Small Organic Molecules for Electrically Re-writable Non-volatile Polymer Memory Devices

The usage of organic materials in the manufacture of electronic polymer memory devices is on the rise. Polymer memory devices are fabricated by depositing a blend (an admixture of organic polymer, small molecules and nanoparticles) between two metal electrodes. The primary aim is to produce devices that exhibit two distinct electrical conductance states when a voltage is applied. These two states can be viewed as the realisation of non-volatile memory. This is an interesting development; however, there are a number of theories that have been proposed to explain the observed electrical behaviour. We have proposed a model that is based on electric dipole formation in the polymer matrix. Here, we investigate further the proposed model by deliberately creating electric dipoles in a polymer matrix using electron donors (8-Hydroxyquinoline, Tetrathiafulvalene and Bis(ethylenedithio)tetrathiafulvalene) and electron acceptors (7,7,8,8-Tetracyanoquinodimethane, Tetracyanoethylene and Fullerene) small molecules.Two types of structures were investigated (i) a metal/blend of polymer and small molecules/metal (MOM), device and (ii) a metal/insulator/blend of small molecules and polymer/semiconductor (MIS) architecture. A blend of polymer and small organic molecules was prepared in methanol and spin-coated onto a glass substrate marked with thin aluminium (Al) tracks; a top Al contact was then evaporated onto the blend after drying - this resulted in a metal-organic-metal structure. The MIS structures consisted of an ohmic bottom Al contact, p-type Si, a polymer blend (two small organic molecules and insulating polymer), followed by polyvinyl acetate and finally a top, circular Al electrode. In-depth FTIR studies were carried out to understand the observed electrical behaviour. An electrical analysis of these structures was performed using an HP4140B picoammeter and an HP 4192A impedance analyser at a frequency of 1 MHz.