The Fabrication And Photoelectric Characteristics Of Vertical Channel Organic Thin-Film Transistor

Organic thin film transistor （OTFT） with a vertical structure and organic light emitting transistors （OLET） combining OTFT with organic light emitting diode have been fabricated in this paper. The devices are prepared using organic semiconductor material copper phthalocyanine （CuPc） as the hole-transporting layer. OTFT and OLET have a thin film A1 gate electrode that was formed using a shadow evaporation mask in the organic semiconductor layers by DC magnetron sputtering thin film deposition. The effective device area （drain-source electrodes overlapping portion） of OTFT and OLET is approximately 4mm². Using Alq₃ as the emissive layer makes OLET with the structure of glass substrate/ITO/Alq3/CuPc/Al/CuPc/Cu. By optimizing the experiment parameters, excellent performances of OTFT and OLET were obtained. Extraction electrode was got with indium pressure method. Static and dynamic characteristics were investigated by using KEITHLEY4200 semiconductor characterization system and oscilloscopes. Carrier injection is analysized using Fowler-Nordheim tunneling model. The drain-source current of the organic thin film transistor with the vertical structure is thin-film Al gate tunneling. The tunneling current is controlled by the gate-source voltage.Experiment data show that there is a good Schottky barrier between gate Al electrode and CuPc film. The drain-source current (I_DS) at a constant drain-source voltage （VDS） decreases with increasing the gate voltage (V_GS); the drain-source current (I_DS) at a constant gate voltage (V_GS) increases with raising the drain-source voltage （VDS）. A typical OTFT characteristic is obtained in the OLET with a small Al gate bias （<1.0V）. There is a high current between source and drain electrode. The luminance of OLET is also controlled by V_GS. The number of hole- carrier injected into the Alq3 light-emitting and I-V characteristics of OTFT and OLET are controlled by relatively small V_G.The electrical characteristics of OTFT are also investigated which have excellent dynamic operation and much larger on/off ratios. The results obtained here show that the OTFT and OLET are suitable element for flexible sheet displays.