The Current Transport Mechanism Analysis Of Zinc Phthalocyanine Thin Film Transistors

The vertical structure organic thin film transistors(VOTFTs)were fabricated using OLED multiple coating system,it has a layered structure ITO/ZnPc/Al/ZnPc/Cu.ITO film as the source was deposited on the glass substrate by RF magnetron sputtering,Al and Cu film as the gate and the drain were prepared using DC magnetron sputtering,and Zinc Phthalocyanine(ZnPc)active layer was formed by vacuum evaporation under a vacuum of 4×10-5Torr.The source temperature of ZnPc was 350?,and the evaporation time was 40 minutes.The thickness of ZnPc film was measured about 82nm by Ambios XP-200 step tester.During the fabrication,the temperature of glass substrate was kept at room temperature.The electrical measurements were performed by semiconductor characteristic analyzer(Keithley 4200-SCS).In the VOTFT,double Schottky barrier is formed between semi-transparent A1 film and the two side ZnPc films,device demonstrates excellent rectifying characteristics.At Vps=3V and VGS=OV,the current density of 1.194mA/cm2 is obtained.The carrier mobility of transistor is calculated for 2.17×10-6cm2/Vs.In this paper,the carrier transport mechanism of the organic thin film transistor was researched and analyzed,and the degradation mechanism of VOTFT was briefly studied.The experimental results show that this device exhibits the unsaturated ?-?characteristics.In the low voltage region,the current-voltage is examined with exponential relationship.With the increasing of the electric field intensity,operation current of the device follows the theory of Fowler-Nordheim tunneling injection.It is decided by the triangle Schottky barrier formed by device structure and conductive properties of ZnPc material.The influence of carrier mobility,threshold voltage and switching current ratio on the performance of device was analyzed The surface morphology and absorption spectra of ZnPc film were tested using atomic force microscope(AFM).?-? characteristics of device based on different Al film thicknesses were also tested,the experimental results exhibit that the device has better electrical characteristics when the Al film thickness is about 20nm.The parameters of the Schottky barrier height for 0.848V and the depletion layer width for 24.7nm were calculated by the C-V characteristic curve.The modulation effect of Schottky barrier height on the current was also analyzed.In this paper,the formation and suppression method of gate leakage current were also described.The short channel of VOTFT makes up for the defect of organic semiconductor materials with low carrier mobility and low conductivity,the operating speed of device is improved.And the high speed,high current density and low driving voltage of organic device are realized.