JP2023106746A - frequency filter - Google Patents

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

The present invention relates to a frequency filter for filtering frequencies used in mobile phone base stations and the like.

In the mobile phone service, radio waves are transmitted and received between a number of base stations installed in the city and mobile phone terminals. In both base stations and terminals, frequency filters are used to filter frequencies by extracting a specific frequency from many frequencies contained in electromagnetic waves received by an antenna.

As an example of such a frequency filter, a surface acoustic wave (SAW) filter is known (see Patent Document 1, for example). A SAW filter has an IDT (Interdigital transducer) formed by interlocking a pair of comb electrodes on the surface of a piezoelectric thin film. There are two types of SAW filters: the resonator type, which consists of one or two IDTs sandwiched between a pair of grating reflectors placed on the surface of a piezoelectric thin film, and the type with two IDTs without a grating reflector. There is a so-called transversal type provided.

A bulk acoustic wave (BAW) filter is known as another example of the frequency filter. A BAW filter consists of a single layer of piezoelectric thin film and a pair of electrodes placed on the front and back sides to sandwich it (herein called a "unit body"). There are those that consist of only one, and those that consist of two sets of unit bodies. The latter is also called SCF (Stacked Crystal Filter) (see Patent Document 2). When an electrical signal converted from an electromagnetic wave is input to one pair of electrodes, an electrical signal of a specific frequency contained in the electrical signal is generated. Output from the other pair of electrodes. Both those consisting of only one set of units and SCFs are free ends where complete reflection occurs by the presence of air or vacuum at both ends, and there is no need to provide reflectors at both ends. Instead of air, there is also an SMR (Solidly Mounted Resonator) with a reflector layer to fix it to the substrate. Each example of the BAW filter described so far functions as a resonator-type frequency filter.

JP 2007-088952 A International publication WO2010/079614 Japanese Patent Application Laid-Open No. 2018-190800

The SAW filter has a low withstand voltage between the combs of the comb-shaped electrodes, and cannot filter high-power high-frequency power. On the other hand, the thickness of the piezoelectric thin film of the BAW filter (each piezoelectric thin film in the SCF) needs to be thinner as the frequency to be filtered is higher, but the pressure resistance of the piezoelectric thin film naturally decreases as it becomes thinner. Therefore, when the frequency to be filtered by the BAW filter is high, there is a problem that it becomes difficult to filter high-power high-frequency power.

A problem to be solved by the present invention is to provide a frequency filter capable of filtering a large amount of high-frequency power.

A frequency filter according to the present invention, which has been made to solve the above problems,
a) a first layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from the polarization of the first layer, or a non-piezoelectric material; A _second layer _composed of A first laminate having a relationship of 0.7 × (v ₂ /v ₁ )d ₁ ≤ d ₂ ≤ 1.5 × ( _{v 2} /v ₁ )d ₁ using the speed of sound v ₁ and the speed of sound v 2 in the second layer and,
b) a first electrode pair consisting of a pair of electrodes provided to sandwich the first laminate in the lamination direction;
c) a third layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from that of the third layer, or a non-piezoelectric material; A _fourth layer consisting of the The thickness _d4 of the fourth layer is 0.7×( _v4 / _v3 )d3 _{≦ d4 ≦ 1.5} ×(v ₄ / _v3 ) _d3 , and the thickness _d1 of the first layer and the thickness _d3 of the third layer are 0.7×( _v3 / _v1 )d1 _{≦ d3} ≦1.5 a second laminate having a relationship of ×(v ₃ /v ₁ )d ₁ ;
d) a second electrode pair consisting of a pair of electrodes provided to sandwich the second laminate in the lamination direction;
and furthermore,
e) a substrate made of an insulating material having one surface in contact with one electrode of the first electrode pair and the other surface in contact with one electrode of the second electrode pair; The electrode and one electrode of the second electrode pair are in direct contact with each other.

The piezoelectric materials forming the first layer and the third layer may be the same material, or may be different materials. Also, if the second layer or the fourth layer are made of a piezoelectric material, those materials may be the same material as the first layer and/or the third layer, or they may be different materials. Further, when both the second layer and the fourth layer are made of piezoelectric material, those materials may be the same material or different materials.

Also, the polarization direction of the first layer and the polarization direction of the third layer may be the same or different. Further, 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. , may be in different directions. Furthermore, 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.

