JP5591977B2 - Piezoelectric thin film resonator, filter, duplexer, communication module, and communication device - Google Patents

Description

  The present invention relates to a thin film bulk acoustic wave resonator (FBAR) used in mobile communication such as a mobile phone, PHS, and wireless LAN, and high-frequency wireless communication. The present invention also relates to a filter, a duplexer, a communication module, and a communication device using a piezoelectric thin film resonator.

  In recent years, an FBAR, which is a resonator using the thickness longitudinal vibration of a piezoelectric material, has attracted attention as a filter element for high-frequency communication.

  FIG. 23 is a plan view of the FBAR. 24 is a cross-sectional view taken along a line AA in FIG. As shown in FIGS. 23 and 24, the FBAR has a structure in which the piezoelectric film 103 is sandwiched between the upper electrode 101 and the lower electrode 102, and a region where the upper electrode 101 and the lower electrode 102 are opposed to each other (hereinafter referred to as resonance). (Referred to as part R1) is a practical resonator. By providing the gap 105 or the acoustic reflector above and below the resonance part R1, it is possible to obtain resonance characteristics with a high quality factor (Q) without attenuating the elastic wave generated in the resonance part R1.

  As shown in FIG. 25, the piezoelectric thin film resonator has a vibration mode (transverse mode) having a propagation component in the lateral direction in a frequency band close to the resonance frequency and antiresonance frequency of the thickness vibration. The transverse mode wave W1 is reflected at the end of the resonance part R1 (reflected wave W2) or transmitted through the end of the resonance part R1 and propagates to the non-resonance part R2. The wave propagating to the non-resonant portion R2 becomes a loss (for example, when the reflection characteristic is displayed on the Smith chart, the Q circle looks small). In view of the actual resonator structure, as shown in FIG. 26 and FIG. 27A, the ends of the upper electrode 101 and the lower electrode 102 are inclined in manufacturing, as shown in FIG. 7B. The apparent acoustic impedance of the piezoelectric film 103 gradually decreases toward the non-resonant portion R2 (note that the acoustic impedance Z is the product of the material density ρ and the sound velocity c, and the sound velocity is a mass added on the piezoelectric film. The apparent acoustic impedance exists for the inherent acoustic impedance without mass addition, defined herein as acoustic impedance = apparent acoustic impedance).

  According to theory, in a resonator using a piezoelectric thin film having a Poisson's ratio of 1/3 or less, if the acoustic impedance of the peripheral portion is smaller than that of the resonant portion, a transverse mode wave is likely to pass through the end portion and become a loss. In addition, it has been found by optical observation that leakage waves exist outside the resonator, and it is a problem to prevent the leakage waves.

For example, Patent Documents 1 and 2 disclose conventional techniques related to the prevention of shear wave leakage. Patent Documents 1 and 2 disclose a configuration in which the periphery of the resonance unit R1 is uniformly surrounded by a layer 106 having different acoustic characteristics, as shown in FIGS. In this configuration, the acoustic impedance around the resonator is larger than the acoustic impedance of the excitation unit, and therefore, it is considered that there is an effect of preventing the leakage of the transverse wave as predicted by theory.
JP 2003-505906 A JP 2006-109472 A

  However, the configurations disclosed in Patent Documents 1 and 2 have the following problems.

  First, the document describes that a change in acoustic characteristics may be provided inside the excitation unit. However, providing a region having a different acoustic characteristic at the location that is originally the excitation unit converts electrical energy into sound waves. In order to increase the portion that is not performed, that is, to reduce the electromechanical coupling coefficient indicating the performance of the resonator, for example, the bandwidth becomes narrow when creating a filter, which is a problem.

  Furthermore, the configuration disclosed in this document is characterized by a structure that surrounds the excitation unit in a frame shape so that the acoustic impedance differs from that of the excitation unit, but the transverse wave confined in the excitation unit is a strong standing wave inside the excitation unit. There is also a problem of forming the mode. 30 and 31 are diagrams showing the electrical characteristics of the basic resonator shown in FIGS. 23 and 24 and the electrical characteristics of the resonator shown in FIGS. 28 and 29. Comparing the electrical characteristics of the two resonators, it can be seen that a large spike-like loss point (spurious) is generated on the lower frequency side than the resonance point due to the generated strong standing wave mode. For example, when a ladder-type filter as shown in FIG. 32 is configured using the resonator, a spike-like loss (spurious) is generated in the pass band as shown in FIG. 33, insertion loss, It becomes a cause of deteriorating an index such as EVM (Error Vector Magnitude).

  An object of the present invention is to add a mass so that the acoustic impedance on the slope is larger than the region inside the slope in the piezoelectric thin film resonator having a slope around the resonance portion, and the acoustic impedance at the opposite sides is different. By designing, it is possible to realize a piezoelectric thin film resonator that suppresses the decrease in the electromechanical coupling coefficient and the increase in the standing wave mode from the conventional example while preventing the energy dissipation of the transverse wave. It is another object of the present invention to realize a filter, a duplexer, a communication module, and a communication device using a piezoelectric thin film resonator.

  A piezoelectric thin film resonator according to the present invention is disposed between a substrate, an upper electrode and a lower electrode disposed on the substrate, and a part of the piezoelectric thin film resonator is opposed to each other, and the upper electrode and the lower electrode. A piezoelectric thin film resonator comprising a mass body disposed on the upper electrode, wherein the mass body is a part of an end of a region of the upper electrode facing the lower electrode It is arranged in.

  According to the present invention, it is possible to realize a piezoelectric thin film resonator that suppresses the decrease in the electromechanical coupling coefficient and the increase in the standing wave mode as compared with the conventional example while preventing the energy dissipation of the transverse wave. In addition, by mounting such a piezoelectric thin film resonator on a filter, duplexer, communication module, and communication device, it is possible to improve filter characteristics or improve communication quality.

