JP2008311873A - Filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-loss and high-performance filter which is improved in a Q value at an anti-resonant frequency of a piezoelectric thin film resonator. <P>SOLUTION: The filter includes a plurality of piezoelectric thin film resonators each having a substrate 10, a bottom electrode 12 provided on the substrate 10, a piezoelectric film 14 provided on the bottom electrode 12, a top electrode 16 which is so formed on the piezoelectric film 14 as to have a portion facing the bottom electrode 12 with the piezoelectric film 14 in-between. The plurality of piezoelectric thin film resonators are provided in a ladder shape, and in parallel resonators P provided in parallel arms among the plurality of piezoelectric thin film resonators, portions (resonating part 20) where the bottom electrode 12 faces the top electrode 16 with the piezoelectric film 14 in-between are in a shape where two ellipses with different ratios of axial lengths are connected by sharing one axis. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a filter, and more particularly to a filter having a plurality of piezoelectric thin film resonators provided in a ladder shape.

  With the rapid spread of wireless devices typified by mobile phones, there is an increasing demand for small and light resonators and filters configured by combining them. Until now, mainly dielectric filters and surface acoustic wave (SAW) filters have been used. Recently, however, piezoelectric thin-film resonance is an element that has particularly good characteristics at high frequencies and that can be miniaturized and made monolithic. Children and filters constructed using them are drawing attention.

  Among the piezoelectric thin film resonators, there are an FBAR (Film Bulk Acoustic Resonator) type and an SMR (Solidly Mounted Resonator) type. An FBAR type piezoelectric thin film resonator has a laminated film structure including a lower electrode, a piezoelectric film, and an upper electrode on a substrate. A gap is formed under the lower electrode in a portion (resonant portion) where the lower electrode and the upper electrode face each other with the piezoelectric film interposed therebetween. Here, the voids in the FBAR are formed in the substrate by wet etching or dry etching or the like (cavity) formed between the lower electrode and the substrate by wet etching the sacrificial layer provided on the substrate surface. There are gaps (via holes). The SMR has an acoustic multilayer film instead of the air gap. In the acoustic multilayer film, a film having a high acoustic impedance and a film having a low acoustic impedance are alternately laminated with a film thickness of λ / 4 (λ: wavelength of elastic wave).

Non-Patent Document 1 discloses an FBAR having a via hole. Patent Document 1 discloses an FBAR having a cavity. FIG. 1 is a cross-sectional view of an FBAR having a via hole, and FIG. 2 is a cross-sectional view of the FBAR having a cavity. Referring to FIG. 1, a lower electrode 12, a piezoelectric film 14, and an upper electrode 16 are sequentially provided on a substrate 10 made of silicon having a SiO ₂ film 11 on the surface. A space 18 (via hole) is provided in the substrate 10 below the portion where the lower electrode 12 and the upper electrode 16 face each other. Referring to FIG. 2, a SiO ₂ film 11 that functions as a support film is provided on a substrate 10 made of silicon so that a void 18 is formed. A lower electrode 12, a piezoelectric film 14, and an upper electrode 16 are sequentially provided on the SiO ₂ film 11. The lower electrode 12 and the upper electrode 16 have a portion on the gap 18 facing each other with the piezoelectric film 14 interposed therebetween.

Here, as the lower electrode 12 and the upper electrode 16, aluminum (Al), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), ruthenium (Ru), rhodium ( Rh), iridium (Ir), chromium (Cr), titanium (Ti), or the like, or a laminated material combining these can be used. As the piezoelectric film 14, aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), or the like can be used. As the substrate 10, silicon, glass, GaAs, or the like can be used.

  When a high-frequency electrical signal is applied between the upper electrode and the lower electrode, elasticity generated by an elastic wave excited by the reverse piezoelectric effect or distortion caused by the piezoelectric effect inside the piezoelectric film sandwiched between the upper electrode and the lower electrode A wave is generated. These elastic waves are converted into electrical signals. Since such an elastic wave is totally reflected on the surface where the upper electrode and the lower electrode are in contact with air, it becomes a longitudinal vibration wave having a main displacement in the thickness direction. The total film thickness H of the laminated film composed of the lower electrode, the piezoelectric film, and the upper electrode (including the mass load film added on the upper electrode) is an integer of 1/2 (1/2 wavelength) of the wavelength λ of the elastic wave A resonance phenomenon occurs at a frequency that is double (n times) (that is, a frequency at which H = nλ / 2). Here, when the propagation speed of the elastic wave determined by the material of the piezoelectric film is V, the resonance frequency F is F = nV / (2H). From this, the resonance frequency F can be controlled by the total film thickness H of the laminated film, and a piezoelectric thin film resonator having a desired frequency characteristic can be obtained.

