JP7329954B2 - Acoustic wave resonators, filters and multiplexers - Google Patents

Description

The present invention relates to acoustic wave resonators, filters and multiplexers, and for example to acoustic wave resonators, filters and multiplexers having a pair of comb electrodes.

A surface acoustic wave resonator is known as an acoustic wave resonator used in communication devices such as smartphones. It is known to bond a piezoelectric substrate forming a surface acoustic wave resonator to a support substrate. It is known to make the thickness of the piezoelectric substrate equal to or less than the wavelength of the surface acoustic wave (for example, Patent Document 1).

JP 2017-034363 A

By bonding the piezoelectric substrate to the support substrate, the temperature characteristics of the surface acoustic wave resonator are improved. Furthermore, loss and spurious can be suppressed by setting the thickness of the piezoelectric substrate to be equal to or less than the wavelength of the surface acoustic wave. However, spurious suppression is not sufficient.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress spurious.

The present invention comprises: a piezoelectric substrate that is a Y-cut X-propagation lithium tantalate substrate rotated by 10° or more and 50° or less; The electrodes are provided on the side of the piezoelectric substrate opposite to the surface on which the pair of comb-shaped electrodes are provided, and have an average particle diameter of 1 to 66 times the average pitch of the plurality of electrode fingers . and a polycrystalline substrate that is a crystal spinel substrate , wherein the thickness of the piezoelectric substrate is equal to or less than twice the average pitch of the plurality of electrode fingers .

The present invention includes a piezoelectric substrate, a pair of comb-shaped electrodes provided on the piezoelectric substrate and having a plurality of electrode fingers for mainly exciting SH waves, and the pair of comb-shaped electrodes of the piezoelectric substrate. a polycrystalline substrate which is a polycrystalline spinel substrate provided on the opposite side of the piezoelectric substrate and has an average grain size of 1 to 66 times the average pitch of the plurality of electrode fingers; The thickness of the elastic wave resonator is not more than twice the average pitch of the plurality of electrode fingers .

In the above configuration, the average particle size may be 40 times or less the average pitch .

In the above configuration, the distance between the surface of the polycrystalline substrate on the side of the piezoelectric substrate and the surface of the piezoelectric substrate on which the pair of comb-shaped electrodes is provided may be less than or equal to twice the average pitch. .

In the above configuration, the piezoelectric substrate may be a Y-cut X-propagation lithium tantalate substrate rotated 36° or more and 42° or less.

In the above configuration, the thickness of the polycrystalline substrate may be at least twice the average pitch and at least the average grain size.

In the above configuration, the piezoelectric substrate and the polycrystalline substrate may be directly bonded.

In the above configuration, an intermediate layer may be provided between the piezoelectric substrate and the polycrystalline substrate.

The present invention is a filter comprising the above elastic wave resonator.

The present invention is a multiplexer including the above filters.

According to the present invention, spurious can be suppressed.

FIG. 1(a) is a plan view of the elastic wave resonator in Example 1, and FIG. 1(b) is a cross-sectional view taken along the line AA of FIG. 1(a). 2A to 2D are cross-sectional views showing the method of manufacturing the elastic wave resonator according to the first embodiment. FIG. 3 is a schematic diagram of a SEM image of a cross section of a polycrystalline spinel substrate. 4(a) and 4(b) show the mean and standard deviation of spurious peaks versus particle size for samples A to C. FIG. FIGS. 5(a) to 5(c) are diagrams showing the pass characteristics of ladder-type filters in samples A to C. FIG. 6A to 6C are cross-sectional views of elastic wave resonators according to Modifications 1 to 3 of Embodiment 1. FIG. FIG. 7A is a circuit diagram of a filter according to the second embodiment, and FIG. 7B is a circuit diagram of a duplexer according to Modification 1 of the second embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1(a) is a plan view of the elastic wave resonator in Example 1, and FIG. 1(b) is a cross-sectional view taken along the line AA of FIG. 1(a). The arrangement direction of the electrode fingers is the X direction, the extending direction of the electrode fingers is the Y direction, and the stacking direction of the supporting substrate and the piezoelectric substrate is the Z direction. The X-direction, Y-direction and Z-direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric substrate. When the piezoelectric substrate is a rotated Y-cut X-propagation substrate, the X-direction is the X-axis direction of the crystal orientation.

