JP4829040B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device used as a filter that passes a specific frequency band in an electronic communication device such as a mobile phone.

  In mobile phones, two types of analog and digital wireless communication systems are used, and the frequencies used range from 800 to 1000 MHz and 1.5 to 2.0 GHz. In these mobile communication devices, a surface acoustic wave element having a structure in which an IDT electrode is arranged in a ladder form on a piezoelectric substrate is used as a component in an RF unit (branching filter) that branches and generates a signal transmitted and received through an antenna. A surface acoustic wave element in which an IDT electrode is formed in a dual mode structure on a piezoelectric substrate is used.

  Here, an important characteristic of the duplexer is an isolation characteristic between the transmission wiring and the reception wiring. This is evaluated as the signal strength leaking to the reception wiring side in the transmission frequency band or the signal strength leaking to the transmission wiring side in the reception frequency band, and the strength of these leakage signals must be less than a predetermined level. In general, the level required in the transmission frequency band is stricter than the level required in the reception frequency band. In order to improve this isolation characteristic, it is indispensable to sufficiently secure the out-of-band attenuation of the surface acoustic wave element, particularly in the transmission frequency band of the surface acoustic wave element for receiving that has a strict requirement. It is necessary to secure sufficient attenuation.

  Therefore, as a duplexer with improved isolation characteristics, a surface acoustic wave element in which a DMS filter (double-mode filter element) is cascade-connected (subordinate connection) is mounted on a wiring board. Has been proposed (see Patent Document 1).

As shown in FIGS. 9 and 10, the wiring board employed in this structure includes an input wiring 21 that inputs a high frequency signal to the surface acoustic wave element 1 and a high frequency that has passed through a filter by the surface acoustic wave element 1. An output wiring 22 for outputting a signal, an input side common ground 24 connected to an input stage ground electrode of the surface acoustic wave element 1 via an input side ground wiring 23, and an output stage ground electrode of the surface acoustic wave element 1 And an output side common ground 26 connected via an output side ground wiring 25, and an inductor wiring 27 connected to the input side common ground 24 and the output side common ground 26.
JP 2003-249842 A

  However, although the duplexer proposed in Patent Document 1 has improved isolation characteristics as compared with the previous duplexer, the isolation between the transmission circuit and the reception circuit to such an extent that a very good reception quality can be secured. In order to satisfy the characteristics, it was necessary to secure a larger out-of-band attenuation.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface acoustic wave device that can secure a sufficient out-of-band attenuation and can be suitably used as a reception filter.

The present invention provides an input electrode, an output electrode, a filter in which an IDT electrode and a reflector are arranged in a dual mode structure on one main surface of a piezoelectric substrate, and two-stage cascaded input stage and output stage filter elements. A surface acoustic wave element having an input stage ground electrode connected to the filter element of the input stage and an output stage ground electrode connected to the filter element of the output stage is mounted on a wiring board. In the surface acoustic wave device, the wiring board includes an input wiring connected to the input electrode, an output wiring connected to the output electrode, and an input-side ground wiring having one end connected to the input stage ground electrode. An input side common ground connected to the input side ground wiring, an output side ground wiring having one end connected to the output stage ground electrode, an output side common ground connected to the output side ground wiring, Input side common graph An inductor wiring connected to de and the output side common ground, comprising a connection binding wire to the output side common ground with electromagnetically coupled with a portion of the input wiring, and the input side common ground wherein an output side common ground, not directly connected, a surface acoustic wave device characterized that it is connected through the inductor line.

Here, an annular conductor is formed along the outer edge of one main surface of the piezoelectric substrate, and a part of the coupling wiring is formed annularly on the wiring substrate corresponding to the annular conductor, the surface acoustic wave element is flip-chip mounted on the wiring substrate while forming a closed space for a portion of the annular conductor and form binding wire to said annular propagates joined SAW It is preferable that a part of the input wiring is formed inside the wiring board and is electromagnetically coupled by facing the coupling wiring.

