Frequency filter

Abstract

To provide a frequency filter that is usable singly as a bandpass filter and has high dielectric strength.SOLUTION: A frequency filter (10) comprises: an input unit (11) composed of a polarized inverted laminate resonator in which a first electrode (121) and a second electrode (122) are arranged so as to sandwich the top and the bottom of a polarized inverted laminate piezoelectric body (110) composed by laminating a plurality of piezoelectric layers (111, 112), each formed from a piezoelectric body and each having an approximately equal basic wave resonance frequency derived by dividing sound velocity by twice of the thickness, in such a manner that the bearing of a polarization component in a direction parallel or perpendicular to the piezoelectric layer is alternately reversed; an output unit (13) composed of a second resonator which is a polarized inverted laminate resonator, with a plurality of piezoelectric layers (131, 132) of the second resonator being laminated in the same direction as a plurality of piezoelectric layers (111, 112) of the first resonator and having an approximately equal basic wave resonance frequency; and a pair of acoustic reflectors (15, 151) provided so as to sandwich the input unit (11) and the output unit (13) in the direction of lamination.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a frequency filter used in communication devices such as smartphones.

Background Art

[0002] In communication devices such as smartphones, a frequency filter is used to extract a specific frequency band from an electromagnetic wave in a wide frequency band converted into a signal current by an antenna. As an example of such a frequency filter, a surface acoustic wave (SAW) filter can be mentioned.

[0003] A SAW filter generally includes a substrate made of a piezoelectric body, an IDT (Inter-Digital Transducer) formed by meshing two comb-shaped electrodes provided on the surface of the substrate with each other, and two grating reflectors provided on the surface of the substrate so as to sandwich the IDT. One SAW filter may be provided with only one IDT, or a plurality of IDTs may be arranged between the two grating reflectors.

[0004] Among SAW filters having a plurality of IDTs, when a signal current is input from a set of comb-shaped electrodes of one of the plurality of IDTs, each IDT vibrates as a resonator, and the plurality of IDTs vibrate as a whole in a plurality of vibration modes and acoustically couple on the substrate (see, for example, Patent Document 1). From such an operation, a SAW filter having a plurality of sets of IDTs is called a multi-mode SAW filter. The multi-mode SAW filter functions as a band filter that passes a signal current obtained by converting an electromagnetic wave within a frequency band having a certain width by vibrating in a plurality of vibration modes. Among band filters using SAW filters, there are also those formed by connecting a plurality of SAW filters each having only one IDT and having different resonance frequencies, but since the multi-mode SAW filter operates as a band filter with only one, the circuit configuration can be simplified.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, since the multi-mode SAW filter operates as a band filter with only one unit, all the voltage of the input signal current is applied to a set of comb-shaped electrodes of one of the plurality of IDTs. Since the comb-shaped electrodes are only separated by a narrow gap (gap), the multi-mode SAW filter has the drawback of low breakdown voltage resistance.

[0007] The problem to be solved by the present invention is to provide a frequency filter that can be used alone as a band filter and has high breakdown voltage resistance.

Means for Solving the Problems

[0008] The frequency filter according to the present invention made to solve the above problems is a) An input section including a first resonator which is a polarization-inverted stacked resonator in which a plurality of piezoelectric layers each made of a piezoelectric material and having substantially equal fundamental wave resonance frequencies, which are values obtained by dividing the sound velocity by twice the thickness, are stacked such that the directions of the components of polarization in a direction parallel or perpendicular to the piezoelectric layers are alternately inverted, and the first electrode and the second electrode are arranged so as to sandwich the polarization-inverted stacked piezoelectric body, or an intermediate electrode stacked resonator in which a plurality of piezoelectric layers each made of a piezoelectric material and having substantially equal fundamental wave resonance frequencies are stacked such that the directions of polarization are aligned, and the first partial electrode and the second partial electrode are alternately arranged above, below, and between the layers of the piezoelectric layers; b) An output section including a second resonator which is a polarization-inverted stacked resonator or an intermediate electrode stacked resonator, in which a plurality of piezoelectric layers of the second resonator are stacked in the same direction as the plurality of piezoelectric layers of the first resonator and have substantially equal fundamental wave resonance frequencies; c) a pair of acoustic reflectors provided so as to sandwich the input part and the output part in the stacking direction; It is characterized by comprising.

[0009] In the present invention, the input part and the output part may be in contact with each other, or an intermediate layer that transmits vibrations generated in the input part to the output part may be sandwiched between the input part and the output part.

[0010] "The fundamental wave resonance frequencies are substantially equal" means that the fundamental wave resonance frequencies of a plurality of piezoelectric layers of a polarization-inverted laminated piezoelectric body or a polarization-aligned laminated piezoelectric body fall within the range of ±10% from their average value. By having substantially equal fundamental wave resonance frequencies for each piezoelectric layer in this way, the entire polarization-inverted laminated resonator or intermediate electrode laminated resonator resonates at a resonance frequency that is an integer (including 1) multiple of the fundamental wave resonance frequency.

[0011] When an AC voltage having a frequency within a frequency band centered on an integer multiple of the fundamental wave resonance frequency is applied between the first electrode and the second electrode of a polarization-inverted laminated resonator, the polarization-inverted laminated piezoelectric body vibrates at the frequency within the frequency band, and when vibrations having a frequency within the same frequency band are applied, an AC voltage having a frequency within the frequency band is generated between the first electrode and the second electrode.

[0012] When an AC voltage having a frequency within a frequency band centered on an integer multiple of the fundamental wave resonance frequency is applied between an adjacent partial first electrode and a partial second electrode of an intermediate electrode laminated resonator, the polarization-aligned laminated piezoelectric body vibrates at the frequency within the frequency band, and when vibrations having a frequency within the same frequency band are applied to the polarization-aligned laminated piezoelectric body, an AC voltage having a frequency within the frequency band is generated between the adjacent partial first electrode and the partial second electrode. When there are a plurality of partial first electrodes, they can be electrically connected to function as one electrode. The same applies to the partial second electrode.

[0013] In the frequency filter according to the present invention, when a voltage of a signal current in which various frequencies are superimposed (typically, a signal obtained by converting an electromagnetic wave received by an antenna) is applied between the first electrode and the second electrode of the input section or between the partial first electrode and the partial second electrode adjacent thereto, vibrations having frequencies within a specific frequency band including a plurality of resonance frequencies that are integer multiples of the fundamental wave resonance frequency and are close to each other occur in the polarization-inverted laminated piezoelectric body or the polarization-aligned laminated piezoelectric body of the input section. This vibration is transmitted to the polarization-inverted laminated piezoelectric body or the polarization-aligned laminated piezoelectric body of the output section. Then, an alternating voltage having a frequency within the specific frequency band is generated between the first electrode and the second electrode of the output section or between the partial first electrode and the partial second electrode adjacent thereto. As a result, the frequency filter according to the present invention functions as a multi-mode band filter having the specific frequency band as a passband.

[0014] According to the frequency filter of the present invention, since a piezoelectric layer exists between the first electrode and the second electrode of the input section or between the partial first electrode and the partial second electrode adjacent thereto, the voltage resistance can be made higher than that of a multi-mode SAW filter in which only a narrow space (gap) exists between the comb-shaped electrodes.

[0015] In the frequency filter according to the present invention, it is preferable that one or both of the pair of acoustic reflectors are acoustic Bragg reflectors. Thereby, it is possible to efficiently prevent the vibration generated in the input section from leaking to the outside of the frequency filter.

[0016] Also, one or both of the pair of acoustic reflectors may be air (that is, without providing any object). Thereby, the structure of the frequency filter can be simplified.

[0017] Furthermore, in the frequency filter according to the present invention, an inductor (coil) may be connected in parallel to the input section and / or in parallel to the output section. As a result, a frequency filter having a passband with a center frequency and / or a width different from those in the case where the inductor is not provided can be obtained.

[0018] Note that the polarization inversion laminated resonator and the intermediate electrode laminated resonator can be used not only as the input part and / or output part in the frequency filter according to the present invention, but also as a band filter by connecting a plurality of resonators having different resonance frequencies to each other, similar to a SAW filter that is not a multi-mode type. These polarization inversion laminated resonators and intermediate electrode laminated resonators have higher voltage resistance than SAW filters that are not multi-mode type for the same reason as the frequency filter according to the present invention. Among these, the polarization inversion laminated resonator has been conventionally used, but the intermediate electrode laminated resonator was first discovered by the present inventor. While it is necessary to fabricate each piezoelectric layer so that the directions of polarization of adjacent piezoelectric layers are different in the polarization inversion laminated resonator, the intermediate electrode laminated resonator can be fabricated more easily because the directions of polarization of each piezoelectric layer are the same.

Advantages of the Invention

[0019] According to the present invention, a frequency filter that can be used as a band filter and has high voltage resistance can be obtained.

Brief Description of the Drawings

[0020]

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Mode for Carrying Out the Invention

[0021] An embodiment of a frequency filter according to the present invention will be described with reference to FIGS. 1 to 22. The frequency filter 10 of the first embodiment shown in FIG. 1 uses a polarization-inverted laminated resonator. The frequency filter 20 of the second embodiment shown in FIG. 2 uses an intermediate electrode laminated resonator. Hereinafter, these two frequency filters 10 and 20 will be described in detail.

[0022] (1) Frequency Filter of the First Embodiment The frequency filter 10 of the first embodiment includes an input section 11 composed of a first input-side piezoelectric layer 111, a second input-side piezoelectric layer 112, a first input-side electrode 121, and a second input-side electrode 122, and an output section 13 composed of a first output-side piezoelectric layer 131, a second output-side piezoelectric layer 132, a first output-side electrode 141, and a second output-side electrode 142.

