WO2017073425A1 - 弾性波共振子、弾性波フィルタ、分波器、通信装置および弾性波共振子の設計方法 - Google Patents
弾性波共振子、弾性波フィルタ、分波器、通信装置および弾性波共振子の設計方法 Download PDFInfo
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- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
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- H03H9/02543—Characteristics of substrate, e.g. cutting angles
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Definitions
- the present disclosure relates to an elastic wave resonator using an elastic wave, an elastic wave filter including the elastic wave resonator, a duplexer including the elastic wave filter, a communication device including the duplexer, and a design of the elastic wave resonator. Regarding the method.
- a surface acoustic wave resonator (SAW resonator) having a piezoelectric substrate and an IDT (Interdigital Transducer) electrode provided on an upper surface of the piezoelectric substrate and exciting a surface acoustic wave (SAW) is known.
- SAW resonator having a piezoelectric substrate and an IDT (Interdigital Transducer) electrode provided on an upper surface of the piezoelectric substrate and exciting a surface acoustic wave (SAW) is known.
- IDT Interdigital Transducer
- Patent Document 1 a capacitive element is connected in parallel to the IDT electrode. By providing such a capacitive element, it is known that the anti-resonance frequency of the SAW can be moved to the low frequency side, and the frequency difference from the resonance frequency to the anti-resonance frequency can be narrowed.
- the SAW resonator is miniaturized by using a reflector also as a capacitive element.
- Patent Document 2 a piezoelectric substrate is not used alone as a SAW resonator, but a bonded substrate obtained by bonding a piezoelectric substrate and a support substrate having a smaller thermal expansion coefficient than the piezoelectric substrate is used as a SAW resonator. ing. By using such a bonded substrate, for example, a temperature change in the electrical characteristics of the SAW resonator is compensated. Patent Document 2 discloses that when a bonded substrate is used, spurious is generated and the cause of the spurious is a bulk wave. Patent Document 2 proposes an electrode structure for canceling out bulk waves.
- the elastic wave resonator includes a piezoelectric substrate and an IDT electrode positioned on the upper surface of the piezoelectric substrate. At least one of the resonance frequency and the antiresonance frequency due to the bulk wave is located between 1 and 4 between the resonance frequency due to the surface acoustic wave and the antiresonance frequency.
- An acoustic wave filter includes a piezoelectric substrate, a support substrate bonded to a lower surface of the piezoelectric substrate, and a plurality of IDT electrodes positioned on the upper surface of the piezoelectric substrate. ing.
- the plurality of IDT electrodes include a first IDT electrode and a second IDT electrode having a thickness different from that of the first IDT electrode.
- a duplexer includes an antenna terminal, a transmission filter that filters a transmission signal and outputs the filtered signal to the antenna terminal, and a reception filter that filters a reception signal from the antenna terminal. Yes. At least one of the transmission filter and the reception filter includes the elastic wave filter.
- a communication apparatus includes an antenna, the duplexer in which the antenna terminal is connected to the antenna, and an IC connected to the transmission filter and the reception filter. ing.
- the resonance frequency and the antiresonance frequency by the surface acoustic wave are the resonance frequency and the antiresonance by the bulk wave.
- the thickness of the electrode finger located on both sides of at least one of the resonance frequencies is specified, and the electrode finger whose one frequency matches a predetermined target frequency with the thickness of the electrode finger specified in the electrode film thickness setting step Specify the pitch.
- FIG. 2 is a cross-sectional view taken along line II-II in FIG. 3A and 3B are diagrams for explaining the principle of the acoustic wave resonator shown in FIG. It is a figure which shows the influence which the thickness of an IDT electrode has on a resonance characteristic.
- FIG. 5A is a diagram showing the influence of the thickness of the piezoelectric substrate on the frequency of the bulk wave spurious.
- FIG. 5B is a diagram showing the influence of the thickness of the piezoelectric substrate on the frequency interval of bulk wave spurious. It is a figure for demonstrating the bulk wave spurious utilized in the elastic wave resonator of FIG.
- FIG. 3 is a flowchart illustrating an example of a procedure of a method for designing the acoustic wave resonator of FIG. 1.
- FIGS. 9A to 9C are schematic views showing a ladder type filter as an example of use of the acoustic wave resonator shown in FIG.
- FIG. 10A and FIG. 10B are diagrams showing the characteristics of an example of a ladder type filter.
- FIG. 10A and FIG. 10B are diagrams showing the characteristics of an example of a ladder type filter.
- It is a schematic diagram which shows the duplexer as an example of utilization of a ladder type filter.
- FIG. 13A to FIG. 13C are schematic diagrams for illustrating various modifications. It is a schematic diagram for showing a modification.
- the elastic wave resonator may have either direction upward or downward, but hereinafter, for the sake of convenience, an orthogonal coordinate system including a D1 axis, a D2 axis, and a D3 axis is defined, and the D3 axis Terms such as the upper surface and the lower surface may be used with the positive side of the direction as the upper side.
- FIG. 1 is a plan view illustrating a configuration of an acoustic wave resonator 1 according to an embodiment of the present disclosure.
- FIG. 2 is a cross-sectional view taken along the line II-II in FIG. However, in FIG. 2, the number of electrode fingers, which will be described later, is depicted fewer than in FIG.
- the elastic wave resonator 1 is a resonator based on a new principle that uses SAW and bulk waves as elastic waves.
- the configuration of the acoustic wave resonator 1 may be basically the same as the configuration of the SAW resonator except for various dimensions. Specifically, it is as follows.
- the acoustic wave resonator 1 includes, for example, a bonded substrate 3 and an electrode unit 5 configured on the upper surface of the bonded substrate 3.
- the elastic wave resonator 1, Other, made of SiO 2 or the like, may have a protective layer for covering the electrode portion 5.
- the bonded substrate 3 includes, for example, a piezoelectric substrate 7 and a support substrate 9 (FIG. 2) bonded to the lower surface of the piezoelectric substrate 7.
- FIG. 1 shows an example of the X axis, the Y axis, and the Z axis of the piezoelectric substrate 7.
- the piezoelectric substrate 7 is composed of, for example, a single crystal substrate having piezoelectricity.
- the single crystal substrate is made of, for example, lithium tantalate (LiTaO 3 ), lithium niobate (LiNbO 3 ), or quartz (SiO 2 ).
- the cut angle may be appropriate.
- lithium tantalate it is a 42 ° ⁇ 10 ° Y plate or a 0 ° ⁇ 10 ° X plate.
- lithium niobate it is a 128 ° ⁇ 10 ° Y plate or a 64 ° ⁇ 10 ° Y plate.
- the piezoelectric substrate 7 is a Y plate of 38 ° or more and 48 ° or less made of lithium tantalate
- the simulation results and the like described later are for a Y plate of 38 ° to 48 ° made of lithium tantalate.
- the main surfaces (upper surface and lower surface) are orthogonal to the Y ′ axis (not shown) rotated around the X axis from the Y axis to the Z axis at an angle of 38 ° to 48 °. .
- the thickness t s (FIG. 2) of the piezoelectric substrate 7 is constant over the entire planar direction of the piezoelectric substrate 7.
- the acoustic wave resonator 1 of this embodiment unlike the SAW resonator, also has a parameter defining the resonator properties the thickness t s.
- the support substrate 9 is made of, for example, a material having a smaller thermal expansion coefficient than the material of the piezoelectric substrate 7. Thereby, the temperature change of the electrical characteristics of the acoustic wave resonator 1 can be compensated.
- a material include a semiconductor such as silicon, a single crystal such as sapphire, and a ceramic such as an aluminum oxide sintered body.
- the support substrate 9 may be configured by laminating a plurality of layers made of different materials.
- the thickness of the support substrate 9 is, for example, constant throughout the planar direction of the support substrate 9, and the size thereof may be appropriately set according to the specifications required for the acoustic wave resonator 1.
- the support substrate 9 is made thicker than the piezoelectric substrate 7. In this case, for example, the effect of temperature compensation is increased, or the strength of the piezoelectric substrate 7 is reinforced.
- the thickness of the support substrate 9 is not less than 100 ⁇ m and not more than 300 ⁇ m.
- the planar shape and various dimensions of the support substrate 9 are, for example, equivalent to the piezoelectric substrate 7.
- the piezoelectric substrate 7 and the support substrate 9 are bonded to each other through an adhesive layer (not shown), for example.
- the material of the adhesive layer may be an organic material or an inorganic material.
- the organic material include a resin such as a thermosetting resin.
- the inorganic material include SiO 2 .
- the piezoelectric substrate 7 and the support substrate 9 may be bonded by so-called direct bonding, in which the bonding surface is bonded without a bonding layer after activation processing with plasma or the like.
- the configuration of the electrode unit 5 is, for example, the same configuration as the electrode unit for a so-called 1-port SAW resonator. That is, the electrode unit 5 includes an IDT electrode 11 and a pair of reflectors 13 located on both sides of the IDT electrode 11.
