Mesoscopic-scale grain formation in HfO2-based ferroelectric thin films and its impact on electrical characteristics

Abstract

Ferroelectric memory devices are expected for low-power and high-speed memory applications. HfO2-based ferroelectric is attracting attention for its CMOS-compatibility and high scalability. Mesoscopic-scale grains, of which size is almost comparable to device size, are formed in HfO2-based ferroelectric poly-crystalline thin films, which largely influences electrical characteristics in memory devices. It is important to study the impact of mesoscopic-scale grain formation on the electrical characteristics. In this work, first, we have studied the thickness dependence of the polarization switching kinetics in HfO2-based ferroelectric. While static low-frequency polarization is comparable for different thickness, dynamic polarization switching speed is slower in thin Hf0.5Zr0.5O2 (HZO) capacitors. Based on the analysis using the NLS model and physical characterization, thinner HZO contains smaller grains with orientation non-uniformity and more grain boundaries than thicker HZO, which can impede macroscopic polarization switching. We have also theoretically and experimentally studied the polar-axis alignment of a HfO2-based ferroelectric thin film. While in-plane polar orientation is stable in as-grown HZO, out-of-plane polarization can be dominant by applying electric field, which indicates the transition from in-plane polar to out-of-plane polar orientation in the ferroelectric phase grains. This is confirmed by calculating kinetic pathway using ab-initio calculation.

Impact of asymmetric electrodes on ferroelectricity of sub-10 nm HZO thin films

“…However, there have been studies indicating that the metastable o-phase may emerge in HZO when the sample is cooled down after annealing [46,47]. The presence of the o-phase can be ascribed to a lower energy barrier between the t-and o-phases as compared to that between the t-and m-phases, which is a consequence of various effects including interface strain, surface energy, oxygen vacancies, doping, etc [46][47][48]. The GIXRD patterns in figure 3(a) show that the m-phase is present in the samples with the Pt BE, which can be attributed to the lack of significant CTE mismatch between HZO and Pt [30].…”

Sharp Transformation across Morphotropic Phase Boundary in Sub‐6 nm Wake‐Up‐Free Ferroelectric Films by Atomic Layer Technology

“…[36,37] The emergence of the o-phase is attributed to a lower kinetic energy barrier between the t-/c-and o-phases than that between the t-/c-and m-phases, which can be deduced from the effects of dopants, interface strain, surface energy, film thickness, and so on. [36][37][38] Compared to HfO 2 , the transition temperature between the t-/c-and m-phases is much lower in ZrO 2 . [36] Therefore, it can be expected that an increase in T HfO2 leads to an increase in the phase transition temperature in the HZ thin film, as depicted in Figure 3g.…”

Flexible aluminum-doped hafnium oxide ferroelectric synapse devices for neuromorphic computing

“…5,6 Among the candidates of the next-generation non-volatile memory, HfO 2based ferroelectric memory has gained significant attention owing to the excellent memory characteristics. [7][8][9][10] Meanwhile, the nonvolatile memories based on HfO 2 ferroelectric materials can be divided into ferroelectric random access memories, ferroelectric field effect transistors and ferroelectric tunneling junctions (FTJs). 11 Among them, the FTJs have gained more attention due to the low power consumption and fast operation speed.…”