[0023] Both the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112 have a polarization P inclined (neither parallel nor perpendicular) to those layers. The components of the polarization P parallel to these layers are in opposite directions to each other, and the components of the polarization P perpendicular to these layers are in the same direction. The first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112 are made of the same piezoelectric material and have the same thickness. As a result, the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112 have substantially equal fundamental wave resonance frequencies, which are values obtained by dividing the sound velocity v, which is a value dependent on the material, by twice the thickness d of those layers, i.e., v / (2d).

[0024] Note that different piezoelectric materials may be used for the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112. In this case, since the sound velocity v is different for each piezoelectric material, the thickness of each layer is set so that the values of the fundamental wave resonance frequency v / (2d) are substantially equal. Also, the directions of polarization P of the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112 only need to have components perpendicular or parallel to these two layers that are opposite to each other. Therefore, the directions of polarization P of these two layers may be perpendicular to these two layers and opposite to each other, or may be parallel to these two layers and opposite to each other, or may be inclined with respect to these two layers and have perpendicular components that are opposite to each other.

[0025] By laminating the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112, an input-side polarization-inverted laminated piezoelectric body 110 is formed. The first input-side electrode 121 and the second input-side electrode 122 are provided so as to sandwich the input-side polarization-inverted laminated piezoelectric body 110 in the lamination direction.

[0026] The first output-side piezoelectric layer 131, the second output-side piezoelectric layer 132, the first output-side electrode 141, and the second output-side electrode 142 of the output unit 13 each have the same configuration as the first input-side piezoelectric layer 111, the second input-side piezoelectric layer 112, the first input-side electrode 121, and the second input-side electrode 122 of the input unit 11. The output-side polarization-inverted laminated piezoelectric body 130 is formed by laminating the first output-side piezoelectric layer 131 and the second output-side piezoelectric layer 132.

[0027] All of the two electrodes on the input unit 11 side (the first input-side electrode 121 and the second input-side electrode 122), and the two electrodes on the output unit 13 side (the first output-side electrode 141 and the second output-side electrode 142) are provided so that a part thereof protrudes outside (laterally) of the laminated piezoelectric body (the input-side polarization-inverted laminated piezoelectric body 110, the output-side polarization-inverted laminated piezoelectric body 130). Also, in order to facilitate wiring to these electrodes, the positions in the in-plane direction (the direction parallel to each layer) where these electrodes protrude from the laminated piezoelectric body are the same for the two electrodes on the input unit 11 side and the same for the two electrodes on the output unit 13 side, but are different between the two electrodes on the input unit 11 side and the two electrodes on the output unit 13 side.

[0028] The input section 11 and the output section 13 are provided so as to be in direct contact in the stacking direction. As a result, the second input-side electrode 122 and the first output-side electrode 141 are electrically connected and have the same electric potential.

[0029] For the materials of the first input-side piezoelectric layer 111, the second input-side piezoelectric layer 112, the first output-side piezoelectric layer 131, and the second output-side piezoelectric layer 132, Sc 1-x Al x AlN (scandium aluminum nitride, 0 < x < 1) can be preferably used. The piezoelectric layer composed of Sc 1-x Al x AlN with a polarization inclined with respect to the layer can be manufactured as follows using the magnetron sputtering apparatus 30 shown in FIG. 3. A target T made of a ScAl alloy is placed on the cathode electrode 31 of the magnetron sputtering apparatus 30. In this state, magnetron sputtering is performed in a gas atmosphere containing nitrogen to generate sputtered particles SP. The generated sputtered particles SP are made to enter the surface of the substrate S fixed to the substrate holder 32 at an angle inclined with respect to the surface, whereby one target piezoelectric layer with a polarization P inclined with respect to the layer is obtained. Then, after rotating the substrate S by 180° around an axis perpendicular thereto, another target piezoelectric layer is manufactured in the same manner as above, whereby the first input-side piezoelectric layer 111, the second input-side piezoelectric layer 112, the first output-side piezoelectric layer 131, and the second output-side piezoelectric layer 132 in which the components of the polarization P parallel to these layers are in opposite directions to each other are obtained.

[0030] The frequency filter 10 further includes an acoustic Bragg reflector 15 that contacts, on a surface of the output portion 13 opposite to the input portion 11 in the stacking direction. The acoustic Bragg reflector 15 is formed by alternately stacking two types of layers having different acoustic impedances. For these two types of layers, for example, a layer made of SiO2 (silicon dioxide) and a layer made of Ta2O5 (tantalum pentoxide) having a higher acoustic impedance than the former can be used. The acoustic Bragg reflector 15 serves to suppress the leakage of vibrations generated by the input-side polarization-inverted stacked piezoelectric body 110 of the input portion 11 to the outside of the frequency filter 10, as will be described later.

