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Purpose and Advantages of Metallization on Single-Crystal CVD Diamond Surfaces (e.g., Au, Ag, Cu, Cr)
Metallization is a critical process that transforms single-crystal CVD diamond from a "super-material" into a functional device component. Its core purpose is to create a robust, functional interface that enables electrical, thermal, and mechanical integration with external systems. It bridges the inherent properties of diamond and the practical requirements of device packaging and operation.
I. Primary Purposes of Metallization
1,Electrical Interfacing & Electrode Fabrication
Purpose: To form ohmic contacts, Schottky contacts, or patterned electrodes for electronic devices (e.g., FETs, diodes), radiation detectors, and electrochemical sensors.
How: Photolithography and metal deposition create precise conductive circuits and bonding pads on the diamond surface.
2,Thermal Integration (Heat Spreading/Dissipation)
Purpose: To enable the reliable, low-thermal-resistance attachment of a diamond heat spreader/sink to a heat-generating device (e.g., laser diode, power amplifier) or a cooling system via soldering or brazing.
How: A metallization stack acts as a solderable layer and diffusion barrier, creating a strong metallurgical bond between the diamond and an external metal mount (e.g., copper, copper-tungsten).
3,Optical Coating
Purpose: To deposit highly reflective metal films (e.g., Au, Ag) on the edges or specific areas of diamond optical windows, lenses, or laser crystals to serve as mirrors or protective coatings.
How: Gold's excellent infrared reflectivity is utilized to create high-performance reflective surfaces on diamond optics.
4,Surface Modification
Purpose: To alter surface properties—such as wear resistance for non-active areas, chemical affinity, or adhesion for subsequent layers—through coatings like chromium.
II. Advantages and Selection of Specific Metal Coatings
The choice of metal depends on the application requirements and the interfacial adhesion chemistry. Metallization is typically a multilayer stack consisting of an "adhesion layer" and a "functional layer."
Metal | Key Advantages | Typical Application & Rationale |
Titanium / Chromium | The Ultimate Adhesion Layer. Ti or Cr reacts with surface carbon atoms to form strong, refractory carbides (TiC, Cr$_3$C$_2$), providing exceptional mechanical anchoring and chemical bonding. This is the essential foundation for most subsequent layers. | Mandatory First Layer: Used as the initial coating for any electrical or thermal connection requiring high adhesion. E.g., the first layer in Ti/Pt/Au or Cr/Pt/Au stacks. |
Gold | The Premium Functional Top Layer. Extremely chemically inert (does not oxidize), offers excellent electrical and thermal conductivity, is highly solderable (e.g., Au-Sn eutectic), and is ideal for wire bonding. | Primary Top Layer: Used for high-frequency electrodes, high-reliability ohmic contacts, optical mirrors, and any application requiring oxidation resistance and easy packaging. |
Silver | High-Performance Alternative. Possesses the highest electrical and thermal conductivity of all metals, with a lower cost than gold. The critical drawback is susceptibility to oxidation and sulfurization, degrading performance and solderability. | Niche Applications: Used for cost-sensitive internal conductive/thermal layers in sealed environments, or for devices requiring ultimate conductivity. Rarely used as an exposed top layer. |
Copper | The Cost-Effective Thermal Champion. Exceptional thermal conductivity (second only to silver) at a much lower cost than Au or Ag. It is the ideal bulk thermal connection layer. Requires protection from oxidation. | Core of Heat Sink Applications: A Ti/Cu or Cr/Cu stack on diamond allows for brazing or sintering to copper substrates, creating a high-performance thermal pathway. |
Platinum / Palladium | Noble Diffusion Barriers. Highly inert metals that effectively prevent interdiffusion between adjacent layers (e.g., Ti and Au) during high-temperature operation or processing, ensuring long-term interfacial stability. | Critical Intermediate Layer: A thin Pt or Pd layer inserted between Ti/Au or Cr/Au dramatically improves device reliability under thermal stress. |
Enables Electrical "Dialogue": It allows the inherently insulating or semiconducting diamond to conduct electrical signals and current, integrating it into circuits.
Unlocks Ultimate Thermal Potential: It facilitates the efficient extraction of heat from the diamond's interior to an external system via low-thermal-resistance, robust bonds. This is the key to its application in 5G, laser, and aerospace thermal management.
Enhances Device Reliability & Lifespan: A robust metallization scheme withstands thermal cycling, mechanical stress, and environmental exposure, ensuring long-term operational stability.
Enables Standard Microfabrication: It allows diamond devices to be processed, packaged, and tested using mature semiconductor industry techniques, promoting scalability and commercialization.
Size Available:
| Crystal growth process: | Mono crystal CVD diamond |
| Color: | Normal grade - Near colorless, Mechanic grade - Brown |
| Advantage: | 1) Regular shape, uniform size. The size can be strictly controlled according to customer needs. |
| 2) High repurchase rate and high cost performance, well received by customers. | |
| 3) No visible growth lines,under 100x microscope, no black spots, no impurities, no crack. | |
| 4) The stress is good, the number of times of reuse is high, and it is not easy to crac | |
| Size | 7*7 8*8 9*9 10*10 11*11 12*12 13*13 14*14 -20*20 Thickness: 0.05-3mm |
| Orientation: | 4pt/100 |
| Shape: | Square,Triangles, rectangles, swords |
| Lateral Dimensions Measured | to smaller side |
| Edges | Laser Cut |
| Laser Kerf | < 3° |
| Lateral Tolerance: | +0.1/-0 mm |
| Roughness, Ra | 1. Two sides polished, Ra <10- 30 nm |
| 2. One side polished, the other size is The other side is the cutting surface, or grow | |
| 3.Both sides are unpolished |
| Thermal Conductivity | ≥600 W/mK |
| Thermal Expansion Coefficient | 4.5-8 ppm/K（adjustable） |
| Density | 5.6 g/cm3 |
| Surface Modification | Chrome, Nickel |
| Transition Layer | Titanium, Platinum |
| Contact Layer | Gold, Copper |
| Crystallographic Orientation | 100 110 111 |
| Miscut for Main Face Orientation | ±3° |
| Common Product Size | 3mm×5mm×0.5mm |
| Transverse Tolerance | ±0.05mm |
| Thickness Tolerance | ±0.1mm |
| Edge Cutting | Laser Cutting |
Picture details:
MCD Diamond CVD Diamond Polished Diamond Rough Diamond Diamond Abrasive PCD & PDC