We demonstrated a novel Ferroelectric Field-Effect Transistor (FeFET) with an IGZO channel, featuring a record-high memory window (MW) of up to 17.8V. A significant advancement is achieved by two strategies. Firstly, the introduction of an intermediate oxygen-deficient channel, which offers sufficient depletion charge to ensure full-loop polarization switching. Secondly, inserting a thin gate interlayer (G.IL), which further increases the MW by the contribution of injected charge through G.IL. With a sub-12nm gate stack thickness and an operation voltage below 15V, the device exhibits promising potential for high-density, low-power non-volatile memory applications.