The increasing interest in non-volatile memory devices has extended the exploration towards new materials, such as organic-inorganic hybrids. Devices based on organic semiconductors and embedded metal nanoparticles (MNPs) were found to display resistive bistability, suitable for programmable electronic applications. Different models were developed to explain the resistive switching mechanism occurring in the devices. Charging/ de-charging of MNPs and concomitant resistivity changes was mainly proposed as mechanism, despite the lack of solid experimental evidence.[ ] In this contribution we report on the role of the space-charge field due to charged MNPs in two-terminal devices, via electrical characterization. Devices comprise 4,4-bis[N-(1-naphthyl)-N-phenyl-amino]diphenyl (α-NPD) with embedded gold nanoparticles (AuNPs). The electrical characterization (current vs bias) of the devices was conducted with and without illumination during operation. Due to the energy level alignment of the chosen materials, the AuNPs behave as deep charge carrier traps. The induced space-charge spontaneously sets the device to the low conductivity state. The de-charging of the AuNPs can then be dynamically induced through illumination, setting the device to a high conductivity state. Despite the ability to optically control the charging state of the AuNPs, the devices do not display any bistability. This finding provides evidence that the commonly proposed MNPs charging/de-charging mechanism can be excluded as the cause for electrical bistability in two-terminal devices, and that other mechanisms, such as filament formation, should be evoked.
|
