Enhancement of crystal anisotropy and ferroelectricity by decreasing thickness in (Al,Sc)N films

Yasuoka, Shinnosuke; Mizutani, Ryoichi; Ota, Reika; Shiraishi, Takahisa; Shimizu, Takao; Yasui, Shintaro; Nishida, Ken; Uehara, Masato; Yamada, Hiroshi; Akiyama, Morito; Imai, Yasuhiko; Sakata, Osami; Funakubo, Hiroshi

doi:10.2109/jcersj2.21184

Cited by 17 publications

(11 citation statements)

References 31 publications

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“…For nonepitaxial films, this was attributed to a change of c ‐to‐ a lattice parameter ratio with decreasing

{Al}_{1 - x} {Sc}_{x} N

film thickness. [ 18 ] As a consequence, the internal parameter u decreased, which is known to result in an increase of the coercive field. [ 11 ] However, XRD measurements (not shown here) of our films reveal no scaling of u .…”

Section: Resultsmentioning

confidence: 99%

“…[ 16,17 ] Very recently, partly ferroelectric switching of

\approx

12 nm‐thick

{Al}_{1 - x} {Sc}_{x} N

was reported by performing positive‐up‐negative‐down (PUND) measurements at room temperature. [ 18 ] The availability of ferroelectric sub‐20 nm films is however crucial in order to reach switching voltages in the low‐single‐digit volt range that is desired for advanced circuits as well as sufficiently small line widths for large‐scale integration. Here we present our recent results on the thickness scaling (from 100 nm down to 10 nm) of epitaxial

{Al}_{0.72} {Sc}_{0.28} N

grown on epitaxial Pt via sputter deposition on GaN/sapphire substrates.…”

Section: Introductionmentioning

confidence: 99%

“…[16,17] Very recently, partly ferroelectric switching of %12 nm-thick Al 1Àx Sc x N was reported by performing positive-up-negative-down (PUND) measurements at room temperature. [18] The availability of ferroelectric sub-20 nm films is however crucial in order to reach switching voltages in the low-single-digit volt range that is desired for advanced circuits as…”

mentioning

confidence: 99%

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Ultrathin Al_1−xSc_xN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Schönweger

Islam

Wolff

et al. 2022

Physica Rapid Research Ltrs

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The high coercive field (E c ) and the high, stable remanent polarization separate the ferroelectric properties recently discovered in materials with wurtzite-type structure from classical ferroelectrics. [1][2][3][4] This raises hopes for particularly good scalability of wurtzite-type-based ferroelectric devices. In addition, the complementary metaloxide semiconductor compatibility and the well-established industrial deposition process make Al 1Àx Sc x N thin films highly attractive for building novel neuromorphic computing and memory devices such as ferroelectric field-effect transistors (FeFET) and ferroelectric tunnel junctions (FTJs). [5][6][7][8][9] Furthermore, it is expected that wurtzite-type ferroelectrics such as Al 1Àx Sc x N introduce ferroelectricity into III-N technology, resulting in a straightforward approach to realize, for example, GaN-embedded memory. Such ferroelectric all-epitaxial all-wurtzite type Al 1Àx Sc x N/GaN heterostructures were demonstrated recently. [10,11] However, a very low film thickness of the ferroelectric layer is needed for following the general trend of miniaturization and increasing storage density in all of the aforementioned devices. In this context, Al 1Àx Sc x N offers high scalability due to its high E c , making it possible to tailor the film thickness to the ultrathin regime to achieve reasonable memory windows and low operating voltages. [12] Furthermore, in terms of device design, ultrathin ferroelectric films are a prerequisite for building FTJs. [7] Reducing the thickness to the ultrathin regime (<30 nm) is often accompanied by a material-specific diminution of remanent polarization (P r ), a drastic increase of E c , or results in a total loss of ferroelectricity. [13][14][15] To our best knowledge, up to now, no thickness scaling study on ferroelectric epitaxial Al 1Àx Sc x N heterostructures was conducted. Also for nonepitaxial heterostructures, only a small number of studies were performed. Below 20 nm film thickness, measurements that suggest ferroelectricity at elevated temperatures or indirectly through scanning nonlinear dielectric microscopy are accessible. [16,17] Very recently, partly ferroelectric switching of %12 nm-thick Al 1Àx Sc x N was reported by performing positive-up-negative-down (PUND) measurements at room temperature. [18] The availability of ferroelectric sub-20 nm films is however crucial in order to reach switching voltages in the low-single-digit volt range that is desired for advanced circuits as

show abstract

“…For nonepitaxial films, this was attributed to a change of c ‐to‐ a lattice parameter ratio with decreasing

{Al}_{1 - x} {Sc}_{x} N

Section: Resultsmentioning

confidence: 99%

“…[ 16,17 ] Very recently, partly ferroelectric switching of

\approx

12 nm‐thick

{Al}_{1 - x} {Sc}_{x} N

{Al}_{0.72} {Sc}_{0.28} N

grown on epitaxial Pt via sputter deposition on GaN/sapphire substrates.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Ultrathin Al_1−xSc_xN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Schönweger

