Revealing the effect of the Schottky barrier on the energy storage performance of ferroelectric multilayers

Different from most of the studies on dielectric energy storage thin films, which mainly talk about domain engineering or interface engineering, our work revealed the effect of the interaction between film and bottom electrode on the energy storage performance of ferroelectric multilayers by fabricating multilayers of BaTiO3 (BT) and SiO2-BaZr0.2Ti0.8O3 (S-BZT) with different layer sequences. With the same periodic number, the multilayers start with the S-BZT layer always have higher voltage endurance, and thus higher energy storage capacity(Wrec), than the multilayers start with BT. The highest Wrec was finally obtained to be 39.37 J/cm3 in BT/S-BZT//(2PN). Such a phenomenon was revealed to be related to the Schottky barrier, which was thought to be caused by the formation of the 2Ti3+-VO. dipoles, in the interface between the LSMO and the S-BZT. Such an assumption was finally proved by the combination of the I-E curves and the C-E curves, and the finite element simulation was also carried out to simulate the electric breakdown process. The result of the simulation fit very well with the experimental result. The reliability and power density of BT/S-BZT//(2PN) are also good. After all, our work opens up a new way to improve the energy storage capacity of dielectric thin films. In addition, the reliability and charge-discharge behavior of the BT/S-BZT//(2PN) is also in good performance.</p

Toward Design Rules for Multilayer Ferroelectric Energy Storage Capacitors – A Study Based on Lead-Free and Relaxor-Ferroelectric/Paraelectric Multilayer Devices

Future pulsed-power electronic systems based on dielectric capacitors require the use of environment-friendly materials with high energy-storage performance that can operate efficiently and reliably in harsh environments. Here, a study of multilayer structures, combining paraelectric-like Ba0.6Sr0.4TiO3 (BST) with relaxor-ferroelectric BaZr0.4Ti0.6O3 (BZT) layers on SrTiO3-buffered Si substrates, with the goal to optimize the high energy-storage performance is presented. The energy-storage properties of various stackings are investigated and an extremely large maximum recoverable energy storage density of ≈165.6 J cm−3 (energy efficiency ≈ 93%) is achieved for unipolar charging–discharging of a 25-nm-BZT/20-nm-BST/910-nm-BZT/20-nm-BST/25-nm-BZT multilayer structure, due to the extremely large breakdown field of 7.5 MV cm−1 and the lack of polarization saturation at high fields in this device. Strong indications are found that the breakdown field of the devices is determined by the outer layers of the multilayer stack and can be increased by improving the quality of these layers. Authors are also able to deduce design optimization rules for this material combination, which can be to a large extend justify by structural analysis. These rules are expected also to be useful for optimizing other multilayer systems and are therefore very relevant for further increasing the energy storage density of capacitors.</p

Epitaxial growth of full range of compositions of (1 1 1) PbZr_1- _xTi_xO₃ on GaN

Integrating functional complex oxides with conventional (“non-oxide”) semiconductors emerges to be an important research field and has been attracting great interest. Because of their superior intrinsic material properties, such as a relatively high dielectric constant and polarization, the utilization of PbZr1- xTixO3 (PZT) materials as a dielectric layer is expected to greatly improve the performance of the GaN high electron mobility transistor. The functional PbZr1- xTixO3 exhibits quite different crystal structures and consequently physical properties depending on the composition. In this work we report the growth of full range of compositions of PZT films on MgO buffered GaN substrates. Besides revealing the temperature effect on phase formation and surface morphology, we demonstrated the strong effect of composition on the growth: pure (1 1 1) phase is formed in Ti-rich PZT (x &gt; 0.48) while pyrochlore impurity phase is found in Zr-rich PZT (x &lt; 0.48). By introducing an ultrathin Ti-rich PZT seed layer, we are able to achieve epitaxial growth of Zr-rich PZT. The epitaxial PZT films of different composition all exhibit good ferroelectric properties, showing great promise for future GaN device applications.</p

Epitaxial ferroelectric oxides on silicon with perspectives for future device applications

Functional oxides on silicon have been the subject of in-depth research for more than 20 years. Much of this research has been focused on the quality of the integration of materials due to their intrinsic thermodynamic incompatibility, which has hindered the flourishing of the field of research. Nevertheless, growth of epitaxial transition metal oxides on silicon with a sharp interface has been achieved by elaborated kinetically controlled sequential deposition while the crystalline quality of different functional oxides has been considerably improved. In this Research Update, we focus on three applications in which epitaxial ferroelectric oxides on silicon are at the forefront, and in each of these applications, other aspects of the integration of materials play an important role. These are the fields of piezoelectric microelectromechanical system devices, electro-optical components, and catalysis. The overview is supported by a brief analysis of the synthesis processes that enable epitaxial growth of oxides on silicon. This Research Update concludes with a theoretical description of the interfaces and the possibility of manipulating their electronic structure to achieve the desired coupling between (ferroelectric) oxides and semiconductors, which opens up a remarkable perspective for many advanced applications. © 2021 Author(s)