The top view which shows the 1st structure of the piezoelectric thin film resonator in embodiment (A) is sectional drawing of the AA part in FIG. 1, (b) is a characteristic figure of an acoustic impedance. Smith chart comparing electrical characteristics of piezoelectric thin film resonators in the embodiment and conventional piezoelectric thin film resonators Characteristic diagram comparing the electrical characteristics of the piezoelectric thin film resonator in the embodiment and the conventional piezoelectric thin film resonator Smith chart comparing electrical characteristics of piezoelectric thin film resonators in the embodiment and conventional piezoelectric thin film resonators The top view which shows the 2nd structure of the piezoelectric thin film resonator in embodiment (A) is a cross-sectional view of the AA portion in FIG. 6, (b) is a characteristic diagram of acoustic impedance The top view which shows the 3rd structure of the piezoelectric thin film resonator in embodiment (A) is a cross-sectional view of the AA portion in FIG. 8, (b) is a characteristic diagram of acoustic impedance Characteristic diagram comparing the electrical characteristics of the piezoelectric thin film resonator in the embodiment and the conventional piezoelectric thin film resonator FIG. 2 is a plan view of a main part showing the configuration of a piezoelectric thin film resonator in Example 1. Sectional drawing of the AA part in FIG. 11A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 2. Sectional drawing of the AA part in FIG. 12A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 3. Sectional drawing of the AA part in FIG. 13A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 4. Sectional drawing of the AA part in FIG. 14A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 5. Sectional drawing of the AA part in FIG. 15A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 6. Sectional drawing of the AA part in FIG. 16A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 7. Sectional drawing of the AA part in FIG. 17A The principal part top view which shows the structure of the piezoelectric thin film resonator in Example 8. Sectional drawing of the AA part in FIG. 18A Sectional drawing which shows the manufacturing process of the piezoelectric thin film resonator of embodiment Sectional drawing which shows the manufacturing process of the piezoelectric thin film resonator of embodiment Sectional drawing which shows the manufacturing process of the piezoelectric thin film resonator of embodiment The block diagram which shows the structure of the duplexer in embodiment The block diagram which shows the structure of the communication module in embodiment The block diagram which shows the structure of the communication apparatus in embodiment Sectional view showing the basic structure of a piezoelectric thin film resonator Plan view showing the configuration of a conventional piezoelectric thin film resonator Sectional drawing of the AA part in FIG. Plan view showing the configuration of a conventional piezoelectric thin film resonator (A) is sectional drawing of the AA part in FIG. 26, (b) is a characteristic figure of an acoustic impedance. Plan view showing the configuration of a conventional piezoelectric thin film resonator (A) is a cross-sectional view of the AA portion in FIG. 28, (b) is a characteristic diagram of acoustic impedance. Smith chart comparing the electrical characteristics of the configuration with and without the mass Characteristic diagram comparing the electrical characteristics of the configuration with and without the mass body Circuit diagram showing the basic configuration of the filter Characteristic diagram comparing the electrical characteristics of the configuration with and without the acoustic characteristic difference

  A piezoelectric thin film resonator according to the present invention is disposed between a substrate, an upper electrode and a lower electrode disposed on the substrate, and a part of the piezoelectric thin film resonator is opposed to each other, and the upper electrode and the lower electrode. A piezoelectric thin film resonator comprising a mass body disposed on the upper electrode, wherein the mass body is a part of an end of a region of the upper electrode facing the lower electrode It is arranged in.

  According to such a configuration, the transverse mode wave can be confined in the piezoelectric film, and mass is not added to some of the boundaries. It is possible to prevent the standing wave intensity from increasing.

  In the piezoelectric thin film resonator according to the aspect of the invention, the mass body may include an apparent acoustic impedance of a part of the piezoelectric film at a boundary between a region where the upper electrode and the lower electrode are opposed to each other and a region outside the region. However, it can be set as the structure arrange | positioned in the position which becomes larger than the apparent acoustic impedance of the said piezoelectric film in the area | region inside the said boundary.

  According to such a configuration, the transverse mode wave can be confined in the piezoelectric film, and mass is not added to some of the boundaries. It is possible to prevent the standing wave intensity from increasing.

  In the piezoelectric thin film resonator according to the aspect of the invention, the mass body may be a boundary that coincides with an end portion of the upper electrode at a boundary between a region where the upper electrode and the lower electrode are opposed to each other and a region outside the region. The apparent acoustic impedance of the piezoelectric film may be different from the apparent acoustic impedance of the piezoelectric film at the boundary that does not coincide with the end portion of the upper electrode.

  With such a configuration, the transverse mode waves can be confined in the piezoelectric film, and the phases of the transverse mode waves reflected at different boundaries of the acoustic impedance are different from each other. An increase in strength can be prevented.

  In the piezoelectric thin film resonator of the present invention, at least a part of the mass body may include a dielectric or a piezoelectric body, and the dielectric or the piezoelectric body may be in contact with the upper electrode.

  According to such a configuration, the position where the mass is added can be positioned at the boundary as much as possible, and by adding the mass, the area contributing to vibration is reduced and the electromechanical coupling coefficient k ^ 2 is reduced. Can be prevented.

  In the piezoelectric thin film resonator according to the aspect of the invention, the upper electrode may include an inclined portion of less than 90 ° at a boundary between a region facing the lower electrode and a region outside the region. it can.

  According to such a configuration, it is possible to prevent a discontinuity in shape due to a step and a manufacturing defect when weighting is performed at the boundary portion, and it is possible to form a high-quality resonator.

  In the piezoelectric thin film resonator of the present invention, the mass body may include titanium (Ti) and gold (Au).

  According to such a configuration, it is possible to confine the transverse wave and simultaneously reduce the series resistance of the resonator, thereby forming a high-Q resonator.

  In the piezoelectric thin film resonator of the present invention, the region where the upper electrode and the lower electrode are formed to face each other has an elliptical shape when viewed in the normal direction of the main plane of the upper electrode; can do.

  According to such a configuration, even if the transverse wave is reflected at the boundary between the resonance part and the non-resonance part, the reflected wave in a specific direction is not intensified, and the standing wave of the transverse mode is strengthened. It can be further suppressed.

  In the piezoelectric thin film resonator of the present invention, the region where the upper electrode and the lower electrode are opposed to each other is a polygon having a non-rectangular shape when viewed in the normal direction of the main plane of the upper electrode. There can be a certain configuration.

  According to such a configuration, even if the transverse wave is reflected at the boundary between the resonance part and the non-resonance part, the reflected wave in a specific direction is not intensified, and the standing wave of the transverse mode is strengthened. It can be further suppressed.

