JPH0567526A - Thin film inductor - Google Patents

Abstract

PURPOSE:To obtain a thin film inductor which has a high inductance and Q and can be used in a wide frequency band by successively forming coil conductor films and an insulating film on a magnetic substrate. CONSTITUTION:Coil conductor films 5 and an insulating film 4 are successively formed on a magnetic substrate 2. For example, after a Cu film having a thickness of 5mum is formed on the surface of a magnetic substrate 2 composed of an Ni-Zn ferrite by a sputtering method, the coil conductor films 5 are formed by patterning the Cu film. After forming the films 5, a photosensitive resin is applied to the surface of the substrate 2 including the films 5 and, after unnecessary parts are removed by exposure and development, the insulating film 4 having a thickness of 5mum is formed by heating and hardening the resin. Then, after a 'Permalloy(R)' film is formed by a sputtering method, a magnetic film 3 having a thickness of 3mum is formed by patterning the 'Permalloy(R)' film. Thereafter, a protective film 6 is formed by forming an Al2O3 film having a thickness of 3mum by a sputtering method after masking the surface of a section for terminals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film inductor, and more particularly to a high frequency thin film inductor.

[0002]

2. Description of the Related Art With the miniaturization and thinning of electronic equipment and communication equipment, miniaturization and integration of magnetic elements such as inductances and transformers have been promoted. Integration is delayed. At present, miniaturization of magnetic elements has been realized using thick film printing technology such as chip inductors. However, since the coil pattern produced by the thick film printing technique has low density and is porous, the electric resistance of the coil conductor portion is high. Also,
Since there is a problem that the tolerance of the obtained characteristics becomes large due to poor dimensional accuracy, there is a limit to integration.

Therefore, a thin film inductor and a transformer which can be integrated with high precision by using a thin film process such as a thin film forming technique or a photolithography technique have been considered.

Conventionally, a thin film inductor has a lower magnetic film 13 on a non-magnetic glass substrate 12 as shown in FIG.
1, the coil conductor film 15, the upper magnetic film 132, and the protective film 16 are sequentially provided, and the coil conductor film 15 is insulated from the upper and lower magnetic films by the insulating film 14. However, the thin film inductor having such a structure has the following problems.

Since the magnetic film is a thin film and the cross-sectional area of the magnetic circuit is small, the inductance is low.

When the coil conductor film is manufactured by the thin film technique, the conductor width and the conductor thickness are smaller than those of a normal winding, so that the resistance becomes large and the Q value (ωL / R) becomes low. Especially at 50 MHz or higher, R significantly increases due to the skin effect and the proximity effect, so that the Q is greatly reduced.

Since the insulating films are present between the coil conductor film and the lower magnetic film and the upper magnetic film, respectively, stray capacitance is generated between the coil conductor film and each magnetic film. As a result, resonance occurs and the inductor cannot be used above the resonance frequency. Since the resonance frequency becomes lower as the stray capacitance C becomes larger, it cannot be used for high frequencies.

[0008]

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and an object thereof is to provide a thin film inductor having a high inductance and a high Q and usable in a wide frequency band.

[0009]

The above objects are achieved by the present invention described in (1) to (7) below. (1) A thin film inductor comprising a coil conductor film on a magnetic substrate in contact with the magnetic substrate, and an insulating film on the coil conductor film.

(2) The thin film inductor according to (1) above, which has a protective film on the insulating film.

(3) The thin film inductor according to (1), wherein a magnetic film is provided on the insulating film, and the magnetic film and the magnetic substrate form a closed magnetic circuit.

(4) The thin film inductor according to (3) above, which has a protective film on the magnetic film.

(5) The thin film inductor according to any one of (1) to (4), wherein the magnetic substrate is made of Ni-Zn ferrite.

(6) The thin film inductor according to any one of (1) to (5), wherein the insulating film is made of a photosensitive resin.

(7) The thin film inductor according to any one of (1) to (6), which is used in a frequency band of 10 MHz or more.

[0016]

In the conventional thin film inductor 11 shown in FIG. 4, the lower magnetic film 131, the coil conductor film 15, the upper magnetic film 132 and the protective film 16 are sequentially provided on the glass substrate 12, and the lower magnetic film 131 is formed. And the upper magnetic film 132 form a closed magnetic circuit. Since the lower magnetic film 131 and the upper magnetic film 132 are made of a metal magnetic material having a low resistance such as permalloy, the insulating film 14 is provided between these magnetic films and the coil conductor film. However, for this reason, stray capacitance is generated between the coil conductor film and each magnetic film, and the resonance frequency becomes low.

