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Sunday, February 20, 2011

Transistor: Heal Thyself!

On SolderSmoke Podcast #130 I mentioned that in the book "The Evening Star" by Henry S.F. Cooper, the author mentioned that during the Magellan mission to Venus, some of the chips on the spacecraft could somehow "heal themselves" after developing problems. Wow! Rigs that fix themselves. I don't know about that. That would kind of take us out of the troubleshooting game, right? Anyway, I was wondering how this "self healing" thing works. Hamilton, KD0FNR has some ideas:

Hi!

I just caught up on SolderSmoke and finished listening to episode 130. FB and great fun! Thanks! You asked a quesiton about logic circuits that had healed themselves on the Venus mission. I can't find an exact reference to it now, but when I interned at a particle accelerator during my MSEE work, engineers frequently talked about using gallium arsenide transistors because they were rad-hard and self-healing. Here's the idea as it was recounted to me in the early '90s:

Radiation can damage transistors by breaking the crystalline lattice inside the semiconductor. Self-healing transistors run very hot so that when a lattice site in the semiconductor crystal is broken by radiation it is 'fixed' by the crystal effectively melting around the broken site. It's similar to your halogen bulb/heat gun fix but on a transistor level and automatically.

I can't find an exact reference that confirms this explanation. The closest I could find was on wiki at: http://en.wikipedia.org/wiki/Radiation_hardening#Fundamental_mechanisms

Maybe other listeners can provide more detail.

Thanks for the mention of my QSO mapper on your show a few years ago! The mapper and my practice exams have continued to evolve and grow, and the latest of each can now be seen at:

Thanks again for the great work that you do!
-- 73 de KD0FNR Hamilton http://copaseticflows.appspot.com http://copaseticflow.blogspot.com

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