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Ultralow sintering temperature and permittivity with excellent thermal stability in novel borate glass-ceramics
Journal of Non-Crystalline Solids 521 (2019) 119527
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Ultralow sintering temperature and permittivity with excellent thermal stability in novel borate glass-ceramics
T
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Juan Xi1, Baobiao Lu1, Jingjing Chen, Guohua Chen , Fei Shang, Jiwen Xu, Changrong Zhou, Changlai Yuan School of Material Science and Engineering, Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Glass-ceramic LTCC Dielectric properties
A novel CuO-ZnO-B2O3-Li2O glass-ceramic was prepared by solid phase method, and. Its phase transition, sintering and dielectric performance was studied. No crystalline phase is observed for the specimen sintered at 560 °C. However, the samples sintered at 580 °C and 600 °C, consist of ZnB4O7 and Cu2B4O7. And the Li2CuB4O8 appears with further increasing temperature. The εr and τf change slightly but the Q × f value alter greatly with firing temperature. The glass-ceramic fired at 620 °C possesses optimum properties with εr = 3.33, Q × f = 17,724 GHz and τf ≈ 0 ppm/°C. Furthermore, the as-prepared glass-ceramic exhibits good co-firing compatibility with Ag and Al electrode. These properties qualify the dielectric material as promising alternatives for wireless communication applications.
1. Introduction
good dielectric properties of εr = 6.7–7.5, tanδ≤1 × 10−3(1-10 MHz) and ultralow sintering temperature(650 °C). However, the τf was too high, which limited its application. Ma et al. [19]presented that CuOB2O3-Li2O glass-ceramics sintered at 625 °C adopted dielectric properties of εr = 5.84 and Q × f = 10,120 GHz, but the τf (−33 ppm/°C) was still large, causing the poor thermal stability. The literature shows that the addition of ZnO in the glass-ceramics can reduce the εr value and increase the Q × f value, resulting perfect dielectric properties [17]. S. Rao et al. reported the 30Li2O-(10-x)ZnO -60B2O3:xCuO (0 ≤ x ≤ 6 mol%) glass system, which had a low permittivity [20]. In summary, we can infer that the CuO-B2O3-Li2O glass-ceramic added ZnO might have comprehensive good microwave dielectric properties. In this work, the CuO-ZnO-B2O3-Li2O (abbreviated to CZBL, similarly hereinafter) glass-ceramics were successfully fabricated by electronic ceramic method By studying the phase evolution, structure and dielectric properties at microwave frequency as a function of firing temperature, a ULTCC material with excellent comprehensive properties was obtained, and the co-firing compatibility between the CZBL glass-ceramics and Ag, Al electrodes was also investigated.
The substrates with short delay time, high density packaging and good compatibility which can realize miniaturization and integration of electronic components, have been drew much attention [1–6].The substrate materials, applied in low temperature co-fired ceramic (LTCC) technology, must exhibit a low permittivity (εr < 10), a high product of quality factor and frequency (Q × f ≥ 5000GHz), a near-zero temperature coefficient of resonance frequency (τf) and low firing temperature (≤ 900 °C) to ensure high signal transmission speed, good frequency selection characteristics and good thermal stability of the frequency as well as co-firing with high thermal conductivity metals such as Cu, Ag and Au [7–10]. Recently, to further conserve energy, shorten delay time and integrate with others, such as semiconductors, metals, and plastics, ultralow temperature (< 650 °C) co-firing ceramic (ULTCC) technology arises at the historic moment [11,12]. To realize ultra-low sintering temperature, two common material systems, i.e. glass+ceramics and ceramics with intrinsic ultralow firing temperature, may be selected [13–16].In practical application of ULTCC technology, the former has higher loss at high frequency. As for the latter, the higher dielectric constants (> 10) will increase the single delay time [14,15], and most materials can react with Ag electrode in the co-fired process. Lately, Yu et al. [17,18]found the borate glass-ceramics showed
⁎
Corresponding author. E-mail address: [email protected] (G. Chen). 1 These authors contributed equally. https://doi.org/10.1016/j.jnoncrysol.2019.119527 Received 12 April 2019; Received in revised form 15 June 2019 Available online 05 August 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.
