Role of electrode-induced oxygen vacancies in regulating polarization wake-up in ferroelectric capacitors

TiN/Hf_0.5Zr_0.5O₂ (HZO) is a popular heterostructure for HZO-based ferroelectric devices. In this study, in-situ synchrotron X-ray techniques were used to examine the ferroelectric wake-up effect of HZO in relation to TiN electrodes. TiN was shown to favor orthorhombic (O)/ferroelectric phase of HZO, while promoting the reconstruction of the TiN/HZO interface through the formation of oxygen vacancy (V_O^′′) states. Real-time changes in polarization under an applied voltage (electrical stress) indicated that V_O^′′ regulates the observed ferroelectric wake-up effects. The changes observed using in-situ X-ray analysis included an intensification of the V_O^′′ signal and the breaking of Hf-O bonds under electrical stress over a period of 1000 s. Stress-driven V_O^′′ increased polarization without degrading the interface, as indicated by the capacitance–voltage (C-V) characteristics of the device. It appears that V_O^′′ woke up HZO polarization without introducing any structural transitions. Despite the fact that V_O^′′ formed concomitantly with the O-phase following TiN capping, it appears that V_O^′′ plays an independent role in regulating polarization under an applied electrical field. Thus, V_O^′′ creates a trade-off between polarization wake-up enhancement and trap states. Furthermore, the results of cyclic polarization-voltage (P-V) measurement show that stress-induced V_O^′′ near the TiN/HZO interface is conducive to enhancing the ferroelectricity with fewer wake-up operation cycles.