Electroceramic Devices Research Articles

Structural Phase Modulation in Lanthanum‐ and Tin‐Cosubstituted Pb(Zr,Ti)O3 Ceramics and its Energy and Pyroenergy Storage Properties

La‐ and Sn‐cosubstituted lead zirconate titanate () ceramics are synthesized using a solid‐state reaction route. These (PLZST) ceramics in pure form are found to exist in dual phase () and single phase (Cc) depending on the amount of La/Sn cosubstitution. PLZST ceramics exhibit thin P–E loops with enhanced polarization when measured at 393 K. Olsen cycle method is used to estimate the pyroenergy harvesting abilities of the samples under study. The estimated maximum energy storage density for PLZST () ceramics at 393 K is 1.16 J cm−3 [efficiency (η) > 96%]. The PLZST ceramics exhibit a remarkable hardness of 9.08 GPa. These results indicate that PLZST ceramics with excellent multifunctional properties are potential candidates in the field of electroceramic devices.

Microwave assisted processing of X8R nanocrystalline BaTiO3 based ceramic capacitors and multilayer devices

BaTiO3 based multilayer ceramic capacitor (MLCC) is an important component in electronic devices. Achieving high dielectric performance, miniaturisation and cost effectiveness are still challenging. Co-sintering ceramic layers with metal electrodes and use of expensive Pt and high-Pd content compositions as electrodes are other key issues. Thus, the major factors that could lead to cost effectiveness of MLCCs are reduction in sintering temperature and using less expensive metal electrodes without compromising dielectric performance and these traits could auger well for the next generation low-cost high performance electroceramic devices – this is the subject matter of the present study.In this work, initially we have fabricated and analysed the dielectric performance of BaTiO3 (BT) ceramics with different BT particle sizes (50 nm, 100 nm and 200 nm). Based on results, 200 nm BaTiO3 was used for further studies due to its superior dielectric performance. Then, to reduce the sintering temperature and improve the dielectric performance of 200 nm BaTiO3 ceramics, Bi2O3 was used as a dopant which acts both as a sintering aid and helps to improve the dielectric performance. A combination of rare earth dopant system (proprietary from the industrial partner Knowles, UK) with Bi2O3 was also added to tune the defect chemistry of BaTiO3 for enhancement in dielectric performance further. A homogeneously mixed BT-based ceramic slurry system (containing the above dopants) with optimum rheology was developed using a non-aqueous medium, dispersant and a binder system. Addition of glass frits for lowering the sintering temperature and its effect on dielectric performance was also investigated on both discs (made using dry pressing of the powders obtained via drying of the slurry) as well as multilayer ceramic capacitors (MLCCs) fabricated through screen printing. Conventional, microwave and hybrid sintering procedures were employed for the densification of the electroceramic devices and these were characterized for density, microstructure, composition and dielectric performance systematically. Conventional sintering resulted in undesired large micron sized surface features which are detrimental to device durability, whereas formation and growth of these features have been demonstrated to be significantly minimised using the rapid microwave assisted sintering procedures for the first time. Further efficient co-sintering of ceramic layers with less expensive (Ag/Pd) alloy has also been accomplished using the microwave methodology. The resultant BaTiO3 based capacitive devices exhibited high dielectric permittivity, superior X8R performance and low dissipation factor, asserting their massive potential for widespread high temperature applications in automotive, sensing and space sectors.

New Opportunities in Metallization Integration in Cofired Electroceramic Multilayers by the Cold Sintering Process

Metallization with high conductivities is critical in the design of high performance multilayer electroceramic devices. Cold sintering offers exciting new opportunities in the integration of different material classes; here we explore novel metal chemistries and demonstrate their integration into ceramic multilayers. The processing is enabled due to the cosintering of both the ceramic and metal powders in fast times and at extremely low sintering temperatures. Metal powders are printed as pastes and formed into multilayers that can be cosintered with the ceramic ZnO; these specific metals include Cu, Fe, and Al. The multilayer structures are assembled and fabricated under a thick film process and enabled by using a polypropylene carbonate binder system that can be removed at low temperatures under N2–H2 forming gas, permitting control of oxidation of the Cu, Fe, and Al. As a result, extremely high conductivity electrodes are fabricated and quantified through the equivalent series resistance (ESR). In addi...

