晶粒尺寸及衬底应力对铁电薄膜特性的影响

Effects of grain size and substrate stress of ferroelectric film on the physical properties

考虑衬底应力、畴壁运动和畴结构变化,建立了修正的Landau-Devonshire热力学模型,计算了生长在不同衬底上的含有纳米晶粒的PbZr0.4Ti0.6O3(PZT)薄膜的电滞回线,研究了矫顽场、剩余极化强度和相对介电常数对晶粒尺寸以及薄膜厚度的依赖关系.结果表明,矫顽场和相对介电常数对晶粒尺寸的依赖关系呈类抛物线状;衬底压应力使矫顽场和剩余极化强度增大,使相对介电常数减小;随着厚度增加,矫顽场先缓慢增加,到200nm急剧增加,到310nm再缓慢增加,这一结果主要取决于介电常数对厚度的依赖.

A modified Landau-Devonshire thermodynamic model is presented, with the contributions of substrate stress, domain wall motion and domain structure transition taken into account. The hysteresis loops of PbZr0.4 Ti0.6 O3 （PZT） films, which are deposited on different substrates, containing nano-scale grain is calculated, and the thickness and grain size dependences of coercive field, remnant polarization and relative permittivity are researched. The results demonstrate that the grain size is dependent on coercive field and relative permittivity as shown in paraboliclike curve, that the pressure stress of substrate enhances the coercive field and remnant polarization, but reduces the relative permittivity, and that the coercive field increases slowly first with the thickness of film, then increases sharply between 200 nm and 310 nm of the thickness, and slowly again after 310 nm. This result is due to the thickness dependence of relative permittivity.