2. Experimental procedures A optimized glass composition of 16CuO-16ZnO-63B2O3-5Li2O (in mass percent) was chosen according to experimental results. The initial
Journal of Non-Crystalline Solids 521 (2019) 119527
J. Xi, et al.
reagent-grade raw materials of CuO and ZnO(≥99%), H3BO3 and Li2CO3(≥99.5%) were dried and weighed according to the above glass composition. The mixed batch was kept in a high temperature furnace at 1150 °C for 1 h to get glass liquid, and then the glass melt is poured into water quenched to obtain glass slag. The glass slag was ball ground for 6 h in a ball mill at a speed of 300 r/min. The glass powders were dried at 100 °C for 8 h and then pressed at 5 MPa to form disk pellets with a diameter of 12 mm and thick of 4–8 mm. The pellets were then sintered at 560–580 °C for 1 h at a heating rate of 4 °C/min. The thermal behavior of the glass powder was characterized by a differential thermal analyzer (DTA, Netzsch STA-449-F3, Germany).The absorption spectrum of the glass was measured using an infrared spectrophotometer (FT-IR, Nicolet 6700, America).The phase evolution was investigated by powder X-ray diffractometer (XRD) (D8-Advance, Bruker, Germany) with Cu Kα radiation(1.5406 Å) in the 2θ range 20–80°.The surface microstructure of the sintered specimens was investigated by a field-emission scanning electron microscope(FE-SEM) (Quanta FEG450, America) equipped with an energy dispersive spectrometer (EDS). The compatibility of co-firing with electrodes was evaluated by using FE-SEM, XRD and EDS. The Archimedes method was employed for measuring density of the glass-ceramic. The dielectric property at microwave frequency was obtained by a Network tester (N5230C, Agilent).The value of τf was gained among 25 °C to 75 °C using the following formula [21]:
τf =
(f75 − f25 ) × 106 50 × f25
ppm/oC
(1)
where f75 and f25were the resonant frequencies at 75 °C and 25 °C, respectively. 3. Results and discussion Fig. 1(a) displays the DTA curve of CZBL glass. The temperature of 485 °C is identified as glass transition temperature. And two obvious exothermic peaks located at 559oCand 640 °C are observed. The first exothermic peak(weak peak) at559oC is ascribed to the crystallization of ZnB4O7and Cu4B2O7 confirmed by the XRD results (seen in Fig. 2), and the second exothermic peak(sharp peak) at 640 °C may be owing to the formation of Li2CuB4O8 as seen in Fig. 2. Fig.1(b)exhibits the room-temperature FT-IR spectrum of CZBL glass. A broad band extending from 3000 to 3625 cm−1 is for hydroxyl or absorbed water group. The absorption peak located at 3424 cm−1 is derived from the asymmetric stretching vibration of OeH. The vibration modes of the borate units are primarily seen in three absorption peak: 1385 cm−1 absorption peak is the strongest, indicating that the boron-oxygen bond (=B-O) in the trihedron has the strongest antisymmetric stretching vibration, the next weaker absorption peak at 1069 cm−1 is due to the stretching vibration of boron atoms in the boron tetrahedron [BO4] connected to non-bridging oxygen (≡B-O). The absorption peak at 704 cm−1 is ascribed to the result of = B-O-B bending deformation vibration of the boron trihedron [BO3] [22]. The XRD profiles of CZBL glass-ceramics sintered at 560–640 °C are shown in Fig. 2.It is clearly that the formation of crystallized phase is dependent on sintering temperature. No crystallization is detected below580°C. Zinc borate (ZnB4O7) and copper borate(Cu2B4O7) are main crystalline phase for the specimens sinteredat 580 °C and 600 °C. The existence of fine size crystallites devotes to broad diffraction peaks. With increasing temperature to 620 °C,the diffraction intensity of crystalline phase increases, indicating that the growth of crystallites and the increase of phase content of ZnB4O7and Cu2B4O7. Meanwhile, the Li2CuB4O8 crystalline phase comes out. With further increasing temperature to 640 °C, crystalline phases are still ZnB4O7, Cu2B4O7 and Li2CuB4O8. However, the intensities of the diffraction peaks for ZnB4O7 and Cu2B4O7 slightly reduce, indicating that the quantity of these two phases decreases.
Fig. 1. DTA curve (a) and FT-IR spectrum (b) of CZBL glass.
Fig. 2. XRD patterns of the obtained CZBL glass-ceramics.
Fig. 3 shows the SEM pictures of the fired CZBL samples. When sintering temperature is under 580 °C, the samples exhibit porous microstructure shown in Fig.3(a)-(b), indicating the sintering process just begin. With increasing temperature from 600 °C to 620 °C, the dense glass-ceramic can be achieved, as seen in Fig. 3(c)- (d). However, 2
Journal of Non-Crystalline Solids 521 (2019) 119527
J. Xi, et al.
Fig. 3. SEM photographs of CZBL specimens sintered at various temperatures. a. 560 °C, b 580 °C, c. 600 °C, d. 620 °C, e. 640 °C.
