Frequency Filters

Abstract

To provide a frequency filter capable of performing filtering to a large, high-frequency power.SOLUTION: A frequency filter 10 comprises a first laminate 11, a first electrode pair 12, a second laminate 13, a second electrode pair 14, and a substrate 15. The first laminate 11 is configured by alternately and repeatedly laminating first layers 111 each formed of a piezoelectric material and a second layers 112 formed of a piezoelectric material and formed of an insulation material having polarization different from that of the first layer or having no piezoelectricity, one by one. The first electrode pair 12 sandwiches the first laminate 11 in a lamination direction. The second laminate 13 is configured by alternately and repeatedly laminating third layers 131 each formed of a piezoelectric material and fourth layers 132 each formed of an insulation material having polarization different from that of the first layer or having no piezoelectricity, one by one. The second electrode pair 14 sandwiches the second laminate 13 in the lamination direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a frequency filter that performs frequency filtering and is used in base stations of mobile phones and the like. [Background technology]

[0002] In mobile phone services, radio waves are transmitted and received between mobile phone terminals and the many base stations installed throughout the city. Both base stations and terminals use frequency filters that filter out specific frequencies from the many frequencies contained in the electromagnetic waves received by the antenna.

[0003] A known example of such a frequency filter is a surface acoustic wave (SAW) filter (see, for example, Patent Document 1). A SAW filter has an IDT (Interdigital Transducer) made of a pair of interdigital electrodes interlocked together, provided on the surface of a piezoelectric thin film. There are two types of SAW filters: a resonator type, which has one or two IDTs sandwiched between a pair of grating reflectors arranged on the surface of the piezoelectric thin film, and a transversal type, which has two IDTs but no grating reflector.

[0004] Also, as another example of a frequency filter, a bulk acoustic wave (BAW) filter is known. There are two types of BAW filters: one consisting of a single unit, with one layer of a piezoelectric thin film and a pair of electrodes on the front and back sides of the thin film sandwiching the thin film (herein referred to as a "unit"), and one consisting of two sets of units stacked on top of each other. The latter is also called an SCF (Stacked Crystal Filter) (see Patent Document 2), and when an electric signal converted from an electromagnetic wave is input to one set of electrodes, an electric signal of a specific frequency contained in the electric signal is output from the other set of electrodes. In both the one consisting of a single unit and the SCF, by having air or vacuum at both ends, they become free ends where complete reflection occurs, and there is no need to provide reflectors at both ends. There is also an SMR (Solidly Mounted Resonator) in which a reflector layer is provided to fix the thin film to a substrate instead of air. All of the examples of BAW filters described so far function as resonator-type frequency filters. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-088952 A [Patent Document 2] International Publication No. WO2010 / 079614 [Patent Document 3] JP 2018-190800 A Summary of the Invention [Problem to be solved by the invention]

[0006] SAW filters have low voltage resistance between the combs of their interdigital electrodes, and are therefore unable to filter high-power, high-frequency power. Meanwhile, the thickness of the piezoelectric thin film in a BAW filter (each piezoelectric thin film in an SCF) needs to be thinner the higher the frequency of filtering, but the voltage resistance of the piezoelectric thin film naturally decreases as it becomes thinner. Therefore, when the frequency of filtering is high, BAW filters have the problem of difficulty in filtering high-power, high-frequency power.

[0007] An object of the present invention is to provide a frequency filter capable of filtering high-power radio frequency power. [Means for solving the problem]

[0008] The frequency filter according to the present invention, which is made to solve the above problems, comprises: a) a first laminate in which a first layer made of a piezoelectric material and having a polarization in a predetermined direction and a second layer made of a piezoelectric material and having a polarization in a direction different from that of the polarization of the first layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one, and a thickness d1 of the first layer and a thickness d2 of the second layer satisfy a relationship of 0.7×(v2 / v1)d1≦d2≦1.5×(v2 / v1)d1, where v1 is the sound velocity in the first layer and v2 is the sound velocity in the second layer; b) a first electrode pair consisting of a pair of electrodes provided so as to sandwich the first stack in the stacking direction; c) a second laminate in which a third layer made of a piezoelectric material and having a polarization in a predetermined direction and a fourth layer made of a piezoelectric material and having a polarization in a direction different from that of the third layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one to a number equal to the total number of the first layers and the second layers, wherein a thickness d3 of the third layer and a thickness d4 of the fourth layer satisfy a relationship of 0.7×(v4 / v3)d3≦d4≦1.5×(v4 / v3)d3 using the sound velocity v3 in the third layer and the sound velocity v4 in the fourth layer, and a thickness d1 of the first layer and a thickness d3 of the third layer satisfy a relationship of 0.7×(v3 / v1)d1≦d3≦1.5×(v3 / v1)d1; d) a second electrode pair consisting of a pair of electrodes provided so as to sandwich the second stack in the stacking direction; and e) A substrate made of an insulating material is provided, one surface of which is in contact with one electrode of the first electrode pair and the other surface of which is in contact with one electrode of the second electrode pair, or one electrode of the first electrode pair and one electrode of the second electrode pair are in direct contact with each other. It is characterized by:

[0009] The piezoelectric materials constituting the first layer and the third layer may be the same or different. Furthermore, if the second layer or the fourth layer is made of a piezoelectric material, the material may be the same or different from the material of the first layer and / or the third layer. Furthermore, if both the second layer and the fourth layer are made of a piezoelectric material, the material may be the same or different.