[0031] In the frequency filter 10 of the present embodiment, nothing is provided in the region 151 that contacts the surface of the input portion 11 opposite to the output portion 13 in the stacking direction. The air present in this region 151 also serves to reflect the vibrations generated in the input portion 11 and suppress their leakage to the outside of the frequency filter 10, similar to the acoustic Bragg reflector 15. As shown in FIG. 4, instead of the air in the region 151, an acoustic Bragg reflector 152 may also be provided on the surface of the input portion 11 opposite to the output portion 13 in the stacking direction. Although the structure becomes more complex by providing such an acoustic Bragg reflector 152, the effect of suppressing the leakage of vibrations to the outside of the frequency filter 10 can be further enhanced. On the other hand, it is also possible to provide a reflection portion by air (without providing the acoustic Bragg reflector 15) at the position of the acoustic Bragg reflector 15 in the frequency filter 10. However, in order to enhance the effect of suppressing the leakage of vibrations to the outside of the frequency filter 10, it is desirable to provide a solid reflector such as an acoustic Bragg reflector (in addition to the substrate 17) at least either above or below in the stacking direction.

[0032] A substrate 17 is provided on the surface of the acoustic Bragg reflector 15 opposite to the input portion 11 in the stacking direction. This substrate 17 serves to support the entire frequency filter 10 and does not contribute to the operation of the frequency filter 10 itself. Therefore, the substrate 17 may be omitted.

[0033] An intermediate layer (not shown) that transmits the vibration generated in the input unit 11 to the output unit 13 may be sandwiched between the input unit 11 and the output unit 13.

[0034] The operation of the frequency filter 10 of the first embodiment will be described. When a voltage of a signal current in which various frequencies are superimposed is applied between the first input-side electrode 121 and the second input-side electrode 122, the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112 vibrate in opposite phases in the direction parallel to the layer because the components parallel to the layer of polarization P are opposite to each other. As a result, in the input-side polarization-inverted laminated piezoelectric body 110, vibrations having one or a plurality of frequencies within a specific frequency band including a plurality of resonance frequencies that are integer multiples of the fundamental wave resonance frequency and are close to each other among those various frequencies are generated. This vibration is conducted to the output-side polarization-inverted laminated piezoelectric body 130. At this time, the air in the acoustic Bragg reflector 15 and the region 151 prevents the vibration from leaking outside the frequency filter 10. Due to the vibration conducted to the output-side polarization-inverted laminated piezoelectric body 130 in this way, an AC voltage having the one or a plurality of frequencies within the specific frequency band is generated between the first output-side electrode 141 and the second output-side electrode 142. Thereby, the frequency filter 10 of the first embodiment functions as a multi-mode type band filter having the specific frequency band as a passband.

[0035] In the frequency filter 10 of the first embodiment, as shown in FIG. 5, an input-side inductor 161 may be provided in parallel with the input unit 11, and an output-side inductor 162 may be provided in parallel with the output unit 13. The center frequency and / or the width of the passband can be adjusted according to the magnitudes of the inductances of these inductors. Only one of the input-side inductor 161 and the output-side inductor 162 may be provided. The input-side inductor 161 and the output-side inductor 162 may have fixed inductances or variable inductances.

[0036] The number of piezoelectric layers each of the input section and the output section has may be more than two layers. For example, in the frequency filter 10A shown in FIG. 6, in the input section 11A and the output section 13A, four piezoelectric layers each (piezoelectric layers 111A to 114A and 131A to 134A) are stacked such that the polarization directions are alternately reversed, and the input-side polarization-reversed stacked piezoelectric body 110A and the output-side polarization-reversed stacked piezoelectric body 130A are used.

[0037] In the above description, for convenience, those denoted by reference numeral 11 were described as the "input section" and those denoted by reference numeral 13 were described as the "output section", but those having the same structure may be used with the roles of the input section and the output section swapped. That is, those denoted by reference numeral 13 may be used as the "input section" and those denoted by reference numeral 11 may be used as the "output section". This point is the same not only for the frequency filter of the first embodiment but also for all the frequency filters shown in this specification.

[0038] (2) Frequency Filter of Second Embodiment As shown in FIG. 2, the frequency filter 20 of the second embodiment includes an input section 21 composed of a first input-side piezoelectric layer 211, a second input-side piezoelectric layer 212, a first input-side electrode 221, and a second input-side electrode 222, and an output section 23 composed of a first output-side piezoelectric layer 231, a second output-side piezoelectric layer 232, a first output-side electrode 241, and a second output-side electrode 242.

[0039] Both the first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212 have a polarization P that is perpendicular to those layers and faces the same direction. Note that the direction of the polarization P only needs to be the same between the first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212, and may be parallel to those layers or may be inclined (neither perpendicular nor parallel) to those layers. The first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212 are made of the same piezoelectric material and have the same thickness, whereby the fundamental wave resonance frequency v / (2d) is substantially equal. Note that the first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212 may be made of different piezoelectric materials, and in that case, the thicknesses of the respective layers are set such that the values of the fundamental wave resonance frequency v / (2d) are substantially equal according to the difference in the sound velocity for each piezoelectric material.