As shown in FIGS. 1( a ) and 1 ( b ), a piezoelectric substrate 12 is laminated on a polycrystalline substrate 10 . The thicknesses of polycrystalline substrate 10 and piezoelectric substrate 12 are T0 and T2, respectively. An elastic wave resonator 20 is provided on the piezoelectric substrate 12 . Acoustic wave resonator 20 has IDT 22 and reflector 24 . The reflectors 24 are provided on both sides of the IDT (Inter Digital Transducer) 22 in the X direction. IDT 22 and reflector 24 are formed by metal film 14 on piezoelectric substrate 12 .

The IDT 22 includes a pair of comb electrodes 18 facing each other. The comb-shaped electrode 18 includes a plurality of electrode fingers 15 and a busbar 16 to which the plurality of electrode fingers 15 are connected. A crossing region 25 is a region where the electrode fingers 15 of the pair of comb-shaped electrodes 18 intersect. The length of the intersection region 25 is the aperture length. A pair of comb-shaped electrodes 18 are provided facing each other such that the electrode fingers 15 are substantially alternated in at least a portion of the intersection region 25 . The elastic waves excited by the plurality of electrode fingers 15 in the intersecting region 25 mainly propagate in the X direction. The pitch of the electrode fingers 15 of one comb-shaped electrode 18 of the pair of comb-shaped electrodes 18 is approximately the wavelength λ of the elastic wave. The wavelength λ of the elastic wave is approximately the pitch of two electrode fingers 15 . The reflector 24 reflects elastic waves (surface acoustic waves) excited by the electrode fingers 15 of the IDT 22 . This confines the acoustic wave within the intersection region 25 of the IDT 22 .

The piezoelectric substrate 12 is a single crystal substrate, such as a lithium tantalate (LiTaO ₃ ) substrate or a lithium niobate (LiNbO ₃ ) substrate, such as a rotated Y-cut X-propagating lithium tantalate substrate or a rotated Y-cut X-propagating niobate substrate. Lithium substrate. The polycrystalline substrate 10 is, for example, a spinel (MgAl ₂ O ₃ ) substrate, a silicon (Si) substrate, or an alumina (Al ₂ O ₃ ) substrate. The X-direction linear expansion coefficient of the polycrystalline substrate 10 is smaller than the X-direction linear expansion coefficient of the piezoelectric substrate 12 . As a result, temperature coefficients such as the resonance frequency of the elastic wave resonator can be reduced.

The metal film 14 is a film containing, for example, Al (aluminum) or Cu (copper) as a main component, such as an Al film or a Cu film. An adhesion film such as a Ti (titanium) film or a Cr (chromium) film may be provided between the electrode fingers 15 and the piezoelectric substrate 12 . The adhesion film is thinner than the electrode finger 15 . An insulating film may be provided to cover the electrode fingers 15 . The insulating film functions as a protective film or temperature compensating layer.

The thickness T0 is, for example, 50 μm to 500 μm. The thickness T2 is, for example, 0.5 μm to 20 μm, and is, for example, 10λ or less and 1λ or less. The number of pairs of two electrode fingers 15 is, for example, 20 to 300 pairs. The duty ratio of the IDT 22 is the thickness of the electrode fingers 15/the pitch of the electrode fingers 15, and is, for example, 30% to 70%. The aperture length of the IDT 22 is, for example, 10λ to 50λ.

[Manufacturing method of Example 1]
2A to 2D are cross-sectional views showing the method of manufacturing the elastic wave resonator according to the first embodiment. As shown in FIG. 2A, the upper surface of the polycrystalline substrate 10 and the lower surface of the piezoelectric substrate 12 are irradiated with ions 54 or the like. The ions 54 are ions of an inert element (for example, rare gas element) such as Ar (argon) ions. Ions 54 or the like are irradiated as an ion beam, a neutralized beam or plasma. As a result, an amorphous layer 10a is formed on the upper surface of the polycrystalline substrate 10 in contact with the polycrystalline substrate 10, and an amorphous layer 12a is formed on the lower surface of the piezoelectric substrate 12 in contact with the piezoelectric substrate 12. FIG. Unbonded bonds are formed (that is, activated) on the surfaces of the amorphous layers 10a and 12a.

