JPH1093371A - Multiple thin film lc filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high efficiency in a thin film capacitor resulting in improving an entire efficiency of a thin film LC device. SOLUTION: In the multiple thin film LC filter consisting of a thin film inductor employing a thin film soft magnetic material and a thin film capacitor employing a thin film dielectric material 19, a structure of very thin comb-lines is adopted for a ground side electrode 18 and a signal side electrode 17 for each thin film capacitor so as to improve the nonuniformity of electric field thereby applying an electric field uniformly between the electrodes even at a high frequency band and improving the efficiency of the thin film capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a thin film inductor,
More particularly, the present invention relates to a lumped-constant multiple-layer thin-film LC filter constituted by a thin-film capacitor using a thin-film dielectric, and particularly to a thin-film LC filter using a high-efficiency thin-film capacitor. The thin-film inductors used here are an inductor using an air-core coil and a high-efficiency inductor using a thin-film magnetic material for a magnetic core. The thin-film capacitor has high efficiency characteristics using a low-loss dielectric, and a high-efficiency thin-film device can be obtained by using it together with the high-efficiency inductor.

[0002] Such a high efficiency thin film LC filter is
It is an electronic device used as a low-pass filter and a band-pass filter, and is used for the oscillating part of a high-frequency circuit and the receiving part of radio waves, and the electronic circuit that needs to prevent noise oscillating from the high-frequency circuit, And to adjust the capacitance of the thin film capacitor in a timely manner to obtain a predetermined filter characteristic or a desired characteristic in a built-in circuit.

[0003]

2. Description of the Related Art Conventionally, an air-core inductor is used as a multiple thin film LC filter, and a spiral coil and a meander coil are used in combination with a chip capacitor and a thin film capacitor. These thin-film LC components tend to be miniaturized with the integration of the systems used,
The chip inductor or chip capacitor component is 302
5 types, 2012 types, 1608 types, 1005
Type and 0530 type, and a small-sized thin-film component such as a thin-film inductor L or a thin-film capacitor has been required.

That is, the chip L and chip C elements are SMT
(Surface mounting technology), so its shape is constant. Therefore, if an electrical equivalent circuit such as the triple LC filter of FIG. 8 is configured by the chip L elements (L1, L2, L3) and the chip C elements (C1, C2, C3), as shown in FIG. When the 1608-based chip C element 23 and the 2012-based chip C element 24 were used, the element arrangement was limited, and the LC filter could not be reduced to the dimensions of individual single elements, 1608 and 2012. Further, the efficiency of the entire device is also limited by the efficiency of each device.

[0005] Therefore, when a thin film LC element is formed using the thin film L and thin film C elements, only necessary elements are arranged on the substrate, so that the size can be greatly reduced as compared with the chip LC element. As a result, a triple LC filter having dimensions of 3025 and 2012 can be formed.

Further, thin film devices are required to have high efficiency in order to cultivate new applications, and a structure in which only necessary elements can be directly arranged has a great merit in terms of increasing the efficiency of the entire device.

Generally, in a circuit design using a magnetic element such as a conventional LC filter, an inductance value and a capacitance value are prepared in advance in accordance with design values. The overall efficiency depends on the characteristics of the individual devices used, and even if several L and C components have high efficiency, if the efficiency of one device is low, the overall efficiency is reduced. Therefore, in thin film devices, high efficiency is required for thin film elements such as individual thin film inductors and thin film capacitors.

[0008]

First, comparing the air-core inductor and the magnetic-core inductor among the thin-film inductors,
To obtain the same inductance, the area of the air-core inductor and the number of windings are required to be about ten times that of the magnetic core inductor. Therefore, the thin film inductor using the air core has problems such as an increase in conductor resistance, low efficiency at low frequency, and susceptibility to stray capacitance caused by the coil. On the other hand, when a magnetic core inductor uses a soft magnetic thin film with high magnetic permeability, it is easy to obtain a large inductance with a small number of windings even at a low frequency. Because it is difficult, it becomes a small and highly efficient thin film inductor.

Next, in general, a thin film capacitor has a capacitance obtained by disposing a dielectric thin film between electrodes. There are several factors that affect the efficiency of a thin film capacitor, such as the composition of the dielectric thin film, the film quality, the electrode surface in contact with the dielectric,
Examples include a capacitor structure and an electrode shape. Especially 100
For an LC filter operating from MHz to several GHz,
There is a problem in that the efficiency of the capacitor is reduced due to the inhomogeneity of the electric field due to the inhomogeneity of the high-frequency current flowing through the electrodes. Therefore, it was necessary to improve the efficiency of the capacitor.

An object of the present invention is to obtain high efficiency in a thin film capacitor, and as a result, to improve the efficiency of the whole thin film LC device.

