David wrote:
I know one thing to watch out for if you are looking for low leakage is gold doping
Anything that increases carrier mobility increases leakage current (all else equal -- i.e., for each particular device geometry). This accounts for the much higher leakage of Schottky and germanium junctions.
Out of curiosity, and I tried to look this up years ago, what doping is used for PNP RF transistors and saturated switches if it is not gold? Does it also increase leakage?
Gold doping doesn't affect the speed of BJTs in the active region very much -- its purpose is to reduce minority carrier lifetime and, thereby, to reduce storage time when a transistor recovers from saturation. I'm not sure how manufacturers deal with this in the case of PNPs. [Note that the list of fast PNP small-signal switching transistors is very short, and the fastest of them are slower than the slowest fast NPN switches.]
And I have another question if you know. How is rb'Cc measured?
One way is to drive the transistor with a medium-high frequency (well down the 1/f portion of its current gain curve -- typically 10-50MHz for small-signal BJTs) and measure the base-collector phase shift. It can also be calculated from fT and Cc-b. There is a JEDEC standard for measuring rb'Cc, but I'm not finding my copy at the moment. It may be posted on the JEDEC web site.
The advantage of the 4117/4118/4119 is that the leakage is already tested to a given specification so no qualification or testing is necessary.
That may be true, but there is nothing in the data published by Vishay, Fairchild, Calogic, or InterFET to indicate this. Spot-checking, along with the part design, should be sufficient to guarantee meeting the spec. I'll try to remember to ask the Vishay process engineer next time I talk to her.
Best regards, Charles _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
