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

Electrically switching organic and polymeric materials have significant advantages over inorganic silicon-and metal-oxide-based memory materials in that their properties can easily be tailored during chemical synthesis and they have a good flexibility. Electronic memories can be divided into two primary categories according to its volatility:volatile and nonvolatile memories. Non-volatile memory, retaining the stored information even when the electrical power supply has been turned off, can be further divided into the write-once read-many times (WORM) memory and the rewritable (Flash) memory.As a non-volatile memory, aWORM memory is capable of holding data permanently and being read from repeatedly, which have broad application prospects. Many D-A type polymeric (composite) materials have been reported as WORM type memory devices, but the ratio and strength of D-A impacting on the memory performance has been rarely reported. The excellent photoconductive and hole-transporting properties of flourene molecules make fluorene-containing polymers widely used as optoelectronic applications, which can be modified by different groups into donors or acceptors. Therefore, several fluorene-containing functional polymers with different strength and ratio of D-A were successfully prepared. Besides, the electrical memory properties of the materials were also studied and some preliminary results were obtained. This thesis was divided into four chapters, as follows:In Chapter1, the device construction and mechanism of WORM memory type materials were briefly introduced. The progress of WORM type polymeric memory applications was reviewed form three aspects:single polymer, doped polymer and carbon-based materials. The problems which are still under studying were also discussed in this chapter.In Chapter2, two polyimides, PCFHI{Poly[(2,7-bis(3,6-di-tert-butyl-9H-carbazole)-9,9-diphenyl-9H-fluorene)-(4.4’-(Hexafluoroisopropylidene)diphthalicimido))]} and PFHI {Poly[(9,9-diphenylene-9H-fluorene)-(4,4’-(Hexafluoroisopropylidene)diphthalicimido)]}, were synthesized through tuning the strength of donor in the fluorene unit by containing carbazolyl. The devices Al/Polymer/ITO and Al/Polymer/Pt has prepared by using the two polymers. showing WORM type and Flash type memory performances. In these two performances. PCFHI with strong donor carbazolyl unit have higher switching ratio than PFHI. The devices resulting different performances were discussed in the end of the chapter.In Chapter3. we designed and synthesized two different D/A propotions polymers. PFD1(D/A=9:1) and PFD2(D/A=27:1)(PFD{Poly[(4,4’-(((9H-fluorene-9,9-diyl) bis(4,1-phenylene))bis(oxy))diphthalonitrile)-(4,4’-(9H-fluorene-9,9-diyl)bis(N,N-diphenylaniline))}), which cotain both triphenylamine(electron donor) and cyan-(electron acceptor) moieties in the C-9position of the fluorene unit through the Yamamoto reaction. The test results found that PFD1with a high proportion receptor performs no memory behavior, but PFD2with the low proportion receptor performs a typical WORM characteristic.In Chapter4, by using the Suzuki coupling reaction, the polymer containg fluorene, P C F C{Poly[((1,1’-biphenyl)-4-carbonitrile)-(9-dihexyl-9H-fluorene)-(9-phenyl-9H-carbazole)]}, weresynthesized. The memory device manufactured with the polymer PCFC film performs a typical WORM characteristic with a turn-on voltage of-1.35V and an ON/OFF ratio of more than10. Both the ON and OFF states are stable under a constant voltage stress and survived up to108read cycles at a read voltage of-1.0V, which suggested that the device has a good fatigue resistance.