It suffices that the first layer and the second layer have a plurality of layers in total. At least one first layer and one second layer may be provided, but a plurality of each of the first layer and the second layer may be provided. Also, one of the first layer and the second layer may be one layer more than the other. The third and fourth layers are the same as the first and second layers.

When one electrode of the first electrode pair and one electrode of the second electrode pair are in direct contact, the two electrodes should be at a common potential (typically grounded). Just do it. Also, these two electrodes may be an integrated (single) electrode.

The frequency filter according to the present invention is a BAW that functions as a transversal type, which has not existed in the past, unlike a BAW that functions as a resonator type. The operation of the frequency filter according to the present invention will be described below.

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 first layer constituting the first laminate is mechanically converted by piezoelectric conversion. It vibrates, but the component of vibration that propagates in the thickness direction (this vibration may be a longitudinal wave or a transverse wave) is the thickness d ₁ and the sound velocity v ₁ (longitudinal wave) among those multiple frequencies. or transverse wave). Moreover, 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 velocity _v2 among the plurality of frequencies. Here, the thickness d ₂ of the second layer has a value of (v ₂ /v ₁ )d ₁ or close to it (0.7 to 1.5 times), so that each second layer of the first stack has the specific (that is, the same frequency as the first layer), and vibrates in the same phase for each frequency. On the other hand, when the second layer is made of an insulating material that does not have piezoelectricity, although the second layer does not vibrate due to the piezoelectric effect, the vibration from the first layer causes the second layer to become the first layer. vibrate strongly at the same specific frequency as As a result, regardless of whether the second layer is made of a piezoelectric material or a non-piezoelectric insulating material, the specific frequency corresponding to the half-integer wavenumber per layer is applied to the entire first laminate. Strong mechanical vibrations occur within a specific centered frequency range.

Strong mechanical vibrations in the frequency range thus generated in the first stack propagate through the substrate to the second stack. In the second laminate, the mechanical vibration propagated from the first laminate excites the third and fourth layers. Here, the thickness _d3 of the third layer has a value of ( _v3 / _v1 ) _d1 or close to it (0.7 to 1.5 times) so that each third layer of the second stack also has a value in said frequency range. vibrate inside. Also, each fourth layer is the same as the third layer by having a thickness d ₄ of (v ₄ /v ₃ )d ₃ or close to it (0.7 to 1.5 times) if it is made of piezoelectric material. It vibrates within a frequency range, and if it is made of an insulating material that does not have piezoelectricity, it receives vibration from the third layer and vibrates within the same frequency range. Accordingly, AC power is generated by piezoelectric conversion between the second electrode pair. By extracting this AC power as an electric signal, the frequency filter according to the present invention extracts, from the second electrode pair, AC power having a frequency within the frequency range among the plurality of frequencies input to the first electrode pair. Acts as a filter.

According to the frequency filter of the present invention, the first layer and the second layer are provided between the first electrode pair on the input side, and the third layer and the second layer are provided between the second electrode pair on the output side. Since each of the fourth layers has a plurality of layers, a piezoelectric member (first laminated body and second laminated body) thicker than the conventional resonator type BAW is placed between the first electrode pair and between the second electrode pair ) can be electrically isolated. Therefore, it is possible to increase the withstand voltage property, and even when the frequency range to be filtered is high, it is possible to perform filtering of high-power high-frequency power.

In the frequency filter according to the present invention,
wherein the second layer is made of a piezoelectric material;
A component of polarization in the first layer parallel to the first layer and a component of polarization in the second layer parallel to the second layer are directed in opposite directions,
and/or
wherein the fourth layer is made of a piezoelectric material;
A configuration can be adopted in which the polarization component of the third layer parallel to the third layer and the polarization component of the fourth layer parallel to the fourth layer are directed in opposite directions.

In this way, a laminate in which the polarization component parallel to each layer is in the opposite direction between the first layer and the second layer and/or the third layer and the fourth layer is formed by magnetron sputtering, for example. This can be easily obtained by making the direction of incidence of particles different for every other layer when fabricating each layer.

In the frequency filter according to the present invention, the electrode on the side of the first electrode pair opposite to the side of the second electrode pair and/or the side of the second electrode pair on the side of the first electrode pair A sound absorbing material may be provided in contact with the electrode on the opposite side. This suppresses reflection of vibration propagating in the first laminate and/or the second laminate at the end surfaces of the laminates provided with the sound absorbing material. Thereby, it is possible to suppress unnecessary resonance from occurring in the first laminate and/or the second laminate.

