Measurement of the effect of write-erase cycling on noise in MNOS memory transistors

p-channel MNOS memory transistors with 25-Å oxide, 550-Å nitride are investigated. Changes in memory characteristics such as high-conductivity and low-conductivity threshold voltages are examined as a function of the number of write-erase cycles taking the amplitude and the duration of the pulses as parameters. Simultaneous measurements of the channel carrier mobility and low-frequency noise spectrum give new information. Changes in noise properties after cycling depend on the amplitude and duration of the write-erase pulses. Beyond about 10⁶write-erase cycles the memory window decays, the channel carrier mobility drops, while the noise exhibits a spectrum in the lowest frequency region. Experimental results are interpreted by the formation, during cycling, of a high density of hole traps distributed in energy and located inside the insulators near the oxide-nitride interface.