High Performance Large Area Bottom Contact Organic Thin Film Transistor

The performance of organic field-effect transistor is not only related to the material selected,but also to the structure of the device.The performance of the top-contact field-effect transistor is generally better than that of the bottom-contact field-effect transistor.However,the bottom contact structure device is more suitable for large-area device array preparation in practical applications,because it is easier to combine with large area patterning technology.How to get high-performance bottom contact transistor is a practical challenge for the application,which mainly restricts the contact between the organic semiconductor and the electrode.Pentacene as the most representative organic small molecule,Since 1980s,pentacene molecules as the organic field effect transistor active layer,has been widely studied.In this paper,we use the pentacene molecule as the active layer to study the performance of the bottom contact thin film transistor device and introduce the induced layer to realize the performance improvement of the bottom contact device.The main contents are as follows:1.We have fabricated and investigated the performance of the pentacene contact transistor and its poor performance.The mobility of the device based on the bottom-contact pentacene transistor is only 10-2cmzV-1s-1,the reason is that the presence of a height difference in the edge region of the gold electrode,resulting in a significant defects in the subsequent deposition of the pentacene film,such as poor film continuity,small grain boundaries,grain boundaries and so on.2.We used p-6P as the induced layer to realize the high-performance bottom contact transistor,and systematically studied the reason of its performance improvement.The p-6P film exhibits a lamellar growth pattern in both the electrode and the channel region,so that it can form a better contact with the gold electrode,and plays a role of weak epitaxial induction on the subsequent deposition of pentacene molecular film.This improvement in morphology improves the performance of the bottom contact device.For the channel length 20?m bottom contact device,we obtained excellent performance with a mobility of more than 1 cm2V-1s-1 and a switch ratio of 106.It is significantly superior to field-effect transistors with only pentacene molecular thin films.3.The resistance information of the device containing the p-6P induced and non-induced layers was analyzed by TLM method,and the reason for the improvement of our device was given.We fabricated the bottom contact field effect transistor with different channel length,calculated and extracted the contact resistance through line transfer method(TLM).According to the results of experimental calculations,the contact resistance of the pentacene thin film transistor with the induced layer is significantly smaller than that of the field effect transistor containing only pentacene molecular film,especially in the case of low gate voltage,the contact resistance is only 40 K(?)cm,and under the same conditions,the contact resistance of the transistor without the induced layer is as high as 200 k(?)cm.4.Using the above method,a high-performance n-type bottom contact thin film transistor was obtained.We selected two representative n-type molecules:PTCDI-Ph and F16CUPc and fabricated the corresponding transistor devices.The results show that the mobility of the n-type bottom contact thin film transistor containing the p-6P induced layer is increased to 0.1?0.5cm2V-1s-1,which is two orders of magnitude higher than that of the corresponding device without the induced layer.It can be seen that our method is equally applicable to n-type organic small molecules.