Elastic wave devices

Abstract

To provide a miniaturized elastic wave device that efficiently attenuates harmonic components. [Solution] An elastic wave device comprising an antenna terminal, a bandpass filter having a predetermined frequency passband, and a band-elimination filter having a predetermined frequency passband, wherein the band-elimination filter comprises a parallel resonator connected between a node between the antenna terminal and the bandpass filter and a ground terminal, and a ground inductor connected in series between the parallel resonator and the ground terminal, and the combined circuit of the parallel resonator and the ground inductor has a first series resonant frequency of 1.9 to 2.4 times the frequency of the passband and a second series resonant frequency of 2.8 to 3.2 times the frequency of the passband.

Description

Technical Field

[0001] The present disclosure relates to an elastic wave device.

Background Art

[0002] With the spread of mobile communication terminals such as smartphones, the demand for elastic wave devices that provide functions such as duplexers is increasing. These elastic wave devices are required to be further miniaturized, and particularly in the case of a transmission filter, characteristics that greatly attenuate harmonic components of the second harmonic and the third harmonic generated from a power amplifier are required.

[0003] Patent Document 1 discloses a method for increasing the separation between a duplexer and two filters. The method for increasing the separation between the filters is such that in the duplexer, the reception filter is coupled to an antenna terminal via a band-stop filter. The band-stop filter separates the transmission path from the reception path so that the separation of the duplexer is increased.

[0004] Patent Document 2 discloses a multiplexer that can be miniaturized and suppresses unnecessary spurious. The multiplexer includes a first filter and a notch circuit. The notch circuit has a stop band in a frequency band that is twice the pass band of the first filter.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, Patent Document 1 does not disclose a specific method for attenuating the second and third harmonic components of one filter, and therefore it is not possible to attenuate the harmonic components. Similarly, Patent Document 2 does not disclose a specific method for attenuating the second and third harmonic components of one filter that suppresses the second harmonic, and therefore it is not possible to attenuate the harmonic components.

[0007] This disclosure was made to solve the above-mentioned problems. The purpose of this disclosure is to provide an elastic wave device that can be miniaturized while attenuating the second and third harmonic components of a bandpass filter. [Means for solving the problem]

[0008] The elastic wave device relating to this disclosure is Antenna terminal and A bandpass filter having a predetermined frequency passband, A band elimination filter having a predetermined frequency pass-through band and Equipped with, The aforementioned band elimination filter is A parallel resonator connected between the node between the antenna terminal and the bandpass filter and the ground terminal, A ground inductor connected in series between the parallel resonator and the ground terminal Equipped with, The combined circuit of the parallel resonator and the ground inductor is, A first series resonant frequency which is 1.9 to 2.4 times the frequency of the aforementioned passband, It has a second series resonant frequency that is 2.8 to 3.2 times the frequency of the aforementioned passband.

[0009] Further comprising a piezoelectric substrate and a package substrate, The plurality of resonators constituting the bandpass filter and the parallel resonators are surface acoustic wave resonators formed on the piezoelectric substrate. In one embodiment of this disclosure, the ground inductor is a metal pattern formed on the package substrate.

[0010] One embodiment of this disclosure is that the band elimination filter further comprises a series resonator connected between the antenna terminal and the bandpass filter.

[0011] When the parallel resonator is represented by the mBVD ​​equivalent circuit model, let the first inductor be L1, the first capacitor connected in series with the first inductor L1 be C1, and the parallel capacitor connected in parallel with the first inductor L1 and the first capacitor C1 be C0. In one embodiment of this disclosure, when the first series resonant frequency is FS1 and the second series resonant frequency is FS2, the ground inductor LS is a value that satisfies the following equations (1) and (2). FS1=1 / (2π*((L1+LS)*C1)^0.5) ···(1) FS2=1 / (2π*(LS*C0)^0.5) ···(2)

[0012] One embodiment of this disclosure is that the thickness of the comb-tooth electrodes of the parallel resonator is smaller than the thickness of the multiple resonators constituting the bandpass filter.

