Postcycling LRS Retention Analysis in HfO2/Hf RRAM 1T1R Device

Low resistance state (LRS) retention after 10<sup>4</sup> and 10<sup>6</sup> pulse cycles is compared to the uncycled LRS retention, based on the (40 × 40 nm)- HfO<sub>2</sub>/Hf bipolar RRAM devices in a 1T1R configuration. The LRS retention after 10<sup>4</sup> pulse cycles does not show degradation, while a larger failure bit tail is seen after 10<sup>6</sup> pulse cycles. The larger failure bit tail is found strongly related to the degradation of the cycled LRS state. From the LRS current fitting with a quantum point contact model, it is found that the total number of oxygen vacancies (V<sub>ox</sub>) in the filament decreases after 10<sup>6</sup> cycles, leaving a narrower switching constriction. The narrower switching constriction therefore suffers more from the self-diffusion of the (V<sub>ox</sub>)'s from the filament into HfO<sub>2</sub> bulk, and results in degradation of the LRS retention.

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