Microwave dielectric properties and compatibility with silver of low-fired Ba 5 Nb 4 O 15 ceramics by BaCu(B 2 O 5 ) add
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ng Wang,a) Minghuia Zhang, and Haibo Yang Electronic Materials Research Laboratory, Key Laboratory of the Ministry of the Education, Xi’an Jiaotong University, Xi’an 710049, China (Received 15 September 2009; accepted 2 February 2010)
The influence of BaCu(B2O5) (BCB) addition on the sintering temperature and microwave dielectric properties of Ba5Nb4O15 ceramics has been investigated. The addition of small amount of BCB can effectively lower the sintering temperature of Ba5Nb4O15 ceramics from 1400 to 875 C and induce no obvious degradation of the microwave dielectric properties. The reduced sintering temperature was attributed to the BCB liquid phase. Typically, the 1.5 wt% BCB-added Ba5Nb4O15 ceramic sintered at 875 C for 2 h exhibited good microwave dielectric properties of Q f ¼ 28,655 GHz, er ¼ 40.2, and tf ¼ 60 ppm/ C. The dielectric ceramic demonstrated stability against the reaction with the Ag electrode, which suggests that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.
I. INTRODUCTION
The development of communication systems such as mobile systems requires the miniaturization of devices. Low-temperature cofired ceramic (LTCC) multilayer devices have been extensively investigated for the miniaturization of microwave dielectric components.1 LTCC multilayer devices consist of alternating microwave dielectric ceramics and internal metallic electrode layers. Ag has been widely used as the metallic electrode, because of its high conductivity and low cost. However, the melting temperature of Ag is low (about 961 C), whereas most of the commercial microwave dielectric ceramics usually need high sintering temperature.2–5 Therefore, for the fabrication of multilayer devices, it is necessary to develop microwave dielectric ceramics with a low sintering temperature, which can be cofired with Ag. Ba5Nb4O15 is the simplest representation of a fivelayer compound derived from the classical perovskite structure.6 The dielectric and luminescence properties of this compound have been investigated, and it has been found to be a useful material in microwave communication applications.7,8 The microwave dielectric properties of Ba5Nb4O15 have been reported by Sreemoolanadhan et al.9,10 Vineis et al. also reported that Ba5Nb4O15 has a quality factor (Q f ) of 26,337 GHz, a relative dielectric a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0216 J. Mater. Res., Vol. 25, No. 9, Sep 2010
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constant (er) of 39.3, and a temperature coefficient of resonant frequency (tf) of 79.1 ppm/ C.11 Ratheesh et al. measured the microwave dielectric properties of Ba5Nb4O15 using the whispering gallery mode technique: Q f ¼ 53,000 GHz at 16 GHz, er ¼ 40, and tf ¼ 78 ppm/ C.12 However, the sintering temperature of Ba5Nb4O15 ceramic was about 1400 C, which is too high to use in LTCC. So it is necessary to reduce the sintering temperature. To lower the firing temperature of B
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