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Egorov, Konstantin V.,Kuzmichev, Dmitry S.,Chizhov, Pavel S.,Lebedinskii, Yuri Yu.,Hwang, Cheol Seong,Markeev, Andrey M. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.15
<P>The plasma-enhanced atomic layer deposition (PEALD) process using Ta(OC2H5), as a Ta precursor and plasma-activated hydrogen as a reactant for the deposition of TaOx films with a controllable concentration of oxygen vacancies (V-o) is reported herein. The V-o concentration control was achieved by varying the hydrogen volume fraction of the hydrogen-argon mixture in the plasma, allowing the control of the leakage current density in the tantalum oxide films within the range of 5 orders of magnitude compared with the Ta2O5 film grown via thermal ALD using the identical Ta precursor and H2O. Temperature-dependent current-voltage measurements combined with Poole-Frenkel emission modeling demonstrated that the bulk trap depth decreases with the increasing hydrogen volume fraction, which could be attributed to the increase of the V-o concentration. The possible chemical change in the PEALD TaOx films grown under different hydrogen volume fractions was confirmed by the in situ X-ray photoelectron spectroscopy (XPS) measurements of the Ta 4f core and valence band spectra. The comparison of the XPS-measured nonstoichiometry and the secondary ion mass spectrometry analysis of the hydrogen content allowed this study to conclude that the nonstoichiometry is largely related to the formation of Ta-V-o sites rather than of Ta-H sites. Such oxygen-deficient TaOx layers were studied for application as an oxygen-deficient layer in a resistance switching random access memory stack (Ta2O5/TaOx) where the actual switching occurred within the stoichiometric Ta2O5 layer. The bilayer memory stack showed reliable resistance switching up to similar to 10(6) switching cycles, whereas the single-layer Ta2O5 memory showed only several hundred switching cycles.</P>
Chernikova, Anna G.,Kozodaev, Maxim G.,Negrov, Dmitry V.,Korostylev, Evgeny V.,Park, Min Hyuk,Schroeder, Uwe,Hwang, Cheol Seong,Markeev, Andrey M. American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.3
<P>Hf0.5Zr0.5O2 thin films are one of the most appealing HfO2-based ferroelectric thin films, which have been researched ettensively for their applications in ferroelectric memory devices. In this work, a 1 mol % La-doped Hf0.5Zr0.5O2 thin-film was grown by plasma-assisted atomic layer deposition and annealed at temperatures of 450 and 500 degrees C to crystallize the film into the desired orthprhornbic phase. Despite the Use of a lower temperature than that used in previous reports, the film showed highly promising ferroelectric properties a remnant polarization of similar to 30 mu C/cm(2) and switching cycle endurance up to 4 x 10(10). The performance was much better than that of undoped Hf0.5Zr0.5O2 thin films, demonstrating the positive influence of La doping. Such improvements were mainly attributed to the decreased coercive field (by similar to 30% compared to the undoped film), which allowed for the use of a lower applied field to drive the cycling tests while maintaining a high polarization value. La doping also decreased the leakage current by similar to 3 orders of magnitude compared to the undoped film, which also contributed to the strongly improved endurance. Nonetheless, the La-doped film required a larger number of wake-up cycles (similar to 10(6) cycles) to reach a saturated remnant polarization value. This behavior might be explained by the increased generation of oxygen vacancies and slower migration of these vacancies from the interface to the bulk region. However, the maximum number of wake-up cycles was less than 0.01% of the total possible cycles, and therefore, initializing the film to the maximum performance state would not be a serious burden.</P>
Egorov, Konstantin V.,Kuzmichev, Dmitry S.,Sigarev, Andrey A.,Myakota, Denis I.,Zarubin, Sergey S.,Chizov, Pavel S.,Perevalov, Timofey V.,Gritsenko, Vladimir A.,Hwang, Cheol Seong,Markeev, Andrey M. The Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.36
<P>The growth per cycle saturation behaviors depending on the precursor pulse duration, reactant pulse duration, and reactant concentration were examined for hydrogen radical enhanced atomic layer deposition (REALD) of TaOx using tantalum-ethoxide as the precursor and plasma-activated hydrogen as the reactant. The chemical state of the TaOx film was dependent on the active hydrogen pulse duration and hydrogen volume fraction in the H2/Ar plasma mixture. The density of the electronic states in the dielectric band gap increased with the increase in the plasma exposure time (6-50 s) and hydrogen volume fraction (7-70%) whereas Ta4f core-level X-ray photoelectron spectroscopy indicated that the observed defects in the TaOx band gap are related to the oxygen deficiency. The <I>ab initio</I> calculations of oxygen deficiency concentrations and the energy spectrum satisfactorily correlated with the experimental data. The demonstrated combination of the growth saturation availability with the precise control of oxygen deficiency concentrations in the PEALD process could be highly useful in fields in which oxide dielectrics with adjustable oxygen deficiencies are required.</P>