A frequency filtering method according to the present invention comprises:
a) a first layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from the polarization of the first layer, or a non-piezoelectric material; A _second layer _composed of A first laminate having a relationship of 0.7 × (v ₂ /v ₁ )d ₁ ≤ d ₂ ≤ 1.5 × ( _{v 2} /v ₁ )d ₁ using the speed of sound v ₁ and the speed of sound v 2 in the second layer and,
b) a first electrode pair consisting of a pair of electrodes provided to sandwich the first laminate in the lamination direction;
c) a third layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from that of the third layer, or a non-piezoelectric material; _A fourth layer _composed of Using the speed of sound _v3 and the speed of sound _v4 in the fourth layer, the relationship is 0.7×( _v4 / _v3 )d3 _{≦ d4} ≦1.5×( _v4 / _v3 ) _d3 , and The thickness _d1 of the first layer and the thickness _d3 of the third layer have a relationship of 0.7×( _v3 / _v1 ) _d1 ≦ _d3 ≦1.5×( _v3 / _v1 ) _d1 . 2 laminates;
d) a second electrode pair consisting of a pair of electrodes provided to sandwich the second laminate in the lamination direction;
and furthermore,
e) a substrate made of an insulating material having one surface in contact with one electrode of the first electrode pair and the other surface in contact with one electrode of the second electrode pair; Using a frequency filter in which the electrode and one electrode of the second electrode pair are in direct contact,
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 input between the two electrodes of the second electrode pair. It is characterized by outputting.

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) are , may be the same or different. If the number of layers on the input side is different from the number of layers on the output side, the voltage of the input AC power is boosted at the same time as filtering (when the number of layers on the output side is greater than the number of layers on the input side). Alternatively, it functions as a transformer for stepping down (when the number of layers on the output side is smaller than the number of layers on the input side) (see Patent Document 3).

According to the present invention, it is possible to obtain a frequency filter capable of filtering high-power high-frequency power.

1 is a schematic configuration diagram showing a first embodiment of a frequency filter according to the present invention; FIG. 4 is a graph showing the relationship between the polarization tilt angle from the normal to the layer and the electromechanical coupling coefficient in a layer composed of Al _1-x Sc _x N (0≦x≦0.45). 4A and 4B are diagrams for explaining the operation of the frequency filter of the first embodiment; FIG. FIG. 3 is a schematic configuration diagram showing a modified example of the frequency filter of the first embodiment; FIG. 5 is a schematic configuration diagram showing another modification of the frequency filter of the first embodiment; FIG. 5 is a schematic configuration diagram showing still another modification of the frequency filter of the first embodiment; FIG. 5 is a schematic configuration diagram showing a second embodiment of a frequency filter according to the present invention; 5 is a graph showing results of calculating filter characteristics of the frequency filters of the first embodiment and the second embodiment; 7 is a graph showing results of calculation of filter characteristics of a plurality of examples in which the number of layers of the first laminated body and the second laminated body are different for the frequency filter of the second embodiment. 10 is a graph showing results obtained by calculation of filter characteristics of a plurality of examples with different impedances connected to the input side and the output side of the frequency filter of the second embodiment; Electron micrographs of cross sections of a portion (a) containing the first laminate and a portion (b) containing the second laminate of the fabricated frequency filter. The (0002) plane pole figure (a) and the graph (b) showing the Ψ scanning curve measured for the first laminate of the fabricated frequency filter. The (0002) plane pole figure (a) and the graph (b) showing the Ψ scanning curve measured for the second laminate of the fabricated frequency filter. 7 is a graph showing the results (a) of measuring the filter characteristics of the manufactured frequency filter, and the results (b) of performing signal processing for removing unnecessary peaks and the like from the measurement data of the obtained filter characteristics. FIG. 5 is a schematic configuration diagram showing a third embodiment of a frequency filter according to the present invention; 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;

Embodiments of the frequency filter according to the present invention are shown using FIGS. 1 to 16. FIG.

(1) First Embodiment A frequency filter 10 of a 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, a 15.

