JP4836748B2 - Bulk acoustic wave resonator, filter device, and communication device - Google Patents

Description

  The present invention relates to a bulk acoustic wave resonator which is a kind of piezoelectric resonator, a filter device using the same, and a communication device, and more particularly, a bulk acoustic wave resonator including a resonance part made of a piezoelectric body formed by a thin film process, and The present invention relates to a filter device using the same and a communication device including the filter device.

  In recent years, a resonator using a thin film thickness longitudinal vibration mode exhibiting piezoelectricity has been proposed. This is a resonator that uses the piezoelectric body to cause longitudinal vibration in the thickness of the input high-frequency electrical signal, and the vibration causes resonance in the thickness direction of the thin film. being called. In addition, since a piezoelectric body formed by a thin film process is used, it is also called a thin film bulk acoustic-wave resonator (FBAR). The bulk acoustic wave resonator has a structure in which a resonance part is formed on a substrate by sequentially laminating a lower electrode, a piezoelectric body, and an upper electrode by a thin film process.

  FIG. 8A shows a cross-sectional view of an example of a bulk acoustic wave resonator. In FIG. 8A, reference numeral 101 denotes a base body, 102 denotes a through hole, 103 denotes a lower electrode, 104 denotes a piezoelectric body, and 105 denotes an upper electrode. The resonating portion is a portion where the lower electrode 103, the piezoelectric body 104, and the upper electrode 105 overlap with each other, and is configured such that an acoustic wave resonates at the resonating portion. Further, the resonance part is acoustically isolated from the base body 101 by the through hole 102. In addition to this, the actual bulk acoustic wave resonator requires a frequency adjustment layer, a protective layer, etc., but in FIG. 8A, they are omitted and only the basic configuration is shown. FIG. 8A shows an example in which two bulk acoustic wave resonators are connected in series.

The resonant frequency of the bulk acoustic wave resonator is determined by the film thickness of each layer constituting the bulk acoustic wave resonator. For example, in the example of FIG. 8A, if the film thicknesses of the lower electrode 103 and the upper electrode 105 are ignored, the resonance is
d = λ / 2
Occurs when the condition is met. Here, d is the film thickness of the piezoelectric body 104, and λ is the wavelength of the acoustic wave propagating through the piezoelectric body 104. When the film thickness of the lower electrode 103 and the upper electrode 105 cannot be ignored, the resonance frequency is slightly lower than when the film thickness can be ignored. Actually, it is necessary to design the bulk acoustic wave resonator in consideration of the protective film and the frequency adjusting film which are omitted in FIG.

Further, similarly to the surface acoustic wave resonator, the bulk acoustic wave resonator has a resonance frequency f0 (frequency at which the impedance is minimized) and an anti-resonance frequency fa (frequency at which the impedance is maximized), and the difference therebetween. (Frequency difference) is determined by an effective electromechanical coupling coefficient (k _eff ² ). The effective electromechanical coupling coefficient is determined by the electromechanical coupling coefficient, which is a material constant of the piezoelectric body, and the material constant and structure of the layers constituting the bulk acoustic wave resonator such as the piezoelectric body, the electrode, and the protective film.

  When a filter is configured using this bulk acoustic wave resonator, as shown in FIG. 8B, a plurality of bulk acoustic wave resonators whose frequencies are slightly shifted are connected in series and in parallel, A so-called ladder-type filter is generally used. In FIG. 8B, 200 is a series resonator in which bulk acoustic wave resonators are connected in series, and 201 is a parallel resonator in which bulk acoustic wave resonators are connected in parallel. Basically, the resonance frequency of each resonator is set so that the resonance frequency f0 of the series resonator 200 and the antiresonance frequency fa of the parallel resonator 201 become the center frequency of the passband of the filter. Further, the antiresonance frequency fa of the series resonator 200 and the resonance frequency f0 of the parallel resonator 201 are blocking frequencies. For this reason, the bandwidth of the ladder filter is substantially equal to the frequency difference of the bulk acoustic wave resonator.

It has also been proposed to obtain a steep attenuation characteristic by changing the effective electromechanical coupling coefficient of each resonator (see Patent Document 1).
JP 2003-22074 A

  When a filter is configured with a bulk acoustic wave resonator, it has been desired to adjust the resonance frequency and the frequency difference in order to obtain desired filter characteristics.

  However, the frequency difference could not be adjusted by changing the film thickness of the resonance part or providing a frequency adjustment film in order to adjust the resonance frequency. In addition, the frequency difference of the bulk acoustic wave resonator is almost determined by the material of the piezoelectric body to be used, and changes slightly even if the material and film thickness of each layer other than the piezoelectric body constituting the bulk acoustic wave resonator are changed. Therefore, there were the following problems.

  1. In order to obtain a desired frequency difference, it is necessary to change the piezoelectric material, so that it is necessary to develop a new material or to develop a special manufacturing process different from the standard.

