An Atomic Force Microscopic Study of Resistive Switching Resonance Activation in ZrO 2 (Y) Films
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An Atomic Force Microscopic Study of Resistive Switching Resonance Activation in ZrO2(Y) Films D. O. Filatova,*, D. A. Antonova, I. N. Antonova, M. A. Ryabovaa, and O. N. Gorshkova aLobachevsky
National State University, Nizhny Novgorod, 603950 Russia *e-mail: [email protected]
Received April 2, 2020; revised April 2, 2020; accepted April 2, 2020
Abstract—Local resistive switching in a contact between the probe of an atomic force microscope (AFM) and ZrO2(Y) films (including with a Ta2O5 sublayer) on conducting substrates has been studied. Switching has been initiated by triangular voltage pulses on which an rf sine-wave signal was imposed. The dependence of the difference between currents through the AFM probe in low- and high-ohmic states of dielectric films on the frequency of the rf sine-wave signal exhibits maxima at characteristic frequencies corresponding to hops of O2– ions between oxygen vacancies in ZrO2(Y) and Ta2O5 at 300 K. This effect is related to the resonance activation of O2– ion migration over oxygen vacancies by an external rf electric field. DOI: 10.1134/S1063784220110079
INTRODUCTION In recent years, resistive switching (RS) has become a subject of much research [1]. The RS effect consists in bistable (multistable) reversible change in the resistivity of a thin (10 nm thick) dielectric film sandwiched in between conducting electrodes to which a voltage is applied [2]. Electron devices exploiting the RS effect are called “memristors” [3]. Today, it is generally believed that the RS mechanism in metal oxides involves forming conductive filaments (consisting of oxygen vacancies) in an electric field between the electrodes [4]. A memristor is switched from a low-resistivity state (LRS) to a high-resistivity state (HRS) when the conductive filament ruptures under the action of a voltage pulse applied to the electrodes (RESET process). The filament can be restored by applying a voltage pulse of opposite polarity, as a result of which a switch from HRS to LRS occurs (the so-called SET process). This is the basic process in the mechanism of a bipolar RS. Memristors are considered promising for fifthgeneration nonvolatile memory devices [5], neuromorphic computers, etc. [6]. However, their application is today limited because of RS parameter instability [7]. The fundamental reason for instability is the stochastic nature of rupture and recovery of filaments in a functional dielectric layer. Since the amount of oxygen vacancies participating in the RS process is countable [8], memristors represent a mesoscopic system in which the fluctuations of any physical parameter may be much larger than its mean value. Conventionally, the RS stability is improved by selecting appropriate functional dielectric materials and mate-
rial for electrodes, grain-boundary geometry in the dielectric, etc. [9–11]. An alternative approach is to select an appropriate switching protocol [12]. Here, we report data for a local RS in ZrO2(Y) films using the AFM method [13]. The process was initiated by applying t
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