Investigation of Ferroelectric Grain Sizes and Orientations in Pt/CaxSr1⁻xBi₂Ta₂O₉/Hf⁻Al⁻O/Si High Performance Ferroelectric-Gate Field-Effect-Transistors.

Abstract

Electron backscatter diffraction (EBSD) was applied to investigate the grain size and orientation of polycrystalline CaxSr1–xBi2Ta2O9 (CxS1–xBT) films in ferroelectric-gate field-effect transistors (FeFETs). The CxS1–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 CxS1–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 CxS1–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 C0.1S0.9BT poly-crystallization was also investigated using the EBSD method.