JP3717477B2 - Spiral inductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spiral inductor provided in an integrated circuit.
[0002]
[Prior art]
In a high-frequency integrated circuit, a spiral inductor is used in which a conductor is formed in a spiral shape for the purpose of impedance matching or the like.
[0003]
[Problems to be solved by the invention]
The conventional spiral inductor has a problem that the thickness of the normal wiring is thin, the conductor is thin, the DC resistance is large, and an inductor having a high Q value (Quality Factor) cannot be obtained. When the thickness of the wiring layer is increased, the thickness of the wirings of other blocks also increases, and the distance between the wirings needs to be increased accordingly, so that the chip area increases. For this reason, it is impossible to increase the thickness of the wiring by increasing the wiring layer.
[0004]
Accordingly, an object of the present invention is to provide a spiral inductor having a high Q value.
[0005]
[Means for Solving the Problems]
According to the present invention, the first wiring formed in a spiral shape in the first wiring layer, the second wiring provided along the entire length of the first wiring in the second wiring layer, There is provided a spiral inductor comprising a plurality of vias connecting two wirings to a first wiring.
[0006]
In this spiral inductor, the portion of the second wiring along the outermost portion of the spiral of the first wiring is formed along the outer edge of the first wiring, and is the outermost portion of the spiral of the first wiring. The portion of the second wiring along the portion located on the inner side is preferably formed along the inner edge of the first wiring.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a spiral inductor according to a first embodiment of the present invention, in which (a) column is a plan view thereof, and (b) column is a cross-sectional view taken along line AA 'in (a) column. In FIG. 1, the wiring 12 is similarly formed in the spiral shape along the wiring 10 in the wiring layer below the wiring layer to which the wiring 10 formed in the spiral shape belongs. A large number of vias 14 are connected between the wiring 10 and the wiring 12. In FIG. 1A, the via 14 is drawn only in a partial region of the wiring 10, but actually the via 14 is formed over the entire region of the wiring 10.
[0008]
Thereby, the substantial thickness of the conductor constituting the spiral inductor is increased and the direct current resistance is decreased without increasing the thickness of the wiring layer, so that the Q value can be increased as shown in FIG.
[0009]
As can be seen from FIG. 2, the Q value as a whole is improved in Example 1, but the degradation of the Q value in the higher frequency region is significant, and cannot be used as an inductor in the higher frequency region. This is because the capacitance between the wiring and the capacitance with respect to the substrate is increased due to the increase in the thickness of the conductor, and the self-resonance frequency is lowered.
[0010]
In the second embodiment of the present invention, attention is paid to the fact that the current flowing in the wiring is unevenly distributed due to the influence of the magnetic field, and by increasing only the portion where the current is unevenly distributed, the inter-wiring capacitance and the substrate are improved Suppress the increase in capacity.
[0011]
FIG. 3 shows a spiral inductor according to a second embodiment of the present invention, FIG. 3 (a) is a plan view thereof, and FIG. 3 (b) is a sectional view taken along line BB 'in FIG. 3 (a). The outer current density is high at the outermost periphery of the spiral of the wiring 16, and the inner current density is high at the innermost periphery. Therefore, the wiring 18 is formed along the outer edge of the wiring 16 at the outermost periphery of the spiral, and is formed along the inner edge of the wiring 16 at the innermost periphery. In portions other than the outermost periphery and the innermost periphery, if the wiring 18 is interrupted, reflection occurs, which is not preferable. Therefore, the distance from both the outer wiring and the inner wiring is taken. A wiring 18 is formed. A via 20 is formed over the entire area of the wiring 18.
[0012]
As can be seen from the graph of FIG. 4, in the second embodiment, the Q value is improved to the same extent as in the first embodiment and the resonance frequency does not decrease.
[0013]
The wiring that realizes the inductor is usually formed in a spiral shape to obtain mutual inductance, but the shape is not limited to a square as in the illustrated example, and may be a circle or a polygon.
[0014]
【The invention's effect】
As described above, according to the present invention, a spiral inductor having a high Q value can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a spiral inductor according to a first embodiment of the present invention.
FIG. 2 is a graph showing a Q value of the spiral inductor of FIG. 1 together with a conventional example.
FIG. 3 is a diagram showing a spiral inductor according to a second embodiment of the present invention.
4 is a diagram showing the Q value of the spiral inductor of FIG. 3 together with the spiral inductor of FIG. 1 and the conventional example.

Claims (1)

A first wiring formed in a spiral shape in the first wiring layer;
A second wiring provided along the entire length of the first wiring in the second wiring layer;
A plurality of vias connecting the second wiring to the first wiring;
A portion of the second wiring along the outermost portion of the spiral of the first wiring is formed along the outer edge of the first wiring;
The portion of the second wiring along the innermost portion of the spiral of the first wiring is a spiral inductor formed along the inner edge of the first wiring.

Images