Surface acoustic wave device

The present invention permits further miniaturization and shortening of a surface acoustic wave device while avoiding the influence of the surface acoustic wave device on the inductance value and performance index (Q value) of the spiral inductor. The chip on which the spiral inductor is formed is flip-chip mounted in a package together with another surface acoustic wave device chip. The package is provided with a hermetically sealed lid. A conductor pattern is formed on a face of the package that opposes the spiral inductor. Further, the overlap between the region of the spiral inductor and the conductor pattern is 7% or less.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device that comprises a chip on which a spiral inductor is formed.

2. Description of the Related Art

A surface acoustic wave device is employed in high-frequency circuit components of cellular phones or other miniature wireless devices, such as in splitters (duplexers) that are connected to a transmission/reception common antenna, for example. In this case, a surface acoustic wave device is constituted such that a SAW filter, which uses a surface acoustic wave element, and a phase shift circuit for separating the transmission and reception frequency bands or a phase matching circuit are mounted in a common package for the sake of miniaturization.

Proposals for further miniaturizing and shortening the height of such a surface acoustic wave device and a variety of proposals for enhancing the characteristics of the phase shift circuit or phase matching circuit to be used in the splitter have been made (Japanese Patent Application Laid Open Nos. H10-126213, 2001-127588, and H8-32402, for example).

The invention that appears in Japanese Patent Application Laid Open No. H10-126213 forms a phase matching circuit in a multilayered structure and implements miniaturization of the splitter by means of a SAW filter cavity structure that is mounted on the multilayered structure. Further, the invention in Japanese Patent Application Laid Open No. 2001-127588 proposes a structure in which an integrated circuit element is mounted on an upper substrate on the opposite side to the base substrate that does not meet the demands to facilitate fabrication and afford additional miniaturization and shortening of conventional structures in which two transmission/reception filters and an integrated circuit element that constitutes a peripheral circuit such as a phase matching circuit are commonly disposed on a base substrate.

In addition, the invention that appears in Japanese Patent Application Laid Open No. H8-32402 provides a solution for the occurrence of a characteristic variation that is caused by a parasitic capacitance produced between the surface of a matching inductance substrate and the lid of the package and for the generation of loss deterioration in a structure in which the surface acoustic wave element and matching inductance are stored in the same package. Therefore, the parasitic capacitance is suppressed by separating the mounted lid and the surface of the matching inductance substrate housed in the package by a distance of 0.5 mm or more.

In the process of examining additional miniaturization and shortening of a surface acoustic wave device that comprises a chip on which a spiral inductor is formed, the present inventors discovered that, in the case of a constitution in which a chip on which a spiral inductor is formed is flip-chip mounted on a cavity substrate face, the influence on the inductance value and performance index (Q value) of the spiral inductor of the distance of the metal (conductor) pattern disposed on the cavity-substrate face facing the spiral inductor and the amount of overlap of the metal (conductor) pattern and therefore discovered a specific distance for the metal (conductor) pattern disposed on the cavity substrate face and a specific amount for the overlap with the metal (conductor) pattern in order to obtain the preferred characteristics.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a surface acoustic wave device with a hermetic structure in which insertion loss is improved without deterioration of the characteristics when shortening is performed, on the basis of these discovered facts. Here, in the description of the present invention, a hermetic structure signifies a hermetically sealed structure.

A surface acoustic wave device that achieves the object of the present invention is, according to a first aspect, a surface acoustic wave device having a chip on which a spiral inductor is formed, wherein the chip on which the spiral inductor is formed is flip-chip mounted in a package together with another surface acoustic wave device chip; the package is provided with a hermetically sealed lid; a conductor pattern is formed on a face of the package that opposes the spiral inductor; and the overlap between the region of the spiral inductor and the conductor pattern is 7% or less.

A surface acoustic wave device that achieves the object of the present invention is, according to a second aspect, a surface acoustic wave device having a chip on which a spiral inductor is formed, wherein the chip on which the spiral inductor is formed is flip-chip mounted in a package together with another surface acoustic wave device chip; the package is provided with a hermetically sealed lid; a conductor pattern is formed on a face of the package that opposes the spiral inductor; and the gap between the spiral inductor and the conductor pattern is at least four or more times the wire width of the spiral inductor.

