JPH0621533A - Noise filter - Google Patents

Abstract

PURPOSE:To obtain a noise filter, which is very small-sized and has superior noise suppressing characteristics. CONSTITUTION:A noise filter is made utilizing the technique of manufacturing an integrated circuit element, spiral epitaxial layers 2a having a second conductivity type (an N-type) opposite to the first conductivity type (a P-type) are formed on a semiconductor wafer 1 having the first conductivity type and a spiral electrode 6a is formed on the spiral epitaxial layer 2a via a dielective film 3. The end part of the spiral epitaxial layer 2a is connected to a reference potential point via a lead-out electrode 8 and both ends of the spiral electrode 6a are connected to a transmission signal passing circuit.

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.

An example of a conventional noise filter is proposed in Japanese Patent Laid-Open No. 233911/1987, and FIG.
, A pair of spiral electrodes through the dielectric 20
21 and 22 are arranged facing each other, and both terminals of one spiral electrode 21
23 and 24 are inserted in series in the transmission signal passing circuit, and one end 25 of the other spiral electrode 22 is grounded. And FIG.
As shown in the equivalent circuit of, a pair of spiral electrodes 21, 22
A distributed capacitor is formed between the two, and a low pass filter with a sharp cutoff is obtained by the inductance of the spiral electrode 21 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 20, and a 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 has been conceived in order to obtain a noise filter which is extremely small and has excellent noise blocking characteristics by utilizing the manufacturing technology of integrated circuit elements.

[0007]

A semiconductor wafer of a first conductivity type is provided with a spiral epitaxial layer of a second conductivity type opposite to the first conductivity type, and a dielectric film is interposed therebetween. A spiral electrode is formed on the spiral epitaxial layer, an end of the spiral epitaxial layer is connected to a reference potential point, and both ends of the spiral electrode are connected to a transmission signal passing circuit.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The noise filter of the present invention will be described in the order of manufacturing steps. As shown in the sectional view of FIG. A crystalline wafer substrate 1 is prepared, and (2) an epitaxial layer 2 of a second conductivity type (for example, N type) opposite to the first conductivity type is grown on the wafer substrate 1, (3) The wafer substrate 1 is exposed to a high temperature oxidizing atmosphere to form a silicon oxide film 3 on the surface of the epitaxial layer 2.

(4) The silicon oxide film 3 is formed by photolithography.
The photoresist is formed on the portion where the extraction electrode is to be formed.
A pattern of 4a is formed, and (5) the photoresist 4a is used as a mask to remove the silicon oxide film 2 to form an opening 5, and then the photoresist 4a is washed off.

(6) By evaporating aluminum in a vacuum,
An aluminum film 6 is deposited on the oxide film 3 and on the openings 5.

(7) Aluminum film 6 is formed by the photolithography method.
A pattern of the spiral photoresist 4b and a pattern of the extraction electrode of the photoresist 4c are formed on the opening 5 and (8) the photoresist 4b, 4c is used as a mask to form the silicon oxide film 3 and the epitaxial layer. After removing 2, photoresists 4b and 4c are washed off.

In this way, the spiral aluminum pattern electrode 6a is formed on the spiral epitaxial layer 2a through the oxide film 3, and the extraction electrode 8 is formed at the end of the spiral epitaxial layer 2a. To do.

The noise filter element formed on the silicon single crystal wafer through the above steps has a planar shape as shown in the plan view of FIG. 2. The noise filter element is divided from the wafer for mounting, and the spiral is formed. Both ends of the aluminum pattern electrode 6a and the extraction electrode 8 are bonded and housed in a case.

When using the noise filter element having such a structure, a direct current voltage is applied between the silicon single crystal wafer substrate 1 and the epitaxial layer 2a via the extraction electrode 8 so that a reverse bias is applied. When applied, the two are in an insulating state, and the spiral epitaxial layer 2a and the spiral aluminum pattern electrode 6a form a spiral electrode which is opposed to and is opposed to the silicon oxide film 2 serving as a dielectric. To do.

