New design approach of vertical inductors for high-frequency integrated circuits

This paper presents a new method for the design of inductors in high-frequency integrated circuits. In order to increase the inductance per unit of area more than one metal layer is used and the spiral inductor is oriented in the vertical instead of the horizontal plane. The inductor is designed in 130 nm BiCMOS technology using five metal layers. Simulations were performed via Sonnet 3D EM software. The inductance at low frequencies was verified with the Greenhouse method using Grover formulas. Good agreement between simulations and analytical calculations was found when the inductance length and metal width was changed. As a first proof of concept, an inductor of 340 pH with self-resonance frequency of 51.7 GHz and a quality factor of 3.14 at 26 GHz was designed, which is well suited for peaking purposes. The designed inductor shows an inductance per unit of area of 377 nH/mm². This is a significant improvement compared to planar inductors.