LaNiO3 Buffer Research Articles

Enhanced energy storage performance in Ag(Nb,Ta)O3 films via interface engineering

Dielectric capacitors with ultrahigh power density and ultra-fast charge/discharge rate are highly desired in pulse power fields. Environmental-friendly AgNbO3 family have been actively studied for its large polarization and antiferroelectric nature, which greatly boost the electric energy storage performance. However, high-quality AgNbO3-based films are difficult to fabricate, leading to a low breakdown field Eb (<1.2 MV/cm) and consequently arising inferior energy storage performance. In this work, we propose an interface engineering strategy to mitigate the breakdown field issue. A Ag(Nb,Ta)O3/BaTiO3 bilayer film is proposed, where the BaTiO3 layer acts as a p-type semiconductor while Ag(Nb,Ta)O3 layer is n-type, together with the n-type LaNiO3 buffer layer on the substrate, forming an n-p-n heterostructure. The n-p-n heterostructure elevates the potential barriers for charge transport, greatly reducing the leakage current. An extremely large breakdown field Eb∼4.3 MV/cm is achieved, being the highest value up to date in the niobate system. A high recoverable energy density Wrec∼62.3 J/cm3 and a decent efficiency η∼72.3% are obtained, much superior to that of the Ag(Nb,Ta)O3 monolayer film (Wrec∼46.4 J/cm3 and η∼80.3% at Eb∼3.3 MV/cm). Our results indicate that interface engineering is an effective method to boost energy storage performance of dielectric film capacitors.

Improvement of the energy storage performance of antiferroelectric Pb,La(Zr,Ti)O3 thin films by the LaNiO3 buffer layer on the metal electrode

Improved energy storage capability is achieved in an antiferroelectric capacitor through the introduction of a LaNiO3 buffer layer on the metal electrode.

Effect of sputtering-target composition on the structure, dielectric, ferroelectric, and energy storage properties of highly (00l)-oriented Ba(ZrxTi1–x)O3 films

It is relatively easy to obtain highly oriented/textured Ba(ZrxTi1–x)O3 (BZT) films by magnetron sputtering, but it is complicated to control the composition of these sputtered oriented films. Here, a series of BZT ceramic targets with different ingredients (x = 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3) and a BaTiO3 (x = 0) target were fabricated by solid-state sintering. Then, the corresponding BZT thin films were deposited on LaNiO3 (LNO) buffered Pt/Ti/(001)Si substrates adopting radio-frequency magnetron sputtering. Benefit from the prefabricated (001)-LNO buffer layer and optimized BZT film preparation process, all BZT films exhibit highly (00l) preferred orientation. However, the degree of orientation, lattice parameter, dielectric properties, ferroelectric behaviors, and energy-storage characteristics are all highly dependent on the Zr content of BZT films sputtered by targets with the same composition. (00l)-oriented BZT films with relatively low Zr content have a better crystalline structure [narrower full width at half maximum (FWHM), larger grains]. It is also found that the rising of the Zr content in (00l)-oriented BZT films will result in a larger out-of-plane lattice parameter, and these results indicate that the doping amount of Zr will strongly change the heterointerface stress/strain states and the growth mode of the oriented films, and then effectively tailor their electric performances.

Optimized Tunability of Barium Strontium Titanate Thin Films onto Different Plates with Proper Buffer Layers

Misfit strain, polarization, permittivity, and tunability of Ba x Sr1−x TiO3 (BST) thin films on various substrates with varied buffer layers are calculated by a modified thermodynamic model. The lattice parameters of the LaAlO3 (LAO), CaTiO3 (CT), BaZr0.25Ti0.75O3 (BZT), and MgO buffer layers grow consecutively as does the thermal expansion coefficient (TEC) of the Si, Ti, Ni, and stainless steel (SS) substrates. When the TEC of substrates is bigger (such as Ni, SS) than that of the films, introducing buffer layers with larger lattice parameters (such as BZT, MgO) can improve the permittivity and tunability. Conversely, inserting buffer layers with smaller lattice parameters (such as LAO, CT) can enhance the dielectric response when the TEC of substrates is smaller (such as Si, Ti) than that of the films. The relationship between the TEC of substrate and the lattice parameter of buffer layer is primarily linear for achieving high tunability. According to several references, introducing LaNiO3 buffer layers can significantly increase the tunability of BST solid solutions prepared on Si‐based substrates, which is in line with the estimated rule. This law offers a guide for choosing the best substrate and buffer layer when producing BST films with strong dielectric response.

