Preparation And Performance Control Of Y-doped HfO₂-based Ferroelectric Thin Films And Laminated Structures

Hafnium oxide（HfO₂）-based thin film is a new type of ferroelectric thin film material.It can also have good ferroelectricity at a very small film thickness and is compatible with advanced CMOS processes.Therefore,it has a good application prospect in the field of ferroelectric memory.Studies have shown that the phase structure of HfO₂ films can be changed by doping to improve the ferroelectricity of the films.However,the HfO₂-based ferroelectric thin films doped with a single element still retain the non-ferroelectric phase to a certain extent,resulting in poor ferroelectricity and endurance,thus limiting their commercial application.The co-doping of HfO₂ films can further promote the non-ferroelectric phase to ferroelectric phase transition in the films,thereby improving the ferroelectricity and endurance of the films.On the other hand,the films can also show good ferroelectricity when HfO₂ and oxides of doping elements are prepared into the laminated structure.The element doping of the HfO₂ layer can promote the nonferroelectric phase-ferroelectric phase transition in the layer,thereby improving its ferroelectric properties.Among various doped materials,the HfO₂-Zr O₂ system has attracted much attention due to its good ferroelectricity and low annealing temperature.Based on this,Hf_0.5Zr_0.5O₂and HfO₂/Zr O₂ laminated ferroelectric thin films are selected as the object,Yttrium（Y）is selected as the second doping element,and the Y-doped Hf_0.5Zr_0.5O₂ and HfO₂/Zr O₂ laminated thin films are prepared by chemical solution deposition in this paper.Through the microstructure characterization and electrical performance test of the films,the relationship between them was explored,and then the structure was further optimized to improve the ferroelectricity and endurance of the HfO₂-based ferroelectric films.The main work of this paper is as follows:（1）Y:Hf_0.5Zr_0.5O₂ ferroelectric thin films were prepared by chemical solution deposition,and the effects of annealing temperature,film thickness and Y doping content on the phase composition,microstructure and electrical properties of the films were investigated.The result shows that appropriate doping of Y element can suppress the formation of monoclinic phase and promote the formation of orthorhombic phase,thereby improving the ferroelectricity of the films.When the annealing temperature is600℃,the film thickness is 58 nm and the Y doping content is 2.5%,the electrical properties of the films are relatively good,in which the remanent polarization P_r is about 15.9μC/cm²,the coercive electric field E_c is about 1.16 MV/cm,and the leakage current density is 1.65×10^-3 A/cm²under an applied electric field of 2 MV/cm.In addition,the P_r of this film can remain above 98%of the original value after 10⁹cycles,indicating a good endurance.（2）Y-doped HfO₂/Zr O₂ laminated ferroelectric thin films were prepared by chemical solution deposition,the effects of the doping method and doping amount of Y element on the phase composition,microstructure and electrical properties of the films were investigated.The result shows that as the film is prepared into a laminated structure and doped with an appropriate amount of Y element in an appropriate doping manner,the formation of the orthorhombic phase in the films can be promoted.When the Y doping mode is（Y:Zr O₂/Y:HfO₂）₂ and the Y doping amount is 1.0%,the electrical properties of the films are relatively good,and the remanent polarization P_ris about 24μC/cm²,the coercive electric field E_c is 1.19 MV/cm,and the leakage current density is 1.73×10^-3 A/cm²under an applied electric field of 2 MV/cm.In addition,the P_r of this film can remain above 90%of the original value after 10⁹cycles,indicating a good endurance.