On the other hand, in the thin film inductor 1 of the present invention shown in FIG. 1, the magnetic substrate 2 is the lower magnetic film 13 in FIG.
The function of 1 is added. Since the magnetic substrate 2 is made of a high resistance soft magnetic material such as Ni-Zn ferrite, the coil conductor film 5 and the magnetic substrate 2 can be in contact with each other as shown in the drawing. .. Therefore, according to the present invention, the lower magnetic film 131 in the configuration shown in FIG.
The stray capacitance between the coil conductor film 15 and the coil conductor film 15 is eliminated. As a result, the resonance frequency becomes high and it becomes possible to use frequencies up to the conventional one. Further, in the present invention, since the substrate can be used as a part of the magnetic path as shown in FIG. 1, a large inductance and a large Q can be obtained. That is, since the substrate is thick, the magnetic flux generated by passing a current through the coil conductor film can be sufficiently passed, so that the leakage magnetic flux is reduced and the inductance and Q are increased.

Further, in the structure shown in FIG. 1, if the insulating film 4 is made of a photosensitive resin, it becomes easier to make the element surface flat as compared with the case of being made of an inorganic material such as SiO ₂ . In addition, since the dielectric constant is smaller than that when an inorganic material is used, the resonance frequency is increased and pinholes and cracks are hardly generated. It should be noted that these effects of the present invention are also realized in the configuration shown in FIG.

[0019]

[Specific Structure] The specific structure of the present invention will be described in detail below. A preferred embodiment of the thin film inductor of the present invention is shown in FIGS.

The thin film inductor 1 shown in FIG. 1 has a coil conductor film 5 on the magnetic substrate 2 in contact with the magnetic substrate 2, and an insulating film 4 on the coil conductor film 5. The magnetic film 3 is provided on the film 4, and the magnetic film 3 and the magnetic substrate 2 form a closed magnetic circuit. Also, on the surface of the magnetic film 3,
A protective film 6 is provided.

Further, the thin film inductor 1 shown in FIG.
Has the same structure as the thin film inductor shown in FIG. 1 except that the magnetic film 3 is not formed and the protective film 6 is provided on the insulating film 4.

<Magnetic Substrate 2> The magnetic substrate 2 is made of a high resistance soft magnetic material, for example, a soft magnetic material having a specific resistance of 10 ⁵ to 10 ⁷ Ω · cm, particularly 10 ⁶ to 10 ⁷ Ω · cm. Preferably. As such a high resistance material, N
i-Zn ferrite is preferred.

The size of the magnetic substrate 2 is not particularly limited and may be appropriately determined according to the application. Usually, the thickness is about 0.2 to 2 mm, preferably about 0.5 to 1 mm, and one side. Is about 1 to 30 mm.

The magnetic substrate 2 may be manufactured by an ordinary sintering method or the like.

<Coil Conductor Film 5> The composition of the coil conductor film 5, the arrangement pattern of conductors, the arrangement density, the number of turns, etc. are not particularly limited and may be appropriately selected according to the required characteristics. For example, the thickness of the coil conductor film 5 is usually 1 to
It is preferably about 10 μm. The composition of the coil conductor film 5 is preferably Cu. However, when photosensitive polyimide is used for the insulating film 4, a Cr film is formed on the surface of the Cu film in order to improve the adhesiveness with the insulating film. It is preferably formed.

<Insulating Film 4> The insulating film 4 is made of an inorganic material such as SiO ₂ which is conventionally used in thin film inductors.
Although it may be made of Al ₂ O ₃ or various kinds of glass, it is preferably made of a photosensitive resin in the present invention. By using a photosensitive resin, it is possible to form an insulating film having fewer pinholes and a smaller dielectric constant than an inorganic material.

The photosensitive resin used in the present invention is not particularly limited, and may be appropriately selected from various positive and negative photosensitive resins.

The thickness of the insulating film 4 on the coil conductor film 5 may be appropriately determined, but is usually about 0.5 to 10 μm.

<Magnetic Film 3> The magnetic film 3 is in contact with the magnetic substrate 2 to form a closed magnetic circuit, and has the function of enhancing the performance as an inductor. In the present invention, the magnetic film 3 does not necessarily have to be provided, and may have a configuration as shown in FIG.

The magnetic film 3 is preferably made of a soft magnetic material having a high magnetic permeability. As such a soft magnetic material, for example, permalloy or a Co-based amorphous alloy such as Co-Nb-Zr-based or Co-Fe-Si-B-based is preferable.

The thickness of the magnetic film 3 is not particularly limited, but is usually about 2 to 6 μm.

