Low-temperature Co-fired Ceramics Applications Research Articles

Phase transition and low-temperature sintering of Zn(Mn1-xAlx)2O4 ceramics for LTCC applications

Thephase transition, sinterability, and microwave dielectric properties of Zn(Mn1-xAlx)2O4 (0.2≤x≤0.9)solid solutions synthesized through a solid-state reaction were investigated. The densification temperature of the solid solutions decreased to 1250°C, which is much lower than that of the end members. All compositions showed a single phase with a tetragonal structure at x≤0.6and a cubic structure at 0.7≤x≤0.9. As the x value increased, the εr value decreased gradually along with an inflection point of a sharp drop at x=0.7. The Q×f value significantly increased initially and reached the maximum value of 14460GHz at x=0.8;it decreased thereafter. Meanwhile, the τf value was near the typical value of about ‒60ppm/°C to ‒80ppm/°C. TiO2and ZnO–B2O3(ZB) glass co-doping can effectively adjust the τf value of Zn(Mn0.2Al0.8)2O4composition, with the highest Q×f value near zero, and can reduce its sintering temperature to 950°C.The (1-y)Zn(Mn0.2Al0.8)2O4-yTiO2(y=0.26)ceramics with 5wt%ZB glass exhibited microwave dielectric properties (εr=12.71,Q×f=8126GHz, and τf=1.02ppm/°C) appropriate for application in low-temperature co-fired ceramics (LTCC).

Crystal structure and physical properties of microwave sintered Sr1−xLaxFe12−xCuxO19 (x=0–0.5) ferrites for LTCC applications

The Sr1−xLaxFe12−xCuxO19 (x=0–0.5) ferrites for use in low temperature co-fired ceramics (LTCC) technology were prepared by improved solid phase method. Dependence of their crystal structure, magnetic, electrical, and dielectric properties on La–Cu substitution amount were investigated. Pure M-type phase is obtained for the ferrites with La–Cu substitution amount x≤0.3. With x further increasing to 0.5, the multiphase structure is formed, where the M-type phase coexists with the LaFeO3 phase and Sr2FeO4−x phase. In single M-type phase region with x≤0.3, the varied magnetic properties can be well explained considering the occupancy effects of La3+ and Cu2+ ions in magnetoplumbite structure. Their electrical transport behavior is found to be correlated with La–Cu substitution amount. Single metal–semiconductor (M–S) transition is clearly observed in the ferrites with a high doping amount as x=0.3. The polarization behavior from 1kHz to 10MHz follows the charge polarization mechanism, and the temperature dependence of real permittivity (ε′–T curves) and dielectric loss (tgδ–T curves) strongly suggests the complicated multiparticle polarization and relaxation.

Microstructure, sintering and properties of CaO–Al2O3–B2O3–SiO2 glass/Al2O3 composites with different CaO contents

CaO–Al2O3–B2O3–SiO2 glass/Al2O3 composites for low temperature co-fired ceramics (LTCC) were prepared by tape casting method, and the effects of CaO content on the microstructure, sintering, and properties were discussed. Results showed that an appropriate CaO addition in CABS glass not only efficiently contributed to a dense glass/ceramic body, but also was endowed with better sintering characteristics, more excellent mechanical and dielectric properties. CABS glass/Al2O3 composites with 9 wt% CaO content sintered at 850 °C for 15 min exhibited bulk density of 3.10 g/cm3, Z-axis shrinkage of 15.3 %, flexural strength of 185 MPa, dielectric constant of 7.99 (at 7 GHz), dielectric loss of 1.8 × 10−3. After being co-fired with Ag electrodes, the glass/ceramic composites could perfectly match with Ag electrodes. It is indicated that this material could be a promising candidate for LTCC application.

Microwave dielectric properties of low-fired Li2MnO3 ceramics co-doped with LiF–TiO2

Li2MnO3 ceramics co-doped with 2wt% LiF and xwt% TiO2 (x=0, 3, 5, 7, 10) were prepared by solid-state reaction for low-temperature co-fired ceramics (LTCC) applications. The sintering temperatures of Li2MnO3 ceramics were successfully lowered to925°C due to the formation of a LiF liquid phase. Their temperature stability was improved by doping with TiO2. A typical Li2MnO3-2wt% LiF-5wt% TiO2 sample with well-densified microstructures displayed optimum dielectric properties (εr=13.8, Q×f= 23,270GHz, τf=1.2ppm/°C). Such sample was compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications in wireless communication systems.

