Scattering parameter approach to power MOSFET design for EMI

Electromagnetic interference (EMI) noise by avalanche oscillations is the major barrier to improve power device performance. Especially the oscillations of three-terminal devices are more complex than two-terminal devices in point of the mutual relationship between devices and external circuit. Scattering parameter (S-parameter) under avalanche condition is obtained to establish stable-unstable criterion with stability factor (K-factor). The stable-unstable criterion clearly indicates the unstable frequency range with each change in MOSFET design. In addition the oscillation mechanism on power MOSFET is modeled with junction capacitance, which is the same as that of diode. For EMI suppression, resonant frequency of external circuit has to be different from unstable frequency of MOSFETs.