Elastic wave devices

Abstract

In an elastic wave device that includes a multi-mode resonator in its receiving filter, the goal is to achieve miniaturization as much as possible while maintaining its characteristics appropriately. [Solution] The circuit pattern includes a multi-mode first resonator 3 and second resonators 4 other than the first resonator 3. A receiving filter 5 is configured from at least one first resonator 3 and a plurality of second resonators 4, and a transmitting filter 6 is configured from a plurality of second resonators 4. The thickness of the conductive metal layer 7 forming the first resonator 3 is made smaller than the thickness of the conductive metal layer 7 forming the second resonator 4.

Description

Technical Field

[0001] The present invention relates to an improvement in an acoustic wave device suitable for use as a frequency filter or the like in mobile communication equipment and the like.

Background Art

[0002] Conventionally, there has been known an acoustic wave device in which a circuit pattern constituting the circuit shown in FIG. 13 is formed by a conductive metal layer on a piezoelectric body of a device chip constituting the acoustic wave device. In FIG. 13, reference numeral 100 denotes a multi-mode (DMS-type) resonator, and reference numeral 101 denotes a non-multi-mode resonator, respectively. The multi-mode resonator 100 has two or more IDT electrodes arranged between reflectors. The non-multi-mode resonator 101 has one IDT electrode arranged between reflectors. In FIG. 13, reference numeral 102 denotes a reception filter, and the reception filter 102 is composed of two multi-mode resonators 100 and a plurality of non-multi-mode resonators 101. Also, in FIG. 13, reference numeral 103 denotes a transmission filter, and the transmission filter 103 is composed of a plurality of non-multi-mode resonators 101. Also, in FIG. 13, reference numeral 104 is a transmission port, reference numeral 105 is a reception port, reference numeral 106 is a ground, and reference numeral 107 is an antenna port.

Summary of the Invention

Problems to be Solved by the Invention

[0003] There is a strong demand for miniaturization of this type of elastic wave device. Slowing down the propagation speed (speed of sound) of the main mode surface acoustic wave excited by the IDT electrode leads to this miniaturization. As the propagation speed (speed of sound) of the surface acoustic wave slows down, the wavelength of the surface acoustic wave becomes shorter, which allows the pitch between the electrode teeth of the comb-shaped electrode constituting the IDT electrode to be set smaller. If the pitch between the electrode teeth of the comb-shaped electrode constituting the IDT electrode becomes smaller, the area in which the resonator is formed on the device chip also becomes smaller. As a result, the device chip itself can also be made smaller.

[0004] The main problem that this invention aims to solve is to provide a new structure for this type of receiving filter that includes a multi-mode resonator, enabling the miniaturization of the elastic wave device while maintaining its characteristics appropriately. [Means for solving the problem]

[0005] In order to achieve the above objectives, in this invention, from a first viewpoint, the elastic wave device is An elastic wave device comprising a single device chip having at least one functional surface made of a piezoelectric material, wherein a circuit pattern made of a conductive metal layer is formed on the functional surface, The circuit pattern includes a multimode first resonator including an IDT electrode, and a second resonator other than the first resonator, which also includes an IDT electrode. The receiving filter is configured with at least one of the first resonators and a plurality of the second resonators, Multiple of the second resonators are used to form a transmitting filter. The thickness of the conductive metal layer forming the first resonator is made smaller than the thickness of the conductive metal layer forming the second resonator.

[0006] The conductive metal layer comprises a first thin film layer, a first thick film layer having a greater thickness than the first thin film layer, and a second layer, wherein the first thin film layer and the first thick film layer are formed so as not to overlap, and the second layer is formed to have portions located on the first thin film layer and the first thick film layer, and further, At least the first resonator, and, if there are two or more first resonators, the inter-resonator wiring that electrically connects the first resonators to each other, are made of the first thin film layer, At least the second resonator and the inter-resonator wiring connecting the second resonators are made of the first thick film layer. One embodiment of this invention involves connecting the first thin film layer and the first thick film layer with the second layer formed in a region other than the regions where the first and second resonators are formed.

[0007] Furthermore, one embodiment of this invention is that the first thick film layer has a thickness that is 1.3 times or more and 1.6 times or less the thickness of the first thin film layer.

