- Email: [email protected]
Microwave dielectric properties of mixtures of glass-forming oxides Zn–B–Si and dielectric ceramics MgTiO3–CaTiO3 for LTCC applications
Journal of Alloys and Compounds 462 (2008) L5–L8
Letter
Microwave dielectric properties of mixtures of glass-forming oxides Zn–B–Si and dielectric ceramics MgTiO3–CaTiO3 for LTCC applications Cheng-Liang Huang a,∗ , Chung-Long Pan a , Wei-Chih Lee b a b
Department of Electrical Engineering, National Cheng-Kung University, Tainan 70101, Taiwan Department of Resource Engineering, National Cheng Kung University, Tainan 70101, Taiwan Received 3 July 2007; received in revised form 25 July 2007; accepted 27 July 2007 Available online 8 August 2007
Abstract Low dielectric constant, low temperature co-fired ceramics (LTCC) using glass-forming oxides (ZnO, B2 O3 and SiO2 ) with/without MgTiO3 –CaTiO3 have been prepared by conventional solid-state route. The crystalline phases were studied by the X-ray diffraction and microstructures by the SEM techniques. The materials of different compositional ratio were characterized at microwave frequencies. The microwave dielectric properties of the specimens were found strongly depended on the Zn–B–Si ratios. A short-sintering-time formulation containing Zn–B–Si in a ratio of 35:25:40 and 15 wt% CaTiO3 can possess promising microwave dielectric properties (εr = 7.05, Q × f = 3500 GHz at 16 GHz, and τ f = 5.93 ppm/◦ C) at 900 ◦ C for 0.5 h. It shows not only better properties in comparison with commercial ones but also leaves out the prior glass preparation. © 2007 Elsevier B.V. All rights reserved. Keywords: LTCC; Microwave dielectric properties; MgTiO3 –CaTiO3 ; Low-temperature sintering
1. Introduction Low temperature co-fired ceramic (LTCC) technology has been playing an important role in modern wireless communication systems. In order to process ceramic with electrode material, such as silver (mp ∼ 961 ◦ C), it is required to sinter the dielectrics at temperatures lower than the melting temperature of the co-fired electrode material. Research on the development of co-fired dielectrics with different dielectric constants has been going for years to fill the need for various RF ranges [1–6]. However, low εr material is still the most popularly used one, such as DuPont 951 (εr ∼ 7.8, Q × f ∼ 700 GHz at 3 GHz, τ f ∼ 8 ppm/◦ C), since it provides fast transmission in communication systems. Zn–B–Si has been demonstrated as an effective sintering aid to reduce the sintering temperature of BaTiO3 from 1300 to 900 ◦ C and still showing good dielectric properties by Hsiang et al. [7]. Based on the 60.3ZnO–27.1B2 O3 –12.6SiO2 glass formulation proposed by Abe et al. [8], composition
∗
Corresponding author. Tel.: +886 6275 7575x62390; fax: +886 6234 5482. E-mail address: [email protected] (C.-L. Huang).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.07.114
70 wt%(60.3ZnO–27.1B2 O3 –12.6SiO2 ) + 30 wt%(95MgTiO3 – 5CaTiO3 ) was firstly prepared by Jantunen et al. [9] through a prior glass preparation followed by a synthesizing condition of 900 ◦ C/80 min. Solid-state route was also introduced to process the same material, which showed better microwave dielectric properties (εr = 8.5, Q ∼ 1100 at 8 GHz, and τ f = 6.2 ppm/◦ C). [10] One advantage is that it avoids the separate, hightemperature, glass-melting step, which carries the risk of component volatilization and consequent variations in chemical composition from batch to batch. Limited alternation in Zn–B–Si ratio was also reported to control its dielectric properties [11]. Still, it needed a sintering time of 80 min, which might be too long to keep away from electrode distortion and diffusion during firing step. Moreover, it is essential to further lower its dielectric constant before putting it to practical applications requiring fast signal transmission at microwave frequencies. In this paper, a more comprehensive study was accomplished through the investigation on the microwave dielectric properties of dielectrics Zn–B–Si–MgTiO3 –CaTiO3 with different compositional ratio. Moreover, the crystalline phase was studied by the X-ray diffraction and microstructure by the SEM techniques.
