Frustration of Negative Capacitance in Al(2)O(3)/BaTiO(3) Bilayer Structure

Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO(3)/BaTiO(3) system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al(2)O(3)/150 nm-thick BaTiO(3) system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al(2)O(3)/epitaxial-BaTiO(3) system showed a typical FE-like hysteresis loop in the polarization – voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al(2)O(3) layer when the BaTiO(3) layer played a role as the NC layer. Therefore, the NC effect in the Al(2)O(3)/BaTiO(3) system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO(3) during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization.