The Fabrication And Property Research Of Organic Piezoelectric Sensor Arrays

Flexible piezoelectric sensors have wide dynamic range,high sensitivity and good mechanical properties.The piezoelectric sensors made of polyvinylidene fluoride（PVDF）and polyvinylidene trifluoroethylene（PVDF-Tr FE）as representatives have attracted much attention in the field of flexible electronics.In view of the existing flexible piezoelectric sensor array research is few,the traditional piezoelectric thin film based on the complex process,expensive film,serious material waste and other problems,this paper based on PVDF and PVDF-Tr FE emulsion solution method,by optimizing the spin coating process to prepare piezoelectric thin film on the flexible substrate.The 4×4 PVDF and PVDF-Tr FE piezoelectric sensor arrays with uniform thickness and consistent properties were fabricated by screen printing process.（1）Study on polarization method and piezoelectric coefficient d₃₃ of piezoelectric thin film.In order to improve the content ofβcrystal phase in the thin film,a polarization system suitable for this study was established based on corona polarization method.A succession of manifestation analyses were performed on the thin film before and after corona polarization,and it was found that the material characteristics（βphase）of the piezoelectric thin film were significantly improved after corona polarization,which tested the availability of the polarization system.Based on the test method of piezoelectric film d₃₃ and the principle of dynamic measurement,a piezoelectric coefficient test platform was built to test the standard commercial samples,and the reliability of the measured value was about 98.14%.（2）Optimization of PVDF piezoelectric film preparation process.In order to obtain the optimal film preparation process,the solvent type,annealing temperature,spin coating thickness,polarization parameters were optimized.By comparing the film forming effects of DMF,NMP and DMSO,it was found that PVDF films prepared by DMF had higher crystallinity and better piezoelectric properties.By analyzing the properties of PVDF films at different annealing temperatures,it was found that the suitable annealing temperature of PVDF was about 100℃.By studying the thickness of PVDF film,it was found that the thicker PVDF film,the better piezoelectric properties;The optimal parameters of corona polarization are 7 k V tungsten grid voltage,3.5 k V grid voltage,1cm distance between grid and sample,and 6 min polarization time by optimizing polarization voltage,grid spacing and polarization time.（3）Fabrication and performance testing of 4×4 PVDF and PVDF-Tr FE piezoelectric sensor arrays.Scanning electron microscopy showed that the thickness of PVDF and PVDF-Tr FE arrays was about 6μm and 6.75μm,respectively,and the thickness of each array point had a small difference within the range of±0.1μm,indicating that the printing uniformity was good.The piezoelectric properties of the PVDF and PVDF-Tr FE flexible sensors fabricated by screen printing have no obvious change after 100 cycles of bending,which proves that the PVDF and PVDF-Tr FE flexible sensors are reliable and reusable.The sensitivity and linearity of each array point were obtained by MATLAB analysis.The sensitivity of PVDF and PVDF-Tr FE arrays ranged from 0.63 m V/N to 0.69 m V/N and 0.89 m V/N to 0.93 m V/N,and the linearity ranged from-0.01 to 0.09 and-0.02 to 0.04,severally.Compared with PVDF array,PVDF-Tr FE array has higher sensitivity and lower linearity.After corona polarization,PVDF and PVDF-Tr FE array d₃₃ increased by 90%and 40%respectively,indicating that the polarization process plays an indispensable part in ameliorating the piezoelectric capability of the devices.Meanwhile,it is remarkable that the d₃₃ difference between polarized PVDF and unpolarized PVDF-Tr FE is very small,indicating that PVDF-Tr FE material itself is far superior to PVDF,of course,the cost of PVDF-Tr FE material is much higher than PVDF,which provides a reference for the selection of materials for preparing piezoelectric devices.