Integrated Passives on LTCC for Achieving Chip-Sized-Modules

This paper describes the design, fabrication and performance of integrated passives devices (IPDs) on LTCC wiring substrates developed for RF-module applications, which have a high quality factor and high self-resonance frequency. A two-layered aerial spiral coil structure and 3D interconnection in the air are used to increase the quality factor of inductors and to reduce the parasitic capacitance in the coils and capacitors. This configuration enables Q-factor of 40 to 60 at 2 GHz for spiral inductors smaller than iquest 0.6 mm, while providing a self-resonance frequency higher than 8 GHz. A Q-factor of 180 at 2 GHz has been achieved for capacitors. The high-Q IPD has been directly fabricated on an LTCC wiring wafer using newly developed multistage plating technology based on a sacrifice layer, which allowed the easy formation of 3D coils and interconnections. The LTCC wiring substrate can offer dense interconnects between the integrated passive circuits and the functional devices mounted above the IPD. This technology combines the advantages of LTCC and IPD and is promising for the miniaturization of future RF-modules.