  2. When bulk acoustic wave resonators having different frequency differences are formed on the same substrate, it is necessary to form two types of piezoelectric bodies on the same substrate, and at the same time, the resonance frequency of each resonator is set to a desired value. For this reason, it is necessary to independently adjust the thicknesses of the piezoelectric bodies and electrodes of the respective resonators, and the design and manufacturing process become very complicated.

  3. By adjusting the thickness of the piezoelectric body and the material and thickness of the electrode, a resonator having a different frequency difference may be realized by using one type of piezoelectric body, but the range that can be adjusted is limited. In order to set the resonance frequency and frequency difference of the resonator to desired values, the design of the thickness and material of the piezoelectric body and electrodes becomes very complicated. Moreover, it is necessary to form piezoelectric bodies and electrodes having different thicknesses on the same substrate, which makes the manufacturing process very complicated.

  As described above, it is very difficult to obtain a resonator having a desired frequency difference. Further, in order to realize a filter having a desired characteristic by combining resonators having adjusted frequency differences as described above, As described above, the design and manufacturing processes are complicated, so that the reliability is poor and the productivity is low.

  The present invention has been devised in view of the problems in the prior art as described above, and its purpose is to provide a bulk acoustic wave resonator that can freely set a frequency difference, and has higher performance and higher productivity. It is to provide.

  Another object of the present invention is to provide a filter device with high productivity and good blocking characteristics, and a communication device with high productivity and good sensitivity.

  The bulk acoustic wave resonator of the present invention is provided on at least one of a resonance part including 1) a piezoelectric body and a pair of electrodes that sandwich the piezoelectric body in a thickness direction, and the thickness direction of the resonance part. And an adjustment film having a thickness of approximately 0.5λ × n.

  However, (lambda) is the wavelength of the acoustic wave which propagates in the thickness direction in the adjustment film | membrane in a use frequency, and n is a natural number.

  In the bulk acoustic wave resonator according to the present invention, 2) in the configuration of 1) described above, the adjustment film is made of a metal material.

  In the bulk acoustic wave resonator according to the present invention, 3) in the configuration of 1) or 2) described above, the adjustment film has a thickness shifted by a predetermined amount from the value of 0.5λ × n, and The resonance frequency or anti-resonance frequency is adjusted to a predetermined target value.

  In the bulk acoustic wave resonator according to the present invention, 4) in any one of the configurations 1) to 3), the peripheral portion of the adjustment film coincides with the peripheral portion in a cross section perpendicular to the thickness direction of the resonant portion. To do.

  The filter device of the present invention includes 5) an input terminal, an output terminal, and a reference potential terminal, on an input / output line connecting the input terminal and the output terminal, or on the input / output line and the reference potential terminal. The bulk acoustic wave resonator according to any one of 1) to 4) above is provided.

  The communication device of the present invention includes at least one of 6) a reception circuit or a transmission circuit, and the filter device described in 5) above is used for the reception circuit or the transmission circuit.

  A communication device of the present invention includes 7) the filter device according to 5) above and at least one of a reception circuit or a transmission circuit.

  According to the bulk acoustic wave resonator of the present invention, the thickness of the adjustment film is approximately 0.5λ × n (λ is the wavelength of the acoustic wave in the adjustment film at the operating frequency, and n is a natural number) due to the configuration of 1). Therefore, it resonates at the same frequency as the resonance frequency designed in the resonance part. As a result, it is possible to change only the effective electromechanical coupling coefficient and the frequency difference according to the thickness of the adjustment film and the material without substantially changing the resonance frequency or the antiresonance frequency. Specifically, in order to adjust the frequency difference with the thickness of the adjustment film, the frequency difference can be reduced by increasing n. For this reason, a frequency difference can be set freely and a higher performance bulk acoustic wave resonator can be provided at low cost. Thus, the bulk acoustic wave resonator according to the present invention is based on the finding that the adjustment film has a frequency difference adjusting function only when the thickness of the adjustment film is approximately 0.5λ × n. is there.

  In addition, the effective electromechanical coupling coefficient and frequency difference can be changed freely by adjusting the thickness and material of the bulk acoustic wave resonator by adjusting the thickness and material without changing the material and film thickness of the resonator. Will be able to. As a result, the degree of freedom in design is increased, and a highly productive bulk acoustic wave resonator having desired characteristics can be provided.

  Further, the frequency difference of the bulk acoustic wave resonator can be further adjusted by setting the thickness of the adjustment film to the above value and selecting the material of the adjustment film. That is, for the adjustment film, when the material is determined based on the target value of the effective electromechanical coupling coefficient of the resonance part, the material of the adjustment film is selected without changing the material and film thickness of the resonance part. Thus, a desired frequency difference based on a desired effective electromechanical coupling coefficient can be obtained. For this reason, a higher performance bulk acoustic wave resonator can be provided at low cost.

  Further, according to the bulk acoustic wave resonator of the present invention, the adjustment film has a function of substantially increasing the thickness of the electrode formed on one side in the thickness direction of the resonance portion by the configuration of 2). As a result, the loss can be reduced.

