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

Abstract

In this study, we investigate the fabrication of integrated chips with microinductors and a micro-tunable capacitor using the standard 0.35 mu m 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