- the IDT electrode 11 is composed of a conductive pattern (conductive layer) formed on the upper surface of the piezoelectric substrate 7, and has a pair of comb-teeth electrodes 15 as shown in FIG.
- the pair of comb-shaped electrodes 15 are, for example, a bus bar 17 (FIG. 1) facing each other, a plurality of electrode fingers 19 extending from the bus bar 17 in the opposing direction of the bus bar 17, and the bus bar 17 between the plurality of electrode fingers 19. And a protruding dummy electrode 21.
- the pair of comb electrodes 15 are arranged so that the plurality of electrode fingers 19 mesh with each other (intersect).
- the bus bar 17 is, for example, formed in a long shape having a substantially constant width and extending linearly in the SAW propagation direction (D1-axis direction, X-axis direction).
- the bus bars 17 of the pair of comb electrodes 15 are opposed to each other in the direction (D2 axis direction) intersecting the SAW propagation direction.
- the plurality of electrode fingers 19 are, for example, formed in an elongated shape having a substantially constant width and extending linearly in a direction orthogonal to the SAW propagation direction (D2 axis direction), and the SAW propagation direction (D1 axis direction). Are arranged at substantially regular intervals.
- the plurality of electrode fingers 19 of the pair of comb-shaped electrodes 15 have a pitch p (for example, a distance between the centers of the electrode fingers 19) of half the SAW wavelength ⁇ at the frequency to be resonated. It is provided so as to be equivalent to the wavelength ( ⁇ / 2).
- the pitch p is not always such a size.
- the SAW wavelength ⁇ is, for example, not less than 1.5 ⁇ m and not more than 6 ⁇ m.
- the pitch p may be relatively small, or conversely, the pitch p may be relatively large. So-called thinning may be performed in which p is an integral multiple of the normal pitch p.
- p when the pitch is simply referred to as “p”, unless otherwise specified, a portion (such as a narrow pitch portion, a wide pitch portion, or a thinned portion) other than the above-described specific portion (a plurality of electrode fingers 19) is excluded. Most) pitch p or an average value thereof.
- the term “electrode finger 19” refers to the electrode finger 19 other than the specific portion.
- the number, length (D2 axis direction) and width (D1 axis direction) of the plurality of electrode fingers 19 may be appropriately set according to the electrical characteristics required for the acoustic wave resonator 1 and the like. In the setting, as understood from the description to be described later, basically, the concept of the SAW resonator can be used. As an example, the number of electrode fingers 19 is 100 or more and 400 or less. The length and width of the electrode fingers 19 are, for example, the same among the plurality of electrode fingers 19.
- the dummy electrode 21 protrudes from the bus bar 17 at an intermediate position of the plurality of electrode fingers 19 in one comb-tooth electrode 15, and the tip thereof has a gap from the tip of the electrode finger 19 of the other comb-tooth electrode 15. Are facing each other.
- the dummy electrodes 21 have the same length and width between the plurality of dummy electrodes 21.
- the reflector 13 is constituted by, for example, a conductive pattern (conductive layer) formed on the upper surface of the piezoelectric substrate 7, and is formed in a lattice shape in plan view. That is, the reflector 13 includes a pair of bus bars (reference numerals omitted) facing each other in a direction crossing the SAW propagation direction, and a direction perpendicular to the propagation direction of the elastic wave (for example, SAW) (D2 axis direction) between these bus bars. And a plurality of strip electrodes (reference numerals omitted).
- the plurality of strip electrodes of the reflector 13 are arranged in the D1 axis direction so as to follow the arrangement of the plurality of electrode fingers 19.
- the number and width of the strip electrodes may be appropriately set according to electrical characteristics required for the acoustic wave resonator 1.
- the pitch of the plurality of strip electrodes is, for example, equal to the pitch of the plurality of electrode fingers 19.
- the distance between the strip electrode at the end of the reflector 13 and the electrode finger 19 at the end of the IDT electrode 11 is, for example, equal to the pitch p of the plurality of electrode fingers 19 (may be an integer multiple of the pitch p). ).
- the conductor layers constituting the IDT electrode 11 and the reflector 13 are made of, for example, metal.
- the metal include Al or an alloy containing Al as a main component (Al alloy).
- Al alloy is, for example, an Al—Cu alloy.
- the conductor layer may be composed of a plurality of metal layers.
- the thickness t e of the IDT electrode 11 and the reflector 13 is, for example, is constant throughout these. As described below, the acoustic wave resonator 1 of this embodiment, the thickness t e is used as a parameter for defining the resonator characteristics.
- the elastic wave resonator 1 having the above-described configuration, first, an action similar to that of the SAW resonator occurs. Specifically, when an electric signal is input to one comb electrode 15 and a voltage is applied to the piezoelectric substrate 7 by the plurality of electrode fingers 19, it propagates along the upper surface in the vicinity of the upper surface of the piezoelectric substrate 7. SAW is induced. The SAW is reflected by the plurality of electrode fingers 19 and the plurality of strip electrodes of the reflector 13. As a result, a SAW standing wave having a pitch p of the electrode fingers 19 of approximately a half wavelength ( ⁇ / 2) is formed. The standing wave generates a charge (an electric signal having the same frequency as that of the standing wave) on the upper surface of the piezoelectric substrate 7, and the electric signal is taken out by the plurality of electrode fingers 19 of the other comb-tooth electrode 15.
- Patent Document 2 discloses that when a piezoelectric substrate is thin like the piezoelectric substrate 7 of the bonded substrate 3, bulk waves cause spurious. In this embodiment, this bulk wave spurious is used to narrow the frequency difference ⁇ f between the resonance frequency and the anti-resonance frequency.
- FIG. 3A and FIG. 3B are diagrams for explaining the principle of the acoustic wave resonator 1.
- the horizontal axis indicates the frequency f (Hz), and the vertical axis indicates the absolute value
- the same reference numerals may be used for the resonance point and the resonance frequency for convenience. Similarly, the same sign may be used for the antiresonance point and the antiresonance frequency.
- a dotted line L0 indicates a resonance characteristic in a normal SAW resonator that is different from the elastic wave resonator 1 of the present embodiment.
- a SAW resonance point f sr where the impedance takes a minimum value
- a SAW anti-resonance point f sa where the impedance takes a maximum value
- the SAW anti-resonance frequency f sa is higher than the SAW resonance frequency f sr .
- the SAW resonator a case where there is no bulk wave spurious between the SAW resonance point f sr and the SAW anti-resonance point f sa is described as an example.
- a solid line L1 indicates the resonance characteristics in the acoustic wave resonator 1 of the present embodiment.
- the bulk wave spurious SP0 appears due to the thin piezoelectric substrate 7.
- the bulk wave spurious SP0 for example, impedance and bulk wave resonance point f br taking a minimum value, the impedance appears as a bulk wave antiresonance point f ba which takes a maximum value.
- the bulk wave spurious SP0 (bulk wave resonance frequency f br and bulk wave antiresonance frequency f ba) is It is located between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa .
- a combination (frequency difference ⁇ f 2 ) with the point f sa is used as a combination of a normal resonance point and an anti-resonance point.
- bulk wave spurious may not be treated as spurious.
- a bulk wave using a resonance point or an anti-resonance point may be referred to as a bulk wave spurious.
- Electrode portion 5 assumes a plurality of elastic wave resonators 1 having different each other thickness t e of (the electrode fingers 19), was determined by simulation calculation resonant characteristics.
- Piezoelectric substrate Materials: lithium tantalate single crystal cut angle: 42 ° Y plate thickness t s: 7.2 [mu] m
- Support substrate Silicon IDT electrode: Material: Al—Cu alloy Thickness t e : Different from 121 to 181 nm by 10 nm.
- Electrode finger pitch p 0.81207 ⁇ m
- Electrode finger duty ratio 0.5 The duty ratio is electrode finger width / p.
- FIG. 4 is a diagram showing the simulation calculation results as described above.
- the horizontal axis indicates the frequency f (MHz), and the vertical axis indicates the absolute value
- a line L51 ⁇ L57, correspondence relationship between the thickness t e of the electrodes is as follows. Incidentally, in parentheses indicates the value of the normalized thickness t e at a pitch p of the electrode fingers 19 normalized thickness t e / 2p.
- a region Rr surrounded by a dotted line indicates a region where resonance points due to SAW of lines L51 to L57 appear.
- a region Ra surrounded by a dotted line indicates a region where anti-resonance points due to SAW of the lines L51 to L57 appear.
- Regions R1 to R4 indicated by arrows indicate regions where bulk wave spurious appears.
- the resonance frequency and anti-resonance frequency (bulk wave spurious region R1 in the example of FIG. 4) by SAW by bulk waves Can be located. Furthermore, the frequency difference ⁇ f 1 between the resonant frequency of the SAW and the anti-resonant frequency of the bulk wave (FIG. 3), or the frequency difference ⁇ f 2 between the resonant frequency of the bulk wave and the anti-resonant frequency of the SAW ( 3) can be adjusted.
