Low-Temperature Sintering of Gahnite Ceramic Using Cu-Nb-O Additive and Evaluation of Dielectric and Thermal Properties
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https://doi.org/10.1007/s11664-020-08346-w Ó 2020 The Minerals, Metals & Materials Society
Low-Temperature Sintering of Gahnite Ceramic Using Cu-Nb-O Additive and Evaluation of Dielectric and Thermal Properties KOICHI SHIGENO ,1,3 SHINJI KANEKO,1 HAJIME NAKASHIMA,1 KENTA SUENAGA,1 and HIROTAKA FUJIMORI2 1.—National Institute of Technology, Ube College, 2-14-1 Tokiwadai, Ube City, Yamaguchi, Japan. 2.—Graduate School of Yamaguchi University, 2-16-1 Tokiwadai, Ube City, Yamaguchi, Japan. 3.—e-mail: [email protected]
Low-temperature sintering of gahnite (ZnAl2O4) ceramic, which has the potential to exhibit higher thermal conductivity than alumina but sinters densely at a moderate temperature of approximately 1500°C, has been investigated. When adding only 5 wt.% Cu-Nb-O additive, the sintering temperature was lowered significantly to 960°C. The sample fired at 960°C for 2 h exhibited a relative permittivity (er) of 9.1, a quality factor multiplied by resonant frequency (Q 9 f) value of 30,000 GHz (at a measurement frequency of approximately 13 GHz), and a temperature coefficient of resonant frequency (sf) of 69 ppm/K, being relatively satisfactory values. However, the thermal conductivity of the sample was 9.3 W/m-K, which exceeds that of conventional low-temperature co-fired ceramic (LTCC) materials but is only one-third of that of the pure gahnite sample (27 W/m-K). Our analysis revealed that the main cause was the incorporation of the Cu component into the gahnite lattice. These results enable the proposal of guidelines for the development of new LTCC materials with high thermal conductivity. Key words: Ceramics, ZnAl2O4, low-temperature sintering, dielectric property, thermal conductivity
INTRODUCTION Low-temperature co-fired ceramics (LTCCs) are dielectric materials that are widely used in small electronic devices such as wiring substrates and integrated circuit packages.1,2 However, the poor thermal dissipation of LTCC materials has been a problem. Aluminum-based oxide ceramics, e.g., with alumina (Al2O3) as the base material, exhibit relatively high thermal conductivity. However, it is necessary to add a large amount (approximately 50% or more of the total amount) of low-softeningpoint glass with low thermal conductivity to achieve low-temperature sintering. Consequently, the majority of these conventional LTCC materials exhibit the shortcoming of low thermal conductivity
(Received April 20, 2020; accepted July 17, 2020)
(of approximately 2 W/m-K to 7 W/m-K).3,4 Recently, the heat generation density of semiconductors, such as light-emitting diodes (LEDs) mounted on LTCC multilayer devices, has been increasing, resulting in a demand for LTCC materials with high thermal conductivity.5 Therefore, in our previous research, utilizing alumina with high thermal conductivity of approximately 30 W/m-K as a base material, we developed additives that could enable sintering at low temperature even when using a small amount. As a result, we developed CuO–TiO2–Nb2O5–Ag2O additive that can sinter alumina at a low temp
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