PLZT Thin Films Research Articles

EFFECT OF OPERATING TEMPERATURE ON THE PERFORMANCE OF RELAXOR-FERROELECTRIC PLZT FILMS-BASED POWER ENERGY-STORAGE DEVICES

Thermal stability is a key factor to determine the applicability of dielectric capacitors in the power energy-storage devices. The effects of operating temperature on the polarization hysteresis, energy-storage performance, and charge-discharge cycling stability of thin-film capacitors have been revealed in this study by investigating the relaxor Pb0.92La0.08(Zr0.52Ti0.48)O3 (PLZT) thin film grown on Pt/Ti/SiO2/Si substrates using a sol-gel spin-coating technique. The PLZT thin films demonstrate good thermal stability of polarization hysteresis and outstanding energy storage properties over a wide temperature range from room temperature to 150C. With increasing operating temperature up to 200C, the polarization hysteresis loops gradually become more slanted and slightly broaden. The fluctuation in recoverable energy density is less than 8%, and the change of energy-storage efficiency is less than 12% at 200C, which may be associated with the high dynamic polar nanoregions (PNRs) in relaxor ferroelectrics. At room temperature, PLZT thin film shows an excellent charge-discharge cycling life with fatigue-free performance after 1010 cycles in both discharge energy-storage density and energy-storage efficiency. However, the reduction of discharge energy-storage density and energy-storage efficiency, performed at an operating temperature of 200C, is about 18% after 1010 charge-discharge cycles. All these results suggest that such PLZT thin film capacitors are very attractive for energy-storage applications operating under high-temperature conditions.

Comparative studies of relaxor-ferroelectric Pb0.92La0.08(Zr0.52Ti0.48)O3 thin films deposited by pulsed laser deposition and sol-gel spin coating

In this study, the energy storage properties of relaxor Pb0.92La0.08(Zr0.52Ti0.48)O3 (PLZT) thin films grown on Pt/Si substrates using pulsed laser deposition (PLD) and sol-gel methods were investigated. The PLZT thin films deposited by PLD possessed a columnar growth microstructure and mixed orientations of (100) and (110) while a dense microstructure and preferred orientation of (100) were achieved by sol-gel deposition. Although the electric breakdown strength (EBD) of the sol-gel-deposited PLZT thin films (EBD=2200 kV/cm) was slightly higher than that of the films deposited using PLD (EBD=2100 kV/cm), the PLD-deposited PLZT thin films had a larger recoverable energy storage density (Ureco) and energy storage efficiency (η), which can be explained by its slimmer polarization loop, higher maximum polarization, and lower remanent polarization. At corresponding EBD values, the Ureco and η values were 33.2 J/cm3 and 67.5% for the PLD-deposited films and 27.5 J/cm3 and 62.2% for the sol-gel-deposited films. Although the sol-gel-deposited PLZT thin films had lower energy storage performance, the sol-gel method remains a promising method for the fabrication of thin films for dielectric energy storage applications due to its unique advantages of low fabrication cost, simple preparation process, and easy control of chemical composition.

Energy storage behavior in flexible antiferroelectric (Pb0.98,La0.02)(Zr0.95,Ti0.05)O3 thin film capacitors prepared via a direct epitaxial lift-off method

Flexible antiferroelectric (AFE) thin film capacitors are important for foldable and wearable electronics. This work demonstrates a direct epitaxial lift-off method to fabricate flexible epitaxial AFE thin film capacitors using (Pb0.98,La0.02)(Zr0.95,Ti0.05)O3 (PLZT) as an example. The flexible PLZT thin film showed the tetragonal structure with coexisting ferroelectricity and antiferroelectricity. An energy storage density (ESD) of 2.6 J/cm3 with an efficiency of 73% was obtained at the low electric field, and a high ESD of 22 J/cm3 with an efficiency of 33% was achieved at the high electric field. Such energy storage performances could be maintained after 103 bending cycles and 105 charging/discharging cycles. This simple method can be used to compose flexible epitaxial thin film capacitors and even other flexible thin film devices.