<Protective Film 6> A protective film 6 is usually provided on the magnetic film 3. The protective film 6 is made of SiO ₂ or Al ₂ O ₃
And the like, and the thickness is preferably about 2 to 10 μm.

<Manufacturing Method> Next, a method of manufacturing the thin film inductor of the present invention will be described. First, a conductor film is formed on the surface of the magnetic substrate 2 by various thin film forming methods such as sputtering. Next, a photosensitive resin film is formed on the conductor film by spin coating, etc., the photosensitive resin is patterned by performing exposure and development, and the conductor film in the region where the photosensitive resin is removed is dry-etched with Ar ions. Remove by. Then, the photosensitive resin is peeled off and the coil conductor film 5 is removed.
And

Next, the insulating film 4 is formed on the coil conductor film 5. When the insulating film 4 is made of a photosensitive resin, first, the photosensitive resin film is formed by spin coating or the like. Then, exposure and development are performed to remove unnecessary portions, and heat curing is performed as necessary to form the insulating film 4.

Since the insulating film 4 is formed by using the coating method such as the spin coating method as described above, it is easy to flatten the element surface even when the coil conductor film 5 is thick.

When the insulating film 4 is made of an inorganic material such as SiO ₂ , the sputtering method may be used.

The magnetic film 3 is preferably formed by a thin film forming method such as a sputtering method. Like the coil conductor film 5, the magnetic film 3 is also formed into a predetermined shape by using a photosensitive resin and etching.

The protective film 6 provided on the magnetic film 3 is also preferably formed by a thin film forming method such as a sputtering method.
Although the protective film 6 is formed so as to cover the entire element, the requirements for shape and dimensional accuracy are not so strict that the terminal portion of the coil conductor film 5 may be masked at the time of sputtering in order to obtain a predetermined shape.

In the structure shown in FIG. 2, the insulating film 4 is used.
Although the protective film 6 is formed after the formation, the protective film 6 may not be formed when the insulating film is made of an inorganic material such as SiO ₂ .

The thin film inductor of the present invention manufactured in this manner can be used in a frequency band of 10 MHz or more, particularly 50 to 300 MHz.

[0041]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention. Example 1 A thin film inductor 1 of the present invention having the structure shown in FIG. 1 was produced.

[0042] The magnetic substrate 2 magnetic substrate 2, 25mm × 25mm × 1mm Ni -Zn ferrites (TDK manufactured K ₅ M material; mu = 300, resistor 2 × 1
0 ⁶ Ω · cm) was used.

Coil conductor film 5 A Cu film having a thickness of 5 μm is formed on the surface of the magnetic substrate by a sputtering method, a photosensitive resin is applied on the Cu film, and then exposure and development are performed for patterning, followed by dryness of Ar ions. The Cu film is etched by etching to form a coil conductor film 5 having a zigzag pattern as shown in FIG.
And The structure of the coil conductor film 5 was as follows, and four coil patterns were formed on the substrate.

Coil thickness: 5 μm Coil width Wc: 200 μm Coil interval Wd: 50 μm Turn length l: 5 mm Number of turns: 15

Insulating film 4 A photosensitive resin (Hoechst AZ-462) is formed on the coil conductor film 5.
0) is applied, exposed and developed to remove unnecessary portions, and then kept at 130 ° C. for 1 hour, further raised to 170 ° C. and kept for 1 hour, further raised to 300 ° C. for 3 hours. It was held and cured to form an insulating film 4. The coil conductor film 5
The thickness of the insulating film 4 between the upper surface of the and the magnetic film 3 was 5 μm.

Magnetic film 3 A permalloy (Ni ₈₀ Fe ₂₀ ) film is formed on the insulating film 4 by a sputtering method, a photosensitive resin film is formed on this film, and after patterning, etching is performed to form a magnetic film having a thickness of 3 μm. This was membrane 3.

Protective film 6 After the surface of the terminal portion of the coil conductor film 5 was masked, an Al ₂ O ₃ film was formed to a thickness of 3 μm by a sputtering method to form a protective film 6. After forming the protective film, it was cut into a size of 10 mm × 10 mm using a dicing saw to obtain four thin film inductors.

Comparative Example 1 A thin film inductor 11 having the structure shown in FIG. 4 was produced.

Glass Substrate 12 A non-magnetic glass substrate (7059 manufactured by Corning Incorporated) having the same dimensions as the magnetic substrate of Example 1 was used.