excessive firing temperature (640 °C) gives rise to a slight increment of porosity, which is due to the result of over-sintering, as seen in Fig.3(e) [23,24]. The bulk densities and permittivity of CZBL specimens sintered at 580–640 °C are displayed in Fig.4(a). The specimen sintered at 560 °C shows the lowest density of 2.34 g/cm3. Enhancing firing temperature makes the density of sample increase. A highest density of 2.75 g/cm3 is obtained when fired at 620 °C. With further increasing sintering temperature to 640 °C, on the contrary, the bulk density is decreased to 2.60 g/cm3 due to over-sintering. This variation trend is well in agreement with the microstructure change presented in Fig.3. Fig. 4(a) displays the permittivity (εr) of glass-ceramics as a function of firing temperature. Obviously, the εr firstly raises and then declines with the increment in sintering temperature, which is consistent with the varying tendency in the bulk density. Therefore, the porosity or densification degree is the main factor affecting the dielectric constant rather than the grain size. The samples sintered at temperatures of 560–580°Chave low εr resulted from their low density. The maximal value of dielectric constant could be gained at 620 °C. The measured dielectric constant of the base glass is 3.01, which is due to the presence of strong nonmetallic polar covalent bonds in the [BO3] and [BO4] groups with low dielectric polarizabilities [25].Moreover, Cu2B4O7, ZnB4O7 and Li2CuB4O8 also own a low εr. As a result, the dielectric
constant for CZBL glass-ceramics is between 3.1 and 3.4, keeping at an ultra-low level compared to the other glass-ceramics [26–29]. Fig. 4(b) illustrates the Q × f values of CZBL samples with firing temperature. The variation in Q × f values is also consistent with that of the bulk density. The dielectric loss at microwave frequency is chiefly affected by inherent loss such as lattice vibration, and by external losses such as porosity, grain size, and phase types. With sintering temperature increasing, the Q × f values of the sample increase and run up to the maximum of 17,724 GHz at 620 °C. The measured Q × f value of CZBL glass is 3875 GHz. And all of Cu2B4O7, ZnB4O7 and Li2CuB4O8 have much higher Q × f value. Therefore, with the increment of firing temperature, the porosity reduces, the grains grow up, and the quantity of the crystal phase increases, resulting in the Q × f value increasing, as shown in Fig.4(b). However, excessive firing temperature (640 °C) leads to the increase of pores and the decrease of crystalline phase, which gives rise to the Q × f value reducing. The τf value of CZBL glassceramic samples is stable in the small range of 0–3 in the temperature range of 560 °C to 640 °C.This finding indicates that dense sample is achieved and has the best comprehensive performance at 620 °C. Fig. 4(c) demonstrates the εr of glass-ceramics upon different testing temperatures at 200KHz. It is observed that the dielectric constant is almost steady between 5.5 and 6 during the temperature of 60 °C to 200 °C, indicating that the CZBL glass-ceramic material possesses good 3
Journal of Non-Crystalline Solids 521 (2019) 119527
J. Xi, et al.
Fig. 4. Bulk density and permittivity (a), Q × f and τf values (b) of CZBL glassceramics sintered at various temperatures, and permittivity of CZBL glassceramics as a function of test temperature (c).
dielectric thermal stability. For ULTCC application, it is necessary to study the co-firing characteristics between glass-ceramic materials and Ag or Al electrodes. The XRD profiles in Fig.5(a) indicate that three crystalline phases (Cu2B4O7, ZnB4O7and Li2CuB4O8), the metals(Ag and Al), and trace amount of Al2O3 attributed to oxidation of aluminum in the air during firing process exist, no any impurity phase appears. It is observed in Fig.5(b) that the big grain with grey dark color is Al2O3, which is consistent with EDS test results. As shown in Fig.5(c), the brighter color region can be confirmed as Ag identified by EDS analysis. The comprehensive analysis results illustrate that the CZBL glass-ceramic do not react with Ag or Al at 620 °C, which makes the CZBL glass-ceramic great potential application in ULTCC field.
Fig. 5. XRD profile (a), BES photograph and EDS result of CZBL material cofired with 20 wt% Al powders (b), and with 20 wt% Ag powders(c) at 620 °C for 1 h.
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Journal of Non-Crystalline Solids 521 (2019) 119527
