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Design and fabrication of biomaterial-based electronic and opto-electronic devices

초록/요약

This thesis discusses the electronic and optoelectronic applications of melanin and silk biomaterials. Silk and melanin have a wide range of applications in fields like soft robotics, bioelectronics, wearable electronics and optoelectronics. This work comprised fabrication along with characterization of melanin particles incorporated in silk hydrogel films. A novel, self- healable and stretchable optoelectronic skin (OE-skin) is synthesized using melanin/silk that is photo-responsive in nature. Characteristics such as stretchability and humidity-dependent conductivity of OE-skin resulted in the fabrication of different sensory applications, for example, humidity and strain sensors. A Melanin/Silk photodetector is fabricated by joining it with p-Si. This photodetector can sense light patterns and it is also skin attachable. Melanin/silk thin films are also fabricated and utilized to create a transparent memristor and an organic electrochemical transistor (OECT) with a high on/off ratio. Both devices were implemented to obtain inhibitory (IPSP) and excitatory (EPSC) synaptic response with pair pulse facilitation (PPF). The first project deals with optoelectronic skins (OE-skin) which are of pivotal importance in robotics and human- machine communications. Here we present an implementation of OE-skin using silk protein and melanin nanoparticles that possess functionalities of the human skin along with photo-responsive characteristics. The fabricated OE-skin is stretchable, conductive, photo-responsive, and self- healable. Free radicals present in the melanin nanoparticles are activated at high humidity which ultimately increases the photoconductivity of OE-skin. On the other hand, Ca2+ ions capture water molecules from the environment that cause stretchability and self-healing in silk/melanin hydrogel layers. OE-skin exhibited an enhanced electrical conductivity upon increasing the humidity and under laser light illumination. These sensing capabilities of OE-skin have been employed to realize multiple sensors such as strain, humidity, and photoconductive sensors. The study suggested that our OE-skin provides a new outlook to the field of prosthetics and skin-attachable devices. In the second project, we fabricated a semiconducting layer by inserting melanin nanoparticles in silk hydrogel. The ionic conductivity of melanin nanoparticles is activated by water-rich silk hydrogel. A biomaterial-silicon junction is formed as Melanin/Silk and p-Si are joined to form a photodetector. The observed charge accumulation/transport behavior at the melanin NP-silk/p-Si junction is associated with the ionic conductive state of the melanin NP-silk composite. The Melanin NP-Silk semiconductor layer is printed on a p-Si substrate that exhibits photoresponse with illumination under different wavelengths. This photodetector when attached with an Ag nanowires incorporated silk layer can be attached with skin. The photo-responsive biomaterial-Si semiconductor junction using light as a stimulus offers a bio-friendly and versatile platform for artificial electronic skin/tissue. In the third project, we incorporated melanin in a silk solution and fabricated a melanin-silk thin film that has a lower bandgap in the range of wide bandgap semiconductors. UV-Vis absorbance results suggest a peak shift towards a higher wavelength and a significant decrease in bandgap as melanin particles are added to the silk matrix. Depending upon applied voltage and frequency, Capacitance-voltage (C-V) curves reveal three specific regions namely inversion, depletion, and accumulation similar to previous reports of biomaterials. The thin film is employed in the construction of an Ag/mel./silk/Au memristor and a biomaterial-based organic electrochemical transistor (OECT) with a high on/off ratio. Moreover, both devices manifest memory storage capabilities as represented by synaptic operation under microsecond pulses. Ag/Mel.-Silk/Au memristor unveils high-performing resistive switching with a low operating voltage and excellent repeatability.

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목차

Chapter 1 1
1. Introduction 1
1-1 History of biomaterials 1
1-2 Definition of biomaterials 2
1-3 Applications of biomaterials 2
1-3-1 Electronic applications 3
1-3-2 Optoelectronic applications 4
1-4 Materials 4
1-4-1 Silk 4
1-4-2 Melanin 5
1-5 Organization of the thesis 5
Chapter 2 7
2. Methods 7
2-1 Preparation of silk protein solution 7
2-2 Preparation of transparent Silk hydrogel 7
2-3 Preparation of Melanin nanoparticles (MNPs) 8
2-4 Fabrication of MNP/silk layers and optoelectronic skin 8
2-5 Fabrication of the OE-skin-based humidity and strain sensor 9
2-6 Fabrication of the MNP/silk-based detector pixels and UV sensor 9
2-7 Sample preparation for Self-heal ability test 11
2-8 Fabrication of Photodetector arrays on Si 11
2-9 Fabrication of Photodetector Device 11
2-10 Preparation of mel./silk solutions 12
2-11 Preparation of mel./silk resistive switching devices 12
2-12 Preparation of mel./silk synaptic transistor devices 12
2-13 Fabrication of mel./silk Capacitor 13
2-14 Characterizations and Measurements 13
Chapter 3 14
3. Utilizing silk protein and melanin biomaterials for photo-responsive optoelectronic skins 14
3-1 Summary 14
3-2 Device construction and basic properties 15
3-3 Absorbance spectra measurement 15
3-4 Scanning electron microscopy 16
3-5 Fourier transform infrared spectroscopy 17
3-6 Peel force measurement 18
3-7 Mechanical properties of OE-skin 19
3-8 Electrical properties of MNP/silk hydrogels 20
3-9 Photocurrent production by MNP/silk hydrogels 23
3-10 Electron paramagnetic resonance analysis 24
3-11 Self-healing ability of OE-skin 25
3-12 Humidity Sensor 27
3-13 Strain sensor 27
3-14 Light signal mapping 28
3-15 UV sensor 29
3-16 Conclusion 30
Chapter 4 31
4. Bio-inspired and skin-attachable melanin-Si photodetectors for image sensing 31
4-1 Summary 31
4-2 Device construction 33
4-3 Reflectance spectra 33
4-4 I-V characteristics 34
4-5 Photoconductivity 36
4-6 Spectral responsivity and External quantum efficiency 38
4-7 Image sensing 40
4-8 Skin attachable PD arrays 41
4-9 Conclusion 45
Chapter 5 46
5. Conductivity-adjustable biosemiconductors for protein-based synaptic devices 46
5-1 Summary 46
5-2 Device structure 47
5-3 SEM analysis 49
5-4 AFM measurement 50
5-5 UV-Vis spectra and bandgap calculation 50
5-6 Capacitance and Dielectric constants 52
5-7 Resistive switching characteristics 53
5-8 Synaptic Transistor 55
5-9 Conclusion 57
References 59
List of publications 67

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