Ferroelectric Si-Doped HfO<sub>2</sub> Device Properties on Highly Doped Germanium

Lomenzo, Patrick D.; Takmeel, Qanit; Fancher, Chris M.; Zhou, Chuanzhen; Rudawski, Nicholas G.; Moghaddam, Saeed; Jones, Jacob L.; Nishida, Toshikazu

doi:10.1109/led.2015.2445352

Cited by 59 publications

(26 citation statements)

References 10 publications

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“…The understandable doubts steadily reduced in the following years as reports of similar properties induced by a wealth of dopants and studies by different groups using unique fabrication methods and various electrode materials suggested some universalityat least for thin film samples. 11,12,13,14,15,16,17,18,19,20 Further "must-haves" for a ferroelectric, beyond a hysteretic curve of polarization P vs. electric field E, such as counter-clockwise switching in a ferroelectric field-effect transistor (FE-FET) 21,22 , piezo- 10,23 and pyroelectricity 24,25 , as well as the experimental proof of the presence of a polar phase 26,27 , solidified the original claim of Böscke et al 10 . The implementation of these new class of fluorite-type ferroelectrics in first devices for memory (transistor 21 and capacitor 28 based), energy harvesting and electrocaloric cooling 29 or supercapacitors 30,31 applications was even faster than the actual proof of the claimed phase behind.…”

Section: Introductionmentioning

confidence: 59%

Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

et al. 2019

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Despite increasing attention for the recently found ferro-and antiferroelectric properties, the polymorphism in hafnia-and zirconia-based thin films is still not sufficiently understood. In the present work, we show that it is important to have a good quality X-ray absorption spectrum to go beyond an analysis of the only the first coordination shell. Equally important is to analyze both EXAFS and XANES spectra in combination with theoretical modelling to distinguish the relevant phases even in bulk materials and to separate structural from chemical effects. As a first step toward the analysis of thin films, we start with the analysis of bulk references. After that, we successfully demonstrate an approach that allows us to extract high-quality spectra also for 20 nm thin films. Our analysis extends to the second coordination shell and includes effects created by chemical substitution of Hf with Zr to unambiguously discriminate the different polymorphs. The trends derived from X-ray absorption spectroscopy agree well with X-ray diffraction measurements. In this work we clearly identify a gradual transformation from monoclinic to tetragonal phase as the Zr content of the films increases. We separated structural effects from effects created by chemical disorder when ration of Hf:Zr is varied and found differences for the incorporation of the substitute atoms between powders and thin films, which we attribute to the different fabrication routes. This work opens the door for further in-depth structural studies to shine light into the chemistry and physics of these novel ferroelectric thin films that show high application relevance.

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Section: Introductionmentioning

confidence: 59%

Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

et al. 2019

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“…Perplexities and confusions arise primarily due to the polymorphic nature of hafnia and also due to the challenges associated with the characterization of the mixed/complex phases in ultrathin films at small length scales 20 . The different sets of growth conditions, including dopant species 5,6,[21][22][23] , substrates 17,[24][25][26] , and capping electrodes 6,21,27 all add some degree of uncertainty in these characterizations. Furthermore, various extrinsic factors such as stress 28 , oxygen vacancies 29,30 , surface energy 31 , and electric fields 32 have been put forward to provide a rationale for the ferroelectricity 33,34 .…”

Section: Introductionmentioning

confidence: 99%

Kinetically stabilized ferroelectricity in bulk single-crystalline HfO2:Y

et al. 2021

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HfO 2 , a simple binary oxide, holds ultra-scalable ferroelectricity integrable into silicon technology. Polar orthorhombic (Pbc2 1 ) form in ultra-thin-films ascribes as the plausible rootcause of the astonishing ferroelectricity, which has thought not attainable in bulk crystals.Though, perplexities remain primarily due to the polymorphic nature and the characterization challenges at small-length scales. Herein, utilizing a state-of-the-art Laser-Diode-heated Floating Zone technique, we report ferroelectricity in bulk singlecrystalline HfO 2 :Y as well as the presence of anti-polar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti-)polar crystallographic signatures and abundant 90 o /180 o ferroelectric domains in addition to the switchable polarization with little wake-up effects. Density-functional theory calculations suggest that the Yttrium doping and rapid cooling are the key factors for the desired phase. Our observations provide new insights into the polymorphic nature and phase controlling of HfO 2 , remove the upper size limit for ferroelectricity, and also pave a new road toward the next-generation ferroelectric devices.

