Indistinguishable From Magic: Manufacturing Modern Computer Chips

https://www.youtube.com/watch?v=NGFhc8R_uO4&t=2070s

It's quite old but I think there is no modern version of it.

I've tried posting to HN a few times but it hasn't gained traction for some reason, but I find it absolutely mind blowing.

I get my DRAM needs at the RAM ranch.

https://dl.acm.org/doi/10.1145/3173574.3174105

Much more impressive are the modifications to the microscope, transforming it into an improvised lithography machine, and the home made plasma etching machine, cobbled together from surplus components.

Of course, the whole thing, starting from the clean room, is extremely impressive -- Intel started their business in a much simpler facility.

It turns out they intentionally drain a bit of the storage capacitor, and amplify that weak signal. Some of that amplified charge is then fed back to storage.

And you are right, that charge on the drain can then be used both to drive some logic and to activate the recharging of the capacitor that was just discharged.

By the way I am being handwavy about "charge" moving about, if you really want to learn the electronics it is more correct to call it a voltage relative to some ground that the charge always moves towards.

Measuring the charge also removes some of the charge -- fast, compared to the leak spead.

DRAM chips have a circuit that writes the value back -- charges the capacitor up if there's supposed to be a charge, drains it if there's not supposed to be a charge.

Refreshes and normal reads are the same, except that normal reads sends the value(s) to the output pin(s) on the chip.

He has "only" shown the basic grid of capacitors and transistors. The chip he shown has no circuit to measure charges or to write them back afterwards. This makes it easier to test the basic grip and the basic capcacitors.

Pretty sure the proper read out and write back circuit comes in the next video.

The capacitance of the wires themselves is typically an order of magnitude greater than that of the storage capacitors. So when the memory is read, the wires are first precharged to some standard voltage. Then the desired row of storage capacitors is connected to the wires, and the charges from the storage capacitors spread onto the wires, changing their voltages very slightly. These voltage deviations from the standard value are amplified by the "sense amplifiers". The amplifiers are sort of like flip-flops. Once they start in a state which "tilts" slightly to "zero" or slightly to "one", they go all the way to the full magnitude zeros and ones. This not only amplifies the signal, but also automatically brings the voltages on the wires and the still connected to them capacitors to the full magnitude, thus "refreshing" the data. The row is disconnected, and the next read cycle can start for some other row.

In the video, an array of 4x5 capacitors and the associated with them switches was fabricated. The capacitors in the video are several hundred times larger (12400 fF) than typical capacitors in a 64 Kbit DRAM (about 50 fF). I assume this is done so that in the later episodes the author could implement the readout electronics outside of the chip.

The important bits here are:

- any two conductive plates close together with an insulator between make a capacitor (1)

- when a capacitor is charged, the energy goes into the electric FIELD

- that's the FIELD of the field effect transistor

- if the field is strong enough, that causes conduction between source and drain (along the "channel")

- the insulator is nanometers thick, so current leaks across it; at that scale, you can detect individual electrons quantum teleporting straight through it.

(1) technically like gravity there is a capacitance between any two objects in the universe, but it's only significant when you have relatively wide and close conductors

I'd pay less for RAM that wasn't "certified" in some official way, at least it works.

This guy is not exactly a regular person. He is a pretty unique case of a talented semiconductor engineer who has a home lab for side hassles. It is not a low effort thing. He runs the equipment 24/7, scrubs all the surfaces in the lab daily to keep it clean.

Still, with the lab and all of the equipment already at hand, it cost him several weeks of work to produce this demonstration of transistors and capacitors, which kind of work, but are still long ways from a "completely complete" 20 bit DRAM chip.

Unfortunately it is simply too much work for one person to maintain a viable semiconductor fabrication process, even when it is done semi-professionally.