[0013] One embodiment of this disclosure is that the bandpass filter is a transmit filter, and further comprises a receive filter formed on the package substrate. [Effects of the Invention]

[0014] According to this disclosure, it is possible to provide an elastic wave device that can be miniaturized while attenuating the second and third harmonic components of a bandpass filter. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a cross-sectional view of the elastic wave device in Embodiment 1. [Figure 2] FIG. 2 is a diagram showing an example of an elastic wave element of the elastic wave device in Embodiment 1. [Figure 3] FIG. 3 is a diagram showing an outline of a main part of the elastic wave device in Embodiment 1. [Figure 4] FIG. 4 is a characteristic diagram of the elastic wave device 1. [Figure 5] FIG. 5 is a circuit diagram showing an mBVD equivalent circuit diagram of the parallel resonator BEFP and a ground inductor LS. [Figure 6] FIG. 6 is a characteristic diagram of another design example of the elastic wave device 1 in Embodiment 1. [Figure 7] FIG. 7 is a diagram showing an outline of a main part of the elastic wave device in Embodiment 2. [Figure 8] FIG. 8 is a characteristic diagram of the elastic wave device in Embodiment 2.

MODE FOR CARRYING OUT THE INVENTION

[0016] Embodiments will be described with reference to the accompanying drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions of such parts are appropriately simplified or omitted.

[0017] Embodiment 1. FIG. 1 is a cross-sectional view of the elastic wave device 1 in Embodiment 1.

[0018] As shown in FIG. 1, the elastic wave device 1 includes a package substrate 2, two chip substrates 3, a plurality of bumps 4, and a sealing portion 5. [[ID=​​​​​ In Figure 1, the top surface of the package substrate 2 is the mounting surface. Multiple conductive pads 2A are formed on the top surface of the package substrate 2. For example, the multiple conductive pads 2A are made of copper. The bottom surface of the package substrate 2 is the mounting surface to a motherboard or the like. Multiple conductive pads 2B are formed on the bottom surface of the package substrate 2. For example, the multiple conductive pads 2B are made of copper. Multiple internal conductors 2C are built into the package substrate 2. For example, the multiple internal conductors 2C are made of copper. Each internal conductor 2C electrically connects to the corresponding conductive pads 2A and conductive pads 2B. In addition, a ground inductor LS is built into the package substrate 2. The ground inductor LS is connected to the ground pad Gnd.

[0021] The chip substrate 3 is mounted on the package substrate 2. For example, the chip substrate 3 is formed from a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz. For example, the chip substrate 3 is formed from piezoelectric ceramics. For example, the chip substrate 3 is formed by joining a piezoelectric substrate and a support substrate. For example, the support substrate is formed from sapphire, silicon, alumina, spinel, quartz, or glass.

[0022] For example, a transmit filter and a receive filter are formed on the main surface (bottom surface in Figure 1) of the two chip substrates 3, respectively.

[0023] The transmit filter is formed to allow electrical signals of a desired frequency band to pass through. For example, the transmit filter includes a ladder filter consisting of multiple series resonators and multiple parallel resonators.

[0024] The receiving filter is formed to allow electrical signals of a desired frequency band to pass through. For example, the receiving filter includes a ladder filter consisting of multiple series resonators and multiple parallel resonators.

[0025] For example, the chip substrate 3 comprises a wiring pattern 3A and a plurality of electrodes 3B. For example, the plurality of electrodes 3B are interdigital transducer (IDT) electrodes (comb-shaped electrodes). The chip substrate 3Tx, which includes the transmitting filter, comprises a parallel resonator BEFP (not shown in Figure 1), which is a parallel resonator of the band elimination filter, as described later. The parallel resonator BEFP is connected to the band elimination filter pad BP. The band elimination filter pad BP is connected to the ground inductor LS via a bump 4 and a conductive pad 2A.

[0026] Each of the multiple bumps 4 is made of gold, conductive adhesive, solder, etc. For example, the height of the bumps 4 is between 20 μm and 50 μm. Each of the multiple bumps 4 electrically connects the conductive pad 2A and the wiring pattern 3A at the corresponding position.

[0027] The sealing portion 5 hermetically seals the chip substrate 3 together with the package substrate 2 while leaving a space 6 between the package substrate 2 and the chip substrate 3. For example, the sealing portion 5 is formed of an insulator such as a synthetic resin. The synthetic resin may be epoxy resin, polyimide, etc.

[0028] Next, an example of the elastic wave element 7 will be explained using Figure 2. Figure 2 shows an example of an elastic wave element in an elastic wave device according to Embodiment 1.

[0029] In Figure 2, the elastic wave element 7 is a SAW (Surface Acoustic Wave) resonator. As shown in Figure 2, the pair of IDT electrodes 7A and the pair of reflectors 7B are formed on the main surface of the chip substrate 3. The pair of IDT electrodes 7A and the pair of reflectors 7B are arranged to excite surface acoustic waves.

