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This thesis describes an investigation into homogeneous KN crystalline films grown on Pt/Ti/SiO2/Si substrates, amorphous KN films grown on TiN/Si substrates using the RF-sputtering method, and the ferroelectic and piezoelectric properties of these KN films. KNbO3 (KN) thin films have been extensively investigated for applications in nonlinear optical, electro-optical and piezoelectric devices. However, the electrical properties of KN films have not yet been reported, because it is difficult to grow stoichiometric KN thin films due to K2O evaporation during growth.

This thesis also reports on the ReRAM properties of a biocompatible KN ReRAM memristor powered by the KN nanogenerator, and finally shows the biological synaptic properties of the KN memristor for application to the artificial synapse of a neuromorphic computing system.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
Wireless nanodevices have been extensively studied in a wide range of biological application fields such as artificial electronic skin, implantable devices and body attached electronic systems [17]. Recently self-powered biomedical devices are advantageous for biological devices driven by piezo-electric nano generators (PNGs), which can transform wasted mechanical energy of the human body into electrical energy [810]. In order to improve the performance of power-supply medical devices, these people need a high-efficiency computing system, but they use a traditional digital computing system based on the Phon Neumann architecture.
Tae-Ho Lee

Chapter 2. Literature Survey

Abstract
Piezoelectric devices such as ultrasonic motors, transformers, piezoelectric sensors, and actuators have been widely used in various industrial areas [1, 2]. Recently, interests in piezoelectric devices has increased considerably with the development of mobile devices. Pb(Zr1 − xTix)O3 (PZT)-based ceramics, thick films, and thin films have been generally used for these piezoelectric devices because of their excellent piezoelectric properties. However, since PZT-based materials contain more than 60 wt% PbO, which is toxic and evaporates during the synthesis process, they can pose serious environmental problems.
Tae-Ho Lee

Chapter 3. Experimental Procedure

Abstract
K2CO3 (99.9% purity, High Purity Chemicals Co., Japan) and Nb2O5 (99.9% purity, High Purity Chemicals Co., Japan) powders were used as starting materials in order to synthesize KNbO3(KN) phase. After stoichiometric weighing, these raw powders were mixed in a zirconia-ball-contained polypropylene jar with ethanol for 24 h, and then dried at 90 °C in an oven.
Tae-Ho Lee

Chapter 4. Results and Discussion

Abstract
Figure 4.1a shows the XRD patterns of the KN thin films grown on the Pt–Si substrate at various temperatures. An amorphous phase was formed in the films grown below 700 °C. The KNb3O8 and KNb5O13 phases, indicated by open circles and open triangles, respectively, were developed in the film grown at 700 °C without formation of the KN phase. Therefore, it was not possible to grow the homogeneous KN film by the sputtering method using the stoichiometric KN target owing to the evaporation of K2O. A similar result was obtained for the NKN film; the amorphous phase was formed for the films grown at temperatures ≤500 °C, and the Na-deficient secondary phase, with a small amount of the NKN phase, was formed in the film deposited at 600 °C, due to the evaporation of K2O and Na2O [13].
Tae-Ho Lee

Chapter 5. Conclusions

Abstract
In this study, Synthesis of a homogeneous KN film was difficult because of the evaporation of K2O during the growth process. The KN film should be deposited at RT to avoid the evaporation of K2O since the K-deficient K2.88Nb5O15 secondary phase was formed in the KN film grown at the very low temperature of 100 °C. Moreover, the annealing of KN films should be conducted at 800 °C, because when the annealing temperature is greater than that, a K-deficient K2.88Nb5O15 secondary phase is also formed. Moreover, a transient KNb3O8 secondary phase was formed when the annealing temperature was less than 800 °C.
Tae-Ho Lee
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