Depolarization electric field and poling voltage‐modulated Pb,La(Zr,Ti)O3‐based self‐powered ultraviolet photodetectors

AbstractTraditional self‐powered ultraviolet photodetectors, which are usually designed based on p‐n junction interfacial effects, exhibit low responsivity and specific detectivity because the photogenerated electrons and holes cannot be separated effectively. Unlike wide band‐gap semiconductor materials, ferroelectrics have large remnant polarization and thus high depolarization electric field throughout the whole bulk region, which can cause effective separation of photogenerated electrons and holes. Based on this, in this study, we prepare Pb0.93La0.07(Zr1‐xTix)0.9825O3 (PLZT) ferroelectric thin films with large remnant polarization and self‐powered ultraviolet photodetectors with Au/PLZT/FTO structure. The results indicate that the photoelectric response performances of the detectors improve as the remnant polarization of the PLZT thin film and positive poling voltage increase. By adjusting the Ti content, due to large remnant polarization of 47.4 μC/cm2 in the PLZT thin films with 80 mol% Ti, the corresponding photodetector exhibits the best self‐powered ultraviolet photoelectric response with the high photo/dark current ratio of 2600, responsivity of 2.05 mA/W, specific detectivity of 5.45 × 1010 Jones, and fast response speed (rise time of 18 ms). These values are superior to those of recently reported self‐powered ultraviolet photodetectors.

Large Quadratic Electro-Optic Effect of the PLZT Thin Films for Optical Communication Integrated Devices

Developing large electro-optic (EO) effect material is crucial technology for developing current levels of optical communication, and the lanthanum-modified lead zirconate titanate (PLZT) transpare...

Self-driven ultraviolet photodetectors based on ferroelectric depolarization field and interfacial potential

Self-powered ultraviolet photodetectors have attracted considerable interest for their reduced sizes and high portability which makes them possible for application in a hazardous environment. In this work, Pb0.95La0.05Zr0.54Ti0.46O3 (PLZT) thin films with a wide bandgap of ∼3.72 eV and large remanent polarization of ∼33.9 μC/cm2 were synthesized by low-cost sol-gel method, based on which, highly sensitive self-powered ultraviolet (UV) photodetectors with a Au/PLZT/FTO structure were developed. It’s found that the responsivity of the devices can be modulated by changing the direction of polarization in the PLZT thin film owing to coupling effects of the depolarization electric field with interfacial barriers at both Au/PLZT and PLZT/FTO contacts. The devices with PLZT in downward polarization state show a remarkable responsivity of 0.011 mA/W at zero bias to illumination of 340 nm-light with fast-response rise time of 98 ms and decay time of 96 ms. The present work sheds light on the design of self-driven photodetectors free of the p-n junction on the basis of ferroelectric oxides.

Comparative study of piezoelectric response and energy-storage performance in normal ferroelectric, antiferroelectric and relaxor-ferroelectric thin films

The energy-storage performance and piezoelectric properties were determined for epitaxial antiferroelectric (AFE) PbZrO3 (PZ), ferroelectric (FE) PbZr0.52Ti0.48O3 (PZT), and relaxor ferroelectric (RFE) Pb0.9La0.1Zr0.52Ti0.48O3 (PLZT) thin films that were deposited on to SrTiO3 buffered Si substrates. The films were investigated by directly measuring the polarization hysteresis loops and piezoelectric strain curves. The square polarization loop with a high remanent polarization and a large piezoelectric coefficient obtained in PZT thin films allow them to be useful for various applications in ferroelectric field effect transistors and/or in MEMS actuators. Meanwhile, there is a jump of about 0.9% in the strain curve of PZ thin films around the field-induced AFE-FE phase transition, which is useful in digital displacement transducers due to a good ON/OFF strain state. The large recoverable energy-storage density, excellent energy-storage efficiency, and low strain hysteresis due to a slim hysteresis loop combine to make PLZT thin films as a potential candidate for a broad range of applications from energy storage to nano-positioning precision systems.

Improvement in piezoelectric properties of PLZT thin film with large cation doping at A-site

This paper reports improved piezoelectric properties of PLZT, designed by partially substituting larger trivalent cation (Bi3+) in place of La3+. For the present investigation, stoichiometric compositions of Pb0.92(La1-yBiy)0.08(Zr0.52Ti0.48)O3 (PLBZT) with y = 0.0, 0.3, 0.5 and 0.7 were prepared by chemical solution deposition method. The XRD results and Raman spectroscopy studies reveal the change in crystal structure with an increase in distortion of the tetragonal unit cell with Bi3+ concentrations. The FESEM study shows a distinct change in the microstructure of PLZT with increasing Bi3+ concentrations. The P-E hysteresis study on all the Bi3+ doped PLZT films give slimmer hysteresis loop, relatively low coercive field (20 kV/cm) and higher switching current (0.5 mA). The polarization fatigue property of PLZT film is improved with Bi3+ doping. The enhanced piezoelectric displacement in Bi3+ doped PLZT yielded almost 3 times higher d33 values than PLZT film at y = 0.5. The substantial enhancement in piezoelectric properties of PLBZT is correlated with the intrinsic contribution of the material that arises from crystal structure and extrinsic contribution that comes from the externally triggered domain wall movement.

