JP2021093609A - Surface acoustic wave filter, duplexer, and module - Google Patents

Abstract

To provide a surface acoustic wave filter, a duplexer, and a module by which high frequency spurious can be suppressed while a Q value is maintained high.SOLUTION: A surface acoustic wave filter is constituted including a carrier substrate 2, a piezoelectric layer 4 formed of a piezoelectric material and provided on the carrier substrate 2, and IDT electrodes 5 formed on the piezoelectric layer 4. The carrier substrate 2 is constituted of an insulator or a semiconductor with high resistance. The piezoelectric layer 4 has a thickness of 0.15 λ to 1.5 λ, in which λ represents the wavelength of an elastic wave determined based on an electrode period of the IDT electrode 5. The piezoelectric layer 4 provided on the carrier substrate 2 includes a plurality of regions with different thicknesses. The surface acoustic wave filter is constituted by forming the IDT electrodes 5 on the respective regions and connecting the IDT electrodes 5 formed on the respective regions. A duplexer and a module are constituted including the surface acoustic wave filter.SELECTED DRAWING: Figure 2a

Description

The present invention relates to surface saw filters, duplexers and modules including them.

In communication equipment terminals such as mobile phone terminals and mobile information terminals, higher Q values are required for elastic wave devices used for antenna filters and duplexers. Surface acoustic wave devices include bulk surface acoustic wave devices and surface acoustic wave devices. Of these surface acoustic wave devices, surface acoustic wave devices are mainly used, but surface acoustic wave devices have a problem that their Q value is lower than that of bulk surface acoustic wave devices.

Therefore, in order to improve this Q value, as described in Patent Document 1, a multilayer film structure is formed in which a thin piezoelectric layer made of lithium tantalate, lithium niobate, etc. is attached onto a substrate made of silicon, sapphire, or the like. As a result, the leakage of elastic waves in the depth direction of the elastic wave substrate is greatly reduced, and as a result, the Q value is significantly improved.

Special Table 2002-534886

However, in a structure in which elastic waves are better confined to a piezoelectric layer, such as the conventional surface acoustic wave device described above, other propagation modes such as longitudinal waves other than surface acoustic waves to be propagated are also excited. Large parasitic resonance (spurious) may occur in a frequency band higher than the passing band. This high frequency spurious adversely affects the attenuation characteristics of the filter. As a result, the passband system used in the mobile communication device may be adversely affected, or the signal transmitted from the system may adversely affect the system in another frequency band. However, it is difficult to suppress this spurious only by adjusting the layer thickness of the piezoelectric layer constituting the elastic wave device.

In view of the above problems, it is an object of the present invention to provide a surface elastic wave filter, a duplexer and a module capable of suppressing high-frequency spurious while maintaining a high Q value.

One aspect of the surface elastic wave filter of the present invention is a resonator provided with a carrier substrate, a piezoelectric layer made of a piezoelectric material provided on the carrier substrate, and an IDT electrode formed on the piezoelectric layer. The carrier substrate is made of a high-resistance semiconductor or an insulator, and the piezoelectric layer has 0. When the wavelength of the elastic wave determined by the electrode period of the IDT electrode is λ. The piezoelectric layer having a thickness of 15λ to 1.5λ and provided on the carrier substrate includes a plurality of regions having different thicknesses, and each of the plurality of regions comprises a resonator having an IDT electrode. It has a resonator formed by connecting the resonators formed on the region of the above.
In this way, by setting the piezoelectric layer of the resonator to a thickness of 0.15λ to 1.5λ, a high electromechanical coupling coefficient and Q value are maintained. In addition, each resonator changes the thickness of the thin piezoelectric layer in which the elastic wave is confined in a plurality of regions, so that the resonance frequency and the anti-resonance frequency are kept substantially constant from the resonance frequency of the fundamental wave. It is a frequency higher than the resonance frequency, and the frequency at which the high-frequency spurious appears is varied and dispersed for each resonator composed in each region. In this way, the frequency at which spurs appear is changed for each resonator having a different thickness of the piezoelectric layer. Therefore, by having a resonator configured by connecting these resonators, spurs having different frequencies can be generated from each other. It is possible to obtain a surface elastic wave filter having less spurious as a whole filter without strengthening each other.