[0040] By laminating the first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212, an input-side polarization-aligned laminated piezoelectric body 210 is formed.

[0041] The first input-side electrode 221 is formed by electrically connecting first input-side partial electrodes 2211 and 2212 provided above and below the input-side polarization-aligned laminated piezoelectric body 210, respectively. The second input-side electrode 222 is provided between the first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212. In this embodiment, the second input-side electrode 222 is composed of a single flat electrode, and this single electrode is regarded as a second input-side partial electrode alternately arranged with the first input-side partial electrodes 2211 and 2212.

[0042] The first output-side piezoelectric layer 231, the second output-side piezoelectric layer 232, the first output-side electrode 241 (first output-side partial electrodes 2411 and 2412), and the second output-side electrode 242 of the output unit 23 each have the same configuration as the first input-side piezoelectric layer 211, the second input-side piezoelectric layer 212, the first input-side electrode 221 (first input-side partial electrodes 2211 and 2212), and the second input-side electrode 222 of the input unit 21. By laminating the first output-side piezoelectric layer 231 and the second output-side piezoelectric layer 232, an output-side polarization-reversed laminated piezoelectric body 230 is formed.

[0043] The input unit 21 and the output unit 23 are provided so as to be in direct contact in the lamination direction. Thereby, the first input-side electrode 221 and the first output-side electrode 241 are electrically connected and have the same electric potential.

[0044] The frequency filter 20 further includes an acoustic Bragg reflector 25 so as to be in contact with the lower surface of the output unit 23, that is, the surface opposite to the input unit 21 in the lamination direction. Also, a substrate 27 is provided under the acoustic Bragg reflector 25. The configurations of the acoustic Bragg reflector 25 and the substrate 27 are the same as those of the acoustic Bragg reflector 15 and the substrate 17 in the first embodiment. Although nothing is provided in the region 251 in contact with the upper surface of the input unit 21, that is, the surface opposite to the output unit 23 in the lamination direction, an acoustic Bragg reflector in contact with this surface may be provided as in the first embodiment.

[0045] The operation of the frequency filter 20 according to the second embodiment will be described. When a voltage of a signal current in which various frequencies are superimposed is applied between the first input-side electrode 221 and the second input-side electrode 222, electric fields perpendicular to those layers and in opposite directions to each other are applied to the first input-side piezoelectric layer 111 and the second input-side piezoelectric layer 112. As a result, the first input-side piezoelectric layer 211 and the second input-side piezoelectric layer 212 vibrate in opposite phases to each other. As a result, in the input-side polarization-conforming laminated piezoelectric body 210, vibrations having one or a plurality of frequencies within a specific frequency band including a plurality of resonance frequencies that are integer multiples of the fundamental wave resonance frequency and are close to each other among those various frequencies are generated. This vibration is conducted to the output-side polarization-conforming laminated piezoelectric body 230, and an alternating voltage having the one or a plurality of frequencies within the specific frequency band is generated between the first output-side electrode 241 and the second output-side electrode 242. Thereby, the frequency filter 20 according to the second embodiment functions as a multi-mode type band filter having the specific frequency band as a passband. Note that the roles of the acoustic Bragg reflector 25 and the air in the region 251 are the same as those in the corresponding parts in the first embodiment.

[0046] As shown in FIG. 7, in the frequency filter 20 according to the second embodiment as well, an input-side inductor 261 may be provided in parallel with the input unit 21, and an output-side inductor 262 may be provided in parallel with the output unit 23. Only one of the input-side inductor 261 and the output-side inductor 262 may be provided. The input-side inductor 261 and the output-side inductor 262 may have a fixed inductance or a variable inductance.

[0047] Also in the frequency filter of the second embodiment, the piezoelectric layers included in each of the input portion and the output portion may be more than two layers. For example, in the frequency filter 20A shown in FIG. 8, the input portion 21A is provided with an input-side polarization-aligned laminated piezoelectric body 210A composed of four piezoelectric layers 211A to 214A, and the output portion 23A is provided with an output-side polarization-aligned laminated piezoelectric body 230A composed of four piezoelectric layers 231A to 234A. These piezoelectric layers 211A to 214A and 231A to 234A are made of the same material, have the same thickness, and are polarized in the same direction. The material and thickness may be different for each piezoelectric layer as long as the fundamental wave resonance frequencies are substantially equal. In the input portion 21A, first input-side partial electrodes 2211A to 2213A and second input-side partial electrodes 2221A and 2222A are alternately provided above and below the input-side polarization-aligned laminated piezoelectric body 210A and between the piezoelectric layers. The first input-side electrodes 221A and the second input-side electrodes 222A are formed by electrically connecting the first input-side partial electrodes 2211A to 2213A to each other and the second input partial electrodes 2221A and 2222A to each other. Similarly, in the output portion 23A, a first output-side electrode 241A in which the first output-side partial electrodes 2411A to 2413A are electrically connected and a second output-side electrode 242A in which the second output-side partial electrodes 2421A and 2422A are electrically connected are formed.

