Nonvolatile memory and opto-electrical characteristics of organic memory devices with zinc oxide nanoparticles embedded in the tris(8-hydroxyquinolinato)aluminum light-emitting layer

Abstract

The nonvolatile organic memory devices based on the tris(8-hydroxyquinolinato)aluminum (Alq3) emitting layer embedded with zinc oxide nanoparticles (ZnO-NPs) are reported. The devices have a typical tri-layer structure consisting of the Alq3/ZnO-NPs/Alq3 layers interposed between indium tin oxide (ITO) and aluminum (Al) electrodes. An external bias is used to program the ON and OFF states of the device that are separated by a four-orders-of-magnitude difference in conductivity. No significant degradation of the device is observed in either the ON or OFF state after continuous stress (∼105s) and multicycle (∼103 cycles) testings. These nanoparticles behave as the charge trapping units, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. Impedance spectroscopy, capacitance–voltage (C–V) and current–voltage (I–V) analysis are used to verify the possible physical mechanism of the switching operation. Moreover, it is found that the location of the ZnO-NPs could affect the memory and opto-electrical characteristics of the devices, such as the ON/OFF ratio, threshold voltage and turn-on voltage, which can be attributed to the influence of the ZnO-NPs and diffused Al atoms in the bulk of the Alq3 layer.