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What? How does adding metal layers allow you to increase the number of transistors? Transistor density is a fixed function of transistor size, and die size is a

What? How does adding metal layers allow you to increase the number of transistors? Transistor density is a fixed function of transistor size, and die size is a variable function ruled mostly by defect density. Unless you are talking about die stacking?

paulmd 11y ago
He's referring to 3D density. Die stacking is one way to do that, and it's the only one that isn't just wild fantasy. Another would be for the die to have multiple layers within a single die - which can't be done with current technology, but isn't physically impossible. Basically what you'd need to do is similar to PCB fabrication - you need to create "blind" and "buried" features within a series of stacked layers. Obviously that capability doesn't exist right now, but you could look at using an ion beam to create a planar mask that targets only a single layer within a multilayer wafer. The particles travel through material without depositing energy until they reach a critical threshold [1], after which they rapidly deposit nearly all of their energy. This allows you to give the beam a specific "depth", in other words it can be targeted in 3D. Perhaps - because it's a particle beam, not an EM wave - it might also be less susceptible to some of the problems caused by the wave nature of light, even in a more conventional application. I know it from proton radiotherapy (a good general rundown of the technology here [2]), and I wonder if it couldn't also be used for something like this. A lot of problems would have to be solved. You'd be talking about a substantially different process from standard wafer production, you'd have to tighten up the Z-resolution, etc. No idea if it'd work or not in the end, but I think it'd be interesting to look. Or alternately maybe we figure out some additive/subtractive method that lets us create multiple layers on a single die another way. For the short terms it's going to be die stacking though. [1] https://en.wikipedia.org/wiki/Bragg_peak https://en.wikipedia.org/wiki/Bragg_peak [2] http://www.aapm.org/meetings/05AM/pdf/18-4016-65735-22.pdf http://www.aapm.org/meetings/05AM/pdf/18-4016-65735-22.pdf
- TheLoneWolfling 11y ago
  Unfortunately, particles are also waves. Look at de Broglie waves. Now, that being said, one real advantage is that the effective wavelength tends to be much smaller. For example, an electron at 0.9c has an effective wavelength of 1.2pm (picometers).

paulmd 11y ago

He's referring to 3D density. Die stacking is one way to do that, and it's the only one that isn't just wild fantasy. Another would be for the die to have multiple layers within a single die - which can't be done with current technology, but isn't physically impossible. Basically what you'd need to do is similar to PCB fabrication - you need to create "blind" and "buried" features within a series of stacked layers. Obviously that capability doesn't exist right now, but you could look at using an ion beam to create a planar mask that targets only a single layer within a multilayer wafer. The particles travel through material without depositing energy until they reach a critical threshold [1], after which they rapidly deposit nearly all of their energy. This allows you to give the beam a specific "depth", in other words it can be targeted in 3D. Perhaps - because it's a particle beam, not an EM wave - it might also be less susceptible to some of the problems caused by the wave nature of light, even in a more conventional application. I know it from proton radiotherapy (a good general rundown of the technology here [2]), and I wonder if it couldn't also be used for something like this. A lot of problems would have to be solved. You'd be talking about a substantially different process from standard wafer production, you'd have to tighten up the Z-resolution, etc. No idea if it'd work or not in the end, but I think it'd be interesting to look. Or alternately maybe we figure out some additive/subtractive method that lets us create multiple layers on a single die another way. For the short terms it's going to be die stacking though. [1] https://en.wikipedia.org/wiki/Bragg_peak https://en.wikipedia.org/wiki/Bragg_peak [2] http://www.aapm.org/meetings/05AM/pdf/18-4016-65735-22.pdf http://www.aapm.org/meetings/05AM/pdf/18-4016-65735-22.pdf

TheLoneWolfling 11y ago
Unfortunately, particles are also waves. Look at de Broglie waves. Now, that being said, one real advantage is that the effective wavelength tends to be much smaller. For example, an electron at 0.9c has an effective wavelength of 1.2pm (picometers).