Time resolved and in-situ structural analysis of a ferroelectric thin film during polarization switching using synchrotron-based diffraction

使用同步加速器衍射对铁电薄膜偏振切换过程中的时间分辨和原位结构进行分析

基本信息

批准号：
18310085
负责人：
SAKATA Osami
金额：
$ 8.31万
依托单位：
Japan Synchrotron Radiation Research Institute
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

A synchrotron-based time-resolved diffraction method has been developed for characterizing a piezoelectric thin film. This was why we needed to complete a time-resolved diffraction system equipped with a ferroelectric test system. We introduced the fenoelectric test system(Toyotechinca FCE-HS100D) for high-speed characterization of polarization in a ferroelectric thin film and modified it for a time-resolved and in-situ measurement. We have succeeded in detection of electrostuction(electuc-field-induced strain) of ferroelectric thin films such as epitaxial Pb(Zr_<0.25>, Ti_<0.75>) O_3(PZT) and polycrystalline BiFeO_3(BFO) films. The electrostnctive strain was induced by an applied electric field having repeated ns-width pulses. In addition, we determined piezoelectric constants from diffraction peak shifts.The apparatus receives a pulse pattern formed by a 508 MHz counter using the RF signals as a clock of the Spring-8 storage ring and applies a pulse electric field to a sample. We use … More d the pulse pattern as a trigger ; accordingly the applied electric fields were synchronized with incident x-rays.A sample was a 750 nm-thick PZT film epitaxially grown on a SrRuO_3 thin film using metal organic chemical vapor deposition. Upper Pt electrodes with a diameter of 100 μm were arrayed in a lattice. One prober touched an upper electiode Pt incident x-rays hit, while the other touched another upper electrode. We aligned a polar direction in the PZT film using an applied voltage of 30 V in advance ; consequently, polarization(+Pr) remamed. We made a Θ-2Θ scan around the PZT 004 Bragg angle and recorded a diffraction- intensity profile as a function of time at each combination of Θ and 2Θ angle using an avalanche photo diode detector for a fixed voltage of 0, 10, 20 30 40 50, 55, 60, 70, and 75 V, respectively. The unipolar-rectangular-shape pulse width of 200 ns was repeatedly applied with a period of 800 ns. Measured time used at each angle was 100 s. An incident slit size used was 15×15μm.We observed that the 004 main peaks were shifted toward the lower angle only when the applied field was on. This indicates that the(004) lattice-plane spacing along the surface normal was lengthened because of electrostriction. The pulse electric-field induced strain Δd / d estimated from the main peak shift for 50 V was 0.0004 ; correspondingly, piezoelectric constant d_<33> was 13 pm / V. Furthermore, our finding is that the other peak appeared at a lower angle. d_<33> obtained from the other peak shift is ca. 50 pm / V. This value almost corresponds to that obtained using AFM measurements.We also applied the time-resolved diffraction method to characterizing a polycrystalline BFO thin film. The applied voltages were 0, 3, 5, 8, 10, 11, and 12 V with a 150 ns width and a 804 ns periodicity. Obtained d_<33> values for the(001) and(110) domain were 27.8 and 26.4 pm / V, respectively. Less

基于同步加速器的时间分辨衍射方法已被开发用于表征压电薄膜，这就是为什么我们需要完成配备铁电测试系统的时间分辨衍射系统（Toyotechinca FCE-HS100D）。）用于铁电薄膜中极化的高速表征，并将其修改为时间分辨和原位测量。外延Pb(Zr_<0.25>,Ti_<0.75>)O_3(PZT)和多晶BiFeO_3(BFO)薄膜等铁电薄膜电致应变的检测具有重复纳秒宽度脉冲的电场此外，我们还根据衍射峰位移确定了压电常数。接收由 508 MHz 计数器使用 RF 信号作为 Spring-8 存储环的时钟形成的脉冲模式，并向样品施加脉冲电场。场与入射 X 射线同步。样品是使用金属有机化学气相沉积在 SrRuO_3 薄膜上外延生长的 750 nm 厚的 PZT 薄膜，直径为 100 nm。 100μm排列成格子状，一个探针接触上部电极Pt入射X射线，而另一个探针接触另一个上部电极，因此我们预先使用30V的施加电压对准PZT薄膜中的极性方向。我们对 PZT 004 布拉格角进行了 θ-2θ 扫描，并记录了每个时间点的衍射强度分布。使用雪崩光电二极管检测器分别在 0、10、20、30、40、50、55、60、70 和 75 V 的固定电压下组合 θ 和 2θ 角，得到 200 ns 的单极矩形脉冲宽度。重复施加 800 ns 的时间，每个角度的测量时间为 100 秒。使用的狭缝尺寸为15×15μm。我们观察到仅当施加场时004主峰向较低角度移动，这表明由于电致伸缩，沿表面法线的(004)晶格面间距被拉长。由50V主峰位移估算出的脉冲电场诱发应变Δd/d为0.0004，相应地，压电常数d_<33>为13 pm / V。此外，我们的发现是，从另一个峰值偏移获得的另一个峰值 d_<33> 约为 50 pm / V。该值几乎与使用 AFM 测量获得的值相对应。还应用时间分辨衍射方法来表征多晶BFO薄膜，施加的电压为0、3、5、8、10、11和12。宽度为 150 ns、周期为 804 ns 的 V 得到的 (001) 和 (110) 域的 d_<33> 值分别为 27.8 和 26.4 pm/V。