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

ABSTRACTLi2MgTiO4 (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B2O3 additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B2O3 additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B2O3 sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B2O3 and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B2O3 sintered at 925°C for 4 h is suitable for LTCC applications.

Microwave dielectric properties of low-fired Li2TiO3–MgO ceramics for LTCC applications

Abstract We fabricated the low-fired Li 2 TiO 3 –MgO ceramics doped with LiF by a conventional solid-state route, and investigated systematically their sintering characteristics, microstructures and microwave dielectric properties. The results showed that temperature stability of Li 2 TiO 3 ceramics were improved by doping MgO. Well microwave dielectric properties for Li 2 TiO 3 –13 wt%MgO (LTM) ceramics with ɛ r = 16.4, Q × f = 87,500 GHz, and τ f = −1.2 ppm/°C were obtained at 1325 °C. Furthermore, addition of LiF enhanced the sinterability and optimized the microwave dielectric properties of LTM ceramics. A typically sample of LTM-4 wt%LiF ceramics with optimum dielectric properties ( ɛ r = 15.8, Q × f = 64,500 GHz, and τ f = −0.2 ppm/°C) were achieved at 850 °C for 4 h. Such sample was compatible with Ag electrodes, suitable for the low-temperature co-fired ceramics (LTCC) applications.

Influences of Li2O–B2O3–SiO2 Glass Addition on Microstructural and Magnetic Properties of LiZnTi Ferrites

Recently, a lot of research has been focusing on the surface mounted microwave gyromagnetic devices fabricated by low-temperature cofired ceramics (LTCC) technique [1-2]. LiZnTi-ferrite materials have been widely applied in microwave gyromagnetic devices, such as circulator, phase shifter in the electronically scanned phased array antennae, due to its low coercivity (Hc), appropriate saturation flux density (Bs) and dielectric constant, all of which can be tailored by various doping strategies [3]. But its high sintering temperature restrains its application in chip microwave gyromagnetic devices. Some low melting point glasses have been used to meet the requirements of sinterability for LTCC technology. The Li 2 O-B 2 O 3 -SiO 2 (LBS) glasses are usually used as a suitable additive for lowing the sintering temperature and dielectric loss of some microwave ceramics, making them suitable for LTCC application [4]. In this paper, the effects of Li 2 O-B 2 O 3 -SiO 2 (LBS) glass addition on the microstructures and properties of low-temperature fired LiTiZn-ferrites have been studied.

Dielectric properties of ultralow-fired Mg4Nb2O9 ceramics co-doped with TiO2 and LiF

The Mg4Nb2O9 co-doped with 20 wt% TiO2 (MNT) and x wt% LiF (1 ≤ x ≤ 8) composite ceramics were prepared by a solid-state reaction method for developing ultralow-fired (≤800 °C) microwave dielectric ceramics. The sintering temperatures of MNT ceramics were successfully lowered to 750 °C due to the formation of liquid phase (LiF). A secondary phase of MgTiO3 was observed at above 700 °C for MNT-8 wt% LiF ceramics. All the composite ceramics have the optimal bulk densities at 800 °C, which corresponds to the maximum Q × f value of 32,000 GHz and ɛr value of 15.7. The well microwave dielectric properties of ɛr = 15.6, Q × f = 25,000 GHz, and τf = −56 ppm/°C were obtained at 750 °C for 5 h for MNT-8 wt% LiF ceramics. This material is compatible with Ag electrodes, suitable for low-temperature co-fired ceramics applications.

Cu<sub>3</sub>TeO<sub>6 </sub>Dielectric Thick Films: Processing by Electrophoretic Deposition and Electrical Characterization

Te-based compounds are promising dielectric candidates for Base-Metal Electrode Multilayer Ceramic Capacitors (BME-MLCCs) and Low-Temperature Co-fired Ceramics (LTCCs) applications due to their low sintering temperature and good dielectric properties. In spite of the possible compatibility with Cu electrodes for microelectronics, data on compounds of the CuO-TeO2 system are scarce. Recently, we have reported the phase formation process of Cu3TeO6 and the first dielectric data for Cu3TeO6 ceramics. Due to the interest for some applications in thick films, in this work Cu3TeO6 thick films were fabricated by electrophoretic deposition (EPD) on platinized silicon substrates under different processing conditions. The relation between processing and film’s quality was established. ~ 50 μm Cu3TeO6 thick films sintered at 860 oC for 5 h exhibit a permittivity of ~2 and dielectric loss of 0.01 at room temperature and the temperature coefficient of the dielectric permittivity is 9.5×103 ppm°C-1 at 1 MHz from 40 °C to 120 °C. It is expected that this dielectric performance, when compared with the one of Cu3TeO6 ceramic counterparts, improves if the density of the films is increased.

