Aren’t transistors physical things? How is it possible to manufacture billions, especially within the small size of a computer chip?
I saw the Apple m2 chip has 20 billion transistors – it just seems incomprehensible that that many can be manufactured.. they could be microscopic, but 20 billion is still an absurd number
In: 2283
they are really really small. In most computers, a transistor is only about 70 ATOMS wide, or about 5 nanometers. at that scale, a 2d plane of transistors that is only 1 square millimeter would hold about 40 billion transistors (assuming they are square). naturally you cant pack them that tight in the real world.
the way we manufacture this is literally using magic crystals, alchemy, and sunlight. UV light is shone through a slide like old slide projectors would use. this slide contains a pattern for a single layer of the chip. this projection of a pattern is then fed backwards through what is effectively a microscope which makes the whole design the size of a single area of a single chip. This is then shone into a UV sensitive coating on a silicon crystal and causes take on the microscopic pattern special “doping” chemicals are then spread over the chip and they soak through into the silicon where the coating is missing changing the properties of the silicon crystal. Rinse and repeat with a new projector pattern. This builds up microscopic layers 1 layer at a time.
here is a good indepth video on the whole process https://www.youtube.com/watch?v=2ehSCWoaOqQ https://www.youtube.com/watch?v=JBYHwRXmEhY
Keep in mind that they aren’t in one line. A square of them makes it much much easier to have so many. A square of 20 billion means a side length of approx 150,000 transistors. Taking a distance of 15nm (Apple uses 5nm, but adding extra for redundancy and variation), gives us a side length of 2mm.
This is really quite small still
Transistors are physical, however, they are not placed individually on a chip (one by one). That would indeed be almost impossible.
The entire chip is created through a lithography process, this is basically like creating old non-digital photographs.
The design of the chip, already having all these transistors, is projected on a light sensitive substrate. This causes chemical changes in the substrate which will eventually become the actual chip.(There are actually multiple layers created sequentially to get a 3D result.)
(In reality, it is much more complex, and you can’t use normal light, etc… but this is the principle.)
The transistors on a chip look nothing like the transistors you can see with your eyes. Using lasers and chemical processes they make tiny parts of the chip behave like transistors, then using even more complicated processes they’ll connect them with different layers of conductive/insulating material.
Modern cpus also have multiple layers of transistors, but then you run in to the problem of dissipating heat from those middle layers
I’ve always had the opinion that our transistors are centuries ahead of where we have any right to be as a civilization. Like if an alien spacecraft surveyed us they be like “WTF these guys are still burning coal but they have nanometer-scale transistors”?
It’s like we mainlined all our skill points into one category.
Physical things can be very small. Atoms are physical things, and you can’t grasp how tiny they are. This isn’t an insult, it’s just the nature of our experience, we evolved to deal with macro sized things.
A transistor is solid-state, it has no moving parts. They can manufacture them so small because of the way they’re made.
There isn’t a person or robot placing 20 billion components on a chip, they’re sort of ‘machined’ into an existing material chemically.
You start with a flat piece of silicon, then paint it with a material that ‘hardens’ when exposed to certain light, called photoresist. You then shine a light on the material, but in a certain pattern called a mask (like shining a flashlight through a mesh screen). This means only certain parts of the photoresist become hardened.
You then immerse the whole thing in a solvent, and the areas that are covered with hard photoresist stay covered, the photoresist dissolves from the rest of the areas, and you’re left with a sort of pattern of exposed and covered silicon. You can then add material to the uncovered areas, filling the gaps, or shoot ions at the silicon to change it’s properties (but again, only the exposed parts). Then you can remove the rest of the photoresist, and are left with some bare silicon, and some with material on it.
If you do this a bunch, over many layers, you end up with a really complex pattern of overlapping materials that create transistors.
The biggest thing is the size. The mask (the mesh they shine the light through) is large, so they have to then shine the light through a huge series of really powerful lenses to shrink the pattern down to microchip size. Think of it like burning things with a magnifying glass.
Without you understanding the process, that’s the best I can do. I would strongly suggest you watch some videos on photolithography, you’ll get an idea of what’s happening better than having me explain it.
Imagine an old-fashioned [slide projector](https://www.youtube.com/watch?v=AkPRHYKjIdo). It has a light source, which shines through a slide, which then goes through a lens and projects a large image on the wall.
When manufacturing chips you do basically the exact same thing, but you use a lens which makes the image *smaller*. Then you add a light-sensitive coating on the material you are trying to make a chip out of. All the black parts in the slide will remain uncoated, but all the white parts in the slide are now protected by the coating. You now wash the chip with an acid which eats away all the material which is *not* protected by the coating. Rinse the entire thing, add a new layer of different chip material, and repeat.
So how do you make the slide? Well, you use a similar process to create a small slide from a very big one! In the very early days the initial slide was hand-cut and could be room-sized, but eventually they just started using fancy high-resolution printers for that.
Modern chip manufacturing is a bit different due to several decades of innovations, but the general concept is still reasonably accurate.
Its possible because they are not individually manufactured. Think of it like spray painting with a stencil. If you put a stencil down of the letter ‘A’ and spray paint over it you get 1 ‘A’. You could also make a stencil with 100 ‘A’s on it and that same single spray will now get you 100 ‘A’s. We basically make transistors with very detailed stencils, ‘spraying’ light and chemicals through them. As we get better at making really detailed stencils we get more transistors per ‘spray’ basically for free.
Transistors used to be an actual thing. If you took the back off a 1970s transistor radio you could count them. Eat one was about the size of a q-tip
Then we figured out how to make the functional equivalent of transistors by etching patterns into layers of silicon. Since then we’ve gotten very good at doing that at microscopic sizes.
So I might argue that a modern chip doesn’t contain transistors, but it contains millions of transistor equivalent silicon circuits.
Answer: Similar to how a book can have a million letters.
Transistors aren’t physical things created and attached to to the chip. They are printed on the chip. It takes many layers, special light, and complicated chemicals, but it is quite like printing.
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