Fabrication And Performance Study Of Flexible Piezoresistive Sensors Based On Bionic Hierarchical Microstructure

With the development of big data,internet of things,artificial intelligence and industrial robots,sensors as data acquisition and feedback systems have attracted extensive attention.Among them,the pressure sensors have developed rapidly in recent years based on the monitoring function of pressure strength,duration,interval and frequency.Flexible pressure sensors with the characteristics of lightweight,portability and wearability show good application prospects in the fields of health care,smart home and data monitoring system.However,as two important sensing parameters of pressure sensors,traded-off between sensitivity and working range in a limited deformation space,for a certain material system,remains a huge challenge.The modulation of micromorphological structure of the sensing layer can increase the additional conductive path and contact change under pressure to significantly improve the sensing performance.Compared with single microrough structure and single porous structure,the sensing layer of hierarchical structure with stronger deformation ability and richer deformation space can optimize the sensitivity and sensing range simultaneously.Furthermore,biological systems show excellent sensing performance with the optimized structures in the long-term evolution,where the lever arm effect of animal ciliary structure under pressure,the stress concentration of microridged structure and dense sensing nerves in fingertip skin make them highly sensitive.Based on micromorphological engineering,combining with hierarchical structure and bionic concept,pressure sensors with high sensitivity in a large pressure range are designed and fabricated in this paper.The research content mainly includes the following two parts.1.Fabrication and research of bionic cilium Zn O SUSM/MXene hierarchical microstructured piezoresistive sensor.Inspired by the sensing mechanism of biological cilia,the construction of 3D spherical spines structure will give full play to the role of this lever arm effect.Under a low-temperature hydrothermal condition,zinc oxide can grow into 3D sea urchin-shape microparticles（Zn O SUSM）with high density spines.However,considering that Zn O has high resistance,the highly conductive and flexible Ti₃C₂T_x（MXene）is further introduced to improve the conduction of the sensing layer and to promote the current transmission among Zn O SUSMs.Compared with the conventional physical blending,composite of Zn O SUSM and MXene,Sg M,which is synthesized by one-step hydrothermal improving the dispersion uniformity due to the in-situ growth of Zn O SUSM.In the Sg M system,Zn O SUSM shows a 3D hierarchical structure with thorny sphere;the loading of flexible MXene not only increases the conductivity but also introduces the microwrinkle structure.The rich microstructures of Zn O SUSM combined with MXene wrinkle lead to a good sensing performance,where the fabricated pressure sensor with a sensing layer thickness of 150μm demonstrated a sensitivity of 89.5 k Pa^-1,the response and recovery time of 62.70 ms/62.63 ms.The related device can successfully explore the signals of human pulse beating,throat swallowing and body movement.In addition,as a proof of concept,it also shows good application prospects in code compilation and pressure threshold alarm system.2.Fabrication and research of skin-inspired#PPM/Zn O NR/MXene hierarchical microstructured piezoresistive sensor.In view of the previous work with a flat sensing film by drop casting,here,the structure of sensing layer with large height variation is introduced to further optimize the sensing performance.Human fingertip skin has good perception for external stimuli,where the microridged structure of epidermal-dermal leads to a good contact and effective stress concentration under loading.Moreover,the dense sensing nerves in the dermis ensure a sensitive and timely perception for external stimuli.Inspired by these characteristics,a single-sided microrough substrate of polydimethylsiloxane（PDMS）with microridge morphology is fabricated by templating.Additionally,zinc oxide nanorod（Zn O NR）array is grown in situ on the substrate to simulate the abundant neural cells.And then,the conductive performance is further improved by conformally loading MXene nanosheets.Finally,the sensing layer with hierarchical structure is assembled with interdigital electrode for the fabrication of pressure sensor.Under compression,based on the stress concentration effect,lever arm effect and contact changing effect,the sensor achieves highly sensitive sensing in a wide working range.The sensor shows the sensitivity up to 10606.9 kpa^-1 and 1882.3 kpa^-1 in the pressure range of 0.15～1.92 k Pa and1.92～17.22 k Pa.Besides,it also shows a rapid response and recovery speed of 62.64ms/62.65 ms.These excellent sensing performances make it have a good detection capacity for the pulse beating,laryngeal muscle movement,body tremor and pressure mapping distribution.