메모리, 이온인지 및 생체적합 기능 브러쉬 고분자의 합성과 물성연구
- 메모리, 이온인지 및 생체적합 기능 브러쉬 고분자의 합성과 물성연구
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- Polymer materials are widely used in biocompatible, ion-sensing and electrical devices, because of their good scalability, mechanical strength, flexibility, and most important of all, ease of processing. As an alternative to the more elaborate processes of vacuum evaporation and deposition of inorganic and organic molecular materials, manufacturers could eventually use ink-jet printers or spin-coater, for example, to deposit polymers on a variety of substrates. In addition, one of advantages of polymer materials is possibility of versatile application by means of simple synthesis. The function of polymer can be changed by addition of specific molecules to polymer backbone or side chain. In particular, polyimide and conjugated polymer are representative optical and electrically useful materials for various fields.
In Chapter II, a new aromatic polyimide containing 4-(Diphenylamino)benzy lidenyliminoethylenyl alcohol (TPAIE) moiety as side groups was synthesized and charaterized. This PI polymer is dimensionally stable up to 280 ？C and thermally stable up to 440 ？C. In devices fabricated with the PI polymer as an active memory layer, the active PI polymer was found to operate at less than ？2 V in electrically bistable unipolar and bipolar switching modes by controlling the compliance current. The PI polymer layer exhibits repeatable writing-reading-erasing capability with high reliability in air ambient conditions as well as at high temperatures up to 130 ？C. This PI polymer also exhibits a high ON/OFF current ratio up to 109. The observed nonvolatile memory behaviors are due to Schottky emission and local filament formation.
In Chapter III, We have synthesized a new thermally and dimensionally stable polyimide, poly(4,4？-amino(4-hydroxyphenyl)diphenylene hexafluoroisopropylidened iphthalimide) (6F-HTPA PI). The 6F-HTPA PI is soluble in organic solvents and thus easily processed with conventional solution coating techniques to produce good quality nanoscale thin films. Devices fabricated with nanoscale thin PI films with thicknesses less than 77 nm exhibit excellent unipolar write-once-read-many-times (WORM) memory behavior with a high ON/OFF current ratio of up to 106, a long retention time and low power consumption, less than ？3.0 V. Furthermore, these WORM characteristics were found to persist even at high temperatures up to 150？C. The WORM memory behavior was found to be governed by trap-limited space-charge limited conduction and local filament formation. The conduction processes are dominated by hole injection. Thus the hydroxytriphenylamine moieties of the PI polymer might play a key role as hole trapping sites in the observed WORM memory behavior.
In Chapter IV, we report the fabrication and operation of novel programmable ？write-read-erase？ memory devices based on nanoscale thin films of a photo-pattenable polyimide (PI), poly(hexafluoroisopropylidenediphthalimide-4-cinnamoyltriphenylami ne (6F-TPA-CI PI) . This PI is easily fabricated by means of conventional solution spin-coating (or roll- or dip-coating) and subsequent drying, and the polymer pattern is well developed by a simple UV photolithography technique.. The devices with the patterned polymer active layer which can be sustainable over the further processing demonstrate excellent programmable, rewritable non-volatile memory characteristics with a high ON/OFF current ratio (105-109) and high electrical stability. This unique feature can make it possible to build 3-dimensional (3D) arrays of devices by spin-coating or dip-coating multiple layers to achieve very high storage densities
In Chapter V, charge-transport characteristics of poly[di(carbazole-9-ethyl)dipropa gylmalonate] (pDCDPM) films which show DRAM characteristic were studied, as a function of temperature and thickness variation. It is found that the ON-state current is dominated by ohmic conduction, and the OFF-state current appears to follow a transition from ohmic to space charge limited conduction with a shallow-trap distribution. Our study proposes that the ON/OFF switching of the devices is mainly governed by a filament mechanism. Films with a thickness of 30−
60 nm were found to exhibit very stable DRAM characteristics without polarity. In addtion, the pDCDPM films possess its memory characteristics when operated at temperatures up to 180 ？C. The filament formation mechanism for the switching process is supported by the metallic property in device？s temperature dependence of the ON-state currents. I also found that the structure change of ？-conjugated polymer could affect filament formation enough to change ON-state current level as well as OFF-state current level.
In Chapter VI, we have synthesized the self-plasticizing all-polymeric ion selective membrane by covalently bonding both ionophore and lipophilic additive moiety through long linker to polymer backbone. The very low Tg of the polymer compensated the reduced mobility due to immobilization thus the flexibility of the polymer which bears both ionophore and lipophilic additive moiety is provided to give an satisfactory potentiometric response to carbonate ion for itself. The optimization of ionophore and lipophilic additive ratio for optimal carbonate ion sensitivity and selectivity to interfering ions was adjusted just by varying the immobilization contents. And by immobilization, the leaching problem of membrane components was solved. Overall as-fabricated ISE by all-polymer ion selective membrane showed good performance. This new type polymer will be a promising candidate for solid-state miniaturized ISE membrane.
In Chapter VII, We have synthesized new brush polymers with various numbers of bristle ends incorporating phosphorylcholine moieties. The polymers are thermally stable up to 175 ？C and form good quality films with conventional spin-, roll-, and dip-coating, and subsequent drying process. Interestingly, all these brush polymers, as a phosphorylcholine-containing polymer, demonstrate for the first time to reveal always a stable molecular multi-bilayer structure in thin films that arise due to the efficient self-assembly of the bristles for temperatures <55 ？C and phosphorylcholine-rich surfaces, and therefore successfully mimic natural cell membrane surfaces. These brush polymer films exhibit excellent water wettability and water sorption under with retaining such the remarkable molecular multi-bilayer structure, and thus have hydrophilic surfaces. These novel multi-bilayer structured films repel fibrinogen molecules and platelets from their surfaces, but also have bactericidal effects on bacteria. Moreover, the brush polymer films were found to provide comfortable surface environments for the successful anchoring and growth of HEp-2 cells, and to exhibit excellent biocompatibility in mice.
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