1. Field of the Invention
The invention relates generally to the field of semiconductor integrated circuit design, and more particularly, to an on-chip high-Q (high quality factor) integrated inductor structure.
2. Description of the Prior Art
The fast growing of the wireless market has created an urgent demand for smaller and cheaper handsets with increased functionality and performance. A major trend of circuit design is to incorporate as many circuit components into integrated circuit form as possible, whereby cost per wafer can be reduced.
Inductors built in semiconductor wafers are widely used in CMOS based radio frequency (RF) circuits such as low-noise amplifiers, voltage-controlled oscillators and power amplifiers. An inductor is a passive electronic component that stores energy in the form of a magnetic field, and an inductor tends to resist any change in the amount of current flowing through it.
One of the most important characteristics of the inductor is the quality factor Q, which relates to the performance of the RF or other circuits and systems. The quality factor Q of an integrated circuit is limited by parasitic losses within the substrate itself. These losses include high resistance through metal layers of the inductor itself. Consequently, in order to achieve a high quality factor, resistance within the inductor should be held to a minimum. One approach to minimizing the resistance of the inductor is increasing the thickness of metal used to fabricate the inductor.
Therefore, integrated inductors fabricated by RF baseline process may have decreased resistance due to much thicker top metal layer (i.e., the topmost level of the damascene copper interconnection). It is easier for one of the skilled in the art to implement a much thicker top metal layer than other metal layers. Taking 0.13 μm RF baseline process as an example, a top metal layer with a thickness of as high as 3 μm is a commonplace. However, such ultra thick metal layer leads to complicated process and relatively lower throughput and higher cost.