Investigation of Ferroelectric Grain Sizes and Orientations in Pt/Ca_xSr_1⁻xBi₂Ta₂O₉/Hf⁻Al⁻O/Si High Performance...

Electron backscatter diffraction (EBSD) was applied to investigate the grain size and orientation of polycrystalline Ca_xSr_1⁻xBi₂Ta₂O₉ (C_xS_1⁻xBT) films in ferroelectric-gate field-effect transistors (FeFETs). The C_xS_1⁻xBT FeFETs with x = 0, 0.1, 0.2, 0.5, and 1 were characterized by the EBSD inverse pole figure map. The maps of x = 0, 0.1, and 0.2 showed more uniform and smaller grains with more inclusion of the a-axis component along the film normal than the maps of x = 0.5 and 1. Since spontaneous polarization of C_xS_1⁻xBT is expected to exist along the a-axis, inclusion of the film normal a-axis component is necessary to obtain polarization versus electric field (P⁻E) hysteresis curves of the C_xS_1⁻xBT when the E is applied across the film. Since memory windows of FeFETs originate from P⁻E hysteresis curves, the EBSD results were consistent with the electrical performance of the FeFETs, where the FeFETs with x = 0, 0.1, and 0.2 had wider memory windows than those with x = 0.5 and 1. The influence of annealing temperature for C_0.1S_0.9BT poly-crystallization was also investigated using the EBSD method.