The extraction electrode 8 is connected to a positive or negative reference potential point of the power source, the end of the spiral epitaxial layer 2a is grounded in an alternating current, and the spiral aluminum pattern electrode 6a is connected to the transmission signal passing circuit. Inserted in series,
The aluminum pattern electrode 6a can form a distributed constant circuit due to the presence of the epitaxial layer 2a that is grounded in an alternating current, and can prevent the propagation of high frequency noise.

The epitaxial layer 2a has a bulk resistance. By adjusting the bulk resistance by changing the thickness and / or width of the epitaxial layer 2a and the impurity concentration, the Q of the distributed constant circuit can be adjusted. it can.

When the Q is high, the attenuation characteristic has a sharp attenuation or resonance point at a specific frequency, but when the Q is low, uniform attenuation can be obtained over a wide frequency band, and thus the spiral is obtained. -Shaped epitaxial layer
By selecting the lengths of 2a and the spiral pattern electrode 6a, the thickness of the oxide film 3, etc., a desired attenuation-specific noise filter can be obtained.

When the voltage of the transmitted signal to be passed is always reverse biased with respect to the substrate 1 of the wafer, the aluminum pattern electrode 6a can be grounded and the transmitted signal can be passed to the epitaxial layer 2a. In this case, when a forward bias surge voltage is generated, the surge voltage can be bypassed to the wafer substrate 1.

By increasing the purity of the silicon single crystal wafer substrate 1 and increasing its specific resistance, it is possible to reduce the influence of capacitive coupling on the epitaxial layer 2a.

(Other Embodiments) The noise filter of the present invention can be used as a component by housing a single element in a case, but as a part of an integrated circuit formed on a semiconductor wafer substrate, a noise filter is used. It can be used by forming a filter and connecting it to a power supply circuit or a transmission signal passing circuit.

If the waveform is distorted by passing the signal through the noise filter constructed as described above, a buffer circuit for performing the Schmitt trigger operation may be provided in a part of the integrated circuit to perform the waveform shaping. It's good.

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

[0023]

As is clear from the description based on the above embodiments, the noise filter of the present invention can be manufactured by a technique similar to that of an integrated circuit, which facilitates miniaturization and mass production. , It is possible to manufacture at low cost, and it is easy to obtain desired damping characteristics.

[Brief description of drawings]

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

FIG. 2 is a plan view of the noise filter of the present invention,

3 (a) is a front view, FIG. 3 (b) is a side view, and FIG. 3 (c) is a rear view showing an example of a conventional noise filter.

FIG. 4 is an equivalent circuit diagram of a conventional noise filter.

[Explanation of symbols]

 1 Silicon Single Crystal Wafer Substrate 2 Epitaxial Layer 2a Spiral Epitaxial Layer 3 Oxide Film 5 Openings 6 Aluminum Film 6a Spiral Aluminum Pattern Electrode 8 Extraction Electrode

Claims (4)

[Claims] 1. A semiconductor wafer of the first conductivity type is provided with a spiral-shaped epitaxial layer of a second conductivity type opposite to the first conductivity type, and the spiral-shaped epitaxial layer is formed through a dielectric film. A spiral electrode is formed on the epitaxial layer, an end of the spiral epitaxial layer is connected to a reference potential point, and both ends of the spiral electrode are connected to a transmission signal passing circuit. noise·
filter. 2. A semiconductor wafer of the first conductivity type is provided with a spiral-shaped epitaxial layer of a second conductivity type opposite to the first conductivity type, and the spiral-shaped epitaxial layer is formed via a dielectric film. Forming a spiral electrode on the epitaxial layer, connecting it to a circuit that allows a transmission signal to be a reverse bias to pass through the spiral epitaxial layer, and connecting the end of the spiral electrode to a reference potential point. Noise filter characterized by. 3. A noise filter is formed as a part of an integrated circuit formed on a semiconductor wafer and is used by being connected to a power supply circuit or a transmission signal passing circuit. The described noise filter. 4. The noise filter according to claim 1, wherein a plurality of noise filters are formed on a semiconductor wafer substrate and are housed in a single case.