JPH04275701A - Low pass filter for integrated circuit - Google Patents

Abstract

PURPOSE:To obtain a filter whose occupancy area is small in an integrated circuit and which can obtain a lower cut-off frequency by providing a ferromagnetic material layer formed in place of an insulating material layer between signal lines at a prescribed section. CONSTITUTION:Under the section where the ferromagnetic material layer 6 is sandwitced between first and second conductor lines 3a and 3b, a comparatively large inductance is generated in the respective conductor lines 3a and 3b. There is capacitance between the respective conductor lines 3a and 3b. As the inductance and the capacitance. which are generated between the respective signal lines, act upon the pair of the signal lines in common, the low passfilter 1 which is formed by combining the both has equal characteristics at the respective lines. Consequently, the low pass filter whose characteristic balances with respect to that of a differential signal lines propagating signals which are mutually complementary, whose occupancy area is small, and which has the sufficiently low cut off frequency is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pass filter for integrated circuits. More particularly, the present invention relates to a novel configuration of a low-pass filter that can be built on a substrate together with semiconductor elements or the like in a monolithic integrated circuit or a hybrid integrated circuit.

0002

2. Description of the Related Art Recent advances in integrated circuit manufacturing technology have been remarkable, and it has become possible to integrate circuits containing almost all types of elements.

FIG. 3 is a circuit diagram showing the configuration of a general low-pass filter used in integrated circuits.

As shown in the figure, a typical low-pass filter consists of an inductor L inserted into a signal line and a capacitor C connected at one end to the signal line. Therefore, when constructing a low-pass filter in an integrated circuit, an inductor and a capacitive element are each formed separately, and these are connected as appropriate to construct a desired low-pass filter.

[0005]

However, both the inductor and the capacitive element constituting the above-described low-pass filter are elements that have problems when manufactured as integrated circuit elements.

That is, an inductor is formed by a coiled conductor line formed on a substrate, and its inductance depends solely on the number of turns of the conductor line. Therefore, if an inductor with a large inductance is manufactured, the area occupied in the integrated circuit will inevitably increase.

[0007] Furthermore, the capacitance of a capacitive element depends exclusively on the dimensions of the element, and it is difficult to incorporate a large capacitive element into an integrated circuit without increasing the area occupied.

For these reasons, when a low-pass filter composed of an inductor and a capacitive element is built into an integrated circuit, the area occupied by the low-pass filter becomes significantly large, and it is difficult to use a low-pass filter with a low cutoff frequency. It was difficult to make.

Furthermore, when creating a circuit in which a low-pass filter is inserted into differential signal lines that propagate mutually complementary signals, low-pass filters with the same characteristics are inserted into a pair of differential signal lines. is difficult to form, and is a constraint on the use of low-pass filters in integrated circuits.

Therefore, the present explanation solves the problems of the above-mentioned prior art, has a sufficiently low cutoff frequency, occupies a small area, and has balanced characteristics for differential signal lines. The purpose is to provide a novel low-pass filter that can be implemented.

[0011]

[Means for Solving the Problems] That is, according to the present invention,
A low-pass filter that is incorporated into an integrated circuit that includes conductor lines formed on a substrate, including a pair of signal lines that are arranged parallel to each other with an insulating layer interposed therebetween, and a pair of signal lines that are connected to each other in a predetermined section. Provided is a low-pass filter for an integrated circuit, comprising a ferromagnetic layer formed between the present invention and the ferromagnetic material layer.

0012

[Operation] The low-pass filter for integrated circuits according to the present invention has the following features:
Its main feature is that it is formed by an inductor similarly formed in each of a pair of signal lines and a capacitance generated between the conductor lines themselves in that section.

Conventional low-pass filters for integrated circuits have been constructed by combining individually manufactured inductors and capacitive elements. Furthermore, when inserting a low-pass filter into the differential signal line, the configuration is such that an individually manufactured low-pass filter is inserted into each signal line.

On the other hand, in the low-pass filter for integrated circuits according to the present invention, a ferromagnetic layer is provided between a pair of conductor lines arranged in parallel, so that the inductance generated in the conductor line and the ferromagnetic It is constituted by the capacitance formed by the conductor line itself in the section sandwiching the body layer. Since the inductance and capacitance generated between each signal line act in common on a pair of signal lines, a low-pass filter formed by combining the two has equal characteristics on each signal line. Therefore, it can be advantageously used as a low-pass filter with balanced characteristics, particularly for differential signal lines that propagate mutually complementary signals.

