Field- and Temperature-Induced Drift in Multi-Level Al-Doped HfO2 RRAM

Abstract

Drift of multi-level conductance states is a key reliability concern for resistive random access memory (RRAM) used in multi-level storage and in-memory computing applications. This work experimentally quantifies how repeated read operations and elevated-temperature storage reshape multiple conductive states in Al5%:HfO₂-based RRAM cells. Systematic read-disturb and multi-temperature retention experiments are performed on one-transistor-one-resistor (1T1R) arrays, and their evolution is analyzed through intra-level transition matrices and a distance-weighted reshuffling factor $F_{r}$ that jointly capture internal reshuffling dynamics beyond median and spread. Read-disturb exhibits a pronounced voltage dependence, with increasing reshuffling as $V_{\mathrm {RD}}$ rises, whereas retention shows a two-phase thermal evolution dominated by an early warm-up reshuffling followed by a slower isothermal regime. Comparing incremental step pulse and verify algorithm (ISPVA) and one-shot programming (OSP) under identical targets and read-stress conditions further shows that both algorithms experience redistribution, but with different directionality and level dependence. These results clarify the distinct statistical signatures of field- and temperature-induced drift and identify the programming algorithm, read-voltage budget, and warm-up handling as key design knobs to improve the number of reliable levels in multi-level RRAM arrays.