Oxygen Vacancy Engineering for Enhanced Remanent Polarization and Memory Window in a-IGZO/HZO Ferroelectric Field-Effect Transistors.

HfO2-derived ferroelectric field-effect transistors (FeFETs) are promising for nonvolatile memory and logic-in-memory applications owing to CMOS compatibility and low-voltage polarization switching. Amorphous InGaZnO (a-IGZO) is attractive for back-end-of-line compatible FeFETs, but inverted bottom-gate devices suffer from incomplete switching under negative gate bias, especially in the nonoverlap metal/ferroelectric/semiconductor (MFS) region where depleted a-IGZO becomes effectively floating and weakens voltage coupling across HfZrOx (HZO). Here, we demonstrate oxygen vacancy (VO)-mediated activation of negative-bias switching in a-IGZO FeFETs. The oxygen-deficient state of the bottom a-IGZO layer was controlled by sputtering oxygen flow ratio and rapid thermal annealing oxygen partial pressure. Depth-profile X-ray photoelectron spectroscopy confirms VO modulation near the a-IGZO/HZO interface. Positive-up-negative-down measurements and area-engineered capacitor test element groups show that VO-rich a-IGZO enhances reversible MFS switching by supplying compensating positive charge under depletion, thereby enlarging the memory window and improving switching behavior. This approach directly mitigates geometry-induced switching loss in practical oxide-semiconductor FeFET architecture.