The MNOS bipolar transistor

Charge-storage effects in MNOS structures have been investigated with regard to application in programmable read-only semiconductor memories utilizing the insulated-gate field-effect transistor as the active circuit component. The surface-potential dependence of both base and collector current in a suitably designed bipolar transistor, however, can be combined with the charge storage effects of the MNOS gate to provide a programmable bipolar transistor. By means of the stored charge in an MNOS gate over the emitter-base junction of a bipolar transistor, the base surface beneath the gate can be stably shifted from accumulation to inversion with the inversion layer beneath the gate of a suitably designed transistor acting as an efficient extention of the emitter junction. This results in a designable increase in collector cmrent at fixed forward emitter-base bias. Examples of both n-p-n and p-n-p transistors performing in this manner are given. The principal advantage of this type of device over conventional MNOS devices lies in its inherent higher transconductance. Performance comparisons between the read speed of conventional MNOS devices and that of the bipolar MNOS will be presented.