JP4443325B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device, and in particular, a surface acoustic wave suitable for a high-frequency filter used in a transmission / reception demultiplexing circuit (hereinafter referred to as a duplexer) of a mobile communication device that is small and requires high power resistance. It relates to the device.

  In recent years, surface acoustic wave devices, particularly surface acoustic wave filters, have been widely used in the communication field, and are particularly compact because they have excellent features such as small size, steep filter characteristics, and excellent mass productivity. It is often used for communication equipment. In order to reduce the size of a mobile communication device, a surface acoustic wave filter is used instead of a conventionally used dielectric filter for a filter constituting a duplexer used in an internal transmission / reception circuit. It is becoming.

  However, since the duplexer is used in the front end of a mobile communication device, high power of 0.8 to 1.2 W is applied during transmission. For this reason, the surface acoustic wave filter that has been used exclusively in the reception circuit in the past has insufficient power resistance, and thus there is a strong demand for improvement in power resistance over the surface acoustic wave filter.

  In general, a surface acoustic wave filter has an interdigital transducer electrode (IDT electrode) that is an excitation electrode formed of aluminum (Al) on the surface of a piezoelectric substrate. This IDT electrode has improved power resistance. Therefore, Al-based alloy films obtained by adding a trace amount of dissimilar metals to Al by sputtering deposition, which has been well-established in the field of semiconductors for a long time, have been used. However, when this is used in a duplexer to which a high power load is applied during transmission, the above-described migration phenomenon occurs between the IDT electrodes, and thus there is a problem that the power resistance is not sufficient.

Migration refers to stress generated in the IDT electrode due to the surface acoustic wave, and distortion occurs. When this exceeds the limit, Al atoms as the electrode material move through the crystal grain boundary of the alloy, resulting in protrusions on the alloy. (Hiroc) and voids.

Therefore, in order to further improve the power durability of the surface acoustic wave filter, for example, as shown in Patent Document 1, it has been proposed to use a film in which titanium (Ti) and Al are alternately laminated as an IDT electrode. Yes. According to this, when power of 4 W is applied to the center frequency in an atmosphere of 100 ° C., the time when the insertion loss is degraded by 0.5 dB from the initial value is defined as the life, and the life of the Al single layer film is normalized by 1, It has been found that the Al-based alloy (adding 1% by mass of Ti to Al) single layer is 100, whereas the film in which Ti and Al are alternately laminated is 3 × 10 ⁷ , extending the life of about 5 digits.

  On the other hand, for duplexers, there is a strong demand for miniaturization. Conventionally, a surface acoustic wave element is mounted in a concave portion of a ceramic package, the pad electrode of the surface acoustic wave element and the terminal portion of the ceramic package are connected by wire bonding technology, and the concave portion is hermetically sealed with a cap or the like. Thus, a so-called package type surface acoustic wave filter, in which a surface acoustic wave filter is manufactured, is common.

On the other hand, in recent years, CSP (Chip Size Package) technology has been actively used for further downsizing, and surface acoustic wave elements are flip-chip mounted on a circuit board, so-called CSP type. As a surface acoustic wave filter, it has been proposed to reduce the space and height required for wire bonding in the conventional package type.
Japanese Patent No. 3430745

  However, a conventional surface acoustic wave device such as a surface acoustic wave filter has a problem that sufficient power durability cannot be obtained only by changing the film structure of the IDT electrode as described above.

  This is because high power is applied to the IDT electrode of the surface acoustic wave device, so that a large amount of heat is generated in the IDT electrode and the migration of the electrode material is accelerated by this heat, so the power resistance of the IDT electrode is insufficient. It is because it ends up.

  Further, if the surface acoustic wave device is of a CSP type in order to reduce the size, the surface on which the IDT electrode of the piezoelectric substrate is formed is face-down mounted toward the circuit substrate, so that high power is applied. There is a problem in that it is difficult to take a heat dissipation measure for releasing the heat generated in the IDT electrode, resulting in a disadvantage in terms of power durability. On the other hand, in a conventional package type surface acoustic wave device, a conductive paste having a good thermal conductivity is used when a surface acoustic wave element is mounted in a recess of the package, and the mounting surface is connected to the ground. As a result, an effective heat dissipation path was secured. In a CSP type surface acoustic wave device, heat can be radiated from the mounting surface side of the surface acoustic wave element only to the circuit board side through a conductor bump having a small cross-sectional area, and it is difficult to secure such an effective heat radiation path. There was a problem that there was.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a CSP type elastic surface that can be suitably used for a surface acoustic wave filter for a duplexer that is small but has excellent power durability. It is to provide a wave device.

  In the surface acoustic wave device of the present invention, 1) a plurality of IDT electrodes and a plurality of electrode pads are formed on one main surface of the piezoelectric substrate, and the one main surface surrounds the plurality of IDT electrodes and the plurality of electrode pads. A surface acoustic wave element having a grounding annular electrode formed thereon is mounted on the upper surface of the circuit board with the one main surface facing the circuit board, and the grounding annular electrode is formed inside or on the lower surface of the circuit board. It is connected to the ground conductor by a through conductor formed inside the circuit board.

