JP3351613B2 - Microwave integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave integrated circuit, and more particularly to a structure of a low impedance line of a monolithic microwave integrated circuit.

[0002]

2. Description of the Related Art Microstrip lines, coplanar lines and the like are basic transmission lines of a microwave integrated circuit, and are basic elements constituting a microwave planar circuit.

A monolithic microwave integrated circuit is a microwave integrated circuit including active elements such as field effect transistors (FETs), resistors, capacitors, inductors, and the like on a semi-insulating substrate such as gallium arsenide (GaAs). A coplanar line is used as a basic transmission line.
Usually, in a microwave circuit, a circuit is configured by a 50 [Ω] system. When a circuit is designed using a coplanar line, the characteristic impedance of the coplanar line is determined by the center conductor width and conductor thickness, the distance between the conductor and the ground conductor, and the dielectric constant of the semi-insulating semiconductor substrate. Therefore, the impedance of the line required for the circuit design is mainly obtained by changing the distance between the center conductor width of the line and the ground conductor.

[0004]

In the monolithic microwave integrated circuit described above, when forming a low impedance line with respect to 50 [Ω], the center conductor width of the coplanar line is fixed and the distance between the center conductor and the ground conductor is reduced. It can be realized by reducing the distance, but it is sometimes difficult to fabricate the device. In addition, it is conceivable that the distance between the center conductor and the ground conductor is fixed and the width of the center conductor is widened.

FIG. 4 shows the structure of a conventional coplanar line. In the figure, reference numerals 23 and 24 denote ground conductors, and the characteristic impedance of the coplanar line is determined by the conductor width of the center conductor 22, the distance between the center conductor thickness and the ground conductor, and the dielectric constant of the semi-insulating semiconductor substrate 21. Is done.

SUMMARY OF THE INVENTION The present invention has been made to reduce the chip size of a monolithic microwave integrated circuit, and it is an object of the present invention to change the conductor thickness of a ground conductor without changing the line width and line interval of a transmission line composed of coplanar lines. To form a low-impedance line, thereby forming a monolithic microwave integrated circuit that is reduced in size and small in chip size.

[0007]

Engaging luma microwave integrated circuit of the present invention According to an aspect of the semi-insulating semiconductor substrate, and at the same intervals on both sides of the center strip conductor and said center strip conductor formed in a predetermined width have thick formed grounding conductor than the center strip conductor, said semi-insulating semiconductor base
A coplanar line formed on a plate
It is characterized by .

[0008]

In the monolithic microwave integrated circuit having the above structure, a strip conductor is provided on a semi-insulating semiconductor substrate.
On both sides of the strip conductor, a ground conductor having the same distance between the strip conductor and the thicker than the conductor thickness of the strip conductor is arranged, and the center conductor width of the line and the distance between the ground conductor and the ground conductor are maintained. By changing the conductor thickness, an arbitrary low impedance line can be formed.

[0009]

【Example】

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG.

In FIG. 1, reference numeral 21 denotes a semi-insulating gallium arsenide substrate, and a center strip conductor 22 is provided on the substrate.
Then, the ground conductors 13 and 14 are arranged so as to sandwich the center strip conductor 22 from both sides. The ground conductors 13 and 14 have conductors thicker than the conductor thickness of the center conductor 22. In the transmission line shown in FIGS. 1 and 4, when the cross-sectional dimension of the line is sufficiently small with respect to the wavelength, the characteristic impedance Z
₀ is represented by the following equation.

[0011]