[0048] (3) Calculation results and experimental results regarding the frequency filters of the first and second embodiments The calculation simulation results and experimental results for the frequency filters of the first and second embodiments are shown below.

[0049] First, an example of the simulation is shown. In this example, in the frequency filter 20 of the second embodiment, a configuration is targeted in which a first inductor 261 and a second inductor 262 are provided, and an intermediate layer 28 is provided between the input portion 21 and the output portion 22 as shown in FIG. 9. The intermediate layer 28 is made of an insulator having no piezoelectricity, and the material and the thickness are set so as to be λ / 2, which is half of the wavelength λ of the vibration having the fundamental wave resonance frequency. The material of each piezoelectric layer is Sc 1-x Al x N(x = 0.4). The inductances L of the first inductor 261 and the second inductor 262p When multiple simulations were performed while changing the value of p L = 6.5 nH, the impedance characteristics shown in FIG. 10 and the filter characteristics shown in FIGS. 11 and 12 were obtained. FIG. 12 is an enlarged view of a part of FIG. 11. In the graph of the impedance characteristics, a plurality of resonances with different resonant frequencies can be seen. In the graph of the filter characteristics, in the frequency range of about 900 to 1050 MHz, the transmission loss is minimized and has a nearly flat shape. Such flat filter characteristics indicate that the frequency filter subjected to the simulation can be suitably used as a band filter that passes an electrical signal having a frequency in the range of about 900 to 1050 MHz.

[0050] Next, in the configuration shown in FIG. 9, for a plurality of examples (= 1%, 4%, 9%, 16%, 25%) in which the electromechanical coupling coefficient k t 2 of each piezoelectric layer is different, the filter characteristics were obtained by simulation. The inductance L p of the first inductor 261 and the second inductor 262, and the thickness of the intermediate layer 28 are the same as those in the simulations of FIGS. 10 to 12. However, in this simulation, in order to eliminate the influence of multiple reflections derived from the substrate 17 and the like, the substrate 27 and the acoustic Bragg reflector 25 were not provided, and both the upper and lower acoustic reflectors were air (nothing was provided). The results of this simulation are shown in FIG. 13. Within the range of the value of the electromechanical coupling coefficient k t 2 used in this simulation, it can be seen that the higher the value, the smaller the transmission loss and the closer to a flat shape in the frequency range of about 600 to 1100 MHz, and it can be suitably used as a band filter.

[0051] Next, in the case of including the first inductor 261, the second inductor 262, and the intermediate layer 28, for a plurality of examples in which the number of piezoelectric layers included in the input portion and the output portion is different, similar to the examples shown in FIGS. 2 and 8, the filter characteristics were obtained by simulation. The inductance L pand the thickness of the intermediate layer 28 is the same as that in the two simulations shown in FIGS. 10 to 12 and FIG. 13. Also, as in the simulation of FIG. 13, both the upper and lower acoustic reflectors were made of air. The results of this simulation are shown in FIG. 14. The numerical values 1 to 5 described in FIG. 14 are the number of piezoelectric layers that the input part and the output part each have (the same number between the input part and the output part). Note that those with a layer number of 1 are those in which electrodes are provided above and below a single-layer piezoelectric layer for each of the input part and the output part, and are not included in the present invention. Those with a layer number of 2 to 5 are included in the present invention, and all have filter characteristics as a band filter. Within this range of the layer number, the bandwidth becomes narrower as the layer number increases.

[0052] Next, the results of manufacturing and evaluating the frequency filter 10 of the first embodiment using the polarization inversion laminated resonator of FIG. 1 and the frequency filter 20 of the second embodiment using the intermediate electrode laminated resonator of FIG. 2 are shown.

[0053] The frequency filter 10 of the first embodiment was manufactured by using the magnetron sputtering apparatus 30 shown in FIG. 3 to form each piezoelectric layer in a gas atmosphere with a pressure of 0.5 Pa in which nitrogen and argon were mixed at a partial pressure ratio of 1:4, with the material of the acoustic Bragg reflector 15 being the ScAl alloy for the substrate S and the target T. The power during film formation was 200 W, the distance between the center of the target T and the lower end of the substrate holder 32 was 13 mm, the size of the target was 3 inches (7.62 cm) in diameter, and the film formation pressure was 10 -4 Pa. As described above, every time a single piezoelectric layer was formed, the substrate S and the formed piezoelectric layer were rotated 180° around an axis perpendicular to the substrate S.

