Pulsed-N2 assisted growth of 5-20 nm thick <i>β</i>-W films

Narasimham, Avyaya J.; Green, Avery; Matyi, R. J.; Khare, Prasanna; Vo, Tuan; Diebold, Alain C.; LaBella, V. P.

doi:10.1063/1.4935372

Cited by 5 publications

(8 citation statements)

References 18 publications

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“…Fig. 5a shows a peak at 29.7 eV related to the W metal element, while Narasimham et al [25] found it at about 30.5 eV to 31.3 eV which is close to the obtained results. Also, the spectra present a symmetrical peak of W 4f incorporated with WO 3 (W 4f 7/2 (35.6 eV)) and (W 4f 5/2 (36.7 eV)).…”

Section: Edx and Xps Studysupporting

confidence: 87%

Study of crystallographic, optical and sensing properties of Na₂WO₄ films deposited by thermal evaporation with several thickness

Abdallah

Kakhia

Shaker

2019

Materials Science-Poland

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Na2WO4 films have been grown at 400 °C using thermal evaporation technique. Their structural properties were characterized by XRD, while their chemical composition was verified by both EDX and X-ray photoelectron spectroscopy (XPS). The evolution of crystallinity was studied as a function of film thickness that ranged from 500 nm to 3000 nm. The grain size increased with increasing film thickness. The surface morphology of the prepared films was studied using scanning electron microscope (SEM) and atomic force microscopy (AFM). It has been observed that the average transmittance of samples in the visible and near infrared range has varied from 90 % to 78 % with the film thickness. The optical band gap of the Na2WO4 films varied from 3.8 eV to 4.1 eV. The crystalline size increased with increasing thickness and showed better sensing response to gases. Thus, this study confirmed the possibility of using Na2WO4 thick films as a sensor element for detection of ethanol (C2H5OH), acetone (C3H6O) methanol (CH3OH) and ammonia hydroxide (NH4OH) vapor at room temperature, where thicker films exhibited sensing properties with a maximum sensitivity at 25 °C in air, especially for NH4OH.

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Section: Edx and Xps Studysupporting

confidence: 87%

Study of crystallographic, optical and sensing properties of Na₂WO₄ films deposited by thermal evaporation with several thickness

Abdallah

Kakhia

Shaker

2019

Materials Science-Poland

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“…2(a) (purple curve), strongly limiting the use of seed and adhesion materials. However, there are reports showing that the presence of oxygen or nitrogen adsorbed onto the surface provides nucleation sites for the growth of metastable β-W [37][38][39].…”

Section: Extension Of Tungsten β Phase Windowmentioning

confidence: 99%

“…Such thin layers impose severe constraints on the choice of thickness and on the etching conditions, possibly leading to a strong distribution of the SOT resistance and efficiency from device to device. We report in this paper the possibility of optimizing the growth of β-W using dopants such as nitrogen and oxygen [37][38][39]. We develop a process in which growing a bilayer of oxygen-and nitrogendoped tungsten, W(O, N), results in process control of the tungsten β phase to more than 10 nm, while concurrently improving the PMA as well as improving the SOT efficiency to −44.4%.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Tungsten β -Phase Window for Spin-Orbit-Torque Magnetic Random-Access Memory

et al. 2021

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Switching induced by spin-orbit torque (SOT) is being vigorously explored, as it allows the control of magnetization using an in-plane current, which enables a three-terminal magnetic-tunnel-junction geometry with isolated read and write paths. This significantly improves the device endurance and the read stability, and allows reliable subnanosecond switching. Tungsten in the β phase, β-W, has the largest reported antidamping SOT charge-to-spin conversion ratio (θ AD ≈ −60%) for heavy metals. However, β-W has a limitation when one is aiming for reliable technology integration: the β phase is limited to a thickness of a few nanometers and enters the α phase above 4 nm in our samples when industryrelevant deposition tools are used. Here, we report our approach to extending the range of β-W, while simultaneously improving the SOT efficiency by introducing N and O doping of W. Resistivity and XRD measurements confirm the extension of the β phase from 4 nm to more than 10 nm, and transport characterization shows an effective SOT efficiency larger than −44.4% (reaching approximately −60% for the bulk contribution). In addition, we demonstrate the possibility of controlling and enhancing the perpendicular magnetic anisotropy of a storage layer (Co-Fe-B). Further, we integrate the optimized W(O, N) into SOT magnetic random-access memory (SOT-MRAM) devices and project that, for the same thickness of SOT material, the switching current decreases by 25% in optimized W(O, N) compared with our standard W. Our results open the path to using and further optimizing W for integration of SOT-MRAM technology.

