A key piece of the ferroelectric hafnia puzzle

Noheda, Beatriz; Íñiguez, Jorgé

doi:10.1126/science.abd1212

Cited by 16 publications

(18 citation statements)

References 11 publications

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“…[18,19] The read voltage used in all I-V measurements (< 500 mV) is well below the coercive voltage of 1 nm Zr:HfO 2 , enabling non-destructive readout. The low J ON (< 10 nA µm −2 ) reported for HfO 2 -based FTJs-due to the lack of an ultrathin Zr:HfO 2 ferroelectric layer only recently established [20][21][22][23][24]40] -prevents practical application into highly-scaled crossbar memories due to insufficient read current. [13] Here, the 1 nm Zr:HfO 2 FTJs can maintain an ON/OFF of 10-higher than most HfO 2 -based FTJs reported thus far (Figure 4a)-for up to 10 3 cycles (Figure 3e).…”

Section: Device Performance Of 1 Nm Hfo 2 -Based Ftjsmentioning

confidence: 99%

One Nanometer HfO₂‐Based Ferroelectric Tunnel Junctions on Silicon

Cheema

Shanker

Hsu

et al. 2021

Adv Elect Materials

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incompatibilities with silicon and modern semiconductor processes. [5] Since the discovery of ferroelectricity in HfO 2 -based thin films in 2011, [6] fluorite-structure binary oxides have attracted considerable interest as they are compatible with complementary metal-oxide-semiconductor (CMOS) processes. [7] Accordingly, HfO 2based ferroelectric memory has received significant attention in recent years, [1,8,9] primarily focused on charge-based ferroelectric random access memory (FeRAM) and ferroelectric field effect transistors (FeFETs). [2,10] Meanwhile, resistiveswitching materials-which exhibit electrically-induced resistance changes in metal-dielectric-metal junctions or heterostructures with multi-dielectric barriershave emerged as promising candidates for novel beyond-CMOS data-centric computing paradigms. [11][12][13] In this context, ferroelectric tunnel junctions (FTJs) present a promising energy-efficient resistive switching memory [12,13] as FTJs exploit the ferroic polarization functionality of the insulating barrier. [14] Voltage-controlled polarization-dependent tunneling through the ferroelectric layer (tunnel electroresistance, TER) can yield much larger ON/OFF conductance ratios [15,16] than, for example, current-controlled magnetic tunnel junctions, [12] another two-terminal tunneling resistive switching device.A critical requirement for FTJs is to achieve a sufficiently high tunneling current (J ON ) at the ON state to ensure that a scaled device can be read rapidly, while still exhibiting a large TER ((J ON -J OFF )/J OFF × 100%). [13] Considering the large band gap of HfO 2 (≈6 eV), the thickness of HfO 2 in the FTJ will need to be reduced to the ultrathin limit for adequate tunnel current. Tunnel junctions implementing CMOS-compatible HfO 2 -based ferroelectric barriers have been recently demonstrated, [17][18][19] but even three nanometer Zr-doped HfO 2 (Zr:HfO 2 ) barriers were found to be too thick to obtain nano-ampere level current in micron-sized capacitors. [20] Therefore, high ON current is a critical consideration; however, the increased ON state current from an ultrathin barrier will coincide with an increased OFF state current. For array-level implementations, where sneak leakage paths can lead to increased power consumption, selector devices may be required in conjunction with the FTJ memory elements to reduce such sneak currents. [13] Here, we demonstrate FTJs utilizing one nanometer Zr:HfO 2 as the ferroelectric barrier, grown by atomic layer deposition (ALD) directly on silicon, thereby scaling down the tunnel barrier ABSTRACT: In ferroelectric materials, spontaneous symmetry breaking leads to a switch-able electric polarization, which offers significant promise for nonvolatile memories. In particular, ferroelectric tunnel junctions (FTJs) have emerged as a new resistive switching memory which exploits polarizationdependent tunnel current across a thin ferroelectric barrier. This work integrates FTJs with com-plementary metal-oxide-semiconductor-compatible Zr-doped HfO 2 (Zr...

