Antiferroelectric Thin Films Research Articles

Effect of bottom electrodes on polarization switching and energy storage properties in Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films

Abstract Polarization switching and energy storage properties of a series of Pb 0.97 La 0.02 Zr 0.95 Ti 0.05 O 3 (PLZT) thin films deposited on (100)-textured LaNiO 3 (LNO)-buffered Si substrates and (111)-textured Pt/Ti/SiO 2 /Si substrates were investigated. It was revealed that the PLZT films deposited on the (100)-textured LNO-buffered Si substrates prefer the (100) textured structure, while the orientation of the films deposited on the (111)-textured Pt-coated Si substrates is random. With respect to the films on the Pt-coated Si substrates, the (100) textured PLZT films have bigger compressive residual stress, larger electrical polarization, better dielectric properties, and better energy storage performances. For the (100)-orientated PLZT films, the energy density ( W s ) and efficiency ( η ) measured at room temperature are about 15.3 J/cm 3 and 56% respectively. Moreover, the better frequency stability in the range from 20 Hz to 10 kHz, and temperature stability in the range from 25 to 270 °C are demonstrated in the (100)-orientated PLZT films. These results indicate that the PLZT films with LNO bottom electrode could be potential candidate for applications in high energy storage density capacitors.

Giant Negative Electrocaloric Effect in Antiferroelectric La-Doped Pb(ZrTi)O3 Thin Films Near Room Temperature.

Antiferroelectric thin films are demonstrated as a new class of giant electrocaloric materials that exhibit a negative electrocaloric response of about -5 K near room temperature. The giant negative electrocaloric effect may open up a new paradigm for light, compact, reliable, and high-efficiency refrigeration devices.

Polarization fatigue in antiferroelectric (Pb,La)(Zr,Ti)O3 thin films: The role of the effective strength of driving waveform

In this study, a critical parameter termed as “effective electric strength” is developed to depict polarization fatigue in antiferroelectric thin films. Specifically, the effect of pulse width, frequency, and magnitude of driving voltage (or field) on polarization fatigue of antiferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) thin films was investigated in detail. By transforming all the waveforms with different pulse-widths/voltages/frequencies into their effective electric strength, a strong correlation between the effective strength and the degree of polarization fatigue in the PLZT films is revealed. For instance, it was found that appreciable fatigue usually occurs when the effective strength is larger than or equal to the voltage of phase transition from antiferroelectric phase to ferroelectric phase. In addition, it is shown that the films are more prone to fatigue for a lower frequency of the same effective strength. Our findings could be well explained in the framework of the local phase decomposition arising from switching induced charge injection.

Ferroelectricity and antiferroelectricity of doped thin HfO2-based films.

The recent progress in ferroelectricity and antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.

PbZrO3-Based Antiferroelectric Thin Film Capacitors with High Energy Storage Density

A series of 400-nm-thick sandwich structured Pb(1+x)ZrO3/(Pb,Eu)ZrO3/Pb(1+x)ZrO3(PZO/PEZO/PZO) antiferroelectric thin films with different Pb excess content (x) (x=0%, 10%, 20%, and 30%) in the PZO precursors have been successfully deposited on Pt(111)/Ti/SiO2/Si substrates by a sol–gel method. The effects of Pb excess content on the dielectric properties, and energy storage performance of the PZO/PEZO/PZO thin films have been investigated in detail. It is found that all the films show a unique perovskite phase structure. With increasing Pb excess content in the PZO precursors, P-E hysteresis loop changes from slanted to square shape. Meanwhile, a larger antiferroelectric to ferroelectric switching field (EAF) and ferroelectric to antiferroelectric switching field (EFA) are observed in the films with higher Pb excess content. When increasing Pb excess content from 0% to 30%, the energy storage density of the sandwich structured films is remarkably improved from 11.4 to 14.8 J/cm3 at 1000 kV/cm.

