Exotic features of a metal/oxide/metal (MOM) sandwich, which will be the basis for a drastically innovative nonvolatile memory device, is brought to light from a physical point of view. Here the insulator is one of the ubiquitous and classic binary-transition-metal oxides (TMO), such as Fe2O3, NiO, and CoO. The sandwich exhibits a resistance that reversibly switches between two states: one is a highly resistive off-state and the other is a conductive on-state. Several distinct features were universally observed in these binary TMO sandwiches: namely, nonpolar switching, non-volatile threshold switching, and current-voltage duality. From the systematic sample-size dependence of the resistance in on-and off-states, we conclude that the resistance switching is due to the homogeneous/inhomogeneous transition of the current distribution at the interface.
No abstract
Hybrid memory systems that incorporate Storage Class Memory (SCM) as non-volatile cache or DRAM data backup are expected to bolster system efficiency and cost because SCM promises higher density than DRAM cache and higher speed than the storage I/F. This paper demonstrates a Cu-based resistive random access memory (ReRAM) cell that meets the SCM performance specifications for a 16Gb ReRAM with 200MB/s write and 1GB/s read [1]. Cell CharacteristicsThe cell in Fig. 1 consists of a Cu-based ion reservoir (IR) over an electrolyte (EL). When a positive bias is applied to the top electrode, ionized Cu is driven from the IR into the EL [2]. Switching from an initial high resistance state (HRS) to a low resistance state (LRS) occurs when the local Cu concentration in the EL becomes sufficient to facilitate electron transport.The cell I-V curve in Fig. 2 illustrates the forming, reset, and set events. While initial forming occurs at 4.2V, the set voltage during subsequent cycles is 2V lower, suggesting the structure is altered upon forming, such that a preferential, lower barrier path is established. This is interpreted as stress-induced channel formation [3]. The forming voltage for the cell materials in Fig. 3 is below the breakdown bias of the EL. Hence, the conductive bridge is formed without breakdown, since metal cations are supplied from an external reservoir; in contrast to oxygen vacancy ReRAM, which relies on soft breakdown to liberate oxygen anions from within the switching region [4]. The estimated number of Cu atoms required to form the conductive bridge ranges from 10-200, based on DFT simulations of a model system in Fig. 4, and the resistance of the bridge in Fig. 5 depends on the quantity of metal transported into the EL, which is inversely related to the set current compliance (I-set). To reset the device, a positive bias is applied to the bottom electrode, to oxidize Cu in the bridge and transport it back to the IR. The onset of reset in Fig. 2 begins at -0.5V, which is ~5x greater than that for similar Ag-based ReRAM cells [5,6].The switching times τ in Fig. 6 follow the form log(τ) ∝ -V , and under nominal conditions, reset occurs slightly faster than set, while forming occurs much slower than set and reset.The virgin and HRS currents both exhibit exponential dependence on voltage, consistent with trap assisted tunneling or hopping-type transport. The activation energy Ea in Fig. 7 is 155meV and is reduced by the applied electric field. While the LRS I-V behavior is roughly linear with voltage, an 8meV Ea suggests the conductance is not purely metallic; and LRS read noise exhibits RTN behavior with a 1/f power spectral density in Fig. 8, characteristic of multiple RTN centers.
Enabling a high-density ReRAM product requires: developing a cell that meets a stringent bit error rate, BER, at low program current, integrating the cell without material damage, and providing a high-drive selector at scaled nodes. We discuss ReRAM performance under these constraints and present a 16Gb, 27nm ReRAM capable of 10 5 cycles with BER < 7x10 -5 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.