JPH0738367A - Noise filter - Google Patents

Abstract

PURPOSE:To obtain the noise filter which is suitable for mass production, is extremely miniature, and has an excellent noise obstructing characteristic. CONSTITUTION:On the surface of an insulated substrate 1, a metallic electrode 21 of the lower half turn of an outside coil is formed, a metallic electrode 31 of the lower half turn of an inside coil is formed through a dielectric layer 22 formed by oxidizing or nitriding the surface of the metallic electrode 21 of the lower half turn of this outside coil, a metallic electrode 41 of the upper half turn of the inside coil through a dielectric layer 32 formed by oxidizing or nitriding the surface of the metallic electrode 31 of the lower half turn of this inside coil, and a metallic electrode 51 of the upper half turn of the outside coil through a dielectric layer 42 formed by oxidizing or nitriding the surface of the metallic electrode 41 of the upper half turn of this inside coil. Subsequently, by forming an artificial distributed constant circuit consisting of the inductance which two flat coils have and the capacitance existing between both coils, a noise extending over a wide frequency band is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise filter which is used in a signal passage circuit or a power supply circuit in electronic equipment to prevent the propagation of noise.

[0002]

2. Description of the Related Art A noise filter is used in a signal passing circuit or a power supply circuit in electronic equipment such as a computer which handles digital signals.

As an example of a conventional noise filter, as shown in FIG. 5, a pair of spiral electrodes 91 and 92 are arranged to face each other with a dielectric 90 interposed therebetween, and both terminals 93 and 94 of one spiral electrode 91 are arranged. It is inserted in series in the transmission signal passing circuit, and one end 95 of the other spiral electrode 92 is grounded. Then, as shown in the equivalent circuit of FIG. 6, a pair of spiral electrodes 91,
A distributed capacitor is formed between 92, and a low pass filter with a sharp cutoff is obtained by the inductance of the spiral electrode 91 that serves as a signal passing circuit.

In such a conventional filter, a material such as ceramic, plastic, glass or mica is used as the dielectric 90, and the spiral electrode is formed by a printing process.

[0005]

In recent years, with the spread of portable electronic devices such as portable telephones and portable personal computers that handle digital signals, there is a demand for miniaturization of noise filters. However, in such a conventional filter, it is difficult to make the dielectric thin to increase the distributed capacitance and to form a long spiral electrode in the printing process, and it is difficult to make the filter extremely compact.

Therefore, the present invention was conceived in order to obtain a noise filter which is extremely small and which has excellent noise blocking characteristics.

[0007]

In the noise filter of the present invention, a metal electrode of the lower half turn of the outer coil is formed on the surface of the insulating substrate, and the metal electrode surface of the lower half turn of the outer coil is oxidized or nitrided. The lower half-turn metal electrode of the inner coil is formed through the dielectric layer, and the upper half-turn of the inner coil is turned through the dielectric layer where the metal electrode surface of the lower half-turn of the inner coil is oxidized or nitrided. Is formed, and the upper half-turn metal electrode of the outer coil is formed through a dielectric layer obtained by oxidizing or nitriding the upper half-turn metal electrode surface of the inner coil.

Further, metal electrodes of the lower half turns of the first coil and the lower half turns of the second coil are alternately formed on the surface of the insulating substrate, and the metal electrodes of the lower half turns of the first and second coils are formed. Metal electrodes of the upper half-turn of the first coil and the upper half-turn of the second coil are alternately formed through the dielectric layer whose surface is oxidized or nitrided to form the first coil and the second coil. It can be formed into a bifilar roll.

[0009]

It is possible to suppress noise over a wide frequency band by forming a pseudo distributed constant circuit consisting of the inductance of the two flat coils and the capacitance existing between the two coils.

[0010]

EXAMPLE A noise filter of the present invention will be described in the order of manufacturing steps. As shown in the sectional view of FIG. 1, (1) an insulating substrate 1 made of glass, synthetic resin or the like is prepared, and (2) the insulating substrate 1 First layer aluminum film 2 on top
Is formed by vapor deposition or sputtering, and (3) the aluminum film 2 of the first layer is etched by a photo-etching method, and as shown in FIG. A first aluminum electrode 21 that corresponds to the lower half turn of the parallel outer coil of the strip and a terminal electrode 23 are formed.

(4) After the end portion of the lower half-turn aluminum electrode 21 of the outer coil is masked with a resist, it is anodized to insulate the remaining surface of the lower half-turn aluminum electrode 21 of the outer coil. First oxide film 22 is formed
Of the dielectric layer.

