Why Chips Die
semiengineering.com
semiengineering.com
Electrons have a lot of great properties for switching. They are massive enough to be localizable into small spaces, but light enough to be cheap (energy-wise) to accelerate up to high speeds. They are ubiquitous, and they interact strongly with matter, electric fields, and magnetic fields.
Light is great for signal transport over long distances in a large part because it interacts so weakly with matter. But that same property makes it difficult to switch.
It's a good question, but there is something often ignored in press-releases about photonic transistors: How exactly does a speedup occur?
For example: Photons do not interact with each other, so a photonic transistor will rely on electrons or holes to effect some sort of interaction between photons. That interaction might occur in a photorefractive material, but ultimately the photorefraction is a result of photons interacting with electrons of the underlying material. So why are the electrons in the photorefractive material faster than the electrons in a conventional transistor? It also might be worth noting that the fastest fT in conventional transistors is around 0.5 THz, so the bar is not particularly low.
FD: I have a patent on photonic transistors from Bell Labs days.
FD2: I have become an old cynic on photonic transistors.
FD3: The above is really a rant on high-speed transistors. Photonic transistors might well have a superiority in different areas, eg quantum computing.
At the fastest speeds, interconnect on crucial lines is engineered as a transmission line, where the inductance balances out the capacitance. When you look at the propagation in the transmission line, the energy of the traveling wave is dominated by the electric and magnetic fields outside the metal. So it is not generally appreciated that transmission-line interconnect is already photonic, and moving at photonic speeds. As you might expect, for most transmission-line geometries, the speed of the signal is not terribly far away from the speed-of-light in the material.
Moreover, the intuition that "metal wires" are slowing down the signal is not taking into account that an "all photonic transmission" still requires some sort of confinement. If you were to eliminate the metal, you would still need some sort of waveguide to confine the photonic energy. Inevitably, the waveguide will have some region of a higher dielectric, which as you know will slow down the propagation and also have some loss. As it turns out, the final propagation speed is close to a transmission line.
So again, it's important to quantify exactly how the speedup occurs by switching to "photonic interconnect", because the reality is that it is already photonic.
Where photonic interconnect might have had a use is where the lines are very long, and the loss associated with a transmission line gets impractically large due to the confining metals. At that point, it's an engineering tradeoff: Converting to and from photons at each end of the line is non-trivial, and not all materials lend themselves to converting photons to electrons. There have been efforts since the 80s to put GaAs on silicon just to address this issue. (I was part of a team that got to 100MHz for GaAs-on-Si. The fact that GaAs-on-Si photonic transmission is still pretty much confined to the lab tells you everything you need to know about the manufacturability.)
Did you end up using that patent in any product? What did happen to it?
Possibly her main long term enemy to chip life as a polymer chemist was not the overall system enemy to long term chip life.
(That was my first thought after reading 'death by design')
For example the graphics back end of a video card is running its framebuffer memory at a different clock rate from the video dot clock, at some point pixel data has to move from one clock domain to the other - metastability failure might cause an occasional bad pixel on the screen, you can do the math, trade latency (and more gates) for reliability so that you see that pixel burble once a year.
Other times it could be worse - I worked on a chip where we did the math on whether the PCI interface would suffer synchroniser failure and what the worst case failure was (maybe bus lockup?), in the end the boss signed off on once a year ... which at the time was ~100 times the mean Win95 uptime
So we do sort of do that math, knowing that you can't 'fix' metastability issues, just make them rare
Apparently chips "age", but they still function because or error mitigation, which is witnessed by a performance drop.
To me it's the only explanation why I see so many computers turn slow, despite the fact that I have reinstalled them, cleaned them, etc. I argued many times against the "just put a SSD and add RAM, windows 10 is just slower", but in my mind, I just cannot explain why a newer OS becomes so much slower and memory hungry and unresponsive, even when running very basic programs.
I think there is a myth that chip will always perform exactly the same as long as they work. Chip engineering sounds much more complicated than it seems, and I cannot trust any IT support person telling me to "upgrade".
I'm sure military-grade chips have different designs and cooling requirements, which doesn't turn them into domestic/obsolete products after 3 years.
After about ten attempts, I was no longer able to get it to POST at all. So I pulled it apart and scavenged its disk’s magnets, which was what I had been planning on doing anyway.
It won't take any longer to startup, it just won't startup in a usable state. Startup/tasks taking longer is definitely the software industry's doing.
https://semiengineering.com/transistor-aging-intensifies-10n... for more.