Electronic device including LTCC inductor

Provided is an electronic device that includes an LTCC inductor including a first sheet disposed on a substrate and including a first conductive pattern, a second sheet disposed on the first sheet and including a second conductive pattern, and a via electrically connecting the first conductive pattern to the second conductive pattern, and a spacer disposed on a lower surface of the first sheet to provide an air gap between the substrate and the first sheet, wherein the first conductive pattern is exposed out of the lower surface of the first sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2009-0066230, filed on Jul. 21, 2009, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The present invention disclosed herein relates to a low temperature cofired ceramic (LTCC) inductor, and more particularly, to an electronic device including an LTCC inductor.

Recently, electronic devices are required to be miniaturized and have high performance. To this end, a three dimensional stacking technology for manufacturing various integrated circuits and passive devices in a single module through a system-in-package process has been widely used.

According to a low temperature cofired ceramic (LTCC) technology, inner electrodes and passive devices are printed on a plurality of green sheets formed of glass-ceramic based material, so as to form a desired circuit, and then, the green sheets are stacked and cofired to manufacture a multi-chip module.

Through the LTCC technology, a circuit substrate and a combination module having high performance and high reliability can be fabricated. At first, the LTCC technology was expected to be used in various fields, but the LTCC technology was limited only to fields requiring special reliability, such as super computer fields or aerospace fields. Thus, the market of the LTCC technology was not expanded because of typical resin multi layered substrates. However, as the mobile communication market has rapidly grown in recent years, the LTCC technology is being widely used to achieve the miniaturization, low cost and high performance of a high frequency analog circuit.

Typical ceramic multi-layered substrates, formed of alumina-based material, require a high temperature firing process. However, according to the LTCC technology, glass-based material is added to perform a low temperature firing process. As such, a firing temperature is decreased to use a high electrical conductive metal, having low cost and low melting temperature, as the material of an interconnection of an inner layer. In addition, the LTCC technology prevents the shrinkage of a green sheet in an x-axis direction and a y-axis direction, so as to fabricate a circuit without modifying an initial design.

The LTCC technology is used for power amplifier modules, engine control units (ECUs) for automobiles, band pass filters, micro antennas, and wireless interfaces of mobile phones, so as to achieve high frequency, high reliability, low cost, miniaturization and low power consumption of a product.

SUMMARY

The present invention provides an LTCC inductor having a high quality factor and a high self resonant frequency characteristic.

Embodiments of the present invention provide electronic devices including: a low temperature cofired ceramic (LTCC) inductor including: a first sheet disposed on a substrate and including a first conductive pattern; a second sheet disposed on the first sheet and including a second conductive pattern; and a via electrically connecting the first conductive pattern to the second conductive pattern; and a spacer disposed on a lower surface of the first sheet to provide an air gap between the substrate and the first sheet, wherein the first conductive pattern is exposed out of the lower surface of the first sheet.

In some embodiments, the LTCC inductor may further include a plurality of sheets including a conductive pattern.

In other embodiments, an upper surface of the substrate may be recessed to form an air cavity that provides an additional air gap between the LTCC inductor and the substrate.

In still other embodiments, the first conductive pattern may include a first conductive line and first and second connections respectively disposed at both ends of the first conductive line, and the second conductive pattern may include a second conductive line and third and fourth connections respectively disposed at both ends of the second conductive line.

In even other embodiments, the first conductive line may cross the second conductive line, the first connection may be electrically connected to the fourth connection through the via, and the second connection may be electrically connected to the third connection through the via.

In yet other embodiments, the electronic devices may further include an input/output terminal electrically connected to one of the first and second conductive lines, wherein the input/output terminal is electrically connected to the substrate.

In further embodiments, the LTCC inductor may be electrically connected to the substrate through the spacer.

In still further embodiments, the second conductive pattern may include the input/output terminal that is electrically connected to the spacer through the via disposed in the first sheet.

In even still further embodiments, the first conductive pattern may include the input/output terminal that is electrically connected to the spacer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the specification, it will be understood that when a layer such as a conductive layer, a semiconductor layer or a dielectric is referred to as being ‘on’ another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Also, though terms like a first, a second, and a third are used to describe a specific grade, grades are not limited to these terms. These terms are used only to discriminate one grade from another grade.

