JP2011114059A - Spiral inductor and method of manufacturing spiral inductor - Google Patents

Abstract

Provided is a spiral inductor capable of avoiding dielectric loss and reducing insertion loss. A semi-insulating substrate 2 provided with a ground conductor, and a dielectric formed on the substrate 2 The film 3, a plurality of supports 4 formed on the dielectric film 3, respectively, and supported by these supports 4, have a spiral conductor pattern on the substrate 2, and have one end 7 a A microstrip line conductor 5 that allows an input signal to pass to the other end 7b. The microstrip line conductor 5 is provided on the back surface of the pattern by a plurality of supports 4 provided along the shape of the conductor pattern. Has a crosslinked structure.
[Selection] Figure 1

Description

  The present invention relates to a spiral inductor and a method for manufacturing a spiral inductor.

  A spiral inductor provided in an MMIC (monicric microwave integrated circuit) forms a planar spiral wiring on a substrate and obtains a desired inductance by the wiring pattern.

  In a spiral inductor formed on a dielectric substrate, a metal layer is directly formed on the dielectric substrate or a dielectric film on the dielectric substrate by vapor deposition.

  2. Description of the Related Art Conventionally, a spiral inductor has been proposed that has a structure in which spiral strip lines are laminated in two layers so that a signal current in a high frequency state can be evenly passed through each strip line (see Patent Document 1). The spiral inductor disclosed in Patent Document 1 is formed on a spiral-shaped first strip line formed on a semi-insulating substrate, and is stacked on the upper surface of the first strip line at a predetermined interval from the upper surface in the vertical direction. A through hole forming line having a plurality of through holes and a spiral-shaped second strip line laminated on the upper surface of the through hole forming line.

  A spiral inductor is also known in which a spiral wiring portion is provided in parallel with a substrate and includes a substrate contact portion that contacts the substrate and a wiring hollow portion having a predetermined gap with respect to the substrate (see Patent Document 2). ). In this spiral inductor, the substrate contact portion is in contact with the substrate via a conductive column. Patent Document 2 discloses that the area of the hollow portion that is not in contact with the substrate and floats in the air is larger than the area of the substrate contact portion.

JP 2004-214414 A JP 2000-21635 A

  However, the microwave is transmitted through a microstrip line formed of a semi-insulating dielectric substrate, a metal pattern on the dielectric film formed on or on the substrate surface, and a ground pattern on the back surface of the substrate. Propagation causes a dielectric loss due to the intrinsic dielectric constant of the semi-insulating substrate or dielectric film, resulting in a problem that the insertion loss increases and the Q value decreases. The Q value refers to the ratio of the impedance of the equivalent circuit to the real part coefficient of the imaginary part coefficient.

  In view of the above problems, an object of the present invention is to provide a spiral inductor capable of avoiding dielectric loss and reducing insertion loss and a method of manufacturing the spiral inductor.

  In order to solve such a problem, according to one aspect of the present invention, a semi-insulating substrate provided with a ground conductor, a plurality of supports each formed on the substrate, and supported by these supports A microstrip line conductor having a spiral conductor pattern on the substrate and allowing a signal input from one end to pass to the other end. There is provided a spiral inductor characterized by having a bridging structure in which the back surface of the pattern is supported by the plurality of supports provided along the shape of the conductor pattern.

  According to another aspect of the present invention, a wiring layer is formed on a semi-insulating substrate provided with a ground conductor, a first resist layer is formed on the wiring layer, and then the substrate surface Forming a plurality of metal layers extending from each opening in a direction perpendicular to the substrate surface, and forming a second resist layer on the metal layers. Etching the second resist layer so as to expose the plurality of metal layers, growing the metal layers, and wiring patterns on the grown metal layers. Forming a layer so that a pattern in a top view of the wiring pattern layer is spiral, and forming a hollow portion between the wiring pattern layer and the substrate surface, the first resist layer And the second Forming a microstrip line having a cross-linking structure composed of any two of the plurality of metal layers and the wiring pattern layer supported by the two metal layers. A method for manufacturing a spiral inductor is provided.

  According to the present invention, air is formed below the microstrip line conductor layer by the bridging structure, so that it is possible to avoid the dielectric loss due to the substrate or the dielectric formed on the substrate, and to reduce the insertion loss. be able to. In addition, the Q value of the inductor can be increased.

