The Structural And Ferroelectric Properties Of Praseodymium/Cerium Doped Hafnium Oxide Ferroelectric Thin Films Fabricated By Solution Method

The ferroelectric field effect transistor?FeFET?is one of the most promising nonvolatile random access memories with the advantages of nonvolatileness,non-destructive readout and high-density integration.Hafnium oxide?HfO₂?based ferroelectric film material is a new ferroelectric film material,which is compatible with advanced CMOS technology.Moreover,it exhibits good ferroelectric properties even with the film thickness scaled down to 3 nm.These advantages make the HfO₂based ferroelectric film suitable for application to FeFET.Doping can enhance the ferroelectric performance of the HfO₂ based ferroelectric film significantly.Chemical solution deposition?CSD?is a method with which is easy to dope,and its advantage is simple,economic and effective.In this thesis,the doped HfO₂ ferroelectric film was choosen as the research object,and two elements of praseodymium?Pr?and cerium?Ce?were selected as dopants,and the films were prepared by CSD method.The main work is as follows:?1?Hafnium oxide films with different Pr doping contents?Pr:HfO₂?were fabricated on?111?Pt/Ti/SiO₂/?100?Si substrate.The ferroelectric orthorhombic phase in the film was confirmed by microstructural characterization,which indicated that the metastable ferroelectric orthorhombic phase could be induced by Pr doping in the HfO₂ films.The P-E?polarization-electrical field?hysteresis loop measurement results demonstrated that the film with 5 mol%Pr exhibited a distinct ferroelectricity,with a maximum remanent polarization?P_r?of 6.9?C/cm² and a coercive field?E_c?of1.2 MV/cm.The C-V?capacitance-voltage?measurements demonstrated that the curve of the 5 mol%Pr doped film exhibited an obvious butterfly shape,furtherly indicating the ferroelectricity in this sample.During endurance performance of the5 mol%Pr doped HfO₂ ferroelectric film,the polarization degraded about 30%after1×10⁸ switching cycles.The leakage current measurements demonstrated that the pure HfO₂ film has the minimum leakage current.?2?Hafnium oxide films with different Ce doping contents?Ce:HfO₂?were fabricated on n-type heavily doped Si.The surface morphology feature,crystal structural and electric properties of the films were characterized.The surfaces of these films were relatively flat,and their surface roughness root mean squares(R_RMS)were all less than 1 nm,indicating the little fluctuations.Moreover,the ferroelectric orthorhombic phase in the film was confirmed by combining methods.The P-E hysteresis loop demonstrated that the ferroelectricity starts to emerge in the film with10 mol%Ce content.Furthermore,the film with 15 mol%Ce exhibited the best ferroelectricity,with a maximum P_r of 16?C/cm² and a 2E_c of 2 MV/cm.The piezoelectricity results demonstrated that the amplitude-voltage curves of the films with 10 mol%and 15 mol%Ce were both with the butterfly shape.The phase-voltage curves demonstrated that the phase for the former could switch for 160owhile that for the later could switch for 180o.