Multifunctional Flexible Temperature Sensors And Their Transient Applications

Flexible temperature sensors refer to temperature sensors that made of flexible or low dimensional materials on flexible substrates,which have excellent mechanical flexibility,enabling seamlessly fit to objects with complex surface structures,thus providing more accurate measurements.Flexible temperature sensors are typically very thin and easy to carry and install,which makes them more suitable for applications that require light loads and portability,such as wearable devices,biomedical devices,smart homes device and etc.In recent years,flexible temperature sensing technology has made significant progress in performance parameters such as sensitivity,accuracy,and response time under the unremitting efforts of researchers.However,with the continuous expansion of flexible temperature sensing applications,simply improving the sensing performance of devices is no longer sufficient to meet the growing demand.The rapid development and widespread application of flexible temperature sensing technology are now facing new problems and challenges.From the perspective of device function,how to simultaneously detect the temperature and position of the heat source and further to improve its spatiotemporal resolution are key technical issues that need to be solved in the applications of flexible temperature sensing arrays,such as wearable electronics and smart electronic skins;From the perspective of device performance,how to overcome the crosstalk of flexible temperature sensors under external stress or deformation and to realize muti-modal coupling sensing are key scientific issues need to be solved for complex sensing environments;From the perspective of application,how to design and develop multifunctional flexible temperature sensors and related functional components(such as energy supply components)is an important challenge for wearable/implantable applications.Based on this,this paper mainly focuses on the study of development and transient applications of multifunctional flexible temperature sensors,designing and optimizing sensing technology from material strategy,structural construction and process design,achieving the preparation and research of flexible temperature sensing arrays with function of heat spot tracing function,flexible temperature sensing arrays with function of high spatiotemporal resolution,flexible implantable dual parameter sensors with function of decupling thermal-mechanical crosstalk,and wireless energy supply devices for implantable temperature sensing applications.The specific work of this dissertation is introduced as follows:1.Design,preparation and research of a flexible heat spot tracker(1)The thermal conductivity properties of different substrate materials were studied by using finite element simulation and weak coupling algorithm of multiple physical fields,and the steady-state temperature distribution formed on different substrates through a heat spot was evaluated.Exploring the key factors affecting the temperature distribution of point heat sources on different substrates.A one-dimensional temperature sensing array was designed and prepared to verify the temperature distribution,and further testing and certificating the temperature distribution rules independent of the heat source.This part of the research establishes the theoretical foundations for the design of a heat spot tracker sensing array.(2)A flexible heat spot tracker(FHST)design strategy was proposed based on a temperature sensing array according to the heat source-independent temperature distribution rules.A corresponding relationship between the response of multiple sensors in a temperature sensing array to a heat spot and the distance of sensors and the heat spot was established.The working mechanism of the FHST for the simultaneous measurement of temperature and position of a heat spot was clarified.(3)FHST based on a temperature sensing array with a low sensing device duty cycle was developed by using a substrate with a large thermal conductivity,such as iron foil.The heat spot tracking performance of FHST in one-dimensional and two-dimensional space were studies,and optimization plans to further improve the accuracy of FHST was proposed based on the analysis and discussion of experimental results.2.Preparation and research of high spatiotemporal resolution flexible temperature sensing array(1)The heat conduction process on the substrate was simulated by using finite element analysis under multiple physical field interfaces such as heat conduction,radiation,and natural convection.The effects of the substrate material’s thermal conductivity,surface emissivity,natural convection coefficient,volumetric specific heat capacity,density,and thermal diffusion coefficient on the response time and spatial resolution of the flexible temperature sensing array were analyzed.Research has shown that sensors have faster response times based on flexible substrates with high thermal diffusion coefficients.The developed flexible temperature sensing array has higher the spatial resolution based on flexible substrates with lower thermal conductivity.The temporal resolution and spatial resolution of the flexible temperature sensing array can be simultaneously improved by selecting the appropriate substrate and further reducing its thickness.