L6
C.-L. Huang et al. / Journal of Alloys and Compounds 462 (2008) L5–L8
Table 1 The microwave dielectric properties of doped 95MCT Addition/S.T
εr
Q × f (GHz)
τ f (ppm/◦ C)
10 wt% B2 O3 /1100 ◦ C 20 wt% B2 O3 /1100 ◦ C 10 wt% SiO2 /1000 ◦ C 20 wt% SiO2 /1000 ◦ C 10 wt% ZnO/1200 ◦ C 20 wt% ZnO/1200 ◦ C
18.32 16.17 14.48 13.7 18.46 19.9
20,540 23,370 11,280 12,800 63,670 66,040
−6.2 −20.04 −20.2 −51.57 −3.78 −11.54
2. Experimental procedure
Table 3 The synthesizing conditions and microwave dielectric properties of the Z35B25S40 ceramics S.T/time
εr
Q × f (GHz) at 16 GHz
τ f (ppm/◦ C)
Shrinkage (%)
890 ◦ C/0.5 h 890 ◦ C/1 h 890 ◦ C/2 h 890 ◦ C/3 h 900 ◦ C/0.5 h 900 ◦ C/1 h 900 ◦ C/2 h 900 ◦ C/3 h
– – 4.73 4.92 4.93 4.92 4.94 4.84
– – 6,500 9,900 7,000 16,400 17,800 19,500
– – −30.27 −34.12 −32.71 −36.51 −25.23 −37.05
2.82 6.27 12.82 13.73 14.27 16.27 16.45 16.00
Density (g/cm3 ) – – 2.77 2.95 2.92 2.91 2.96 2.94
Samples were synthesized by conventional solid-state methods from highpurity oxide (>99.9%) powders: MgO, CaCO3 , TiO2 , ZnO, B2 O3 and SiO2 . The starting materials were mixed according to an appropriate stoichiometry, and ground in distilled water for 10 h in a balling mill with agate balls. Mixtures were all dried and calcined at 850 ◦ C for 4 h. The calcined powders together with 5 wt% solution of PVA as a binder were re-milled for 5 h. The powders were then uniaxially pressed into pellets with 11 mm diameter and 5 mm height and sintered under appropriate conditions. The densities of the sintered specimens were measured by the liquid displacement method using deionized water as the liquid (Archimedes method). The dielectric constants εr and the quality values Q at microwave frequencies were measured using the Hakki–Coleman [12] dielectric resonator method as modified and improved by Courtney [13]. A HP8757D network analyzer and a HP8350B sweep oscillator were employed in the measurement. The temperature coefficient of resonant frequency τ f at microwave frequency was measured in the temperature range from 20 to 80 ◦ C. The microstructure observation of the sintered surface was performed by scanning electron microscopy (SEM, JEOL-JSM-6400, Japan). The crystalline phases of the sintered ceramics were also identified by XRD using Cu K␣ (λ = 0.15406 nm) radiation with a Siemens D5000 diffractometer operated at 40 kV and 40 mA.
3. Results and discussion
Fig. 1. X-ray diffraction patterns of Z35B25S40 with various amounts of CT addition sintered at 900 ◦ C/0.5 h (* CaTiO3 ).
