Patent Grant
8199451
1. Field of the Invention
The present invention relates to an ESD protection device and a composite electronic component thereof, and in particular, to an ESD protection device which is useful in a high-speed transmission system and, which can advantageously be combined with a common mode filter.
2. Description of the Related Art
In recent years, size reduction and performance improvement of electronic apparatuses have been rapidly in progress. Furthermore, much effort has been made to increase transmission speed (an increased frequency exceeding 1 GHz) and to reduce driving voltage as typically seen in high-speed transmission systems such as USB2.0, S-ATA2, and HDMI. On the other hand, the withstand voltage of electronic components used in electronic apparatuses decreases consistently with the size reduction of electronic apparatuses and the reduced driving voltage therefore. Thus, it has been important to protect electronic components from overvoltage typified by electrostatic pulses generated when a human body comes into contact with a terminal of an electronic apparatus.
In order to protect electronic components from such electrostatic pulses, a method of providing a banister or the like between the ground and a line to be subjected to static electricity has generally been used, and a method of adopting a surge absorber including long-lasting electrodes has been proposed (see Patent Documents 1 to 3). However, the use, in a high-speed transmission system, of the barrister or the like, which has a large electrostatic capacitance, not only increases a discharge starting voltage but also degrades signal quality.
On the other hand, an antistatic component with a low electrostatic capacitance has been proposed which includes an electrostatic protection material filled between opposite electrodes. For example, Patent Document 4 discloses an electric circuit protecting device (antistatic component) including a voltage varying polymer material disposed between electrodes, by applying a polymer material containing conductive particles into the gap area between the electrodes by stencil printing and thermally treating and solidifying the polymer material. Furthermore, Patent Document 5 discloses an antistatic component including an electrostatic protection material layer formed between a pair of electrodes by, in order to enhance an electrostatic inhibition effect, kneading metal particles with a passive layer formed on the surface thereof, a silicone-containing resin, and an organic solvent to obtain electrostatic protection material paste and applying the electrostatic protection material paste to between the opposite electrodes by screen printing before drying. Moreover, Patent Document 6 discloses an electric circuit protecting device (antistatic component) including a voltage dependent resistor layer composed mainly of zinc oxide and formed by providing ceramic paste containing metal oxide, a resin component, and a solvent component, subjecting the ceramic paste to screen printing so as to fill the gap between electrode paste films, and burning the ceramic paste at a high temperature.
However, the antistatic components described in Patent Documents 4-6 still provide high discharge starting voltages and fail to offer sufficient electrostatic absorption characteristics. Moreover, in the antistatic components described in Patent Documents 4-6, if any electrode is damaged during discharge, the electrodes may be short-circuited or the gap distance between the electrodes may vary, resulting in a significant variation in discharge starting voltage. Thus, these antistatic components cannot withstand repeated use.
The present invention has been made in view of the above circumstances. An object of the present invention is to provide an ESD protection device having a low discharge starting voltage and offering improved durability against repeated use, and a composite electronic component combined with the ESD protection device. Another object of the present invention is to provide an ESD protection device having excellent heat resistance and weather resistance, and allowing a further reduction in the thickness thereof, improvement of productivity, and a reduction in costs and a composite electronic component combined with the ESD protection device.
To accomplish the above-described objects, the present inventors conducted earnest studies. The present inventors have thus found that in what is called a gap type ESD protection device in which an electrostatic protection material is filled between opposite electrodes, a reduction in discharge starting voltage and improvement of durability against repeated use can be achieved by controlling the relationship of the gap distance between the electrodes and the electrode thickness under specific conditions. As a result, the present inventors have completed the present invention.
That is, an ESD protection device according to the present invention comprises a base having an insulating surface, electrodes disposed on the insulating surface and facing but spaced apart from each other, and a functional layer disposed on at least between the electrodes, wherein a gap distance ΔG between the electrodes ranges from 0.5 μm to 10 μm, and a thickness ΔT of each of the electrodes meets a relationship of ΔG/ΔT=1 to 30.
Here, the term “gap distance ΔG” means the shortest distance between the electrodes. The term “thickness of the electrode ΔT” means the thickness of each of the electrodes near the gap between the electrodes. Furthermore, the term “durability” means performance evaluated based on the number of discharges occurring during repeated electrostatic discharge tests in examples described below.
As a result of measurement of the characteristics of the ESD protection devices configured as described above, the present inventors have found that, compared to the conventional antistatic elements, the discharge starting voltage of the ESD protection devices were reduced and their durability were improved. The details of the mechanism of these effects have not been clarified yet. However, for example, the mechanism can be assumed to be as follows.