[0011]

In a thin film capacitor, a capacitance is generated by arranging a dielectric between electrodes, and when the area of the electrodes is large, a uniform electric field is generated between the electrodes by a DC electric field, but a high frequency band of GHz is used. In this case, the eddy current loss and skin depth (magnetic flux penetration depth) become thin, so that the electric field becomes non-uniform in the electrode surface. The non-uniformity is considered to be remarkable mainly at the center and the edge of the large area, and is estimated to be one of the causes of the reduction in the efficiency of the high frequency band of the thin film capacitor. Therefore, in the present invention, in a multiple thin film LC filter composed of a thin film inductor using a thin film soft magnetic material and a thin film capacitor using a thin film dielectric, the efficiency Q of the dielectric and insulator used is reduced by miniaturizing the electrodes and conductors. , The non-uniformity of the electric field is improved, the electric field is evenly applied between the electrodes even in a high frequency band, and the efficiency of the thin film capacitor is improved.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. The present invention is characterized by using a thin film inductor represented by a thin film coil as shown in FIG. 1 and a thin film capacitor having a thin film dielectric sandwiched between thin film conductors as represented by FIG. FIG. 3 shows an example of a plan view of a thin film triple LC filter using the thin films L and C handled in the present invention.

In FIG. 1, 5 is a magnetic material, 6 is a conductor coil, and 7 is a substrate. In FIG. 2, 8 is an upper electrode, 9 is a dielectric layer, 10 is a lower electrode, and 11 is a substrate. FIG.
12 is a thin film inductor (L1, L2, L3), and 13
Is a thin film capacitor (C1, C2, C3), 14 is a signal line electrode, and 15 is a ground line electrode.

The thin film triple LC filter shown in FIG.
Various coil shapes such as a solenoid (helix) type, a spiral type, and a meander type can be used for the coil portion of the inductor according to the inductance value. As shown in the schematic diagram, the capacitor section is configured such that an inductor and a capacitor are arranged adjacent to each other and are connected between conductors connecting L1 and L2 like C1 or L2 and L3 like C2. There are various forms such as a connecting conductor serving as a capacitor or being formed on an electrode portion like C3.

In such a thin film capacitor of the multiple thin film LC filter, the electrode portion is divided into a comb shape or a step shape so that an eddy current distribution at a center portion and an end portion of the electrode in a high frequency band is different. Suppress the inhomogeneity of the resulting electric field,
The efficiency of the thin film capacitor can be improved.

FIGS. 4 and 5 show a thin film capacitor having a comb-shaped electrode and a stepped electrode according to the present invention. 16 is a substrate, 17
Is a signal line electrode and a step-like electrode, 18 is a comb capacitor electrode of the present invention, and 19 is a thin film dielectric. FIG. 4 shows that the electrode on the signal line side is integrated and the capacitor electrode side is comb-shaped.
Has a step-like electrode on the signal line side and a comb-like electrode on the capacitor electrode side.

Hereinafter, the effect obtained by improving the efficiency of the thin film capacitor in the thin film LC filter having the above thin film capacitor will be described. The thin film capacitor has a comb-shaped electrode, on which a dielectric thin film is formed, and further, an electrode also serving as a signal line is formed. FIG.
7 is a sectional view of the thin film capacitor of the present invention. In FIG. 6, the signal lines are formed without division, whereas in FIG. 7, the signal lines disposed above are divided in a stepwise manner.
In the case of FIG. 6, the electrodes are arranged so that the signal lines surround the electrodes, so that the eddy current around the lower electrode is divided for each electrode, and the generation of an electric field to the electrodes is effective.

On the other hand, in FIG. 7, since the upper electrode is arranged in a stepwise manner corresponding to the lower comb-like electrode, inhomogeneity of the electric field due to the generation of the eddy current hardly occurs. However, efficiency is improved. Further, FIG. 6 shows that the lower electrode is covered by the upper signal line electrode, so that the thickness of the dielectric layer between the electrodes is not uniform and the thin film capacitance value varies, or the electrodes are likely to be short-circuited. In No. 7, since the electrode surface is flat, uniformity of the electrode thickness is maintained, and there is little problem such as short circuit. Therefore, it is more effective to make the ground-side electrode comb-shaped, and further to make the signal-side electrode stepwise in accordance with the ground-side electrode.

The multi-layered thin film LC filter according to the present invention improves the characteristic efficiency of the thin film capacitance so that a large amount of attenuation cannot be obtained due to low efficiency.
Since steep attenuation characteristics cannot be obtained, it can be applied to new application fields that could not be used. That is, there are thin-film filters such as a low-pass filter and a band-pass filter. For example, ± 30 MH, which is weak in conventional surface acoustic wave filters
It can also be used in the field of a wideband bandpass filter of about z. That is, the hermetic seal of the surface acoustic wave filter is a component necessary for covering the surface acoustic wave element portion, and is a factor of cost increase. In this regard, the multiple thin film LC filter according to the present invention uses the same thin film process as the surface acoustic wave filter for the manufacturing process, but has no cost increase factors such as hermetic sealing and is low in cost. Further, the overall thickness of the thin film LC filter is as thin as several tens of μm, which is two orders of magnitude smaller than the thickness of several mm of the hermetic seal. As a result, the size of the entire system can be reduced.