  In the surface acoustic wave device according to the present invention, 2) in the configuration of 1), the grounding annular electrode has a quadrangular shape, and the through conductor is connected to the side thereof. .

  In the surface acoustic wave device according to the present invention, 3) In the configuration of 1), the plurality of IDT electrodes and the plurality of electrode pads form a plurality of filters, and the grounding annular electrode is the plurality of filters. It is characterized by being formed so as to individually enclose the.

  In the surface acoustic wave device according to the present invention, 4) in the configuration of 3), the grounding annular electrodes formed so as to individually surround the plurality of filters are in contact with each other. It is.

  In the surface acoustic wave device according to the present invention, the size of the grounding annular electrode formed so as to individually surround a plurality of filters is different in each of 5) 3) and 4) above. It is characterized by.

  In the surface acoustic wave device according to the present invention, 6) in each of the configurations 1) to 6), at least one of the IDT electrodes is electrically connected to the annular ring electrode for grounding through a resistor. It is characterized by this.

  According to the surface acoustic wave device of the present invention, 1) a plurality of IDT electrodes and a plurality of electrode pads are formed on one main surface of the piezoelectric substrate, and a plurality of IDT electrodes and a plurality of electrode pads are surrounded on the one main surface. A surface acoustic wave element having a grounding annular electrode formed thereon is mounted on the upper surface of the circuit board with one main surface facing the grounding electrode, and the grounding annular electrode is a grounding conductor formed inside or on the lower surface of the circuit board. In addition to being connected by a through conductor formed inside the circuit board, the heat generated in the IDT electrode is diffused through the grounding annular electrode formed so as to surround the IDT electrode. Since the through conductor connected to the annular electrode can be transmitted to the ground conductor of the circuit board and radiated from the ground conductor, even the CSP type surface acoustic wave device has its elastic surface It can be satisfactorily dissipate heat generated by the IDT electrode of the element, so that it is possible to suppress the occurrence of migration in the IDT electrode, an excellent surface acoustic wave device power durability.

  According to the surface acoustic wave device of the present invention, 2) when the grounding annular electrode has a quadrangular shape and the through conductor is connected to the side thereof, the grounding annular electrode is connected to the IDT electrode. Since it can be connected to the conductor pattern extending to the grounding annular electrode at the shortest distance, heat can be radiated more efficiently.

  According to the surface acoustic wave device of the present invention, 3) the plurality of IDT electrodes and the plurality of electrode pads form a plurality of filters, and the grounding annular electrode is formed so as to individually surround the plurality of filters. In this case, since the ground annular electrode serves as an electromagnetic shield for each filter, the electromagnetic coupling between the filters can be eliminated, and interference between the filters can be suppressed. In particular, in the case of a transmission filter and a reception filter in which a plurality of filters constitute a duplexer, interference between the filters means that a transmission signal amplified by a power amplifier leaks to the reception side. If such a leak occurs, a signal that must be received is disturbed, so interference between filters must be avoided.

  When the plurality of filters are, for example, a transmission filter and a reception filter, the surface acoustic wave device can be suitably used as a duplexer. Further, when the plurality of filters are, for example, a GSM filter and a DCS filter, the surface acoustic wave device can be reduced in size as compared with the case where two filters are formed on separate piezoelectric substrates. It can be suitably used as one that can reduce the mounting area.

  Further, according to the surface acoustic wave device of the present invention, 4) When the grounding annular electrodes formed so as to individually surround the plurality of filters are in contact with each other, there is a difference in the amount of heat generated by the plurality of filters. In addition, a filter with a large amount of heat generation can dissipate heat by using both the through-hole conductors of the grounding annular electrode surrounding itself and the grounding annular electrode surrounding the filter with low heat generation, so that it has better heat dissipation. Structure. Further, since the installation area of the grounding annular electrode can be reduced by contact as compared with the case where a plurality of grounding annular electrodes are not in contact with each other, the surface acoustic wave device can be reduced in size. In this case as well, each filter is electromagnetically cut off, and interference between the filters is suppressed.

  Further, according to the surface acoustic wave device of the present invention, 5) When the size of the grounding annular electrode formed so as to individually surround the plurality of filters is different, the grounding for surrounding the filter that generates a large amount of heat. By enlarging the annular electrode, more through conductors can be provided around the filter that generates a large amount of heat, so that heat can be efficiently released to the circuit board side.

  According to the surface acoustic wave device of the present invention, 6) When at least one of the IDT electrodes is electrically connected to the grounding annular electrode through the resistor, the heat generated in the IDT electrode is used for grounding. Although it is possible to escape through the annular electrode, the resistor can prevent the high frequency signal from escaping from the IDT electrode, so that the characteristics of the IDT electrode and the characteristics of the filter formed thereby are not affected. However, heat can be radiated well.

  Hereinafter, a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings schematically showing examples of embodiments. In the drawings described below, the same portions are denoted by the same reference numerals.

