Ultrashort SONOS memories

We report the operational characteristics of ultrashort SONOS memories down to ∼30-nm effective gate length. Good sub-threshold swing, good drain-induced barrier lowering (∼120 mV/decade), and ∼2.4 V of memory window down to the smallest dimensions demonstrate the improvements that result from a thin tunneling oxide and a large trapping center density. The use of distributed defects and thin tunneling oxide is reflected in a memory window that is stable up to at least 10⁵ cycles for the smallest devices. The smallest structures tested employ ∼75 electrons for memory storage, which allows for device to device reproducibility. The capture and emission processes asymmetries point to the differences in the energy parameters of the two processes. The smallest structures, however, do show loss of retention time compared to the larger structures, for the same oxide-nitride-oxide stack thickness, and this is believed to arise from higher leakage due to higher defects distribution in the gate insulators from process-induced damage. All tested devices, down to ∼30-nm effective gate length, show very good endurance characteristics.