How are scientists able design processors with such large amounts of transistors? Do they do it with automation? How is it possible to do something like this at that scale?
In: Physics
There are two related questions here:
1) How do they design things with millions of transistors?
2) How do they manufacture things with at that scale?
Answers:
1) Hierarchy and Automation.
When a designer designs a processor, they are not choosing to place individual transistors, they are placing more complex devices that (generally) have already been designed. The most basics of these are logic gates, which are collections of transistors that map onto the boolean logic functions: AND, OR and NOT. From these gates, you can build more complex devices: multiplexers, encoders & decoders, full and half adders, registers etc. The designers job is generally to decided which versions of these devices are needs, and how they are to be connected in order to make the processors match the desired specifications (power, space, speed and cost).
Once the designer is finished, the automation takes over to do the layout. Layout is actually a hard problem (NP-Hard to be specific but not ELI5), as the individual connections between registers need to as short as possible but not overlap. In most cases, there will be simulations done before the design is manufacturer and the design may manually adjust components with CAD tools to get the performance they desire. The same CAD tools would be used to design the standard devices used throughout the hierarchy.
2) Photolithography.
First, a bit about how transistors work. Transistors work because it’s it relative easy to make “doped” silicons, which makes it easier or harder for electrons to pass through it. By alternating between the two kinds of doped silicons, you can create or close a channel between them by applying an electromagnetic field. This allows them to operate as voltage controlled switches. You can get these effects with extreme small layers of silicons, at the scale of 10s of molecules thick. At that scale, UV light can be used to crave and etch away shapes in a layer. So the basic process goes like this: A layer of silicons or metal connector is applied to the wafer, then UV light is used to etch away the parts they don’t need, and this is repeated countless times until all of the required layers are created, then a protective layer is applied. However, this isn’t done for individual transistors that are joined together at a later point. Instead, an entire device is built together, at once on a chip, and they are small enough that a multiple chips at built in at once on a single wafer.
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