Research Of Switching Dynamics And Electrical Characteristics In PZT Thin Film With Ferroelastic Superdomain Structure

In recent years,various electronic devices which based on ferroelectric thin films have been widely used.The foundation of these ferroelectric devices is the switching dynamics.The essence of switching dynamics is the movement of domain and domain wall.Thus,the functional characteristics of ferroelectric devices with diverse domain structures are different from each other.Ferroelastic superdomain structure is a kind of special domain structure formed by nanodomain self-assembly.There are abundant intermediate polarization states and complex polarization characteristics in this structure.Therefore,the study on its switching dynamics and electrical characteristics is impotant for the development of ferroelectric inductors and solving the problems of insufficient adjustable states of ferroelectric artificial synapses.However,the switching dynamics of ferroelastic superdomain is difficult to be observed by conventional methods.Its switching dynamics and electrical properties are still need to be explored.In this thesis,the epitaxial Pb Zr_0.2Ti_0.8O₃（PZT）thin film was prepared,and the switching dynamics test systems were designed and built.Then,the switching dynamic and negative capacitance effect of the film were studied by using the test systems.The model of giant inductor based on electrically induced polar vortices was proposed,and the inductance characteristic of the PZT thin film was studied.The main research contents and results are as follows:（1）The PZT thin film was prepared by pulsed laser deposition,and their growth quality and orientation,domain configuration,general electrical properties were tested.The results showed that high quality and orientation along the（111）direction of the PZT thin film,besides there were single band ferroelastic superdomain structure with neatly arranged nano domains inside.The polarization intensity of the thin film was near 120μC/cm²,leakage current was only p A magnitude,fatigue performance was outstanding.In addition,the thin film had polymorphic polarization characteristics,the resistance state change under small electric field could reach 10³.（2）The switching dynamics test system was designed and built.The system achieved the output of ns-level pulses and the monitoring of ps-level signals.On the basis of this system,the ultra-fast switching dynamics test system which based on step waveform was built.Through step waveform design,ps-level ultra-fast output and observation were achieved,and the electrical characteristics of ferroelectric materials or other dielectric materials could be observed.（3）The switching dynamics of（111）-PZT thin film was studied by the test system.The results showed that there were abundant polarization intermediate states and continuous polarization reversal in the film,and the ferroelastic polarization reversal were obvious under the action of low electric field.The negative capacitance effect of the film was significant and the transient voltage drop could reach 0.8 V.（4）A giant inductor based on electrically induced polar vortices was proposed.The dynamics of the induced polar vorties and inductance characteristics in（111）-PZT thin film were studied.The results showed that the inductance and capacitance of the（111）-PZT film could be controlled by the external electric field,and its inductance density could reach 800 m H/cm².