  According to the present invention, a coupling wiring that is electromagnetically coupled to the input wiring is provided, and this is connected to the output-side common ground, so that a sufficient out-of-band attenuation can be ensured and can be suitably used as a reception filter. A surface acoustic wave device is obtained.

  This is presumably because part of the input current flows to the output side common ground via the coupling wiring due to magnetic field coupling between the input wiring and the coupling wiring, and the leakage signal entering the surface acoustic wave element is reduced. . Further, the potential of the second common ground (output side common ground) having a low potential can be brought close to the potential of the first common ground (input side common ground) having a high potential. It is thought that this is because the characteristics are exhibited.

An embodiment of the present invention will be described.
The surface acoustic wave device of the present invention includes an input stage and an output stage in which an input electrode 11, an output electrode 12, an IDT electrode and a reflector are arranged in a dual mode structure on one main surface of the piezoelectric substrate 10 shown in FIG. The filter element is connected in two stages in cascade, the input stage ground electrode 14 connected to the input stage filter element 13, and the output stage ground electrode 16 connected to the output stage filter element 15. The surface acoustic wave element 1 is mounted (not shown) on the wiring board 2 shown in the schematic explanatory diagram of FIG.

  The surface acoustic wave device 1 includes a piezoelectric substrate 10 made of a material such as a lithium tantalate single crystal, a lanthanum-gallium-niobium single crystal having a langasite-type crystal structure, and a lithium tetraborate single crystal on a principal surface of silver, An IDT electrode and other electrodes are formed of copper or the like.

  Specifically, as shown in FIG. 1, the IDT electrode is composed of a pair of comb electrodes having a plurality of electrode fingers intersecting each other, and three IDT electrodes 131, 132, 133 are arranged side by side. The input mode filter element 13 having a dual mode structure in which reflectors 134 are arranged on both sides (both sides in the SAW propagation direction) and three IDT electrodes 151, 152, and 153 are arranged side by side. A double-mode output stage filter element 15 having reflectors 154 disposed on both sides (both sides in the SAW propagation direction) is cascaded in two stages.

  In the IDT electrode 132 in the middle of the three IDT electrodes 131, 132, 133 arranged side by side in the input stage filter element 13, one of the pair of comb electrodes is connected to the input electrode 12, and the other Is connected to the input stage ground electrode 14. In the IDT electrode 131, one of the pair of comb electrodes is connected to the IDT electrode 151 of the output stage filter element 15, and the other is connected to the input stage ground electrode 14. Similarly, in the IDT electrode 133, one of the pair of comb electrodes is connected to the IDT electrode 153 of the output stage filter element 15, and the other is connected to the input stage ground electrode 15. The reflector 134 has a function of reflecting the leaky surface acoustic wave from the IDT electrode. By confining the energy of the surface acoustic wave excited by the IDT electrode between the two reflectors, the longitudinal first-order mode and the longitudinal third-order mode are separated and excited, and the resonance frequency difference between these two modes is used to DMS. Implement a filter.

  In the IDT electrode 152 in the middle of the three IDT electrodes 151, 152, and 153 arranged side by side in the output stage filter element 15, one of the pair of comb electrodes is connected to the output electrode 12. The other is connected to the output stage ground electrode 16. In the IDT electrode 151, one of the pair of comb electrodes is connected to the IDT electrode 131 of the input stage filter element 13, and the other is connected to the output stage ground electrode 16. Similarly, in the IDT electrode 153, one of the pair of comb electrodes is connected to the IDT electrode 133 of the input stage filter element 13, and the other is connected to the output stage ground electrode 16. The reflector 154 has a function of reflecting the leaky surface acoustic wave from the IDT electrode. By confining the energy of the surface acoustic wave excited by the IDT electrode between the two reflectors, the longitudinal first-order mode and the longitudinal third-order mode are separated and excited, and the resonance frequency difference between these two modes is used to DMS. Implement a filter.

  Note that the path from the IDT electrode 131 to the IDT electrode 151 is connected to the path from the IDT electrode 133 to the IDT electrode 153. This makes it difficult for the phase of the signal transmitted through each path to shift.

