Second (or step 2), a negative pulse is applied to create the con

Second (or step 2), a negative pulse is applied to create the conducting filament at LRS (approximately 20 kΩ). A negative forming voltage, which determines the conducting filament size, is reduced learn more from 2.6 to 1.1 V with a 100-ns pulse width. However, a conventional negative forming voltage (-2.6 V) is shown in blue line, this changes HRS (approximately 15 MΩ) to LRS (approximately 10 kΩ). Quantum-size effect and percolation models of RESET for different

switching materials have been explained to understand the conducting filaments [135, 136]. Another method of reducing CC can be used to control the conducting filament size, which can be achieved by adjusting the resistivity of the bulk TaO x layer. The resistivity can reduce the forming current by controlling the oxygen Pinometostat mouse content of TaO x [120]. In this case, the conducting filament size becomes smaller and oxygen vacancy becomes larger when the oxygen content is increased. The observed switching is due to the change of barrier RAD001 mw height on the application of voltage. When positive voltage was applied, O2- ions migrate from bulk and accumulate near the TE. Oxidation reaction increases the barrier height and device comes to the HRS. On the other hand, when negative voltage was applied on the TE, O2- ions move away from TE and reduction reaction lowers the barrier height which brings the device into LRS. Hence, the barrier height change

on the application of bias voltage due to redox reaction is responsible for the observed switching.

Several kinds of electrode materials were examined and found that the materials having high work function show stable resistance switching behavior. The significant for improvement in the retention characteristics at 150°C under the small current operation of 80 μA by two-step forming are obtained as compared to single-step forming. Two-step electroforming process is very critical to have controlled conducting filament diameter as well as the RRAM could be operated as low current at 80 μA. The W/TiO x /TaO x /W memory device showed good bipolar resistive switching characteristics with different CCs from 10 to 100 μA (Figure 12[41]). The low-resistance state decreases with increasing CCs from 10 to 100 μA (Figure 12a,b), which will be useful for multi-level data storage applications. As the filament diameter increases with higher CCs, the low-resistance state decreases, and the value of RESET voltage increases. The RESET current can be scaled down to 23 μA at a low CC of 10 μA. Figure 13a,b shows the device-to-device uniformity of LRS/HRS and SET/RESET voltage, respectively. The cumulative probability distribution is small for both LRS/HRS as well as set/reset voltage. The resistance ratio of HRS/LRS is >100, and the device can be operated below ±5 V. The device can be switched more than 104 AC cycles with stable LRS, as shown in Figure 14a.

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