HfO₂-based resistive random-access memory (RRAM) with a Ti buffer layer has been extensively studied as an emerging nonvolatile memory (eNVM) candidate because of its excellent resistive switching (RS) properties and CMOS process compatibility. However, a detailed understanding of the nature of Ti thickness-dependent RS and systematic thermal degradation research about the effect of post-metallization annealing (PMA) time on oxygen vacancy distribution and RS performance still needs to be included. Herein, the impact of Ti buffer layer thickness on the RS performance of the Al/Ti/HfO₂/TiN devices is first addressed. Consequently, we have proposed a simple strategy to regulate the leakage current, forming voltage, memory window, and uniformity by varying the thickness of the Ti layer. Moreover, it is found that the device with 15 nm Ti shows the minimum cycle-to-cycle variability (CCV) and device-to-device variability (DDV), good retention (10⁵ s at 85 °C), and superior endurance (10⁴). In addition, thermal degradation of the Al/Ti(15 nm)/HfO₂/TiN devices under different PMA times at 400 °C is carried out. It is found that the leakage current increases and the forming voltage and memory window decrease with the increase in PMA time due to the thermally activated oxidation of the Ti. However, when the PMA time increases to 30 min, the Ti can no longer capture oxygen from HfO₂ due to the formation of self-limited TiO_x. Therefore, the device shows superior thermal stability with a PMA time of 90 min at 400 °C and no degradation of the memory window, uniformity, endurance, or retention. This work demonstrates that the Ti/HfO₂-based RRAM shows superior back-end-of-line compatibility with high thermal stability up to 400 °C for over an hour.

Al alloying/doping in HfO₂-based resistive random-access memory (RRAM) has been proven to be an effective method for improving the low-resistance state (LRS) retention. However, a detailed understanding of Al concentration on oxygen vacancy migration and resistive switching (RS) behaviors still needs to be included. Herein, the impact of Al concentration on the RS properties of the TiN/Ti/HfAlO/TiN RRAM devices is addressed. Firstly, it is found that the forming voltage, SET voltage, and RESET voltage can be regulated by varying the Al doping concentration. Moreover, we have demonstrated that the device with 15% Al shows the minimum cycle-to-cycle variability (CCV) and superior endurance (over 10⁶). According to density-functional theory (DFT) calculations, it is found that the increased operation voltage, improved uniformity, and improved endurance are attributed to the elevated migration barrier of oxygen vacancy through Al doping. In addition, LRS retention characteristics of the TiN/Ti/HfAlO/TiN devices with different Al concentrations are compared. It is observed that the LRS retention is greatly enhanced due to the suppressed lateral diffusion process of oxygen vacancy through Al doping. This study demonstrates that Al alloying/doping greatly affects the RS behaviors of HfO₂-based RRAM and provides a feasible way to improve the RS properties through changing the Al concentration.

This work systematically investigates the impact of a pre-annealed ZrO₂ interfacial layer on the ferroelectric behavior of Hf_0.5Zr0.₅O₂ (HZO) capacitors. The remanent polarization (2Pr) value of HZO capacitors, including configurations such as W/HZO/TiN/p⁺ Si, W/HZO/(pre-annealed) ZrO₂/TiN/p⁺ Si, W/HZO/SiO₂/TiN/p⁺ Si, and W/HZO/SiO₂/p⁺ Si, exhibits significant variations. The W/HZO/(pre-annealed) ZrO₂/TiN/p⁺ Si capacitor demonstrates superior ferroelectric performance, with a 2Pr value of ~32 µC/cm². Furthermore, by optimizing the thickness combination of HZO and the pre-annealed ZrO₂ interfacial layer, a capacitor with a 10 nm HZO and 2 nm ZrO₂ achieves the largest 2Pr value. The pre-annealing process applied to ZrO₂ is found to play a very important role in inducing the orthorhombic phase and thus enhancing ferroelectricity. This enhancement is attributed to the pre-annealed 2 nm ZrO₂ interfacial layer acting as a structural guide for the subsequent HZO orthorhombic phase, thereby improving the ferroelectric performance of HZO capacitors. These findings provide a comprehensive explanation and experimental verification of the impact of pre-annealed ZrO₂ on ferroelectric devices, offering novel insights for the optimization of ferroelectric properties.