The Design And Fabrication Of Flexible And Stretchable Sensors Based On Force-electric Coupling

Stretchable electronics based on inorganic functional thin film with specific mechanical structure enable the novel devices with not only high electrical performance but also deformability and stretchability.Stretchable electronics have drawn much attention of the researchers and have been intensively studied in many fields such as wearable radio frequency identification,wearable flexible sensors and flexible batteries.However,some key scientific and technical issues in the design and fabrication of stretchable electronics are still in preliminary research stage,and further related researches are urgently demanded.In the perspective of device fabrication,conventional device fabrication methods,including growth of thin film and nano fabrication techniques,are difficult to be directly realized on the polymeric organic substrate of the stretchable electronic device,making it necessary to propose new fabrication methods with the considerations of the material properties of the stretchable electronics.In the perspective of device performance,the deformation of stretchable devices requires the development of the methods for regulating the coupling between the applied force and electronic properties at the rigid-flexible interface under large deformation.In this thesis,several studies focusing on these issues are presented as follows.A temperature-dependent and velocity-dependent transfer printing approach based on thermosensitive adhesive material are proposed for the construction of the rigid-flexible interface in stretchable devices.By studying the influences of peeling velocity and temperature on the energy release rate in the device-stamp interface,the modulation of the energy release rate in a wide range(0-951.1 J/m~2)is achieved,which expands the application range of functional materials for the transfer-printing technique.Based on this method,a stretchable neural electrode array is prepared on polydimethylsiloxane(PDMS)substrate,which can be used to collect the electroencephalogram(ECo G)signals and steady state visually evoked potentials(SSVEP)on the rat cortex.A"cut-transfer-release"method is further developed based on thermosensitive adhesive material to prepare a three-dimensional serpentine antenna.Results of finite element analyses(FEA)and experiments show that the antenna can maintain a stable RF performance at the 5.6 GHz frequency band under uniaxially tensile strain of 200%,and demonstrates effective resistance to the human hand touch on RF performance.To study the force-electric coupling characteristics of functional material in stretchable electronic devices,a force-electric coupling model for the polyvinylidene fluoride(PVDF)thin film with serpentine mesh design is established based on the analysis of the dependence of polarization on the strain distribution in the film.Based on the proposed model,a stretchable piezoelectric micromotion sensor is designed and fabricated,showing the stretchability of 27.5%as well as the voltage and current output sensitivity of 72 V/?and 272.73 n A/?,respectively.The capabilities of the sensor to achieve voice recognition,including speech pattern recognition with machine learning,are demonstrated.Furthermore,a structural design of three-dimensional hierarchical microhelix suitable for multidimensional stretchable electronic devices is presented.By combining the three-dimensional helical configuration with the fractal serpentine design,the stretchable electronic device with this structure design shows high stretchability in both the axial and radial directions.Two applications of this structural design,including stretchable LED circuits and epidermal electronic system,are demonstrated.The epidermal electronic system can not only collect fingertip electrocardiogram(ECG)signals,skin conductance and fingertip touch signals,but also achieve human emotion and tactile recognition with machine learning.In view of the mismatch between stretchable electronic devices and current commercial data acquisition system,a wearable wireless data acquisition system is developed to support the above wearable applications.Compared with heavy multiparameter ambulatory physiologic monitoring system used in hospital,the system has some advantages,including low energy consumption,light weight and small size,whose the ability to collect high-fidelity electrophysiological signals including ECG,electroencephalogram(EEG)and Surface Electromyography(s EMG)signals,and the capability of immunity to motion artifacts are illustrated.