Sintering and Microwave Dielectric Properties of $ZnWO_4$

$ZnWO_4$ 소결특성 및 고주파 유전특성

In this study, development of a new LTCC material using non-glassy system was attempted with repsect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. However, presence of liquid phases usually decrease dielectric properties, especially the quality factor. Therefore, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, $ZnWO_4$ was turned out the suitable LTCC material. $ZnWO_4$ can be sintered up to 98% of full density at $1050^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 15.5, 74380GHz, and $-70ppm/^{\circ}C$, respectively. In order to modify the dielectric properties and densification temperature, $B_{2}O_{3}$ and $V_{2}O_{5}$ were added to $ZnWO_4$. 40 mol% $B_{2}O_{3}$ addition reduced the dielectric constant from 15.5 to 12. And the temperature coefficient of resonant frequency was improved from -70 to $-7.6ppm/^{\circ}C$. However, sintering temperature did not change due to either lack of liquid phase or high viscosity of liquid phase. Incorporation of small amount of $V_{2}O_{5}$ in $ZnWO_{4}-B_{2}O_{3}$ system enhanced liquid phase sintering. 0.1 wt% $V_{2}O_{5}$ addition to the $0.6ZnWO_{4}-0.4B_{2}O_{3}$ system, reduced the sintering temperature down to $950^{\circ}C$. Dielectric constant, quality factor, and temperature coefficient of resonant frequency were 9.5, 16737GHz, and $-21.6ppm/^{\circ}C$, respectively.