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Section: Device Performance Of 1 Nm Hfo 2 -Based Ftjsmentioning

confidence: 99%

One Nanometer HfO₂‐Based Ferroelectric Tunnel Junctions on Silicon

Cheema

Shanker

Hsu

et al. 2021

Adv Elect Materials

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“…For example, theoretical work suggests that hafnia’s ferroelectricity may not be proper in character 6 – 8 , yet it is switchable, which sets this compound apart from all ferroelectrics used so far in applications. Further, the nature of its (anti)polar instabilities is such that very narrow domains, and very narrow domain walls, occur naturally in it 9 , 10 ; in effect, this makes HfO 2 a quasi-2D ferroelectric, and may explain the resilience of its polar phase in nanometric samples. In fact, unlike traditional materials, HfO 2 seems to improve its ferroelectric properties as the samples decrease in size; moreover, the first reports of ferroelectricity in thick films or bulk samples are very recent 11 , 12 .…”

Section: Introductionmentioning

confidence: 99%

Piezoelectricity in hafnia

et al. 2021

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Because of its compatibility with semiconductor-based technologies, hafnia (HfO2) is today’s most promising ferroelectric material for applications in electronics. Yet, knowledge on the ferroic and electromechanical response properties of this all-important compound is still lacking. Interestingly, HfO2 has recently been predicted to display a negative longitudinal piezoelectric effect, which sets it apart from classic ferroelectrics (e.g., perovskite oxides like PbTiO3) and is reminiscent of the behavior of some organic compounds. The present work corroborates this behavior, by first-principles calculations and an experimental investigation of HfO2 thin films using piezoresponse force microscopy. Further, the simulations show how the chemical coordination of the active oxygen atoms is responsible for the negative longitudinal piezoelectric effect. Building on these insights, it is predicted that, by controlling the environment of such active oxygens (e.g., by means of an epitaxial strain), it is possible to change the sign of the piezoelectric response of the material.

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“…Along with the distinct piezoelectric origins ( 27 ), unconventional ferroelectric origins have also been attributed to fluorite-structure binary oxides ( 12 , 13 ). First-principles calculations suggest that 2D fluorite-structure Pca 2 1 slabs maintain switchable polarization because of their improper nature ( 12 ); indeed, for improper ferroelectric transitions, the primary nonpolar structural distortion, from which the spontaneous polarization indirectly arises, is impervious to electrostatic depolarization effects ( 28 ).…”

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confidence: 99%

Emergent ferroelectricity in subnanometer binary oxide films on silicon

Cheema

Shanker

Hsu

et al. 2022

Science

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The critical size limit of voltage-switchable electric dipoles has extensive implications for energy-efficient electronics, underlying the importance of ferroelectric order stabilized at reduced dimensionality. We report on the thickness-dependent antiferroelectric-to-ferroelectric phase transition in zirconium dioxide (ZrO 2 ) thin films on silicon. The emergent ferroelectricity and hysteretic polarization switching in ultrathin ZrO 2 , conventionally a paraelectric material, notably persists down to a film thickness of 5 angstroms, the fluorite-structure unit-cell size. This approach to exploit three-dimensional centrosymmetric materials deposited down to the two-dimensional thickness limit, particularly within this model fluorite-structure system that possesses unconventional ferroelectric size effects, offers substantial promise for electronics, demonstrated by proof-of-principle atomic-scale nonvolatile ferroelectric memory on silicon. Additionally, it is also indicative of hidden electronic phenomena that are achievable across a wide class of simple binary materials.

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A key piece of the ferroelectric hafnia puzzle

Abstract: A key piece of the ferroelectric hafnia puzzle Dipolar slices explain the origin of ferroelectricity in a material now used for memory devices. Science, 369(6509),

Cited by 16 publications

References 11 publications

One Nanometer HfO₂‐Based Ferroelectric Tunnel Junctions on Silicon

One Nanometer HfO₂‐Based Ferroelectric Tunnel Junctions on Silicon

Piezoelectricity in hafnia

Emergent ferroelectricity in subnanometer binary oxide films on silicon

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A key piece of the ferroelectric hafnia puzzle

Abstract: A key piece of the ferroelectric hafnia puzzle Dipolar slices explain the origin of ferroelectricity in a material now used for memory devices. Science, 369(6509),

Cited by 16 publications

References 11 publications

One Nanometer HfO2‐Based Ferroelectric Tunnel Junctions on Silicon

One Nanometer HfO2‐Based Ferroelectric Tunnel Junctions on Silicon

Piezoelectricity in hafnia

Emergent ferroelectricity in subnanometer binary oxide films on silicon

Contact Info

Product

Resources

About

One Nanometer HfO₂‐Based Ferroelectric Tunnel Junctions on Silicon

One Nanometer HfO₂‐Based Ferroelectric Tunnel Junctions on Silicon