[0008] Furthermore, one embodiment of this invention is to make the first thick film layer 18% of the wavelength of the main mode surface acoustic wave. [Effects of the Invention]

[0009] According to this invention, it is possible to miniaturize a receiving filter as much as possible while properly maintaining the characteristics of an elastic wave device that includes a multimode resonator. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a plan view of a device chip constituting an elastic wave device according to one embodiment of the present invention, showing only the contours of the first resonator, second resonator, capacitance, and external connection pads formed on the functional surface. [Figure 2]FIG. 2 is a planar configuration diagram of the device chip, and shows only portions other than the first resonator in the first thin film layer formed on the functional surface. [Figure 3] FIG. 3 is a planar configuration diagram of the device chip, and shows only portions other than the second resonator in the first thick film layer formed on the functional surface. [Figure 4] FIG. 4 is a planar configuration diagram of the device chip, and shows only the second layer formed on the functional surface. [Figure 5] FIG. 5 is an enlarged view showing a main part on the functional surface of the device chip. [Figure 6] FIG. 6 is a cross-sectional configuration diagram taken along line A-A in FIG. 5. [Figure 7] FIG. 7 is a cross-sectional configuration diagram taken along line B-B in FIG. 5. [Figure 8] FIG. 8 is a configuration diagram showing an example of the second resonator formed on the functional surface of the device chip constituting the elastic wave device. [Figure 9] FIG. 9 is a configuration diagram showing an example of a circuit formed on the functional surface of the device chip. [Figure 10] FIG. 10 shows simulation results of insertion loss characteristics of an elastic wave device. [Figure 11] FIG. 11 shows simulation results of insertion loss characteristics of an elastic wave device. [Figure 12] FIG. 12 shows simulation results of insertion loss characteristics of an elastic wave device. [Figure 13] FIG. 13 is a configuration diagram showing an example of a circuit provided in a conventional elastic wave device. Description of Embodiments

[0011] Hereinafter, typical embodiments of the present invention will be described with reference to FIG. 1 to FIG. 12. The elastic wave device 1 according to the present embodiment is suitable for use as a frequency filter or the like in mobile communication equipment and the like.

[0012] The acoustic wave device 1 according to this embodiment includes a single device chip 2 having at least one functional surface 2a made of a piezoelectric material, that is, a circuit pattern made of a conductive metal layer 7 formed on the functional surface 2a of one single device chip 2.

[0013] As shown in Figures 6 and 7, typically, the device chip 2 has the functional surface 2a made of the piezoelectric material and a back surface 2b opposite to the functional surface 2a. As shown in Figure 1, the device chip 2 further has four side surfaces 2c and has a flat hexahedral shape.

[0014] As the piezoelectric material, lithium tantalate or lithium niobate is typically used. The device chip 2 may also be configured by laminating sapphire, silicon, alumina, spinel, quartz, glass or the like on the piezoelectric material.

[0015] On the other hand, the circuit pattern includes a multimode first resonator 3 including an IDT electrode, and a second resonator 4 other than the first resonator 3 including an IDT electrode.

[0016] At the same time, at least one said first resonator 3 and a plurality of said second resonators 4 constitute a receiving filter 5, and a plurality of said second resonators 4 constitute a transmitting filter 6.

[0017] The acoustic wave device 1 having a CSP (Chip Size Package) structure is configured by mounting the device chip 2 on a package substrate or the like (not shown) using bumps or the like (not shown) such that a space is formed under the first resonator 3 and the second resonator 4.

[0018] Furthermore, a Wafer Level Package (WLP) elastic wave device 1 is constructed by forming a wall layer (not shown) on the functional surface 2a of the device chip 2 that surrounds the first resonator 3 and the second resonator 4, and a cover layer (not shown) on the wall layer that works in cooperation with the wall layer and the functional surface 2a to form an internal space for housing the first resonator 3 and the second resonator 4.

[0019] The circuit pattern is typically formed on the functional surface 2a by a conductive metal layer 7 formed by photolithography. To facilitate understanding of the structure of such circuit patterns, each of the layers that constitute them is shown separately in Figures 1 through 4. Figure 1 shows only the outlines of the circuit pattern, which consists of the first resonator 3 (formed by the first thin film layer 7a), the second resonator 4 (formed by the first thick film layer 7b), the capacitance 8, and the external connection pad 9, on the functional surface 2a of the device chip 2. Figure 2 shows only the first thin film layer 7a on the functional surface 2a of the device chip 2, excluding the first resonator 3 described later. Figure 3 shows only the first thick film layer 7b on the functional surface 2a of the device chip 2, excluding the second resonator 4 described later. Figure 4 shows only the second layer 7c, which will be described later, on the functional surface 2a of the device chip 2. Figure 5 shows a magnified view of the key parts on the functional surface 2a of the device chip 2.

