JPH0730356A - Noise filter - Google Patents

Abstract

PURPOSE:To provide an extremely compact noise filter with an excellent noise blocking characteristic suitable to mass production. CONSTITUTION:A lower half turn 32 of an outside coil 3 is formed on the surface of an insulating substrate 1, and a lower half turn 42 of an inside coil 4 is formed through a dielectric layer 22 on the lower half turn 32 of the outside coil 3. An upper half turn 44 of the inside coil 4 is formed through a dielectric layer 23 on the lower turn 42 of the inside coil 4, and an upper half turn 34 of the outside coil 3 is formed through a dielectric layer 24 on the upper half turn 44 of the inside coil 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small 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. 7, 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 connected. 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. 8, 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 electrodes 91 and 92 arranged facing each other on both sides of the dielectric 20 are formed by a printing process. ing.

[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 size extremely small.

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

[0007]

According to the noise filter of the present invention, the lower half turn of the outer coil is formed on the surface of the insulating substrate, and the inner half is formed on the lower half turn of the outer coil through the dielectric layer. The lower half turn of the coil is formed, the upper half turn of the inner coil is formed on the lower half turn of the inner coil, and the upper half turn of the inner coil is formed on the upper half turn of the inner coil. The upper half turn of the outer coil is formed.

Further, lower half turns of the first coil and lower half turns of the second coil are alternately formed on the surface of the insulating substrate,
An upper half turn of the first coil and an upper half turn of the second coil are alternately formed on the lower half turns of the first and second coils through a dielectric layer, and the first coil and the second coil are formed. The coil may be bifilar wound.

[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 coils and the electrostatic capacitance existing between the two coils.

[0010]

EXAMPLE (First Example) The first example of the noise filter shown in the equivalent circuit of FIG. 3 will be described in the order of manufacturing steps. As shown in the sectional view of FIG. Prepare insulating substrates such as resin, ceramics, and high-purity silicon wafers. In particular, a high-purity silicon wafer 1 having a large bulk resistance is suitable for the insulating substrate.

(2) After forming the first silicon oxide film 21 on the silicon wafer 1 by chemical vapor deposition (CVD) or by oxidizing the silicon wafer 1 in an oxidizing atmosphere, (3) On this silicon oxide film 21, a metal capable of withstanding the next chemical vapor deposition process by sputtering or vapor deposition, for example, a metal film of aluminum, gold, tungsten, molybdenum, tantalum, niobium, or the like.
3a is formed, (4) on the metal film 3a, a pattern of a plurality of parallel photoresists 51 whose both ends are shifted downward by a half pitch is formed, (5) using this photoresist 51 as a mask, A plurality of parallel first metal electrodes 32 shown in (1) of FIG.
After forming, the photoresist 51 is removed. This first metal electrode 32 forms the lower half turn of the outer coil.

(6) As shown in (2) of FIG. 2, the entire surface of each of the plurality of parallel first metal electrodes 32 excluding both end portions 31, 33 is subjected to a second chemical vapor deposition method to form a second metal electrode. After forming the silicon oxide film 22, (7) a second metal film 4a is formed on the second silicon oxide film 22, and (8) a first parallel film is formed on the second metal film 4a. A pattern of a plurality of parallel photoresists 52, which are shorter than the first parallel metal electrode 32 and whose both ends are shifted downward by a half pitch, on the metal electrode 32;
And a pattern of a photoresist 52 exposing both end portions 31 and 33 of each metal electrode 32 is formed, and (9) using the photoresist pattern 52 as a mask, as shown in (3) of FIG. After forming the parallel second metal electrodes 42 and the both ends 31, 33 of each first metal electrode 32, a photoresist is formed.
Remove 52. This second metal electrode 42 forms the lower half turn of the inner coil.

