Electrical And Optical Modulation On Ferroelectric Properties Of P(VDF-TrFE) Thin Film

Ferroelectric poly(vinylidene fluoride-co-trifluoroethylene)copolymers(P(VDF-TrFE))have excellent polarization and high Curie temperature compared with other small organic ferroelectric molecules,and it is also flexible,thermally stable,easy to be processed.These properties make it promising to be used in the fields of microelectronics such as sensors,memories,photovoltaics,and artificial skin.However the high coercivity of P(VDF-TrFE)limits its application in microelectronics,which requests low operate voltage and power consumption.For inorganic ferroelectric counterpart,several methods have been widely explored to modulate their properties.Such as the strain engineering through the mismatch between substrates and films,the electrostatic interactions between defect dipoles(such as oxygen vacancy)and polarizations,and the interface engineering based on the different screening abilities of metals and semiconductors.However,these routes have been rarely explored for the organic ferroelectrics,especially for P(VDF-TrFE)polymer.Considering P(VDF-TrFE)is an organic polymer,which is difficult to couple with rigid substrate and is of minor charged defects,so we use the interface engineering to modulate the properties of P(VDF-TrFE)thin films in this thesis.Specifically,two kinds of interfaces,namely ferroelectric/metal and ferroelectric/semiconductor,have been constructed by spin coating P(VDF-TrFE)films on typical metal substrate Au and semiconductor substrate Nb:SrTiO3(NSTO).We found that the ferroelectric properties such as ferroelectric loop and switching dynamics of P(VDF-TrFE)polymers could be modulated by the selection of electrodes,and furthermore by the UV light illumination due to the excellent UV light absorption of Nb:SrTiO3 and the semi-transparent nature of P(VDF-TrFE)polymer filmsThe first part mainly explores the polarization performance and switching dynamics of P(VDF-TrFE)by means of the P-E loop and the measurement of PUND(positive up negative down)under different voltages and under different directions.We have found that films grown on NSTO substrates are easier to be switched under the negative voltage compared to positive voltage because of asymmetric electrodes.While films grown on Au substrate have minor difference in switching dynamics under different voltages.In the second part,we study the hysteresis loops,switching kinetic curves,polarization current curves(?-?)and capacitance voltage(C-V)curve of P(VDF-TrFE)film under 365 nm ultraviolet(UV)light illumination.We found that P(VDF-TrFE)films are easier to be switched after introducing the UV light.Specifically,the coercive field of the film grown on the NSTO substrate could be significantly reduced up to?18%upon UV light illumination.