JPH10224122A - High-frequency circuit, and method for adjusting characteristic of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-frequency circuit which drastically reduces the length of a stub that is used with a same frequency, maintaining a high-frequency characteristic and miniaturizes the measures of an MIC and an MMIC in a microwave.a millimeter wave, and a method for adjusting its characteristics. SOLUTION: A square stub which is formed by a microstrip line is formed on a GaAs diaphragm 21 in line width at which characteristic capacitor in a desired frequency is 50Ω. An insulating film 25 is formed on the square stub, and a metallic layer 26 which is an upper layer is formed in the form of partially covering a middle position of the square stub, and an MIM capacitor 23 consists of the film 25 and the layer 26 and a metallic layer 24 that forms the stub. The capacitor 23 penetrates the diaphragm 21 and connected to a rear ground metallic layer 29 through via holes 28a and 28b, by wiring pad parts 27a and 27b which are brought out from the layer 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency circuit and a method for adjusting characteristics thereof, and more particularly to a structure of a high-frequency distributed constant circuit constituted by microstrip lines and a method for adjusting characteristics thereof.

[0002]

2. Description of the Related Art FIG. 8 is a perspective view showing a high-frequency circuit using a microstrip line having a conventional structure. In this figure, 11 is a semi-insulating gallium arsenide (GaAs) substrate, 12 is a square stub, 13 is a microstrip line, 14 is a back ground metal layer, wm 'is the width of a microstrip line, and wm is the width of a square stub. , L1 is the length of the square stub.

As shown in FIG. 8, a square stub 12 is made of a metal layer having a width wm (μm) so as to have a characteristic impedance of 50Ω. Semi-insulating gallium arsenide substrate 11
Is a semi-insulating GaAs having a thickness of 50 μm and a relative dielectric constant of 13. When it is desired to configure this as a band rejection filter at 30 GHz, wm = 34.4 and L1 = 5 in FIG.
80 (unit μm).

[0004]

However, in the above-described conventional high-frequency circuit, the length of the rectangular stub is extremely long even in the above-described configuration. Microwave / millimeter-wave MIC using compound semiconductor such as GaAs
(Monolitic IntegratedCir
unit) and MMIC (Microwave Mon)
oliticIntegrated Circuit
In t), the miniaturization of the circuit greatly affects the cost reduction. However, this rectangular stub is one of the long elements in the circuit, and is an obstacle to miniaturization.

The present invention eliminates the above-mentioned problems and can greatly reduce the length of a stub used at the same frequency while maintaining high-frequency characteristics. It is an object of the present invention to provide a high-frequency circuit capable of reducing the size of a circuit and a method for adjusting the characteristics of the circuit.

[0006]

In order to achieve the above object, the present invention provides: [1] In a high frequency circuit having a microstrip line, a part of a metal layer forming a microstrip line on a substrate is partially replaced by a capacitor. A metal layer formed above the metal layer as another metal layer; and a MIM capacitor having an insulating film formed between the two metal layers, wherein the MIM capacitor is formed on the upper side. The ground is formed by the formed metal layer.

[2] The high-frequency circuit according to [1], wherein the MIM capacitor is formed in a part of an open stub. [3] In the high-frequency circuit according to the above [1] or [2], the metal layer formed on the upper side is connected to a back ground metal layer by a via hole penetrating the substrate, and the MIM capacitor is grounded. That's what I did.

[4] The high-frequency circuit according to [1], [2] or [3], wherein the substrate is made of semi-insulating gallium arsenide. [5] In the method for adjusting characteristics of a high-frequency circuit, a part of a metal layer forming a microstrip line on a substrate is used as one metal layer of a capacitor, and a metal layer formed above this metal layer is used as another metal layer. A MIM capacitor having a metal layer and an insulating film formed between the two metal layers;
This MIM capacitor includes a high-frequency circuit grounded by a metal layer formed on the upper side, and adjusts the size of the metal layer formed on the upper side after circuit fabrication to adjust circuit characteristics. is there.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view of a high-frequency circuit using a microstrip line according to a first embodiment of the present invention, FIG. 2 is an enlarged view of the vicinity of a capacitor in FIG. 1, and FIG. 3 is a sectional view taken along line AA in FIG. .

In FIG. 1, 21 is a semi-insulating gallium arsenide (GaAs) substrate, 22 is a square stub, and 23 is a MIM.
(Metal-Insulating Film-Metal) Capacitors, 27a and 27b are wiring pads, 28a and 28b are via holes, 29 is a backside ground metal layer, wm 'is a microstrip line width, wm is a stub width, and L0 is a MIM capacitor. The length of the stub on the nearer side, Lmim is the dimension in the stub longitudinal direction of the MIM capacitor, and L2 is the length of the stub on the tip side of the MIM capacitor.

