| Sensor technology is one of the three pillars of the modern information industry.In recent years,with the improvement of flexible electronics technology and three-dimensional high-density system packaging process,research and development of sensors that can be used for intelligent environmental protection,human activity,health care,smart wear and other areas has become the most promising field.Miniaturized,intelligent and bionic novel flexible pressure sensors with high sensitivity,low detection limit,fast response,low cost and good mechanical stability are necessary in practical applications.In this paper,we select sycamore bark with graded microstructure and air-laid paper with rough porous structure as the flexible substrate,and PEDOT:PSS,a conductive polymer,as the active material.Several novel micro-nanostructured flexible pressure sensors are designed and fabricated by optimizing the preparation process of different micro-nanostructured flexible sensitive layers.The performance of piezoresistive flexible pressure sensors is tested and the pressure-sensitive sensing principle is discussed.Finally,we successfully realize the monitoring of human activities and physiological signals.The main content are as follows:（1）A top electrode with natural sycamore bark microstructure is prepared by PDMS casting process and PEDOT:PSS spin-coating film formation method,and a copper forked finger electrode prepared on PET substrate by screen printing technique is used as the bottom electrode.We design and prepare a biomimetic sycamore bark microstructure flexible pressure sensor.The results show that this flexible pressure sensor has a high sensitivity of 5.375 k Pa-1and a wide pressure response range（0-80 k Pa）,which is 180 times more sensitive than that of the flat structured flexible pressure sensor.In addition,it has a fast response time of 60 ms and a detection limit of less than 4 Pa,and still maintains excellent performance even after 3500cycles.（2）A PEDOT:PSS films are deposited on a rough and porous air-laid paper by one-step impregnation method,and assembled with a copper forked finger electrode on a PET substrate to obtain top-bottom and sandwich structure flexible pressure sensors,respectively.Then,the sensitivity of the two sensors are compared.The test results show that,compared with the sandwich structure,the top-bottom sensor has a smaller contact area and larger initial resistance,and achieves a higher current response at the same pressure with a 3-fold increase in sensitivity.The sensitivity is as high as 29.027 k Pa-1in 0-120 k Pa,with a wide response range of 0～250 k Pa,and maintains good response performance after 1000 cycles.The response time for the applied pressure signal is 160 ms and the recovery time after unloading pressure is 70 ms,which can be fully used for the monitoring of human physiological signals.（3）An all-paper pressure sensor is prepared by screen printing technique and solution method with copper electrodes on filter paper substrate and assembled with top conductive polymer（PEDOT:PSS）sensing paper.The sensor has a maximum sensitivity of 768.07 k Pa-1,a response range of 0～250 k Pa,and a cycling stability of 5000 cycles.As fabricated large-area sensor array（4×4）can detect spatial pressure distribution,while a sensing mechanism based on the piezoresistive principle is proposed.Our application experiments demonstrate that this sensor can be used to monitor relevant physiological signals of the human body（e.g.,joint flexion,human pulse,cheek bulge,etc）.This pressure sensor is simple to fabricate,has high sensing performance,and has great potential for application in a new generation of green,degradable,and portable electronic products. |
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