  Further, according to the bulk acoustic wave resonator of the present invention, by adjusting the material of the adjustment film having a thickness of approximately 0.5λ × n and the size of n by the configuration of 3), A desired frequency difference is obtained without changing the film thickness and the like, and the thickness of the adjustment film is shifted from the value of 0.5λ × n by a predetermined amount, thereby maintaining a desired frequency difference and a desired resonance frequency or counter-frequency. A resonance frequency can also be obtained. For this reason, it becomes possible to provide a bulk acoustic wave resonator having higher performance and higher design freedom at a low cost.

  In addition, according to the bulk acoustic wave resonator of the present invention, it is possible to prevent the occurrence of parasitic capacitance due to the adjustment film by the configuration 4) and to achieve high performance that resonates at a desired resonance frequency. Further, since the adjustment film can be formed and processed simultaneously with the electrode, desired characteristics can be obtained without increasing the number of steps, and the productivity can be increased.

  Further, according to the filter device of the present invention, the bulk acoustic wave resonator of each configuration having a high degree of design freedom is used as the resonator constituting the filter device by the configuration of 5). Compared to a filter device using a technical FBAR, a filter having a high degree of design freedom can be configured. In addition, since such a filter device can be manufactured simply by adding the adjustment film forming step, a high-performance filter device with better blocking characteristics can be provided at low cost, and the productivity is high. be able to.

  Further, according to the communication device of the present invention, the filter device adjusted to have a desired characteristic can be used with the configuration of 6), so that the removal performance of unnecessary waves in the circuit can be improved. It is possible to achieve high performance. In addition, since a circuit can be configured using a low-cost filter device, a communication device with better performance can be provided at low cost.

  Furthermore, according to the communication device of the present invention, the communication device can be configured by using the low-cost filter device adjusted to have the desired characteristics by the configuration of 7). Can be provided.

  Hereinafter, embodiments of a bulk acoustic wave resonator, a filter device, and a communication device of the present invention will be described in detail with reference to the drawings.

  An example of an embodiment of a bulk acoustic wave resonator of the present invention is shown in FIG. 1 (a) as a plan view, and FIG. 1 (b) as a cross-sectional view taken along line A-A 'in FIG. In the drawings, the dimensions of each part are appropriately enlarged so that the structure of the bulk acoustic wave resonator can be easily understood. FIG. 1 shows a conventional bulk acoustic wave resonator on the left side and a bulk acoustic wave resonator of the present invention on the right side, and these two resonators are connected in series.

  In FIGS. 1A and 1B, 11 is a substrate, 12 is a through hole, 13 is a lower electrode, 14 is a piezoelectric body, 15 is an upper electrode, and 16 is an adjustment film. On the substrate 11, a lower electrode 13 and an upper electrode 15 are stacked to sandwich a piezoelectric body 14 in the thickness direction and apply a voltage from the thickness direction. The lower electrode 13 and the upper electrode 15 constitute a pair of electrodes that sandwich the piezoelectric body 14 in the thickness direction. In addition, the portion where the lower electrode 13, the piezoelectric body 14, and the upper electrode 15 overlap in the thickness direction is a portion responsible for acoustic wave resonance, and is referred to as a resonance portion. This resonance part is acoustically separated from the base 11 by the through hole 12. The adjustment film 16 is provided so as to be in direct contact with the upper electrode 15.

  In the bulk acoustic wave resonator of the present invention, since the adjustment film 16 is formed on the resonance part, the effective electromechanical coupling coefficient of the bulk acoustic wave resonator is changed, and as a result, the frequency difference can be adjusted. it can.

  Usually, the frequency adjustment film or the like provided on the resonance part cannot change the frequency difference, and shifts the resonance frequency and the antiresonance frequency only in one direction on the low frequency side. Further, when the thickness is 0.25 × λg with respect to the wavelength λg in the thickness direction at the operating frequency, it functions as a reflective layer that reflects the acoustic wave propagating through the resonance part to the resonance part side. It was known that the work of shifting would disappear. For this reason, in order to adjust the frequency, a film having a thickness exceeding 0.25 × λg was not formed. And such a frequency adjustment film could not change the frequency difference.

  However, as a result of extensive studies by the inventor, the adjustment film 16 is formed on the resonance portion, and the thickness of the adjustment film 16 is 0.5λ × n (where λ propagates through the adjustment film 16 at the operating frequency in the thickness direction). It was found that the following excellent characteristics can be obtained by setting the wavelength of the acoustic wave and n is a natural number. In other words, the adjustment film 16 can adjust the frequency difference that could not be adjusted in the past without substantially changing the resonance frequency even though the film is formed on the resonance part. It is.

  Note that the thickness of the adjustment film 16 is approximately 0.5λ × n, and specifically includes a range of ± 15% from the value of 0.5λ × n.

  Hereinafter, each part will be described in detail.

The substrate 11 has a function of supporting a bulk acoustic wave resonator, and a mirror-polished Si wafer having a thickness of about 0.05 to 1 mm and a diameter of about 75 to 200 mm is usually used. The Si wafer is particularly suitable because it is easy to handle and has many corresponding thin film processing apparatuses, which makes it easy to manufacture. As the substrate 11, a wafer such as Si, Al ₂ O ₃ , SiO ₂ , glass, or the like having good compatibility with a thin film process can be used in addition to a Si wafer.