A surface acoustic wave device that achieves the object of the present invention is, according to a third aspect, a surface acoustic wave device according to aspect 1 or 2, wherein the surface acoustic wave device comprises two surface acoustic wave elements, one of which is a reception surface acoustic wave filter that passes a reception signal that is received from a common antenna, and the other is a transmission surface acoustic wave filter that passes a transmission signal that is supplied to the common antenna; and the chip on which the spiral inductor is formed has a capacitor formed in parallel with the spiral inductor and possesses the function of a phase shift circuit connected to the input side of the reception surface acoustic wave filter.

A surface acoustic wave device that achieves the object of the present invention is, according to a fourth aspect, a surface acoustic wave device according to aspect 3, wherein the conductor pattern on the face opposing the spiral inductor is a conductor for a connection with the reception surface acoustic wave filter, and a ground conductor.

A surface acoustic wave device that achieves the object of the present invention is, according to a fifth aspect, a surface acoustic wave device having a chip on which a spiral inductor is formed, comprising a first chip in which the spiral inductor is formed on an insulator substrate; and a second chip on which a surface acoustic wave device chip is formed, wherein the second chip is flip-chip mounted on the first chip so that the spiral inductor and the surface acoustic wave device chip lie opposite each other; the edges of the first chip and second chip are sealed by means of a hermetic structure; and the region of the spiral inductor and the region of the opposing surface acoustic wave device chip are formed without overlap.

A surface acoustic wave device that achieves the object of the present invention is, according to a sixth aspect, a surface acoustic wave device, wherein the surface acoustic wave device chip comprises two surface acoustic wave elements, one of which is a reception surface acoustic wave filter that passes a reception signal that is received from a common antenna, and the other is a transmission surface acoustic wave filter that passes a transmission signal that is supplied to the common antenna; and the chip on which the spiral inductor is formed has a capacitor formed in parallel with the spiral inductor and possesses the function of a phase shift circuit connected to the input side of the reception surface acoustic wave filter.

The characteristics of the present invention will become more evident from the embodiments of the invention that are described hereinbelow with reference to the drawings.

As a result of the present invention, it is possible to avoid the influence on the inductance value and performance index (Q value) of the spiral inductor of the distance of the metal (conductor) pattern that is disposed on a cavity substrate face facing the spiral inductor and the amount of overlap with the metal (conductor) pattern. As a result, further miniaturization and shortening of the surface acoustic wave device are possible.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described hereinbelow with reference to the drawings. Further, the embodiments described hereinbelow permit an understanding of the present invention but the technological scope of the present invention is not limited to these embodiments.

Here, prior to the description of the embodiments, facts discovered by the present inventors, which constitute the fundamental principles of the present invention, will first be described.

FIG. 1shows a chip on which only an inductor is mounted in order to illustrate the fundamental principles of the present invention.FIG. 1Ais a planar view of a chip on which only a spiral inductor2is mounted, andFIG. 1Bis a side cross-sectional view along the line A—A.

In the case of the chip8inFIG. 1, a spiral inductor2is formed, by means of copper wiring that has an internal diameter of 0.225, a wire width of 0.01 mm, a wire gap of 0.01 mm and 4.5 turns, on an insulator substrate1that consists of a glass substrate or of a silicon substrate covered by an insulating film of silicon oxide film. The chip8comprises signal pickups3outside the spiral and at the center thereof respectively.

The circumference of the spiral inductor2is buried by an insulator4with a relative permittivity of 2.8 and a cover5of 0.001 mm is formed at the top of the spiral inductor2. In addition, bumps7are formed on electrode pads6that are wired from the signal pickups3, thereby constituting the chip8. The material of the bumps7is Au or can be any solder material as long as similar characteristics suited to the object of the present invention are obtained.

FIG. 2illustrates a constitution in which a chip8, on which only the spiral inductor2shown inFIG. 1is mounted, is flip-chip mounted in the package.

FIG. 2Ais a planar view,FIG. 2Bis a side cross-sectional view, andFIG. 2Cis an enlarged view of a portion18ofFIG. 2B. As shown in these figures, the chip8is mounted on the die-attach face10of a ceramic package9by means of a flip-chip construction method, and a package lid91covers and hermetically seals the ceramic package9via sealing material92. The material of the ceramic package9may be any of alumina or LTCC (low temperature cofired ceramics).

Further,FIG. 3shows the face opposing the spiral inductor2. As shown inFIG. 3A, the face12opposing the spiral inductor2is a region of the nonconductor part9bwhere a metal pattern is not formed. The portion of the chip8excluding the region where the spiral inductor2is formed has a portion13that overlaps the metal pattern9a.

