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

Low resistance state (LRS) retention after 10
⁴
and 10
⁶
pulse cycles is compared to the uncycled LRS retention, based on the (40 × 40 nm)- HfO
₂
/Hf bipolar RRAM devices in a 1T1R configuration. The LRS retention after 10
⁴
pulse cycles does not show degradation, while a larger failure bit tail is seen after 10
⁶
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
_ox
) in the filament decreases after 10
⁶
cycles, leaving a narrower switching constriction. The narrower switching constriction therefore suffers more from the self-diffusion of the (V
_ox
)'s from the filament into HfO
₂
bulk, and results in degradation of the LRS retention.