Symmetrical inductor

A symmetrical inductor includes a first metal layer, the first metal layer having a first conductive segment disposed on a first side of a line, and a second conductive segment disposed on a second side of the line, the second conductive segment and the first conductive segment being symmetrical to the line; a second metal layer, the second metal layer having a third conductive segment disposed on the first side of the line, and a fourth conductive segment disposed on the second side of the line, the fourth conductive segment and the third conductive segment being symmetrical to the line; a first contact plug for connecting the first conductive segment with a first end of the third conductive segment; a second contact plug for connecting the first conductive segment with a second end of the third conductive segment; a third contact plug for connecting the second conductive segment with a first end of the fourth conductive segment, the third contact plug and the first contact plug being symmetrical to the line; and a fourth contact plug for connecting the second conductive segment with a second end of the fourth conductive segment, the fourth contact plug and the second contact plug being symmetrical to the line.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to an inductor, and more particularly, to a symmetrical inductor.

2. Description of the Prior Art

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. The inductor is usually used with capacitors in various wireless communications applications for providing stable currents, switched phases, filtering and resonance. In its simplest form, the inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns, the thickness, the length and the radius of the coil. The inductance also depends on the type of material around which the coil is wound. In a semiconductor manufacturing process, at least two metal layers with specifically designed layout patterns and a plurality of contact plugs for connecting these two metal layers are used to form a wire loop, thus fabricating an inductor onto an integrated circuit chip.

Referring toFIG. 1,FIG. 1is a schematic diagram of an inductor according to the prior art. As shown inFIG. 1, a differential inductor10includes a first metal layer, which consists of a first conductive segment12and a second conductive segment14. The first conductive segment12and the second conductive segment14are interlaced with each other to form an approximate circle pattern with two overlapping regions A and B. The inductor10further includes a second metal layer, which consists of a third conductive segment20and a fourth conductive segment24. The third conductive segment20is disposed under the overlapping region A of the first conductive segments12and the second conductive segment14, and the fourth conductive segment24is disposed under the overlapping region B of the first conductive segments12and the second conductive segment14. The inductor10further includes a dielectric layer (not shown) disposed between the first metal layer and the second metal layer, and a plurality of contact plugs16,18,22,26penetrating through the dielectric layer to connect the first metal layer and the second metal layer. For example, the portions of the second conductive segment14and the third conductive segment20at the overlapping region A are connected with each other via the contact plugs16and18. The portions of the first conductive segment12and the fourth conductive segment24at the overlapping region B are connected with each other via the contact plugs22and26.

The inductor10cannot provide a symmetrical structure at the overlapping regions of the first conductive segment12and the second conductive segment14. For example, at the overlapping region A, the second conductive segment14connects to the third conductive segment20via the contact plugs16,18, however, the first conductive segment12does not need any contact plugs to connect to the second metal layer. At the overlapping region B, the first conductive segment12connects to the fourth conductive segment24via the contact plugs22,26, however, the second conductive segment14does not need any contact plugs to connect to the second metal layer. In this case, different parasitic resistance values occur in the asymmetrical inductor10, and two differential signals (V+, V−) at the two ends of the inductor10become asymmetrical to result in phase differences and phase noises, thus deeply affecting the electronic circuit characteristics.

SUMMARY OF INVENTION

It is therefore an object of the claimed invention to provide a symmetrical inductor to solve the above-mentioned problems.

According to the claimed invention, the symmetrical inductor includes a first metal layer, the first metal layer having a first conductive segment disposed on a first side of a line, and a second conductive segment disposed on a second side of the line, the second conductive segment and the first conductive segment being symmetrical to the line; a second metal layer, the second metal layer having a third conductive segment disposed on the first side of the line, and a fourth conductive segment disposed on the second side of the line, the fourth conductive segment and the third conductive segment being symmetrical to the line; a first contact plug for connecting the first conductive segment with a first end of the third conductive segment; a second contact plug for connecting the first conductive segment with a second end of the third conductive segment; a third contact plug for connecting the second conductive segment with a first end of the fourth conductive segment, the third contact plug and the first contact plug being symmetrical to the line; and a fourth contact plug for connecting the second conductive segment with a second end of the fourth conductive segment, the fourth contact plug and the second contact plug being symmetrical to the line.

