Gate Engineering Effect in Ferroelectric Field‐Effect Transistors with Al‐Doped HfO2 Thin Film and Amorphous Indium‐Gallium‐Zinc‐Oxide Channel

Abstract This work investigates the mechanism for the memory window (MW) suppression of the ferroelectric‐thin film transistors (FETFTs) with an amorphous indium‐gallium‐zinc ( a ‐IGZO) channel. a ‐IGZO generally has an n‐type character with a high bandgap (>3 eV) and a high density of gap states, hindering the carrier type inversion. Therefore, the negative ferroelectric (FE) bound charges at the FE layer/ a ‐IGZO interface must be compensated by the positive charges of the oxygen vacancy in the a ‐IGZO layer. In contrast, accumulated electrons can compensate for the positive FE‐bound charges. Such a bound charge compensation mechanism complicates the FETFT operation and precise understanding. Experiments and simulations confirm that feasible FE switching in the bottom‐TiN or P ++ ‐Si/Al‐doped HfO 2 / a ‐IGZO/top‐TiN structure can occur only when the countercharges in the a ‐IGZO layer compensate the positive and negative bound charges. More importantly, the Al‐doped HfO 2 / a ‐IGZO interface generally involves electron trapping, which hinders FE switching and achieving a MW for the TiN gate case. When replacing the TiN gate with the P ++ ‐Si gate, the suppressed FE polarization by the depolarization effect from the SiO 2 interface layer can mitigate electron accumulation. Consequently, the P ++ ‐Si bottom electrode (BE) is more advantageous than the TiN BE regarding a MW of FETFT.