> One major problem that Re6Se8Cl2 faces is that rhenium is one of the rarest elements on Earth. This makes Re6Se8Cl2 very expensive and unlikely to ever make its way into a commercial product.
I call BS. It is rare, true. But it is found in reasonable concentrations in some minerals (alongside molybdenum) that are already being mined and we just need to learn to extract rhenium out of it. For high perf semiconductors you only need microscopic amounts of it anyway.
As to costs, majority of the costs are not in substrates anyway, however costly they are. The costs are in IP and in processing. I suspect even if silicon was as expensive as gold it would not meaningfully change the cost of current high-end CPUs that go into our phones.
(edited, I mistakenly wrote ruthenium where I meant rhenium)
Its concentration in minerals is not reasonable, but extremely small.
The yearly production per human is a barely visible grain with a volume of about a quarter of a cubic millimeter. If each human would want to have a ring of rhenium, that would need all the global production accumulated during one thousand years.
All of it is heavily contended for various applications like gas turbine blades, so the price is in the same range as for platinum-group elements, which are in fact much more abundant.
If the semiconductor layers would have thicknesses in the tens of nanometer range, i.e. they would be deposited on some crystallographically compatible substrate, then such a semiconductor might be usable for expensive devices.
Nevertheless, developing a deposition method that can recycle all the non-deposited rhenium may be not easy. The deposition methods normally used frequently deposit far more substance on the equipment walls than on the semiconductor wafer. When depositing pure inert metals like gold or platinum, there are relatively easy methods to recover them, e.g. by dissolving in acid everything else. Such a complex substance containing rhenium might be obtained from a chemical reaction during the deposition, but it may be difficult to find precursors that are also easy to recycle.
That low price was only in 2020, as a result of the huge air traffic decrease caused by COVID-19.
The price of rhenium fluctuates wildly and a few years ago there was a maximum at $10 per gram.
It is unlikely that it will ever return to the COVID-19 price.
The problem with rhenium is not the current price, but the minuscule production, for which there is very little hope that it could be increased much.
If instead of being used in a few military and commercial airplanes and in a few industrial applications, like thermocouples or catalysts, there would be demand to use it in something used by everybody, the price would increase quickly.
> The price of rhenium fluctuates wildly and a few years ago there was a maximum at $10 per gram.
You lost sight of the simple fact I mentioned, you only need a very small amount of it and you add it to a CPU that costs hundreds of dollars already. So the impact on the cost of the CPU would be negligible.
Even at the highest cost of rhenium you have mentioned, even if you needed a full gram of it (which I don't believe, this is going to be more like milligrams or even micrograms), you still only change the cost of the CPU slightly, at most.
This before you account for inevitable improvements in obtaining the Rhenium itself.
Price of gold is ~$60/gram, so this is not especially expensive in the grand scheme of rare metals even if it's significantly more expensive than copper.
My intuition matches yours. It's abundant enough to find its way into alloys for jet engine blades at single digit percentages: https://www.thenakedscientists.com/articles/science-features... And if used in chips, you don't need to make the full substrate with this material, just a few hundred nanometers at the top, in the active area.
People don't have understanding of what expensive is. Even at hundreds or thousands of dollars per gram it could be pretty much irrelevant to the end result cost if you only need a layer that is couple nanometers in width.
The cost of the raw materials is a rounding error compared to all other aspects of semiconductor manufacturing.
The entire industry is a game of "value-add". The blank silicon wafers start out with effectively zero (or negative) value. The raw materials are worthless to the business. Only once validated features (process layers) begin to accumulate do those raw materials begin to inherit some sense of value.
You can be amazed of its density, but that is safer to do with the lighter, but much cheaper, tungsten.
Most chemical elements with atomic numbers equal or greater than that of lutetium are very slightly radioactive (with a few exceptions like iridium, gold, mercury and lead). Rhenium is one of the most radioactive of them, but it is several orders of magnitude less radioactive than thorium and uranium.
Nevertheless, its radioactivity is so weak that it can be handled safely with bare hands. Even so, making some jewelry kept permanently on the skin is unlikely to be a good idea.
> Rhenium is one of the most radioactive of them, but it is several orders of magnitude less radioactive than thorium and uranium.
Rhenium does have one stable isotope, which comprises 37,4% of naturally ocurring Rhenium. 62,6% is radioactive Rh-187 with a half-life of 10^10 years. That's a bit longer than U-235 or U-238.
But unlike uranium, Rh-187 decays into stable osmium.
Yeah, rhenium radioactivity is pretty much irrelevant for health.