Lower magnetic film 131 It is formed in the same manner as the magnetic film 3 of Example 1, and has a thickness of 5 μm.
And

Insulating film 14 Before forming the coil conductor film 15, an insulating film having a thickness of 5 μm is formed in the same manner as the insulating film 4 of the first embodiment, and after forming the coil conductor film 15, the insulating film 4 of the first embodiment is formed again. The insulating film 14 was formed in the same manner as. The thickness of the insulating film existing between the upper surface of the coil conductor film 15 and the upper magnetic film 132 was 5 μm.

Coil Conductor Film 15 This was formed in the same manner as the coil conductor film 5 of Example 1.

Upper magnetic film 132 It was formed in the same manner as the magnetic film 3 of Example 1.

Protective film 16 It was formed in the same manner as the protective film 6 of Example 1.

<Evaluation> For each thin film inductor of Example 1 and Comparative Example 1, an impedance analyzer (HP
4285A), the inductances L and Q and the resonance frequency were measured. The results are shown in Table 1 below. In addition,
The measured value is an average value of four thin film inductors.

[0056]

[Table 1]

[Embodiment 2] The insulating film 4 was formed by the steps 1 to 3 of the above-mentioned Embodiment 1, and the protective film 6 was further formed by the steps to fabricate a thin film inductor having the structure shown in FIG.

Comparative Example 2 A thin film inductor was manufactured by forming the insulating film 14 through the steps 1 to 3 of Comparative Example 1 and further forming a protective film through the steps.

<Evaluation> The characteristics of each thin film inductor of Example 2 and Comparative Example 2 were measured in the same manner as in Example 1 above. The results are shown in Table 2 below.

[0060]

[Table 2]

[Third Embodiment] In the thin film inductor of the first embodiment, the material of each film is changed to the one shown below.

Insulating film: Toray Photo Nice (photosensitive polyimide)

However, as the coil conductor film, C having a thickness of 5 μm is used.
After forming the u film by sputtering, a 300 A Cr film is formed by sputtering to improve the adhesion between the coil conductor film and the insulating film, and then a photosensitive resin mask is formed and dry etching is performed The coil conductor film of the pattern was used.

Magnetic film: Co ₈₄ Nb _12.5 Zr _3.5 (μ = 2
000)

The magnetic film had a thickness of 5 μm, was formed by a sputtering method, and was then heat-treated at 200 ° C. for 1 hour in vacuum.

Comparative Example 3 Using the insulating film material and the magnetic film material used in Example 3, a thin film inductor having the structure shown in FIG. 4 was manufactured according to Comparative Example 1. However, a Cr film similar to that in Example 3 was formed above and below the coil conductor film. Further, the magnetic film was heat-treated in the same manner as in Example 3.

<Evaluation> The thin film inductors of Example 3 and Comparative Example 3 were evaluated in the same manner as in Example 1. The results are shown in Table 3 below.

[0068]

[Table 3]

From the above examples and comparative examples, the effects of the present invention are clear. That is, Table 1, Table 2 and Table 3
As shown in, the thin film inductor of the present invention has a large L and a high Q as compared with the inductor of the comparative example. And 30
It can also be used at a frequency of 0 MHz.

[0070]

According to the present invention, a thin film inductor having high inductance and Q and usable in a wide frequency band is realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a thin film inductor of the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of the thin film inductor of the present invention.

FIG. 3 is a plan view showing an example of a coil conductor film pattern of the thin film inductor of the present invention.

FIG. 4 is a sectional view showing an example of a conventional thin film inductor.

[Explanation of symbols]

 1 Thin Film Inductor 2 Magnetic Substrate 3 Magnetic Film 4 Insulating Film 5 Coil Conductor Film 6 Protective Film 11 Thin Film Inductor 12 Glass Substrate 131 Lower Magnetic Film 132 Upper Magnetic Film 14 Insulating Film 15 Coil Conductor Film 16 Protective Film

Claims (7)

[Claims] 1. A thin film inductor comprising a coil conductor film on a magnetic substrate in contact with the magnetic substrate, and an insulating film on the coil conductor film. 2. The protective film is provided on the insulating film.
The thin film inductor described in. 3. The thin film inductor according to claim 1, wherein a magnetic film is provided on the insulating film, and the magnetic film and the magnetic substrate form a closed magnetic circuit. 4. The protective film is provided on the magnetic film.
The thin film inductor described in. 5. The thin film inductor according to claim 1, wherein the magnetic substrate is made of Ni—Zn ferrite. 6. The thin film inductor according to claim 1, wherein the insulating film is made of a photosensitive resin. 7. The thin film inductor according to claim 1, which is used in a frequency band of 10 MHz or more.