Influence of Bottom Electrodes on the Ferroelectric Stability of AlScN Film at High Temperatures

ABSTRACT The effect of high‐temperature annealing on the ferroelectric properties of AlScN films is studied using different bottom electrodes. When the bottom electrode has compressive residual stress, tensile strain develops in the AlScN layer after thermal annealing, while the compressive stress in the electrode relaxes. This reduces the switching barrier of AlScN, leading to a lower coercive field (E C ). Specifically, when a 90 nm‐thick HfN 0.4 thin film with strong (002) texture is used as the bottom electrode, significant tensile strain is applied to the AlScN layer after annealing due to the coherent AlScN/HfN 0.4 interface. The 700°C annealing also increases the defect concentration within the AlScN film, and these defects lead to a pronounced reduction in the E C , from 7.0 to 5.7 MV/cm. However, annealing at 900°C causes a phase transformation in the HfN 0.4 layer, which results in severe structural damage to the AlScN and leads to premature breakdown before polarization switching. Conversely, the thinner (< 30 nm) HfN 0.4 layer, lacking a clear (002) texture, prevents the formation of a coherent interface with the AlScN layer, resulting in minimal changes in E C and maintaining stable ferroelectric switching even after annealing at 900°C.