Impact of fatigue behavior on energy storage performance in dielectric thin-film capacitors

The polarization hysteresis loops and the dynamics of domain switching in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT), antiferroelectric PbZrO3 (PZ) and relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films deposited on Pt/Ti/SiO2/Si substrates were investigated under various bipolar electric fields during repetitive switching cycles. Fatigue behavior was observed in PZT thin films and was accelerated at higher bipolar electric fields. Degradation of energy storage performance observed in PZ thin films corresponds to the appearance of a ferroelectric state just under a high bipolar electric field, which could be related to the nonuniform strain buildup in some regions within bulk PZ. Meanwhile, PLZT thin films demonstrated fatigue-free in both polarization and energy storage performance and independent bipolar electric fields, which are probably related to the highly dynamic polar nanodomains. More importantly, PLZT thin films also exhibited excellent recoverable energy-storage density and energy efficiency, extracted from the polarization hysteresis loops, making them promising dielectric capacitors for energy-storage applications.

High-performance energy storage and breakdown strength of low-temperature laser-deposited relaxor PLZT thin films on flexible Ti-foils

The microstructure, ferroelectric, electric-field breakdown strength, and energy-storage properties of relaxor Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films grown on flexible Ti foils using pulsed laser deposition were systematically investigated. Low temperature deposited PLZT thin films showed very slim polarization hysteresis loops with a high difference between maximum and remanent polarizations and low remanent polarization through modulating the film structure with a small columnar-grain size. An ultrahigh recoverable energy density (Ureco) of 40.9 J/cm3, excellent energy efficiency (η) of 80.2% and large breakdown strength (EBD) of 3000 kV/cm were achieved in a PLZT film deposited at the low temperature of 480 °C. More importantly, this film shows excellent charge-discharge cycling endurance with a small variation of both Ureco and η values (less than 3%) after 1010 cycles and good thermal stability under a wide operating temperature range from room temperature to 200 °C. These results indicate that the relaxor PLZT films deposited on thin Ti foils, even at low temperature, are a promising strategy to enhance energy-storage performance for pulse-power energy-storage systems with broad temperature range applications, especially in applications where the device weight is critical (lightweight) due to the thin and low density of Ti foils.

Experimental evidence of breakdown strength and its effect on energy-storage performance in normal and relaxor ferroelectric films

Normal-ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) and relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin-films are deposited on SrRuO3-covered SrTiO3/Si substrates. An ultrahigh recoverable energy-storage density (Ureco) of 68.2 J/cm3 and energy efficiency (η) of 80.4% are achieved in the PLZT thin-films under a large breakdown strength (EBD) of 3600 kV/cm. These values are much lower in the PZT thin-films (Ureco of 10.3 J/cm3 and η of 62.4% at EBD of 1000 kV/cm). In addition, the remanent polarization (Pr) and dielectric-constant are also investigated to evaluate the breakdown strength in thin-films. Polar nano-regions (PNRs) are created in the PLZT thin-films to enable relaxor behavior and lead to slim polarization loops along with very small Pr. The excellent operating temperature of energy-storage performance and also the breakdown strength obtained in the PLZT thin-films are mainly ascribed to the presence of PNRs. Moreover, both PZT and PLZT thin-films exhibit superior performance up to 1010 times of charge-discharge cycling.

Enhancement of relaxor behavior by La doping and its influence on the energy storage performance and electric breakdown strength of ferroelectric Pb(Zr0.52Ti0.48)O3 thin films