It is a top view of the spiral inductor which concerns on embodiment of this invention. (A) is the fragmentary sectional view along the VV 'line of FIG. 1, (b) is the fragmentary sectional view along the WW' line of the same figure. It is a top view in the middle of the manufacturing process of a spiral inductor. It is a top view which shows the conductor pattern of a microstrip line. It is a figure for comparing the cross-sectional structure of the spiral inductor which concerns on embodiment of this invention, and the cross-sectional structure of the spiral inductor by a prior art example. It is a figure for comparing the frequency characteristic of Q value of each spiral inductor by an Example and a prior art example. It is a figure for comparing the frequency characteristic of the insertion loss of each spiral inductor by an Example and a prior art example. (A), (b) is a figure for demonstrating the preparation method of the lead wiring of a spiral inductor, respectively. (A)-(d) is a figure for demonstrating the manufacturing process of a spiral inductor, respectively. (A)-(c) is a figure for demonstrating the process of growing a metal layer, respectively. (A), (b) is a figure for comparing the cross-sectional structure of the spiral inductor which concerns on the modification of embodiment of this invention, and the cross-sectional structure of the spiral inductor by a prior art example, respectively.

  Hereinafter, a spiral inductor according to an embodiment of the present invention and a method for manufacturing the spiral inductor will be described with reference to FIGS. In the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

  The spiral inductor according to the embodiment of the present invention is an MMIC planar spiral inductor that mainly operates in the microwave band. The method for manufacturing a spiral inductor according to the present embodiment is a method for forming the spiral inductor in the MMIC.

  FIG. 1 is a top view of a spiral inductor according to this embodiment. 2A is a partial cross-sectional view taken along the line VV ′ of FIG. 2, and FIG. 2B is a partial cross-sectional view taken along the line WW ′ of FIG. The spiral inductor 1 includes a semi-insulating substrate 2, a dielectric film 3 formed on the substrate 2, and a plurality of first metal layers 4 (supports) each formed in a column shape on the dielectric film 3. Body) and a microstrip line 5 (micro microstrip line conductor) having a spiral conductor pattern and supported by these first metal layers 4.

  For the substrate 2, a semi-insulating compound semiconductor substrate is used. Semi-insulating means that the electron mobility is high, the impurity density is sufficiently low, and the resistance value is high. GaAs (gallium arsenide) is used as the compound semiconductor. The substrate 2 has a ground layer or ground wiring (ground conductor) (not shown).

  The first metal layers 4 are each formed in an island shape along the shape of the conductor pattern of the microstrip line 5. The first metal layer 4 is obtained by applying a resist film on the dielectric film 3 and then patterning the resist film by forming a plurality of openings. In FIG. 3, the top view of the board | substrate 2 after the process in which the 1st metal layer 4 was formed in island shape is shown. Gold (Au) is vapor-deposited in openings represented by a plurality of small squares to grow a gold plating layer, and respective support pillars are formed. Next, a resist film is applied and patterned, and the column heads of the support columns are wired to each other by gold vapor deposition. Thereafter, when all the resist films are removed, the second metal layer 6 remains on the substrate 2, and the microstrip line 5 is obtained in a spiral shape when viewed from above. FIG. 4 shows the conductor pattern after the microstrip line 5 made of the second metal layer 6 is formed. By depositing gold having excellent conductivity, the substrate 2 is not affected electromagnetically.

  Further, as represented by the hatched portions in FIG. 1, the pattern back surface of the microstrip line 5 is supported by the stigma of each first metal layer 4 at a plurality of locations. Each first metal layer 4 that is a support column functions as a pier or abutment, and the conductor pattern of the microstrip line 5 between any two first metal layers 4 functions as a bridge girder. Each of the microstrip lines 5 includes a plurality of support columns that support the microstrip lines 5 and a bridge that spans between adjacent support columns along the shape of the conductor pattern except for the portions of the support columns. Having a crosslinked structure.

  The spiral inductor 1 has an outer end 7a disposed outside the spiral winding, and an inner end 7b disposed inside the spiral winding. A lead wire 8 formed in advance below the conductor pattern of the microstrip line 5 is connected to the inner end 7b. An insulating film is formed between the conductor pattern and the lead wiring 8. By passing the lead-out wiring 8 under the conductor pattern, the two conductors can be crossed in a three-dimensional manner without being short-circuited.

  An example in which the spiral inductor 1 having such a configuration is used in an impedance matching circuit will be described. One end of the microstrip line 5 is grounded to a ground layer to function as an inductor. A high frequency signal input from the external end 7a of the microstrip line 5 or the wiring end 9 of the lead-out wiring 8 is passed to the other end of the microstrip line 5, that is, the wiring end 9 or the external end 7a. A wiring layer (not shown) connected to the ground wiring is formed on the substrate 2, and this wiring layer is in contact with one end portion of the conductor pattern of the microstrip line 5. An inductor component acts on the signal voltage.

