JPH06124843A - High frequency use thin film transformer - Google Patents

Abstract

PURPOSE:To miniaturize a high frequency use thin film transformer and improve the performance by suppressing inductance reduction and the rapid increase of high frequency conductor resistance and improving the coupling between primary and secondary conductors. CONSTITUTION:Top and bottom magnetic layers 8 and 14 are connected at a through hole 15 and a primary and a secondary conductors 10 and 12 are permitted to be covered vertically and horizontally in the longitudinal direction by a magnetic body which has a closed magnetic circuit. The closed magnetic circuit structure remarkably reduces diamagnetic field, which causes inductance deterioration, in the magnetic layers 8 and 14, permits the interval between the adjacent conductors to be extremely small and the thin film transformer is miniaturized. At the same time, leakage flux is reduced, a rapid increase of the high frequency conductor resistance due to eddy current generated by the interlinkage of the leakage flux and the conductors 10 and 12 is suppressed and a high Q value is allowed. Primary side and secondary side conductors 8 and 14 are arranged in the closed magnetic circuit structured magnetic body and a high coupling coefficient is allowed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductor / transformer which is suitable for a converter, a switching power supply, etc. and has a small size and excellent high frequency characteristics.

[0002]

2. Description of the Related Art In recent years, demands for downsizing and weight reduction of electronic equipment components are strict, and downsizing is an essential issue even in switching power supplies and the like that can obtain high-quality power. Miniaturization has been promoted by making components such as transformers and capacitors smaller.
In semiconductor components and capacitor components, thin film technology has been used for a long time, as represented by LSI and multilayer ceramic capacitors, and has sufficiently met the demand for miniaturization of component parts.
On the other hand, transformers are the most difficult to miniaturize so far, and it is difficult to suppress the increase in loss due to higher frequencies, which was the first cause of hindering the miniaturization of power supplies. Therefore, it is no exaggeration to say that the volume of the high-frequency switching power supply is currently determined by the transformer. Therefore, in recent years, research on a thin film transformer using a thin film forming technique has been advanced in order to cope with higher frequencies, and development of a small power source in which a switching frequency is increased to a MHz band has been strongly desired.
(For example, T.YACHI, M.MINO, A.TAG
O, and K. YANAGISWAWA, PESC'9
1 RECORDS, pp. 20-26, 1991,
Yamaguchi, Onuma, Imagawa, Torio, The Institute of Electrical Engineers of Japan, MAG
-91-62, 1991. FIG. 8 is a plan view of a zigzag folded thin film transformer manufactured by a conventional thin film forming technique (a).
And a schematic view (b) taken along the line XX 'of the plan view. In the figure, 1 is a substrate, 2 is a lower magnetic layer, 3 is a primary-side conductor, 4 is a secondary-side conductor, 5 is an upper magnetic layer, and each layer is formed through an insulating layer and is insulated from each other. Has been done. Conventionally, the fabrication of this type of thin film transformer has been performed as follows. That is, the substrate 1 having an insulating surface
On top of Permalloy, CoZrRe, CoZrNb, Co
A magnetic layer of FeSiB or the like is formed by a thin film forming method such as a sputtering method, and is patterned to form a flat lower magnetic layer 2
Forming an insulating layer on top of which a photoresist, Si
Made of O ₂ , SiO, Al ₂ O ₃ , polyimide resin, etc.,
After this is flattened, a conductor layer of Cu, Ag, Al or the like is formed by an electron beam evaporation method, a sputtering method or the like, and patterned to form a zigzag-shaped primary conductor 3. Further, an insulating layer is again formed on this and flattening is performed. And 1
A through hole is formed in the external connection terminal portion of the secondary conductor 3 by an ion beam etching method or the like, and a window of the terminal portion is opened. Further, a conductor layer is formed by an electron beam vapor deposition method, a sputtering method or the like, and the through hole portion is filled and patterned to form a zigzag-shaped secondary conductor 4. Then, an insulating layer is formed thereon and planarized, then a magnetic layer is formed and patterned to form a flat upper magnetic layer 5. Finally, a window is opened in the external terminal portion of the primary side and secondary side conductor layers by an ion beam etching method or the like to complete. In the thin film transformer manufactured in this way, 1
The coupling between the secondary conductor 3 and the secondary conductor 4 is performed by connecting the upper and lower magnetic layers 2, 2.
The structure is such that they are coupled by the leakage flux between the five.