  In the piezoelectric thin film resonator of the present invention, the inclined portion may be formed by dry etching.

  According to such a configuration, the inclination can be formed with high accuracy.

  In the piezoelectric thin film resonator of the present invention, the dielectric may be made of silicon oxide (SiO 2).

  In the piezoelectric thin film resonator of the present invention, the upper electrode and the lower electrode may be configured such that at least a portion in contact with the piezoelectric film is formed of ruthenium (Ru).

(Embodiment)
FIG. 1 is a plan view of a first configuration of the piezoelectric thin film resonator according to the present embodiment. FIG. 2A is a cross-sectional view taken along line AA in FIG. FIG. 2B shows the acoustic impedance in the piezoelectric thin film resonator shown in FIGS. 1 and 2A. As shown in FIGS. 1 and 2, the piezoelectric thin film resonator of the present embodiment includes an upper electrode 11 and a lower electrode 12 that sandwich a piezoelectric film 13 on a substrate 14. A region where the upper electrode 11 and the lower electrode 12 face each other is the resonance portion R1, and a non-resonance region around the region is the non-resonance portion R2. A gap 15 or an acoustic multilayer film (not shown) is formed below the resonance part R1. The wave generated in the resonance part R1 is reflected at the end of the resonance part R1 (reflected wave W11) or leaks to the non-resonance part R2 (leakage wave W12).

  The feature of the present embodiment is that a mass body 16 is provided along the inclined portion 11a of the upper electrode 11 at the boundary between the resonance portion R1 and the non-resonance portion R2, as shown in FIG. The mass body 16 can be made of a dielectric material, a piezoelectric material, a metal, or the like. By providing the mass body 16 in this manner, the acoustic impedance of the inclined portion 11a is increased, and the elastic wave W11 generated in the resonance portion R1 is confined in the resonance portion R1.

  At this time, it is also characterized in that at least a part of the periphery of the resonance part R1 is provided with a region to which the mass body 16 is not added. In the configuration shown in FIGS. 1 and 2, an arc-shaped (see FIG. 1) mass body 16 is added only to the end portion of the upper electrode 11, and the mass body 16 is added to a portion facing the end portion. Absent. As described above, by adding the mass body 16 only to a part of the outer periphery of the resonance part R1, a part of the elastic wave W11 is transmitted to the non-resonance part R2 through a portion where the mass body 16 is not added (leakage wave W12). Thus, it is possible to suppress the standing waves from strengthening in the resonance part R1.

  3, FIG. 4 and FIG. 5 show the results of experiments confirmed for the suppression of the occurrence of standing waves. As shown in FIG. 3 to FIG. 5, compared with the characteristics of the conventional resonator shown in FIG. 23 and FIG. 24, the mass body is provided only in a part around the resonance part R1 as in the present embodiment (the present invention). By adding 16, the reflection coefficient in the vicinity of the antiresonance point was increased, and it was confirmed that leakage of transverse waves could be prevented. Further, as shown in FIGS. 28 and 29, it was confirmed that the generation of standing waves can be suppressed as compared with the configuration in which the mass body is added to the entire periphery of the resonance part R1.

  FIG. 6 is a plan view of a second configuration of the piezoelectric thin film resonator according to the present embodiment. Fig.7 (a) is sectional drawing of the AA part in FIG. FIG. 7B shows acoustic impedance in the piezoelectric thin film resonator shown in FIGS. 6 and 7A. In this configuration, a mass body is added to the entire periphery of the resonance portion R1, and further, a mass body 17 added to the inclined portion 11a of the upper electrode 11 and a mass body 18 added to the inclined portion 11b facing the inclined portion 11a. , The mass is different from each other. By adopting such a configuration, the acoustic impedances at the sides opposite to each other on the outer periphery of the resonance part R1 are different, so that the phases of the reflected waves do not coincide with each other, and the transverse standing waves are prevented from strengthening each other. it can.

  FIG. 8 is a plan view of a third configuration of the piezoelectric thin film resonator in the present embodiment. Fig.9 (a) is sectional drawing of the AA part in FIG. FIG. 9B shows acoustic impedance in the piezoelectric thin film resonator shown in FIGS. 8 and 9A. This configuration is characterized in that at least a part of a portion of the mass body that contacts the upper electrode 11 is a dielectric or a piezoelectric body. In the configuration shown in FIG. 8, the piezoelectric body 19 is provided between the mass body 20 and the upper electrode 11. By adopting such a configuration, the mass body 20 can be disposed as far as possible outside the resonance part R1, and the addition of the mass body 20 reduces the area contributing to vibration and reduces the electromechanical coupling coefficient. Can be prevented. At this time, if a metal is laminated on the piezoelectric body 19 (or dielectric), the same effect can be obtained with a smaller film thickness than when only a dielectric having a low mass is added.

  10 shows a case where a mass body is added to the inside of the resonance part R1 using a piezoelectric FEM simulator (FEM: finite element method) (prior art shown in FIGS. 28 and 29), and the resonance part. The result of having calculated each electrical characteristic when a mass body is added so that it may touch the outer side of R1 (3rd structure of this Embodiment shown in FIG.8 and FIG.9) is shown. As shown in FIG. 10, the electromechanical coupling coefficient k 2 can be easily estimated from the difference between the resonance frequency and the antiresonance frequency, and k 2 in the piezoelectric thin film resonator of the present embodiment is 6.4. %, K ^ 2 in the conventional piezoelectric thin film resonator was 5.9%, and it was confirmed that there was a difference of 0.5% between the two. The difference of k ^ 2 is a difference of about 4 MHz at a frequency of 2 GHz, which is an important difference in a communication device (such as a mobile phone terminal) that requires a wideband filter.

  Examples of the piezoelectric thin film resonator according to the present embodiment will be described below. Examples of the first configuration of the piezoelectric thin film resonator according to the present embodiment are Examples 1 to 3, Examples of the second configuration are Examples 4 and 5, and Examples of the third configuration are examples. Examples 6-8.