- the thickness of the piezoelectric substrate 7 is changed, the frequency of the bulk wave spurious changes. Therefore, the thickness of the piezoelectric substrate 7, without thickening or thinning the thickness t e of the electrode portion 5, the bulk wave spurious is located between the resonant frequency and the antiresonant frequency by SAW. That is, in the realization of the acoustic wave resonator 1 of the present embodiment, adjustment of the thickness t e is not essential.
- Bulk wave spurious appears not only in one frequency region but also in a plurality of frequency regions R1 to R4.
- the bulk wave spurious positioned between the resonance frequency and the anti-resonance frequency by the SAW may be a bulk wave spurious in any region.
- the thickness t e of the electrode portion 5 as described above not only qualitative influence on the resonance characteristics are also shown an example of a quantitative impact.
- the anti-resonance frequency f sa region Ra
- the anti-resonance frequency f b2a due to the bulk wave in the region R2
- the frequency difference (f b2a ⁇ f sa ) A list is shown.
- the reason why the bulk wave spurious in the region R2 is used instead of the bulk wave spurious in the region R1 is that, as described above, no bulk wave spurious occurs in the region R1 for the lines L51 and L52.
- the thickness t e a practical range It was done.
- a line L51 that has a small bulk wave spurious R1 and does not appear to be located between the resonance frequency and the anti-resonance frequency of the SAW can be regarded as a resonance characteristic of the conventional SAW resonator.
- the difference Delta] f s of the frequency between the SAW resonant frequency and SAW antiresonance frequency is about 100 MHz.
- the frequency difference ⁇ f 1 between the bulk wave resonance frequency and the SAW anti-resonance frequency is about 30 MHz.
- the electrode part 5 of the acoustic wave resonator 1 may be made thicker than the electrode part 5 of a normal SAW resonator.
- the thickness t e of the electrode portion 5 (the electrode fingers 19) is set so that the excitation efficiency of the SAW is highest.
- the normalized thickness t e / 2p normalized by the pitch p of the electrode fingers 19 and the thickness t e is about 0.070. Therefore, for example, if the normalized thickness t e / 2p is 0.075 or more, the bulk wave may be considered. If the normalized thickness t e / 2p exceeds 0.080, the normalized thickness t e / 2p ( 0.07) of a normal SAW resonator is about 15% thicker, and the error range is reduced. It is well over, and it can be said that bulk waves are considered almost certainly.
- the thickness t e of the electrode portion 5 is 0.06 or less and 0.09 or more normalization thickness, loss is increased, a thickness which is not employed in the conventional design. Thus, it can be said that the bulk wave is taken into consideration even when it is too thick and too thin.
- the thickness of the electrode finger 19 refers to the thickness near the center of the intersecting region of the electrode finger 19.
- Electrode finger pitch Although not particularly illustrated, when the pitch p of the electrode finger 19 is changed, the frequencies of both the SAW standing wave and the bulk wave standing wave (bulk wave spurious) change. That is, if the pitch p is reduced, the frequency of the standing wave of the SAW and the standing wave of the bulk wave is increased, and accordingly, the resonance frequency and the antiresonance frequency due to the SAW and the bulk wave are increased. This is obvious from the principle of excitation of standing waves by the IDT electrode 11.
- the pitch p is assumed as the pitch p.
- the pitch p is set similarly to the case where the SAW resonance frequency f sr or the SAW anti-resonance frequency f sa to be obtained in the acoustic wave resonator 1 is obtained in a normal SAW resonator. Then, to calculate the thickness t e of the electrode fingers 19 capable of obtaining a difference Delta] f 1 or Delta] f 2 of a desired frequency under that assumption.
- the electrode fingers 19 when the thickness t e of the electrode fingers 19 is thick, since the resonant frequency and the antiresonant frequency of the SAW is moved to the lower frequency side, the electrode fingers 19 so that these frequencies increases The pitch p is reduced. Conversely, when the thickness t e of the electrode fingers 19 is thin, since the resonant frequency and the antiresonant frequency of the SAW is moved to the high frequency side, the pitch p of the electrode fingers 19 so that these frequencies is low Widened.
- the piezoelectric substrate It is easy to use a bulk wave spurious having a relatively low frequency while adopting materials that are actually used or easy to use as the material 7 and the cut angle. Accordingly, it is considered that the pitch p of the electrode fingers 19 is often narrower in the acoustic wave resonator 1 than the pitch p of a normal SAW resonator.
- the pitch p may be referred to less than a half wavelength lambda 0/2, it is assumed that except where such conditions are caused by manufacturing errors.
- the manufacturing error of the pitch p is, for example, 50 nm.
- the difference Delta] f 1 or Delta] f 2 of a desired frequency is obtained.
- adjustment of only the pitch p of the electrode fingers 19 is sufficient.
- the anti-resonance frequency or resonance frequency due to the bulk wave substantially matches the bulk wave anti-resonance frequency f ba or the bulk wave resonance frequency f br that is being obtained. It is also possible. In this case it would be an adjustment of the thickness t e only of the electrode fingers 19. Of course, both the adjustment of the thickness t e and the pitch p can occur even if not needed.
- the modes in the vibration direction are, for example, a mode that vibrates in the D3 axis direction, a mode that vibrates in the D2 axis direction, and a mode that vibrates in the D1 axis direction.
- Each mode in each vibration direction has a plurality of order modes. This order mode is defined, for example, by the number of nodes and antinodes in the depth direction (D3 axis direction).
- the acoustic wave resonator 1 of the plurality of SAW resonators (present embodiment having different thickness t s of the piezoelectric substrate 7 together, which does not have any adjustment of the thickness t e and the pitch p of the electrode fingers 19 )
- the influence of the thickness of the piezoelectric substrate 7 on the frequency of the bulk wave in each mode was examined. Specifically, the frequency of the bulk wave in each mode generated in the piezoelectric substrate 7 having various thicknesses was calculated by simulation calculation.
- FIG. 5 (a) is a diagram showing the simulation calculation results as described above.
- the horizontal axis (t s ) indicates the thickness of the piezoelectric substrate 7.
- Vertical axis (f) shows a bulk wave having a frequency (appearing as an elastic wave resonator 1, the bulk wave resonance frequency f br).
- a plurality of lines L11 to L17 indicate frequencies of a plurality of types of bulk waves in which at least one of the vibration direction mode and the order mode is different from each other.
- the plots of the lines L15, L16, and L17 are made halfway, but in reality, as with the lines L11 to L14, a line in which the frequency decreases as the thickness increases continues. Further, although not shown, there are an infinite number of lines having the same tendency as L11 to L17 in the line L17 and subsequent lines (line L18, line L19). Further, in a normal bonded substrate, the thickness of the piezoelectric substrate 7 is often recommended to be 20 ⁇ m. That is, the thickness of a normal bonded substrate is even thicker than the thickness range shown in FIG.
- the frequency of the bulk wave of any mode increases as the thickness of the piezoelectric substrate 7 is reduced.
- the line L11 and the line L12 indicate the frequencies of the bulk waves having the same vibration direction mode and different order modes. As indicated by the arrows, the frequency interval between the two bulk waves increases as the thickness of the piezoelectric substrate 7 is reduced. The same applies to other bulk waves (for example, lines L13 and L14) having the same vibration direction mode and different order modes.
- FIG. 5B is a diagram showing the relationship between the thickness of the piezoelectric substrate 7 and the frequency interval of bulk waves having different order modes in the same vibration direction mode as described above. This figure is obtained from the simulation calculation result.
- the horizontal axis Df indicates the frequency interval.
- the vertical axis t s / 2p indicates the normalized thickness of the piezoelectric substrate 7. Normalized thickness t s / 2p is divided by the 2 times the pitch p of the electrode fingers 19 and the thickness t s of the piezoelectric substrate 7 (the same basically wavelength of SAW lambda in this case), in dimensionless quantity Yes (no unit).
- each plot shows the frequency interval of the bulk wave obtained by simulation calculation, and the line shows an approximate curve.
- the frequency interval of the bulk wave when the normalized thickness of the piezoelectric substrate 7 is reduced increases rapidly as the normalized thickness of the piezoelectric substrate 7 is reduced. For example, when the normalized thickness t s / 2p is 5 or more, the frequency interval does not change much. On the other hand, when the normalized thickness t s / 2p is 3 or less, the frequency interval increases rapidly. When the normalized thickness t s / 2p is 3 or less, the slope of the curve approaches a constant value.
- the thickness t s (normalized thickness t s / 2p) of the piezoelectric substrate 7 is made relatively thin, the frequency interval between the bulk wave spurious becomes wide. Therefore, the SAW resonance frequency f sr and the SAW anti-resonance frequency f In the frequency region between and around sa , only the frequency of the bulk wave spurious that is to be used for narrowing ⁇ f is positioned, and other bulk wave spurs that are truly spurious are moved away from the frequency region. it can.
- the bulk wave spurious (line L11) having the lowest frequency among the infinite number of bulk wave spurs is likely to approach the resonance frequency and anti-resonance frequency to be realized in the elastic wave resonator 1. This makes it easy to select the bulk wave spurious signal having the lowest frequency as the bulk wave spurious signal used to narrow ⁇ f. The effect of this will be described later.
