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Design >> RF Design >> instantaneous circuit breakdown
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Message started by aaron_do on Apr 24^th, 2013, 1:41am

Title: instantaneous circuit breakdown
Post by aaron_do on Apr 24^th, 2013, 1:41am

Hi all,

I have a high power circuit which breaks down in a matter of seconds upon slightly changing a bias voltage. Of the normal breakdown mechanisms experienced by mosfets, im thinking this is a gate dielectric breakdown. Other mechanisms which I know of are either result in slow degradation, or can be recovered from.

Are there any thoughts on this?

Thanks,
Aaron

Title: Re: instantaneous circuit breakdown
Post by RFICDUDE on Apr 24^th, 2013, 4:25am

Over voltage from drain to source could cause "punch through" where the D-S depletion regions run into each other and form a high conductance path.

I guess you could tell the difference between gate oxide breakdown and punch through by measuring the gate-source, gate-drain and drain source resistances. If the G-S and G-D resistance is high and D-S low then maybe it is punch through.

During the bias change does the gate voltage go up or down and what happens at the D and S during the change?

Title: Re: instantaneous circuit breakdown
Post by aaron_do on Apr 24^th, 2013, 8:05am

Hi RFICDUDE,

Unfortunately there's no way for me to check those things. However, isnt punchthrough recoverable from? I only made a small change in the bias point.

Thanks,
Aaron

Title: Re: instantaneous circuit breakdown
Post by RFICDUDE on Apr 24^th, 2013, 7:23pm

I suppose the recovery is totally dependent on the maximum current drawn under the condition.

I guess the question is "what changes a lot with a small change in bias?"

Accessing the breakdown voltage conditions are fairly straight forward. Beyond that, you would look at mechanism that exponentially increase current to the point of physical breakdown.

Title: Re: instantaneous circuit breakdown
Post by loose-electron on Apr 24^th, 2013, 8:38pm

got schematic, bias voltages and process limitations?

you want answers you got to give us information

Title: Re: instantaneous circuit breakdown
Post by aaron_do on Apr 24^th, 2013, 9:05pm

Hi all,

thanks for the replies.

I guess what I'm trying to say is that in my case, there's a tipping point. The current shouldn't change much as its just a small change in the biasing (and it actually shouldn't directly affect current anyway). Also, after the breakdown, the circuit no longer functions and there is a small leakage current from the supply.

From analyzing the circuit, its possibly a high VDS (punch through), a high VGD (gate dielectric), or even high current at high VDS (HCI). But my thinking is that if there isn't an enormous current, then the circuit should be able to recover from punch through. Also, HCI is more of a long-term degradation mechanism. That leaves gate dielectric breakdown. From personal experience, I feel that this is most likely the cause as the circuit will seem OK until the break point is reached, at which point it will just die...

So just curious if any other explanations are possible. Also, sorry that I can't provide schematics as its a little sensitive.

regards,
Aaron

Title: Re: instantaneous circuit breakdown
Post by Frank Wiedmann on Apr 25^th, 2013, 12:24am

Changing the bias point might result in positive feedback, perhaps based on effects that are not correctly included in your simulation models. Thermal runaway would be an example for such a problem.

Title: Re: instantaneous circuit breakdown
Post by aaron_do on Apr 25^th, 2013, 7:55am

Quote:

Changing the bias point might result in positive feedback, perhaps based on effects that are not correctly included in your simulation models. Thermal runaway would be an example for such a problem.

thanks. That might be a posibility too...

Aaron