The dielectric, thermal properties and crystallization mechanism of Li–Al – B–Si – O glass – Ceramic systems as a new ULTCC material

Abstract Li–Al–B–Si–O (LABS) glass-ceramics with a sintering temperature of 600 °C were studied for ultra-low temperature co-fired ceramics (ULTCC) applications. The crystal phase of LABS glass-ceramics is dendritic β-spodumene. The permittivity and dielectric loss of LABS glass-ceramics are e r = 5.8 and tg δ = 1.3 × 10 −3 at 10 MHz, respectively. The coefficient of thermal expansion (CTE) of LABS glass-ceramics is 3.23 ppm/°C, which is close to that of silicon. The dielectric and thermal properties of LABS glass-ceramics are closely correlated to the degree of its crystallization. The permittivity decreases continually while the dielectric loss decreases first and slightly increases with the increasing of crystallization of β-spodumene. The CTE of LABS glass-ceramics decreases as β-spodumene crystallized from LABS glass. The crystallization kinetic and mechanism of LABS glass-ceramics indicate that the β-spodumene crystallizes in a two-dimensional interfacial growth mechanism due to the migration of Li-ions. The diffusion coefficients derived from energy-dispersive X-ray spectroscopy (EDS) results indicated that both Al and Ag electrodes have good compatibilities with ULTCC tapes, which could reduce the cost of multilayer electro-ceramic devices dramatically by using the ULTCC and base metallization.

Synergistically-enhanced ion track formation in pre-damaged strontium titanate by energetic heavy ions

Latent ion tracks created by energetic heavy ions (12 MeV Ti to 946 MeV Au) in single crystal SrTiO3 are investigated using Rutherford backscattering spectrometry and scanning transmission electron microscopy. The results demonstrate that pre-existing irradiation damage, introduced via elastic collision processes, interacts synergistically with the electronic energy deposition from energetic heavy ions to enhance formation of latent ion tracks. The average amorphous cross-section increases with the level of pre-damage and is linearly proportional to the electronic energy loss of the ions, with a slope dependent on the pre-damage level. For the highest energy ions (629 MeV Xe and 946 MeV Au), the tracks are continuous over the pre-damaged depth, but become discontinuous beyond the pre-damaged region. This work provides new understanding and insights on ion-solid interactions that significantly impact the interpretation of latent track formation processes, models of amorphization, and the fabrication of electro-ceramic devices.

Tape casting system for ULTCCs to fabricate multilayer and multimaterial 3D electronic packages with embedded electrodes

A 3D multilayer structure built by two ultra-low temperature co-fired ceramic (ULTCC) compositions with silver embedded electrodes are co-fired at a temperature of 450°C. The 3D multilayer module is prepared by laminating the ULTCC green tapes with a new binder system, which organics can be completely burned out at temperature of 250°C before the sintering of the ULTCC 3D modulus. High-density microstructures are achieved for the sintered module. In this study, the ULTCC feasible binder system is introduced. Also, ULTCC multilayers and multimaterial structures with surface and embedded silver electrodes are fabricated. This research opens up a new horizon for fabrication of electroceramic devices with embedded electrodes in multimaterial devices.

Preserving nickel electrode conductivity during sintering process using lithium carbonate coatings

The resistance of nickel particles can be decreased by five orders of magnitude when coated with lithium carbonate during sintering in an oxidative atmosphere. The resistance is within a range, in which use is suitable for electrodes in the electroceramic devices. The coated powders have the potential to replace the precious metals (e.g. Pt and Ag) in multilayer electroceramic devices. A systematic study of the influence of sintering atmosphere and temperature on the morphology of Li2CO3-coated Ni particles was investigated via TEM (transmission electron microscopy), SEM-FIB (scanning electron microscopy - focused ion beam) imaging, and TGA (thermogravimetric analysis). The results suggested that the Li2CO3 decomposes and produces CO in the presence of residual carbon; CO, as a reducing agent, decreases the amount of NiO phases formed during sintering. At the same time, the NiO phase was doped with Li+, resulting in a decrease in its resistivity. The combination of these two processes decreased the resistance of the final Ni electrodes from 140 kΩ to 1 Ω. The effect and role of these two mechanisms were separated, and it is shown that both of them are equally useful in the preservation of electrical conductivity.