In order to study the effect of Zn–B–Si (ZBS) addition ratio on the microwave dielectric properties of 95MgTiO3 –5CaTiO3 (95MCT) ceramics, additions ZnO, B2 O3 and SiO2 were individually added to 95MCT to investigate their influence on the
microwave dielectric properties of the specimens (Table 1). Although the case of Zn–B–Si mixture would be more complicate than that of individual ones, it still can provide a rough inspiration as initial reference. As illustrated in Table 1, ZnO
Table 2 The microwave dielectric properties of 0.2 wt%(95MCT)–0.8 wt%(Zn–B–Si) ceramics at different Zn–B–Si ratios sintered for 2 h Composition
Sintering temperature ( ◦ C)
εr
Q × f (GHz) at 16 GHz
τ f (ppm/◦ C)
Shrinkage (%)
Density (g/cm3 )
Z60B25S15/95MCT
890 880 870 860
10.17 9.7 8.9 7.01
8270 8450 7880 4650
15.3 17.2 14.3 12.2
12.65 10.71 9.32 6.88
1.70 1.59 1.51 1.57
Z55B25S20/95MCT
890 880 870 860
8.72 8.67 7.44 5.33
5400 3380 3130 3040
9.9 8.5 6.3 6.5
13.23 11.98 9.21 6.70
2.04 1.96 1.72 1.60
Z45B25S30/95MCT
890a 880 870 860
– 8.29 7.94 5.34
– 4490 3460 3180
– 8.2 5.1 2.3
– 13.71 12.55 6.92
– 1.83 1.61 1.58
Z35B25S40/95MCT
890a 880 870 860
– 7.91 7.54 5.55
– 4850 4440 2990
– 6.5 4.2 3.3
– 14.33 12.70 7.53
– 1.85 1.70 1.65
a
Melted.
C.-L. Huang et al. / Journal of Alloys and Compounds 462 (2008) L5–L8
can be as a Q × f promoter. SiO2 addition not only possesses the lowest εr value but also provides a large negative shift in τ f . Moreover, it can provide a most effective temperature reduction. According to the foregoing results, we chose B remaining
L7
unchanged and varying the Zn–Si contents to offer different Zn–B–Si ratio for investigation. The microwave dielectric properties of the 0.2 wt%(95MCT) –0.8 wt%(Zn–B–Si) specimens strongly depend on the Zn–B–Si
Fig. 2. (a) SEM micrographs of boundary between silver electrode and the Z35B25S40/15CT formulation sintered at 900 ◦ C/0.5 h and EDS at (b) spot A and (c) spot B.
L8
C.-L. Huang et al. / Journal of Alloys and Compounds 462 (2008) L5–L8
Table 4 The microwave dielectric properties of the Z35B25S40-CT ceramics Composition Z35B25S40 Z35B25S40/5CT Z35B25S40/10CT Z35B25S40/15CT Z35B25S40/20CT Z35B25S40 Z35B25S40/5CT Z35B25S40/10CT Z35B25S40/15CT Z35B25S40/20CT
S.T/time
εr
900 ◦ C/0.5 h
4.93 5.48 6.21 7.05 7.83
900 ◦ C/1 h
4.92 5.66 6.21 7.19 7.93
τ f (ppm/◦ C)
Shrinkage (%)
Density (g/cm3 )
7,000 – 3,200 3,500 2,700
−32.71 −12.34 −3.86 5.93 24.45
14.27 12.55 12.26 15.00 13.18
2.92 2.88 2.87 2.95 2.94
16,400 – 4,200 4,500 3,500
−36.51 −13.95 −5.29 6.31 14.37
16.27 13.18 14.91 15.18 15.00
2.91 2.9 2.93 2.92 3.00
Q × f (GHz) at 16 GHz
ratios (Table 2). With the increase of Si content, the εr value decreased, the τ f value shifted toward negative as expected. Moreover, the sintering temperature was also lowered since Z45B25S30 and Z35B25S40 were already melted at 890 ◦ C. The Z35B25S40/95MCT had an εr of 7.91, a Q × f of 4847 GHz (at 16 GHz), and a τ f of 6.5 ppm/◦ C. Detected main phases were similar to that reported by Jantunen et al. [10]. In order to be as a new low εr LTCC material compatible with DuPont 951, pure Z35B25S40 was also investigated. Table 3 illustrates the synthesizing conditions and microwave dielectric properties of the Z35B25S40. As observed, 890 ◦ C was not high enough to fully sinter the specimen. Its shrinkage still remained low (∼13.73%) as increasing the sintering time up to 3 h. On the contrary, 900 ◦ C seemed to be an appropriate temperature since a much higher shrinkage could be obtained even for a 0.5 h-sintered specimen (14.27%). It could possess a low εr and a high Q × f as