J. Xi, et al.
4. Conclusions
of multilayer ceramic chips with Ag/Pd electrodes, Ceram. Int. 27 (2001) 889–893. [11] H.T. Yu, J.S. Liu, W.L. Zhang, S.R. Zhang, Ultra-low sintering temperature ceramics for LTCC applications: a review, J. Mater. Sci. Mater. Electron. 26 (2015) 9414–9423. [12] J. Dhanya, E.K. Suresh, R. Naveenraj, R. Ratheesh, Synthesis and characterization of Na5M(MoO4)4 (M=Y, Yb) microwave ceramics for ULTCC applications, Ceram. Int. 44 (2018) 6699–6704. [13] C.J. Dileep Kumar, T.K. Sowmya, E.K. Sunny, Raghu,“influence of nature of filler on densification of Anorthite-based Crystallizable glass+ceramic system for low temperature Cofired ceramics application,”, J. Am. Ceram. Soc. 92 (3) (2009) 595–600. [14] H.C. Xiang, Y. Tang, L. Fang, H. Porwal, C.C. Li, A novel ultra-low temperature cofired Na2BiZn2V3O12 ceramic and its chemical compatibility with metalelectrodes, J. Mater. Sci.Mater. Electron. 28 (2017) 1508–1513. [15] D. Zhou, C.A. Randall, L.X. Pang, H. Wang, X.G. Wu, J. Guo, G.Q. Zhang, L. Shui, X. Yao, Microwave Dielectric Properties of Li2(M2+)2Mo3O12 and Li3(M3+) Mo3O12 (M=Zn, Ca, Al, and In) Lyonsite-Related-Type Ceramics with Ultra-Low Sintering Temperatures, J. Am. Ceram. Soc. 94 (3) (2011) 802–805. [16] N. Joseph, J. Varghese, T. Siponkoski, M. Teirikangas, M.T. Sebastian, H. Jantunen, Glass-Free CuMoO4 Ceramic with Excellent Dielectric and Thermal Properties for Ultralow Temperature Cofired Ceramic Applications, ACS Sustain. Chem. Eng. 4 (2016) 5632–5639. [17] W. H, K. Yu, K. Ju, M. Wang, A novel glass-ceramic with ultra-low sintering temperature for LTCC application, J. Am. Ceram. Soc. 97 (3) (2014) 704–707. [18] H.T. Yu, J.S. Liu, M.S. Zeng, Structure and dielectric properties of zinc borate glass–ceramics modified by magnesium, J. Mater. Sci. Mater. Electron. 27 (2016) 7109–7114. [19] M.S. Ma, Z.Q. Fu, Z.F. Liu, Fabrication and microwave dielectric properties of CuOB2O3-Li2O glass-ceramic with ultra-low sintering temperature, Ceram. Int. 43 (2017) S292–S295. [20] S. Rao, J. Raju, N. Raju, Dielectric studies of Li2O-ZnO-B2O3 glasses doped with copper ions, J. Chem. Pharm. Sci. 9 (1) (2016) 620–621. [21] T. Nishikawa, K. Wakino, H. Tamura, IEEE MTT-S International Microwave Symposium Digest, 87 (1987), pp. 277–280. [22] S.G. Motke, S.P. Yawale, S.S. Yawale, Infrared spectra of zinc doped lead borate glasses, Bull. Mater. Sci. 25 (1) (2002) 75–78. [23] X.F. Luo, L.C. Ren, Y.S. Xia, Y.K. Hu, W.Y. Gong, M.C. Cai, H.Q. Zhou, Microstructure, sinterability and properties of CaO-B2O3-SiO2 glass/Al2O3 composites for LTCC application, Ceram. Int. 43 (2017) 6791–6795. [24] Y.F. Hu, X.G. Miao, Comparison of hydroxyapatite ceramics and hydroxyapatite/ borosilicate glass composites prepared by slip casting, Ceram. Int. 30 (2004) 1787–1791. [25] M. Ohsahi, H. Ogawa, A. Kan, E. Tanaka, Microwave dielectric properties of low temperature sintered Li3AlB2O6 ceramic, J. Eur. Ceram. Soc. 25 (2005) 2877–2881. [26] V. Chaware, R. Deshmukh, C. Sarode, S. Gokhale, G. Phatak, Low-Temperature Sintering and Microwave Dielectric Properties of Zn2SiO4 Ceramic Added with Crystalline Zinc Borate, J. Mater. Sci.Mater. Electron 44 (7) (2015) 2312–2320. [27] M. He, S.R. Zhang, X.H. Zhou, B. Li, J. Wan, Dielectric and microwave properties of ZrO2 doped CaO-SiO2-B2O3 ceramic matrix composites, J. Alloys Compd. 509 (2011) 4260–4263. [28] D.F. He, C. Gao, Effect of boron on crystallization, microstructure and dielectric properties of CBS glass-ceramics, Ceram. Int. 44 (2018) 16246–16255. [29] L.S. Xie, C.W. Zhong, Z.X. Fang, Y. Zhao, B. Tang, S.R. Zhang, Microwave dielectric properties of Li2OxMgOZnOB2O3SiO2 glass-ceramics (x= 3050wt%), J. Ceram. Soc. Jpn. 126 (3) (2018) 163–169.