  1 to 3 show a first example of an embodiment of a surface acoustic wave device according to the present invention. FIG. 1 shows a piezoelectric substrate of a surface acoustic wave element constituting the surface acoustic wave device according to the present invention. FIG. 2 is a plan view showing a top surface of a circuit board on which the piezoelectric substrate is mounted, and FIG. 3 is a diagram showing the invention in which a surface acoustic wave element is mounted on the circuit board. FIG. 3 is a cross-sectional view of the surface acoustic wave device taken along the line AA ′ in FIG. 1 and the line BB ′ in FIG. 2.

  In FIG. 1, 1 is a piezoelectric substrate, 2 is an IDT electrode formed on one main surface of the piezoelectric substrate 1, and 3 is electrically connected to an IDT electrode 2 formed on one main surface of the piezoelectric substrate 1. In addition, electrode pads 4 functioning as input / output terminals are grounding annular electrodes formed on one main surface of the piezoelectric substrate 1 so as to surround the plurality of IDT electrodes 2 and the plurality of electrode pads 3. A surface wave device is configured. The first example is an example in which a duplexer using a ladder type surface acoustic wave filter is configured, and a plurality of IDT electrodes 2 and a plurality of electrode pads 3 are used as a plurality of filters on the piezoelectric substrate 1 for transmission. The filter 5 and the reception filter are configured, and the grounding annular electrode 4 is formed so as to individually surround the transmission filter 5 and the reception filter 6. In the first example, the IDT electrode 2 constituting the transmission filter 5 generates heat during operation when high power is input, and the grounding annular electrode 4 is formed in a square shape.

  On the other hand, in FIG. 2, 11 is a circuit board, 12 is an input / output through conductor formed on the circuit board 11 corresponding to the electrode pad 3 and functions as an input / output terminal, and 13 is grounded to the upper surface of the circuit board An annular conductor for grounding formed corresponding to the annular electrode 4 for use, 14 is a through conductor formed corresponding to the annular electrode 4 for grounding inside the circuit board 11, and 15 is formed on the lower surface of the circuit board 11, This is a ground conductor to which the through conductor 14 is connected. The ground conductor 15 may be formed inside the circuit board 11 in some cases.

  In FIG. 3, 1 is a piezoelectric substrate, 4 is an annular electrode for grounding, 5 is a filter for transmission, 6 is a filter for reception (IDT electrode 2 and electrode pad 3 are not shown), and 11 is a circuit. A substrate, 14 is a through conductor, 15 is a ground conductor (the input / output through conductor 12 and the ground annular conductor 13 are not shown), and 21 is a surface acoustic wave device mounted on the circuit board 11. It is a sealing resin that stops.

  Thus, in the surface acoustic wave device of the present invention, a plurality of IDT electrodes 2 and a plurality of electrode pads 3 are formed on one main surface of the piezoelectric substrate 1, and the plurality of IDT electrodes 2 and a plurality of electrode pads 3 are formed on the one main surface. A surface acoustic wave element in which an annular electrode 4 for grounding is formed so as to surround the electrode pad 3 is mounted on the upper surface of the circuit board 11 so that one main surface thereof is opposed to the circuit board 11. Is connected to a ground conductor 15 formed on the inside or the lower surface of the circuit board 11 by a through conductor 14 formed inside the circuit board 11. As a result, the heat generated in the IDT electrode 2 is diffused through the grounding annular electrode 4 formed so as to surround the IDT electrode 2, and the circuit board is connected to the through conductor 14 connected to the grounding annular electrode 4. 11 can be transmitted to the ground conductor 15 and dissipated from the ground conductor 15, so that even the CSP type surface acoustic wave device can dissipate the heat generated by the IDT electrode 2 of the surface acoustic wave element satisfactorily. As a result, the occurrence of migration in the IDT electrode 2 can be suppressed, and the surface acoustic wave device excellent in power durability can be obtained.

  Further, when the grounding annular electrode 4 and the through conductor 14 are connected, the grounding annular conductor 13 is formed on the upper surface of the circuit board 11 so as to correspond to the grounding annular electrode 4 as in the first example. When the grounding annular electrode 4 and the through conductor 14 are connected to the grounding annular electrode 4 and the grounding annular conductor 13, the IDT electrode 2 and the electrode pad 3 are hermetically sealed in the space inside the grounding annular electrode 4 and the grounding annular conductor 13, respectively. Even if an external force is applied to the piezoelectric substrate 1, it can be received by the grounding annular electrode 4 and the grounding annular conductor 13 to prevent adverse effects on the operation of the IDT electrode 2. The surface acoustic wave device is excellent in reliability.

  Further, when the grounding annular electrode 4 has a quadrangular shape and a through conductor 14 is connected to the side thereof as in the first example, the grounding annular electrode 4 is connected to the grounding annular electrode 4 from the IDT electrode 2. Since the conductor pattern extending to the electrode 4 can be connected at the shortest distance, heat can be radiated more efficiently.

  Further, as in the first example, a plurality of IDT electrodes 2 and a plurality of electrode pads 4 constitute, for example, a transmission filter 5 and a reception filter 6 as a plurality of filters, and the grounding annular electrode 4 is supplied with these transmission electrodes. When the trust filter 5 and the reception filter 6 are formed so as to surround the filter 5 and the reception filter 6, the grounding annular electrode 4 serves as an electromagnetic shield for each filter 5, 6. 6 can be eliminated, and interference between the filters 5 and 6 can be suppressed.

