On the Charge Sheet Superjunction (CSSJ) MOSFET

This paper provides more insight into the operation of the charge sheet superjunction (CSSJ) proposed recently, whose specific on-resistance for a given breakdown voltage is even lower than that of a Superjunction (SJ). It is shown how the SJ and the CSSJ both evolve from a simple Gamma-shaped p+-n junction in which the heavily doped region surrounds the lightly doped region; the peak field in such a 2-D junction is less than that in a plane junction. The phenomena underlying the I- V and C -V characteristics of the CSSJ MOSFET are clarified with the help of charge and potential simulations. A simple analytical model is developed for the drain-source capacitance of the CSSJ MOSFET; the model is shown to apply to SJ MOSFET as well. It is argued that the insulator charges providing the charge sheet essential for CSSJ operation will not present the same reliability problems as those due to trapped charge in the gate insulator of small-signal MOSFETs; this is because the insulator field distribution in a CSSJ differs significantly from that in a small-signal MOSFET. The insight provided in this paper should build a strong motivation for the practical implementation of the new structure.

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