Engineering silver nanomaterials : from transparent conductors to resistive switching devices

Abstract

Metal nanomaterials have been considered to be crucial in electronic devices, due to their unique properties such as high electrical conductivity, small size, optical transparency and flexibility. Ag nanomaterials have been widely studied in transparent conductors and memory devices. Although Ag nanoparticle electrodes have been employed to build memory devices, the requirement for better performance and underlying mechanisms worth continuing to study. Moreover, several works have focused on fabricating transparent conductor based on Ag NW networks, while the thermal stability of devices still shows great room for improvement. In this dissertation, memory devices and transparent conductors based on Ag NWs and Ag nanoparticles have been fabricated through spin coating and vacuum filtration, and the electronic performance and thermal properties have been studied. The thesis includes the following parts: (1) In the study of graphene oxide enhanced transparent conductors, the thermal stability of single Ag NW and Ag NW networks have been investigated. The result shows that the first break of Ag NWs junctions during heat treatment is the main reason for resistance increase. Based on microscopic results that graphene oxide can reduce the break of junctions, graphene oxide protected Ag NW networks with multilayers structure are fabricated and the thermal stability as well as electrical stability have been tested. (2) Loose Ag NW network structure is utilized to fabricate threshold switching devices with a selectivity of 100 times and endurance of 160 cycles by modifying the junctions between bare Ag NWs. The temperature and Ag NWs density effect are also investigated to understand the mechanism. The result displays that the mechanism for threshold switching behavior is the conductive filaments formed by migration of Ag and the electrical performance of Ag NW networks can be modified by controlling the loose structure. (3) In fabricating non-volatile memory devices, SrTiO3 nanocomposite was employed as the active layer and Ag nanoparticles electrodes were formed by sputter coating. Similar to threshold switching behavior, the mechanism for non-volatile behavior is the formation of conductive filaments caused by the migration of Ag from top electrodes. This work proves a new insight in the potential application of Ag nanomaterials in memory devices and transparent conductors.