  In the surface acoustic wave device of the present invention, the piezoelectric substrate 1 constituting the surface acoustic wave element is a substrate made of a piezoelectric material such as lithium tantalate, for example, a 36 ° ± 3 ° Y-cut X propagation lithium tantalate single unit. Crystal, 42 ° ± 3 ° Y-cut X-propagation lithium tantalate single crystal, 64 ° ± 3 ° Y-cut X-propagation lithium niobate single crystal, 41 ° ± 3 ° Y-cut X-propagation lithium niobate single crystal, A 45 ° ± 3 ° X-cut Z-propagation lithium tetraborate single crystal can be suitably used because it has a large electromechanical coupling coefficient and a small frequency temperature coefficient. The thickness of the piezoelectric substrate 1 is preferably about 0.1 mm to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate 1 tends to break, and if it exceeds 0.5 mm, the component dimensions tend to be large and it is difficult to achieve downsizing of the surface acoustic wave device.

  The plurality of IDT electrodes 2 formed on one main surface of the piezoelectric substrate 1 constitutes a ladder type filter connected in a ladder shape in series and in parallel with each other, so that the transmission filter 5, the reception filter 6, etc. The filter constitutes a surface acoustic wave filter having a steep and low-loss filter characteristic. A plurality of electrode pads 3 are formed on the same main surface of the piezoelectric substrate 1, and these electrode pads 3 serving as grounding terminals or signal input / output terminals for transmission or reception are provided on the IDT electrode 2. Are electrically connected.

  In addition, although the example which comprised the transmission filter 5 and the reception filter 6 was shown in the 1st example, this can be used suitably as a duplexer. In addition, when the PCS half band filter is used as a constituent filter, for example, the bandwidth specification of the PCS band is strict, so the pass band is divided into two bands, a low band and a high band. The filter and the high band filter can be formed on the same piezoelectric substrate 1.

  Further, the grounding annular electrode 4 formed on the same main surface of the piezoelectric substrate 1 so as to surround the plurality of IDT electrodes 2 and the plurality of electrode pads 3 has the electrode pads 3 on the upper surface of the circuit board 11. Each of the input / output through conductors 12 formed in correspondence with each other is connected via a conductor bump (not shown), and the grounding annular electrode 4 is formed on the upper surface of the circuit board 11 in correspondence therewith. For example, a soldering material such as solder is used to connect the grounding annular conductor 13 so as to seal the inside in an annular shape. As a result, a predetermined space can be secured on the operating surface side of the surface acoustic wave element and the airtightness of the space can be maintained, so that the surface acoustic wave element can be stably operated while suppressing the influence of the external environment. In addition, the operation can be performed stably over a long period of time, and a highly reliable surface acoustic wave device can be obtained.

  Further, each IDT electrode 2 and each electrode pad 3 is sealed by sealing, for example, nitrogen gas, which is an inert gas, in the inside of the ring-shaped hermetic electrode 4 and the ring-shaped ring conductor 13 hermetically sealed. Since deterioration due to oxidation or the like of each input / output through conductor 12 can be effectively prevented, higher reliability can be achieved.

  The grounding annular electrode 4 is connected to the grounding conductor 15 formed on the lower surface of the circuit board 11 by the through conductor 14 through the grounding annular conductor 13, so that the heat generated in the IDT electrode 2 as described above. Can be dissipated well.

  Such a grounding annular electrode 4 is formed into a rectangular shape on one main surface of the piezoelectric substrate 1 so as to surround the plurality of IDT electrodes 2 and the plurality of electrode pads 3, thereby forming the piezoelectric substrate. The filter (5, 6) composed of a plurality of IDT electrodes 2 and a plurality of electrode pads 3 can be effectively arranged on the inside using a large area. . At this time, when a plurality of filters are configured, it is preferable to form the plurality of filters so as to be individually surrounded by the grounding annular electrode 4.

  The grounding annular electrode 4 is preferably formed with a width of, for example, 0.05 mm to 0.15 mm in consideration of sealing performance with brazing material such as solder and alignment accuracy. If the width is smaller than 0.05 mm, it tends to be difficult to satisfy the sealing performance by solder and the reliability by mechanical stress. In addition, providing the grounding annular electrode 4 with a larger width than necessary makes it difficult to effectively arrange the plurality of IDT electrodes 2 and the plurality of electrode pads 3 using a large area inside. What is necessary is just to set suitably according to the characteristic and specification which are requested | required of a surface acoustic wave apparatus.

  The IDT electrode 2, the electrode pad 3, and the grounding annular electrode 4 are made of Al, Al-based alloy, copper, copper alloy, gold, gold alloy, tantalum, tantalum alloy, or a laminated film of layers made of these materials. Alternatively, a laminated film of a layer made of these materials and a layer made of a material such as titanium or chromium can be used. As a film forming method, a sputtering method or an electron beam evaporation method can be used. After film formation, a photoresist is spin-coated to a thickness of about 0.5 μm, and then a desired electrode pattern is patterned with a stepper (reduction projection exposure machine). Next, an unnecessary portion of resist is formed with a developing device. After melting with an alkali developer and exposing a desired electrode pattern, the electrode is etched by a RIE (Reactive Ion Etching) apparatus, and the IDT electrode 2 of the desired electrode pattern, the electrode pad 3, the annular electrode 4 for grounding Get.

