<reportingsjr>
kristianpaul: an entire pic18 clone? 0.0 wow
<reportingsjr>
that is awesome
<azonenberg>
reportingsjr: i got most of the way through a pic12 implementation in an evening
<azonenberg>
then abandoned because i realized the architecture was annoyingly inefficient
<azonenberg>
i wanted something pipelined
<reportingsjr>
azonenberg: how do you do that??
<azonenberg>
verilog on an fpga, obvs
<azonenberg>
no, my fab process isnt that advanced ;)
<reportingsjr>
haha
<berndj>
azonenberg, do you expect diy semi fab to be more suited to small / high speed devices, or to power devices?
<berndj>
(once you get over the hump of "works at all")
<azonenberg>
berndj: MEMS are the easiest since they're least susceptible to trace metal contamination
<azonenberg>
Then power
<azonenberg>
because power is easy to do with large process sizes
<berndj>
you don't think they're more fussy about impurities, and inhomogeneities thereof?
<azonenberg>
Once you get MOS devices to work, no
<azonenberg>
in fact, i think big ones would be *less* suscpetible
<berndj>
(otherwise you have atrocious SOA)
<azonenberg>
a single particle of something is a smallesr portion of the device
<berndj>
i hope you're right
<azonenberg>
I have no idea, thats just a guess
<azonenberg>
MEMS are my field, cmos is a longer term goal
<berndj>
yeah - you just don't want that single particle to be more conductive than the rest, and to hog all the current
<azonenberg>
Of course
<azonenberg>
But the asusmption is that you dont have the particle embedded in the device
<azonenberg>
i.e. that it was a bump in photoresist etc
<azonenberg>
Also, not much dust is conductive
<azonenberg>
its mostly organics (and, more importantly, not stuck very hard to anything)
<berndj>
reason i ask is after looking over some opensourceecology.org - and realizing that they're probably dependent on semi power devices more than on any single other semi tech
<azonenberg>
i'd be more concerned about metal ions
<azonenberg>
getting rid of those is gonna be a pita
<berndj>
yeah, i was thinking more about non-uniformities of dopants
<azonenberg>
TMAH is a little toxic to be recommending for amateur level fab
<azonenberg>
i want to explore use of straight ammonia as a developer
<azonenberg>
and dopant difusion isnt really likely to be a problem
<azonenberg>
Spin coating gives a very even film of doped SiO2
<azonenberg>
HF etch that away through windows in photoresist
<berndj>
where do you draw the line between "calculated risk" and "hey kids, try this at home"?
<azonenberg>
then coat with undoped sio2 and diffuse
<azonenberg>
berndj: Its different for each person, depends on facilities and experience
<berndj>
i get the feeling you just can't get away without dealing with murderdeathkill substances
<azonenberg>
And at least MEMS are possible with nothing worse than line-level voltages (120/240 AC), vacuum, KOH, and 3% HF
<berndj>
you've already accepted HF, i'm not sure how much worse you can go!
<azonenberg>
plus some common solvents
<azonenberg>
thats the thing, its extremely dilute hf sold OTC
<azonenberg>
bad, but not THAT bad
<azonenberg>
CVD is a definite no
<berndj>
i was going to ask if there's a material difference between 3% and 30%
<azonenberg>
Yes
<azonenberg>
Among other things, 3% doesnt fume noticeably
<berndj>
but F- diffusing through your skin is one problem
<azonenberg>
Yeah, thats the BIG one
<azonenberg>
the concentration is 10x lower
<azonenberg>
so you have a lot more time to rinse it off
<berndj>
you don't ALSO need it to be frothing and desiccating or whatever it does
<azonenberg>
before it does any damage
<azonenberg>
and there's less F- to neutralize after the fact
<berndj>
does HF desiccate stuff?
<azonenberg>
I dont think so
<azonenberg>
the 3% doesnt at least
<azonenberg>
its an aqueous solution :P
<berndj>
yeah, there's 97% of pre-desiccated stuff!
<berndj>
anyways nothing like fuming H2SO4
<azonenberg>
oh, no
<azonenberg>
i want nothing to do with that
<azonenberg>
the only acid i'm using in my lab besides 3% hf is concentrated (30%) HCl
<azonenberg>
and from what i hear it's much more mild than concentrated h2so4
<berndj>
our high school science teacher turned a blind eye when us A students wanted to "try something"...
