Enhanced ferroelectric switching speed of Si-doped HfO2 thin film tailored by oxygen deficiency

Abstract

Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. Various studies have examined the relationship between oxygen deficiency and the phase transformation from a nonpolar phase to a polar phase in HfO2 thin films. However, there are few reports on the effects of oxygen deficiencies on the switching dynamics of the ferroelectric phase itself. Herein, we report the oxygen- deficiency induced enhancement of ferroelectric switching properties of Si-doped HfO2 thin films. By controlling the annealing conditions, we controlled the oxygen deficiency concentration in the ferroelectric orthorhombic HfO2 phase. Rapid high-temperature (800 °C) annealing of the HfO2 film accelerated the characteristic switching speed compared to low-temperature (600 °C) annealing. Scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) revealed that thermal annealing increased oxygen deficiencies, and first-principles calculations demonstrated a reduction of the energy barrier of the polarization flip with increased oxygen deficiency. A Monte Carlo simulation for the variation in the energy barrier of the polarization flipping confirmed the increase of characteristic switching speed.

On the switching dynamics of epitaxial ferroelectric CeO2–HfO2 thin film capacitors

“…The KAI model is considered appropriate for epitaxial films in classical ferroelectric materials since it describes homogeneous domain nucleus formation and unhindered domain wall motion as the limiting step similar to high-purity bulk materials [ 43 , 48 , 49 ]. However, multiple recent studies have demonstrated that the NLS model is a better fit for HfO 2 thin films [ 34 , 35 , 50 , 51 ]. This model assumes inhomogeneous formation of nuclei in different regions of the film with a characteristic distribution.…”

“…On the one hand, the stabilizing effect of oxygen deficiency is agreed upon [ 49 , 62 – 64 ]. On the other hand, the influence on the switching kinetics is controversial, including reports of no direct influence [ 65 ] and switching speed enhancements [ 35 , 64 ]. In the present study, we found faster switching with close to KAI model dynamics for the sample with the higher oxygen content.…”

“…The differences in switching kinetics are further examined by comparing the recorded polarization transients to common switching models. This approach has been employed before for HfO 2 ferroelectric systems [33], although in most publications discrete probing pulses are used [34][35][36]. Regarding the appropriate model, a wide variety has been proposed in literature, including the Kolgomorov-Avrami-Ishibashi (KAI) model [37][38][39], Inhomogeneous-Field-Mechanism (IFM) model [40,41], multi-grain Landau-Khalatnikov (LK) model [42] and the Nucleation-Limited-Switching (NLS) model [43][44][45][46][47].…”

Negative Capacitance and Switching Dynamics Control Via Non-Ferroelectric Elements

“…Since the discovery of ferroelectricity more than 100 years ago, many applications have been developed based on its unique property to change the polarization state/orientation using an external electric field. , Based on this bi-stability, ferroelectric (FE) materials became the core of FE random access memory or FE field-effect transistor (FEFET) electronic devices. − Even if non-volatility is a key characteristic, the dynamic of polarization switching − also plays an important role for binary digital devices and determines important parameters such as the writing speed, writing voltage, stability in time, or fatigue.…”

Polarization Switching Kinetics in Thin Ferroelectric HZO Films

“…The NLS model has also been employed to study the impact of different parameters of HfO 2 on its switching speed. In particular, it has been shown that concentration of oxygen vacancies [ 14 , 15 ], HZO film thickness [ 16 ], and Zr alloy concentration in Hf 1−x Zr x O 2 thin films [ 17 ] affect polarization switching kinetics. On the other hand, the impact of several physical phenomena in HfO 2 on time dependence of polarization switching has been examined in the frame of the NLS model.…”