rbanffy•4d
Thinner Films Conduct Better Than Copperieee.org
23 comments
  • adrian_b•4d

    Because copper is no longer a good enough conductor when it it is used in very thin layers, the latest and densest CMOS fabrication processes have begun to replace copper with other metals for the first 2 metal layers, which are the thinnest.

    It is not known with certainty what metals are currently used by Intel or TSMC, though cobalt and ruthenium have been considered as the most promising choices.

    There has been a lot of speculation about whether the choice of cobalt for the thinnest metal layers has been an important cause of Intel's woes with their "10 nm" CMOS fabrication process.

    While there were chances for this hypothesis to be true, the actual reasons for Intel's failure to achieve the predicted clock frequencies and fabrication yields with their "10 nm" processes remain unknown, because Intel has never published any information about this.

    Whichever was the reason, eventually Intel has succeeded to fix this fabrication process, even if only around 5 years later than in their initial plan, after rebranding it in "Intel 7", at least from the point of view of the achievable performances, which have culminated in Raptor Lake Refresh, though perhaps Intel's incapacity of predicting accurately the reliability behavior as a function of the supply voltage, as demonstrated in many failures of Raptor Lake/Alder Lake CPUs, may indicate that they have never succeeded to understand the exact characteristics of this fabrication process.

    • q3k•4d

      > It is not known with certainty what metals are currently used by Intel or TSMC, though cobalt and ruthenium have been considered as the most promising choices.

      Wait, shouldn't that be easy to find out? Section/delayer a chip and throw it under a SEM-EDX system?

      • adrian_b•2d

        There are companies that specialize in studying semiconductor chips made with recent manufacturing processes.

        They write reports with the results of their investigations, which are sold at hefty prices.

        So the competitors in this domain certainly know exactly what metals are used. This does not mean that these facts are published anywhere in the open literature.

        In general, trade secrets about what is in a product have rarely any value against well-funded competitors. They may work only to prevent the appearance of new entrants in the market.

        The secrecy maintained by many companies about how their products really work is very annoying, because it hurts only their customers, never their competitors.

        The only trade secrets that are enforceable are those about how something is made, not about what it is or what it contains.

      • IlikeKitties•4d

        Der8auer on Youtube is the most likely candidate to figure it out if he so choses.

      • hnuser123456•4d

        Alright, who here has the delidding tools and SEM? Let's crack this egg

  • croemer•4d

    Correct title is "New Films Conduct Better the Thinner They Get"

  • sopchi•4d

    The research described was done at Stanford by Profs Eric Pop and Krishna Saraswat. Paper in Science: https://www.science.org/doi/10.1126/science.adq7096

  • deepsun•4d

    I wonder if that's only about direct current. The higher frequency is AC, the more it conducts on sides of the wire (hence insulated strands). So I wouldn't be surprised by their discovery if we talked about very high frequency AC.

    But since it all reversed here it might by opposite for AC in their case.

    UPDATE: paper says something about RF (radio frequency), but I'm not sure I understand what it means, looks more like manufacturing process.

  • dieselerator•4d

    The research looks detailed and interesting. However, I don't follow this summary article.

    Digital circuits dissipate most of the energy charging and discharging capacitance. It must necessarily dissipate that as heat (except for a minor amount of electro-magnetic radiation). The interconnect resistance hardly matters. Of course RC relay can be a factor for some circuits. We can hope this reasearch leads to improvement there.

    Power supply bus resistance can lead to voltage drops, but this research apparently studies layers much too thin for that application.

    Did I missing something?

    • mystified5016•4d

      The interconnect resistance does matter as resistance is a function of cross-sectional area. It's related to the physical size of the conductor. Lower resistance conductors can be physically smaller while carrying the same amount of current.

      But the real trick is if you can increase your switching speed, you lose less energy in the transistor. All the time in between 0 and 1, the transistor is burning energy as heat rather than conducting current. Lower R in your interconnect means your RC time constant goes down and your switching speed goes up. Your transistor spends less time in the linear region and wastes less energy.

      But yes, these are pretty small effects on the whole. That's really just where the industry is at: incremental improvements until the Next Big Thing comes along.

      Additional nit: up to 50% of the energy put into gate capacitance could be recovered. It's not necessary to waste 100%, it's just dramatically cheaper and easier. Honestly I doubt there's any practical benefit as the chip would become quite a lot larger.

      • rbanffy•4d

        > Honestly I doubt there's any practical benefit as the chip would become quite a lot larger.

        There will be at some point when area becomes too small to accommodate the heating and the added complexity becomes a way to shrink the entire chip to sizes that wouldn’t be possible otherwise.

  • larkost•4d

    The linked article does not go into many details about what they are measuring. So I have to wonder: could this property be used to make thinner wires for conducting electricity in bulk (e.g.: hosing wires, or transmission lines) by stacking lots of very thin layers into a cable. I imagine there would be a good amount of development work to make manufacturing such a layered cable, so it would not be right around the corner. But is there any physical barrier to such a development?

  • infogulch•4d

    Cool! Or lukewarm. Or both since they tested from 5K to 300K. And found that the thin films (5-18nm) 'behaved like' metals wrt temperature dependence of resistivity, where thicker films of the same material (80nm) 'behaved like' insulators.

    I wonder how traditional superconductor materials would fare in a super thin film regime like this.

  • bee_rider•4d

    The title here is sort of confusing-thinner films? Thinner than what? And what are these thin films made of?

    Maybe something like “thin film semi metals conduct better than copper” would be better?

    • motorest•4d

      > The title here is sort of confusing-thinner films? Thinner than what? And what are these thin films made of?

      You answer all your questions if you read the first paragraph of the article. The second paragraph even specified the exact material and thickness.

      • themaninthedark•4d

        The only thing I think that the title could make clearer is that this is at or below nm scale, but that too is in the first paragraph.

    • jonasenordin•4d

      Conductivity: Film at Eleven

    • NikkiA•4d

      "New niobium thin film conducts better than copper" would have been my choice, but it would probably get butchered by the autofilter to something as useless as the current title anyway, because 'new' is probably elided, as would 'than'.