| Description |
Scaling limitation of current memory technology requires invention of a new class of memory that has high density, fast programming and access time, as well as good nonvolatility. Resistive switching memories or memristors are good candidates for such application. Anticipated advantages of these devices include long retention time, high access speed, endurance, low power, high density, and scalability. Memristors were first proposed theoretically by L. Chua in 1971, but it did not come into practical implementation until 2008 when researchers in the HP lab fabricated and recognized the first ever memristor. There are several significant contributions within the scope of this research work. This thesis work demonstrates the fabrication, characterization, and experimental validation of the operating principle of a gate controlled memristive device. We used electrochemical metallization (ECM)-based memristors. The fabricated gated memristors are among the first of its kind. In-depth studies of the switching layers used in the fabricated gated memristors are also presented prior to the fabrication process. Firstly, two insulating layers, i.e., Cu2-xS and Ag2-xS, are selected to be used in our devices. Using advanced characterization techniques such as atomic force microscopy, growth of metallic conductive filaments was observed under various voltage magnitudes and polarities. Secondly, a batch of two-terminal memristors (Ag/Ag2-xS/Au) was fabricated to study the time-dependent switching behavior of Cu2-xS and Ag2-xS layers. These devices did not have any gate electrodes. After these initial studies, three- terminal gated memristors were designed and fabricated. Our memristor was Pt/Cu2-xS/Pt-based with an additional Pt-electrode called "gate". These devices exhibit very low sub-threshold slope (~2 mV/dec) with/without gate electric field. The turn on/off voltage of the device can be tuned by application of a gate electric field. A numerical simulation model was also developed to explain the gate electric field effect observed in our fabricated Pt/Cu2-xS/Pt-based gated memristor. Finally, we extended our study to understand switching in some 2D layered materials so that they can be potentially applied to future memristors. In summary, we successfully added gate electrode to conventional ECM-based memristor and experimentally validated the fact that the gate electric field can indeed change the switching characteristics of such device. The experimental results were explained with the aid of numerical simulation for better understanding of the underlying principle of operation of gated ECM-based memristors. |