  The lower electrode 13 is a member having a function of applying a high-frequency voltage to the piezoelectric body 14, and is formed of a metal material such as W, Mo, Au, Al, or Cu. The lower electrode 13 is formed with a predetermined thickness on the substrate 11 by a thin film process such as sputtering or CVD, and is processed into a predetermined shape by a photolithography technique or the like. In addition, since the lower electrode 13 has a function of forming a resonance part, the thickness of the lower electrode 13 takes into consideration the inherent acoustic impedance, density, sound speed, wavelength, etc. of the material in order to exhibit the necessary resonance characteristics of the bulk acoustic wave resonator. Therefore, it is necessary to design precisely. The optimum electrode thickness varies depending on the operating frequency, the required characteristics of the resonator, the material of the piezoelectric body 14, the electrode material, the configuration of other members provided in contact with the resonance part, etc., but when the resonance frequency is 2 GHz, 0.01. About 0.5 μm.

  The piezoelectric body 14 is made of, for example, a piezoelectric material such as ZnO, AlN, or PZT, and expands and contracts according to the high-frequency voltage applied by the lower electrode 13 and the upper electrode 15 to convert an electrical signal into mechanical vibration. Has function. The piezoelectric body 14 is formed with a predetermined thickness on the lower electrode 13 by a thin film process such as a sputtering method or a CVD method, and is processed into a predetermined shape by a photolithography technique or the like. In order for the bulk acoustic wave resonator to exhibit the necessary resonance characteristics, the thickness of the piezoelectric body 14 needs to be precisely designed in consideration of the inherent acoustic impedance, density, sound speed, wavelength, etc. of the material. The optimum thickness varies depending on the operating frequency, the required characteristics of the resonator, the material of the piezoelectric body 14, the material of the lower electrode 13 and the upper electrode 15, and the like, when the resonance frequency is 2 GHz, it is about 0.3 to 2.0 μm. is there.

  The upper electrode 15 is a member having a function of applying a high-frequency voltage to the piezoelectric body 14 together with the lower electrode 13, and is formed of a metal material such as W, Mo, Au, Al, or Cu. The upper electrode 15 is formed with a predetermined thickness on the piezoelectric body 14 by a thin film process such as a sputtering method or a CVD method, and is processed into a predetermined shape by a photolithography technique or the like. In addition, since the upper electrode 15 has a function of forming a resonance part simultaneously with the function as an electrode, the thickness of the upper electrode 15 is not limited to the specific acoustic impedance of the material, It is necessary to design precisely considering density, sound speed, wavelength, and the like. The optimum electrode thickness varies depending on the operating frequency, the required characteristics of the resonator, the material of the piezoelectric body 14, the electrode material, and the like, but is about 0.01 to 0.5 μm when the resonance frequency is 2 GHz.

  The lower electrode 13 and the upper electrode 15 are not a single layer of metal material, but a laminate of a plurality of metal layers, a substrate, a piezoelectric body 14 in order to improve conductivity and obtain necessary acoustic characteristics. A layer to which an adhesion layer and a buffer layer are added is also used.

  In addition, as described above, the resonance part formed by sandwiching the piezoelectric body 14 from above and below by the lower electrode 13 and the upper electrode 15 causes the acoustic wave to resonate due to the thickness longitudinal vibration. In addition, it is necessary to design precisely considering the required characteristics of the resonator, the material of the piezoelectric body 14, the material of the lower electrode 13 and the upper electrode 15, and the like. The resonance part is a part where the lower electrode 13, the piezoelectric body 14, and the upper electrode 15 overlap each other, and each of the lower electrode 13, the piezoelectric body 14, and the upper electrode 15 may be formed wider than the resonance part. Usually, the overall thickness is designed to be approximately λ / 2 (λ is the wavelength of the acoustic wave at the operating frequency). In addition, the planar shape is rectangular in the example shown in FIG. 1, but may be a circular shape, an indefinite shape, or a trapezoidal shape to prevent unnecessary vibration (spurious). Further, since the area becomes a factor for determining the impedance of the resonator, it is necessary to design it precisely like the thickness. When used in a 50Ω impedance system, the electrical capacitance of the resonance unit is usually designed to have a reactance of approximately 50Ω at the operating frequency. For example, in the case of a 2 GHz vibrator, the area of the resonance part is about 100 μm × 100 μm to 200 μm × 200 μm.

The through-hole 12 is formed by, for example, forming a resonance part in the base 11, forming a photoresist pattern on the back side of the base 11 by a photolithography technique, and etching the base 11 by deep-RIE or anisotropic wet etching. Can be formed. In this case, an etching stop layer such as SiO ₂ , SiNx, or AlN may be provided between the lower electrode 13 and the substrate 11.

