AVS 60th International Symposium and Exhibition
    Electronic Materials and Processing Wednesday Sessions
       Session EM+PS-WeM

Invited Paper EM+PS-WeM5
Ionic Memory - Materials and Devices

Wednesday, October 30, 2013, 9:20 am, Room 102 A

Session: Oxides and Dielectrics for Novel Devices and Ultra-dense Memory II
Presenter: M.N. Kozicki, Arizona State University
Correspondent: Click to Email
There is widespread agreement within the semiconductor industry that existing high density non-volatile memory technologies are reaching their scaling limits and will ultimately be replaced by some variant of resistive random access memory (RRAM). This paper discusses advances in ionic RRAM, which relies on ion transport and redox reactions in thin solid electrolyte/dielectric films. Emphasis is placed on a technology known as Conductive Bridging Random Access Memory (CBRAM), a recently commercialized ionic memory based on the Programmable Metallization Cell (PMC) platform. In this technology, metallic cations are typically the mobile species. An ion current will flow if (1) the electrolyte is placed between two conductive layers, at least one of which can supply ions, (2) the ion-supplying electrode is made positive with respect to the opposing electrode, and (3) a sufficient bias is applied to overcome the internal potential barrier. The ion current feeds the reduction reaction, resulting in the formation of a metallic filament within the electrolyte/dielectric. The filament has a conductivity that is much higher than the surrounding material and hence it allows the resistance of the structure to be reduced by several orders of magnitude. The resistance of the conducting filament depends on the total number of metal ions that are reduced, which in turn depends on the charge supplied by the external circuit. Thus, the on-state resistance can be controlled by programming current and time. Control over the on-state resistance means that it is possible to create multiple discrete resistances levels to represent more than one binary digit per cell. If one electrode is electrochemically inert, the resistance-change process can be reversed by applying an opposite bias to that used for programming which dissolves the conducting pathway via oxidation of the metal in the filament. It is this electrode asymmetry that allows the deposition/dissolution process to be cycled repeatedly. We have also studied stackable diode-isolated arrays, in which each cell has one resistive switching element and one integrated Zener diode formed by the junction of the Cu filament of the device on-state and a doped silicon (n-type) electrode. The diode reduces “sneak path” currents via low resistance on-state devices in an array, but the reverse breakdown of the Zener element allows the cells to be erased by reverse bias.