JP2012090207A - Air bridge structure of coplanar line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily use a plurality of air bridges while suppressing the influence of the cross capacity of the signal line of a coplanar line and the air bridges.SOLUTION: In an air bridge structure 100, a lower layer wiring layer 8 is provided with hole areas 12A and 12B formed by notching positions facing each other across a signal line 1 in ground lines 2A and 2B respectively, also an upper layer wiring layer 7 is provided with an upper layer ground electrode 13A electrically connected with the ground line 2A of the lower layer wiring layer 8 at the upper position of the hole area 12A and an upper layer ground electrode 13B electrically connected with the ground line 2B of the lower layer wiring layer 8 at the upper position of the hole area 12B, and the ground lines 2A and 2B are electrically connected through the upper layer ground electrodes 13A and 13B by an air bridge 3.

Description

  The present invention relates to a high-frequency circuit technology, and more particularly to an air bridge structure for connecting ground electrodes of a coplanar line.

  An air bridge structure used for a coplanar (hereinafter referred to as CPW line: Coplanar Waveguide) line on a high dielectric constant substrate such as a semiconductor integrated circuit is an indispensable connection structure for satisfactorily grounding the CPW line. The CPW line has a structure having two ground electrodes on both sides of the signal line. In order to keep these ground electrodes at the same potential, it is necessary to connect the two by some method. A simple way to do this is the air bridge structure. The normal air bridge structure is a CPW line, that is, a wiring layer different from the signal line and the wiring layer constituting the ground electrode, and is a connection structure in which two ground electrodes are connected by an air bridge at the shortest distance.

  In such an air bridge structure, since the signal line and the air bridge cross each other, a cross capacitance is generated between them, which is often a problem. That is, since the air bridge is connected to the nearest ground electrode, the cross capacitance between the signal line and the air bridge behaves as a parallel capacitance to the signal line. For this reason, the characteristic impedance of the CPW line decreases at the air bridge portion, causing a delay in signal propagation. Further, signal reflection occurs at a location where the air bridge exists due to a local decrease in characteristic impedance.

  If these effects of the air bridge may adversely affect the operation of the integrated circuit, a circuit design that takes into account the influence of the air bridge must be performed in advance. However, in reality, since the position and number of air bridges are determined by the convenience of the circuit layout, it is difficult to accurately consider at the stage of circuit design. Therefore, it is necessary to perform circuit design and layout work alternately to reflect the circuit design while gradually determining the arrangement of the air bridge.

  In order to solve the problem in such an air bridge structure, several techniques have been conventionally proposed. As a first conventional technique, there is a method of reducing parasitic capacitance by miniaturizing wiring. This is because the use of a fine CPW line inevitably reduces the cross capacitance of the air bridge.

  As a second conventional technique, a method for compensating for the cross capacitance generated in the air bridge can be considered. As one of them, there is a method of increasing the inductance component of the wiring by narrowing the signal line width of the CPW line only at a place where an air bridge is present (for example, see Patent Document 1). Since the characteristic impedance of the wiring is given by the square root of the inductance-to-capacitance ratio per unit length of the line, if the inductance of the signal line is increased in proportion to the size of the cross capacitance, the characteristic impedance is maintained at a constant value. Signal reflection can be prevented.

  As a third conventional technique, there is a method in which a part of a microstrip line is introduced to make an air bridge unnecessary. This is because the microstrip line has only one ground electrode and essentially does not require an air bridge.

Japanese Patent No. 2569697

Aikawa et al., “Monolithic microwave integrated circuit”, pp. 51, IEICE, ISBN88552-145-9, 1997/01/25

However, in such a conventional technique, although the influence of the cross capacitance between the signal line of the coplanar line and the air bridge is suppressed to some extent, there is a problem that a large number of air bridges cannot be used easily.
For example, in the first prior art, since the miniaturization of the line is a trade-off with the line loss, it is necessary to select and refine a part of the line. At this time, the pitch conversion of the CPW line is necessary, and a new parasitic effect accompanying the pitch conversion needs to be reflected in the circuit design. In addition, in the case of a circuit that handles high power, the miniaturization of the line is limited by the power rating, so there is a limit to the miniaturization of the line.

