Process alternatives for manufacturing integrated inductors

New interest has recently arisen on inductors integrated monolithically together with CMOS electronics. The reason for the current attention lies in the demand for higher level of integration and increased operation frequency. Earlier efforts to make advantage of inductors in addition to other passive elements led to conclusion that the high conductivity of silicon and the large area required for the device would restrict their use. General development of integrated circuit fabrication technology has now made it possible to reappraise the use of integrated inductors.

Two important process related aspects which affect the quality factor of inductors are the series resistance and parasitic capacitance of the structure. We have worked on reducing the resistance by using alternative metallization for the inductors and at the same time born in mind the demand for integration. We also have tried different oxide thicknesses between silicon substrate and the device to reduce parasitic capacitance. For alternative metallizations electroplated gold and thick sputter deposited aluminium have been used. Comparison between the quality of inductors as well as manufacturability of each process has been made.