Improved sintering behavior and microwave dielectric properties of SnO2-based ceramics and their LTCC materials with ultrawide temperature stability

Abstract

Microwave dielectric ceramics with simple composition, a low permittivity (εr), high quality factor (Q × f) and temperature stability, specifically in the ultrawide temperature range, are vital for millimetre-wave communication. Hence, in this study, the improvements in sintering behavior and microwave dielectric properties of the SnO2 ceramic with a porous microstructure were investigated. The relative density of the Sn1-xTixO2 ceramic (65.1%) was improved to 98.8%, and the optimal sintering temperature of Sn1-xTixO2 ceramics reduced from 1525 °C to 1325 °C when Sn4+ was substituted with Ti4+. Furthermore, the εr of Sn1-xTixO2 (0 ≤ x ≤ 1.0) ceramics increased gradually with the rise in x, which can be ascribed to the increase in ionic polarisability and rattling effects of (Sn1-xTix)4+. The intrinsic dielectric loss was mainly controlled by rc (Sn/Ti–O), and the negative τf of the SnO2 ceramic was optimised to near zero (x = 0.1) by the Ti4+ substitution for Sn4+. This study also explored the ideal microwave dielectric properties (εr = 13.7, Q × f = 40,700 GHz at 9.9 GHz, and τf = −7.2 ppm/°C) of the Sn0.9Ti0.1O2 ceramic. Its optimal sintering temperature was decreased to 950 °C when the sintering aids (ZnO–B2O3 glass and LiF) were introduced. The Sn0.9Ti0.1O2-5 wt% LiF ceramic also exhibited excellent microwave dielectric properties (εr = 12.8, Q × f = 23,000 GHz at 10.5 GHz, and τf = −17.1 ppm/°C). At the ultrawide temperature range (−150 °C to +125 °C), the τε of the Sn0.9Ti0.1O2-5 wt% LiF ceramic was +13.3 ppm/°C, indicating excellent temperature stability. The good chemical compatibility of the Sn0.9Ti0.1O2-5 wt% LiF ceramic and the Ag electrode demonstrates their potential application for millimetre-wave communication.