In this kind of gap type ESD protection devices, discharge typically occurs in a conductive path in which the resistivity between the electrodes arranged opposite each other exhibits the smallest value. The discharge starting voltage tends to decrease as the gap distance decreases. According to the present inventors' knowledge, during high voltage discharge, the electrodes may be damaged though the level of the damage varies depending on the gap distance or a material forming the gap. For example, the electrode may be partly melted probably by locally generated heat, with the gap-side end surface of the electrode deformed. As a result, in many cases, the electrode may be damaged in such a way that the gap distance ΔG between the electrodes increases. The electrodes with the thus increased gap distance ΔG fail to discharge at an initially set voltage when static electricity is applied to the device again.
In contrast, in the ESD protection device configured as described above, the gap distance ΔG between the electrodes is set to a relatively small value, that is, from 0.5 μm to 10 μm, and the thickness ΔT of each of the electrodes meets the relationship of ΔG/ΔT=1 to 30. Thus, the gap distance ΔG is reduced, and the thermal capacity of the electrodes is increased. This improves a heat diffusion effect based on thermal conductance through the electrodes themselves. Thus, the discharge starting voltage is reduced, and the electrodes are inhibited from being damaged by local heat caused by discharge. Furthermore, the thickness of the electrode ΔT is set to be sufficiently large for a conductive path. Thus, even if any electrode is partly damaged, for example, even if the lower end surface of the electrode is damaged, unless the upper end surface of the electrode is damaged, the upper end surface of the electrode maintains the initially set gap distance ΔG. That is, the thickness of the electrode serves to inhibit (compensate for) a variation in gap distance ΔG possibly caused by damage to the electrode during discharge. Therefore, the initially set gap distance ΔG is maintained over time, thus improving durability. However, the effects of the present invention are not limited to those described above.
Here, the functional layer is preferably a composite in which a conductive inorganic material is discontinuously dispersed in a matrix of an insulating inorganic material. Instead of the above-described conventional organic-inorganic composite film, a composite of an insulating inorganic material and a conductive inorganic material is thus adopted as an electrostatic protection material to significantly improve heat resistance and weather resistance against an external environment including temperature and humidity. Furthermore, such a composite can be formed by using a thin-film formation method for an inorganic material such as a sputtering method or a deposition method. Thus, compared to the forming of an organic-inorganic composite film of about several tens of μm by application based on stencil printing or screen printing and the following drying, the forming of the composite facilitates a reduction in film thickness, improves productivity, and reduces costs.
In the specification, the term “composite” used herein means a state in which a conductive inorganic material is dispersed in a matrix of an insulating inorganic material, and includes a concept in which not only a state in which a conductive inorganic material is uniformly or randomly dispersed in a matrix of an insulating inorganic material, but also a state in which clusters of a conductive inorganic material are dispersed in a matrix of an insulating inorganic material, that is, a state typically called a sea-island structure. Furthermore, the term “insulating” used herein means that the resistivity is greater than or equal to 0.1 Ωcm, and the word “conductive” means that the resistivity is smaller than 0.1 Ω·cm. What is called “semi-conductive” is included in the former word “insulating” as long as the specific resistivity of a material in question is greater than or equal to 0.1 Ωcm.
Furthermore, the insulating inorganic material is preferably at least one species selected from the group consisting of Al2O3, TiO2, SiO2, ZnO, In2O3, NiO, CoO, SnO2, V2O5, CuO, MgO, ZrO2, AlN, BN, and SiC. These metal oxides are excellent in the insulating property, heat resistance, and weather resistance and thus functions effectively as a material forming the insulating matrix of the composite. As a result, the metal oxides can be formed into a high-performance ESD protection device that is excellent in the discharge property, heat resistance, and weather resistance. Moreover, the metal oxides are inexpensively available, and the sputtering method is applicable to these metal oxides. Thus, the metal oxides serve to improve productivity while reducing costs.
Moreover, the above-described conductive inorganic material is preferably at least one species of metal selected from the group consisting of C, Ni, Cu, Au, Ti, Cr, Ag, Pd, and Pt, or a metal compound thereof. By blending any of the metals or metal compounds in a matrix of an insulating inorganic material so that the metal or metal compound is discontinuously dispersed, a high-performance ESD protection device is obtained which is excellent in the discharge property, heat resistance, and weather resistance.
Furthermore, the above-described electrodes is preferably at least one species of metal selected from the group consisting of Cu, Au, Cr, Al, Ag, Zn, W, Mo, Ni, Co, and Fe, or a metal compound thereof. As these metals or the metal compounds thereof have low resistivity, by forming the electrodes using these metals or the metal compounds thereof, a high-performance ESD protection device is obtained which is excellent in the discharge property and the heat resistance.
