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Electrical conductivity in oxygen-deficient phases of transition metal oxides from first-principles calculations

Desjarlais, Michael P.; Thompson, A.P.; Brennecka, Geoff; Marinella, Matthew

Density-functional theory calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula are applied to predict electrical conductivity in Ta2Ox (0 x 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (VOn; n=0,1+,2+). Our calculations of DC conductivity at 300K agree well with experimental measurements taken on Ta2Ox thin films and bulk Ta2O5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta2O5 electronic structure provide further theoretical basis to substantiate VO0 as a donor dopant in Ta2O5 and other metal oxides. Furthermore, this dopant-like behavior appears specific to neutral VO cases in both Ta2O5 and TiO2 and was not observed in other oxidation states. This suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for VO0 in transition metal oxides.

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TYPE SAND Report YEAR 2013
DOIOSTI

A CMOS Compatible, Forming Free TaOx ReRAM

ECS Transactions (Online)

Stevens, James E.; Mickel, Patrick R.; Hughart, David R.; Marinella, Matthew

Resistive random access memory (ReRAM) has become a promising candidate for next-generation high-performance non-volatile memory that operates by electrically tuning resistance states via modulating vacancy concentrations. Here, we demonstrate a wafer-scale process for resistive switching in tantalum oxide that is completely CMOS compatible. The resulting devices are forming-free and with greater than 1x105 cycle endurance.

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TYPE Journal Article YEAR 2013
OSTIDOI

Optimizing TaOx memristor performance and consistency within the reactive sputtering "forbidden region"

Applied Physics Letters

Lohn, Andrew J.; Stevens, James E.; Mickel, Patrick R.; Marinella, Matthew

Standard deposition processes for depositing ReRAM oxides utilize mass flow of reactive gas to control stoichiometry and have difficulty depositing a precisely defined sub-stoichiometry within a "forbidden region" where film properties are discontinuous with mass flow. We show that by maintaining partial pressure within this discontinuous "forbidden region," instead of by maintaining mass flow, we can optimize tantalum oxide device properties and reduce or eliminate the electroforming step. We also show that defining the partial pressure set point as a fraction of the "forbidden region" instead of as an absolute value can be used to improve wafer-to-wafer consistency with minimal recalibration efforts. © 2013 AIP Publishing LLC.

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TYPE Journal Article YEAR 2013
DOIOSTIScopus
Results 276–300 of 376
Results 276–300 of 376