Research And Application Of High Performance Organic Thin Film Transistor

Organic thin-film field effect transistors?OTFTs?have the property of light,low cost and moderate processing condition,even can be prepared on the flexible substrates.A bright future and promising prospect could be presented in the large area preparation of the flexible electronics,active drive circuits,sensors and RFID,et al.With the advancement of the scientific researches on OTFTs,the performance of the devices has been greatly improved.However,as compared with inorganic transistor devices,OTFTs still exist some disadvantages,such as a higher threshold voltage,the lower crystalline of organic semiconductor,the poor stability.Based on pentacene as the active layer,this dissertation carried out the related researches in the following three aspects.?1?We studied the interface between the electrode and the organic semiconductor when taking advantage of Cu I as the modification layer.By inserting the ultra-thin CuI layer into the interface between Cu and pentacene,we researched the value and the distribution of contact resistance and its impact on device performance especially on the field effect mobility by use of transfer-line method?TLM?.CuI particles optimized the connection between grains with various sizes,reduced the roughness on the surface of the pentacene,decreased the contact resistance of the device as well.Doping contact generated during the interface increases the probability of carriers tunnel through the schottky barrier by means of field emission.In addition,contact doping layer forms the receptor layer,thus increasing the injection area of hole density,reducing the defect density in those area.As a result,due to the contact optimizing between the metal electrode and organic active layer,we effectively decreased the injection barrier,so that threefold enhancements on the field effect mobility had achieved,as 1.27cm²/Vs??2?We adopted solution method to fabricate the novel inorganic/organic composite insulating layer.By comparing with the performance of various insulation materials,we found that SiO₂ insulating layer prepared by sol-gel method kept a much higher dielectric constant which obviously resulted in the low voltage operating characteristics of OTFTs devices.However,sol-gel method could produce a couple of pinhole-size holes inside and outside the thin film,those holes could become the charge traps easily and give rise to the irregular decrease in thin film thickness,so as to generate some points where local high electric field applied.Meanwhile,breakdown can easily happen,and the gate leakage current density increased.In order to further improve the performance of the device,we spin coating a crosslinked PVP polymer solution on sol gel-SiO₂ dielectric layer.The sticky crosslinked PVP polymer solution soundly filled the former uneven defect,which improved the surface roughness of insulation layer,film quality and crystallinity of the organic semiconductor layer,and greatly reduced gate leakage current.Moreover,PVP decreased the hydroxyl groups,so that reduced the trap density in the interface.Also,it improved the conductive channel quality in the interface near organic layer and the stability of devices.By use of solution method,we prepared inorganic/organic compound insulation materials with good dielectric properties,which formed a fine interface with a lower trap density and a higher crystallinity of organic semicondor,so as to realize the preparation of OTFT devices with the low voltage,low power consumption and high field effect mobility.The solution method tends to be simple and low cost,presenting a promising prospect for application.?3?We researched on the lable-free biosensor based on OTFTs.By use of the mercapto group?-SH?modified single-stranded DNA?ssDNA1?as the curing material on gold electrode,chemical bonds of Au-SH enabled a strong connection between DNA molecule and gold after dropping ssDNA1 on the surface of gold electrodes,so that ssDNA1 could be effectively cured on the surface of gold by chemical absorption.When dropping the complementary ss DNA2 and uncomplementary ssDNA3 on the devices cured by ssDNA1,respectively,we were enable to differentiate the completely matched and mismatched DNA from targeted DNA efficiently,according to the various electrical performance of hybrid devices.Meanwhile,experiments shown that probes cured by different concentrations of ssDNA1 could affect the response of the sensor.Its sensitivity can be optimized by changing the concentration of ssDNA1 probe.This dissertation had some researches on the interfacial problems,such as interface between electrode/organic semiconductor,organic semiconductor/dielectric layer,existed in the process of OTFTs development.As a consequence,we optimized the interfaces and fabricated high performance OTFTs,also futher exploited applications in the field of biosensors based on OTFTs.