JP2000357774A - Plurality of conductor lines, inductor element and monolithic microwave integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-loss line structure which can avoid making a high resistance due to the skin effect of a high frequency current. SOLUTION: A plurality of parallel conductors 12, 13 are formed on a board 11 to constitute a line. Currents in phase are flowed or voltages in phase are applied on the parallel conductors 1. The parasitic resistance of the plurality of conductors line can be reduced at high frequencies. The plurality of conductors line is spirally wound to form inductor elements and a monolithic microwave IC involving them can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line, an inductor element and an integrated circuit which operate in a microwave or millimeter wave region such as mobile communication, satellite communication or satellite broadcasting.
It is intended to reduce the loss of the line and the inductor element, and to realize the high performance of the integrated circuit.

[0002]

2. Description of the Related Art In order to realize a compact high-frequency circuit, a monolithic microwave integrated circuit (Monolithic Microwave Int.) In which active elements operating at a high frequency and passive elements such as inductors, capacitors and resistors are integrally formed on a semiconductor substrate.
egrated Circuit, hereafter monolithic microwave IC
Has been put to practical use. Conventional monolithic microwave ICs are described, for example, in Masayoshi Aikawa et al., "Monolithic Microwave Integrated Circuit (MMIC)" (published in 1997, The Institute of Electronics, Information and Communication Engineers). In order to improve the performance of the monolithic microwave IC such as high gain and high output, it is essential to reduce the loss of the line as well as the performance of the active element.

FIG. 2 shows an example of a line 22 used in a conventional monolithic microwave IC. FIG.
2A is a plan view, and FIG. 2B is a cross-sectional view. The line 22 is formed on an interlayer film 24 covering the Si substrate 21, and a surface protection film 25 is further formed thereon.

[0004] In a conventional line, as the frequency increases, the resistance of the conductive wire becomes different from the DC resistance. This is a phenomenon in which the resistance value increases because the region where the current flows in the conductor of the line is narrowed only near the surface due to the effect of the skin effect.

The thickness at which the current density decreases to 1 / e of the surface is called the skin depth δ, which depends on the operating frequency f and is expressed as δ = √ (2ρ / 2πfμ). Here, ρ and μ are the resistivity and the magnetic permeability of the conductive wire, respectively.

For example, a frequency f used in mobile communication
= 2 GHz, Al conducting wire ρ = 2.75 × 10 ⁻⁸ Ω · m, μ
In the case of = μ ₀ = 4π × 10 ⁻⁷ H / m, δ = 1.87 × 1
0 ⁻⁶ m = 1.87 μm, and the line width (W ′) of the conductor is δ
Even if it is spread more than about, the resistance does not decrease much. On the other hand, if the line width (W ′) of the conductor is increased, the parasitic capacitance C per unit length between the conductor and the substrate increases, so that the dielectric loss increases, and eventually the loss cannot be reduced.

Since there is a relation of Z = √ (εμ ′) / C between the parasitic capacitance C per unit length and the characteristic impedance Z of the line, the line width (W ′) of the line is It must be determined in consideration of the characteristic impedance, and cannot be infinitely wide. Where ε and μ 'are interlayer films, respectively.
24 are the permittivity and magnetic permeability.

A conventional spiral-shaped inductor element using such a line is described in, for example, Shin Chagi et al., “Study of spiral inductor equivalent circuit modeling” (IEICE Technical Report ED92-1).
19, NW92-122, ICD92-140 / 1993-01, pp. 45-52). In the case of a conventional spiral-shaped inductor element having a conductor wire width of 10 μm, the frequency range is 0.1 to 10 GHz.
At z, there is a tendency for the resistance to increase with frequency due to the skin effect. Also in this case, even if the line width of the conductor is further increased, the loss cannot be reduced.

[0009]

As described above, the flow of the current flowing through the conductor of the line is uniquely determined by giving the resistivity and the frequency. On the other hand, since the parasitic capacitance C and the characteristic impedance Z are determined by the line width of the conductor, there is a restriction that the line width cannot be increased as much as possible in order to reduce the high-frequency resistance R. Therefore, conventionally, in order to reduce the high-frequency resistance R of a line, a method other than manufacturing a line using a metal having a low resistivity ρ and a wire having a line width of 2 to 3 times or less the skin depth δ is used. There was no.

The present invention has been made to solve the above-mentioned conventional problems, and provides a low-loss line structure capable of preventing a high resistance from being caused by a skin effect of a high-frequency current, and a low-loss line structure formed by using this line structure. And a monolithic microwave IC.

