Diamond wafers: efficient solutions for thermal conductivity and heat dissipation

With the continuous development of technology, more and more high-power electrical appliances and high-power microelectronic components are gradually emerging, and people's demand for electronic products to be lightweight and high-performance is increasing. The power density of semiconductor components continues to increase, and the heat flux will also increase. Common heat dissipation materials can no longer solve the heat dissipation problem well. How to cool down the materials has become the primary challenge.

So in the field of heat conduction and dissipation, how to choose materials?At present, popular heat dissipation solutions mainly include graphite sheets, graphene, thermal conductive interface materials, heat pipes and soaking plates, and semi-solid die-casing parts. However, natural graphite heat dissipation film products are relatively thick and have low thermal conductivity, making it difficult to meet the heat dissipation needs of future high-power and high integrated density devices. At the same time, they also do not meet people's high-performance requirements for ultra-thin and long endurance. Therefore, the search for new materials with super thermal conductivity is of great significance. This requires such materials to have extremely low thermal expansion rate, ultra-high thermal conductivity, and lightweight volume. Diamond, graphene and other carbon materials just meet the requirements, they have a high thermal conductivity, and their composite materials are a class of thermal and heat dissipation materials with great application potential, which have become the focus of attention.

Faced with various limitations of traditional packaging materials, various new heat dissipation materials have been developed, which have low thermal expansion rate and very light weight. Diamond, as a representative of the above materials, is the substance with the highest thermal conductivity in nature. It is often said that the thermal conductivity of diamond is five times that of copper. There are actually various types of diamonds, such as Ia, Ib, IIa, IIb, etc. For type I and II diamonds, they are distinguished by the different UV and infrared absorption spectra of diamonds, while type A and type B are distinguished by the different electron paramagnetic resonance absorption. The thermal conductivity of different types of diamond is also different, and the thermal conductivity of the same type of diamond may not be the same. The thermal conductivity of diamond is related to the integrity of its internal structure and the type and content of impurities it contains. The thermal conductivity of the same type of diamond also varies at different temperatures, as shown in the table below:

Diamond type             172K               80K

        Ia                      600-1000     2000-4000

        IIa                    2000-2200       15000

The thermal conductivity of diamond is not fixed and has a range of variation. As diamond heat sinks, the main types are IIa single crystal diamond and polycrystalline diamond with required thermal conductivity, with a thermal expansion coefficient of about 0.8 × 10-6/K and insulation at room temperature. Diamond is a cubic crystal structure, where each carbon atom forms a covalent bond with four other carbon atoms in an SP3 hybrid orbital, forming a tetrahedron. Because all valence electrons are confined to the covalent bond region and there are no free electrons, diamond is non-conductive. High thermal conductivity is associated with high conductivity. Unlike metals that rely on peripheral electrons for heat transfer, the thermal conductivity of diamond is mainly due to the propagation of carbon atom vibrations (i.e. phonons).

The average free path of phonons is determined by the collision between phonons and the scattering of phonons by defects in the solid. Impurity elements, dislocations, cracks and other crystal defects in diamond, as well as residual metal catalysts and lattice orientations, can collide with phonons and cause scattering, thereby limiting the average free path of phonons and reducing thermal conductivity.

When the composition of a substance is simpler, the structure is simpler, and there are fewer impurities, the phonon motion is faster, and the heat transfer rate is also faster. This is because the introduction of the second component and impurities can cause lattice distortion, distortion, and dislocations, disrupt the integrity of the crystal, and increase the scattering probability of phonons or electrons. Diamond is composed of only a single element of carbon and has a very simple structure. Among the four types of diamonds, Ia, Ib, IIa, and IIb, IIa is the purest and has the least impurities, thus having the highest heat transfer rate.

In addition, diamond also has the characteristics of high electrical resistivity, high breakdown field strength, low dielectric constant, and low thermal expansion. It has obvious advantages in the heat dissipation of high-power optoelectronic devices, which also indicates that diamond has huge application potential in the field of heat dissipation.

CSMH focuses on the production and research and development of diamond materials, mastering mature diamond cooling solutions and successful cases for high-power devices. Its core products include diamond heat sinks, diamond windows, diamond wafers, diamond heterojunction integrated composite substrates, AlN thin films, etc. Currently, it has applications in high-power LEDs, lasers, 5G communication, aerospace, new energy vehicles, GPUs, and other fields.