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Comment by dragontamer | Hacker News Reader

I agree. Cooling of CPUs is awful use of this tech. Why would anyone turn down thermal conductivity? Just always be sucking heat out.

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The most obvious application would be electrically controlled insulators.

If it's winter or summer, insulate the house.

But if outdoors is 72F (or 21C or another ideal temperature), let the ideal temperature into the house.

Temperature controlled crystal oscillators are another application IMO. Applications where we have a 'target temperature', and easy access to differing temperatures (ex inside the oven vs outside the oven vs the heat from a heater)

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Perhaps another application is insulation of batteries. You want good thermal conductivity when the battery is in active use at high power draw to sink heat to the environment, but also you may want to insulate it when it's idle and freezing outside, to reduce how much self-discharge is needed to maintain its minimum temperature.

However, it might be simpler to do this with moving parts or phase-change materials, etc

> Why would anyone turn down thermal conductivity?

Why do you think CPU dies can still only be cooled directly over the parts that are generating heat? If I read the article correctly, this tech isn't just the ability to turn off thermal conductivity that already existed, it's the ability to add thermal conductivity that you couldn't before.

We already have high-quality thermal conductors and its name is copper. And copper runs throughout the inside of all of our chips.

I have severe doubts that any "heat semiconductor" would have the same thermal-conductance as copper (or copper heatpipes, and other such heat-devices we have today).

But copper is conductive, so it will conduct electricity too. This could possibly be placed in areas where copper can't be, maybe even much closer to (or even directly contacting) the actual copper traces in the chip.

Unfortunately I don't know enough about CPU manufacturing to speculate much more than that.

You're asking for a thermal jumper.

I don't know much about the inside of CPUs either. But I know that at the PCB-level, we use these devices to carry heat but not electricity.

https://www.vishay.com/en/product/60157/

Copper is still better at conducting heat. But just a little bit of thermal-jumper to make that small electrical separation is all you need.

Datasheet: https://www.vishay.com/docs/60157/thjp.pdf

In any case, modern material science provides us with plenty of useful insulators, conductors, thermal-conductors (but not electrical), semiconductors, and now semi-heat conductors (erm, thermal semiconductor?)

I don't expect the thermal semiconductor to be replacing any of the other materials we already use. Instead, we will find new discoveries and applications for things I can barely imagine.

If you want to conduct heat but not electricity, there's always diamond.

You're right, I forgot that diamond is very easy to grow on silicon during the CPU manufacturing process.

...this was sarcasm, just in case it wasn't already painfully obvious to the downvoters.

This requires a layer of gold below it, and a layer of graphene above it. If you’re worried about shorting things out, this isn’t your solution.

Oof. Good to know.

modern houses should be well-insulated, using heat exchange ventilators and heat pumps get proportionately more efficient in these conditions. i will be shocked if this is ever viable economically.

One possibility you lose from a well insulated house is the heat collection potential of your roof on a cold day. The roof is receiving close to 1,000w/m2 and that energy is just wasted.

Passive houses use a lot of tricks around the angles light enters a home and skylights etc to collect that energy, but a system that uses little energy and doesn’t have moving parts so it can last the lifetime of the home should allow for more options and thus lower costs.

PS: Solar thermal systems work well and have a fairly short payback period, but involve both moving parts and fluids.

> Cooling of CPUs is awful use of this tech. Why would anyone turn down thermal conductivity?

Well, you could build logic gates out of these switching elements ;)

You could switch the thermal sink between multiple radiators to give each one a lower duty cycle.

Heat naturally flows to the lowest temperature object connected by the lowest thermal-resistance (or highest thermal conductivity).

If you have a radiator at 80C, and a 2nd radiator at 60C and both are connected to HotPlate-X, the heat will naturally find itself going to the 60C, while the 80C will more naturally find its own heat radiating out to the environment quicker.

You don't need a thermal-semiconductor to just have heat flow around. That's just... heat physics.

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There seems to be some practical applications for this new "thermal semiconductor". Though the next questions are that of cost, performance, etc. etc.

it (the insulator) seems very small. I think, a lot of chips have multiple temperature sensors across the whole chip to decide when to clock down.

If I have 4 cores, and 1 is going flat out, I could see insulating the unused (or lesser used) cores. The idea being give the hot part the full cooling capacity.

That seems like the obvious idea. But maybe I'm misunderstanding or forgetting something fundamental.

> The idea being give the hot part the full cooling capacity.

Isn't it also to prevent the hot part from heating the other, cooler parts? This could be used to give each part of a CPU its own independent cooling. That'd be pretty cool.

You can use this to equalize temperatures on one chip, using it like a changeable heat-shield, so instead of hotspots, you artifically keep some heat from escaping from colder areas too fast which could prevent stress induced cracking. It's better to keep whole chip at 70*C than a one small area at 70 and other areas at 30. Then when heat load from that one small spot vanishes or is moved to other spot, you can change your heat mask on the fly.

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