Thermal, Electronic, and Quantum Diamond Grades

Suppliers do sell named thermal, electronic, and quantum-oriented diamond products. The names identify different jobs, not successive steps on one universal purity scale. The question is what the material must do, and which measurements demonstrate that it can do it.

Three jobs, three sets of evidence

The following numbers come from the Element Six Diamond Handbook 2024. They describe named products, not industry-wide definitions.

Product family	Principal job	Relevant specifications and one product example
Thermal	Spread heat away from a hotspot	Thermal conductivity, area, thickness, finish, and assembled thermal resistance. E6 TM150 and TM180 list conductivity above 1500 and above 1800 W/(m K) respectively at 300 K.
Electronic	Support devices or epitaxy	Impurity background, orientation, extended defects, and surface quality. E6 ELSC specifies substitutional nitrogen below 5 ppb.
Quantum application	Create, read, or control color centers	Nitrogen and NV-center densities, coherence, optical behavior, and sometimes isotope composition. E6 DNV-B1 lists approximately 800 ppb substitutional nitrogen before treatment and 300 ppb NV.

Thermal products include polycrystalline plates and single-crystal options. The form-factor decision is discussed in single-crystal versus polycrystalline CVD diamond.

Nitrogen and 12C depend on the quantum task

About 1.1% of natural carbon is 13C, whose nuclear spin can contribute to decoherence in some color-center experiments. An isotope-engineering study reduced the 13C fraction to about 0.3%. That result is a research example, not a mandatory specification for every quantum material.

Indeed, the E6 DNV-B1 datasheet gives a natural 13C fraction of 1.1%, along with the nitrogen and NV figures above. A single-defect experiment may benefit from a very low background of paramagnetic impurities; an NV-ensemble sensor may instead require enough nitrogen to generate a useful density of centers. Neither goal is captured by the phrase “quantum grade means the lowest possible nitrogen.”

Why “higher purity is always better” fails

• An electronic device may need a low uncontrolled impurity background while also requiring deliberate doping, such as boron, for its electrical function. Electronic grade does not mean that all devices use undoped material.
• An NV-ensemble sensor deliberately retains a nitrogen source. More total purity does not automatically improve its signal or sensitivity.
• A diamond plate with exceptional bulk conductivity may still perform poorly in a package if the bond or interface adds thermal resistance.

Can one grade replace another?

Do not assume so. A high-purity single crystal can be a starting point for a quantum device without having the required color-center density or coherence. A high-conductivity plate can be a promising heat spreader without a viable bond. An epitaxial substrate still needs orientation, defect, geometry, and surface data, as set out in the wafer evaluation checklist.

When writing a specification, state the test object (material, device, package, or system), the measurable property, measurement temperature and method, spatial coverage, lot statistics, and unacceptable defect classes. Ask for data from the product and process you plan to buy, not an exceptional coupon from another product line.

Is quantum grade always “above” electronic grade? No. Their intended functions and acceptance tests differ; E6’s DNV-B1 and ELSC nitrogen figures make the distinction concrete.

Is electronic-grade diamond inherently conductive? Undoped high-purity diamond is generally insulating. Conductive devices use controlled doping and contacts; evaluate their measured electrical performance.