Study On Perofrmances Of Organic Heterojunction Field-effect Transistors

Since the first organic field-effect transistor (OFET) was reported in1986, considerableprogress has been achieved in the development of the performance and preparation of organic fieldeffect transistors in the past30years. Compared with the traditional inorganic semiconductors,organic semiconductors have the advantages of simple preparation process, low cost, goodcompatibility with large-area flexible substrates. Therefore organic semiconductors are with thepotential of wide applications, which can be applied in many fields. Currently, researchers mainlyfocused on improving the device performance of organic field-effect transistors. In contrast, littlework has been devoted to the research of multi-functional devices. This article focuses on the studyof multi-functional OFET devices. The main research contents are as follows:First, this thesis reviews the development of OFET, discusses the significance of research inOFET and the research progress in OFET, as well as summarize the problems to be solved and thefuture direction of development in OFETs. Secondly, we give a brief introduction of the basicstructure and classifications of OFET, and then summarize various kinds of commonly usedmaterials, such as the organic semiconductor layer materials, insulating layer materials, substratematerials and electrode materials. In addition, the author briefly introduce the working principle ofOFET by taking P-type OFET as an example, and provide electrical models of OFET and mainperformance parameters. On the basis, several charge transport mechanisms are introduced in theorganic semiconductors. Finally, the methods of preparation OFET as well as their advantages anddisadvantages are summarized.Then, high performance N-type F16CuPc/CuPc heterojunction OFET device was preparedwith the electron mobility of0.94×10-2cm2/Vs. This value is much higher than the mobility ofOFET with F16CuPc (the mobility of3.1×10-3cm2/Vs). Meanwhile, the device can remain in anormally-on state. Device performance enhancement was attributed to dipole effects originatingfrom the F16CuPc/CuPc interface. The role of the dipoles has been discussed. On the other hand,ambipolar transistors are obtained by preparing F16CuPc/CuPc heterojunction OFET with MoO3modified electrodes. The mobility of electrons and holes is2.5×10-3cm2/Vs and3.1×10-3cm2/Vs,respectively. By analyzing the change of the electrical properties of the interface between theelectrodes and the semiconductor layer, the electrical properties of ambipolar transistor attribute tothe lowered contact resistance and increased electron injection barrier. The thesis also prepared organic non-volatile field-effect transistor memory device withPentacene/P13/Pentacene heterostructure which exhibits good P-type characteristics. Thefield-effect mobility, the threshold voltage and the on/off current ratio are0.21cm2/Vs,4.4V and104, respectively. The memory window is around80V with program/erase bias pulses of120V.When applying different write voltages, devices exhibit good multibit storage characteristics, whichenables a2bit data storage capacity with the data retention time exceeds10000s. These goodstorage characteristics are attributed to stable dipole layer originating from the Pentacene/P13interfaces. In this paper, the role of the dipoles has been discussed. Furthermore, the light alsocontributes to the formation of dipoles, resulting in the shifts in the threshold voltage of the device.On the basis of this study, the author has prepared a flexible nonvolatile organic field-effecttransistor based on flexible PET substrate, the device shows good storage characteristics. Thememory window is about40V. The data retention time can reach more than10000s. In addition,the memory devices exhibits almost no change in the programmed/erased Vtheven after10000bending cycles with a bending radius of10mm.Finally, work in this article is summarized, and the development trends and prospects in theheterojunction OFETs are discussed.