Introduction to Diamond Wafers: Monocrystalline vs Polycrystalline

Currently, diamond wafers are widely used in high-tech industries due to their notable hardness and unique properties for electronic, optical, and even cutting and polishing purposes. In particular, diamond wafers are valued for their extraordinary resistance to extreme conditions such as high temperatures and intense mechanical stress. The most popular types of diamond wafers are monocrystalline and polycrystalline; both types have distinct features and advantages in certain applications.

What Are Diamond Wafers?

A diamond wafer is a thin, flat piece of synthetic diamond material, generally prepared by methods such as CVD or HPHT. These wafers are cut to a specific size and are primarily used as substrates in various industrial and scientific applications. The hardness and thermal conductivity of diamond make it a material suitable for areas where conventional materials might fail.

Fig. 1 CVD Diamond Wafer

Monocrystalline Diamond Wafers

The monocrystalline diamond wafer is made from a single, continuous diamond crystal. In other words, the entire wafer is produced from one uniform structure where all atoms align in the same manner. This uniformity confers monocrystalline diamonds with unique properties, including:

• High Thermal Conductivity: Their high thermal management capabilities make monocrystalline diamonds suitable for applications in high-power electronics or heat dissipation.

• High Mechanical Strength: Monocrystalline diamonds exhibit exceptionally high strength due to their crystal structure, making them effective in applications such as cutting, grinding, and drilling.

• Optical Clarity: These wafers can be utilised in precision optics, owing to their ability to transmit light with minimal distortion. This provides significant benefits in laser technology and specialised imaging equipment.

The growth of monocrystalline diamonds is considerably more time-consuming and expensive than other forms, but the final product finds strong demand in critical performance applications such as high-end semiconductor manufacturing, quantum computing, and aerospace.

Applications of Monocrystalline Diamond Wafers:

• High-Performance Electronics: Utilised in power devices and heat sinks.
• Semiconductor Industry: As substrates for advanced semiconductor devices.
• Optics and Lasers: These include laser windows and high-precision lenses.
• Industrial Cutting and Drilling: Involving tools that require extreme levels of wear resistance.

Polycrystalline Diamond Wafers

Conversely, polycrystalline diamond wafers are fabricated by collecting diamond crystals that are fused together. These crystals, although diamond, are not aligned in a single continuous structure. The result is a material that varies in mechanical and thermal properties compared to monocrystalline diamond.

Fig. 2 Polycrystalline Diamond [1]

Key features of polycrystalline diamond wafers include:

• Lower Cost: Polycrystalline diamonds are generally less expensive than their monocrystalline counterparts, due to a more efficient growth process. This ultimately makes polycrystalline diamond wafers an economical choice for many applications.

• High Abrasive Strength: Although it does not feature a single-crystal structure, polycrystalline diamond is extraordinarily tough and thus finds extensive use in cutting, grinding, and drilling where high wear resistance is required.

• Versatility: The areas of applicability for polycrystalline diamonds are much wider because of their flexibility in production and their cost efficiency.

However, polycrystalline diamond wafers tend to have lower thermal conductivity and less optical clarity than their monocrystalline counterparts. Consequently, they cannot be employed in high-precision optics or scenarios where superior heat management is necessary.

Applications of Polycrystalline Diamond Wafers:

• Industrial Cutting Tools: Applied to tools used in machining, mining, and other abrasive applications.
• Heat Sinks: Where high thermal conductivity is less critical.

• Wear-resistant coatings for components operating in severe environmental conditions.

Comparison: Monocrystalline vs Polycrystalline Diamond Wafers

Here is a refined comparison table with a clearer structure and specific data points where applicable:

Key Takeaways:

• Thermal conductivity: Monocrystalline diamonds are significantly better in heat dissipation, making them ideal for high-power electronics or environments requiring effective heat management.
• Mechanical strength: While both types are strong, monocrystalline diamonds tend to outperform polycrystalline in terms of uniformity and tensile strength.
• Cost-efficiency: Polycrystalline diamond wafers are much more cost-effective, making them an attractive choice for industrial applications where top performance is not as critical.
• Optical clarity: Monocrystalline diamonds excel in optics due to their uniform crystal structure, while polycrystalline diamonds are less transparent.

Conclusion

The choice between monocrystalline and polycrystalline diamond wafers usually depends on specific application needs. Monocrystalline diamonds are much better for high-precision applications in semiconductor manufacturing, advanced electronics, and optics due to their improved performance in thermal conductivity and mechanical strength. Polycrystalline diamond wafers are suitable for situations that require durability for applications such as industrial cutting and drilling.

As research and technology further improve, the role that diamond wafers will play in many industries will continue to increase, making these materials essential in the development of more efficient, durable, and complex technologies. For further information, please check Stanford Advanced Materials (SAM).

Reference:

[1] Sobolev, Nikolay & Tomilenko, A. & Bul'bak, Taras & Logvinova, Alla. (2019). Composition of Hydrocarbons in Diamonds, Garnet, and Olivine from Diamondiferous Peridotites from the Udachnaya Pipe in Yakutia, Russia. Engineering. 5. 10.1016/j.eng.2019.03.002.