- FIG. 6 is a diagram showing the relationship between the thickness of the piezoelectric substrate 7 and the frequency of the bulk wave as shown in FIG. 5 (a). In the range where the thickness of the piezoelectric substrate 7 is relatively thin, The frequency of the bulk wave is shown.
- FIG. 6 is obtained based on the simulation calculation.
- the simulation conditions are shown below.
- Piezoelectric substrate Material: Lithium tantalate single crystal Cut angle: 42 ° Y plate
- Support substrate Silicon IDT electrode: Material: Al—Cu alloy Thickness t e : 121 nm
- Electrode finger pitch p 0.80413 ⁇ m
- Electrode finger duty ratio 0.5 The duty ratio is electrode finger width / p.
- the horizontal axis represents the normalized thickness t s / 2p
- the vertical axis represents the normalized frequency f ⁇ 2p.
- the normalized frequency f ⁇ 2p is a product of the frequency f and twice the pitch p of the electrode fingers 19 (here, basically the same as the wavelength ⁇ of the SAW).
- a line L21 indicates a bulk wave having the lowest frequency in the illustrated range (a range where t s / 2p is 1 or more and 3 or less and its surroundings). This bulk wave will be referred to as a first order mode bulk wave in the first vibration direction mode. Note that the vibration direction of the first vibration direction mode is a bulk wave that vibrates substantially in the D3 axis direction in lithium tantalate.
- the line L21 is generated on the lowest frequency side of the bulk waves that can be generated.
- Line L22 indicates a bulk wave having the same mode of vibration direction as the bulk wave of line L21, the order (frequency from another viewpoint) being the second lowest after the bulk wave of line L21.
- This bulk wave is referred to as a second order mode bulk wave in the first vibration direction mode.
- the line L23 is a bulk wave having the lowest frequency in the illustrated range among the bulk waves having different vibration direction modes from the bulk waves of the lines L21 and L22. This bulk wave will be referred to as the first order mode bulk wave in the second vibration direction mode.
- the line L23 has a higher frequency than the line L21, but intersects the line L22, and has a frequency lower than that of the line L22 in a range where the normalized thickness t s / 2p is thinner than the intersection.
- the vibration direction of the second vibration direction mode is a bulk wave that vibrates substantially in the D2 axis direction in lithium tantalate.
- the lines L21 to L23 correspond to the lines L11 to L13 in FIG.
- a bulk that draws a line (lower frequency) located below the line L21 in the illustrated range There are no waves. Further, in the illustrated range, there is no bulk wave that draws a line located between the line L21 and the line L22 or the line L23. In other words, the other bulk waves are located above the lines L22 and L23 (the frequency is high) in the illustrated range.
- the SAW resonance frequency f sr is located on the lower frequency side than the line L21 and the SAW anti-resonance frequency f sa is within the region surrounded by the lines L21 to L23, the frequency difference ⁇ f is reduced. L21 bulk wave spurious can be used.
- the thickness t s (normalized thickness t s / 2p) of the piezoelectric substrate 7 may be set so as to have such a frequency relationship.
- the product has only one value as the normalized thickness t s / 2p, so that the frequency of the lowest frequency bulk wave spurious and then The SAW antiresonance frequency fsa falls within the low-frequency bulk wave frequency.
- the next lowest bulk wave frequency is that of line L22 or line L23 (both at the intersection).
- the region on the lower frequency side than the line L21 or the region surrounded by the lines L21 to L23 is a region where other bulk waves are not generated as described above, but this region is a region surrounded by any combination of other lines. It is a unique area that is extremely wide even compared. This is because the thickness of the piezoelectric substrate 7 in addition to the advantage in the vertical axis direction of the graph that no bulk wave spurious is generated in a certain frequency range (for example, a range around the SAW resonance frequency f sr or the SAW anti-resonance frequency f sa ). Even if there is some variation, it is possible to realize the advantage in the horizontal direction of the graph that no bulk wave spurious is generated.
- Normalized thickness t s / 2p may be a 1 to 3.
- the bulk wave spurious (line L21) having the lowest frequency can be used as described above.
- t s / 2p When t s / 2p is less than 1, for example, the loss of SAW increases.
- the frequency of the SAW is easily affected by the state of the lower surface of the piezoelectric substrate 7, and the variation in frequency characteristics among the plurality of elastic wave resonators 1 increases. For example, it becomes difficult to ensure the strength of the piezoelectric substrate 7. In other words, when t s / 2p is 1 or more, such inconvenience is eliminated or reduced.
- the frequency interval between the bulk waves having different modes is relatively wide. Also, for example, when considering the actual SAW propagation speed, the lowest bulk wave spurious frequency is easily located between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa .
- the normalized thickness t s / 2p of 1 or more and 3 or less is merely an example of the range.
- the normalized thickness t s / 2p is less than 1 or more than 3, and the bulk frequency spurious with the lowest frequency is used.
- the frequency may be located between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa .
- Twice (2p) the pitch p in the acoustic wave resonator 1 is, for example, 1.5 ⁇ m or more and 6 ⁇ m or less. Therefore, t s is, for example, 1.5 ⁇ m or more 18 ⁇ m or less.
- the purpose of such other effects associated with thinning of the piezoelectric substrate 7 e.g. increase in the temperature compensation effect of the supporting substrate 9), and thinner than the above range, t s is the less 1.5 ⁇ m than 10 ⁇ m May be.
- Figure 7 is a view corresponding to FIG. 6 in the case of increasing the thickness t e of the IDT electrode 11 than the FIG.
- FIG. 7 is obtained based on the simulation calculation as in FIG. The simulation conditions different from FIG. 6 are shown below.
- IDT electrode Thickness t e : 201 nm
- Electrode finger pitch p 0.75768 ⁇ m
- Lines L31 to L33 correspond to lines L21 to L23. That is, the lines L31 to L33 correspond to the first order mode of the first vibration direction mode, the second order mode of the first vibration direction mode, and the first order mode of the second vibration direction mode. Yes.
- the horizontal axis in the figure is the same as in FIG. That is, the thickness and pitch of the IDT electrode 11 are values before adjustment.
- the line L31 has shown the simulation result when the line L32 and the line L33 set the above-mentioned thickness in the case of the same thickness as FIG.
- the result of FIG. 7 shows that the above-mentioned singular range surrounded by the lines L21 to L23 in FIG. 5 can be shifted to a desired position by adjusting the thickness and pitch of the IDT electrode 11. Yes. That is, the singular region can be shifted to the high frequency side or to the low frequency side. Furthermore, the thickness range of the piezoelectric substrate 7 that can utilize the bulk wave spurious signal having the lowest frequency can be adjusted so as to be in a realizable region, or the thickness range can be expanded.
- FIG. 8 is a flowchart illustrating an example of a design procedure of the pitch p or the like of a thickness t e and the electrode fingers 19 of the electrode portion 5.
- the acoustic wave resonator 1 includes a mode using the SAW resonance frequency f sr and the bulk wave antiresonance frequency f ba (frequency difference ⁇ f 1 ), and a bulk wave.
- the resonance frequency f br and the SAW anti-resonance frequency f sa are used. The former will be described as an example.
- step ST1 various setting conditions or design values of the acoustic wave resonator 1 are initialized.
- the material, the cut angle and the thickness t s of the piezoelectric substrate 7 and the material, the thickness t e , the intersection width, the pitch p, the duty ratio and the number of the electrode fingers 19 are appropriately selected.
- the value of the temporary The thickness t e and the pitch p is changed after step ST1.
- the SAW resonance frequency f sr or the SAW anti-resonance frequency f sa SAW resonance frequency f sr in the procedure of FIG. 8) to be obtained in the acoustic wave resonator 1 is obtained. This may be done in the same manner as in a normal SAW resonator.
- step ST2 resonance characteristics are calculated based on the design conditions or design values set in step ST1. Specifically, for example, simulation calculation is performed to calculate the SAW resonance frequency f sr , the bulk wave antiresonance frequency f ba, and the frequency difference ⁇ f 1 therebetween.
- step ST3 the difference Delta] f 1 frequency calculated in step ST2 is, whether to match to the difference Delta] f t of a target frequency is determined. Note that the determination of whether or not they match here includes determination of whether or not the difference between the two is within a predetermined allowable range. The same applies to steps ST6 and ST9 described later. If it is determined that they do not match, the process proceeds to step ST4. If it is determined that they match, the process skips steps ST4 and ST5 and proceeds to step ST6.
- step ST5 the same calculation as in step ST2 is performed. Then, the process returns to step ST3. Thus, until an affirmative determination is made in step ST3, the change of the design value of the thickness t e is performed.
- step ST6 it is determined whether or not the SAW resonance frequency f sr matches the target resonance frequency f tr . If it is determined that they do not match, the process proceeds to step ST7. If it is determined that they match, the process skips steps ST7 and ST8 and proceeds to step ST9.