Ultra-low sintering temperature ceramics for LTCC applications: a review

During past over 30 years, low temperature co-fired ceramic (LTCC) technology has been developed to meet with the requirements of small, light weight and multifunctional electronic components through enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrode. A recent technology is to develop new dielectrics with ultra-low sintering temperature (usually <650 °C) to save energy, reduce processing time, and to enable further integrations with semiconductors, metals or even plastics. In this review, we summarized the materials with ultra-low sintering temperature developed in past over 10 years, which will be helpful for those researchers to not only develop new materials but also improve all technologies in ultra-LTCC fields.

Effect of La–CO substitution on the crystal structure and magnetic properties of low temperature sintered Sr1−xLaxFe12−xCoxO19 (x=0–0.5) ferrites

The La–Co substituted Sr1−xLaxFe12−xCoxO19 (x=0–0.5) ferrites with appropriate Bi2O3 additive were prepared at a low sintering temperature of 890°C compatible with LTCC (low temperature co-fired ceramics) systems, and the effect of La–Co substitution on their crystal structure and magnetic properties was investigated. The results show that the pure M-type phase is successfully obtained when the La–Co substitution amount x does not exceed 0.3. However, the single M-type phase structure transforms to multiphase structure with further increased x, where the α-Fe2O3 phase and La2O3 phase coexist with the M-type phase. Moreover, the saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC of the ferrites depend on the La–Co substitution amount strongly, which are suggested to be determined by the partially substitution of La3+–Co2+ ions for Sr2+–Fe3+ ions with x not higher than 0.3. It is found that the obtained Sr1−xLaxFe12−xCoxO19 (x=0.2 and 0.3) ferrites can provide improved magnetic properties (Ms>62emu/g, Ha>1400kA/m, and Hci>320kA/m) as low temperature sintered M-type hexaferrites for microwave LTCC applications.

Low-Temperature Sintering and Microwave Dielectric Properties of Zn2SiO4 Ceramic Added with Crystalline Zinc Borate

The physical and dielectric properties of composites of known microwave materials, Zn2SiO4 and Zn3B2O6, prepared by solid-state reaction, were investigated with the purpose of developing a low-loss dielectric material for low-temperature co-fired ceramic applications. An off-stoichiometric phase of Zn2SiO4 with extra SiO2 was used to avoid the occurrence of unreacted ZnO. During sintering, zinc borate was found to partially react with residual SiO2 to form Zn2SiO4. The residual zinc borate was converted to a boron-rich glassy phase which helped to reduce the sintering temperature of the composite. Good relative sintering density (>90%) at temperatures below the melting temperature of zinc borate is indicative of a sintering mechanism of diffusion-based mass transfer. Composites containing 15 wt.% zinc borate, 2.5 wt.% lithium carbonate and 20 wt.% zinc borate in zinc silicate had dielectric constants of 6.8 and 6.1, quality factors (Q×f) of 48,800 and 94,300 GHz when sintered at 900°C and 950°C, respectively. These quality factor results are close to the best values reported for zinc silicate at these sintering temperatures.

Novel zinc manganese oxide-based microwave dielectric ceramics for LTCC applications

Low-temperature co-fired ceramics (LTCCs), with a Zn(Mn1−xTix)3O7 (0≤x≤1.0) composition, were prepared using a conventional solid-state method. A novel ZnMn3O7 ceramic was obtained, with a ZnMn2O4 spinel structure, εr of 7.32, Q×f of 13,667GHz, and τf of −58.33ppm/°C. The effect of various dopant concentrations on the microstructure and microwave dielectric properties of the material was investigated. Results showed that the increase in dopant concentration changed the phase composition, improved the microwave dielectric properties, and reduced the sintering temperature of the Zn(Mn1−xTix)3O7 by a factor of 250°C. The dielectric constant of Zn(Mn1−xTix)3O7 varied from 7.32 to 33.08 at x=0.8. However, the maximum value was reduced to 27.67 at x=1.0. Moreover, the value of Q×f increased significantly up to a maximum value of 18,934GHz, whereas τf changed gradually from −58.33ppm/°C to +289.25ppm/°C. In addition, promising LTCC materials with stable temperature characteristics and co-firing compatibility with silver electrodes can be obtained in the nominal Zn(Mn1−xTix)3O7 (x=0.68) ceramics with 5wt% ZnO–B2O3 glass sintered at 900°C. This material possesses the following microwave dielectric properties: εr of 18.2, Q×f of 12,018GHz, and τf of −3.98ppm/°C.

