A Comparative Study on the Ferroelectric Performances in Atomic Layer Deposited Hf0.5Zr0.5O2 Thin Films Using Tetrakis(ethylmethylamino) and Tetrakis(dimethylamino) Precursors.

The chemical, physical, and electrical properties of the atomic layer deposited Hf0.5Zr0.5O2 thin films using tetrakis(ethylmethylamino) (TEMA) and tetrakis(dimethylamino) (TDMA) precursors are compared. The ligand of the metal-organic precursors strongly affects the residual C concentration, grain size, and the resulting ferroelectric properties. Depositing Hf0.5Zr0.5O2 films with the TDMA precursors results in lower C concentration and slightly larger grain size. These findings are beneficial to grow more ferroelectric-phase-dominant film, which mitigates its wake-up effect. From the wake-up test of the TDMA-Hf0.5Zr0.5O2 film with a 2.8 MV/cm cycling field, the adverse wake-up effect was well suppressed up to 105 cycles, with a reasonably high double remanent polarization value of ~40 µC/cm2. The film also showed reliable switching up to 109 cycles with the 2.5 MV/cm cycling field without involving the wake-up effect but with the typical fatigue behavior.

Alternative interpretations for decreasing voltage with increasing charge in ferroelectric capacitors.

Recent claim on the direct observation of a negative capacitance (NC) effect from a single layer epitaxial Pb(Zr0.2,Ti0.8)O3 (PZT) thin film was carefully reexamined, and alternative interpretations that can explain the experimental results without invoking the NC effect are provided. Any actual ferroelectric capacitor has an interfacial layer, and experiment always measures the sum of voltages across the interface layer and the ferroelectric layer. The main observation of decreasing ferroelectric capacitor voltage (VF) for increasing ferroelectric capacitor charge (QF), claimed to be the direct evidence for the NC effect, could be alternatively interpreted by either the sudden increase in the positive capacitance of a ferroelectric capacitor or decrease in the voltage across the interfacial layer due to resistance degradation. The experimental time-transient VF and QF could be precisely simulated by these alternative models that fundamentally assumes the reverse domain nucleation and growth. Supplementary experiments using an epitaxial BaTiO3 film supported this claim. This, however, does not necessarily mean that the realization of the NC effect within the ferroelectric layer is impractical under appropriate conditions. Rather, the circuit suggested by Khan et al. may not be useful to observe the NC effect directly.