In the above-described aspect of the present invention, the thickness of the plurality of regions of the piezoelectric layer is stepwise so that the thickness of the region having the next smallest thickness is 10% or more smaller than the thickness of a certain region. It is preferable that the IDT electrodes are set so as to have a small thickness reduction and the IDT electrodes formed on the plurality of regions are connected in series or in parallel.
By making the thicknesses of the piezoelectric layers different by 10% or more in this way, the frequencies of spurious generated by the resonators in the regions where the thicknesses of the piezoelectric layers are different can be dispersed without strengthening each other. Further, by connecting the resonators in the regions having different thicknesses of the piezoelectric layers in series or in parallel, further spurious suppression becomes possible.

In each aspect of the present invention described above, it is preferable that the piezoelectric vibration excited by the piezoelectric layer is in SH mode.
As described above, in the configuration in which the piezoelectric vibration excited by the piezoelectric layer is in the SH mode and spurious is likely to be generated, an effective effect for suppressing spurious can be obtained.

In each of the above-described aspects of the present invention, one or a plurality of intermediate layers that serve at least one of the functions of facilitating the coupling between the carrier substrate and the piezoelectric layer or increasing the speed of sound of elastic waves are provided. It is preferable to prepare.
By providing such an intermediate layer, it is possible to improve the bond strength with the carrier substrate or obtain the effect of preventing leakage of surface acoustic waves to be propagated.

By realizing the module including the surface elastic wave filter of each aspect of the present invention described above, it is possible to provide a module in which high frequency spurious is suppressed.

Even when the duplexer is realized by including the surface elastic wave filter of each aspect of the present invention described above, the duplexer in which high-frequency spurious is suppressed can be provided.

Even when the module is realized by including the duplexer of the present invention described above, it is possible to provide a module in which high-frequency spurious is suppressed.

According to the present invention, a high Q value is maintained by setting the piezoelectric layer of the surface acoustic wave device (resonator) to a thickness of 0.15λ to 1.5λ. In addition, by changing the thickness of the thin piezoelectric layer in which the elastic wave is confined by the resonator, the frequency at which the high-frequency spurious appears is set to the resonator while keeping the anti-resonance frequency substantially constant from the resonance frequency of the fundamental wave. It can be changed for each. In this way, since the frequency at which spurious appears can be changed for each resonator having a different thickness of the piezoelectric layer, the resonators are connected to form a resonator, and the resonator is used for surface elasticity. By constructing the wave filter, it is possible to obtain a surface elastic wave filter having less spurious without intensifying spurs having different frequencies from each other.

It is sectional drawing and schematic drawing which shows typically one of the resonators which are the constituent elements which make up the surface elastic wave filter of this invention. It is sectional drawing and schematic drawing which shows typically the resonator which has the piezoelectric layer of the thickness different from FIG. 1a. It is sectional drawing and schematic drawing which shows typically the resonator which has a thickness different from the resonator of FIG. 1a and FIG. 1b. FIG. 5 is a cross-sectional view schematically showing an embodiment of a resonator used in the present invention composed of the resonators shown in FIGS. 1a to 1c. FIG. 5 is a cross-sectional view schematically showing another embodiment of the resonator used in the present invention composed of the resonators shown in FIGS. 1a and 1b. It is sectional drawing which shows typically the conventional resonator for comparison with the resonator used in this invention. FIG. 5 is a cross-sectional view schematically showing a conventional resonator having a piezoelectric layer having a thickness different from that of FIG. 2c. 2 is a cross-sectional view schematically showing a conventional resonator having a piezoelectric layer having a thickness different from that of FIGS. 2c and 2d. It is a block diagram which shows the resonator of this invention which is constructed by connecting the resonators shown in FIGS. 1a to 1c in series. FIG. 5 is a configuration diagram showing a resonator of the present invention configured by connecting the resonators shown in FIGS. 1a to 1c in parallel. FIG. 5 is a configuration diagram showing a resonator of the present invention configured by connecting the resonators shown in FIGS. 1a and 1b in series. FIG. 5 is a configuration diagram showing a resonator of the present invention configured by connecting the resonators shown in FIGS. 1a and 1b in parallel. It is a top view which shows the resonator shown in FIG. 3a more concretely. It is a top view which shows the resonator shown in FIG. 3b more concretely. FIG. 5 is a partially enlarged view of FIG. 4 for explaining the relationship between the resonance frequency and the electrode period in the resonator. It is a correlation diagram which shows the relationship between the thickness of the piezoelectric layer in a resonator and the sound velocity of an elastic wave. 3 is a characteristic diagram showing an amount of attenuation with respect to the frequency of the conventional resonator shown in FIGS. 3c to 3e. It is a characteristic diagram which shows the admittance with respect to the frequency of the resonator shown in FIG. 3a. It is a characteristic diagram which shows the admittance with respect to the frequency of the resonator shown in FIG. 3b. It is a characteristic diagram which shows the admittance with respect to the frequency of the resonator shown in FIG. 3c. It is a characteristic diagram which shows the admittance with respect to the frequency of the resonator shown in FIG. 3d. FIG. 3 is a process diagram showing an example of a process of forming piezoelectric layers having different thicknesses constituting the resonator shown in FIG. 2a. It is a block diagram which shows an example of the surface elastic wave filter of this invention constructed in a rudder structure. It is a block diagram which shows another example of the surface elastic wave filter of this invention constructed in a rudder structure. It is a block diagram which shows an example of the module constructed by using the surface elastic wave filter of this invention. It is a block diagram which shows an example of the duplexer constructed by using the surface elastic wave filter of this invention. It is a block diagram which shows an example of the module configured by using the duplexer of FIG.