(2)According to the above theoretical basis,flexible temperature sensing arrays were developed by using iron foil and polyimide(PI)as substrates.The two substrates show large differences in thermal conductivity.The temporal and spatial resolution performance of flexible temperature sensing devices based on two substrates was studied and analyzed,and the significance of substrate material strategy in regulating the high spatiotemporal resolution performance of temperature sensing was verified and elucidated.(3)In order to further improve the spatial resolution of the sensing array,a heat conduction limitation design based on the grid structure was proposed.Finite element simulation was used to study the limiting effect of the air in the grid cavity on the heat conduction of the substrate,thereby improving the spatial resolution of the sensing array.A scheme of optimizing the grid structure was proposed to further improve spatial resolution by taking one-dimensional heat conduction limited structures as an example.3.Flexible transient temperature-strain dual-parameter sensor for implantable applications(1)The preparation of temperature-strain dual-parameter decoupled sensors was proposed the signal crosstalk problem of flexible temperature sensing devices.The physical,mechanical flexibility,process compatibility and degradation characteristics of related materials were analyzed,and the significance of using semiconductor germanium as the sensing functional layer was clarified.By using transfer printing technology combined with micro/nano processing and spin on glass(SOG)technology,a germanium based serpentine wire structure with a thickness of 200 nm was completely transferred to an iron substrate,and further completing the preparation of the flexible transient temperature-strain dual-parameter sensor.(2)The temperature and strain responses of the prepared sensors were tested and studied,and the results showed that the temperature coefficient of resistance(TCR)of the sensor is stress independent and the gauge factor(GF)is temperature independent.Based on this,an experimental scheme was designed for the continuous effect of temperature and strain,verifying the feasibility of temperature strain dual parameter decoupling based on germanium thin films,and elucidating the signal calibration mechanism of flexible temperature sensors involving strain.(3)The transient and degradation characteristics of germanium were analyzed and studied.By designing a comparative experiment with the degradation of semiconductor silicon,the bubble-free nature of the transient degradation of germanium was verified.A cytotoxicity test was conducted on germanium,and the results showed its good biocompatibility.The accelerated degradation(pH=7.4,90℃)test results showed that the device can completely degrade and disappear after 49 days.4.Wireless electromagnetic coupling energy transmitter for implantable temperature sensing integration applications.(1)By analyzing and comparing various energy supply methods for implantable temperature sensing integrated applications elucidated the advantages of wireless electromagnetic coupling energy transmission.To address the teasers of rapid degradation rate and potential safety hazards in traditional metal coils,a strategy of preparing sensing coils through heavily doped silicon was proposed;The working mechanism of wireless electromagnetic coupling was analyzed,and the coil structure design was analyzed and optimized.(2)Two methods,including thin film transfer and wet thinning,were used to prepare silicon coils on flexible substrates,and the advantages and disadvantages of the two preparation methods were compared and analyzed.The performance of the prepared silicon coil was characterized and tested using impedance analyzer and vector network analyzer,and the factors which affecting the coil output were studied and analyzed.The feasibility of using heavily doped silicon coils for wireless energy transmission has been verified by successfully driving and illuminating light-emitting diodes(LED)through a wireless energy transmission device.(3)The effect of doping concentration on the degradation rate of silicon was studied and analyzed.Degradation experiments were compared between silicon-based coils and magnesium-based coils with the same structure,which proved the mildness of the degradation process.The cell adhesion and cytotoxicity of phosphorus doped Si coils were tested and characterized,elucidating their biocompatibility.In summary,this dissertation is based on the development and optimization of multifunctional,high-performance,and energy integrated flexible temperature sensors,with the goal of expanding their applications in the field of implantable electronics.By clarifying the functional development,performance improvement,and transient applications of flexible temperature sensors,revealing the material selection,structural design,and working principle innovation required to achieve multi-functional flexible temperature sensing.Based on this,the design and preparation of flexible temperature sensing electronics for single heat source tracing,high spatiotemporal resolution,dual parameter decoupling,and wireless energy supply integration were proposed and implemented.The dissertation research will provide an important foundation for the application of multifunctional flexible temperature technology in the field of wearable/implantable electronics.