The recent leap in computational power has come with an increasingly steep toll: heat. As nanometer-scale transistors switch at gigahertz and architectures stack vertically, hotspots within the chip can rise tens of degrees above the rest of the circuit, forcing clock speed reductions and shortening device lifespan. Classic solutions—fans, heat sinks, vapor chambers, even liquid or immersion cooling—work but arrive too late: the heat is already born inside the silicon. The fundamental question is obvious: what if we could spread that heat from within, just nanometers from the transistor, before it concentrates?
A team at Stanford University, led by Professor Srabanti Chowdhury, claims to have found a practical route with an unexpectedly promising material: diamond. Not the gem—from single crystal and thick—but polycrystalline diamond deposited as a very thin film, on the order of microns, grown directly on devices at only 400°C. That threshold matters: below 1,000°C, interconnections and dielectric layers of modern chips are no longer destroyed. If scalable for industry, the concept of a diamond “blanket” or thermal scaffold could drastically lower internal temperatures, enabling higher performance, more 3D integration, and less energy consumption.
Why diamond—and why now
Diamond has long been known in thermal management for a key property: its thermal conductivity can exceed 2,200–2,400 W/m·K in single-crystal form, up to six times that of copper. In polycrystalline form, accessible via industrial processes, top values typically range from 300 to 2,200 W/m·K, still well above silicon and most chip dielectric materials. Additionally, it is electrically insulating and has a low dielectric constant, minimizing signal penalties when integrated in places where traditional insulators are used.
Until now, the obstacle was processing: growing high-quality diamond required temperatures that would ruin the rest of the circuit. Stanford’s innovation comes from two fronts: controlled grain size from the start—large crystals that conduct well horizontally, rather than “forests” of inefficient columns—and low-temperature growth (≈400°C), achieved through a deposition chemistry that incorporates oxygen to “clean” the non-diamond carbon during growth. The result is a coating layer that can also cover device sides, bringing a “thermal diffuser” within nanometers of hotspots.
An invisible heat bridge: the silicon carbide trick
Integrating different materials often introduces a bottleneck: the interfacial thermal resistance (TBR). At that boundary, phonons—the vibrational “packages” carrying heat—rebound if the crystalline lattices do not “communicate” well, blocking thermal flow. Chowdhury’s team saw something unexpected when growing diamond on GaN devices with silicon nitride as a coating: the TBR dropped to record levels. The explanation came from studying the interface: silicon carbide (SiC) formed by intermixing, acting as a “phonon bridge” connecting the two materials. This detail, more akin to basic science than applied engineering, had immediate impact: it significantly improved heat evacuation without impairing transistor operation.
First test: RF GaN transistors
GaN HEMTs are ideal candidates for new thermal management: they are three-dimensional, operate at extremely high power densities, and their electronic channel—where heat originates—is just tens of nanometers below the surface. Any “break” in device physics is immediately measurable.
Using a “blanket” of micrometer-thick polycrystalline diamond around the transistor and keeping processes under 400°C, results included: 50–70°C reductions in channel temperature and performance improvements in the X-band (8–12 GHz) when the device was less hot. It wasn’t all free: some high-frequency parameters declined slightly, but the thermal balance—and thus reliability—improved enough to attract industry interest.
Looking at silicon: thermal scaffolding for 3D stacking
However, the real battlefield lies with CMOS computing chips and their future 3D stacking. High-bandwidth memory (HBM) and AI accelerators are already stacked in “plants,” promising performance but multiplying thermal challenges: heat must be extracted from each layer, not just the top.
This is where “thermal scaffolding” comes in: interleaving ultra-thin layers of diamond inside the chip’s “backend,” directly above transistors, to spread heat laterally, and connecting them via thermal pillars (copper or diamond) that conduct heat vertically (downward) toward better diffusers and cooling circuits. In prototypes with hot load testing, this scaffold reduced temperatures by up to tenfold compared to unstructured chips—a reduction external heat sinks cannot match because they arrive too late at hotspots.
Current solutions: still necessary but insufficient
The industry isn’t starting from scratch: denser coolers, more efficient fans, optimized vapor chambers, liquids circulating in microchannels, phase change materials, or even immersion in dielectric fluids have all pushed the limits. But all these techniques act after heat is generated and from a distance—not at the source. In stacked chips like “skyscrapers of silicon,” heat that isn’t dissipated inside cannot easily be recovered outside. The promise of diamond is to complement this arsenal by controlling heat closer to its source.
