Polymeric materials used in memory devices have attracted significant scientific interest due to their several advantages, such as low cost, solution processability, and possible development of three-dimensional stacking devices. Polythiophenes, including tethered alkyl substituted polythiophenes and block copolymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and composites, are one of the most attractive polymeric systems for memory applications because of their commercial availability, high conductivity, and mechanical strength. In this article, recent studies of functional polythiophene for memory applications are reviewed, mostly focusing on the role of the materials in the memory functionality, optimizing the chemical structure of the polythiophene and the component of each layer in memory device. A critical summary of the proposed mechanisms, including filament formation, electric field-induced charge transfer and reductionoxidation (redox) driven, is given to explain the resistive switching phenomena in the polythiophene system. In addition, the challenges facing the research and development in the field of polythiophene electronic memories are summarized. POLYM. ENG. SCI., 54:2470-2488, 2014. V C 2013 Society of Plastics Engineers
INTRODUCTIONOver the past few decades, thin films of polymer semiconductors are being intensively investigated for electronics applications because of their remarkable advantages including their adaptability to low-temperature processing on flexible substrates, low cost, amenability to high-speed fabrication, and tunable electronic properties that are not feasible to produce using standard inorganic electronics. Polymer semiconductor devices such as light-emitting diodes [1], photovoltaic cells [2,3], thin-film transistors [4,5], chemical and photo sensors [6][7][8], organic/ polymer nonvolatile memory device [9] are potential candidates for future flexible electronic-device applications. Among these applications, polymer nonvolatile memory device appears highly attractive owing to its potential usage in data storage media. In particular, polymer memory devices have attracted a lot of attention due to their simple structure, three-dimensional stacking capability, good scalability, high mechanical flexibility [10,11]. Unlike current memory devices storing data by means of encoding "0" and "1" as the amount of charge stored in electric circuits, polymer nonvolatile devices store information in an entirely different manner, utilizing the conductivity response of the active layer to the applied voltage, in which the low and high resistive states are assigned to "ON" (or "LRS") and "OFF" (or "HRS"), respectively [12]. Among the nonvolatile memory types, the write-once read-many times (WORM) memory and the hybrid rewritable (write-read-erase-read) memory are usually observed in polymeric memory performance. Depending on the electrical polarity required for resistance switching, the switching behaviors can be classified into two types including polarity dep...
