Experimental study of single-electron phenomena in silicon nanocrystal memories

In this paper we present experimental evidence for single-electron phenomena in solid-state memories based on silicon nanocrystals as storage elements. The stepwise evolution of the channel current of a written memory cell biased in the subthreshold regime is monitored by means of a purposely designed low noise acquisition system with a bandwidth of 1 kHz. Each channel current step-up is ascribed to a single-electron emission from the silicon nanocrystal to the silicon substrate and each current step-down is ascribed to a single-electron capture from the silicon substrate into the silicon nanocrystal. The effect of the measurement system bandwidth on the detection of single-electron events is discussed and a procedure for extracting the threshold voltage shift associated to these events is proposed. It is shown that single-electron charging and discharging events in a memory cell with an area of 4.5 x 10(-10) cm2 can cause threshold voltage shift at room-temperature of the order of several millivolts. Qualitative explanation for the observed threshold voltage shift distribution is given.