FIG. 3Bis a transparent view of the chip8in a state where the front and rear sides of the chip inFIG. 1Ahave been reversed. A state rendered by the superposition ofFIGS. 3A and 3Bis shown inFIG. 3C.

When a packaged inductance element was created as above and the inductance characteristic was measured, the inductance value was 7.6 nH and the performance index (Q value) was approximately 25.

Next, as a comparative example, the whole of the face opposing the spiral inductor2shown inFIG. 3Awas formed as the metal pattern9aand the influence on the Q value in the event of a variation in the distance between the spiral inductor2and the metal pattern9aof the face opposing the spiral inductor was examined.

FIG. 4is a graph showing the influence on the Q value in the event of a variation in the distance between the spiral inductor2and the metal pattern9aof the face opposing the spiral inductor in a state where there is a metal pattern9aof a fixed area on the face opposing the spiral inductor2at a frequency of 880 MHz by means of an electromagnetic field simulation.

It can be seen, from the results of the electromagnetic field simulation inFIG. 4, that, in comparison with the constitution ofFIG. 3A, the same Q value (=25) is obtained by separating the face opposing the spiral inductor2and the metal pattern9aby a distance of 40 μm or more (therefore, four or more times the spiral inductor wire width).

Next,FIG. 5shows a chip8in which capacitors are inserted in the chip constitution ofFIG. 1in parallel between the signal pickups3and spiral inductor2.FIG. 5Ais a planar view andFIG. 5Bis a side cross-sectional view along the line A—A. That is, parallel plate capacitors14are formed between the signal pickups3and spiral inductor2such that the respective capacitances are 3.4 pF. The capacitors14are approximately 0.08 mm2. A filter for an equivalence circuit is configured by means of this constitution. The remaining constitution is analogous to that ofFIGS. 1 to 3.

With a filter of this constitution, when the insertion loss was measured, same had a minimum value of approximately −2.5 dB. Next, as a comparative example, when the chip8ofFIG. 5is hermetically sealed in the package9, the metal pattern9ais formed on the face opposing the spiral inductor2in order to generate an overlap in 40% of the area of the spiral inductor2. The remaining constitution is analogous to that ofFIGS. 1 to 3.

Further, likewise, by means of an electromagnetic simulation, the influence on filter insertion loss when the distance between the spiral inductor2and the metal pattern9aof the face opposing the spiral inductor is changed at a frequency of 880 MHz was measured.

FIG. 6is a graph of simulation results that shows the relationship between the distance between the spiral inductor2and metal pattern9aof the face opposing the spiral inductor, and filter insertion loss. It can be seen fromFIG. 6that the spiral inductor2and the metal pattern9aof the face opposing the spiral inductor that overlaps a region of approximately 40% must be separated by a distance of 40 μm or more as per the earlier example (four times the wire width of the spiral inductor2) to render the same insertion loss (−2.5 dB).

It can be seen from the above examination that, irrespective of the Q value of the spiral inductance or the filter insertion loss, in cases where the spiral inductor2is flip-mounted in the package, when there is an overlap with the metal pattern on the face opposing the spiral inductor, the influence can be avoided by retaining a gap that is four or more times the wire width of the spiral inductor.

Here, a splitter (duplexer) is assumed for an application example of a package in which a chip, in which the examined spiral inductor2is formed on an insulator substrate, is flip-chip mounted in accordance with the present invention.

FIG. 7shows constitutional examples of a duplexer. The constitution shown inFIG. 7comprises a reception surface acoustic wave (SAW) filter21that passes a reception signal that is received by a common antenna24, and a transmission surface acoustic wave (SAW) filter22that passes a transmission signal that is supplied to the common antenna24.

InFIG. 7A, the phase shift circuit23is provided on the input side of the reception surface acoustic wave filter21so that the passband of the reception surface acoustic wave filter21is the blocked bandwidth of the transmission surface acoustic wave filter22.

Meanwhile, inFIG. 7B, the maximum electrical power can be transmitted by matching the characteristic impedance of the common antenna24and transmission and reception surface acoustic wave filters21and22by means of each of the impedance matching circuits41.

In addition, the example shown inFIG. 8shows a constitutional example of a typical reception balance filter. A reception signal that is received by an antenna (not shown) is inputted by a reception SAW filter25to a low noise amplifier27via a balance-type impedance-matching circuit26.