In the second prior art, the signal propagation speed in the coplanar line is reduced. This is because the propagation speed of the signal is determined by the propagation constant β, and its value is inversely proportional to the square root of the inductance capacity product per line unit length. For this reason, if the characteristic impedance is compensated for by the second prior art, the delay time of the CPW line further increases.
In the third prior art, it is necessary to separately consider the parasitic effect due to CPW microstrip conversion (see, for example, Non-Patent Document 1), which is different from the design burden for reflecting the influence of the air bridge in the circuit design. Result without.

  The present invention is to solve such problems, and provides an air bridge structure that can easily use a plurality of air bridges while suppressing the influence of the cross capacitance between the signal line of the coplanar line and the air bridge. The purpose is that.

  In order to achieve such an object, an air bridge structure according to the present invention includes a signal line formed on a high dielectric constant substrate and first and second ground lines arranged across the signal line. A lower wiring layer constituting a coplanar line and an upper wiring layer constituting an air bridge that crosses the upper part of the signal line and electrically connects the first and second ground lines, The first and second ground lines have first and second hole regions formed by cutting out positions facing each other across the signal line, and the upper wiring layer has the first hole. A first upper ground electrode electrically connected to the first ground line of the lower wiring layer at an upper position of the region, and a second ground line of the lower wiring layer electrically connected to the first hole line of the second hole region. And a second upper ground electrode connected to the air In Tsu di is obtained by the between the first and second ground lines through the first and second upper ground electrode to be electrically connected to each other.

  In this case, a first contact for electrically connecting the first ground line and the first upper-layer ground electrode is further provided at a position adjacent to the first hole area in the first ground line. And a second contact for electrically connecting the second ground line and the second upper ground electrode at a position adjacent to the second hole area in the second ground line. Good.

  The first contact is formed at a position adjacent to the first hole region in the first ground line so as to surround the first hole region, and the second contact is formed with the second ground. You may form so that a 2nd hole area | region may be enclosed in the position adjacent to a 2nd hole area | region among lines.

Further, the capacitance between the signal line above the CPW line and the first and second ground lines in the portion where the air bridge structure is not formed in the CPW line is Ca, and a high dielectric constant substrate The inter-line capacitance between the internal signal line and the first and second ground lines is Cb, and the signal line above the CPW line and the first in the part where the air bridge structure is formed in the CPW line. And Cc between the signal line and the second ground line and between the signal line and the air bridge, and between the signal line and the first and second ground lines inside the high dielectric constant substrate. When the line-to-line capacitance is Cd and the distance between the signal line and the first and second ground lines is L, only the distance L that satisfies the formula Cc−Ca _(L) = Cb−Cd _(L) In the air bridge structure Line and may be formed by releasing the first and second ground lines.

  According to the present invention, the influence of the cross capacitance generated between the signal line and the air bridge can be suppressed without thinning the signal line of the CPW line. Therefore, the disturbance of the characteristic impedance and delay time of the CPW line in the vicinity of the air bridge can be suppressed, and an excellent air bridge structure can be realized. In addition, since a complicated circuit design such as a parasitic effect by CPW microstrip conversion is not required, a plurality of air bridges can be easily used.

It is a top view which shows the structure of the air bridge structure concerning one Embodiment. It is a top view which shows the shape of a coplanar track | line. FIG. 3 is a sectional view taken along line III-III in FIG. 1. It is IV-IV sectional drawing of FIG. This is an example in which a plurality of air bridge structures are densely arranged. It is an example of the air bridge structure which has the hole area | region which consists of a substantially elliptical shape.

Next, an embodiment of the present invention will be described with reference to the drawings.
[Air bridge structure]
First, an air bridge structure of a coplanar (hereinafter referred to as CPW line: Coplanar Waveguide) line according to the present embodiment will be described with reference to FIGS. FIG. 1 is a plan view showing a configuration of an air bridge structure according to an embodiment. FIG. 2 is a plan view showing the shape of the coplanar line. 3 is a cross-sectional view taken along the line III-III in FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG.

 The CPW line includes a signal line 1 made of a conductive film formed on the high dielectric constant substrate 9, and a ground line (first ground line) 2A made of a conductive film and sandwiching the signal line 1 therebetween. And a ground line (second ground line) 2B. A high-frequency signal input from the input terminal 4 consisting of one end of the signal line 1 and the ground lines 2A and 2B can be taken out from the output terminal 5 consisting of the other end of the signal line 1 and the ground lines 2A and 2B. Is laid out.

