Investigation of the wake-up process and time-dependent imprint of Hf0.5Zr0.5O2 film through the direct piezoelectric response

Abstract

Ferroelectric HfO2-based thin films, which have been attracting a great deal attention because of their potential use in various applications, are known for their unique properties, such as a large time-dependent imprint and wake-up effect, which differentiate them from conventional ferroelectric materials. In this study, direct piezoelectric measurement was employed to investigate the state of polarization during the retention and wake-up process without applying an electric field. The polarization-electric field hysteresis loop of a sputtered Hf0.5Zr0.5O2 (HZO) film with a thickness of 10 nm showed a time-dependent imprint at room temperature during polarization retention, and the internal electric field that generated the imprint gradually increased from 0.05 to 0.6 MV/cm. While a space charge density of more than 1 μC/cm2 is required to form such an internal electric field, it was found that the magnitude of the direct piezoelectric response did not change at all during polarization retention. On the other hand, both the remanent polarization and direct piezoelectric response increased during the wake-up process. Based on the difference in the variation over time of these two characteristics, we concluded that the non-ferroelectric layer exists at the interface between the HZO film and TaN electrode and gradually transitions to ferroelectric phases through the electric field cycle.

Understanding of polarization reversal and charge trapping under imprint in HfO2-FeFET by charge component analysis

“…There have been many reports on imprint in metal-ferroelectric-metal (MFM) capacitors with ferro-HfO 2 [15][16][17][18][19][20][21][22][23][24][25] and the origins of imprint such as diffusion of defects (oxygen vacancies) 15) and electron trapping at the interface between the electrode and ferro-HfO 2 [16][17][18][19][20][21]23) have been discussed. Compared to MFM capacitors, FeFET shows more complex imprint behavior, because FeFET has metal-ferroelectricinsulator-Si (MFIS) structure and there exists a SiO 2 interfacial layer (IL-SiO 2 ) with low dielectric constant between the ferroelectric layer and the channel.…”

A Study on Imprint Behavior of Ferroelectric Hafnium Oxide Caused by High‐Temperature Annealing

“…Imprint is correlated with an internal electric field that may be caused by charge injection, trapping, migration, and inhomogeneous redistribution of charges in the FE materials as well as at the interfaces of electrodes and the FE layer. [ 26,28,30 ] Yuan et al explained that in FE HZO, carrier injection followed by electron detrapping results in internal field variation and consequently leads to imprint behavior. [ 32 ] In order to improve endurance and retention characteristics, and therefore the performance of ‐based FE memory devices, it is necessary to have a deep understanding of the imprint issue.…”

“…[19][20][21] Many research groups have investigated the imprint issue in FE HfO 2 . [22][23][24][25][26][27][28][29][30][31][32][33] The temperature-as well as time-dependent imprint phenomena, which is the main cause of data retention loss, require further research in order to understand the physical mechanism behind it.…”

Enhanced Endurance and Imprint Properties in Hf0.5Zr0.5O2−δ Ferroelectric Capacitors by Tailoring the Oxygen Vacancy

“…Previous reports indicate a significant increase in the leakage current before breakdown, which originates from the migration and generation of defects. , In addition, imprint effects in HfO 2 -based ferroelectric capacitors have been more severe but less studied in the past decade. The imprint is considered to be caused by the alteration of the internal bias field, which might be triggered by charged defects, , especially charged oxygen vacancies . Since the oxygen vacancies are the most common defects in HfO 2 , it is crucial to comprehensively investigate the impact of oxygen vacancies on endurance and the imprint effect of HfO 2 -based films.…”