(111)取向0.7PMN-0.3PT薄膜机电耦合性能

铁电薄膜由于其优异物理性能,而被广泛应用于微电子、光电子、微机电领域。在铁电薄膜理论研究方面,热力学理论可以有效地预测铁电薄膜的相结构、极化特性和机电性能等,且已在(001)取向铁电薄膜的研究中取得了较好的应用,而对于(111)取向铁电薄膜的研究报道非常少。因此,本文通过对序参量坐标转换的方法,构建了(111)取向薄膜的热力学势能函数及其机电性能计算方法。基于此,研究了(111)取向0.7PMN-0.3PT铁电薄膜的相结构及其机电性能。研究结果表明,(111)取向0.7PMN-0.3PT铁电薄膜的相结构主要存在沿晶轴方向三个极化可互换的对称相:顺电相PE、菱方相R和单斜相M_A(或M_B)。在应变和外电场的调控下,(111)取向0.7PMN-0.3PT薄膜展现出优良的机电性能,在R和M_A相变点处,介电常数ε11、ε22、ε33和面外压电系数d33取得了极大值。在外电场E₃分别为0、50 kV/cm、100 kV/cm和200 kV/cm时,面外介电常数ε33的峰值分别为4 382、2 646、2 102和1 600,面外压电系数d33的峰值分别为303.8 pm/V、241.9 pm/V、219.7 pm/V和195.1 pm/V。应变和外电场能够较好地调控薄膜的机电耦合性能,可为优异机电耦合性能的器件制备提供参考。

Electromechanical Coupling Performance of ( 111 )-Oriented 0.7PMN-0.3PT Thin Film

Due to its excellent physical properties,ferroelectric thin films are widely used in the fields of microelectronics,optoelectronics,and microelectromechanics.In terms of theoretical research on ferroelectric thin films,the phenomenological theory of thermodynamics can effectively predict the phase structure,polarization characteristics and electromechanical properties of ferroelectric thin films,and has been well applied in the research of(001)-oriented ferroelectric thin films.However,there are very few research reports on(111)-oriented ferroelectric thin films.Therefore,the thermodynamic potential energy function and the calculation method of electromechanical properties of the(111)-oriented thin film by transforming order parameters of the system was constructed in this paper.Based on constructed theory,the phase structure and electromechanical properties of(111)-oriented 0.7PMN-0.3PT ferroelectric thin film were studied.The results reveal that the phase structures of the(111)-oriented 0.7PMN-0.3PT ferroelectric thin film mainly have three symmetrical phases with interchangeable polarizations along the crystal axis,they are paraelectric phase PE,rhombohedral phase R and monoclinic phase M_A(or M_B).By the controling of misfit strain and external electric field,the(111)-oriented 0.7PMN-0.3PT thin film exhibits excellent electromechanical properties.At the boundary of the R-M_A phase transformation,the dielectric constantsε₁₁,ε₂₂,ε₃₃ and the out-of-plane piezoelectric coefficient d₃₃ have achieved a maximum value.With the external electric field E 3=0,50 kV/cm,100 kV/cm and 200 kV/cm,the peak values of the out-of-plane dielectric constantε₃₃ are 4382,2646,2102 and 1600,respectively,and the peak values of the out-of-plane piezoelectric coefficient d₃₃ are 303.8 pm/V,241.9 pm/V,219.7 pm/V and 195.1 pm/V.The misfit strain and external electric field can better control the electromechanical coupling performance of the film,which provide a reference for the preparation of devices with excellent electromechanical coupling performance.