[0003]

FIG. 9 is a cross-sectional view showing the magnetic field distribution of the above-mentioned zigzag-shaped thin film transformer of the conventional example. The magnetic flux distribution generated when a current is passed through the primary side conductor 3 is indicated by arrows. It is shown in. In addition, in the figure

[0004]

[Equation 1]

The former represents the direction of current flowing from the back side of the paper to the front side in the vertical direction of the paper surface, and the latter represents the opposite direction. In such a thin-film transformer, as shown in the figure, since currents antiparallel to each other flow in the adjacent conductors, the magnetic fields from the conductors 3 and 4 cause the magnetic layers 2 and 5 to be antiparallel to each other. It is divided into regions where a magnetic field is generated, so that the inductance reduction due to the demagnetizing field appears. Therefore, if the conductor spacing is large, the problem is relatively small, but if the spacing between adjacent conductors is narrowed in order to reduce the size, the inductance will drop significantly, which is extremely important in developing a small zigzag thin film transformer. It was a big problem. In addition, the magnetic flux leaking between the upper and lower magnetic layers 2 and 5 intersects with the conductors 3 and 4, whereby
The eddy current was generated during the period 4, causing a rapid increase of the conductor resistance at high frequency, and was a factor of decreasing the performance characteristic value Q value (ωL / R). Further, since the primary side conductor 3 and the secondary side conductor 4 are coupled by the magnetic flux flowing between the upper and lower magnetic layers 2 and 5 having a large gap, the coupling as a transformer is small. For this reason, the zigzag structure is not suitable for small thin film transformers, and research and development is currently being carried out mainly on spiral structure thin film transformers and spiral coil thin film transformers, which have a large effect on downsizing. (For example, T.YACHI, M.MINO, and K.YA
NAGISAWA, PESC'91 RECORDS,
pp. 20-26, 1991. Yamaguchi, Onuma, Imagawa,
Toriu, The Institute of Electrical Engineers of Japan Material, MAG-91-62, 19
91. ).

In order to overcome the above-mentioned problems and to reduce the size and improve the performance of the thin film transformer, the present invention suppresses the reduction of the inductance and the rapid increase of the conductor resistance at high frequency, and the primary and secondary side conductors. It is an object of the present invention to propose a new structure which can improve the coupling between the two and is particularly suitable for a zigzag thin film transformer.

[0007]

In order to achieve the above object, in the high frequency thin film transformer of the present invention, the shape of the magnetic body, that is, the magnetic layer forming the transformer is made uneven, and the upper and lower magnetic layers form a conductor longitudinal direction. The upper and lower left and right sides of the conductor are surrounded by a magnetic body having a closed magnetic circuit structure, and further, in the above-mentioned configuration, to enhance the coupling between the primary and secondary side conductors. In addition, the primary side conductor or the secondary side conductor has a rectangular coaxial cross-section structure surrounding the upper and lower sides of the secondary side conductor or the primary side conductor in the longitudinal direction.

[0008]

In the high frequency thin film transformer of the present invention, the magnetic layers to be formed are made uneven, and the upper and lower magnetic layers surround the upper and lower sides of the conductor in the longitudinal direction, and the conductor is surrounded by a magnetic material having a closed magnetic circuit structure. Have a structure. As a result, the demagnetizing field in the magnetic layer, which has been a cause of inductance reduction, is significantly reduced by using a closed magnetic circuit structure, and the spacing between adjacent conductors is made extremely small, reducing the size of the zigzag thin film transformer. Enable At the same time, by making the magnetic body a closed magnetic circuit structure, the leakage flux is reduced, and the surge of the conductor resistance at high frequencies due to the eddy current generated by the leakage flux and the conductor intersecting each other is suppressed, and the transformer having a high Q value is suppressed. Can be provided. On the other hand, in comparison with the conventional thin film transformer in which the primary and secondary conductors of the transformer are coupled by the leakage magnetic flux between the upper and lower magnetic layers having the open magnetic circuit structure, the primary in the magnetic body of the closed magnetic circuit structure is increased. The coupling coefficient of the thin film transformer is improved by adopting a structure in which the side / secondary side conductors are installed. Furthermore, by making the structure of the conductor a rectangular coaxial sectional shape, the coupling between the primary side and the secondary side is further improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