1a to 1c are a cross-sectional view (shown on the right side) and a schematic view (shown on the left side) schematically showing one of the resonators for forming the surface elastic wave filter of the present invention, respectively. The resonators 1A, 1B, and 1C are provided between the carrier substrate 2, the piezoelectric layers 4 having different thicknesses, the IDT electrode 5 formed on the piezoelectric layer 4, and the carrier substrate 2 and the piezoelectric layer 4. It is provided with the intermediate layer 3 provided. Each resonator 1A, 1B, 1C excites the main vibration in SH mode.

The carrier substrate 2 is made of a high-resistance semiconductor or insulator, and for example, silicon having a non-amorphous crystalline form or crystalline sapphire is used. The material used for the carrier substrate 2 is not limited to these, and other materials such as polycrystalline silicon, polycrystalline Al ₂ O ₃ , and polycrystalline sapphire can be used as long as they can solve the problems of the present invention. May be good.

Lithium tantalate (LiTaO ₃ ) (hereinafter sometimes referred to as LT) or lithium niobate (LiNbO ₃ ) (hereinafter sometimes referred to as LN) is used for the piezoelectric layer 4. However, the piezoelectric layer 4 is not limited to those made of these materials, and those made of other materials can also be used.

For the IDT electrode 5, for example, Al, Au, Cu, Ni, Pt, Ti, Cr, Ag or an alloy thereof can be used, but other metals or alloys may be used.

The intermediate layer 3 is a layer provided for at least one of the purposes of increasing the bonding strength between the carrier substrate 2 and the piezoelectric layer 4 or increasing the propagation speed of elastic waves. When provided for the purpose of increasing the bonding strength between the carrier substrate 2 and the piezoelectric layer 4, for example, silicon dioxide (SiO ₂ ) or the like is used for the intermediate layer 3. Further, when providing the intermediate layer 3, for example, aluminum nitride (AlN) or boron nitride aluminum _{(B X Al 1-X N} ) or the like is used as a high-speed layer of the elastic wave.

When manufacturing such an elastic wave device 1, it is effective to use a piezoelectric layer 4 as thin as possible in order to improve the Q value. As the piezoelectric layer 4, for example, an LT having a Y-cut X propagation of 15 ° to 52 ° is used.

The points that the resonators 1A, 1B, and 1C shown in FIGS. 1a to 1c are different from each other are that the thicknesses t1, t2, and t3 of the piezoelectric layer 4 are different from each other (t1> t2> t3). As shown in FIG. 2a, the resonator for forming the surface elastic wave filter of the present invention is provided with, for example, resonators 1A, 1B, and 1C as an integral resonator. Then, the thickness of the piezoelectric layer 4 in the region where the resonators 1A, 1B, and 1C are arranged is configured to be different by at least two types. Alternatively, for example, as shown in FIG. 2b, for example, the resonators 1A and 1B may be provided as an integral resonator, and the thickness of the piezoelectric layer 4 in the region where the resonators 1A and 1B are arranged may be different. Good. When there are three resonators as shown in FIG. 2a, the spurious suppression effect can be suppressed to some extent even if the thickness of the piezoelectric layer in the three regions is configured to be only two types (for example, t1 = t2> t3). ..

2c to 2e show resonators 6X, 6Y, and 6Z having a conventional configuration in which the thickness of the piezoelectric layer 4 is different (the thickness of the piezoelectric layer 4 is t1, t2, and t3, respectively). These resonators 6X, 6Y, and 6Z are comparative examples shown for explaining the spurious suppression effect according to the present invention.

