【作者】 刘学璋；

【导师】 余志明；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 金刚石的热导率为铜的4-5倍,密度比传统的金属封装材料小,具优良的高温性能、抗辐射性能和化学稳定性。铜具良好的导电性,有良好的延展性和可塑性,易焊接。金刚石/铜基复合材料由于其高导热性在大功率电真空器件中有广泛的应用。对于金刚石/铜基复合材料来说,充分发挥金刚石导热性能的前提是使金刚石在铜基中沿导热方向形成并联式结构。化学气相沉积(CVD)能生长出连续的金刚石膜,是实现这种并联结构复合材料的理想方法。但是,铜是既不溶碳也不能形成碳化物基体,且与金刚石热膨胀系数差异很大,严重影响CVD金刚石/铜基复合材料的制备。为此,本文就改善CVD金刚石在铜基体上形核生长、增强CVD金刚石与铜结合等进行了基础研究,并首次提出了两种制备CVD金刚石并联结构/铜复合材料的方法。1根据水溶液体系中纳米金刚石颗粒与铜基体间相互作用,通过热处理调控纳米金刚石(Nanodiamond)表面的含氧官能团,使其在水溶液中与铜基体产生强静电作用。在静电作用下,纳米金刚石颗粒可均匀吸附于铜基表面。这种纳米金刚石在铜基体的静电吸附可使CVD金刚石形核密度达1011cm-2,比一般热丝CVD金刚石的形核率提高近2个数量级。2提出一种Nanodiamond/n-Pt复合层增强形核并改善金刚石/铜结合状态的方法。在静电吸附的纳米金刚石层表面蒸镀一层约40nm厚的Pt,然后在此Nanodiamond/n-Pt复合层上沉积金刚石。该方法可使金刚石膜牢固结合于铜基体,SEM显示金刚石膜与铜基体间无明显的过渡层；Raman光谱的峰偏移计算金刚石膜的应力为-7.56GPa,与热应力的理论数值接近,表明金刚石/铜间结合良好。3考察了Ti、W(可形成碳化物型)与Ni(碳溶解型)过渡层对金刚石膜生长、结合性能的影响。Ti过渡层既能与金刚石形成碳化物,又能与铜基体形成扩散,能显著提高金刚石膜的结合；与Ti过渡层相比,W过渡层上沉积的金刚石膜与铜基体结合较差；因C原子在Ti中的固溶度远大于W,同等沉积条件下,Ti过渡层上生长的金刚石膜中非金刚石相比W过渡层上的多。Ni过渡层上可沉积出晶体颗粒接近热力学形态的高质量金刚石膜,其中非金刚石相的含量小于5.56%,但结合不佳。4研究了铜模板通道内CVD金刚石的生长行为。当沉积气压为2.OkPa时,可生长出连续的金刚石膜。而金刚石晶粒尺寸随模板通道长径比的增加而大体呈线性降低,当通道的长径比为2.0时,金刚石膜表面光滑,晶粒完全细化,变成典型的球形纳米晶金刚石膜；通过气源强制输送可明显改善模板通道内金刚石的质量,约在600μm通道深度处的CVD金刚石的结晶完整性仍较好。气源强制输送主要改善了金刚石沉积过程中的[CH3]加成速率,进而提高了通道内金刚石生长的均匀性；模板法原位生长可获得金刚石/铜微通道复合材料,采用纳米金刚石增强形核与过渡层增强结合,铜微通道基片表面可生长出连续、光滑的金刚石膜,CVD金刚石膜与基片结合牢固。微通道的直径为0.236mm,通道间的距离为2mm。5采用钨丝((?)1mm)为芯材沉积出高质量金刚石/W预制棒,溅射钛过渡层后,将金刚石/W预制棒纵向排成阵列,铜粉填充于预制棒之间,经真空热压烧结制备成致密的金刚石并联结构/铜基复合材料。通过热模拟讨论了该复合材料的导热性能,热源远端表面的热流量分布显示,金刚石膜层的热流量显然高于其它部分。随着金刚石/W预制棒数量的增加,复合材料热源远端表面上的温度开始均匀,单个金刚石/W预制棒的影响范围开始耦接在一起,复合材料上表面的热流量分布趋于均匀。图89幅,表更多还原

【Abstract】 The thermal conductivity of diamond is4or5times of Cu and its density is lower than traditional metal packing materials. At the same time, diamond has exceptional high temperature performance, radiation resistant property and chemical stability. Copper has excellent electrical conductivity, malleable and plastic properties which make it easy to weld. Diamond/Cu composite material is widely used in the field of high power Electron Device due to its high thermal conductivity.For Diamond/Cu composite material, to make the most of diamond’s thermal conductivity performance is based on forming its paralleling structure along the heating conduction direction in copper substrate. The chemical vapor deposition (CVD) technique is an ideal solution to fabricate such composite material since continuous diamond film can be deposited during this process. However, it is a difficult endeavor to deposit diamond film on Cu substrate using chemical vapor deposition (CVD) technique, namely:①Copper has a cubic crystal structure. It is immiscible with carbon, and does not form any carbide, which results in low nucleation density and poor quality of diamond film;②the high thermal stress originated from the large mismatch of thermal expansion coefficients damages the bonding property between diamond film and Cu substrate. In order to improve the nucleation and growth of diamond on Cu substrate and enhance its cohesion between CVD diamond and copper, we have done some fundamental researches and come up with two ways to fabricating CVD diamond with paralleling structure/Cu composite material for the first time.1Based on the interaction between nanoparticles and substrate surfaces in solvent system, modified nanodiamond was homogeneously charged on the Cu substrate by electrostatic self-assembly, which