Supramolecular block copolymers: PCBM composite for resistor-type memory device application
Date Issued
2011
Date
2011
Author(s)
Lian, Shiang-Lin
Abstract
Recently years, polymeric materials use to the memory device applications as an emerging area. The donor-acceptor type polymers have attracted a significant interest for memory device applications due to their tunable electronic properties through molecular design. However, the effects of the different polymer structure on the pure polymer memory characteristics and the application of functional block copolymer composites being used to disperse and control fullerene domain size through specified physical interaction on the nanomaterials composite memory characteristics have not yet been explored. In this thesis, we explore fluorene-based conjugated rod-coil block copolymer and thiophene-containing side-chain polymers with the different block ratio effect of pure copolymer and nanocomposites on resistive type memory device application.
In the first part of this thesis (chapter 2), the optoelectronic, morphology and the memory device properties of diblock (with two different ratio 10/37, 10/68) and triblock (with the ratio41/40/41) poly[2,7-(9,9-dihexylfluorene)](PF)-block-poly(2-vinylpyridine)(P2VP) copolymers are reported. The pure copolymer PF10-b-P2VP37, PF10-b-P2VP68 and P2VP41-b-PF40-b-P2VP41 device exhibit SRAM, SRAM, and DRAM characteristic, respectively. The three pure polymers device exhibit high ON/OFF ratio (107) and threshold voltage about -4V. The switching effect is based on the fluorene moieties transport ability with coexisting P2VP as the charge trap sites. The electric volatile is attributed to the back transferring of shallow trap depth. For the composite system, the varied PCBM content of PCBM: PF-b-P2VP composite device exhibit volatile memory behavior, WORM, or conductor behaviors. The optical absorption and photoluminescence indicated the charge transfer between copolymer and PCBM, which lead to memory characteristics. However, the non-volatile type memory characteristic is associated with the high electron affinity of PCBM. We also compare the memory behavior with different block length and the difference between diblock and triblock copolymer. In the case of PCBM: diblock copolymer composite, by loading less content of PCBM in PF10-b-P2VP68 matrix could achieve the memory performances which need loading more PCBM content for PF10-b-P2VP37. This results is due to the longer P2VP block length of PF10-b-P2VP68, it probably attract more amount PCBM approach copolymer, thus, the distance of isolated domain size in the electrical connected channel between two electrodes is decrease. The morphology and the photoluminescence quenching relativity of these two diblock composites also agree with this result. In addition, the triblock: PCBM composite devices have significant lower threshold voltage than diblock: PCBM composite. It is due to the P2VP41-b-PF40-b-P2VP41 have higher π-π interchain stacking and stack together favorably leading the charge transfer between P2VP41-b-PF40-b-P2VP41 and PCBM is probably easier than diblock composite. This study indicate that the device electrical characteristic could be tune by varied the loading PCBM content or the design of copolymer architecture.
In the second part of this thesis (chapter 3), supramolecular composite thin films of thiophene-containing side-chain polymers PT-b-P2VP: [6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PCBM) were prepare for memory device. The optical absorption and photoluminescence results indicate that the formation charge transfer between PT-b-P2VP and PCBM. The memory device exhibited the WORM type characteristics with threshold voltage -4 ~ -4.6 and ON/OFF ratio 103 ~105. The switching behavior can be explained by the charge injection dominated thermal emission for OFF state and the field induced charge transport in the ON state. This study provide the novel nanomaterials memory device application through the physical interaction between functional block copolymer and fullerene controlling domain size.
Subjects
polymer memory
resistor-type memory
block copolymer
PCBM
supramolecular interaction
Type
thesis
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