The first laminate 11 includes a first layer 111 made of a piezoelectric material and a second layer 112 made of a piezoelectric material, which are arranged from the substrate 15 side to form the first layer 111 , the second layer 112 , the first layer 111 and the second layer 112 . Multiple (four) layers are alternately stacked in the order of The first layer 111 has a polarization P ₁ =(p _x , p _y ) in a direction tilted (neither parallel nor perpendicular to the layer) with respect to the layer. Here, p _x indicates the component of polarization P ₁ in the direction parallel to the layer, and p _y indicates the component of polarization P ₁ in the direction perpendicular to the layer. The polarization P ₂ of the second layer 112 is tilted with respect to the layer, and the component in the direction parallel to the layer is −p _x (that is, the direction opposite to that of the first layer 111) and the component in the direction parallel to the layer is p _y (that is, the same direction as the first layer 111) (P ₂ =(-p _x , p _y )).

Al _1-x Sc _x N (0≦x≦0.45) having a wurtzite structure is used for the piezoelectric material of the first layer 111 and the second layer 112 in this embodiment. When x exceeds 0.45, other piezoelectric materials having a wurtzite structure, such as ZnO, may be used instead of Al _1-x Sc _x N, which is a non-piezoelectric material. A piezoelectric material having a wurtzite structure is deposited by depositing particles of the piezoelectric material from a direction inclined to the surface of the substrate using, for example, a magnetron sputtering method. It has the advantage that the layers can be easily produced. When using this method to fabricate the first laminate 11, the operation of depositing the particles of the piezoelectric material after rotating the substrate by 180° about an axis perpendicular to the substrate is repeated.

Note that when Al _1-x Sc _x N is used for the piezoelectric material of the first layer 111 and the second layer 112 , the directions of the polarizations P ₁ and P ₂ are from the perpendicular to the first layer 111 and the second layer 112 . It is preferable that the direction is inclined by 27° to 43°. By tilting in such a direction, it is possible to increase the value of k′ ₁₅ ² among the electromechanical coupling coefficients (see FIG. 2), and as will be described later, the transverse wave generated in the first laminate 11 can be reduced. Strength can be increased.

Although both the first layer 111 and the second layer 112 have the same thickness in this embodiment, the thicknesses of both may be slightly different. Specifically _, the thickness d _{1 of the first layer 111 and the thickness d 2 of} the second layer 112 are 0.7×( v ₂ /v ₁ ) d ₁ ≤ d ₂ ≤ 1.5 × (v ₂ /v ₁ )d ₁ , the thickness d ₁ of the first layer 111 and the thickness d ₂ of the second layer 112 are You just have to decide. When the first layer 111 and the second layer 112 are made of the same piezoelectric material as in this embodiment, v ₁ =v ₂ , so the relationship 0.7d ₁ ≦d ₂ ≦1.5d ₁ should be satisfied. When the first layer 111 and the second layer 112 are made of different piezoelectric materials, the speed of sound is obtained for each piezoelectric material, and from the above relationship, the thickness _d1 of the first layer 111 and the thickness of the second layer 112 are _d2 should be determined.

The first electrode pair 12 is composed of a pair of electrodes 121 and 122 provided so as to sandwich the first laminate 11 in the lamination direction.

The second laminate 13 includes a third layer 131 made of a piezoelectric material and a fourth layer 132 made of a piezoelectric material, which are arranged from the substrate 15 side to form a third layer 131 , a fourth layer 132 , a third layer 131 and a fourth layer 132 . Multiple (four) layers are alternately stacked in the order of In this embodiment, the second laminate 13 has the same configuration as the first laminate 11 . That is, Al _1-x Sc _x N (0≦x≦1), which is the same piezoelectric material, is used for both the third layer 131 and the fourth layer 132, and the polarization of the third layer 131 is P ₁ =( p _x , p _y ), and the polarization of the fourth layer 132 is P ₂ =(−p _x , p _y ). Also, the thickness of the third layer 131 and the thickness of the fourth layer 132 are the same. The second laminate 13 can also have a modified configuration similar to the first laminate 11 . Alternatively, only one of the first layered body 11 and the second layered body 13 may be deformed, or the first layered body 11 and the second layered body 13 may be deformed differently from each other.

The second electrode pair 14 is composed of a pair of electrodes 141 and 142 provided so as to sandwich the second laminate 13 in the lamination direction.

