Improved LTCC spiral inductor structures for RF-system-in-package applications

Abstract

Highly compact system integration is one of the key issues for realization of the next generation mobile communication handset because it needs backward compatibility and convergence including WLAN, GPS, and even Bluetooth as well as various mobile communications. Contrary to digital circuits, being composed of several different technologies such as GaAs circuits for power amplifiers and switches, Si circuits for IF and baseband analog circuit, and ceramic components such as filter and resonator, the RF part of the mobile handset is more feasible to be integrated in a near future with a SIP (system in package) technology rather than SoC (system on a chip) technology. This thesis reports novel low temperature co-fired ceramics (LTCC) inductor structures for RF System-In-Package (SIP) applications. Passive components occupy a large part of total area in RF system and it is desirable to reduce the area occupied by the passive components and improve the better performance. LTCC technology is capable of embedding passive components, particularly inductors and capacitors, within the multilayer circuit. The fully embedded structure renders placement freedom and space efficiency of the passive devices in the RF system. This thesis proposes fully embedded multilayer spiral inductors for high density integration and, more importantly, fully embedded LTCC spiral inductors incorporating air cavity. The proposed structures are aimed to reduce the shunt capacitance and to improve the Q-factor and SRF of the embedded inductors. With a same dimension and number of turns, the 3D spiral inductor has better performance than the conventional spiral inductor: the embedded 3D spiral inductor improves SRF by 20%, Q-factor by 14%, and effective inductance by 13% compared to the conventional embedded spiral inductor. Moreover the spiral inductor with air cavity incorporated reveals also improved performance than the conventional spiral inductor: the spiral inductor incorporating air ...