  The circuit board 11 is composed of an insulating board in which a plurality of insulating layers made of ceramics, glass, resin, etc. are laminated, and an annular conductor for grounding 13 or an input / output through conductor 12, A conductor pattern or a through conductor pattern for forming a desired wiring including the through conductor 14 and the ground conductor 15 is made of metal conductor such as Au, Cu, Ag, Ag-Pd, W or the like by screen printing, vapor deposition or sputtering. It is formed by a combination of a film forming method and etching. Each conductor pattern or each through conductor pattern may be plated with Ni, Au, or the like on the surface if necessary for good bonding with the surface acoustic wave element.

  The circuit board 11 in the first example is manufactured by laminating two insulating layers. For these insulating layers, for example, ceramics mainly composed of alumina, glass ceramics that can be sintered at a low temperature, or glass epoxy resins mainly composed of organic materials are used. A green sheet is produced by forming a slurry in which a metal oxide such as ceramics and an organic binder are homogeneously kneaded with an organic solvent into a sheet. After forming a desired conductor pattern and through conductor pattern, these green sheets are laminated. It is produced by integrally forming by firing and then firing.

  Conductive bumps connecting the electrode pads 3 and the input / output through conductors 12 are formed of a conductive material such as solder or gold. In the case of forming with solder, for example, after applying cream solder to the end of the electrode pad 3 or the input / output through conductor 12 by screen printing, the solder bump can be melted to form a conductor bump. In the case of forming with gold, for example, a gold wire can be wire-bonded to the electrode pad 3 or the end of the input / output through conductor 12 and cut into a short length to form a conductor bump. In connection with this conductor bump, pressure bonding may be performed while applying heat, ultrasonic waves, or the like. According to this, reliable and good connection is possible.

  The through conductor 14 formed on the circuit board 11 is used to connect the grounding annular electrode 4 to the ground conductor 15 for electrical grounding and to provide good heat dissipation, and is mounted on the upper surface of the circuit board 11. The surface acoustic wave element is formed corresponding to the grounding annular electrode 4. The through conductor 14 is arranged near the intersection of the wiring pattern connected to the ground from the IDT electrode 2 having a large calorific value or from the parallel resonator to the ground, or the reflector of the IDT electrode 2 having a large calorific value. When it is electrically connected to the grounding annular electrode 4, it is preferable to make it near the connecting portion because the heat radiation path is short and the heat radiation effect is enhanced.

  In particular, when the grounding annular electrode 4 is formed in a square shape, the grounding annular electrode 4 can be effectively disposed and used up to the corner of the piezoelectric substrate 1, and the IDT electrode 2 and the electrode pad 3 can be used. Since it can be effectively arranged on the inside using a large area, it is preferably arranged at a position corresponding to the side and connected to the grounding annular electrode 4. In addition, the size of the through conductor 14 is advantageous when the diameter is large in consideration of heat dissipation, but if it is too large, thermal expansion between the through conductor 14 made of, for example, ceramics and metal that is an insulating material of the circuit board 11 The coefficient difference becomes large, and cracks such as cracks are generated in the insulating layer in the vicinity of the through conductor 14, which may cause a decrease in connection reliability. Therefore, the diameter of the through conductor 14 is preferably about 50 to 200 μm here.

  The ground conductor 15 formed inside or on the lower surface of the circuit board 11 is connected to an external electronic circuit to ground the surface acoustic wave device, and generates heat generated by the operation of the IDT electrode 2 in the surface acoustic wave device. It has a function to dissipate heat well to the outside. Such a ground conductor 15 is preferably located at a position where it can be connected through the shortest path in order to efficiently release the heat generated by the IDT electrode 2 to an external electronic circuit. That is, it is desirable that the ground conductor 15 and the grounding annular electrode 4 are linearly connected by the through conductor 14. Further, since the ground conductor 15 is a main path for releasing the heat generated by the IDT electrode 2 to an external electronic circuit, it is desirable that the ground conductor 15 which is a connection surface thereof is as large as the design allows.

  The sealing resin 21 functions as an exterior protective material for hermetically sealing the surface acoustic wave element mounted on the circuit board 11 and protecting it from the external environment and external force. The surface acoustic wave element is formed from the other principal surface of the piezoelectric substrate 1 (which is the upper surface in FIG. 1) to the upper surface of the circuit substrate 11 so as to form the outer shape of the surface acoustic wave device. Thus, the piezoelectric substrate 1 mounted on the upper surface of the circuit board 11 is sealed with an epoxy resin, a biphenol resin, a polyimide resin, or a resin in which a filler such as alumina, aluminum nitride, or silicon nitride is mixed as a solid filler. By sealing with the resin 21, the piezoelectric substrate 1 and the electrical connection portion can be protected from mechanical impacts, moisture, chemicals, and the like, and a highly reliable surface acoustic wave device can be obtained.

