The Fabrication And Electrical Properties Of Flexible Small Organic Molecule Thin Film Field Effect Transistors

The thin film field-effect transistors(TFTs)are the most basic components in various integrated circuits.Compared with conventional thin film transistor devices,the flexible TFTs have been studied because of their advantages of low cost,light weight,flexibility,low power consumption and large area production.With years of efforts,the performance of flexible transistor devices has been significantly improved.There have been significant developments in areas such as flexible displays,electronic printing,bio-compatible sensors,large-scale integrated circuit and digital communications,etc.In recent years,the wearable flexible electronics and biocompatible flexible sensors have been gotten great attention in the market and laboratory.However,The problems such as the roughness of flexible substrates,the preparation process of flexible devices and the poor stability of the performance of flexible devices need to be solved.In this paper,the preparation process of flexible devices was studied.A flexible substrate with high flatness was prepared by spin coating process.Flexible thin-film transistors were fabricated on flexible substrates using vacuum evaporation deposition and magnetron sputtering deposition processes.The flexible substrate preparation process was explored.The effects of the preparation process of flexible substrate,dielectric layer and annealing on the electrical properties of the device were studied.The main contents are as follows:Firstly,in order to solve the problem of large roughness of the flexible substrate and obtain a flexible substrate material with a small roughness,a polyimide(PI)solution was used as a raw material.The polydimethylsiloxane(PDMS)buffer layer which was compatible with the flexible device was prepared on the glass by a spin coating process.Polyimide solution was spin-coated upon the buffer layer and then annealed to prepare a flexible polyimide substrate.The relationship between the spin coating rate and the polyimide film thickness was studied.The optimum spin coating rate was 3000 r/min and the thickness of polyimide substrate was 5.4?m.The surface morphology and surface roughness of the substrate were characterized,the RMS was 0.5nm.Secondly,the flexible small organic molecule Dinathto-thieno-thiophene(DNTT)thin film transistor device was prepared by vacuum evaporation deposition coating process.The effects of common dielectric layers of Al2O3 with Al2O3-SAM(self-assembled monolayer)composite dielectric layers on the performance of flexible devices was compared.The performance of the flexible device was optimized because of the smaller roughness of the composite dielectric layer.The effect of the thickness of different dielectric layers on the performance of the device was studied,a thicker composite dielectric layer could effectively improve the device performance.The effect of annealing on the performance of the flexible organic small molecule thin film transistor was investigated.The optimal annealing temperature was determined to be about 70? by annealing the flexible device in N2,the device mobility reaches 0.99cm2V-1s-1.Finally,in order to prepare high performance flexible organic-inorganic heterojunction thin film field effect transistor devices,N-type flexible a-IGZO oxide thin film transistors were fabricated by magnetron sputtering deposition process.The compatibility of oxide films on polyimide flexible substrates was explored.The a-IGZO was combined with small organic molecules,and vertical structure was adopted without any interface modification,the small organic molecule Dinathto-thieno-thiophene(a-DNTT)was evaporated directly on the surface of a-IGZO film to prepare a vertical structure of high-performance flexible organic-inorganic heterojunction thin film transistor devices.The device exhibit an outstanding electrical performance as high as 3.50 cm2 V-1 s-1 and 0.36 cm2 V-1 s-1 for electrons and holes.The morphology of the initial molecular layer and oxide film of small organic molecules were characterized.The transport properties of the electron carrier and hole enhancement mode of the flexible a-IGZO/DNTT bipolar device were tested and the mechanism was explained.