Effective driving voltage on polarization fatigue in (Pb,La)(Zr,Ti)O3 antiferroelectric thin films

Polarization fatigue in (Pb0.97La0.02)(Zr0.95Ti0.05)O3 (PLZT) antiferroelectric thin films deposited onto silicon wafers is studied by investigating the effect of the peak/average/root-mean-square cycling voltage through varying the waveform of the electrical excitation. Interestingly, it is found that the fatigue behavior of the film is determined by the root-mean-square voltage of the external driving excitation rather than by the peak or average voltages. Our results can be well explained in the framework of the local phase decomposition model and indicate that the root-mean-square voltage should be considered as the effective driving voltage determining the polarization fatigue in PLZT antiferroelectric films.

Development of High Energy Capacitors Using La-Doped PbZrO3 Anti-Ferroelectric Thin Films

Chemical solution-derived anti-ferroelectric (AFE) thin films for energy storage devices were investigated. In order to evaluate dielectric properties(dielectric constant and loss, leakage current density), anti-ferroelectric properties(energy storage density and loss, energy storage efficiency) of anti-ferroelectric thin films with lanthanum (La) as a dopant, ∼1 μm-thick anti-ferroelectric (PbLa)ZrO3 (PLZO) films as a function of La doping concentration (0 ∼ 6 mol.%) were deposited on Pt/Ti/SiO2/Si substrate. With the increase of La-doping concentration, the energy storage loss was reduced from ∼8.8 J/cm3 to ∼6.6 J/cm3, and the efficiency was increased from ∼59.2% to ∼80.7%. In terms of the lowest leakage current density, the maximum energy storage performance was observed in La 2 mol.% doped PLZO thin film capacitor with the energy storage density ∼16.9 J/cm3, energy loss ∼8.4 J/cm3 and energy storage efficiency ∼66.8% at an applied electric field ∼1 MV/cm with frequency ∼1 kHz at room temperature.

Electric-field tunable electrocaloric effects from phase transition between antiferroelectric and ferroelectric phase

In this letter, orthorhombic Pb(Nb,Zr,Sn,Ti)O3 (PNZST) and tetragonal (Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) thin films were deposited on LaNiO3/Pt(111)/TiO2/SiO2/Si(100) substrates via a sol-gel method. The electrocaloric effect (ECE) of PNZST and PLZST films originated from phase transition between AFE and ferroelectric were studied, based on their pyroelectric results. A large tunable ECE near room temperature was realized in these films under the function of electric field. As the applied electric field increased, the temperature corresponding to the peak of ECE was decreased for the orthorhombic PNZST films, while the temperature was increased for the tetragonal PLZST films. The maximum ECE of 0.040 K · cm/kV in PNZST films and 0.048 K · cm/kV in PLZST films was received at 323 and 305 K, respectively. The results indicated that AFE thin films had the potential for application in tunable cooling devices near room temperature.

Ferroelectric and antiferroelectric properties of Si-doped HfO2 thin films

Ferroelectric and antiferroelectric HfO2 nano-films were prepared by changing silicon doping concentration, and their basic properties conpared in terms of polarization hysteresis, capacitance-voltage and leakage-voltage behavior, as well as the effect of temperature on phase stability. Antiferroelectric thin film exhibits a higher dielectric constant than the ferroelectric film, and is characterized by the double polarization hysteresis loops due to reversible antiferroelectric-ferroelectric phase transition induced during loading and unloading processes of electric field. No antiferroelectric-paraelectric phase transition is observed at measuring temperatures up to 185 ℃. The negative differential resistivity effect observed in leakage measurements is attributed to the contributions from slow response mechanisms like polarization relaxation.

Effect of residual stress on energy storage property in PbZrO3 antiferroelectric thin films with different orientations

The effect of residual stress on energy storage property was investigated for a series of PbZrO3 thin films on SrTiO3 and Si substrates. Compressive or tensile residual stress influences the critical electric field EA for the ferroelectric-to-antiferroelectric phase transition, thus for films with (110)/(101) orientation, energy density W of films on SrTiO3 is 38% larger than films on Si; in contrast, (001)-oriented PbZrO3 films on SrTiO3 show slightly smaller W compared to films on Si. We conclude that the different responses of W to stress are related to the different constrain states in films with different orientations.

