Study On Organic Field-effect Transistors

Organic field-effect transistors(OTFTs) has been of great scientific and technological interest for sevel decades.While for many years electronic materials rearch has been dominated by organic semiconductor materials,dielectric materials acting as the other important part of OTFTs are payed attention to.dielectric materials can change the electrical property of OTFTs significantly and is irrepalceable.PMMA[poly(methyl methacrylate)] has been a promising organic dielectric material for OTFTs. Researchers have done many studies on the thickness and the surface morphology of PMMA thin film. But only few research on the trap charges and the mechanism of leakage current.We study the dentisity of traps and the mechanism of leakage current though the C-V(capacitance-voltage) curve,C-F(capacitance-frequency) curve and J-V(current-voltage) curve of MIS structure whose insulater material is PMMA film. The molecular of PMMA and the preparation technology are changed to find their realationship between the electrical property. The main contents include:(1) The PMMA film is prepared by spin-coating different concentrations of PMMA - chloroform solution and we find out that when the solution concentration is 20mg / ml , a large area of PMMA film without pinhole can be prepared.(2) The effect of molecular weight on the electrical property of PMMA is researched. The PMMA layer is spin coated from a 20mg/ml dilution of PMMA in chloroform.The critical electric field is more than 1.8MV/cm and the thickness is 220nm. When the molecular is 996K,we get the minimum unit area current,which is 6.0×10-9A/cm2.While the molecular is 350K,we get bigger unit area current, which is 8.5×10-9A/cm2. Schottky emission accounts for the leakage current versus electric field strength behavior in high electric fields and the Schottky barrier height is 0.9eV calculated by linear fitting. The trap density decreases with the molecular weight increasing.996k molecular weight PMMA has the least trap density, which is 4.7×1010A/cm2.(3)When the annealing temperature is 130℃,the PMMA thin film has good electrical property.The capacitance of unit area is 9.6nf/cm2 and the leakage current of perarea is as low as 4.7×1010/cm2.(4)When the annealing time is 180 minute,the PMMA film has good electrical performance than other annealing tim.(5)The OTFTs using the best preparation process prepared PMMA film present good transistor characteristic.They have higher carrier mobility and on/off current ratio,and lower threshold voltage is found.