Diamond

• Manufacturing process of diamond materials

1. Natural diamond mining

Natural diamond is obtained through mining, which is costly and unsuitable for large-scale semiconductor applications. The purity of diamond material is usually required to be above 6N (99.9999%),

2. Synthetic diamond

High Temperature and High Pressure (HPHT) Method: This method simulates the formation conditions of natural diamonds. Under high temperatures (1500-2000°C) and high pressures (5-10 GPA), metal catalysts (such as nickel and iron) are used to induce phase changes in carbon sources like graphite, converting graphite into diamond crystals. This process yields high-quality single-crystal diamonds, which are relatively small in size and difficult to dope.

Chemical Vapor Deposition (CVD): Microwave Plasma Chemical Vapor Deposition (MPCVD) uses carbon-containing gases (methane) to decompose at high temperatures (around 1000℃) and low pressures (<1 ATM). Carbon atoms deposit on the substrate to form diamond films. CVD can produce large-area, high-quality diamond films and can achieve N-type or P-type semiconductor properties through doping. Due to the absence of electrode contamination and high plasma density, MPCVD has become the mainstream method for preparing high-quality single-crystal diamonds, suitable for semiconductor applications

3. Epitaxial growth: epitaxial growth on a diamond substrate to form high quality single crystal diamond film. This method can further improve the crystal quality and electrical properties of diamond materials.
4. Backing and doping technology

Substrate selection: Silicon, silicon carbide (SIC) or diamond itself as the substrate, surface treatment (such as ultrasonic treatment) is required to enhance the nucleation density.

Type P doping: Boron (B) atoms replace carbon atoms to form the host energy level, and the hole mobility can reach 450 CM²/ (V·S).

N-type doping: phosphorus (P) or nitrogen (N) atoms are introduced and activated by high temperature annealing. The electron mobility is about 1800 CM²/ (V·S).

The diamond single crystal is cut into wafers (the thickness is usually 100-300ΜM) and polished, cleaned and surface treated.

5. Device manufacturing

Wafers are prepared by laser cutting, ion beam etching or mechanical polishing, with a thickness of 0.3-1 MM. Surface hydrogenation (H-TERMINATION) reduces the surface state density and improves device performance. High-power electronic devices or quantum devices are manufactured by lithography, etching and other processes.

• Material properties of diamond materials

1. Electrical properties

With an ultra-wide band gap (5.47 EV), diamond is the material with the widest band gap among the current elemental semiconductor materials, which enables diamond devices to support high temperature, high voltage and high frequency, and high power electronic devices.

Diamond has high electron mobility and hole mobility of 2800CM²/ (V·S) and 1800CM²/ (V·S), respectively, which is conducive to the realization of high frequency and high speed electronic devices

High breakdown field strength: Diamond has a very high breakdown field strength, can withstand high voltage without breakdown, suitable for the manufacture of high power devices

2. Thermal performance

Diamond is one of the materials with the highest thermal conductivity in nature. At room temperature, the thermal conductivity can reach 2000W/ (M·K), which is three times that of silicon, five times that of copper and seven times that of GAN. It can effectively solve the heat dissipation problem of electronic devices and is suitable for high power heat dissipation.

High temperature stability (>500°C), low thermal expansion coefficient as low as 1.1×10⁻⁶/℃, high temperature resistance (>500℃) and radiation resistance, can work in extreme environment.

3. Optical properties

Diamond has wide spectral transparency, full band transmission from ultraviolet to infrared (0.2-25 ΜM), high refractive index (2.42), especially in the deep ultraviolet (DUV) field, can be used to manufacture high performance optical window and lens materials, suitable for optical devices.

4. Mechanical properties

Mechanical properties: Diamond has extremely high hardness (Mohs hardness 10) and good mechanical stability, which can ensure the durability of electronic devices in harsh environment.

5. Chemical stability

Chemical stability: acid and alkali resistant, suitable for sensors in harsh environments.

• Technical index advantages of diamond materials

1. High power electronic devices

The ultra-wide band gap and high thermal conductivity of diamond materials support the high performance of high power electronic devices.

2. High frequency devices

The high carrier mobility of diamond material supports the high performance of high frequency devices.

3. Quantum computing

Nitrogen vacancy (NV) centers in diamond materials perform better than other materials in quantum computing.

4. Optical devices

Diamond material with wide light transmittance range and high refractive index is suitable for optical device applications.

• Industry applications

1. High frequency communication and 5G/6G

RF power amplifier: used in 5G base stations and millimeter wave radar, supporting higher frequency bands (24-100 GHZ) and low signal loss.

Optical communication module: diamond photoelectric detector improves the optical fiber communication rate to 800G level.

Field-effect transistor (FET): Cut-off frequency (Fₜ) exceeds 100 GHZ, suitable for 5G millimeter-wave base stations and satellite communications.

Terahertz (THZ) devices: THZ emitters and detectors are developed using high carrier velocity (saturation velocity 2.7 x 10⁷ CM/S)

2. New energy vehicles and power electronics

Power devices: Diamond-based MOSFET and IGBT can reduce the loss of electric vehicle inverter, shorten the charging time, and improve the battery life.

Heat dissipation system: integrated diamond microchannel heat dissipation module, so that the junction temperature of GAN device is reduced from 676℃ to 182℃.

3. Extreme environment and cutting-edge technology

Aerospace: High temperature and high pressure characteristics are suitable for rocket engine sensors and satellite electronic systems.

Quantum computing: Diamond is used as a solid state carrier, and the nitrogen vacancy center (NV color center) in diamond can realize the efficient storage and processing of optical quantum states.

4. Consumer electronics

Mobile phone / GPU cooling: The diamond cooling GPU tested by Nvidia can increase AI performance by three times; Huawei Diamond chip cooling patent layout

5. High power electronic devices

Thyristor and IGBT: power conversion for electric vehicles and smart grid, achieving low on-resistance (<1 MΩ·CM²) and high switching frequency (> 100 KHZ).

Schottky diode: reverse breakdown voltage up to 5000 V, forward current density>100 A/CM²

6. Optical devices

Deep ultraviolet detector: response wavelength <260 NM, used for flame monitoring and biomedical imaging.

Diamond laser: room temperature single photon emission is achieved through nitrogen vacancy (NV) color center to promote quantum communication.

8. Package substrate

Diamond’s high thermal conductivity makes it a high-performance packaging substrate material, which can effectively reduce the temperature of electronic devices

• Future development trends

1. Efficiency improvement

The hybrid device is developed by combining GAN and SIC to take into account both high frequency and high power performance

2. High frequency device development

Diamond-based high frequency electronic devices are studied for 5G communications and radar systems.

3. Quantum technology development

Diamond materials are being promoted in the field of quantum computing and quantum sensors.

4. Environmental protection and recycling

Develop environmentally friendly diamond manufacturing process and promote the recycling of diamond materials.

Diamond, with its excellent electrical, thermal, and optical properties, has become a core material for next-generation semiconductor technology. Despite challenges such as high preparation costs and difficulties in doping, its irreplaceability in high-power power electronics, quantum computing, and extreme environments continues to drive technological advancements. In the future, large-scale production of high-quality CVD diamonds and hetero-integration technologies (such as diamond/SIC composite structures) will accelerate their industrialization process.