Gating of Two Dimensional Materials Using Solid Polymer Electrolytes and Ferroelectrics

Two-dimensional (2D) materials, particularly graphene and transition metal dichalcogenides (TMDs), have been the subject of many recent studies because of their unique mechanical and electrical properties. All the bonds are in-plane, and the layers are separated by a van der Waals gap. While most properties can be characterized by measuring the unmodified materials, many electrical properties require the charge state of the material to be modulated. For traditional semiconductors, this is achieved by field-effect gating through a dielectric combined with substitutional doping. However, the lack of dangling surface bonds makes the deposition of a gate dielectric challenging, and methods for controlled substitutional doping have not yet been developed. Solid polymer electrolytes (SPEs), which consist of a salt dissolved in a polymer, offer a relatively simple solution. By using the SPE in the place of a gate dielectric, ions in the SPE are driven to close proximity (∼1 nm) of the material surface to induce image charges in the 2D material. The ion and corresponding image charge layers are collectively known as an electrostatic (or electric) double layer (EDL). The EDL can induce charge carrier densities in the material in excess of 10^14 cm^−2 . The work presented in this dissertation details ways of using EDL-induced sheet charges to open up new applications in the field of nanoelectronics. By tuning the Erich Kinder glass transition temperature of the SPE, the EDL retention time can be increased by six orders of magnitude at room temperature while still achieving charge carrier densities in excess of 10^14 cm^−2 , enabling unique hardware security. We also investigate applying large electric fields over the SPE, which causes volumetric change in 2D electronics due to ion intercalation. 2D devices typically are top-gated by the SPE. However, in this work, backgating by an SPE is demonstrated for the first time. As well, we explore partial switching of the ferroelectric material HfZrO2 The objective is to use the ferroelectric in conjunction with a 2D channel to form a two-terminal resistive processing unit for use in hardware-based neural networks.