Improved Polarization-Retention-Endurance in Hf_0.5Zr_0.5O₂ Films by ZrO₂ Capping via Electrostatic Effects

Ferroelectric hafnia is one of the most promising materials for next generation of non-volatile memory devices. Several strategies have demonstrated to be of interest to improve its functional properties. Interface engineering, realized by the introduction of additional layer in the capacitor structure, is demonstrated as a promising strategy. However, interface layers can have multiple implications, such as changes in the chemistry of the interfaces and an increase of depolarization field, whose effects are difficult to discriminate. The role of HfO2 and ZrO2 capping is explored on polarization, retention, endurance, and leakage properties of Hf0.5Zr0.5O2 epitaxial films. In HfO2 capped films, lower polarization is observed, and endurance and retention are also comparably worse than in ZrO2 capped films. Complementary under illumination ferroelectric characterization and capacitance measurements indicate a reduction of defects and interface capacitance contribution in ZrO2 capped films. For both cappings, the interfaces with the Hf0.5Zr0.5O2 layer are shown to be compositionally sharp and the phase of Hf0.5Zr0.5O2 (HZO) grains is replicated on the capping layer, indicating that electrostatic effects prevail and that the use of interface layers with high permittivity, here ZrO2, is crucial to favor good functional properties.