Today, among the existing semiconductor materials, diamond is one of the most promising semiconductor materials. Usually, it is used as diamond thermal management material. The article will mainly discuss the diamond from 3 parts: what is diamond, diamond material properties and its applications.
1. What Is Diamond?
Diamond has been discovered by mankind for more than two thousand years. It is known as the “King of Gems”, but its value is far more than that. Diamond is composed of carbon atoms and belongs to the cubic crystal system. The crystal structure is:
there are four carbon atoms in a face-centered cubic unit cell, which are located at one quarter of the diagonal of the four spaces. Through the sp3 hybridization, each carbon atom forms a covalent bond with the other four carbon atoms, forming a tetrahedron.
2. Diamond Material Properties
What are the properties of diamond? Because of the special crystal structure and strong carbon-carbon bond effect, diamond has many outstanding characteristics and superior physical, chemical, electronic, optical, thermal and mechanical properties than other existing semiconductor materials. It has a wide band gap, high thermal conductivity, high breakdown field strength, high carrier mobility, high temperature resistance, acid and alkali resistance, corrosion resistance and radiation resistance. All these advantages make it play an important role in the field of in high power, high frequency, high temperature, etc. Traditional semiconductor materials, such as silicon and gallium arsenide, will encounter bottlenecks in these fields due to their own characteristics.
However, diamond transfers heat through lattice vibration, and the quantum energy of vibration produced by carbon atoms is greater, resulting in a high vibration frequency, so the thermal conductivity is very high. The thermal conductivity of natural single crystal diamond at room temperature (25℃) can reach 22 W/(cm·K). By contrast, the thermal conductivity of metal copper is about 4 W/(cm·K), while the traditional semiconductor material silicon has a thermal conductivity less than 2 W/(cm·K). The thermal conductivity of diamond grown artificially by CVD method usually can reach 15 W/(cm·K) at room temperature.(*The data is from PAM-XIAMEN)
3. Applications of Diamond Material Property – High Thermal Conductivity
Due to its low coefficient of thermal expansion and high insulation, material properties of diamond can be used as excellent heat sinks for power electronic devices and solid microwave power devices, improving the working temperature and working power of the device. CVD polycrystalline diamond has a lower cost than single crystal diamond and has high thermal conductivity and lower surface roughness. It is convenient to be introduced into the structure of semiconductor power devices. Due to CVD diamond material properties, which has a broader application field, the heat dissipation capacity of the device is significantly improved.
Taking gallium nitride (GaN) power devices as an example: high frequency and high power gallium nitride (GaN) devices fabricated with diamond heat sink can reduce the devices’ self-heating effect. It is expected to solve the problem of rapid decline in power density along with increases in the total power and frequency.
In the field of heat sink applications, with a thermal conductivity of more than 22 W/(cm·K). The CVD diamond heat dissipation material with a thermal conductivity over 22W/(cm*K) is particularly suitable for thermal management of high power density radio frequency (RF) and application specific integrated circuit (ASIC) devices.
The CVD diamond heat sink needs to use a time domain thermal reflectance measurement system (TDTR) to measure thermal conductivity. The research results of diamond material properties by PAM-XIAMEN show that the quality of diamond has a greater impact on the thermal conductivity. The fewer internal impurities and defects, the closer the thermal conductivity to that of natural diamond.