- step ST7 the design value of the pitch p of the electrode finger 19 is changed so that the SAW resonance frequency f sr approaches the target resonance frequency f tr . That is, if f sr ⁇ f tr , the design value of the pitch p is narrowed so that the SAW resonance frequency f sr moves to the high frequency side. Conversely, if f sr > f tr , the design value of the pitch p is widened so that the SAW resonance frequency f sr moves to the low frequency side.
- the amount of change at this time may be set as appropriate, may be a fixed amount, or may be adjusted according to the magnitude of the difference between f sr and f tr .
- step ST8 the same calculation as in step ST2 is performed. Then, the process returns to step ST6. Thus, the design value of the pitch p is changed until an affirmative determination is made in step ST6.
- step ST9 it is determined whether or not the bulk wave antiresonance frequency fba matches the target antiresonance frequency fta .
- the pitch p slightly affects ⁇ f 1 , this determination is confirmed.
- step ST9 If it is determined in step ST9 that they do not match, the process returns to step ST3. Thereby, step ST3 and subsequent steps are repeated until both the frequency difference ⁇ f 1 and the SAW resonance frequency f sr (and thus the bulk wave anti-resonance frequency f ba ) match the target value. If it is determined that they match, the design procedure is completed.
- step ST6 the determination in step ST6 and the determination in step ST9 are reversible. That is, the step of matching the SAW resonance frequency f sr with the target value and the step of matching the bulk wave antiresonance frequency f ba with the target value may be regarded as the same step. Similarly, when using the frequency difference ⁇ f 2 , the step of matching the SAW anti-resonance frequency f sa with the target value and the step of matching the bulk wave resonance frequency f br with the target value are regarded as the same step. It's okay.
- FIG. 9A schematically shows an elastic wave filter 51 including the elastic wave resonator 1.
- the acoustic wave filter 51 is a so-called ladder-type resonator filter, and one or more (two in FIG. 9 (a)) series resonators 53A and 53B and one or more (in FIG. 9 (a)) connected to the ladder type. 3) parallel resonators 55A to 55C.
- these symbols A, B, or C may be omitted.
- Each of the series resonator 53 and the parallel resonator 55 is, for example, a one-port resonator including the IDT electrode 11 and the reflectors 13 on both sides thereof.
- the plurality of resonator IDT electrodes 11 and a pair of reflectors 13 (electrode portions 5) are provided on a common piezoelectric substrate 7, for example.
- the one or more series resonators 53 are connected in series between, for example, a pair of terminals 57 (wiring may be used instead of the terminals). That is, one of the pair of comb electrodes 15 is directly or indirectly connected to one of the pair of terminals 57, and the other of the pair of comb electrodes 15 is connected to the other of the pair of terminals 57 in series or indirectly. Has been.
- the one or more parallel resonators 55 are connected between, for example, a pair of terminals 57 (in front of or behind any one of the series resonators 53) and a reference potential portion. That is, one of the pair of comb electrodes 15 is connected between the pair of terminals 57, and the other of the pair of comb electrodes 15 is connected to the reference potential portion.
- the series resonator 53 and the parallel resonator 55 are configured such that the anti-resonance frequency of the parallel resonator 55 matches the resonance frequency of the series resonator 53.
- a filter is formed between the pair of terminals 57 with the antiresonance frequency of the parallel resonator 55 and the resonance frequency of the series resonator 53 as the center of the passband.
- At least one of the one or more series resonators 53 and the one or more parallel resonators 55 is configured by the elastic wave resonator 1 of the present embodiment.
- one of the parallel resonators 55 is constituted by the elastic wave resonator 1 of the present embodiment, and the series resonator 53 and other
- the parallel resonator 55 may be configured by a conventional SAW resonator 59.
- the elastic wave resonator 1 of the present embodiment is used for the parallel resonator 55 as described above, the difference ⁇ f in frequency can be narrowed, so that the rise of the attenuation amount on the low frequency side of the pass band can be made steep, and the elastic wave filter 51. The filter characteristics are improved.
- the elastic wave resonator 1 according to this embodiment may be used as the parallel resonator 55 having the highest resonance frequency.
- one of the series resonators 53 is configured by the elastic wave resonator 1 of the present embodiment, and the other The series resonator 53 and the parallel resonator 55 may be configured by a conventional SAW resonator 59.
- the elastic wave resonator 1 of the present embodiment is used for the series resonator 53 in this way, the frequency difference ⁇ f can be narrowed, so that the fall of the attenuation amount on the high frequency side of the passband can be sharpened, and the elastic wave filter The filter characteristic of 51 is improved.
- the elastic wave resonator 1 of this embodiment may be used for the series resonator 53 having the lowest resonance frequency.
- the conventional SAW resonator 59 is provided with an IDT electrode for exciting a surface acoustic wave, and unlike the surface acoustic wave resonator 1, between the resonance frequency and the anti-resonance frequency of the surface acoustic wave, Bulk wave spurious is not located, or three or more are located. That is, the resonance frequency and antiresonance frequency of the bulk wave include 0 or 5 or more between the resonance frequency and antiresonance frequency of the surface acoustic wave.
- the elastic wave resonator 1 of the present embodiment may be applied to both the series resonator 53 and the parallel resonator 55. In this case, the steepness of the change in attenuation can be improved on both the low frequency side and the high frequency side of the pass band.
- 9B and 9C only one of the plurality of parallel resonators 55 or only one of the plurality of series resonators 53 is the elastic wave resonator 1 of the present embodiment. However, two or more or all of them may be the elastic wave resonator 1 of the present embodiment.
- the elastic wave resonator 1 of the present embodiment is applied only to some of the one or more series resonators 53 and one or more parallel resonators 55.
- the SAW resonator 59 various bulk wave spurious frequencies are moved away from the pass band. Surrounding spurious can be reduced.
- the difference Delta] f s of the frequency of the SAW resonator 59 is, for example, by a piezoelectric substrate 7 is relatively thin (for example, a thickness of 1 [lambda ⁇ 3 [lambda]), surrounded by a line L21 ⁇ L23 in FIG. 6 It is located in the range.
- the elastic wave resonator 1 of the present embodiment is applied to all or a relatively large number of resonators, for example, the effect of the steepening as described above can be increased.
- the acoustic wave resonator 1 When applying the elastic wave resonator 1 of this embodiment only some of the plurality of parallel resonators 55 as shown in FIG. 9 (b), the acoustic wave resonator 1 has a thickness t e and the electrode of the electrode portion 5 The pitch p of the finger 19 is different from other parallel resonators 55 (SAW resonators 59).
- the elastic wave resonator 1 of this embodiment is applied to only a part of the plurality of series resonators 53 as shown in FIG. 9C, the elastic wave resonator 1 has the thickness t of the electrode portion 5.
- e and the pitch p of the electrode fingers 19 are different from those of the other series resonators 53 (SAW resonators 59).
- a SAW resonator 59 as a parallel resonator 55, the SAW resonator 59 as series resonators 53, the thickness t e of the electrode portion 5 is the same.
- the plurality of IDT electrodes 11 constituting the one or more series resonators 53 and the one or more parallel resonators 55 are different in thickness from the first IDT electrode 11 and the first IDT electrode 11. It is possible to determine whether or not the elastic wave resonator 1 of the present embodiment is provided depending on whether or not the IDT electrode 11 is included. As already described, when using a bulk wave spurious having a relatively low frequency while adopting a material that is actually used or easy to use as the material and cut angle of the piezoelectric substrate 7, in the elastic wave resonator 1, as compared to the SAW resonator 59, increasing the thickness t e of the electrode portion 5, there is a high probability that the pitch p of the electrode fingers 19 is narrowed.
- the IDT electrodes 11 having different thicknesses may be appropriately formed.
- the conductor layer for the thick (or thin) IDT electrode 11 may be formed and etched, and then the conductor layer for the thin (or thick) IDT electrode 11 may be formed and etched.
- the remaining thickness of the thick IDT electrode 11 and the entire thin IDT electrode 11 are formed.
- the conductor layer may be formed and etched.
- both may be formed in separate steps, or a part of the steps for forming the thick IDT electrode 11 may be formed. You may make it common with the step for.
- the filter characteristics were examined assuming specific conditions of the filter 51.
- the configuration of the filter 51 includes a series resonator 53A and three resonators, a parallel resonator 55A and a parallel resonator 55B.
- the elastic wave resonator 1 of the present embodiment is applied to the parallel resonator 55A.
- all the resonators are normal SAW resonators 59.
- ⁇ f 2 shown in FIG. 3 is used as the frequency difference ⁇ f, and models of the example and the comparative example are made for two types of cases (case 1 and case 2) having different sizes, and simulation calculation is performed. The results were compared.
- Case 1 (Comparative Example 1 and Example 1) are shown below.
- Piezoelectric substrate Materials: lithium tantalate single crystal cut angle: 42 ° Y plate thickness t s: 2 [mu] m
- Support substrate Silicon IDT electrode: Material: Al—Cu alloy Thickness t e : Comparative Example 1: 121 nm
- Electrode finger pitch p Comparative Example 1: 0.79115 ⁇ m
- Example 1 0.75325 ⁇ m
- Electrode finger duty ratio 0.5
- Case 2 (Example 2) was adjusted pitch p as further Delta] f 2 than Case 1 is small, the thickness t e like.