The substrate 15 is a plate material made of an insulating material, and has one surface in contact with one electrode 122 of the first electrode pair 12 and the other surface in contact with one electrode 141 of the second electrode pair 14 . For the substrate 15, for example, a quartz plate can be used. Quartz has an acoustic impedance close to that of Al _1-x Sc _x N, so it is suitable as a material for the substrate 15 especially when the first laminate 11 and the second laminate 13 are made of Al _1-x Sc _x N. It can be used preferably. The thickness of the substrate 15 is not particularly limited, but the thickness should be such that the vibration generated in the first laminate 11 is not excessively damped when it is transmitted to the second laminate 13 as will be described later.

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

An AC power signal containing multiple frequencies to be filtered is input between electrodes 121 and 122 of the first electrode pair 12 . Then, each first layer 111 and each second layer 112 constituting the first laminate 11 mechanically vibrate due to piezoelectric conversion. At that time, the polarization P ₁ of the first layer 111 and the polarization P ₂ of the second layer 112 are in opposite directions to each other. It vibrates parallel to the layers and in opposite phases (180° out of phase). As a result, transverse wave vibration propagates in the thickness direction (the direction perpendicular to the first layer 111 and the second layer 112) in the first laminate 11 (see FIG. 3). The vibration of this transverse wave is centered on a specific frequency determined by the thicknesses of the first layer 111 and the second layer 112 and the speed of sound (depending on the material of those layers) among the multiple frequencies of the input AC power. It is strongly generated at vibration frequencies within a specified frequency range (which may be the same as or deviated from the specified frequency).

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

As described above, the frequency filter 10 of the first embodiment has a frequency (the oscillation frequency) within the specific frequency range among the AC power signals including a plurality of frequencies input to the first electrode pair 12. It operates as a frequency filter in which the AC power signal is output from the second electrode pair 14 .

Although the first electrode pair 12 is assumed to be the input side and the second electrode pair 14 is assumed to be the output side in the above description, the same applies when the second electrode pair 14 is assumed to be the input side and the first electrode pair 12 is assumed to be the output side. works similarly.

In the frequency filter 10 of the first embodiment, the first layer 111 and the second layer 112 are made of piezoelectric layers having polarization tilted with respect to these layers. 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 polarizations P of the first layer 111 and the second layer 112 are arranged to be opposite to each other. Alternatively, one of the first layer 111 and the second layer 112 is a piezoelectric layer having a polarization P perpendicular to the layer, and the other layer is a vertical component opposite to the polarization P in the one layer. A piezoelectric layer may be used which has a slope with respect to the other layer. In either case, longitudinal wave vibration is generated in the first stack 11 . A configuration similar to these may be applied to the third layer 131 and the fourth layer 132 (see FIG. 4).

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. Also in this case, the polarizations P of the first layer 111 and the second layer 112 are made to be opposite to each other. Alternatively, one of the first layer 111 and the second layer 112 is a piezoelectric layer having a polarization P parallel to that layer, and the other layer is a parallel component in the opposite direction to the polarization P in the one layer. A piezoelectric layer may be used which has a slope with respect to the other layer. In either case, transverse wave vibration is generated in the first laminate 11 in the same manner as in the first embodiment. A configuration similar to these may be applied to the third layer 131 and the fourth layer 132 (see FIG. 5).

As still another modification, instead of providing the substrate 15 in the frequency filter 10 of the first embodiment, as shown in FIG. and one electrode of the second electrode pair 14 (corresponding to the electrode 141 in the first embodiment). In this case, the vibration generated in the first laminate 11 propagates to the second laminate 13 via the electrode 151 . Such an electrode 151 can also be applied when the first layer 111 to the fourth layer have polarization as shown in FIGS. 4 and 5 or other polarizations.

(2) Second Embodiment Next, a frequency filter 20 according to a second embodiment will be described. As shown in FIG. 7, the frequency filter 20 of the second embodiment is obtained by adding a first sound absorbing material 21 and a second sound absorbing material 22 to the frequency filter 10 of the first embodiment. The first sound absorbing material 21 is provided so as to be in contact with the electrode 121 on the side of the first electrode pair 12 opposite to the second electrode pair 14 side. The second sound absorbing material 22 is provided so as to be in contact with the electrode 142 on the side of the second electrode pair 14 opposite to the first electrode pair 12 side. 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 that of the first layer 111, and have uneven end faces. Sound waves are absorbed by being scattered at the end face having such unevenness.

Instead of providing both the first sound absorbing material 21 and the second sound absorbing material 22, only one of the first sound absorbing material 21 and the second sound absorbing material 22 may be provided. Also, the first sound absorbing material 21 and/or the second sound absorbing material 22 may be combined with the configuration of each modification of the first embodiment described above.