Coating Ni particles to preserve their conductivity during sintering in oxidizing atmospheres

In this study, a new Ni electrode was introduced which was able to preserve its electrical conductivity during sintering in oxidizing atmosphere. The Ni electrode was manufactured from Ni nanoparticles, which were coated by Li salts, namely Li2CO3, LiOH, and LiF, with an innovative coating method. The coating process is schematically shown in the graphical abstract. After the confirmation of a successful coating on Ni particles by SEM (Scanning Electron Microcopy) imaging, the Ni particles with Li2CO3 coating demonstrated the greatest preservation in conductivity among the other salts. Thus they were selected for further investigation; the effect of Li2CO3 percentage, sintering program, and pO2 on electrode resistance were systematically studied. The results suggest that the coating can reduce the resistance by five orders of magnitude at oxidizing atmosphere (e.g. pO2=2×10−4atm). The reduced resistances were as low as 1Ω, suitable to be used as an electrode. SEM and FIB (Focused Ion Beam) cross section imaging were used to document the Ni oxidation, the sintering process of Ni particles, and the Li2CO3 decomposition. Finally, two mechanisms were speculated to be the reasons of the conductivity conservation and the importance of this invention in the reducing of oxygen vacancies in electroceramic devices was discussed.

Value-addition of ZnO used in glazing industry for varistor application

The feasibility of using industrial-grade (IG) ZnO raw materials to produce electroceramics has been examined. A certain degree of agglomeration of particles was observed with sizes ranging in the hundreds of nanometer. The morphology of IG particles was less crystallographically defined compared to the reagent-grade powders. The apparent particle densities were also significantly different. The examined composition was of typical varistor in the ZnO-Bi2O3-CoO system. The solution-coated samples sintered much slower than the oxide samples. This could be caused by compositional change of the eutectic system. The varistor properties were dependent on the sintering temperature. At 1,000°C, the varistor fabricated from the IG powders yielded a breakdown field as high as 4500 V cm−1, comparing to 3600 V cm−1 from the oxide route; whereas the coefficients of non-linearity were in the same range for both. These comparable varistor properties have demonstrated the potential for fabrication of electroceramic devices.

Crystallization and grain growth characteristics of yttria-stabilized zirconia thin films grown by pulsed laser deposition

Knowledge about the crystallization and grain growth characteristics of metal oxide thin films is essential for effective microstructural engineering by thermal post-annealing and the integration to Si-based miniaturized electroceramic devices. Finite size and interface effects may cause fundamentally different behavior compared to three dimensional macroscopic systems. This work presents a comprehensive investigation of the crystallization kinetics and microstructural evolution upon thermal post-annealing of amorphous 200 nm and 1.2 μm thin films of 8 mol% yttria-stabilized zirconia grown by pulsed laser deposition (PLD) using ex- and in-situ X-ray diffraction, Raman spectroscopy, and electron microscopy techniques. The layers exhibit a remarkably low crystallization temperature of 200–250 °C while exposure to energetic electrons induces the formation of randomly dispersed ~ 20 nm sized crystallites already at ambient temperature. The isothermal amorphous to crystalline phase transformation kinetics can be described quantitatively by the Johnson–Mehl–Avrami–Kolmogorov model. They reveal characteristics of a three dimensional growth under cation bulk diffusion control with heterogeneous nucleation that changes from continuous to instantaneous initial seeding at temperatures above 300 °C. Large (> 100 nm) equiaxed grains are formed rapidly without a stabilization of transient nanocrystals during the thermally induced phase transformation. A stagnation of normal grain growth resulting in a logarithmic normal size distribution is observed once the average grain dimensions approach the film thickness. The results on the crystallization and grain growth of the PLD-grown YSZ films are evaluated with regards to the fabrication of YSZ solid electrolyte membranes for Si-supported micro solid oxide fuel cells and gas sensors.

Effect of Sr doping on phase transition and electric behaviour of (Pb0.70Sr0.30)(Zr0.70Ti0.30)O3 ceramics

The ferroelectric (FE) materials are continuously attracting considerable attention due to the interesting combination of their mechanical, electrical and chemical properties and their application in microelectromechanical devices (piezoelectric transformers, motors and transducers). To be more specific, their excellent electrostrictive properties coupled with domain mobility, high Curie point and good stability make these ‘new materials’ important components of electroceramic devices. It is already known that the electrical behaviour of these FE materials largely depends on random elasto-electric fields connected with the diffusion of phase transition and defects distribution. The aim of this article is the exposition of phase transition dependence on Sr2+ homovalent dopant in (Pb0.70Sr0.30)(Zr0.70Ti0.30)O3 ceramics investigated by electrical methods. We demonstrate that electrical examination can be effectively used for drawing decisive applications conclusions from the grain and grain boundary parameters distribution. Modification of FE materials with isovalent ions, but with radii bigger than the original atom, significantly affect its properties, particularly the (Pb,Sr)(Zr,Ti) O3 real part of electrical permittivity shows the change of phase transition from FE to relaxor.