As described above, the semi-insulating GaAs having a thickness t0
The characteristic capacitor at the desired frequency is 50Ω on the substrate 21.
A square stub 22 as an open stub formed of a microstrip line is formed with a line width of. An insulating film 25 formed thereon and an upper metal layer 26 are further formed so as to cover a part of the intermediate position of the rectangular stub 22, and these insulating film 25 and metal layer 26 (FIG. And a metal layer 24 forming the stub 22 to form an MIM capacitor 23.

The MIM capacitor 23 has wiring pad portions 27a and 27b drawn from the upper metal layer 26.
GaAs via via holes 28a and 28b
It penetrates through the s-substrate 21 and is connected to the back surface ground metal layer 29. FIG. 4 shows an equivalent circuit including dimensions of this type.
become that way. In FIG. 4, 40A is port 1, 40
B is a port 2, 41 is an open stub at the tip of the MIM capacitor, 42 is a stub of the portion forming the MIM capacitor (half toward the tip), 43 is a stub of the portion forming the MIM capacitor (half at the base). , 44 is MI
An open stub on the base side of the M capacitor, 45 and 47 are microstrip lines, and 46 is a microstrip T
Junction 48 is an MIM capacitor.

Here, semi-insulating GaAs having a thickness of 50 μm is used.
When a function as a band rejection filter at 30 GHz is realized on the substrate 21 using this circuit, the insulating film 25 is made of silicon nitride having a thickness of 1000 ° (relative permittivity = 6). At this time, the values shown by the symbols in FIG. 4 are wm = 34.4 and L0 = 10 when the specific dimensions (unit: μm) are used.
0, L1 = 150, wmin = 34.4, Lmim = 6
Becomes (At this time, the MIM capacitor has a capacitance of 0.1 pF). L0 + Lmim + L1 = 256 μm
And a conventional rectangular stub length L0 =
It can be seen that the overall length is greatly reduced as compared with 480 μm.

As shown in FIG. 3, according to the present invention, an MIM capacitor having a very small capacitance is formed by forming an insulating film and a metal layer on a square stub and a part thereof, By connecting the constituent metal of the capacitor to the ground metal layer on the back surface of the substrate through the via hole, the capacitor is branched from the rectangular stub to form a grounded capacitor. Also, 30
The characteristics of the structure (dimensions described above) of the present invention formed in expectation of the blocking characteristics at GMz are as shown in FIG.

FIG. 5 shows the S parameter in FIG. 4. The horizontal axis represents the frequency (GHz), and the vertical axis represents the dB (S
11), dB (S22) or dB (S21), dB (S
12) are shown. The dotted line shows the S parameter of the conventional structure without the MIM capacitor. Here, dB (S11) and dB (S22) include:
An S parameter representing the reflection characteristic at port 1 or port 2 is shown, and dB (S21) and dB (S12) include:
S-parameters indicating transmission characteristics from port 1 to port 2 or port 2 to port 1 are shown. In FIG. 5, an enlarged view of the band is shown.

As is clear from FIG. 5, it can be seen that the circuit operates at the same center rejection frequency as the prior art. As described above, according to the first embodiment, the configuration in which the MIM capacitor in which one electrode is grounded is provided by branching from the rectangular stub, so that it is used at the same frequency while maintaining high-frequency characteristics. The length of the rectangular stub can be greatly reduced, and MIC in microwave and millimeter waves,
This can greatly contribute to miniaturization of the size of the MMIC.

Next, a second embodiment of the present invention will be described. In this embodiment, in the structure shown in the first embodiment, the capacitor upper metal layer shown as the upper metal layer 26 in FIG. 3 is trimmed by means such as ion milling to change the size, thereby obtaining the capacitance. Is configured to be able to be adjusted.

Hereinafter, a method of adjusting the capacitance will be described with reference to FIG. As shown in FIG. 6, the upper metal layer 26 is formed so as to cover desired dimensions to be obtained after trimming and other circuit portions not to be etched.
Patterning is performed with the photoresist 50. In this state, by exposing the exposed metal layer by ion milling, the portion 51 of the upper metal layer 26 that is not covered with the photoresist 50 is removed.

By adjusting the size of the upper metal layer 26 of the MIM capacitor by trimming according to the method described above, the area of the metal layer 24 forming the stub and the area of the upper metal layer 26 opposite to each other are changed. It is possible to adjust the capacitance of the capacitor. Also, M
Even after the trimming of the IM capacitor 23, there is no change in the shape of the metal layer 24 forming the stub, so that only the capacitance of the MIM capacitor changes, and no change occurs in the circuit characteristics of the microstrip line.

An example in which this adjustment is applied to a structure having specific dimensions shown in FIG. 3 will be described. As described in the first embodiment, in an example of operating as a 30 GHz band rejection filter, the dimensions of the opposed portions of the upper and lower metal layers of the capacitor are wmim = 34.4 and Lmim = 6 (μm).
Here, this Lmim is adjusted. According to the method by ion milling described in the preceding section, L
Adjust mim to 4 μm. At this time, the capacitance of the MIM capacitor changes from 0.1 pF to 0.075 pF, but constants for other circuit elements do not change. FIG. 7 shows the change in the characteristics at this time.