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, the vibration propagating in the first laminate 11 and/or the second laminate 13 is Reflection at the end faces of these laminates provided with the sound absorbing material is suppressed. Thereby, it is possible to suppress unnecessary resonance from occurring in the first laminated body 11 and/or the second laminated body 13 .

(3) Calculation and Experimental Examples Regarding the Frequency Filters of the First and Second Embodiments First, the frequency filter 10 of the first embodiment and the frequency filter 20 of the second embodiment (both of The filter characteristics were calculated for each of the two laminates (the number of layers is four). A filter characteristic is indicated by an insertion loss value for each frequency. In this calculation, all of the first layer 111, the second layer 112, the third layer 131, and the fourth layer 132 in both the first embodiment and the second embodiment are 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 polarization inclination angle of 43° from the direction perpendicular to the layer). The sound velocities v1-v4 of the transverse waves in the first layer 111-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, signal processing is used to eliminate the effects of reflection on the end face, thereby forming the first sound absorbing material 21 and the second sound absorbing material 22 in a pseudo manner. 2 A state in which the sound absorbing material 22 exists is reproduced.

FIG. 8 shows the calculation results of the filter characteristics. In the first embodiment, a large number of spike-like peaks can be seen in gentle peaks having a frequency width of several tens to 200 MHz. This spike-like peak is caused by unnecessary resonance occurring in the first laminated body 11 and the second laminated body 13 in the frequency filter 10 of the first embodiment. On the other hand, in the second embodiment, only gentle peaks are seen, and spike-like peaks are not seen. This is because unnecessary resonance is suppressed in the frequency filter 20 of the second embodiment due to 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 (located on the upper side in the graph of FIG. 8), and suppresses signal loss.

For the frequency filter 20 of the second embodiment, the number of layers of the first laminate 11 (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 number of layers of the third layer 131 and the second layer 131) The filter characteristics were calculated for each of the cases where the sum of the number of layers of the four layers 132) was set to 2, 3, and 4, respectively. Here, when the number of layers is three, the number of layers of the first layer 111 and the third layer is two, and the number of layers of the second layer 112 and the fourth layer 132 is one. Calculation results are shown in FIG. In addition, when the number of layers is 4, the calculation result of the second embodiment in FIG. 8 is the same. As the number of layers of the first laminated body 11 and the second laminated body 13 increases, the passband becomes narrower and the insertion loss becomes smaller, thereby suppressing signal loss.

It was confirmed by calculation that the filter characteristics of the frequency filter 20 of the second embodiment (the number of layers of the first laminate 11 and the number of layers of the second laminate are four each) are changed by adjusting the impedance matching. Here, a case where an electrical resistance of R = 50Ω is inserted on the input side and the output side of the frequency filter 20, and a case where an electrical resistance of R = 50Ω and an inductance of L = 16nH are inserted on the input side and the output side respectively. The filter characteristics were calculated. Calculation results are shown in FIG. Insertion loss is smaller when R=50Ω electrical resistance and L=16nH inductance are inserted than when only R=50Ω electrical resistance is inserted. Insertion loss can be reduced by adjusting impedance matching. Confirmed to be improved.

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

The manufacturing method is as follows. First, the electrodes 122 and 141 were produced by vapor-depositing a metal material on both surfaces of the substrate 15 . Next, the substrate 15 was mounted on the substrate holder of the magnetron sputtering apparatus 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 are made incident on the surface of the electrode 122 from a direction inclined with respect to the substrate 15 in a nitrogen gas atmosphere, thereby forming the first layer 111. formed one. Subsequently, after rotating the substrate 15 by 180° about an axis perpendicular to it, one second layer 112 was formed by injecting particles onto the surface of the first layer 111 in the same manner as described above. By performing this operation twice more, the first laminate 11 was produced.

Next, the substrate 15 was mounted again so that the electrode 141 faced the sputtering target side, and particles were made incident on the surface of the electrode 141 in the same manner as described above, thereby forming one third layer 131 . Subsequently, after rotating the substrate 15 by 180° about an axis perpendicular to it, one fourth layer 132 was formed by injecting particles onto the surface of the third layer 131 in the same manner as described above. By performing this operation twice more, the second laminate 13 was produced. Finally, electrodes 121 and 142 were fabricated by vapor-depositing a metal material on the surface of the first laminate 11 opposite to the substrate 15 and the surface of the second laminate 13 opposite to the substrate 15. .