  A signal input from the input electrode 11 is divided into two by the IDT electrode 131 and the IDT 133 via the IDT electrode 132. That is, a surface acoustic wave (SAW) propagates from the IDT electrode 132 to the IDT electrode 131 and the IDT electrode 133. One of the signals divided by the input stage filter element 13 is transmitted from the IDT electrode 131 to the IDT electrode 151 in the filter element 15 of the output stage, and the other divided signal is transmitted from the IDT electrode 133 to the filter element of the output stage. 15 to the IDT electrode 153. Further, the signal from the IDT electrode 151 and the signal from the IDT electrode 153 merge at the IDT electrode 152. That is, a surface acoustic wave (SAW) propagates from the IDT electrode 151 and the IDT electrode 153 to the IDT electrode 152. A signal is output from the output electrode 16.

  The surface acoustic wave element 1 shown in FIG. 1 has an annular conductor 17 formed along the outer edge of one main surface of the piezoelectric substrate 10 for flip chip mounting (face-down mounting). Further, a conductive pattern (not shown in FIG. 2) formed in an annular shape corresponding to the annular conductor 17 is soldered to form a sealed space for propagating the surface acoustic wave. However, in the present invention, the mounting method of the surface acoustic wave element 1 is not limited to flip chip mounting (face-down mounting).

  The wiring board 2 in the surface acoustic wave device according to the present invention includes an insulating base 20 and various wirings formed on or inside the insulating base 20 as shown in FIG. Specifically, the various wirings include an input wiring 21 connected to the input electrode 11, an output wiring 22 connected to the output electrode 12, an input-side ground wiring 23 having one end connected to the input stage ground electrode 14, and An input-side common ground 24 connected to the input-side ground wiring 23, an output-side ground wiring 25 connected at one end to the output stage ground electrode 16, an output-side common ground 26 connected to the output-side ground wiring 25, An inductor wiring 27 connected to the input-side common ground 24 and the output-side common ground 26, and a coupling wiring 28 that is electromagnetically coupled to a part of the input wiring 21 and is connected to the output-side common ground 26 are included. . FIG. 2 is a schematic explanatory view showing only various wirings of the wiring board 2 in one embodiment of the present invention and extending it in the stacking direction for easy understanding.

  Examples of the constituent material of the insulating base 20 include ceramics such as alumina, glass ceramics that can be fired at low temperature, and resins such as FR4, and are not particularly limited. Since various wirings formed on the insulating base 20 are formed by simultaneous firing with the insulating base 20, the constituent material is selected according to the firing temperature of the material forming the insulating base 20. For example, when the insulating base 20 is made of ceramics such as alumina, various wirings are mainly composed of a high melting point material such as tungsten or molybdenum, and when the insulating base 20 is made of glass ceramics, As the various wirings, those mainly composed of a low resistance material such as copper, silver, or gold are used.

  As shown in FIG. 2, an input pad 211 and an input ground pad 212 are formed on the surface of the insulating base 20 as an entrance for inputting a high-frequency signal sent from a semiconductor element. Since the transmission line of the high frequency signal is composed of such a pair, the input pad 211 and the input ground pad 212 are also a pair. The input ground pad 212 is connected to the input side common ground 24.

  One end of the input wiring 21 is connected to the input pad 211, and the other end of the input wiring 21 is an input-side connection pad provided on the surface of the insulating base 20 corresponding to the input electrode 11 of the surface acoustic wave element 1. The high-frequency signal is transmitted from the input pad 211 to the input electrode 11 of the surface acoustic wave element 1 through the input wiring 21 and the input-side connection pad 213. The input wiring 21 is a wiring on the path between the input pad 211 and the input side connection pad 213, and is usually formed inside the insulating substrate 20 and includes the input wiring pattern 214.

