Enhanced Ferroelectricity Achieved in Sub-6-nm Hf 0.5 Zr 0.5 O 2 Films by Using WO x Inserted W Electrodes

HfO₂-based ferroelectric thin films have attracted a deal of interest due to its potential in industry. However, achieving high performance in sub-6-nm films is challenging due to pronounced interface effects. This work demonstrates that WO_x inserted in W bottom electrode can effectively suppress the “dead layer”, and subsequently reduce the oxygen vacancies in Hf_0.5Zr_0.5O₂ (HZO) film without sacrificing the required stress and surface energy for high proportion of ferroelectric phase. The optimized 5-nm-thick HZO film exhibits a 20.9% increase in 2P_r (51.4 μ C/cm² under 2.0 V), a 22.3% reduction in 2E_c and a over 40% decrease in leakage current. Furthermore, excellent endurance characteristics (no significant P_r degradation over 10⁹ cycles under ±2.5-4.0 MV/cm @100 kHz) and film uniformity (yield > 95%) are achieved. This approach is expected to be effective for 4 nm and 3 nm HZO ferroelectric thin films, offering valuable insights for the scaling of high-performance ferroelectric devices.