  In the surface acoustic wave device according to the present invention, the grounding electrode pad 3 of the transmission filter 5 has a plurality of through conductors shifted in the vertical direction from the upper surface to the lower surface of the circuit board 11 as conductors in the circuit board 11. It is preferable to connect to stepped through conductors connected in steps by layers. According to this, the stepped through conductor in which the parasitic inductance generated in the ground conductor of the transmission filter 5 (more specifically, the low-pass filter) constituted by the IDT electrode 2 is connected in a stepped manner in the circuit board 11. , So that the parallel resonator of the transmission filter 5 (low-pass filter) overlaps the frequency band of the reception filter 6 (more specifically, the high-pass filter). Since the impedance of the transmission filter 5 can be reduced, it is possible to effectively block a signal that passes through a band that overlaps the high frequency side frequency band. Therefore, the high frequency of the transmission filter 5 (low frequency side filter) The out-of-side band attenuation characteristics can be greatly improved. As such a stepped through conductor, for example, a plurality of through conductors may be formed with a diameter of about 0.05 mm to 0.2 mm. For the purpose of increasing the inductance of the stepped through conductor, the through conductor has a diameter of 0.1 mm or less. What is necessary is just to form.

  In the surface acoustic wave device of the present invention, the electrode pad 3 of the reception filter 6 is preferably connected to a linear through conductor formed linearly on the circuit board 11 from the upper surface to the lower surface. According to this, the linear through conductor formed linearly in the circuit board 11 with respect to the parasitic inductance generated in the ground conductor of the reception filter 6 (more specifically, the high-pass filter) constituted by the IDT electrode 2. To reduce the impedance in the band overlapping the frequency band of the transmission filter 5 (low-pass filter) for the parallel resonator of the reception filter 6 (high-pass filter). Therefore, it is possible to effectively block a signal that passes through a band that overlaps the low frequency side frequency band. Therefore, the low frequency side out-of-band attenuation characteristic of the reception filter 6 (high frequency side filter) can be achieved. Can be improved satisfactorily. As such a linear through conductor, for example, a linear through conductor (or a plurality of through conductors connected in a straight line) may be formed with a diameter of about 0.05 mm to 0.2 mm. For the purpose of reducing the size, the through conductor may have a diameter of 0.1 mm or more.

  Next, FIG. 4 shows a second example of the embodiment of the surface acoustic wave device of the present invention. The IDT of the piezoelectric substrate of the surface acoustic wave element constituting the surface acoustic wave device of the present invention similar to FIG. It is a top view which shows the surface in which the electrode was formed. 4, the same reference numerals are given to the same parts as in FIG. 1. In this example, the grounding annular electrodes 4 that individually surround the plurality of transmission filters 5 and reception filters 6 are in contact with each other. The transmission filter 5 and the reception filter 6 are each surrounded by the same grounding annular electrode 4.

  According to the second example having such a structure, the surface acoustic wave element and the surface acoustic wave device can be further reduced in size while having the same heat dissipation as compared with the first example.

  Next, FIG. 5 and FIG. 6 show a third example of the embodiment of the surface acoustic wave device of the present invention, and the piezoelectric of the surface acoustic wave element constituting the surface acoustic wave device of the present invention similar to FIG. It is a top view which shows the surface in which the IDT electrode of the board | substrate was formed, and a top view which shows the upper surface of the circuit board in which the piezoelectric substrate similar to FIG. 2 is mounted. 5 and 6, the same reference numerals are given to the same portions as those in FIGS. 1 and 2, and in this example, grounding that individually surrounds the transmission filter 5 and the reception filter 6 that are a plurality of filters. The annular electrodes 4 are in contact with each other and have different sizes, and the transmitting filter 5 and the receiving filter 6 are respectively surrounded by annular portions of the same size of the grounding annular electrode 4. It is what has been. In this example, the size (inner area) of the annular portion surrounding the transmission filter 5 is larger (wider) than the size of the annular portion surrounding the reception filter 6.

  According to the third example having such a structure, the IDT electrode 2 of the transmission filter 5 to which high power is directly applied can be designed as a large electrode, and more around the transmission filter 5 having a larger calorific value. Since the through conductor 15 can be provided and connected to the grounding annular electrode 4, it is possible to improve the power durability while suppressing an increase in the size of the surface acoustic wave device.

  Next, FIG. 7 shows a fourth example of the embodiment of the surface acoustic wave device of the present invention. The IDT of the piezoelectric substrate of the surface acoustic wave element constituting the surface acoustic wave device of the present invention similar to FIG. It is a top view which shows the surface in which the electrode was formed. In FIG. 7, the same reference numerals are assigned to the same parts as in FIG. 1. In this example, the transmission filter 5 and the reception filter 6, which are a plurality of filters, are individually surrounded by the grounding annular electrode 4. At least one of the plurality of IDT electrodes 2 is electrically connected to the grounding annular electrode 4 via the resistor 7. In this example, the grounding annular electrode 4 is formed so as to surround the transmission filter 5 and the reception filter 6, and a signal line that is not directly connected to the grounding annular electrode 4 among the respective IDT electrodes 2. What is connected is electrically connected to the grounding annular electrode 4 through the resistor 7 via the signal line. The resistor 7 may be formed of a high resistance semiconductor such as silicon, titanium oxide, or copper oxide. Alternatively, a thin film resistor such as tantalum nitride may be used.

