Anodization Behavior of Glassy Metallic Hafnium Thin Films

Abstract

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...

Electrolyte-Dependent Modification of Resistive Switching in Anodic Hafnia

“…Hafnium dioxide is typically a compact oxide with a high dielectric constant, large bandgap, and high chemical and thermal stability [ 20 ]. Anodic formation of Hf oxide directly on Hf parent metal thin films already showed admirable electrical properties for electronic applications [ 21 , 22 ]. Therefore, the use of inexpensive, simple, and fast electrochemical methods for fabrication of the oxide layer necessary in MIM structures such as Pt/HfO 2 /Hf may present some advantages for being used in ReRAMs competing with more expensive fabrication methods such as sputtering [ 18 , 23 , 24 ].…”

Memristive Characteristics of Composite Hafnium/Tantalum Anodic Oxides

“…However, is important to note that this is not always the case, and amorphous Hf and Ta films with particular anodization characteristics were already reported. [ 43,44 ]…”

Downstream analytics quantification of ion release during high-voltage anodisation of niobium

“…Moreover, the oxide grows at both interfaces, the metal/oxide interface and the oxide/electrolyte interface, as dictated by anionic and cationic transport numbers. An exception is found for Zr and Hf which have very low transport numbers [4]. The thin oxide layers formed during anodisation are transparent and the phenomenon of optical interference is responsible for the apparent colours of the films on Hf, Nb, Ta, Ti and Zr [5].…”