I just can’t wrap my head around millions of those memory cells being packed in the memory chips in flash drives like sd cards and ssds, how is it possible to make something so small?
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Photolithography. Imagine a video projector, but instead of projecting a huge image to a canvas, the optics resemble backwards binoculars, shrinking the projected image to a few square millimeters of silicon.
On the chip, a layer of light-sensitive lacquer is exposed to one pattern at a time, excess lacquer is then washed off, and metal or chemicals are deposited into the resulting grooves. They make up wires, insulators, or change the electrical properties of the silicon itself. Many cycles of exposure and chemical treatment eventually build up complete circuits at an unimaginably tiny scale. Several square meters of human-readable circuitry can be put on a single tiny chip.
There’s more to it, including the use of short wavelength ultraviolet light to get the details small enough, and advanced techniques to make chips with so many layers that the circuitry is essentially perpendicular to the surface.
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