No surprise, SiC is very conductive.
These numbers look bad but note they're per cm, not per m as usual. Copper is ~4 W/cm/K.
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Interesting that it peaks around room temperature, then drops so sharply at higher temperatures. Not that you'll be able to operate so high, with a plastic packaged device.
What is it about plastic packaging that dies so suddenly at 150C+, anyway? Local expansion ripping the bondwires out? You can solder the buggers at nearly 300C, and they don't always fail. (Not that they necessarily use the same compound in TO-247s and SOT-23s.) Soldering likely has less gradient than operation, particularly under high heat fluxes --> high thermal gradient between die surface and backing plate. Maybe that's it.
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Silicon also peaks in conductivity, but lower (LN2 temps), and is only ~1.3 W/cm/K at RT. So you need bigger dies for the power alone, but more importantly, for the Rds(on) at Vds(max). Consequence: fuckoff massive Qg.
SiC just performs that much better, but also has yield problems (persistent defects -- screw defects IIRC, from the bulk substrate, even after epitaxy and annealing), making large area devices impractical.
I wonder if SiC transistors are any good as RF amps. Not going to threaten GaN of course, but Superjunction Si is already quite good, and damn cheap compared to the alternatives.
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
"John Larkin" wrote in message
news:78lptddgtam4jvoibfbh7b0kep46kdqs0k@4ax.com...
>
> I've been pushing (ie, blowing up) come Cree SiC power fets, the 1200
> volt 280 mohm part in TO247. It sure looks like thermal runaway.
>
> Just for fun I ground one down.
>
> https://www.dropbox.com/s/hnu2b7qlfw98bwq/Cree_Chip.JPG?raw=1
>
> No wonder it blows up. The actual chip is tiny, so all the heat is in
> one spot. Why bother to put it in that giant TO247 package?
>
> A healthy mosfet die would use most of the available area.
>
> https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?raw=1
>
> I've ordered some ST SiC parts. They have similar capacitance and
> twice the Rds-on, but Ron barely changes with temperature. The Cree
> Rds-on takes off radically with temperature, so the ST wins above
> 150C.
>
> I'll gring down an ST part too.
>
> We are considering getting an x-ray machine. It will inspect BGA
> solder joints and will count parts, loose in trays or on reels.
> Engineering could use it to snoop inside parts like this, maybe.
>
>
>
> --
>
> John Larkin Highland Technology, Inc
> picosecond timing precision measurement
>
> jlarkin att highlandtechnology dott com
> http://www.highlandtechnology.com
>