[0030] For example, a pair of IDT electrodes 7A and a pair of reflectors 7B are formed from an aluminum-copper alloy. For example, a pair of IDT electrodes 7A and a pair of reflectors 7B are formed from suitable metals such as titanium, palladium, or silver, or alloys thereof. For example, a pair of IDT electrodes 7A and a pair of reflectors 7B are formed from a laminated metal film in which multiple metal layers are stacked.

[0031] The IDT electrode 7A comprises a plurality of electrode fingers 7D and a busbar 7E. The plurality of electrode fingers 7D are arranged longitudinally. The busbar 7E connects the plurality of electrode fingers 7D so that they face each other. One of a pair of reflectors 7B is adjacent to one side of the pair of IDT electrodes 7A. The other of the pair of reflectors 7B is adjacent to the other side of the pair of IDT electrodes 7A. For example, the pair of IDT electrodes 7A and the pair of reflectors 7B are deposited and patterned using the same process as the wiring pattern 3A (not shown in Figure 2).

[0032] Next, the main components of the elastic wave device in Embodiment 1 will be explained using Figure 3. Figure 3 is a diagram showing an overview of the main components of the elastic wave device in Embodiment 1.

[0033] As shown in Figure 3, a ladder-type filter constituting the transmit filter is formed on the chip substrate 3Tx which includes the transmit filter. The ladder-type filter includes multiple series resonators S1 to S4 and multiple parallel resonators P1 to P3. The transmit filter is, for example, an LTE band 8 transmit filter with a passband of 880 MHz to 915 MHz.

[0034] A parallel resonator BEFP, which constitutes a band-elimination filter BEF, is formed on the chip substrate 3Tx containing the transmit filter. The parallel resonator BEFP has a resonant frequency that is higher than the passband frequency of the transmit filter. Since the resonant frequency of the parallel resonator BEFP is higher than that of the transmit filter, it may be formed with a thinner film thickness than the film thickness of the IDT electrode of the resonator included in the ladder-type filter that constitutes the transmit filter. This is because a thinner film thickness makes it lighter, which increases the speed of sound and allows for greater resolution of fine patterns.

[0035] On chip board 3Tx, the band-elimination filter pad BP is not connected to any resonators other than the parallel resonator BEFP. That is, on chip board 3Tx, the band-elimination filter pad BP is connected only to the parallel resonator BEFP. The parallel resonator BEFP is connected to the ground inductor LS via the band-elimination filter pad BP, bump 4, and conductive pad 2A.

[0036] The package substrate 2 includes a ground inductor LS that constitutes a band-elimination filter BEF. The ground inductor LS is composed of a metal pattern formed within the package substrate 2. The metal pattern of the ground inductor LS may be patterned on only one layer of the package substrate 2, or it may be patterned across multiple layers. In other words, the band-elimination filter BEF is composed of a pattern that spans both the package substrate 2 and the chip substrate 3Tx.

[0037] Here, the inductance value LS of the ground inductor LS is set such that the first series resonant frequency of the combined circuit of the parallel resonator BEFP and the ground inductor LS is 1.9 to 2.4 times the passband frequency of the transmit filter, and the second series resonant frequency of the combined circuit of the parallel resonator BEFP and the ground inductor LS is 2.8 to 3.2 times the passband frequency of the transmit filter. For example, the inductance value LS of the ground inductor LS can be set to 2nH.

[0038] Figure 4 is a characteristic diagram of elastic wave device 1. The vertical axis represents attenuation, and the horizontal axis represents frequency. In this example, the first series resonant frequency m1 is 2.10 GHz, which is 2.34 times the passband of the transmit filter, and the second series resonant frequency m2 is 2.75 GHz, which is 3.06 times the passband of the transmit filter. It can be seen that the attenuation near the second and third harmonics of elastic wave device 1 can be greatly increased with a single band-elimination resonator and a single inductor.

[0039] Next, we will explain the relationship between the capacitance and inductance of the parallel resonator BEFP and the ground inductor LS using Figure 5. Figure 5 shows the mBVD ​​equivalent circuit diagram of the parallel resonator BEFP and the ground inductor LS. The mBVD ​​equivalent circuit is an abbreviation for Modified Butterworth-Van Dyke equivalent circuit and is a common equivalent circuit model for elastic wave devices. For simplicity, the resistive component is omitted here.

[0040] In Figure 5, capacitors C0 and C1, and inductor L1 are the mBVD ​​equivalent circuits of the parallel resonator BEFP. The ground inductor LS is connected between the parallel resonator BEFP and the ground terminal Gnd.