As shown in FIG. 2(b), when the amorphous layers 10a and 12a are stuck together while maintaining a vacuum, dangling bonds are bonded to form a strong bond. Thereby, the polycrystalline substrate 10 and the piezoelectric substrate 12 are joined. Since such bonding is performed at room temperature (for example, 100° C. or lower and −20° C. or higher, preferably 80° C. or lower and 0° C. or higher), thermal stress can be suppressed. Whether or not the bonding is performed at normal temperature can be confirmed by the temperature dependence of the residual stress. In other words, the residual stress is the lowest at the temperature at which it is joined. An amorphous layer 30 consisting of the amorphous layers 10a and 12a is formed.

The amorphous layer 10a is mainly composed of constituent elements of the polycrystalline substrate 10 and contains an element (for example, Ar) for surface activation. When the polycrystalline substrate 10 is a spinel substrate, the amorphous layer 10a is mainly composed of Mg (magnesium), Al (aluminum) and O (oxygen), and contains elements for surface activation. The amorphous layer 12a is mainly composed of the constituent elements of the piezoelectric substrate 12 and contains an element for surface activation. When the piezoelectric substrate 12 is a lithium tantalate substrate, the amorphous layer 12a is mainly composed of Ta (tantalum), Li (lithium) and O, and contains elements for surface activation. The amorphous layer 10a hardly contains constituent elements other than the polycrystalline substrate 10 among the constituent elements of the piezoelectric substrate 12 . For example, the amorphous layer 10a contains little Ta and Li. Amorphous layer 12 a contains almost no elements other than the constituent elements of piezoelectric substrate 12 among the constituent elements of polycrystalline substrate 10 . For example, the amorphous layer 12a hardly contains Mg and Al.

The thickness of the amorphous layers 10a and 12a is preferably greater than 0 nm, more preferably 1 nm or more. Thereby, the bondability between the polycrystalline substrate 10 and the piezoelectric substrate 12 can be improved. The thickness of the amorphous layers 10a and 12a is preferably 10 nm or less, more preferably 5 nm or less. Thereby, deterioration of the characteristics of the elastic wave resonator can be suppressed. Since the amorphous layer 30 is much thinner than the polycrystalline substrate 10 and the piezoelectric substrate 12, the polycrystalline substrate 10 and the piezoelectric substrate 12 are substantially directly bonded. Polycrystalline substrate 10, piezoelectric substrate 12, and amorphous layers 10a and 12a can be observed using a TEM (Transmission Electron Microscope) method.

As shown in FIG. 2C, the upper surface of the piezoelectric substrate 12 is flattened by, for example, CMP (Chemical Mechanical Polishing). As a result, the thickness of the piezoelectric substrate 12 becomes T2. As shown in FIG. 2(d), an IDT 22 made of a metal film 14 and a reflector 24 are formed on the upper surface of the piezoelectric substrate 12. As shown in FIG.

FIG. 3 is a view of a copy of a SEM (Scanning Electron Microscope) image of a cross section of a polycrystalline spinel substrate. A plurality of crystal grains 50 and grain boundaries 52 between the crystal grains 50 can be observed. The average grain size of polycrystalline substrate 10 is measured as follows. The diameter of a circle equal to the cross-sectional area of the crystal grain 50 is defined as the grain size. The grain size of the crystal grains 50 in the 90 μm×90 μm SEM image is measured, and the average grain size is calculated.

