Low temperature sintering of Zn4B6O13 based substrates, their microstructure and dielectric properties up to the THz range

Abstract

Tape casting was used to prepare green tapes based on pure and doped Zn4B6O13 ceramics that are destined for LTCC high frequency substrates. In order to broaden the sintering temperature range, three additives which were based on Zn2SiO4–Li2TiO3, AlF3–CaB4O7–Li2TiO3 and Zn2SiO4–MgTiO3, were selected using heating microscope studies. Differential thermal analysis was used to establish the optimal firing profiles. The microstructure and composition of the sintered ceramics were examined by scanning electron microscopy, energy dispersive spectroscopy and the X-ray diffraction method. Owing to the low sintering temperatures and good compatibility with commercial Ag thick films, multilayer substrates based on green tapes made of the developed materials can be cofired at 900–920 °C. The dielectric properties were studied in a broad range up to the THz frequencies. The most advantageous properties for LTCC substrates, such as high densification degree, a low dielectric permittivity (6.9 at 1 THz) and a low dissipation factor (0.005 at 1 THz) were exhibited by the Zn4B6O13 ceramic to which 10% Zn2SiO4 and 5% MgTiO3 were added.