On the Importance of the Work Function and Electron Carrier Density of Oxide Electrodes for the Functional Properties of Ferroelectric Capacitors

Abstract

It is important to understand the effect of the interfaces between the oxide electrode layers and the ferroelectric layer on the polarization response for optimizing the device performance of all‐oxide ferroelectric devices. Herein, the effects of the oxide La0.07Ba0.93SnO3 (LBSO) as an electrode material in an PbZr0.52Ti0.48O3 (PZT) ferroelectric capacitor are compared with those of the more commonly used SrRuO3 (SRO) electrode. SRO (top)/PZT/SRO (bottom), SRO/PZT/LBSO, and SRO/PZT/2 nm SRO/LBSO devices are fabricated. Only marginal differences in crystalline properties, determined by X‐ray diffraction and scanning transmission electron microscopy, are found. High‐quality polarization loops are obtained, but with a much larger coercive field for the SRO/PZT/LBSO device. In contrast to the SRO/PZT/SRO device, the polarization decreases strongly with increasing field cycling. This fatigue problem can be remedied by inserting a 2 nm SRO layer between PZT and LBSO. It is argued that strongly increased charge injection into the PZT occurs at the bottom interface, because of the low PZT/LBSO interfacial barrier and the much lower carrier density in LBSO, as compared with that in SRO, causing a low dielectric constant, depleted layer in LBSO. The charge injection creates a trapped space charge in the PZT, causing the difference in fatigue behavior.

Ferroelectricity Improvement in Ultra‐Thin Hf0.5Zr0.5O2Capacitors by the Insertion of a Ti Interfacial Layer

“…This phenomenon has been already described in the literature for other ferroelectric‐based stacks with different electrodes. [ 32 ] The obtained results show that the presence of the Ti layer clearly increases the value of 2 P r . The highest 2 P r is obtained for Sample 2 and the lowest for Sample 0.…”

Low-temperature grapho-epitaxial La-substituted BiFeO3 on metallic perovskite

“…of BPBO is larger than that of SRO (0.58 kΩ/sq. ), which possibly contribute to an additional source of voltage drop across the capacitor that enhances the coercive fields 42 . This further opens the possibility of tuning the BPBO conductivity through different doping and future aspects of the low-temperature BFO.…”

“…Lower value of polarization in 450 °C BLFO is consistent with the analysis of HAADF-STEM polarization mapping. As explained above, the electrical properties of the electrode may play an important role in deciding the voltage distribution and screening effect across the electrode interfaces 42,47 . In our case, the BPBO has low carrier concentration as well as higher resistivity that potentially serve as an additional voltage drop and impact the switching voltage, however, these parameters (such as electrode conductivity and carrier mobility) can be further improved by tuning the Bi/Pb substitution 48 in BPBO lattice though the epitaxial quality should not compromise at low temperature.…”