Integrated circuit spiral inductor

DETAILED DESCRIPTION The object of the present invention is to provide high Q inductors and transformers, and methods of making thereof, that eliminate the problems of conventional inductors and transformers.
Another object of the present invention is to provide high Q inductors and transformers that are suitable for integration in VLSI IC chips, consume a small IC area, and operate at high frequencies.
These and other objects of the inventions are achieved by a spiral inductor and a method of making thereof.
The spiral inductor comprises a substrate; a dielectric layer having a spiral trench; and a first spiral metal coil formed in the spiral trench over the liner to increase an aspect ratio thereof.
A ferromagnetic liner lines the bottom and sides of the trench, and a cap layer may cap the first metal coil so that the first spiral metal coil is enclosed by the cap and liner layers.
In addition, an underpass contact is formed in the dielectric layer below one end of the first metal coil.
This one end of the first metal coil extends into a via formed in the dielectric layer to connect to the underpass contact.
Ferromagnetic core lines are formed in a core surrounded by the first metal coil.
These core lines are electrically separated from each other.
In another embodiment of the present inventions, a second metal coil is formed in the dielectric layer.
The second metal coil may be vertically stacked over the first metal coil or adjacent thereto.
In the latter case, a ferromagnetic bridge is formed below, and contacts, the two adjacent metal coils.
The ferromagnetic bridge may also be formed below the first metal coil in the vertically stacked coils configuration.
The ferromagnetic bridge reduces magnetic flux penetration into the substrate.
This increases the quality factor Q by increasing the inductance L.
In the vertically stacked configuration, an overpass contact may be formed in the dielectric layer above the second metal coil.
The two vertically stacked or adjacent coils may each have a pair of ports to form a spiral transformer