Fabrication, RF Characteristics and Mechanical Stability of Self-Assembled 3D Microwave Inductors

We present a method for the fabrication of vertical inductors for radio-frequency and microwave applications. This process uses five levels of lithography and electroplating, with no substrate removal, high temperatures or serial process steps. Rotation of the inductors perpendicular to the substrate is achieved by surface tension driven self-assembly, giving separation from the substrate and therefore increasing substantially the Q and self-resonant frequencies. Meander and spiral air-bridged inductors of up to 5.5 nH are demonstrated. The Q of 2 nH inductors shows an increase from 4 to 20 after having undergone the self-assembly process. Mechanical sensitivity is evaluated through finite element modelling, and the maximum displacements indicated are below 10 nm for 1 g of loading. Mechanical resonance frequencies are found within the 6-15 kHz range. (C) 2002 Elsevier Science B.V. All rights reserved.