FIG. 11 shows an electron micrograph of a cross section of the frequency filter 10 produced. 11(a) is an enlarged view of the first laminate 11 side, and FIG. 11(b) is an enlarged view of the second laminate 13 side. Note that FIG. 11A is upside down from the schematic diagram shown in FIG. From these electron micrographs, it can be seen that both the first laminate 11 and the second laminate 13 have four layers oriented alternately 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 micrograph.

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 an angle (tilt angle) with respect to a line perpendicular to the substrate 15, and φ indicates an azimuth angle. The Ψ scanning curve is obtained by obtaining the X-ray diffraction intensity while changing Ψ along the straight line in (a). From these figures, the polarization direction (the same direction as the z-axis of the Al _1-x Sc _x N crystal) has an average tilt angle of 32.2° in the first layer 111 and an average tilt angle of 32.2° in the second layer 112 . The azimuth angle is 26.8°, which is almost 180° different from the polarization of the first layer 111 . Similarly, regarding the second laminate 13, the (0002) plane pole figure shown in FIG. 13(a) and the Ψ scanning curve shown in FIG. is 24.6° in the fourth layer 132, and the tilt angle in the fourth layer 132 is 22.3° on average and the azimuth angle differs from the polarization in the third layer 131 by approximately 180°.

Filter characteristics of the fabricated frequency filter 10 were measured using a network analyzer. The results are shown in FIG. 14(a). Comparing this measurement result with the calculation result (Fig. 8), the measurement result shows that the induced loss is smaller than the calculation result in the frequency range below 300MHz. It is considered that this is due to the occurrence of vibration of longitudinal waves in addition to transverse waves. In addition, in this measurement result, as in the calculation result, a spike-like peak due to reflection at the end surface of the laminate is observed.

Therefore, signal processing was performed by subjecting the obtained measurement data to fast Fourier transform and then to inverse fast Fourier transform. The results are shown in FIG. 14(b). It was confirmed that the effects of longitudinal waves and the effects of reflection at the end face of the laminate can be eliminated by such signal processing.

(4) Third Embodiment In each of the embodiments described so far, all the layers (piezoelectric layers) constituting the first laminate and the second laminate are made of a piezoelectric material. A first laminated body and/or a second laminated body may be used in which layers (non-piezoelectric layers) made of an insulating material having no piezoelectricity are provided at regular intervals, that is, piezoelectric layers and non-piezoelectric layers are alternately laminated. In the frequency filter 30 illustrated in FIG. 15, the first laminate 31 has a structure in which a first layer (piezoelectric layer) 111 and a second layer (non-piezoelectric layer) 313 are alternately laminated. It has a configuration in which a third layer (piezoelectric layer) 131 and a fourth layer (non-piezoelectric layer) 333 are alternately laminated. It should be noted that the polarization direction of the piezoelectric layer is not limited to the illustrated one. 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 those illustrated. Furthermore, the number of layers of the first laminate 31 and the second laminate 33 is not limited to the illustrated one, and may be two layers, three layers, or five layers or more. Configurations other than the first laminated body 31 and the second laminated body 33 are the same as those of the frequency filter 10 of the first embodiment, and modifications similar to those of the first and second embodiments are possible.

(5) Others In each of the embodiments described so far, the first laminate and the second laminate have the same number of layers, but the first laminate and the second laminate have different numbers of layers. also acts as a frequency filter. However, in that case, 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. When the number of layers is 4 (one each of the third layer 131 and the fourth layer 132), when an AC electric signal is input between the electrodes 121 and 122 of the first electrode pair 12, the second electrode pair Between the electrodes 141 and 142 of 14, a frequency-filtered AC electrical signal having a higher voltage than the input AC electrical signal is output. When an alternating electrical signal is input between the electrodes 141 and 142 of the second electrode pair 14 with the same configuration, a lower voltage than the input alternating electrical signal is applied between the electrodes 121 and 122 of the first electrode pair 12 An alternating electrical signal having voltage and filtered frequency is output. Note that the configuration shown in FIG. 16 is an example, and modifications such as the number of layers, the direction of polarization, the presence or absence of non-piezoelectric layers, the presence or absence of the substrate 15, etc. are possible, as in the first to third embodiments. be.