  For example, after the upper electrode 15 is formed, the adjustment film 16 is formed with a predetermined thickness on the upper electrode 15 by a thin film process such as sputtering or CVD, and is processed into a predetermined shape by a photolithography technique or the like. . The material and thickness of the adjustment film 16 must be selected so that the bulk acoustic wave resonator exhibits the necessary resonance characteristics. The optimum thickness varies depending on the operating frequency, the required characteristics of the resonator, the material of the piezoelectric body 14, the electrode material, and the like, but is about 0.5 to 2.0 μm when the resonance frequency is 2 GHz.

The material of the adjustment film 16 is not particularly limited, but a metal material such as W, Mo, Au, Al, or Cu and an insulator material such as SiO ₂ or SiNx are desirable from the viewpoint of compatibility with the thin film process. Further, when the material of the adjustment film 16 is a metal material, the same effect as that of increasing the thickness of the upper electrode 15 can be obtained by electrically connecting the upper electrode 15 and the adjustment film 16, so that the conductivity of the electrode can be increased. This is desirable because the rate can be substantially improved. Further, the adjustment film 16 and the upper electrode 15 may be continuously formed and processed at the same time to have the same outer shape. In this case, since the number of steps can be reduced, a device can be manufactured at a lower cost.

  Furthermore, when the peripheral edge portion of the adjustment film 16 is made to coincide with the peripheral edge portion in the cross section perpendicular to the thickness direction of the resonance portion, parasitic capacitance due to the addition of the adjustment film is not generated. Will not deteriorate. Here, the peripheral portion of the adjustment film 16 refers to the peripheral portion of the adjustment film 16 on the resonance portion side in the thickness direction. That is, when the adjustment film 16 is in contact with the resonance part as shown in FIG. 1, the peripheral part of the part in contact with the resonance part is referred to, and the reverse taper shape and reverse taper shape may be formed therefrom. In the case where the peripheral portion of the adjustment film 16 in contact with the resonance portion does not coincide with the peripheral portion in the section perpendicular to the thickness direction of the resonance portion (FIG. 2A), the resonance frequency of the portion indicated by A in the figure However, since it differs from other parts, this part may become a parasitic capacitance that does not contribute to resonance. On the other hand, in the case where the peripheral portion of the adjustment film 16 in contact with the resonance portion is made to coincide with the peripheral portion in the cross section perpendicular to the thickness direction of the resonance portion (FIG. 2B), such a portion is Therefore, characteristic deterioration due to parasitic capacitance is eliminated.

  In addition, the resonance part, the substrate, other materials and structures, the manufacturing process, etc. in the bulk acoustic wave resonator of the present invention are not particularly limited to the above examples, and further, the protective film, the package, the resonance part and the external connection There is also no particular limitation on the configuration and structure of wiring and electrodes for connecting to a terminal portion (not shown) for connecting, and a filter by connecting a plurality of resonance portions. The same applies to the bulk acoustic wave resonator described below.

  For example, in FIG. 1, the resonance part is acoustically isolated from the base 11 by the through-hole 12, but layers of high impedance material and layers of low impedance material having a thickness of 0.25λg are alternately arranged. An acoustic multilayer reflective film formed by laminating may be provided between the resonance portion and the substrate 11.

  Further, although the adjustment film 16 is formed on the upper electrode 15 in FIG. 1, it may be provided between the lower electrode 13 and the substrate 11 or may be provided on both. Further, an adhesion layer and a buffer layer can be added between the adjustment film 16 and the upper electrode 15 or the lower electrode 13. Further, the adjustment film may be composed of a plurality of layers.

  FIG. 3 shows a simulation result of the relationship between the thickness of the adjustment film 16 and the resonance frequency (resonance frequency f0 and antiresonance frequency fa) of the bulk acoustic wave resonator. In the simulation, adjustment was made of Al on the resonance part composed of the piezoelectric body 14 having a material of ZnO and a thickness of 0.92 μm, and the upper electrode 15 and the lower electrode 13 having a material of W and a thickness of 0.1 μm. The case where the film 16 was formed was used as a model. In the drawing, the resonance frequency and the antiresonance frequency when there is no adjustment film 16 are indicated by broken lines.

  As can be seen from FIG. 3, the frequency difference (fa−f0) is smaller when the adjustment film 16 is present than the resonance frequency without the adjustment film 16. That is, the effective electromechanical coupling coefficient is reduced by the adjustment film 16. In this way, by forming the adjustment film 16, the frequency difference can be changed without changing the material, film thickness, etc. of the resonance part of the bulk acoustic wave resonator. That is, the effective electromechanical coupling coefficient of the resonance unit can be set to a predetermined target value.

  Further, it is desirable that the thickness of the adjustment film 16 is approximately 0.5λ × n. FIG. 3A shows the case where n = 1. As can be seen from FIG. 3, there is a close relationship between the thickness of the adjustment film 16 and the resonance frequency. When the film thickness of the adjustment film 16 is approximately in the vicinity of 0.5λ, the resonance is almost the same as that without the adjustment film 16. Have a frequency. Therefore, it is possible to obtain a bulk acoustic wave resonator in which only the frequency difference is changed without substantially changing the resonance frequency or the anti-resonance frequency, and it is possible to provide a bulk acoustic wave resonator having a high degree of design freedom at a low cost. It becomes like this.