It is an advantage of the present invention to design layout patterns of the inductor into a fully symmetrical structure. The first conductive segment and the second conductive segment of the first metal layer are disposed at either side of the line and symmetrical to the line. The third conductive segment and the fourth conductive segment of the second metal layer are disposed at either side of the line and symmetrical to the line. In addition, the contact plugs symmetrical to the line are also used to connect the first metal layer and the second metal layer. Therefore, the fully symmetrical inductor of the present invention can effectively prevent the problems of different parasitic resistance values, asymmetrical signals, phase differences and phase noises.

These and other objects of the claimed invention will be apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

DETAILED DESCRIPTION

Referring toFIG. 2,FIG. 2is a schematic diagram of an inductor according to a first embodiment of the present invention. As shown inFIG. 2, a differential inductor30includes a first metal layer, which consists of a spiral-shaped first conductive segment32and a spiral-shaped second conductive segment34symmetrical to a line L. The first conductive segment32and the second conductive segment34form at least an approximate circle pattern, and the line L is a diameter of the circle pattern. The inductor30further includes a second metal layer, which consists of a third conductive segment38and a fourth conductive segment44symmetrical to the line L. A portion of the first conductive segment32is disposed above the third conductive segment38, and a portion of the second conductive segment34is disposed above the fourth conductive segment44. Alternatively, in other embodiments of the present invention, the second metal layer is disposed above the first metal layer. As a result, a portion of the first conductive segment32is disposed under the third conductive segment38, and a portion of the second conductive segment34is disposed under the fourth conductive segment44. The inductor30further includes at least a dielectric layer (not shown) disposed between the first metal layer and the second metal layer, and a plurality of contact plugs36,40,42,46penetrating through the dielectric layer to connect the first metal layer and the second metal layer. For example, the first conductive segment32comprises at least a first contact point and a second contact, and the second conductive segment34comprises at least a third contact point and a fourth contact point. The first contact point of the first conductive segment32and the third contact point of the second conductive segment34are symmetrical to the line L. The second contact point of the first conductive segment32and the fourth contact point of the second conductive segment34are symmetrical to the line L, too. The contact plug36connects the first contact point of the first conductive segment32to a first end of the third conductive segment38. The contact plug40connects the second contact point of the first conductive segment32to a second end of the third conductive segment38. The contact plug42connects the third contact point of the second conductive segment34to a first end of the fourth conductive segment44. The contact plug46connects the fourth contact point of the second conductive segment34to a second end of the fourth conductive segment44.

Since the patterns of the first metal layer, the second metal layer and the contact plugs connecting the first metal layer and the second metal layer are symmetrical to the line, the inductor of present invention provides a fully symmetrical structure for the two differential signals (V+, V−) to improve the quality of the inductor and prevent the problems of phase noises. In addition, the present invention may further design rounded corners in the first conductive segment and the conductive segment of the first metal layer, thus preventing currents flowing through the inductor from collecting at the corners to increase local resistance and reduce the quality factor of the inductor. It is worth noticing that the inductor of the present invention is not limited to have the approximate circle pattern. Other inductor patterns comprising a plurality of metal layers, conductive segments and contact plugs symmetrical to a certain line are all applicable in the present invention.

