I have read that electrostatic charges produced by human body can be as high as up to a several thousand volts.
How exactly damage of transistors happens
MOSFET NPN
Electrostatic voltage applied to the drain or source thus causing a reverse biasing of either PN junction with a voltage > breakdown voltage
BJT NPN
Electrostatic voltage applied to emitter or collector thus causing collector-base or emitter-base be in a reverse bias with a voltage > breakdown voltage
Am I correct?
Then, why FETs are subjects to be damaged in particular. I often hear about protection against electrostatics for FETs, but for BJT not so often, and not in mention for diodes, also very rare, although they are also PN junction devices.
Best Answer
At the moment of discharge, there is current flowing from the charged object, through the transistor, and finally to ground or other lower potential.
Ohm's law is in effect here, and the higher the resistance, the higher will be the voltage observed across the two terminals of the "device under destruction".
FET's have a very high resistance on their gate lead. For MOS FET's, that resistance is extremely high. A BJT has a much lower resistance, although, when you are dealing with static discharge, there's no assurance you won't blow that up as well.
As a side effect, BJT circuits usually have relatively small resistors across their terminals to bias the device, and that will limit the IR drop even further.