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

Abstract

Low resistance state (LRS) retention after 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> pulse cycles is compared to the uncycled LRS retention, based on the (40 × 40 nm)- HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Hf bipolar RRAM devices in a 1T1R configuration. The LRS retention after 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> pulse cycles does not show degradation, while a larger failure bit tail is seen after 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ox</sub> ) in the filament decreases after 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cycles, leaving a narrower switching constriction. The narrower switching constriction therefore suffers more from the self-diffusion of the (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ox</sub> )'s from the filament into HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk, and results in degradation of the LRS retention.