[0010] In addition, the polarization direction of the first layer and the polarization direction of the third layer may be the same or different. In addition, when the second layer or the fourth layer is made of a piezoelectric material, the polarization directions of the second layer and the third layer, or the polarization directions of the fourth layer and the first layer may be the same or different. In addition, when both the second layer and the fourth layer are made of a piezoelectric material, the polarization directions of the second layer and the fourth layer may be the same or different.

[0011] There may be multiple first and second layers in total. There may be at least one first and second layer, but there may be multiple first and second layers each. Also, either the first or second layer may have one more layer than the other. The third and fourth layers are the same as the first and second layers.

[0012] When one electrode of the first electrode pair and one electrode of the second electrode pair are in direct contact with each other, the two electrodes may be at a common potential (typically, grounded).The two electrodes may also be an integrated (single) electrode.

[0013] The frequency filter according to the present invention is a BAW that functions as a transversal type, unlike a BAW that functions as a resonator type. The operation of the frequency filter according to the present invention will be described below.

[0014] In the frequency filter according to the present invention, when AC power including a plurality of frequencies is input between the two electrodes of the first electrode pair, each of the first layers constituting the first laminate vibrates mechanically by piezoelectric conversion, and the vibration component propagating in the thickness direction (which may be a longitudinal wave or a transverse wave) becomes strong at a specific frequency determined by the thickness d1 and the sound speed v1 (which differs depending on whether the wave is a longitudinal wave or a transverse wave) among the plurality of frequencies. In addition, when the second layer is made of a piezoelectric material, the second layer vibrates strongly at a specific frequency determined by the thickness d2 and the sound speed v2 among the plurality of frequencies. Here, by having the thickness d2 of the second layer be (v2 / v1)d1 or a value close thereto (0.7 to 1.5 times), each of the second layers of the first laminate vibrates at the specific frequency (i.e., the same frequency as the first layer) with the same phase for each frequency. On the other hand, when the second layer is made of an insulating material having no piezoelectricity, the second layer does not vibrate due to the piezoelectric effect, but receives vibration from the first layer and vibrates strongly at the same specific frequency as the first layer. As a result, whether the second layer is made of a piezoelectric material or an insulating material having no piezoelectricity, strong mechanical vibrations are generated throughout the first laminate within a specific frequency range centered on the specific frequency corresponding to a wave number that is a half integer number per layer.

[0015] Thus, the strong mechanical vibration in the frequency range generated in the first laminate is propagated to the second laminate via the substrate. In the second laminate, the third and fourth layers are excited by the mechanical vibration propagated from the first laminate. Here, the thickness d3 of the third layer is (v3 / v1)d1 or a value close to it (0.7 to 1.5 times), so that each third layer of the second laminate also vibrates within the frequency range. Furthermore, when each fourth layer is made of a piezoelectric material, the thickness d4 of the fourth layer is (v4 / v3)d3 or a value close to it (0.7 to 1.5 times), so that the fourth layer vibrates within the same frequency range as the third layer, and when the fourth layer is made of an insulating material that does not have piezoelectricity, the fourth layer vibrates within the same frequency range upon receiving the vibration from the third layer. As a result, AC power is generated between the second electrode pair by piezoelectric conversion. By extracting this AC power as an electric signal, the frequency filter according to the present invention functions as a frequency filter that extracts AC power having a frequency within the frequency range from the second electrode pair among the multiple frequencies input to the first electrode pair.

[0016] According to the frequency filter of the present invention, since it has multiple first and second layers between the first electrode pair on the input side, and multiple third and fourth layers between the second electrode pair on the output side, it is possible to electrically insulate the first electrode pair and the second electrode pair by piezoelectric members (first and second laminates) that are thicker than those of the conventional resonator-type BAW. Therefore, it is possible to increase the voltage resistance and to filter high-power radio frequency power even when the frequency range for filtering is high.

[0017] In the frequency filter according to the present invention, the second layer is made of a piezoelectric material; a component of the polarization in the first layer parallel to the first layer and a component of the polarization in the second layer parallel to the second layer are oriented in opposite directions to each other, and / or the fourth layer is made of a piezoelectric material; A component of the polarization in the third layer parallel to the third layer and a component of the polarization in the fourth layer parallel to the fourth layer are oriented in opposite directions to each other. The following configuration can be adopted.

[0018] In this way, a laminate in which the components of polarization parallel to each layer are in opposite directions between the first and second layers and / or the third and fourth layers can be easily obtained, for example, by setting the particle incidence direction to a different direction for every other layer when producing each layer using a magnetron sputtering method.

