the Hearth @Felthry@awoo.space

from where i'm sitting, it's six western characters in a box!
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well, we woke up last night at like 1 AM and threw up

took some medicine and got back to sleep around 2:30 and have been okay since but... that was an unpleasant experience

not sure what it was that we ate last night that caused such a reaction

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tails
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i love my friends 💚 -F

dammit i can't fit all the sauces i want on here, just remembered tzatziki should be here
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condiment of choice (no further context given)

as of today, it's been one year since we moved here to oregon
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cases of the latter that i can think of off the top of my heads are:
- changing Ōkami's visual style from as-photorealistic-as-the-PS2-can-manage to the beautiful game it is now
- changing the protagonist of Wild Arms 3 from Jet (Generic Anime Protagonist Guy™) to Virginia (Actually Interesting Character With Good Motivations And Story Arc™)
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sometimes you hear about changes being made to a game partway through development and you think "why the fuck did they do that, it would have been so much better the other way"

but sometimes it's exactly the opposite, and you think "why the fuck did they ever plan on doing it the first way, the new way is so much better"
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anyway after two weeks of working on that and several long meetings poring over kLayout and/or Cadence trying to line up photomicrographs of the hot spots with the layout files and figure out why the *fuck* the hot spot would *possibly* be *there* of all places, we've identified a plan for fixing it and, with luck, we'll have working wafers in a couple weeks

after identifying the problem in the first wafers we got, we immediately told the foundry to stop production on the next batch they were working on, and it's looking like we may be able to salvage those by changing one layer that hasn't yet been deposited, which is a major relief--we're not too up to speed on the financials but it seems like those wafers cost several thousand dollars so far, so losing them would be unfortunate for the company wallet (and it's a startup company, so that wallet isn't looking too great to begin with)
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and best of all, this liquid crystal is cheap

our work paid $135 for 1 mL of liquid crystal dissolved in 10 mL of carrier solvent (here, ethanol, though i'm kind of wishing we got the one dissolved in dichloromethane instead, or even the 1 mL of pure liquid crystal with no solvent; we've had some difficulties with the ethanol)

That may sound like a lot of money for very little stuff, but almost none of the stuff actually gets used. we could probably do this whole process several thousand times with what we have in that bottle, it's a very thin film of liquid crystal

compare that to spending $10k on a thermal camera, then another $6k on infrared-rated microscope lenses (yes, really), and even *then* having relatively poor temperature resolution making it difficult to pinpoint the hot spot
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What's happening here is a phase transition in the liquid crystal; the stuff we bought is specially formulated to transition from its optically-active nematic phase to its transparent disordered phase at 29 °C, quite close to room temperature. It's very sensitive; temperature differences of less than 0.1 °C can be detected with it--of course, it's limited to telling you whether the temperature is above or below 29 °C, but that's all we really need.

By very carefully adjusting the voltage applied to the chip, we can get to a point where the black spots just barely appear, where the hottest points on the die are *just* above 29 °C. And that tells us, with reasonable accuracy (subject to thermal conduction and heatsinking effects of metal layers on the die, anyway, which can change the apparent location of the hotspot by a few microns) exactly where the fault is located.
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As it turns out, liquid crystals have an interesting property that can be exploited here.

We placed, using an ordinary paintbrush, a very thin film of specially-formulated liquid crystal over the surface of the die. Then, by illuminating the die with polarized light, and putting a cross-polarized filter in the optical path of the microscope, the film of liquid crystal turns rainbow-colored as it rotates the polarization of light passing through it.

Then we apply power to the die, carefully adjust the voltage until the breakdown just starts.... and as if by magic, black spots appear in the rainbow pattern right on top of the hot spots.
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So, based on the principle that the heat is generated where the current is flowing, right at the point of the breakdown, we can find where the problem is if only we have a method of identifying where the heat is located.

One's first thought may be a thermal camera, and that would indeed work, but three problems make it relatively impractical:
- Thermal cameras are expensive
- You need special microscope lenses designed to be apochromatic down to near infrared, which are also expensive
- The materials that make up an IC are relatively thermally conductive, and so the temperature differences we need to look at are quite small

So a thermal camera isn't the best option. But then, what else could we use?
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So we had a problem with an IC our company is in the process of designing, where you could only apply 18 volts across its power rails before it started to break down and conduct huge amounts of current (it's supposed to be powered by 25 volts)

this is a relatively complex device, so it was important to find out *where* on the die the anomalous current was flowing, so we could match that up with the layout and identify what part needs work

conveniently, however, all that current generates heat.
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someone remind us to ramble about it sometime when we have more energy
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it turns out the process of debugging a semiconductor die is *fascinating* and also what we've been doing at work the past couple weeks
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if there's oregano, is there also washingtano and californiano?
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one singular scissor
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