| Summary: | 博士 === 國立臺灣大學 === 化學工程學研究所 === 104 === Recently, organic-based memory devices have received extensive scientific interest due to the rapid growth of the next-generation consumer electronic devices. Organic memory devices with the solution process, high transparency and well mechanical property are required, apart from their advantages such as flexibility, scalability, and material variety. A typical type of charge-trapping OFET memory is organic floating-gate memory. In this device, charges are stored in a metal nanoparticles called a floating gate, located within the insulating gate dielectric, and completely surrounded by insulator. In general, floating gate materials are gold nanoparticles (Au NPs), which required either high vacuum deposition or multiple processing steps to combine the charge-trapping sites with tunneling layer. Besides, the Au NPs possessed a strong absorption in the visible region due to their strong surface plasmon resonance effects. The devices with the Au NPs showed a lower transparency than that of the devices without the Au NPs. On the other hand, organic memory should be engineered to be durable enough to withstand high levels of strain for the wearable device applications. Therefore, efforts to develop stretchable types of transistor memory for advanced electronic circuits are important. The following summarize the important discovery of this thesis:
1. Conjugated Polymer Nanoparticles as Nano Floating Gate Electrets for High Performance Non-volatile Organic Transistor Memory Devices (chapter 2): A nano-floating gate material by using conjugated polymer nanoparticles (CPN) as the discrete trapping sites embedded in an insulating polymer was demonstrated. The nanoparticles of polyfluorene (PF) and poly(fluorene-alt-benzo[2,1,3]thiadiazole (PFBT) with average diameters of around 50-70 nm prepared from repcrecipitation method were used as a charge-trapping sites, while hydrophilic Poly (methacrylic acid) PMAA served as a matrix and a tunneling layer. The transistor memory device revealed a controllable threshold voltage shift, indicating effectively electron-trapping by the PF CPN. The memory device had a large memory window (35 V), retention time longer than 10^4 s with a high ON/OFF ratio of >10^4. In addition, the memory device performance using conjugated polymer nanoparticle NFG was much higher than that of the corresponding polymer blend thin films of PF/polystyrene (PS).
2. High Performance Transparent Transistor Memory Devices Using Nano-Floating Gate of Polymer/ZnO Nanocomposites (chapter 3) : The transparency of the device with metal NPs is restricted to 60~70% due to the light absorption in the visible region caused by the surface plasmon resonance effects of metal NPs. To address this issue, we demonstrated a novel NFGM using the blends of hole-trapping poly (9-(4-vinylphenyl) carbazole) (PVPK) and electron-trapping ZnO NPs as the charge storage element. The memory devices exhibited a remarkably programmable memory window up to 60 V during the program/erase operations, which was attributed to the trapping/detrapping of charge carriers in ZnO NPs/PVPK composite. Furthermore, the devices showed the long-term retention time (>10^4s) and high ON/OFF ratio of >10^4, indicating excellent electrical reliability and stability. Additionally, the fabricated transistor memory devices exhibited a relatively high transparency of 90% at the wavelength of 500 nm.
3. Elastomeric substrate with wrinkled surfaces for intrinsically stretchable organic thin film transistor (chapter 4): We employed the fluoroelastomer with the wrinkle surface as substrate for the intrinsically stretchable transistor, and this material is also used as the gate dielectric layer. Poly(selenophene-alt-3,6-dithophene-2-yl-2,5-bis-(2-octyldodecyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione) (PSeDPP) with a high mobility as well as an air stability was selected to be the semiconducting layer. CNT and PU/PEDOT:PSS blend solution were used as the stretchable source/drain and gate electrode, respectively. The substrate could dissipate the applied strain on the semiconducting layer, and the transistor device was transformed to become the wrinkled structure after stretching, leading to a high endurance under strain. The device with high electrical mobility of ∼0.73 (cm^2 V^-1S^-1 and on-off ratio of 10^4 was stable over 2000 cycles of stretching under a 30% uniaxial strain.
Our study demonstrated new methods to fabricate solution processable organic transistor memory devices with a high performance. Besides, an intrinsically stretchable transistor with a high device durability at stretching was obtained, which could be applied to stretchable electronics.
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