Mixed Al and Si doping in ferroelectric HfO2 thin films

Lomenzo, Patrick D.; Takmeel, Qanit; Zhou, Chuanzhen; Chung, Ching‐Chang; Moghaddam, Saeed; Jones, Jacob L.; Nishida, Toshikazu

doi:10.1063/1.4937588

Cited by 38 publications

(25 citation statements)

References 18 publications

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“…To better understand the meaning of these values obtained in a sub-5 nm film, Fig. 5 summarizes the polarization and endurance values reported in literature 6,[8][9][10][46][47][48][49][50][51][52][53][54][55][56][57][58][59] for polycrystalline HfO 2 films doped with different atoms. The recent use of La as a dopant has allowed a notable increase in endurance without loss of polarization (empty triangles) in >5 nm films.…”

Section: Resultsmentioning

confidence: 99%

High polarization, endurance and retention in sub-5 nm Hf_0.5Zr_0.5O₂ films

et al. 2020

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Ferroelectric HfO 2 is a promising material for new memory devices, but significant improvement of its important properties is necessary for practical application. However, previous literature shows that a dilemma exists between polarization, endurance and retention. Since all these properties should be simultaneously high, overcoming this issue is of the highest relevance. Here, we demonstrate that high crystalline quality sub-5 nm Hf 0.5 Zr 0.5 O 2 capacitors, integrated epitaxially with Si(001), present combined high polarization (2P r of 27 µC cm −2 in the pristine state), endurance (2P r > 6 µC cm −2 after 10 11 cycles) and retention (2P r > 12 µC cm −2 extrapolated at 10 years) using the same poling conditions (2.5 V). This achievement is demonstrated in films thinner than 5 nm, thus opening bright possibilities in ferroelectric tunnel junctions and other devices.This journal is

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Section: Resultsmentioning

confidence: 99%

High polarization, endurance and retention in sub-5 nm Hf_0.5Zr_0.5O₂ films

et al. 2020

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“…For example, the overview STEM image in Figure 3a reveals discontinuous bands of darker contrast that run through the middle of the 10 nm Si:HfO 2 dielectric. Even though these results suggest a nonuniform dopant distribution, [23] atomic resolution STEM reveals formation of crystalline HfO 2 grains between the two TiN electrodes without obvious formation of secondary phases (Figure 4). [22] The integrated line profile of the image intensity reveals two major dips near the center of the film, which indicate layering.…”

Section: Chemical Compositionmentioning

confidence: 96%

“…In a more heavily doped thicker film, many more prominent layers are revealed (not shown). Even though these results suggest a nonuniform dopant distribution, [23] atomic resolution STEM reveals formation of crystalline HfO 2 grains between the two TiN electrodes without obvious formation of secondary phases (Figure 4). Consistent with prior reports for Gd:HfO 2 , [19] some grains in Si:HfO 2 were observed to relax toward tetragonal-like symmetry at the electrode interfaces (see Figure 4).…”

Section: Chemical Compositionmentioning

confidence: 96%

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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“…Nevertheless, it is important to note that our ideal scenario is strongly reminiscent of how most FE hafnia films are actually grown, via atomic layer deposition (ALD), where the dopant ratio is achieved by performing a dopant oxide ALD cycle after a certain number of

{HfO}_{2}

cycles . ALD‐grown films are then subject to thermal treatment to induce crystallization; whereas dopants may diffuse at this step, the resulting samples still present a modulation in dopant concentration along the growth direction, thus displaying diffuse dopant layers . Hence, when the ALD samples are subject to the wake‐up treatment—i.e., the application of alternate electric fields, typically along the out‐of‐plane direction—they are (according to our results) suitably preconditioned to yield the FE‐o phase.…”

mentioning

confidence: 99%

Effect of Dopant Ordering on the Stability of Ferroelectric Hafnia

Dutta

Aramberri

Schenk

et al. 2020

Physica Rapid Research Ltrs

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Films of all-important compound hafnia (HfO2) can be prepared in an orthorhombic ferroelectric (FE) state that is ideal for applications, e.g. in memories or negative-capacitance field-effect transistors. The origin of this FE state remains a mystery, though, as none of the proposed mechanisms for its stabilization -from surface and size effects to formation kinetics -is fully convincing. Interestingly, it is known that doping HfO2 with various cations favors the occurrence of the FE polymorph; however, existing first-principles works suggest that doping by itself is not sufficient to stabilize the polar phase over the usual non-polar monoclinic ground state. Here we use first-principles methods to reexamine this question. We consider two representative isovalent substitutional dopants, Si and Zr, and study their preferred arrangement within the HfO2 lattice. Our results reveal that small atoms like Si can adopt very stable configurations (forming layers within specific crystallographic planes) in the FE orthorhombic phase of HfO2, but comparatively less so in the non-polar monoclinic one. Further, we find that, at low concentrations, such a dopant ordering yields a FE ground state, the usual paraelectric phase becoming a higher-energy metastable polymorph. We discuss the implications of our findings, which constitute a definite step forward towards understanding ferroelectricity in HfO2.

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Mixed Al and Si doping in ferroelectric HfO2 thin films

Cited by 38 publications

References 18 publications

High polarization, endurance and retention in sub-5 nm Hf_0.5Zr_0.5O₂ films

High polarization, endurance and retention in sub-5 nm Hf_0.5Zr_0.5O₂ films

Si Doped Hafnium Oxide—A “Fragile” Ferroelectric System

Effect of Dopant Ordering on the Stability of Ferroelectric Hafnia

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Mixed Al and Si doping in ferroelectric HfO2 thin films

Cited by 38 publications

References 18 publications

High polarization, endurance and retention in sub-5 nm Hf0.5Zr0.5O2 films

High polarization, endurance and retention in sub-5 nm Hf0.5Zr0.5O2 films

Si Doped Hafnium Oxide—A “Fragile” Ferroelectric System

Effect of Dopant Ordering on the Stability of Ferroelectric Hafnia

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High polarization, endurance and retention in sub-5 nm Hf_0.5Zr_0.5O₂ films

High polarization, endurance and retention in sub-5 nm Hf_0.5Zr_0.5O₂ films