Example 1
FIG. 11A is a plan view of a principal part of the first example of the resonator according to the present embodiment. 11B is a cross-sectional view taken along the line AA in FIG. 11A. The piezoelectric thin film resonator according to the present embodiment is formed in the substrate 14, the piezoelectric film 13, the upper electrode 11 and the lower electrode 12 disposed so as to sandwich the piezoelectric film 13, and the non-resonant portion R 2 on the upper electrode 11. The contact electrode 21 made of the low resistance electrode (Au, Al, etc.) and the mass body 16a disposed on the inclined portion 11a on the upper electrode 11 are provided. The mass body 16a is formed along the end portion of the upper electrode 11 as shown in FIG. 11A, and is not formed at a portion facing the end portion.

  The mass body 16a is composed of a piezoelectric body, a dielectric body, or a metal. The mass body 16a includes, for example, aluminum nitride (AlN), lead zirconate titanate (PZT), silicon oxide (SiO2), titanium oxide (TiO2), ruthenium (Ru), molybdenum (Mo), gold (Au), It can be formed of any one of titanium (Ti), copper (Cu), tungsten (W), and aluminum (Al), or a synthetic material containing any one of them as a main component. Further, the film thickness, width, and arrangement of the mass body 16a can be obtained, for example, by simulation using the general-purpose piezoelectric analysis software described above, and more preferably derived from experiments. The inclined portions 11a and 11b in the upper electrode 11 and the inclined portion 12a in the lower electrode 12 can be formed by cutting using an ion milling device. The mass body 16a can be formed by dry etching or wet etching after being deposited using a sputtering method.

  With this configuration, the elastic wave W11 generated in the resonance unit R1 is not confined in the resonance unit R1, and leaks to the non-resonance unit R12 as a leakage wave W12. It is possible to prevent the presence waves from strengthening each other.

(Example 2)
FIG. 12A is a plan view of a principal part of a second example of the resonator according to the embodiment. 12B is a cross-sectional view taken along the line AA in FIG. 12A. The configuration shown in the present embodiment is different from the configuration shown in the first embodiment in the shape of the mass body. In this embodiment, as shown in FIG. 12A, the shape of the mass body 16b extends not only to the end portion of the upper electrode 11, but also to a portion facing the end portion. . Furthermore, the mass body 16b does not surround the entire periphery of the resonance part R1, but is provided with an opening 16c in part. From this opening 16c, part of the elastic wave W11 leaks to the non-resonant part R12 as a leaky wave W12.

  With this configuration, the elastic wave W11 generated in the resonance unit R1 is not confined in the resonance unit R1, and leaks to the non-resonance unit R12 as a leakage wave W12. It is possible to prevent the presence waves from strengthening each other.

(Example 3)
FIG. 13A is a plan view of a principal part of a third example of the resonator according to the present embodiment. 13B is a cross-sectional view taken along the line AA in FIG. 13A. The configuration shown in the present embodiment is different from the configuration shown in the first embodiment in the shape of the mass body. In this embodiment, as shown in FIG. 13A, the shape of the mass body 16d is formed to extend not only to the end portion of the upper electrode 11 but also to a portion facing the end portion. . Furthermore, the mass body 16d does not surround the entire periphery of the resonance part R1, but is provided with openings 16e (similar to the opening 16c of Example 2) and 16f in part. From the openings 16e and 16f, part of the elastic wave W11 leaks to the non-resonant part R12 as a leaky wave W12.

  With this configuration, the elastic wave W11 generated in the resonance unit R1 is not confined in the resonance unit R1, and leaks to the non-resonance unit R12 as a leakage wave W12. It is possible to prevent the presence waves from strengthening each other.

Example 4
FIG. 14A is a plan view of relevant parts of a fourth example of the resonator according to the present embodiment. 14B is a cross-sectional view taken along the line AA in FIG. 14A. The piezoelectric thin film resonator of the present embodiment is formed in the substrate 14, the piezoelectric film 13, the upper electrode 11 and the lower electrode 12 disposed so as to sandwich the piezoelectric film 13, and the non-resonant portion R <b> 2 on the upper electrode 11. Contact electrode 21 made of a low-resistance electrode (Au, Al, etc.), a first mass body 17a disposed on the inclined portion 11a of the upper electrode 11, and a second electrode disposed on the inclined portion 11b of the upper electrode 11. Mass body 18a. The first mass body 17a is made of a piezoelectric body, a dielectric body, or a metal. The second mass body 18a is made of a piezoelectric material, a dielectric material, or a metal made of a material different from that of the first mass body 17a. The first mass body 17a and the second mass body 18a include, for example, aluminum nitride (AlN), lead zirconate titanate (PZT), silicon oxide (SiO2), titanium oxide (TiO2), ruthenium (Ru), molybdenum ( One of Mo or gold (Au), titanium (Ti), copper (Cu), tungsten (W), and aluminum (Al), or a synthetic material mainly containing any one of them. Can do. Further, the film thickness, width, and arrangement of the first mass body 17a and the second mass body 18a can be obtained from, for example, a simulation using the general-purpose piezoelectric analysis software described above, and more optimally derived from an experiment. It is desirable. The inclined portion 11a of the upper electrode 11 and the inclined portion 12a of the lower electrode 12 can be formed by cutting using an ion milling device. Further, the first mass body 17a and the second mass body 18a can be formed by dry etching or wet etching after being deposited using a sputtering method.

  By adopting such a configuration, the acoustic impedances at the sides facing each other on the outer periphery of the resonance part R1 are different, so the phase of the elastic wave W11 (reflected wave) reflected by the first mass body 17a and the second mass body The phase of the elastic wave W13 (reflected wave) reflected by 18a does not coincide with each other, and it is possible to suppress the standing wave of the transverse wave from strengthening.

(Example 5)
FIG. 15A is a plan view of a principal part of a fifth example of the resonator according to the embodiment. FIG. 15B is a cross-sectional view taken along the line AA in FIG. 15A. The configuration shown in the present embodiment is different from the configuration shown in Embodiment 4 in that a part of the contact electrode 21 is extended onto the inclined portion 11b instead of the second mass body 18a. The first mass body 17a is formed of a material different from that of the contact electrode 21, and can be formed of, for example, the material described in the column of Example 4.

  In the present embodiment, since the end portion 21a of the contact electrode 21 is formed so as to be positioned on the inclined portion 11b, the acoustic impedance at the sides facing each other on the outer periphery of the resonance portion R1 is different. The phase of the elastic wave W11 (reflected wave) reflected by 17a and the phase of the elastic wave W13 (reflected wave) reflected by the end 21a of the contact electrode 21 do not coincide with each other, and the standing wave of the transverse wave strengthens. Can be suppressed.

