Ferroelectric phase transitions in nanoscale HfO 2  films enable giant pyroelectric energy conversion and highly efficient supercapacitors

Hoffmann, Michael; Schroeder, Uwe; Kuenneth, Christopher; Kersch, Alfred; Starschich, S.; Böttger, U.; Mikolajick, Thomas

doi:10.1016/j.nanoen.2015.10.005

Cited by 197 publications

(182 citation statements)

References 45 publications

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“…The phase transition to the m-phase is an irreversible process, and this can be confirmed from the color contour maps for the cooling in Figure S1 of the Supporting Information. [9,41] Typically, a phase transition from the t-phase to the o-phase at T c is visible. Once formed, the m-phase does not transform back during subsequent cooling down as shown in Figure S1 of the Supporting Information.…”

Section: In Situ X-ray Diffractionmentioning

confidence: 99%

“…[8,9,11,37,42] This property is known to be observed in HfO 2 thin films that contain a relatively higher doping concentration compared to the ferroelectric films. It was suggested that the double polarization-electric field hysteresis in Si and Al-doped HfO 2 and for Hf 1-x Zr x O 2 thin films originate from the electric field induced phase transition from the t-phase to a polar phase, which can be the o-phase.…”

Section: Wwwadvelectronicmatdementioning

confidence: 99%

“…[1,2] Numerous functionalities and devices have been proposed or demonstrated, including ferroelectric random access memory, [3] ferroelectric field effect transistor, [4][5][6] negative capacitance field effect transistor, [7] pyroelectric energy harvester, [8][9][10][11] infrared sensor, [8,9,12] electrocaloric cooler, [7][8][9][10] and electrostatic supercapacitor. [1,2] Numerous functionalities and devices have been proposed or demonstrated, including ferroelectric random access memory, [3] ferroelectric field effect transistor, [4][5][6] negative capacitance field effect transistor, [7] pyroelectric energy harvester, [8][9][10][11] infrared sensor, [8,9,12] electrocaloric cooler, [7][8][9][10] and electrostatic supercapacitor.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Park

Chung

Schenk

et al. 2018

Adv Elect Materials

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crystalline phase in doped HfO 2 thin film. [17,18] However, this phase cannot be observed in the phase diagram of bulk HfO 2 and ZrO 2 , [19,20] even when doped with elements that are used in the thin film counterparts. [21] Therefore, multiple factors were suggested as origin of the stabilization of the ferroelectric phase. Materlik et al. suggested that the o-phase can be stabilized due to surface energy effects, [22] and Park et al. comprehensively examined the surface energy model and their experimental observations. [23] In the latter study, it was confirmed that the o-phase can be stabilized within the nuclei formed during the atomic layer deposition (ALD) process, but the interface/grain boundary effect is not sufficient to stabilize the o-phase within the final grain size after annealing. [23] Therefore, it was suggested that the crystalline phase of the initial nuclei can remain even after crystallization, implying that the phase transformation to the monoclinic phase (m-phase, space group: P2 1 /c) can be kinetically suppressed. [23,24] Stress in thin films was also suggested as a possible origin, [1,25,26] and Shiraishi et al. experimentally proved that the polymorphism of Hf 0.5 Zr 0.5 O 2 thin films is strongly affected by the thermal expansion coefficient (TEC) of the used substrate. [27] However, the detailed mechanism of the formation of the unexpected o-phase is not yet resolved.It is generally known that the structure and electrical properties of perovskite ferroelectrics are strongly coupled. [28][29][30] The ferroelectric properties of doped HfO 2 thin films are also believed to be determined by their crystalline structure. ParkThe ferroelectricity in fluorite oxides has gained increasing interest due to its promising properties for multiple applications in semiconductor as well as energy devices. The structural origin of the unexpected ferroelectricity is now believed to be the formation of a non-centrosymmetric orthorhombic phase with the space group of Pca2 1 . However, the factors driving the formation of the ferroelectric phase are still under debate. In this study, to understand the effect of annealing temperature, the crystallization process of doped HfO 2 thin films is analyzed using in situ, high-temperature X-ray diffraction. The change in phase fractions in a multiphase system accompanied with the unit cell volume increase during annealing could be directly observed from X-ray diffraction analyses, and the observations give an information toward understanding the effect of annealing temperature on the structure and electrical properties. A strong coupling between the structure and the electrical properties is reconfirmed from this result.

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Section: In Situ X-ray Diffractionmentioning

confidence: 99%

Section: Wwwadvelectronicmatdementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Park

Chung

Schenk

et al. 2018

Adv Elect Materials

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“…[36][37][38] This was shown for bulk ceramics and was exploited to stabilize a higher-k hafnia phase in thin films for application to gate and capacitor dielectrics. [41] Consequently, the phase evolution as well as the evolution of the dielectric behavior with increasing Si content can be explained based on the phenomenological theory of ferroelectrics by Landau and Devonshire model. Hoffmann et al showed that Si doping lowers the Curie or Curie-Weiss temperatures.…”