[0019] The frequency filter according to the present invention may further include a sound absorbing material in contact with an electrode of the first electrode pair on the opposite side to the second electrode pair and / or an electrode of the second electrode pair on the opposite side to the first electrode pair. This prevents vibrations propagating through the first laminate and / or the second laminate from being reflected at the end faces of the laminates on which the sound absorbing material is provided. This prevents unnecessary resonance from occurring in the first laminate and / or the second laminate.

[0020] The frequency filtering method according to the present invention comprises the steps of: a) a first laminate in which a first layer made of a piezoelectric material and having a polarization in a predetermined direction and a second layer made of a piezoelectric material and having a polarization in a direction different from that of the polarization of the first layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one, and a thickness d1 of the first layer and a thickness d2 of the second layer satisfy a relationship of 0.7×(v2 / v1)d1≦d2≦1.5×(v2 / v1)d1, where v1 is the sound velocity in the first layer and v2 is the sound velocity in the second layer; b) a first electrode pair consisting of a pair of electrodes provided so as to sandwich the first stack in the stacking direction; c) a second laminate in which a third layer made of a piezoelectric material and having a polarization in a predetermined direction and a fourth layer made of a piezoelectric material and having a polarization in a direction different from that of the third layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one, wherein the thickness d3 of the third layer and the thickness d4 of the fourth layer satisfy the relationship of 0.7×(v4 / v3)d3≦d4≦1.5×(v4 / v3)d3 using the sound velocity v3 in the third layer and the sound velocity v4 in the fourth layer, and the thickness d1 of the first layer and the thickness d3 of the third layer satisfy the relationship of 0.7×(v3 / v1)d1≦d3≦1.5×(v3 / v1)d1; d) a second electrode pair consisting of a pair of electrodes provided so as to sandwich the second stack in the stacking direction; and e) A substrate made of an insulating material is provided, one surface of which is in contact with one electrode of the first electrode pair and the other surface of which is in contact with one electrode of the second electrode pair, or one electrode of the first electrode pair and one electrode of the second electrode pair are in direct contact with each other. Using a frequency filter, The present invention is characterized in that AC power including a plurality of frequencies is input between the two electrodes of the first electrode pair, and AC power having one of the plurality of frequencies is output between the two electrodes of the second electrode pair.

[0021] In the frequency filtering method according to the present invention, the total number of the first and second layers (the number of layers on the input side) and the total number of the third and fourth layers (the number of layers on the output side) may be the same or different. When the number of layers on the input side is different from the number of layers on the output side, the filter also functions as a transformer that boosts (when the number of layers on the output side is greater than the number of layers on the input side) or lowers (when the number of layers on the output side is less than the number of layers on the input side) the voltage of the input AC power (see Patent Document 3). Effect of the Invention

[0022] According to the present invention, a frequency filter capable of filtering high-power high-frequency power can be obtained. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic configuration diagram showing a first embodiment of a frequency filter according to the present invention. [Diagram 2] 1 is a graph showing the relationship between the inclination angle of polarization from a line perpendicular to a layer made of Al1-xScxN (0≦x≦0.45) and the electromechanical coupling coefficient. [Diagram 3] FIG. 4 is a diagram for explaining the operation of the frequency filter according to the first embodiment. [Figure 4] FIG. 4 is a schematic configuration diagram showing a modified example of the frequency filter of the first embodiment. [Diagram 5] FIG. 4 is a schematic configuration diagram showing another modified example of the frequency filter of the first embodiment. [Figure 6] FIG. 4 is a schematic configuration diagram showing still another modified example of the frequency filter of the first embodiment. [Figure 7] FIG. 4 is a schematic configuration diagram showing a second embodiment of a frequency filter according to the present invention. [Figure 8] 5 is a graph showing the results of calculating filter characteristics for the frequency filters of the first and second embodiments. [Figure 9] 10 is a graph showing the results of calculating filter characteristics for a number of examples of the frequency filter according to the second embodiment, in which the first laminate and the second laminate have different numbers of layers. [Figure 10] 10 is a graph showing the results of calculating filter characteristics for a number of examples of different impedances connected to the input side and the output side of the frequency filter according to the second embodiment. [Figure 11] Electron microscope photographs showing cross sections of a portion (a) including a first laminate and a portion (b) including a second laminate of the produced frequency filter. [Figure 12] 1A is a pole figure of the (0002) plane measured for the first laminate of the produced frequency filter, and FIG. 1B is a graph showing a Ψ scanning curve. [Figure 13] 1A is a pole figure of the (0002) plane measured for the second laminate of the produced frequency filter, and FIG. 1B is a graph showing a Ψ scanning curve. [Figure 14]6A is a graph showing the results of measuring the filter characteristics of the manufactured frequency filter, and FIG. 6B is a graph showing the results of signal processing for removing unnecessary peaks and the like from the measurement data of the obtained filter characteristics. [Figure 15] FIG. 11 is a schematic configuration diagram showing a third embodiment of a frequency filter according to the present invention. [Figure 16] FIG. 4 is a schematic configuration diagram showing an example in which the number of layers of a first laminate and the number of layers of a second laminate are different. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 1 to 16 show an embodiment of a frequency filter according to the present invention.