[0041] In elastic wave device 1, the capacitance of capacitor C0 was set to 1.68 pF, the capacitance of capacitor C1 to 0.28 pF, the inductance of inductor L1 to 19.1 nH, and the inductance of ground inductor LS to 2.0 nH.

[0042] In this case, it may be desirable to change the first series resonant frequency m1 and the second series resonant frequency m2 of the combined circuit of the parallel resonator BEFP and the ground inductor to set the attenuation pole to an arbitrary other frequency. Also, due to constraints on the chip board layout or depending on the filter design method, it may be necessary to use different sizes for the parallel resonator BEFP. In such cases, the ground inductance LS can be found as the solution to the following simultaneous equations (1) and (2), using the capacitances C0, C1, and L1 in the mBVD ​​equivalent circuit of the parallel resonator BEFP described in Figure 5, with the first series resonant frequencies being FS1 and FS2, respectively. FS1=1 / (2π*((L1+LS)*C1)^0.5) ···(1) FS2=1 / (2π*(LS*C0)^0.5) ···(2)

[0043] This makes it possible to efficiently suppress spurious signals near the second and third harmonics of the elastic wave device 1, by setting the first series resonant frequency of the parallel resonator BEFP to a frequency 1.9 to 2.4 times the passband of the transmitting filter, and the second series resonant frequency of the parallel resonator BEFP to a frequency 2.8 to 3.2 times the passband of the transmitting filter.

[0044] Next, another design example of the elastic wave device 1 will be described. Figure 6 is a characteristic diagram of another design example of the elastic wave device 1 in Embodiment 1. The vertical axis in Figure 6 represents attenuation. The horizontal axis in Figure 6 represents frequency.

[0045] Another design example of elastic wave device 1 involves setting the inductance of the ground inductor LS to 3nH and optimizing the resonant frequency and capacitance C0 of the parallel resonator BEFP. The other configurations are the same as those of elastic wave device 1 shown in Figures 4 and 5.

[0046] As shown in Figure 6, in this design example, by setting the inductance value of the ground inductor LS to 3nH, the first series resonant frequency M3 of the combined circuit of the parallel resonator BEFP and the ground inductor LS was set to 1795MHz, which is exactly twice the passband center frequency of 897.5MHz of the LTE band 8 transmit filter with a passband of 880MHz to 915MHz, and the second series resonant frequency M4 was set to 2693MHz, which is exactly three times the passband center frequency.

[0047] In other words, by setting the inductance value of the ground inductor LS to 3nH, it was possible to position the attenuation poles to correspond to the centers of the second and third harmonics of the LTE Band 8 transmission bandwidth.

[0048] This demonstrates that, in another design example of elastic wave device 1, a single band-elimination resonator and a single inductor significantly improve the attenuation of the second and third harmonics in the passband of elastic wave device 1, and efficiently suppress the second and third harmonic spurious signals generated from the power amplifier.

[0049] According to Embodiment 1 described above, it is possible to provide a miniaturized elastic wave device that efficiently attenuates the second and third harmonic components of a bandpass filter.

[0050] Embodiment 2. Figure 7 shows an overview of the main components of the elastic wave device in Embodiment 2. Parts identical or corresponding to those in Embodiment 1 are denoted by the same reference numerals. Descriptions of these parts are omitted.

[0051] As shown in Figure 7, the elastic wave device in Embodiment 2 includes a series resonator BEFS that constitutes a band-elimination filter BEF, connected in series between the series resonator S4 of the ladder-type filter constituting the transmit filter and the antenna terminal ANT, on a chip substrate 3Tx including a transmit filter.

[0052] The series resonator BEFS has a resonant frequency that is higher than the passband frequency of the transmitting filter. The series resonator BEFS has an anti-resonant frequency that is higher than the first series resonant frequency of the combined circuit of the parallel resonator BEFP and the ground inductor LS, and lower than the second series resonant frequency. Since the series resonator BEFS is higher than the transmitting filter, it may be formed with a thinner film thickness than the film thickness of the IDT electrode of the resonator included in the ladder-type filter that constitutes the transmitting filter. This is because a thinner film thickness makes it lighter, which increases the speed of sound and allows for greater resolution of fine patterns.

[0053] The anti-resonant frequency of the series resonator BEFS is 2.267 GHz. The other configurations of the elastic wave device in Embodiment 2 are the same as those of another design example in Embodiment 1, so their description is omitted.

