Microscopic mechanism of imprint in hafnium oxide-based ferroelectrics

Yuan, Peng; Mao, Ge‐Qi; Cheng, Yan; Xue, Kaiping; Zheng, Yi; Yang, Yang; Jiang, Pengfei; Xu, Youqian; Wang, Yuan; Wang, Yuhao; Ding, Yaxin; Chen, Yuting; Dang, Zhiwei; Tai, Lu; Gong, Tiancheng; Luo, Qing; Miao, Xiangshui; Liu, Qi

doi:10.1007/s12274-021-4047-y

Cited by 23 publications

(26 citation statements)

References 41 publications

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“…For the same compound orthorhombic HfO 2 , estimated coercive field values include 15.5 MV/cm and 13.4 MV/cm . The fact that experimental ε C is ∼1 MV/cm has been attributed to domain wall dynamics, which will reduce the coercive field to much lower values. It was also speculated that a strain gradient due to the film deposition process may reduce the required electric field for switching .…”

Section: Resultsmentioning

confidence: 99%

Ferroelectricity in HfO₂ from a Coordination Number Perspective

et al. 2022

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Ferroelectricity observed in thin-film HfO 2 , either doped with Si, Al, and so forth or in the Hf 0.5 Zr 0.5 O 2 form, has gained great technical significance. While a trilinear coupling between phonon modes could explain its ferroelectric distortion, from a practical perspective, one may be concerned with a theory that is more straightforward to predict similar ferroelectric candidates through some apparent features of HfO 2 and ZrO 2 . In this work, we propose that the 7 cation coordination number of HfO 2 /ZrO 2 lies at the heart of this ferroelectricity, which stems from the proper ionic radii of Hf/Zr compared with O. Among the numerous compounds with a non-centrosymmetric nature, for example, the mm2 point group, HfO 2 and ZrO 2 are special in that they are close to the border of 7 and 8 cation coordination, such that the 8-coordination tetragonal intermediate phase could greatly reduce the switching barrier. Other 7-coordination candidates, including SrI 2 , TaON, YSBr, and YOF, are also studied in comparison to HfO 2 /ZrO 2 , and six switching paths are analyzed in detail for the Pca2 1 phase. A rule of the preferred switching path in terms of the ionic radii ratio and coordination number has been established. We also show the possible route from the ferroelectric Pca2 1 phase to the monoclinic P2 1 /c phase in HfO 2 , which is relevant to the fatigue phenomenon.

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Section: Resultsmentioning

confidence: 99%

Ferroelectricity in HfO₂ from a Coordination Number Perspective

et al. 2022

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“…Such asymmetric treatment is quite common and recently it was reported that the abundant oxygen vacancies around the TE interface may be related to the imprint phenomenon in HZO‐ferroelectrics. [ 27 ] In our device, the impact of bombardment is only prominent in the topmost ZrO 2 layer of ≈2 nm thick. As shown in Figure 1e, TE sputtering bombards the ZrO 2 layer with a depth of about 1.1 nm.…”

Section: Wake‐up Free Ferroelectric Capacitors Through Designmentioning

confidence: 99%

Designing Wake‐Up Free Ferroelectric Capacitors Based on the HfO₂/ZrO₂ Superlattice Structure