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“…This disparity in spin Hall angles for the different phases has led to recent work 5,6 to resolve the origin of the high spin Hall angle in β-W. Since the growth of β-W requires the addition of O [7][8][9] , N 10,11 , F 12,13 , or Si 14 impurities to stabilize the crystal lattice, it has been unclear if the high spin Hall angle was intrinsic or extrinsic. The intrinsic spin Hall effect is due to strong relativistic spin-orbit interactions in the material that act to separate spins and produce a transverse spin current when a charge current is applied.…”

Section: Introductionmentioning

confidence: 99%

Impact of impurities on the spin Hall conductivity in β -W

McHugh

Goh

Gradhand

et al. 2020

Phys. Rev. Materials

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While the metastable β (A15) phase of tungsten has one of the largest spin Hall angles measured, the origin of this high spin Hall conductivity is still unclear. Since large concentrations of oxygen and nitrogen are often used to stabilize β tungsten, it is not obvious whether the high spin Hall conductivity is due to an intrinsic or extrinsic effect. In this work, we have examined the influence of O and N dopants on the spin Hall conductivity and spin Hall angle of β-W. Using multiple first principles approaches, we examine both the intrinsic and extrinsic (skew scattering) contributions to spin Hall conductivity. We find that intrinsic spin Hall conductivity calculations for pristine β-W are in excellent agreement with experiment. However, when the effect of high concentrations (11 at.%) of O or N interstitials on the electronic structures is taken into account, the predicted intrinsic spin Hall conductivity is significantly reduced. Skew scattering calculations for O and N interstitials in β-W indicate that extrinsic contributions have a limited impact on the total spin Hall conductivity. However, we find that the spin-flip scattering at O and N impurities can well explain the experimentally found spin-diffusion length within the range of 1-5 nm. To explain these findings, we propose that dopants (O and N) help to stabilize β-W grains during film deposition and afterwards segregate to the grain boundaries. This process leads to films of relatively pristine small β-W grains and grain boundaries with high concentrations of O or N scattering sites. This combination provides high spin Hall conductivity and large electrical resistance, leading to high spin Hall angles. This work shows that engineering grain boundary properties in other high spin Hall conductivity materials could provide an effective way to boost the spin Hall angle.

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Pulsed-N2 assisted growth of 5-20 nm thick β-W films

Cited by 5 publications

References 18 publications

Study of crystallographic, optical and sensing properties of Na₂WO₄ films deposited by thermal evaporation with several thickness

Study of crystallographic, optical and sensing properties of Na₂WO₄ films deposited by thermal evaporation with several thickness

Optimization of Tungsten β -Phase Window for Spin-Orbit-Torque Magnetic Random-Access Memory

Impact of impurities on the spin Hall conductivity in β -W

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Pulsed-N2 assisted growth of 5-20 nm thick β-W films

Cited by 5 publications

References 18 publications

Study of crystallographic, optical and sensing properties of Na2WO4 films deposited by thermal evaporation with several thickness

Study of crystallographic, optical and sensing properties of Na2WO4 films deposited by thermal evaporation with several thickness

Optimization of Tungsten β -Phase Window for Spin-Orbit-Torque Magnetic Random-Access Memory

Impact of impurities on the spin Hall conductivity in β -W

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Study of crystallographic, optical and sensing properties of Na₂WO₄ films deposited by thermal evaporation with several thickness

Study of crystallographic, optical and sensing properties of Na₂WO₄ films deposited by thermal evaporation with several thickness