Ultrathin High- $Q$ 2-D and 3-D RF Inductors in Glass Packages

Embedded inductors in ultrathin glass substrates were modeled, designed, fabricated, and characterized. Various 2-D and 3-D topologies were explored to obtain the tradeoffs in inductance density, quality (Q) factor, size, and self-resonant frequency (SRF). Single-layer spiral inductors were modeled and designed to formulate an inductor library that is optimized for high inductance densities. These include variations in the number of turns, conductor linewidth and spacing, and the ratios of inner diameter and outer diameter of the spiral. In order to optimize the inductor topology for higher Q factors, various types of 3-D topologies with 300-μm glass were studied through modeling, fabrication, and model validation. Inductance densities, Q, and SRF were measured for various topologies. Higher inductance densities of 10-20 nH/mm
²
with a Q factor of 30-40 are obtained for spiral inductors on glass, making them more suitable for module miniaturization when Q-factor requirements are not stringent. For higher Q factors, 3-D solenoid and daisy-chain topologies are found to be more suitable in spite of their low inductance densities of 3 nH/mm
²
, making them a better choice for applications where better channel selectivity, precise phase-switching, and lower insertion loss are needed.