I'm interested into know what semiconductor manufacturing process use the most common PIC and AVR microcontrollers, in particular 8 bit microcontrollers.
Obviously they are not at the same level of modern CPUs and GPUs (~20 nm), what is the gap between these two "categories"? Are microcontrollers still in the order of micron?
Is the microcontrollers frequency limit (tens of MHz) only due to the worst manufacturing process or are they other factors that affect their maximum operating frequency?
Is just the extremely high cost of better manufacturing process that prevents its use in cheap microcontrollers? Or are there other reasons?
Best Answer
Finer processes require lower supply voltages, which tends to lead to lower core than I/O voltages, and multiple pins being required for power supplies. For example, 3.3V maximum on the I/O and 1.x V on the core. That's inconvenient in a small system.
Also, a lot of the die is used up by the (fixed-size) I/O bonding pads and drivers, so making the rest of the chip finer does not yield as big returns in terms of reduced chip acreage.
The mask sets are much cheaper for the coarser processes (maybe tens of thousands of dollars rather than ~$1M for a state-of-the art mask set), so it makes it more practical to have a wide range of different products.
Microchip PIC products are actually produced in at least one fab (Gresham OR) that was previously used to make (at that time) state-of-the-art memory chips (Fujitsu).