  FIG. 5A is a diagram showing a cross-sectional structure taken along line AA ′ of FIG. FIG. 5B is a diagram showing a cross-sectional structure when a conventional spiral inductor as a comparative example is cut along a portion corresponding to the line AA ′. The spiral inductor as a comparative example was formed on the semi-insulating substrate 2, the dielectric film 3 on the substrate 2, the first metal layer 50 formed on the dielectric film 3, and the first metal layer 50. It consists of the 2nd metal layer 51, and this 2nd metal layer 51 is arrange | positioned in the top view spiral shape.

  In the prior art, the cross-sectional view of AA ′ is as shown in FIG. 5B. In this embodiment, first, as shown in FIG. 3, the first metal layer 4 (represented by a small square) is formed. It arrange | positions at island shape and forms a crosslinked structure in the 2nd metal layer 6 after that. At this time, a cross-sectional view taken along the line A-A ′ of the spiral inductor 1 according to the present embodiment is as shown in FIG. Since the bridging structure portion is disposed in the air, the dielectric loss due to the substrate 2 or the dielectric film 3 is reduced.

  In the prior art, as shown in FIG. 5B, a plated metal layer 51 is provided on the first metal layer 50 formed on the dielectric film 3 on the substrate 2. On the other hand, in the spiral inductor 1 according to this embodiment, the first metal layer 4 is arranged in an island shape, and each island is bridged by the second metal layer 6. With this structure, air below the second metal layer 6 becomes air, so that dielectric loss due to the dielectric can be avoided and insertion loss can be reduced. This also makes it possible to obtain an inductor with a high Q value.

  FIG. 6 is a diagram illustrating the frequency characteristic of the Q value according to the example and the frequency characteristic of the Q value according to the comparative example. FIG. 7 is a diagram illustrating frequency characteristics of insertion loss according to the embodiment and frequency characteristics of insertion loss according to the comparative example. In FIG. 6, the larger the Q value on the vertical axis in the high frequency region, the smaller the signal loss. MAG (Maximum Available Gain) on the vertical axis in FIG. 7 represents the maximum available gain. According to the present embodiment, the insertion loss and the Q value can be improved as shown in FIGS.

  A manufacturing method of the spiral inductor 1 having such a structure will be described with reference to FIGS.

  FIG. 8A is a top view of a portion used as the lead wiring 8 during the manufacturing process of the spiral inductor 1, and FIG. It is a figure which shows a structure. The above-described symbols represent the same elements as those described above.

  A dielectric film 3 is formed on the substrate 2, and the dielectric film 3 is patterned to provide openings. A step of forming the lead wiring 8 is performed by performing patterning by depositing metal on the dielectric film 3 or the like. Thereafter, a silicon nitride film (SiN) 10 is formed on the dielectric film 3 including the lead wiring 8. Holes are formed in the silicon nitride film 10 using resist patterning. An exposed portion of the lead wiring 8 is connected to the substrate 2 through the dielectric film 3 and functions as a wiring layer.

  Subsequently, a resist is applied to the entire surface of the nitride film layer.

  FIG. 9A to FIG. 9D are diagrams for explaining the manufacturing process of the spiral inductor 1. The above-described symbols represent the same elements as those described above. As shown in FIG. 9 (a), holes are formed in a plurality of locations on the resist layer 11 (first resist layer), each serving as a pier position.

  That is, a wiring layer is formed on the substrate 2, and after the resist layer 11 is formed on the wiring layer, the openings 12 are formed at a plurality of locations serving as bridging legs.

  Titanium / platinum / gold (Ti / Pt / Au) or gold (Au) is deposited on the resist layer 11 having the openings 12. That is, a plurality of pad metals (metal layers) extending from each opening 12 in a direction orthogonal to the surface of the substrate 2 are formed by plating. As shown in FIG. 9B, the metal 13 scattered in an island shape is visually recognized from above on the substrate 2.

  As shown in FIG. 9C, a second resist layer 14 (second resist layer) is formed so as to cover these metals 13. Thereafter, etching is performed using a pattern positioned at each metal 13 as a mask to form an opening in the second resist layer 14 to expose the underlying metal 13. That is, openings are patterned in the second resist layer 14 and etched so that a plurality of metal layers are exposed. FIG. 9D shows a state where the metal 13 is exposed.

