Development and Optimization of Multifunctional Electronic Devices Based on Soft Materials = 유연 재료 기반 다기능 전자소자의 개발 및 최적화

다국어 초록 (Multilingual Abstract)

Development and Optimization of Multifunctional Electronic Devices Based on Soft Materials Baeksang Sung Dept. of Creative Convergence Engineering Graduate School Hanbat National University Advisor : Jonghee Lee The trend in wearable and implantable electronic devices is shifting from rigid to soft material-based platforms, driven by the advancements in next-generation healthcare and biomonitoring technologies. This transition is essential for mitigating discomfort caused by mechanical mismatch with the human body and for enhancing device performance. However, in-depth research is required concerning the biocompatibility, compatibility, and performance optimization of the substrates and components when configuring soft electronic devices. Therefore, this study discusses material selection considering the human-device interface and the performance optimization design of corresponding components. The first section focused on fabricating a strain sensor utilizing cellulose, a material with skin-like mechanical properties and high biocompatibility as the main substrate. To enhance the low durability of cellulose, it was crosslinked with plant-derived tannic acid (TA), achieving both skin-like Young's modulus and improved durability. The addition of TA also imparted UV-blocking and antibacterial properties, proving its suitability as a substrate material for next-generation biocompatible soft electronic devices. The second section addressed the low luminance issue of organic light-emitting diode (OLED), which is suitable for phototherapy and optogenetics applications, by fabricating a polydimethylsiloxane (PDMS) based porous pyramid film capable of reducing internal reflection within the OLED. The introduction of this film resulted in approximately 50% efficiency improvement for the OLED, alongside expectations for improved uniform light distribution and reduced angular dependence even under deformation, demonstrating the OLED's sufficient applicability as a light source for bio-integrated soft optoelectronic devices. The third section addressed the structural instability of bio-derived optical films in wet environments by fabricating a crosslinked gelatin/chitosan-based micro-lens array (Bio-MLA) film optimized for moisture resistance and mechanical compliance. The introduction of this film resulted in an electroluminescence (EL) intensity enhancement of approximately 31% even after rehydration, alongside the achievement of skin-like mechanical properties, demonstrating its potential as a robust and biocompatible light extraction solution for phototherapeutic OLED applications. The fourth section designed a novel humidity sensing platform to enhance the sensitivity of the respiration sensor. To overcome the performance limitations caused by the length (L) and width (W) of the widely used interdigitated electrode (IDE) for humidity sensing, a silicon oxide wafer-based vertical type humidity sensor was developed. The novel vertical type humidity sensor, utilizing an ultra-thin silicon oxide film as a dielectric layer, outputs the humidity-dependent conductivity change of the hydroxyethyl cellulose (HEC) sensing layer as an amplified capacitance change, resulting in an approximately 20-fold amplified capacitance change compared to the IDE Type, thereby improving sensitivity. Furthermore, its sufficient applicability in analyzing human respiration characteristics confirmed its potential as a next-generation high-sensitivity respiration sensor. In conclusion, these studies discuss both the seamless human-device interaction design essential for soft electronic devices and the optimization strategies for the embedded components, making significant academic and technical contributions to the advancement of the next-generation soft electronic device field.

목차 (Table of Contents)

• List of Tables ⅳ
• List of Figures ⅴ
• ABSTRACT ⅸ
• Ⅰ. Introduction 1
• Ⅱ. Research Background 4
• 2.1 Soft electronics 4
• 2.2 Design of soft electronic device 5
• 2.2.1 Mechanical properties of soft material 5
• 2.2.2 Biocompatibility of soft material 6
• 2.2.3 Integration of soft electronic device 8
• 2.3 Soft electronic device for human-device interaction 8
• 2.3.1 Strain sensor 9
• 2.3.2 Soft optoelectronic device 11
• 2.3.3 Humidity sensor 13
• Ⅲ. Cellulose-based strain sensor 16
• 3.1 Introduction 16
• 3.2 Experiment 18
• 3.2.1 Materials 18
• 3.2.2 Fabrication process of TAC conductive hybrid film 19
• 3.2.3 Characterization 19
• 3.3 Results and discussion 20
• 3.4 Conclusion 38
• Ⅳ. Soft optical property enhancement film for OLEDs 39
• 4.1 Introduction 39
• 4.2 Experiment 41
• 4.3 Results and discussion 44
• 4.3.1 J-V-L, EQE, and C.E characteristics of Devices A, B, and C 45
• 4.3.2 Angular-dependent EL characteristics of Devices A, B, and C 48
• 4.3.3 TEOLEDs with optical properties-enhancement film at different resonan-
• ce conditions 50
• 4.3.4 Angular dependence characteristics of Devices D, E, and F 52
• 4.4 Conclusion 54
• Ⅴ. Bio-derived Optical film for OLED Light extraction 55
• 5.1 Introduction 55
• 5.2 Experiment 57
• 5.2.1 Fabrication of Bio-MLA Film 57
• 5.2.2 Characterization of Bio-MLA Film 59
• 5.2.3 OLED Fabrication and Measurement 59
• 5.3 Results and discussion 60
• 5.4 Conclusion 66
• Ⅵ. Vertical-type capacitive humidity sensor 67
• 6.1 Introduction 67
• 6.2 Experiment 69
• 6.2.1 Humidity-Sensitive Materials and Sensor Fabrication 69
• 6.2.2 Humidity testing system 70
• 6.3 Results and discussion 71
• 6.3.1 Detection Mechanism of the Vertical-Type Humidity Sensor 71
• 6.3.2 Equivalent Circuits Calculation 74
• 6.3.3 Electrical Characteristics of the Sensor 78
• 6.3.4 Universality of the Sensing Platform 83
• 6.3.5 Application: Respiration Monitor 84
• 6.4 Conclusion 87
• 6.5 Supporting information 87
• 6.5.1 Humidity-dependent electrical properties of HEC 87
• 6.5.2 Derivation of Potential Distribution (V(x)) 88
• 6.5.3 Calculation of Leff 91
• 6.5.4 Correlation between V(x) and Leff 93
• 6.5.5 Calibration for the difference between measured and calculated 94
• 6.5.6 Hysteresis of vertical humidity sensor 95
• 6.5.7 Capacitance-to-resistance conversion capability 95
• Reference 96
• 국문 요약 117