I would worry more about radioactivity as a failure mode for these transistors. Given how fast these are and how few atoms are supposed to be there, the question is if a single atom in the lattice undergoing fission can
a) blow up the lattice enough to disrupt it
b) make it no longer perform the function because the atom that is there has different chemical properties
Are you discounting the cost of development of technology to support the new semiconductor material? that along with it's rarity is what I suspect they're talking about.
I remember when people were super excited for graphene and nanotubes in semiconductors. What happened to that? Seems like a lot of things stop dead in its tracks when it comes to mass manufacturing.
Mass manufacturing is really hard, it's not really a surprise that many things that we can do on lab scale can't be made to work (in an economical fashion) at mass production scale.
We're incredibly lucky that copper and silicon are so (relatively) easy to work with.
Imagine if even basic electrical systems needed wires made of rhodium and semiconductors only worked at cryogenic temperatures. We'd never have gotten over the "technological activation energy" in the 1800s.
Copper was not always easy to work with in semiconductor chips. When I started in the industry in the 1990's all the wiring was aluminum. Articles about copper for wiring were research projects and which company would be the first to get it to mass production.
IBM was the first in 1997 and then others followed.
That's how technology is. Things start out hard and with a lot of work and time we invent new methods.
Aluminum was once worth more than gold. Then we invented new processes of extraction and refinement.
Can I ask an un-related question? In a CPU with thousands of pins, how come they use N pins for ground, N pins for VCC, when it seems simpler to have continuous bar-shaped contacts? Then pins would only be necessary for signals that actually changed. I see this in computer power supplies as well, they use N separate wires to carry V+ and N more for GND, but if you need more current why not use a thicker wire and only have 2?
> In a CPU with thousands of pins, how come they use N pins for ground, N pins for VCC, when it seems simpler to have continuous bar-shaped contacts?
I can't speak to cpus with thousands of pins, but with significantly smaller chips that often have N>1 vcc or ground, it's typically due to layout convenience. The multiple vcc may be on e.g. opposite sides of the chip, and that makes it easier to route a pure vcc signal to a spot that needs it. It's easier to route outside the chip than inside the chip, because there's more space.
This improves the impedance of high speed signal transmission - at high speeds the currents want to flow through the ground path as close to the signal path as is possible. Said another way - designers work to reduce the total area inside the electric circuit to support high switching speeds. The additional power pins in high pin count chips serve to reduce the distance between high speed signal paths and their return ground paths. This is actually true for both ground and vcc, but is easier to visualize when working with signals and their grounds.
I've never seen it on large logic chips, but this is pretty common on power ICs. Look up TI's HotRod QFNs for a particularly well-marketed example. Of course, the fab processes here are basically stone-age (for example, 0.6um BCD is still very common), so such things are easier to do and more beneficial for high-power parts.
> if you need more current why not use a thicker wire and only have 2
How do you route that current in one pin to the two locations the two pins handled? You've just moved the point where the split happens from on the motherboard to on the chip package.
you could have 2 bus bars around all 4 sides of the CPU, and tap off them at the point where the die has its connectors to the "body" (enclosure?) of the package. All the die pics I've seen, the tiny gold signal wires still route around the edges (i.e. they don't join the die in the center). So a thicker bus should work for the main voltage supply. But as the sibling commenter said, it has to do with signal impedance.
You are looking at wire bonded chips. Wire bonding is still used for chips in older process nodes and lower number of IO. This article says up to 800 IOs
But all the high performance chips in leading edge process nodes like 3nm are flip chips. The last time I worked on a wire bond chip was in 130nm in 2004.
With a wire bond chip you can only have IO for signals and power/ground around the periphery. Some wire bond chips have 2 rings of IO pads but it makes the wire bond angles complicated. It's difficult to jump over other wire bonds to get closer to the center.
Flip chips have a series of bumps above the top layer of the chip. These bumps are then connected to a small PCB inside a package or some other kind of interposer.
The transistors are on the bottom of the die and then up to 18 layers of metal are built on top. In a wire bond chip the heat has to go up through all that metal stackup which is usually encased in a glob top which isn't great for heat transfer.
In contrast a flip chip has the die mounted upside with the top layer mounted to the PCB and the side with transistors is on top and can be directly mounted to a heat sink. Intel and AMD used to have bare die around 2000 but then mounted heat spreaders on top because sometimes people would mount the heat sink incorrectly and crack the corner of the die when tightening down non-uniformly.
With a flip chip we can have over 15,000 IO in the chip. The flip chip bumps can be all over the die not just the periphery. Not only can we put IO in the center but the density of the bumps can be much higher compared to the pad points where a wire bonder would attach.