Another aspect of the present invention provides a composite electronic component effectively combined with the ESD protection device according to the present invention and including an inductor device and an ESD protection device that are provided between two magnetic bases, wherein the inductor device comprises an insulating layer composed of resin and a conductor pattern formed on the insulating layer, the ESD protection device comprises an underlying insulating layer formed on the magnetic bases, electrodes disposed on the underlying insulating layer and facing but spaced apart from each other, and a functional layer disposed on at least between the electrodes, and wherein a gap distance ΔG between the electrodes ranges from 0.5 μm to 10 μm, and a thickness ΔT of each of the electrodes meets a relationship of ΔG/ΔT=1 to 30.
Moreover, yet another aspect of the present invention provides a composite electronic component effectively combined with the ESD protection device according to the present invention and including a common mode filter layer and an ESD protection device layer that are provided between two magnetic bases, wherein the common mode filter layer includes a first insulating layer and a second insulating layer both composed of resin, a first spiral conductor formed on the first insulating layer, and a second spiral conductor formed on the second insulating layer, and the ESD protection device layer includes a first ESD protection device connected to one end of the first spiral conductor, and a second ESD protection device connected to one end of the second spiral conductor, and wherein the first and second spiral conductors are formed on respective planes perpendicular to a stacking direction and arranged so as to be magnetically coupled together, and each of the first and second ESD protection devices comprises an underlying insulating layer formed on the magnetic base, electrodes disposed on the underlying insulating layer and facing but spaced apart from each other, and a functional layer disposed on at least between the electrodes, and wherein a gap distance ΔG between the electrodes ranges from 0.5 μm to 10 μm, and a thickness ΔT of each of the electrodes meets a relationship of ΔG/ΔT=1 to 30.
The present invention provides an ESD protection device with a low discharge starting voltage and improved durability and a composite electronic component combined with the ESD protection device. Moreover, the present invention allows the heat resistance to be improved and enables films in the device and component to be thinned, compared to the prior art. As a result, the present invention can improve productivity and reduce costs.
Embodiments of the present invention will be described below. Positional relationships such as vertical and lateral positions are based on those shown in the drawings unless otherwise specified. Moreover, dimensional scales for the drawings are not limited to those shown in the drawings. Furthermore, the embodiments described below are examples based on which the present invention will be described. The present invention is not limited to the embodiments.
The base 2 has the insulating surface 2a. Here, the base 2 having the insulating surface 2a is a concept including, besides a substrate composed of an insulating material, a substrate with an insulating film produced on a part or the entirety of the substrate. The dimensions and shape of the base 2 are not particularly limited provided that the base 2 can support at least the electrodes 3a and 3.b and the functional layer 4.
A specific example of the base 2 may include a ceramic substrate and a single-crystal substrate composed of a low-dielectric-constant material with a dielectric constant of 50 or lower, preferably 20 or lower, such as NiZn ferrite, alumina, silica, magnesia, and aluminum nitride. Other preferred example may include any of well-known substrates with an insulating film formed on the surface thereof and composed of a low-dielectric-constant material with a dielectric constant of 50 or lower, preferably 20 or lower, such as NiZn ferrite, alumina, silica, magnesia, and aluminum nitride. An applicable method for forming an insulating film is not particularly limited to a specific one, and may be a well-known technique such as a vacuum deposition method, a reactive deposition method, a sputtering method, an ion plating method, or a gas phase method such as CVD or PVD. Furthermore, the thickness of the substrate and the insulating film can be set as appropriate.
The paired electrodes 3a and 3b are disposed on the insulating surface 2a of the base 2 away from each other. In the present embodiment, the paired electrodes 3a and 3b are oppositely arranged at a substantially central position as seen in a plan view, with a gap distance ΔG between the electrodes 3a and 3b.