  Moreover, according to the present Example, since it is the structure which integrated the 2nd mass body 18a and the contact electrode 21 in Example 4, a manufacturing man-hour can be reduced.

  In the present embodiment, the second mass body 18a and the contact electrode 21 shown in Embodiment 4 are integrally formed. However, any one of the first mass body 17a and the second mass body 18a is used. Any one may be used as long as it is formed of the same material as the contact electrode 21 and formed integrally with the contact electrode 21.

(Example 6)
FIG. 16A is a plan view of a principal part of a sixth example of the resonator according to the embodiment. 16B is a cross-sectional view taken along the line AA in FIG. 16A. The piezoelectric thin film resonator of the present embodiment is formed in the substrate 14, the piezoelectric film 13, the upper electrode 11 and the lower electrode 12 disposed so as to sandwich the piezoelectric film 13, and the non-resonant portion R <b> 2 on the upper electrode 11. The contact electrode 21 made of a low resistance electrode (Au, Al, etc.), a third mass body 19a, and a fourth mass body 20a are provided. The third mass body 19a is desirably arranged from a position near the non-resonant part R2 on the inclined part 11a of the upper electrode 11 to the non-resonant part R2. In the present embodiment, it is disposed at a position in contact with the piezoelectric film 13 in the vicinity of the end portion of the upper electrode 11 from the inclined portion 11a. The third mass body 19a is preferably formed of a piezoelectric body or a dielectric body. The fourth mass body 20a is formed by being stacked on the third mass body 19a. The third mass body 19a and the fourth mass body 20a include, for example, aluminum nitride (AlN), lead zirconate titanate (PZT), silicon oxide (SiO2), titanium oxide (TiO2), ruthenium (Ru), Molybdenum (Mo), gold (Au), titanium (Ti), copper (Cu), tungsten (W), and aluminum (Al) can be used. The film thickness, width, and arrangement of the third mass body 19a and the fourth mass body 20a can be obtained from, for example, a simulation using the general-purpose piezoelectric analysis software described above, and more optimally derived from an experiment. It is desirable. The inclined portion 11a of the upper electrode 11 and the inclined portion 12a of the lower electrode 12 can be formed by cutting using an ion milling device. In addition, the third mass body 19a and the fourth mass body 20a can be formed by dry etching or wet etching after being deposited using a sputtering method.

  With such a configuration, the third mass body 19a and the fourth mass body 20a can be arranged at the maximum outside in the resonance part R1, and the area contributing to vibration is reduced by the addition of the mass body. And it can prevent that an electromechanical coupling coefficient falls. At this time, if a metal is laminated on the third mass body 19a, the same effect can be obtained with a smaller film thickness than when only a dielectric having a low mass is added.

(Example 7)
FIG. 17A is a plan view of relevant parts of a seventh example of the resonator according to the present embodiment. FIG. 17B is a cross-sectional view taken along line AA in FIG. 17A. The configuration shown in the present embodiment is different from the configuration shown in the sixth embodiment in that the second mass body 18a (see the fourth embodiment is provided) on the inclined portion 11b formed at a position facing the inclined portion 11a in the upper electrode 11. ). Other configurations are the same as the configurations shown in the sixth embodiment. Further, the specific configuration of the second mass body 18a has been described in the fourth embodiment, and is omitted. The mass of the second mass body 18a may be at least different from the total mass of the third mass body 19a and the fourth mass body 20a.

  With such a configuration, the third mass body 19a and the fourth mass body 20a can be arranged at the maximum outside in the resonance part R1, and the area contributing to vibration is reduced by the addition of the mass body. And it can prevent that an electromechanical coupling coefficient falls. At this time, if a metal is laminated on the third mass body 19a, the same effect can be obtained with a smaller film thickness than when only a dielectric having a low mass is added.

  Further, since the acoustic impedances at the sides facing each other on the outer periphery of the resonance part R1 are different, the phase of the elastic wave W11 (reflected wave) reflected by the third mass body 19a and the fourth mass body 20a and the second mass body The phase of the elastic wave W13 (reflected wave) reflected by 18a does not coincide with each other, and it is possible to suppress the standing wave of the transverse wave from strengthening.

(Example 8)
FIG. 18A is a plan view of a principal part of an eighth example of the resonator according to the present embodiment. 18B is a cross-sectional view taken along the line AA in FIG. 18A. The configuration shown in the present embodiment is different from the configuration shown in Embodiment 7 in that a part of the contact electrode 21 is extended onto the inclined portion 11b instead of the second mass body 18a. The first mass body 17a is formed of a material different from that of the contact electrode 21, and can be formed of, for example, the material described in the column of Example 4.

  In the present embodiment, since the end portion 21a of the contact electrode 21 is formed so as to be positioned on the inclined portion 11b, the acoustic impedance at the sides facing each other on the outer periphery of the resonance portion R1 is different. The phase of the elastic wave W11 (reflected wave) reflected by 17a and the phase of the elastic wave W13 (reflected wave) reflected by the end 21a of the contact electrode 21 do not coincide with each other, and the standing wave of the transverse wave strengthens. Can be suppressed.

  Moreover, according to the present Example, since it is the structure which integrated the 2nd mass body 18a and the contact electrode 21, a manufacturing man-hour can be reduced.

  In the present embodiment, the second mass body 18a and the contact electrode 21 shown in the seventh embodiment are integrally formed. However, any one of the first mass body 17a and the second mass body 18a is used. Any one may be used as long as it is formed of the same material as the contact electrode 21 and formed integrally with the contact electrode 21.

  In the piezoelectric thin film resonators of Examples 1 to 8, the upper electrode 11 and the lower electrode 12 are made of, for example, aluminum (Al), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum ( Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), or the like can be used. For the piezoelectric film 13, aluminum nitride (AlN), lead zirconate titanate (PZT), lead titanate (PbTiO3), or the like can be used. The substrate 14 can be made of silicon, glass, or the like. The piezoelectric film 13 preferably contains aluminum nitride (AlN). Since AlN has a high sound speed, a resonator having a good Q value can be realized. Moreover, it is preferable that at least one of the lower electrode 12 and the upper electrode 11 includes a ruthenium (Ru) film. Since Ru is a material having a high acoustic impedance, a resonator having a good Q value can be realized.