As for your original question about some kind of continuous bar shaped contact we have a power grid underneath on every layer to distribute the power across the chip. This has to go from the top layer Metal18 down through vias to the transistors below Metal1.
Modern chips have multiple voltages in multiple voltage domains. The DDR and PCIE sections have their own voltage requirements. The standard cells that are the combination logic within a CPU operate on much lower voltages. We have dynamic voltage control where the voltage is lowered to save power. We have voltage islands where the USB port can be shut off if nothing is plugged in or CPU core 1 is active while cores 2-4 are off saving power. This requires dedicated power / ground bumps and head switches to disconnect power to sections of the chip.
I don't think we could manufacture your concept of a "bar shaped contact" because the process DRC (Design Rule Check) stuff is very rigid about what can be manufactured. Certain shapes, widths, and turns decrease the yield so they aren't allowed.
Yes, "bump" is the actual technical name. You can click on the wikipedia link I posted to flip chip.
You can see a diagram here of the layer stack up. You can see that the solder bump on the top that connects to the outside world is huge compared to the internal metal layers.
A standard cell in 5nm is around 200nm in height. The width can vary but this way all the cells go together like Lego bricks. Each metal layer going up from Metal1 to the top gets wider and thicker. By the time you get up to Metal18 or so it is probably 20 times wider and thicker than M1. This is useful because those upper layer metals distribute the power and ground and a chip wide clocks. The large top layer metal is also required for the huge bumps above that connect to the outside world.
I think the current minimum bump pitch is around 130 microns. You can see these with your eye and don't need a microscope. Do the math on a chip that is 25mm by 25mm and a pitch of 130 microns and you can determine how many bumps you could fit on the chip.
This is the program I use everyday. It has a list price of over $1 million for a single license. My company has about 800 licenses but we probably get discounts of 60%
I worked at ASML San Diego for about a year as a bottom-rank software engineer (contractor) for 7nm. The scale and complexity of the thing was mind blowing. I worked on the seed laser team, alongside the team that did the molten-tin gun. I think that domain is a rare case where the users (people like you) have a higher knowledge burden than the manufacturer. I can't imagine what actually goes on (in Taiwan and elsewhere) to actually use the machines and sign off the wafers as good-to-go.
That is really cool. I've been in the industry for over 25 years and I've never been to a fab. The number of jobs and specialization is so high that you need thousands of experts in their area but they have little knowledge about someone else's job. I know very little about all the equipment used to make chips. The people next to me that write Verilog know very little about DRC violations that I described. It takes a team of thousands of engineers to make this stuff.
I think they're talking about copper electrical wiring not semiconductor use. If we couldn't use simple copper to bootstrap our energy intensive aluminum industry in the 1800s we might be using rhodium.
Perhaps not trivial in chip interconnects, but it's fairly abundant and a rather workable material in general (hence the bronze age). Faraday probably wouldn't have gotten very far if copper was a gas at room temperature or only occured in trace amounts and there were no other ductile, solid conductive materials on Earth.
For sure. When you look at a used car lot or a smartphone for a few hundred dollars, it is easy to forget that they are the product of a system involving (at least!) hundreds of thousands of people working together in a system that has been studied and optimized for decades. Maybe we'll eventually reach consumer grade graphene processors, but if we do it will probably take decades for the technology to advance through the technology readiness levels.
I think what happened is we found something rare with interesting properties, then we sort of cost-optimized with other materials until we found something cheaper with similar properties.
I think the germanium point contact transistor was sold, but eventually got us via practical methods to the silicon chips we have now. We have had more expensive exotic materials like gallium arsenide.
So I think his comment in the article will happen:
“Now that we know what structural and electronic properties are needed to achieve the new transport regime discovered in this work, there is good likelihood that we will find earth-abundant alternatives to this rhenium-based material that also show impressive transport properties,” Delor says.
I think about this sometimes. Also, what if Pythagoras' formula didn't exist or was some king of hypothesis or a very long formula: where would technology be?
It's also turned out that carbon nanotubes are toxic in a similar fashion to asbestos. While a completed chip would be sealed, it does raise concerns about the safety of manufacture. Similar concerns have been raised about graphene.
It's possible, but cleanroom suits are primarily designed to protect the product from the employees. They keep foreign contaminants out of the manufacturing environment. They're not necessarily capable of protecting the employees from the hazards of the manufacturing environment itself, nor do they necessarily account for the removal of hazardous material before venting the production area to the atmosphere. It might further add to the costs of the fabrication facility.
