Device Fabrication And Electrical Characteristics Of Vertical Organic Thin Film Transistors

Traditional organic thin film transistors (OTFTs), the planar-type organic field-effect transistors (OFETs), are of disadvantages such as low current modulation and high operation voltages due to the limitation of channel length and low carrier mobility of organic materials. Therefore, vertical OTFTs have been proposed, which perform high current modulation for relative low operation voltages resulted from the shorter pathways for carrier transport as compared to the planer OFETs. One of the most promising vertical device structures is the metal-base organic transistor (MBOT).In this study, devices structured in metal / 2-Amino-4-phenylphenol / metal with various anodes and cathodes are fabricated. It is found that the current - voltage (I - V) characteristics of the two terminal devices is strongly dependent on the energy structure of the materials. Furthermore, devices with the same metal electrodes perform much different I - V characteristics for top-injection and bottom-injection, due to the differences between the metal / organic / metal interface resulted from the deposition order. Based on these results, MBOT device consists of Au / 2-Amino-4-phenylphenol / Ca / 2-Amino-4-phenylphenol / Au is fabricated. The static current gainβand the on / off ratio reach 150 and 5×10⁵ resectively.MBOT device consists of ITO / PEDOT : PSS / m-MTDATA / Pentacene / NPB / Al / Pentacene / Au has been fabricated, which performs higher current modulation (6.7 mAcm^-2) and on/off ratio (23) as compared to that of the device without PEDOT : PSS / m-MTDATA (0.76 mAcm-2, 6.5), due to the efficient charge carrier injection in the emitter electrode / emitter interface. The insertion of PEDOT : PSS / m-MTDATA modifies the ITO electrode surface and decreases the hole injection barrier from ITO to the emitter, resulting in the improvement in the device performance.Hot-carrier transistor device consists of Au / Pentacene / Al / LiF / CaO / Pentacene / Au has been fabricated, which performs much higher static current gainβ(300) as compared to that of the device without CaO layer (35). And theβvalue is almost independent on the base voltage (Vb). The CaO layer in the base / emitter interface is considered as electron blocking layer from the base to the emitter, which singnificantly depresses the unwanted minority charge carrier transmission in the base / emitter interface.Flexible organic transistor PI / PEDOT∶PSS / P3HT / LiF / Al / Pentacene / Au with PEDOT∶PSS emitter electrode has fabricated on PI substrate. By testing the electrical characteristics and flexibility of the device, conducting polymer is proved to be of much potential applications in flexible organic electronics. The current modulation and the static current gainβreach as high as 240 and 120 mAcm-2 respectively.