On Thu, 6 Apr 2017 22:23:43 -0400, you wrote: >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.
I mentioned this in connection with some manufacturers using gold doping in transistors which would not normally be expected to have gold doping. So you end up with a bunch of lessor named 2N3904s which meet the 2N3904 specifications but are useless if you were looking for low leakage diodes. >> 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. I thought there was a more sophisticated way but that sure sounds like something Tektronix would have done for grading parts. The JEDEC standard is probably what I need to find or at least start with. Thank you for the tip. >> 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 If they are not being tested, then where is the maximum specified leakage number coming from? For a small signal bipolar transistor it will typically be 25nA, 50nA, or 100nA, but the InterFET datasheet (1) shows 10pA maximum and 1pA maximum for the A versions. When this discussion of low leakage input protection started, I did a quick search for inexpensive alternatives to the 4117/4118/4119 JFETs and came up with nothing; all of the inexpensive JFETs are much worse until you get to premium devices. (1) I only picked the InterFET datasheet because it was the most readily available of the ones you mentioned. The current Fairchild and Linear Systems datasheets show the same thing. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