3a to 3d are block diagrams showing the resonators 6A to 6D of the present invention configured by using the resonators 1A, 1B, and 1C. The resonator 6A of FIG. 3a shows an example in which resonators 1A, 1B, and 1C having different thicknesses of the piezoelectric layer 4 are connected in series. The resonator 6B of FIG. 3b shows an example in which resonators 1A, 1B, and 1C having different thicknesses of the piezoelectric layer 4 are connected in parallel. The resonator 6C of FIG. 3c shows an example in which resonators 1A and 1B having different thicknesses of the piezoelectric layer 4 are connected in series. The resonator 6D of FIG. 3d shows an example in which resonators 1A and 1B having different thicknesses of the piezoelectric layer 4 are connected in parallel.

FIG. 4 is a plan view showing more concretely the resonator 6A configured by connecting the resonators 1A, 1B, and 1C in series as shown in FIG. 3a. Each resonator 1A, 1B, 1C is configured by providing reflectors 7 on both sides of an IDT electrode 5, which is a comb-shaped electrode. The resonators 1A, 1B, and 1C are connected in series with each other, and a first port 8A is provided at one end of the series connection circuit, and a second port 9A is provided at the other end.

FIG. 5 is a plan view showing more concretely the resonator 6B configured by connecting the resonators 1A, 1B, and 1C in parallel as shown in FIG. 3b. Each resonator 1A, 1B, 1C is configured by providing reflectors 7 on both sides of an IDT electrode 5, which is a comb-shaped electrode. A first port 8B is provided at one end of the IDT electrodes 5 connected in parallel to each other of the resonator 6B, and a second port 9B is provided at the other end.

When two resonators 1A and 1B are connected in series to form a resonator 6C (see FIG. 3c), the resonator 1C is excluded from FIG. When two resonators 1A and 1B are connected in parallel to form a resonator (see FIG. 3d), the resonator 1C is excluded from FIG.

For example, as shown in FIG. 4, when a high-frequency signal is input between the first port 8A and the second port 9A, an electric field is generated between the individual electrodes of the IDT electrode 5, and the surface acoustic wave is excited to be piezoelectric. It propagates on the layer 4 and is reflected by the reflector 7 to generate an electrical resonance. The resonance frequency f _R is determined by λ, which is the wavelength of the surface acoustic wave propagating in the piezoelectric layer 4, and the electrode period P, and the electrode period P (see FIG. 6) is determined by P = λ / 2. ..

Next, according to the present invention, when the thickness of the piezoelectric layer 4 on which the IDT electrode 5 is provided is different, the verification result that the spurious suppressing effect is obtained will be described. This verification was performed by simulation. That is, as shown in FIGS. 2c to 2e, the thickness of each piezoelectric layer 4 of the resonators 6X, 6Y, and 6Z is made uniform with t1, t2, and t3, respectively, and the present invention shown in FIGS. 3a to 3d. The spurious suppression effect was compared with the resonators 6A to 6D. Here, as a constituent material of the surface elastic wave filter to be verified, silicon having a thickness of 200 μm was used for the carrier substrate 2 in common with the resonator of the present invention and the resonator of the conventional example.

The materials of the resonator of the present invention and other components of the conventional resonator are as shown in Table 1. That is, Al was used for the IDT electrode 5, LT was used for the piezoelectric layer 4, and silicon dioxide was used for the intermediate layer 3. Further, the period P (= λ / 2) of the IDT electrode 5 is 0.9 μm (λ = 1.8 μm), the thickness of the piezoelectric layer 4 of the resonator 1A is 0.3λ (0.54 μm), and the resonator 1B. The thickness of the piezoelectric layer 4 was set to 0.25λ (0.45 μm), and the thickness of the piezoelectric layer 4 of the resonator 1C was set to 0.2λ (0.36 μm). The thickness of the intermediate layer 3 of the resonator 1A was 0.08λ (0.14 μm), and the thickness of the intermediate layer 3 of the resonators 1B and 1C was 0.06λ (0.11 μm). The thickness of the IDT electrode 5 was 0.08λ (0.14 μm).

FIG. 8 is a characteristic diagram showing the admittance (dB siemens) for the frequencies of the resonators 6X, 6Y, and 6Z of the comparative examples shown in FIGS. 3c to 3e in one graph. The resonators 6X, 6Y, and 6Z have a configuration in which three resonators 1A, 1B, and 1C are connected in parallel, respectively. As shown in FIG. 8, when the thickness of the piezoelectric layer 4 is different as shown in 1A, 1B, and 1C of Table 1 (the thickness of the piezoelectric layer 4 of the resonator 6A is t1, 6B is t2, and 6C is t3). _{The resonance frequency f R} and the anti-resonance frequency f _A of the fundamental wave near 2 GHz hardly change. However, the frequency at which high-frequency spurious emission near 2.8 GHz is generated shifts to a higher side as the thickness of the piezoelectric layer 4 becomes thinner.