[experiment]
When the thickness T2 of the piezoelectric substrate 12 is set to be equal to or less than the wavelength λ of the elastic wave, the spurious caused by the bulk wave is reduced. However, spurious suppression at frequencies higher than the anti-resonance frequency is not sufficient. Therefore, a ladder-type filter having acoustic wave resonators was fabricated using spinel substrates having different average particle diameters as supporting substrates. The fabricated ladder-type filter has five series resonators and four parallel resonators. Other manufacturing conditions are as follows.
Polycrystalline substrate 10: Polycrystalline spinel substrate manufactured using a sintering method Thickness T0: 150 μm
Piezoelectric substrate 12: 42° rotated Y-cut X-propagation lithium tantalate substrate Thickness T2: 1.3 μm
The conditions for one elastic wave resonator among the plurality of elastic wave resonators in the ladder-type filter are as follows. In other acoustic wave resonators, the filter characteristics are appropriately adjusted so as to be desired.
Elastic wave wavelength λ: 1.6 μm
Logarithm of IDT22: 100 pairs Aperture length: 25λ
Duty ratio: 50%
The wavelength λ of the elastic wave is approximately twice the average pitch of the electrode fingers 15 of the IDT 22 .

The average grain sizes of the polycrystalline substrates 10 of samples A to C are as follows.
Sample A: 17 μm
Sample B: 30 μm
Sample C: 54 μm

We measured the spurious and transmission characteristics of the ladder-type filter that we fabricated. 4(a) and 4(b) show the mean and standard deviation of spurious peaks versus particle size for samples A to C. FIG. The spurious peak average value indicates the average value of the spurious peak values within the wafer plane in each sample, and the standard deviation indicates the standard deviation of the spurious peak values within the wafer plane for each sample. λ is the pitch of the two electrode fingers 15 . As shown in FIGS. 4(a) and 4(b), the smaller the particle size, the smaller the average value of the spurious peaks and the smaller the standard deviation.

FIGS. 5(a) to 5(c) are diagrams showing the pass characteristics of ladder-type filters in samples A to C. FIG. FIG. 5(a) is a broadband pass characteristic, FIG. 5(b) is an enlarged view around the passband, and FIG. 5(c) is an enlarged view around the stopband. As shown in FIG. 5(a), the pass band of the fabricated ladder-type filter is the 2.4 GHz band (2.4025 GHz to 2.4815 GHz). be the stopband.

As shown in FIG. 5(b), samples A to C have approximately the same passband loss. The passband differs depending on the sample, but this is because the resonance frequency and anti-resonance frequency of the elastic wave resonator are not optimized for each sample. As shown in FIG. 5(c), sample C has large spurious emissions around the communication bands of bands 41 and 42. As shown in FIG. In sample B, the spurious is smaller than in sample C. Sample A has even smaller spurious.

When the thickness T2 of the piezoelectric substrate 12 is set to be equal to or less than the wavelength λ of the elastic wave, the spurious around the passband caused by the bulk wave is suppressed. However, suppression of spurious generated in a band of frequencies higher than the passband is not sufficient. By reducing the grain size of the polycrystalline substrate 10 as shown in FIG. 5C, the spurious can be suppressed. It is considered that this is because unwanted waves such as bulk waves are scattered in the polycrystalline substrate 10 .

[Modification 1 of Embodiment 1]
6A is a cross-sectional view of an elastic wave resonator according to Modification 1 of Embodiment 1. FIG. As shown in FIG. 6A, an intermediate layer 11 is provided between a polycrystalline substrate 10 and a piezoelectric substrate 12. As shown in FIG. The thickness of the intermediate layer 11 is T1. The intermediate layer 11 is an insulating layer such as a silicon oxide layer, a silicon nitride layer, an aluminum oxide layer, or an aluminum nitride layer. When the sign of the temperature coefficient of elastic modulus of the intermediate layer 11 is opposite to the sign of the temperature coefficient of elastic modulus of the piezoelectric substrate 12, the intermediate layer 11 functions as a temperature compensation film. A silicon oxide film (which may contain an additive such as fluorine) is used as the temperature compensation film. Further, the intermediate layer 11 may function as a bonding layer that bonds the polycrystalline substrate 10 and the piezoelectric substrate 12 together. Other configurations are the same as those of the first embodiment, and description thereof is omitted.

[Modification 2 of Embodiment 1]
FIG. 6B is a cross-sectional view of an elastic wave resonator according to Modification 2 of Embodiment 1. FIG. As shown in FIG. 6B, the lower surface of polycrystalline substrate 10 is bonded to support substrate 13 . The support substrate 13 is, for example, a sapphire substrate, an alumina substrate, a quartz substrate, or a crystal substrate. Other configurations are the same as those of the first embodiment, and description thereof is omitted.

