Interface engineering of oxidized Mo electrodes for imprint stability and enhanced endurance in hafnia-based ferroelectric devices

Abstract

Engineering stable electrode interfaces is crucial for achieving reliable hafnia-based ferroelectric devices for next-generation nonvolatile memory applications. In particular, imprint—a bias-induced shift of the polarization–electric field (P–E) hysteresis—can severely impact device stability. Here, we systematically compare tantalum nitride (TaN) and oxidized molybdenum (MoO_x) bottom electrodes with MoO_x-rich surfaces in metal–ferroelectric–metal capacitors to elucidate the role of interface electronic structures and work function in modulating imprint behavior, endurance, and tunneling performance. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses reveal that short-time high-temperature oxidation of Mo produces Mo⁶⁺-rich surfaces with work functions exceeding 5.5 eV, significantly suppressing charge trapping and oxygen vacancy migration at the HZO interface. Capacitors with MoO_x-rich electrodes maintain stable imprint voltages and remanent polarization over 10⁶ switching cycles, while TaN-based devices exhibit significant imprint evolution and polarization degradation. Interface trap density measurements confirm that oxidized Mo electrodes achieve a nearly 55% reduction in trap formation compared to TaN counterparts after extended cycling. Furthermore, in ferroelectric tunnel junctions (FTJs), MoO_x-rich electrodes enable stable diode-like behavior, high tunneling electroresistance (TER), and robust endurance with minimal degradation up to 10⁷ cycles. These results demonstrate that oxidized Mo electrodes with MoO_x-rich surfaces provide chemically stable, high-work-function interfaces that effectively mitigate degradation mechanisms, offering a robust strategy for enhancing the performance, reliability, and scalability of ferroelectric memory and logic devices.