In the following description, the technical terms are used only for explain a specific exemplary embodiment while not limiting the present invention. The terms of a singular form may include plural forms unless referred to the contrary. The meaning of “include,” “comprise,” “including,” or “comprising,” specifies a property, a region, a fixed number, a step, a process, an element and/or a component but does not exclude other properties, regions, fixed numbers, steps, processes, elements and/or components.

Additionally, the embodiment in the detailed description will be described with sectional views and/or plan views as ideal exemplary views of the present invention. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Accordingly, shapes of the exemplary views may be modified according to manufacturing techniques and/or allowable errors. Therefore, the embodiments of the present invention are not limited to the specific shape illustrated in the exemplary views, but may include other shapes that may be created according to manufacturing processes. For example, although an etch region is illustrated as a right-angled region, the etch region may be actually round or have a predetermined curvature. Areas exemplified in the drawings have general properties, and are used to illustrate a specific shape of a device region. Thus, this should not be construed as limited to the scope of the present invention.

FIGS. 1 through 3are schematic views illustrating an electronic device including a low temperature cofired ceramic (LTCC) inductor according to an embodiment of the present invention.

Referring toFIGS. 1 through 3, the LTCC inductor is mounted on a substrate150. The LTCC inductor may include first and second sheets110and120that may be green sheets. The green sheet may be formed by mixing ceramic powder, a dispersant, solvent, a polymer binder, a plasticizer, and, if necessary, an additive in a predetermined ratio.

FIG. 2is a plan view illustrating the lower surface of the first sheet110. The lower surface of the first sheet110may be provided with first conductive patterns114that may be formed of at least one selected from the group consisting of Au, Ag, and Cu. The first conductive patterns114may be formed through a typical LTCC process such as a screen printing process and an ink jet printing process. The first conductive pattern114may include a first conductive lines115and first and second connections116and117that are connected to both ends of the first conductive lines115. The first conductive lines115may be oblique and parallel to each other.

The lower surface of the first sheet110may be provided with mounting portions145that may be spaced apart from the first conductive patterns114and that may be formed together with the first conductive patterns114through the same process as that of the first conductive patterns114. The shape of the mounting portions145is not limited to the shape ofFIG. 2, provided that a shape is adapted for mounting. That is, the shape of the mounting portions145may be varied according to a connection method to a substrate.

FIG. 3is a plan view illustrating the upper surface of the second sheet120. Second conductive patterns124may be disposed on the upper surface of the second sheet120, and formed through the same process as that of the first conductive patterns114. The second conductive pattern124may include a second conductive lines125and third and forth connections126and127connected to both ends of the second conductive lines125. The second conductive lines125may be oblique and parallel to each other. The second conductive lines125may cross the first conductive lines115. The second conductive patterns124may further include input/output terminals128and129that may be connected to the second conductive lines125. The input/output terminals128and129may be used as members that are electrically connected to the substrate150that will be described later.

Referring toFIGS. 1 through 3, the first sheet110may be provided with first via holes130that may be disposed on the first and second connections116and117. The first via holes130may be formed by punching portions of the first sheet110. First preliminary vias131may be formed by filling the first via holes130with conductive paste.

The second sheet120may be provided with second via holes135that may be disposed under the third and fourth connections126and127. The second via holes135may be formed through the same process as that of the first via holes130. Second preliminary vias136may be formed by filling the second via holes135with conductive paste. The second preliminary vias136and the first preliminary vias131constitute vias139through which the first conductive patterns114may be electrically connected to the second conductive patterns124.

According to the current embodiment, the first conductive patterns114, the second conductive patterns124, and the vias139may be electrically connected to each other to constitute a solenoid type inductor. That is, the third connections126are electrically connected to the second connections117through the vias139, and the fourth connections127are electrically connected to the first connections116through the vias139. Thus, an electrical signal input through the input terminal128repeatedly passes through the first conductive patterns114, the vias139, and the second conductive patterns124, and then, arrives at the output terminal129. Thus, according to the current embodiment, the first conductive patterns114, the vias139, and the second conductive patterns124may constitute a solenoid type LTCC inductor. The first conductive patterns114and the second conductive patterns124are modified to adjust the number of turns or the thickness of the LTCC inductor and vary inductance. The thickness of a dielectric between the first conductive patterns114and the second conductive patterns124may be adjusted, or an additional dielectric sheet may be provided to vary inductance. Thus, an inductor having large inductance, which is difficult to fabricate on an integrated circuit, is easily fabricated using an external inductor.

