Comment by philipkglass | Hacker News Reader

Comment by philipkglass | Hacker News Reader

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It's possible that the inkjet printed transistor is both replicable and impractical for building a full microprocessor.

The inkjet transistor article says "A total of 216 devices were tested with a yield of greater than 95%, thus demonstrating the true scalability of the process for achieving integrated systems." But 95% yield on the transistor level implies vanishingly low yield at the device level when you need thousands of transistors to build a full microprocessor.

Even the new MoS2 microprocessor discussed in the Ars article wasn't fabricated all at once. It was built up from sub-components like shift registers containing fewer transistors, then those components were combined to make a full microprocessor. See for example "Supplementary Fig. 7 | Yield analysis of wafer-level 8-bit registers." in the supplementary information:

https://static-content.springer.com/esm/art%3A10.1038%2Fs415...

The yield of 8-bit registers, each consisting of 144 transistors, can reach 71% on the wafer.

My knowledge of transistors is pretty limited[0]. Does the yield percentage refer to number of successful chips on a substrate or look more at the total number of successful transistors? (Or confusing hybrid-term like rain forecasts) I believe your comment implies the latter? So the number of successful processors is quite low? How many failed transistors can you have in a working microprocessor? (Probably not an easy to answer question?)

[0] Am I remembering correctly that this is your area?

Yield would be the amount of functioning chips. This may be chips, entire packages or even a complexer answere where good chips also need to be below certain leakage. Cores and caches could be disabled and the list of potential yield increasing tooling is always increasing when wafers nowadays costs thousands of dollars.

I’ll add chip designers add redundancy. When errors are detected in testing, they can disable sections of the chip by lasering fuses. That allows routing the circuit through a higher quality area. Quality is measured by not only that the circuit produces correct data but also within tolerances of timing and voltage. IIRC RAM is approximately 10% redundant. A good quality chip will use what meets the spec and leave good transistors unused. A poor quality chip will disable bad ones and only use the ones that meet spec.

if you could print transistors, you could make computers the way Wozniak made them - a bunch of chips with a ton of wiring.

You can do that easily and cheaply today without a fancy transistor printer.

You can find Apple II schematics easily enough online. All the chips are common, off-the-shelf parts still available today. You can send the KiCAD drawings (also available) to a company like PCBWay and have PCBs made very cheaply and in small quantity. Then all you have to do is solder in the chips and other components and connect the board to a power supply.

You can even make a Mac SE/30 "from scratch" - it's mind blowing how many PCBs and chips people have made for retro computing. https://youtu.be/zc3sPoqOFG8?si=iIamSEB00mnxfQdL

Wow, thank you for this! At some point I really want to get my own Mac SE/30. I have a Mac Classic (inherited from my uncle) I still need to work on. This video is really exciting for anyone who wants to fix one of these vintage machines but ends up with a motherboard PCB that's been severely damaged by battery leakage.

I think the appeal is the you can print out a couple of pages of chips and wire them up, not send out for chips and PCBs.

You can order a whole batch of chips and wire them up on breadboards without sending away to have a PCB made. The PCB step is the last one when you want to finalize your computer and package it up.

Ben Eater actually has a free course on YouTube [1] all about building a breadboard computer!

[1] https://youtube.com/playlist?list=PLowKtXNTBypGqImE405J2565d...

There's just a different emotional sense between manufacturing the lego bricks yourself versus mail ordering the magic blocks that you can assemble into a finished product.

Lego bricks is an apt analogy. I don't know how many people would actually care to manufacture their own Lego bricks but millions of people enjoy putting Lego together.

Sam Zeloof [1] actually went through the exercise of making his own semiconductors from scratch. It's a lot of chemistry and experimentation and quite interesting as an exercise, but not at all practical for building your own computer.

Printable transistors would take away the nasty chemistry bits that Sam had to deal with but otherwise wouldn't help much with making practical devices. Computers have a lot of very standard, "Lego brick" or jellybean components. Stuff like muxes/demuxes, shift registers, adders, and the like. These are the components you can buy off the shelf to build your own computer. Building these yourself on giant sheets of paper with a printer might be interesting but you'd get a far less practical, usable computer out of the deal.

[1] https://www.youtube.com/@SamZeloof/videos

I don't know much about this topic but you still need the magic bricks in the printer to make the magic bricks though, no? I guess this can be either depressing or relieving but I'm in the former category, I wish you could do this stuff from sand or something, without relying on modern technology, would be fun.

In my mind the printer counts as a tool so it's a different category. Also you could always do the same by hand with a mask. The feature size might be a bit larger though.

As to doing it all "from sand". You can! At least sort of. It's always a question of how far down the stack you want to take it. After all you probably need to source rare earths from somewhere that isn't your backyard.

Check out pictures of the old processes before automated VLSI. It was all done by hand including crystalizing the silicon. You'll need a clean room and a bunch of weird supplies though.

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