New Resistive Switching Phenomena in Devices with Limited Active Metal Source
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New Resistive Switching Phenomena in Devices with Limited Active Metal Source Mohini Verma, Yuhong Kang, Tanmay Potnis, Sushil Khadka, Tong Liu, and Marius Orlowski Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A.
ABSTRACT To better understand the mechanisms of creation and rupture of conductive filaments in resistive switching devices such as Cu/TaOx/Pt, with Cu and Pt being the active and inert electrodes, respectively, a device with limited supply of active metal electrode has been manufactured and electrically characterized. The limited supply of active metal has been realized by depositing a thin (delta) Cu layer (δ-Cu), 6 nm and 12 nm thick, on TaOx, resulting in a Pt/δCu/TaOx/Pt device structure. The limited active metal supply i) has a direct impact on the onresistance (Ron) of the Cu bridge, and leads, after several conventional set-reset cycles, to ii) pulsating behavior, when device turns on and off repeatedly, to iii) symmetric switching behavior with respect to applied voltage polarity, when the device can be set and reset both at positive and negative bias, and to iv) volatile switching behavior. INTRODUCTION Solid electrolyte materials using ionic transport between an oxidizable anode and inert cathode are among the most promising candidates to replace the conventional floating-gate device based non-volatile memory beyond the 11 nm technology node [1-3]. A single Cu/TaOx/Pt switch relies on electrochemical deposition and rupture of a conductive filament (CF) of the active Cu electrode [4,5]. The Cu/TaOx/Pt resistive devices are typically set by positive voltages (assuming that the bottom Pt electrode is grounded) and reset in bipolar mode [6]. When a Cu CF is established between the electrodes under the positive SET voltage, the device switches more or less abruptly from a high-resistance state (HRS) Roff (1-800MΩ) to a low-resistance state (LRS) Ron (80-2000Ω). Cu+ ion flux together with the stopping power of the inert electrode is responsible for the formation of a metallic filament consisting of Cu atoms in the matrix of the (TaOx) electrolyte [7]. Every time a cell undergoes a SET operation a significant number of Cu atoms is being transferred from the active (Cu) to the inert (Pt) electrode. In a RESET cycle some of the Cu atoms deposited on Pt electrode may get oxidized and transferred back to the Cu electrode. Nevertheless, owing to the initial asymmetry of electrodes, after several SET-RESET cycles, a net transfer of Cu atoms to the inert electrode is bound to take place. In this context two questions arise: (i) What is the impact on the switching behavior of the cell if the supply of active metal atoms is limited? and (ii) What is the role of the Cu atoms deposited on the inert electrode on the cell switching behavior? The latter question is, of course, relevant also for conventional (Cu/TaOx/Pt) devices. In order to answer these questions a novel device structure Pt/δCu/TaOx/Pt with limited Cu supply
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