[0054] Regarding the fabricated frequency filter 10, X-rays were incident from a direction inclined by an inclination angle χ from a direction perpendicular to the piezoelectric layer on the combined input-side polarization-inverted laminated piezoelectric body 110 and output-side polarization-inverted laminated piezoelectric body 130, and X-ray diffraction measurement was performed while changing the inclination angle χ. The results are shown in FIG. 15. In this figure, the positive and negative of the inclination angle χ mean that X-rays were incident from directions 180° different from each other in a direction parallel to the piezoelectric layer. From this measurement result, it is shown that the four piezoelectric layers of the input-side polarization-inverted laminated piezoelectric body 110 and the output-side polarization-inverted laminated piezoelectric body 130 are inclined at an inclination angle centered on +45.5° or -49.6° of the c-axis. Since the direction of the c-axis corresponds to the direction of the polarization P, this result suggests that the polarization P in the desired direction is formed in each piezoelectric layer.

[0055] FIG. 16 shows a micrograph of a longitudinal section taken of the fabricated frequency filter 10. From this micrograph, it can be seen that the crystals grow in a zigzag pattern corresponding to the direction of the inclination of the c-axis in each piezoelectric layer.

[0056] FIG. 17 shows the results of measuring the filter characteristics of the fabricated frequency filter 10. Here, two measurements were made: one without the input-side inductor 161 and the output-side inductor 162 (``L p none'' in FIG. 17) and the other with the input-side inductor 161 and the output-side inductor 162 of 12.7 nH (``L p present''). All of these measurement results show that this frequency filter 10 operates as a band filter with a passband width of approximately 200 MHz centered around approximately 600 MHz. The case of ``L p present'' is preferable because the pass loss in the passband is smaller than that of ``L p none''.

[0057] For the fabrication of the frequency filter 20 of the second embodiment, the magnetron sputtering apparatus 30 shown in FIG. 3 was used after changing the orientation of the substrate holder 32 so that the surface of the substrate S was substantially parallel to the surface of the target T. The acoustic Bragg reflector 25 was fabricated by forming each piezoelectric layer in a gas atmosphere with a pressure of 0.5 Pa in which nitrogen and argon were mixed at a partial pressure ratio of 1:4, using the ScAl alloy as the material of the substrate S and the target T. The power during film formation was 200 W, the distance between the surface of the target T and the surface of the substrate S was 20 mm, the size of the target was 3 inches (7.62 cm) in diameter, and the film formation pressure was 10 -4 Pa.

[0058] FIG. 18 shows a micrograph of a longitudinal section of the fabricated frequency filter 20. From this micrograph, it can be seen that crystals grow in a direction perpendicular to the layer in each piezoelectric layer. This corresponds to the c-axis and the polarization P being oriented in a direction perpendicular to the layer in each piezoelectric layer.

[0059] FIG. 19 shows the results of measuring the filter characteristics of the fabricated frequency filter 20. In this measurement, the input-side inductor 261 and the output-side inductor 262 were not used. This measurement result shows that this frequency filter 20 operates as a band filter with a passband width of approximately 4000 MHz centered around approximately 900 MHz.

[0060] As described above, the embodiments of the frequency filter according to the present invention have been described. However, the frequency filter according to the present invention is not limited to the above embodiments, and various modifications are possible.

[0061] For example, in the above embodiment, the number of piezoelectric layers provided in the input section and the number of piezoelectric layers provided in the output section are the same, but they may be different from each other.

[0062] In the above embodiment, when the input section includes a polarization-inverted laminated piezoelectric body, an output section including a polarization-inverted laminated piezoelectric body is used. When the input section includes a polarization-aligned laminated piezoelectric body, an output section including a polarization-aligned laminated piezoelectric body is used. However, one of the input section and the output section may include a polarization-inverted laminated piezoelectric body, and the other may include a polarization-aligned laminated piezoelectric body.

[0063] (4) Embodiments of intermediate electrode laminated resonators Next, the intermediate electrode laminated resonators used as the input sections 21, 21A and the output sections 23, 23A in the frequency filters 20, 20A of the second embodiment will be described.

[0064] The intermediate electrode laminated resonator 50 shown in FIG. 20 has the same configuration as the input section 21 and the output section 23 in the frequency filter 20 of the second embodiment. That is, the intermediate electrode laminated resonator 50 includes a polarization-aligned laminated piezoelectric body 510 formed by laminating a first piezoelectric layer 511 and a second piezoelectric layer 512 that are both perpendicular to the layers and have the same-direction polarization P and have substantially equal fundamental resonance frequencies, and first partial electrodes 5211, a second electrode (second partial electrode) 522, and first partial electrodes 5212 that are alternately arranged above, below, and between the layers of the polarization-aligned laminated piezoelectric body 510. The first partial electrodes 5211 and 5212 are electrically connected to form a first electrode 521.