  Among the CPW lines, the signal line 1 and the ground lines 2 </ b> A and 2 </ b> B are configured by the lower wiring layer 8 located on the surface of the high dielectric constant substrate 9. In the center of the CPW line, an air bridge 3 made of a conductive member that crosses the upper portion of the signal line 1 and electrically connects the ground lines 2A and 2B is disposed. The air bridge 3 is electrically connected to the ground lines 2A and 2B via contacts 11A and 11B made of a conductive member. The air bridge 3 and the contacts 11A and 11B are constituted by an upper wiring layer 7 located above the lower wiring layer 8.

  The air bridge structure 100 according to the present embodiment has a hole region (first region) formed by cutting out positions facing each other across the signal line 1 of the ground lines 2A and 2B in the lower wiring layer 8 as described above. ) (Hole area) 12A and hole area (second hole area) 12B.

The upper wiring layer 7 has an upper layer ground electrode (first upper layer ground electrode) 13A electrically connected to the ground line 2A of the lower wiring layer 8 at a position above the hole region 12A. An upper layer ground electrode (second upper layer ground electrode) 13B electrically connected to the ground line 2B of the lower wiring layer 8 is provided at an upper position of the region 12B. , 13B are electrically connected between the ground lines 2A, 2B.
In the example of FIG. 2, the hole regions 12 </ b> A and 12 </ b> B are formed by cutting out the side portion on the signal line 1 side of the ground lines 2 </ b> A and 2 </ b> B into a rectangular shape.

  The upper layer ground electrodes 13A and 13B are arranged at the same height as the air bridge 3 in the upper wiring layer 7 and at positions above the hole regions 12A and 12B so as to cover the hole regions 12A and 12B. Has been. These upper-layer ground electrodes 13A and 13B may be formed of a conductive member separate from the air bridge 3, and then electrically connected to the air bridge 3, or may be collectively formed of the same conductive member as the air bridge 3. Good.

The contacts 11A and 11B are arranged in the hole areas 12A and 12B, that is, the positions adjacent to the notches in the ground lines 2A and 2B. The ground lines 2A and 2B of the lower wiring layer 8 and the peripheral portions of the upper ground electrodes 13A and 13B are electrically connected to each other.
Further, the contact 11A is formed at a position adjacent to the hole area 12A in the ground line 2A so as to surround the hole area 12A, and the contact 11B is positioned at a position adjacent to the hole area 12B in the ground line 2B. Alternatively, it may be formed so as to surround the hole region 12B.
The CPW line and the air bridge structure 100 may be manufactured using existing semiconductor manufacturing process technology such as monolithic microwave integrated circuit technology.

Next, the operation of the hole regions 12A and 12B will be described in detail.
As shown in FIG. 3, in the vicinity of the III-III cross section of the CPW line where the air bridge structure 100 is not formed, the line-to-line capacitance between the signal line 1 and the ground lines 2A and 2B as the capacity above the CPW line. 21 (Ca) is generated, and an inter-line capacitance 22 (Cb) is generated between the signal line 1 and the ground lines 2A and 2B as a capacitance inside the high dielectric constant substrate 9. Usually, since the relative permittivity of the dielectric substrate has a value at least several times larger than 1, Cb is several times larger than Ca.

  Further, as shown in FIG. 4, in addition to the signal line 1 and the ground lines 2 </ b> A and 2 </ b> B, the air bridge 3, the hole region is located in the vicinity of the IV-IV cross section where the air bridge structure 100 is formed in the CPW line. 12A, 12B, and contact 6 exist. Therefore, in the vicinity of the IV-IV cross section, the capacitance between the signal line 1 and the ground lines 2A and 2B and between the signal line 1 and the air bridge 3 is the capacitance above the CPW line. In addition, an inter-line capacitance 24 (Cd) is generated between the signal line 1 and the ground lines 2A and 2B as a capacitance inside the high dielectric constant substrate 9. Usually, the dielectric constant of the dielectric substrate has a value that is at least several times larger than 1, so Cc is several times larger than Cd.

  Here, when Ca and Cc are compared, Cc has a larger value than Ca due to the influence of the cross capacitance generated at the intersection of the signal line 1 and the air bridge 3, and the value of the cross capacitance is the difference Cc between the two capacitances. It is represented by -Ca.