  According to the fourth example having such a structure, the resistor 7 has a high impedance with respect to the high-frequency signal input to the IDT electrode 2. No high frequency signal leaks to 4. On the other hand, since it has a low impedance in terms of direct current, it is in a conducting state and operates as a heat dissipation path from the IDT electrode 2 to the grounding annular electrode 4, so that heat generated in the IDT electrode 2 can be radiated more efficiently. Therefore, the power durability of the surface acoustic wave device can be further enhanced.

  Such a resistor 7 may be connected to at least one of the plurality of IDT electrodes 2, more specifically, to the IDT electrode 2 having the largest amount of heat that is not directly connected to the grounding annular electrode 4. The IDT electrode 2 may be connected via a signal line as in this example, or may be directly connected to the bus bar portion of the IDT electrode 2.

  Next, examples of the surface acoustic wave device of the present invention will be described.

  The surface acoustic wave device uses a 38.7 ° Y-cut X-propagation lithium tantalate single crystal substrate as a piezoelectric substrate, and an Al (99% by mass) -Cu (1% by mass) Al alloy is formed on this main surface. The IDT electrode 2 pattern, the electrode pad pattern as the input / output electrode, the wiring pattern for electrically connecting them, and the grounding annular electrode were formed. These patterns were prepared by forming an Al alloy thin film by a sputtering method as follows, and then performing photolithography using a stepper, an RIE (reactive ion etching) apparatus, or the like to obtain predetermined patterns.

  First, a lithium tantalate wafer serving as a piezoelectric substrate was ultrasonically cleaned with an organic solvent such as acetone or IPA (isopropyl alcohol) to clean organic components. Next, the substrate was sufficiently dried by a clean oven, and then the IDT electrode, electrode pad, wiring, and grounding annular electrode were formed.

  In these formations, an Al—Cu thin film having the above composition was formed using a sputtering apparatus, and then a photoresist was spin-coated to a thickness of about 0.5 μm, and patterning was carried out to each desired pattern using a stepper. Next, after undesired portions of the resist are melted with an alkali developer by a developing device to expose each desired pattern, the Al—Cu thin film is etched by an RIE device, and a desired IDT electrode, electrode pad, An annular electrode for wiring and grounding was formed.

  Thereafter, a protective film for protecting them was formed. Here, a silicon oxide film is formed by a sputtering apparatus, and then resist patterning is performed by photolithography, and an input / output electrode window opening corresponding to an electrode pad and an annular electrode for grounding are supported by an RIE apparatus or the like. Etching with the opening portion for the annular electrode was performed to form a protective film pattern.

  Next, an opening pattern of a portion where a resistor for connecting the IDT electrode and the grounding annular electrode is formed on the protective film is formed by photolithography, and after etching the protective film of this portion with an RIE apparatus, the resistor is removed. It was prepared by the lift-off method. The resistor was formed by sputtering using silicon to which boron was added.

Here, the resistor is formed by independently patterning, but the protective film itself may be formed of a semiconductor thin film such as silicon, and thereby the IDT electrode and the grounding annular electrode may be electrically connected. In this case, the step of patterning the resistor again can be omitted. Also, when etching the IDT electrode, an Al—Cu thin film is left extremely thin between the IDT electrode and the grounding annular electrode, and then a resist stripping process using oxygen plasma or CVD (chemical) using oxygen plasma is performed. In the protective film manufacturing process by the chemical vapor deposition method, the remaining Al—Cu ultrathin film is oxidized to form CuAlO ₂ that is a high-resistance semiconductor, which can be used as a resistor. Furthermore, the IDT electrode is formed of a single-layer Al—Cu thin film here, but Ti or Cu or the like may be provided as a base layer to form a laminated film. When Ti or Cu is used for the base layer, Can oxidize the ultra-thin layer of Ti or Cu left using the same process to make a high-resistance semiconductor such as titanium oxide or copper oxide, so this may be used as a resistor. .

  Next, the piezoelectric substrate was diced along dicing lines and divided for each surface acoustic wave element chip. Then, the chip electrode pad and the grounding annular electrode, the input / output through conductor and the grounding annular conductor on the circuit board are temporarily attached with solder balls, and then joined through a reflow process to hermetically seal the IDT electrode. A stopped surface acoustic wave filter was obtained.

  Here, the circuit board is manufactured by laminating a plurality of insulating layers. For these insulating layers, for example, ceramics mainly composed of alumina, glass ceramics that can be fired at a low temperature, or glass epoxy resins mainly composed of organic materials are used. A green sheet made of ceramics, etc. is manufactured, and after providing a desired wiring pattern and through conductor, these green sheets are laminated and bonded together to form an integral body and fired.

  The surface acoustic wave device of the present invention obtained as described above is about 3 hours superior to the conventional surface acoustic wave device in a test in which a power of 32 dBm is applied at an environmental temperature of 50 ° C. Obtained power durability.

