Preparation And Properties Of Poly (Vinlidene Fluoride)Based Composites With Alternating Stacking Structure Of Positive And Negative Permittivity Layers

The requirement of consumers for the portability of electronic products has given birth to the revolution of circuit board packaging technology.Scientific embedded packaging technology will greatly improve the compatibility between capacitor and circuit board.The use of embedded capacitor in circuit will bring its excellent dielectric performance into play,which is bound to promote the development of the whole circuit board technology.The traditional ceramic dielectric materials have many defects,which limit their application in embedded circuit board.Therefore,the research and development of new dielectric materials is increasingly urgent.In this paper,a new sandwich structure composite with negative permittivity was prepared and studied,which aims to achieve the breakthrough of permittivity in the traditional sandwich structure composite while maintaining its low dielectric loss.The nano-sized Ba(Fe0.5Ta0.5)O3 powder was prepared by oxalate coprecipitation method.The single-layer BFT/PVDF composite was prepared by hot pressing technology and its dielectric properties were studied.The results showed that the introduction of BFT ceramic powder improved the dielectric properties of the composite significantly,and the dielectric constant of the composite was as high as 120.Then negative permittivity was found in Ni/PVDF composite,and on this basis,BFT/PDF-Ni/PVDF-BFT/PVDF sandwich structure composite with negative permittivity middle-layer was prepared.It was found that the permittivity of the sandwich structure composite was further increased to 170,which was consistent with the performance of series capacitor model.The dielectric loss was kept at 0.29 due to the existence of interlayer ohmic barrier.The sandwich structure BFT/PVDF-Ti3SiC2/PVDF-BFT/PVDF composite and BFT/PVDF-Ti3AlC2/PVDF-BFT/PVDF composite with negative permittivity middle-layer were prepared by using Ti3SiC2 and Ti3AlC2 ceramics instead of Ni respectively.It was found that the permittivity of the material was further improved at low frequency,which was due to the high volume ratio of Ti3SiC2 and Ti3AlC2 with layered filler resulting in.The dielectric constant of 50 vol.%BFT/PVDF-77 vol.%Ti3AlC2/PVDF-50 vol.%BFT/PVDF is 290 and the dielectric loss is only 0.53.Through the study of sandwich structure BFT/PVDF-Ti3AlC2/PVDF-BFT/PVDF composite with different layer thickness,it is found that the dielectric constant of the composite increases with the increase Ti3AlC2/PVDF layer thickness.When the thickness of sandwich structure composite's middle-layer Ti3AlC2/PVDF is 0.6 mm and the thickness of upper and lower layers BFT/PVDF is 0.15 mm,the dielectric constant of the composite is 720 and the dielectric loss is 0.49.The obvious increase of the dielectric constant is attributed to the way of adjusting the thickness of the layer.When the absolute value of the capacitance of the negative permittivity layer is close to that of the positive permittivity layer,the total capacitance and permittivity of the material will be significantly increased.The reason why the material can keep low loss is that the good insulation of BFT/PVDF layer blocks the conductive path.Finally,the composite shows excellent dielectric properties,which combines the enhancement of negative permittivity layer to dielectric constant and the inhibition of positive permittivity layer to dielectric loss.