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

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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