Specific examples of a material forming the electrodes 3a and 3b includes, for example, Cu, Au, Cr, Al, Ag, Zn, W, Mo, Ni, Co, Fe, Pd, Ti, and Pt, or an alloy thereof. However, the present invention is not particularly limited to these materials. In view of providing a high-performance ESD protection device which is excellent in the discharge property and the heat resistance, the electrodes 3a and 3b are preferably that one which the resistivity of the metal materials forming the electrodes 3a and 3b are low, in particular, the resistivity of the metal materials forming the electrodes 3a and 3b is preferably less than 10*10−8 Ωm in at room temperature. Specific examples of the metal materials with low resistivity includes, for example, at least one species of metal selected from the group consisting of Cu (1.7*10−8 Ωm), Au (2.2*10−8 Ωm), Cr (2.6*10−8 Ωm), Al (2.8*10−8 Ωm), Ag (1.6*10−8 Ωm), Zn (5.9*10−8 Ωm), W (3.5*10−8 Ωm), Mo (5.1*10−8 Ωm), Ni (7.2*10−8 Ωm), Co (7.0*10−8 Ωm), and Fe(9.8*10−8 Ωm) or a metal compound thereof. The more preferable resistivity is less than 5*10−8 Ωm in at room temperature. Furthermore, in view of providing the electrodes 3a and 3b which is excellent in the low resistivity and the film-forming property, the particularly preferable material forming the electrodes 3a and 3b is at least one species of metal selected from the group consisting of Cu, Au, Cr, Al, and Ag, or an alloys thereof. In the present embodiment, each of the electrodes 3a and 3b is formed to be rectangular as seen in a plan view. However, the shape of the electrode is not particularly limited but may be like comb teeth or a saw. A method for forming the electrodes 3a and 3b (a method for forming the gap between the electrodes 3a and 3b) is not particularly limited. Any well-known technique can be appropriately selected. Specific examples of the well-known technique include a pattern forming method using laser or ion beams and a pattern forming method utilizing photolithography.
In order to ensure low-voltage initial discharge and to inhibit possible short circuiting between the electrodes 3a and 3b while maintaining easily-processability for gap formation, the gap distance ΔG between the electrodes 3a and 3b is set to the ranges of 0.5 to 10 μm, more preferably the ranges of 0.5 to 8 μm. On the other hand, in order to inhibit possible damage to the electrodes 3a and 3b and a possible variation in gap distance ΔG during discharge to improve durability, the thickness ΔT of each of the electrodes 3a and 3b is set to meet the relationship of ΔG/ΔT=1 to 30, more preferably 2 to 20. Specifically, although depending on the gap distance ΔG between the electrodes 3a and 3b, the thickness ΔT of each of the electrodes 3a and 3b is preferably set to the ranges of 0.1 to 1
The functional layer 4 is disposed between the electrodes 3a and 3b. In the present embodiment, the functional layer 4 is stacked on the insulating surface 2a of the base 2 and on the electrodes 3a and 3b. The dimensional shape and the position disposed of the functional layer 4 are not particularly limited as long as they are designed such that initial discharge occurs between the electrodes 3a and 3b via the functional layer 4 itself when overvoltage is applied to the device.
The functional layer 4 is composed of a composite of a sea-island structure including an aggregate of island-like conductive inorganic materials 4b discontinuously dispersed in a matrix of an insulating inorganic material 4a. In the present embodiment, the functional layer 4 is formed by sequential sputtering. More specifically, a layer of the conductive inorganic material 4b is partially (incompletely) formed on the insulating surface 2a of the base 2 and/or the electrodes 3a and 3b by sputtering. Subsequently, the insulating inorganic material 4a is sputtered to form a composite of a stack structure including the layer of the conductive inorganic materials 4b dispersed like islands and the insulating inorganic material 4a covering the conductive inorganic material 4b.
Specific examples of the insulating inorganic material 4a forming the matrix include metal oxide and metal nitride. However, the present invention is not limited to these examples. In view of the insulating property and costs, preferable materials include Al2O3, TiO2, SiO2, ZnO, In2O3, NiO, CoO, SnO2, V2O5, CuO, MgO, ZrO2, MN, BN, and SiC. One of these materials may be exclusively used or two or more of these materials may be used together. Among the materials, in view of a high insulating property applied to the insulating matrix, Al2O3, SiO2, or the like is preferably used. On the other hand, in view of semi-conductivity applied to the insulating matrix, TiO2 or ZnO is preferably used. By applying the semi-conductivity to the insulating matrix results in an ESD protection device allowing the discharge to be started at a lower voltage. A method of applying the semi-conductivity to the insulating matrix is not particularly limited. For example, TiO2 or ZnO may be used exclusively or together with any other insulating inorganic material 4a. In particular, during sputtering in an argon atmosphere, oxygen in TiO2 is likely to be insufficient, and electric conductivity tends to increase. Thus, TiO2 is particularly preferably used in order to apply the semi-conductivity to the insulating matrix.
Specific examples of the conductive inorganic material 4b include metal, alloy, metal oxide, metal nitride, metal carbide, and metal boride. However, the present invention is not limited to these examples. In view of the conductivity, preferable materials include C, Ni, Cu, Au, Ti, Cr, Ag, Pd, and Pt or an alloy thereof.
Preferred combinations of the insulating inorganic material 4a and the conductive inorganic material 4b include, but not particularly limited to, a combination of Cu and SiO2 and a combination of Au and SiO2. An ESD protection device composed of these materials is excellent in electrical characteristics but also allows the accurate and easy formation of a composite of a sea-island structure including an aggregate of discontinuously dispersed island-like conductive inorganic materials 4b. This very advantageously facilitates processing and reduces costs.
