Flexible Sensing Devices:Material Characterization,Structural Design And System Application

With the development of the mobile internet and the improvement of the medical diagnosis level,the wearable and implanted sensing devices attract lots of attention.Some applications scenarios,especially for implantations use,the electronic devices would attach with the soft tissues.In order to monitor the physiological signals of the body without leading to any harm,the electronic devices should be soft and biocompatible;the flexibility,even stretchability of the devices are also needed,which could ensure the well attachment with the tissues to achieve the precisely monitoring.Compared with traditional rigid electronic system,the flexible electronic system are integrated with different devices on the soft substrate,which requires special system architecture,materials and fabrication process.The devices should work stable during bending process;in some more challenging applications,the stretchability of the devicesare needed.Actually,some achievements of the flexible devices have already been made,including OLED,energy storage devices,sensors,and gradually replace the rigid based electronic devices in some applications.But there are still some key issues need to be discussed in-depth in flexible sensing system,including:(1)the materials selection principles;(2)sensors structures design concept;(3)the integration of the multiple sensingdevices and the extraction of the signals.The explorations of these key issues are conducted in this thesis and the main achievements are highlighted as follows:(1)The mechanical properties of the materials(PDMS,metals,organic semiconducting polymers)are investigated with different test methods,including strain-stress curve,buckling method and nano indentation.The mechanical properties of the organic semiconducting polymers in different forms(film,wire and bulk)are studied in details.By analyzing the mechanical properties of the materials,we also tried to reveal the relationship between the molecular structure and flexibility.This work would be beneficial for molecular design of the polymers which may apply to the flexible electronic devices.These test methods are equally applicable to materials that can be used in flexible electronic devices,enabling deeper understanding of material properties and facilitating precise control of device performance.(2)A high-resolution skin-like sensor based on the carbon nanotubes and PDMS is presented.The CNTs-PDMS based micro-structure arrays could realize the resolution of 50 um,and sensing the deformation by monitoring the conductive change of the sensor.Based on this strain sensor,different sensations including touch,pressure,temperature and even pain,could be imitated.The sensor could not only distinguish different sensation,but also could detect three-dimensional deformation.In order to achieve the real-time detection,the circuit and the software were also developed.(3)A pressure sensor based on PDMS,ITO and polypyrrole(ppy)nano particles with high sensitivity was demonstrated.The ppy nano particles were made by microfluidic system,from which the size of the particles could be well controlled.The ppy particles were spray coated on the ITO electrodes,and a layer of air gap was sandwiched between two ITO electrodes.During the pressing process,the resistance between the electrodes could decrease several orders,which showed very high sensitivity(?102 kPa-1).(4)A flexible system designed for robotic hand were demonstrated.The sensing system covered the surface of the robot hand and integrated with different sensors,including temperature sensors,pressure sensors and strain sensors,which could achieve the precise movement monitoring of the robot hand and skin sensations imitation.During the fabrication process of the system,a liquid metal based encapsulation method of the flexible devices was put forward,showing good repeatability and reliability.