JP2000059112A - Small-sized transmission line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the effective capacity between a signal and a return line without varying the inductance of the whole transmission line by embedding an insulating medium in a signal line so that a direct current can not be propagated from the signal line to the return line. SOLUTION: An AC current 105 is carried by the return line 102 which allows it to flow reversely to the signal line 101. The signal and return lines are formed of conductive materials and the circumferential medium 103 is made of an insulating material. The mean distance as to capacitive coupling decreases because of the presence of a tab 111 of a conductive material, which increases the length-directional capacity of the transmission line. Further, a notch 112 prevents the current from flowing along the length, so the current path of a signal and a return signal is restricted by outside edges of two conductors which do not have the tab 111 and the current path has no variation from the geometric shape which does not have the tab 111. Consequently, a magnetic field is not varied and the length-directional inductance of the transmission line, therefore, has no variation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a small transmission line.

[0002]

2. Description of the Related Art FIGS. 1A and 1B are sectional views and FIG.
The known structure shown in (plan view) is used as a transmission line (or waveguide). It has one or more metal lines 101 that carry an AC current or signal and one or more metal lines 102 that carry a return signal having equal and opposite currents. The direction of the current is indicated by arrows 105, which are indicated by the arrowheads and arrowheads as shown in FIG. 1 (a), incoming and outgoing current directions, and FIG. The line indicating either as a "signal" line or a "return" line is arbitrary, since the direction of the current is switched every half cycle. A typical transmission line is uniform along its length, and a three-dimensional transmission line is usually described as a two-dimensional shape extruded in the length dimension. In that case, the following relationship holds, and FIG.
Independent of the two-dimensional section shown in (b): CL = εμ = 1 / c ² Equation 1 Lossless transmission line (this is roughly the case in most cases)
The following relationship applies: c = (CL) ^−1/2 Equation 2 where C and L are the capacitance and inductance per transmission line length. The variable c is the speed of light in the medium, the speed at which a signal is sent through the transmission line.

For a metal line on an integrated circuit that is first embedded in silicon dioxide, the dielectric constant is ε = 4.0.
e ₀ and c = 1.50e ¹⁰ cm / s. When the signal frequency is 5 GHz, the wavelength is 3 cm. The above relationship shows that if the capacitance is increased without changing the inductance, the speed of the signal will decrease. However, in the past, any change in capacitance has been offset so that the inductance changes correspondingly so as not to change both c and wavelength.

Considering the case of FIG. 1, as the lines move closer together, the capacitance between the signal carrying line and the return signal increases. However, by allowing the two current paths to be close together, their contribution to the magnetic field cancels out more accurately (because they are in opposite directions), thereby reducing the overall field strength and, therefore, The inductance per length of the transmission line is reduced. Since c was expected to be unchanged in FIG. 2, the inductance per length is reduced by the same factor that the assumed capacity per length was increased.

[0005]

An object of the present invention is to solve the above-mentioned problems.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a signal line comprising one or more parallel conductive paths carrying an alternating current along its length, and one or more signal lines carrying an alternating current in a direction opposite to the direction of the signal line. A return signal line consisting of a conductive path parallel to the signal line, a return and signal medium embedded so that DC cannot pass from the signal line to the return line, and an insulation medium in which the entire transmission line is not significantly reduced. A non-uniform conductive means coupled to the signal and return lines to increase the effective capacitance between the signal line and the return line, and a semiconductor substrate, wherein the insulating medium comprises a transmission line structure disposed on the semiconductor substrate. Including.

The present invention also provides a signal line comprising a semiconductor substrate and one or more parallel conductive paths carrying an alternating current over the length of the semiconductor substrate, and a direction opposite to the direction of the signal line over the semiconductor substrate. A return signal line comprising a conductive path parallel to one or more signal lines for carrying an alternating current, an insulating medium having a return and signal line embedded therein so that DC cannot pass from the signal line to the return line, and an inductance of the entire transmission line The non-uniform conductive means coupled to the signal and return lines to increase the effective capacitance between the signal and return lines without significantly reducing the transmission line structure made of insulating material. Integrated circuits.