High performance LaNiO3-buffered, (001)-oriented PZT piezoelectric films integrated on (111) Si

Integration of high-performance lead zirconate titanate (PZT) piezoelectric films onto (111) Si substrates is beneficial for the development of piezoelectric micro-electro-mechanical systems (Piezo-MEMS) because of (111) Si's isotropic mechanical properties and desirable etching characteristics. These features will greatly reduce complications in micro-device fabrication and patterning of PZT/Si heterostructures. However, piezoelectric performance of a PZT film is usually dominated by its preferred crystalline orientation, with (001) being superior than (110) and (111). Such a vectorial dependence seriously restricts applications of PZT films grown on (111) Si, which are usually not (001)-textured. In this work, highly (001)-oriented PZT thick films (∼1.5 μm) with a 53/47 Zr/Ti ratio were prepared on (111) Si substrates via a multi-layer buffering technique, i.e., through the use of a (111)Pt/Ti bi-layer and a LaNiO3 buffer layer. The PZT films were sputter-deposited at a low temperature (350 °C) and then crystallized in a (001) texture via a rapid thermal annealing (RTA). The e31,f transverse piezoelectric coefficient was up to ∼11.6 C/m2 for PZT films with a RTA time of 2 minutes. Such an e31,f value is comparable to that of PZT films grown on (100) Si. This work opens up many possibilities for Piezo-MEMS by demonstrating the desirable combination of a large piezoelectricity in (001) PZT with a good patternability of (111) Si.

Room temperature tunability of ferroelectricity and dielectricity in La and Mn codoped BiFeO3 nanoflakes: Implications for electronic devices applications

This study sheds a light on the in-situ growth of nanoflakes structure in Bi0.9La0.1Fe0.5Mn0.5O3 (BLFMO) thin film. The BLFMO thin films of various thicknesses were grown on LaNiO3 (LNO) coated Si (100) substrates using pulsed laser deposition technique. A long-range crystal structure of the as prepared BLFMO thin films was studied by X-ray diffraction measurements, which shows that the LNO buffer layer allows growth for a specific orientation. The compact and densely packed nanoflake structures in BLFMO thin film samples were confirmed by surface morphological investigations. To measure the polarization versus electric field (p-E) loop of BLFMO chip samples, a standard bipolar sinusoidal waveform with its magnitude of 250 kV/cm was applied at the frequency of 1 kHz. The maximum saturation and remnant polarizations of 104.50 μC/cm2 and 86.24 μC/cm2 respectively were probed for a critical thickness (420 nm) of the BLFMO layer. The voltage polarity-dependent leakage current behavior of Ag/BLFMO/LNO thin-film capacitor is thoroughly explored in detail. The value of leakage current density was observed from 1.16 × 10−4 to 2.24 × 10−5 J/cm2 for BLFMO thin films at an external applied electric field of 300 kV/cm. The highest tunability ∼60.20% and minimum temperature capacitance coefficient ∼1.23 × 10−3 were also observed for the same critical thickness of proposed chip element. The present study may open up a new opportunity to fabricate thin film based ferroelectric memory devices.

