Synthesis and Applications of High Performance Polyimides and Their Hybrid Materials
Date Issued
2015
Date
2015
Author(s)
Li, Meng-Hsien
Abstract
Polyimides (PI) are high performance and functional polymers widely used in the fields of optoelectronics and semiconductor fabrications due to their good thermal stability, chemical resistance and outstanding mechanical strengths. Polyimide/inorganic hybrid materials have been commonly used to enhance the physical properties, such as thermal, mechanical, and optical properties. However, the development of polyimide/silica hybrid films with the multi-functionality of high optical transmittance, superior thermal stability, excellent mechanical strength, and photo-patternable remains challenges. In addition, the incorporation of electroactive moiety into polyimides for electrical device applications has not been fully explored yet. In this thesis, we firstly explored the preparation of photosensitive PI/silica hybrid films with high thermal/mechanical properties. Sequentially, through blending with small conjugated molecules, the developed polyimide-based supramolecules could be used in organic field effect transistor memory devices as a charge storage layer. The detailed results and discussion are described as following： In Chapter 2, we synthesized the polyimide/silica hybrid optical films with high optical transmittances, high mechanical strength and high thermal stability. The polyimides were prepared using the monomers of soft aromatic dianhydride, 4,4’-oxydiphthalic anhydride (ODPA) with ether group and diamine, 2,2’-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FOH) with hydroxyl and hexafluoroisopropylidene group, then followed with tetramethyl orthosilicate, (TMOS) for sol-gel reaction, and followed by the thermal imidization to obtain polyimide/silica hybrid optical films with different silica content. To explore the photosensitive application of polyimide, we introduced 3-(trimethoxysilyl) propyl methacrylate (MPTMS) with vinyl group and photo-initiator Irgacure-819 to prepare negative-type photoresist patterns. The experimental results showed that the thermal-resistance and mechanical strength of the hybrid materials as increasing the silica content. In addition, the hybrid films achieved high thermal stability (the coefficient of thermal expansion (CTE) could be as low as 17.92 ppm/oC), good optical transparency (>85 % at 410 nm, thickness >20 μm), and exceptional mechanical properties (tensile Strength = 93.07 MPa, tensile Modulus = 4.28 GPa and elongation = 2.99 %). Additionally, a clear negative-tone image with resolution 50 μm in 7 μm thickness film could be obtained. In Chapter 3, the nonvolatile memory characteristics of p-type pentacene-based organic field-effect transistor (OFET) using the synthesized polymer electrets PI(6FOH-ODPA) and its supremolecules were systematically studied. The supramolecular materials were prepared by hydrogen-bonding 1-aminopyrene with the hydroxyl functional group of the PI(6FOH-ODPA). The effect of the 1-aminopyrene composition on the hole-trapping capability of the PI(6FOH-ODPA) electret was investigated. Under the operating voltage in ± 30 V, the prepared devices exhibited a memory window of 20.56 V and hole-mobility of up to 10-1 cm2V-1s-1. Furthermore, the devices showed a long charge-retention time for 104 s with the ON/OFF current ratio of around 103~104 and multiple switching stability over 100 cycles. This reveals that the device has potential applications in nonvolatile memory devices. The relationship between the charge transfer effect of polyimide/1-aminopyrene and their memory characteristics was also discussed. This thesis demonstrated that the polyimides modified with the inorganic, photosensitive or electroactive moieties could be potentially used in different electrical/photonic applications.
Subjects
polyimide hybrid materials
photosensitive polyimide
OFET memory device
1-aminopyrene
Type
thesis
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