  On the other hand, by changing the size of the hole region 12, the distance L between the signal line 1 and the ground lines 2A and 2B in FIG. 3 can be increased to an arbitrary size. In other words, the inter-line capacitance Cd is expressed as a function of the distance L between the signal line 1 and the ground lines 2A and 2B, and the inter-line capacitance Cd can be decreased by increasing the distance L. At this time, the inter-line capacitance Ca also decreases at the same time, but the amount of change is small due to the already described difference in dielectric constant.

Therefore, it can be seen that the condition for removing the influence of the cross capacitance is that the signal line 1 and the ground lines 2A and 2B are separated to a distance L that satisfies the following expression (1).
Cc-Ca _(L) = Cb-Cd _(L) (1)
Except for the case where the cross capacitance is extremely large, Cc and Ca are smaller than Cb and Cd, and therefore it is easy to find the distance L that satisfies the equation (1). That is, it can be seen that in the air bridge structure 100 according to the present embodiment, the cross capacitance is corrected without changing the shape of the signal line 1 in the vicinity of the air bridge 3.

  The hole regions 12A and 12B are covered with the upper wiring layer 7 constituting the upper ground electrodes 13A and 13B. That is, the ground lines 2A and 2B originally existing in the hole regions 12A and 12B are lifted to the upper wiring layer 7 above the hole regions 12A and 12B by the contacts 11A and 11B as the upper layer ground electrodes 13A and 13B. That's right. Therefore, the functions of the ground lines 2A and 2B originally existing in the hole regions 12A and 12B are replaced by the upper layer ground electrodes 13A and 13B. In other words, the gap of the CPW line (the distance between the signal line 1 and the ground lines 2A and 2B) is effectively kept constant between the input terminal 4 and the output terminal 5, and depends on the hole region 12. It can also be seen that the impact is minimized.

[Effects of the present embodiment]
As described above, in the present embodiment, in the air bridge structure 100, the hole region 12A formed by cutting out the positions facing each other across the signal line 1 of the ground lines 2A and 2B in the lower wiring layer 8. , 12B respectively, and an upper layer ground electrode 13A electrically connected to the ground line 2A of the lower layer wiring layer 8 at the upper position of the hole region 12A and an upper position of the hole region 12B. An upper ground electrode 13B that is electrically connected to the ground line 2B of the lower wiring layer 8 is provided, and the ground lines 2A and 2B are electrically connected by the air bridge 3 via the upper layer ground electrodes 13A and 13B. It is a thing.

More specifically, a contact 11A for electrically connecting the ground line 2A and the upper layer ground electrode 13A is provided at a position adjacent to the hole area 12A in the ground line 2A, and an empty space in the ground line 2B. A contact 11B for electrically connecting the ground line 2B and the upper layer ground electrode 13B is provided at a position adjacent to the hole region 12B.
Further, the contact 11A is formed at a position adjacent to the hole area 12A in the ground line 2A so as to surround the hole area 12A, and the contact 11B is positioned at a position adjacent to the hole area 12B in the ground line 2B. These are formed so as to surround the hole region 12B.

  Thereby, the influence of the cross capacitance generated between the signal line 1 and the air bridge 3 can be suppressed without thinning the signal line 1 of the CPW line. Therefore, according to the air bridge structure 100 according to the present embodiment, the disturbance of the characteristic impedance and delay time of the CPW line in the vicinity of the air bridge 3 can be suppressed, and an excellent air bridge structure can be realized. In addition, since a complicated circuit design such as a parasitic effect by CPW microstrip conversion is not required, a plurality of air bridges can be easily used.

  FIG. 5 is an example in which a plurality of air bridge structures are densely arranged. Due to the effects of the air bridge structure 100 according to the present embodiment described above, as shown in FIG. The high-density air bridge 3 functions to prevent electromagnetic waves from being radiated from the CPW line. Therefore, the air bridge structure according to the present invention becomes more useful as the high frequency at which electromagnetic waves are easily radiated from the line.