desired. However, it also had a large negative τ f , which needed to be compensated to put it into practical applications. CaTiO3 (CT) was then chosen as a compensator due to its large positive τ f (∼800 ppm/◦ C). Fig. 1 shows the X-ray diffraction patterns of Z35B25S40 with various amounts of CT addition. In addition to CT, detected main phases consisted of SiO2 , Zn2 SiO4 , Zn4 B6 O13 , and ZnSiO3 . The phases of specimen with different content of CT were similar to each other but slightly different in phase fractions. The microwave dielectric properties of the Z35B25S40-CT ceramics are demonstrated in Table 4. All of the specimens seemed to be fully sintered by examining their densities. The Z35B25S40/15CT (addition of 15 wt% CT) had an εr of 7.05, a Q × f of 3500 GHz (at 16 GHz), and a τ f of 5.93 ppm/◦ C at 900 ◦ C/0.5 h. Although it possessed a lower Q × f, it also showed a lower εr , a closer to zero τ f , and a shorter-sintering-time, in comparison with that of Z35B25S40/95MCT. Moreover, a structure of a silver electrode sandwiched by the Z35B25S40/15CT formulation was accomplished to investigate the diffusion or the reaction between electrode and ceramic. Fig. 2(a) shows the SEM micrograph of the mentioned structural boundary. EDS (Fig. 2b and c) was recorded at spots 1 m from boundary to ceramic as well as to electrode. Spot A showed a composition of almost silver free (<3 atom%) while silver was detected as main composition (>97 atom%) at spot B. It indicates no diffusion or reaction takes place at boundary, which makes it a very promising candidate for LTCC applications.
4. Conclusions Microwave dielectric properties of glass-forming oxides (ZnO, B2 O3 and SiO2 ) with/without MgTiO3 –CaTiO3 were investigated. A conventional solid-state-prepared formulation containing Zn–B–Si in a ratio of 35:25:40 and 15 wt% CaTiO3 is proposed as a possible LTCC dielectric. In comparison with commercial ones, it possesses better microwave dielectric properties (εr = 7.05, Q × f = 3500 GHz at 16 GHz, and τ f = 5.93 ppm/◦ C) and a less sintering time (0.5 h). Moreover, significant diffusion or reaction was not observed at the boundaries between electrode and dielectric. Acknowledgements This work was co-sponsored by the Delta Electronics, Inc., Taiwan and the National Science Council of the Republic of China under Grant NSC-95-2221-E-006-117. References [1] R. Umemura, H. Ogawa, A. Yokoi, H. Ohsato, A. Kan, J. Alloys Compd. 424 (2006) 388–393. [2] J. Wang, Z. Yue, Z. Gui, L. Li, J. Alloys Compd. 392 (2005) 263–267. [3] Q. Zeng, W. Li, J.L. Shi, J.K. Guo, M.W. Zuo, W.J. Wu, J. Am. Ceram. Soc. 89 (2006) 1733–1735. [4] D.-K. Kwon, M.T. Lanagan, T.R. Shrout, J. Am. Ceram. Soc. 88 (2005) 3419–3422. [5] H.K. Shin, H. Shin, S.Y. Cho, K.S. Hong, J. Am. Ceram. Soc. 88 (2005) 2461–2465. [6] C.L. Huang, M.H. Weng, Mater. Lett. 43 (2000) 32–35. [7] H.-I. Hsiang, C.-S. Hsi, C.-C. Huang, S.-L. Fu, Sintering behavior and dielectric properties of BaTiO3 ceramics with glass addition for internal capacitor of LTCC, J. Alloys Compd. 459 (2008) 307–310. [8] M. Abe, T. Nanataki, S. Yano, US Patent 5,493,262, 20 February 1996. [9] H. Jantunen, R. Rautioaho, A. Uusimaki, S. Leppavuori, J. Eur. Ceram. Soc. 20 (2000) 2331–2336. [10] H. Jantunen, R. Rautioaho, A. Uusimaki, S. Leppavuori, J. Am. Ceram. Soc. 83 (2000) 2855–2857. [11] H. Jantunen, A. Uusimaki, R. Rautioaho, S. Leppavuori, J. Am. Ceram. Soc. 85 (2002) 697–699. [12] B.W. Hakki, P.D. Coleman, IEEE Trans. Microwave Theory Tech. 8 (1960) 402–410. [13] W.E. Courtney, IEEE Trans. Microwave Theory Tech. 18 (1970) 476– 485.
