# Why Chipmakers Are Turning to Diamond Substrates

An episode of [The Hardware Podcast with Fexingo: Chips, Devices, and Electronics Engineering Conversations](https://invisiblenetwork.ai/podcast/1896799982), 24 Jun 2026, 7:54.

Audio: https://audio.fexingo.com/business/the-hardware-podcast/episode-0070.mp3

For decades, silicon has been the workhorse of chipmaking, but it's hitting a thermal wall. In this episode, Lucas and Luna explore why chip designers are now experimenting with diamond substrates — a material that conducts heat five times better than copper. They look at how companies like Akashic Systems and Stanford researchers are fabricating thin-film diamond layers directly on CMOS wafers, potentially lowering operating temperatures by 20°C. The hosts break down the cost challenge, the scalability question, and why this isn't just a lab curiosity: a startup just raised $40 million to commercialize diamond wafers for AI accelerators. If current roadmaps hold, the first commercial chips with embedded diamond layers could tape out as soon as 2028. #DiamondSubstrates #ChipThermalManagement #SemiconductorMaterials #AkashicSystems #StanfordEngineering #CMOS #AIChips #ThermalConductivity #WaferFabrication #ChipDesign #Technology #FexingoBusiness #BusinessPodcast #HardwarePodcast #ChipsAndDevices #SemiconductorInnovation #DataCenterCooling #MaterialScience Keep every episode free: buymeacoffee.com/fexingo

## Transcript

Lucas: You ever hold a piece of silicon and think, this thing is great — until it gets hot.
Luna: All the time. I mean, thermal management is basically the hidden job of every chip designer now.
Lucas: Right. And the conventional solutions — copper heat sinks, vapor chambers, liquid cooling — they're all Band-Aids on a material that just doesn't conduct heat well. Silicon's thermal conductivity is about 150 watts per meter-kelvin. That's okay for a phone chip. It's not okay for an AI accelerator running at 700 watts.
Luna: So what's the alternative? I've heard people whisper about diamond.
Lucas: Exactly. Diamond, in its crystalline form, has a thermal conductivity of roughly 2,000 watts per meter-kelvin. That's more than five times copper. And it's an electrical insulator, so it won't short anything. The idea is to put a thin layer of diamond right underneath the hot spots on a chip — or even use diamond as the substrate itself.
Luna: But diamond is expensive. And hard to work with. How do you even grow it on silicon?
Lucas: That's been the barrier for decades. But there's been real progress in the last few years. The key technique is chemical vapor deposition, or CVD. You start with a small diamond seed crystal, then you pump in methane and hydrogen gas, and you essentially grow a diamond film atom by atom. Temperatures are around 800°C, which is compatible with standard CMOS processing — you just have to do it before you add the metal layers.
Luna: So you're not replacing silicon entirely. You're adding diamond as a layer.
Lucas: Exactly. The most practical approach is to grow a polycrystalline diamond film on the backside of the silicon wafer, after the transistors are built but before packaging. That film acts as a heat spreader, pulling heat away from the transistors and into the package. A Stanford group published a paper last year showing a 15 to 20 degree Celsius reduction in junction temperature for a test chip, just by adding a 10-micron diamond layer.
Luna: Twenty degrees is huge. That's the difference between throttling and not throttling.
Lucas: Especially for data center GPUs. Right now, companies like NVIDIA are pushing 700-plus watts on a single accelerator. If you can drop the hotspot temperature by even 10 degrees, you can either run the chip faster or extend its life. And there's a startup called Akashic Systems that just raised 40 million dollars to commercialize exactly this — diamond wafers for AI chips.
Luna: Akashic Systems — I've seen their name. They're based in Santa Clara?
Lucas: Yeah. They claim they can produce 200-millimeter diamond wafers with a thickness of about 100 microns, and they're working on 300 millimeter. The cost is still high — a diamond wafer might be five to ten times the cost of a silicon wafer — but if you're building a 30,000-dollar GPU, that incremental cost is manageable. And the performance gain is direct: lower temperature means higher clock speeds, or lower leakage current.
Luna: What about the flatness? Diamond is hard, but can you polish it to the nanometer-level flatness you need for lithography?
Lucas: That's been a challenge. Diamond is chemically inert and extremely hard, so polishing is slow and expensive. But Akashic uses a process called 'ion beam planarization' — essentially, you shoot argon ions at the surface to smooth it out. They've demonstrated roughness below one nanometer RMS, which is good enough for most back-end processes. You wouldn't do front-end lithography on diamond directly; you'd bond it to silicon first.
Luna: Bonding is another potential trouble spot. Thermal expansion mismatch — diamond expands less than silicon when heated.
Lucas: Right. If you bond a thick diamond layer to a silicon wafer and then heat it up, you get stress that can warp the wafer or cause delamination. The trick is to keep the diamond layer thin — under 50 microns — and use a graded interface, like a silicon carbide intermediate layer. Several groups have shown that a thin diamond film, say 10 to 20 microns, stays adhered through standard reflow temperatures up to 300 degrees Celsius.
Luna: So the roadmap seems to be: first, diamond as a backside heat spreader in high-end chips. Then maybe diamond interposers for chiplets? And eventually, maybe diamond substrates for specialized devices like RF amplifiers?
Lucas: That's exactly the trajectory. In fact, the US Defense Advanced Research Projects Agency, DARPA, has a program called 'Thermal Management of Advanced Microelectronics' that's funding several groups to integrate diamond. They're targeting GaN-on-diamond for high-power RF amplifiers — that's a big deal for radar and 5G base stations. GaN itself is great for power, but it gets incredibly hot. Diamond substrates can keep junction temperatures below 150 degrees.
Luna: And what about the consumer side? Will we see diamond in phones?
Lucas: Probably not directly — the cost doesn't make sense for a five-dollar chip. But as the technology scales, you might see diamond used in the packaging of flagship phone processors, where thermal headroom can save battery life. There's also work on embedding diamond nanoparticles in thermal interface materials, which is cheaper and could improve thermal paste performance by 30 percent.
Luna: It's interesting that a lot of this progress is coming from startups, not the big fabs.
Lucas: That's true. TSMC and Intel are watching, but they're not investing heavily because the existing cooling solutions are 'good enough' for now. But as power densities keep rising — we're already seeing designs with 2,000 watts per square centimeter in some hot spots — even the best liquid cooling can't keep up. Diamond is one of the few materials that can handle that flux passively.
Luna: So it's really a question of when, not if.
Lucas: I think so. The first commercial chips with embedded diamond layers could tape out as soon as 2028. That's just two years from now. And once the process is proven, the cost will come down as volume increases — you know how that works.
Luna: Yeah, it's the classic semiconductor learning curve. And it reminds me of something: if you're finding value in these deep dives into hardware, and you want to help us keep making them ad-free, a small contribution goes a long way.
Lucas: Absolutely. These shows take a lot of research, and listener support is what lets us stay independent. You can chip in at buy me a coffee dot com slash fexingo. Even a couple of dollars a month genuinely makes a difference.
Luna: Alright, back to diamond. So Lucas, given the cost and integration challenges, what's the single most promising application you see in the next three years?
Lucas: I'd put my money on GaN-on-diamond for 5G infrastructure. The combination of higher power density and better thermal management directly translates to smaller base stations or higher data rates. And the government funding is there. That's a concrete use case where diamond's cost is justified by the system-level savings.
Luna: Makes sense. And it's not just about cooling — it's about enabling architectures that were previously impossible.
Lucas: Exactly. Diamond gives you back thermal headroom that you can trade for performance, reliability, or size reduction. That's a powerful lever when you're designing the next generation of chips.

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