Micromachined High Q Inductors for High Frequency Applications

To meet requirements in mobile communication and microwave integrated circuits, miniaturization of the inductive components that many of these systems require is of key importance. At present, active circuitry is used which simulates inductor performance and which has high Q-factor and inductance; however, such circuitry has higher power consumption and higher potential for noise injection than passive inductive components. An alternate approach is to fabricate integrated inductors, in which lithographic techniques are used to pattern an inductor directly on a substrate or a chip. However, integrated inductors can suffer from low Q-factor and high parasitic effects due to substrate proximity. To expand the applications of integrated inductors, these characteristics must be improved. High Q integrated spiral inductors are investigated using olymer/metal multilayer processing techniques and surface micromachining techniques. These inductors have spiral geometry with an air core and a large air gap (4Oim height) between the coils and the substrate (to reduce substrate capacitance), and thick, highly conductive electroplated copper conductor lines (to increase the quality factor). Various inductor geometries are investigated by designing and fabricating several inductors with differing core areas and numbers of turns. The fabricated inductors have a Q-factor of 40-75 at 300-700 MHz and an inductance at these frequencies between 30-7OnH.

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