ION MODULATED ORGANIC TRANSISTORS - Doria

Nikolai Kaihovirta3. RESULTS AND DISCUSSIONSV [V]20100-10-2010 -4WRITEREAD"1"abs(I D)[A]10 -610 -8"0"0 50 100 150 200t [s]Figure 3.10. The figure illustrates the difference between applying a highreduction potential versus a high oxidation potential in a PEDOT/PSS basedECT. For the former the recovery of the current is almost complete, while thelatter results in a terminated electronic conductivity. The WRITE-pulse is ±25V, 5 s and the READ-pulse is -2 V, 2 s.Overoxidation was utilized for demonstrating write-once read manytimes (WORM) memory functionality by using the ECT device structure(subsequently denoted as WORM-ECT). In a WORM-device, informationis permanently stored once and read several times. Such memory-devicesare considered favorable for e.g., archiving purposes. Organic WORMdeviceshave been demonstrated before [73-75]. I-V characteristics for theWORM-ECT are shown in Figure 3.11. By applying a high negativepotential at the gate-electrode (WRITE-pulse: -25 V, 30 s) the transistorchannel is overoxidized. In other words, the high-conducting state (“1”) istransformed into a low-conducting state (“0”). The permanent “0” state isfurther illustrated by characterizing the WORM-ECT roughly one monthafterwards. From Figure 3.11 it is apparent that the “0” state is notcompletely stable. The variation in conductivity is due to the ionicconductivity in the WORM-ECT, which is sensitive to a change in theambient humidity.33