[0020] Figure 9 shows an example of such a circuit pattern configuration. In Figure 9, reference numeral 3 indicates the first resonator, which is a multi-mode type (DMS type), and reference numeral 4 indicates the second resonator, which is not a multi-mode type. The multi-mode first resonator 3 has two or more IDT electrodes placed between the reflectors. In the second resonator 4, which is not a multi-mode type, one IDT electrode is placed between the reflectors. In Figure 9, reference numeral 5 indicates a receiving filter, which consists of two multimode first resonators 3 and multiple non-multimode second resonators 4. In Figure 9, reference numeral 6 indicates a transmitting filter, and the transmitting filter 6 is composed of multiple non-multimode second resonators 4. In Figure 9, reference numeral 10 denotes the transmit port, reference numeral 11 denotes the receive port, reference numeral 12 denotes the ground, and reference numeral 13 denotes the antenna port.

[0021] Figure 8 shows an example of the configuration of a second resonator 4. The second resonator 4 has an IDT electrode 4a and a reflector 4b formed so as to sandwich the IDT electrode 4a. The IDT electrode 4a consists of electrode pairs, and each electrode pair is formed by connecting multiple electrode fingers 4c, which are arranged in parallel so that their length intersects the propagation direction x of the surface wave that becomes the main mode, with a busbar 4d at one end of each pair. The reflector 4b is formed by connecting the ends of multiple electrode fingers 4e, which are arranged in parallel so that their length intersects the propagation direction x of the elastic wave, with a busbar 4f. Although not shown in the diagram, the IDT electrode and reflector constituting the first resonator 3 have a substantially similar structure to those in Figure 8.

[0022] Furthermore, in this embodiment, as shown in Figures 6 and 7, the thickness of the conductive metal layer 7 (first thin film layer 7a) forming the first resonator 3 is made smaller than the thickness of the conductive metal layer 7 (first thick film layer 7b) forming the second resonator 4. The thickness of the conductive metal layer 7 referred to here is the distance between the contact interface of the conductive metal layer 7 with the functional surface 2a and the upper surface of the conductive metal layer 7 opposite this contact interface.

[0023] More specifically, in this embodiment, the conductive metal layer 7 comprises a first thin film layer 7a, a first thick film layer 7b having a greater thickness than the first thin film layer 7a, and a second layer 7c. As shown in Figures 2 and 3, the first thin film layer 7a and the first thick film layer 7b are formed so as not to overlap. On the other hand, as shown in Figure 4, the second layer 7c is formed to have portions located on the first thin film layer 7a and the first thick film layer 7b. In the manufacturing process of the elastic wave device 1, either the first thin film layer 7a or the first thick film layer 7b is formed on the wafer that will become the device chip 2, then the other layer is formed, and then the second layer 7c is formed.

[0024] At least the first resonator 3, and, if there are two or more first resonators 3, the inter-resonator wiring 14 (see Figure 2) that electrically connects the first resonators 3 to each other, are made of the first thin film layer 7a. In the illustrated example, two first resonators 3 and the inter-resonator wiring 14 that electrically connects them are made of the first thin film layer 7a. In the illustrated example, a portion of the external connection wiring 15 for connecting the first resonators 3 to the outside is also made of the first thin film layer 7a.

[0025] Furthermore, at least the second resonator 4 and the inter-resonator wiring 16 (see Figure 3) connecting the second resonators 4 to each other are made of the first thick film layer 7b. In the illustrated example, multiple second resonators 4 and the inter-resonator wiring 16 that electrically connect them are made of the first thick film layer 7b. In the illustrated example, a portion of the external connection wiring 17 for connecting the second resonators 4 to the outside is also made of the first thick film layer 7b.

[0026] Furthermore, as shown in Figure 4, the first thin film layer 7a and the first thick film layer 7b are connected by the second layer 7c, which is formed in a region other than the formation region 18 of the first resonator 3 and the second resonator 4. As a result, the two first resonators 3 and the multiple second resonators 4 are connected to form a single receiving filter 5 as a whole.

