Transient Negative Capacitance Effect in Atomic-Layer-Deposited Al2O3 /Hf0.3 Zr0.7O2 Bilayer Thin Film

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)O-3 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-Hf0.3Zr0.7O2 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/Hf0.3Zr0.7O2 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.