[Embodiment 1] FIG. 1 is a plan view (a) of a thin film transformer showing a first embodiment of the present invention and a schematic view (b) taken along the line YY 'of the plan view. In the figure, 6 is a substrate, 7 is an insulating layer, 8 is a lower magnetic layer, 9 is an insulating layer, 10 is a primary side conductor, 11 is an insulating layer, 12 is a secondary side conductor, 13 is an insulating layer, and 14 is an upper part. Magnetic layer, 15 is a through hole of the magnetic layer, 16 and 17 are primary side external connection terminals, 18 and 19
Is a secondary side external connection terminal.

Next, the manufacturing method of this embodiment will be described in detail. First, SiO 2 is formed on the substrate 6 by sputtering or the like.
An insulating layer 7 such as ₂ is formed. On top of that Permalloy, Co
A magnetic film of ZrRe, CoFeSiB or the like is deposited by a sputtering method or the like and patterned by an ion beam etching method or the like to form the lower magnetic layer 8. Then, the same as above
O ₂ or the like is deposited and a flattening process is performed to form the insulating layer 9. Subsequently, a conductor layer of Cu or the like is formed on the insulating layer 9 by an electron beam vapor deposition method or the like, and the conductor layer is patterned by an ion beam etching method or the like to form a primary conductor 10 having a zigzag shape. At this time, the primary side external connection terminal 1
6 and 17 are manufactured at the same time. Then, the same as above
O ₂ or the like is deposited and flattening treatment is performed to form the insulating layer 11.
At this time, through holes penetrating the insulating layer 11 are formed in the external connection terminals 16 and 17 of the primary side conductor 10 by an ion beam etching method or the like. After that, a conductor layer of Cu or the like is formed on the insulating layer 11 by an electron beam evaporation method or the like to fill the through holes, and the conductor layer is patterned by an ion beam etching method or the like to form a zigzag shape. The secondary conductor 12 is formed. At this time, the external connection terminals 18 and 19 of the secondary conductor are simultaneously manufactured. Further, similarly to the above, SiO ₂ or the like is deposited and flattened to form the insulating layer 13. Then, in order to connect the upper and lower magnetic layers, a through hole portion 15 penetrating the insulating layers 9, 11, and 13 in the adjacent void portion of the conductor 12 and the outer peripheral portion of the conductor.
Are formed by ion beam etching or the like. FIG. 2 shows a pattern diagram of the through hole portion 15. Further, a magnetic film is formed by a sputtering method or the like to form a magnetic layer in the through hole portion 15 and the magnetic layer is patterned to form the upper magnetic layer 14. Finally, through holes penetrating the insulating layer 13 are formed in the terminals 16 to 19 of the zigzag-shaped conductors 10 and 12 as external terminals to obtain the thin film transformer of the present invention.

The operation of the embodiment configured as described above is shown in FIG.
This will be described in comparison with the conventional example. In this embodiment, the upper and lower magnetic layers 8 and 14 are continuous with each other so as to surround the primary and secondary side conductors vertically and horizontally in the longitudinal direction by the through hole portion 15 to form a closed magnetic circuit structure. FIG. 3 shows a case where the magnetic film permeability, the conductor width, the conductor thickness, and the magnetic film thickness of the magnetic layer constituting the thin film transformer are constant and the conductor spacing on the left and right adjacent primary or secondary sides is changed. FIG. 6 is a diagram in which the relationship between the inductance value and the conductor spacing is calculated, and the cases of the present embodiment and the conventional example are shown together.

In the calculation of the inductance, a magnetic path that circulates around each conductor is assumed, the magnetic resistance R thereof is calculated, and the reciprocal of the sum thereof is calculated. The magnetic resistance R can be expressed by the following equation.

