Retention Improvement of HZO-Based Ferroelectric Capacitors with TiO2 Insets.

ABSTRACT

The influence of the bottom TiO2 interfacial layer grown by atomic layer deposition on the ferroelectric properties of the TiN/Hf0.5Zr0.5O2/TiN capacitors is systematically investigated. We show that the integration of the TiO2 layer leads to an increase in the polar orthorhombic phase content in the Hf0.5Zr0.5O2 film. In addition, the crystalline structure of the Hf0.5Zr0.5O2 film is highly dependent on the thickness of the TiO2 inset, with monoclinic phase stabilization after the increase of TiO2 thickness. Special attention in this work is given to the key reliability parameters-retention and endurance. We demonstrate that the integration of the TiO2 inset induces valuable retention improvement. Using a novel approach to the depolarization measurements, we show that the depolarization contribution to the retention loss is insignificant, which leaves the imprint effect as the root of the retention loss in TiN/TiO2/Hf0.5Zr0.5O2/TiN devices. We believe that the integration of the insulator interfacial layer suppresses the scavenging effect from the bottom TiN electrode, leading to a decrease in the oxygen vacancy content in the Hf0.5Zr0.5O2 film, which is the main reason for imprint mitigation. At the same time, although the observed retention improvement is very promising for the upcoming technological integration, the field cycling testing revealed the endurance limitations linked to the phase transitions in the TiO2 layer and the rise of the effective electric field applied to the Hf0.5Zr0.5O2 film.