Electronic Memory Effects in Zinc Oxide Nanoparticle -Polystyrene Devices with a Calcium Top Electrode
- PDF / 359,234 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 113 Downloads / 192 Views
0965-S09-11
Electronic Memory Effects in Zinc Oxide Nanoparticle -Polystyrene Devices with a Calcium Top Electrode Frank Verbakel1,2, Stefan C. J. Meskers1,2, and René A. J. Janssen1,2 1 Molecular Materials and Nanosystems, Eindhoven University of Technology, P.O. Box 513, Eindhoven, 5600 MB, Netherlands 2 Dutch Polymer Institute (DPI), P.O. Box 902, Eindhoven, 5600 AX, Netherlands ABSTRACT Diodes with an active layer of solution processed zinc oxide (ZnO) nanoparticles and polystyrene are studied. Poly(3,4-ethylenedioxythiophene)- polystyrenesulfonate (PEDOT:PSS) on indium doped tin oxide (ITO) is used as the bottom electrode and aluminum or calcium are used as top electrode. Pristine devices show diode behavior in their current-voltage characteristics. The conductivity of the device in reverse bias can be raised three orders of magnitude by applying a positive voltage or by illumination with UV light. In this high conductivity state we observe reversible electronic memory effects. The electronic memory effects are attributed to a reversible electrochemical process at the PEDOT:PSS/ZnO interface. Memory effects in diodes with Al and Ca metal electrode are found to be very similar, consistent with the view that the memory effects arise at the PEDOT:PSS/ZnO interface.
INTRODUCTION Electronic memories based on field induced resistive switching of organic and polymeric thin films in a diode configuration attract considerable attention [1,2]. Similar memory effects have also been observed in molecular materials containing inorganic nanoparticles or metal interlayers [3-7]. We have recently shown that thin films of ZnO nanoparticles embedded in a polystyrene (PS) matrix show memory effects in their current voltage characteristics when sandwiched between ITO/PEDOT:PSS bottom and aluminum (Al) top electrodes [8]. The conductivity in these mixed ZnO:PS hybrid layers is due to a percolating pathway of ZnO nanoparticles [9,10]. Memory effects in the conductivity [11,12] and persistent photoconductivity [13] have been reported for bulk ZnO and are also known for other metal oxides [14,15]. Similar to bulk ZnO [16,17], the nanoparticle blends show a forming step under influence of UV illumination or a high forward bias to reach high conductivity. After this forming, reversible memory effects can be induced by applying a voltage [8]. These memory effects have been ascribed to electrochemistry involving the PEDOT:PSS/ZnO interface. The electronic memory effects in organic and polymer diodes have recently been related to the specific use of Al as top electrode [5,18]. Filaments of Al, formed during the evaporation of the top electrode at pinholes in the active layer can support high current densities. The switching effects are then ascribed to Al2O3, formed during evaporation on the end of the Al filament [18]. In view of these reports on the involvement of the Al top electrode in the memory effects, we investigated the role of Al in ZnO:PS memories. We prepared devices with a calcium (Ca) top electrodes and show that the electr
Data Loading...