Large piezoelectric strain with ultra-low strain hysteresis in highly c-axis oriented Pb(Zr0.52Ti0.48)O3 films with columnar growth on amorphous glass substrates

Abstract Thin films of PbZr0.52Ti0.48O3 (PZT) with largely detached columnar grains, deposited by pulsed laser deposition (PLD) on amorphous glass substrates covered with Ca2Nb3O10 nanosheets as growth template and using LaNiO3 electrode layers, are shown to exhibit very high unipolar piezoelectric strain and ultra-low strain hysteresis. The observed increase of the piezoelectric coefficient with increasing film thickness is attributed to the reduction of clamping, because of the increasingly less dense columnar microstructure (more separation between the grains) with across the film thickness. A very large piezoelectric coefficient (490 pm/V) and a high piezoelectric strain (~0.9%) are obtained in 4-µm-thick film under an applied electric field of 200 kV/cm, which is several times larger than in usual PZT ceramics. Further very low strain hysteresis (H≈2–4%) is observed in 4 to 5 µm thick films. These belong to the best values demonstrated so far in piezoelectric films. Fatigue testing shows that the piezoelectric properties are stable up to 1010 cycles. The growth of high quality PZT films with very large strain and piezoelectric coefficients, very low hysteresis and with long-term stability on a technologically important substrate as glass is of great significance for the development of practical piezo driven microelectromechanical actuator systems

Energy Storage Performance and Electric Breakdown Field of Thin Relaxor Ferroelectric PLZT Films Using Microstructure and Growth Orientation Control

Thin relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films were deposited on Si substrates using Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) nanosheets as the growth template layer and SrRuO3 (SRO) as the base electrode layer, using pulsed laser deposition. XRD and cross-sectional SEM results show that the structure of the PLZT layers changes from very dense with (001)-orientation to columnar with (110)-orientation for CNOns and TiOns, respectively. The recoverable energy-storage density (Ureco) is nearly proportional to the critical electric breakdown field (EBD), which increases with PLZT film thickness. A very high Ureco value of 58.4 J cm-3 and energy-storage efficiency (η) of 81.2% were obtained at an EBD of 3400 kV cm-1 for the 1000 nm thick PLZT film on CNOns/Si, significantly higher than for the film on TiOns/Si (Ureco = 44.0 J cm-3 and η = 59.6% for EBD = 2800 kV cm-1). This excellent energy storage performance in the PLZT/SRO/CNOns/Si is due to the dense film structure and nearly hysteresis-free relaxor behavior. These results are important for improving the performance of relaxor-ferroelectric thin films for high-power capacitor applications

Effect of a thin (doped) PZT interfacial layer on the properties of epitaxial PMN-PT films

Pure perovskite phase, (001)-oriented, epitaxial thin films of (Pb(Mg1/3Nb2/3)O3)0.67-(PbTiO3)0.33 (PMN-PT) were fabricated on single crystal, (001)-oriented SrTiO3 substrates using a hard (Fe-doped) and soft doped (Nb-doped) PZT(52/48) interfacial layer. The effect of different interface layers on the structural and ferroelectric properties of the PMN-PT films was investigated in detail. A significant self-bias voltage in the PMN-PT films can be introduced by using an appropriate interfacial layer. There are significant differences in polarization for different types of doped and undoped interface layers and a doubling of the relative dielectric constant was observed for the Nb-doped interfacial layer. Device properties remain stable up to at least 108 cycles

Effect of fabrication conditions on phase formation and properties of epitaxial (PbMg1/3Nb2/3O3)0.67-(PbTiO3)0.33 thin films on (001) SrTiO3

The pulsed laser deposition process of 300nm thick films of Pb(Mg1/3Nb2/3)O3)0.67-(PbTiO3)0.33 on (001)-oriented SrTiO3 was studied by varying deposition pressure, substrate deposition temperature, laser fluence on the target and target-substrate distance. Perovskite phase pure, (001)-oriented, epitaxial smooth films were obtained in a narrow range of deposition parameters. The ferroelectric and dielectric properties of films fabricated within this parameter range still vary significantly. This shows the sensitivity of the system for growth conditions. The best film has a polarization value close to that expected for a (001) poled, stress free single crystal film. All films show deposition conditions dependent variations in the self-bias field. The self-bias is very stable during long cycling for films made at optimum deposition conditions. The piezoelectric coefficients of the films are strongly reduced with respect to bulk single crystal values due to the film clamping. The properties variations are ascribed to changes in the grain boundary properties in which film defects are expected to accumulate. Notably slight off-stoichiometry may cause localized screening charges, affecting specifically the polarization and dielectric constant