- 10 (a) and 10 (b) show the simulation results of the filter characteristics of case 1.
- FIG. 10 (a) and 10 (b) show the simulation results of the filter characteristics of case 1.
- FIG. 10B is an enlarged view of the low frequency side in FIG.
- the line L51 indicates the comparative example 1
- the line L52 indicates the example 1.
- a normal SAW resonator can be used even if the acoustic wave resonator 1 that uses the bulk wave spurious as a resonance point or anti-resonance point is used for the filter 51 instead of capturing the bulk wave spurious as a spurious. It was confirmed that the filter 51 functions as a filter in the same manner as the filter 51 including only 59. It was also confirmed that the effect of steepening the change in attenuation at the end of the passband (rising on the low frequency side in this embodiment) can be obtained by narrowing the frequency difference ⁇ f.
- f L is a frequency when the attenuation is 0.6 dB
- f A is a frequency when the attenuation is 10 dB
- f D is f L ⁇ f A. Therefore, high steepness as f D is small.
- Example 1 has higher steepness than Comparative Example 1. Specifically, both dB / f D are Example 1 / Comparative Example 1 ⁇ 100 ⁇ 2.29 / 1.16 ⁇ 100 ⁇ 198%, and the steepness is approximately doubled.
- the magnitude of ⁇ f 2 is adjusted in consideration of the attenuation characteristic on the lower frequency side as compared with the first embodiment.
- the attenuation characteristic on the low frequency side outside the pass band of the filter can be improved.
- FIG. 11 is a schematic diagram showing a duplexer 101 as an example of use of the acoustic wave resonator 1.
- the duplexer 101 filters, for example, the transmission signal from the transmission terminal 105 and outputs it to the antenna terminal 103, and filters the reception signal from the antenna terminal 103 and outputs it to the pair of reception terminals 107.
- a reception filter 111 A reception filter 111.
- the transmission filter 109 has the same configuration as the elastic wave filter 51 described with reference to FIG. That is, the transmission filter 109 has one or more series resonators and one or more parallel resonators connected in a ladder shape. At least one of these resonators is constituted by an elastic wave resonator 1. In the example of FIG. 11, one series resonator and one parallel resonator are configured by the elastic wave resonator 1, and the other series resonator and the other parallel resonator are configured by the conventional SAW resonator 59. The case is illustrated.
- the IDT electrode 11 and the pair of reflectors 13 (electrode portions 5) constituting the plurality of resonators are provided on the same piezoelectric substrate 7, for example.
- the reception filter 111 includes, for example, a SAW resonator 59 and a SAW filter 61 connected in series with each other.
- the IDT electrode 11 and the pair of reflectors 13 constituting these are provided, for example, on the same piezoelectric substrate 7.
- the piezoelectric substrate 7 on which the reception filter 111 is configured may be the same as or different from the piezoelectric substrate 7 on which the transmission filter 109 is configured.
- the SAW filter 61 is, for example, a longitudinally coupled multimode (including a double mode) type resonator filter, and includes a plurality of IDT electrodes 11 arranged in the SAW propagation direction and a pair of electrodes arranged on both sides thereof. And a reflector 13.
- FIG. 12 is a block diagram illustrating a main part of a communication device 151 as an example of use of the acoustic wave resonator 1.
- the communication device 151 performs wireless communication using radio waves.
- the communication device 151 uses the elastic wave resonator 1 by including the duplexer 101 described above. Specifically, it is as follows.
- a transmission information signal TIS including information to be transmitted is modulated and increased in frequency (conversion to a high frequency signal of a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153, and the transmission signal TS Is done. Unnecessary components other than the transmission passband are removed from the transmission signal TS by the bandpass filter 155, amplified by the amplifier 157, and input to the duplexer 101 (transmission terminal 105). Then, the duplexer 101 removes unnecessary components other than the transmission passband from the input transmission signal TS, and outputs the transmission signal TS after the removal from the antenna terminal 103 to the antenna 159.
- the antenna 159 converts the input electric signal (transmission signal TS) into a radio signal (radio wave) and transmits it.
- a radio signal (radio wave) received by the antenna 159 is converted into an electric signal (reception signal RS) by the antenna 159 and input to the duplexer 101.
- the duplexer 101 removes unnecessary components other than the reception passband from the input reception signal RS and outputs the result to the amplifier 161.
- the output received signal RS is amplified by the amplifier 161, and unnecessary components other than the reception passband are removed by the band pass filter 163. Then, the reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 153 to be a reception information signal RIS.
- the transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) including appropriate information, for example, analog audio signals or digitized audio signals.
- the passband of the radio signal may conform to various standards such as UMTS (Universal Mobile Telecommunications System).
- the transmission passband and the reception passband usually do not overlap each other.
- the modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more thereof.
- the direct conversion system is illustrated in FIG. 12, but may be other appropriate ones, for example, a double superheterodyne system.
- FIG. 12 schematically shows only the main part, and a low-pass filter, an isolator or the like may be added at an appropriate position, and the position of an amplifier or the like may be changed.
- the acoustic wave resonator 1 includes the piezoelectric substrate 7 and the IDT electrode 11 located on the upper surface of the piezoelectric substrate 7. Between the resonant frequency f sr and the anti-resonance frequency f sa by SAW, at least one of the resonance frequency f br and anti-resonance frequency f ba by bulk waves are located.
- a resonance characteristic having a frequency difference ⁇ f 2 with respect to the resonance frequency f sa can be realized. Since ⁇ f 1 or ⁇ f 2 is narrower than the frequency difference ⁇ f s between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa , the resonance characteristic having a narrower frequency difference ⁇ f compared to the SAW resonator is obtained. Realized.
- the elastic wave resonator 1 is epoch-making because it uses a bulk wave treated as a spurious in a SAW resonator to realize resonance characteristics based on the concept of inversion. Unlike the conventional SAW resonator or bulk wave resonator, the elastic wave resonator 1 is not based on one type of elastic wave but uses two types of elastic waves (SAW and bulk wave). This is also technological.
- the acoustic wave filter 51 includes one or more series resonators 53 and one or more parallel resonators 55 connected in a ladder shape, and at least one of these resonators is a main resonator. It consists of the elastic wave resonator 1 of embodiment.
- the acoustic wave resonator 1 having a narrow frequency difference ⁇ f is included, and as described with reference to FIGS. 10A and 10B, the rise of the attenuation at the end of the passband or The fall can be sharpened and the filter characteristics are improved.
- the rise of the attenuation amount on the low frequency side of the pass band can be sharpened.
- the fall of the attenuation amount on the high frequency side of the pass band can be sharpened.
- the acoustic wave filter 51 is located on the piezoelectric substrate 7, the support substrate 9 bonded to the lower surface of the piezoelectric substrate 7, and the upper surface of the piezoelectric substrate 7. And a plurality of IDT electrodes 11 constituting one or more series resonators 53 and one or more parallel resonators 55 connected in a ladder shape.
- the plurality of IDT electrodes 11 are different in thickness from the first IDT electrode 11 (the IDT electrode 11 constituting the SAW resonator 59) and the first IDT electrode 11 (for example, thicker than the first IDT electrode 11). 2nd IDT electrode 11 (IDT electrode 11 which comprises the elastic wave resonator 1).
- the first IDT electrode 11 constitutes a normal SAW resonator 59 in which no bulk wave spurious is located between the SAW resonance frequency and the SAW anti-resonance frequency, and the second IDT electrode 11 allows the SAW resonance frequency to be formed.
- the elastic wave resonator 1 of this embodiment in which a bulk wave spurious is located between the SAW anti-resonance frequency and the SAW anti-resonance frequency can be configured. By providing the acoustic wave resonator 1, the above-described various effects are exhibited. Further, by mixing the SAW resonator 59 and the elastic wave resonator 1, it is possible to combine the advantages of both.
- the method of designing the acoustic wave resonator 1 is that the SAW resonance frequency f sr and anti-resonance frequency f sa are bulk when the pitch p of the electrode fingers 19 of the IDT electrode 11 is a predetermined initial value.
- a wave due to the resonance frequency f br and anti-resonance frequency f electrode thickness setting step of specifying a thickness t e of the electrode fingers 19 located on at least one of both sides of ba (step ST3 ⁇ ST5), identified by the electrode film thickness setting step in the thickness t e of the electrode fingers 19, the step of said one frequency (f br or f ba) identifies a pitch p of the electrode fingers 19 that matches a predetermined target frequency (step ST6 ⁇ ST8. where step ST6 And ST9 may be identified with each other as described above).
- the elastic wave resonator 1 of at least the present embodiment in which one is located in the bulk wave resonance frequency f br and bulk wave antiresonance frequency f ba between the SAW resonant frequency f sr and SAW antiresonant frequency f sa is Realized. Also, varying the thickness t e of the electrode fingers 19, while the SAW resonance frequency f sr and SAW antiresonant frequency f sa changes, since the frequency of the bulk wave spurious hardly changes, the difference ⁇ f of the desired frequency Is easy to realize.
