Memory applications of a thiophene-based conjugated polymer: capacitance measurements

Abstract

Capacitance-voltage (C-V) and transient capacitance characteristics of devices based on a thiophene-based conjugated polymer have been studied. C-V characteristics showed a hysteresis behaviour similar to one previously observed in current-voltage (I-V) measurements. The hysteresis behaviour has been explained by considering accumulation of space charges in the polymer layer near the electrodes of the device. The amount of space charges has been found to increase with voltage amplitude. An asymmetry has been observed in charge distribution under forward and reverse bias directions. A voltage pulse was applied to 'write' a state, which has been 'read' by measuring the capacitance of the device. The polymer has been found to retain the stored data for more than 2 h. The slow relaxation of the stored charges, as evident from capacitance transients, has been identified to be responsible for memory applications of the polymer-based devices. We have established that the displacement current due to capacitance variation can generate the observed hysteresis in the I-V characteristics of the devices and hence memory effect in polymer-based devices.