<berndj>
the H2SO4 + sugar trick was pretty neat
<azonenberg>
lol
<azonenberg>
in terms of carbonizing organic matter (experimenters included)
<azonenberg>
hcl is much less nasty than h2so4
<berndj>
but tbh (and i was younger and stupider then) i did fubar a little bit once - made nitric acid in my lungs!
<azonenberg>
um, yeah
<azonenberg>
no2 == nasty
<berndj>
coughed like hell and i imagine i spat/coughed a trace of blood
<berndj>
no >5-minute-term problems though
<azonenberg>
Never got a dose nearly that heavy
<berndj>
yeah, we did something pretty dumb.  neat HNO3 onto some metal shavings i think
<azonenberg>
worst i got was some stinging eyes for a few seconds from vapor
<azonenberg>
no splashes, had goggles and i think a face shield on
<berndj>
goggles?  lol
<berndj>
how did i ever survive chem class
<azonenberg>
This was decapping ICs
<azonenberg>
heat sample to 150C on hot plate
<berndj>
*which i still need to do
<azonenberg>
one drop conc. HNO3 on center
<azonenberg>
let it react, grab with tweezers/forceps and swish particles off in acetone
<azonenberg>
repeat until die is exposed
<azonenberg>
the quantities were small and we were quite careful
<azonenberg>
and from now on i have no plans to repeat the experiment outside a fume hood
<berndj>
i always forget, acetone has THREE carbons
<berndj>
mnemonic: acet-foo is meth-foo + 1, and it's a ketONE
<azonenberg>
ochem <shudder/>
<berndj>
i've forgotten a lot of it.  majored in biochem among others
<azonenberg>
never even took college chem
<azonenberg>
majored in comp sci :p
<berndj>
now THERE is some nasty stuff
<azonenberg>
nasty stuff? You want nasty stuff?
<berndj>
stuff that'll give you cancer, guaranteed, if you just look at it wrong
<azonenberg>
If you get this stuff on you, you wont survive long enough to get cancer :P
<berndj>
i like that "hypergolic with no measurable delay" part
<azonenberg>
"with test engineers"
<berndj>
and ignites asbestos
<azonenberg>
Yep
<berndj>
of all things
<azonenberg>
Probably near the top of materials i do not want to get anywhere near :p
<berndj>
i wonder if that's the closest analog to hollywood action movie "acid" pools
<azonenberg>
I dont even know what state it's in at room temperature
<azonenberg>
is it liquid?
<berndj>
i imagine H2SO4 might also work for that
<azonenberg>
no, boils at 11.7C
<azonenberg>
h2so4 would work, yes
<azonenberg>
this stuff would be vapor
<azonenberg>
Though if released anywhere near anything organic, it'd look like a ball of fire :p
<azonenberg>
This stuff is so nasty that it burns asbestos creating smoke made of HF
<azonenberg>
"the operator is confronted with the problem of coping with a  metal-fluorine fire. For dealing with this situation, I have always  recommended a good pair of running shoes."
<berndj>
if HF is the combustion *product*...
<azonenberg>
Yeah
<azonenberg>
Then the original stuff is even worse
<berndj>
maybe you can placate it by feeding it metallic potassium?
<azonenberg>
From a significant distance away, i hope?
<berndj>
then it will "only" be a fluorine-alkali fire
<berndj>
or a nuke: turn the fluorine and chlorine into neon and argon, respectively
<azonenberg>
lol
<berndj>
they'll be glad the lab only got nuked
<azonenberg>
Yeah
<azonenberg>
Suffice it to say, thats top on the list of substances i never want to work with
<berndj>
i know you're going for MEMS first, but have you got a plan for what dopants to use?
<azonenberg>
but the end result is doped SiO2, you etch with HF
<azonenberg>
and drive in with thermal diffusion
<berndj>
oh and regarding vacuum chambers
<azonenberg>
Yeah?
<berndj>
i suspect stainless steel is going to be prohibitively expensive
<azonenberg>
Was planning to use a glass bell jar for the evaporator
<berndj>
what problems could one expect from other steel?
