Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf0.5Zr0.5O2 Thin Films

Mehmood, Furqan; Mikolajick, Thomas; Schroeder, Uwe

doi:10.1002/pssa.202000281

Cited by 23 publications

(9 citation statements)

References 31 publications

(52 reference statements)

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“…This phase transition is related to the wake-up effect in ferroelectricity, as reported in the previous studies. [12,[16][17][18][19][20] Although the ferroelectric properties stem from the orthorhombic structure, the orthorhombic structure in the as-deposited or as-annealed film is not needed for exhibiting ferroelectricity. Thus, structural changes by the electric field, including phase transition and domain switching, play a key role in fluorite oxide-based ferroelectric materials, and studies on epitaxial films are a suitable platform to clarify these phenomena.…”

Section: Resultsmentioning

confidence: 99%

“…[11][12][13] In particular, HfO 2 -based materials often require a certain number of electric field cycles to exhibit ferroelectricity. [12][13][14][15][16][17][18][19] Particularly, this so-called wakeup effect relates to the structural change in the electric field. Previous studies have shown a 90 domain rotation from inplane to out-of-plane polarizations using scanning transmission electron microscopy (STEM), selected area electron diffraction, and microarea X-ray diffraction (XRD) studies.…”

Section: Introductionmentioning

confidence: 99%

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Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf_0.5Zr_0.5O₂: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Shiraishi

Tashiro

Mimura

et al. 2021

Physica Rapid Research Ltrs

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The ferroelectric phase transformation from the tetragonal phase to the orthorhombic phase, induced by an electric field, is demonstrated in a 5%YO1.5‐doped Hf0.5Zr0.5O2 epitaxial film which is grown on Sn‐doped In2O3‐covered (111) yttria‐stabilized zirconia by the pulsed laser deposition method at room temperature and subsequent heat treatment. Although X‐ray diffraction shows the film to consist of a paraelectric tetragonal phase after the heat treatment, polarization–electric field (P–E) measurements reveal a hysteresis loop attributed to the ferroelectricity. To clarify the discrepancy between the crystal structure and electric characteristics, the crystal structure after electric field loading is determined by scanning transmission electron microscopy and synchrotron X‐ray diffraction measurements. Both structural characterizations clearly reveal that the application of an electric field promotes the phase transition from the paraelectric tetragonal phase to the ferroelectric orthorhombic phase. This ferroelectric transition is irreversible, as the ferroelectric phase remains after the removal of the electric field. These results facilitate the elucidation of the mechanism by which ferroelectricity is displayed in HfO2‐based fluorite ferroelectric materials and imply unimportance of the orthorhombic phase for as‐prepared films.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf_0.5Zr_0.5O₂: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Shiraishi

Tashiro

Mimura

et al. 2021

Physica Rapid Research Ltrs

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“…This hinders a comprehensive solution to the problem. For wake-up, three main mechanisms have been proposed: field-driven phase change, where the nonpolar tetragonal phase (T-phase) and monoclinic phase (M-phase) convert to the polar O-phase during cycling; , domain depinning caused by the redistribution of trapped charges, including oxygen vacancies; ,, and rotation of the initially in-plane aligned ferroelectric domains to the out-of-plane direction . Evidence of phase change has previously been obtained via in situ high-resolution transmission electron microscopy (HRTEM), in which evidence of a structural transformation from T-phase to O-phase during electric field cycling has been reported .…”

Section: Introductionmentioning

confidence: 99%

“…A domain-depinning mechanism was supported by a range of electrical measurements. Through temperature-dependent voltage cycling measurements, Mehmood et al suggest that the wake-up can be separated into two stages: charge redistribution and ferroelectric domain depinning, followed by a phase change in the electrode interfacial regions after 10 4 cycles . In contrast, by means of synchrotron XRD and scanning transmission electron microscopy (STEM), Shimizu et al revealed ferroelastic domain switching as a contributor to wake-up during the initial application of an electric field on an epitaxial film .…”

Section: Introductionmentioning

confidence: 99%

Enhanced Switching Reliability of Hf_0.5Zr_0.5O₂ Ferroelectric Films Induced by Interface Engineering

Huang,

Saini,

et al. 2023

ACS Appl. Mater. Interfaces

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Ferroelectric materials have been widely researched for applications in memory and energy storage. Among these materials and benefiting from their excellent chemical compatibility with complementary metal−oxide−semiconductor (CMOS) devices, hafnia-based ferroelectric thin films hold great promise for highly scaled semiconductor memories, including nonvolatile ferroelectric capacitors and transistors. However, variation in the switched polarization of this material during field cycling and a limited understanding of the responsible mechanisms have impeded their implementation in technology. Here, we show that ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) capacitors that are nearly free of polarization "wake-up"�a gradual increase in switched polarization as a function of the number of switching cycles�can be achieved by introducing ultrathin HfO 2 buffer layers at the HZO/electrodes interface. High-resolution transmission electron microscopy (HRTEM) reveals crystallite sizes substantially greater than the film thickness for the buffer layer capacitors, indicating that the presence of the buffer layers influences the crystallization of the film (e.g., a lower ratio of nucleation rate to growth rate) during postdeposition annealing. This evidently promotes the formation of a polar orthorhombic (O) phase in the as-fabricated buffer layer samples. Synchrotron X-ray diffraction (XRD) reveals the conversion of the nonpolar tetragonal (T) phase to the polar orthorhombic (O) phase during electric field cycling in the control (no buffer) devices, consistent with the polarization wake-up observed for these capacitors. The extent of T−O transformation in the nonbuffer samples is directly dependent on the duration over which the field is applied. These results provide insight into the role of the HZO/ electrodes interface in the performance of hafnia-based ferroelectrics and the mechanisms driving the polarization wake-up effect.

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“…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.…”

mentioning

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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Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf_0.5Zr_0.5O₂ Thin Films

Cited by 23 publications

References 31 publications

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf_0.5Zr_0.5O₂: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf_0.5Zr_0.5O₂: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Enhanced Switching Reliability of Hf_0.5Zr_0.5O₂ Ferroelectric Films Induced by Interface Engineering

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

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Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf0.5Zr0.5O2 Thin Films

Cited by 23 publications

References 31 publications

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf0.5Zr0.5O2: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf0.5Zr0.5O2: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Enhanced Switching Reliability of Hf0.5Zr0.5O2 Ferroelectric Films Induced by Interface Engineering

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

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Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf_0.5Zr_0.5O₂ Thin Films

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf_0.5Zr_0.5O₂: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf_0.5Zr_0.5O₂: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

Enhanced Switching Reliability of Hf_0.5Zr_0.5O₂ Ferroelectric Films Induced by Interface Engineering

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