Study Of The Electrical Characteristics Of Pentacene-based Organic Thin-film Transistor

Thin film transistors based on pentacene as active layer are studied in this thesis,we improved the performance of the devices by choosing pentacene as active layer,improving the morphology of pentacene thin film and choosing the electrodes,all the devices using top contact configuration with bottom gate.Firstly,we have prepared organic thin film transistors(OTFTs) with pentacene, CuPc,and P3HT as the active layer respectively,we found that the electrical characteristics of OTFT based on pentacene are better than others,whose mobility is 0.0948cm~2/Vs,whereas the mobility of OTFT based on CuPc is 0.0029cm~2/Vs,and the output characteristic of is OTFT based on P3HT not stable,thus we eventually chose pentacene as the active layer to fabricate OTFTs for its merit in this thesis.Secondly,we have studied the effect of pentacene morphology on the performance of OTFTs.We have formed pentacene thin film with different deposition rate,the mobility of device prepared with 0.03nm/s deposition rate is 0.1064cm~2/Vs,but the mobility of device prepared with 0.13nm/s deposition rate is 0.0485cm~2/Vs,obviously, the former is better.From the AFM images we found that pentacene thin film with low deposition rate has a lager grain size and less grain boundaries which make the transportation of carriers easier.However,the parasitic resistance of pentacene thin film with high deposition rate is much larger because of the energy barrier and traps at grain boundaries,and corresponded to which the performance of OTFTs is not good.In addition,we have also studied the effect on the performance of OTFTs by annealing prepared OTFTs,we annealed the prepared OTFTs at 50℃,80℃,and 100℃for 10 hours in vacuum oven,and we compared the four devices.The device annealed at 80℃has the best characteristics with the mobility of 0.1804cm~2/Vs,the device unannealed has the worst characteristics with the mobility of 0.0417cm~2/Vs.And we observed and analyzed the pentacene morphology at different annealing temperatures.Finally,the effect on the performance of OTFTs with different metal electrodes is studied.We used Au and Al as source/drain electrode to fabricate OTFTs respectively. The former has the better performance,because the energy between Al and pentacene is not suitable and possibly Al reacted with pentacene.However,Au is very stable and much suitable to pentacene.Therefore the contact barrier and contact resistance between Au and pentacene are smaller so that hole injection from metal Au to pentacene is much easier than from metal Al to pentacene,and the performance of device with Au source/drain electrode is improved.