Lithium metaborate as a lightweight ultra low temperature cofired ceramic substrate for high speed communication systems

The research is aimed at fabrication, and structural, microstructural, thermal and dielectric characterization of new, inexpensive, lightweight, low permittivity substrates based on metaborate LiBO 2 , with a special focus on their applicability in the terahertz frequency range suitable for high-speed 6G communication systems and feasibility in ULTCC (ultra-low temperature cofired ceramics) technology beneficial for miniaturization, integration and cost reduction. Conventional solid state reaction methods are used for LiBO 2 synthesis and sintering of pure LiBO 2 ceramics and LiBO 2 ceramics containing two dopants − AlF 3 -CaB 4 O 7 and AlF 3 -CaB 4 O 7 -Li 2 TiO 3 . The structure, composition, microstructure and sintering behavior are investigated using XRD analysis, EDS analysis, Raman spectroscopy, scanning electron microscopy, thermal analysis, dilatometric measurements and heating microscope studies. Inexpensive starting materials, compatibility with cheap commercial Ag conductors and ultra low sintering temperature (650-710 °C) determines low fabrication costs of the developed substrates. LiBO 2 ceramics show very good dielectric properties in the terahertz range: a very small relative permittivity (4.5–5.2 at 1 THz), stable in a broad frequency range and a relatively small dielectric loss. The applied dopants facilitate processing due to restriction of the reactivity with water and mitigation of excessive shrinkage and warpage during sintering.