[0027] Typically, the device chip 2 is configured to be a rectangular plate with sides of 0.5 to 1 mm and a thickness of 0.15 to 0.2 mm, and the contour of the functional surface 2a is rectangular when viewed from a direction perpendicular to the functional surface 2a. Furthermore, the first thin film layer 7a typically has a thickness of 500 to 600 nm. Furthermore, the first thick film layer 7b typically has a thickness of 800 to 1000 nm. Furthermore, the second layer 7c typically has a thickness of 2 to 4 μm. In each figure, the thickness of the components of the elastic wave device 1 is exaggerated to make it easier to understand the device's structure.

[0028] In this type of elastic wave device 1, there is a strong demand for miniaturization. Slowing down the propagation speed (speed of sound) of the main mode surface acoustic wave excited by the IDT electrode leads to this miniaturization. As the propagation speed (speed of sound) of the surface acoustic wave slows down, the wavelength of the surface acoustic wave becomes shorter, so the pitch y (see Figure 8) between the electrode fingers 4c of the comb-shaped electrode constituting the IDT electrode 4a can be set to a smaller size. If the pitch y between the electrode fingers 4c of the comb-shaped electrode constituting the IDT electrode 4a becomes smaller, the resonator formation region 18 on the device chip 2 also becomes smaller. As a result, the device chip 2 itself can also be made smaller. It is known that the propagation speed (speed of sound) of the surface acoustic wave slows down as the thickness of the conductive metal layer 7 increases. From this viewpoint, it is preferable to increase both the thickness of the first thin film layer 7a and the thickness of the first thick film layer 7b. However, if both the thickness of the first thin film layer 7a and the thickness of the first thick film layer 7b are increased, the reflectivity of surface acoustic waves in the IDT electrodes constituting the multi-mode first resonator 3, which has two or more IDT electrodes arranged between the resonators, will increase, resulting in a deterioration of the characteristics of the first resonator 3. In this embodiment, the thickness of the conductive metal layer 7 (first thin film layer 7a) forming the first resonator 3 is made smaller than the thickness of the conductive metal layer 7 (first thick film layer 7b) forming the second resonator 4. This makes it possible to minimize the formation region 18 of the second resonator 4 (the area required for the formation of the second resonator 4 on the functional surface 2a of the device chip 2) while properly maintaining the characteristics of the first resonator 3. This enables miniaturization of the elastic wave device 1, which includes a multimode first resonator 3 in the receiving filter 5, as much as possible.

[0029] Figures 10 to 12 show the simulation results of the insertion loss characteristics in the circuit pattern shown in Figure 9. In Figures 10 to 12, the dashed lines show the characteristics when the thickness of the conductive metal layer 7 constituting the first resonator 3 and the conductive metal layer 7 constituting the second resonator 4 are both set to a thickness of 18% of the wavelength of the main mode surface acoustic wave (h / λ: 18%) (the propagation speed of the surface acoustic wave (speed of sound) is 3365 m / s). Typically, the thickness of the conductive metal layer constituting the resonator is around 10% of the wavelength of the main mode's surface acoustic wave (h / λ: 10%). In Figure 10, the solid line shows the characteristics where the thickness of the conductive metal layer 7 (first thin film layer 7a) constituting the first resonator 3 is set to 12% of the wavelength of the main mode surface acoustic wave (h / λ: 12%) (the propagation speed of the surface acoustic wave (speed of sound) is 3746 m / s), and the thickness of the conductive metal layer 7 (first thick film layer 7b) constituting the second resonator 4 is set to 18% of the wavelength of the main mode surface acoustic wave (h / λ: 18%, the propagation speed of the surface acoustic wave (speed of sound) is 3365 m / s). The first thick film layer 7b has a thickness 1.5 times that of the first thin film layer 7a. When the vertical axis represents loss characteristics and the horizontal axis represents frequency, it was found that in the frequency range from 617 MHz to 652 MHz, the insertion loss characteristics are superior when the thickness of the conductive metal layer 7 (first thin film layer 7a) constituting the first resonator 3 is made smaller than the thickness of the conductive metal layer 7 (first thick film layer 7b) constituting the second resonator 4.

[0030] In Figure 11, the solid line shows the characteristics where the thickness of the conductive metal layer 7 (first thin film layer 7a) constituting the first resonator 3 is 13.8% of the wavelength of the main mode surface acoustic wave (h / λ: 13.8%), and the thickness of the conductive metal layer 7 (first thick film layer 7b) constituting the second resonator 4 is 18% of the wavelength of the main mode surface acoustic wave (h / λ: 18%). The first thick film layer 7b has a thickness 1.3 times that of the first thin film layer 7a.

