Flexible Quasi‐van der Waals Ferroelectric Hafnium‐Based Oxide for Integrated High‐Performance Nonvolatile Memory

Abstract

Ferroelectric memories with ultralow-power-consumption are attracting a great deal of interest with the ever-increasing demand for information storage in wearable electronics. However, sufficient scalability, semiconducting compatibility, and robust flexibility of the ferroelectric memories remain great challenges, e.g., owing to Pb-containing materials, oxide electrode, and limited thermal stability. Here, high-performance flexible nonvolatile memories based on ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) via quasi-van der Waals heteroepitaxy are reported. The flexible ferroelectric HZO exhibits not only high remanent polarization up to 32.6 µC cm −2 without a wake-up effect during cycling, but also remarkably robust mechanical properties, degradation-free retention, and endurance performance under a series of bent deformations and cycling tests. Intriguingly, using HZO as a gate, flexible ferroelectric thin-film transistors with a low operating voltage of ±3 V, high on/off ratio of 6.5 × 10 5 , and a small subthreshold slope of about 100 mV dec −1 , which outperform reported flexible ferroelectric transistors, are demonstrated. The results make ferroelectric HZO a promising candidate for the next-generation of wearable, low-power, and nonvolatile memories with manufacturability and scalability.

An Overview of Ferroelectric Hafnia and Epitaxial Growth

“…Among them, atomic layer deposition (ALD) has been frequently used due to its wide industrial coverage. This technique initially results in amorphous hafnia thin films [49,[61][62][63] capped by a metal electrode (usually TiN), and further subjected to rapid thermal annealing to achieve polycrystalline hafnia thin films. [61] The confinement strain during fast annealing suppresses the conventional tetragonal to monoclinic phase transition, resulting in an alternative pathway from tetragonal to orthorhombic phase.…”

“…[81,105,106] In fact, the wake-up effect is usually accompanied by redistribution of oxygen vacancies and defects in HZO film, which traps charges, pins the domains, and prevents them from switching. [61,107] Thus, it has also been proposed that the wake-up effect can be attributed to the diffusion and redistribution of the oxygen vacancies by repetitive electric field cycling. Kashir et al have investigated the effect of ozone dosage, which influence the defects, on the wake-up of HZO films.…”

Ferroelectrics Based on HfO2 Film

“…Because of this, studies on the formation of ferroelectric HfO 2 thin film on PI films have reported poor physical and ferroelectric properties [64,68]. Recently, a mica substrate with high thermal resistance was used for flexible ferroelectric HfO 2 film but had a problem with poor versatility [69]. Therefore, to employ ferroelectric HfO 2 on a flexible device, it will be necessary to introduce a fundamentally low-temperature process.…”

Flexible and Stretchable Memristive Arrays for in-Memory Computing

“…The emergence of the Internet of Things (IoT) and artificial intelligence (AI) technology has promoted the rapid development of flexible and stretchable intelligent systems, such as electronic skin (e-skin) (Yang et al, 2019;Wang et al, 2020b), soft robotics (Wang et al, 2018b;Park et al, 2020b), and wearable devices (Liu et al, 2020). In the ideal scenarios, these systems should be able to undergo complex deformations in response to external stimuli, such as bending, twisting, and shearing (Wang et al, 2020c;Wang et al, 2021b;Raeis-Hosseini and Rho, 2021).…”