We demonstrate, for the first time, excellent ferroelectricity, and endurance of 4 nm-thick and $65\mathrm{~nm}\times 45\mathrm{~nm}$ size Hf0.5 Zr0.5 O2 (HZO) capacitors with Mo electrodes. We show 1) the crystallization temperature is as low as 400 °C, which is critical for BEOL FeRAM; 2) benefits from thickness scaling, low operation voltage (1.2 V) and high endurance (>10¹⁰ cycles) are achieved; 3) the wake-up effect is further reduced to 20% and the beginning of fatigue is delayed by an order of magnitude by adding a 1 nm CeO2 stressor layer; and 4) direct measurements of ferroelectricity with ultra-high polarization switching $(\sim 108 \mu\mathrm{C}/\mathrm{cm}^{2})$ in devices scaled down to $95\mathrm{~nm}\times 85\mathrm{~nm}$ size. This study advances the understanding of scaling effect in HZO capacitors.