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The influence of the inductor thickness on the Q factor has been analyzed in detail by the 3-D electromagnetic simulator HFSS. For spiral inductors based on the CMOS compatible Cu/SiO2 interconnect technology, the improvement of the Q factor can be realized by increasing the metal layer thickness due to the decrease of the series resistance. However, such improvement of the Q factor becomes slender as the thickness over a certain value because of the skin effect and proximity effect. Considering both the effectiveness of improving Q by increasing the thickness and the process challenge to state-of-the-art CMOS technology, we recommend that the reasonable thickness of the interconnect top-metal-layer for inductors can be set to be from 4 μm to 6μm.