Sputter deposition and characterization of “epi-poly” Pb(Zr, Ti)O3 thin film on (100) Si substrate for MEMS applications

Monocrystalline Pb(Zr, Ti)O3 (mono-PZT) thin films are suitable for specific microelectromechanical systems applications. However, these films are more brittle than general polycrystalline PZT thin films. Herein, we focus on an epitaxial PZT thin film with multiple variants in the in-plane direction. Such a unique crystalline structure is expected to have properties intermediate between the mono- and polycrystalline PZT thin films. Such a film is called as “epi-poly” thin film in this paper. We formed an LaNiO3 buffer layer with three variants as an underlayer. PZT was then sputter-deposited onto it. Thus, a (100)-oriented epi-poly PZT thin film with three variants was obtained. Its piezoelectricity, ∣e 31,f ∣, dielectric constant, ε r33, dielectric loss, and tanδ were measured to be approximately 9 C m−2, 750–800, and 0.02, respectively. Nano-indentation tests on the epi-poly and mono-PZT thin films indicated that the former had superior mechanical robustness than that of the latter.

Ferroelectric and dielectric properties of BF-PT/LNO thin films on different substrates

Ferroelectric 0.7BiFeO3–0.3PbTiO3 (BF-PT) thin films were prepared by the sol–gel method on Pt/Ti/SiO2/Si, stainless steel (SS) and Ti substrates, respectively, with LaNiO3 (LNO) buffer layers. The performance of the BF-PT films on SS is significantly better than that on the Ti substrates and is comparable to the films on the Pt/Ti/SiO2/Si substrates. The BF-PT films on SS substrates have the good crystallinity with a pure perovskite structure. Moreover, the dielectric loss and remnant polarization (Pr) of BF-PT on SS are of 4.48% (at the frequency of 103 Hz) and 28.9 μC/cm2, respectively, revealing good dielectric and ferroelectric properties. It is found that BF-PT deposited on SS has the good fatigue resistance relative to the films on Ti substrates. The reduction of polarization is of about 22% after the electrical switching of 1.33 × 108 cycles. Experiments show that BF-PT thin films deposited on SS substrates exhibit superior ferroelectric, dielectric, and fatigue resistance properties.

{001}-textured Pb(Zr, Ti)O3 thin films on stainless steel by pulsed laser deposition

In this work, we report nearly single oriented {001}-textured ferroelectric PbZr0.52Ti0.48O3 thin films grown by pulsed laser deposition onto AISI 304 stainless steel substrates. Pt, Al2O3, and LaNiO3 buffer layers promote the PbZr0.52Ti0.48O3 {001} texture and protect the substrate against oxidation during deposition. The dominant {001} texture of the PbZr0.52Ti0.48O3 layer was confirmed using x-ray and electron backscatter diffraction. Before poling, the films exhibit a permittivity of about 350 at 1 kHz and a dielectric loss below 5%. The films display a remanent polarization of about 16.5μCcm−2 and a high coercive field of up to Ec=135.9kVcm−1. The properties of these PbZr0.52Ti0.48O3 thin films on stainless steel are promising for various MEMS applications such as transducers or energy harvesters.

Enhanced energy storage properties and temperature stability of fatigue-free La-modified PbZrO3 films under low electric fields

Electrostatic energy-storage capacitors, with their ultrahigh storage density and high temperature stability, have been receiving increasing attention of late for their ability to meet the critical requirements of pulsed power devices in low-consumption systems. In such a context, this work reports on the successful production of anti-ferroelectric (AFE) thin films with excellent energy storage performance under a relatively low electric field. In particular, La-doped PbZrO3 thin films were fabricated using a sol-gel method, yielding a recoverable energy storage density of 34.87 J cm−3 with an efficiency of 59.23% at room temperature under the electric field of ∼800 kV cm−1. The temperature dependence of the energy storage property was demonstrated from room temperature to 210°C, indicating a stable density variation between 34.87 and 27.98 J cm−3. The films also exhibited excellent anti-fatigue property (endurance of up to 3×109 cycles and the recoverable energy storage density varied from 39.78 to 29.32 J cm−3 combined with an efficiency of 61.03%`-44.95% under the test frequencies from 10 to 5000 Hz). All results were obtained using compact films with a high polarization (Pmax) of approximately 103.7 µC cm−2 and low remnant polarization (Pr∼7 µC cm−2), which was owing to the combination of LaNiO3 buffer layers and vacancies at Pb sites. These results illustrate the great potential of pulsed power devices in low-consumption systems operating in a wide range of temperatures and long-term operations.