The total thickness of the functional layer 4 is not particularly limited but can be appropriately set. In order to allow a further reduction in film thickness to further reduce the size of an electronic apparatus using the ESD protection device 1 while improving the performance of the electronic apparatus, the total thickness is preferably set to the ranges of 10 nm to 10 μm, more preferably the ranges of 15 nm to 1 μm, most preferably the ranges of 15 to 500 nm. Furthermore, a very thin composite made of an inorganic material and having a thickness of the ranges of 10 nm to 1 μm can be formed by application of the well-known thin-film formation method such as the sputtering method or the deposition method. This improves the productivity of the ESD protection device 1, while reducing the costs thereof. When the layer of the discontinuously dispersed island-like conductive inorganic materials 4b and the layer of matrix of the insulating inorganic material 4a are formed as in the present embodiment, the thickness of the layer of the conductive inorganic material 4b is preferably the ranges of 1 to 10 nm. The thickness of the layer of the insulating inorganic materials 4a is preferably the ranges of 10 nm to 10 μm, more preferably the ranges of 10 nm to 1 μm, most preferably the ranges of 10 to 500 nm.
A method for forming the functional layer 4 is not limited to the above-described sputtering method. The functional layer 4 can be formed by using the well-known thin-film formation method to apply the above-described insulating inorganic material 4a and conductive inorganic material 4b onto the insulating surface 2a of the base 2 and/or the electrodes 3a and 3b. That is, the ESD protection device 1 is very advantageous in that the functional layer 4 is composed of, instead of the above-described organic-inorganic composite film formed by the conventional printing method, the composite of the insulating inorganic material 4a and the conductive inorganic material 4b, which can be formed into layers by the sputtering method, the deposition method, or the like. The ESD protection device 1 according to the present embodiment may be configured such that application of a voltage between the electrodes 3a and 3b causes part of the electrodes 3a and 3b to disperse into the functional layer 4, resulting in the containment, in the functional layer 4, of the material forming the electrodes 3a and 3b.
In the ESD protection device 1 according to the present embodiment, the functional layer 4 containing the island-like conductive inorganic material 4b discontinuously dispersed in the matrix of the insulating inorganic material 4a functions as an electrostatic protection materials of a low-voltage discharge type. Specifically, when an electrostatic voltage is applied to between the paired electrodes 3a and 3b, discharge occurs at a point at which high energy concentrates and which is located in any path formed by the conductive inorganic material 4b discontinuously dispersed like islands in the matrix of the insulating inorganic material 4a; the path is located between the electrodes 3a and 3b. Electrostatic discharge energy is thus absorbed. High-voltage discharge may cause the electrodes or functional layer to be partially destroyed after discharge. However, the discontinuously dispersed island-like conductive inorganic materials 4b form a large number of current paths, enabling static electricity to be absorbed a number of times.
In particular, in the ESD protection device 1 according to the present embodiment, the gap distance ΔG between the electrodes 3a and 3b and the thickness ΔT of each of the electrodes 3a and 3b are controlled under the specific conditions. The gap distance ΔG is set to a relatively small value. Furthermore, the electrodes 3a and 3b have a relatively increased thermal capacity, providing appropriate a heat diffusion action. Thus, the discharge starting voltage is reduced, and the durability against repeated use is improved.
Furthermore, the present embodiment adopts the composite composed at least of the insulating inorganic material 4a and the conductive inorganic material 4b, as the functional layer 4 functioning as an electrostatic protection material of a low-voltage discharge type. Thus, compared to the conventional ESD protection device with the organic-inorganic composite film, the ESD protection device 1 is very excellent in heat resistance and weather resistance. Moreover, since the functional layer 4 is formed by the sputtering method, the ESD protection device 1 serves to improve productivity while reducing costs.
The ESD protection device 1 according to the first embodiment adopts, as the functional layer 4, the composite in which the conductive inorganic materials 4b are discontinuously dispersed in the matrix of the insulating inorganic material 4a. However, the functional layer 4 may be a composite in which metal particles, for example, Ag, Cu, Ni, Al, or Fe or particles of a conductive metal compound are dispersed in high insulating resin such as silicone resin and epoxy resin.
The functional layer 7 is a composite in which conductive inorganic materials 4b (not shown in the drawings) are dispersed in a matrix of an insulating inorganic material 4a (not shown in the drawings). In the present embodiment, the functional layer 7 is formed by sputtering a target containing the insulating inorganic material 4a (or a target containing the insulating inorganic material 4a and the conductive inorganic materials 4b) onto an insulating surface 2a of a base 2 and/or electrodes 3a and 3b and then applying a voltage to between the electrodes 3a and 3b to allow part of the electrodes 3a and 3b to disperse randomly into the insulating inorganic material 4a. Thus, the functional layer 7 according to the present embodiment contains at least the conductive inorganic materials 4b, that is, the material forming the electrodes 3a and 3b.