La-doped Pb1-xLax(Zr0.52Ti0.48)O3 (PLZT) thin films with dopant concentrations of up to 12% were fabricated on (111)Pt/Ti/SiO2/Si substrates by a sol-gel spin-coating method to investigate the effects of La content on the phase transition, ferroelectric and energy-storage performance properties of PZT thin films. The compositional-induced relaxor behavior was increased with the doping of La, due to the presence of polar nano-regions (PNRs). The existence of PNRs in the relaxor ferroelectric, as opposed to the microscopic long-range ordered domains in the normal ferroelectric, induced the difference between the polarizations of the normal and relaxor ferroelectrics. The results indicated that the decrease in remanent polarization and coercive field in the PLZT thin films with increasing La content was associated with the phase transition from normal ferroelectric behavior in undoped PZT to relaxor behavior in PLZT thin films due to the substitution of Pb2+ ions by La3+ ions. The maximum recoverable energy-storage density (27.5 J/cm3) and efficiency (62.2%) were obtained for the 8% La-doped film due to the large electric breakdown strength (2200 kV/cm) and slimmer polarization hysteresis loop. Because of the thinner films (250 nm), the low driven voltage of 55 V can be used to charge the thin film capacitors to obtain the above energy-storage properties. Moreover, an excellent charge-discharge cycling life with fatigue-free performance up to 1010 cycles was also realized in the thin films. All of the excellent results indicated that the relaxor PLZT thin films with 8% La doping possess excellent potential for low voltage operation advanced capacitors with high energy-storage performance.

Lanthanum modified lead zirconate titanate thin films by sol-gel and plasma annealing for integrated passive nanophotonic devices

Lanthanum modified lead zirconate titanate (PLZT) thin films were prepared by sol-gel and the plasma annealing process. The PLZT thin films are pure perovskite phase and highly crystalline. The polarization-electric loops confirmed quadratic PLZT thin films. The optical properties were determined by a spectroscopic ellipsometry analyzer, showing an absorption coefficient of near zero and an energy gap of around 3.6 eV. The insertion losses of the optical devices based on PLZT films are less than 5 dB. These films have the potential to be applied in the field of integrated nanophotonic devices.

Phase transition and energy storage behavior of antiferroelectric PLZT thin films epitaxially deposited on SRO buffered STO single crystal substrates

Abstract(Pb0.98, La0.02)(Zr0.95, Ti0.05)O3 (PLZT) thin films of 300 nm thickness were epitaxially deposited on (100), (110), and (111) SrTiO3 single crystal substrates by pulsed laser deposition. X‐ray diffraction line and reciprocal space mapping scans were used to determine the crystal structure. Tetragonal ((001) PLZT) and monoclinic MA ((011) and (111) PLZT) structures were found, which influenced the stored energy density. Electric field‐induced antiferroelectric to ferroelectric (AFE→FE) phase transitions were found to have a large reversible energy density of up to 30 J/cm3. With increasing temperature, an AFE to relaxor ferroelectric (AFE→RFE) transition was found. The RFE phase exhibited lower energy loss, and an improved energy storage efficiency. The results are discussed from the perspective of crystal structure, dielectric phase transitions, and energy storage characteristics. Besides, unipolar drive was also performed, providing notably higher energy storage efficiency values due to low energy losses.

Tuning the energy storage performance, piezoelectric strain and strain hysteresis of relaxor PLZT thin films through controlled microstructure by changing the ablation rate

Relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) films with a thickness of 1.2 μm were deposited on LaNiO3-buffered Ca2Nb3O10-nanosheet/Si. It was revealed how structural modification of a PLZT film, fabricated using pulsed laser deposition under various ablation rates, can be used to tune its energy-storage performance and piezoelectric-strain. A highest unipolar piezoelectric-strain of 0.71% with extremely low strain-hysteresis of 1.9% and corresponding normalized-strain of 142 pm/V under an electric field of 500 kV/cm were observed in the film deposited at an ablation rate of 50 Hz, and such film consists of vertical columnar-structure. Whereas, the film deposited at a low ablation rate of 10 Hz with dense-structure had the higher recoverable energy-storage density (50.2 J/cm3) and energy-storage efficiency (82.2%) due to the larger electric-breakdown strength (3150 kV/cm). The strongly improved performance by choosing an appropriate film structure is important for practical applications in pulse-power energy-storage as well as for the development of piezo-driven microelectromechanical-systems.

Imprint behavior and polarization relaxation of PLZT thin films

Thickness dependence of imprint and polarization dynamics of Pb1-xLax(Zr1-yTiy)1-x/4O3 (PLZT) thin films is reported in this work. Asymmetries in the histograms of the local piezoresponse reveal an imprint effect in the studied films whose origin could be associated to Schottky barriers near the film-substrate interface. Time-resolved spectroscopic measurements shows that the local polarization relaxation follows the exponential dependence . A maximum relaxation time τ ≈ 2.18 s was observed for the 350 nm thick film. A similar thickness dependence between grain size, correlation length (ξ) and relaxation time (τ) suggest an intrinsic relationship between them.

