RF Power Amplifier, 2nd Edition

10.14 Planar Spiral Inductors

10.14.1 Geometries of Planar Spiral Inductors

Planar spiral inductors are the most widely used RF IC inductors. Figure 10.17 shows square, octagonal, hexagonal, and circular planar spiral inductors. A planar spiral inductor consists of a low-resistivity metal trace (aluminum, copper, gold, or silver), silicon dioxide (SiO) of thickness , and a silicon substrate, as shown in Fig. 10.18. A metal layer embedded in silicon dioxide is used to form the metal spiral. The topmost metal layer is usually the thickest and thus most conductive. In addition, a larger distance of the topmost metal layer to the substrate reduces the parasitic capacitance , increasing the SRF , where is the metal trace area. The substrate is a thick silicon (Si), gallium arsenide (GaAs), or silicon germanium (SiGe) layer of thickness of the order of 500–m. The thin silicon dioxide (SiO) of ...