Integrated Micro-Supercapacitor: Design, Fabrication, and Functionalization

Owing to the advantages of high power density, fast charge/discharge rates as well as long lifetime, micro-supercapacitor (MSC) has drawn much attention for its potential application in miniaturized electronics. Many efforts have been devoted to the design and fabrication of high-performance MSCs. On the other hand, the integration of MSCs with multiple functional materials and devices has emerged with the development of portable and wearable microelectronics. To date, the biggest challenge in research is to develop a reliable and smart fabrication technology/strategy, which can integrate diverse objective materials into compact devices. Rolled-up nanotechnology is a unique approach to self-assemble 2D nanomembranes into 3D structures by using strain engineering. This self-assembly process smartly combines top-down and bottom-up methods to pattern functional nanomaterials into ordered 3D micro- and nanostructure arrays. One promising advantage of this approach is that such a self-assembled structure can endow micro-devices with functionality and high performance under a limited footprint area. The first part of this thesis focuses on the fabrication of planar interdigital MSCs with thermo-responsive function. Based on this work, the second part involves the research on novel tubular MSC which was fabricated by employing shapeable materials and strain engineering. A polymeric framework consisting of swelling hydrogel and polyimide layers ensures excellent ion transport between electrodes and provides efficient self-protection of the tubular MSC against external compression. Such tubular device also exhibits excellent areal capacitance, and an improved cycling stability compared to that of planar MSCs. The third part introduces the step-by-step experiments towards the fabrication and optimization of inorganic strained layer-based tubular MSC. Al2O3/Ni/Cr/Al2O3 strained nanomembrane is designed and can successfully drive the rolling up of MnO2 electrodes with a high yield under magnetic fields.:Chapter 1. Introduction 1 1.1. General background 1 1.2. Motivation of this work 2 1.2.1. Integration of micro-supercapacitors 2 1.2.2. Thermo-responsible micro-supercapacitors 2 1.2.3. 3D tubular functional micro-supercapacitors 2 1.3. Dissertation structure 3 Chapter 2. Overview of micro-supercapacitors 5 2.1. Introduction to MSCs 5 2.1.1. Capacitor 5 2.1.2. Electric double-layer capacitor 5 2.1.3. Pseudocapacitor 7 2.2. MSC configuration 8 2.3. Fabrication strategies of interdigital MSCs 9 2.4. Fabrication methods of active materials 12 2.5. Functionalization of supercapacitors 15 2.5.1. Tribo/piezoelectric driven self-charging function 15 2.5.2. Solar cell driven self-charging function 16 2.5.3. Electrochromic function 18 2.5.4. Self-healing function 19 2.5.5. Sensing function 20 2.5.6. Stretchable function 21 2.5.7. Thermo-responsive function 22 2.5.8. Photo-switchable function 23 2.6. Conclusion and outlook 23 Chapter 3. Overview of rolled-up technology 27 3.1. 3D self-assembly of the inorganic nanomembrane 27 3.1.1. Introduction 27 3.1.2. Rolled-up nanomembranes for capacitors 28 3.1.2. Rolled-up nanomembranes for Li-ion batteries 30 3.2. 3D self-assembly of the polymeric layers 32 3.2.1. Introduction 32 3.2.2. Self-assembled polymeric layers for microelectronics 35 Chapter 4. Experimental methods 39 4.1. Deposition methods 39 4.1.1. Photolithography 39 4.1.2. Electron beam evaporation 39 4.1.3. Atomic layer deposition 40 4.1.4. Electrochemical deposition 41 4.2. Characterization methods 43 4.2.1. Scanning electron microscopy and focused ion beam milling 43 4.2.2. Electrochemical characterization 43 Chapter 5. An integrated MSC with thermo-responsible function 47 5.1. Introduction 47 5.2. Fabrication and characterization of thermo-responsible MSCs 47 5.2.1. Single thermo-responsible MSCs 47 5.2.2. The array of thermo-responsible MSC 51 5.3. Conclusion 53 Chapter 6. Self-assembly of 3D tubular MSCs 55 6.1. Introduction 55 6.2. Fabrication of tubular MSCs 57 6.2.1. Diagram of processing flow 57 6.2.2. Polymeric layer stack 58 6.2.3. Microelectrodes, self-assembly and capsulation 59 6.3. Results and discussion 60 6.3.1. On-chip and free-standing sample morphology 60 6.3.2. Electrochemical characterization of tubular MSCs 64 6.3.3. Self-protection function of tubular structures 72 6.3.4. Assembly of tubular structures in series/parallel 76 6.4. Conclusion 80 Chapter 7. Tubular nanomembranes for MSCs 81 7.1. Introduction 81 7.2. Self-assembly of Al2O3/Ti/Cr/Al2O3 strained nanomembranes 82 7.2.1. Fabrication method 82 7.2.2. Results and discussion 83 7.3. Self-assembly of Al2O3/Ni/Cr/Al2O3 strained nanomembranes 87 7.3.1. Fabrication method 87 7.3.2. Results and discussion 88 7.4. Conclusion 92 Chapter 8. Summary and outlook 93 8.1. Summary 93 8.2. Outlook 94 Bibliography 95 List of Figures 109 List of Tables 117 Theses 119 Acknowledgment 121 Publications and presentations 123 Curriculum Vita 12