Effect of static charge imbalance on forward blocking voltage of superjunction power MOSFET

The superjunction power device will carry high currents in on-state and also switch from off to on state and vice versa. Gate voltage, above threshold will inject a large amount of majority carriers through the n drift region depending on the drain voltage. This will create an on state charge imbalance condition in the device affecting its forward blocking voltage (FBV). In order to study the effect of the on-state charge imbalance, investigation of the I_D-V_D characteristics of CoolMOS up to the first breakdown is carried out for all the three cases drift layer doping densities with the help of simulation by 1) N=P, 2) P>N and 3) N>P. It is observed here that there is a considerable effect on the FBV of the CoolMOS in all three cases. Investigation using potential contours and electric field profile is also carried out to analyze this effect. In order to summarize the ON state and. OFF state charge imbalance behavior at one glance for all the three cases, we have defined a new curve FBV-V_G for SJ MOSFET.