Polymer CMOS Circuits Based On Rare Earth Metal Contacts

As the building blocks of the future organic electronics,organic field-effect transistors(OFETs)have not yet been well developed.A critical issue arises from the poor contact between the metal and the organic semiconductor,significantly affecting the device performance and stability.Complementary MOS(CMOS)circuits call for well-paired PMOS and NMOS characteristics as well as good stability.Compared with the relatively matured P-type OFETs,the N-type counterparts still demonstrate very poor performance.This severely hinders the development of organic CMOS circuits,in which the contact engineering is the key.To improve the performance of organic CMOS circuits,this thesis focuses on the contact engineering in N-type OFETs by taking CMOS inverter as an example.After a systematic literature suvey,we concluded that the rare-earth metal of scandium(Sc)is a promising candidate of the source/drain electrode for N-type polymer OFETs.The main content of this thesis is descrbied as follows:By means of fabricating DPPT-TT OFETs with gold(Au)and scandium(Sc)contacts,we found that the Sc-contacted devices exhibited superior N-type OFET charactertics.By means of fabricating DPPT-TT and N2200 OFETs with Sc contacts,we found that N2200 devices displayed better,unipolar N-type OFETs characteristics with much improved performance parameters.By varying the thickness of the Au and Sc contact electrodes,we found that the morphology of the semiconductor film deterioated as the contact thickness increased and the device performance also degraded.So,a thickness of 20 nm was believed to be the optimized value for the contact electrodes.By varying the annealing temperature of the polymer semiconductor film,we found that hightemperature annealing may cause defect formation,leading to structural and energetic disorder.So,annealing at 150℃ for 1h was believed to the optimized condition for DPPT-TT.Finally,by modifying the contact eletrodes from Au to Sc,we found that the rare-earch metal of Sc can indeed improve the contact performance in N-type OFETs and thus resulted in much enhanced performance for the constituted CMOS circuits.