The total thickness of the functional layer 7 is not particularly limited but can be appropriately set. However, in order to allow a further reduction in film thickness, the total thickness is preferably set to the ranges of 10 nm to 10 μm, more preferably the ranges of 10 nm to 1 μm, and most preferably the ranges of 10 to 500 nm.
In the ESD protection device 6 according to the present embodiment, the composite in which the granular conductive inorganic materials 4b are discontinuously dispersed in the matrix of the insulating inorganic material 4a is adopted as the functional layer 7 functioning as an electrostatic protection material of a low-voltage discharge type. This configuration exerts effects similar to those of the above-described first embodiment.
As shown in
The first and second magnetic base 11a and 11b physically protect the composite functional layer 12 and serves as a closed magnetic circuit for the common mode filter. Sintered ferrite, composite ferrite (a resin containing powdery ferrite), or the like can be used as a material for the first and second magnetic bases 11a and 11b.
As shown in
As shown in
The common mode filter layer 12a includes insulating layers 16a to 16e, a magnetic layer 16f, an adhesive layer 16g, a first spiral conductor 17 formed on an insulating layer 16b, a second spiral conductor 18 formed on an insulating layer 16c, a first extraction conductor 19 formed on the insulating layer 16a, and a second extraction conductor 20 formed on the insulating layer 16d.
The insulating layers 16a to 16e insulate conductor patterns from one another or each of the conductor patterns from the magnetic layer 16f. The insulating layers 16a to 16e also serve to maintain the flatness of the underlying surface on which each conductor pattern is formed. A preferable material for the insulating layers 16a to 16e is a resin offering excellent electric and magnetic insulating properties as well as appropriate processability. That is, the preferable material is a polyimide resin or an epoxy resin. As the conductive patterns, Cu, Al, or the like, which is excellent in conductivity and processability, is preferably used. The conductor patterns can be formed by an etching method or an additive method (plating) using photolithography.
An opening 25 penetrating the insulating layers 16a to 16e is formed in a central area of each of the insulating layers 16a to 16e and inside the first and second spiral conductors 17 and 18. The interior of the opening 25 is filled with a magnetic substance 26 forming a closed magnetic circuit between the first magnetic base 11a and the second magnetic base 11b. Composite ferrite or the like is preferably used as the magnetic substance 26.
Moreover, the magnetic layer 16f is formed on the surface of the insulating layer 16e. The magnetic substance 26 in the opening 25 is formed by hardening pasted composite ferrite (a resin containing magnetic powder). However, during hardening, the resin contracts to create recesses and protrusions in the opening portion. To allow the number of recesses and protrusions to be reduced as much as possible, the paste is preferably applied not only to the interior of the opening 25 but also to the entire surface of the insulating layer 16e. The magnetic layer 16f is formed in order to ensure such flatness of the magnetic layer 16f.
The adhesive layer 16g is required to stick the magnetic base 11b onto the magnetic layer 16f. The adhesive layer 16g also serves to reduce the recesses and protrusions on the surfaces of the magnetic base 11b and the magnetic layer 16f to allow tighter contact. A material for the adhesive layer 16g is not particularly limited but may be an epoxy resin, a polyimide resin, a polyamide resin, or the like.
The first spiral conductor 17 corresponds to the inductor device 14a shown in
The second spiral conductor 18 corresponds to the inductor device 14b shown in
Both the first and second spiral conductors 17 and 18 have the same planar shape and are provided at the same position as seen in a plan view. The first and second spiral conductors 17 and 18 overlap perfectly and are strongly magnetically coupled together. In the above-described configuration, the conductor patterns in the common mode filter layer 12a forms a common mode filter.
The ESD protection device layer 12b includes an underlying insulating layer 27, a first gap electrode 28 and a second gap electrode 29 formed on the surface of the underlying insulating layer 27, and an electrostatic absorption layer 30 covering the first and second gap electrodes 28 and 29. A layer structure near the first gap electrode 28 functions as the first ESD protection device 15a shown in
As shown in
a) and 8(b) are views showing an example of the layer structure near the first gap electrode 28 in the ESD protection device layer 12b.
The ESD protection device layer 12b includes an underlying insulating layer 27 formed on the surface of the magnetic base 11a, paired electrodes 28a and 28b included in the first gap electrode 28, and an electrostatic absorption layer 30 disposed between the electrodes 28a and 28b.
