[论文解读] Microscopic piezoelectric behavior of clamped and membrane (001) PMN-30PT thin films

A. Brewer, S. Lindemann+14 more|arXiv (Cornell University)|Oct 16, 2021

Ferroelectric and Piezoelectric Materials参考文献 21被引用 10

一句话总结

本研究证明，将(001)-取向的PMN-30PT薄膜从其Si衬底上释放可消除机械夹持效应，从而实现从菱面体(R)相到四方(T)相的完整极化旋转，并恢复体材料类似的巨大压电性能，d33 > 1000 pm/V。相比之下，受夹持的薄膜仅表现出有限的R到单斜(Ma)相转变，这是由于衬底引起的应变和畴抑制导致d33 < 100 pm/V。

ABSTRACT

Bulk single-crystal relaxor-ferroelectrics, like Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), are widely known for their large piezoelectricity. This is attributed to polarization rotation which is facilitated by the presence of various crystal symmetries for compositions near a morphotropic phase boundary (MPB). Relaxor-ferroelectric thin films, which are necessary for low-voltage applications, suffer a reduction in their piezoelectric response due to clamping by the passive substrate. To understand the microscopic behavior of this adverse phenomenon, we employ AC electric field driven in-operando synchrotron x-ray diffraction (XRD) on patterned device structures to investigate the piezoelectric domain behavior under an electric field for both a clamped (001) PMN-PT thin film on Si and a (001) PMN-PT membrane released from its substrate. In the clamped film, the substrate inhibits the field induced rhombohedral (R) to tetragonal (T) phase transition resulting in a reversible R to Monoclinic (M) transition with a reduced longitudinal piezoelectric coefficient d33 < 100 pm/V. Releasing the film from the substrate results in recovery of the R to T transition and results in a d33 > 1000 pm/V. Using diffraction with spatial mapping, we find that lateral constraints imposed by the boundary between active and inactive material also inhibits the R to T transition. Phase-field calculations on both clamped and released PMN-PT thin films simulate our experimental findings. Resolving the suppression of thin film piezoelectric response is critical to their application in piezo-driven technologies.

研究动机与目标

• 理解夹持的PMN-30PT薄膜中压电响应抑制的微观起源。
• 研究衬底机械夹持如何抑制极化旋转和相变。
• 确定活性区与非活性区之间侧向边界在限制畴演化中的作用。
• 证明自由悬挂的PMN-30PT膜可恢复体材料类似的压电响应。
• 通过衬底和几何结构工程建立最大化薄膜器件压电响应的设计原则。

提出的方法

• 对图案化夹持和膜状PMN-30PT薄膜进行原位同步辐射X射线衍射(XRD)，施加交流电场。
• 采用空间分辨XRD测绘分析电极区域内的局部应变和相变。
• 采用相场模拟模拟夹持和释放薄膜中的极化旋转和相变演化。
• 使用双光束激光干涉仪(DBLI)测量夹持薄膜和膜状薄膜的纵向压电系数d33。
• 对004衍射峰进行L扫描，以追踪不同电场下动态相变过程。
• 将实验XRD数据与夹持和未夹持条件下R、M和T相的热力学自由能计算结果相关联。

实验结果

研究问题

• RQ1 衬底夹持如何影响(001)-PMN-30PT薄膜中的极化旋转路径？
• RQ2 非活性区域引起的侧向机械约束在抑制压电响应中起什么作用？
• RQ3 通过去除衬底夹持，是否可以在薄膜中恢复完整的R→T相变？
• RQ4 夹持薄膜与自由悬挂膜在微观畴结构和相变方面有何不同？
• RQ5 相邻非活性区域产生的侧向应变场在多大程度上抑制了活性区域的畴重新取向？

主要发现

• 夹持的PMN-30PT薄膜在电场作用下表现出可逆的R到单斜(Ma)相转变，纵向压电系数d33 ≈ 30 pm/V，表明压电响应受到严重抑制。
• 在去除衬底后，PMN-30PT膜恢复从R相到T相的完整极化旋转，d33 ≈ 1100 pm/V，接近体单晶材料的数值。
• 空间分辨XRD显示，相邻非活性区域引起的侧向夹持通过限制畴演化而降低压电响应，其影响在电极边缘附近最强。
• 通过使用小循环PE环的“棘轮”过程，可逐步实现单斜相和四方相的成核与生长，从而在固溶相界附近观察到R→T相变。
• 相场模拟定量再现了实验中的相变演化，证实衬底夹持稳定了Ma相并抑制了T相的形成。
• 本研究识别出侧向机械约束是除衬底夹持外的第二个响应抑制因素，表明孤立岛状结构可能进一步增强压电响应。