acted as pre-existing sp3seeds. The nucleation density is greater than1011cm-2, which is2times higher than other reports.2A novel method of enhancing diamond nucleation and binding property through forming a Nanodiamond/n-Pt composite layer was proposed. After coating a platinum layer of40nm thickness to the copper substrate seeded with nanodiamond particles, adherent diamond film was then deposited on Cu substrate. As can be seen from the SEM images, there is no distinctly metallic interlayer between diamond film and Cu substrate. The residual stress in diamond film calculated from the shift of Raman spectrum is-7.56GPa, which is comparable with the thermal stress.3The influence of those interlayers like Ti, W and Ni on diamond growth and binding property has been discussed in details. Ti can not only form a relatively strong carbide bond with diamond film but also has reasonable diffusion ability in Cu substrates, so it can distinguishably improve the binding property of diamond/Cu. Compared with Ti, W shows poor binding property. However, the dissolution of carbon in Ti is higher than W, so the sp2carbon content of diamond film deposited on Ti interlayer is distinctly higher than diamond film on W interlayer under the same CVD conditions. High-quality diamond film with its crystalline grains close to the thermal equilibrium shape was deposited on Ni interlayer. The sp2carbon content is less than5.56%, but poor in cohesion performance.4The growth behaviors of diamond film in the holes (or channels) of a Cu template were investigated. Under the pressure of2.0kPa, continuous diamond film was obtained. Increasing the aspect ratio of the holes, the diamond grain size linearly decreases. When the aspect ratio is2.0, the deposited diamond film was smooth and quasi-spherical nanocrystalline. Forced transportation of gas source can improve the quality of diamond deposited in the hole. Even at the depth of about600μm, diamond grains still show perfect crystallinity. Forced transportation of gas source is able to enhance the addition rate of [CH3] during the diamond deposition, and then the quality of diamond in the holes pores can be improved. CVD diamond/Cu micro-channel composite material was directly deposited by Cu template. By nanoseeding and forming an interlayer, continuous and smooth diamond film was obtained, which has a excellent cohesion performace with the Cu substrate. The diameter of micro-channels is0.236mm, and the distance between channels is2mm.5High quality columnar diamond bar was deposited by using W wire as core substrate. After sputtering a Ti interlayer, diamond bars were longitudinally arranged in order with copper powder filling in the prepared paralleling structure diamond/Cu composite by vacuum hot-press sintering method. The thermal conductivity performance of CVD diamond/Cu composite material for directional thermal conductivity was discussed by thermal simulation. Heat flow distribution of the far end surface of composite material shows that heat transfer rate of diamond film layer is obviously higher than other parts. With the increase of the diamond rod, the surface temperature distribution becomes uniform, and the influence range of a single diamond rod begins to couple with each other, while the heat flow distribution of composite material on the far end surface also tends to be uniform.更多还原