Reliability of MNOS integrated circuits

Recent advances in silicon nitride deposition techniques have led to the metal-silicon nitride-silicon dioxide-slilicon (MNOS) integrated circuit technology as an alternative and supplement for the existing MOS technology. Applications of MNOS field effect transistors have been proposed for both logic circuits (as an alternative for stable MOS transistors) and non-volatile memory arrays. The MNOS transistor for logic circuit applications combines the low surface state density of the thermal oxide (300 -- 500 Å) -- silicon interface with the passivation properties and high dielectric constant of the silicon nitride layer (500 -- 700 Å). On the other hand the same basic transistor structure with a thin thermal oxide (∼50 Å) has recently been shown to exhibit hysteresis behavior of turn on voltage as a function of applied gate voltage, resulting from charge storage at the silicon nitride-silicon dioxide interface. The storage function associated with the hysteresis characteristic leads to the potential application of variable turn on voltage MNOS transistors in random access and alterable read only semiconductor memories.