Structures, phase transformations, and dielectric properties of (1−x)Bi2Zn2/3Nb4/3O7–xBi1.5NiNb1.5O7 pyrochlore ceramics prepared by aqueous sol–gel method

As a candidate of thermostable low temperature co-fired ceramics (LTCC) material, (1−x)Bi2Zn2/3Nb4/3O7–xBi1.5NiNb1.5O7 (0.0⩽x⩽1.0) ceramics with improved dielectric properties have been prepared via aqueous sol–gel method. The relations of phase equilibrium, crystal structure and dielectric properties of the composites were investigated systematically. Phase transformation, from orthorhombic zirconolite-like to cubic pyrochlore structure, occured with the increasing Bi1.5NiNb1.5O7 content. The phase stability of the orthorhombic and cubic pyrochlore phase in the (1−x)β-BZN–xBNN system was dependent on the Bi3+ content as well as the distribution and variety of divalent cations, such as Ni2+/Zn2+ ratio. The phase boundaries were located around x=0.1 and x=0.6 for orthorhombic and cubic phases, respectively. Near-zero temperature coefficient of dielectric constant (τε) was obtained and the dielectric constant (εr) was in the range of 80–165 in this system, which were strongly correlated with phase composition. The (1−x)β-BZN–xBNN ceramic with x=0.2 satisfied the EIA (Electronic Industries Association) specification NP0 (τε≤± 30ppm/°C between −55 and 125°C) exhibited excellent dielectric properties of εr=105.6, small dielectric tangent (tanδ)∼10−4, τε=−11.1ppm/°C with the low-firing temperature of 900°C within the two-phase region, which can be a promising candidate for LTCC and multilayer components applications in high frequency and microwave range.

Li2Zn3Ti4O12–Ba3(VO4)2 microwave dielectric ceramics sintered at a low temperature without glass addition

The microstructure and microwave dielectric properties of the (1−x)Li2Zn3Ti4O12–xBa3(VO4)2 composite ceramics prepared via a solid-state reaction method have been investigated systematically by using an X-ray diffractometer (XRD), a scanning electron microscope equipped with an energy dispersive spectrometer and a microwave network analyzer. The XRD results exhibited that the Li2Zn3Ti4O12 and Ba3(VO4)2 ceramic could coexist well in the sintered bodies, and no other secondary phase was detected. The microstructure and microwave dielectric properties of the composite ceramics were found to be obviously dependent on the sintering temperature and phase composition. With the addition of the Ba3(VO4)2 phase, the sintering temperature of the Li2Zn3Ti4O12 ceramic could be reduced effectively and its temperature coefficient of resonant frequency (τf) value could also be adjusted to near zero together with a comparable quality factor (Q × f) value. Excellent microwave dielectric properties of dielectric constant er ~ 16.9, Q × f ~51,322 GHz and τf ~+3.3 ppm/°C were obtained in the 0.4Li2Zn3Ti4O12–0.6Ba3(VO4)2 composite ceramic, when sintered at 950 °C for 4 h. The good chemical compatibility between the 0.4Li2Zn3Ti4O12–0.6Ba3(VO4)2 composite ceramic and silver electrode indicates that the as-prepared composite ceramic is suitable for low-temperature cofired ceramic (LTCC) applications.

Effect of Li2O–V2O5 addition on the sintering behavior and microwave dielectric properties of Li3(Mg1−xZnx)2NbO6 ceramics

The effect of Zn2+ substitution on the structure and microwave dielectric properties of Li3Mg2NbO6 ceramic was investigated. The compositions of Li3(Mg1−xZnx)2NbO6 (0≤x≤0.1) ceramics were prepared by the solid-state reaction method. The phase structure, microstructure and microwave dielectric properties of Li3(Mg1−xZnx)2NbO6 ceramics were analyzed via an X-ray diffraction, a scanning electron microscope as well as a network analyzer. All samples sintered at 1080–1240°C for 4h remained a single orthorhombic structure, which could be indexed according to the Li3Mg2NbO6 phase (JCPDS-PDF #86-0346). The microwave dielectric properties of Li3(Mg1−xZnx)2NbO6 ceramics exhibited significant dependence on the sintering condition, microstructure and composition. Excellent microwave dielectric properties (εr~17.2, Q×f~142,331GHz, τf~−23.2ppm/°C) were obtained in the x=0.08 sample sintered at 1120°C for 4h in air. In addition, the 0.17Li2O–0.83V2O5 composition was added as a sintering aid to lower the sintering temperature. The 0.5wt% 0.17Li2O–0.83V2O5 added Li3(Mg0.92Zn0.08)2NbO6 ceramic showed fairly good microwave dielectric properties of εr~14, Q×f~83,395GHz, τf~−37.2ppm/°C when sintered at 925°C for 2h. Furthermore, there was no chemical reaction between Ag electrode and the sintering aid added sample, which further demonstrates that the Li3(Mg0.92Zn0.08)2NbO6 ceramic modified with 0.17Li2O–0.83V2O5 would be a promising candidate material for low-temperature cofired ceramic (LTCC) applications.

