For instance, Apple supposedly required a deal where they only paid TSMC for usable chips per N3 wafer, and not for the entire wafer.
https://arstechnica.com/gadgets/2023/08/report-apple-is-savi...
The next iPhone generation is said to be a return to form with all models using the same SOC on the revised version of the 3nm node.
> Code from the operating system also indicates that the entire iPhone 16 range will use a new system-on-chip – t8140 – Tahiti, which is what Apple calls the A18 chip internally. The A18 chip is referenced in relation to the base model iPhone 16 and 16 Plus (known collectively as D4y within Apple) as well as the iPhone 16 Pro and 16 Pro Max (referred to as D9x internally)
https://www.macrumors.com/2023/12/20/ios-18-code-four-new-ip...
[1] https://semiwiki.com/semiconductor-manufacturers/tsmc/322688...
[2] https://semiengineering.com/sram-scaling-issues-and-what-com...
[3] https://semiengineering.com/sram-in-ai-the-future-of-memory/
I can see why AMD started putting the SRAM on top.
From what I can gather the key aspects are that decreased feature sizes lead to more variability between transistors, but also to less margin between on-state and off-state. Thus a kind of double-whammy. In logic circuits you're constantly overwriting with new values regardless of what was already there, so they're not as sensitive to this, while the entire point of a memory circuit is to reliably keep values around.
Alternate transistor designs such as FinFET, Gate-all-around and such can provide mitigation of some of this, say by reducing transistor-to-transistor variability by a factor, but can't get around root issue.
[1]: https://semiengineering.com/sram-scaling-issues-and-what-com...
The N3 process is in the A17 Pro, the M3, M3 Pro, and M3 Max. The A17 Pro name seems to imply you won't find it trickle down on the regular iPhones next year. So we'll see that processor only this year in phones, since Apple discontinues their Pro range of phones every year; only the regular phones trickle downrange lowering their prices. The M3 devices are all Macs that needed an upgrade due to their popularity: the Macbook Pro and Macbook Air. They made three chips for them, but they did not make an M3 Ultra for the lower volume desktops. With the announcement of an M4 chip in iPads today, we can expect to see the Macbook Air and Macbook Pro upgraded to M4 soon, with the introduction of an M4 Ultra to match later. We can now expect those M3 devices to be discontinued instead of going downrange in price.
That would leave one device with an N3 process chip: the iMac. At its sale level, I wouldn't be surprised if all the M3 chips that will go into it will be made this year, with the model staying around for a year or two running on fumes.