Liquid-Solid Hybrid Memory Device Achieved by Unique Features of Ionic Liquids

Abstract

Ionic liquids (ILs), non-volatile liquids composed of cations and anions, have various attractive properties for electronic devices, such as wide potential windows. Combining ILs with electronic devices is presumed to be able to provide new options for realizing a sustainable internet of things society because such liquid-solid hybrid devices have the capability to act as a key in realizing further possibilities that cannot be achieved with all-solid-state devices. In this paper, we describe the development of IL-supplied conducting-bridge random access memory (IL-CBRAM) whose operating mechanism is the Cu filament formation/rupture caused by redox reactions in ILs as an electrochemical reaction field. Although the introduction of liquids into solid-state processes is challenging, we successfully demonstrated the reproducible memory operation of IL-CBRAM with a Cu/SiO2/Pt structure and a microfabricated pore filled with IL in the SiO2 layer. We also improved the wettability of the IL to SiO2 by exposing it to Ar plasma, which was essential not only to obtain an IL thin film from the droplet but also to ensure pore filling by the IL before Cu deposition. The present device fabrication process for IL-CBRAM is highly reliable and compatible with conventional vacuum processes.