JP3029929B2 - Noise filter - Google Patents

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 for a signal passing circuit or a power supply circuit in an electronic apparatus and which blocks noise propagation.

[0002]

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

As an example of a conventional noise filter, as shown in FIG. 6, a pair of spiral electrodes 21 and 22 are arranged to face each other via a dielectric 20 and both terminals 23 and 24 of one spiral electrode 21 are connected. An arbitrary one end 25 of the other spiral electrode 22 is grounded by being inserted in series into the transmission signal passing circuit. Then, as shown in the equivalent circuit of FIG.
A low-pass filter having a sharp cutoff is obtained by forming a distributed capacitance between the capacitors 22 and the inductance of the spiral electrode 21 serving as a signal passing circuit.

In such a conventional filter, a material such as ceramic, plastic, glass, or mica is used as the dielectric 20, and spiral electrodes which are opposed to both surfaces of the dielectric 20 are formed by a printing process.

[0005]

In recent years, as portable electronic devices handling digital signals, such as portable telephones and portable personal computers, have become widespread, noise filters have also been required to be reduced in size. However, in such a conventional filter, there is a limit in increasing the distributed capacitance by reducing the thickness of the dielectric, and in forming a long spiral electrode by a printing process, and it is difficult to significantly reduce the size.

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

[0007]

According to the noise filter of the present invention, a first spiral electrode is formed on an insulating substrate, and the first spiral electrode is formed on the insulating substrate and on the first spiral electrode.
Forming an electric conductor layer, and forming the first spiral on the dielectric layer;
A second spiral electrode is formed so as to partially overlap the spiral electrode . In addition, a semiconductor substrate with high purity and high bulk resistance can be used as the insulating substrate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of a noise filter according to the present invention will be described in the order of manufacturing steps. As shown in the sectional view of FIG. 1, (1) First, glass, synthetic resin, high purity An insulating substrate 1 such as a silicon wafer is prepared. In particular, a high-purity silicon wafer having a large bulk resistance is suitable for the insulating substrate 1.

(2) A first silicon oxide film (SiO ₂ film) is formed on the silicon wafer 1 by chemical vapor deposition (CVD).
After forming the silicon wafer 2, (3) On the silicon oxide film 2 of the silicon wafer 1,
A metal film 3 such as a metal, for example, gold, tungsten, molybdenum, tantalum, or niobium, which can withstand the next chemical vapor deposition process, is deposited. A pattern of a photoresist 4 is formed. (5) A first spiral metal electrode 3a is formed using the photoresist 4 as a mask.
Wash off.

(6) After forming the second silicon oxide film 5 on the first spiral metal electrode 3a and the exposed first silicon oxide film 2 by a chemical vapor deposition method, An aluminum film 6 is deposited on the second silicon oxide film 5.

(8) On the aluminum film 6, a pattern of a spiral photoresist 7 having a width larger than the interval between the electrodes is formed along the center line between the adjacent first spiral metal electrodes 3a. (9) Using this photoresist 7 as a mask, a second spiral aluminum electrode having a terminal electrode 6b at the end
After the formation of 6a, the pattern of the photoresist 7 is washed off. (10) The first silicon oxide film 5 on the surface of both ends or one end of the first spiral metal electrode 3a is removed by etching to expose and form the terminal electrodes 3b and 3c.

The planar shape of the noise filter element formed on the silicon wafer 1 serving as an insulating substrate through such a series of steps is as shown in the plan view of FIG. The cross section cut along the line BB in the figure is
This is as shown in the sectional view of FIG. The silicon wafer 1 is divided and bonded to the terminal electrodes 3b, 3c, and 6b of the two spiral metal electrodes 3a and 6a and housed in a package.

(Second Embodiment) In the first embodiment described above, both sides of the second spiral metal electrode 6a are overlapped on both electrodes adjacent to the first spiral metal electrode 3a. Has formed,
As shown in the cross-sectional view of FIG. 3, only one side of the second spiral metal electrode 6a, that is, at least a part thereof is overlapped to form two spiral metal electrodes 3a, 6a.
The connection between them may be changed.

As a method of packaging the noise filter manufactured by the steps of the first and second embodiments,
As shown in FIG. 4, a silicon oxide film 13 is formed on the entire surface of the chip 12 of the divided silicon wafer by a chemical liquid phase method, and the silicon oxide film 13 on the terminal electrode is removed by etching to form a hole. Drilling and sealing the hole to the extent that it swells on the surface with solder 14 allows the projecting solder 14 to directly contact the land of the printed wiring board, which is convenient for surface mounting. In addition, another insulating material such as a synthetic resin may be used for the protective film on the surface of the chip 12,
A laser beam may be used for perforating the protective film.

(Third Embodiment) On the surface of a silicon wafer on which an integrated circuit has already been formed,
An embodiment in which the noise filter is formed three-dimensionally will be described.

As shown in FIGS. 5A and 5B,
On the silicon wafer 10 on which the integrated circuit 11 has already been formed,
A silicon oxide film 2 is formed by a chemical vapor method, and a noise filter is formed on the silicon oxide film 2 through the steps described in the first and second embodiments.

