When can we say that transistor suffers from OVERSTRESS?

[allennlowaton]

Good day guys.
I am curious to know about this overstress occurring in the transistors.
I have read somewhere that when 2VDD is detected on the gate, overstress had occurred already.
Please share your valuable insights regarding this.

Thank you.

 

[embeddedlover]

When you excessive voltage due to high potential chance of high current flowing through the device is high causing overstress...
If u take the case of amplifier we have active, cut off, saturation regions....
If u operate transistor in saturation region for more time there is chance of damage....(which we call p1bB, p3dB points)

 

[eladla]

I never heard the term overstressed used, but there are several issues with overbiasing a MOS transistor.
One problem is hot electron injection - where electrons (or holes, but less common because of smaller mobility) travel very fast near the drain side and colide and become embedded in the oxide layer.
This is a problem because for each electron that is embedded in the oxide, we will need to have an extra hole to compensate for it at the gate node. i.e. Vth goes up with enough trapped electrons!
Other problems are oxide break down, due to very high vertical electrical field. If the oxide physically breaks down, the capacitance between the gate and channel is gone and the field-effect is dead.
Hope this is what you were looking for.

 

[embeddedlover]

Overstressed is a terminology used incase of applying something to any device beyond it's limits.....
We havn't heard it because it was never mentioned in our good old text books....
Now it is commonly used in datasheets & articles too....term may not sound technical but gives clear understanding....

 

[eladla]

I get what you are saying, but the problem with non-technical terms is that it`s not always clear how they link in to the technical terms.
If I see the word overstress voltage on a datasheet, I`ll ask myself "Is this distructive? Does the device break down? What type of breakdown?"
and if it breaks down, why not just call it a breakdown?
If someone tells you "Your device has been overstressed!" What does that mean exactly?
Should I toss my transistor in the trash or should I just make it a cup of hot cocoa and give it a foot massage?
In the same process a huge power transistor might be ok with 2Vdd, and a minimal feature size NMOS might be toast. There is no real rule of thumb.
I don`t see the point of dumbing down EE. We are all pros and should be able to handle this information.

 

[embeddedlover]

Here it is basically effect & cause relationship....

Finally as you told it is breakdown but the cause is overstress....
what happened in overstress is all you have explained....

There is no specific terminology other than overstress to explain a condition when it is operated out of range of specifications....