Study On Dielectric Properties Of Hf_1-xZr_xO₂ Ferroelectric Thin Films Based On Composition-Graded Control

Hafnium oxide has attracted extensive research since it was found to have the advantages of ferroelectric in 2011 and highly compatibility with CMOS process,no pollution and miniaturization.With the full application of 5G network,a large number of servers and signal towers have increased requirements for microwave modulators such as phase shifters.However,the ferroelectric materials used in most of the previous phase shifters were the traditional ferroelectric materials,which has the fatal shortcomings of difficult miniaturization,incompatibility with CMOS process and high energy consumption.Hafnium oxide materials can be a good solution to the above problems,so the introduction of new hafnium oxide based ferroelectric materials into this field is imperative! The main requirements of phase shifters for ferroelectric thin films materials lie in high tunability,low dielectric loss,low leakage current and strong fatigue resistance.With the development of the research on hafnium oxide based ferroelectric thin films,its disadvantages are gradually highlighted: the tuning ratio and dielectric loss of ferroelectric thin films are in a state of contradiction,which is related to the reversal speed of the internal ferroelectric domains;the hafnium oxide based ferroelectric thin films has poor fatigue resistance and can not maintain long-term stable work.Composition-graded materials can concentrate the advantages of various materials with similar compositions and solve the problems mentioned above.In this paper,the concept of "composition-graded" is firstly combined with HZO(hafnium,zirconium oxygen)ferroelectric films,which is widely studied at present,to prepare homogeneous HZO ferroelectric films and composition-graded HZO ferroelectric films with different hafnium and zirconium ratios.The main contents are as follows:(1)Firstly,HZO homogeneous ferroelectric thin films with hafnium zirconium ratio of 7:3,5:5 and 3:7 was prepared.The effects of different hafnium and zirconium ratios on the properties of HZO ferroelectric thin films were studied.It was confirmed that the non-ferroelectric monoclines in HZO thin films decreased with the increase of zirconium content.It is found that HZO ferroelectric film with hafnium zirconium ratio of 5:5 has excellent ferroelectric performance,high residual polarization value and excellent tunability,but poor fatigue performance and high dielectric loss.In contrast,HZO ferroelectric film samples with hafnium zirconium ratio of 3:7 and hafnium zirconium ratio of 7:3 have better fatigue performance and low dielectric loss,but lower tunability,and larger leakage current of 3:7 sample.(2)Secondly,according to the deposition sequence of different hafnium zirconium ratio along the thickness direction when HZO film was deposited,the upper and lower composition gradient structures were prepared;And the properties of the composition gradient thin films and the hafnium zirconium ratio of 5:5 HZO ferroelectric thin films were compared.It is found that there is no significant difference in the crystalline properties of the composition-graded films and the homogeneous film.In terms of electrical properties,it is found that the composition-graded thin films not only maintain excellent ferroelectric properties and high tunability,but also effectively improve the shortcomings of homogeneous ferroelectric thin films such as poor fatigue performance and high dielectric loss.(3)To investigate the dielectric loss in depth,the domain inversion test,NLS model fitting and dielectric loss test are combined.The test results were compared with the theoretical calculation results,it is found that the lower dielectric loss of the compositiona-graded films relative to the HZO ferroelectric films with a hafniumzirconium ratio of 5:5 is due to the faster establishment of the polarization of the internal dipole and the shorter time required for the ferroelectric domain to flip.The test results are in good agreement with the fitting results of the NLS model,proving that the physical mechanism of the dielectric loss change lies in the domain flipping speed inside the ferroelectric thin films.