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

Abstract

We re-examine the dominant factors of the memory window (MW) and reliability of HfO2 FeFET using a new technique to extract both spontaneous polarization $(\mathrm{P}_{\mathrm{s}})$ and interface trap charges $(\mathrm{Q}_{\mathrm{t}})$ by one-time current measurement of an FeFET during the memory operation. FeFET characteristics are strongly affected by unstable $\mathrm{Q}_{t}$ (unrelated to ferroelectric) which causes $\mathrm{V}_{\mathrm{th}}$ instability just after programming, and stable $\mathrm{Q}_{1}$ which compensates most of electric(E)- field generated by $\mathrm{P}_{\mathrm{s}}$. Stable $\mathrm{Q}_{\mathrm{t}}$ is coupled to $\mathrm{P}_{\mathrm{s}}$ with constant ratio (~90%), and reduce MW to the value much lower than the coercive voltage $(\mathrm{V}_{\mathrm{c}})$ limitation. Unlike the conventional model, $\mathrm{P}_{\mathrm{s}}$ increase and stabilization are still effective to improve MW and retention, respectively. During cycling, MW is degraded by $\Delta \mathrm{P}_{\mathrm{s}}$ reduction as well as the increase of the compensation ratio $(\Delta \mathrm{Q}_{\mathrm{t}}/\Delta \mathrm{P}_{\mathrm{s}})$ which can be mitigated by suppressing charge injection/ejection via interfacial $\mathrm{SiO}_{2}$.