Improved properties of Pb(Zr0.52Ti0.48)O3 films by hot plate annealing on LaNiO3 bottom electrode

Pb(Zr0.52Ti0.48)O3 (PZT) perovskite ferroelectric thin films were fabricated on LaNiO3 buffer silicon substrate by sol–gel spin coating technique. The thickness of PZT films was about 150 nm, and the thickness of LNO films as electrodes was about 120 nm. The prepared PZT thin films were annealed by hot plate annealing and conventional electric furnace annealing at various temperatures for 30 min. The microstructure of annealed films was analyzed by different techniques. The obtained results demonstrated that the perovskite phase can be achieved in films by both methods of annealing. Structural and morphological characterizations substantiated that hot plate annealing method can facilitate the formation of perovskite phase of PZT films than the electric furnace annealing. Consequently, the films annealed using hot plate exhibited more excellent electrical properties. The higher dielectric permittivity, remnant polarization, and the lower dielectric dissipation were observed for the thin films annealed at 550 °C by the hot plate. The values of remnant polarization and coercive field of PZT annealed on the hot plate were 36.4 μC/cm2 and 168 kV/cm, respectively. These results demonstrated that the crystallization of ferroelectric PZT films was improved by hot plate annealing.

Design of flexible inorganic BiFe0.93Mn0.07O3 ferroelectric thin films for nonvolatile memory

Flexible ferroelectric memories, endowing with high data storage density, provide a chance for the next-generation wearable electronics. Here, flexible inorganic Mn-doped BiFeO3 thin films were directly integrated on fluorophlogopite mica (F-Mica) substrates by an easy and low-cost all solution chemical solution deposition (AS-CSD) route. The integration of LaNiO3 buffer layer can improve the film surface density and uniformity. The flexible characteristic can be achieved by reducing the thickness of F-Mica substrates for the ferroelectric thin films. In contrast to BiFe0·93Mn0·07O3/LaNiO3/Si thin film deposited on rigid substrates (Si), the BiFe0·93Mn0·07O3/LaNiO3/F-mica fabricated on F-Mica show better ferroelectric performances due to the improved crystal growth and less defects. More importantly, the obtained BiFe0·93Mn0·07O3/LaNiO3/F-mica ferroelectric thin films still show large remnant polarization of Pr ∼64 μC/cm2 (deterioration of ∼7.2%), good antifatigue properties up to 1.2 × 108 cycles and outstanding retention behaviors for 1.6 × 104 s after continuous bending. This work will provide a feasible route to fabricate flexible inorganic ferroelectric thin films through low-cost solution method and show attractive comprehensive performances in next-generation wearable smart devices.

Space charge limited conduction in pulsed laser deposited BaTiO3/LaNiO3 hetero-junctions

We report the charge transport mechanism in BaTiO3 (BTO) thin film deposited on LaNiO3 (LNO) buffer layer using pulsed laser deposition technique thus, forming the metal – insulator – metal junction (Au/BTO/LNO). The temperature dependent Current density- Voltage (J-V) characteristics were measured, analyzed and compared with the La0.67Ca0.33MnO3 (LCMO) buffered BTO film (Au/BTO/LCMO). Although the mechanism was found to be space charge limited conduction (SCLC) as in case of BTO/LCMO but the absence of Ohmic region in Log J-Log V plot indicates higher injection rate. Various parameters such as trap density, activation energy, and ratio of free to trapped carriers (θ) were extracted out from the fitted J-V plot and subsequently their temperature dependence was studied and compared with BTO/LCMO. Higher current density, lower activation energy, lower trap density and higher ratio of free to trapped carriers (θ) were observed in BTO/LNO in contrast to BTO/LCMO. Furthermore, the lower activation energy indicates the presence of shallow trap level.