[0025] (1) First embodiment The frequency filter 10 of the first embodiment shown in FIG. 1 includes a first laminate 11, a first electrode pair 12, a second laminate 13, a second electrode pair 14, and a substrate 15.

[0026] The first laminate 11 is a laminate of a first layer 111 made of a piezoelectric material and a second layer 112 made of a piezoelectric material, the first layer 111, the second layer 112, the first layer 111, and the second layer 112 alternately stacked in this order from the substrate 15 side. The first layer 111 has a polarization P1=(p x , p y ), where p x is the component of polarization P1 parallel to the layer, p y The polarization P2 of the second layer 112 is inclined with respect to the layer, and the component in the direction parallel to the layer is −p x (i.e., the opposite direction to the first layer 111) and the component in the direction parallel to the layer is p y (i.e., the same direction as the first layer 111) (P2=(-p x , p y )).

[0027] In this embodiment, the piezoelectric material of the first layer 111 and the second layer 112 is Al, which has a wurtzite structure. 1-x Scx N (0≦x≦0.45) is used. If x exceeds 0.45, Al becomes a non-piezoelectric material. 1-x Sc x Instead of N, other piezoelectric materials having a wurtzite structure, such as ZnO, may be used. The advantage of a piezoelectric material having a wurtzite structure is that a piezoelectric layer having a polarization inclined with respect to the layer can be easily produced by depositing particles of the piezoelectric material from an inclined direction with respect to the surface of the substrate, for example, using a magnetron sputtering method. When producing the first laminate 11 using this method, the substrate is rotated 180° around an axis perpendicular to the substrate, and then the operation of depositing particles of the piezoelectric material is repeated.

[0028] The piezoelectric material of the first layer 111 and the second layer 112 is Al. 1-x Sc x When using N, the directions of the polarizations P1 and P2 are preferably inclined at 27° to 43° from the perpendicular line to the first layer 111 and the second layer 112. By inclining in such a direction, the electromechanical coupling coefficient k' 15 2 The value of can be increased (see FIG. 2), and the strength of the transverse waves generated in the first laminate 11 can be increased, as described later.

[0029] In this embodiment, the first layer 111 and the second layer 112 have the same thickness, but the thicknesses of the two layers may be slightly different. Specifically, the thickness d1 of the first layer 111 and the thickness d2 of the second layer 112 may be determined so that the thickness d1 of the first layer 111 and the thickness d2 of the second layer 112 are in a relationship of 0.7×(v2 / v1)d1≦d2≦1.5×(v2 / v1)d1 using the sound velocity v1 in the first layer 111 and the sound velocity v2 in the second layer 112. When the first layer 111 and the second layer 112 are made of the same piezoelectric material as in this embodiment, v1=v2, so the relationship of 0.7d1≦d2≦1.5d1 may be satisfied. When the first layer 111 and the second layer 112 are made of different piezoelectric materials, the thickness d1 of the first layer 111 and the thickness d2 of the second layer 112 may be determined from the above relationship after determining the sound velocity for each piezoelectric material.

[0030] The first electrode pair 12 is made up of a pair of electrodes 121, 122 disposed to sandwich the first stack 11 in the stacking direction.

[0031] The second laminate 13 is a laminate in which a third layer 131 made of a piezoelectric material and a fourth layer 132 made of a piezoelectric material are alternately laminated in multiple layers (four layers) in the order of the third layer 131, the fourth layer 132, the third layer 131, and the fourth layer 132 from the substrate 15 side. In this embodiment, the second laminate 13 has the same structure as the first laminate 11. That is, the material of the third layer 131 and the fourth layer 132 is the same piezoelectric material, Al. 1-x Sc x N (0≦x≦1), and the polarization of the third layer 131 is P1=(p x , p y ), and the polarization of the fourth layer 132 is P2=(-p x , p y ) The third layer 131 and the fourth layer 132 have the same thickness. The second laminate 13 can also have a deformed configuration similar to the first laminate 11. It is also possible that only one of the first laminate 11 and the second laminate 13 has a deformed configuration, or that the first laminate 11 and the second laminate 13 have different deformed configurations.

[0032] The second electrode pair 14 is made up of a pair of electrodes 141, 142 disposed to sandwich the second stack 13 in the stacking direction.

[0033] The substrate 15 is a plate made of an insulating material, one surface of which is in contact with one electrode 122 of the first electrode pair 12, and the other surface of which is in contact with one electrode 141 of the second electrode pair 14. For example, a quartz plate can be used for the substrate 15. Quartz has an acoustic impedance of Al 1-x Sc x Since the acoustic impedance of the first laminate 11 and the second laminate 13 is close to that of N, 1-x Sc x When the substrate 15 is made of N, it can be suitably used as the material for the substrate 15. The thickness of the substrate 15 is not particularly limited, but the thickness is set to a level that does not excessively attenuate vibrations generated in the first laminate 11 when they are transmitted to the second laminate 13, as described below.

[0034] Next, the operation of the frequency filter 10 of the first embodiment will be described with reference to FIG.