(10) As shown in (4) of FIG. 2, both ends 31 of the plurality of parallel first and second metal electrodes 32, 42,
A third silicon oxide film 23 is formed on the entire surface except 33 and 41 and 43 by a chemical vapor deposition method, and then (11) the third silicon oxide film 23 is formed.
On the silicon oxide film 23 and exposed metal electrode
A third metal film 4b is formed on both ends 31, 33 and 41, 43 of 32, 42, and (12) the left ends connecting the ends 41, 43 of the parallel second metal electrode 42. A pattern of a plurality of parallel photoresists 53 shifted downward by a half pitch and a pattern of the photoresist 53 exposing both end portions 31, 33 of each first metal electrode 32 are formed. (13) This photoresist Using the pattern of 53 as a mask, as shown in FIG. 2 (5), after forming a plurality of parallel third metal electrodes 44 and both ends 31, 33 of the first metal electrodes 32, The photoresist 53 is removed. At this time, the lower half turn of the second metal electrode 42 and the third turn
The flat inner coil 4 is formed by the upper half turn of the metal electrode 44.

(14) As shown in (6) of FIG. 2, both end portions 31, 33 of the plurality of parallel first metal electrodes 32 and both terminal portions 40, 45 of the flat inner coil are arranged. After forming a fourth silicon oxide film 24 on the entire surface except for the chemical vapor deposition method, (15)
A fourth metal film 3b is formed on the fourth silicon oxide film 24 and on both ends 31, 33 of the exposed metal electrode 32, and (16) the parallel first metal electrodes 32 are formed. Each end of 31, 33
And a pattern of a plurality of parallel photoresists 54 shifted by a half pitch to the lower left and connecting the two, and a photoresist 54 for exposing both terminal portions 30, 35, 40, 45 of the first and second metal electrodes. And (17) in FIG. 2 (7)
As shown in FIG. 3, the pattern of the photoresist 54 is used as a mask to form a plurality of parallel fourth metal electrodes 34, both terminal portions 40 and 45 of the inner coil 4, and both terminal portions of the outer coil 3. After forming 30, 35, the photoresist 54 is removed. At this time, the lower half turn of the first metal electrode 32 and the fourth turn
The flat outer coil 3 is formed by the upper half turn of the metal electrode 34.

Through such a series of steps, silicon
On the wafer 1, it is possible to form the flat inner coil 4 and the outer coil 3 having the third silicon oxide film 23 having the coil pitches overlapped as the winding core. Then, the exposed ends 30, 35 and 40, 45 of each coil are used as terminal electrodes.

Finally, the silicon wafer 1 is divided into elements, and the terminal electrodes 30 and 3 of the two flat coils 3 and 4 are divided.
Bond and coat 5, or 40, 45 respectively, or package.

The inductance of the flat first coil 3 and the electrostatic capacitance formed between the flat second coil 4 are set to desired values, and as shown in the equivalent circuit of FIG. Then, a pseudo distributed constant circuit is formed.

(Second Embodiment) The inner coil 4 and the outer coil 3 are partially widened to face each other, one of the coils is shortened, and the other coil is formed elongated to widen the width. A hybrid circuit is formed by a series circuit of a pseudo distributed constant circuit having a large electrostatic capacitance formed in a portion and a lumped constant circuit of the inductance of the elongated coil.

(Third Embodiment) As shown in the plan view of FIG. 4, the inner coil 4 and the outer coil 3 are offset from each other so as to straddle adjacent electrodes of the inner coil 4. Both sides of the outer coil 3 are overlapped, and the terminal electrode 30,
Form 35 and 40.

(Fourth Embodiment) In the third embodiment described above, both side portions of the outer coil 3 are formed so as to straddle over both adjacent electrodes of the inner coil 4. However, only one side of the electrode of the outer coil 3, that is,
It may be formed so that at least a part thereof overlaps, and the coupling state between the electrodes of the two coils 3 and 4 may be changed.

(Fifth Embodiment) In the third embodiment, both side portions of the outer coil 3 are formed so as to overlap the adjacent electrodes of the inner coil 4 and overlap each other. The second coil 4 may be formed between the adjacent electrodes of the first coil 3 to form the two coils 3 and 4 in a bifilar winding, as shown in the plan view of FIG. In this case, 2
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, the silicon on which the 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 first to fifth embodiments.

By thus forming the noise filter three-dimensionally, the area of the silicon wafer can be effectively used.