- FIGS. 13A to 13C show a book in which at least one of the bulk wave resonance frequency f br and the bulk wave anti resonance frequency f ba is located between the SAW resonance frequency f sr and the SAW anti resonance frequency f sa.
- Various modifications of the elastic wave resonator 1 according to the embodiment are shown.
- an additional film 201 having a shape substantially equivalent to the shape of the electrode finger 19 (electrode part 5) in a plan view is provided. May be.
- the additional film 201 may be made of a conductor or may be made of an insulator.
- the additional film 201 can also be provided under the electrode finger 19.
- Such an additional film 201 contributes to, for example, increasing the reflection coefficient of the elastic wave at the electrode finger 19.
- a protective layer (not shown) is formed thicker than the electrode finger 19, and the material of the protective layer (for example, SiO 2 ) and the material of the electrode finger 19 (for example, Al or Al alloy) are acoustically approximated. It is effective when In the case where the additional film 201 is made of an insulator, the additional film 201 does not necessarily have the same shape as the electrode portion 5 in plan view. For example, the electrode finger 19 and the dummy electrode 21 (see FIG. 1). ) May be located between them.
- the electrode finger 203 may be considered to be configured by the electrode finger 19 (metal layer) and the additional film 201 (which may be a conductor or an insulator).
- the thickness t e of the electrode finger 19 without significantly changing the frequency of the bulk wave spurious, or alter the resonant frequency and the antiresonant frequency by SAW, the bulk wave spurious The frequency with high excitation efficiency was shifted.
- the cut angle of the piezoelectric substrate 7 by changing the cut angle of the piezoelectric substrate 7, it is possible to shift the frequency at which the excitation efficiency of the bulk wave is high. Thereby, the magnitude of the bulk wave may be adjusted. For example, in a Y-plate of a lithium tantalate single crystal, the higher the cut angle, the higher the frequency at which the bulk wave excitation efficiency is shifted to the higher frequency side.
- only one bulk wave spurious is located between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa .
- two bulk wave spurious signals (two bulk wave spurious signals SP1 and SP2 in the illustrated example) are positioned. May be.
- a resonance characteristic having a frequency difference ⁇ f 1 is realized between the SAW resonance frequency f sr and the anti-resonance frequency f ba of the bulk wave spurious SP1, or the resonance frequency f br of the bulk wave spurious SP2 and the SAW anti-resonance frequency f.
- the resonance characteristic of the frequency difference ⁇ f 2 can be realized with sa .
- the bulk wave spurious is 3 or more (when the resonance frequency and the anti-resonance frequency of the bulk wave are 5 or more), adjustment by the film thickness and pitch of the IDT electrode becomes substantially difficult.
- both of them may be used as shown in FIG. 13C, or one of them may be located near the resonance frequency or anti-resonance frequency of the surface acoustic wave. The influence may be reduced, or the influence may be reduced by placing the excitation efficiency of the bulk wave at a very low frequency.
- the bulk wave spurious does not have to be located between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa in both the resonance frequency f br and the anti-resonance frequency f ba .
- the bulk wave antiresonance frequency f ba may be positioned between the SAW resonance frequency f sr and the SAW antiresonance frequency f sa, and the frequency difference
- the bulk wave resonance frequency f br may be positioned between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa .
- the frequency difference between the bulk wave resonance frequency f br and the bulk wave anti-resonance frequency f ba is narrower than the frequency difference ⁇ f s between the SAW resonance frequency f sr and the SAW anti-resonance frequency f sa.
- both the bulk wave resonance frequency fbr and the bulk wave antiresonance frequency fba are often located between the SAW resonance frequency fsr and the SAW antiresonance frequency fsa .
- the elastic wave resonator 1 is used as a ladder type filter as the elastic wave filter 5 has been described as an example, but is not limited thereto.
- the acoustic wave filter 51 the acoustic wave resonator 1 can also be used in a filter including the longitudinally coupled resonator 13 such as the reception filter 111 shown in FIG.
- a longitudinally coupled (series connection) resonator 13 and a parallel resonator 58 disposed between a reference potential are provided between terminals 103 and 107.
- the filter 51 ⁇ / b> A may be provided, and the elastic wave resonator 1 may be used as the parallel resonator 58.
- Such a parallel resonator 58 has an antenna terminal 103 rather than the resonator 13 as shown in FIG. It may be arranged on the receiving side 107 or on the receiving terminal 107 side.
- the shape of the IDT electrode is not limited to the illustrated one.
- the IDT electrode may not have a dummy electrode.
- the IDT electrode may be subjected to so-called apodization in which the length of the electrode finger or the like changes in the SAW propagation direction.
- the bus bar may be inclined with respect to the SAW propagation direction.
- the elastic wave resonator according to the present embodiment can narrow the frequency difference ⁇ f between the resonance frequency and the anti-resonance frequency without providing a capacitive element connected in parallel to the IDT electrode.
- a capacitive element connected in parallel to the IDT electrode may be provided.
- the support substrate is not an essential requirement.
- the support substrate when the support substrate is bonded to the lower surface of the piezoelectric substrate, for example, the strength of a wafer on which a large number of acoustic wave resonators (thin piezoelectric substrates) are taken in the manufacturing process can be improved. Further, the support substrate may not have a temperature compensation function.
- the bulk wave spurious used for the resonance point or anti-resonance point is not limited to the bulk wave spurious having the lowest frequency (for example, line L21 in FIG. 6).
- a bulk wave spurious having the second lowest frequency for example, the line L21 or the line L23 in FIG. 6) may be used.
- the design method described with reference to FIG. 8, estimates the resonance characteristics by simulation calculations, were identified (thickness t e and the pitch p in the embodiment) various sizes that satisfy the conditions (step ST3, ST6 and ST9).
- a prototype may be manufactured and the resonance characteristics may be measured, and various dimensions that satisfy various conditions may be specified. That is, the design method of the present embodiment is not limited to that realized by software.
- various dimensions of a normal SAW resonator are assumed, and various dimensions that satisfy various conditions are specified by changing the dimensions.
- various dimensions of the elastic wave resonator may be calculated from the beginning, or adjustment may be performed based on the calculation result.