  As shown in FIG. 3B, as the thickness of the adjustment film 16 is increased as n of 0.5λ × n, the resonance frequency does not change, and the frequency difference further decreases. It was confirmed by simulation.

  Furthermore, the resonance frequency and the antiresonance frequency can be set to predetermined target values by shifting the thickness of the adjustment film 16 from the value of 0.5λ × n by a predetermined value. This is useful when the ladder type filter is configured by combining bulk acoustic wave resonators, and the resonance frequency of the series resonator and the parallel resonator is shifted so as to satisfy the filter characteristics. Conventionally, for this purpose, a frequency adjusting film is added on the upper electrode 15 or the film thickness of the upper electrode 15 is reduced by etching. On the other hand, in the bulk acoustic wave resonator of the present invention, the adjustment film 16 can change the resonance frequency and the anti-resonance frequency itself in addition to the effective electromechanical coupling coefficient and the frequency difference. As is clear from FIG. 3, as the thickness of the adjustment film 16 is increased, both the resonance frequency and the antiresonance frequency are shifted to the lower frequency side. Therefore, the adjustment film 16 can adjust the frequency difference and adjust the resonance frequency and the anti-resonance frequency. For example, in FIG. 3, the thickness of the adjustment film 16 may be 0.50λ in order to make the antiresonance frequency coincide with the resonator without the adjustment film 16. In order to make the resonance frequencies coincide with each other, the thickness of the adjustment film 16 may be set to 0.52λ. Furthermore, in order to make the anti-resonance frequency of the resonator without the adjustment film 16 coincide with the resonance frequency of the resonator with the adjustment film 16, the thickness of the adjustment film 16 may be set to 0.45λ. . That is, when the thickness of the adjustment film 16 is 0.50λ, the anti-resonance frequency fa is the same as that without the adjustment film, and the resonance frequency f0 is higher by about 20 MHz. That is, the bulk acoustic wave resonator has the same anti-resonance frequency and a small frequency difference of about 20 MHz (small effective electromechanical coupling coefficient). Further, when the thickness of the adjustment film 16 is 0.52λ, it has the same resonance frequency f0 as that without the adjustment film and has an anti-resonance frequency lower by about 20 MHz. That is, the bulk acoustic wave resonator has the same resonance frequency and a small frequency difference of about 20 MHz (small effective electromechanical coupling coefficient). Furthermore, when the thickness of the adjustment film 16 is 0.45λ, it has the same resonance frequency f0 as the antiresonance frequency fa without the adjustment film, and at the same time, the frequency difference is about 20 MHz smaller (the effective electromechanical coupling coefficient is small). ) Becomes a bulk acoustic wave resonator. As is clear from this, according to the adjustment film 16 of the present invention, it is possible to adjust the resonance frequency toward the high frequency side, which is impossible with the conventional frequency adjustment film.

  Thus, the result of having simulated the impedance characteristic of the bulk acoustic wave resonator when adjusting the film thickness of the adjustment film | membrane 16 is shown in FIG.

  FIG. 4A shows the relationship between the bulk acoustic wave resonator having the same antiresonance frequency fa and a small frequency difference of about 20 MHz, and the impedance characteristics of the bulk acoustic wave resonator without the adjustment film 16. FIG. 4B shows a relationship between a bulk acoustic wave resonator having the same resonance frequency f0 and a small frequency difference of about 20 MHz, and a bulk acoustic wave resonator without the adjustment film 16. 4A and 4B, the solid line indicates the characteristic when the adjustment film 16 is not provided, and the broken line indicates the characteristic when the adjustment film 16 is provided. The simulation results shown in FIG. 4 show that the piezoelectric resonance frequency fa of the bulk acoustic wave resonator shown in FIG. 4A is equal to the resonance frequency f0 of the bulk acoustic wave resonator shown in FIG. The film thickness of the body 14 is changed.

  As described above, the adjustment film 16 adjusts the frequency difference and shifts the thickness of the adjustment film 16 from the value of 0.5λ × n by a predetermined value so that the resonance frequency and the anti-resonance frequency can be reduced to the low frequency side and the high frequency side. Can be adjusted. In addition, since it is possible to adjust the resonance frequency without changing the material and film thickness of the resonance part of the bulk acoustic wave resonator, the productivity and reliability should be high. it can.

  As described above, the amount of change in the frequency difference can be adjusted by the magnitude of n, but can also be adjusted by the material of the adjustment film 16. In the above example, the case where Al is used as the adjustment film 16 is illustrated, but the effective electromechanical coupling coefficient and the amount of change in the frequency difference depend on the material used for the adjustment film 16. Hereinafter, a method for adjusting the frequency difference depending on the material will be described.