InFIGS. 7 and 8above, the phase shift circuit23and impedance matching-circuits41and26have a constitution in which inductance is included in the circuit. Therefore, when a constitution34comprising these circuits and a SAW filter is housed in a single hermetically sealed package, an application of the present invention according to the principles of the invention described earlier is feasible.

FIG. 9shows an embodiment in which the present invention is applied to the phase shift circuit23shown inFIG. 7A.FIG. 9Ais a planar constitutional view of a chip that corresponds to the phase shift circuit shown inFIG. 5.

InFIG. 9B, the phase shift circuit23and the transmission and reception SAW filters21and22shown inFIG. 7Aof a duplexer are made a single package constitution34.

The transmission SAW filter22and the reception SAW filter21are disposed in the package9in respective regions15and16. In addition, a chip8, which constitutes the phase shift circuit23, is mounted in the package9in accordance with the present invention. Each of the chips8constituting the transmission SAW filter22, reception SAW filter21, and phase-shift circuit23are mounted on the bottom face of the ceramic package9by means of the flip chip construction method.

FIG. 10illustrates the flip-chip mounting in the package9of only the chip8constituting the phase shift circuit23for the sake of simplification.

As shown in the planar view ofFIG. 9Aand the side cross-sectional view ofFIG. 10C, the chip8constituting the phase shift circuit23forms the spiral inductor2on a glass substrate1by means of copper wiring with an internal diameter of 0.225 mm, a wire width of 0.01 mm, a wire gap of 0.01 mm and 4.5 turns, and signal pickups3are provided outside the spiral inductor2and at the center thereof respectively. In addition, parallel plate capacitors14are constituted so that the respective capacitances in parallel between the signal pickups3and spiral inductor2are 3.4 pF. The capacitors14are approximately 0.08 mm2. The circumference of the spiral inductor2is buried in an insulator4with a relative permittivity of 2.8 and a cover5of 0.001 mm is provided at the top of the spiral inductor2. Next, bumps7are formed on pads6, which are wired from the signal pickups3, to render a single chip8.

The chip8constituting the phase shift circuit23is further mounted on the die-attach face10of the ceramic package9via the bumps7by means of the flip chip construction method. At such time, the gap11between the spiral inductor2and die-attach face10is 0.02 mm.

Here, a metal (conductor) pattern for a connection with the antenna24and reception SAW filter21exists on the die-attach face10opposite the chip8that constitutes the phase shift circuit23.FIG. 11illustrates this state.

InFIG. 11, the metal (conductor) pattern9a1, which connects to the antenna24and reception SAW filter21, and the ground metal (conductor) pattern9a2exist in the region of the die-attach face10facing the chip8that constitutes the phase shift circuit23.

Therefore, there are cases where the region opposite the spiral inductor2and the region of the metal (conductor) pattern9a1or the ground metal (conductor) pattern9a2overlap.

FIG. 12illustrates a case where the region opposite the spiral inductor2and the region of the ground metal (conductor) pattern9a2overlap. ‘A’ inFIG. 12represents the ground metal (conductor) pattern9a2as a surface area, ‘B’ represents the surface area of the spiral inductor2, and therefore ‘C’ shows the overlap of surface area A of the ground metal (conductor) pattern9a2and the surface area B of the spiral inductor2. The amount of overlap between the two surface areas can be determined.

Here, as shown inFIG. 9, the spiral inductor2is flip-flop mounted in the ceramic package9together with the reception SAW filter21and transmission SAW filter22and then the package9is sealed to render a single product.

The insertion loss of the reception SAW filter21and transmission SAW filter22of this product is measured and thus the relationship between the variation in the surface area of the metal face (ground pattern) on the face opposing the spiral inductor2and the accompanying insertion loss is determined.FIG. 13is a graph illustrating this relationship. The horizontal axis represents the ratio of the area of overlap of the opposing ground pattern9a2in relation to the total area of the spiral inductor2as a percentage (A/B). The vertical axis represents the variation in the insertion loss (−2.5 dB) with respect to when the insertion loss is 0 in cases where there is no overlap between the spiral inductor2and ground pattern9a2.

Based on the measurement results, the planar overlap between the ground pattern9a2on the die-attach face10and the spiral inductor2must be made 7% or less in order to make the insertion loss difference with respect to a case where there is absolutely no overlap 0.1 dB or less.