  The input side ground connection pad 231 is provided on the surface of the insulating base 20 corresponding to the input stage ground electrode 14 of the surface acoustic wave element 1. The input-side ground connection pad 231 is connected to the input-side ground wiring 23 formed inside the insulating base 20, and the input-side common ground 24 provided on the back surface of the insulating base 20 through the input-side ground wiring 23. It is connected to the. Although three IDT electrodes are provided in the filter element 13 of the surface acoustic wave element 1 shown in FIG. 1, the ground sides of each are joined and connected to one input stage ground electrode 14. The input stage ground electrode 14 is connected to the input side ground connection pad 231 by a solder bump or the like.

  An output-side connection pad 221 and an output-side ground connection pad 251 are provided on the surface of the insulating base 20 so as to receive a high-frequency signal that has passed through the surface acoustic wave element 1. The output side connection pad 221 is connected to the output wiring 22 formed inside the insulating base 20, and is connected to the output pad 222 formed on the back surface of the insulating base 20 via the output wiring 22. The output wiring 22 refers to a wiring of a path between the output side connection pad 221 and the output pad 222.

  The output side ground connection pad 251 is provided on the surface of the insulating base 20 corresponding to the output stage ground electrode 16 of the surface acoustic wave element 1, and is provided on the back surface of the insulating base 20 via the output side ground wiring 25. The output side common ground 26 is connected. Although three IDT electrodes are provided in the filter element 15 of the surface acoustic wave element 1 shown in FIG. 1, the ground sides are joined together and connected to one output stage ground electrode 16. The output stage ground electrode 16 is connected to the output side ground connection pad 251 by a solder bump or the like.

  The input side common ground 24 and the output side common ground 26 are connected by an inductor wiring 27 while being separated in high frequency. If the input-side common ground 24 and the output-side common ground 26 are not connected, the signal in the pass band will not propagate, and if connected without using the inductor wiring 27, signal leakage from the input wiring to the output wiring will be large. This is because it becomes.

  Then, the output pad 222 and the output-side common ground 26 form a pair and are connected to the transmission line of the external circuit to output a high-frequency signal.

  Inside the insulating substrate 20 constituting the wiring board 2, a coupling wiring 28, which is a characteristic part of the present invention, is provided, and a coupling wiring pattern 281 that is a part of the coupling wiring 28 is a part of the input wiring 21. It is provided at a position where it is electromagnetically coupled to a certain input wiring pattern 214. FIG. 3 illustrates an example in which an input wiring pattern 214 that is a part of the input wiring 21 and a coupling wiring pattern 281 that is a part of the coupling wiring 28 are formed in the same layer. The coupling wiring 28 means a wiring including the coupling wiring pattern 281 and the via-hole conductor 282.

  Here, the thickness of the input wiring pattern 214 and the combined wiring pattern 281 is usually about 5 to 10 μm. In this embodiment, the length L and the distance D of the region (coupled region) where the input wiring 21 (input wiring pattern 214) and the coupled wiring 28 (coupled wiring pattern 281) are close to each other must not have excessive dielectric loss. In consideration of the fact that the bonding amount is not too small, the length L is preferably 100 to 1000 μm and the distance D is 50 to 300 μm.

  The coupling wiring 28 is not sensitive to the inductance component, but if it becomes too long, the potential of the output-side common ground 26 that is a low potential cannot be brought close to the potential of the input-side common ground 24 that is a high potential, and the elastic surface It is preferable that the total length of the coupling wiring 28 is 3000 μm or less because the effect that the inherent performance of the wave element 1 can be exhibited and the out-of-band attenuation can be increased.

  Furthermore, the connection point between the coupling wiring 28 and the output side common ground 26 is preferably close to the connection point between the output side ground wiring 25 and the output side common ground 26, and if it is too far, the low potential of the output side common ground 26 is reduced. It cannot be brought close to the high potential of the input-side common ground 24, and the effect that the inherent performance of the surface acoustic wave device 1 can be exhibited and the out-of-band attenuation can be increased is reduced. Accordingly, these distances are preferably 2000 μm or less.

  Here, as shown in FIG. 1 to FIG. 4, a structure in which a part of the input wiring pattern formed in the same layer and a part of the coupling wiring pattern are electromagnetically coupled, and the length of the coupling region is shown. The filter insertion loss was evaluated from 1.81 GHz to 1.93 GHz for L of 600 μm and the interval D of 75 μm. The result is shown in FIG.