Section: Landau Theory and Internal Bias Fieldsmentioning

confidence: 99%

Si Doped Hafnium Oxide—A “Fragile” Ferroelectric System

Richter

Schenk

Park

et al. 2017

Adv Elect Materials

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152

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a wealth of different elements from the periodic table [7][8][9] have since exhibited ferroelectric properties. In their original publication, Böscke et al. [10] used ≈10 nm thick films of Si:HfO 2 and found the electrical behavior to evolve from paraelectric (PE) to ferroelectric (FE) and antiferroelectriclike to paraelectric again with a continuous increase in the Si dopant concentration. A similar electric evolution has also been shown for aluminum doping [11] and for (Hf,Zr)O 2 . [6,12] For the latter, an advanced understanding of the phase stabilization could be established, assisted in part by the very wide concentration window over which the changes occur. Ab initio calculations [13] interrogated the impact of surface energy in this system, revealing a phase transition from monoclinic pure HfO 2 to orthorhombic Hf 0.5 Zr 0.5 O 2 to tetragonal pure ZrO 2 for 10 nm film thickness, which aligns well the experimental observations. Moreover, inclusion of an electric field effect explained the antiferroelectriclike polarization hysteresis of pure ZrO 2 as the result of a fieldinduced phase transition from a nonpolar tetragonal to a polar orthorhombic phase. [6,13,14] Thus, instead of the term antiferroelectricity, field-induced ferroelectricity (FFE) is becoming a more precise and commonly used way to describe this behavior. While Si:HfO 2 and Al:HfO 2 have quickly been used in applications such as ferroelectric field effect transistors in 28 nm technology [15,16] and 3D capacitors, [17] basic material studies of doped ferroelectric HfO 2 have lagged those of the (Hf,Zr) O 2 system. By exploring a wide Si concentration range in fine steps, this work aims to gain insight into the phase transformations that occur in a doped HfO 2 system. Results and Discussion Impact of Annealing ConditionsAs a first step, planar capacitor stacks (Figure 1) with ≈36 nm thick HfO 2 films are deposited using a 22:1 HfO 2 :SiO 2 cycle ratio. As shown later, this results in a Si content that is slightly higher than the one that has produced the highest remanent polarization P r values in this study (Figure 7). As visible in Figure 2, the P r (measured under an electric field of 4 MV cm −1 and 10 kHz) increases for anneals at higher temperatures.Silicon doped hafnium oxide was the material used in the original report of ferroelectricity in hafnia in 2011. Since then, it has been subject of many further publications including the demonstration of the world's first ferroelectric field-effect transistor in the state-of-the-art 28 nm technology. Though many studies are conducted with a strong focus on application in memory devices, a comprehensive study on structural stability in these films remains to be seen. In this work, a film thickness of about 36 nm, instead of the 10 nm used in most previous studies, is utilized to carefully probe how the concentration range impacts the evolution of phases, the dopant distribution, the field cycling effects, and their interplay in the macroscopic ferroelectric response of the films. Si:HfO 2 appear...

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“…Not only the paired, but also the unpaired vacancies might contribute to the desired phase stabilization. Here, some preliminary results have been published[40], shown inFig 1b. 6.25ani.-% V O in HfO 2 lowers the ferroelectric phase by 15 meV/f.u.…”

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confidence: 95%

A computational study of hafnia-based ferroelectric memories: from ab initio via physical modeling to circuit models of ferroelectric device

et al. 2017

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Abstract. The discovery of ferroelectric properties of binary oxides revitalized the interest in ferroelectrics and bridged the scaling gap between the state-of-the-art semiconductor technology and ferroelectric memories. However, before hitting the markets, the origin of ferroelectricity and in-depth studies of device characteristics are needed. Establishing a correlation between the performance of the device and underlying physical mechanisms is the first step toward understanding the device and engineering guidelines for a novel, superior device. Therefore, in this paper a holistic modeling approaches which lead to a better understanding of ferroelectric memories based on hafnium and zirconium oxide is addressed. Starting from describing the stabilization of the ferroelectric phase within the binary oxides via physical modeling the physical mechanisms of the ferroelectric devices are reviewed. Besides, limitations and modeling of the multi-level operation and switching kinetics of ultimately scaled devices as well as the necessity for Landau-Khalatnikov approach are discussed. Furthermore, a device level model of ferroelectric memory devices that can be used to study the array implementation and their operational schemes are addressed. Finally, a circuit model of the ferroelectric memory device is presented and potential further applications of ferroelectric devices are outlined.

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Ferroelectric phase transitions in nanoscale HfO 2 films enable giant pyroelectric energy conversion and highly efficient supercapacitors

Cited by 197 publications

References 45 publications

Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Si Doped Hafnium Oxide—A “Fragile” Ferroelectric System

A computational study of hafnia-based ferroelectric memories: from ab initio via physical modeling to circuit models of ferroelectric device

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Ferroelectric phase transitions in nanoscale HfO 2 films enable giant pyroelectric energy conversion and highly efficient supercapacitors

Cited by 197 publications

References 45 publications

Effect of Annealing Ferroelectric HfO2 Thin Films: In Situ, High Temperature X‐Ray Diffraction

Effect of Annealing Ferroelectric HfO2 Thin Films: In Situ, High Temperature X‐Ray Diffraction

Si Doped Hafnium Oxide—A “Fragile” Ferroelectric System

A computational study of hafnia-based ferroelectric memories: from ab initio via physical modeling to circuit models of ferroelectric device

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Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction