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China Just Made the World's Fastest Transistor and It Is Not Made of Silicon
(www.zmescience.com)
this post was submitted on 05 May 2025
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A half life of 2×10^19 years still means 100 events per gram per year, 100 new defects in the chip every year.
Modern CPUs have transistors at least in the tens of millions, the most advanced have billions. A gram of bismuth has ~2*10^21 atoms. Pre-existing impurities would probably be a bigger factor by orders of magnitude.
100 per gram of the bismuth part of the transistors per years. But even decades old transistors have volume measured in nanometers cubed which implies a negligible mass.
Assume the transistors are 10 nm, the volumic mass of bismuth is 9750 kg/m^3 = 9.75 * 10^-6 kg/nm, which means, assuming the bismuth part of the transistor is 10 nm^3 it weigh 9.75 * 10^-6 * 10 kg = 9.75 * 10^-5 kg.
100 event per gram per year is 1000 event per kg per year, which means approximately 1000 * 10^-5 = 10^-2 event per 10^-5 kg per year or 1 event per 100 000 years per transistor. assuming there is a billion transistors in a chip that's 10^9 * 10^-5 = 10^4 event per year in a chip.
A bismuth atom has a radius of approximately 160 picometers = 0.16 nm. To simplify, let's assimilate the atoms to cubes of volume 0.16 nm^3. Then, per our previous assumption, a transistor in our chip has a side 10 / 0.16 = 62.5 atoms long which means it contains 62.5^3 = 244 140.625 atoms of bismuth, let's round it down to 244 140 atoms, which means the billion transistors of the chip contain 10^9 * 244 140 =~ 2.441 * 10^14 atoms of bismuth.
Which means that 1000 atoms decay per year out of ~ 2.441 * 10^14 atoms (1000 / ~ 2.441 * 10^14) * 100 =~ 4.096 * 10^-10 % of the bismuth. At this rate it would take well over 5 * 10^9 years, or 5 billion years, for half a percent of the material to have decayed.
TL;DR: AstroStelar [he/him] is right, for all intent and purposes bismuth is stable.
I'm not a material scientist but I'm not sure every single atomic decay will result in defect
Every decay will result in at least one crystal defect. Alpha particles don't travel very far, so it probably cause another crystal defect nearby, and maybe a short chain reaction. I'm sure they can work around it but I don't think it will be easier to deal with than the defects due to ion migration they already have to deal with in Silicon.
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