(5) The second layer aluminum film 3 is again formed on the surface, and (6) the second layer aluminum film 3 is etched by a photo-etching method, as shown in FIG. As shown, on the surface of the first aluminum electrode 2a, the second half which hits the lower half turn of a plurality of parallel inner coils whose both ends are shifted downward by a half pitch.
The aluminum electrode 31 is formed.

(7) Both ends of the aluminum electrode 21 in the lower half turn of the outer coil and both ends of the second aluminum electrode 31 corresponding to the lower half turn of the inner coil are masked with a resist, and then anodized. An insulating oxide film 32 is formed on the remaining surface of the aluminum electrode 31 in the lower half turn of the inner coil to form a second dielectric layer.

(8) Again, the third layer aluminum film 4 is formed on the surface, and (9) the third layer aluminum film 4 is etched by the photoetching method, as shown in FIG. As shown, on the surface of the second aluminum electrode 31 so as to straddle the adjacent second aluminum electrode 31, both ends are offset by a half pitch to the lower left. Aluminum electrode 41
And terminal electrodes 43 and 44 are formed. At this time, a flat inner coil is formed by the lower half turn of the second aluminum electrode 31 and the upper half turn of the third aluminum electrode 41.

(10) After masking the ends of the aluminum electrode 21 in the lower half turn of the outer coil and the terminal electrodes 43, 44 of the third aluminum electrode 41 corresponding to the upper half turn of the inner coil with resist, anodization Then, an insulating oxide film 42 is formed on the surface of the aluminum electrode 41 in the upper half turn of the inner coil to form a third dielectric layer. (11) A fourth layer aluminum film 5 is formed on the surface, and (12) a fourth layer aluminum film 5 is formed by photoetching.
As shown in FIG. 2 (4), the upper surface of the third aluminum electrode 41 is exposed to the upper half turn of a plurality of parallel outer coils whose left ends are shifted downward by a half pitch. 4 aluminum electrode 51 and outer coil terminal electrode ☆
To form. At this time, the first aluminum electrode 21
The lower half turn and the upper half turn of the fourth aluminum electrode 51 form a flat outer coil, and both ends of the outer coil serve as the terminal electrodes 23 and 52 of the outer coil.

Through the series of steps described above, the insulating substrate 1
A noise filter including a flat inner coil and a flat outer coil having a third dielectric layer having coil pitches overlapping each other as a winding core can be formed on the upper portion. Then, both exposed ends of both coils are used as terminal electrodes.

Aluminum electrodes 21, 31, 4 of each coil
1 and 51 have a resistance according to the film thickness and width, and by adjusting the resistance by changing the thickness and / or width of each aluminum electrode 21, 31, 41, 51, a pseudo distribution The Q of the constant circuit can be adjusted.

When Q is high, the attenuation characteristic has a sharp attenuation or resonance point at a specific frequency, but when Q is low, uniform attenuation can be obtained over a wide frequency band. By selecting the length, thickness and width of the Num electrode and the thickness of the dielectric layer (insulating oxide film), a desired attenuation-specific noise filter can be obtained.

If the capacitance between the aluminum electrodes of the two coils is too large, the length of either one of the aluminum electrodes may be made shorter or narrower than the other.

Finally, the insulating substrate 1 is divided into element units, and each terminal electrode is bonded and coated or packaged.

When using the noise filter element thus constructed, one end of the inner coil is connected to the reference potential point via the terminal electrode, for example, grounded, and the outer coil passes the transmission signal. When inserted in series in the circuit, the outer coil is
A distributed constant circuit can be formed to prevent the propagation of high frequency noise.

(Second Embodiment) The inner coil and the outer coil are partially widened to face each other, one of the coils is shortened, and the other coil is formed elongated so that the widened portion is formed. A hybrid circuit is formed which is a series circuit of a pseudo distributed constant circuit having a large electrostatic capacity and a lumped constant circuit of the inductance of an elongated coil.

(Third Embodiment) As shown in the plan view of FIG. 3, the inner coil A and the outer coil B are displaced from each other so as to straddle adjacent electrodes of the inner coil A. Both sides of the outer coil B are overlapped, and the terminal electrode 43,
23 and 52 are formed.

(Fourth Embodiment) In the third embodiment described above, both side portions of the outer coil B are formed so as to extend over both adjacent electrodes of the inner coil A. But only on one side of the outer coil B electrode, ie
At least a part of the coils may be formed so as to overlap with each other, and the coupling state between the electrodes of the two coils A and B may be changed.

