small dielectric constant, etc. The potential applications of cBN based polycrystalline materials as ceramic substrate, heat sink and microwave window materials need to be developed urgently. In this thesis, cBN polycrystalline materials were sintered under high temperature and high pressure conditions. The influences of grain, grain boundary phase, and defects on the sintering and functional properties of cBN based polycrystalline materials were studied through microstructure observation and investigations on the materials’electrical, thermal, and optical properties. Meanwhile, the preparation of silver electrode with ohmic contact and some properties of low melting glass frits for surface metallization of cBN based polycrystalline materials were generally researched. The main results of this thesis are as follows:1. cBN based polycrystalline materials could be rapidly sintered from cBN micro-powders under high temperature and high pressure conditions, and they showed near-ultraviolet(UV) light-emitting properties. The photoluminescence intensities of Si-cBN polycrystalline materials increased with the increase of Si additions. Heat treatment showed little effect on the luminescence properties of pure polycrystalline cBN sintered materials, but significantly improved the near-UV photoluminescence intensity of Si-cBN polycrystalline materials. The short-wavelength light emission and spectral vibration structure of cBN polycrystalline materials were directly related to the phonon interaction of cBN crystals. Moreover, n-type shallow doping of cBN polycrystalline materials was realized by Si during the high temperature and high pressure sintering process.2. Mg was an effective additive for improving the relative densities of cBN polycrystalline materials. As-prepared Mg-cBN polycrystalline materials had low electrical resistivity (within the semiconducting range) and near-UV light-emitting property. Heat treatment displayed a greater impact on the surface morphology of Mg-cBN polycrystalline materials than the adjustment of cBN grain morphology within the specimens. The interaction between phonons of annealing-related MgO crystals and phonons of hBN led to phonon replica structure. 3. Al reacted with cBN to form grain boundary phase, AlN and AlB12, which significantly promoted the sintering of Al-cBN polycrystalline materials and showed notable influence on their thermal conductivities and optical absorption properties. When the amount of Al was increased, Al-cBN polycrystalline materials maintained increasing density and thermal conductivity, and their optical absorption characteristics were dominated by those of AlN. Existence of grain boundary phase in general resulted in the lower thermal conductivities and the narrower bandgap for Al-cBN polycrystalline materials.4. Al-cBN polycrystalline materials had high volume resistivities and good resistance stability at high voltage, high stability of dielectric properties at high frequency and the similar dielectric properties as growth-sintered type cBN polycrystals. The investigations on the electrical and dielectric properties of Al-cBN polycrystalline materials revealed the I-V relation exhibited a quadratic nonlinear growth at low voltage and an e exponential growth at high voltage, and indicated an e exponential decline of dielectric constant, the product of dielectric constant and dissipation vs porosity were existed.5. Ohmic contact with cBN polycrystalline materisls were formed using silver paste. With the increase of Si addition in cBN based polycrystalline materisls, the Ohmic contact character of the electrodes gradually weakened.更多还原