Development Of Flexible Circuit And Sensor Based On Liquid Metal Patterning

With the rapid development of the Internet of Things,people's demand for flexible wearable devices is increasing.Compared with traditional rigid devices,flexible wearable devices have better fit and comfort.Through physical,chemical and biological information obtained from human skin,flexible wearable devices can monitor human physiological parameters and environmental state in real time.Therefore,it has a great application prospect in the field of medical care and health as well as in daily life.Liquid metal is one of the preferred conductor materials for flexible electronic equipment due to its excellent conductivity,free deformation and other properties.The patterning of liquid metal is a hot topic for researchers,and the patterning methods of liquid metal should be adopted according to the requirements of different patterning structures.In this paper,the patterning methods of two kinds of liquid metals in silicone elastic substrates are introduced,and flexible circuits and flexible sensors are prepared respectively according to the advantages of these two patterning methods.Porous graphene was ablated on commercial polyimide film(PI)tape using CO₂ infrared laser.With porous graphene as a rough surface with microstructure,the liquid metal can selectively deposit preset circuit patterns on the surface ablated by PI,and then transfer the deposited patterns to the flexible substrate for packaging processing to complete the preparation of flexible circuits.Through the demonstration of embedded chip LED lamp,it is verified that the flexible circuit prepared has good bending,fitting and stretchability.The liquid metal direct injection method and vacuum pressure differential injection method are analyzed and discussed theoretically.It is found that it is difficult and complicated to use direct injection method to inject liquid metal into microchannel.In contrast,the vacuum pressure difference is more suitable for filling the narrow liquid metal micro-channel with complex and changeable curves.The optimal design of vacuum pressure differential injection method for the sensor microchannel was carried out at the liquid metal injection end of the sensor micro-channel.A wide slot and two stepped buffer flow channels are added at the injection port of the micro flow channel.Through simulation and experiment,it is verified that the design of the liquid storage buffer structure can slow down the pressure in the flow passage and prevent the fluid leakage.It can make the liquid metal penetrate into the micro flow passage more gently and fill the flow passage.Using the improved vacuum pressure difference injection method to fill the hollow micro channel of silica gel elastic body with liquid metal,the single channel resistance tension sensor and the plane cross finger capacitive sensor were prepared.The sensitivity of the resistance sensor is GF_R=2.05,the response time is (?)??0.14 s,the plane cross finger capacitive sensor is GF_c=1.The experimental value agrees with the theoretical analysis value.In order to improve the sensitivity of the sensor and reduce the influence of temperature on the stability of the sensor,a single channel resistance sensor was optimized and a Whiston bridge circuit was introduced to design the liquid metal microchannel in the sensor.The experimental results show that the improved sensor not only reduces the influence of temperature on data drift,but also increases the sensitivity GF_R=2.05 to GF_v=4.94.The response sensitivity of the sensor has been greatly improved.The above two flexible electronic manufacturing technologies have the advantages of low cost and high efficiency,and can be compatible with industrial mass production.They realize the liquid metal curved surface patterning and the preparation of highly sensitive flexible sensors respectively,which can be applied to electronic tattoos,electronic skin,VR/AR sensing equipment and bionic robots,etc.It has a wide range of applications and a good development prospect in the fields of telemedicine,artificial intelligence and human-computer interaction.