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

TiN/Hf0.5Zr0.5O2 (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.