HfO_(2)-based ferroelectric thin film and memory device applications in the post-Moore era:A review

The rapid development of 5G,big data,and Internet of Things(IoT)technologies is urgently required for novel non-volatile memory devices with low power consumption,fast read/write speed,and high reliability,which are crucial for high-performance computing.Ferroelectric memory has undergone extensive investigation as a viable alternative for commercial applications since the post-Moore era.However,conventional perovskite-structure ferroelectrics(e.g.,PbZr_(x)Ti_(1-x)O_(3))encounter severe limitations for high-density integration owing to the size effect of ferroelectricity and incompatibility with complementary metal-oxide-semiconductor technology.Since 2011,the ferroelectric field has been primarily focused on HfO_(2)-based ferroelectric thin films owing to their exceptional scalability.Several reviews discussing the control of ferroelectricity and device applications exist.It is believed that a comprehensive understanding of mechanisms based on industrial requirements and concerns is necessary,such as the wake-up effect and fatigue mechanism.These mechanisms reflect the atomic structures of the materials as well as the device physics.Herein,a review focusing on phase stability and domain structure is presented.In addition,the recent progress in related ferroelectric memory devices and their challenges is briefly discussed.

Domain Wall Evolution in Hf_(0.5)Zr_(0.5)O_(2)Ferroelectrics under Field-Cycling Behavior

HfO_(2)-based ferroelectrics have evoked considerable interest owing to the complementary metal-oxide semiconductor compatibility and robust ferroelectricity down to a few unit cells.However,the unique wake-up effect of HfO_(2)-based ferroelectric films severely restricts the improvement of their performance.In particular,the domain structure is an important characteristic of ferroelectric materials,which still has not been well understood in HfO_(2)-based ferroelectrics.In this work,a Hf_(0.5)Zr_(0.5)O_(2) ferroelectric thin film is grown on a typical Si substrate buffered with TiN electrode.The 90°domains of the Pca21 ferroelectric phase with head-to-tail and tail-to-tail structures can be observed by Cs-corrected scanning transmission electron microscope under their pristine condition.After waking up,the 180°domain is displayed in the ferroelectric phase.The remarkable differences in domain walls for 90°and 180°domains are characterized by qualitatively mapping the polarization distributions at the atomic scale.The domain wall changes from the[101]of the Hf_(0.5)Zr_(0.5)O_(2) film to the[001]of the Hf_(0.5)Zr_(0.5)O_(2) film.This result provides fundamental information for understanding the domain structure of HfO_(2)-based ferroelectrics.

Robustly stable intermediate memory states in HfO_(2)-based ferroelectric field-effect transistors

Multilevel ferroelectric field-effect transistors(FeFETs)integrated with HfO_(2)-based ferroelectric thin films demonstrate tremendous potential in high-speed massive data storage and neuromorphic computing applications.However,few works have focused on the stability of the multiple memory states in the HfO_(2)-based FeFETs.Here we firstly report the write/read disturb effects on the multiple memory states in the Hf_(0.5)Zr_(0.5)O_(2)(HZO)-based FeFETs.The multiple memory states in HZO-based FeFETs do not show obvious degradation with the write and read disturb cycles.Moreover,the retention characteristics of the intermediate memory states in HZO-based FeFETs with unsaturated ferroelectric polarizations are better than that of the memory state with saturated ferroelectric polarization.Through the deep analysis of the operation principle of in HZO-based FeFETs,we speculate that the better retention properties of intermediate memory states are determined by the less ferroelectric polarization degradation and the weaker ferroelectric polarization shielding.The experimental and theoretical evidences confirm that the long-term stability of the intermediate memory states in HZO-based FeFETs are as robust as that of the saturated memory state,laying a solid foundation for their practical applications.