Letter
Microwave dielectric properties of mixtures of glass-forming oxides Zn–B–Si and dielectric ceramics MgTiO3–CaTiO3 for LTCC applications Cheng-Liang Huang a,∗ , Chung-Long Pan a , Wei-Chih Lee b a b
Department of Electrical Engineering, National Cheng-Kung University, Tainan 70101, Taiwan Department of Resource Engineering, National Cheng Kung University, Tainan 70101, Taiwan Received 3 July 2007; received in revised form 25 July 2007; accepted 27 July 2007 Available online 8 August 2007
Abstract Low dielectric constant, low temperature co-fired ceramics (LTCC) using glass-forming oxides (ZnO, B2 O3 and SiO2 ) with/without MgTiO3 –CaTiO3 have been prepared by conventional solid-state route. The crystalline phases were studied by the X-ray diffraction and microstructures by the SEM techniques. The materials of different compositional ratio were characterized at microwave frequencies. The microwave dielectric properties of the specimens were found strongly depended on the Zn–B–Si ratios. A short-sintering-time formulation containing Zn–B–Si in a ratio of 35:25:40 and 15 wt% CaTiO3 can possess promising microwave dielectric properties (εr = 7.05, Q × f = 3500 GHz at 16 GHz, and τ f = 5.93 ppm/◦ C) at 900 ◦ C for 0.5 h. It shows not only better properties in comparison with commercial ones but also leaves out the prior glass preparation. © 2007 Elsevier B.V. All rights reserved. Keywords: LTCC; Microwave dielectric properties; MgTiO3 –CaTiO3 ; Low-temperature sintering
1. Introduction Low temperature co-fired ceramic (LTCC) technology has been playing an important role in modern wireless communication systems. In order to process ceramic with electrode material, such as silver (mp ∼ 961 ◦ C), it is required to sinter the dielectrics at temperatures lower than the melting temperature of the co-fired electrode material. Research on the development of co-fired dielectrics with different dielectric constants has been going for years to fill the need for various RF ranges [1–6]. However, low εr material is still the most popularly used one, such as DuPont 951 (εr ∼ 7.8, Q × f ∼ 700 GHz at 3 GHz, τ f ∼ 8 ppm/◦ C), since it provides fast transmission in communication systems. Zn–B–Si has been demonstrated as an effective sintering aid to reduce the sintering temperature of BaTiO3 from 1300 to 900 ◦ C and still showing good dielectric properties by Hsiang et al. [7]. Based on the 60.3ZnO–27.1B2 O3 –12.6SiO2 glass formulation proposed by Abe et al. [8], composition
∗
Corresponding author. Tel.: +886 6275 7575x62390; fax: +886 6234 5482. E-mail address: [email protected] (C.-L. Huang).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.07.114
70 wt%(60.3ZnO–27.1B2 O3 –12.6SiO2 ) + 30 wt%(95MgTiO3 – 5CaTiO3 ) was firstly prepared by Jantunen et al. [9] through a prior glass preparation followed by a synthesizing condition of 900 ◦ C/80 min. Solid-state route was also introduced to process the same material, which showed better microwave dielectric properties (εr = 8.5, Q ∼ 1100 at 8 GHz, and τ f = 6.2 ppm/◦ C). [10] One advantage is that it avoids the separate, hightemperature, glass-melting step, which carries the risk of component volatilization and consequent variations in chemical composition from batch to batch. Limited alternation in Zn–B–Si ratio was also reported to control its dielectric properties [11]. Still, it needed a sintering time of 80 min, which might be too long to keep away from electrode distortion and diffusion during firing step. Moreover, it is essential to further lower its dielectric constant before putting it to practical applications requiring fast signal transmission at microwave frequencies. In this paper, a more comprehensive study was accomplished through the investigation on the microwave dielectric properties of dielectrics Zn–B–Si–MgTiO3 –CaTiO3 with different compositional ratio. Moreover, the crystalline phase was studied by the X-ray diffraction and microstructure by the SEM techniques.
