Vanadium Oxide Based RRAM Device

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Vanadium Oxide Based RRAM Device

Zhenni Wan1*, Robert B. Darling1 and M. P. Anantram1 1

Department of Electrical Engineering, University of Washington, Seattle, WA, 98105, USA.

ABSTRACT Forming-free bipolar resistive switching characteristics in a Vanadium oxide based sandwich structure is observed for the first time. The bottom conducting layer is the common ground electrode for all devices. The top conducting layer acts as an active element with an additional Cr/Al/Cr electrode patterned on its top for making contact. Different from the typical metal/transition metal oxide/metal sandwich structure based resistive memories, our device exhibits a low resistance state (LRS) in its virgin state, and can be switched to a high resistance state (HRS) when a positive bias of +2.5V is applied to the top electrode. Following this, the device can be reset to a LRS when a negative bias of approximately 2.5V is applied. A significant decrease of switching voltages is observed when the diameter of the top contact decreases, indicating an electric field enhanced switching mechanism. Simulation using TCAD confirms that electric field beneath the top metal contact increases due to fringing. The results suggest future applications in low power integrated non-volatile memories.

INTRODUCTION Electroforming in resistive random access memory (RRAM) usually requires a large voltage that is a few times higher than the switching voltage. This causes severe electrical and mechanical stresses to the MIM memory element [1]. It is also generally a slow process compared to the subsequent resistive switching. Reducing or even eliminating the forming step is valuable for practical applications. Vanadium pentoxide has been intensively studied in the past few decades due to its special electrical and chemical properties. Its orthorhombic layered structure, which promises a large capacity for conducting and intercalating metal ions, especially lithium and sodium ions, is promising as a cathode material in lithium-ion batteries [2, 3]. The dangling vanadium-oxygen bonds also suggest that the oxidation states could be easily reduced by electrochemical reactions that might enable interfacial resistive switching. Irreversible resistive switching has been discovered in Cr/V2O5/Cr devices before[4], but a reversible and stable resistive switching has not yet been reported. In the present study, we report a reversible bipolar switching in ITO/V2O5/ITO structures for the first time. EXPERIMENTAL DETAILS

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A commercial ITO coated glass slide with a sheet resistance of 10Ω/sq is used as substrate and bottom contact. A thin film of V2O5 with a thickness of 300nm is deposited using a sol-gel process. The top layer of ITO (160nm) is deposited by magnetron sputtering and the corresponding sheet resistance is 50-80Ω/sq. After

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