[0014]

[Equation 2]

Where ι is the length of the magnetic material, μ ₀ is the magnetic permeability of the vacuum,

[0016]

[Equation 3]

Is the relative permeability of the magnetic material, and A is the cross-sectional area of the magnetic material. Further, in the calculation, only the primary side conductor was used and the influence of the secondary side conductor was ignored.

First, in a zigzag thin film transformer having a conventional structure, a magnetic path is assumed as shown in FIG.
Calculate _{1 to} R ₄ .

[0019]

[Equation 4]

Since there are 2N conductors 101, the required inductance L is

[0021]

[Equation 5]

It is expressed as follows. Where N is the number of zigzag turns of the conductor 101, a is the length of one side of the zigzag square thin film transformer, t _m is the thickness of the magnetic film of the magnetic layer 102, and g is the upper and lower magnetism through the insulating layer 100. The gap of the layer 102, μ ₀ is the magnetic permeability of the vacuum,

[0023]

[Equation 6]

Is the relative magnetic permeability of the magnetic layer 102.

Further, in the case of the structure of the present invention, FIG.
Assuming a magnetic path as shown in (b), the calculation is performed by approximating the conductor 101 with a length of 2 aN covering the magnetic layer 102.

[0026]

[Equation 7]

Then,

[0028]

[Equation 8]

Here, N is the number of zigzag turns of the conductor 101, a is the length of one side of the zigzag square thin film transformer, t is the covering thickness of the magnetic layer 102, and g ′ is the conductor 101.
And the thickness of the insulating layer 100, μ ₀ is the magnetic permeability of the vacuum,

[0030]

[Equation 9]

Is the relative permeability of the magnetic layer 102, and d is the conductor 10.
1 is the width of the insulating layer 100 that surrounds 1.

The conductor spacing [m in FIG. 3 obtained from the above equation
In the graph showing the relationship between [m] and the inductance [H], the solid line indicates the calculated value of the inductance according to the technique of the present invention, and the ● mark indicates the measured value. On the other hand, the broken line indicates the calculated value of the inductance according to the conventional technique. In the prior art, currents that are antiparallel to each other flow in adjacent conductors, and therefore the magnetic field from the conductors divides the magnetic layer into regions where magnetic fields that are antiparallel to each other are generated. It will decrease significantly. On the other hand, in this example, the decrease in inductance due to the demagnetizing field in the magnetic layer, which is seen in the prior art, is not seen,
On the contrary, the inductance increases until the conductor spacing is about 20 μm. The actual measurement data shows a value slightly larger than the calculated value because the calculation does not consider the inductance of the air core.

Further, as a result of comparing the coupling coefficient between the primary side and the secondary side, it was about 0.1 to 0.2 in the prior art, but it is extremely high from 0.90 to 0.96 in this embodiment. A high value was obtained.

As described above, the present technique is superior to the conventional technique in all measured ranges, and it is possible to reduce the size by narrowing the conductor pitch, which is difficult with the conventional technique, and narrowing the pitch. At the same time, since the leakage flux between the upper and lower magnetic layers is significantly reduced, the conductor resistance is not sharply increased due to the leakage flux, and the coupling coefficient is significantly improved.

[Second Embodiment] A second embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 4 is a plan view (a) of the thin film transformer showing the configuration and Z of the plan view.
It is a schematic diagram (b) of a -Z 'sectional structure. In the figure, 20 is a substrate, 21 is an insulating layer, 22 is a lower magnetic layer, 23 is an insulating layer,
24 is a primary side conductor, 25 is a secondary side conductor, 26 is an insulating layer,
27 is an upper magnetic film, 28 is a through hole portion of the magnetic layer, 5
Reference numerals 0 and 51 are primary side external connection terminals, and 52 and 53 are secondary side external connection terminals. A pattern diagram of the through hole portion 28 for connecting the upper and lower magnetic layers is shown in FIG. 5 as in the first embodiment. The difference from the first embodiment is that the primary conductor and
The arrangement of the next-side conductor is changed from the vertical arrangement to the horizontal arrangement to simplify the conductor forming process.
Is common by a through hole portion 28 to form a closed magnetic circuit structure that surrounds the upper and lower sides of the primary and secondary side conductors 24 and 25 in the longitudinal direction.