Since the first conductive patterns114disposed on the lower surface of the first sheet110are exposed to air, the LTCC inductor according to the current embodiment has less parasitic capacitance than that of an embedded LTCC inductor mounted in a substrate. A quality factor (hereinafter, referred to as a Q value) of an inductor is the ratio of inductive reactance to the resistance of the inductor at a given frequency. The Q value of an inductor denotes the efficiency of the inductor. Typically, as a frequency is increased in a GHz level band, the Q value is increased and then decreased after reaching the maximum value, so as to form a parabola. At this point, a region where the Q value is increased or decreased according to frequency variation depends on a resistance component and a parasitic capacitance component of an inductor. That is, when parasitic capacitance is decreased, a Q value is improved. According to the current embodiment, since the first conductive patterns114are exposed to air that has low permittivity, the LTCC inductor according to the current embodiment has less parasitic capacitance than that of an embedded LTCC inductor, so as to obtain a high Q value.

Furthermore, the LTCC inductor according to the current embodiment has a high self resonant frequency characteristic. A self resonant frequency is a frequency in which the function of an inductor is lost due to increase in parasitic components. That is, since the LTCC inductor according to the current embodiment reduces parasitic capacitance, a self resonant frequency is increased.

A firing process is performed in the state where the second sheet120is disposed on the first sheet110. The firing process may be performed at a low temperature of about 1000° C. or less, like a typical LTCC process. The LTCC inductor is completed through the firing process.

The LTCC inductor is disposed on the substrate150that includes a silicon substrate, a PCB substrate, or an IC chip. The upper surface of the substrate150may be recessed to form an air cavity151that provides an additional space between the substrate150and the LTCC inductor. The air cavity151is not limited to the shape illustrated inFIG. 1, and thus, may be any structure providing an additional space. According to the current embodiment, the air cavity151may have one of a V-shaped vertical cross section, a U-shaped vertical cross section, and a tetragonal vertical cross section. The air cavity151may be formed through a wet etch process, a dry etch process, or a photo process. According to the current embodiment, a wet etch process using an etch solution including potassium hydroxide (KOH), tetramethyl ammonium hydroxide (TMAH), and ethylene diamine pyrocatechol (EDP) is performed to form the air cavity151.

Spacers140may be disposed between the LTCC inductor and the substrate150. The spacers140provide an air gap between the substrate150and the LTCC inductor. Accordingly, an air layer is maintained under the exposed first conductive patterns114. Thus, a high Q value and a high self resonant frequency can be obtained as described above. The spacers140are not limited to the shapes illustrated inFIG. 1, provided that the substrate150is spaced apart from the LTCC inductor. For example, the spacers140may be solder balls, Cu pillars, stud bumps, or polymer balls. According to the current embodiment, the spacers140may be disposed on the mounting portions145. That is, solder paste is applied on the mounting portions145and the substrate150, and solder balls are disposed therebetween, so as to provide an air gap between the LTCC inductor and the substrate150.

According to the current embodiment, the substrate150is electrically connected to the input terminal128and the output terminal129through wires160.

FIG. 4is a graph illustrating a Q value of the LTCC inductor according to the current embodiment. Referring toFIG. 4, while a typical embedded solenoid inductor has the maximum Q value of about 35, the LTCC inductor having a spacer and an air cavity has the maximum Q value of about 52, and thus, the Q value is increased by about 40%. Further, as the number of turns is increased, a Q value of the typical embedded solenoid inductor is quickly decreased, but the LTCC inductor still has a high Q value. In addition, the LTCC inductor according to the current embodiment has a high self resonant frequency. InFIG. 4, a self resonant frequency is a frequency where a Q value is zero.

FIGS. 5 through 7are a cross-sectional view and plan views illustrating an electronic device including an LTCC inductor according to an embodiment. Since the current embodiment is similar to the previous one except for electrical connection structure of the LTCC inductor, and the configuration of spacers240, a description of the same part as that of the previous embodiment will be omitted.