The underlying insulating layer 27 functions as the insulating surface 2a according to the above-described first embodiment. The underlying insulating layer 27 is composed of an insulating material. In the present embodiment, the underlying insulating layer 27 covers the entire surface of the magnetic base 11a because this arrangement is easy to manufacture. However, the underlying insulating layer 27 has only to lie under at least the electrodes 28a and 28b and the electrostatic absorption layer 30 and need not necessarily cover the entire surface of the magnetic base 11a. Preferable specific examples of the underlying insulating layer 27 include not only a film formed of a low-dielectric-constant material with a dielectric constant of 50 or lower, preferably 20 or lower, such as NiZn ferrite, alumina, silica, magnesia, or aluminum nitride, but also an insulating film composed of any of these low-dielectric-constant material and formed on any of various well-known substrates. A method for producing the underlying insulating layer 27 is not particularly limited but may be a well-known technique such as the vacuum deposition method, reactive deposition method, sputtering method, ion plating method, or gas phase method such as CVD or PVD. Furthermore, the film thickness of the underlying insulating layer 27 can be appropriately set.
The electrodes 28a and 28b correspond to the electrodes 3a and 3b in the above-described first embodiment. Duplicate descriptions are thus omitted. The gap distance ΔG between the electrodes 28a and 28b and the thickness ΔT of the gap electrode 28 are set to have a relationship similar to that between the gap distance ΔG between the electrodes 3a and 3b and the thickness ΔT of each of the electrodes 3a and 3b according to the above-described first embodiment.
The electrostatic absorption layer 30 is composed of a composite of a sea-island structure including an aggregate of conductive inorganic materials 33 discontinuously dispersed in a matrix of an insulating inorganic material 32. The electrostatic absorption layer 30 corresponds to the functional layer 4 in the above-described first embodiment. Furthermore, the insulating inorganic material 32 and the conductive inorganic materials 33 correspond to the insulating inorganic material 4a and conductive inorganic materials 4b in the above-described first embodiment. Duplicate descriptions of these materials are omitted.
In the ESD protection device layer 12b, the electrostatic absorption layer 30 functions as an electrostatic protection material of a low voltage discharge type. The electrostatic absorption layer 30 is designed such that when overvoltage such as static electricity is applied to the component, initial discharge occurs between the electrodes 28a and 28b via the electrostatic absorption layer 30. Furthermore, the insulating inorganic material 32 according to the present embodiment functions as a protection layer protecting the paired electrodes 28a and 28b and the conductive inorganic materials 33 from any upper layer (for example, the insulating layer 16a).
As described above, the composite electronic component 100 according to the present embodiment contains an ESD protection device of a low voltage type offering a reduced electrostatic capacitance, a reduced discharge starting voltage, and an improved durability against repeated use. Thus, the composite electronic component can function as a common mode filter having an advanced electrostatic protection function.
Furthermore, according to the present embodiment, the insulating inorganic material 32 and the conductive inorganic materials 33 are used as materials for the ESD protection device layer 12b, and none of the various materials forming the ESD protection device layer 12b contain resin. Thus, the ESD protection device layer 12b can be formed on the magnetic base 11a. Moreover, the common mode filter layer 12a can be formed on the ESD protection device layer 12b. A thermal treatment process at 350° C. or higher is required to form the common mode filter layer 12a using what is called a thin film formation method. A thermal treatment process at 800° C. is required to form the common mode filter layer 12a using what is called a stacking method of sequentially stacking ceramic sheets with respective conductive patterns formed thereon. However, when the insulating inorganic material 32 and the conductive inorganic material 33 are used for the ESD protection device layer, an ESD protection device can be reliably formed which can function normally while withstanding the thermal treatment process. Moreover, the ESD protection device can be formed on the sufficiently flat surface of the magnetic base. Thus, the fine gap of the gap electrode can be stably formed.
Additionally, according to the present embodiment, the gap electrodes are formed at the positions where the gap electrodes do not two-dimensionally overlap the first and second spiral conductors and the like forming the common mode filter to avoid the conductor patterns thereof. This prevents possible vertical impacts when the ESD protection device is partially electrostatically destroyed. Thus, a more reliable composite electronic component can be provided.
Moreover, according to the present embodiment, as shown in
The present invention will be described below in detail with reference to examples. However, the present invention is not limited to the examples.
As shown in
Then, as shown in
First, Au was deposited on parts of the surface of the base 2 with the electrodes 3a and 3b formed thereon by sputtering to form a layer of conductive inorganic materials 4b in which thin Au films of thickness 3 nm were discontinuously dispersed like islands. The sputtering was carried out using a multi-target sputter apparatus (trade name: ES350SU; manufactured by EIKO Engineering Co., Ltd.) under conditions including an argon pressure of 10 mTorr, an input power of 20 W, and a sputter time of 40 seconds.
