Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

Perovskite lead-free dielectrics for energy storage applications

The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in the near future.

Homogeneous/Inhomogeneous-Structured Dielectrics and their Energy-Storage Performances.

Piezoelectric materials that can function at high temperatures without failure are desired for structural health monitoring and/or nondestructive evaluation of the next generation turbines, more efficient jet engines, steam, and nuclear/electrical power plants. The operational temperature range of smart transducers is limited by the sensing capability of the piezoelectric material at elevated temperatures, increased conductivity and mechanical attenuation, variation of the piezoelectric properties with temperature. This article discusses properties relevant to sensor applications, including piezoelectric materials that are commercially available and those that are under development. Compared to ferroelectric polycrystalline materials, piezoelectric single crystals avoid domain-related aging behavior, while possessing high electrical resistivities and low losses, with excellent thermal property stability. Of particular interest is oxyborate [ReCa4O (BO3)3] single crystals for ultrahigh temperature applications (>1000°C). These crystals offer piezoelectric coefficients deff, and electromechanical coupling factors keff, on the order of 3–16 pC/N and 6%–31%, respectively, significantly higher than those values of α-quartz piezocrystals (~2 pC/N and 8%). Furthermore, the absence of phase transitions prior to their melting points ~1500°C, together with ultrahigh electrical resistivities (>106 Ω·cm at 1000°C) and thermal stability of piezoelectric properties (< 20% variations in the range of room temperature ~1000°C), allow potential operation at extreme temperature and harsh environments.

Piezoelectric Materials for High Temperature Sensors

Recent development in lead-free perovskite piezoelectric bulk materials

Perovskite solid solution in the (1−x)[0.4BiScO3–0.6BaTiO3]+x (K1/2Bi1/2)TiO3 [BSBT–KBTx] system was synthesized using conventional sintering and hot-isostatic pressing. Dielectric properties of BSBT ceramics with different dopant levels of KBT were characterized as a function of temperature and frequency for potential use of high-temperature capacitors. The BSBT ceramics with KBT exhibited high dielectric permittivities (ɛr) (>1700 at RT) and low dielectric loss over the temperature range from 100° to 300°C, with flat temperature coefficients of permittivity (TCɛs). In addition, BSBT ceramics with increasing KBT were observed to possess dielectric relaxation characteristics at temperatures (>RT) as observed in lead-based relaxors. Furthermore, high energy densities, being on the order of 4.0 J/cm3 at 220 kV/cm was observed for the BSBT–KBT20 ceramics from the electric-field polarization behavior.

High-Temperature Dielectrics in the BiScO3–BaTiO3–(K1/2Bi1/2)TiO3 Ternary System

K4CuNb8O23 doped K0.45Na0.55NbO3 (KNN-KCN) ferroelectric ceramics were found to exhibit asymmetrical polarization hysteresis loops, related to the development of an internal bias field. The internal bias field is believed to be the result of defect dipoles of acceptor ions and oxygen vacancies, which lead to piezoelectric "hardening" effect, by stabilizing and pinning of the domain wall motion. The dielectric loss for the hard lead-free piezoelectric ceramic was found to be 0.6%, with mechanical quality factors Q on the order of >1500. Furthermore, the piezoelectric properties were found to decrease and the coercive field increased, when compared with the undoped material, exhibiting a typical characteristic of "hard" behavior. The temperature usage range was limited by the polymorphic phase transition temperature, being 188degC. The full set of material constants was determined for the KNN-KCN materials. Compared with conventional hard PZT ceramics, the lead-free possessed lower dielectric and piezoelectric properties; however, comparable values of mechanical Q, dielectric loss, and coercive fields were obtained, making acceptor modified KNN based lead-free piezoelectric material promising for high-power applications, where leadfree materials are desirable.

Characterization of Hard Piezoelectric Lead-Free Ceramics

BaCu(B2O5) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B2O5) phase was formed at 700°C and melted above 850°C. The BaCu(B2O5) ceramic sintered at 810°C had a dielectric constant (ɛr) of 7.4, a quality factor (Q×f) of 50 000 GHz and a temperature coefficient of resonance frequency (τf) of −32 ppm/°C. As the BaCu(B2O5) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B2O5) was added to the Ba(Zn1/3Nb2/3)O3 (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B2O5) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q×f=16 000 GHz, ɛr=35, and τf=22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B2O5) ceramic sintered at 875°C for 2 h.

Synthesis of BaCu(B2O5) Ceramics and their Effect on the Sintering Temperature and Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Ceramics

Zn 2 SiO 4 ceramics synthesized by the conventional solid-state method exhibited a low Q × f value, possibly due to the formation of a ZnO second phase. However, with a small ZnO reduction from the Zn 2 SiO 4 ceramics, the ZnO second phase disappeared and grain growth occurred due to the formation of a Si-rich liquid phase. Specimens with a large grain size exhibited an improved Q × f value. In particular, the ceramics with nominal composition Zn 1.8 SiO 3.8 sintered at 1300°C exhibited improved microwave dielectric properties of e r = 6.6, Q × f = 147000 GHz, and τ f = -22 ppm/°C.

Effect of Zn/Si Ratio on the Microstructural and Microwave Dielectric Properties of Zn2SiO4 Ceramics

Re 3 Ga 5 O 12 (Re: Nd, Sm, Eu, Dy, Yb, and Y) garnet ceramics were synthesized and their microwave dielectric properties were investigated for advanced substrate materials in microwave integrated circuits. The Re 3 Ga 5 O 2 ceramics sintered at 1350°-1500°C had a high-quality factor (Q xf) ranging from 40 000 to 192173 GHz and a low-dielectric constant (e r ) of between 11.5 and 12.5. They also exhibited a relatively stable temperature coefficient of resonant frequency (if) in the range of -33.7 to - 12.4 ppm/°C. In particular, the Sm 3 Ga 5 O 12 ceramics sintered at 1450°C exhibited good microwave dielectric properties of e r = 12.4, Qxf= 192173 GHz, and τ f = -19.2 ppm/°C.

Jong Bong Lim

Papers

High-Temperature Dielectrics in the BiScO3–BaTiO3–(K1/2Bi1/2)TiO3 Ternary System

Characterization of Hard Piezoelectric Lead-Free Ceramics

Synthesis of BaCu(B2O5) Ceramics and their Effect on the Sintering Temperature and Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Ceramics

Effect of Zn/Si Ratio on the Microstructural and Microwave Dielectric Properties of Zn2SiO4 Ceramics

Synthesis and Microwave Dielectric Properties of Re3Ga5O12 (Re: Nd, Sm, Eu, Dy, Yb, and Y) Ceramics