Fig. 4 (a) Endurance property under operation pulses (6 V, 20 ms) and (-4.5 V, 20 ms). (b) Retention property of the representative three conductance states.
The endurance and long-term retention property are also investigated, as shown in Fig. 4. The fatigue could be observed at 102~ 103 endurance cycles, but no dielectric breakdown was observed even after 106pulses, as shown in Fig. 4a . Three representative conductance states were selected for retention tests, and each state was monitored by a 3 V bias every 5 seconds. As seen from Fig. 4b , all the three states successfully lasted 1000 seconds without noticeable degradation at room temperature.