FIG. 14illustrates a case where the overlap of the spiral inductor2is not with the ground pattern9a2but instead with the signal pattern9a1. InFIG. 14, ‘D’ represents the surface area of the signal pattern9a1and ‘E’ denotes the overlap between the spiral inductor2and the area of the signal pattern9a1.

The insertion loss of the reception SAW filter21and transmission SAW filter22is measured andFIG. 15shows the relationship between the variation in the surface area of the metal face (signal pattern9a1) on the face opposing the spiral inductor2and the accompanying insertion loss. Here, as perFIG. 13, the horizontal axis represents the ratio (E/B) of the area of overlap of the opposing signal pattern9a1in relation to the total area of spiral inductor2as a percentage. The vertical axis represents the variation in the insertion loss (−2.5 dB) with respect to when the insertion loss is 0 in cases where there is no overlap between the spiral inductor2and signal pattern9a1.

Based on the measurement results, it can be seen that, with respect to the overlap with the signal pattern9a1, the planar overlap between the ground pattern9a2on the die-attach face10and the spiral inductor2must be made 7% or less as per the ground pattern overlap in order to make the preferred insertion loss difference 0.1 dB or less.

The above embodiment was a constitution in which the spiral inductor2was mounted in the package together with the transmission SAW filter21and reception SAW filter22likewise by means of flip-chip mounting and then the lid91was hermetically sealed. Meanwhile,FIG. 16is another embodiment according to the present invention, which is an example of a constitution in which only the transmission and reception SAW filters are flip-chip mounted and which especially facilitates fabrication and represents a structure that further enables miniaturization.FIG. 16Ais a perspective view in which a twin-layer structure is split into upper and lower layers to facilitate comprehension.FIG. 16Bis a side cross-sectional view along the line B—B of the lower layer inFIG. 16A.

InFIG. 16, the spiral inductor2is formed in the center of an insulator substrate1by means of copper wiring that has an internal diameter of 0.225 mm, a wire width of 0.01 mm, a wire gap of 0.01 mm and 4.5 turns, and signal pickups3are provided outside the spiral inductor2and at the center thereof respectively, whereby a chip8of lower-layer is constituted.

Parallel plate capacitors14are formed in parallel between the signal pickups3and spiral inductor2so that the respective capacitances are 3.4 pF. The capacitors14are approximately 0.08 mm2. The circumference of the spiral inductor2is buried in an insulator4with a relative permittivity of 2.8 and a cover5of 0.001 mm is provided at the top of the spiral inductor2. In addition, pads28are constituted at the circumference of the spiral inductor2and through-holes29are formed for through wiring. As a result, a chip8having the spiral inductor2, which is to become the lower layer, is constituted.

Meanwhile, a plurality of bumps7is formed on a single chip18formed with transmission and reception SAW filter (transmission filter30and reception filter31) patterns and mounted on a chip, whose lower layer constitutes an inductor and capacitor, to face the chip18by means of the flip chip construction method.

After mounting, the peripheral edge of the chip is rendered a hermetic structure by means of metal33. At such time, the gap40between the pattern face of the spiral inductor2and the face opposing the spiral inductor is approximately 20 μm and the face32opposing the spiral inductor2is in a state where a metal pattern is not present. In this case, the face32opposing the spiral inductor2is a region without a metal pattern and hence the size of the gap40need not be four or more times that of the wire width (0.01 mm) of the spiral inductor2.

Here, in the above description of the embodiments, the shape of the spiral inductor2is shown as an entirely circular spiral. However, the application of the present invention is not limited to such a case.FIG. 17shows other spiral shapes that may substitute the circular spiral (FIG. 17A).

Although a spiral inductor2with the circular layout ofFIG. 17Awas employed in the description of the embodiments of the present invention, the effect of the present invention may also be obtained by means of a spiral inductor with any of the layouts shown inFIG. 17.

Moreover, a resistor part can be formed in series with or in parallel with the inductor part of the chip where the spiral inductor of the present invention is formed and countermeasures to alleviate damage caused by ESD (electrostatic discharge) of the surface acoustic wave device chip can also be taken.

INDUSTRIAL APPLICABILITY

As a result of the application of the present invention as described hereinabove with reference to the drawings, it is possible to provide a surface acoustic wave device with a shortened hermetic structure with improved insertion loss and for which there is no characteristic deterioration, which makes a substantial contribution to miniaturization of devices in which a surface acoustic wave device is mounted.