Memristors have emerged as promising candidates for non-volatile memory, neuromorphic computing, and logic applications, owing to their distinctive resistive switching (RS) behavior. The electrical performance and reliability of memristors are critically influenced by the insulating material in the metal-insulator-metal (MIM) stack. Among various oxide-based insulators, hafnium dioxide (HfO₂) [1] and aluminum oxide (Al₂O₃) [2] have been extensively studied in valence change mechanism (VCM)-based memristors, where a Ti scavenging layer facilitates the formation and migration of oxygen vacancies. However,optimizing the thickness and combination of these oxides remains a challenge. A major limitation in memristor technology is variability, which occurs both device-to-device and cycle-to-cycle (within the same device), compromising the switching uniformity, endurance, and long-term stability. This work investigates the impact of HfO₂ and Al₂O₃ thickness on the resistive switching performance of TiN/10 nm Ti/insulator/W memristors (Fig. 1). Different insulator stack configurations were evaluated to analyze device-to-device and cycle-to-cycle variability (Fig. 2) and the stability of the resistive switching behavior (Fig. 3). The results provide valuable insights into how both the combination of HfO₂ and Al₂O₃, and the HfO₂ thickness, influence the formation and migration of oxygen vacancies, ultimately affecting the reliability and long-term performance of the devices.