Re-Examination of Vth Window and Reliability in HfO2 FeFET Based on the Direct Extraction of Spontaneous Polarization and Trap Charge during Memory Operation

We re-examine the dominant factors of the memory window (MW) and reliability of HfO ₂ FeFET using a new technique to extract both spontaneous polarization (Ps) and interface trap charges (Qt) by one-time current measurement of an FeFET during the memory operation. FeFET characteristics are strongly affected by unstable Qt (unrelated to ferroelectric) which causes Vth instability just after programming, and stable Q1 which compensates most of electric(E)- field generated by Ps. Stable Qt is coupled to Ps with constant ratio (~90%), and reduce MW to the value much lower than the coercive voltage (Vc) limitation. Unlike the conventional model, Ps increase and stabilization are still effective to improve MW and retention, respectively. During cycling, MW is degraded by Ps reduction as well as the increase of the compensation ratio (Qt/Ps) which can be mitigated by suppressing charge injection/ejection via interfacial SiO2.