In this work, the CuO-ZnO-B2O3-Li2O system glass-ceramic has been developed. The dielectric properties depend upon sintering temperature and phase compositions. The glass-ceramic sintered at 620 °C for 60 min, possessing three crystalline phases of Cu2B4O7, ZnB4O7and Li2CuB4O8 as well as outstanding frequency thermal stability, displays an ultralow dielectric constant of 3.33 and a high Q × f value of 17,724 GHz. The as-obtained glass-ceramic do not react with Ag and Al electrodes. These excellent performances would enable this novel dielectric material to applied in high-speed wireless communication field. Conflicts of interest The authors declare no conflicts of interest. Acknowledgements This work was financially supported by National College Students Innovation and Entrepreneurship Training Program (Nos. 201810595014, 201810595015). References [1] M.T. Sebastian, R. Ubic, H. Jantunen, Low loss dielectric materials and their properties, Int. Mater. Rev. 60 (7) (2015) 392–412. [2] D. Szwagierczak, B. Synkiewicz, J. Kulawik, Low dielectric constant composites based on B2O3 and SiO2 rich glasses, cordierite and mullite, Ceram. Int. 44 (2018) 14495–14501. [3] O. Dernovsek, A. Naeini, G. Preu, W. Wersing, M. Eberstein, W.A. Schiller, LTCC glass-ceramic composites for microwave application, J. Am. Ceram. Soc. 21 (2001) 1693–1697. [4] D.H. Jiang, J.J. Chen, B.B. Lu, J. Xi, G.H. Chen, A new glass–ceramic with low permittivity for LTCC application, J. Mater. Sci. Mater. Electron. 29 (2018) 18426–18431. [5] D.H. Jiang, J.J. Chen, B.B. Lu, J. Xi, F. Shang, J.W. Xu, G.H. Chen, Preparation, crystallization kinetics and microwave dielectric properties of CaO-ZnO-B2O3-P2O5 -TiO2 glass-ceramics, Ceram. Int. 45 (2019) 8233–8237. [6] C.C. Xia, D.H. Jiang, G.H. Chen, Y. Luo, B. Li, C.L. Yuan, C.R. Zhou, Microwave dielectric ceramic of LiZnPO4 for LTCC applications, J. Mater. Sci. Mater. Electron. 28 (2017) 12026–12031. [7] M.T. Sebastian, H. Jantunen, Low loss dielectric materials for LTCC applications: a review, Int. Mater. Rev. 53 (2) (2008) 57–90. [8] M.T. Sebastian, H. Wang, H. Jantunen, Low temperature co-fired ceramics for LTCC application: a review, Curr.Opin. Solid. State. Mater. Sci. 20 (2016) 151–170. [9] Y.G. Wang, G.N. Zhang, J.S. Ma, Research of LTCC/cu, ag multilayer substrate in microelectronic packaging, Mater. Sci. Eng. B 94 (2002) 48–3. [10] R.Z. Zuo, L.T. Li, Z.L. Gui, Interfacial development and microstructural imperfection
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Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Ultralow sintering temperature and permittivity with excellent thermal stability in novel borate glass-ceramics
T
⁎
Juan Xi1, Baobiao Lu1, Jingjing Chen, Guohua Chen , Fei Shang, Jiwen Xu, Changrong Zhou, Changlai Yuan School of Material Science and Engineering, Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Glass-ceramic LTCC Dielectric properties
A novel CuO-ZnO-B2O3-Li2O glass-ceramic was prepared by solid phase method, and. Its phase transition, sintering and dielectric performance was studied. No crystalline phase is observed for the specimen sintered at 560 °C. However, the samples sintered at 580 °C and 600 °C, consist of ZnB4O7 and Cu2B4O7. And the Li2CuB4O8 appears with further increasing temperature. The εr and τf change slightly but the Q × f value alter greatly with firing temperature. The glass-ceramic fired at 620 °C possesses optimum properties with εr = 3.33, Q × f = 17,724 GHz and τf ≈ 0 ppm/°C. Furthermore, the as-prepared glass-ceramic exhibits good co-firing compatibility with Ag and Al electrode. These properties qualify the dielectric material as promising alternatives for wireless communication applications.
1. Introduction
good dielectric properties of εr = 6.7–7.5, tanδ≤1 × 10−3(1-10 MHz) and ultralow sintering temperature(650 °C). However, the τf was too high, which limited its application. Ma et al. [19]presented that CuOB2O3-Li2O glass-ceramics sintered at 625 °C adopted dielectric properties of εr = 5.84 and Q × f = 10,120 GHz, but the τf (−33 ppm/°C) was still large, causing the poor thermal stability. The literature shows that the addition of ZnO in the glass-ceramics can reduce the εr value and increase the Q × f value, resulting perfect dielectric properties [17]. S. Rao et al. reported the 30Li2O-(10-x)ZnO -60B2O3:xCuO (0 ≤ x ≤ 6 mol%) glass system, which had a low permittivity [20]. In summary, we can infer that the CuO-B2O3-Li2O glass-ceramic added ZnO might have comprehensive good microwave dielectric properties. In this work, the CuO-ZnO-B2O3-Li2O (abbreviated to CZBL, similarly hereinafter) glass-ceramics were successfully fabricated by electronic ceramic method By studying the phase evolution, structure and dielectric properties at microwave frequency as a function of firing temperature, a ULTCC material with excellent comprehensive properties was obtained, and the co-firing compatibility between the CZBL glass-ceramics and Ag, Al electrodes was also investigated.