[0054] Figure 8 is a characteristic diagram of the elastic wave device in Embodiment 2. The vertical axis in Figure 8 represents attenuation. The horizontal axis in Figure 8 represents frequency. As shown in Figure 8, it can be seen that the harmonic attenuation characteristics of the elastic wave device have been improved. By setting the inductance value of the ground inductor LS to 3nH, the first series resonant frequency M5 of the combined circuit of the parallel resonator BEFP and the ground inductor LS was set to 1795MHz, and the second series resonant frequency M6 was set to 2693MHz. Furthermore, the anti-resonant frequency M7 of the series resonator BEFS was set to 2.267GHz. As a result, it can be seen that spurious signals near the second and third harmonics of the elastic wave device were efficiently suppressed while also ensuring attenuation between the second and third harmonics.

[0055] According to Embodiment 2 described above, it is possible to efficiently attenuate the second and third harmonic components of a bandpass filter while also ensuring attenuation between the second and third harmonics, thereby providing a miniaturized elastic wave device.

[0056] While several aspects of at least one embodiment have been described, it should be understood that various modifications, alterations, and improvements will be readily conceivable to those skilled in the art. Such modifications, alterations, and improvements are intended to be part of and within the scope of this disclosure.

[0057] It should be understood that the embodiments of the methods and apparatus described herein are not limited to their application to the structural and arrangement details of the components described above or illustrated in the accompanying drawings. The methods and apparatus can be implemented in other embodiments and carried out or performed in various ways. Specific implementation examples are given herein for illustrative purposes only and are not intended to limit the scope of the invention.

[0058] The expressions and terms used in this disclosure are for illustrative purposes only and should not be considered limiting. The use herein of “includes,” “equips,” “possesses,” “contains,” and variations thereof means the inclusion of the items listed herein and their equivalents, as well as the supplementary items.

[0059] The reference to “or” can be interpreted as meaning that any term written using “or” refers to one, more than one, or all of the terms written.

[0060] References to front / back, left / right, top / bottom / top / bottom, width / height, and front / back are all intended for convenience of description. Such references do not mean that the components of this disclosure are limited to any single positional or spatial orientation. Accordingly, the above description and drawings are illustrative only. [Explanation of Symbols]

[0061] 1 Elastic wave device, 2 Package substrate, 2A Conductive pad, 2B Conductive pad, 2C Internal conductor, 3 Chip substrate, 3A Wiring pattern, 3B Electrode, 4 Bump, 5 Encapsulation, 6 Space, 7 Elastic wave element, 7A IDT electrode, 7B Reflector, 7D Electrode finger, 7E Busbar, BEFP Parallel resonator, LS Ground inductor, BEFS Series resonator

Claims

1. Antenna terminal and A bandpass filter having a predetermined frequency passband, A band elimination filter having a predetermined frequency pass-through band and Equipped with, The aforementioned band elimination filter is A parallel resonator connected between the node between the antenna terminal and the bandpass filter and the ground terminal, A ground inductor connected in series between the parallel resonator and the ground terminal Equipped with, The combined circuit of the parallel resonator and the ground inductor is, A first series resonant frequency which is 1.9 to 2.4 times the frequency of the passband, An elastic wave device having a second series resonant frequency that is 2.8 to 3.2 times the frequency of the aforementioned passband.

2. Further comprising a piezoelectric substrate and a package substrate, The plurality of resonators constituting the bandpass filter and the parallel resonators are surface acoustic wave resonators formed on the piezoelectric substrate. The elastic wave device according to claim 1, wherein the ground inductor is a metal pattern formed on the package substrate.

3. The elastic wave device according to claim 1 or 2, further comprising a series resonator connected between the antenna terminal and the bandpass filter as the band elimination filter.

4. When the parallel resonator is represented by the mBVD ​​equivalent circuit model, let the first inductor be L1, the first capacitor connected in series with the first inductor L1 be C1, and the parallel capacitor connected in parallel with the first inductor L1 and the first capacitor C1 be C0. The elastic wave device according to claim 1 or 2, wherein, when the first series resonant frequency is FS1 and the second series resonant frequency is FS2, the ground inductor LS is a value that satisfies the following equations (1) and (2). FS1=1 / (2π*((L1+LS)*C1)^0.5) ...(1) FS2=1 / (2π*(LS*C0)^0.5)...(2)

5. The elastic wave device according to claim 1 or 2, wherein the thickness of the comb-tooth electrodes of the parallel resonator is smaller than the thickness of the plurality of resonators constituting the bandpass filter.

6. The elastic wave device according to claim 1 or 2, further comprising a bandpass filter which is a transmit filter and a receive filter formed on the package substrate.

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