Measured reverse base damage of NPN

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I remember there was some discussion if low reverse currents can damage
a bipolar transistor. I got a new toy (HP 4142B with 3 SMUs) and did
some quick testing.

It seems that even 1uA reverse current starts to destroy the
transistor. Here's a graph that shows hFE as a function of amp-seconds
from the base:
https://plot.ly/~msyrjala/3/#/

I also did an another test with 0.1 for 2000s and 1mA for 2000s:
https://plot.ly/~msyrjala/9/

The reverse voltage increased during the test from 7.5 to 7.9V
https://plot.ly/~msyrjala/11/#/

The quick test was limited to 2000s, i.e. 2mAs, but I'll do a longer run
to see if the detoriation depends on the charge only or does current
have some effect.

(Unfortunately transistors _were_ harmed during the tests.)

--
mikko OH2HVJ

Re: Measured reverse base damage of NPN
On 10/17/2018 10:10 AM, Mikko OH2HVJ wrote:
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Were they new transistors out of the box? Can the graphs be explained by  
something other than physical damage to the structure like  
charge-storage effect or some kind of wear-in process that would occur  
when a new transistor is used in any configuration?

Re: Measured reverse base damage of NPN
On 10/17/2018 10:52 AM, bitrex wrote:
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Forward-active beta varies for different amounts of constant current  
thru the base-emitter junction there's nothing unusual about that. AFAIK  
it doesn't matter which direction the current is going to affect it.

Re: Measured reverse base damage of NPN

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Yes, they were out of the box. The effect was visible even after hours
no backwards BE current, I would expect any charge storage to clear
within that time - on the other hand heating seems to help.

Here's one paper I found about the subject - it mentions 'interface states
created in the oxide over the emitter-base junction during the stress'
as being one generally assumed reason for additional base current.

http://downloads.hindawi.com/journals/apec/2001/053209.pdf

I guess the interface/surface states could be cleared up by heat ?

So - add a heater or cover your bases!

--
mikko

Re: Measured reverse base damage of NPN
Mikko OH2HVJ wrote:
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   It is well known (since before the Apollo mission) that the damage  
can be annealed out.

Re: Measured reverse base damage of NPN
On 10/18/2018 01:54 AM, Robert Baer wrote:
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Yeah it just seemed like an awful large droop for such a small amount of  
charge which is why I was trying to explore whether it could be  
accounted for by a measurement error.

Re: Measured reverse base damage of NPN

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1uA, to 0.05 A*s:
https://plot.ly/~msyrjala/17/

100/1000uA
https://plot.ly/~msyrjala/9

The resolution of the latter graph is not that good, but to me it looks
like the 1uA current causes damage slower.

--
mikko

Re: Measured reverse base damage of NPN
On 10/17/18 10:10 AM, Mikko OH2HVJ wrote:
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Yikes.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Measured reverse base damage of NPN

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recovers.




Re: Measured reverse base damage of NPN

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...

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Don't have a heating chamber at home, using the one in kitchen for
electronics causes distortion and our sauna at home has a hard limit

next to plastic.

hFE curves before heating (hFE~10%5 for Ic=1mA, Vce=3V)
https://plot.ly/~msyrjala/13/

The performance drop at low currents is especially gruesome!

After heating (hFE~17%7 for Ic=1mA, Vce=3V)
https://plot.ly/~msyrjala/15/

Heat cures!

--
mikko OH2HVJ


Re: Measured reverse base damage of NPN
On Wednesday, October 17, 2018 at 2:39:29 PM UTC-4, Mikko OH2HVJ wrote:
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t  
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Fun... here's a silly question.  
Can you cure 'em with C-E voltage/current heating?  

Heal thyself, physician.  

George H.

Re: Measured reverse base damage of NPN
On 10/17/18 1:38 PM, tom wrote:
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Pease says someplace that Widlar used to use his cigar on metal can  
transistors for exactly this.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: Measured reverse base damage of NPN
On Thursday, October 18, 2018 at 6:23:33 AM UTC+11, Phil Hobbs wrote:
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ge
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run

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There was reputed to be an HP pulse generator which worked much better afte
r the service engineer stubbed out his cigarette on the output transistor.

Other people's cigarettes worked equally well.

--  
Bill Sloman, Sydney

Re: Measured reverse base damage of NPN
Mikko OH2HVJ wrote:
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   You may find that the amount of measurable damage depends on the  
product of time and revers current, not unlike radiation damage or ionic  
contamination.


Re: Measured reverse base damage of NPN
On Wednesday, October 17, 2018 at 10:10:16 AM UTC-4, Mikko OH2HVJ wrote:
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downloads.hindawi.com/journals/apec/2001/053209.pdf

Re: Measured reverse base damage of NPN
On 17/10/2018 15:10, Mikko OH2HVJ wrote:
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Good work! Last year I did a few simple experiments too and noticed the  
same rapid initial decline in beta which then tends to level off. But I  
never thought to look for changes in breakdown voltage.

piglet


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