  According to FIG. 5, the band whose out-of-band attenuation is −50 dB or less is from 1.85 GHz to 1.91 GHz. Further, as a comparative example, the insertion loss of the filter was evaluated from 1.81 GHz to 1.93 GHz for a conventional surface acoustic wave device having a structure as shown in FIGS. As a result, as shown in FIG. 11, the band with an out-of-band attenuation of −50 dB or less was 1.89 GHz to 1.91 GHz. Therefore, it can be seen that the filter characteristics (out-of-band attenuation characteristics) are improved by the present invention, and the out-of-band attenuation is sufficiently secured.

  In order to design so as to have such characteristics, first, a structure having no coupling wiring as shown in FIGS. 9 and 10 is used, and the out-of-band is adjusted by adjusting the inductance of the input ground wiring 23 and the output ground wiring 25. A wiring board having a desired filter characteristic in which the above is attenuated is designed. Then, a coupling wiring 28 that is electromagnetically coupled to a part of the input wiring 21 and has one end connected to the output-side common ground 26 is provided. At this time, the out-of-band attenuation can be sufficiently secured by adjusting the coupling amount by setting the length L and the interval D of the coupling region to the preferable ranges as described above. Such an effect appears due to the following two points.

  As a first consideration, a signal that enters a surface acoustic wave element due to magnetic field coupling between a part of the input wiring and a part of the coupling wiring causes a part of the input current to flow to the output side common ground via the coupling wiring. This is a point that is considered to be small.

  As another consideration, in the conventional wiring structure, the potential at the connection point between the output side ground wiring and the output side common ground is lower than the potential at the connection point between the input side ground wiring and the input side common ground. . That is, the surface acoustic wave element operates in a state where the first-stage common ground (input-side common ground) and the second-stage common ground (output-side common ground) are different from each other. Is not demonstrated. On the other hand, in the structure of the present invention, the electric potential coupling between the input wiring having the highest potential and the coupling wiring increases the potential of the coupling wiring, and the potential of the output-side common ground to which the coupling wiring is connected also increases. To do. As a result, the potential of the output-side common ground having a low potential approaches the potential of the input-side common ground, the original performance of the surface acoustic wave device is exhibited, and the out-of-band attenuation is increased.

Next, another embodiment of the present invention will be described.
In this surface acoustic wave device, as shown in FIGS. 6 and 7, an annular coupling wiring pattern 282 is formed on the surface of the insulating base 20, and a part of the coupling wiring pattern 282 and the input wiring pattern 214 are sandwiched between insulating layers. The other part of the wiring board 2 has substantially the same structure as that of the embodiment shown in FIGS. 1 to 4. In this embodiment, the distance between the part of the input wiring 21 and the part of the coupling wiring 28 (distance between the facing regions) is several tens to several hundreds μm, preferably 20 to 20 in consideration of the dielectric loss and the coupling amount. 100 μm. Further, preferably area opposed to is 5000~30000μm ^2.

  As shown in FIG. 1, the annular conductor 17 is independently formed along the outer edge of the one principal surface of the piezoelectric substrate 10 of the surface acoustic wave element 1, and the coupling wiring pattern 282 is formed so as to correspond to the annular conductor 17. Is formed on the wiring substrate (insulating base 20), so that the surface acoustic wave element 1 is joined to the annular conductor and the coupling wiring pattern 282 to form a sealed space for propagating the surface acoustic wave. It is flip-chip mounted on the insulating substrate 20).

  According to such a form, formation of the sealed space for propagating the surface acoustic wave and formation of the coupling electrode can be performed simultaneously.

Here, as shown in FIGS. 6 and 7, an annular coupling wiring pattern 282 is formed on the surface of the insulating base 20, and a part of the coupling wiring pattern 282 and a part of the input wiring pattern 214 are sandwiched between the insulating layers. And an insertion loss of a filter from 1.81 GHz to 1.93 GHz for a structure in which the area of the coupling region is 9750 μm ² and the interval D is 40 μm. Until evaluated. The result is shown in FIG.

