Electrical Characteristics Investigation Of Ferroelectric Polymer PVDF And Its Composite Film

The ferroelectric material Poly（vinylidene fluoride）（PVDF）,which has the advantages of high residual polarization,good thermal stability and rapid polarization response time,has possible application in sensors,capacitors and infrared detection.Among the three main crystal phases of PVDF,theβcrystal phase with the highest strong spontaneous polarization by an all trans（TTT）configuration is considered as an important ferroelectric and piezoelectric material.In this dissertation,the process parameters required for optimized PVDF film,which is prepared by spin-coating,are selected properly in terms of solvent type,solution concentration and annealing temperature.The induction of Mo S₂nanosheets with high specific surface area and surface S vacancy defects is considered as possibility to modulate the conductivity behavior of PVDF film.The resistance transition mechanism of composite PVDF/Mo S₂films is also discussed.1,Focus on the high polarization field in PVDF film,the different solution concentration witch N,N-Dimethylformamide（DMF）,N-Methyl pyrrolidone（NMP）and acetone respectively,are comparatively characterized in surface roughness and uniform thickness and then annealing temperature.The optimal process parameters for higher componentβphase and better film quality are determined as DMF solution in concentration of 40 mg/ml and annealing temperature of 160℃.The obvious hysteresis phenomenon is observed in I-V curve of the PVDF film by the applied cyclic scan voltage.The value of short-circuit current I_scand the open-circuit voltage V_ochas shown an increase with the maximum cycle voltage value.The mechanism discussion is ascribed to the enhancement of residual polarization intensity inβ-phase PVDF film.2,The composite PVDF/Mo S₂film is prepared by introducing the Mo S₂nanosheets obtained via sonication assisted liquid-phase exfoliation and its conductive behavior is discussed.The hysteresis characteristic similar with single layer PVDF film is also observed with the current on/off ratio at 2.5×10².The mechanism in composite film by nonlinear fitting of I-V curves indicates that the conductance properties is depending on the common effect of dielectric PVDF and conductive Mo S₂and switching behavior is due to the reversed polarization field of PVDF and the carrier capture/release by V_s-rich surface defect of Mo S₂nanosheets.The conclusion has demonstrated the possible application of Fe-RRAM.