The reason for this can be explained as follows. As shown in FIG. 7, when the thickness of the piezoelectric layer 4 becomes thin, the speed of sound of elastic waves in the piezoelectric layer 4 becomes large. Spurious is often caused by simultaneous excitation of vibrations in different vibration modes, but in a structure in which a thin piezoelectric layer 4 is formed on a carrier substrate 2, the dependence of the speed of sound in the piezoelectric layer 4 on the piezoelectric layer thickness. Depends on the vibration mode. That is, in the vibration mode of the fundamental wave, the degree of increase in the speed of sound due to the thinning of the film thickness is larger than the degree of increase in the speed of sound due to the thinning of the film thickness in the spurious vibration mode. Therefore, it can be explained that the frequency at which spurious is generated increases as the thickness of the piezoelectric layer 4 becomes thinner. As shown in FIG. 5, the difference between the maximum admittance and the minimum admittance in the spurious generation frequency band in these resonators 6X, 6Y, and 6Z was 32 dB.

FIG. 9 is a characteristic diagram showing the admittance with respect to the frequency of the resonator 6A shown in FIGS. 3a and 4, that is, the resonators 1A, 1B, and 1C having different thicknesses connected in series. As described above, the difference between the maximum admittance and the minimum admittance in each spurious generation frequency band was 20 dB, which was significantly smaller than that of the individual resonators 6X, 6Y, and 6Z. In this way, the difference between the maximum admittance and the minimum admittance in the spurious generation frequency band, in other words, the reason why the sprias is significantly reduced, is that the resonance frequencies and anti-resonance frequencies of the resonators 1A, 1B, and 1C in the resonator 6A are almost the same. It is the same, and by changing the thickness of the piezoelectric layer 4, the spurious frequencies higher than the frequency and anti-resonant frequency are dispersed differently, and the resonators 1A, 1B, and 1C are electrically connected in series. This is because the level is reduced as a result of synthesizing the spears dispersed in the resonators 1A, 1B, and 1C for each region where the thickness of the piezoelectric layer 4 is different.

FIG. 10 is a characteristic diagram showing the admittance with respect to the frequency of the resonator 6B shown in FIGS. 3b and 5, that is, the resonators 1A, 1B, and 1C having different thicknesses connected in parallel. In the case of the resonator 6B as well, the difference between the maximum admittance and the minimum admittance in the spurious generation frequency band was 20 dB, which was significantly smaller than that of the individual resonators 6X, 6Y, and 6Z. The reason why the spurious is significantly reduced is that the spurious frequency is increased in each region where the thickness of the piezoelectric layer 4 of each resonator 1A, 1B, 1C is different, as in the case of the resonator 6A shown in FIG. This is because the dispersed spurs of the resonators 1A, 1B, and 1C were synthesized because they were dispersed differently and these resonators 1A, 1B, and 1C were connected in parallel.

FIG. 11 is a characteristic diagram showing the amount of attenuation with respect to the frequency of the resonator 6C shown in FIG. 3c, that is, the resonator 6C configured by connecting the resonators 1A and 1B having different thicknesses in series. In the case of the resonator 6C as well, the difference between the maximum admittance and the minimum admittance in the spurious generation frequency band was 25 dB, which was smaller than that of the individual resonators 6X, 6Y, and 6Z. The reason for the decrease in spurious is that the frequency at which spurious is generated is dispersed in each region where the thickness of the piezoelectric layer 4 is different, as in the case of the resonators 6A and 6B shown in FIGS. 8 and 9. Is. The reason why the degree of suppression of sprias is smaller in the case of the resonator 6C having two types of piezoelectric layer 4 thicknesses than in the case of the resonators 6A and 6B having three types of piezoelectric layer 4 thicknesses. This is because the strength of the spear generated in the individual regions having different thicknesses of the piezoelectric layer 4 is higher in the case of the resonator 6C than in the case of the resonators 6A and 6B.

FIG. 12 is a characteristic diagram showing admittance with respect to the frequency of the resonator 6D shown in FIG. 3d, that is, the resonator 6D configured by connecting the resonators 1A and 1B having different thicknesses in parallel. In the case of the resonator 6D as well, the difference between the maximum admittance and the minimum admittance in the spurious generation frequency band was 25 dB, which was smaller than that of the individual resonators 6X, 6Y, and 6Z. As described above, the reason why the spurious of the resonator 6D is suppressed and the reason why the spurious is larger than that of the resonators 6A and 6B are the same as in the case of the resonator 6C shown in FIG.