  In the piezoelectric thin film resonator of the present embodiment, the lower electrode 12 is arranged on the gap 15 formed through the substrate 14. However, the gap is formed on the surface of the substrate 14, and the lower electrode 12 is formed on the gap. It is good also as a structure which arranges the lower electrode 12 in this.

  Further, the piezoelectric thin film resonator in the present embodiment is not limited to the FBAR type piezoelectric thin film resonator, but may be an SMR (solidly mounted resonator) type piezoelectric thin film resonator.

  Furthermore, the drawings shown in the embodiments describe only the main part of the resonator, and other members may be provided. For example, a dielectric film may be provided as a reinforcement or etching stop layer under the lower electrode 12, or a passivation film or a dielectric film for frequency adjustment may be provided on the upper electrode 11.

[2. Method for manufacturing piezoelectric thin film resonator]
19A to 19C are diagrams for explaining a manufacturing process of the piezoelectric thin film resonator. The illustrated piezoelectric thin film resonator has a configuration in which a gap is formed between the surface of the substrate 14 and the lower electrode 12 in the piezoelectric thin film resonator shown in the fourth embodiment.

  First, as shown in FIG. 19A, a sacrificial layer film 30 made of magnesium oxide (MgO) is formed on a substrate 14 made of an Si substrate (or quartz substrate) by a sputtering method or a vacuum evaporation method. The thickness of the substrate 14 is, for example. The thickness was about 20 to 100 nm. The sacrificial layer 30 is not particularly limited as long as it is a material that can be easily dissolved by an etching solution, such as zinc oxide (ZnO), germanium (Ge), titanium (Ti), silicon oxide (SiO 2), in addition to MgO.

  Next, the sacrificial layer 30 is patterned into a desired shape by photolithography and etching. Here, the upper electrode 11 and the lower electrode 12 are patterned into an elliptical shape that is substantially equal to the shape of the overlapping portion.

  Next, as illustrated in FIG. 19B, the lower electrode 12, the piezoelectric film 13, the upper electrode 11, and the weighting layer are sequentially formed on the substrate 14 and the sacrificial layer 30. The lower electrode 12 is formed by sputtering, and the lower electrode 12 is patterned into a desired shape by photolithography and etching. Subsequently, AlN as the piezoelectric film 13 is formed by sputtering using an Al target in an Ar / N2 mixed gas atmosphere. Then, the Ru film of the upper electrode 11 is formed by sputtering. Furthermore, if the weighting layer is Ti, for example, sputtering film formation is performed. The laminated film thus formed is subjected to a photolithography technique and an etching process (wet etching or dry etching), and the weighting layer, the upper electrode 11 and the piezoelectric film 13 are patterned into a desired shape. The sputtering conditions are set so that the stress of the laminated film composed of the lower electrode 12, the piezoelectric film 13, and the upper electrode 11 becomes a compressive stress. The central portion of the lead portion of the upper electrode 11 in contact with the membrane is formed on the gap formed in the next step, and both end portions of the lead portion of the upper electrode 11 are formed outside the gap.

  Next, as shown in FIG. 19C, an etching solution introduction hole is formed in the lower electrode 12 by a photolithography technique using resist patterning, and the etching solution is introduced from the etching solution introduction hole to remove the sacrificial layer 30 by etching. By doing so, the air gap 31 is formed. The etchant introduction hole may be formed at the same time when the lower electrode 12 is etched. Here, the stress of the laminated film composed of the lower electrode 12, the piezoelectric film 13, and the upper electrode 11 is set to be a compressive stress. By satisfying such a stress condition, at the end of the etching of the sacrificial layer 30, the laminated film swells and a dome-shaped gap 31 can be formed between the lower electrode 12 and the substrate 14.

[3. (Duplexer configuration)
A duplexer is mounted in mobile communication (high-frequency wireless communication) such as a mobile phone terminal, a PHS (Personal Handy-phone System) terminal, and a wireless LAN system. The duplexer has a transmission function and a reception function for communication radio waves and the like, and is used in a wireless device in which frequencies of a transmission signal and a reception signal are different.

  FIG. 20 shows a configuration of a duplexer including the piezoelectric thin film resonator according to the present embodiment. The duplexer 52 includes a phase matching circuit 53, a reception filter 54, and a transmission filter 55. The phase matching circuit 53 is an element for adjusting the phase of the impedance of the reception filter 54 in order to prevent the transmission signal output from the transmission filter 55 from flowing into the reception filter 54 side. An antenna 51 is connected to the phase matching circuit 53. The reception filter 54 is configured by a band-pass filter that allows only a predetermined frequency band of the reception signal input via the antenna 51 to pass. An output terminal 56 is connected to the reception filter 54. The transmission filter 55 is configured by a band pass filter that allows only a predetermined frequency band among the transmission signals input via the input terminal 57 to pass. An input terminal 57 is connected to the transmission filter 55. Here, the reception filter 54 and the transmission filter 55 include the piezoelectric thin film resonator in the present embodiment.

  As described above, the piezoelectric thin film resonator according to the present embodiment is provided in the reception filter 54 and the transmission filter 55, thereby preventing the occurrence of spike-like loss (spurious) in the passband, and the insertion loss, EVM (Error Vector Magnitude) can be reduced.

[4. (Configuration of communication module)
FIG. 21 shows an example of a communication module including the piezoelectric thin film resonator of the present embodiment or the above duplexer. As shown in FIG. 21, the duplexer 62 includes a reception filter 62a and a transmission filter 62b. The reception filter 62a is connected to reception terminals 63a and 63b corresponding to, for example, balanced output. The transmission filter 62b is connected to the transmission terminal 65 via the power amplifier 64. Here, the reception filter 62a and the transmission filter 62b include the piezoelectric thin film resonator in the present embodiment.

  When performing a reception operation, the reception filter 62a passes only a signal in a predetermined frequency band among reception signals input via the antenna terminal 61, and outputs the signal from the reception terminals 63a and 63b to the outside. Further, when performing a transmission operation, the transmission filter 62b passes only a signal in a predetermined frequency band among transmission signals input from the transmission terminal 65 and amplified by the power amplifier 64, and outputs the signal from the antenna terminal 61 to the outside. To do.

