Study On The Preparation And Electrical Properties Of Sr,La Doped Hf_0.5Zr_0.5O₂ Ferroelectric Films

HfO₂ based films are a new type of ferroelectric thin film materials which are fully compatible with CMOS process,and because of the advantages of no pollution,high degree of miniaturization and wide band gap,they are regarded as ideal materials for preparing large storage capacity ferroelectric memory.However,HfO₂-based Fe RAM shows poor endurance due to hard breakdown at the saturated electric field,which has become the main bottleneck restricting its commercial application.At present,most studies have used a single element doping to stabilize the orthorhombic ferroelectric phase in HfO₂thin films,but the material still contains a high content of monoclinic phase after doping,which is probably the key reason for its hard breakdown and failure.The ferroelectric properties and endurance of HfO₂-based films can be improved by doping the second or more elements to further promote the transition of monoclinic phase to orthogonality phase.In this paper,Zr-doped HfO₂(Hf_0.5Zr_0.5O₂,HZO)ferroelectric thin films was taken as the research object.Two elements,strontium(Sr)and lanthanum(La),are selected as the second doping elements.The structure and performance of the film are adjusted through the composite doping,to reduce the coercive electric field and leakage current of the HfO₂-based thin film,and obtain a HfO₂-based ferroelectric thin film with good ferroelectricity and endurance.The work of this paper mainly includes the following two aspects:(1)The effects of annealing temperature,film thickness and Sr doping content on the phase composition,microstructure and electrical properties of Sr:Hf_0.5Zr_0.5O₂ferroelectric thin films were studied which is prepared by chemical solution deposition(CSD).The results show that the ferroelectric properties of the films are the best when the annealing temperature is 500^oC,the thickness of the films is 26 nm and the doping content of Sr is 0.50%:the remanent polarization(P_r)of the films is about 15?C/cm²,the coercive field(E_c)is 1.1 MV/cm,the leakage current density is8.6×10^-4A/cm²,and shows good fatigue properties(P_rdecrease within 1%after 10⁹cycles).This is because when a certain amount of Sr is doped,the monoclinic phase formation could be inhibited,and the content of tetragonal phase gradually stabilized,which encouraged the formation of orthorhombic phase,so the ferroelectricity is improved;At the same time,the crystallinity of the film increases,the grain size increases with the shorter leakage current channel and the decrease of grain boundary,so the leakage current density decreases.(2)La:Hf_0.5Zr_0.5O₂ ferroelectric thin films were prepared by chemical solution deposition,and the effects of annealing temperature and La doping content on the phase composition,microstructure and electrical properties of the thin films were studied.The results show that the ferroelectric properties of the films are the best when the annealing temperature is 600^oC and the doping content of La is 1.50%:the P_rof the films is about 17.9?C/cm²,the E_cis 0.83 MV/cm,and the leakage current density is in the order of 10^-3A/cm²,and the P_rdecrease below 4%after 10⁹cycles.Because,doping a certain amount of La can promote the phase transformation of monoclinic phase and tetragonal phase,to form more orthorhombic phase,which is beneficial to improve the ferroelectric properties;At the same time,doping can improve the crystallinity of the film,increase the grain size,and decreases the leakage current density.