Islam

Wolff

et al. 2022

Physica Rapid Research Ltrs

View full text Add to dashboard Cite

show abstract

“…(Al 1– x Sc x )N thin films exhibit a unique ferroelectric property: large remanent polarization ( P r ) values beyond 100 μC/cm 2 . In particular, it is reported that the P r values exceeding 100 μC/cm 2 are preserved without remarkable degradation even in considerably thin (around 10 nm) films . These results promise next-generation memory devices using ultrathin ferroelectric (Al 1– x Sc x )N films, especially ferroelectric tunnel junctions (FTJs), because large P r values are thought to contribute to large on/off resistance ratios …”

Section: Introductionmentioning

confidence: 88%

“…In particular, it is reported that the P r values exceeding 100 μC/cm 2 are preserved without remarkable degradation even in considerably thin (around 10 nm) films. 8 These results promise next-generation memory devices using ultrathin ferroelectric (Al 1−x Sc x )N films, especially ferroelectric tunnel junctions (FTJs), because large P r values are thought to contribute to large on/off resistance ratios. 9 The ferroelectric properties of conventional ferroelectric materials such as Pb(Zr,Ti)O 3 and HfO 2 -based films are affected by various factors, such as chemical composition and mechanical strain.…”

Section: ■ Introductionmentioning

confidence: 97%

Tunable Ferroelectric Properties in Wurtzite (Al_0.8Sc_0.2)N via Crystal Anisotropy

Yasuoka

Mizutani

Ota

et al. 2022

ACS Appl. Electron. Mater.

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The effect of pure mechanical strain on ferroelectricity was investigated for (001)-one-axis-oriented (Al0.8Sc0.2)N films deposited on (111)Pt-coated substrates with different thermal expansion coefficients. The mechanical lattice strains were successfully controlled by using substrates with different thermal expansion coefficients, though the composition of the films is the same. The changes in the remanent polarization (P r) and coercive field (E c) values of these films can be understood by the internal parameter u representing crystal anisotropy of a wurtzite structure. These results suggest that the ferroelectric properties of (Al1–x Sc x )N films can be tuned via crystal anisotropy.

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Probing of Polarization Reversal in Ferroelectric (Al,Sc)N Films Using Single‐ and Tri‐Layered Structures With Different Sc/(Al+Sc) Ratio

Yasuoka,

Shimizu,

Okamoto

et al. 2024

Adv Materials Inter

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Wurtzite‐(Al,Sc)N films are promising candidates for ferroelectric memory devices owing to their outstanding properties. However, there are many challenges on the way to practical applications, including lowering an electric field required for polarization switching. Understanding the switching kinetics, especially the starting point of polarization reversal, is key to designing materials with desired properties. Here, the impact of Sc concentration and segregation on the switching kinetics for (Al,Sc)N capacitors is investigated by evaluating time‐ and field‐dependences of the switching polarization for the tri‐layered (Al,Sc)N films with various Sc/(Al+Sc) ratios. The remanent polarization of stacked films slightly decreased compared to those of the single‐layered films with the same average Sc/(Al+Sc) ratio, while their coercive fields depended on the average Sc content in (Al,Sc)N. The ferroelectric switching behavior suggests the possibility of nucleation originating from the Sc‐rich region and the sequential switching mechanism for individual layers, which is unique to multilayered films. This shows a possibility that nucleations of the polarization switching start not from the interface between the (Al,Sc)N films and the electrodes. The unique switching kinetics in tri‐layered (Al,Sc)N films have provided new insights into the field of ferroelectric switching in wurtzite‐nitrides.

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Enhancement of crystal anisotropy and ferroelectricity by decreasing thickness in (Al,Sc)N films

Cited by 17 publications

References 31 publications

Ultrathin Al_1−xSc_xN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Ultrathin Al_1−xSc_xN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Tunable Ferroelectric Properties in Wurtzite (Al_0.8Sc_0.2)N via Crystal Anisotropy

Probing of Polarization Reversal in Ferroelectric (Al,Sc)N Films Using Single‐ and Tri‐Layered Structures With Different Sc/(Al+Sc) Ratio

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Enhancement of crystal anisotropy and ferroelectricity by decreasing thickness in (Al,Sc)N films

Cited by 17 publications

References 31 publications

Ultrathin Al1−xScxN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Ultrathin Al1−xScxN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Tunable Ferroelectric Properties in Wurtzite (Al0.8Sc0.2)N via Crystal Anisotropy

Probing of Polarization Reversal in Ferroelectric (Al,Sc)N Films Using Single‐ and Tri‐Layered Structures With Different Sc/(Al+Sc) Ratio

Contact Info

Product

Resources

About

Ultrathin Al_1−xSc_xN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Ultrathin Al_1−xSc_xN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Tunable Ferroelectric Properties in Wurtzite (Al_0.8Sc_0.2)N via Crystal Anisotropy