W-doping induced antiferroelectric to ferroelectric phase transition in PbZrO3 thin films prepared by chemical solution deposition

We reported on W-doping induced antiferroelectric to ferroelectric phase transition in PbZrO3 (PZO) thin films prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. The phase transition has been studied through polarization-electric field hysteresis loop, capacitance-voltage characteristic, and Raman scattering measurements. Suitable amount W-doping increased the saturated polarization of antiferroelectric W-doped PZO thin films, whereas the ferroelectric W-doped PZO thin films exhibited higher dielectric constant with a high dielectric-bias voltage tunability of about 70%. With increasing W-doping content, the orientation of the thin films changed from preferred (111)Cubic to complete (100)Cubic, due to W-doping-induced lattice distortion, meanwhile the Curie temperature dropped, and dielectric maximum broadened. Our study demonstrates that W-doping is an effective way to tailor the electrical properties of PZO thin films through the induced antiferroelectric-ferroelectric phase transition.

Enhanced polarization switching and energy storage properties of Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films with LaNiO3 oxide top electrodes

Polarization switching and energy storage properties of highly (100) oriented antiferroelectric (AFE) (Pb,La)(Zr,Ti)O3 thin films (≤250 nm) deposited via a sol-gel process with both LaNiO3 and Pt top electrodes were investigated. By using LaNiO3 top electrodes, the energy density as well as energy efficiency can be enhanced by 4.6 J/cm3 and 11%, respectively. Furthermore, the films with LaNiO3 top electrodes are more capable of providing high energy density over a wide temperature regime above room temperature compared to Pt. This work clearly highlights that oxide top electrodes can greatly improve the energy storage performance of antiferroelectric thin film capacitors.

Structure and improved electrical properties of Pr-doped PbZrO3 antiferroelectric thin films with (111) preferential orientation

Pr-doped PbZrO3 antiferroelectric thin films have been fabricated on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. All the thin films with different Pr doping contents crystallized in perovskite phase with strong (111)-preferred orientation. When Pr doping amount was 1 mol%, the thin film exhibited a large saturation polarization of 59.4 μC cm−2, a high energy storage density of 14.2 J cm−3 at about 600 kV cm−1, and a dielectric constant of about 354 at 1 kHz. The high (111) orientation and occupying site of Pr ions were suggested to be responsible for the improved electrical properties of the thin films.

Electromechanical properties and fatigue of antiferroelectric (Pb, La) (Zr, Sn, Ti)O3 thin film cantilevers fabricated by micromachining

Electromechanical cantilevers comprising antiferroelectric (Pb, La) (Zr, Sn, Ti)O3 (PLZST) thin films were fabricated through bulk micro-machining process on silicon wafers, and their electromechanical properties including strain-fatigue behaviors of the antiferroelectric thin film cantilevers were investigated. The antiferroelectric cantilevers showed the distinct digital actuation characteristics with the strain generated due to the antiferroelectric–ferroelectric transformation. The maximum displacement per unit voltage around the phase switching field reached 16.7μm/V, significantly larger than the typical piezoelectric cantilevers. Moreover, the antiferroelectric PLZST cantilevers exhibited superior strain-fatigue resistance compared to the similar piezoelectric microstructures. These results show the promising future of antiferroelectric materials in micro electromechanical systems.

Effect of Nb doping on preferential orientation, phase transformation behavior and electrical properties of PbZrO3 thin films

Undoped and Nb-doped (1, 3, 5, 7 and 9mol%) PbZrO3 antiferroelectric thin films were deposited on Pt(111)/Ti/SiO2/Si substrates by using a sol–gel method. All the thin films had a perovskite phase structure and exhibited a distinct preferential orientation, phase transformation behavior and electrical properties, due to the effect of Nb doping. On the extent of Nb dopant, orientation of the films was changed from (100) to (111) gradually. Meanwhile, with increasing Nb content, a gradual change from AFE to ferroelectric at room temperature was observed. Dielectric constant as a function of Nb content was also reported. The dielectric constant increased with Nb content up to 7mol% and then decreased at 9mol% Nb. Dielectric loss remained quite low (less than 0.05) in the whole frequency or voltage ranges.

