Study On The Electrical Properties Of Strains-regulated Ferroelectric Negative Capacitance

Among various ferroelectric thin film materials,lead zirconate titanate PbZr_1-xTi_xO₃(PZT)epitaxial thin films have many advantages,such as excellent dielectric properties,piezoelectric properties,and ferroelectric properties.Therefore,the preparation and research of this material has become a research hotspot for scholars.This paper uses the Landau-Ginzburg-Devonshire theory to conduct a theoretical study on the negative capacitance effect in the epitaxial PZT ferroelectric film.The main research contents and results are as follows:1.The PZT ferroelectric thin film grown on the cubic substrate induces isotropic biaxial misfit strain,and this chapter shows that the negative capacitance effect of the PZT ferroelectric thin film with different composition(x(28)0.,90.,80.,50.4)under this strain.The transient negative capacitance effect is accompanied by polarization reversal and nucleation all the time.Low temperature,compressive strain and the imbalance of Zr/Ti ratio can be conducive to the stability of transient negative capacitance effect.Under high temperature and tensile strain,the polarization reversal rate is faster.In the ferroelectric-dielectric capacitor combined system,the compressive strain enhances the static negative capacitance effect of the system,and tensile strain is more conducive to obtain non-hysteresis gain.The imbalance of the Zr/Ti ratio enhances the static negative capacitance effect and its capacitance enhancement effect,while it is conducive to the hysteresis characteristics of the system.2.The PZT ferroelectric thin film grown on the orthogonal substrate induces anisotropic in-plane misfit strain,and this chapter shows that the negative capacitance effect of the PZT ferroelectric thin film with different composition(x(28)0.,90.,80.,50.4)under this strain.The regulation of uniaxial in-plane misfit strain(a special anisotropic in-plane misfit strain)on the negative capacitance effect shows similar characteristics to the isotropic biaxial misfit strain.The difference between them is that the transient negative capacitance effect is more sensitive to temperature regulation under uniaxial in-plane misfit strain.Under the regulation of compressive strain,the isotropic biaxial misfit strain is better to help stabilize the transient negative capacitance.However,under the regulation of tension strain,the uniaxial misfit tension strain is the better one.In the ferroelectric-dielectric capacitor combination system and under the regulation of compressive strain,the uniaxial in-plane misfit strain is better to obtain non-hysteresis gain,while the capacitance enhancement effect weakened.Under the regulation of tensile strain,it is easy for the isotropic biaxial misfit tensile strain to obtain the linear relationshipQ-V,while the uniaxial in-plane misfit tensile strain can improve this linear relationship to non-hysteresis characteristics,and the advantage of this is that the capacitance enhancement effect is more obvious.3.Due to the difference of thermal expansion coefficients between thin film and the substrate,the isotropic biaxial thermal strain can be induced by PbZr_0.2Ti_0.8O₃ferroelectric thin film which deposited on three different substrates of Si,c-Al₂O₃and Mg O.The transient negative capacitance effect of this strain on the ferroelectric is studied.On the Mg O deposition substrate,study shows that the lower the deposition temperature,the more significant the ferroelectric negative capacitance effect.Under the same deposition temperature,the larger the thermal expansion coefficient,the more significant the ferroelectric negative capacitance effect,which also shows that compared to the tensile heat strain,the compression heat strain is better to help stabilize the transient negative capacitance effect.