FIG. 13 is a process diagram showing an example of a process of forming the piezoelectric layer 4 so that the thickness is different from that of t1, t2, and t3. As shown in FIG. 13A, a resist 10a is formed on the surface of the piezoelectric layer 4 in a region 4a where the thickness is not reduced, that is, a region where the thickness should be t1. Then, the region 4b on which the resist 10a is not formed is etched by irradiation with ions 11 such as argon gas ions to form a thin region 4c of the piezoelectric layer 4 as shown in FIG. 13 (b). .. Subsequently, when a region of a thinner piezoelectric layer is obtained, resists 10a and 10b are left or newly formed in the regions 4a and 4c to be left as the thicknesses t1 and t2, as shown in FIG. 13 (c). , The remaining region 4d is irradiated with ions 11 to perform etching. As a result, as shown in FIG. 13D, the resists 10a and 10b are removed after forming the region 4e having a thickness of t3, which is thinner than the region 4c.

After forming a plurality of regions 4a, 4c, and 4e having different thicknesses in the piezoelectric layer 4 in this way, IDT electrodes 5 are formed in the respective regions 4a, 4c, and 4e by using a photolithography technique.

The thicknesses t1, t2, and t3 of the regions 4a, 4b, and 4c having different thicknesses of the piezoelectric layer 4 are the regions 4b (the regions 4b) having the next smallest thickness with respect to the thickness t1 (t2) of a certain region 4a (4b). It is preferable to set the thickness t2 (t3) of 4c) so as to be smaller by 10% or more with a gradual decrease in thickness. Theoretically, if a slight difference in thickness is provided, the spurious frequencies will be displaced and dispersed, so that the difference between the maximum spurious attenuation amount and the minimum spurious attenuation amount will decrease. However, by providing the above-mentioned difference of 10% or more as a difference in thickness to some extent, the frequencies of spurious generated in each region 4a, 4b, and 4c can be clearly dispersed so as not to overlap, so that the maximum attenuation is achieved. This is because the difference between the amount and the minimum attenuation amount is large because the degree of decrease is large. In the above numerical example,
t2 / t1 = 0.25 / 0.3 = 0.83
t3 / t2 = 0.2 / 0.25 = 0.80
The difference in thickness between the regions 4a and 4c of the piezoelectric layer 4 is 1-0.83 = 0.17 (17%), and the difference in thickness between the regions 4c and 4e of the piezoelectric layer 4 is 1-0. .80 = 0.20 (20%).

When the piezoelectric layer 4 is made of LT, the intermediate layer 3 is made of silicon dioxide, and the carrier substrate 2 is made of silicon, the thickness of the piezoelectric layer 4 is preferably 1.5 λ or less. This is because when the thickness of the piezoelectric layer 4 is larger than 1.5λ, the guiding action of guiding the surface acoustic wave along the piezoelectric layer 4 due to the thinning of the piezoelectric layer 4 is reduced, resulting in a decrease in the Q value.

The thickness of the piezoelectric layer 4 is preferably 0.15λ or more for the following reasons. When, for example, an LT of 42 ° Y-cut X propagation is used as the piezoelectric layer 4, silicon dioxide is used for the intermediate layer 3, and silicon is used for the carrier substrate 2, when the thickness of the piezoelectric layer 4 is changed, electromechanical coupling is performed. The coefficient K2 (%) changes. As described above, when the piezoelectric layer 4 is provided on the carrier substrate 2 via, for example, an intermediate layer 3 having a thickness of 0.08λ, the thickness of the piezoelectric layer 4 is 0.15λ and the electromechanical coupling coefficient K2 shows a peak. If it is smaller than 0.15λ, the change in the electromechanical coupling coefficient K2 starts to deteriorate significantly, so that the characteristics become unstable and the yield decreases. Therefore, the thickness of the piezoelectric layer 4 is preferably 0.15λ or more.

In the above example, the case where silicon dioxide is used as the intermediate layer 3 has been described, but if a material for speeding up the propagation of elastic waves such as aluminum nitride or boron nitride aluminum is used as the intermediate layer 3, the surface to be propagated is used. It is possible to increase the propagation speed of surface acoustic waves and improve the characteristics at higher frequencies.