Honestly asbestos (and by analogy graphene) would be some of the more benign chemicals involved in semiconductor manufacturing. It regularly uses carcinogens, things that will cause miscarriages in pregnant women and acids strong enough to cause bone damage after being absorbed through the skin.
Looking into this a bit and I discovered I have carbon nanotubes in my house already [1] and I never would have guessed. Since the nanotubes are pure carbon, I'm not sure it would cause a similar immune response to asbestos, but the "black lung" issue is still likely a risk. Lungs don't like powders in general.
Normally a manufacturing process is doing well if 90% of the chips on a wafer are usable. Carbon nanotube based circuits manufacture are doing well if 90% of transistors were working. That needs to be solved before they're practical.
I can't help but assume that anything being described as using graphene, carbon nanotubes, crypto, blockchain, bitcoin and - to some degree - AI is a scam.
I feel like the only person I've heard talking about graphene and actually demonstrating any practical application is Robert Murray-Smith. This guy is like he fell down the popular science rabbit hole 20 years ago and emerged naked but for a towel screaming "Eureka".
I work with a company that has a couple of patents on a carbon nanotube based sensing system for hydrocarbons. This company is making and selling units every day, like this shit is real man.
These units are installed out in the field all around the world and are tied into a dashboard for customers to see if any of their projects are experiencing leaks.
I agree that the carbon nano-tech revolution that we were promised by pop-sci writers hasn't materialized but that doesn't mean that it isn't a genuinely useful substance.
"This means processing speeds in devices based on them could reach femtoseconds, a million times as fast as the speeds achievable with current gigahertz electronics"
> “Now that we know what structural and electronic properties are needed...there is good likelihood that we will find earth-abundant alternatives to this rhenium-based material.”
Unfortunately the rarest of rare materials, but the above quote does point out that it shows us what’s possible even if it isn’t viable yet.
Rhenium is used in industry already in metal aloys. It costs around $10000 per Kg. [1] And the US produced 8 tons of it in 2020 [2]. A modern cpu weighs 60g. If we were to make CPUs out of pure Rhenium we could make 133 000 a year at a cost of just $600 each for raw materials. If these things are really a million times faster than the current best in breed silicon ones they will have no trouble competing commercially. $600/ one million is not very much money at all and 133000 times one million is a LOT of compute. Furthermore, the CPUs will not be pure Rhinium.
Gold was extensively used in chip manufacturing previously, and wasn't cost prohibitive.
The 60g figure is for the packaging, not the chip. The actual chips are tiny and weight much less than that, probably under 1g for most processors.
This new semiconductor isn't pure rhenium, it's a compound, and hence less than 1g would be needed, or about $10 per chip, maximum.
Realistically, this new semiconductor would be deposited as an extremely thin layer on top of something cheaper like silicon or quartz. The material cost per chip would be measured in cents.
The cost of depositing an expensive substance like a rhenium compound on a semiconductor wafer is significantly greater than that of the substance that remains deposited on the wafer.
Depending on the kind of deposition method used, for depositing a certain amount on the wafer, a much greater quantity is used, which ends deposited on the equipment, or as chemical precursors mixed and reacted or unreacted.
Due to the rhenium cost and scarcity, all the rhenium compounds that are not deposited on the wafer must be recycled. That can raise the cost a lot.
Finding a compatible substrate for deposition, with an appropriate crystal structure, can be very difficult.
That’s extremely interesting. So there is a considerable manufacturing process waste factor that reduces yield.
I had been thinking that viability of yield could be an issue too as it would have the same wafer fabrication yield, wafer sort yield, and packaging yield that silicon does. And as a new and profoundly expensive material there is going to be an appreciable learning curve.
Is that what you’re referring to? Or is there more to it even than that?
That's not really how market works though, if you could make processors that were a million times faster than current ones, there would be demand for much more than 133 000 a year and many people would be ready to pay more than 600$ for them. For comparison, I find on a random Google result that 50 tons of silicon are used per year for CPUs "in the US".
The price of rhenium would skyrocket to million dollars per kg, and as long as production would stay the same (assuming it's limited by raw resource availability rather than just extraction methods) it would keep getting higher.
The current relatively low price of rhenium (relative to its rarity) is simply due to low demand.
Sure, assuming (1) we can actually produce a rhenium CPU, and (2) we are unable to increase the production of rhenium then, yes, the price of rhenium will increase.
But it will increase precisely because we have a working rhenium CPU in production in the first place, which is what the article disputes is possible (due to its current rarity).
Furthermore, the price would skyrocket only if people are actually willing to pay a high price for these rhenium CPUs, which again means they’re worth the money.
> The current relatively low price of rhenium (relative to its rarity) is simply due to low demand.