Referring toFIG. 3,FIG. 3is a schematic diagram of an inductor according to a second embodiment of the present invention. As shown inFIG. 3, a differential inductor50includes a first metal layer, which consists of a spiral-shaped first conductive segment52and a spiral-shaped second conductive segment54symmetrical to a line L. The first conductive segment52and the second conductive segment54form at least an approximate circle pattern, and the line L is a diameter of the circle pattern. The inductor50further includes a second metal layer58, and at least a dielectric layer (not shown) disposed between the second metal layer58and the first metal layer52,54. Portions of the first conductive segment52and the second conductive segment54are disposed above the second metal layer58. Alternatively, in other embodiments of the present invention, the second metal layer58is disposed above the first metal layer52,54. As a result, portions of the first conductive segment52and the second conductive segment54are disposed under the second metal layer58. The inductor50further includes a plurality of contact plugs56,60penetrating through the dielectric layer to connect the first metal layer52,54and the second metal layer58. For example, the first conductive segment52comprises at least a first contact point, and the second conductive segment54comprises at least a second contact point. The first contact point of the first conductive segment52and the second contact point of the second conductive segment54are symmetrical to the line L. The contact plug56connects the first contact point of the first conductive segment52to a first end of the second metal layer58. The contact plug60connects the second contact point of the second conductive segment54to a second end of the second metal layer58.

Since the patterns of the first metal layer, the second metal layer and the contact plugs connecting the first metal layer and the second metal layer are symmetrical to the line, the inductor of present invention provides a fully symmetrical structure for the two differential signals (V+, V−) to improve the quality of the inductor and prevent the problems of phase noises. In addition, the present invention may further design rounded corners in the first conductive segment and the conductive segment of the first metal layer, thus preventing currents flowing through the inductor from collecting at the corners to increase local resistance and reduce the quality factor of the inductor. It is worth noticing that the inductor of the present invention is not limited to have the approximate circle pattern. Other inductor patterns comprising a plurality of metal layers, conductive segments and contact plugs symmetrical to a certain line are all applicable in the present invention.

Referring toFIG. 4,FIG. 4is a schematic diagram of an inductor according to a third embodiment of the present invention. As shown inFIG. 4, a differential inductor70includes a first metal layer, which consists of a spiral-shaped first conductive segment72and a spiral-shaped second conductive segment74symmetrical to a line L. The first conductive segment72and the second conductive segment74form at least an approximate circle pattern, and the line L is a diameter of the circle pattern. The inductor70further includes a second metal layer78, and at least a dielectric layer (not shown) disposed between the second metal layer78and the first metal layer72,74. Portions of the first conductive segment72and the second conductive segment74are disposed above the second metal layer78. Alternatively, in other embodiments of the present invention, the second metal layer78is disposed above the first metal layer72,74. As a result, portions of the first conductive segment72and the second conductive segment74are disposed under the second metal layer78. The inductor70further includes a plurality of contact plugs76,80penetrating through the dielectric layer to connect the first metal layer72,74and the second metal layer78. For example, the first conductive segment72comprises at least a first contact point, and the second conductive segment74comprises at least a second contact point. The first contact point of the first conductive segment72and the second contact point of the second conductive segment74are symmetrical to the line L. The contact plug76connects the first contact point of the first conductive segment72to a first end of the second metal layer78. The contact plug80connects the second contact point of the second conductive segment74to a second end of the second metal layer78.

Since the patterns of the first metal layer, the second metal layer and the contact plugs connecting the first metal layer and the second metal layer are symmetrical to the line, the inductor of present invention provides a fully symmetrical structure for the two differential signals (V+, V−) to improve the quality of the inductor and prevent the problems of phase noises. In addition, the present invention may further design rounded corners in the first conductive segment and the conductive segment of the first metal layer, thus preventing currents flowing through the inductor from collecting at the corners to increase local resistance and reduce the quality factor of the inductor. It is worth noticing that the inductor of the present invention is not limited to have the approximate circle pattern. Other inductor patterns comprising a plurality of metal layers, conductive segments and contact plugs symmetrical to a certain line are all applicable in the present invention.

In contrast to the asymmetrical inductor of the prior art, the present invention designs layout patterns of the inductor into a fully symmetrical structure. The first conductive segment and the second conductive segment of the first metal layer are disposed at either side of the line and symmetrical to the line. The third conductive segment and the fourth conductive segment of the second metal layer are disposed at either side of the line and symmetrical to the line. In addition, the contact plugs symmetrical to the line are also used to connect the first metal layer and the second metal layer. Therefore, the fully symmetrical inductor of the present invention can effectively prevent the problems of different parasitic resistance values, asymmetrical signals, phase differences and phase noises.