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The Improvement Mechanism Of The Electrical Properties Of Pentacene Organic Thin Film Transistors By Modifying Insulation Layers

Posted on:2011-03-06Degree:MasterType:Thesis
Country:ChinaCandidate:Y GuoFull Text:PDF
GTID:2178360305471292Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
The main research of this thesis is to enhance and improve the electrical properties of pentacene organic thin film transistors (OTFTs), and the mechanism of the performance improvement.Firstly, we review the history and the development of OTFTs and summarized the research results of OTFTs in the laboratory and current use situation in real life, then discusse the existing problems and research direction of OTFTs. And content in the next we introduce the basic knowledge of OTFTs, including common device structures, OTFTs works, material selection and preparation, and crafts.Second, the electrical properties of organic thin film transistors with the modification layers are investigated.In this section, the properties of OTFTs without and with the interface modification layer PhTMS OTFTs but with different active layer thickness are studied. We find that the OTFTs device with the modified interface by PhTMS and 40nm thickness active layer has the best performance. The field-effect mobility of this OTFTs is 4×10-2cm2/ Vs, the on/off current ratio is 1.87×102, the threshold voltage is-10.3V. When the thickness of the active layer is 30nm, the field-effect mobility of this OTFTs is 3.4 x 10-2cm2/Vs, on/off current ratio is 1.38×102, the threshold voltage is 2.74V. For non-modified layer OTFTs, the device's field-effect mobility is 5.66×10-3cm2/Vs, on/off current ratio is 0.52 x 102, the threshold voltage is 3.94V. After analyzing of the performance of these devices, we find that the modified surface of processed insulator layer forms an organic buffer layer between the insulating layer and the active layer film, which has a good compatibility consistency to improve the device performance. In addition, after PhTMS modified, larger pentacene grain size makes the grain density per unit area decrease, while the density of the grain boundaries decreases within the film, which reduces the role of trap states within the film and improves the device performance. Finally, we find when the pentacene film thickness is 40nm the pentacene film has a larger grain size.Finally, the growth mechanism of pentacene on the modified surface of the insulator layer is studied in order to discover the improvement mechanism of the modification layer. In this chapter, AFM diagram of pentacene thin films with different thickness on SiO2 with and without modified by PhTMS are detected..By comparing the AFM diagram after PhTMS modified, we find that in the initial stage of the growth of pentacene film is island-based. Pentacene molecules are stacked in one direction in the growth process, and grown along the long axis perpendicular to the substrate surface. When pentacene is grown on SiO2 with modification, in the early stages, the film growth shows a layer-island growth mode which is mixed with the vertical and tilted growths.It is shown by AFM that after modified, pentacene molecules grow with perpendicular to the ground more easily. The component of film phase increases. Without the interface modification layer, the film phase and three-phase inalics are mixed in pentanece thin film. In the film phase the distance between molecules will decrease and the conjugated degree is higher, which lets the carrier transfer more effectively in the film and improve the performance of OTFTs device. In addition, after PhTMS modified, when deposited pentacene film, the grain size can grow larger. The grain density per unit area and grain boundary density will decreases, which will greatly increase the charge carrier mobility and improve the device performance.
Keywords/Search Tags:Organic thin film transistors, Interface modification, Field-effect mobility, Threshold voltage, On/off current ration
PDF Full Text Request
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