Development of Transparent and Flexible Resistive Switching Materials

Abstract

In conventional circuit boards, 77% of the weight is in the substrate. New electronics built on thin and flexible substrates will open up exciting possibilities in lightweight devices, including wearable electronics, Internet of Things, and healthcare & medical applications. Recently, flexible resistive switching memories with high transparency, light weight, and excellent flexibility, have been of great interest because of the emerging need for wearable electronic devices. Flexible substrates are much rougher and more sensitive to high-temperature fabrication as compared to conventional rigid substrates such as silicon. The rough surface induces the degradation of memory performance, current leakage, and even electrical shorting. Meanwhile, current physical fabrication methods, such as atomic layer deposition and pulsed laser deposition, have low yield and limitation on mass-production, which are critical for decreasing fabrication costs. The major obstacles for solution-processed fabrication techniques are the high-temperature annealing of amorphous precursor films, which can cause dilation of the plastic substrate, undesired cracks, particle growth due to the melting point depression and deterioration of particle morphology during annealing. In contrast to conventional physical deposition methods, in this project, a novel approach based on solution-processed resistive switching components has been developed. To bypass high-temperature annealing process, the strategy is to fabricate well-crystalline colloidal nanocrystals and then disperse them into suitable solvents to form colloidal nanocrystal arrays for dielectric layers and the electrodes of resistive switching memory. Such colloidal nanocrystal arrays can be directly deposited into ordered films at room temperature; and finally organic ligands are removed by UV treatment, which can bypass the grain growth and cracks formation. This approach is critical to improve the flexibility and electrical performance of the devices. In detail, the thesis focus on the studies: (a) fabrication of transparent electrodes composed of silver nanowires (AgNWs) network embedded in a polymer, such as colourless polydimethylsiloxane (PDMS) with high electrical, optical, and mechanical stability and flexibility;(b) synthesis of perovskite oxide (BaTiO3, SrTiO3, and BiFeO3) nanomaterials by hydrothermal method; and (c) fabrication of flexible and transparent resistive memory devices. The current study provides a systematically understanding of controlling the shape and size of perovskite materials by hydrothermal method towards future high performance resistive switching memories design.