[sdiy] $100 Chip fab service

mskala at ansuz.sooke.bc.ca mskala at ansuz.sooke.bc.ca
Wed May 2 20:11:33 CEST 2018

On Wed, 2 May 2018, cheater00 cheater00 wrote:
> Why would the characteristics differ? They're monolithic on a single chip,
> and chips from different wafers will likely have the exact same

Everything varies in a semiconductor process if it isn't deliberately
controlled, and if you build something that depends on an unspecified
parameter and it doesn't work because that parameter changed, too bad -
you have no recourse, because the manufacturer never promised you that.

> characteristics. Sure, stuff needs to be characterised, but once you have
> that you're free to go. Bear in mind you get several orders of magnitude
> more transistors than in a normal synth module.. so this opens a lot of
> possibilities.

I don't think there's reason to think the transistors in this service will
ever be accurately characterized with respect to analog parameters,
because they are not meant to be used that way.

Even in the best case where you know exactly how the transistors behave,
so what?  As others have commented, they're going to be low-voltage only,
and you're not going to be able to connect to them from outside the chip
except through an ADC/DAC combo - and it's not clear how you're going to
build the ADC and DAC inside the chip at all.  You're unlikely to have any
real ability to build passives because doing those in a semiconductor
process is difficult at best and this process isn't designed to do them.

I don't know what kind of "possibilities" this is supposed to open up.
Digital ones,I guess.  There's overlap with what FPGAs do, but this must
have some value those don't provide or it wouldn't be offered.  It's
probably also meant as an educational opportunity for people who are
learning to design (digital) ICs, in which case the question of whether
there may be more efficient ways to build the same circuits is not the
real issue.  Trying to build *analog* stuff with this service seems like
a pipe dream.

Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.

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