Quantifying Endurance-Driven Loss of Polarization-to-Channel Charge Coupling in HfO2-Based Ferroelectric Field-Effect Transistors

Hafnium-oxide (HfO2)-based ferroelectric field-effect transistors are promising for nonvolatile memory and in-memory computing; however, endurance degradation remains difficult to quantify because polarization switching and charge trapping simultaneously influence the threshold voltage. Here, we combine transfer characteristics, switching-current-derived polarization, capacitance–voltage measurements, and physics-based modeling to evaluate pulse-width-dependent operation and cycling degradation in metal–ferroelectric–insulator–semiconductor FeFETs. Nearly symmetric polarization reversal produces strongly asymmetric low- and high-threshold-voltage evolution, consistent with polarity-dependent trapping and detrapping. We extract the apparent channel-coupled charge density using the measured MFIS capacitance and define an apparent polarization-to-channel coupling factor by comparison with the ferroelectric switching charge. Endurance cycling reduces the channel-coupled charge density from 0.71 to 0.09 μC cm–2 after 104 cycles, while substantial polarization remains. The coupling factor correspondingly decreases from approximately 3.5 to 0.9%, indicating that memory-window collapse is primarily associated with trap-assisted screening and loss of effective channel coupling. This operational metric distinguishes retained polarization from its diminishing transistor-level effectiveness.