The growing demand for heat dissipation in materials
With the continuous advancement of technology, an increasing number of high-power electrical appliances and high-power microelectronic components have emerged. Along with the growing demand for thinner, lighter electronics and higher performance efficiency, the power density of semiconductor components is constantly increasing, leading to greater heat flux. Ordinary heat dissipation materials can no longer effectively solve thermal issues, making heat dissipation a primary challenge.
So, in the field of thermal conduction and dissipation, how should materials be selected?
Currently, popular heat dissipation solutions include graphite sheets, graphene, thermal interface materials, heat pipes, vapor chambers, and semi-solid die-cast components. However, natural graphite thermal films are relatively thick and have low thermal conductivity, making it difficult to meet the heat dissipation requirements of future high-power, high-integration-density devices. They also fail to satisfy demands for ultra-thinness, light weight, and long battery life. Therefore, finding new ultra-thermal-conductive materials is of great significance. Such materials must have extremely low thermal expansion coefficients, ultra-high thermal conductivity, and a lightweight, thin profile. Carbon materials such as diamond and graphene meet these requirements—they possess very high thermal conductivity, and their composites are highly promising as thermal conduction and dissipation materials, currently attracting significant research attention.
The growing demand for heat dissipation in materials
With the continuous advancement of technology, an increasing number of high-power electrical appliances and high-power microelectronic components have emerged. Along with the growing demand for thinner, lighter electronics and higher performance efficiency, the power density of semiconductor components is constantly increasing, leading to greater heat flux. Ordinary heat dissipation materials can no longer effectively solve thermal issues, making heat dissipation a primary challenge.
So, in the field of thermal conduction and dissipation, how should materials be selected?
Currently, popular heat dissipation solutions include graphite sheets, graphene, thermal interface materials, heat pipes, vapor chambers, and semi-solid die-cast components. However, natural graphite thermal films are relatively thick and have low thermal conductivity, making it difficult to meet the heat dissipation requirements of future high-power, high-integration-density devices. They also fail to satisfy demands for ultra-thinness, light weight, and long battery life. Therefore, finding new ultra-thermal-conductive materials is of great significance. Such materials must have extremely low thermal expansion coefficients, ultra-high thermal conductivity, and a lightweight, thin profile. Carbon materials such as diamond and graphene meet these requirements—they possess very high thermal conductivity, and their composites are highly promising as thermal conduction and dissipation materials, currently attracting significant research attention.
金刚石的导热率（W/mk）
金刚石类型 | 在172K下 | 在80K下 |
Ia | 600~1000 | 2000~4000 |
IIa | 2000~2200 | 15000 |
The thermal conductivity of diamond is not fixed; it has a certain range of variation. The main types used as diamond heat spreaders are type IIa single-crystal diamond and polycrystalline diamond that meets thermal conductivity requirements. Their coefficient of thermal expansion is approximately 0.8×10⁻⁶/K, and they are electrically insulating at room temperature.
Principle of Diamond Thermal Conduction
Diamond has a cubic crystal structure, in which each carbon atom forms covalent bonds with four other carbon atoms through sp³ hybrid orbitals, creating a regular tetrahedron. Since all valence electrons are confined to the covalent bond regions and there are no free electrons, diamond does not conduct electricity. High thermal conductivity is typically associated with high electrical conductivity, but unlike metals, which rely on free electrons for heat transfer, diamond’s thermal conductivity arises primarily from the propagation of carbon atom vibrations, i.e., phonons.
The mean free path of phonons is determined by collisions between phonons and by the scattering of phonons from defects within the solid. Crystal defects such as impurity elements, dislocations, and cracks, as well as residual metal catalysts and lattice orientation, can all collide with phonons and cause scattering, thereby limiting the phonon mean free path and reducing thermal conductivity.
When a material has a purer composition, a simpler structure, and fewer impurities, phonons can move more rapidly, leading to faster heat transfer. This is because the introduction of secondary components and impurities can induce lattice distortion, strain, and dislocations, compromising crystal integrity and increasing the scattering probability of phonons or electrons. Diamond is composed solely of the single element carbon and has a very simple structure. Among the four types of diamond—Ia, Ib, IIa, and IIb—type IIa is the purest and contains the fewest impurities, thus exhibiting the highest heat transfer rate.
In addition, diamond possesses high electrical resistivity, high breakdown field strength, low dielectric constant, and low thermal expansion. These characteristics give it a clear advantage in addressing heat dissipation issues in high-power optoelectronic devices, indicating that diamond has enormous potential for applications in thermal management.