[0031] In Figure 12, the solid line shows the characteristics where the thickness of the conductive metal layer 7 (first thin film layer 7a) constituting the first resonator 3 is 11.3% of the wavelength of the main mode surface acoustic wave (h / λ: 11.3%), and the thickness of the conductive metal layer 7 (first thick film layer 7b) constituting the second resonator 4 is 18% of the wavelength of the main mode surface acoustic wave (h / λ: 18%). The first thick film layer 7b has a thickness 1.6 times that of the first thin film layer 7a.

[0032] It was found that when the first thick film layer 7b has a thickness 1.3 times that of the first thin film layer 7a, and when it has a thickness 1.6 times that of the first thin film layer 7a, an improvement in insertion loss characteristics similar to or slightly less than the simulation results (Figure 10) when the thickness is 1.5 times that of the first thin film layer 7a can be expected. On the other hand, when the thickness of the first thick film layer 7b is less than 1.3 times the thickness of the first thin film layer 7a, it is considered that there will be no significant difference from the characteristics shown by the dashed lines in Figures 10 to 12. On the other hand, when the first thick film layer 7b has a thickness greater than 1.6 times that of the first thin film layer 7a, the speed of sound of the surface acoustic waves excited by the IDT electrodes of the multi-mode first resonator 3 increases, causing the pitch between the electrode fingers constituting the IDT electrodes of the multi-mode first resonator 3 to become larger, and the formation region of the first resonator 3 to become too large. Based on the above, it is preferable that, at least when the thickness of the conductive metal layer 7 constituting the second resonator 4 is set to a thickness that is 18% of the wavelength of the main mode surface acoustic wave (h / λ: 18%), the first thick film layer 7b has a thickness that is 1.3 times or more and 1.6 times or less of the thickness of the first thin film layer 7a.

[0033] Naturally, the present invention is not limited to the embodiments described above, but includes all embodiments that can achieve the objectives of the present invention. [Explanation of Symbols]

[0034] 1. Elastic wave device 2 device chips 2a Functional aspect 2b Back 2c side 3 1st resonator 4 Second resonator 4a IDT electrode 4b reflector 4c electrode finger 4D bus bar 4e electrode finger 4F Bus Bar 5. Receiving filter 6. Transmission filter 7 Conductive metal layer 7a 1st thin film layer 7b 1st thick film layer 7c 2nd layer 8 Capacitance 9 pads 10 Sending Ports 11 Incoming Port 12 Grand 13 Antenna Ports 14 Inter-resonator wiring 15 External connection wiring 16 Inter-resonator wiring 17 External connection wiring 18. Resonator formation region

Claims

1. An elastic wave device comprising a single device chip having at least one functional surface made of a piezoelectric material, wherein a circuit pattern made of a conductive metal layer is formed on the functional surface, The circuit pattern includes a multimode first resonator including an IDT electrode, and a second resonator other than the first resonator, which also includes an IDT electrode. The receiving filter is configured with at least one of the first resonators and a plurality of the second resonators, Multiple of the second resonators are used to form a transmitting filter. An elastic wave device wherein the thickness of the conductive metal layer forming the first resonator is smaller than the thickness of the conductive metal layer forming the second resonator.

2. The conductive metal layer comprises a first thin film layer, a first thick film layer having a greater thickness than the first thin film layer, and a second layer, wherein the first thin film layer and the first thick film layer are formed so as not to overlap, and the second layer is formed to have portions located on the first thin film layer and the first thick film layer. At least the first resonator, and, if there are two or more first resonators, the inter-resonator wiring that electrically connects the first resonators to each other, are made of the first thin film layer, At least the second resonator and the inter-resonator wiring connecting the second resonators are made of the first thick film layer. The elastic wave device according to claim 1, wherein the first thin film layer and the first thick film layer are connected by the second layer formed in a region other than the region where the first and second resonators are formed.

3. The acoustic wave device according to claim 2, wherein the first thick film layer has a thickness of 1.3 times or more and 1.6 times or less the thickness of the first thin film layer.

4. The acoustic wave device according to claim 2, wherein the first thick film layer has a thickness that is 18% of the wavelength of the main mode surface acoustic wave.

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