  According to FIG. 8, the band where the out-of-band attenuation is −50 dB or less is changed from 1.84 GHz to 1.91 GHz, and the filter characteristics (out-of-band attenuation characteristics) are significantly improved compared to the characteristics of FIG. 11. Recognize. Although it is better than the filter characteristic shown in FIG. 5, the adjustment of the coupling amount is more suitable than the filter shown in FIG.

It is a schematic explanatory drawing of the structure of the surface acoustic wave element in one Embodiment of this invention. It is the schematic explanatory drawing which took out only the various wiring of the wiring board in one Embodiment of this invention, and was extended in the lamination direction. It is a schematic sectional drawing which shows the electromagnetic coupling state of the coupling wiring pattern and input wiring pattern which are shown in FIG. It is the schematic of the wiring structure of one Embodiment of this invention. 5 is a graph showing filter characteristics of the surface acoustic wave device shown in FIGS. 1 to 4. It is the schematic explanatory drawing which took out only the various wiring of the wiring board in other embodiment of this invention, and was extended in the lamination direction. It is a schematic sectional drawing which shows the electromagnetic coupling state of the coupling wiring pattern shown in FIG. 6, and an input wiring pattern. It is a graph which shows the filter characteristic of the surface acoustic wave apparatus shown in FIG. 6 and FIG. As a comparative example, it is a schematic explanatory diagram in which only various wirings of a wiring board not provided with a coupling wiring are taken out and extended in the stacking direction. It is the schematic of the wiring structure of the form of a comparative example. It is a graph which shows the filter characteristic of the surface acoustic wave apparatus as a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave element 10 ... Piezoelectric substrate 11 ... Input electrode 12 ... Output electrode 13 ... Input stage filter element 14 ... Input stage ground electrode 15 ... Output stage filter Element 16: Output stage ground electrodes 131, 132, 133, 151, 152, 153... IDT electrodes 134, 154... Reflector 2. ··· Input pad 212 ··· Input grounding pad 213 ··· Input side connection pad 214 ··· Input wiring pattern 22 ··· Output wiring 221 · · Output side connecting pad 222 ··· Output pad 23 ··· Input side grounding wiring 231 .. Input side ground connection pad 24... Input side common ground 25... Output side ground wiring 251... Output side ground connection pad 26. 28 ... coupling line 281 and 282 ... bonds wiring pattern

Claims (2)

A filter in which an input electrode, an output electrode, an IDT electrode and a reflector are arranged in a dual mode structure on one main surface of the piezoelectric substrate, and two-stage filter elements of the input stage and the output stage are connected in cascade; A surface acoustic wave formed by mounting a surface acoustic wave element formed with an input stage ground electrode connected to a stage filter element and an output stage ground electrode connected to the output stage filter element on a wiring board. A device,
The wiring board includes an input wiring connected to the input electrode, an output wiring connected to the output electrode, an input-side ground wiring having one end connected to the input stage ground electrode, and an input-side ground wiring Connected input side common ground, output side ground wiring having one end connected to the output stage ground electrode, output side common ground connected to the output side ground wiring, the input side common ground and the output side and an inductor connected commonly wired to ground, comprising a connection binding wire to the output side common ground with electromagnetically coupled with a portion of said input lines, said input side common ground and the output side common ground and it is not directly connected, a surface acoustic wave device characterized that it is connected through the inductor line. An annular conductor is formed along the outer edge of one main surface of the piezoelectric substrate, and a part of the coupling wiring is formed annularly on the wiring substrate corresponding to the annular conductor,
The surface acoustic wave element is flip-chip mounted on the wiring substrate while forming a closed space for a portion of the annular conductor and form binding wire to said annular propagates joined SAW ,
2. The surface acoustic wave device according to claim 1, wherein a part of the input wiring is formed inside the wiring board and is electromagnetically coupled by facing the coupling wiring.

Images