Composite Cu/VO and VO/Cu Nanofilaments in Cu/Ta2O5/Pt Devices

Abstract

Formation of nanofilament conductive path in solid electrolytes is a promising phenomenon exploited in reversible resistive switching. 1 Widely researched metal oxide resistive switching memory is one of the most competitive candidates for future generations of nonvolatile memory applications due to its simple cross-point structure, fastswitchingspeed,highscalabilitypotential,andcompatibilitywith CMOS technology. The mechanism of resistive switching random access memory (RRAM) has been widely attributed to formation and rupture of conductive filaments assumed to consist of metal precipitates such as (Cu, Ag, Ni) or oxygen vacancies. 2 Specifically, switching of a resistive Cu/TaOx/Pt device can be based on the formation of two types of CFs in the same device: Cu and oxygen vacancy (Vo) filaments depending on the polarity of switching voltage. 3 The two types of conduction can be distinguished by different values of the temperature coefficient (α) of resistance defined as R(T) = R(To) [1 + α(T-To)]. For TaOx formed by physical vapor deposition (PVD), the temperature coefficient α of the on-resistance Ron is α(Cu-CF) = 0.0033 K −1 for Cu CF and α(Vo-CF) = 0.001 K −1 for Vo CF. 3 The α(Cu-CF) in oxygen deficient TaOx is close to the bulk value of Cu, α(Cu) =0.0039 K −1 . In this paper, we present evidence for composite Cu and VO single CF observed in Cu/Ta2O5/Pt devices with a Ta2O5 deposited by atomic layer deposition (ALD). The characterization of the temperature dependence of the filament resistance is an effective way of exploring the properties of the elusive nano-filaments. 4‐7 In Ni/HfO2/p + Si devices an α(Ni-CF) = 0.0063 K −14 which is close to the temperature coefficient of solid Ni nanowire (30 nm diameter) of α(Ni-NW). = 0.0048 K −1 . 5 In Ref. 6 the temperature coefficient of the resistance has been measured in the range of 100 K to 300 K on Ag CF in Ag/La-BFO/Pt devices and a difference has been found for bipolar α(Ag-bipolar) = 0.00194 K −1 and for unipolar characteristics α(Ag-unipolar) = 0.00177 K −1 . In Ni/ZrO2/Pt devices it was found that α(Ni-CF) varies between 0.00127 K −1 and 0.00220 K −1 , 7 indicating that the Ni CFs are metallic and close to the α coefficients of Ni nanowire with 10‐30 nm diameter. 5,8,9