Industry and defense aligned—for once
Heat management doesn’t recognize competition. That’s why manufacturers and suppliers who rarely collaborate have come together: Applied Materials, Samsung, Micron, TSMC, and more. Meanwhile, DARPA’s THREADS program (Technologies for Heat Removal in Electronics at the Device Scale) targets cooling at the device level for high-power RF modules and RF amplifiers, aiming for 6–8 times the current power densities. The motivation is simple: in defense, thermal margin equates to performance and reliability.
Key figures (and how to interpret them)
- Thermal conductivity: Single-crystal diamond hits 2,200–2,400 W/m·K; high-quality polycrystalline ranges from 300 to 2,200 W/m·K depending on thickness, orientation, and process. Copper hovers around 400 W/m·K.
- Processing temperature: reducing from approximately 900–1,000°C to around 400°C enables integration into finished chips without damaging interconnects.
- Interface: formation of SiC at the diamond/silicon nitride/GaN boundary drops TBR to record lows (m²·K/GW); it effectively unblocks phonon flow.
- Practical impact: measured device temperature drops of –50 to –70°C; up to –90% reduction in thermal ramp-up in prototype 3D thermal scaffolding with thermal loads.
Unresolved issues
Not everything is solved. A key challenge is achieving atomically smooth surfaces atop the diamond coating, essential for stacking metals and dielectrics without defects. Repeatability at wafer scale, grain variability in complex geometries, and compatibility with standard manufacturing flows (BEOL) also require fine engineering work. These are engineering problems, not insurmountable physics issues, which explains growing industrial interest: if scalable, this process could open the way toward cooler 3D stacks and denser chips.
Why this fits into the AI era
Thermal demands are rising beyond traditional computing. Generative AI accelerators reach power densities that challenge current cooling solutions. For example, next-generation GPU servers approach 15 kW per chassis; stacking HBM memory around logic chips generates heat pathways that limit scaling unless additional cooling is provided. Integrating diamond inside chips doesn’t replace data center liquid cooling, but it alleviates the peaks and hotspots that ultimately dictate performance limits.
What this could mean for users—and the industry
- More sustained performance: less “thermal throttling” during long workloads.
- Higher reliability: operating cooler reduces leakage, electromigration, and aging of materials.
- More compact chassis: if heat is spread from within, metal and volume outside can potentially be reduced.
- New 3D architectures: solving layer-by-layer thermal bottlenecks enables higher stacking and shorter signal paths.
Editorial: a pragmatic approach to gain time against heat
For years, the industry has fantasized about diamond transistors. They may appear in niche applications but are not necessary to win this battle. The approach of “diamond as a thermal dielectric” appears more realistic: it preserves existing electronics, relies on known chemistry, and adds functionality where current materials merely insulate without aiding heat flow. If, as initial tests suggest, the process is scalable and interfaces controllable, it’s reasonable to expect “diamond blankets” becoming a critical piece of the thermal puzzle for the next decade.
Frequently Asked Questions
Does the “diamond inside” chip replace external heatsinks and liquid cooling?
No. It acts at the source, diffusing hotspots where heat originates, and complements external systems. Together, they provide more margin before thermal throttling occurs.
Why is reducing the TBR at the interface so important?
Because even with excellent thermal conduction, if phonons rebound at the chip boundary when crossing to the diamond, heat flow stalls. Forming SiC at the interface creates a “phonon bridge” that facilitates this transfer and unlocks the full benefit of diamond.
Can it be integrated into advanced CMOS chips without disrupting current processes?
That’s the promise of processing at ≈400°C: staying below the damage threshold for interconnects and dielectrics, integrating in the “backend” manufacturing flow. Engineering challenges remain (planarity, variability), but the compatibility is promising.
Where would this have the most immediate impact?
Primarily in high-power RF devices (GaN HEMT) and 3D stacks of computing and memory (HBM + logic), where hotspots and long thermal paths currently limit performance.
Sources
• Technical analysis and dissemination of low-temperature polycrystalline diamond growth for “thermal blankets” in RF and CMOS, with results in GaN HEMTs, 3D thermal scaffolding, and industry collaborations.
• DARPA’s THREADS program (Technologies for Heat Removal in Electronics at the Device Scale) focusing on device-level cooling of high-power RF modules.
• Study with record low TBR interfaces in diamond/Si₃N₄/GaN, key to the SiC-based “phonon bridge”.
• Research into interlayer diamond and thermal pillars for SoC and 3D stacking, with conductivities of polycrystalline diamond and proof-of-concept of “thermal scaffolding”.
• Recent coverage of the “diamond blanket” method and its temperature reductions in experiments and simulations.