Access Rate-Dependent Endurance Behavior of Ferroelectric Hafnium Zirconium Oxide Capacitors
Fluorite-structured ferroelectrics, such as hafnium zirconium oxide ($Hf_{1-x}Zr_{x}O_{2}$), are among the most promising materials for developing the next generation of low-power nonvolatile memories. Emulating realistic operating scenarios for ferroelectric memories requires performing access rate-dependent endurance tests. The access rate-dependent reduction of the switched polarization cannot be described as a mere superposition of fatigue and imprint effects, which are observed in conventional endurance and retention tests, respectively. The interplay between these degradation mechanisms and its correlation with the delay time in between the programming pulses remains unclear. Combining electrical testing through voltage pulses with ab initio and drift-diffusion simulations provides a comprehensive perspective on the microscopic origin of the access rate-dependent reduction of the switched polarization of ferroelectric capacitors based on product-relevant 5 nm thick $Hf_{0.5}Zr_{0.5}O_{2}$ films. The role of oxygen vacancy defects accumulating at the electrode-ferroelectric interface with delay time in reducing the fraction of switchable domains is elucidated considering electron transfer processes which change the defect charge state. Building upon this theoretical understanding, a physics-based model to extrapolate the long-term access rate-dependent endurance performance is developed and experimentally verified for temperatures up to 135°C and delay times up to 2 ms.