[0011]

Therefore, according to the present invention, a line includes a plurality of parallel conductors formed on a substrate as at least a part of the line, and a current in phase with the plurality of parallel conductors. Or a common-mode voltage is applied to reduce the high-frequency parasitic resistance compared to a single line having the same parasitic capacitance.

Further, a spiral shape is formed by this line, that is, a plurality of conductor lines, to constitute an inductor element.

Further, a monolithic microwave IC is formed by forming the plurality of conductor lines or inductor elements on a substrate.
Is composed.

The plurality of conductive lines are manufactured using a semi-insulating semiconductor substrate such as GaAs or InP used in the prior art or a Si semiconductor substrate as a substrate and using a conventional semiconductor manufacturing process. Can be.

In addition, when the monolithic microwave IC includes an active element, a plurality of conductor lines, and a matching circuit for impedance matching between the two, and the matching circuit includes an inductance element as a component, As the inductance element, the inductor element can be used depending on the used frequency band, and the plural conductor lines having a required length can be used depending on the used frequency band.

As the frequency increases, the region where the current flows through the conductor narrows only near the surface. In the multiple conductive lines of the present invention, the width of the conductor is not increased to twice or more than twice or three times the skin depth δ, but the number of the conductors is increased. And the loss can be reduced.

Further, by forming the inductor element using the plurality of conductive lines, it is possible to reduce the loss of the inductor element.

Further, the reduction of the loss results in a monolithic microwave IC having an inductor element having higher performance such as higher gain, lower noise and lower power consumption.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a plurality of parallel conductors formed on a substrate as at least a part of a line, and the plurality of parallel conductors have the same phase. This is a multi-conductor line that reduces the high-frequency parasitic resistance compared to a single line with the same parasitic capacitance by applying current or applying the same-phase voltage. it can.

According to a second aspect of the present invention, each of the plurality of parallel conductors is disposed on a plane parallel to the surface of the substrate, and each of the plurality of conductors is equidistant from the substrate. It is arranged with keeping.

According to a third aspect of the present invention, each of a plurality of parallel conducting wires is stacked and arranged on a substrate.
The parasitic capacitance between the line and the substrate can be reduced.

According to a fourth aspect of the present invention, the inductor element is formed by forming a helical shape with the plurality of conductor lines according to any one of the first to third aspects. Can be configured.

According to a fifth aspect of the present invention, there is provided a monolithic microwave provided with a plurality of conductor lines according to any one of the first to third aspects or an inductor element having a spiral shape of the plurality of conductor lines. It is an IC that can achieve high gain, low noise, and low power consumption.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 shows the structure of a multi-conductor line of the present invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view. The plural conductor lines are constituted by two parallel conductors, a first conductor 12 and a second conductor 13, and these parallel conductors 12, 13 are formed on an interlayer film 14 covering the Si substrate 11. The surface is further covered with a surface protective film 15.

The line width w of the first conductor 12 and the second conductor 13 is:
It is 4.5 μm, and the space s between them is 3 μm. Here, a voltage in the same direction with respect to the potential of the substrate 11 is applied to the first conductor 12 and the second conductor 13. In other words, the first
The in-phase AC signal is passed through the lead wire 12 and the second lead wire 13.

As the substrate 11, a P-type Si substrate is used. Al wiring is used for the first conductor 12 and the second conductor 13. The Al wiring referred to here is a laminate of a Ti / TiN barrier layer, an Al layer obtained by adding Si and Cu to Al, and a Ti / TiN barrier layer, and has a total thickness t of about 2 μm. The interlayer film 14 is made of p-T which is a kind of silicon oxide film.
An EOS film having a thickness of 6 μm is used. Surface protective film 15
Deposits a 4.3 μm polyimide film.

The effect of the multiple conductor lines will be described in comparison with the conventional single line of FIG. The conventional single line of FIG.
A single conductor having a line width w ′ = 12 μm formed on the substrate 21
22.

Referring to the parasitic capacitance between the substrate and the substrate, the multi-conductor line (FIG. 1) of the present invention has a total line width of 9 μm.
And the area of the bottom surface is smaller because the line width is smaller than that of the single conductor line (FIG. 2). However, since the number of the lines is two, the area of the side surface is increased. Therefore, the parasitic capacitance with the substrate becomes almost the same.

On the other hand, the parasitic resistance R of the conventional single conductor line is smaller at direct current and low frequency, but as the frequency increases, the current of the conventional single conductor line increases due to the skin effect. As a result, the parasitic resistance R greatly increases.

