Effect of crystallization on microwave dielectric properties of stoichiometric cordierite glasses containing B 2 O 3 and
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Effect of crystallization on microwave dielectric properties of stoichiometric cordierite glasses containing B2O3 and P2O5 Jenn-Ming Wua) and Hong-Lin Huang Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, Taiwan 30043, Republic of China (Received 12 July 1999; accepted 11 October 1999)
The effect of crystallization on microwave dielectric properties of cordierite glasses containing B2O3 and P2O5 additions was investigated. Two glasses containing 5 wt% B2O3/5 wt% P2O5 and 7.5 wt% B2O3/7.5 wt% P2O5 were studied. Both glasses were sintered to nearly full density at temperatures as low as 860 °C. The frequency constant and quality factor of ␣ cordierite are, respectively, about five times and two times larger than those of glassy phase and cordierite. The temperature coefficients of resonant frequency are estimated to be about −13, −55, and −15 ppm/°C for glassy phase, cordierite, and ␣ cordierite, respectively. As a result of the microwave dielectric properties of the individual phase, cordierite glasses containing ␣ cordierite possess the best microwave properties.
I. INTRODUCTION
Ceramic dielectrics possess excellent properties such as high relative dielectric constant, high dielectric quality factor (Q), and a near-zero temperature coefficient of resonant frequency in the microwave range. The promising electrical properties of dielectric ceramic resonators reduce the size of filter and oscillator components in microwave systems ranging from cellular phones to global positioning technologies.1 Multilayer structures have been developed to increase the volume efficiency2–4 further in order to reduce the size of microwave devices. In producing miniaturized devices, it is important to lower the sintering temperature of the dielectric in order to be able to cofire with low loss conductors such as silver and palladium. Addition of low melting glass5,6 is one of the most effective and least expensive methods to achieve the goal. In order to sinter microwave dielectric ceramics at temperature lower than 900 °C with glass additives, the amount of glass additives may need to be at the 20– 30 wt% level. In this case, the microwave properties of the glass additives become an important factor in determining the final properties of the devices. However, most low melting glasses7 especially those containing alkali metal oxides have high dielectric loss in the microwave region.8,9 In addition, the degree of disorder affects dielectric loss of ionic crystals,10,11 and glasses possess higher dielectric loss than their crystalline counterparts. It is beneficial that the glass additives are not only low
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J. Mater. Res., Vol. 15, No. 1, Jan 2000
melting but also capable of transforming into the crystalline phase. It was reported that some of the aluminosilicate-based glasses, such as cordierite and celsian, show low dielectric loss in the microwave region,12,13 which is of potential in application as glass
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