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Abstract
Description
以下、本開示の実施形態に係る弾性波共振子について、図面を参照して説明する。なお、以下の説明で用いられる図は模式的なものであり、図面上の寸法比率等は現実のものとは必ずしも一致していない。
図1は、本開示の実施形態に係る弾性波共振子1の構成を示す平面図である。図2は、図1のII-II線における断面図である。ただし、図2において、後述する電極指の数は図1よりも少なく描かれている。
図3(a)および図3(b)は、弾性波共振子1の原理を説明するための図である。図3(a)および図3(b)において、横軸は周波数f(Hz)を示しており、縦軸はインピーダンスの絶対値|Z|(Ω)を示している。
なお、このSAW共振子は、SAW共振点fsrとSAW***振点fsaとの間にバルク波スプリアスが存在しない場合を例に説明している。
以下では、弾性波共振子1の各種の寸法がSAWおよびバルク波による共振特性に及ぼす影響を示し、上述した新たな原理を利用するための各種の寸法の具体的な設定方法について説明する。
電極部5(電極指19)の厚みteを互いに異ならせた複数の弾性波共振子1を想定して、共振特性をシミュレーション計算によって求めた。
圧電基板:
材料:タンタル酸リチウム単結晶
カット角:42°Y板
厚みts:7.2μm
支持基板:シリコン
IDT電極:
材料:Al-Cu合金
厚みte:121~181nmまで10nmずつ異ならせた。
電極指のピッチp:0.81207μm
電極指のデューティー比:0.5
なお、デューティー比は、電極指の幅/pである。
(nm) (MHz) (MHz) (MHz)
121 2533.1 2573.6 40.5
131 2520.7 2573.6 52.9
141 2506.7 2572.1 65.4
151 2492.0 2572.1 80.1
161 2474.9 2572.1 97.2
171 2455.9 2570.5 114.7
181 2436.6 2570.5 133.9
また、電極部5の厚みteが正規化厚みで0.06以下や0.09以上となると、ロスが大きくなり、通常の設計では採用しない厚みである。このように、厚すぎる場合および薄すぎる場合であってもバルク波を考慮しているといえる。
なお、通常のSAW共振子において、電極指19の厚みとは、電極指19の交差領域の中心付近における厚みを指すものとする。
特に図示しないが、電極指19のピッチpを変化させると、SAWの定在波およびバルク波の定在波(バルク波スプリアス)の双方の周波数が変化する。すなわち、ピッチpを小さくすれば、SAWの定在波およびバルク波の定在波の周波数は高くなり、ひいては、SAWおよびバルク波による共振周波数および***振周波数は高くなる。これは、IDT電極11による定在波の励振の原理から自明である。
本願発明者は、鋭意遂行を重ねた結果、種々の周波数のバルク波スプリアスが以下のメカニズムで発生していることを推定した。
図6を参照して、圧電基板7の厚みの影響を定量的に評価して、圧電基板7の厚みの範囲の例について述べる。
圧電基板:
材料:タンタル酸リチウム単結晶
カット角:42°Y板
支持基板:シリコン
IDT電極:
材料:Al-Cu合金
厚みte:121nm
電極指のピッチp:0.80413μm
電極指のデューティー比:0.5
なお、デューティー比は、電極指の幅/pである。
上述の例では、支持基板9としてSi基板を用いた場合を例に説明したが、サファイア基板を用いた場合についても、同様であることを確認している。具体的には、図6で示す線L21~L23を数式で表すと、傾き等を定める各係数に違いはあるが、同様の傾向が示される。具体的には、正規化厚みをx、正規化周波数をyとすると、支持基板としてSi基板を用いた場合には線L21~L23の近似式は以下の通りとなる。
L21:y = 71.865x4 - 706.82x3 + 2641.5x2 - 4567.1x + 6518.1
L22:y = 466.89x4 - 2884x3 + 6768x2 - 7310.5x + 7544.4
L23:y = -66.245x3 + 689.86x2 - 2546x + 6941.6
同様にサファイア基板を用いた場合には線L21~L23の近似式は以下の通りとなる。
L21:y = 33.795x4 - 419.77x3 + 1966.9x2 - 4212.8x + 6990.5
L22:y = -54.624x3 + 625.48x2 - 2533.6x + 7334.6
L23:y = -258.23x3 + 1477.7x2 - 2912.2x + 6418.1
既に述べたように、例えば、電極部5の厚みteを厚くするとSAW共振周波数fsrおよびSAW***振周波数fsaは低くなる。また、この周波数の低下は、電極指19のピッチpを狭くすることによって補償できる。この際、バルク波は、高次のモードほど、周波数が高くなる。その結果、例えば、バルク波スプリアスを利用することがより容易化される。このことを以下に示す。
IDT電極:
厚みte:201nm
電極指のピッチp:0.75768μm
図8は、電極部5の厚みteおよび電極指19のピッチp等の設計手順の一例を示すフローチャートである。
以下、弾性波共振子1の利用例として、弾性波フィルタ、分波器および通信装置について説明する。
図9(a)は、弾性波共振子1を含む弾性波フィルタ51を模式的に示している。弾性波フィルタ51は、いわゆるラダー型共振子フィルタであり、ラダー型に接続された1以上(図9(a)では2つ)の直列共振子53Aおよび53Bならびに1以上(図9(a)では3つ)の並列共振子55A~55Cを有している。なお、以下では、これらの符号のA、BまたはCを省略することがある。
フィルタ51の具体的条件を想定してそのフィルタ特性を調べた。フィルタ51の構成は、直列共振子53Aと、並列共振子55Aおよび並列共振子55Bの3つの共振子を有するものとした。実施例においては、並列共振子55Aに本実施形態の弾性波共振子1を適用した。比較例においては、全ての共振子を通常のSAW共振子59とした。また、周波数の差Δfとして図3に示すΔf2を用い、その大きさを異ならせた二種類のケース(ケース1、ケース2)について、実施例および比較例のモデルを作り、シミュレーション計算を行ない、その結果を比較した。
圧電基板:
材料:タンタル酸リチウム単結晶
カット角:42°Y板
厚みts:2μm
支持基板:シリコン
IDT電極:
材料:Al-Cu合金
厚みte:
比較例1:121nm
実施例1:181nm
電極指のピッチp:
比較例1:0.79115μm
実施例1:0.75325μm
電極指のデューティー比:0.5
比較例1 実施例1
fL(MHz) 2392.5 2391.3
fA(MHz) 2384.4 2387.2
fD(MHz) 8.1 4.1
dB/fD 1.16 2.29
図11は、弾性波共振子1の利用例としての分波器101を示す模式図である。
図12は、弾性波共振子1の利用例としての通信装置151の要部を示すブロック図である。
図13(a)~図13(c)は、SAW共振周波数fsrとSAW***振周波数fsaとの間にバルク波共振周波数fbrおよびバルク波***振周波数fbaの少なくとも一方が位置する本実施形態の弾性波共振子1の種々の変形例を示している。
の側に配置してもよいし、受信端子107の側に配置してもよい。
Claims (16)
- 圧電基板と、
該圧電基板の上面上に位置しているIDT電極と、
を有しており、
弾性表面波による共振周波数と***振周波数との間に、バルク波による共振周波数および***振周波数の少なくとも一方が1個以上4個以下位置している
弾性波共振子。 - 最も周波数が低いバルク波による共振周波数および***振周波数の少なくとも一方が弾性表面波による共振周波数と***振周波数との間に位置している
請求項1に記載の弾性波共振子。 - 前記IDT電極の電極指のピッチをpとし、前記電極指の厚みをteとしたときに、電極指の正規化厚みte/2pが0.08を超えている、
請求項1または2に記載の弾性波共振子。 - 前記IDT電極の電極指のピッチは、弾性表面波の伝搬速度を弾性表面波の共振周波数で除して得られる波長の半分よりも小さい
請求項3に記載の弾性波共振子。 - 前記圧電基板は、タンタル酸リチウムの単結晶基板からなる、カット角が38°以上48°以下のY板であり、
前記IDT電極の電極指のピッチをpとし、前記圧電基板の厚みをtsとしたときに、前記圧電基板の正規化厚みts/2pが1以上3以下である
請求項1~4のいずれか1項に記載の弾性波共振子。 - ラダー型に接続された1以上の直列共振子および1以上の並列共振子を有しており、
前記1以上の直列共振子および前記1以上の並列共振子の少なくとも1つは、請求項1~5のいずれか1項に記載の弾性波共振子からなる
弾性波フィルタ。 - 前記1以上の直列共振子および前記1以上の並列共振子は、前記弾性波共振子のIDT電極と厚みが異なるIDT電極を有し、弾性表面波による共振周波数と***振周波数との間に、バルク波による共振周波数および***振周波数が位置していないか、5個以上位置している、弾性表面波共振子を含んでいる
請求項6に記載の弾性波フィルタ。 - 前記弾性波共振子のIDT電極の厚みが前記弾性表面波共振子のIDT電極の厚みよりも厚い
請求項7に記載の弾性波フィルタ。 - 前記1以上の直列共振子の少なくとも1つは前記弾性波共振子からなる
請求項6~8のいずれか1項に記載の弾性波フィルタ。 - 前記1以上の並列共振子の少なくとも1つは前記弾性波共振子からなる
請求項6~9のいずれか1項に記載の弾性波フィルタ。 - 圧電基板と、
該圧電基板の下面に貼り合わされている支持基板と、
前記圧電基板の上面上に位置している複数のIDT電極と、
を有しており、
前記複数のIDT電極は、第1のIDT電極と、当該第1のIDT電極と厚みが異なる第2のIDT電極とを含んでいる
弾性波フィルタ。 - 複数のIDT電極は、ラダー型に接続された1以上の直列共振子および1以上の並列共振子を構成している
請求項11に記載の弾性波フィルタ。 - 前記複数のIDT電極は、縦結合型の共振子と、前記縦結合型の共振子と基準電位との間に接続された並列共振子とを構成しており、
前記第1のIDT電極は、前記並列共振子を構成しており、前記第2のIDT電極は、前記縦結合型の共振子を構成している
請求項11に記載の弾性波フィルタ。 - アンテナ端子と、
送信信号をフィルタリングして前記アンテナ端子に出力する送信フィルタと、
前記アンテナ端子からの受信信号をフィルタリングする受信フィルタと、
を有しており、
前記送信フィルタおよび前記受信フィルタの少なくとも一方は、請求項6~13のいずれか1項に記載の弾性波フィルタを含んでいる
分波器。 - アンテナと、
前記アンテナに前記アンテナ端子が接続されている請求項14に記載の分波器と、
前記送信フィルタおよび前記受信フィルタに接続されているICと、
を有している通信装置。 - IDT電極の電極指のピッチが所定の初期値である場合において弾性表面波による共振周波数および***振周波数がバルク波による共振周波数および***振周波数の少なくとも一方の両側に位置する前記電極指の厚みを特定する電極膜厚設定ステップと、
前記電極膜厚設定ステップで特定した前記電極指の厚みで、前記一方の周波数が所定の目標周波数に一致する前記電極指のピッチを特定するステップと、
を有している弾性波共振子の設計方法。
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JP2019121879A (ja) * | 2017-12-28 | 2019-07-22 | 太陽誘電株式会社 | マルチプレクサ |
WO2020050402A1 (ja) * | 2018-09-07 | 2020-03-12 | 株式会社村田製作所 | 弾性波装置、弾性波フィルタ及び複合フィルタ装置 |
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JPWO2017073425A1 (ja) | 2018-08-09 |
US20180323769A1 (en) | 2018-11-08 |
CN107852144A (zh) | 2018-03-27 |
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