Thickness scaling of FeFETs with Hf0.5Zr0.5O2 (HZO) from 11 down to $4.6\mathrm{~nm}$ is systematically studied in this work in terms of the memory characteristics and the memory window (MW) narrowing mechanism. The HZO thickness scaling leads to low-voltage operation, higher $I_{\text{on}}/I_{\text{off}}$ ratio, lower S.S., and better endurance. It is also found, for the first time, that with reducing cycling voltage the dominant narrowing mechanism changes from MOS interface degradation to ferroelectric fatigue, which can be recovered by a high-voltage pulse. Based on this finding, we propose and demonstrate a method to improve endurance by utilizing this recovery, which is more effective in thinner HZO FeFETs.