Guidelines for improving resistance to CO 2 of materials for solid state electrochemical systems

Alkali earth oxides are present in many ionic and mixed conductors with a potential application in solid state electrochemical or electroceramic devices. Hence, study has been made of the relative risks of carbonation of selective materials based on thermodynamic predictions, with emphasis on ATiO 3 electroceramics, with A = Ca, Sr, Ba, and proton conductors based on AMO 3 perovskites with A = Sr or Ba and M = Ce or Zr. Predictions show that slight A-site deficiency lowers the activity of alkali earth oxide and enhances resistance to CO 2; this is confirmed by experimental findings. Thermodynamic predictions also indicate that the high stability of (Ba,Sr)TiO 3 and (Ba,Sr)ZrO 3 perovskites contributes to attain reasonable resistance to CO 2, in spite of the ready carbonation of BaO and SrO. However, these materials show wide gap between the upper and lower limits of resistance to CO 2. This gap provides interpretation for the effects of powder preparation and/or ceramic processing on resistance to CO 2. It is also shown that the lower and upper limits of resistance to CO 2 correlate with the structural tolerance factor of these perovskites.

Nanoferroelectric perovskite oxides with unusual morphology produced by different synthesis procedures

We report in the present paper some original results of a joint research performed in the framework of the COST Action 539 ELENA. In search of higher miniaturisation of electroceramic devices a new outlook seems to arise from ceramics with unusual morphology that might present a new kind of circular or toroidal ferroelectric ordering of dipoles. Completely new perspectives in data storage can be expected if a close control of size confinement and dimensionality as well as of the chemical composition and the phase purity is reached. We succeeded in the fabrication of BaTiO3 hollow nanoparticles and nanowires, and Bi4Ti3O12 platelets. The use of soft chemistry and solid state methods allowed to produce coreshell powders and ferroelectric-ferromagnetic composites with completely new functional properties.

Local impedance and microchemical analysis of electrical heterogeneities in multilayer electroceramic devices

We present an experimental methodology for locating and studying local failure sites in multilayer electroceramic devices at the submicron-length scale. In particular, the inhomogeneous degradation of multilayer ceramic capacitors is studied using a judicious combination of scanning electron microscopy (SEM), local-probe electrical measurements, focused ion beam (FIB) extraction, and transmission electron microscopy (TEM). Voltage-contrast SEM permits the identification of regions of different electrical potential within degraded multilayer devices. The local impedance from specific regions is measured in situ between a tungsten probe and the internal device electrodes, while impedance spectra are extracted for more detailed analysis. Because implementation occurs in dual-beam FIB/SEM, these locally defective sites can be extracted and thinned to electron transparency for further investigation by TEM. In this study, degraded sites in BaTiO3 multilayer capacitors are found to be associated with local oxygen deficiencies in BaTiO3, as measured by electron energy loss spectroscopy.

Zinc oxide-based ceramic varistors

ZnO-based varistors are electroceramic devices with an extremely high non-linear electrical response, originated on a functional microstructure with well defined characteristics. In the present paper the development of these materials since its discovery in the earlier seventies is reviewed. In spite of the important technological progress achieved, several essential features of its functional microstructure remain however unsolved.