In the embodiment constructed as described above, although the inductance value is slightly reduced as compared with the first embodiment,
The coupling coefficient of the transformer is 0.90 as in the first embodiment.
A value of 0.96 is obtained. As described above, the effects of the present invention can be obtained even if the primary side / secondary side conductors are horizontally arranged and the process is simplified, and miniaturization can be achieved by narrowing the conductor spacing and narrowing the pitch, which has been difficult in the prior art. It is possible. At the same time, the leakage flux between the upper and lower magnetic layers 22 and 27 is remarkably reduced, so that the conductor resistance is not sharply increased due to the leakage flux and the coupling coefficient is remarkably improved.

[Embodiment 3] A third embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 6 is a plan view (a) of the zigzag folded thin film transformer showing the structure and a schematic sectional view (b) taken along the line α-α ′ of the plan view. The present embodiment is common in having the same magnetic structure as the first embodiment, and is characterized in that the structure of the primary side and secondary side conductors has a rectangular coaxial sectional shape. In the figure, 30 is a substrate,
31 is an insulating layer, 32 is a lower magnetic layer, 33 is an insulating layer, 34
Is a primary side conductor, 35 is a secondary side conductor, 36 is an insulating layer, 37
Is an upper magnetic layer, 38 is a magnetic layer through hole portion, 39, 4
Reference numeral 2 is a primary side external connection terminal, and 40 and 41 are secondary side external connection terminals.

Next, the manufacturing method of this embodiment will be described in detail. First, Si is sputtered on the substrate 30.
An insulating layer 31 such as O ₂ is formed. Permalloy on it,
A magnetic film of CoZrRe, CoFeSiB, or the like is deposited by a sputtering method or the like and patterned by an ion beam etching method or the like to form the lower magnetic layer 32. After that, SiO ₂ or the like is deposited in the same manner as above and a planarization process is performed to form the insulating layer 33. Subsequently, a conductor layer of Cu or the like is formed on the insulating layer 33 by an electron beam evaporation method or the like, and the conductor layer is patterned by an ion beam etching method or the like to form a rectangular lower side portion of the secondary conductor 35 having a zigzag shape. In addition, terminals 39 and 42 for secondary side external connection are formed. After that, SiO ₂ or the like is deposited in the same manner as above, and a flattening process is performed to form the insulating layer 3
6 Next, in the insulating layer 36, of the secondary conductor 35,
Through holes are formed by ion beam etching or the like in the region where the rectangular side wall is formed and the primary side conductor portion. Then, after forming a conductor layer of Cu or the like by an electron beam evaporation method or the like, patterning is performed by an ion beam etching method or the like, and a rectangular side wall portion of the secondary side conductor 35 and the primary side conductor 3 are formed.
4 and primary side external connection terminals 40 and 41 are formed. An insulating layer is formed thereon and flattened in the same manner as above, followed by patterning to form an insulating layer on the upper part of the primary side conductor 34, and then on the rectangular side wall of the secondary side conductor 35 with an ion beam. A through hole is formed by an etching method or the like. Then, after forming a conductor layer of Cu or the like by an electron beam evaporation method or the like, patterning is performed by an ion beam etching method or the like to produce a rectangular upper side portion of the secondary side conductor 35. Then, through holes 38 as shown in FIG. 7 are formed in the void portions of the adjacent coaxial conductors and the conductor outer peripheral portion by an ion beam etching method or the like. Then, a magnetic layer is formed in the through hole portion 38, and this magnetic layer is patterned to form an upper magnetic layer 37.
Finally, through holes penetrating the insulating film are opened in the connecting terminals 39 to 42 to form external terminals to obtain the thin film transformer of the present invention.

In the zigzag folded thin-film transformer of the example thus manufactured, the value of the inductance is almost the same as that of the example 1, which is significantly improved as compared with the conventional example. On the other hand, the coupling coefficient is
The coupling coefficient was further improved and values of 0.97-0.99 were obtained.

