Preparation And Performance Improvement Of Bottom Contact Transistors Based On Weakly Epitaxial Growth Of Rubrene Films

Organic field effect transistors（OFETs）have broad application prospects in flexible circuits,RFID tags,sensors,and other fields.In recent years,the mobility of organic semiconductors has been greatly improved,but the operating frequency of organic transistors is still far below the target of 1 GHz,due to limitations such as contact resistance and channel length.At the same time,bottom contact structure transistors are still one of the main structures used in the large-scale application of organic transistors,due to the process requirements of refined electrode patterns.However,the contact resistance of bottom contact transistors is usually high,which seriously affects the performance and operating frequency of transistors.Therefore,it is very important to effectively improve the contact resistance in bottom contact transistors for their performance.In this thesis,the effects of Mo O₃ buffer layers,UV-treated electrodes,and the combined effects of molybdenum oxide and silver oxide buffer layers on the performance of bottom contact transistors were studied using weakly epitaxial Rubrene thin films as the research object.Finally,we designed a new sandwich structure transistor and further improved its performance using electrode modification.In this thesis,the effects of Mo O₃ buffer layers,UV-treated electrodes,and the combined effects of molybdenum oxide and silver oxide buffer layers on the performance of bottom contact transistors are studied using weakly epitaxial Rubrene thin films as the research object.Finally,we design a new sandwich structure transistor and further improved its performance using electrode modification.In the first part,we first analyze the morphology of thin films in the bottom contact and top contact structure,and find that the silver electrode with the bottom contact structure would have an impact on the growth of p-6P thin films.At higher substrate temperatures,the electrode channels will hinder the growth of p-6P,and the grains near the electrodes are independent from each other,unable to form a continuous p-6P thin film.This impact is most severe in the channels;when we decrease the substrate temperature,due to the increased interaction between p-6P and the silicon wafer,the grains of p-6P in the channel can connect with each other at 200°C,forming a smooth and continuous bimolecular layer film,suitable for use as an epitaxial inducing layer.In addition,by comparing the performance of top contact transistors and bottom contact transistors,it can be found that the performance of bottom contact transistors is poor and the mobility is low.We calculate their contact resistance by changing the length of the channel.In the second part,the effects of Mo O₃ buffer layer,UV-treated electrodes,and the combined effects of molybdenum oxide and silver oxide buffer layers on the performance of bottom contact transistor devices are studied.Analysis of the electrode surface shows that Mo O₃ can not only improve charge injection,but also improve the morphology of Rubrene on the electrode surface,the continuity of the film in bottom contact transistor,and improve transistor performance by reducing surface energy.When the thickness of Mo O₃ is 3 nm,the electrode improvement effect is the best.The contact resistance of the bottom contact transistor is reduced by 90%,and the mobility is increased by 270%.UV treatment of silver electrodes can form silver oxide on the electrode surface,and suitable silver oxide can be used to improve the contact effect of bottom contact transistors.When the electrode is exposed to ultraviolet light,treatment for 10 s has the best improvement effect,reducing the contact resistance by 75%,and increasing the mobility by 160%.Adding Mo O₃ to the UV-treated electrodes can further improve the performance of the transistor.After adding 3 nm Mo O₃,the contact resistance of the transistor is further reduced by 56%,and the mobility is increased by60%.In the third part,a sandwich type bottom contact transistor is designed by changing the preparation order of each functional layer of the transistor.By controlling the thickness of p-6P around the bottom contact transistor electrode,the contact effect of the bottom contact transistor is improved.The bottom contact transistor with a sandwich structure reduces the contact resistance by more than 40%and increases the mobility by more than 50%.Finally,the electrode was modified to further improve the device performance of the sandwich transistor.The device contact resistance obtained by improving Mo O₃ is low,with a minimum of 8.57×10³ kΩ;The combined improvement of molybdenum oxide and silver oxide buffer layer results in a high device mobility of up to 2.9×10^-2 cm²/Vs。...