Electrical and Energy Storage Performance of Eu‐Doped PbZrO3 Thin Films with Different Gradient Sequences

The Eu‐doped compositionally graded multilayer PbZrO3 antiferroelectric thin films have been deposited on Pt(111)/Ti/SiO2/Si substrates by a sol–gel method. The effect of gradient sequence on microstructure, electrical properties, and energy storage performance has been investigated in detail. X‐ray diffraction patterns confirm that both thin films have crystallized into a unique perovskite phase. Down‐graded thin films have bigger grain sizes than up‐graded films, which is attributed to the influence of the gradient sequence of the thin films layer. The dielectric constant of down‐graded films is found to be higher than that of up‐graded films. Compared with up‐graded thin films, the energy storage density of down‐graded films is enhanced due to double hysteresis loop with small hysteresis switch, and high polarization.

Effect of Eu Doping on the Electrical Properties and Energy Storage Performance of PbZrO3 Antiferroelectric Thin Films

Undoped and Eu‐doped (1, 3 and 5 mol%) PbZrO3 (PZ) antiferroelectric (AFE) thin films have been deposited on Pt (111)/Ti/SiO2/Si substrates by a sol–gel method. The effect of Eu doping on phase transformation and energy storage performance of PZ thin films have been investigated in detail. It has been seen that on extent of Eu dopant the Curie temperature and electric field‐induced phase transformation can be altered. The energy storage properties have been found to be strongly dependent on Eu doping content. With the increase of Eu contents, recoverable energy storage density has been enhanced followed by their subsequent reduction. A maximum energy density (~18.8 J/cm3 at ~900 kV/cm) and minimum energy loss (~7.3 J/cm3) have been achieved on 3 mol% Eu‐doped PZ thin films.

Nonlinear dielectric thin films for high-power electric storage with energy density comparable with electrochemical supercapacitors

Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb(0.97)La(0.02))(Zr(0.90)Sn(0.05)Ti(0.05))O(3) (PLZST) antiferroelectric ceramic thin films, Pb(Zn(1/3)Nb(2/3))O(3-)Pb(Mg(1/3)Nb(2/3))O(3-)PbTiO(3) (PZN-PMN-PT) relaxor ferroelectric ceramic thin films, and poly(vinylidene fluoride) (PVDF)-based polymer blend thin films. The results showed that these thin film materials are promising for electric storage with outstandingly high power density and fairly high energy density, comparable with electrochemical supercapacitors.

Phase Transformation Properties of Highly (100)‐Oriented PLZST 2/85/12/3 Antiferroelectric Thin Films Deposited on Nb–SrTiO3 Single‐Crystal Substrates

In this work, (Pb0.97La0.02)(Zr0.85Sn0.12Ti0.03)O3 (PLZST 2/85/12/3) antiferroelectric (AFE) thin films with a thickness of ~700 nm were successfully fabricated on (100)‐oriented Nb–SrTiO3 single crystal via a sol–gel technique. X‐ray diffraction and scanning electron microscopy results showed that the obtained AFE films had a highly (100)‐preferred orientation and displayed a uniform surface microstructure. Electrical measurements, such as P–E loops, the electric‐field, and temperature‐dependent dielectric properties, demonstrated a mixture of AFE and FE phases in PLZST 2/85/12/3 films deposited on Nb–SrTiO3 substrates.

Dielectric Properties of Pb&lt;sub&gt;0.97&lt;/sub&gt;La&lt;sub&gt;0.02&lt;/sub&gt;Zr&lt;sub&gt;0.95&lt;/sub&gt;Ti&lt;sub&gt;0.05&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Antiferroelectric Thin Films Prepared at Different Annealing Temperatures

Pb0.97La0.02Zr0.95Ti0.05O3 (PLZT) antiferroelectric thin films were prepared on Pt (111)/ Ti/SiO2/Si (100) substrates by a sol-gel process. The influences of annealing temperature on the structures and dielectric properties of the PLZT antiferroelectric thin films were investigated. And the phase structure and crystal orientation were studied by X-ray diffraction analyses (XRD). The antiferroelectric characterization of the PLZT thin films annealed at different temperature was demonstrated by P(polarization)-E(electric field) and C(capactitance)-E(electric field) curves. The maximum polarizations for the films annealed at 650°C, 700°C and 750°C were 35μC/cm2, 42μC/cm2 and 47μC/cm2, respectively. The temperature dependent of the dielectric constant and loss was measured under the frequency 1, 10, 100 and 1000 kHz. The films annealed at 700°C have high (100)-preferred orientation and excellent dielectric properties.