In the above three embodiments, the primary side / secondary side conductors are provided as the thin film transformer with the number of foldings N times. However, the primary side conductor and the secondary side conductor are connected to the external terminal portion. It is also possible to connect them in series with each other and use them as a thin film inductor having a number of folds of 2N. Needless to say, the improvement of the coupling coefficient due to the coaxial cross-sectional shape of the conductor structure has the same effect not only in the zigzag structure thin film transformer but also in the spiral structure thin film transformer.

[0041]

As is clear from the above description, according to the high frequency thin film transformer of the present invention, there is no decrease in the inductance due to the narrowing of the conductor spacing, which is noticeable in the conventional structure. Rather, it has the characteristic that the inductance improves due to the narrow spacing. Furthermore, the structure of the present invention significantly improves the coupling coefficient between the primary and secondary conductors, and the characteristics of the transformer are significantly improved. Therefore, with the structure of the present invention, it is possible to provide a thin film transformer that achieves a narrower spacing and a higher coupling coefficient, and at the same time has a small size and high performance. According to the second aspect of the present invention, in particular, the coupling coefficient can be further improved.

[Brief description of drawings]

1A is a plan view of a first embodiment of the present invention, and FIG. 1B is a schematic view of a YY ′ cross-sectional structure of the plan view.

FIG. 2 is a pattern diagram of a through hole portion of a magnetic layer of Example 1 of the present invention.

FIG. 3 is a graph showing a calculated value and a measured value (the thin film transformer of the present invention and the thin film transformer of the prior art) showing the relationship between the conductor spacing and the inductance.

4A is a plan view of a second embodiment of the present invention, and FIG. 4B is a schematic view of the ZZ ′ cross-sectional structure of the plan view.

FIG. 5 is a pattern diagram of a through hole portion of a magnetic layer of Example 2 of the present invention.

6A is a plan view of a third embodiment of the present invention, and FIG. 6B is a schematic sectional view taken along the line α-α ′ of the plan view.

FIG. 7 is a pattern diagram of a through hole portion of a magnetic layer of Example 3 of the invention.

8A is a plan view of a zigzag folded thin film transformer according to the prior art, and FIG. 8B is a schematic view of a sectional structure taken along line XX ′ of the plan view.

FIG. 9 is a schematic sectional view showing a magnetic field distribution of a zigzag thin film transformer according to a conventional technique.

10A and 10B are magnetic path structure model diagrams used for calculation.

[Explanation of symbols]

 6 ... Substrate 7, 9, 11, 13 ... Insulating layer 8 ... Lower magnetic layer 10 ... Primary side conductor 12 ... Secondary side conductor 14 ... Upper magnetic layer 15 ... Through hole part of magnetic layer 16, 17 ... Primary side External connection terminals 18, 19 ... Secondary side external connection terminals 20 ... Substrates 21, 23, 26 ... Insulating layer 22 ... Lower magnetic layer 24 ... Primary conductor 25 ... Secondary conductor 27 ... Upper magnetic layer 28 ... Through hole portion of magnetic layer 50, 51 ... Primary side external connection terminal 52, 53 ... Secondary side external connection terminal 30 ... Substrate 31, 33, 36 ... Insulating layer 32 ... Lower magnetic layer 34 ... Primary conductor 35 ... Secondary-side conductor 37 ... Upper magnetic layer 38 ... Magnetic layer through-hole portion 39, 42 ... Primary-side external connection terminal 40, 41 ... Secondary-side external connection terminal

Claims (2)

[Claims] 1. A thin film transformer comprising magnetic layers disposed above and below primary side and secondary side conductors having a structure in which at least two or more conductors are arranged in parallel with each other. A high-frequency thin-film transformer having a cross-sectional structure that surrounds the upper and lower sides and the left and right sides in the longitudinal direction of the conductor. 2. The high frequency thin film transformer according to claim 1, wherein the primary-side conductor or the secondary-side conductor has a cross-sectional structure that surrounds the secondary-side conductor or the primary-side conductor in the longitudinal direction in the vertical direction. High frequency thin film transformer.