L6
C.-L. Huang et al. / Journal of Alloys and Compounds 462 (2008) L5–L8
Table 1 The microwave dielectric properties of doped 95MCT Addition/S.T
εr
Q × f (GHz)
τ f (ppm/◦ C)
10 wt% B2 O3 /1100 ◦ C 20 wt% B2 O3 /1100 ◦ C 10 wt% SiO2 /1000 ◦ C 20 wt% SiO2 /1000 ◦ C 10 wt% ZnO/1200 ◦ C 20 wt% ZnO/1200 ◦ C
18.32 16.17 14.48 13.7 18.46 19.9
20,540 23,370 11,280 12,800 63,670 66,040
−6.2 −20.04 −20.2 −51.57 −3.78 −11.54
2. Experimental procedure
Table 3 The synthesizing conditions and microwave dielectric properties of the Z35B25S40 ceramics S.T/time
εr
Q × f (GHz) at 16 GHz
τ f (ppm/◦ C)
Shrinkage (%)
890 ◦ C/0.5 h 890 ◦ C/1 h 890 ◦ C/2 h 890 ◦ C/3 h 900 ◦ C/0.5 h 900 ◦ C/1 h 900 ◦ C/2 h 900 ◦ C/3 h
– – 4.73 4.92 4.93 4.92 4.94 4.84
– – 6,500 9,900 7,000 16,400 17,800 19,500
– – −30.27 −34.12 −32.71 −36.51 −25.23 −37.05
2.82 6.27 12.82 13.73 14.27 16.27 16.45 16.00
Density (g/cm3 ) – – 2.77 2.95 2.92 2.91 2.96 2.94
Samples were synthesized by conventional solid-state methods from highpurity oxide (>99.9%) powders: MgO, CaCO3 , TiO2 , ZnO, B2 O3 and SiO2 . The starting materials were mixed according to an appropriate stoichiometry, and ground in distilled water for 10 h in a balling mill with agate balls. Mixtures were all dried and calcined at 850 ◦ C for 4 h. The calcined powders together with 5 wt% solution of PVA as a binder were re-milled for 5 h. The powders were then uniaxially pressed into pellets with 11 mm diameter and 5 mm height and sintered under appropriate conditions. The densities of the sintered specimens were measured by the liquid displacement method using deionized water as the liquid (Archimedes method). The dielectric constants εr and the quality values Q at microwave frequencies were measured using the Hakki–Coleman [12] dielectric resonator method as modified and improved by Courtney [13]. A HP8757D network analyzer and a HP8350B sweep oscillator were employed in the measurement. The temperature coefficient of resonant frequency τ f at microwave frequency was measured in the temperature range from 20 to 80 ◦ C. The microstructure observation of the sintered surface was performed by scanning electron microscopy (SEM, JEOL-JSM-6400, Japan). The crystalline phases of the sintered ceramics were also identified by XRD using Cu K␣ (λ = 0.15406 nm) radiation with a Siemens D5000 diffractometer operated at 40 kV and 40 mA.
3. Results and discussion
Fig. 1. X-ray diffraction patterns of Z35B25S40 with various amounts of CT addition sintered at 900 ◦ C/0.5 h (* CaTiO3 ).
In order to study the effect of Zn–B–Si (ZBS) addition ratio on the microwave dielectric properties of 95MgTiO3 –5CaTiO3 (95MCT) ceramics, additions ZnO, B2 O3 and SiO2 were individually added to 95MCT to investigate their influence on the
microwave dielectric properties of the specimens (Table 1). Although the case of Zn–B–Si mixture would be more complicate than that of individual ones, it still can provide a rough inspiration as initial reference. As illustrated in Table 1, ZnO
Table 2 The microwave dielectric properties of 0.2 wt%(95MCT)–0.8 wt%(Zn–B–Si) ceramics at different Zn–B–Si ratios sintered for 2 h Composition
Sintering temperature ( ◦ C)
εr
Q × f (GHz) at 16 GHz
τ f (ppm/◦ C)
Shrinkage (%)
Density (g/cm3 )
Z60B25S15/95MCT
890 880 870 860
10.17 9.7 8.9 7.01
8270 8450 7880 4650
15.3 17.2 14.3 12.2
12.65 10.71 9.32 6.88
1.70 1.59 1.51 1.57
Z55B25S20/95MCT
890 880 870 860
8.72 8.67 7.44 5.33
5400 3380 3130 3040
9.9 8.5 6.3 6.5
13.23 11.98 9.21 6.70
2.04 1.96 1.72 1.60
Z45B25S30/95MCT
890a 880 870 860
– 8.29 7.94 5.34
– 4490 3460 3180
– 8.2 5.1 2.3
– 13.71 12.55 6.92
– 1.83 1.61 1.58
Z35B25S40/95MCT
890a 880 870 860
– 7.91 7.54 5.55
– 4850 4440 2990
– 6.5 4.2 3.3
– 14.33 12.70 7.53
– 1.85 1.70 1.65
a
Melted.