  As described above, the piezoelectric thin film resonator or duplexer according to the present embodiment is provided in the reception filter 62a and the transmission filter 62b of the communication module, thereby preventing the occurrence of spike-like loss (spurious) in the passband and inserting Loss and EVM (Error Vector Magnitude) can be reduced.

  The configuration of the communication module shown in FIG. 21 is an example, and the same effect can be obtained even when the piezoelectric thin film resonator of the present invention is mounted on a communication module of another form.

[5. Configuration of communication device]
FIG. 22 shows an RF block of a mobile phone terminal as an example of a communication device including the piezoelectric thin film resonator of the present embodiment. The configuration shown in FIG. 22 shows the configuration of a mobile phone terminal that supports a GSM (Global System for Mobile Communications) communication scheme and a W-CDMA (Wideband Code Division Multiple Access) communication scheme. Further, the GSM communication system in the present embodiment corresponds to the 850 MHz band, 950 MHz band, 1.8 GHz band, and 1.9 GHz band. In addition to the configuration shown in FIG. 22, the mobile phone terminal includes a microphone, a speaker, a liquid crystal display, and the like, but they are not shown in the description of the present embodiment because they are not necessary. Here, the reception filters 73a, 77, 78, 79, and 80 and the transmission filter 73b include the piezoelectric thin film resonator according to the present embodiment.

  First, the received signal input via the antenna 71 selects an LSI to be operated by the antenna switch circuit 72 depending on whether the communication method is W-CDMA or GSM. When the input received signal is compatible with the W-CDMA communication system, switching is performed so that the received signal is output to the duplexer 73. The reception signal input to the duplexer 73 is limited to a predetermined frequency band by the reception filter 73 a, and a balanced reception signal is output to the LNA 74. The LNA 74 amplifies the input received signal and outputs it to the LSI 76. The LSI 76 performs demodulation processing on the audio signal based on the input received signal and controls the operation of each unit in the mobile phone terminal.

  On the other hand, when transmitting a signal, the LSI 76 generates a transmission signal. The generated transmission signal is amplified by the power amplifier 75 and input to the transmission filter 73b. The transmission filter 73b passes only a signal in a predetermined frequency band among input transmission signals. The transmission signal output from the transmission filter 73 b is output from the antenna 71 to the outside via the antenna switch circuit 72.

  In addition, when the received signal to be input is a signal corresponding to the GSM communication system, the antenna switch circuit 72 selects any one of the reception filters 77 to 80 according to the frequency band and outputs the received signal. To do. A reception signal whose band is limited by any one of the reception filters 77 to 80 is input to the LSI 83. The LSI 83 performs a demodulation process on the audio signal based on the input received signal, and controls the operation of each unit in the mobile phone terminal. On the other hand, when transmitting a signal, the LSI 83 generates a transmission signal. The generated transmission signal is amplified by the power amplifier 81 or 82 and output from the antenna 71 to the outside via the antenna switch circuit 72.

  As described above, by providing the communication device with the piezoelectric thin film resonator of the present embodiment or the communication module including the piezoelectric thin film resonator, occurrence of spike-like loss (spurious) in the pass band can be prevented. Insertion loss and EVM (Error Vector Magnitude) can be reduced.

[6. Effects of the embodiment, etc.]
According to the present embodiment, at the boundary between the region where the upper and lower electrodes are formed to face each other and the region outside the upper electrode 11, the acoustic impedance of a part of the boundary is larger than the acoustic impedance of the region inside it. By adding the mass body 16 on the top, it is possible to confine transverse mode waves in the piezoelectric film 13 and not add mass to some boundaries. It is possible to prevent the strength of the standing wave in the transverse mode from increasing. Therefore, it is possible to suppress the decrease in the electromechanical coupling coefficient as compared with the conventional example while preventing the energy dissipation of the transverse wave, and to prevent the bandwidth from being narrowed. Further, an increase in the standing wave mode can be suppressed, and a large spike-like loss point (spurious) can be prevented from being generated on the lower frequency side than the resonance point.

  Further, at the boundary between the region where the upper and lower electrodes are opposed to each other and the region outside the region, the acoustic impedance at a location where the acoustic impedance matches the end of the upper electrode 11 at the boundary does not match the end of the upper electrode 11. Since the transverse mode waves can be confined in the piezoelectric film 13 and the phases of the transverse mode waves reflected at different boundaries of the acoustic impedance are different from each other. An increase in strength can be prevented.

  Further, by adopting a configuration in which at least a part of the mass body includes a dielectric or a piezoelectric body and the dielectric or piezoelectric body is in contact with the upper electrode 11, the position where the mass is added is positioned as close to the boundary as possible. It is possible to reduce the area that contributes to vibration by adding mass and to prevent the electromechanical coupling coefficient k ^ 2 from decreasing.

  Further, the mass body is arranged by providing the upper electrode 11 with the inclined portions 11a and 11b having an inclination angle of less than 90 ° at the boundary between the region where the upper and lower electrodes are opposed to each other and the outer region. In this case, it is possible to prevent the discontinuity of the shape due to the step and the manufacturing defect, and it is possible to form a high-quality resonator.

  Further, when the mass body loaded so as to increase the acoustic impedance at the boundary that does not coincide with the end of the upper electrode 11 is composed of the low resistance electrode containing Ti and Au, the transverse wave can be confined in the resonance part R1. At the same time, the series resistance of the resonator can be reduced, and a high-Q resonator can be formed.

  In addition, since the region where the upper and lower electrodes are opposed to each other has an elliptical shape, even if a transverse wave is reflected at the boundary between the resonance part R1 and the non-resonance part R2, reflected waves in a specific direction are strengthened. It is possible to further suppress the strengthening of the standing wave in the transverse mode.

  In addition, since the region formed by facing the upper and lower electrodes is a non-rectangular polygonal shape, even if a transverse wave is reflected at the boundary between the resonance part R1 and the non-resonance part R2, a reflected wave in a specific direction is generated. It is possible to further suppress the strengthening of the standing wave in the transverse mode without strengthening each other.

  Further, since the inclined portions 11a and 11b are formed by the dry etching process, the inclined portions can be formed with high accuracy.

