| In recent years,flexible sensors which can conformal to curved surfaces such as human skin have shown great potential in robotics,wearable electronics and health monitoring applications,and can be used as human-computer interaction interfaces.The flexible sensors can enhance the measurement accuracy because they can conformally attach to complex curved surface such as human skin and thus extend its applications.Among several common sensor types,the temperature sensor array is particularly worthy of attention because it plays an important role in several key potential applications,such as health monitoring of electronic devices,human body temperature mapping,and smart logistic monitoring for internet of things(Io Ts)purpose.Among different fabrication technology of flexible sensors,the printing method is known as a green technology for its low-cost and low energy consumption compared to the traditional lithography based technology which is high energy consumption,high pollution,and high cost.Therefore,to manufacture electronic devices and circuits by using printing methods has gained more and more research attention,but it faces a major challenge that most of the printing methods results in low spatial resolution,which cannot fulfill the requirement of manufacturing high-performance,high-resolution electronic devices.Electrohydrodynamic(EHD)jet printing technology is a promising technology among the numerous printing methods.Compared with the traditional piezoelectric inkjet printing method,electrohydrodynamic(EHD)jet printing technology can increase the printing resolution by two orders of magnitude,so it is suitable for high-performance,high-resolution flexible electronic products,increasing the level of integration of printed electronic products.In this thesis,we study the fabrication of high-resolution flexible temperature sensor arrays using the electrohydrodynamic(EHD)jet printing,and realize all-printed flexible device.The research work includes the following two aspects:1.Optimize the printing conditions by adjusting the various parameters of electrohydrodynamic(EHD)jet printing.By spin-coating the water-soluble material PVA on the PEN flexible substrate,which has been widely used to improve the printing quality of the hydrophilic ink on the hydrophobic substrate,the printed line resolution is largely enhanced.A flexible temperature sensor is realized by measuring the temperature induced resistance change of the device.The line width of temperature sensor is about 8 μm,and has good resistance-temperature linearity,allowing it to apply for various scenarios.2.After completing the fabrication and characterization of a single device,an 8×8 temperature sensor array was fabricated on a one inch square flexible substrate by electrohydrodynamic(EHD)jet printing technology.Via holes are used as part of the sensor array for wire interconnection between different layers.In this thesis,we use high voltage of EHD jetting system to burn the via holes on the flexible substrate with hole diameter down to 5 μm.To our knowledge,this is the highest resolution achieved so far for via hole fabrication compared with other non-lithography technologies.We further prove the reliability of our design by conducting a heat transfer simulation by using finite element method(FEM).Finally,to demonstrate the practical application of printed flexible temperature sensor array,we use it to map the temperature distribution of the heat objects and to detect body temperature distribution of the human body. |
