Fabrication of thin-film organic memory elements

A flexible organic memory unit will be a key element when manufacturing future RFID circuits on flexible substrates. Although the research of memory devices using organic materials dates back almost 40 years, the performance of these devices has remained low when compared to their inorganic counterparts. The main problem limiting the application of these devices is that their operation tends to degrade in air and under stress of successive read-write cycles. Furthermore, the physical phenomena affecting their stability are many times unclear. In this study many different aspects related to the sample preparation were studied in order to identify which of them had an influence on the performance and stability of the devices. The test device structure consisted of two metal electrodes and an organic layer between them. As the organic film different polymer materials including block polymers, poly(3-hexyl thiophene) (P3HT), and polystyrenes were tested in various compositions. The film thickness varied from a few tens of nanometres to ~200 nm. During the work, different electrode materials, interface effects, film thickness, device area, substrate materials, impurity effects, and curing parameters etc. were studied. Results from the electrical characterisation showed that electrical switching took place in all of the tested materials but not in all fabrication parameter combinations. One of the most important aspects in the sample preparation affecting the device performance was the purity of processing environment. The importance of the dust particles in constituting conducting paths to charge carriers and thereby enabling electrical conductivity was identified. In addition to the purity of the processing environment the interface effects played a major role in the operation of the devices.