Researchers claim first functioning graphene-based chip
spectrum.ieee.org
spectrum.ieee.org
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.
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.
I guess my Google-fu is good enough, because I've been unable to find where I read about it.
That doesn't make the computers unstable. It just makes the data less fit for long-term storage. And even then, people manage.
This is what goes wrong.
error(x + y) > error(x) + error(y)
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.
In practice this is done using non-linear effects of transistors[1], however the exact details of those effects are individual to each transistor and is also temperature dependent.
Since the multiplication circuit relies on different transistors behaving identically, compensation circuitry and trimming is required, which will never be perfect.
[1]: https://www.analog.com/media/en/training-seminars/tutorials/...
Look deep enough, and every modern digital circuit is emulated by an analog circuit, just because the components are analog in their nature, and the 0s and 1s are an interpretation of analog data. That includes digital computers.
Does this make digital computers inherently unstable? Clearly, simple enough computations both of digital and analog kind are good enough to be useful. So there must be a breaking point further away, but on what axis?
In digital logic, this process happens at every gate. Hence the reliability of digital logic.
Analogue logic doesn't do this. So analogue logic is only useful if the noise introduced at each step is lower than the error from your source data was already (at whatever point in the computation you have reached). If there is a way round this, I don't know it.
That's why I think the original comment was about a specific, limited meaning of "analog computation" that does not allow for emulating anything digital. But I struggle to come up with one that doesn't throw the baby of being universal out with the bath water of emulating digital computations.
Which sounds at the very least imprecise to me, considering that I'm writing it on a digital (and therefore analog) computer.
Good explanation on the issue is here:
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.
Why? We are single digit gigahertz, so terahertzes should be ~ 100 times faster?
At a glance, the article doesn't make it clear whether the "terahertz" speed refers to switching frequency or gain bandwidth (fT). You can definitely get transistors with fT in the hundreds of gigahertz range right now.
I don't think this is accurate. Are you saying that in digital computers each individual transistor switches faster than the clock rate of, say, 3 GHz? I think there is one clock signal that is distributed to all transistors and they turn on/off synchronously at this rate. The GHz number on the processor advertisement is the switching rate of all transistors, not some hypothetical 'system rate' which would somehow be much lower?? Please clarify or correct me if I am mistaken.
Imagine an adder made up of logic gates. The gates aren't inherently synchronous - they don't have a clock input - signals appear at their inputs and some time later propagate to their outputs.
To make the adder synchronous you need flip flops at the inputs/outputs and a clock.
If you squint a bit you can view most designs as blobs of async logic sandwiched between sync elements (gated by the clock).
We can see that a signal might have to go through a lot of gates/transistors between flip-flops and so the gates (and their underlying transistors) will necessarily need to be able to switch faster than the clock.
(Technically, many gates do switch more than once per cycle since their inputs change at different times. But their outputs are only latched at the end of the cycle, so any extra switching is ignored.)
The problem is that when you pack them together, they get far too hot to permit dennard scaling to reach the limits of the individual transistor.
So the transistors switch fast individually, but the speed of the chip is limited by the slowest path in any stage, where you wait for every transistor on the path in series
One reason that clock speeds are going above 5 GHz these days is that chips are getting smaller. That means shorter signal propagation distances.
That number depends not just on the number of transistors, but also on the routing delay (are the interconnect wires between transistors long or short? How high is the resistance/capacitance?), and a lot of low-level details of the fabrication process that are extremely not public
But say you buy a brand new CPU and it's clocked at 5 GHz, you can easily get a rough estimate of how long the critical path is, since 1/5GHz = 0.2ns
What you can't easily get is the speed of the transistors or the number of transistors in the critical path, that info is not public, and you could only make a very rough guesstimate.
It's my understanding modern processors do indeed do this to varying degrees.
Each clock stage has many layers of transistors
This THz comment relates to analog circuits, which is supposedly around a factor 10 higher with this new tech.
If you want to learn more, read about Fmax and Ft of transistors.
*1000 times
It is intended only for the highest end network gear, the range is very limited, and requires very special and expensive cables.
It sure is hard to compete with half a century of Si advancement, though. Especially given how many STEM-brains get attracted to software instead, nowadays…
It's just common sense. You won't earn decent money at semiconductor company and given the niche, you will be sentenced to whims of one or two (if you are lucky) companies operating in your region. If you find that your employer doesn't treat you well, you cannot exactly leave and bootstrap your own chip making business.
Software is more democratised and you have much better chances to grow wealth of your family in that area. Although corrupt regulators are doing their best to pull as many ladders as they can to limit ways workers can go their own way (like changed IR35 legislation in the UK that massively limits how small service based business can operate).
Contrast that with software where you and I could go start a business now and potentially unseat a major player somewhere with enough talent and dedication.
Its obvious which one is going to have more mobile employees.
Or am I being too synical?
Market forces (more demand than supply) are what push coding salaries into the stratosphere
Or you work at a foundry-less IP house. There are many of those.
The sad fact is that nasty and exotic chemicals provide ways to make many manufacturing processes cheaper and run large batches. When you're pushing the limits of everything and the stakes are high, you can't really take them off the table.
the researchers said "functioning semiconductor".
https://arxiv.org/pdf/2308.12446
They did make a proof-of-concept device: "The electrical properties of the SEG were measured by characterizing a fabricated top-gated SEG FET."
"The second major advantage of Si is the existence of a native oxide (silicon dioxide, SiO2), which is used as an insulator"
So they use a tube furnace?
> “The chips we use cost about [US] $10, the crucible about $1, and the quartz tube about $10,” said de Heer.
Tube furnaces do not cost $10 except when you build it yourself and do not count the thousands of dollars of equipment you have sitting around.
For reference, carbon makes up about 0.18% of the earth's mass, whereas silicon makes up 27.7%. The moon basically has zero carbon, and the regolith is 20% silicon.
I don't know if that's possible in reality though, since things like cache space are important regardless of your clock speed and there's no point in being able to do fast logic if you can't pipe in enough data.
De Heer says that it will take time to develop this technology. “I compare this work to the Wright brothers’ first 100-meter flight. It will mainly depend on how much work is done to develop it.”
Something to look forward to!
That's fine for experiments. It has zero value for making devices with billions of components. Unless there is something akin to lithograph techniques you can't make products economically.
FTA: “Then a high-frequency current is run through a copper coil around the quartz tube, which heats the graphite crucible through induction. The process takes about an hour.”
Are you saying Graphene can be found in nature?
Looks like that's sort-of a real thing? https://www.americanscientist.org/article/mass-producing-gra...
> Researchers at Rutgers University are making sheets of graphene out of ordinary graphite flakes and some sulfuric or nitric acid.