STUDY OF ORGANIC FIELD-EFFECT TRANSISTORS FROM POLY-3- OCTYLTHIOPHENE SOLUTIONS ON DIFFERENT GATE DIELECTRICS

摘要

We compared several gate dielectrics useful for organic thin film transistors (OFET) on flexible substrates: spun on benzocylobutene and poly-imide, anodically grown Al_2O_3, reactively sputtered Ta_2O_5 and mixed Ta_2O_5/SiO_2; for comparison we included thermally grown SiO_2. Commercially available P3OT and P3HT have been applied as organic semiconductors, mainly via spin coating, additionally we tested ink-jet printing. Although organic dielectrics revealed good coverage, they failed at very thin films. With respect to electrical behavior as gate dielectrics Ta_2O_5/SiO_2-films turned out to be best, because of its high permittivity accompanied by excellent insulation characteristics. Nevertheless, it introduces problems with mechanical stresses and susceptibility to cracking. Anodically grown Al_2O_3 might be a good candidate from an overall point of view, but we ended up with a strong dependency of breakdown behavior on area due to defects that prevented successful OFET preparation. We built up OFETs on Ta_2O_5, Ta_2O_5/SiO_2, and BCB with the Ta_2O_5 ones exhibiting very low gate voltages of 3 V for full operation with a I_(on)/I_(off)-ratio of about 300.