| 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. |
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