By starting from a uniform geometry along the length, C can be increased without decreasing L.
The structure of FIG. 2 accomplishes this with a pattern of alternating tabs 111 and notches 112 on the two inner edges of the transmission line metal. The average distance to capacitive coupling is significantly reduced by the presence of the tub, which increases C. Notch 11
Because 2 prevents current flow in the longitudinal direction, the current paths of the signal and return signals are regulated to remain on the outer edges of the two conductors as if no tab had been added. Since the current path is essentially unchanged from the untabbed geometry, the magnetic field is not changed,
Therefore, L is not changed. Equation 2 of this structure adds a lower value for the signal rate c, while Equation 1 adds nothing more. The wavelength λ of the signal on the transmission line is proportional to c.

In integrated circuits, there are practical reasons to reduce both. Delay lines are used to increase the flight time of the signal, which reduces the required length of the delay line. It is desirable when the phase of the signal is sometimes shifted by a given fraction (fraction) of the wavelength,
The reduced wavelength of the signal in this configuration reduces the length of the transmission line required to achieve this shift.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings.
This will be described in detail. 2A and 2B show an embodiment of the present invention. AC current 105 is applied to one or more signal lines 1
It is carried by one or more return lines 102 carrying current in the direction opposite to 01. The signal and return lines may generally be comprised of any conductive material, such as metal,
The surrounding medium 103 is usually made of an insulating material. Tab 1
11 is also a conductive material, connected to the signal and return lines, the presence of which destroys the uniformity of the transmission line along its length. The average distance for capacitive coupling is C
Is significantly reduced by the presence of tabs. Because notch 112 prevents current from flowing longitudinally, signal and return signal current paths 105 are limited to stay on the outer edges of the two conductors as if no tabs were added. . Since the current path is essentially unchanged from the tab-free geometry, the magnetic field is not changed and therefore L is not changed. The effect on the signal speed and wavelength λ of the transmission line is both reduced by a factor equal to the square root of the ratio r,
C is thereby increased. In integrated circuits, there are practical reasons for reducing both. The delay line is reduced to increase the flight time of the signal, which reduces the required length of the delay line. Desirable when the phase of a signal may be shifted by a given fraction of wavelength,
The reduced wavelength of the signal in this configuration reduces the line length required to achieve this shift. Integrated circuit (I
In C), a ratio of r = 300 is achievable with current processes using standard techniques. This speed (1 / r)
By multiplying by ^1/2 = 0.058, 8.7 × 10 ⁸ c
The m / sec and wavelength are 0.17 cm at 5 GHx.

FIGS. 3A and 3B show a modification of the present invention applicable to a transmission line on an IC in which a metal and an insulator are successively patterned on a chip. This structure is similar to that shown in FIGS. 1A and 1B except that an additional metal 122 is used. The main feature of this structure is that the increased capacitive coupling makes this second layer 12
2, which is patterned into a series of strips 123, 124 that need not be rectangular in shape. The strips are generally directed generally transverse to the lines 101, 102 with gaps 106 between each such that no current flows in the strips in the same direction as the lines 101,102. The preferred embodiment is via 12
1 that couples each of the strips to either the signal line or the return line of the transmission line. This helps to maximize the capacitance C per length of the transmission line, which may be the fat portion 1 of each of the strips.
24 and approximately equal to that between the signal (or return signal) line above it. For a small gap 131 between the two metal layers, the capacitance is high. To maximize capacity, most of the area of the line 102 is underneath the strip 12
Must have part of four. Other than this standard,
The exact shape of the strip is quite arbitrary. Thick piece 1
A rectangle having a uniform width equal to the width of 24 will work just as in this case. 4 (a),
(B) shows a structure including features from both the structures of FIGS. The tab 11 connected to the signal line 101 fills most of the area between the metal first level signal line and the return line. Strip 12 of second layer of metal 122
3 extends below both the tub and the signal line and is attached to the return line with conductive vias 121. This structure uses both the area of the signal line and the area between the signal line and the return line for capacitive coupling between the two metal layers.

FIGS. 5A and 5B show signal lines 101. FIG.
Shows the structure where the return line 102 is in another metal layer. Each line extends toward the opposite line and has a series of tabs 111, 123 on its own level overlapping it as shown. FIG. 6 is a variation of FIG. 2 (b), where the tabs 111 are interleaved to achieve higher capacity.

The present invention is embodied in the structure of an IC, wherein the surrounding medium 103 is comprised of typical semiconductor process materials such as silicon, silicon dioxide, silicon nitride, plastic, air, and the like. The invention is also embodied in a multilayer PCB (Printed Circuit Board), where the surrounding medium is a non-metallic component of the PCB. The signal and return lines are on one side of the insulating layer, and the spaced metal lines are on the other side. Another simple embodiment of the invention is in a cable. Specific examples of this are tabs reaching inward from outer conductors and / or tabs reaching out from inner conductors.