[Modification 3 of Embodiment 1]
FIG. 6C is a cross-sectional view of an elastic wave resonator according to Modification 3 of Embodiment 1. FIG. As shown in FIG. 6(c), the bottom surface of the polycrystalline substrate 10 is bonded to the support substrate 13. As shown in FIG. Other configurations are the same as those of Modification 1 of Embodiment 1, and description thereof is omitted.

The polycrystalline substrate 10 and the piezoelectric substrate 12 may be directly bonded as in the first embodiment and its second modification, or the polycrystalline substrate 10 and the piezoelectric substrate 12 may be directly bonded as in the first and third modifications of the first embodiment. Intermediate layer 11 may be provided between substrate 12 . The polycrystalline substrate 10 may be bonded to the support substrate 13 as in the second and third modifications of the first embodiment.

According to the first embodiment and its modification, the polycrystalline substrate 10 is provided on the side opposite to the side of the piezoelectric substrate 12 on which the pair of comb-shaped electrodes 18 are provided, and the average grain size is the average of the plurality of electrode fingers 15 . It is less than or equal to 66 times the pitch (ie 33λ). Thereby, as shown in FIGS. 4(a) to 5(c), the spurious on the high frequency side of the passband can be suppressed.

The average grain size of the polycrystalline substrate 10 is preferably 40 times (that is, 20λ) or less, more preferably 20 times or less, the average pitch of the electrode fingers 15 . Thereby, spurious can be suppressed more. In order to scatter unnecessary waves in the polycrystalline substrate 10, the average grain size is preferably at least 1 time the average pitch of the electrode fingers 15, more preferably at least 2 times. The average pitch of the electrode fingers 15 can be calculated by dividing the length of the acoustic wave resonator 20 in the X direction by the number of electrode fingers 15 . The average grain size of polycrystalline substrate 10 can be calculated by the method described with reference to FIG. If the grain sizes of 20 or more crystal grains 50 are averaged, the precision will be higher. If the grain sizes of 50 or more crystal grains 50 are averaged, the accuracy is further improved.

The polycrystalline substrate 10 is a polycrystalline spinel substrate (that is, a polycrystalline substrate containing MgAl ₂ O ₃ as a main component). Thereby, spurious can be suppressed more. The main component means containing to the extent that the effects of Example 1 and its modifications are exhibited, including intentionally or unintentionally added impurities, for example, 50 atomic % or 80 atomic % of the constituent elements It is to include above.

The distance between the upper surface of the polycrystalline substrate 10 (the surface on the side of the piezoelectric substrate 12) and the upper surface of the piezoelectric substrate 12 (the surface on which the pair of comb-shaped electrodes is provided) (for example, T2 in Example 1 and its Modified Example 2, Example T2+T1) of Modifications 1 and 3 of 1) is four times or less the average pitch of the electrode fingers 15 . By thinning T2 or T2+T1 in this way, the spurious caused by bulk waves can be suppressed. However, as shown in FIG. 5(c), spurious suppression at frequencies higher than the passband is not sufficient. Therefore, the average grain size of the polycrystalline substrate 10 is reduced. This suppresses spurious at frequencies higher than the passband. The distance between the upper surface of the polycrystalline substrate 10 and the upper surface of the piezoelectric substrate 12 is preferably two times or less the average pitch of the electrode fingers 15, and more preferably 0.2 times or more.

The thickness T2 of the piezoelectric substrate 12 is preferably twice or less the average pitch of the electrode fingers 15, more preferably 1.6 times or less, and preferably 0.2 times or more. Thereby, the spurious caused by the bulk wave can be suppressed. Also, loss can be suppressed.

When the piezoelectric substrate 12 is a Y-cut X-propagation lithium tantalate substrate rotated by 10° or more and 50° or less, the comb-shaped electrode 18 mainly excites SH (Shear Horizontal) waves. More preferably, the piezoelectric substrate 12 is a 36° or more and 42° or less rotated Y-cut X-propagating lithium tantalate substrate. The SH wave is a wave that displaces parallel to the surface of the piezoelectric substrate 12 and perpendicular to the propagation direction of the SH wave. At this time, bulk waves are likely to be excited. Therefore, it is preferable to use the polycrystalline substrate 10 .

