In Operando Optical Tracking of Oxygen Vacancy Migration and Phase Change in few Nanometers Ferroelectric HZO Memories

Abstract

Ferroelectric materials offer a low-energy, high-speed alternative to conventional logic and memory circuitry. Hafnia-based films have achieved singledigit nm ferroelectricity, enabling further device miniaturization. However, they can exhibit nonideal behavior, specifically wake-up and fatigue effects, leading to unpredictable performance variation over consecutive electronic switching cycles, preventing large-scale commercialization. The origins are still under debate. Using plasmon-enhanced spectroscopy, a non-destructive technique sensitive to <1% oxygen vacancy variation, phase changes, and single switching cycle resolution, the first real-time in operando nanoscale direct tracking of oxygen vacancy migration in 5 nm hafnium zirconium oxide during a pre-wake-up stage is provided. It is shown that the pre-wake-up leads to a structural phase change from monoclinic to orthorhombic phase, which further determines the device wake-up. Further migration of oxygen ions in the phase changed material is then observed, producing device fatigue. These results provide a comprehensive explanation for the wake-up and fatigue with Raman, photoluminescence and darkfield spectroscopy, combined with density functional theory and finite-difference time-domain simulations.

Pure ZrO2 Ferroelectric Thin Film for Nonvolatile Memory and Neural Network Computing

“…After the wake up, an increase in the o-phase fraction can be observed, which can account for the increased ferroelectricity shown in Figure b. In Figure g, the o/t phases are preferred over the m/r phases, which is related to the in-plane tensile strain induced by the low thermal expansion coefficient of RuO 2 electrodes. , In the wake-up process, other phases transit to the o phase as a result of the electric field stimuli and V O migration. ,− , …”

“…The polarization of the device shows a small degradation over 10 4 s and is expected to be retained for >10 years. During the electric field cycling in the wake-up process, the redistribution of oxygen vacancies may cause the depinning of ferroelectric dipoles and/or phase transitions from non-ferroelectric (such as t or m phase) to ferroelectric (such as o phase). − These phenomena will increase the total amount of switchable ferroelectric dipoles and, accordingly, enhance the ferroelectricity.…”

“…23,37 In the wake-up process, other phases transit to the o phase as a result of the electric field stimuli and V O migration. 30,[46][47][48]52 The cross-sectional EDS mappings of the device in the pristine and woken-up states are shown in panels h and i of Figure 2, respectively. Consistent with the findings of a previous report, 37 decreased oxygen signals at both the top and bottom interfaces can be observed.…”

Electrically induced cancellation and inversion of piezoelectricity in ferroelectric Hf0.5Zr0.5O2

“…Hence, we can confidently exclude that phenomena related to imprint (such as charge redistribution) account for the sign change of d 33 . Electrical cycling during the wake-up phase has also been suggested to trigger a crystalline phase transition from the non-ferroelectric monoclinic or tetragonal P4 2 /nmc to the polar orthorhombic Pca2 1 phase via oxygen vacancy migration 11 , 51 , 52 . Here, we can rule out that the capacitors contain a majority of non-ferroelectric phase(s).…”

Recent Research for HZO-Based Ferroelectric Memory towards In-Memory Computing Applications

“…In-memory computing improves latency and energy by performing calculations without physical separation from the storage where the data are located. Ferroelectric-based non-volatile memory with independent switching mechanisms and high-power efficiency has recently been recognized for its potential in neuromorphic and in-memory computing [17][18][19][20][21][22].…”