[0035] An AC power signal including multiple frequencies to be filtered is input between the electrodes 121 and 122 of the first electrode pair 12. Then, each of the first layers 111 and each of the second layers 112 constituting the first laminate 11 vibrates mechanically due to piezoelectric conversion. At that time, since the components of the polarization P1 of the first layer 111 and the polarization P2 of the second layer 112 parallel to those layers are in the opposite directions to each other, the first layer 111 and the second layer 112 vibrate parallel to those layers and in opposite phases (phases differing by 180°). As a result, a transverse wave vibration propagating in the thickness direction (direction perpendicular to the first layer 111 and the second layer 112) is generated in the first laminate 11 (see FIG. 3). This transverse wave vibration occurs strongly at a vibration frequency (which may be the same as the specific frequency or may deviate from the specific frequency) within a specific frequency range centered on a specific frequency determined by the thicknesses of the first layer 111 and the second layer 112 and the speed of sound (which depends on the materials of those layers) among the multiple frequencies of the input AC power.

[0036] The vibration of the transverse waves at the vibration frequency thus generated strongly in the first laminate 11 propagates to the second laminate 13 via the substrate 15. In the second laminate 13, each of the third layers 131 and each of the fourth layers 132 is excited by the vibration of the transverse waves propagated from the substrate 15. As a result, AC power having the vibration frequency is generated by piezoelectric conversion between the electrodes 141 and 142 of the second electrode pair 14. By extracting this AC power from the second electrode pair 14, an AC power signal at the vibration frequency is extracted.

[0037] As described above, the frequency filter 10 of the first embodiment operates as a frequency filter in which an AC power signal having a frequency (the vibration frequency) within the specific frequency range is output from the second electrode pair 14, out of an AC power signal including a plurality of frequencies input to the first electrode pair 12.

[0038] Here, the first electrode pair 12 is described as the input side and the second electrode pair 14 is the output side, but the operation is similar to that described above even when the second electrode pair 14 is the input side and the first electrode pair 12 is the output side.

[0039] In the frequency filter 10 of the first embodiment, the first layer 111 and the second layer 112 are piezoelectric layers having a polarization inclined with respect to these layers. Instead, as shown in FIG. 4, a piezoelectric layer having a polarization P perpendicular to the first layer 111 and the second layer 112 may be used. In this case, the polarization P of the first layer 111 and the second layer 112 is made to be in the opposite directions. Alternatively, one of the first layer 111 and the second layer 112 may be a piezoelectric layer having a polarization P perpendicular to the layer, and the other layer may be a piezoelectric layer having a perpendicular component in the opposite direction to the polarization P of the one layer and inclined with respect to the other layer. In either case, a longitudinal wave vibration is generated in the first laminate 11. A similar configuration may be applied to the third layer 131 and the fourth layer 132 (see FIG. 4).

[0040] Alternatively, as shown in FIG. 5, the first layer 111 and the second layer 112 may be piezoelectric layers having a polarization P parallel to those layers. In this case, the polarization P in the first layer 111 and the second layer 112 is made to be in the opposite directions. Alternatively, one of the first layer 111 and the second layer 112 may be a piezoelectric layer having a polarization P parallel to that layer, and the other layer may be a piezoelectric layer having a parallel component in the opposite direction to the polarization P in the one layer and inclined with respect to the other layer. In either case, transverse wave vibrations are generated in the first laminate 11 as in the first embodiment. A similar configuration may be applied to the third layer 131 and the fourth layer 132 (see FIG. 5).

[0041] As yet another modified example, instead of providing the substrate 15 in the frequency filter 10 of the first embodiment, an electrode 151 serving as one electrode of the first electrode pair 12 (corresponding to the electrode 122 in the first embodiment) and one electrode of the second electrode pair 14 (corresponding to the electrode 141 in the first embodiment) may be provided between the first laminate 11 and the second laminate 13 as shown in Fig. 6. In this case, vibrations generated in the first laminate 11 are propagated to the second laminate 13 via the electrode 151. Such an electrode 151 can be applied to cases where the first layer 111 to the fourth layer have polarizations as shown in Figs. 4 and 5 or other polarizations.

[0042] (2) Second embodiment Next, a frequency filter 20 of the second embodiment will be described. As shown in FIG. 7, the frequency filter 20 of the second embodiment further includes a first sound absorbing material 21 and a second sound absorbing material 22 in addition to the frequency filter 10 of the first embodiment. The first sound absorbing material 21 is provided so as to contact the electrode 121 on the side opposite to the second electrode pair 14 of the first electrode pair 12. The second sound absorbing material 22 is provided so as to contact the electrode 142 on the side opposite to the first electrode pair 12 of the second electrode pair 14. Both the first sound absorbing material 21 and the second sound absorbing material 22 are made of a material having the same acoustic impedance as the first layer 111, and have unevenness formed on the end surface. Sound waves are scattered at the end surface having such unevenness, thereby absorbing sound.

[0043] Instead of providing both the first sound-absorbing material 21 and the second sound-absorbing material 22, it is also possible to provide only one of the first sound-absorbing material 21 and the second sound-absorbing material 22. Also, the first sound-absorbing material 21 and / or the second sound-absorbing material 22 may be combined with the configurations of the modified examples of the first embodiment described above.

