Highly sensitive sensors based on advanced materials for flexible and wearable electronic devices

  • Liming Chen

Student thesis: Phd

Abstract

Flexible and wearable sensing technology is becoming increasingly important in personal healthcare and population health management. However, currently many wearable sensors are cumbersome, fragile and rigid, with obvious limitations, such as low sensitivity, slow response, low durability, and incompatibility with soft human skin surfaces. Advanced materials, such as graphene, hexagonal boron nitride (h-BN), MXene, metal nanoparticles (e.g., gold, silver, copper and nickel), have shown great potential in wearable sensing applications due to their excellent electromechanical properties. However, there remain challenges to apply these sensing materials to real world wearable applications. (1) The physical interaction between sensing material and the substrate is weak, fail to be used for a long time; (2) The electrical signal analysis of the sensor is still in its infancy, and the relationship between electrical signals and external stimuli is not clear; (3) Most wearable sensors are passive and require a rigid input power supply; (4) A single sensor unit cannot simulate the real complex touch sense of the human skin, which requires a sensor array to achieve multipoint sensory and perception. This thesis proposes several effective strategies to solve these problems. Firstly, efficient and low-cost surface modification strategies were used to form robust chemical interaction between the sensing materials and flexible substrates through hydrogen bonds, covalent bonds, and topological structures. The solid adhesion interconnection networks endow stable and durable sensing capabilities to the prepared sensors. The developed sensors were then applied to flexible and wearable electronic devices to monitor individuals' daily activities and health status in real-time, such as joint bending, speaking, running, watching TV, coughing, fever, runny and stuffy nose. Secondly, interdisciplinary knowledge of materials science, electrical engineering, physics and chemistry is applied to promote signal output analysis. Taking the h-BN-based humidity sensor as an example, I successfully clarified the relationship between impedance output and resistance & capacitance, and the relationship between resistance/capacitance and humidity changes. This showcases the interdisciplinary investigation (material science and electronic engineering) of a humidity sensor and its practical applications. Thirdly, high-performance flexible triboelectric nanogenerators (TENGs) as flexible power sources are developed and integrated into a self-powered humidity sensor. The liquid metal nanoparticles film helps a typical TENG to greatly enhance contact surface, and thus increases the charge density by more than three times. The proposed charge excitation system offers a strong electric field, which causes the extra abundant positive/negative charge on tribo-surfaces due to quantum tunnelling effect, led to the maximum ~134-fold enhancement of output power density. Finally, a capacitive sensor array is constructed, by introducing TENG's structure to fabricating a self-powered sensor array. In summary, the thesis made significant progress in developing highly sensitive and fast response wearable sensors.
Date of Award31 Dec 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorWuliang Yin (Supervisor) & Xuqing Liu (Supervisor)

Keywords

  • Ttriboelectric nanogenerator
  • Health monitoring
  • Electronics
  • Nickel electroless deposition
  • Wearable sensor
  • 2D material

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