Design And Preparation Of Donor-Acceptor Type Fluorene-containing Functional Polymers For Memory Devices

Rather than encoding "0"and "1" as a charge stored in the cell of a silicon device, polymer memories store data in an entirely different form, such as in a high-and low-conductivity response to an applied voltage. Advantages of polymer memories include simplicity in device structure, good scalability, ease of processing, low-cost potential,3D stacking capability and large capacity for data storage. The Donor-Acceptor polymeric (composite) materials with the intrinsic switching behavior provide great interest because the memory characteristics could be adjusted over a wide range of modifications on chemical structures. In this thesis, we designed and synthesized a series of new D-A type fluorene-containing functional polymeric materials, and the structures and electrical memory properties of these materials were investigated.In Chapter1, briefly introduce the construction, type, and characteristic curve of storage device, and the synthesis and memory properties of D-A type fluorene-containing functional polymers were reviewed in this chapter.In Chapter2, a new soluble conjugated polymer, poly[{9-(4-methoxyphenyl)-9H-carbazole}(9,9-dioctylfluorene)(2,5-diphenyl-1,3,4-oxadiazole)](PCFO), was synthesized through the Suzuki coupling reaction. The absolute fluorescence quantum yield of PCFO was measured using the integrating sphere of a photoluminescence spectrofluorometer, and changed from49.1%for a dilute tetrahydrofuran solution to16.2%for a thin film due to the existence of a strong fluorescence quenching effect in the solid state. The HOMO-LUMO bandgap (3.07eV) calculated from the electrochemical measurement is nearly identical to the optical bandgap (3.06eV) estimated from the ultraviolet/visible absorption onset data. This film was attached to aluminum and indium-tin oxide contacts to fabricate a memory device with typical bistable electrical switching, nonvolatile write-once read-many-times(WORM) memory performance, a turn-on voltage of-2.3V and an ON/OFF ratio of105.In Chapter3, We designed and synthesized a novel conjugated polymer poly [(tripheny-lamine)-(9,9-dioctylfluorene)-9,9-bis[4-(3,4-dicyanophenoxy)phenyl]fluorine](PAFF) which contains both triphenylamine (electron donor) and cyan-(electron acceptor) moieties. In the UV/vis absorption (or photoluminescence) spectrum of a thin film of the sample, there is only a small red-shift of the position of its maximum compared to the dilute solution. As the polarity of the solvent increased, the emission band of PAFF was observed to get broader and become red shifted.The memory device manufactured with the polymer film performs a typical WORM characteristic with a turn-on voltage of-1.5V and an ON/OFF ratio of104. In Chapter4, MWNTs and GO were covalently functionalized with the conjugated polymer PCF-OH. The fluorescence emission exhibited by composite was considerably quenched as compared to PCF-OH. The decreased absolute fluorescence quantum yields of the samples in dilute solution further confirmed that this quenching phenomenon. The Raman spectra show that the D and G bands of composite have different degrees of changes. The memory performance is being tested.