On the other hand, the multi-conductor line has a larger resistance at a direct current and a low frequency than a single conductor line, but has a smaller line width at a higher frequency, so that the resistance does not increase as much as a single conductor line. As a result, for example, when compared at a frequency of 2 GHz used in mobile communication, in the case of a plurality of conductor lines,
The parasitic resistance R can be reduced by 20% as compared with the conventional single conductor line.

In this embodiment, a case is shown in which a plurality of conductor lines are constituted by two conductors, but the parasitic resistance can be further reduced by further increasing the number of conductors. In this embodiment, the conductors 12 and 13 constituting the plural conductor lines are arranged on the plane equidistant from the substrate 11, but one of the conductors (or a part thereof) is disposed between the interlayer film. The same effect can be obtained by disposing so as to overlap with the other conductive wire via.

As the substrate 11, in addition to the P-type silicon substrate used in this embodiment, for example, a semi-insulating semiconductor substrate such as GaAs or InP, an N-type silicon substrate, or a silicon substrate on an insulator (Silicon-On). A similar effect can be obtained by using an -Insulator substrate). When a semi-insulating semiconductor substrate is selected as the substrate, the potential can be stabilized by adding a ground conductor to the back surface.

The same effect can be obtained by using a Cu wiring or an Au wiring other than the Al wiring used in this embodiment as the first conductive line 12 and the second conductive line 13 constituting the plural conductive lines. is there.

As the interlayer film 14, in addition to the p-TEOS film used in this embodiment, for example, another silicon oxide film such as an NSG film, or a silicon oxide film containing B or P such as a PSG film or a BPSG film. A similar effect can be obtained by using a fluorine-added silicon oxide film such as an FSG film, an organic film such as a silicon nitride film, a polyimide or the like, or a laminate thereof.

Further, the same effect can be obtained by depositing a film similar to the above-mentioned interlayer film other than the polyimide film used in this embodiment as the surface protective film 15.

(Second Embodiment) In the second embodiment,
An inductor element configured using a plurality of conductor lines will be described.

As shown in FIG. 3, this inductor element is configured by spirally winding the plural conductor lines of the first embodiment on a Si substrate 31. As in the first embodiment, the plural conductor lines have a first conductor 32 and a second conductor 33 having a line width W = 4.5 μm arranged in parallel with a space s = 3 μm therebetween. A signal of the same phase flows through the first conductor 32 and the second conductor 33. Where these wires intersect each other, contacts 34 and 45 and the underlying wire 36
Is used. The outer size is lx = 200 μm and ly = 200 μm, respectively.

FIG. 4 shows an example of a conventional inductor element for comparison. This inductor element is also an inductor element in which the line 42 is spirally wound, but differs from FIG. 3 in that the line is constituted by a single conductor 42. The conventional inductor element of FIG. 4 is similar to the conventional line of FIG.
A line is constituted by a single conducting wire 42 having a line width w = 12 μm on 41. The outer size is lx = 200 μm and ly = 200 μm as in FIG.

The inductor element composed of a plurality of conductor lines of this embodiment and the inductor element composed of a conventional single conductor line are almost the same with respect to the parasitic capacitance between the substrate and the substrate. The parasitic capacitance is almost the same because, in the case of a plurality of conductor lines, the total line width is 9 μm, which is smaller than the conventional single conductor line, and the parasitic capacitance at the bottom portion is reduced, but the side surface of the space portion is reduced. This is because the parasitic capacitance increases.

The value of the inductance is slightly smaller in this embodiment, but is substantially the same. The reason why the inductance value is slightly different is that there is a space, but the distance between the outsides of the pair of conducting wires is set to 12 as in the conventional example.
If the space is narrowed while maintaining a value of μm, the inductance value can be made even closer to the conventional inductance value.

Regarding the parasitic resistance R, at DC and low frequencies, the inductor element using the conventional line is smaller,
As the frequency increases, in the conventional inductor element using a single conductor line, the current concentrates on both side surfaces of the conductor due to the skin effect, and the parasitic resistance R greatly increases.

On the other hand, the inductor element using the plural conductor lines of this embodiment has
Although the resistance is higher than the conventional example, the line width is small, so that even if the frequency increases, the resistance does not increase as much as the conventional example.

As a result, when compared at a frequency of 2 GHz used in mobile communication, for example, the inductor element using the plural conductor lines of this embodiment has a parasitic resistance R reduced by 20% as compared with the conventional inductor element. it can. Further, the Q value, which is an index indicating the power loss, is improved from 6.0 to 7.2.

In this embodiment, the conductors 32 and 33 constituting a plurality of conductor lines are arranged on a plane equidistant from the substrate 31, but one of the conductors (or a part thereof) is provided with an interlayer film. The same effect can be obtained by arranging it so as to overlap with the other conductive wire with an intervening space.