[0044] According to the frequency filter 20 of the second embodiment, by providing the first sound-absorbing material 21 and / or the second sound-absorbing material 22, it is possible to prevent vibrations propagating through the first laminate 11 and / or the second laminate 13 from being reflected at the end faces on which the sound-absorbing materials of those laminates are provided. This makes it possible to prevent unnecessary resonance from occurring in the first laminate 11 and / or the second laminate 13.

[0045] (3) Calculation and Experimental Examples Regarding the Frequency Filters of the First and Second Embodiments First, the filter characteristics were calculated for the frequency filter 10 of the first embodiment and the frequency filter 20 of the second embodiment (both of which have four layers in the first laminate 11 and the second laminate). The filter characteristics are represented by the value of insertion loss for each frequency. In this calculation, the first layer 111, the second layer 112, the third layer 131, and the fourth layer 132 of both the first and second embodiments are made of Al. 1-x Sc x N (x=0.4), with a thickness of 3.8 μm and an electromechanical coupling coefficient k'152 of 12% (corresponding to a case where the inclination angle of polarization from the direction perpendicular to the layers is 43°). The sound velocities v1 to v4 of the transverse waves in the first layer 111 to the fourth layer 132 are all 3795 m / s. In the second embodiment, instead of actually providing the first sound-absorbing material 21 and the second sound-absorbing material 22, the influence of reflection at the end faces is removed by signal processing to simulate the presence of the first sound-absorbing material 21 and the second sound-absorbing material 22.

[0046] The calculation results of the filter characteristics are shown in FIG. 8. In the first embodiment, many spike-like peaks are seen among gentle peaks having a frequency width of several tens to 200 MHz. These spike-like peaks are due to unnecessary resonance occurring in the first laminate 11 and the second laminate 13 in the frequency filter 10 of the first embodiment. In contrast, in the second embodiment, only gentle peaks are seen, and no spike-like peaks are seen. This is because the unnecessary resonance is suppressed in the frequency filter 20 of the second embodiment by the presence of the first sound-absorbing material 21 and the second sound-absorbing material 22. On the other hand, the first embodiment has a smaller insertion loss than the second embodiment (it is on the upper side in the graph of FIG. 8), and signal loss is suppressed.

[0047] For the frequency filter 20 of the second embodiment, the filter characteristics were calculated for each of the cases where the number of layers of the first laminate 11 (the sum of the number of layers of the first layer 111 and the second layer 112) and the number of layers of the second laminate 13 (the sum of the number of layers of the third layer 131 and the fourth layer 132) were 2, 3, and 4. Here, when the number of layers was 3, the number of layers of the first layer 111 and the third layer was 2, and the number of layers of the second layer 112 and the fourth layer 132 was 1. The calculation results are shown in FIG. 9. Note that, when the number of layers was 4, the calculation results were the same as those of the second embodiment in FIG. 8. As the number of layers of the first laminate 11 and the second laminate 13 increases, the passband becomes narrower and the insertion loss becomes smaller, thereby suppressing signal loss.

[0048] It was confirmed by calculation that the filter characteristics change by adjusting the impedance matching for the frequency filter 20 of the second embodiment (the number of layers of the first laminate 11 and the second laminate are each four). Here, the filter characteristics were calculated for the case where an electrical resistance of R=50Ω was inserted on each of the input side and output side of the frequency filter 20, and for the case where an electrical resistance of R=50Ω and an inductance of L=16nH were inserted on each of the input side and output side. The calculation results are shown in FIG. 10. The insertion loss was smaller when an electrical resistance of R=50Ω and an inductance of L=16nH were inserted than when only an electrical resistance of R=50Ω was inserted, and it was confirmed that the insertion loss was improved by adjusting the impedance matching.

[0049] Next, the results of fabricating the frequency filter 10 of the first embodiment (the first laminate 11 and the second laminate each have four layers) will be described. For the substrate 15, a plate material made of quartz and having both the front and back surfaces perpendicular to the z-axis was used.

[0050] The manufacturing method is as follows. First, the electrodes 122 and 141 were manufactured by depositing a metal material on both sides of the substrate 15. Next, the substrate 15 was mounted on a substrate holder of a magnetron sputtering device with the electrode 122 side facing the sputtering target side. Then, particles generated by sputtering a sputtering target made of an alloy of Al and Sc were made to be incident on the surface of the electrode 122 from a direction inclined with respect to the substrate 15 under a nitrogen gas atmosphere, thereby forming one first layer 111. Next, the substrate 15 was rotated 180° on an axis perpendicular thereto, and the particles were made to be incident on the surface of the first layer 111 in the same manner as above, thereby forming one second layer 112. This operation was performed two more times to manufacture the first stack 11.

[0051] Next, the substrate 15 was reattached so that the electrode 141 faced the sputtering target side, and particles were made to be incident on the surface of the electrode 141 in the same manner as above, to form one third layer 131. Next, the substrate 15 was rotated 180° about an axis perpendicular to it, and particles were made to be incident on the surface of the third layer 131 in the same manner as above, to form one fourth layer 132. This operation was repeated two more times to produce the second laminate 13. Finally, metal materials were vapor-deposited on the surface of the first laminate 11 opposite the substrate 15 and on the surface of the second laminate 13 opposite the substrate 15, respectively, to produce electrodes 121 and 142.