[0065] The intermediate electrode laminated resonator 50A shown in FIG. 21 has the same configuration as the input section 21A and the output section 23A in the frequency filter 20A of the second embodiment. That is, the intermediate electrode laminated resonator 50A includes a polarization-aligned laminated piezoelectric body formed by laminating four piezoelectric layers 511A to 514A that are all perpendicular to the layers and have the same-direction polarization P and have substantially equal fundamental resonance frequencies, and three first partial electrodes 5211A to 5213A and two second partial electrodes 5221A and 5222A that are alternately provided above, below, and between the layers of the polarization-aligned laminated piezoelectric body. The three first partial electrodes 5211A to 5213A are electrically connected to form a first electrode 521A. The two second partial electrodes 5221A and 5222A are electrically connected to form a second electrode 522A.

[0066] These intermediate electrode laminated resonators 50 and 50A are easy to fabricate in that each piezoelectric layer has polarization in the same direction.

[0067] These intermediate electrode laminated resonators 50 and 50A can be used as a frequency filter (band filter) 60 that allows a signal current within a frequency band having a certain width to pass through by connecting a plurality of them in a "ladder type" as shown in FIG. 22 by a known method related to resonators.

Explanation of Reference Numerals

[0068] 10, 10A, 20, 20A, 60... Frequency filter 11, 11A, 21, 21A... Input section 110, 110A... Input-side polarization-reversed laminated piezoelectric body 111, 211... First input-side piezoelectric layer 112, 212... Second input-side piezoelectric layer 111A~114A, 131A~134A, 211A~214A, 231A~234A... Piezoelectric layer 121, 221, 221A... First input-side electrode 122, 222, 222A... Second input-side electrode 13, 13A, 23, 23A... Output section 130, 130A... Output-side polarization-reversed laminated piezoelectric body 131, 231... First output-side piezoelectric layer 132, 232... Second output-side piezoelectric layer 141, 241, 241A... First output-side electrode 142, 242, 242A... Second output-side electrode 15, 152, 25,... Acoustic Bragg reflector 161, 162... Input-side inductor 162, 262... Output-side inductor 17, 27... Substrate 210, 210A... Input-side polarization-aligned laminated piezoelectric body 2211, 2212, 2211A~2213A... First input-side partial electrode 2221A, 2222A... Second input-side partial electrode 230, 230A... Output-side polarization-aligned laminated piezoelectric body 2411, 2412, 2411A to 2413A... First output side partial electrodes 2421A, 2422A... Second output side partial electrodes 30... Magnetron sputtering apparatus 31... Cathode electrode 32... Substrate holder 50, 50A... Intermediate electrode laminated resonator 510... Polarization - consistent laminated piezoelectric body 511... First piezoelectric layer 512... Second piezoelectric layer 511A to 514A... Piezoelectric layers 521, 521A... First electrode 5211, 5212, 5211A to 5213A... First partial electrodes 522... Second electrode (second partial electrode) 522A... Second electrode 5221A to 5223A... Second partial electrodes P... Polarization S... Substrate SP... Sputtering particles T... Target

Claims

1. a) An input section comprising a first resonator which is a polarization-inverted stacked resonator in which a plurality of piezoelectric layers each made of a piezoelectric material and having substantially equal fundamental wave resonance frequencies, which are values obtained by dividing the speed of sound by twice the thickness, are stacked such that the directions of the polarization components in a direction parallel or perpendicular to the piezoelectric layers are alternately reversed, and first and second electrodes are arranged so as to sandwich the upper and lower portions of the polarization-inverted stacked piezoelectric body, or an intermediate electrode stacked resonator in which a plurality of piezoelectric layers each made of a piezoelectric material and having substantially equal fundamental wave resonance frequencies are stacked such that the directions of polarization are aligned, and first partial electrodes and second partial electrodes are alternately arranged above and below the polarization-aligned stacked piezoelectric body and between the respective layers of the piezoelectric layers; b) An output section comprising a second resonator which is a polarization-inverted stacked resonator or an intermediate electrode stacked resonator, wherein the plurality of piezoelectric layers of the second resonator are stacked in the same direction as the plurality of piezoelectric layers of the first resonator and have substantially equal fundamental wave resonance frequencies; c) A pair of acoustic reflectors provided so as to sandwich the input section and the output section in the stacking direction. A frequency filter characterized by comprising the above.

2. The frequency filter according to claim 1, wherein one or both of the pair of acoustic reflectors are acoustic Bragg reflectors.

3. The frequency filter according to claim 1 or 2, further characterized in that an inductor is connected in parallel to the input section and / or in parallel to the output section.

4. An intermediate electrode stacked resonator characterized by comprising a polarization-aligned stacked piezoelectric body in which a plurality of piezoelectric layers each made of a piezoelectric material and having substantially equal fundamental wave resonance frequencies are stacked such that the directions of the polarization components in a direction parallel or perpendicular to the piezoelectric layers are aligned; and first partial electrodes and second partial electrodes alternately arranged above and below the polarization-aligned stacked piezoelectric body and between the respective layers thereof. An intermediate electrode stacked resonator characterized by comprising the above.

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