| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 100 === Polymer transistor type memory devices have recently attracted significant scientific interest for flexible electronic applications due to the advantages such as low cost, solution process and flexibility. The dominant mechanism in transistor type memory is the charges trapping due to polymer electrets, interfacial defects or nano-crystal floating gate. However, the nanofibers based nonvolatile memory devices or flexible memory devices have not been fully explored yet. In this thesis, we explored the following two subjects to address the above issues: (1) nonvolatile field-effect transistor memory based on ES nanofibers. (2) flexible nonvolatile transistor memory devices based on polyimides (PIs) Electrets.
Nonnvolatile Field-Effect Transistor Memory Based on Electrospun Nanofibers (chapter 2) : We have demonstrated the memory characteristics of ES nanofibers based on F8T2. The effects of the geometry and diameter of the ES nanofibers on charge transport and charge storage ability were explored. The narrow ES nanofibers showed higher mobility than those with a large diameter, because the improved orientation and crystallinity. The large ES nanofiber exhibited a larger memory window, attributed to the heterogeneities in the amorphous-crystalline interfaces in the F8T2 ES nanofibers. The devices of the ES nanofibers with the smallest diameter showed the highest charge carrier mobility of 9.8×10-3 and on-off ratio of 3.6×103 at Vg = 0 V. From the stability testing of the WRER cycles, the good on/off ratios could be maintained for at least 100 cycles, showing good stability. This study demonstrated that the morphology of ES nanofibers have a significant influence on electrical charge storage ability and their resulted memory characteristics.
Flexible Nonvolatile Transistor Memory Devices Based on PIs Electrets (chapter 3) : OFET memory devices were fabricated with 2,5-Bis (4-aminophenylenesulfanyl) selenophene-4,4’- (hexafluoroisopropylidene) diphthalic anhydride (APSP-6FDA) and 2,5-Bis (4-aminophenylenesulfanyl) thiophene-4,4’- (hexafluoroisopropylidene) diphthalic anhydride (APST-6FDA) as the electrets, c-PDMS as the blocking layer and F8T2 as the conducting layer. The wider memory operation window (83V) and higher hole mobility (1.29x10-3 cm2V-1s-1) were observed in APSP-6FDA based devices than those of APST-6FDA based devices attributed to the higher electron density in selenophene than thiophene. Moreover, retention test and WRER test showed a long term stability at least 10000s and durability for repeated operation more than 100 cycles. During the bending test of various curvature radius and repeated bending, the hole mobility could be kept in the same level as that in flat state until r = 3 mm and can maintain at least 3000 bending cycles under the curvature r =13 mm. The threshold voltage shift was also kept in a similar level after 3000 bending cycles and increased considerably when curvature radius was smaller than 3 mm, due to more interface defects after the hard bending. The above results demonstrated the potential applications of the materials for flexible nonvolatile memory devices.
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