Fully embedded LTCC spiral inductors incorporating air cavity for high Q-factor and SRF

In this paper, a new fully-embedded LTCC spiral inductor is proposed by incorporating an air cavity between the spiral and ground plane for high quality factor (Q-factor) and high self-resonant frequency (SRF). The disadvantage of fully embedded structure without an air cavity is the reduction of size efficiency in the RF system, since its structure needs a lot of layers to decrease parasitic capacitance between the spiral and ground plane for high Q-factor and SRF. The air cavity employed under the spiral reduces the shunt parasitic capacitance of the inductor, and results in high Q-factor and high SRF of the embedded inductors. The measured results of the optimized spiral inductor with the embedded air cavity show a maximum Q of 51 and SRF of 9.1 GHz, while those of the conventional spiral inductor describe a maximum Q of 43 and SRF of 8 GHz with effective inductance of 2.7 nH.