(Other Embodiments) As a method of packaging the noise filter manufactured by the steps of the first to fifth embodiments, as shown in FIG. 6, the whole surface of the chip A of the divided silicon wafer is shown. Then, a silicon oxide film B is formed by a chemical liquid phase method, the silicon oxide film B on the terminal electrode is removed by etching to form a hole, and the hole is sealed with solder C to the extent that it rises on the surface. Since C can be brought into direct contact with the land of the printed wiring board, it is convenient for surface mounting. It should be noted that another insulating material such as synthetic resin may be used for the protective film on the surface of the chip B, and a laser beam may be used for perforating the protective film.

Each metal electrode of the inner coil and the outer coil
32, 34, 42, and 44 have resistances according to film thickness and width, and the resistance of the pseudo distributed constant circuit is adjusted by changing the thickness and / or width to adjust the resistance. be able to.

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 characteristics can be obtained over a wide frequency band. , The bulk resistance of the silicon wafer that becomes the insulating substrate, the length of the metal electrode that forms the coil,
By selecting the thickness, width, and thickness of the silicon oxide film to be the insulating oxide film, it is possible to obtain a noise filter having a desired attenuation characteristic.

In each of the embodiments described above, each of the metal electrodes 32, 34 or 42, 44 forming the two coils is formed by one layer, but a silicon oxide film is interposed between the metal electrodes 32, 34 or 42, 44. By connecting and forming a plurality of layers, the inductance and / or the capacitance can be increased.

When it is desired to increase the inductance of the coil, a magnetic insulator such as ferrite may be used as the insulating substrate.

Although the noise filter of the present invention can be used as a single component by housing a single element in a case, it can be used for other circuits formed on an insulating substrate such as a printed wiring board or an IC card. A noise filter can be formed as a part and can be used by connecting to a power supply circuit or a transmission signal passing circuit.

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

In order to prevent the dielectric layer 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 gap. Operating below the threshold voltage,
Just connect a Zener diode.

As the dielectric layer existing between the two coils, a silicon nitride film (Si ₃ N ₄ film) having a relatively large dielectric constant may be used instead of the silicon oxide film.

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 32, 34, 42, and 44 forming a coil, and is highly insulating. It can be sufficiently used as a 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. Further, it is suitable for mass production without requiring new facility investment, can be manufactured at low cost, and it is easy to obtain elements having various attenuation characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a noise filter according to the present invention in the order of manufacturing steps;

FIG. 2 is a plan view showing the state of the noise filter according to the first embodiment of the present invention during the manufacturing process,

FIG. 3 is an equivalent circuit diagram of the noise filter of the present invention,

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

FIG. 5 is a plan view showing still another embodiment of the noise filter according to the present invention,

FIG. 6 is a sectional view showing an example of packaging of the noise filter of the present invention manufactured in each of the embodiments,

FIG. 7 is a surface view showing an example of a conventional noise filter.
(a), side view (b), back view (c),

FIG. 8 is an equivalent circuit diagram of a conventional noise filter.

[Explanation of symbols]

 1 silicon wafer (insulating substrate) 3 outer coil 4 inner coil 21, 22, 23, 24 dielectric layer (silicon oxide film) 32, 34 metal electrode forming outer coil 42, 44 inner coil formed Metal electrode

Claims (2)

[Claims] 1. A lower half turn of the outer coil is formed on a surface of an insulating substrate, and a lower half turn of the inner coil is formed on the lower half turn of the outer coil through a dielectric layer. The upper half turn of the inner coil is formed on the lower half turn of the inner coil via the dielectric layer, and the upper half turn of the outer coil is formed on the upper half turn of the inner coil via the dielectric layer. Noise
filter. 2. A lower half turn of the first coil and a lower half turn of the second coil are alternately formed on the surface of the insulating substrate, and a dielectric layer is formed on the lower half turns of the first and second coils. A noise filter, characterized in that the upper half-turns of the first coil and the upper half-turns of the second coil are alternately formed, and the first coil and the second coil are formed in a bifilar winding.