Dielectric and thermodynamic properties of Ba-doped photoetchable glasses for three dimensional RF microsystem packaging

Abstract

Photoetchable glasses (PEGs) are employed in packaging of radio frequency (RF) microsystems. However, their widescale adoption has been limited by intrinsic high dielectric losses. The present study reports results of systematic investigation of dielectric and thermodynamic properties of Barium (Ba) ion substituted Li–Al–Si-based PEGs. It is demonstrated that UV absorption characteristics remain largely unchanged upon Ba ion doping. Crystallization behavior of PEGs were determined by digital scanning calorimetry. After annealing at different temperatures, the structure and morphology of precipitated crystal phases were analyzed by x-ray diffraction and electron microscopy. Results reveal that the optimal annealing temperature was 565 °C, after which dielectric properties were measured to experience a dielectric constant and minimum dielectric loss of 4.7 and 3 × 10−3, respectively. Concomitantly, the influence of temperature on dielectric properties at constant frequency was investigated. Raman spectroscopy analyses exhibit that the incorporation of Ba ions do not participate in structural changes but rather dissociate within the glass network as network modifiers, influencing the dielectric properties of Ba-doped PEG. The improvement in dielectric and thermodynamic properties demonstrated here confirms the value of PEGs as preferred interposer materials in three-dimensional RF microsystem packaging.