Bai

Xue

Huang

et al. 2022

Adv Elect Materials

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In contrast to traditional ferroelectrics such as perovskite Pb(Zr,Ti)O 3 , SrBi 2 Ta 2 O 9 , and organic polyvinylidene fluoride polymers, a special wake-up phenomenon has been widely observed in hafnia-based ferroelectric capacitors, which implies that the switchable polarization is subject to variation during the initial period of capacitor lifetime. [13] Although the spontaneous polarization is actually being enhanced during wake-up, [14] the variable device parameter can cause severe problems in applications. It has been reported that the crystallization temperature is highly relevant to the wakeup process. [13,[15][16][17] In particular, a high crystallization temperature could effectively render wake-up-free ferroelectric capacitors based on HZO. [17] Therefore, raising the processing temperature is a potential solution to get rid of the wake-up phenomenon.Nevertheless, using high crystallization temperature leads to other serious problems. On the one hand, hafnia-ferroelectric capacitors usually involve TiN or TaN electrodes, which are oxygen scavenger materials at high temperature. [18] On the other hand, high temperature crystallization tends to generate the thermodynamically stable monoclinic P2 1 /c phase (m-phase) for HfO 2 or HZO, which is paraelectric. [16,19] The robust stability of monoclinic phase hinders its transformation into the ferroelectric orthorhombic Pca2 1 phase (o-phase). Hence, in most published works, the crystallization temperature was controlled at around 500 °C. [17,20,21] In this work, we attempt a special design for the ferroelectric layer that can avoid the above two problems, thus permitting a higher crystallization temperature. First of all, the concept of HfO 2 /ZrO 2 superlattice enables crystallization from the ZrO 2 side. This is possible when ZrO 2 is adjacent to an inert electrode and the heat source is only from that electrode side during rapid thermal annealing (RTA). Standard RTA instruments typically possess heating modes from upper lamps, lower lamps and both. As is well-known, the m-phase of ZrO 2 can be less stable than its tetragonal phase due to surface energy consideration, as long as the grain dimension is sufficiently small. [22][23][24] Hence, even high temperature RTA may not transform nanoscale ZrO 2 into m-phase. Secondly, an inert electrode like Pt can be selected in conjunction with the ZrO 2 layer that isThe wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at a higher temperature has been reported to be effective in eliminating wakeup, but high temperature may yield the monoclinic phase or generate more oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of Hf 0.5 Zr 0.5 O 2 (HZO) superlattice ferroelectrics, which involves heating from the Pt/ZrO 2 interface side. It is demonstrated that 600 °C annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up...

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“…[ 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

{HfO}_{2}

‐based FE memory devices, it is necessary to have a deep understanding of the imprint issue. Here, the imprint is defined as the shift of coercive voltages during cycling and after annealing at high temperatures (from 100 to 200 °C).…”

Section: Introductionmentioning

confidence: 99%

“…[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.…”

Section: Introductionmentioning

confidence: 99%

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

Sünbül

Lehninger

Lederer

et al. 2023

Physica Status Solidi (a)

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Hafnium oxide is found to be a favorable material for ferroelectric nonvolatile memory devices. Its compatibility with complementary metal–oxide–semiconductor processes, the relatively low crystallization temperature when zirconium‐doped, and the thickness scaling are among the advantageous properties of hafnium oxide. Different requirements must be fulfilled for different applications of hafnium oxide. Herein, high‐temperature annealing and operation conditions are analyzed in order to investigate nonvolatile memories for automotive applications. A strong imprint behavior (shift in coercive voltages) is observed after annealing hafnium–zirconium–oxide thin films at temperatures varied between 100 and 200 °C. The imprint behavior is a significant challenge in many applications. Therefore, to reduce/recover the undesirable imprint behavior caused by high‐temperature treatment, two different ways are successfully examined and delineated here: endurance cycling and applying high electric fields.

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Microscopic mechanism of imprint in hafnium oxide-based ferroelectrics

Cited by 23 publications

References 41 publications

Ferroelectricity in HfO₂ from a Coordination Number Perspective

Ferroelectricity in HfO₂ from a Coordination Number Perspective

Designing Wake‐Up Free Ferroelectric Capacitors Based on the HfO₂/ZrO₂ Superlattice Structure

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

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Microscopic mechanism of imprint in hafnium oxide-based ferroelectrics

Cited by 23 publications

References 41 publications

Ferroelectricity in HfO2 from a Coordination Number Perspective

Ferroelectricity in HfO2 from a Coordination Number Perspective

Designing Wake‐Up Free Ferroelectric Capacitors Based on the HfO2/ZrO2 Superlattice Structure

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

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Ferroelectricity in HfO₂ from a Coordination Number Perspective

Ferroelectricity in HfO₂ from a Coordination Number Perspective

Designing Wake‐Up Free Ferroelectric Capacitors Based on the HfO₂/ZrO₂ Superlattice Structure