The cylindrical devices with tunable positive, infinite, and negative capacitance for dynamic random access memory

Due to a stray field formation from the alternating ferroelectric bound charges of the multidomain state of the ferroelectric thin films, the negative capacitance effect can emerge in the ferroelectric/dielectric bilayer devices. However, the capacitance behavior of the thin ferroelectric/dielectric stacked films in the nanoscale cylindrical structure deviated from the negative capacitance state to unpredicted other states. This work confirmed that the thin (2.0 - 3.0 nm) ferroelectric Hf_0.33Zr_0.67O₂ layer could have a positive capacitance, infinite capacitance, or negative capacitance by controlling the thickness of the stacked dielectric Al₂O₃ layer thickness (1.0 - 3.0 nm). A detailed analytical model and numerical simulation based on phase-field modeling, considering the ferroelectric polarization bound charge compensation by the injected/trapped interfacial carriers and the geometry effect of the cylinder, precisely identified the change of the inhomogeneous stray field energy, which played a crucial role in determining the capacitance state. Further analysis of the models revealed that the capacitance variation is strongly correlated to the extent of the initial polarization charge compensation of the ferroelectric domains and leakage mechanisms. This work provides guidelines for developing the next-generation capacitors in dynamic random access memory.