[0052] FIG. 11 shows an electron microscope photograph of a cross section of the fabricated frequency filter 10. FIG. 11(a) shows an enlarged view of the first laminate 11 side, and FIG. 11(b) shows an enlarged view of the second laminate 13 side. Note that FIG. 11(a) is upside down compared to the schematic diagram shown in FIG. 1. These electron microscope photographs show that both the first laminate 11 and the second laminate 13 have four layers that are alternately oriented in a zigzag pattern. The polarization of each layer is oriented in the direction indicated by the arrow in the right margin of the electron microscope photograph.

[0053] FIG. 12(a) shows the (0002) plane pole figure measured for the first laminate 11 of the fabricated frequency filter 10, and FIG. 12(b) shows the Ψ scanning curve. In these figures, Ψ indicates the angle (tilt angle) with respect to a line perpendicular to the substrate 15, and φ indicates the azimuth angle. The Ψ scanning curve was obtained by changing Ψ along the straight line in (a) to obtain the X-ray diffraction intensity. From these figures, it is clear that the polarization direction (Al 1-x Sc x 13(a) and the Ψ-scan curve shown in FIG. 13(b), the polarization direction of the third layer 131 has an average tilt angle of 24.6°, and the polarization direction of the fourth layer 132 has an average tilt angle of 22.3°, and the azimuth angle of the third layer 131 is different from that of the fourth layer 132 by approximately 180°.

[0054] The filter characteristics of the fabricated frequency filter 10 were measured using a network analyzer. The results are shown in Figure 14(a). Comparing the measurement results with the calculation results (Figure 8), the measurement results show that the induction loss is smaller than the calculation results in the frequency range of 300 MHz or less. This is thought to be due to the occurrence of longitudinal wave vibrations in addition to transverse waves. Also, the measurement results show spike-shaped peaks due to reflections at the end faces of the laminate, just like the calculation results.

[0055] Therefore, we performed signal processing by performing a fast Fourier transform on the obtained measurement data and then an inverse fast Fourier transform. The results are shown in Figure 14(b). It was confirmed that this type of signal processing can eliminate the effects of longitudinal waves and reflections at the end faces of the laminate.

[0056] (4) Third embodiment In each embodiment described above, all layers constituting the first laminate and the second laminate are made of piezoelectric material (piezoelectric layers), but it is also possible to use a first laminate and / or a second laminate in which every other layer is made of an insulating material that does not have piezoelectricity (non-piezoelectric layer), that is, in which piezoelectric layers and non-piezoelectric layers are alternately laminated. In the frequency filter 30 illustrated in FIG. 15, the first laminate 31 has a configuration in which a first layer (piezoelectric layer) 111 and a second layer (non-piezoelectric layer) 313 are alternately laminated, and the second laminate 33 has a configuration in which a third layer (piezoelectric layer) 131 and a fourth layer (non-piezoelectric layer) 333 are alternately laminated. The direction of polarization of the piezoelectric layer is not limited to that illustrated. Also, the stacking order of the first layer 111 and the second layer 313 and the stacking order of the third layer 131 and the fourth layer 333 may be reversed from that illustrated. Furthermore, the number of layers of the first laminate 31 and the second laminate 33 is not limited to that shown in the figure, and may be two layers, three layers, or five layers or more. The configuration other than the first laminate 31 and the second laminate 33 is similar to that of the frequency filter 10 of the first embodiment, and modifications similar to those of the first and second embodiments are possible.

[0057] (5) Other In each embodiment described so far, the first laminate and the second laminate have the same number of layers, but even if the first laminate and the second laminate have different numbers of layers, they function as a frequency filter. In that case, however, when an AC electric signal is introduced into either the first electrode pair or the second electrode pair, the AC electric signal output from the other has a voltage different from that at the time of input. This is because a frequency filter having such a structure functions as a transformer as described in Patent Document 3. For example, as shown in FIG. 16, in the case where the number of layers of the first laminate 41 is 2 (one first layer 111 and one second layer 112) and the number of layers of the second laminate 43 is 4 (one third layer 131 and one fourth layer 132), which is greater than the number of layers of the first laminate 41, when an AC electric signal is input between the electrodes 121 and 122 of the first electrode pair 12, an AC electric signal having a higher voltage than the input AC electric signal and having a filtered frequency is output between the electrodes 141 and 142 of the second electrode pair 14. In the case of having the same configuration, when an AC electric signal is input between electrodes 141 and 142 of second electrode pair 14, an AC electric signal having a lower voltage than the input AC electric signal and whose frequency has been filtered is output between electrodes 121 and 122 of first electrode pair 12. Note that the configuration shown in Fig. 16 is only one example, and similarly to the first to third embodiments, modifications are possible in terms of the number of layers, the direction of polarization, the presence or absence of a non-piezoelectric layer, the presence or absence of a substrate 15, and the like.

