JPH0212008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an interdigital capacitor made of a microwave integrated circuit.

FIG. 1 is a block diagram of a conventional interdigital capacitor of this type. In FIG. 1, 1 is a dielectric substrate, 2 is a ground conductor, 3 is a first strip conductor, and 4 is a second strip conductor. A plurality of fingers 5 are provided at one ends of the first and second strip conductors, and are arranged to face each other and interlock with each other alternately.

In FIG. 1, the width of the finger 5 is w,
The length is l, and the distance between two adjacent fingers is s.
When the dielectric constant of the dielectric substrate 1 is ε _r , the capacitance C per unit length generated between two adjacent fingers is generally given by the following equation.

C=ε ₀ (1+ε _r )K/K′ (1) However k=tan ² πa/4b k'=1−k ² a=w/2 b=w+s/2 ε ₀ is the dielectric constant in vacuum.

In Figure 1, if the total number of fingers is N,
The total capacity C _T is given by the following formula.

C _T =C(N-1)l (2) To obtain a large capacitance value from equations (1) and (2), N, l
There is a method of increasing N and l, but in the microwave band, as N and l are increased, the dimensions of the capacitor part cannot be ignored compared to the wavelength, resulting in negative effects such as the capacitor not operating as a capacitor. Another way to obtain a large capacitance is to increase the capacitance C per unit length between two adjacent fingers. By the way, C is a function of s/w, and in particular in the range of s≧0 and w≧0, C is a monotonically decreasing function of s/w. Therefore, in order to increase C, it is sufficient to decrease s or increase w.
If w is increased, the shape becomes larger, and similar to the above problem arises, such as the capacitor not operating as a capacitor in the microwave band, so the value of w cannot be made extremely large. Therefore, it is considered desirable to obtain a large capacity by reducing s.

However, when the dimension s is reduced to a level similar to the working precision of a microwave integrated circuit, the finger 5 provided on the first strip conductor 3 and the second
Since the fingers 5 provided on the strip conductor 4 may come into contact with each other, there is a restriction on the minimum value of the dimension s.

As mentioned above, in conventional interdigital capacitors of this type, there is a restriction on the minimum value of the dimension s due to problems with the machining accuracy of microwave integrated circuits, and this has the drawback that it may not be possible to obtain the desired large capacity. It was hot.

In order to eliminate this drawback, the present invention arranges the fingers provided on the first strip conductor and the fingers provided on the second strip conductor so as to be insulated through a film made of an insulator. , the drawings will be explained in detail below.

FIG. 2 is a block diagram of an interdigital capacitor according to the present invention, and FIG. 3 is a sectional view taken along AA' of FIG. A film 10 made of an insulator is formed between the finger 7 provided on the first strip conductor 6 and the finger 9 provided on the second strip conductor 8.
are placed. In FIG. 2, even if the distance s between the finger 7 provided on the first strip conductor 6 and the finger 9 provided on the second strip conductor 8 is made small, the film 10 made of an insulator is Finger 7 and Finger 9
There is no problem of contact between the two. Therefore, there is no restriction on the minimum value of the dimension s, making it possible to obtain a large capacity. In particular, if a film 10 made of an insulator is used that has a small dielectric constant and a small thickness d, the influence of the film 10 made of an insulator can be reduced, and the design formula for this kind of interdigital capacitor in the past can be reduced. can be applied as is.

FIG. 4 is a sectional view of another embodiment of the interdigital capacitor according to the present invention. As shown in FIG. 4, the fingers 7 and 9 may overlap each other with a film 10 made of an insulator interposed therebetween.

Although the above description has been made for the case where all the fingers have the same width, the present invention may be used when the fingers have different widths. Moreover, although the case where the spacing between all adjacent fingers is equal has been described, it may be used when the spacing is different.

The invention may also be used in monolithic microwave integrated circuits.

As described above, in the interdigital capacitor according to the present invention, the first
The finger provided on the strip conductor and the second
Since the film 10 made of an insulator is placed between the fingers provided on the strip conductor of the strip conductor for insulation, it is possible to reduce the spacing between adjacent fingers or to arrange them one on top of the other. It has the advantage of increasing capacity.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional interdigital capacitor of this type, Fig. 2 is a block diagram of an interdigital capacitor according to the present invention, Fig. 3 is a cross-sectional view along AA' of Fig. 2, and Fig. 4 is a block diagram of an interdigital capacitor according to the present invention. FIG. 3 is a sectional view of another embodiment of the interdigital capacitor according to the present invention. In the figure, 1 is a dielectric substrate, 2 is a ground conductor, 3 is a first strip conductor, 4 is a second strip conductor, 5 is a finger, 6 is a first strip conductor, 7 is a finger, and 8 is a second strip conductor. 9 is a finger, and 10 is a film made of an insulator. In the drawings, the same or corresponding parts are designated by the same reference numerals.

Claims (1)

[Claims] 1 a dielectric substrate, a first strip conductor having a plurality of fingers formed on the dielectric substrate, and a first strip conductor provided on the fingers of the first strip conductor and covering the entire finger portion; a film made of an insulator, and a plurality of fingers formed on the film made of the insulator and arranged alternately with the plurality of fingers of the first strip conductor, and formed on the dielectric substrate. and a second strip conductor.