Research On Flexible Pressure Sensor Based On Liquid Metal

In the past decades,human skin-inspired flexible electronics have attracted tremendous research attention due to their potential applications in health monitoring and diagnostics,robotics,and prosthetics.Flexible pressure sensors are currently an important direction for the development of flexible electronics.They have the advantages of simple mechanism,low cost,easy signal acquisition and conversion.Liquid metal is a material that can deform while maintaining high conductivity simultaneously,which overcomes the wrinkles and fracture failure caused by traditional solid materials.Particularly,flexible pressure sensors should be able to work under normal and deformed states,so liquid metal based flexible sensors have great application prospects and development space potential.The main performance indicators of flexible pressure sensors are sensitivity,force measurement range,and response time.Also,the microstructures have proven to be the main means to improve performance.Tactile sensors manufactured by low-cost and efficient technology are critical for intelligent robotics and real-time health monitoring.However,conventional methods such as photolithography and surface stencil methods are limited due to their less efficiency and low repeatability.To overcome these limitations,we prepared a highly sensitive capacitive pressure sensor,by using parallel femtosecond laser writing technology and chemical etching to prepare microstructures.Compared with photolithography and surface template method,our technique is fast,efficient,highly repeatable,and customized in terms of structure.In addition,traditional stretchable pressure sensors cannot distinguish between out-of-plane pressure and in-plane stretch because the mechanism of change is the same,so it faces a defect.When the sensor is in the stretch state,it cannot accurately measure the static and dynamic pressure response simultaneously and this causes a severe problem of signal interference.Therefore,it is necessary to design a stretchable pressure sensor that is not sensitive to stretching,which will help to expand the application range of pressure sensors.Based on these facts,a porous carbon material is used as a pressure sensing layer,and a liquid metal is patterned as an electrode layer on Ecoflex.Finally,a tension insensitive pressure sensor has been assembled.Initially,a high-performance flexible capacitive pressure sensor based on liquid metal is prepared.The sensor uses parallel femtosecond laser writing technology and assists chemical etching to form a microstructure on a silicon dioxide mold.The microstructure of the silicon dioxide mold is transferred to PDMS to form a microarch PDMS.The dielectric layer is composed of two micro arch PDMS in cross arrangement.Considering the micro-arch PDMS,the electrodes are made by printing liquid metal.The prepared flexible pressure sensor shows a sensitivity of 1.2 kPa^-1（for an applied pressure of<10 kPa）,which is significantly higher than that of a non-microstructured sensor and an order of magnitude higher than that of an unstructured sensor.In addition,the response time of the pressure sensor is shorter than 36 ms,and there is no significant difference in performance after 10,000 cycles of 250 Pa pressure.At the same time,the device is small,lightweight,highly sensitive,easy to manufacture,and has great application potential in intelligent electronic devices as well as human-machine interfaces.Secondly,a tension insensitive pressure sensor based on liquid metal has been assembled.Using PDMS,carbon black,and sodium chloride as raw materials to prepare porous pressure sensing layers,Ecoflex and liquid metal are used as electrode stretching layers,and finally encapsulated into pressure sensors.In terms of pressure,the device has higher sensitivity（2.27 kPa-1）,faster response time（20 ms）,and higher cycle stability.In terms of stretching,when the device is stretched to 200%,the change is resistance is negligible,similarly the resistance of the sensor in 0%,20%,42%,79%,100%,and 150%tensile changes is not much variant,indicating that the device has good tensile stability.Considering these prominent features,the device has great application potential for human motion detection,vocalization detection,wearable flexible sensing devices include electronic skin（E-skin）as well as Artificial intelligence（AI）in healthcare.