Flexible resistive switching bistable memory devices using ZnO nanoparticles embedded in polyvinyl alcohol (PVA) matrix and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)

The resistive switching memory effects in metal-insulator-metal devices with aluminium (Al) as top electrode (TE) and bottom electrode (BE). A solution processed active layer consisting of zinc oxide (ZnO) nanoparticles embedded in an insulating polyvinyl alcohol (PVA) matrix and polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been studied by using flexible polyethylene terephthalate (PET) substrates. The current–voltage (I–V) measurements of hybrid Al/ZnO–PVA/PEDOT:PSS/Al/flexible PET substrate device exhibited a non-volatile bistable resistive switching behaviour, which is attributed to the trapping, storage and transport of charges in the electronic states of the ZnO nanoparticles. The performance of hybrid device is significantly enhanced over control Al/PEDOT:PSS/Al and Al/ZnO–PVA/Al devices due the presence of PEDOT:PSS polymer. This PEDOT:PSS improves the performance of oxygen ions (holes) migration toward BE and protect back oxygen vacancies (electrons) migrate toward BE from ZnO–PVA composites which may reduces the leakage current, as a result, increased the ‘ON state/OFF state’ current ratio of 7.9 × 10(3) times. The fabricated hybrid device showed high ON/OFF switching current ratio larger than five orders of magnitude with low operating voltages. It is observed that, the existence of two conducting states, namely, low conductivity state (OFF state) and high conductivity state (ON state), exhibiting bistable behaviour. The state of the device was maintained even after removal of the applied bias, indicating the non-volatile memory. The observed current–time response showed good memory retention behaviour of the fabricated devices. The excellent stability and retention performances of hybrid device verify the reliability of this device and demonstrate their potential for application in non-volatile bistable memory device. The carrier transport mechanism of the bistable behaviour for the fabricated non-volatile organic bistable devices structures is described on the basis of the I–V experimental results by analyzing the effect of space charge and electronic structure. Interestingly, the device performance was not degraded and remains identical even after bending the device from 60–120° angles, which indicates high potential for flexible non-volatile bistable memory device applications. This demonstration provides a class of memory devices with the potential for future flexible electronics applications.