For the IC embodiment, nichrome is preferred for the conductive layer 122. Because it is a formable metal. The invention can be practiced by shaping nichrome strips to interrupt the current path from the tub to the signal or return line. By cutting more strips, the wavelength and speed of the line gradually increases. This can be done after the rest of the process and while the lines are being measured so that very accurate delays or phase shifts are achieved.

The small transmission lines 101 and 102 are connected to the tab 11
It has a non-uniform conductive geometry including ones and notches 112. Tough 111 and notch 112 increase the capacitance of lines 101 and 102 without increasing inductance.
This creates a delay in the signal transmitted on lines 101,102.

[Brief description of the drawings]

FIG. 1A is a sectional view of a conventional technique, and FIG. 1B is a plan view thereof.

FIG. 2A is a sectional view of an embodiment of the present invention, and FIG.

FIG. 3 (a) shows a cross-sectional view of an alternative embodiment of the present invention, and FIG. 3 (b) shows a plan view thereof.

FIG. 4 (a) is a cross-sectional view of a second alternative embodiment of the present invention.
The plan view is shown in FIG.

FIG. 5 (a) is a cross-sectional view of a third alternative embodiment of the present invention.
The plan view is shown in FIG.

FIG. 6 shows a plan view of a fourth alternative embodiment of the present invention.

[Explanation of symbols]

 101, 102 Metal line 103 Medium 105 Current path 106, 131 Gap 111, 123 Tab 112 Notch 121 Via 122 Conductive layer 123, 124 Strip

Claims (7)

[Claims] 1. A signal line comprising one or more parallel conductive paths capable of carrying an alternating current along its length, and carrying an alternating current in a direction parallel to the signal line and opposite to the direction of the signal line. A return signal line consisting of one or more conductive paths, an insulating medium in which return and signal lines are embedded so that no direct current can pass from the signal line to the return line, and without significantly reducing the inductance of the entire transmission line. A transmission line structure comprising a non-uniform conductive means coupled to the signal and return lines to increase the effective capacitance between the signal and return lines, and a semiconductor substrate, wherein the insulating medium is disposed on the semiconductor substrate. 2. A multilayer printed circuit board having alternating layers of metal lines and insulating material, the insulating layer having a first layer of signal and return lines on one side and signal and return lines on the other side. A second layer of spaced metal lines oriented transversely with respect to the signal and return lines to increase capacitance between the signal and return lines, separated from each other by an insulating material. A cable structure including the lines and at least one set of conductive tabs extending from one line toward another line, wherein the tabs are interconnected to increase capacitance between a signal line and a return line. The transmission line according to claim 1, wherein the transmission line is directed at: 3. The non-uniform conductive means comprises a pattern of conductive strips which are transverse to the signal and return lines to increase the capacitance between the signal and return lines. The conductive strip is separated by a gap to prevent current from being induced inductively therein, and the insulating medium is a printed circuit board.
The described transmission line. 4. A signal line comprising a semiconductor substrate and one or more parallel conductive paths carrying an alternating current over the semiconductor substrate in a longitudinal direction; and a signal line parallel to the signal line and extending over the semiconductor substrate. A return signal line consisting of one or more conductive paths carrying an alternating current in the opposite direction, an insulating medium in which the return and signal lines are embedded so that no direct current can pass from the signal line to the return line, and a significant inductance of the entire transmission line. The non-uniform conductive means coupled to the signal and return lines to increase the effective capacitance between the signal and return lines without reducing the substrate, the substrate comprising an integrated transmission line structure of insulating material. circuit. 5. The integrated circuit according to claim 4, wherein the insulating material is an insulating layer on the substrate. 6. The non-uniform conductive means comprises a pattern of conductive strips that traverse the signal and return lines to increase the capacitance between the signal and return lines. 6. The integrated circuit of claim 5, wherein said conductive strips are separated by gaps to prevent currents being induced inductively therein. 7. The device further includes a via extending from the conductive strip to either the signal line or the return line, the via for electrically connecting the strip to a respective signal or return line. 7. The integrated circuit according to claim 6, wherein the integrated circuit is filled with a conductive material.