Unveiling Cryogenic Performance (4 to 300 K) Towards Ultra-Thin Ferroelectric HZO: Novel Kinetic Barrier Engineering and Underlying Mechanism

We perform comprehensive and in-depth investigation into the cryogenic characteristics of ferroelectric (FE) HZO thin films with varying thicknesses (3/5/7/10 nm) across a broad temperature range (4300 K), assisted by the first-principles calculations as well as extensive material and electrical characterizations. We discover: (1) 3 and 5 nm HZO films exhibit distinct temperature dependence in remnant polarization (P_r) and coercive field (E_c) as compared with 7 and 10 nm ones owning to different phase transition mechanisms. (2) The concentration and location of V_o²⁺ emerge as pivotal factors influencing the trap-assisted-tunneling process, and thereby the temperature-dependent behaviors of P_r and E_c. (3) V_o²⁺ possesses a lower migration energy barrier as compared with V_o, and oxygen vacancy concentration can be engineered through O₃ pulse duration during ALD deposition of HZO. Building upon these insights, we propose and experimentally demonstrated, for the first time, an innovative cryogenic barrier engineering approach for P_r enhancement, particularly valuable for ultra-thin HZO films.