[0058] In addition to the multiple embodiments and their modifications described above, various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0059] 10, 20, 30... frequency filters 11, 31, 41...First laminate 111…1st layer 112...Second layer 12...First electrode pair 121, 122...electrodes of the first electrode pair 13, 33, 42...Second laminate 131...Third layer 132…4th layer 14...Second electrode pair 141, 142...electrodes of the second electrode pair 15...Substrate 151...electrode serving as one electrode of the first electrode pair and one electrode of the second electrode pair 21…First sound absorbing material 22…Second sound absorbing material 313...Second layer (non-piezoelectric layer) 333...4th layer (non-piezoelectric layer)

Claims

1. a) A first layer made of a piezoelectric material and having a polarization oriented in a predetermined direction and a second layer made of a piezoelectric material and having a polarization oriented in a direction different from that of the polarization of the first layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one, and the thickness of the first layer is d 1 and the thickness d of the second layer 2 is the sound speed in the first layer v 1 and the sound speed in the second layer v 2 Using 0.7×(v 2 / v 1 )d 1 ≦d 2 ≦1.5×(v 2 / v 1 )d 1 A first laminate having a relationship of b) a first electrode pair consisting of a pair of electrodes provided so as to sandwich the first stack in the stacking direction; c) A third layer made of a piezoelectric material and having a polarization in a predetermined direction and a fourth layer made of a piezoelectric material and having a polarization in a direction different from that of the third layer or made of an insulating material having no piezoelectricity are alternately laminated one by one, and the number of layers is the same as the total number of the first layers and the second layers, and the thickness d of the third layer is 3 and the thickness d of the fourth layer 4 is the sound speed in the third layer v 3 and the sound speed in the fourth layer v 4 Using 0.7×(v 4 / v 3 )d 3 ≦d 4 ≦1.5×(v 4 / v 3 )d 3 and the thickness d of the first layer 1 and the thickness d of the third layer 3 is 0.7×(v 3 / v 1 )d 1 ≦d 3 ≦1.5×(v 3 / v 1 )d 1 A second laminate having the following relationship: d) a second electrode pair consisting of a pair of electrodes provided so as to sandwich the second stack in the stacking direction; and e) A substrate made of an insulating material is provided, one surface of which is in contact with one electrode of the first electrode pair and the other surface of which is in contact with one electrode of the second electrode pair, or one electrode of the first electrode pair and one electrode of the second electrode pair are in direct contact with each other.

1. A frequency filter comprising:

2. the second layer is made of a piezoelectric material; a component of the polarization in the first layer parallel to the first layer and a component of the polarization in the second layer parallel to the second layer are oriented in opposite directions to each other, and / or the fourth layer is made of a piezoelectric material; A component of the polarization in the third layer parallel to the third layer and a component of the polarization in the fourth layer parallel to the fourth layer are oriented in opposite directions to each other.

2. The frequency filter according to claim 1 .

3. 3. The frequency filter according to claim 1, further comprising a sound-absorbing material in contact with an electrode of the first electrode pair on the side opposite the second electrode pair and / or an electrode of the second electrode pair on the side opposite the first electrode pair.

4. a) A first layer made of a piezoelectric material and having a polarization oriented in a predetermined direction and a second layer made of a piezoelectric material and having a polarization oriented in a direction different from that of the polarization of the first layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one, and the thickness of the first layer is d 1 and the thickness d of the second layer 2 is the sound speed in the first layer v 1 and the sound speed in the second layer v 2 Using 0.7×(v 2 / v 1 )d 1 ≦d 2 ≦1.5×(v 2 / v 1 )d 1 A first laminate having a relationship of b) a first electrode pair consisting of a pair of electrodes provided so as to sandwich the first stack in the stacking direction; c) A third layer made of a piezoelectric material and having a polarization in a predetermined direction and a fourth layer made of a piezoelectric material and having a polarization in a direction different from that of the third layer or made of an insulating material that does not have piezoelectricity are alternately laminated one by one, and the thickness of the third layer is d 3 and the thickness d of the fourth layer 4 is the sound speed in the third layer v 3 and the sound speed in the fourth layer v 4 Using 0.7×(v 4 / v 3 )d 3 ≦d 4 ≦1.5×(v 4 / v 3 )d 3 and the thickness d of the first layer 1 and the thickness d of the third layer 3 is 0.7×(v 3 / v 1 )d 1 ≦d 3 ≦1.5×(v 3 / v 1 )d 1 A second laminate having the following relationship: d) a second electrode pair consisting of a pair of electrodes provided so as to sandwich the second stack in the stacking direction; and e) A substrate made of an insulating material is provided, one surface of which is in contact with one electrode of the first electrode pair and the other surface of which is in contact with one electrode of the second electrode pair, or one electrode of the first electrode pair and one electrode of the second electrode pair are in direct contact with each other. Using a frequency filter, A frequency filtering method comprising the steps of: inputting AC power including a plurality of frequencies between two electrodes of the first electrode pair; and outputting AC power having one of the plurality of frequencies between two electrodes of the second electrode pair.

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