The substrates with short delay time, high density packaging and good compatibility which can realize miniaturization and integration of electronic components, have been drew much attention [1–6].The substrate materials, applied in low temperature co-fired ceramic (LTCC) technology, must exhibit a low permittivity (εr < 10), a high product of quality factor and frequency (Q × f ≥ 5000GHz), a near-zero temperature coefficient of resonance frequency (τf) and low firing temperature (≤ 900 °C) to ensure high signal transmission speed, good frequency selection characteristics and good thermal stability of the frequency as well as co-firing with high thermal conductivity metals such as Cu, Ag and Au [7–10]. Recently, to further conserve energy, shorten delay time and integrate with others, such as semiconductors, metals, and plastics, ultralow temperature (< 650 °C) co-firing ceramic (ULTCC) technology arises at the historic moment [11,12]. To realize ultra-low sintering temperature, two common material systems, i.e. glass+ceramics and ceramics with intrinsic ultralow firing temperature, may be selected [13–16].In practical application of ULTCC technology, the former has higher loss at high frequency. As for the latter, the higher dielectric constants (> 10) will increase the single delay time [14,15], and most materials can react with Ag electrode in the co-fired process. Lately, Yu et al. [17,18]found the borate glass-ceramics showed
⁎
Corresponding author. E-mail address: [email protected] (G. Chen). 1 These authors contributed equally. https://doi.org/10.1016/j.jnoncrysol.2019.119527 Received 12 April 2019; Received in revised form 15 June 2019 Available online 05 August 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.
2. Experimental procedures A optimized glass composition of 16CuO-16ZnO-63B2O3-5Li2O (in mass percent) was chosen according to experimental results. The initial
Journal of Non-Crystalline Solids 521 (2019) 119527
J. Xi, et al.
reagent-grade raw materials of CuO and ZnO(≥99%), H3BO3 and Li2CO3(≥99.5%) were dried and weighed according to the above glass composition. The mixed batch was kept in a high temperature furnace at 1150 °C for 1 h to get glass liquid, and then the glass melt is poured into water quenched to obtain glass slag. The glass slag was ball ground for 6 h in a ball mill at a speed of 300 r/min. The glass powders were dried at 100 °C for 8 h and then pressed at 5 MPa to form disk pellets with a diameter of 12 mm and thick of 4–8 mm. The pellets were then sintered at 560–580 °C for 1 h at a heating rate of 4 °C/min. The thermal behavior of the glass powder was characterized by a differential thermal analyzer (DTA, Netzsch STA-449-F3, Germany).The absorption spectrum of the glass was measured using an infrared spectrophotometer (FT-IR, Nicolet 6700, America).The phase evolution was investigated by powder X-ray diffractometer (XRD) (D8-Advance, Bruker, Germany) with Cu Kα radiation(1.5406 Å) in the 2θ range 20–80°.The surface microstructure of the sintered specimens was investigated by a field-emission scanning electron microscope(FE-SEM) (Quanta FEG450, America) equipped with an energy dispersive spectrometer (EDS). The compatibility of co-firing with electrodes was evaluated by using FE-SEM, XRD and EDS. The Archimedes method was employed for measuring density of the glass-ceramic. The dielectric property at microwave frequency was obtained by a Network tester (N5230C, Agilent).The value of τf was gained among 25 °C to 75 °C using the following formula [21]:
τf =
(f75 − f25 ) × 106 50 × f25
ppm/oC
(1)
where f75 and f25were the resonant frequencies at 75 °C and 25 °C, respectively. 3. Results and discussion Fig. 1(a) displays the DTA curve of CZBL glass. The temperature of 485 °C is identified as glass transition temperature. And two obvious exothermic peaks located at 559oCand 640 °C are observed. The first exothermic peak(weak peak) at559oC is ascribed to the crystallization of ZnB4O7and Cu4B2O7 confirmed by the XRD results (seen in Fig. 2), and the second exothermic peak(sharp peak) at 640 °C may be owing to the formation of Li2CuB4O8 as seen in Fig. 2. Fig.1(b)exhibits the room-temperature FT-IR spectrum of CZBL glass. A broad band extending from 3000 to 3625 cm−1 is for hydroxyl or absorbed water group. The absorption peak located at 3424 cm−1 is derived from the asymmetric stretching vibration of OeH. The vibration modes of the borate units are primarily seen in three absorption peak: 1385 cm−1 absorption peak is the strongest, indicating that the boron-oxygen bond (=B-O) in the trihedron has the strongest antisymmetric stretching vibration, the next weaker absorption peak at 1069 cm−1 is due to the stretching vibration of boron atoms in the boron tetrahedron [BO4] connected to non-bridging oxygen (≡B-O). The absorption peak at 704 cm−1 is ascribed to the result of = B-O-B bending deformation vibration of the boron trihedron [BO3] [22]. The