(Fifth Embodiment) In the third embodiment, both side portions of the outer coil B are formed so as to extend over both adjacent electrodes of the inner coil A, but FIG. As shown in the plan view of FIG. 2, the second coil B is formed between the adjacent electrodes of the first coil A, the terminal electrodes 23, 52, 43 and 44 are provided to connect the two coils A and B to the bifilar. It may be configured in a roll. In this case, the capacitance between the two coils can be reduced.

(Sixth Embodiment) When a noise filter is three-dimensionally formed on the surface of a silicon wafer on which an integrated circuit is already formed, a silicon on which an integrated circuit is already formed is formed.
A silicon oxide film is formed on the wafer by a chemical vapor deposition method, and a noise filter is formed on the silicon oxide film through the steps described in the above embodiments.

When the noise filter is three-dimensionally formed in this manner, the area of the silicon wafer can be effectively used.

(Seventh Embodiment) In each of the above-described embodiments, the metal electrodes 21, 51 or 31, 41 forming the two coils are formed one layer each, but a silicon oxide film or the like is used. Insulation layer of
Alternatively, the capacitance can be increased.

(Other Embodiments) The noise filter of the present invention can be used as one component by housing a single element in a case, but it is formed on an insulating substrate such as a printed wiring board or an IC card. A noise filter can be formed as a part of the other circuits to be used and connected to a power supply circuit or a transmission signal passing circuit.

Further, by forming a plurality of noise filters on the insulating substrate and housing them in a single case, it is possible to prevent the propagation of noise generated by a transmission signal of a plurality of bits by a single component.

In order to prevent the dielectric layer 42 interposed between the two coils from being destroyed by static electricity, a discharge gap is provided between the metal electrodes, or a plurality of diodes connected in series are connected to form a forward direction. It is sufficient to operate below the threshold voltage or to connect a Zener diode.

Although aluminum is used as the electrodes of both coils in the above embodiments, other conductive materials may be used, and an aluminum oxide film may be used as a dielectric. However, the nitride film may be made of a dielectric material.

A high-purity semiconductor substrate, for example, a high-purity silicon wafer, has a bulk resistance extremely higher than that of metal conductors such as metal electrodes 21, 31, 41, 51 forming a coil, and is highly insulated. It can be sufficiently used as a substrate.
Incidentally, an insulating film such as SiO ₂ may be formed on the surface of the silicon wafer and then used as an insulating substrate.

The noise filter of the present invention, when a silicon wafer is used as an insulating substrate, is manufactured and inspected by a conventionally used integrated circuit manufacturing apparatus.
It becomes possible to package it, and there is no need to install new equipment.

[0035]

As is apparent from the description based on the above embodiments, the noise filter of the present invention can be manufactured by a technique similar to the manufacturing technique of an integrated circuit, and therefore can be easily miniaturized. It is suitable for mass production, can be manufactured at low cost, and can easily obtain desired damping characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a noise filter of the present invention in the order of manufacturing steps,

2 is a plan view of the noise filter shown in FIG. 1 in the order of manufacturing steps;

FIG. 3 is a plan view showing another embodiment of the noise filter of the present invention,

FIG. 4 is a plan view showing still another embodiment of the noise filter according to the present invention,

FIG. 5A is a front view showing an example of a conventional noise filter, FIG. 5B is a side view, FIG.

FIG. 6 is an equivalent circuit diagram of a conventional noise filter.

[Explanation of symbols]

 1 Insulating substrate 22, 32, 41 Insulating oxide film 21, 51 Outside coil electrode 31, 41 Inside coil electrode 23, 52 Outside coil electrode terminal electrode 43, 44 Outside coil electrode terminal electrode

Claims (2)

[Claims] 1. A lower half-turn metal electrode of the outer coil is formed on the surface of the insulating substrate, and the lower half-turn metal electrode surface of the outer coil is oxidized or nitrided to form a metal layer under the inner coil. A metal electrode with a half turn is formed, and a metal electrode with an upper half turn of the inner coil is formed through a dielectric layer obtained by oxidizing or nitriding the surface of the metal electrode of the lower half turn of the inner coil. A noise filter characterized in that a metal electrode of the upper half turn of the outer coil is formed through a dielectric layer obtained by oxidizing or nitriding the surface of the metal electrode of the turn. 2. A metal electrode of the lower half turns of the first coil and the lower half turn of the second coil is alternately formed on the surface of the insulating substrate, and the metal electrode of the lower half turns of the first and second coils is formed. Metal electrodes of the upper half turn of the first coil and the upper half turn of the second coil are alternately formed through a dielectric layer whose surface is oxidized or nitrided, and the first coil and the second coil are bifilar. A noise filter characterized by being formed into a winding.