<azonenberg>
They outgas more but my guess is that at the pressures we'd be doing it wouldnt matter too much
<berndj>
hmm. i guess there's room for stuff to hide in the rust that would invariably build up
<berndj>
HF scrubdown!
<berndj>
i found my first arc welding experiment harder than i thought
<berndj>
major problem: the stick moves in the time that you flip the shade glass down
<azonenberg>
Yeah
<azonenberg>
I had trouble doign that in class
<azonenberg>
i want to try using an auto-darkening lens
<berndj>
gas welding was easy by comparison, but no use for making a vacuum chamber
<azonenberg>
they basically have a phototransistor that darkens an LCD-based (?) shutter
<azonenberg>
reacts in a few microseconds or something
<azonenberg>
so the dose of UV etc you get is minimal
<azonenberg>
you dont even see the flash
<berndj>
yeah, i think i'll have to do that.  they're just expensive enough to require a "yes, i really want to do this" decision
<azonenberg>
from what i hear nobody professional uses the old-school ones for anything :p
<berndj>
yeah, it's fast in darkening, but takes milliseconds to open up again
<azonenberg>
Yep
<azonenberg>
heck, half a second would be fine for brightening lol
<berndj>
i'd just like to either a) understand the mechanism properly, or b) see every last ANSI/ISO mark on it
<berndj>
don't want to depend on a battery or solar cell for eye safety
<azonenberg>
Lol, i know what you mean
<azonenberg>
I think most of them start out at shade 4 ish anyway, so thats a start
<azonenberg>
and i think they have a test button
<berndj>
hmm, i didn't know that, that would give me more confidence
<azonenberg>
in any case i would say buy a good name brand
<berndj>
i hear your warning about pressure vessels, but frankly i'd be more scared of a bell jar than of a (well-anchored and made of malleable) steel sphere
<azonenberg>
Put a screen over it
<berndj>
and yes, shock waves can kill
<berndj>
so there'd be a screen too
<azonenberg>
also, how big of one are you talking about?
<berndj>
big enough for telescope mirrors :)
<azonenberg>
If its like 8" across and a foot high, the total energy released in an implosin wouldnt be that bad
<azonenberg>
Something big enough for scope mirrors? Oh
<azonenberg>
Yeah, that would be problematic if it went poof
<berndj>
8 inch diameter disks would be okay, but ideally i'd like to go bigger
<azonenberg>
i meant 8" diameter jar
<azonenberg>
which would give you maybe a 4" diameter plating area
<berndj>
where are the other 4 inches?
<berndj>
surely the glass isn't 2 inches thick...
<azonenberg>
no lol
<azonenberg>
mounting for the electrodes, etc
<berndj>
ah yes. feedthroughs
<azonenberg>
as well as the actual sucking hole to evacuate the chamber
<berndj>
spark plugs :)
<berndj>
i like how ClF3's NFPA 704 says "will not burn"
<berndj>
not as a fuel, no!
<azonenberg>
Yeah
<azonenberg>
But it will oxidize anything in sight
<azonenberg>
heck, i think some fluorinating agents can oxidize oxygen to a higher oxidation stat elol
<berndj>
heck, oxidizing argon
<azonenberg>
XeF2
<azonenberg>
The fact that it exists is scary :p
<berndj>
did you ever consider basing a diy semi fab process on anything other than silicon?
<azonenberg>
Not really
<berndj>
i think the obvious candidates would be ZnO, SiC, CuO
<azonenberg>
I am mostly doing mems though
<azonenberg>
CuO is a possibility but its a lot harder to work with
<azonenberg>
in terms of etching etc
<berndj>
is silicon the only game in town for meme?
<azonenberg>
Its not, but the existence of KOH for anisotropic etching is a major win
<azonenberg>
easy to obtain, not too toxic, and gives you nice slopes or vertical sidewalls
<berndj>
eew, i can still smell acetone on my fingers while eating supper
<azonenberg>
shouldnt be possible
<azonenberg>
the stuff is so incredibly volatile
<berndj>
was cleaning a pot (water didn't work)
<azonenberg>
must be vapor in the room or something
<azonenberg>
but not liquid
<berndj>
can't smell it now.  maybe some bitterant that i'm confusing for acetone itself!