XRD profiles of CZBL glass-ceramics sintered at 560–640 °C are shown in Fig. 2.It is clearly that the formation of crystallized phase is dependent on sintering temperature. No crystallization is detected below580°C. Zinc borate (ZnB4O7) and copper borate(Cu2B4O7) are main crystalline phase for the specimens sinteredat 580 °C and 600 °C. The existence of fine size crystallites devotes to broad diffraction peaks. With increasing temperature to 620 °C,the diffraction intensity of crystalline phase increases, indicating that the growth of crystallites and the increase of phase content of ZnB4O7and Cu2B4O7. Meanwhile, the Li2CuB4O8 crystalline phase comes out. With further increasing temperature to 640 °C, crystalline phases are still ZnB4O7, Cu2B4O7 and Li2CuB4O8. However, the intensities of the diffraction peaks for ZnB4O7 and Cu2B4O7 slightly reduce, indicating that the quantity of these two phases decreases.
Fig. 1. DTA curve (a) and FT-IR spectrum (b) of CZBL glass.
Fig. 2. XRD patterns of the obtained CZBL glass-ceramics.
Fig. 3 shows the SEM pictures of the fired CZBL samples. When sintering temperature is under 580 °C, the samples exhibit porous microstructure shown in Fig.3(a)-(b), indicating the sintering process just begin. With increasing temperature from 600 °C to 620 °C, the dense glass-ceramic can be achieved, as seen in Fig. 3(c)- (d). However, 2
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Fig. 3. SEM photographs of CZBL specimens sintered at various temperatures. a. 560 °C, b 580 °C, c. 600 °C, d. 620 °C, e. 640 °C.
excessive firing temperature (640 °C) gives rise to a slight increment of porosity, which is due to the result of over-sintering, as seen in Fig.3(e) [23,24]. The bulk densities and permittivity of CZBL specimens sintered at 580–640 °C are displayed in Fig.4(a). The specimen sintered at 560 °C shows the lowest density of 2.34 g/cm3. Enhancing firing temperature makes the density of sample increase. A highest density of 2.75 g/cm3 is obtained when fired at 620 °C. With further increasing sintering temperature to 640 °C, on the contrary, the bulk density is decreased to 2.60 g/cm3 due to over-sintering. This variation trend is well in agreement with the microstructure change presented in Fig.3. Fig. 4(a) displays the permittivity (εr) of glass-ceramics as a function of firing temperature. Obviously, the εr firstly raises and then declines with the increment in sintering temperature, which is consistent with the varying tendency in the bulk density. Therefore, the porosity or densification degree is the main factor affecting the dielectric constant rather than the grain size. The samples sintered at temperatures of 560–580°Chave low εr resulted from their low density. The maximal value of dielectric constant could be gained at 620 °C. The measured dielectric constant of the base glass is 3.01, which is due to the presence of strong nonmetallic polar covalent bonds in the [BO3] and [BO4] groups with low dielectric polarizabilities [25].Moreover, Cu2B4O7, ZnB4O7 and Li2CuB4O8 also own a low εr. As a result, the dielectric
constant for CZBL glass-ceramics is between 3.1 and 3.4, keeping at an ultra-low level compared to the other glass-ceramics [26–29]. Fig. 4(b) illustrates the Q × f values of CZBL samples with firing temperature. The variation in Q × f values is also consistent with that of the bulk density. The dielectric loss at microwave frequency is chiefly affected by inherent loss such as lattice vibration, and by external losses such as porosity, grain size, and phase types. With sintering temperature increasing, the Q × f values of the sample increase and run up to the maximum of 17,724 GHz at 620 °C. The measured Q × f value of CZBL glass is 3875 GHz. And all of Cu2B4O7, ZnB4O7 and Li2CuB4O8 have much higher Q × f value. Therefore, with the increment of firing temperature, the porosity reduces, the grains grow up, and the quantity of the crystal phase increases, resulting in the Q × f value increasing, as shown in Fig.4(b). However, excessive firing temperature (640 °C) leads to the increase of pores and the decrease of crystalline phase, which gives rise to the Q × f value reducing. The τf value of CZBL glassceramic samples is stable in the small range of 0–3 in the temperature range of 560 °C to 640 °C.This finding indicates that dense sample is achieved and has the best comprehensive performance at 620 °C. Fig. 4(c) demonstrates the εr of glass-ceramics upon different testing temperatures at 200KHz. It is observed that the dielectric constant is almost steady between 5.5 and 6 during the temperature of 60 °C to 200 °C, indicating that the CZBL glass-ceramic material possesses good 3
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Fig. 4. Bulk density and permittivity (a), Q × f and τf values (b) of CZBL glassceramics sintered at various temperatures, and permittivity of CZBL glassceramics as a function of test temperature (c).