When carrying out the present invention, the intermediate layer 3 may be eliminated and the piezoelectric layer 4 and the carrier substrate 2 may be directly bonded. Also in this case, the effect of improving the Q value by the guiding action of the surface acoustic wave by thinning the piezoelectric layer 4 can be obtained as in the case where the intermediate layer is provided. However, the effect may be inferior to the case where the intermediate layer 3 is present.

Further, when carrying out the present invention, two layers, a first layer and a second layer, may be provided as the intermediate layer 3. In that case, a high-speed layer can be used as the first layer on the piezoelectric layer 4 side, and a layer for strengthening the bond can be used as the second layer on the carrier substrate 2 side. That is, by using aluminum nitride, boron nitride, or the like as the first layer and silicon dioxide or the like as the second layer, the effects of improving the Q value and improving the bond strength can be obtained. In addition, it is also possible to use silicon dioxide as the first layer and aluminum nitride, boron nitride aluminum or the like as the second layer. It is also possible to adopt a layer structure of three or more layers as the intermediate layer 3.

Further, a silicon polycrystalline layer may be provided on the bonding layer between the piezoelectric layer 4 and the carrier substrate 2. Providing a silicon polycrystalline layer in the bonding layer has the effect of suppressing high-frequency leakage current, and when the piezoelectric layer is thinned near the high-frequency wavelength, it has the effect of suppressing high-frequency noise.

FIG. 14a shows a surface elastic wave filter assembled in a ladder shape by resonators S1 to S4 forming series arms and resonators P1 to P3 forming parallel arms. This surface elastic wave filter has an input port 13 and an output port 14 at both ends of resonators S1 to S4 connected in series with each other. The resonators P1, P2, and P3 forming the parallel arm are inserted between the line 15 connecting the resonators S1 to S4 forming the series arm and the ground 16, respectively. In this configuration, by providing the piezoelectric layers having different thicknesses to each of the resonators S1 to S4 constituting the series arm, the effect of reducing spurious can be obtained. The effect of reducing spurious can be obtained even if the thicknesses of the piezoelectric layers 4 of two or more resonators of the resonators S1 to S4 are different.

The effect of reducing spurious can be obtained even if the thickness of the piezoelectric layer of all or two resonators P1 to P3 forming the parallel arm is different from that of the resonators S1 to S4 forming the series arm. Even if two or more of the resonators S1 to S4 forming the series arm and two or more of the resonators P1 to P3 forming the parallel arm are configured with different thicknesses of the piezoelectric layer 4, the spurious is generated. The effect of reduction can be obtained. The number of resonators S1 to S4 and P1 to P3 assembled in the ladder type is arbitrarily changed according to the application.

FIG. 14b shows a surface elastic wave filter of a modified example of FIG. 14a, and two resonances of a part of the resonators S1 to S4 and P1 to P3 of FIG. 14a (in this example, the first-stage resonator S1 of the series arm). It is divided into vessels S11 and S12, and the thicknesses of the piezoelectric layers 4 of these resonators S11 and S12 are made different, and they are connected in series with each other. The thickness of the piezoelectric layer 4 of the other resonators S2 to S4 and P1 to P3 is the same. By dividing a part of the resonators and making the thickness of the divided piezoelectric layers different in this way, it is possible to reduce the spurious generated in the resonators S11 and S12, and the influence of the spurious is reduced. can do. Even if the resonators S11 and S12 are connected in parallel with each other, the effect of reducing spurious can be obtained.

In the surface elastic wave filter of FIG. 14b, at least a part of the other resonators S2 to S4 and P1 to P3 are also configured by having different thicknesses of the piezoelectric layers 4 and connecting them in series or in parallel with each other. However, the influence of spurious can be reduced. All the resonators S1 to S4 and P1 to P3 may be divided into resonators having different piezoelectric layer thicknesses and connected in series or in parallel. However, if the number of divided resonators is increased, the resonators may be divided. In some cases, it may be preferable to divide only a part of the resonator and connect it in series or in parallel due to design optimization because the required area is increased.

FIG. 15 shows an example of the module 21 by the receiving filter 20 using the surface elastic wave filter according to the present invention configured as shown in FIGS. 3a to 3d or 14a or 14b, for example. This module 21 is used in a mobile communication device that handles a plurality of different transmission / reception signals. This module 21 includes a plurality of receiving filters 20 configured by a surface elastic wave filter according to the present invention corresponding to each frequency, a low noise amplifier (LNA) 22 provided corresponding to each receiving filter 20, and a plurality of receiving filters. A switch circuit 23 inserted between the 20 and an antenna port (not shown) is included.

