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231Power Semiconductors

suffer this disadvantage because their current fl

ow is in the form of majority carriers. The

mobility of majority carriers in silicon decreases with increasing temperature.

This inverse relationship dictates that the carriers slow down as the chip gets hotter. In

effect, the resistance of the silicon path is increased, which prevents the concentrations of

current that lead to hot spots. In fact, if hot spots do attempt to form in a MOSFET, the

local resistance increases and defocuses or spreads out the current, rerouting it to cooler

portions of the chip.

Because of the character of its current fl