Designing Wake-Up Free Ferroelectric Capacitors Based on the HfO2/ZrO2 Superlattice Structure

The wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at a higher temperature has been reported to be effective in eliminating wake-up, but high temperature may yield the monoclinic phase or generate more oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of Hf0.5Zr0.5O2 (HZO) superlattice ferroelectrics, which involves heating from the Pt/ZrO2 interface side. It is demonstrated that 600 degrees C annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up free nature and a switchable remnant polarization value of 27.4 mu C cm(-2). On the other hand, heating from the TiN/HfO2 side, or using 500 degrees C annealing temperature, could yield ferroelectric devices that require a wake-up process. The special configuration of Pt/ZrO2 is verified by comparative studies with several other superlattice structures and HZO solid-state solutions. It is discovered that heating from the Pt/HfO2 side at 600 degrees C leads to high leakage current and a memristor behavior. The mechanisms of ferroelectric phase stabilization and memristor formation have been discussed. The unidirectional heating method can also be useful for other hafnia-based ferroelectric devices.