Preparation and properties of thin amorphous tantalum films formed by small e-beam evaporators

Stella, Kevin; Bürstel, Damian; Franzka, Steffen; Posth, Oliver; Diesing, Detlef

doi:10.1088/0022-3727/42/13/135417

Cited by 35 publications

(24 citation statements)

References 47 publications

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“…The very low evaporation rates achievable with the mini e-gun are desirable especially for ultra-thin film applications. 17 A total Hf thin film thickness of 50 nm was obtained on a 40 × 40 mm 2 substrate. The base pressure of the e-beam chamber was 5 × 10 −7 Pa and the Hf deposition took place in vacuum (10 −6 Pa) at room temperature.…”

Section: Methodsmentioning

confidence: 99%

Anodization Behavior of Glassy Metallic Hafnium Thin Films

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Gavrilović-Wohlmuther

et al. 2015

J. Electrochem. Soc.

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Glassy metallic Hf thin films were obtained using electron beam deposition at room temperature due to the low energy received by Hf atoms during the film formation process. The amorphous nature of the Hf films suggested by XRD was confirmed by low temperature electrical conductivity measurements where a negative temperature coefficient of resistivity was identified. Anodic oxidations using a scanning droplet cell microscopy were performed on a typical crystalline (hexagonal) Hf film obtained by sputtering and on the glassy Hf. A decrease of the oxide formation factor by 30% (from 2.4 to 1.7 nm V −1 ) was evidenced on the amorphous Hf. Electrochemical impedance spectroscopy on both samples revealed almost identical capacitances while the electrical permittivities were found to differ by 40%. The dielectric constant of the HfO 2 decreased from 33.5 on the crystalline parent metal sample to 19.8 on the amorphous one. The unexpected 10% deviation was attributed to a smoother defect-free oxide/metal interface in the case of Hafnium dioxide has a high dielectric constant, a relatively large bandgap, larger heat of formation as compared to SiO 2 , good chemical and thermal stability on Si and large barrier heights at interfaces with Si. Its modern applications are diverse, most recent ones focused on electronic devices. The chosen methods for obtaining hafnia thin films are also varied, most common one being reactive sputtering.1 Doping of sputtered hafnia with elements such as Ce has led to an increase in the dielectric constant and a decrease of the leakage currents, while Si doping revealed intrinsic ferroelectricity due to a non-centrosymmetric orthorhombic phase with direct applications in ferroelectric memories.2,3 Cathodoluminescence due to oxygen vacancies was also recently found in ion beam sputtered HfO 2 and first steps toward fabrications of hafnia micro-light emitting devices were already taken. 4,5 The resistance switching behavior due to formation and rupture of conductive paths within HfO 2 deposited by atomic layer deposition was exploited for random access memory fabrication. 6 Since these are only a few examples of most recent applications of HfO 2 , still the predominant effort is put into using it as high-k material for gate oxides for replacing SiO 2 gates in MOS-FET structures.7 For a typical operation voltage of 1-1.5 V, the leakage current through HfO 2 dielectric films was found to be several orders of magnitude lower than that of SiO 2 for the same equivalent oxide thickness of 0.9-2 nm.8-10 However, clearly a weak point in using thermally grown or vapour phase deposited HfO 2 as gate dielectrics arises from its poor interfacing with semiconductors which has led to a fervent investigation of hafnium-based complex oxides in recent years. 7Nowadays it is common knowledge that the anodic oxides on valve metals (e.g. Al, Hf, Ta, Nb etc.) are some of the most compact oxides available due to their growth mechanism obeying a high field regime.11 However, their use for electronic devices is weakly ex...

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Section: Methodsmentioning

confidence: 99%

Anodization Behavior of Glassy Metallic Hafnium Thin Films

Mardare

Siket

Gavrilović-Wohlmuther

et al. 2015

J. Electrochem. Soc.

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“…The effective thickness of the metallic nanostripe that allowed the best fit was 12 nm. This means that either some of the Ta in contact with the SiO 2 substrate is oxidized and/or that the Ta became very resistive as a thin layer [23]. Figure 2(a) shows small deviations between simulations and experiments for the largest voltage pulses.…”

Section: B Details Of the Computer Simulationsmentioning

confidence: 96%

Joule heating in ferromagnetic nanostripes with a notch

et al. 2015

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The temperature in a ferromagnetic nanostripe with a notch subject to Joule heating has been studied in detail. We first performed an experimental real-time calibration of the temperature versus time as a 100 ns current pulse was injected into a Permalloy nanostripe. This calibration was repeated for different pulse amplitudes and stripe dimensions and the set of experimental curves were fitted with a computer simulation using the Fourier thermal conduction equation. The best fit of these experimental curves was obtained by including the temperature-dependent behavior of the electrical resistivity of the Permalloy and of the thermal conductivity of the substrate (SiO 2 ). Notably, a nonzero interface thermal resistance between the metallic nanostripe and the substrate was also necessary to fit the experimental curves. We found this parameter pivotal to understand our results and the results from previous works. The higher current density in the notch, together with the interface thermal resistance, allows a considerable increase of the temperature in the notch, creating a large horizontal thermal gradient. This gradient, together with the high temperature in the notch and the larger current density close to the edges of the notch, can be very influential in experiments studying the current assisted domain wall motion.

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“…The resistivity of these thin films is 209 μΩcm (10 nm) and 193 μΩcm (15 nm) at room temperature. Moreover, it shows a negative temperature coefficient of resistance (TCR) [43], which is characteristic of high-resistivity disordered metals and has been reported for the β-Ta phase [20,44] and the amorphous Ta as well [21,22]. We inject a charge current from the Py electrode to the left side of the Cu channel.…”

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confidence: 99%

Unveiling the mechanisms of the spin Hall effect in Ta

et al. 2018

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Spin-to-charge current interconversions are widely exploited for the generation and detection of pure spin currents and are key ingredients for future spintronic devices including spin-orbit torques and spin-orbit logic circuits. In case of the spin Hall effect, different mechanisms contribute to the phenomenon and determining the leading contribution is peremptory for achieving the largest conversion efficiencies. Here, we experimentally demonstrate the dominance of the intrinsic mechanism of the spin Hall effect in highly-resistive Ta. We obtain an intrinsic spin Hall conductivity for β-Ta of -820±120 (ħ/e) Ω -1 cm -1 from spin absorption experiments in a large set of lateral spin valve devices. The predominance of the intrinsic mechanism in Ta allows us to linearly enhance the spin Hall angle by tuning the resistivity of Ta, reaching up to -35±3 %, the largest reported value for a pure metal.Condensed matter systems with strong spin-orbit coupling (SOC) are extensively studied in the emerging field of spin-orbitronics due to the novel effects and functionalities originated from the interplay between the charge and the spin of electrons. The spin Hall effect (SHE) in heavy metals [1,2] and Edelstein effect in Rashba interfaces [3,4,5] or in the Dirac surface states of topological insulators [3,6] are some of the phenomena discovered in this field. They all lead to spin-to-charge current interconversions, which are essential for future spin-orbit-based technological applications such as spin-orbit torques for magnetization switching [7,8,9,10] or spin-orbit logic [11,12].

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Preparation and properties of thin amorphous tantalum films formed by small e-beam evaporators

Cited by 35 publications

References 47 publications

Anodization Behavior of Glassy Metallic Hafnium Thin Films

Anodization Behavior of Glassy Metallic Hafnium Thin Films

Joule heating in ferromagnetic nanostripes with a notch

Unveiling the mechanisms of the spin Hall effect in Ta

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