  FIG. 6 is an example of an air bridge structure having a hole region having a substantially elliptical shape. In the present embodiment, the case where the hole regions 12A and 12B are formed of rectangular cutouts has been described as an example. However, the shape of the cutouts is not limited to a rectangular shape. Other shapes such as a polygonal shape, a circular shape, an elliptical shape, a substantially circular shape, a semicircular shape, a substantially semicircular shape, a semielliptical shape, and a substantially semielliptical shape may be used.

In the present embodiment, the inter-line capacitance between the signal line 1 and the ground lines 2A and 2B above the CPW line in the part where the air bridge structure 100 is not formed in the CPW line is set as Ca. The inter-line capacitance between the signal line 1 and the ground lines 2A and 2B inside the high dielectric constant substrate 9 is Cb, and the CPW line is located above the CPW line in the portion where the air bridge structure 100 is formed. The inter-line capacitance between the signal line 1 and the ground lines 2A and 2B and between the signal line 1 and the air bridge 3 is Cc, and the signal line 1 and the ground lines 2A and 2B in the high dielectric constant substrate 9 are provided. Is a distance satisfying the expression Cc−Ca _(L) = Cb−Cd _(L) where Cd is a line-to-line capacitance between the signal line 1 and the ground line 2A and 2B. L only, air The signal line 1 and the ground line 2A in the ridge structure 100 may be formed away and 2B.

  Thereby, the influence of the cross capacitance between the signal line 1 and the air bridge 3 in the air bridge structure 100 can be completely removed, and an extremely excellent air bridge structure can be realized.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 100 ... Air bridge structure, 1 ... Signal line, 2A ... Ground line (1st ground line), 2B ... Ground line (2nd ground line), 3 ... Air bridge, 4 ... Input terminal, 5 ... Output terminal, DESCRIPTION OF SYMBOLS 7 ... Upper layer wiring layer, 8 ... Lower layer wiring apparatus, 9 ... High dielectric constant board | substrate, 11A ... Contact (1st contact), 11B ... Contact (2nd contact), 12A ... Hole area | region (1st hole) Region), 12B ... hole region (second hole region), 13A ... upper layer ground electrode (first upper layer ground electrode), 13B ... upper layer ground electrode (second upper layer ground electrode), Ca, Cb, Cc , Cd: capacitance between lines, L: distance.

Claims (4)

A lower wiring layer constituting a coplanar line comprising a signal line formed on a high dielectric constant substrate and first and second ground lines arranged across the signal line;
An upper wiring layer constituting an air bridge that crosses the upper portion of the signal line and electrically connects the first and second ground lines;
The lower wiring layer has first and second hole regions formed by cutting out positions facing each other across the signal line among the first and second ground lines,
The upper wiring layer includes a first upper layer ground electrode electrically connected to the first ground line of the lower wiring layer at an upper position of the first hole region, and the second hole region. A second upper layer ground electrode electrically connected to the second ground line of the lower wiring layer at an upper position of
The air bridge electrically connects the first and second ground lines via the first and second upper layer ground electrodes. In the air bridge structure according to claim 1,
A first contact for electrically connecting the first ground line and the first upper-layer ground electrode is further provided at a position adjacent to the first hole area in the first ground line. Prepared,
A second contact for electrically connecting the second ground line and the second upper layer ground electrode is further provided at a position adjacent to the second hole area in the second ground line. An air bridge structure characterized by comprising. In the air bridge structure according to claim 2,
The first contact is formed at a position adjacent to the first hole region in the first ground line so as to surround the first hole region,
The air bridge is characterized in that the second contact is formed at a position adjacent to the second hole area in the second ground line so as to surround the second hole area. Construction. In the air bridge structure according to any one of claims 1 to 3,
The inter-line capacitance between the signal line and the first and second ground lines above the coplanar line in a portion of the coplanar line where the air bridge structure is not formed is Ca, The coplanar in the portion where the air bridge structure is formed in the coplanar line, where Cb is a line capacitance between the signal line and the first and second ground lines inside the high dielectric constant substrate. The line-to-line capacitance between the signal line and the first and second ground lines above the line and between the signal line and the air bridge is Cc, and the inside of the high dielectric constant substrate A line capacitance between a signal line and the first and second ground lines is Cd, and a distance between the signal line and the first and second ground lines is L. A distance L which satisfies the equation _{Cc-Ca (L) = Cb} -Cd (L), the said signal line in the air bridge structure and the first and second ground lines are formed apart Air bridge structure characterized by

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