Transverse piezoelectric properties of {110}-oriented PLZT thin films

Preferentially {110}-oriented thin films of lead lanthanum zirconate titanate, (Pb, La) (Zr, Ti)O3 [PLZT] having compositions (7/65/35), (7/60/40) and (7/56/44) across the morphotropic phase boundary with a thickness of 1.5µm were prepared on platinised silicon substrates (111) Pt/Ti/SiO2/Si by sol-gel spin coating technique. The crystallographic orientation and crystalline phases were analysed by X-ray diffraction and Raman spectroscopy respectively. The dependence of the transverse piezoelectric coefficient, of the PLZT thin films on their composition and texture have been investigated. PLZT (7/60/40) thin films having a higher tetragonal content was found to exhibit optimum piezoelectric characteristics. By combining the results obtained from the dielectric and polarisation-electric field (P-E) studies, the domain switching mechanism responsible for have been established.

Ultra Uniform Pb0.865La0.09(Zr0.65Ti0.35)O₃ Thin Films with Tunable Optical Properties Fabricated via Pulsed Laser Deposition.

Ferroelectric thin films have been utilized in a wide range of electronic and optical applications, in which their morphologies and properties can be inherently tuned by a qualitative control during growth. In this work, we demonstrate the evolution of the Pb0.865La0.09(Zr0.65Ti0.35)O3 (PLZT) thin films on MgO (200) with high uniformity and optimized optical property via the controls of the deposition temperatures and oxygen pressures. The perovskite phase can only be obtained at the deposition temperature above 700 °C and oxygen pressure over 50 Pa due to the improved crystallinity. Meanwhile, the surface morphologies gradually become smooth and compact owing to spontaneously increased nucleation sites with the elevated temperatures, and the crystallization of PLZT thin films also sensitively respond to the oxygen vacancies with the variation of oxygen pressures. Correspondingly, the refractive indices gradually develop with variations of the deposition temperatures and oxygen pressures resulted from the various slight loss, and the extinction coefficient for each sample is similarly near to zero due to the relatively smooth morphology. The resulting PLZT thin films exhibit the ferroelectricity, and the dielectric constant sensitively varies as a function of electric filed, which can be potentially applied in the electronic and optical applications.

Dependence of dielectric and photovoltaic properties of Pt/PLZT/LNO on the temperature and La doping content

In this study, Pb1−xLax(Zr0.52Ti0.48)O3/LaNiO3 (PLZT/LNO) heterostructures with different doping contents of La (x = 0.02–0.15) were prepared on a Si substrate by sol–gel process. First, the effects of the La doping content on the crystal structure, electric hysteresis loop, and dielectric performance of the PLZT thin film were investigated. With the increase in the La doping content, the results revealed that the XRD diffraction peaks of the PLZT thin film shifted to large angles, indicative of the decrease in the film grain size; meanwhile, the residual polarization intensity and coercive field strength of the thin film decreased. The dielectric-temperature spectrum revealed that with the increase in the La doping content, the Curie temperature of the PLZT thin film gradually decreased, while the relative dielectric constant tended to first decrease and then increase. When x (La) was 0.08, the constant reached the minimum. Furthermore, the dependences of the photovoltaic characteristics of the PLZT thin films on the temperature and La doping content were investigated. Under the same test temperature, the open-circuit voltage of the PLZT film tended to first increase and then decreased with the increase in the La doping content. When x (La) = 0.08, the open-circuit voltage reached the maximum. For PLZT with the same doping content of La, the open-circuit voltage also increased first and then decreased with increasing temperature. When T = 223 K and x (La) = 0.08, the open-circuit voltage reached the maximum of around 693 mV.

Effect of La and W dopants on dielectric and ferroelectric properties of PZT thin films prepared by sol–gel process

La or W-doped lead zirconate titanate thin films (PLZT or PZTW) were prepared on platinized silicon substrates by sol–gel process. The effects of La or W dopant on the phase development, microstructure, dielectric and ferroelectric characteristics of films were studied. For PLZT films, the optimum doping concentration was found to be 2 mol%. While for PZTW films, the dielectric and ferroelectric properties were found to be improved as the doping concentration increased. The fatigue properties of PLZT and PZTW thin films were also investigated, the results showed that A- or B-site donor doping could improve the fatigue properties of PZT thin films. The theory of oxygen vacancy was used to explain the performance improvement caused by donor doping.