C.-L. Huang et al. / Journal of Alloys and Compounds 462 (2008) L5–L8
can be as a Q × f promoter. SiO2 addition not only possesses the lowest εr value but also provides a large negative shift in τ f . Moreover, it can provide a most effective temperature reduction. According to the foregoing results, we chose B remaining
L7
unchanged and varying the Zn–Si contents to offer different Zn–B–Si ratio for investigation. The microwave dielectric properties of the 0.2 wt%(95MCT) –0.8 wt%(Zn–B–Si) specimens strongly depend on the Zn–B–Si
Fig. 2. (a) SEM micrographs of boundary between silver electrode and the Z35B25S40/15CT formulation sintered at 900 ◦ C/0.5 h and EDS at (b) spot A and (c) spot B.
L8
C.-L. Huang et al. / Journal of Alloys and Compounds 462 (2008) L5–L8
Table 4 The microwave dielectric properties of the Z35B25S40-CT ceramics Composition Z35B25S40 Z35B25S40/5CT Z35B25S40/10CT Z35B25S40/15CT Z35B25S40/20CT Z35B25S40 Z35B25S40/5CT Z35B25S40/10CT Z35B25S40/15CT Z35B25S40/20CT
S.T/time
εr
900 ◦ C/0.5 h
4.93 5.48 6.21 7.05 7.83
900 ◦ C/1 h
4.92 5.66 6.21 7.19 7.93
τ f (ppm/◦ C)
Shrinkage (%)
Density (g/cm3 )
7,000 – 3,200 3,500 2,700
−32.71 −12.34 −3.86 5.93 24.45
14.27 12.55 12.26 15.00 13.18
2.92 2.88 2.87 2.95 2.94
16,400 – 4,200 4,500 3,500
−36.51 −13.95 −5.29 6.31 14.37
16.27 13.18 14.91 15.18 15.00
2.91 2.9 2.93 2.92 3.00
Q × f (GHz) at 16 GHz
ratios (Table 2). With the increase of Si content, the εr value decreased, the τ f value shifted toward negative as expected. Moreover, the sintering temperature was also lowered since Z45B25S30 and Z35B25S40 were already melted at 890 ◦ C. The Z35B25S40/95MCT had an εr of 7.91, a Q × f of 4847 GHz (at 16 GHz), and a τ f of 6.5 ppm/◦ C. Detected main phases were similar to that reported by Jantunen et al. [10]. In order to be as a new low εr LTCC material compatible with DuPont 951, pure Z35B25S40 was also investigated. Table 3 illustrates the synthesizing conditions and microwave dielectric properties of the Z35B25S40. As observed, 890 ◦ C was not high enough to fully sinter the specimen. Its shrinkage still remained low (∼13.73%) as increasing the sintering time up to 3 h. On the contrary, 900 ◦ C seemed to be an appropriate temperature since a much higher shrinkage could be obtained even for a 0.5 h-sintered specimen (14.27%). It could possess a low εr and a high Q × f as desired. However, it also had a large negative τ f , which needed to be compensated to put it into practical applications. CaTiO3 (CT) was then chosen as a compensator due to its large positive τ f (∼800 ppm/◦ C). Fig. 1 shows the X-ray diffraction patterns of Z35B25S40 with various amounts of CT addition. In addition to CT, detected main phases consisted of SiO2 , Zn2 SiO4 , Zn4 B6 O13 , and ZnSiO3 . The phases of specimen with different content of CT were similar to each other but slightly different in phase fractions. The microwave dielectric properties of the Z35B25S40-CT ceramics are demonstrated in Table 4. All