Referring toFIGS. 5 through 7, the LTCC inductor is mounted on a substrate250. The LTCC inductor may include first and second sheets210and220that may be green sheets. The green sheet may be formed by mixing ceramic powder, a dispersant, solvent, a polymer binder, a plasticizer, and, if necessary, an additive in a predetermined ratio.

FIG. 6is a plan view illustrating the lower surface of the first sheet210. The lower surface of the first sheet210may be provided with first conductive patterns214that may be formed of at least one selected from the group consisting of Au, Ag, and Cu. The first conductive patterns214may be formed through a typical LTCC process such as a screen printing process and an ink jet printing process. The first conductive pattern214may include a first conductive lines215and first and second connections216and217that are connected to both ends of the first conductive lines215. The first conductive lines215may be oblique and parallel to each other.

FIG. 7is a plan view illustrating the lower surface of the second sheet220. Second conductive patterns224may be disposed on the lower surface of the second sheet220, and formed through the same process as that of the first conductive patterns214. The second conductive pattern224may include a second conductive lines225and third and forth connections226and227connected to both ends of the second conductive lines225. The second conductive lines225may be oblique and parallel to each other. The second conductive lines225may cross the first conductive lines215. The second conductive patterns224may further include an input terminal228and an output terminal229that may be connected to the second conductive lines225. The input terminal228and the output terminal229may be used as members that are electrically connected to the substrate250that will be described later.

Referring toFIGS. 5 through 7, the first sheet210may be provided with first via holes230that may be disposed on the first and second connections216and217. The first via holes230may be formed by punching portions of the first sheet210. First vias231may be formed by filling the first via holes230with conductive paste. The first conductive patterns214may be electrically connected to the second conductive patterns224through the first vias231.

The first sheet210may be provided with second via holes237that may be disposed under the input terminal228and the output terminal229. The second via holes237may be formed through the same process as that of the first via holes230. Second vias238may be formed by filling the second via holes237with conductive paste.

According to the current embodiment, the first conductive patterns214, the second conductive patterns224, and the first vias231may be electrically connected to each other to constitute a solenoid type inductor. That is, the third connections226are electrically connected to the first connections216through the first vias231, and the fourth connections227are electrically connected to the second connections217through the vias231. Thus, an electrical signal input through the input terminal228repeatedly passes through the first conductive patterns214, the first vias231, and the second conductive patterns224, and then, arrives at the output terminal229. Thus, according to the current embodiment, the first conductive patterns214, the first vias231, and the second conductive patterns224may constitute a solenoid type LTCC inductor. The first conductive patterns214and the second conductive patterns224are modified to adjust the number of turns or the thickness of the LTCC inductor and vary inductance. The thickness of a dielectric between the first conductive patterns214and the second conductive patterns224may be adjusted, or an additional dielectric sheet may be provided to vary inductance. Thus, an inductor having large inductance, which is difficult to fabricate on an integrated circuit, is easily fabricated using an external inductor.

Since the first conductive patterns214disposed on the lower surface of the first sheet210are exposed to air, the LTCC inductor according to the current embodiment has less parasitic capacitance than that of an embedded LTCC inductor mounted in a substrate. A quality factor (hereinafter, referred to as a Q value) of an inductor is the ratio of inductive reactance to the resistance of the inductor at a given frequency. The Q value of an inductor denotes the efficiency of the inductor. Typically, as a frequency is increased in a GHz level band, the Q value is increased and then decreased after reaching the maximum value, so as to form a parabola. At this point, a region where the Q value is increased or decreased according to frequency variation depends on a resistance component and a parasitic capacitance component of an inductor. That is, when parasitic capacitance is decreased, a Q value is improved. According to the current embodiment, since the first conductive patterns214are exposed to air that has low permittivity, the LTCC inductor according to the current embodiment has less parasitic capacitance than that of an embedded LTCC inductor, so as to obtain a high Q value.

Furthermore, the LTCC inductor according to the current embodiment has a high self resonant frequency characteristic. A self resonant frequency is a frequency in which the function of an inductor is lost due to increase in parasitic components. That is, since the LTCC inductor according to the current embodiment reduces parasitic capacitance, a self resonant frequency is increased.

