Investigation of ferroelectric grain sizes and orientations in Pt/Ca x Sr 1-x Bi 2 Ta 2 O 9 /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 Ca x Sr 1-x Bi 2 Ta 2 O 9 (C x S 1-x BT) films in ferroelectric-gate field-effect transistors (FeFETs). The C x S 1-x BT 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 x S 1-x BT 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 x S 1-x BT 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 0.1 S 0.9 BT poly-crystallization was also investigated using the EBSD method.