| Summary: | 博士 === 國立臺灣大學 === 化學工程學研究所 === 102 === Organic-based memory devices have received extensive scientific interest due to their advantages of flexibility, scalability, and material variety. A typical configuration of OFET memory devices is a conventional transistor with an additional charge storage layer ( named as the electret) between a semiconductor layer and dielectric layer. However, there is no systematic study on the above structure effects. In this thesis, we report the nonvolatile transistor memory device characteristics of n-type organic semiconducting nanowires, and reveal the geometry effects on memory characteristics. We further explored the effects of donor-acceptor charge transfer of polyimide electrets on the memory characteristics. In addition, high dielectric constant PI/TiO2 and polymer/graphene oxide (GO) composites as charge-storage dielectrics for the low-voltage nonvolatile memory devices were also investigated. The following summarize the important discovery of this thesis.
1. Self-Assembled Nanowires of Organic N-type Semiconductor for Nonvolatile Transistor Memory Devices (Chapter 2): Organic nonvolatile transistor-type memory devices using self-assembled nanowires of n-type semiconductor, N,N’-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI). The BPE-PTCDI nanowires with small diameters induced high electrical field and resulted in a large memory window (the shifting of the threshold voltage). The value of BPE-PTCDI nanowire based memory devices on the bare substrate could reach 51 V, which was significantly larger than that (~ 5 V) of thin film. The memory window was further enhanced to 78 V with the on/off ratio of 2.1x104 and the long retention time (104 s), using the hydrophobic surface.
2. Nonvolatile Organic Field-Effect Transistor Memory Devices Using Polymer Electrets with Different Thiophene Chain Lengths (Chapter 3): Synthesis of poly(5-hexyl-2-vinylthiophene) (PVT) and poly(5-Hexyl-5”-vinyl-2,2’:5,2” -terthiophene) (PVTT) as charge storage electrets for memory devices using BPE-PTCDI. The mobility of the memory device using PVTT electret was significantly smaller compared with that of PVT because its large torsional angle hindered the molecular packing of BPE-PTCDI. Besides, the highest HOMO energy level of PVTT facilitated the charges transfer from BPE-PTCDI and led to the largest memory window of 81V.
3. Thiophene and Selenophene Donor-Acceptor Polyimides as Polymer Electrets for Nonvolatile Transistor Memory Devices (Chapter 4): Nonvolatile memory characteristics of n-type BPE-PTCDI-based organic field-effect transistors (OFET) using the polyimide electrets of poly[2,5-bis(4-aminophenylenesulfanyl) -selenophene-hexafluoroisopropylidenediphthalimide] (PI(APSP-6FDA)), poly[2,5-bis(4-aminophenylenesulfanyl)-thiophene-hexafluoroisopropylidene -diphthalimide] (PI(APST-6FDA)), and poly (4,4’-oxydianiline-4,4’ -hexafluoroisopropylidenediphthalic anhydride) (PI(ODA-6FDA)). The device with PI(APSP-6FDA) exhibited the largest memory window because the highest HOMO energy level and heavy-atom effect facilitated the charges transferring from BPE-PTCDI and trapping in the PI electret.
4. Nonvolatile Transistor Memory Devices using High Dielectric Constant Polyimides Electrets (Chapter 5): The memory characteristics of pentacene-based OFET using polyimide electrets of PI(6FDA-TPA-CN), PI(DSDA-TPA-CN), and PI(BTDA-TPA-CN), consisted of electron-donating 4,4′-diamino-4〃 -cyanotriphenylamine (TPA-CN) and different electron-accepting dianhydrides The higher dipole moment and larger torsion angle of PI(6FDA-TPA-CN) resulted in the more stable charge transfer complex and accompanied with the largest memory window of 84 V of the fabricated device.
5. Nonvolatile Transistor Memory Devices Based on High-k Electrets of Polyimide/TiO2 Hybrids (Chapter 6): Novel nonvolatile memory behaviors of BPE-PTCDI-based OFET using the new polyimides (PIs), (poly[9,9-bis(4-(4-amino-3-hydroxyphenoxy)phenyl)fluorene-oxydiphthalimide]) PI(F-ODPA) and (poly[4,4’-bis(4-amino-3-hydroxyphenylthio)diphenyl sulfide -oxydiphthalimide]) PI(3S-ODPA) and their PI/TiO2 hybrids as electrets were reported. The OFET memory device derived from PI(F-ODPA) with π-conjugated fluorene moiety exhibited larger memory window (8.6V), and could be further enhanced by introducing TiO2 (up to 20wt%) into the PIs.
6. High-k Polymer/Graphene Oxide Dielectrics for Low-Voltage Flexible Nonvolatile Transistor Memories (Chapter 7): Solution-processable nonvolatile transistor memories on flexible ITO-PEN substrate were demonstrated using the electrets of poly(methacrylic acid) (PMAA) and graphene oxide (PMAA-GO) composites. The hydrogen bonding interaction effectively dispersed GO sheets in the high-k PMAA matrix. Besides, the fabricated transistor memories have a low operation voltage, a large threshold voltage shift, a long retention ability of up to 104 s, and good stress endurance of at least 100 cycles.
Our study revealed the significance of the nano-morphology and donor/acceptor structure of the electrets on the OFET memory characteristics for advanced data storage applications.
|
|---|