A firing process is performed in the state where the second sheet220is disposed on the first sheet210. The firing process may be performed at a low temperature of about 1000° C. or less, like a typical LTCC process. The LTCC inductor is completed through the firing process.

The LTCC inductor is disposed on the substrate250that includes a silicon substrate, a PCB substrate, or an IC chip. The upper surface of the substrate250may be recessed to form an air cavity251that provides an additional space between the substrate250and the LTCC inductor. The air cavity251is not limited to the shape illustrated inFIG. 5, and thus, may be any structure providing an additional space. According to the current embodiment, the air cavity251may have one of a V-shaped vertical cross section, a U-shaped vertical cross section, and a tetragonal vertical cross section. The air cavity251may be formed through a wet etch process, a dry etch process, or a photo process.

The spacers240may be disposed between the LTCC inductor and the substrate250. The spacers240provide an air gap between the substrate250and the LTCC inductor. Accordingly, an air layer is maintained under the exposed first conductive patterns214. Thus, a high Q value and a high self resonant frequency can be obtained as described above. The spacers240are not limited to the shapes illustrated inFIG. 5, provided that the substrate250is spaced apart from the LTCC inductor.

According to the current embodiment, the spacers240may be formed of conductive materials such as solder balls to electrically connect the LTCC inductor to the substrate250. That is, unlike the previous embodiment, the spacers240provide an air gap between the LTCC inductor and the substrate250, and simultaneously, electrically connect the LTCC inductor to the substrate250. The spacers240are electrically connected to the second vias238that are electrically connected to the input terminal228and the output terminal229. To this end, a pad255may be disposed on the substrate250. Thus, the LTCC inductor is electrically connected to the substrate250.

FIGS. 8 through 10are a cross-sectional view and plan views illustrating an electronic device including an LTCC inductor according to an embodiment. Since the current embodiment is similar to the embodiment of theFIG. 1except for electrical connection structure of the LTCC inductor, and the configuration of spacers340, a description of the same part as that of the embodiment of theFIG. 1will be omitted.

Referring toFIGS. 8 through 10, the LTCC inductor is mounted on a substrate350. The LTCC inductor may include first and second sheets310and320that may be green sheets. The green sheet may be formed by mixing ceramic powder, a dispersant, solvent, a polymer binder, a plasticizer, and, if necessary, an additive in a predetermined ratio.

FIG. 9is a plan view illustrating the lower surface of the first sheet310. The lower surface of the first sheet310may be provided with first conductive patterns314that may be formed of at least one selected from the group consisting of Au, Ag, and Cu. The first conductive patterns314may be formed through a typical LTCC process such as a screen printing process and an ink jet printing process. The first conductive pattern314may include a first conductive line315and first and second connections316and317that are connected to both ends of the first conductive line315. The first conductive lines315may be oblique and parallel to each other. The first conductive patterns314may further include input/output terminals318and319. The input/output terminals318and319may be connected to the first conductive lines315. The input/output terminals318and319may be used as members that are electrically connected to the substrate350that will be described later.

FIG. 10is a plan view illustrating the upper surface of the second sheet320. Second conductive patterns324may be disposed on the upper surface of the second sheet320, and formed through the same process as that of the first conductive patterns314. The second conductive pattern324may include a second conductive line325and third and forth connections326and327connected to both ends of the second conductive line325. The second conductive lines325may be oblique and parallel to each other. The second conductive line325may cross the first conductive line315.

Referring toFIGS. 8 through 10, the first sheet310may be provided with first via holes330that may be disposed on the first and second connections316and317. The first via holes330may be formed by punching portions of the first sheet310. First preliminary vias331may be formed by filling the first via holes330with conductive paste.

The second sheet320may be provided with second via holes335that may be disposed under the third and forth connections326and327. The second via holes335may be formed through the same process as that of the first via holes330. Second preliminary vias336may be formed by filling the second via holes335with conductive paste. The second preliminary vias336and the first preliminary vias331constitute vias339through which the first conductive patterns314may be electrically connected to the second conductive patterns324.

