how is it possible for computer chips to have billions of transistors?

Question

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

Answer 1

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.