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Buries the lede a bit? Near the end is "Conventional GFETs [graphene transistors] do not use semiconducting graphene, making them unsuitable for digital electr
by ajb 3y ago
Buries the lede a bit? Near the end is "Conventional GFETs [graphene transistors] do not use semiconducting graphene, making them unsuitable for digital electronics requiring a complete transistor shutdown. [...] the SEC [material] developed by his team allows for a complete shutdown, meeting the stringent requirements of digital electronics."
As far as I heard before, this was the problem with graphene transistors, they had a nonlinear response but did not shut down the current flow, making them not useful for digital logic, only analog circuits. But, it's a while since I read about this so maybe someone else already achieved this before.
- deleted 3y ago[deleted]
- j16sdiz 3y agoThat's the "bandgap" thing mentioned in the article. They exists, but very unreliable.
- singularity2001 3y agoSemi analog transistor would be perfectly fine for AI operations though? ( matrix multiplication, sigmoid, tanh etc )
- marcosdumay 3y agoAnalog or digital are properties of the signals you put on the circuits, not of the transistors. You can do digital manipulation with non-gapped transistors too. You just can't use the extremely intense when active but self-limiting designs we use today. Besides, unless we get some very creative new insights, analog computers are a dead-end.
- lbourdages 3y agoI've been trying to find the source for a while, but I recall reading about a fundamental property of analog computers that makes them inherently unstable (as in, noise will always win on the long run), unlike digital computers. No matter how good the design is, little bits of noise add up in complex analog computers and the output is inexact. I guess my Google-fu is good enough, because I've been unable to find where I read about it.
- marcosdumay 3y agoAre you thinking about the property of analog data that it can't be stored, reprocessed, or copied without the noise increasing? That doesn't make the computers unstable. It just makes the data less fit for long-term storage. And even then, people manage.
- lbourdages 3y agoNo, it wasn't about storage. It was really during calculations, you can't prevent the noise from affecting the results, from a fundamental level.
- fooker 3y agoFor any complicated calculation, you need to store and propagate multiple intermediate results. This is what goes wrong. error(x + y) > error(x) + error(y)
- imtringued 3y agoFloating point calculation is "noisy" and yet there are models that use smaller and smaller floating point numbers without losing much accuracy.
- marcosdumay 3y agoOh, ok. You can't. I'm not sure you can find a citation though, it's like searching for a source that the sky is blue. Keep in mind that digital calculations have noise too. The digitization noise behaves in a completely different way, but any single computer has a finite precision whatever the technology behind it. Infinite precision doesn't exist on the real world.
- jari_mustonen 3y agoCould this be the reason why human (and things with brains) need to sleep from time to time? Sleep would reset the accumulating noice from the brain.
- 3y ago
- imtringued 3y agoLeaky ReLU is the best though.
- ajb 3y agoYes, analogue computing. It's a world of pain though, each individual operator in each individual device is going to have a slightly different level of accuracy, which is also going to be affected by temperature, so you need to learn a whole new set of analytical skills and operational practices to ensure that your model works correctly on each one at a customer location. And that's not even thinking about the testability at shipment of the devices being in spec, and that they are at all operating temperatures and over the lifetime of the device.
- happytiger 3y agoI believe what you are referring to is called the Bandgap problem. Good explanation on the issue is here: https://www.allaboutcircuits.com/technical-articles/graphene-field-effect-transistor-gfet-construction-benefits-challenges/ https://www.allaboutcircuits.com/technical-articles/graphene... Convenience quote of relevant section: > Lack of Bandgap Despite being a fast and efficient transistor, the GFET does not have a bandgap. The gapless structure means that the valence and conduction bands meet at zero volts, hence making graphene to behave like a metal. In semiconductor materials such as silicon, the two bands are separated by a gap which behaves like an insulator under normal conditions. Usually, the electrons require some additional energy to jump from the valence band to the conduction band. In FETs, a bias voltage enables a current to flow through the band which acts as an insulator in the absence of the bias. Unfortunately, the absence of a band gap in GFET makes it hard to turn off the transistor since it cannot behave as an insulator. The inability to completely switch it off results in an on/off current ratio of about 5, which is quite low for logic operations. Consequently, using GFETs in digital circuits is a challenge. However, this is not a problem with analog circuits hence making the GFET suitable for amplifiers, mixed-signal circuits, and other analog applications. Multiple parties are researching ways to address these bandgap challenges, including techniques such as the negative resistance approach and the bottom-up synthesis technique of fabrication.