Preparation And Study Of PHT Ferroelectric Thin Films On Pt/Si Substrates

Ferroelectric thin films have been widely used in microelectronic devices due to their excellent ferroelectric,piezoelectric,dielectric,pyroelectric and optoelectronic properties.However,traditional ferroelectric thin films with perovskite structure like Pb(Zr_xTi_1-x)O₃（PZT）,when they are integrated on silicon substrate,there exists some problems such as size effect,poor compatibility and bad fatigue performance.In order to meet the increasingly complex working environment,people have higher requirements on the compatibility,stability and service life of ferroelectric thin films.Compared with the traditional perovskite ferroelectric material PZT,Pb(Zr_xTi_1-x)O₃（PHT）has the similar ferroelectric and dielectric properties,but better fatigue performance,which can be used to prepare ferroelectric memory（Fe RAM）with better performance.In this paper,we take PHT as the research object.The Pb(Hf_xTi_1-x)O₃ thin films are deposited on Pt/Ti/SiO₂/Si substrates by using pulsed laser deposition technique（PLD）.The Pb(Hf_0.48Ti_0.52)O₃ films are considered as the key research for its component near the morphotropic phase boundary（MPB）.Moreover,the effect of Hf doping on the structure and properties of the films was investigated by changing the content of Hf in the films.The main research work and conclusions are as follows:1、The Pb(Hf_0.48Ti_0.52)O₃ films are fabricated on Pt/Si substrates and its best growth condition is studied.The results show that the growth atmosphere and temperature have an important influence on the structure and properties of films.When the oxygen pressure is 20 Pa and the growth temperature is 500 ℃,the crystal quality of the films is best.At this time,the remna nt polarization and the relative dielectric constant of the film are 80.97 μC/cm² and 542 respectively.The leakage current density(≈2×10^-9A/cm²)is less than that of the films grown at other oxygen pressure and temperature.2、In order to reduce the lattice mismatch and thermal mismatch between the substrates and the films,the Pb(Hf_0.48Ti_0.52)O₃ thin films are prepared by inserting the low temperature self-buffered layer,and the effects of the self-buffered layer on the structure and properties of films are investigated.The experimental results show when the growth temperature of self-buffered layer is 300 ℃,the main diffraction peak of the film is（111）,which is same as that of the Pt/Si substrate.Not only that,the XRD scanning pattern show the reflections form a doublet and singlet for T and R phases respectively,which means the coexistence of two phases.Compared with the films without self-buffered layer,the electrical properties of epitaxial Pb(Hf_0.48Ti_0.52)O₃ thin films on the low temperature self-buffered layer（300 ℃）have been improved obviously.The remnant polarization and relative dielectric constant are increased to 93.23 μC/cm² and 712.Furthermore,the leakage current density is reduced(≈1×10^-9A/cm²),and the fatigue performance of the reactor is also improved obviously.3、The effects of Hf doping on the structure and properties of PHT thin films with self-buffered layer are investigated.There exits two phases in Pb(Hf_0.48Ti_0.52)O₃ films.When the content of Hf increased to x=0.52,the PHT changes from two phases to rhombohedral phase;when the Hf content continued to increase to x=0.7,the films can keep a rhombohedral structure unchanged.The results show that the increase of the Hf doping will lead to the structure of PHT changes to rhombohedral structure,which is similar to PZT.The PHT films near MPB（x=0.48）have best ferroelectric and dielectric properties,even if its leakage current is little worse than other components.After 2.15×10¹⁰ switching cycles,all PHT films with different compositions deposited on low temperature self-buffer layer exhibit good fatigue properties.From all the above results,it can been seen obviously that the PHT films near MPB show the most excellent electrical performance.