Robust and Postless Air-Suspended High Q Integrated Inductors on Silicon

In this paper, integrated air-suspended inductors were newly developed on silicon substrate for on-chip radio frequency (RF) circuit and system applications. For the improvement of Q-factors and self-resonant frequencies of the integrated inductors, they were designed and fabricated by using air-suspended spiral conductor lines, photoresist sacrificial layer, and electroplating technique. For forming the air-suspended conductor lines without selectively etching the substrate and using any metal or insulating posts, the conductor lines were designed to have a shape of ‘U’ at the center of each conductor line. In comparison of the fabricated conventional planar and air-suspended inductors, an increase of 25% in the Q-factor was achieved for the air-suspended inductors. The self-resonant frequency was also increased about 10 to 15% compared with the planar ones. The proposed inductor geometry and fabrication processes were developed for integrating with metal-insulator-metal (MIM) RF capacitors.