In addition to the multiple embodiments and modifications thereof described so far, various modifications are possible within the scope of the gist of the present invention.

10, 20, 30... frequency filters 11, 31, 41... first laminate 111... first layer 112... second layer 12... first electrode pairs 121, 122... electrodes 13, 33, 42... of the first electrode pairs Second laminate 131 Third layer 132 Fourth layer 14 Second electrode pair 141, 142 Second electrode pair electrode 15 Substrate 151 One electrode of the first electrode pair and one of the second electrode pair Electrode 21 that also serves as an electrode of the first sound absorbing material 22 second sound absorbing material 313 second layer (non-piezoelectric layer)
333... Fourth layer (non-piezoelectric layer)

Claims (4)

a) a first layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from the polarization of the first layer, or a non-piezoelectric material; A _second layer _composed of A first laminate having a relationship of 0.7 × (v ₂ /v ₁ )d ₁ ≤ d ₂ ≤ 1.5 × ( _{v 2} /v ₁ )d ₁ using the speed of sound v ₁ and the speed of sound v 2 in the second layer and,
b) a first electrode pair consisting of a pair of electrodes provided to sandwich the first laminate in the lamination direction;
c) a third layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from that of the third layer, or a non-piezoelectric material; A _fourth layer consisting of the The thickness _d4 of the fourth layer is 0.7×( _v4 / _v3 )d3 _{≦ d4 ≦ 1.5} ×(v ₄ / _v3 ) _d3 , and the thickness _d1 of the first layer and the thickness _d3 of the third layer are 0.7×( _v3 / _v1 )d1 _{≦ d3} ≦1.5 a second laminate having a relationship of ×(v ₃ /v ₁ )d ₁ ;
d) a second electrode pair consisting of a pair of electrodes provided to sandwich the second laminate in the lamination direction;
and furthermore,
e) a substrate made of an insulating material having one surface in contact with one electrode of the first electrode pair and the other surface in contact with one electrode of the second electrode pair; A frequency filter, wherein an electrode and one electrode of the second electrode pair are in direct contact. wherein the second layer is made of a piezoelectric material;
A component of polarization in the first layer parallel to the first layer and a component of polarization in the second layer parallel to the second layer are directed in opposite directions,
and/or
wherein the fourth layer is made of a piezoelectric material;
2. The method according to claim 1, wherein a component of polarization in said third layer parallel to said third layer and a component of polarization in said fourth layer parallel to said fourth layer are directed in opposite directions to each other. frequency filter. Further, an electrode of the first electrode pair on the side opposite to the second electrode pair and/or an electrode of the second electrode pair on the side opposite to the first electrode pair 3. A frequency filter according to claim 1 or 2, comprising a sound absorbing material in contact with the . a) a first layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from the polarization of the first layer, or a non-piezoelectric material; A _second layer _composed of A first laminate having a relationship of 0.7 × (v ₂ /v ₁ )d ₁ ≤ d ₂ ≤ 1.5 × ( _{v 2} /v ₁ )d ₁ using the speed of sound v ₁ and the speed of sound v 2 in the second layer and,
b) a first electrode pair consisting of a pair of electrodes provided to sandwich the first laminate in the lamination direction;
c) a third layer made of a piezoelectric material, the polarization of which is oriented in a predetermined direction, and an insulating material made of a piezoelectric material, the polarization of which is oriented in a direction different from that of the third layer, or a non-piezoelectric material; _A fourth layer _composed of Using the speed of sound _v3 and the speed of sound _v4 in the fourth layer, the relationship is 0.7×( _v4 / _v3 )d3 _{≦ d4} ≦1.5×( _v4 / _v3 ) _d3 , and The thickness _d1 of the first layer and the thickness _d3 of the third layer have a relationship of 0.7×( _v3 / _v1 ) _d1 ≦ _d3 ≦1.5×( _v3 / _v1 ) _d1 . 2 laminates;
d) a second electrode pair consisting of a pair of electrodes provided to sandwich the second laminate in the lamination direction;
and furthermore,
e) a substrate made of an insulating material having one surface in contact with one electrode of the first electrode pair and the other surface in contact with one electrode of the second electrode pair; Using a frequency filter in which the electrode and one electrode of the second electrode pair are in direct contact,
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 input between the two electrodes of the second electrode pair. A frequency filtering method characterized by outputting.

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