  From the above results, according to the surface acoustic wave device of the present invention, it was confirmed that the heat generated in the IDT electrode can be efficiently dissipated, thereby being excellent in power durability.

  In addition, this invention is not limited to the example of the above embodiment, A various change may be added in the range which does not deviate from the summary of this invention. For example, in the above embodiment, the electrode pad 3 of the piezoelectric substrate 1 is connected to the end of the input / output through conductor 12 of the circuit board 11, but the electrode pad 3 is formed on the upper surface of the circuit board 11. An electrode pad corresponding to the above may be formed and connected thereto.

  Further, in order to improve the isolation between the transmission filter 5 and the reception filter 6 in the circuit board 11, a matching circuit using meandering phase lines, inductors and capacitors may be arranged. According to this, since the impedance characteristic of the reception filter 6 viewed from the antenna terminal approaches infinitely in the transmission frequency band and the transmission signal can be prevented from flowing into the reception filter 6, the isolation characteristic is excellent. It becomes possible to.

It is a top view which shows the surface in which the IDT electrode of the piezoelectric substrate which comprises the surface acoustic wave apparatus which shows the 1st example of embodiment of the surface acoustic wave apparatus of this invention was formed. It is a top view which shows the 1st example of embodiment of the surface acoustic wave apparatus of this invention which shows the upper surface of the circuit board in which the piezoelectric substrate is mounted which comprises the surface acoustic wave apparatus. FIG. 3 is a cross-sectional view taken along the line A-A ′ of FIG. 1 and the line B-B ′ of FIG. 2, showing a first example of the embodiment of the surface acoustic wave device of the invention. It is a top view which shows the surface in which the IDT electrode of the piezoelectric substrate which comprises the surface acoustic wave apparatus which shows the 2nd example of embodiment of the surface acoustic wave apparatus of this invention was formed. It is a top view which shows the surface in which the IDT electrode of the piezoelectric substrate which comprises the surface acoustic wave apparatus which shows the 3rd example of embodiment of the surface acoustic wave apparatus of this invention was formed. It is a top view which shows the 1st example of embodiment of the surface acoustic wave apparatus of this invention which shows the upper surface of the circuit board in which the piezoelectric substrate is mounted which comprises the surface acoustic wave apparatus. It is a top view which shows the surface in which the IDT electrode of the piezoelectric substrate which comprises the surface acoustic wave apparatus which shows the 4th example of embodiment of the surface acoustic wave apparatus of this invention was formed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2 ... IDT electrode 3 ... Electrode pad 4 ... Ground electrode 5 ... Transmission filter 6 ... Reception filter 7 ... Resistor
11 ... Circuit board
12 ... Input / output through conductors
13 ... Ground conductor for grounding
14 ... Penetration conductor
15 ... Grounding conductor
21 ... Sealing resin

Claims (5)

A piezoelectric substrate;
A transmission filter having a first IDT electrode formed on one main surface of the piezoelectric substrate;
A receiving filter having a second IDT electrode formed on one main surface of the piezoelectric substrate;
A first grounding annular electrode formed on one main surface of the piezoelectric substrate and surrounding the transmission filter;
A second annular electrode for grounding formed on one principal surface of the piezoelectric substrate and surrounding the receiving filter;
A circuit board having a mounting surface on which the piezoelectric substrate is mounted, and on which the piezoelectric substrate is mounted such that the mounting surface and one main surface of the piezoelectric substrate face each other;
A first grounding annular conductor formed on the mounting surface of the circuit board so as to correspond to the first grounding annular electrode;
A second grounding annular conductor formed on the mounting surface of the circuit board so as to correspond to the second grounding annular electrode;
The piezoelectric substrate is interposed between the first grounding annular electrode and the first grounding annular conductor and between the second grounding annular electrode and the second grounding annular conductor, respectively. And a brazing material for joining the circuit board ,
A plurality of through conductors which are connected before Symbol first, second ground annular conductor,
A grounding conductor formed in or on the lower surface of the circuit board and connected to the plurality of through conductors,
The first grounding annular electrode is made larger than the second grounding annular electrode, and the number of through conductors connecting the first grounding annular conductor and the grounding conductor is the second grounding electrode. A surface acoustic wave device having more than the number of through conductors connecting the annular conductor for ground and the ground conductor.   2. The surface acoustic wave device according to claim 1, wherein each of the first and second grounding annular electrodes has a rectangular frame shape, and the through conductor is connected to each side thereof.   The transmission filter is a ladder type filter including a first parallel resonator, the reception filter is a ladder type filter including a second parallel resonator, and the first parallel resonator is the first filter. 2. The surface acoustic wave device according to claim 1, wherein the second parallel resonator is connected to the first grounding annular electrode, respectively, and the second parallel resonator is connected to the second grounding annular electrode.   2. The surface acoustic wave device according to claim 1, wherein a portion of the first and second grounding annular electrodes located between the transmission filter and the reception filter is shared.   The first IDT electrode is electrically connected to the first grounding annular electrode via a resistor made of silicon, titanium oxide, copper oxide, or tantalum nitride. The surface acoustic wave device according to any one of claims 1 to 4.

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