  Next, titanium / platinum / gold or the like is vapor-deposited on the second resist layer 14 having an opening pattern to grow each metal layer. FIG. 10A is a view showing a substrate cross-sectional structure in a state where the second resist layer 14 is formed. The above-mentioned codes are the same. An electrode is connected to the plating layer 16 on the metal layer 15, and a voltage is applied from the electrode to the plating layer 16 to grow the plating layer 16 in an upward direction perpendicular to the substrate surface. Reference numeral 17 denotes a wiring layer. FIG. 10B shows a substrate cross-sectional structure in a state where the plating layer 16 is grown.

  Then, a wiring pattern layer is formed on each of the grown plating layers 16 so that the pattern of the wiring pattern layer viewed from above is spiral. Thereby, the wiring pattern layer is obtained as the microstrip line 5 as shown in FIG.

  Finally, as shown in FIG. 10C, the first resist layer 11 and the second resist layer 14 are formed so that a hollow portion is formed between the spiral wiring pattern layer and the surface of the substrate 2. Are removed by etching. The plating layer 16 functions as the second metal layer 6.

  In this way, the microstrip line 5 having a cross-linking structure including any two of the plating layers 16 and the wiring pattern layer is created.

  According to the method for manufacturing a spiral inductor according to the present embodiment, a hollow structure is obtained, and air under the second metal layer 6 becomes air, so that dielectric loss due to the dielectric can be avoided, and insertion loss Can be reduced. In addition, the Q value of the inductor can be increased.

(Modification)
In the example of FIG. 1 and FIG. 2, the first metal layer 4 is formed on the dielectric film 3 after the dielectric film 3 is formed on the substrate 2, but according to the embodiment of the present invention. In the spiral inductor, the first metal layer 4 as a support may be directly formed on the substrate 2.

  FIG. 11A is a diagram showing a cross-sectional structure when a spiral inductor according to a modification is cut along a plane orthogonal to the signal transmission direction. FIG. 11B is a view showing a cross-sectional structure of the same portion of the conductor pattern of the conventional spiral inductor as a comparative example as the conductor pattern of FIG. The above-described symbols represent the same elements as those described above.

  In FIG. 11B, the first metal layer 50 is formed on the substrate 2. Also in the spiral inductor according to this modification, the first metal layer 4 (not shown in the figure) is arranged in an island shape on the substrate 2, and each island is bridged by the second metal layer 6. With this structure, air below the second metal layer 6 becomes air, so that dielectric loss due to the substrate 2 can be avoided and insertion loss can be reduced. In addition, an inductor having a high Q value can be obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  In the above embodiment, the shape of the spiral is not limited to a square, but may be a polygon such as an octagon close to a circle. The cross-sectional shape of the first metal layer 4 (support column or pier) as a support was a quadrangle, but this cross-sectional shape can be variously changed according to the opening shape of the resist film. A structure other than the column may be used as the support.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Spiral inductor, 2 ... Board | substrate, 3 ... Dielectric film, 4 ... 1st metal layer, 5 ... Microstrip line (microstrip line conductor), 6 ... 2nd metal layer, 7a ... Outer end, 7b ... Inner end , 8 ... Lead wiring, 9 ... Wiring edge, 10 ... Silicon nitride film, 11 ... Resist layer (first resist layer), 12 ... Opening, 13 ... Metal, 14 ... Resist layer (second resist layer), 15 ... Metal layer, 16 ... Plating layer, 17 ... Wiring layer.

Claims (2)

A semi-insulating substrate provided with a ground conductor;
A plurality of supports each formed on the substrate;
A microstrip line conductor supported by these supports, having a spiral-shaped conductor pattern on the substrate, and allowing a signal input from one end to pass to the other end,
The microstrip line conductor has a bridge structure in which a back surface of a pattern is supported by the plurality of supports provided along the shape of the conductor pattern. Forming a wiring layer on a semi-insulating substrate provided with a ground conductor, forming a first resist layer on the wiring layer, and then forming openings at a plurality of locations on the substrate surface; ,
A step of laminating and forming a plurality of metal layers extending from each opening in a direction perpendicular to the substrate surface;
Forming a second resist layer on these metal layers, patterning openings in the second resist layer, and etching to expose the plurality of metal layers;
Growing these metal layers,
Forming a wiring pattern layer on the plurality of grown metal layers so that a top view pattern of the wiring pattern layer is spiral;
A step of removing the first resist layer and the second resist layer so that a hollow portion is formed between the wiring pattern layer and the substrate surface,
A method for manufacturing a spiral inductor, characterized in that a microstrip line having a bridge structure composed of any two of the plurality of metal layers and the wiring pattern layer supported by the two metal layers is formed. .

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