<azonenberg>
Then again i always wear gloves when using acetone or other solvents in nontrivial amounts
<azonenberg>
all of that defatting is kinda unpleasant lol
<berndj>
NaOH is the bugger there
<azonenberg>
naoh is worse, yeah
<azonenberg>
turns your fat into soap
<berndj>
turns your fingers into soap until you rinse with vinegar
<berndj>
ok, so anisotropic etching gives you the high aspect ratios - steep walls.  right?  if you make, say, a little gear, how do you get it unstuck from the bottom of the pit?
<azonenberg>
You'd need to build it on a sacrificial layer
<azonenberg>
there are a couple of options
<azonenberg>
One is SOI
<azonenberg>
and then etch away the oxide
<berndj>
sacrificial layer? doesn't that imply CVD?
<azonenberg>
Not really
<azonenberg>
you can do a lot with evaporation afaik
<azonenberg>
you can spin coat sio2
<azonenberg>
its solid-phase deposition
<azonenberg>
liquid*
<berndj>
hmm.  what is the gear made of then - SiO2?  i had assumed it would be Si, but i guess that's a spurious assumption
<azonenberg>
You could do polysilicon by evaporation or sputtering
<azonenberg>
But then you cant do anisotropic etch
<azonenberg>
thats something i'm very interested in solving
<azonenberg>
but dont yet have an answer to
<berndj>
what sort of aspect ratios do you work with?  i'm not sure i interpret SEM-grams properly
<azonenberg>
Right now? I havent tried going too far
<azonenberg>
hoping for 10:1 with KOH on <110>
<berndj>
ok, so that steep
<azonenberg>
In metal layers, much shallower
<azonenberg>
maybe 30-45 degree slope
<azonenberg>
since the etch is isotropic
<berndj>
and you can't play games with photoresist layers?
<azonenberg>
I want to explore something similar to DRIE using multiple photoresist depositions
<azonenberg>
spin coat, expose, develop,  etch a little
<azonenberg>
strip resist
<azonenberg>
coat (including sidewalls of undercut area)
<azonenberg>
expose, develop, etch again
<azonenberg>
it will use a lot of PR but if i do a couple of steps i may be able to improve aspect ratios (assuming i get good alignment)
<azonenberg>
But the idea is the same
<azonenberg>
DRIE uses an isotropic etch followed by protection of sidewalls
<azonenberg>
then repeats the cycle
<azonenberg>
so if i did it right i'd get something that looked very much like a Bosch process feature
<azonenberg>
make sense?
<azonenberg>
Its an idea i've had for a while but havent had time to explore much
<berndj>
yeah
<berndj>
though full of jargon i'll have to look up :]
<azonenberg>
note the rounded cutouts on the sidewalls
<azonenberg>
Each iteration of the process you do an isotropic etch (which has undercut because its isotropic) and then follow with a passivation process
<azonenberg>
the passivation protects sidewalls but is quickly eroded in the bottom of the pit
<berndj>
oooh, so DRIE is a bit like FIB but with ions more reactive than Pd / Pt / W / etc?
<azonenberg>
Not exactly
<azonenberg>
That's RIE in general
<berndj>
so... higher energies?
<azonenberg>
RIE is generally mildly anisotropic because the ions are being blasted into the wafer from a vertical direction
<azonenberg>
But sometimes they bounce and etch sidewalls
<azonenberg>
DRIE = deep RIE = higher aspect ratios
<azonenberg>
You start out with a short RIE step
<azonenberg>
giving you a mostly vertical etch with some undercut
<azonenberg>
Then you passivate the entire hole
<azonenberg>
You then do more RIE
<azonenberg>
The KE of the ions knocks the passivation off the bottom
<azonenberg>
but the undercut is slow enough it doesnt attack the passivation much
<azonenberg>
since that actino is only chemical and not as mechanical
<azonenberg>
Then when you've etched long enough that the passivation is significantly thinned, you re-passivate
<azonenberg>
and do another etch step
<azonenberg>
and keep going
<azonenberg>
My process would be similar except instead of using chemical passivation removed by the KE of the etch
<azonenberg>
i'd be using photoresist passivation removed by light shining down the hole during the repeated exposure step
<azonenberg>
The profile of the resulting feature would be nearly identical (though given the need for a lot of expose-align steps i dont think more than 4-5 would be feasible in a realistic amount of time)
<azonenberg>
But if i just need say a 5x improvement in anisotropy it might help
<berndj>
i hope you don't get trouble from sidewall reflection / diffraction
<azonenberg>
No idea
<azonenberg>
Just ran the idea past a guy i work with - he thinks the alignment will be a PITA but it will likely work
<lekernel>
"Temperature Sensor Diode: The ***2N2222*** diode is indicated"
<lekernel>
lol? are they talking about a standard 2N2222 transistor?