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

(Appendix 1)
Piezoelectric thin film comprising: a substrate; an upper electrode and a lower electrode disposed on the substrate and partially disposed to face each other; and a piezoelectric film disposed between the upper electrode and the lower electrode A resonator comprising a mass body disposed on the upper electrode, wherein the mass body is disposed at a part of an end portion of the upper electrode facing the lower electrode. vessel.

(Appendix 2)
The mass body has an apparent acoustic impedance of a part of the piezoelectric film at a boundary between a region where the upper electrode and the lower electrode are opposed to each other and a region outside the region, in a region inside the boundary. The piezoelectric thin film resonator according to appendix 1, wherein the piezoelectric thin film resonator is disposed at a position larger than an apparent acoustic impedance of the piezoelectric film.

(Appendix 3)
The mass body has an apparent acoustic impedance of the piezoelectric film at a boundary that coincides with an end of the upper electrode at a boundary between a region where the upper electrode and the lower electrode are opposed to each other and a region outside the region. 2. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is arranged so that an apparent acoustic impedance of the piezoelectric film at a boundary that does not coincide with an end portion of the upper electrode is different.

(Appendix 4)
The piezoelectric thin film resonator according to any one of appendices 1 to 3, wherein at least a part of the mass body includes a dielectric or a piezoelectric body, and the dielectric or the piezoelectric body is in contact with the upper electrode.

(Appendix 5)
The piezoelectric thin film resonance according to any one of appendices 1 to 3, wherein the upper electrode includes an inclined portion of less than 90 ° at a boundary between a region facing the lower electrode and a region outside the region. vessel.

(Appendix 6)
The piezoelectric thin film resonator according to appendices 1 to 4, wherein the mass body includes titanium (Ti) and gold (Au).

(Appendix 7)
The piezoelectric thin film resonance according to any one of appendices 1 to 3, wherein the region formed by facing the upper electrode and the lower electrode is an elliptical shape when viewed in the normal direction of the main plane of the upper electrode. vessel.

(Appendix 8)
The region formed by the upper electrode and the lower electrode facing each other is a polygon having a non-rectangular shape when viewed in the normal direction of the main plane of the upper electrode. Piezoelectric thin film resonator.

(Appendix 9)
The piezoelectric thin film resonator according to appendix 8, wherein the inclined portion is formed by a dry etching process.

(Appendix 10)
The piezoelectric thin film resonator according to any one of supplementary notes 1 to 3, wherein the piezoelectric film is made of aluminum nitride (AlN).

(Appendix 11)
The piezoelectric thin film resonator according to appendix 4, wherein the dielectric is made of silicon oxide (SiO2).

(Appendix 12)
10. The piezoelectric thin film resonator according to appendices 1 to 9, wherein at least a portion of the upper electrode and the lower electrode that are in contact with the piezoelectric film is formed of ruthenium (Ru).

(Appendix 13)
A filter comprising the piezoelectric thin film resonator according to any one of appendices 1 to 12.

(Appendix 14)
A duplexer comprising the filter according to appendix 13.

(Appendix 15)
A communication module comprising the filter according to appendix 13 or the duplexer according to appendix 14.

(Appendix 16)
A communication device comprising the communication module according to attachment 15.

  The piezoelectric thin film resonator of the present invention is useful for an apparatus capable of receiving or transmitting a signal having a predetermined frequency.

11 Upper electrode 12 Lower electrode 13 Piezoelectric film 14 Substrate 16 Mass

Claims (15)

A substrate,
An upper electrode and a lower electrode disposed on the substrate and partially disposed to face each other;
A piezoelectric thin film resonator comprising a piezoelectric film disposed between the upper electrode and the lower electrode,
Comprising a mass disposed on the upper electrode;
The upper electrode includes an inclined portion of less than 90 ° at a boundary between a region facing the lower electrode and a region outside the region,
The mass body is disposed on the inclined portion,
In the mass body, the mass body on the inclined portion of the end portion of the upper electrode and the mass body on the inclined portion facing the end portion are made of different materials, respectively.
Piezoelectric thin film resonator. The mass body is
The apparent acoustic impedance of a part of the piezoelectric film at the boundary between the region where the upper electrode and the lower electrode are opposed to each other and the region outside the region is apparent from the apparent acoustic impedance of the piezoelectric film in the region inside the boundary. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is disposed at a position larger than the acoustic impedance of the piezoelectric thin film resonator. The mass body is
An apparent acoustic impedance of the piezoelectric film at a boundary that coincides with an end of the upper electrode at a boundary between a region where the upper electrode and the lower electrode are opposed to each other and a region outside the region, and the upper electrode 2. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is arranged so that an apparent acoustic impedance of the piezoelectric film at a boundary that does not coincide with an end of the piezoelectric film is different. The mass body is
The piezoelectric thin film resonator according to any one of claims 1 to 3, wherein at least a part includes a dielectric or a piezoelectric body, and the dielectric or the piezoelectric body is in contact with the upper electrode. The mass body is
The piezoelectric thin film resonator according to claim 1, comprising titanium (Ti) and gold (Au).   4. The piezoelectric thin film according to claim 1, wherein a region formed by facing the upper electrode and the lower electrode has an elliptical shape when viewed in a normal direction of a main plane of the upper electrode. Resonator.   The region formed by facing the upper electrode and the lower electrode is a polygon having a non-rectangular shape when viewed in the normal direction of the main plane of the upper electrode. Piezoelectric thin film resonator. The inclined portion is
The piezoelectric thin film resonator according to claim 7, wherein the piezoelectric thin film resonator is formed by a dry etching process. The piezoelectric film is
The piezoelectric thin film resonator according to claim 1, which is made of aluminum nitride (AlN). The dielectric is
The piezoelectric thin film resonator according to claim 4, wherein the piezoelectric thin film resonator is made of silicon oxide (SiO2). The upper electrode and the lower electrode are
The piezoelectric thin film resonator according to claim 1, wherein at least a portion in contact with the piezoelectric film is made of ruthenium (Ru).   A filter comprising the piezoelectric thin film resonator according to claim 1.   A duplexer comprising the filter according to claim 12. A communication module comprising the filter according to claim 12 or the duplexer according to claim 13 .   A communication device comprising the communication module according to claim 14.

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