In FIG. 7, a dotted line indicates a state before the adjustment [(w
mim = 34.4, Lmim = 6 (μm)], and the solid line after adjustment [(wmim = 34.4, Lmim = 4 (μm)])
The characteristic in the case of is shown. That is, FIG.
FIG. 4 shows S parameters of the high-frequency circuit of FIG. 4 when the metal layer of the IM capacitor is dimensionally changed by ion milling. The horizontal axis represents frequency (GHz), and the vertical axis represents dB (S11) and dB (S
22) or dB (S21) and dB (S12).

Here, dB (S11) and dB (S22)
Has S representing the reflection characteristic at port 1 or port 2.
Parameters are indicated, dB (S21), dB (S12)
5 shows S parameters representing transmission characteristics from port 1 to port 2 or port 2 to port 1. FIG. 7 shows an enlarged view of the band. As is apparent from FIG. 7, the size of the metal layer of the MIM capacitor was changed by ion milling, and as a result, the center rejection frequency was 30.
It has changed from 0 GHz to 32.2 GHz.

As described above, according to the second embodiment, the MIM
By adjusting the dimensions of the capacitor by trimming the upper metal layer, it is possible to adjust the high frequency characteristics.
Note that this adjustment does not affect the characteristics of other circuit elements. In the embodiment of the present invention, the rectangular stub has been described as an application as a band rejection filter. However, the reduced rectangular stub can be used for a parallel stub as a capacitive component when forming an impedance matching circuit.

It should be noted that the present invention is not limited to the above embodiment, but various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0025]

As described above, according to the present invention, the following effects can be obtained. (A) The length of the open stub used at the same frequency can be significantly reduced while maintaining high-frequency characteristics, and the size of the MIC and MMIC in microwaves and millimeter waves can be reduced.

(B) After the circuit is formed, the area of the opposing metal layer can be changed, so that the capacitance of the capacitor can be adjusted. Further, only the capacitance of the capacitor changes without changing the shape of the strip line, and no change occurs in the circuit characteristics of the microstrip line.

[Brief description of the drawings]

FIG. 1 is a perspective view of a high-frequency circuit using a microstrip line according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of the vicinity of a capacitor in FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is an equivalent circuit diagram when the present invention is applied to an open stub connected in parallel to a microstrip line.

FIG. 5 is a diagram showing S parameters in the circuit of FIG. 4;

FIG. 6 is a diagram illustrating a manner of adjusting a capacitance according to a second embodiment of the present invention.

7 is a diagram showing S parameters of the high-frequency circuit of FIG. 4 when the dimensions of the metal layer of the MIM capacitor of the present invention are changed by ion milling.

FIG. 8 is a perspective view showing a high-frequency circuit using a microstrip line having a conventional structure.

[Explanation of symbols]

 Reference Signs List 21 semi-insulating GaAs substrate 22 rectangular stub 23 MIM (metal-insulating-metal) capacitor 24 metal layer forming stub 25 insulating film 26 upper metal layer 27a, 27b wiring pad 28a, 28b via hole 29 backside ground metal layer wm Stub width wm ′ Microstrip line width L0 Length of stub on the front side of MIM capacitor Ldim Length of stub in longitudinal direction of MIM capacitor L2 Length of stub on tip side of MIM capacitor 50 Photoresist 51 Photoresist 51 Covered with photoresist Untouched part

Claims (5)

[Claims] In a high frequency circuit having a microstrip line, a part of a metal layer forming a microstrip line on a substrate is used as one metal layer of a capacitor, and a metal layer formed above the metal layer is used as another metal layer. A high-frequency circuit comprising: a MIM capacitor having one metal layer and an insulating film formed between the two metal layers, wherein the MIM capacitor is grounded by the metal layer formed on the upper side. . 2. The high-frequency circuit according to claim 1, wherein said MIM capacitor is formed in a part of an open stub. 3. The high-frequency circuit according to claim 1, wherein the metal layer formed on the upper side is connected to a backside grounded metal layer by a via hole penetrating the substrate, and the MIM capacitor is grounded. A high frequency circuit characterized by the following. 4. The high frequency circuit according to claim 1, wherein said substrate is made of semi-insulating gallium arsenide. 5. A method for adjusting characteristics of a high-frequency circuit, comprising:
A part of the metal layer forming the microstrip line on the substrate is used as one metal layer of the capacitor, the metal layer formed above the metal layer is used as the other metal layer, and the two metal layers are insulated from each other. A MIM capacitor having a film formed thereon, the MIM capacitor including a high-frequency circuit grounded by a metal layer formed on the upper side, and adjusting a size of the metal layer formed on the upper side after circuit fabrication; A method for adjusting characteristics of a high-frequency circuit, comprising adjusting characteristics of the circuit.