<lekernel>
I built quite a few small radio transmitters with those when I was a kid :-)
<lekernel>
didn't know it's apparently good for measuring cryogenic temperatures
<lekernel>
I'm very surprised by the apparent simplicity of those devices. I guess the devil is in the details ...
<azonenberg>
i knew they used diodes for measuring temperatures
<azonenberg>
but i didnt know it worked that low
<azonenberg>
the bandgap varies with temperature
<azonenberg>
and by extension the forward voltage
<lekernel>
well, I can easily try to build one based on bicycle pumps and duct tape and see what happens :-)
<azonenberg>
Whats your intended application?
<lekernel>
hopefully, reaching cryogenic temperatures at some point :)
<bart416>
azonenberg, VT as temperature reference works right down to absolute zero :P
<reportingsjr>
lekernel: a transistor can function as a diode if you tie the base and the collector together
<lekernel>
yes
<lekernel>
but I was just surprised they use such a common part
<bart416>
It sounds logical to use a common part
<bart416>
Easy to do quality testing
<bart416>
And a 2N2222 is pretty damn reliable
<reportingsjr>
yep
<reportingsjr>
very easy to source too
<lekernel>
yes, but it was never meant to be used as a cryogenic thermometer probe
<lekernel>
it's good to know it apparently does a nice job at this
<bart416>
lekernel, name one electronic component that hasn't been abused yet
<bart416>
people have been making point contact transistors out of germanium diodes
<bart416>
Then proceeded to use a 555 timer as audio amplifier
<bart416>
To finish it off with some nice LED as light sensitive receiver
<reportingsjr>
haha
<reportingsjr>
I wouldn't call it abuse
<reportingsjr>
just finding different uses
<bart416>
lol
<bart416>
"tactical misplacement of components" xD
<lekernel>
yes, but this 2N2222 probe is (a) done by an apparently very serious company (b) in a domain few electronics engineers are knowledgeable about
<bart416>
lekernel, we have an ancient analog circuit design professor hanging around the lab that does weird things like that...
<lekernel>
if I asked you how to build a cheap cryogenic temperature probe, I guess you'd have a hard time figuring out "just use a 2N2222" :-)
<bart416>
To be honnest I'd use 4, lol
<reportingsjr>
lekernel: I don't see why a large company would not be allowed to use a solution like this
<lekernel>
I'm not saying it's bad or should be banned, I'm saying it's remarkable
<bart416>
In the end it's still an engineer designing it lekernel
<bart416>
And all engineers like quick, easy, reliable and cheap solutions
<bart416>
And if that person happens to have used a 2N2222 as temperature sensor before and he has a stack of them around when making the prototype, then why the hell not :P
<berndj>
but why not just use a 1N400x?
<berndj>
are they harder to find than 2N2222?
<bart416>
transistors are easier to use as temperature sensors
<berndj>
and since they're using the transistor as a diode anyway...
<bart416>
Check the scale of influence of VT ;)
<bart416>
the Is of a diode and transistor are quite different
<berndj>
hmm, you're still taking advantage of its transistorness
<berndj>
ok never mind i said anything :)
<bart416>
np
<bart416>
Had to think about it as well for a minute, lol
<lekernel>
nah, usually, electronics companies avoid using components for unintended purposes, because doing so tends to result in a "let's see if it works with this week's parts" kind of production
<bart416>
Maybe that's one of the reasons they went for the 2N2222