Transient Negative Capacitance Effect in Atomic‐Layer‐Deposited Al₂O₃/Hf_0.3Zr_0.7O₂ Bilayer Thin Film

Abstract The negative capacitance (NC) effect is now attracting a great deal of attention in work towards low‐power operation of field effect transistors and extremely large capacitance density in dynamic random access memory. However, to date, observation of the NC effect in dielectric/ferroelectric bilayer capacitors has been limited to the use of epitaxial ferroelectric thin films based on perovskite crystal structures, such as Pb(Zr,Ti)O₃ and BaTiO₃, which is not compatible with current complementary metal oxide semiconductor technology. This work, therefore, reports on the transient NC effect in amorphous‐Al₂O₃/polycrystalline‐Hf_0.3Zr_0.7O₂ bilayer systems prepared using atomic layer deposition. The thin film processing conditions are carefully tuned to achieve the appropriate ferroelectric performances that are a prerequisite for the examination of the transient NC effect. Capacitance enhancement is observed in a wide voltage range in 5–10 nm thick Al₂O₃/Hf_0.3Zr_0.7O₂ bilayer thin films. It is found that the capacitance of the dielectric layer plays a critical role in the determination of additional charge density induced by the NC effect. In addition, inhibition of the leakage current is important for stabilization of nonhysteretic charge–discharge behavior of the bilayers. The mean‐field approximation combined with classical Landau formalism precisely reproduces the experimental results.