of the specimens seemed to be fully sintered by examining their densities. The Z35B25S40/15CT (addition of 15 wt% CT) had an εr of 7.05, a Q × f of 3500 GHz (at 16 GHz), and a τ f of 5.93 ppm/◦ C at 900 ◦ C/0.5 h. Although it possessed a lower Q × f, it also showed a lower εr , a closer to zero τ f , and a shorter-sintering-time, in comparison with that of Z35B25S40/95MCT. Moreover, a structure of a silver electrode sandwiched by the Z35B25S40/15CT formulation was accomplished to investigate the diffusion or the reaction between electrode and ceramic. Fig. 2(a) shows the SEM micrograph of the mentioned structural boundary. EDS (Fig. 2b and c) was recorded at spots 1 m from boundary to ceramic as well as to electrode. Spot A showed a composition of almost silver free (<3 atom%) while silver was detected as main composition (>97 atom%) at spot B. It indicates no diffusion or reaction takes place at boundary, which makes it a very promising candidate for LTCC applications.
4. Conclusions Microwave dielectric properties of glass-forming oxides (ZnO, B2 O3 and SiO2 ) with/without MgTiO3 –CaTiO3 were investigated. A conventional solid-state-prepared formulation containing Zn–B–Si in a ratio of 35:25:40 and 15 wt% CaTiO3 is proposed as a possible LTCC dielectric. In comparison with commercial ones, it possesses better microwave dielectric properties (εr = 7.05, Q × f = 3500 GHz at 16 GHz, and τ f = 5.93 ppm/◦ C) and a less sintering time (0.5 h). Moreover, significant diffusion or reaction was not observed at the boundaries between electrode and dielectric. Acknowledgements This work was co-sponsored by the Delta Electronics, Inc., Taiwan and the National Science Council of the Republic of China under Grant NSC-95-2221-E-006-117. References [1] R. Umemura, H. Ogawa, A. Yokoi, H. Ohsato, A. Kan, J. Alloys Compd. 424 (2006) 388–393. [2] J. Wang, Z. Yue, Z. Gui, L. Li, J. Alloys Compd. 392 (2005) 263–267. [3] Q. Zeng, W. Li, J.L. Shi, J.K. Guo, M.W. Zuo, W.J. Wu, J. Am. Ceram. Soc. 89 (2006) 1733–1735. [4] D.-K. Kwon, M.T. Lanagan, T.R. Shrout, J. Am. Ceram. Soc. 88 (2005) 3419–3422. [5] H.K. Shin, H. Shin, S.Y. Cho, K.S. Hong, J. Am. Ceram. Soc. 88 (2005) 2461–2465. [6] C.L. Huang, M.H. Weng, Mater. Lett. 43 (2000) 32–35. [7] H.-I. Hsiang, C.-S. Hsi, C.-C. Huang, S.-L. Fu, Sintering behavior and dielectric properties of BaTiO3 ceramics with glass addition for internal capacitor of LTCC, J. Alloys Compd. 459 (2008) 307–310. [8] M. Abe, T. Nanataki, S. Yano, US Patent 5,493,262, 20 February 1996. [9] H. Jantunen, R. Rautioaho, A. Uusimaki, S. Leppavuori, J. Eur. Ceram. Soc. 20 (2000) 2331–2336. [10] H. Jantunen, R. Rautioaho, A. Uusimaki, S. Leppavuori, J. Am. Ceram. Soc. 83 (2000) 2855–2857. [11] H. Jantunen, A. Uusimaki, R. Rautioaho, S. Leppavuori, J. Am. Ceram. Soc. 85 (2002) 697–699. [12] B.W. Hakki, P.D. Coleman, IEEE Trans. Microwave Theory Tech. 8 (1960) 402–410. [13] W.E. Courtney, IEEE Trans. Microwave Theory Tech. 18 (1970) 476– 485.