For stuff previously needed in low quantities it's usually the reverse - price goes down as more is needed. Initially prices are high because manufacturing equipment has to be maintained even if idle, wages have to be paid, and because of logisticical overhead for the small quanitites. A second price drop occurs as we get into mass-manufacturing and better processes are found.
Rhenium is a byproduct of mining and refinement, but I suspect it is often not captured because the small quanitites needed don't make it economically interesting - you would invest in infrastructure to extract it and immediately crash the price. That would change if there was a stable demand of higher quantities.
Also depending on how easily you can scale these semiconductors down, you may not need such complex cores. CPUs today are complex to (amongst other things) improve IPC - but if you’re really talking a 10^6 improvement in clock speed, I would guess that even a simple in-order core would perform better, and be much smaller.
DRAM latency will remain a problem, no way you can make CPU a million times faster without bringing in memory on the same chip. And you could probably only have a few kB close enough to the core to keep up in frequency.
Most probably you'd see this tech in highly specialized interfacing circuits, like current GaAs chips.
Fiber optic regeneration could benefit from faster electricals on longer shoots, you can only amplify so many times before the noise is amplified too much to ignore so they use optical to electrical to optical circuits. A much faster electrical path could make for some really cool high speed regeneration.
I can also imagine Juniper using them in an ASIC and charging a ton.
If desirable CPUs are made of Rhenium with an effective production line and that the raw supply is so tight, the price certainly won't stay at $10000/Kg, and probably will align with equivalent computation power/watt of traditional designs. Any investor will see that it will only make miner rich without that much return miles aways, and walk away.
This ignore the law of offer and demand. If the supply doesn't change, but there is a lot more demand because now the semiconductor industry also want some, the price will shot up.
processing speeds in devices based on them could reach femtoseconds
That would also mean switching times that allow rectifying infrared light. I.e. capturing light energy with um-sized antennas instead of bandgap traps.
They also seem to say that it cannot be used directly for improving CPUs as they are designed today:
> “[…] they are not necessarily compatible with current hardware used in the semiconductor industry,” […] the applications for these semiconductors “would likely be different than those for traditional semiconductors.”
A slightly important sentence, if you're caught up on the "...using Unobtainium" issue:
> Although the new material is made using one of the rarest elements on Earth, the researchers suggest counterparts made from more abundant materials may be discovered that operate comparably fast.
Yes, it is expensive if you want millions of chips, but imagine those militar and trading operations who would be willing to pay for that speedup as an edge, hope they manufacture something soon. I just wonder how resusable is stuff like EUV when you change the semiconductor material...
Could this mechanism possibly be related to the Boson Peak anomaly in disordered materials? Potentially extra acoustic excitation mode caused by interactions of transient large-cluster vibrations.
> One major problem that Re6Se8Cl2 faces is that rhenium is one of the rarest elements on Earth. This makes Re6Se8Cl2 very expensive and unlikely to ever make its way into a commercial product.
Something doesn't add up.
Rhenium price seems to be $2k/kg. Gold price is $62k/kg. Silver price is $0.8k/kg. So Rhenium is about 3 times as expensive as silver and 30 times cheaper than gold.
My understanding (from binge watching Asianometry) is that the rare earth metals are not mined directly.
Instead they are extracted from ores in the tailings of large scale mining operations like coal or copper and refined by specialty processors.
It is not commercially viable to mine the rare earth elements on their own. Because the price is only $2k/kg, it makes more sense to build a business around all the coal (or whatever) that has to be moved to get a kg of a rare earth.
Because you still have to move all that dirt.
Basically, the price reflects only the costs of refining, marketing, and distribution. Extraction is sunk cost.
Technetium has very similar properties with rhenium, but as its name says it must be made artificially, because due to its low lifetime all that has existed when the Solar System has been formed has disintegrated a long time ago.
Manganese has significantly different properties (due to smaller atomic size and greater electronegativity), so just substituting it in the same chemical formula would not create the same crystal structure and any properties would be different.
Nevertheless, it is likely that other substances with similar properties will be found, but it remains to be seen if any of them are stable enough and cheap enough to be used in practical devices.
I call BS. It is rare, true. But it is found in reasonable concentrations in some minerals (alongside molybdenum) that are already being mined and we just need to learn to extract rhenium out of it. For high perf semiconductors you only need microscopic amounts of it anyway.
As to costs, majority of the costs are not in substrates anyway, however costly they are. The costs are in IP and in processing. I suspect even if silicon was as expensive as gold it would not meaningfully change the cost of current high-end CPUs that go into our phones.
(edited, I mistakenly wrote ruthenium where I meant rhenium)