<azonenberg>
There was some undercut of the mask in a few spots, and the Cr hardmask was too thin so it got eaten through
<azonenberg>
And the etch was far from aligned to the crystal axes
<azonenberg>
But for a first attempt i dont think its bad at all
<azonenberg>
But we're a way out from having a working CPU
<azonenberg>
I have done full 8-bit designs on FPGAs (and am working on a 32-bit now)
<azonenberg>
In terms of home fab so far we've done basic 2D copper interconnect wiring and i just got the beginnings of a silicon etch process working
<azonenberg>
transistors are still further down the roadmap
<flowr>
how many Mhz can someone get up to, with a homebrew CPU of transistors?
<azonenberg>
flowr: First you have to have specs for the transistors (switching speeds etc)
<azonenberg>
Then you have to do the gate-level design and find critical paths
<azonenberg>
then you can compute the maximum delay along that path and that gives you the max frequency
<flowr>
critical paths = bottle neck?
<azonenberg>
flowr: yeah, pretty much
<azonenberg>
biggest delay between a pair of flipflops
<azonenberg>
including gates and wiring
<azonenberg>
My guess is, >10 MHz using discrete transistors is not happening
<azonenberg>
even thats high
<flowr>
have you done any homebrew computers this way?
<azonenberg>
if you integrate it you may have a chance
<azonenberg>
I've used FPGAs
<azonenberg>
and am now working from the other end up on home chip fab
<azonenberg>
But we dont even have functional transistors yet
<flowr>
home chip fab? You mean, making your own ICs?
<azonenberg>
flowr: Yeah, thats what the channel is about lol
<flowr>
but I mean, small ones :P
<flowr>
or is that what you mean? :O
<azonenberg>
flowr: Small as in low gate count? Yes
<azonenberg>
Small as in 22nm? No, our chips are huge dimension wise :p
<flowr>
that's what I thought :P
<azonenberg>
most of my test dies are a few mm across and the components are in a ~0.5mm disk in the middle
<azonenberg>
But i havent actually fabricated anything more complex than test patterns in copper wiring
<azonenberg>
and, most recently, the beginnings of a MEMS device
<azonenberg>
hoping for a simple working MEMS unit by end of this calendar year and logic gates some time in 2012
<flowr>
what does one have to do, to get past 20Mhz, if one is soldering one's own gates on a circuit board?
<flowr>
Do you need pretty small transistors to get past 20Mhz?
<azonenberg>
flowr: No, you need them close together
<azonenberg>
I mean, getting a single gate that fast is easy
<azonenberg>
getting a string of gates end to end that fast is harder
<flowr>
is it because the copper wire between them?
<flowr>
of*
<azonenberg>
flowr: Routing delay is significant, yes
<azonenberg>
especially in FPGA designs due to the less efficient routing it can be >50% of your total path delay
<azonenberg>
If you have fast gates and long wires (like a breadboarded design) it will be even worse
<azonenberg>
Making a working cpu is entirely feasible
<azonenberg>
making it fast is hard
<azonenberg>
I havent really looked into what transistor speeds etc would be in a homebrew fab process yet
<azonenberg>
its so far out that i have more pressing things to worry about