Further, in this embodiment, the outer shape of the inductor element is formed as a quadrangle, but the same effect can be obtained with an arbitrary polygon such as an octagon, a circle or a spiral.

Although a Si substrate is used as a substrate in this embodiment, a semi-insulating semiconductor substrate such as GaAs or InP or a silicon substrate (Silicon-
The same effect can be obtained by using an on-insulator substrate.

(Third Embodiment) In the third embodiment,
A monolithic microwave IC will be described.

FIG. 5 shows an example of a monolithic microwave IC for amplification of one stage of a transistor. Si substrate
On 51, a transistor element 52 as an active element, inductor elements 53 to 56 as passive elements, capacitor elements 57 to 510,
There are pads 511 to 515 for input / output of signals and power, etc., and these elements are connected by the conventional single conductor line 516 or the plural conductor lines 517 to 519 described in the first embodiment as necessary. Have been. The signal is input from the pad 511, and only the AC component is passed by the capacitor element 57. Similarly, only the AC component is passed by the capacitor element 510 and the output is taken out from the pad 512. The bias voltage of the transistor element 52 is supplied from the pad 513 through the inductor element 56, and the bias voltage of the transistor element 52 from the pad 514 through the inductor element 55. The input matching circuit of the inductor element 53, the capacitor element 58 and the multi-conductor line 517 matches the input of the transistor element 52, and the inductor element 54, the capacitor element 59 and the multi-conductor line 51 are used.
The output matching circuit 9 is used to match the output of the transistor element 52, thereby configuring a circuit with a small loss.

By using inductor elements formed of a plurality of conductor lines as described in the second embodiment for the inductor elements 53 and 54 included in these matching circuits, and using a plurality of conductor lines as the lines, The loss can be further reduced as compared with the conventional monolithic microwave IC. By reducing the loss, it is possible to achieve higher performance such as higher gain, lower noise, and lower power consumption of the monolithic microwave IC.

In this embodiment, a Si substrate is used as a substrate, but a semi-insulating semiconductor substrate such as GaAs or InP or a silicon substrate on an insulator (Silicon-On-Insulat) is used.
or a substrate) has the same effect. Further, in addition to the elements shown in this embodiment, the performance can be further improved by integrating passive elements such as resistance elements and other elements on the same substrate and devising a circuit configuration. Further, the monolithic microwave IC having a circuit configuration other than that shown in this embodiment can also use the plural conductor lines of the present invention or the inductor element using the same, thereby achieving low loss.

[0052]

As is apparent from the above description, according to the present invention, the parasitic resistance R of the line at high frequencies can be reduced, and the loss of the inductor element in which the line is spirally wound can be reduced. Further, it is possible to increase the gain and lower the power consumption of the monolithic microwave IC using the line or the inductor element, and to realize the high performance of the IC.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a multi-conductor line according to a first embodiment of the present invention;

FIG. 2 is a configuration diagram of a conventional single conductor line,

FIG. 3 is a plan view of an inductor element using a plurality of conductor lines according to a second embodiment of the present invention;

FIG. 4 is a plan view of a conventional inductor element;

FIG. 5 is a plan view of a monolithic microwave IC according to a third embodiment of the present invention.

[Explanation of symbols]

 11, 21, 31, 41, 51 Si substrate 12, 32 First conductor 13, 33 Second conductor 14, 24 Interlayer film 15, 25 Surface protective film 22, 42 Conductor 34, 35, 44, 45 Contact 36, 46 Lower layer conductor 52 Transistor element 53-56 Inductor element 57-59, 510 Capacitor element 511-515 Pad 516 Conventional line 517-519 Multiple conductor line

Claims (5)

[Claims] A plurality of parallel conductors formed on a substrate are provided as at least a part of a line, and an in-phase current is applied to the plurality of parallel conductors or an in-phase voltage is applied to the plurality of parallel conductors to thereby form the same line. A multi-conductor line characterized in that high-frequency parasitic resistance is reduced as compared with a single line having a parasitic capacitance. 2. The multi-conductor line according to claim 1, wherein each of the plurality of parallel conductors is disposed on a plane parallel to a surface of the substrate. 3. The multi-conductor line according to claim 1, wherein each of the plurality of parallel conductors is stacked and disposed on a substrate. 4. An inductor element having a spiral shape formed by a plurality of conductor lines according to any one of claims 1 to 3. 5. A monolithic microwave comprising a plurality of conductor lines according to any one of claims 1 to 3, or a spiral-shaped inductor element formed by the plurality of conductor lines. Integrated circuit.