Towards ultrahigh-Q and temperature-stable microwave dielectric ceramics via trilayer cofired architecture: A case study of Mg4Nb2O9/TiO2/Mg4Nb2O9

Microwave dielectric ceramics (MWDCs), as the key materials for microwave components in wireless communication systems, are required to possess appropriate dielectric constant (epsilon(r)), low dielectric loss (high Qxf value) and near-zero temperature coefficient of resonant frequency (tau(f)). However, it remains very difficult for many typical composite ceramic systems to develop temperature-stable and high-Q MWDCs through conventional solid-state reaction method (the mixed route), because not all the introduced temperature compensators can well coexist with the matrices. Herein, as for the typical Mg4Nb2O9-TiO2 system, a trilayer cofired MWDC with Mg4Nb2O9/TiO2/Mg4Nb2O9-sandwich architecture was newly designed to realize excellent microwave dielectric characteristics. The effects of TiO2 stacking content on the microwave dielectric properties of the cofired architectures were studied systematically. The chemical reactions between the matrix Mg4Nb2O9 and the temperature compensator TiO2 were effectively confined to a narrow region (approximately 35 mu m in depth) at the Mg4Nb2O9/TiO2 interfaces. It could be beneficial for the cofired ceramic architectures to optimize the microwave dielectric properties of epsilon(r) similar to 14.21 and tau(f) similar to -3.13 ppm/degrees C at a small TiO2 content of 1.49 vol%, together with an ultrahigh Qxf value similar to 134 660 GHz which is more than eight times that of the counterparts prepared by conventional solid-state mixed route. The current work can provide new insights into making full use of existing MWDC systems, especially those with very large tau(f) values, and thereby facilitating the development of high-performance dielectric resonators and multilayer components for further commercial applications.