Smart Sensors and Neuromorphic Resistive Memory Devices for Intelligent Wearable Electronics

Abstract

Recently there has been a growing interest in the realization of smart sensors and neuromorphic resistive memory devices by process from the field of printed electronics with low cost, and high-throughput printing techniques. These devices can easily by integrated and interfaced with a Human-machine interface (HMI) and have the potential to revolutionize the spread of electronic applications. Printed Electronics has emerged as one of the most promising alternative manufacturing technologies because of its ambient manufacturing processing. This thesis focuses on the fabrication of Printed, flexible, and stretchable electronic devices by utilization of printed techniques. Materials are synthesized to make them printable through printed techniques for the realization of electronic devices and circuits. The printed techniques used in device manufacturing are Spray Coating, Inkjet material printing, Screen Printing, and spin coating. In this work, I have used different substrates according to to the manufacturing process requirement in the glass substrate and flexible and stretchable substrate. The main substrates utilized in the fabrication of devices are glass, PDMS, PET, and biomaterials. The fabricated devices were characterized against their electrical, mechanical, optical, and chemical behavior to verify the device fabrication approach and performance. Resistive random-access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, and are currently considered to be one of the next-generation alternatives to traditional memory. I have fabricated different memristors based on device structure ITO/ZnO/Fe2O3/Ag to solve sneak current problem in a crossbar array and soft and flexible resistive memory device Cu/(PAA-Na+:H2O): (NaOH)/Cu to improve retention time, on/off ratio and endurance cycles. Neuromorphic computing has emerged as a promising avenue towards building the next generation of intelligent computing systems. It has been proposed that memristive devices, which exhibit history-dependent conductivity modulation, could efficiently represent the synaptic weights in artificial neural networks. I have fabricated solid-state and liquid-based neuromorphic computing resistive memory devices. The solid-state structure is based on structure ITO/ZnO/GaN/Ag and ITO/GeO2/Ag are fabricated using spin coating and RF sputtering technology. These works show the memory importance to block sneak current in a crossbar array. At the same time, Neuromorphic behavior has been explored to show its importance to implement hardware-based artificial intelligence systems. On the other hand, soft and liquid-based neuromorphic resistive memory devices are emerging field, which helps to open a gateway for soft circuits. To introduce a simple device structure to perform neuromorphic computing we fabricated a discrete channel device, which helps to improve our understanding of soft neuromorphic computing devices using structure Cu/BMIM FeCl4: H2O/Cu. The large-scale integration of soft memory devices can be enabled by introducing soft and flexible device structures in a crossbar array structure Cu/Ag@AgCl/Cu. These results open a gateway for the implementation of soft and flexible brain-like miking systems. Several types of printed devices are fabricated and discussed in this thesis includes: Humidity Sensor, Piezo, and Triboelectric Nanogenerator, and its stretchability achieved up to 54.5%. To measure humidity in a wide range with high sensitivity, inkjet printing, Screen-printing, and spin coating technique are utilized to fabricate humidity sensor, which helps to monitor real-time humidity applications using inner eggshell membrane, and GaN. The snake shad is used to fabricate the Piezoelectric and Triboelectric nanogenerator for energy harvesting to power electronic devices. Inkjet-printed self-healable strain sensor based on Graphene and Magnetic Iron Oxide on polyurethane substrate. The prototype of printed electronic devices and circuits fabricated by utilizing solution-processed materials are good achievements and a way to future printed flexible and stretchable electronics.