An improved NMOS controlled thyristor

Earlier work has shown that a traditional NMOS MCT (MOS controlled thyristor) is not a viable concept. The advantage of the higher current handling capability of the NMOS transistor, as compared to PMOS, is lost because of the presence of a parasitic bipolar transistor giving a shorting effect of the n-emitter/p-base junction. It is shown that this can be avoided by the introduction of a p-doped layer beneath the source and drain areas. This will decrease the current gain of the parasitic bipolar transistor. Devices have been fabricated and characterized. It was found that the geometry and doping levels of the NMOS MCT cells and the buried layer must be selected very carefully so as not to cause any degradation of the thyristor on-state behavior or turn-off action