The module 21 may also include other passive elements and circuits required when forming a receiving circuit. Further, the module 21 may be configured by combining with other circuits.

As shown in FIG. 15, even in the module 21 using the surface elastic wave filter 20 of the present invention, the module 21 in which high-frequency spurious is suppressed can be realized.

FIG. 16 shows an example of a duplexer 27 using a transmission filter 25 and a reception filter 26 configured by using the surface elastic wave filter according to the present invention. As the transmission filter 25 and the reception filter 26 shown in FIG. 16, for example, a surface acoustic wave filter having resonators 6A to 6D of FIGS. 3a to 3d, or a surface acoustic wave filter configured as shown in FIGS. 14a or 14b was used. It is a thing. The duplexer 27 is used in a mobile communication device in which the frequency band of the transmission signal and the frequency band of the reception signal are close to each other. The transmission filter 25 is inserted between an antenna port 28 connected to an antenna (not shown) and a transmission circuit connection port 29 connected to a transmission circuit (not shown). The reception filter 26 is inserted between the antenna port 28 and the reception circuit connection port 30 connected to a reception circuit (not shown). The antenna port 28 and the ground are connected by an appropriate impedance element 31, and this element 31 is also included in a part of the duplexer 27. By constructing the duplexer 27 using the surface elastic wave filter of the present invention in this way, the duplexer 27 in which high-frequency spurious is suppressed can be realized.

FIG. 17 shows an example of the module 33 configured by using the duplexer 27 according to the present invention. This module 33 is used in a mobile communication device that handles a plurality of different transmission / reception signals. The module 33 includes a plurality of duplexers 27 shown in FIG. 16, a power amplifier 35 inserted into a transmission circuit 34 provided corresponding to each duplexer 27, and a reception circuit 36. A switch circuit 37 is inserted between the plurality of duplexers 27 and an antenna port (not shown), and this switch circuit 37 is also included in the module 33.

The module 33 may also include other passive elements and circuits required when forming a transmission / reception circuit. Further, the module 33 may be configured by combining the duplexer 27 and a circuit other than the power amplifier 35.

As shown in FIG. 17, even in the module 33 using the duplexer 27 including the surface elastic wave filter of the present invention, the module 33 in which the high frequency spurious is suppressed can be realized.

The present invention has been described above, but the present invention is not limited to the above-described embodiment, and various modifications and additions can be made without departing from the gist of the present invention.

1A to 1C ... Resonator 2 ... Carrier substrate 3 ... Intermediate layer 4 ... Piezoelectric layer 5 ... IDT electrode 7 ... Reflectors 6A to 6D ... Resonators 21, 33 ... Module 27 ... Duplexers S1 to S4, S11, S12, P1 to P3 ... Resonator t1, t2, t3 ... Region where the resonator is arranged

Claims (7)

A surface elastic wave filter having a carrier substrate, a piezoelectric layer made of a piezoelectric material provided on the carrier substrate, and a resonator having an IDT electrode formed on the piezoelectric layer.
The carrier substrate is composed of a high resistance semiconductor or an insulator.
The piezoelectric layer has a thickness of 0.15λ to 1.5λ, where λ is the wavelength of the elastic wave determined by the electrode period of the IDT electrode.
The piezoelectric layer provided on the carrier substrate includes a plurality of regions having different thicknesses.
A resonator having an IDT electrode in each of the plurality of regions is configured.
A surface elastic wave filter having a resonator formed by connecting resonators formed on the plurality of regions. In the surface elastic wave filter according to claim 1,
The thickness of the plurality of regions of the piezoelectric layer is gradually reduced so that the thickness of the region having the next smallest thickness is reduced by 10% or more with respect to the thickness of a certain region. Set,
A surface elastic wave filter including a portion in which IDT electrodes formed on the plurality of regions are connected in series or in parallel. In the surface elastic wave filter according to claim 1 or 2.
A surface elastic wave filter in which the main vibration of the piezoelectric vibration excited by the piezoelectric layer is in SH mode. In the surface elastic wave filter according to any one of claims 1 to 3,
A surface acoustic wave filter comprising one or a plurality of intermediate layers between the carrier substrate and the piezoelectric layer, which serve at least one of the functions of facilitating the coupling between the two and increasing the speed of sound of a surface acoustic wave. A module including the surface elastic wave filter according to any one of claims 1 to 4. A duplexer comprising the surface elastic wave filter according to any one of claims 1 to 4. A module configured to include the duplexer according to claim 6.

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