dielectric thermal stability. For ULTCC application, it is necessary to study the co-firing characteristics between glass-ceramic materials and Ag or Al electrodes. The XRD profiles in Fig.5(a) indicate that three crystalline phases (Cu2B4O7, ZnB4O7and Li2CuB4O8), the metals(Ag and Al), and trace amount of Al2O3 attributed to oxidation of aluminum in the air during firing process exist, no any impurity phase appears. It is observed in Fig.5(b) that the big grain with grey dark color is Al2O3, which is consistent with EDS test results. As shown in Fig.5(c), the brighter color region can be confirmed as Ag identified by EDS analysis. The comprehensive analysis results illustrate that the CZBL glass-ceramic do not react with Ag or Al at 620 °C, which makes the CZBL glass-ceramic great potential application in ULTCC field.
Fig. 5. XRD profile (a), BES photograph and EDS result of CZBL material cofired with 20 wt% Al powders (b), and with 20 wt% Ag powders(c) at 620 °C for 1 h.
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4. Conclusions
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In this work, the CuO-ZnO-B2O3-Li2O system glass-ceramic has been developed. The dielectric properties depend upon sintering temperature and phase compositions. The glass-ceramic sintered at 620 °C for 60 min, possessing three crystalline phases of Cu2B4O7, ZnB4O7and Li2CuB4O8 as well as outstanding frequency thermal stability, displays an ultralow dielectric constant of 3.33 and a high Q × f value of 17,724 GHz. The as-obtained glass-ceramic do not react with Ag and Al electrodes. These excellent performances would enable this novel dielectric material to applied in high-speed wireless communication field. Conflicts of interest The authors declare no conflicts of interest. Acknowledgements This work was financially supported by National College Students Innovation and Entrepreneurship Training Program (Nos. 201810595014, 201810595015). References [1] M.T. Sebastian, R. Ubic, H. Jantunen, Low loss dielectric materials and their properties, Int. Mater. Rev. 60 (7) (2015) 392–412. [2] D. Szwagierczak, B. Synkiewicz, J. Kulawik, Low dielectric constant composites based on B2O3 and SiO2 rich glasses, cordierite and mullite, Ceram. Int. 44 (2018) 14495–14501. [3] O. Dernovsek, A. Naeini, G. Preu, W. Wersing, M. Eberstein, W.A. Schiller, LTCC glass-ceramic composites for microwave application, J. Am. Ceram. Soc. 21 (2001) 1693–1697. [4] D.H. Jiang, J.J. Chen, B.B. Lu, J. Xi, G.H. Chen, A new glass–ceramic with low permittivity for LTCC application, J. Mater. Sci. Mater. Electron. 29 (2018) 18426–18431. [5] D.H. Jiang, J.J. Chen, B.B. Lu, J. Xi, F. Shang, J.W. Xu, G.H. Chen, Preparation, crystallization kinetics and microwave dielectric properties of CaO-ZnO-B2O3-P2O5 -TiO2 glass-ceramics, Ceram. Int. 45 (2019) 8233–8237. [6] C.C. Xia, D.H. Jiang, G.H. Chen, Y. Luo, B. Li, C.L. Yuan, C.R. Zhou, Microwave dielectric ceramic of LiZnPO4 for LTCC applications, J. Mater. Sci. Mater. Electron. 28 (2017) 12026–12031. [7] M.T. Sebastian, H. Jantunen, Low loss dielectric materials for LTCC applications: a review, Int. Mater. Rev. 53 (2) (2008) 57–90. [8] M.T. Sebastian, H. Wang, H. Jantunen, Low temperature co-fired ceramics for LTCC application: a review, Curr.Opin. Solid. State. Mater. Sci. 20 (2016) 151–170. [9] Y.G. Wang, G.N. Zhang, J.S. Ma, Research of LTCC/cu, ag multilayer substrate in microelectronic packaging, Mater. Sci. Eng. B 94 (2002) 48–3. [10] R.Z. Zuo, L.T. Li, Z.L. Gui, Interfacial development and microstructural imperfection
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