Then, silicon dioxide was deposited, by the sputtering method, almost all over the surface of the base 2 with the electrodes 3a and 3b and the conductive inorganic materials 4b formed thereon so as to entirely cover the layer of the electrodes 3a and 3b and the conductive inorganic materials 4b in the thickness direction. Thus, a layer of an insulating inorganic material 4a of thickness 600 nm was formed. The sputtering was carried out using a multi-target sputter apparatus (trade name: ESU350; manufactured by EIKO Engineering Co., Ltd.) under conditions including an argon pressure of 10 mTorr, an input power of 400 W, and a sputter time of 40 minutes.
The above-described operations resulted in the formation of the functional layer 4 having the island-like conductive inorganic materials 4b discontinuously dispersed in the matrix of the insulating inorganic material 4a. Thereafter, as shown in
An ESD protection device 1 in Example 2 was obtained by performing operations similar to those in Example 1 except that the thickness of each of the electrodes 3a and 3b was changed to 0.2 p.m.
An ESD protection device 1 in Example 3 was obtained by performing operations similar to those in Example 1 except that the thickness of each of the electrodes 3a and 3b was changed to 0.4
An ESD protection device 1 in Example 4 was obtained by performing operations similar to those in Example 3 except that the gap distance ΔG between the electrodes 3a and 3b was changed to 2 p.m.
An ESD protection device 1 in Example 5 was obtained by performing operations similar to those in Example 1 except that the gap distance ΔG between the electrodes 3a and 3b was changed to 2.5 μm.
An ESD protection device 1 in Comparative Example 1 was obtained by performing operations similar to those in Example 1 except that the gap distance ΔG between the electrodes 3a and 3b was changed to 5 μm and that the formation of the functional layer 4 was omitted.
An ESD protection device 1 in Comparative Example 2 was obtained by performing operations similar to those in Example 1 except that the gap distance ΔG between the electrodes 3a and 3b was changed to 5 μm and that the sputtering of the conductive inorganic material 4b during the formation of the functional layer 4 was omitted.
An ESD protection device in Comparative Example 3 was obtained by performing operations similar to those in Example 1 except that the gap distance ΔG between the electrodes 3a and 3b was changed to 5 μm.
An ESD protection device in Comparative Example 4 was obtained by performing operations similar to those in Example 1 except that the gap distance ΔG between the electrodes 3a and 3b was changed to 3.5 p.m.
<Electrostatic Discharge Tests>
Then, an electrostatic test circuit shown in
The electrostatic discharge tests were carried out based on electrostatic discharge immunity tests and noise tests specified in the international standards IEC 61000-4-2, in conformity with the human body model (discharge immunity: 330Ω; discharged capacity: 150 pF; applied voltage: 8 kV; contact discharge). Specifically, as shown in the electrostatic test circuit in
The discharge starting voltage is the voltage at which an electrostatic absorption effect is manifested in an electrostatic absorption waveform observed while a voltage of 0.4 kV is increased at 0.2-kV increments during static electricity tests. A peak voltage is the maximum voltage value of the electrostatic pulse obtained when the static electricity tests based on the IEC 61000-4-2 are carried out at a charging voltage of 8 kV. Moreover, a clamping voltage is a voltage value obtained 30 nanoseconds after the wave front value of the electrostatic pulse observed when the static electricity tests based on the IEC 61000-4-2 are carried out based on contact discharge at a charging voltage of 8 kV.
The electrostatic capacitance (pF) was measured at 1 MHz. Furthermore, for discharge immunity, electrostatic discharge tests were repeated. The number of repetitions was counted until the ESD protection device stopped functioning. The discharge immunity was then evaluated based on the number of repetitions. Table 1 shows the results of the evaluation.
ESD protection devices 1 in Examples 6-8 were obtained by performing operations similar to those in Example 3 except that Ag, Au, and Al instead of Cu were used as the metal forming the electrodes 3a and 3b. Table 2 shows the results of the evaluation.
As described above, the ESD protection device and the composite electronic component combined with the ESD protection device according to the present invention offer a reduced discharge starting voltage and have improved durability against repeated use. Moreover, the ESD protection device and the composite electronic component allow improvements of heat resistance and weather resistance, and allow a further reduction in film thickness, improvement of productivity, and a reduction in costs. The ESD protection device and the composite electronic component can be effectively utilized for various electronic or electric devices and various apparatuses, facilities, systems, and the like including the electronic or electric devices. In particular, the ESD protection device and the composite electronic component can be widely and effectively utilized to prevent possible noise in high-speed differential transmission signal lines and video signal lines.
| Number | Date | Country | Kind |
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