The thickness T2 of the polycrystalline substrate 10 is preferably twice or more the average pitch of the electrode fingers 15, more preferably four times or more. Moreover, T2 is preferably equal to or larger than the average particle size, and more preferably equal to or larger than twice the average particle size. As a result, unwanted waves can be diffused and spurious can be suppressed.

FIG. 7A is a circuit diagram of a filter according to Example 2. FIG. As shown in FIG. 7A, one or more series resonators S1 to S3 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The elastic wave resonator of Example 1 can be used for at least one of the one or more series resonators S1 to S3 and the one or more parallel resonators P1 and P2. The number of resonators of the ladder-type filter and the like can be set as appropriate. The filter may be a multimode filter.

[Modification 1 of Embodiment 2]
FIG. 7B is a circuit diagram of a duplexer according to Modification 1 of Embodiment 2. FIG. As shown in FIG. 7B, a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A receive filter 42 is connected between the common terminal Ant and the receive terminal Rx. The transmission filter 40 allows the signal in the transmission band among the high-frequency signals input from the transmission terminal Tx to pass through the common terminal Ant as the transmission signal, and suppresses the signals of other frequencies. The reception filter 42 allows signals in the reception band among the high-frequency signals input from the common terminal Ant to pass through the reception terminal Rx as reception signals, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

A duplexer has been described as an example of a multiplexer, but a triplexer or a quadplexer may be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

REFERENCE SIGNS LIST 10 polycrystalline substrate 11 intermediate layer 12 piezoelectric substrate 13 support substrate 15 electrode fingers 18 comb-shaped electrode 20 elastic wave resonator 22 IDT

Claims (10)

a piezoelectric substrate that is a Y-cut X-propagating lithium tantalate substrate rotated 10° or more and 50° or less ;
a pair of comb-shaped electrodes provided on the piezoelectric substrate and having a plurality of electrode fingers to excite elastic waves;
A polycrystalline spinel substrate provided on the side of the piezoelectric substrate opposite to the surface on which the pair of comb-shaped electrodes is provided, having an average grain size of 1 to 66 times the average pitch of the plurality of electrode fingers , and a polycrystalline spinel substrate A polycrystalline substrate that is
with
The elastic wave resonator , wherein the thickness of the piezoelectric substrate is not more than twice the average pitch of the plurality of electrode fingers . a piezoelectric substrate;
a pair of comb-shaped electrodes provided on the piezoelectric substrate and having a plurality of electrode fingers for mainly exciting SH waves;
provided on the side of the piezoelectric substrate opposite to the surface on which the pair of comb-shaped electrodes are provided, having an average grain size of 1 to 66 times the average pitch of the plurality of electrode fingers, and being a polycrystalline spinel substrate; a polycrystalline substrate;
with
The elastic wave resonator, wherein the thickness of the piezoelectric substrate is not more than twice the average pitch of the plurality of electrode fingers. 3. The elastic wave resonator according to claim 1, wherein said average grain size is 40 times or less as large as said average pitch. 4. The distance between the surface of the polycrystalline substrate on the side of the piezoelectric substrate and the surface of the piezoelectric substrate provided with the pair of comb-shaped electrodes is not more than twice the average pitch. The elastic wave resonator according to . The elastic wave resonator according to any one of claims 1 to 4, wherein the piezoelectric substrate is a Y-cut X-propagation lithium tantalate substrate rotated 36° or more and 42° or less. The acoustic wave resonator according to any one of claims 1 to 5, wherein the thickness of the polycrystalline substrate is at least twice the average pitch and at least the average grain size. 7. The elastic wave resonator according to claim 1, wherein said piezoelectric substrate and said polycrystalline substrate are directly bonded. 7. The elastic wave resonator according to claim 1, further comprising an intermediate layer provided between said piezoelectric substrate and said polycrystalline substrate. A filter comprising the elastic wave resonator according to any one of claims 1 to 8. A multiplexer including the filter of claim 9.

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