Ferroelectric Diode Effect with Temperature Stability of Double Perovskite Bi2NiMnO6 Thin Films.

Double perovskite Bi2NiMnO6 (BNMO) thin films grown on p-Si (100) substrates with LaNiO3 (LNO) buffer layers were fabricated using chemical solution deposition. The crystal structure, surface topography, surface chemical state, ferroelectric, and current-voltage characteristics of BNMO thin films were investigated. The results show that the nanocrystalline BNMO thin films on p-Si substrates without and with LNO buffer layer are monoclinic phase, which have antiferroelectric-like properties. The composition and chemical state of BNMO thin films were characterized by X-ray photoelectron spectroscopy. In the whole electrical property testing process, when the BNMO/p-Si heterojunction changed into a BNMO/LNO/p-Si heterojunction, the diode behavior of a single diode changing into two tail to tail diodes was observed. The conduction mechanism and temperature stability were also discussed.

Effect of LaNiO&lt;sub&gt;3&lt;/sub&gt; Buffer Layer on the Electrical and Optical Properties of Nonpolar ZnO Film Deposited on (100) Si Substrate

Nonpolar ZnO films are deposited on (100) Si substrate using LaNiO3 conducting buffer layer by radio frequency sputtering. X-ray diffraction results show that ZnO films are (110) and (002) orientation with and without LaNiO3 buffer layer. The current behavior of ZnO/LaNiO3 heterojunction exhibits ohmic conduction which is different from the diode-like rectification current behavior of ZnO film using insulated buffer layers. The photoluminescence properties indicate that the (110)-oriented nonpolar ZnO film has better band-edge emission than that of (002)-oriented polar ZnO film. It is suggested that LaNiO3 buffer layer can be used to deposit silicon-based ZnO film with well ohmic contact electrode in optoelectronic devices.

Effects of LNO buffer layers on electrical properties of BFO-PT thin films on stainless steel substrates

Ferroelectric 0.7BiFeO3-0.3PbTiO3 (BFO-PT) thin films were deposited on LaNiO3 (LNO) coated stainless steel (SS) substrates by the sol-gel method. XRD results indicate that both LNO and BFO-PT thin films have the perovskite structure and the film crystallinity is improved with increasing the LNO thickness. The dielectric loss of BFO-PT thin films is reduced significantly with addition of LNO buffer layers, achieving about 4% at the frequency of 1 kHz, much lower than that of >20% for BFO-PT thin films directly deposited on SS substrates. BFO-PT thin films reveal the strong ferroelectricity with remnant polarization (Pr) of about 35 μC/cm2 for LNO of 390 nm. Moreover, addition of LNO buffer layers mitigates the polarization deterioration after the 1.33 × 108 switching cycles resulting in the improved anti-fatigue properties of BFO-PT thin films. Our results indicate that BFO-PT/LNO multilayer thin films on SS substrates maintain excellent dielectric and ferroelectric properties.

Controlled spalling and flexible integration of PZT film based on LaNiO3 buffer layer

As a functional ferroelectric material, PbZr0.53Ti0.47O3 (PZT) film is widely used in many electronic devices. However, with the rapid development of intelligent terminal, traditional PZT device cannot meet the demand for flexible wearable devices. In this work, a high-quality flexible PZT film is fabricated by the controlled spalling technology (CST) for the first time, which is novel, simple and cost-efficient. LaNiO3 (LNO) film by sol-gel process is used as the buffer layer for the PZT film growth due to good lattice match and low cost. The PZT film on silicon substrate is successfully transferred onto a flexible one by electroplating Ni stressor layer. LNO buffer layer thickness has an important influence on the spalled silicon depth and Ni stressor layer thickness during the spalling process. The exfoliated PZT film based on sandwich capacitor structure Au/PZT/Au with an area of 1 cm2 exhibits good ferroelectric properties under different mechanical deformation. Moreover, the ferroelectric response of flexible PZT film does not show obvious deterioration after repeated operation cycles. Therefore, the flexible PZT thin film has a good application prospect on wearable ferroelectric microelectronics.

