Preparation And Characterization Of PZT Ferroelectric Thin Films By Magnetron Sputtering At Medium And Low Temperatures

Originated from its excellent ferroelectricity,piezoelectricity and pyroelectricity and other characteristics,ferroelectric thin films play an increasingly important role in many core and emerging fields such as big data,mobile computing and automation control.Lead zirconate titanate(Pb(Zr,Ti)O3 or PZT)is one of the key materials for scientific research and commercial applications because of its excellent ferroelectric,piezoelectric,pyroelectric properties,high Curie temperature,easy being doped and good stability.However,the preparation temperature of PZT thin film via magnetron sputtering is relatively high.So if we can reduce the preparation temperature of the PZT thin film,it can be better integrated with the CMOS-Si technology,which has very important significance in both theoretical and practical applications.BaTiO3 and PZT materials are typical perovskite-type(ABO3)ferroelectric materials,and BaTiO3 is a dielectric material with low dielectric loss and leakage current and good ferroelectricity.And the low-temperature preparation process of BaTiO3 is being perfect.In our work,PZT/BaTiO3 bilayer films are prepared in order to combine the advantages of both BaTiO3 and PZT films.The Ferroelectric and dielectric properties of PZT/BaTiO3 bilayer films can be improved by the polarization coupling formed between the PZT and BaTiO3 layers and a space charge layer formed in the BaTiO3 layer near the bottom electrode.In the part of experimental research,we use a multi-target rf sputtering deposition system to prepare PZT/BaTiO3 bilayer ferroelectric thin films and PZT single-layer ferroelectric thin films at meddle and low temperature(350?,500?),and then this films undergo rapid annealing process(RTP).PZT single and PZT/BaTiO3 bilayer ferroelectric thin films with excellent electrical properties were obtained.The main research contents are summarized as follows:1.Preparation and characterization of PZT/BaTiO3 bilayer ferroelectric thin films.(1)Study on properties of PZT/BaTiO3 bilayer films at low and middle temperatures.It is found that 500? is the in-situ growth temperature of the PZT/BaTiO3 bilayer film.And we explored that PZT thin films can be prepared at 350? combining rapid annealing,and good electrical properties of this PZT films can be obtained.(2)The PZT/BaTiO3 bilayer film shows the comprehensive characteristics of the PZT material and the BaTiO3 material.The PZT/BaTiO3 bilayer film exhibits the following characteristics compared with the PZT single-layer film:PZT/BaTiO3 bilayer films have more slender hysteresis loops,significantly higher pressure resistance but lower polarization intensity,significantly reduced leakage current and dielectric constant.(3)The total thickness of the PZT/BaTiO3 bilayer film was fixed.It was found that as the proportion of BaTiO3 layer increased,the shape of the hysteresis loop was more slender,ie,the breakdown field strength was significantly increased and the polarization intensity was significantly reduced,and the leakage current density shows a decreasing trend as the increased thickness of the BaTiO3 layer in the bilayer film.2.Middle and low temperature preparation and performance characterization of PZT films.(1)The PZT film samples prepared at a low temperature of 350? exhibited excellent electrical properties after RTP,Its saturation polarization can reach 116?C/cm2 at an electric field of about 760kV/cm,which is related to the retained fine grain of PZT thin film after RTP.(2)The PZT thin film samples prepared at a low temperature of 350? are easily polarized after annealing,indicating good ferroelectric properties,which is related to the fine grains that remain in the PZT thin films after annealing.In addition,through the ferroelectric tests with different frequencies,it was found that the equivalent circuit of this PZT thin film sample is a parallel circuit composed of linear and nonlinear capacitors and ideal ferroelectrics.(3)The PZT film deposited at a low temperature of 350? exhibits extremely excellent piezoelectric performance by means of RTP.In a cycle test of 6V-20V-6V,the transversal piezoelectric coefficient value |e31,f| is between 14.1-15.8 C/m2,and the figure of merit FOM is 18.26-22.93GPa.(4)The PZT film prepared at 350? have good fatigue properties after RTP,and±Pr respectively drops to-78%and-74%of initial value after 108 cycles.