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“…17,21,22 By characterizing MFS capacitors, it has been reported that semiconductor substrates have a significant effect on the ferroelectric properties. 23,24 On the other hand, there are two concerns with the characterization of separate MFS capacitors as a method to predict the ferroelectricity of ferroelectric gates insulators in FeFETs. First, high doping concentration in the order of 10 19 to 10 20 cm -3 is usually employed in the semiconductor substrates of MFS capacitors (called here as MFS + ) to minimize the substrate depletion.…”

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confidence: 99%

Evaluation of polarization characteristics in metal/ferroelectric/semiconductor capacitors and ferroelectric field-effect transistors

Toprasertpong

Tahara

Takenaka

et al. 2020

Applied Physics Letters

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In this study, we propose a measurement technique for evaluating ferroelectric polarization characteristics in ferroelectric field-effect transistors (FeFETs). Different from standard metal/ferroelectric/metal capacitors, the depletion and inversion phenomena in semiconductor substrates have to be carefully taken into account when evaluating the ferroelectric properties using fast voltage sweep as input. The non-equilibrium deep depletion is found to be the limiting factor for the accurate evaluation of ferroelectric properties in metal/ferroelectric/semiconductor capacitors. By connecting the source, drain, and substrate of the FeFET together during the polarization measurement, the deep depletion can be suppressed and the ferroelectricity of the ferroelectric gate can be accurately evaluated. The present technique is a powerful method for capturing the polarization states in FeFETs, enabling new approaches for device characterization and fundamental study, and overcomes the limitation found in the conventional polarization measurement on 2-terminal metal/ferroelectric/semiconductor capacitors.Ferroelectric field-effect transistors (FeFETs), in which ferroelectric thin films are employed as FET gate insulators, are promising for non-volatile memory devices 1-3 and synaptic devices in computing-in-memory applications. 4-6 A substantially increasing interest in FeFETs can be seen after the discovery of ferroelectric HfO 2 7 thanks to its scalability and CMOS compatibility, 3 with FeFETs having excellent performance being continuously reported. [8][9][10][11] So far, the characterization of FeFETs is mainly limited to the standard evaluation of I d -V g characteristics and threshold voltage shift ∆V T as well as their retention and endurance properties. 3,5,[8][9][10][11][12][13][14][15][16][17] On the other hand, the ferroelectric properties of the ferroelectric gate insulators are usually evaluated in an indirect manner, by preparing separate metal/ferroelectric/metal (MFM) capacitors for characterization. 3,5,8,[14][15][16] It is usually assumed that the ferroelectric properties of the separately-prepared MFM capacitors can well reproduce those of the ferroelectric gate insulators in the FeFETs. However, it is questionable whether MFM capacitors can represent the ferroelectricity of the ferroelectric gate insulators, particularly for metal/ferroelectric/semiconductor (MFS, or sometimes called MFIS if the dielectric insulator layer should be emphasized)-type FeFETs, as it is well recognized that the ferroelectric properties of HfO2 is strongly dependent on the underlying and capping layers. [17][18][19][20] To carry out more accurate characterization, MFS capacitors are frequently employed to reproduce the same substrate condition as the ferroelectric gates in FeFETs. 17,21,22 By characterizing MFS capacitors, it has been reported that semiconductor substrates have a significant effect on the ferroelectric properties. 23,24 On the other hand, there are two concerns with the characterization of separate MFS capaci...

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Ferroelectric Si-Doped HfO₂ Device Properties on Highly Doped Germanium

Cited by 59 publications

References 10 publications

Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

Kinetically stabilized ferroelectricity in bulk single-crystalline HfO2:Y

Evaluation of polarization characteristics in metal/ferroelectric/semiconductor capacitors and ferroelectric field-effect transistors

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Ferroelectric Si-Doped HfO2 Device Properties on Highly Doped Germanium

Cited by 59 publications

References 10 publications

Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

Kinetically stabilized ferroelectricity in bulk single-crystalline HfO2:Y

Evaluation of polarization characteristics in metal/ferroelectric/semiconductor capacitors and ferroelectric field-effect transistors

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Ferroelectric Si-Doped HfO₂ Device Properties on Highly Doped Germanium