Fabrication of Integrated Chip with Microinductors and Micro-Tunable Capacitors by Complementary Metal–Oxide–Semiconductor Postprocess

In this study, we investigate the fabrication of integrated chips with microinductors and a micro-tunable capacitor using the standard 0.35 µm single polysilicon four-metal (SPFM) complementary metal–oxide–semiconductor (CMOS) and a postprocess. Two inductors-planar spiral and conical spiral-are fabricated and tested. The postprocess has two main steps: One step is the removal of a metal from sacrificial layers and the etching holes in structures using phosphoric acid. The other is the etching of a silicon substrate using tetramethyl ammonium hydroxide (TMAH) to increase the distance between the inductors and the silicon substrate, thereby reducing substrate loss and increasing the quality ( Q ) factor of the inductors. Experimental results show that the maximum Q factors of the conical spiral and planar spiral inductors were 4.6 at 3.5 GHz and 4.7 at 4 GHz, respectively, following the postprocess. The self-resonance frequency of the conical spiral inductor exceeded that of the planar spiral inductor.