Development of Materials Integration Strategies for Electroceramic Film-Based Devices Via Complementary In Situ and Ex Situ Studies of Film Growth and Interface Processes

We review our studies of film growth and interface processes performed using complementary in situ and ex situ characterization techniques that provide valuable information critical to the development of materials integration strategies for the fabrication of electroceramic film-based devices. Specifically, we review our work performed using in situ time-of-flight ion scattering and recoil spectroscopy (TOF-ISARS) / X-ray photoemission spectroscopy (XPS) / spectroscopic ellipsometry (SE), in conjunction with ex situ TEM and other techniques to study film growth and interface processes critical to the fabrication of non-volatile ferroelectric memories (NVFRAMs), dynamic random access memories (DRAMs), and high frequency devices based on high-K thin films. TOF-ISARS involves three distinct but closely related experimental methods, namely: ion scattering spectroscopy, direct recoil spectroscopy and mass spectroscopy of recoiled ions, which provide monolayer-specific information on film growth and surface segregation processes. Spectroscopic Ellipsometry enables investigation of buried interfaces. XPS provides valuable information on the chemistry of surface and interfaces. Specifically, we discuss: a) studies of oxidation of Ti-Al layers and synthesis and properties of La 0.5 Sr 0.5 CoO 9 /Ti-Al heterostructured layers for integration of PZT capacitors with Si substrates, and b) studies of BaSr x Ti 1 m x O 3 layer integration with Si substrates relevant to DRAMs, high frequency devices and high-K gate oxides for integrated circuits. This review shows the power of combined in situ / ex situ analytical techniques to provide valuable information for material integration strategies for electroceramic thin film-based devices.

Direct‐Write Fabrication of Zinc Oxide Varistors

Zinc oxide (ZnO)‐based pastes with tailored rheological properties have been developed for direct‐write fabrication of thick‐film varistor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 × 104 Pa·s. Upon aging, the pastes attained printable, steady‐state viscosities of approximately 3 × 102 Pa·s at 10 s−1. Square and rectangular elements were patterned on dense alumina substrates and sintered at varying temperatures between 800° and 1250°C. Varistor elements fired at 900°C exhibited nonlinearity coefficients (α= 30) that were equivalent to high‐density (>95%) varistors formed by cold isostatic pressing at 100 MPa (15 ksi) of a similar chemically derived powder heat‐treated under analogous conditions.

Direct‐Write Fabrication of Pb(Nb,Zr,Ti)O3 Devices: Influence of Paste Rheology on Print Morphology and Component Properties

Lead niobium zirconate titanate (PNZT) pastes with tailored rheological properties have been developed for direct‐write fabrication of thick‐film capacitor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 × 106 cP. On aging, the degree of shear thinning and the low shear apparent viscosity decreased. Pastes prepared from as‐received powders attained printable, steady‐state viscosities of ∼2 × 105 cP after 50 days of aging. In contrast, pastes prepared from dispersant‐coated powders showed no measurable rheological changes after 1 day of aging. Square elements were patterned on dense alumina substrates or Teflon sheets. Leveling behavior as a function of time for single line prints, and the resulting surface topographies of dried PNZT films were measured by laser profilometry. PNZT layers sintered at varying temperatures between 950° and 1050°C for 5 h in either air or a lead‐rich atmosphere yielded porous microstructures as revealed by scanning electron microscopy (SEM). Such layers exhibited dielectric constants (K) of 1400–1570 at 1 kHz with dissipation factors (D) of less than 4.1%.

Routes to net shape electroceramic devices and thick films

The net shape fabrication of a range of electroceramic devices and thick films is described. The fabrication routes involve producing homogeneous and formable ceramic dough using a viscous polymer processing technique, with various subsequent shape-forming operations to produce devices with sizes ranging from tens of millimetres to tens of microns. The advantages of these processing routes are discussed and examples of large (>1 mm) planar and 3-D components (hemispheres, tubes and helices) and structures with small (<150 μm) feature sizes (thick films and microrod arrays) are presented.

Monolayer-mediated patterning of integrated electroceramics

Integrated electroceramic thin-film devices on semiconducting or insulating substrate materials offer a wide variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electrical, electromechanical, magnetic and optical functions. Thus the ability to pattern such electroceramic thin films is a critical technology for future device realization. Patterned oxide thin-film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment i.e., a subtractive method. We review here an upset technology, a different way of patterning, by an additive approach, which allows for the selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective functionalization is achieved through microcontact printing (μ-CP) of self-assembled monolayers of the chemical octadecyltrichlorosilane on substrates of current technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron-scale dielectric oxide devices have been fabricated by this method, with lateral resolution as fine as 0.5 μm. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)O3 [PZT], LiNbO3, and Ta2O5. A multilevel example is also given which combines selective MOCVD deposition of metal electrodes and sol-gel patterned PZT for Pt//PZT//Pt//Si(100) ferroelectric memory cells.