Next, the downsizing of the system is closely related to the higher operating frequency, and high frequency noise is generated. That is, because of the miniaturization, a high frequency propagates between adjacent strip lines, and noise enters other unrelated signal lines and power supply lines. Several hundreds of these noises are reduced.
The thin film LC filter of the present invention, which exhibits a high attenuation of −30 dB in a wide band of MHz to 2 GHz, is effective.

[0021]

An embodiment of the present invention will be described below. As a thin film capacitor, a conventional thin film capacitor including a flat plate electrode and a thin film capacitor including a comb-shaped electrode according to the present invention (FIG. 4)
) Were manufactured, and filter characteristics were compared and examined.
Thin film triple LC consisting of the equivalent circuit of FIG. 8 manufactured by the present invention
In the filter, the value of the thin film inductor used is L1 = 15.
0nH, L2 = 150nH, L3 = 150nH,
The thin film capacitor has C1 = 30 pF, C2 = 13 pF,
It was adjusted to have a value of C3 = 14 pF, and was manufactured in a thin film process. The width of the comb-shaped electrode can be 50 to 500 μm, but this time, the width is 500 μm, and the width between the electrodes is 20 to 100 μm.
It was set to 100 μm for a possible set value of μm.

FIG. 1 shows the obtained low-pass filter characteristic results.
0. As can be seen from FIG. 10, the conventional plate electrode has a low Q value of about 10, so that when a low-pass filter is formed, the cutoff of filter characteristics from 100 MHz to 200 MHz is poor. On the other hand, in the thin film capacitor according to the present invention, the Q value was improved to about 50 when the electrode on the ground side was formed in a comb shape and the electrode on the signal side was covered thereon.
As a result, as shown in FIG. 10, the cutoff of the filter characteristics around 200 MHz was greatly improved.

Next, as a thin film capacitor, a thin film capacitor having a conventional flat plate electrode and a thin film capacitor having a comb-like ground side electrode and a step-like signal side electrode as shown in FIG. . FIG.
FIG. 1 shows the measurement results of the triple LC filter characteristics. The values of the thin films L and C are the same as in the embodiment. The width of the comb electrode on the ground side is 50 to 500 μm as in the first embodiment.
Is 500 μm with respect to the settable width of
Was set to 100 μm for a settable width of from 100 μm. The electrode on the signal side is formed narrower than the electrode on the ground side so as to form a film on the electrode on the ground side. As a result, the width of the electrode on the signal side becomes wider.

As can be seen from FIG. 11, the thin film C of the present invention has a Q value improved to about 100 as compared with the conventional flat plate electrode, so that the filter characteristic is cut off from 100 MHz to 200 MHz and the gain is further increased. Was.

[0025]

According to the equivalent circuit of the triple LC filter as shown in FIG. 1, an integrated thin film LC filter is manufactured using a thin film process, and the filter characteristics, attenuation and attenuation band are evaluated to evaluate the effect of the present invention. confirmed. Each value shown in the figure is a representative example, C1 to C3 are capacitance values of a thin film capacitor, and L1 to L3 are inductance values of a thin film inductor. Specifically, FIG. 4 shows a schematic plan view thereof.

According to the present invention, as shown in FIG.
By adopting a configuration in which two or three thin film spiral coils are arranged in series and thin film capacitors are arranged between thin film inductors, high efficiency is obtained in the thin film capacitor, and as a result, the efficiency of the whole thin film device is improved. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing a typical thin-film inductor element.

FIG. 2 is a perspective view showing a typical thin film capacitance.

FIG. 3 is a schematic diagram of a thin film triple LC filter using thin films L and C.

FIG. 4 is an external perspective view of a comb-shaped electrode thin film capacitor.

FIG. 5 is a configuration diagram of a thin-film capacitor including comb-like and step-like electrodes.

6 is a cross-sectional view of the comb-shaped electrode thin film capacitor of FIG.

FIG. 7 is a cross-sectional view of the comb-like and step-like electrode thin film capacitors of FIG.

FIG. 8 is an equivalent circuit diagram of a triple LC filter.

FIG. 9 is a schematic diagram of an arrangement of L elements and C elements of a triple LC filter equivalent circuit wiring.

FIG. 10 is a characteristic diagram showing a comparison of characteristics of a triple LC filter using a thin film capacitor including a conventional flat plate electrode and a comb-shaped electrode of the present invention.

FIG. 11 is a characteristic diagram showing a comparison of characteristics of a triple LC filter using a conventional flat plate electrode and a thin film capacitor including a comb-like electrode and a step-like electrode of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 5 Magnetic body 6 Conductor coil 7 Substrate 8 Upper electrode 9 Dielectric layer 10 Lower electrode 11 Substrate 12 Thin film inductor 13 Thin film capacitor 14 Signal line electrode 15 Ground line electrode

Claims (2)

[Claims] 1. A multi-layered thin film LC filter, wherein a ground side and a signal side electrode of the thin film capacitor have a structure miniaturized in a comb or step shape.
C filter. 2. The method according to claim 1, wherein when forming the signal line on or around the electrode structure miniaturized in the shape of a comb or step, the capacitor electrode miniaturized in the shape of a comb or step is connected to the signal line. A multi-layer thin film LC filter, wherein a film is arranged so as to enclose the same.