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

When the noise filter manufactured by the steps of the first to third embodiments is operated in the normal mode, the first one of the two spiral metal electrodes is used.
When the end of the spiral metal electrode is connected to a reference potential point, for example, grounded, and the second spiral metal electrode is inserted in series in the transmission signal passage circuit, the second spiral metal electrode Due to the presence of the grounded first metal electrode, a distributed constant circuit can be formed and propagation of high frequency noise can be prevented.

In order to operate the noise filter in the common mode, two spiral metal electrodes may be inserted in series in the transmission signal passage circuit.

Each of the spiral metal electrodes 3a and 6a has a resistance corresponding to the film thickness and width, and the thickness and / or
Alternatively, by adjusting the resistance by changing the width, the Q of the distributed constant circuit can be adjusted.

When Q is high, the attenuation characteristic has a steep attenuation or resonance point at a specific frequency, but when Q is low, uniform attenuation characteristics can be obtained over a wide frequency band. By selecting the bulk resistance of the silicon wafer as the insulating substrate, the length, thickness and width of the spiral metal electrode, and the thickness of the silicon oxide film as the insulating oxide film, noise and noise with the desired attenuation characteristics can be obtained. A filter can be obtained.

If the capacitance between the two spiral metal electrodes is too large and / or if the inductance of one spiral electrode is insufficient, the length of one spiral electrode is made longer than the other. You just have to do it.

(Other Embodiments) In each of the embodiments described above, the two spiral metal electrodes 3a and 6a are formed one by one. However, a silicon oxide film is interposed between the two spiral metal electrodes 3a and 6a. By forming a plurality of layers by connection, inductance and / or capacitance can be increased.

If it is desired to increase the inductance of the spiral metal electrode, a magnetic insulator such as ferrite may be used as the insulating substrate.

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

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

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

Further, by forming a plurality of noise filters on the insulating substrate and enclosing them in a single package, the propagation of noise generated from a transmission signal of a plurality of bits can be prevented by a single component.

In order to prevent the dielectric layer between the two spiral metal electrodes from being destroyed by static electricity, a discharge gap is provided between the electrodes, or a plurality of diodes connected in series are connected to each other to set a forward threshold voltage. All you have to do is operate it below or connect a Zener diode.

As the dielectric layer existing between the two spiral metal electrodes, 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 an extremely high bulk resistance as compared with metal conductors such as the spiral metal electrodes 3a and 6a, and can be sufficiently used as an insulating substrate. it can.

The noise filter of the present invention is a silicon filter.
If the wafer is configured as an insulating substrate, it can be manufactured, inspected, and packaged by a conventionally used integrated circuit manufacturing apparatus, and there is no need to provide new equipment.

[0033]

As is clear from the description based on the above embodiment, according to the noise filter of the present invention, the noise filter can be manufactured by a technique similar to the integrated circuit manufacturing technique, so that miniaturization is easy. It is suitable for mass production and can be manufactured at low cost without requiring new capital investment, and it is easy to obtain elements having various attenuation characteristics.

[Brief description of the drawings]

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

FIG. 2 is a plan view (a) and a cross-sectional view (b) of the noise filter manufactured in the process of FIG.

FIG. 3 is a sectional view showing a second embodiment of the noise filter according to the present invention;

FIG. 4 is a sectional view showing an example of a state in which a noise filter manufactured by the steps of the first and second embodiments is packaged;

FIG. 5 is a sectional view of a third embodiment of the noise filter according to the present invention;

FIG. 6 is a surface view showing an example of a conventional noise filter.
(a), side view (b), back view (c),

FIG. 7 is an equivalent circuit diagram of a conventional noise filter.

[Explanation of symbols]

1 Silicon wafer (insulating substrate) 2, 5 Silicon oxide film or silicon nitride film (dielectric layer) 3a, 6a Spiral metal electrode 3b, 3c, 6b Terminal electrode 4, 7, 7a Photoresist

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-108209 (JP, A) JP-A-2-280410 (JP, A) JP-A-2-215213 (JP, A) JP-A-2- 196406 (JP, A) JP-A-62-233911 (JP, A) JP-A-60-257161 (JP, A) JP-A-3-121720 (JP, U) Patent 2860211 (JP, B2) (58) Field (Int.Cl. ⁷ , DB name) H03H ⁷ /01-7/075 H01F 17/00 H01F 27/00 Patent file (PATOLIS)

Claims (7)

(57) [Claims] A first spiral electrode is formed on an insulating substrate, and the first spiral electrode is formed on the insulating substrate and on the first spiral electrode.
A dielectric layer is formed on the dielectric layer, and the first spa
A noise filter, wherein a second spiral electrode is formed so as to partially overlap the spiral electrode. 2. At least one of the spiral electrodes
2. The noise filter according to claim 1, wherein one end is grounded, and both ends of the other spiral electrode are connected in series to a transmission signal passage circuit to operate in a normal mode. 3. The noise filter according to claim 1, wherein both ends of the spiral electrode are connected in series to a transmission signal passage circuit to operate in a common mode. 4. The noise filter according to claim 1, wherein a high-purity semiconductor substrate is used as the edge substrate. 5. The noise filter according to claim 1, wherein a magnetic insulator substrate is used as the insulating substrate. 6. The noise filter according to claim 1, wherein a plurality of noise filters are formed on an insulating substrate and integrated. 7. The noise filter according to claim 1, wherein the noise filter is formed on a substrate on which an integrated circuit is formed.