  FIG. 5 shows an example of simulation results of (a) frequency difference and (b) effective electromechanical coupling coefficient when the adjustment film 16 made of various materials is formed on the above-described bulk acoustic wave resonator. When the adjustment film 16 is not provided, the bulk acoustic wave resonator has a frequency difference of 83 MHz and an effective electromechanical coupling coefficient of 8.2%. However, when Al is used as the material of the adjustment film 16, the frequency difference is 60 MHz. , 5.8%, and 24MHz, 2.3% when W is used. Thus, since the frequency difference and effective electromechanical coupling coefficient of the bulk acoustic wave resonator in which the adjustment film 16 is formed depend on the material of the adjustment film 16, the material of the adjustment film 16 in the bulk acoustic wave resonator of the present invention is different. It is desirable that the selection is made based on a desired effective electromechanical coupling coefficient.

  Thus, it has been confirmed that the frequency difference of the bulk acoustic wave resonator can be adjusted also by the material of the adjustment film 16.

  Next, a filter device using the bulk acoustic wave resonator of the present invention will be described.

  FIG. 6 is an equivalent circuit diagram showing an example of the embodiment of the filter device of the present invention.

  In the filter device of the present invention, as shown in FIG. 6A, the bulk acoustic wave resonator 100 of the present invention is connected between the input / output line connecting the input terminal In and the output terminal Out and the reference potential terminal. do it. Further, as shown in FIG. 6B, a bulk acoustic wave resonator 100 may be connected on the input / output line. Further, the bulk acoustic wave resonator 100 may be connected both between the input / output line connecting the input terminal In and the output terminal Out and the reference potential terminal and on the input / output line. That is, the bulk acoustic wave resonator of the present invention may be used for at least one of the plurality of series resonators 200 and parallel resonators 201 as shown in FIG.

  Here, the reference potential terminal is connected to the reference potential, and FIG. 6 shows an example in which the reference potential terminal is connected to the ground potential.

  Further, as a filter device of the present invention using the bulk acoustic wave resonator of the present invention, in addition to the ladder type filter device in which the above resonators are electrically coupled, the lattice type filter device There are a stacked crystal filter device and a coupled resonator filter device in which resonators are acoustically coupled, and these filter devices also have the same effect. .

  Next, the characteristics of such a filter device will be described.

  The bulk acoustic wave resonator having the characteristics shown in FIG. 4A with the adjustment film 16 is replaced with a parallel resonator (201 in FIG. 8B) of the ladder filter, and the adjustment film of FIG. By using a bulk acoustic wave resonator having the characteristics shown in the case of 16 as a series resonator (200 in FIG. 8B), the bulk acoustic wave resonator without the adjustment film 16 is used as a series resonator and a parallel resonance. Compared to the case of using both of the elements, the passband width is narrower, and the impedance change between resonance and antiresonance becomes steeper, so that a filter having steeper attenuation characteristics can be obtained. Further, for example, a bulk acoustic wave resonator having characteristics with the adjustment film 16 of FIG. 4B is used in the case where the ladder filter series resonator 200 does not have the adjustment film 16 of FIG. By using a bulk acoustic wave resonator having characteristics for the parallel resonator 201, compared with the case where the bulk acoustic wave resonator without an adjustment film is used for both the series resonator and the parallel resonator, A filter having a steeper attenuation characteristic can be obtained.

  In the example of FIG. 4, the bulk acoustic wave resonator used for the series resonator of the ladder filter and the bulk acoustic wave resonator used for the parallel resonator have an antiresonance frequency of the series resonator and a resonance frequency of the parallel resonator. The example in which the resonance frequency is shifted by changing the film thickness of the piezoelectric body 14 has been described. However, the present invention is not limited to this example. For example, the configuration including the film thickness of the resonance portion may shift the resonance frequency by adjusting the film thickness of the adjustment film 16 using the same bulk acoustic wave resonator. In this case, since the frequency shift of the series resonator and the parallel resonator can be obtained only by the frequency adjustment function of the adjustment film 16 without changing the film thickness of the piezoelectric body 14, the productivity is high. .

  Next, an example in which a communication device is formed using the filter device of the present invention will be described.

  FIG. 7 is a block diagram illustrating a communication apparatus according to an embodiment of the communication apparatus of the present invention.

  In FIG. 7, a transmission circuit Tx and a reception circuit Rx are connected to an antenna 140 via a duplexer 150. The high-frequency signal to be transmitted is removed from the unnecessary signal by the filter 210, amplified by the power amplifier 220, and then radiated from the antenna 140 through the isolator 230 and the duplexer 150. The high-frequency signal received by the antenna 140 is amplified by the low-noise amplifier 160 through the duplexer 150, the unnecessary signal is removed by the filter 170, re-amplified by the amplifier 180, and converted to a low-frequency signal by the mixer 190. Is done.

  In FIG. 7, if the filter device of the present invention is used for any one of the duplexer 150, the filter 170, and the filter 210, the degree of freedom in design is high, so that desired characteristics and high productivity can be achieved. .

  Note that although the communication device having the transmission circuit Tx and the reception circuit Rx has been described with reference to FIG. 7, the communication device may have either the transmission circuit Tx or the reception circuit Rx.