(Equation 1) Here, V ₀ is the speed of light, C is the capacitance per unit length, C
₀ is the capacitance per unit length when the dielectric is removed in FIGS. The electric field distribution of the line shown in Figure 1 Figure 2 also shows the electric field distribution of the line shown in FIG. 3 in FIG. As can be seen from the drawing, in the line shown in FIG. 1, since the thickness of the ground conductors 13 and 14 is made larger than the center conductor thickness 22, energy concentrates between the center conductor 22 and the ground conductors 13 and 14. The capacitance per unit length is increased as compared with the conventional structure shown in FIG. If the relative dielectric constant of the insulating protective film is close to the relative dielectric constant of the semi-insulating semiconductor substrate, the concentration of energy becomes more remarkable. As can be seen from equation (1), the larger the capacitance per unit length of the line, the lower the impedance of the line. Therefore, in the conventional structure shown in FIG. 4, a low impedance line is formed by changing the center conductor width or the interval between the center conductor and the ground conductor. However, the line structure becomes difficult or the circuit scale becomes large. There were drawbacks such as. On the other hand, in the structure according to the present invention shown in FIG. 1, a low-impedance line can be formed by changing the thickness of the ground conductor without changing the width of the center conductor and the distance between the center conductor and the ground conductor. A monolithic microwave integrated circuit with a small chip size can be realized.

FIG. 5 shows the characteristics of the monolithic microwave integrated circuit according to the present invention.

In FIG. 5 , a curve 101 represents the characteristics of the line shown in FIG. 1 according to the present invention. The substrate thickness of the semi-insulating gallium arsenide substrate 21 shown in FIG. The distance between the conductors 13 and 14 is 50
[Μm] and the relative dielectric constant is 12.9. The relative dielectric constant of the insulating film is 7.0, and the center strip conductor 2
The conductor width of No. 2 is 75 [μm], and the conductor thickness is 2 [μm]. A point 102 is a characteristic of the line having the conventional structure shown in FIG. 4, and the thickness of the gallium arsenide substrate 21 is 400 [μm].
The distance between the center strip conductor 22 and the ground conductors 23 and 24 is 50 [μm], and the relative dielectric constant is 12.9. The relative permittivity of the insulating film is 7.0, the conductor width of the center strip conductor 22 is 75 [μm], and the conductor thickness is 2 [μm].
It is. As is apparent from FIG. 3, it is possible to form a coplanar line having an arbitrary low impedance by changing the thickness of the ground conductor while keeping the distance between the center conductor and the ground conductor and the width of the center conductor constant. it can.

(Embodiment 2) In a microwave integrated circuit (not shown), the distance between a strip conductor formed on an insulating substrate and the strip conductor on both sides of the strip conductor is equal to each other, and is greater than the conductor thickness of the strip conductor. A thicker ground conductor is provided, and by changing the thickness of the ground conductor, an arbitrary low impedance line can be formed as compared with a conventional coplanar line.

Although gallium arsenide is used as the semi-insulating semiconductor substrate in the above embodiment, it goes without saying that other materials can be used. Also strip conductor
Further, an insulating film may be provided on the ground conductor.

[0016]

As described above, according to the present invention ,
It is possible to provide a microwave integrated circuit having a small low impedance line in comparison with the traditional coplanar line.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a monolithic microwave integrated circuit according to the present invention.

FIG. 2 is a schematic diagram showing an electric field distribution of the monolithic microwave integrated circuit according to the present invention.

FIG. 3 is a block diagram of a conventional monolithic microwave integrated circuit.
Area view.

FIG. 4 shows a conventional monolithic microwave integrated circuit.
The schematic diagram which shows a field distribution.

FIG. 5 illustrates characteristics of a monolithic microwave integrated circuit.
Diagram.

[Explanation of symbols]

 13, 14, 23, 24: ground conductor 21: semi-insulating semiconductor substrate 22: center strip conductor 101, 102: impedance of transmission line

Claims (3)

(57) [Claims] [Claim 1 further comprising a semi-insulating semiconductor substrate, the thick formed grounding conductor than the same distance on both sides and the center strip conductor of the center strip conductor and said center strip conductor formed in a predetermined width, The semi-insulating semiconductor
A coplanar line formed on a substrate.
And a microwave integrated circuit. 2. A comprises a semi-insulating semiconductor substrate, a ground conductor formed thicker than the same distance on both sides and the center strip conductor of the center strip conductor and said center strip conductor formed in a predetermined width, The semi-insulating semiconductor
A coplanar line formed on a substrate.
And a monolithic microwave integrated circuit. 3. The monolithic microwave integrated circuit according to claim 2 , further comprising an insulating film covering the center strip conductor and the ground conductor.