Influence of Al2O3/SiO2 ratio on the microstructure and properties of low temperature co-fired CaO–Al2O3–SiO2 based ceramics

In this work, in order to obtain the materials for low temperature co-fired ceramics applications, CaO–Al2O3–SiO2 (CAS) based ceramics were synthesized at a low sintering temperature of 900 °C. The influences of Al2O3/SiO2 ratio on the microstructure, mechanical, electrical and thermal properties were studied. According to the X-ray diffractomer and scanning electron microscopy results, the addition of the Al2O3 is advantageous for the formation of the desired materials. Anorthite(CaAl2Si2O8) is the major crystal phase of the ceramics, and the SiO2 phase is identified as the secondary crystal phase. No new crystal phase appears in the ceramics with the increasing Al2O3 content. More or less Al2O3 addition would all worsen the sintering, mechanical and dielectric properties of CAS based ceramics. The ceramic specimen (Al2O3/SiO2 = 20/18.5) sintered at 900 °C shows good properties: high bending strength = 145 MPa, low dielectric constant = 5.8, low dielectric loss = 1.3 × 10−3 and low coefficient of thermal expansion value = 5.3 × 10−6 K−1. The results indicate that the prepared CAS based ceramic is one of the candidates for low temperature co-fired ceramic applications.

Structural evolution and microwave dielectric properties of MgO–LiF co-doped Li2TiO3 ceramics for LTCC applications

In this study, MgO–LiF co-doped Li2TiO3 ceramics were prepared by the conventional solid-state ceramic route. Continuous solid solutions between Li2TiO3, LiF and MgO were formed across the entire compositional range. With increasing MgO content, the degree of long range order decreased, and the crystalline structure transformed from monoclinic phase to cubic phase. The addition of LiF significantly promoted the sinterability of Li2TiO3 based ceramics and successfully reduced the sintering temperature. The Qf and τf values could be further optimized by doping MgO. Well-densified structure with excellent microwave dielectric properties of εr=23.21, Qf=131,668GHz, and τf=−0.46ppm/°C was obtained for 0.87Li2TiO3–0.05MgO–0.08LiF ceramics sintered at 950°C. In addition, Li2TiO3–MgO–LiF ceramics were compatible with Ag electrodes, making them suitable for low-temperature co-fired ceramic (LTCC) applications.

Preparation and microwave dielectric properties of Li(Mg1–xCox)PO4 ceramics for low-temperature cofired ceramic applications

Li(Mg1–xCox)PO4 (x=0–0.09) ceramics were prepared by the conventional solid-state ceramic method. The formation of single-phase Li(Mg1–xCox)PO4 solid solutions is confirmed by the X-ray diffraction (XRD) patterns. Co2+ substitution for Mg2+ can lower the sintering temperature and enhance the Qf value of LiMgPO4 ceramics. The LiMg0.95Co0.05PO4 ceramic sintered at 875°C reaches a maximum relative density of 97.4% and shows the microwave dielectric properties of εr=6.97, Qf=111,200GHz, and τf=–53.8ppm/°C. The negative τf value can be tuned nearly to zero by adding TiO2. The LiMg0.95Co0.05PO4–TiO2 composite ceramic with 16.1wt% TiO2 sintered at 875°C for 2h shows a near-zero τf value of +0.8ppm/°C, together with an εr value of 9.97 and a Qf value of 58,200GHz. The composite ceramic does not react with the commonly used electrode material silver and is a promising candidate for low-temperature cofired ceramic applications.

A new microwave dielectric ceramics for LTCC applications: Li2Mg2(WO4)3 ceramics

A novel microwave dielectric ceramics Li2Mg2(WO4)3 (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the Li2Mg2(WO4)3 ceramics were investigated. The optimal sintering temperature of dense Li2Mg2(WO4)3 ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: e r = 7.72, Q × f = 29,600 GHz (f = 6.0 GHz), and τ f = −15.5 ppm/°C. Moreover, the Li2Mg2(WO4)3 ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application.