Flexible vibrational energy harvesting devices using strain-engineered perovskite piezoelectric thin films

The material properties of Pb(Zr,Ti)O3 (PZT) thin film with a LaNiO3 (LNO) buffer layer on an ultra-thin Ni-Cr-based austenitic steel metal foil substrate are systematically investigated for flexible piezoelectric vibrational energy harvesting device applications. The use of the flexible austenitic metal foil substrate with a high thermal expansion coefficient results in the large compressive stress in the deposited PZT thin film, and subsequently produces much enhanced ferroelectric polarization of the film. The measured polarization value of the PZT film on the flexible metal foil substrate is over 50 µC/cm2, showing a great improvement in comparison with the film on the conventional Pt/Ti/SiO2/Si substrate. Simultaneously, the LNO buffer layer prevents any undesirable reactions, provides uniform nucleation sites and promotes easy crystallization of the PZT thin film, achieving the highly dense and uniform microstructure of the film with a smooth surface. Using the strain-engineered PZT thin film, a small-scale and flexible vibrational energy harvester is fabricated using a simple punching process without any complex microelectromechanical system (MEMS) or etching processes. The maximum power and the corresponding peak voltage of the device are 5.6 µW and 690 mV, respectively, which are much higher values than those of MEMS-based vibrational energy harvester. The improved device performance of our flexible small-scale vibrational energy harvester is due to the enhanced PZT film properties by the stress engineering, the increased flexure and deflection of the flexible structure, and the easy vibrational sensitivity at low acceleration of 0.5g, compared to the MEMS-based device integrated with conventional Si-based substrates. The results prove that our strain-tuned PZT thin film-based flexible vibrational piezoelectric energy harvester is a promising candidate for autonomous power systems and future small-scale mobile platforms.

Textured Bi1/2Na1/2TiO3‐BaTiO3 Lead‐Free Films with Enhanced Piezoelectric Property and Depolarization Temperature

AbstractFuture microelectromechanical systems will need environmentally friendly lead‐free piezoelectrics in the form of thin films, like Bi1/2Na1/2TiO3 (BNT); however, its application is limited due to the relatively low depolarization temperature (Td). In this work, not only enhanced piezoelectric properties, but also higher Td, are achieved in (001)‐textured 0.94Bi1/2Na1/2TiO3‐0.06BaTiO3 (BNT‐BT6) thin films on widely used platinized Si wafers with a LaNiO3 buffer layer. The piezoelectric coefficient a33,eff is increased by 65% to 43 pm V−1 in the textured films from 26 pm V−1 in the nontextured counterparts. The texturing also raises the Td to ≈140 °C, about 40 °C higher than that in nontextured films. The increase of Td is attributed to the in‐plane tensile thermal stress and the (001)‐textured structure. The present work provides a guideline to improve piezoelectric properties and the thermal stability of BNT‐based lead‐free piezoelectric thin films.

Flexible high energy density capacitors using La-doped PbZrO3 anti-ferroelectric thin films

Flexible high energy density capacitors were fabricated by depositing 6 mol. % La-doped anti-ferroelectric PbZrO3 thin films using chemical solution deposition on ultra-thin metal foil substrates. The integration of a LaNiO3 buffer layer on the flexible austenitic metal foil substrate resulted in substantial improvements in microstructure uniformity and density of the La-doped PbZrO3 thin film capacitors. The recoverable energy density and the energy loss of the flexible thin film capacitors were 15.2 ± 0.2 J/cm3 and 4.8 ± 0.2 J/cm3 at 1 MV/cm, respectively. The La-doped PbZrO3 flexible thin film capacitors showed no noticeable degradation in ferroelectric hysteresis behavior and the energy storage density even after 1000 bending cycles.