[0015] The inductance generated in the conductor line by sandwiching a ferromagnetic material between a pair of mutually laminated signal lines is significantly larger than the inductance parasitic on the conductor line in a normal integrated circuit. The conductor line in this section effectively functions as an inductor.

The low-pass filter according to the present invention as described above only requires forming a ferromagnetic layer between a pair of signal lines, and occupies an extremely small area on an integrated circuit.

[0017] The present invention will now be described in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and is not intended to limit the technical scope of the present invention in any way.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a specific example of the structure of a low-pass filter for integrated circuits according to the present invention.

As shown in the figure, this low-pass filter for integrated circuits includes a first conductor line 3a formed on a substrate 1 via an insulator layer 2, and an insulator layer 4 on the conductor line. It mainly consists of a second conductor layer 3b formed therebetween and a ferromagnetic layer 6 buried in an insulator layer 4. Note that the second conductor line 3b is covered with a protective insulating layer 5. Further, it is assumed that the first conductor line 3a and the second conductor line 3b propagate mutually complementary differential signals.

In the low-pass filter 1 having the above configuration, in the section F where the ferromagnetic layer 6 is sandwiched between the first and second conductor lines 3a and 3b, each conductor line 3a
, 3b, a relatively large inductance L occurs. Further, there is a capacitance C between each conductor line 3a and 3b.

FIG. 2 is a circuit diagram showing an equivalent circuit of the low-pass filter for integrated circuits shown in FIG. 1.

As shown in the figure, a capacitance C is formed between the conductor lines 3a and 3b, and a capacitance C is formed between the conductor lines 3a and 3b.
By sandwiching the ferromagnetic layer 6 between the conductor lines 3a,
Inductance L is generated in 3b. Therefore, the conductor lines 3a and 3b form a distributed constant type low-pass filter.

Note that the characteristics of this low-pass filter are 1
In addition to the dimensions, spacing, and shape of the pair of conductor lines 3a and 3b, adjustment can also be made by the thickness of the ferromagnetic layer 6 interposed between them.

Although FIG. 1 shows the most basic configuration example, in addition to the structure shown in FIG. By adding an additional layer and using it as a ground pattern for shielding,
The balance of characteristics for each conductor line 3a, 3b is further improved.

[Production Example] A low-pass filter having the structure shown in FIG. 1 was actually produced.

First, SiN is deposited on the substrate 1 by the CVD method.
An insulator layer 2 with a thickness of 1 μm was formed by depositing. Subsequently, Au was deposited by vapor deposition to form a first conductor line 3a having a thickness of 1 μm. Next, after forming an insulator layer 4b with a thickness of 1 μm, ferrite is applied to the section F and an insulator is applied to the other areas to a thickness of 1 μm.
The insulator layer 4a and the ferromagnetic layer 6 were formed by depositing to a depth of .mu.m. Furthermore, after depositing an insulator with a thickness of 1 μm to form an insulator layer 4c, Au was deposited again to form a second conductor line 3b, and finally, an insulator layer 5 was formed. The thickness of the second conductor line 3b is formed to be the same as that of the first conductor line, and the line width of each conductor line is 12
It was set as μm.

When the characteristics of the low-pass filter manufactured as described above were measured, the cutoff frequency was 230.
A cutoff characteristic of 24 dB/oct was obtained at MHz.

[0028]

As explained above, the low-pass filter for integrated circuits according to the present invention functions as an effective low-pass filter with a small occupied area due to its unique structure.
It also emits less noise.

Furthermore, since this low-pass filter is formed of one inductor and capacitive element that are common to a pair of signal lines, it is possible to form a low-pass filter with uniform characteristics for the differential signal lines. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a specific configuration example of a low-pass filter for an integrated circuit according to the present invention.

FIG. 2 is a diagram showing an equivalent circuit of the low-pass filter shown in FIG. 1;

FIG. 3 is a circuit diagram showing a general configuration of a low-pass filter.

[Explanation of symbols]

1. Substrate, 2, 4, 5 Insulator layer, 3a, 3b Conductor line, 6 Ferromagnetic layer

Claims (1)

[Claims] 1. A low-pass filter built into an integrated circuit including a conductor line formed on a substrate, comprising: a pair of signal lines arranged parallel to each other with an insulating layer interposed therebetween; 1. A low-pass filter for an integrated circuit, comprising: a ferromagnetic layer formed between a pair of signal lines.