  With such a configuration, loss in the circuit is reduced and unnecessary wave removal performance is enhanced by a steeper filter device, so that a communication device with higher sensitivity can be provided.

  A specific example of the bulk acoustic wave resonator of the present invention will be described below with reference to FIG. Here, a bulk acoustic wave resonator that resonates at 2 GHz was fabricated.

  First, a lower electrode 13 made of W having a thickness of 0.1 μm was formed on a high-resistance Si substrate 11 by sputtering. The lower electrode 13 was patterned by wet etching. Thereafter, a piezoelectric body 14 made of a 0.9 μm ZnO film was formed by sputtering. Patterning of the ZnO film was performed by photolithography and wet etching with dilute hydrochloric acid. Then, an upper electrode 15 made of W having a thickness of 0.1 μm and an adjustment film 16 made of Al having a thickness of 1.68 μm (= 0.5λ) are formed thereon by sputtering, and similarly dry etching by photolithography and RIE. Then, pattern formation was performed. A bulk acoustic wave resonator without the adjustment film 16 was also formed on the same substrate 11 at the same time. With respect to the bulk acoustic wave resonator of the present invention as shown in FIG. 1 manufactured as described above, the resonance characteristics thereof were measured with an impedance analyzer. As a result, the parallel resonant frequency of the bulk acoustic wave resonator without the adjustment film 16 was 2. The bulk acoustic wave resonator formed with the adjustment film 16 had a parallel resonance frequency of 2.110 GHz and a frequency difference of 52 MHz, whereas the frequency difference was .114 GHz and the frequency difference was 70 MHz.

  In the same process, when the adjustment film 16 having a thickness of 1.67 μm (= 0.52λ) was produced, the parallel resonance frequency was 2.058 GHz and the frequency difference was 52 MHz.

  It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, AlN, PZT, or the like may be used as a piezoelectric material, and a CVD method or a sol-gel method (a method in which a material solution is spin-coated on a substrate and baked to obtain a piezoelectric material), etc. Can also be used. In particular, when a ferroelectric material having a large electromechanical coupling coefficient such as PZT is used, a bulk acoustic wave resonator having a large frequency difference (difference between the resonance frequency and the antiresonance frequency) can be realized. Moreover, the filter using it can be used suitably for the radio | wireless communication apparatus which has a wide pass-band width and uses a broadband spectrum.

An example of the bulk acoustic wave resonator of this invention is shown, (a) is a top view, (b) is sectional drawing of the A-A 'part of (a). (A), (b) is sectional drawing which shows the other example of the bulk acoustic wave resonator of this invention, respectively. (A), (b) is a diagram which shows an example of the simulation result of the relationship between the adjustment film | membrane thickness of the bulk acoustic wave resonator of this invention, a resonance frequency, and an antiresonance frequency, respectively. (A), (b) is a diagram which shows an example of the simulation result of the impedance characteristic of the bulk acoustic wave resonator of this invention, respectively. (A), (b) is a diagram which shows an example of the simulation result of the relationship between the adjustment film | membrane thickness, a frequency difference, and an effective electromechanical coupling coefficient, respectively of the bulk acoustic wave resonator of this invention. (A), (b) is an equivalent circuit diagram which respectively shows an example of embodiment of the filter apparatus of this invention. It is a block diagram which shows an example of embodiment of the communication apparatus of this invention. (A), (b) is sectional drawing which shows an example of the conventional bulk acoustic wave resonator, respectively, and a circuit diagram which shows the circuit structure of a ladder type filter using the same.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Base | substrate 12 ... Through-hole 13 ... Lower electrode 14 ... Piezoelectric body 15 ... Upper electrode 16 ... Adjustment film

Claims (7)

A resonating unit including a piezoelectric body and a pair of electrodes that sandwich the piezoelectric body in the thickness direction;
An adjustment film made of a metal material provided on at least one side in the thickness direction of the resonance part, and having a thickness of (0.425 to 0.575) λ × n;
A bulk acoustic wave resonator comprising:
(Where λ is the wavelength of the acoustic wave propagating in the thickness direction through the adjustment film at the operating frequency, and n is a natural number.) The bulk acoustic wave resonator according to claim 1 , wherein the adjustment film is made of Al . The bulk acoustic wave resonator according to claim 1, wherein the adjustment film has a thickness of 0.5λ .   The bulk acoustic wave resonator according to claim 1, wherein a peripheral edge portion of the adjustment film coincides with a peripheral edge portion in a cross section perpendicular to the thickness direction of the resonance portion.   5. An input / output line having an input terminal, an output terminal, and a reference potential terminal, on the input / output line connecting the input terminal and the output terminal, or between the input / output line and the reference potential terminal. A filter device provided with the bulk acoustic wave resonator according to claim 1.   A communication device having at least one of a reception circuit or a transmission circuit, wherein the filter device according to claim 5 is used in the reception circuit or the transmission circuit.   A communication device comprising the filter device according to claim 5 and at least one of a reception circuit or a transmission circuit.

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