According to the current embodiment, the first conductive patterns314, the second conductive patterns324, and the vias339may be electrically connected to each other to constitute a solenoid type inductor. That is, the third connections326are electrically connected to the second connections317through the vias339, and the fourth connections327are electrically connected to the first connections316through the vias339. Thus, an electrical signal input through the input terminal318repeatedly passes through the first conductive patterns314, the vias339, and the second conductive patterns324, and then, arrives at the output terminal319. Thus, according to the current embodiment, the first conductive patterns314, the vias339, and the second conductive patterns324may constitute a solenoid type LTCC inductor. The first conductive patterns314and the second conductive patterns324are modified to adjust the number of turns or the thickness of the LTCC inductor and vary inductance. The thickness of a dielectric between the first conductive patterns314and the second conductive patterns324may be adjusted, or an additional dielectric sheet may be provided to vary inductance. For example, as shown inFIG. 11, an additional dielectric sheet360may be formed between the first sheet310and the second sheet320. Thus, an inductor having large inductance, which is difficult to fabricate on an integrated circuit, is easily fabricated using an external inductor.

Since the first conductive patterns314disposed on the lower surface of the first sheet310are exposed to air, the LTCC inductor according to the current embodiment has less parasitic capacitance than that of an embedded LTCC inductor mounted in a substrate. A quality factor (hereinafter, referred to as a Q value) of an inductor is the ratio of inductive reactance to the resistance of the inductor at a given frequency. The Q value of an inductor denotes the efficiency of the inductor. Typically, as a frequency is increased in a GHz level band, the Q value is increased and then decreased after reaching the maximum value, so as to form a parabola. At this point, a region where the Q value is increased or decreased according to frequency variation depends on a resistance component and a parasitic capacitance component of an inductor. That is, when parasitic capacitance is decreased, a Q value is improved. According to the current embodiment, since the first conductive patterns314are exposed to air that has low permittivity, the LTCC inductor according to the current embodiment has less parasitic capacitance than that of an embedded LTCC inductor, so as to obtain a high Q value.

Furthermore, the LTCC inductor according to the current embodiment has a high self resonant frequency characteristic. A self resonant frequency is a frequency in which the function of an inductor is lost due to increase in parasitic components. That is, since the LTCC inductor according to the current embodiment reduces parasitic capacitance, a self resonant frequency is increased.

A firing process is performed in the state where the second sheet320is disposed on the first sheet310. The firing process may be performed at a low temperature of about 1000° C. or less, like a typical LTCC process. The LTCC inductor is completed through the firing process.

The LTCC inductor is disposed on the substrate350that includes a silicon substrate, a PCB substrate, or an IC chip. The upper surface of the substrate350may be recessed to form an air cavity351that provides an additional space between the substrate350and the LTCC inductor. The air cavity351is not limited to the shape illustrated inFIG. 8, and thus, may be any structure providing an additional space. According to the current embodiment, the air cavity351may have one of a V-shaped vertical cross section, a U-shaped vertical cross section, and a tetragonal vertical cross section. The air cavity351may be formed through a wet etch process, a dry etch process, or a photo process.

The spacers340may be disposed between the LTCC inductor and the substrate350. The spacers340provide an air gap between the substrate350and the LTCC inductor. Accordingly, an air layer is maintained under the exposed first conductive patterns314. Thus, a high Q value and a high self resonant frequency can be obtained as described above. The spacers340are not limited to the shapes illustrated inFIG. 8, provided that the substrate350is spaced apart from the LTCC inductor.

According to the current embodiment, the spacers340may be formed of conductive materials such as solder balls to electrically connect the LTCC inductor to the substrate350. That is, unlike the embodiment ofFIG. 1, the spacers340provide an air gap between the LTCC inductor and the substrate350, and simultaneously, electrically connect the LTCC inductor to the substrate350. The spacers340are electrically connected to the input/output terminals318and319. To this end, pads355may be disposed on the substrate350. Thus, the LTCC inductor is electrically connected to the substrate350.

According to the embodiments of the present invention, the conductive patterns of the lower sheet of the LTCC inductor are exposed to air, and the spacers or the air cavity are disposed between the LTCC inductor and the substrate, thus obtaining a high quality factor and a high self resonant frequency characteristic.