Ladder type filters are mainly used as filters using piezoelectric thin film resonators. The ladder filter has a series resonator connected in series between the input terminal Tin and the output terminal Tout, and a parallel resonator connected in parallel, and functions as a bandpass filter. FIG. 3A and FIG. 3B show equivalent circuit diagrams of the series resonator S and the parallel resonator P, respectively. FIG. 3C shows the frequency characteristics of the series resonator S and the parallel resonator P. Passing amount of the series resonator S has a maximum value at the resonance frequency f _rs, the minimum value at the antiresonance frequency f _{the as.} The amount of passage through the parallel resonator P has a minimum value at the resonance frequency f _rp and a maximum value at the anti-resonance frequency f _ap . FIG. 4A is an equivalent circuit diagram of a ladder type filter in which the series resonator S and the parallel resonator P are configured in one stage. FIG. 4B shows the pass characteristic of this filter. By setting the resonance frequency _frs of the series resonator S and the antiresonance frequency f _ap of the parallel resonator P to be substantially the same frequency, a bandpass filter can be configured.

In Patent Documents 2 to 4, a lower electrode and an upper electrode are opposed to each other with a piezoelectric film interposed therebetween in order to suppress a spurious mode (unnecessary vibration) called an inharmonic mode generated by an elastic wave propagating in a horizontal direction on a substrate. A technique for controlling the contour shape of a portion (resonant portion) is disclosed.
ELECTRONICS LETTERS JULY 1981 p507-p509 JP 60-189307 A JP 2005-33262 A JP 2003-17974 A JP 2000-31552 A

  Since the piezoelectric thin film resonator causes the piezoelectric film itself to resonate and vibrate, a high-quality piezoelectric film with little loss during excitation is required. In order to form such a high quality piezoelectric film, high energy is required at the time of film formation. For example, in the film formation using the MOCVD (Metal Organic Chemical Vapor Deposition) method, it is necessary to heat the substrate to 1000 ° C. or more. In the film formation using the PECVD (Plasma Enhanced Chemical Vapor Deposition) method, In addition, it is necessary to heat the substrate at 400 ° C. or higher. Even in film formation using sputtering technology, there is an increase in substrate temperature due to sputtering of the insulating film. For this reason, the piezoelectric film has a strong film stress.

  In the piezoelectric thin film resonator, the elastic wave is a longitudinal vibration wave having a main displacement in the thickness direction of the piezoelectric film. However, if the piezoelectric film has a strong film stress, deformation in the thickness direction during excitation is hindered. Thereby, the resonance sharpness (Q value) at the anti-resonance frequency is deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a low-loss and high-performance filter by improving the Q value at the antiresonance frequency of a piezoelectric thin film resonator.

  The present invention provides a substrate, a lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode, and a portion facing the lower electrode with the piezoelectric film interposed therebetween. A plurality of piezoelectric thin film resonators, wherein the plurality of piezoelectric thin film resonators are provided in a ladder shape, and the plurality of piezoelectric thin film resonators provided on a parallel arm among the plurality of piezoelectric thin film resonators The piezoelectric thin film resonator has a shape in which two ellipses with different length ratios of shafts are connected by sharing a single axis at a portion where the lower electrode and the upper electrode face each other across the piezoelectric film. It is a filter characterized by having. ADVANTAGE OF THE INVENTION According to this invention, the Q value of the antiresonance frequency of the piezoelectric thin film resonator provided in the parallel arm among the piezoelectric thin film resonators provided in the ladder type can be improved. For this reason, it becomes possible to improve the loss in the pass band of the filter.

  In the above configuration, one of the two ellipses may be an ellipse having the one axis as a minor axis, and the other ellipse may be an ellipse having the one axis as a major axis. According to this configuration, loss in the pass band of the filter can be improved.

  In the above configuration, the lower electrode may have an ellipse whose major axis is the one axis, and the upper electrode may have an ellipse whose minor axis is the one axis. According to this configuration, the stress applied to the piezoelectric film can be suppressed. Therefore, the Q value of the antiresonance frequency can be improved, and the loss in the pass band of the filter can be improved.

  In the above configuration, the ellipse having the short axis as the one axis may have a ratio of the short axis length to the long axis length of 7: 8-10. According to this configuration, the Q value of the antiresonance frequency can be further improved, and the loss in the passband of the filter can be further improved.

  The said structure WHEREIN: The part which the said lower electrode and the said upper electrode oppose on both sides of the said piezoelectric film can be set as the structure provided on the space | gap provided in the said board | substrate.

  The said structure WHEREIN: The part which the said lower electrode and the said upper electrode oppose on both sides of the said piezoelectric film can be set as the structure contained in the said space | gap. According to this configuration, the resonance characteristics of the piezoelectric thin film resonator can be improved.

  In the above structure, the piezoelectric film may be formed of aluminum nitride or zinc oxide exhibiting orientation with a (002) direction as a main axis.

  ADVANTAGE OF THE INVENTION According to this invention, the Q value of the antiresonance frequency of the piezoelectric thin film resonator provided in the parallel arm among the piezoelectric thin film resonators provided in the ladder type can be improved. For this reason, a filter with improved loss in the passband can be obtained.

  First, in order to realize a low-loss filter, a simulation performed on the piezoelectric thin film resonator constituting the filter will be described. FIG. 5A is a top view of the piezoelectric thin film resonator used in the simulation, and FIG. 5B is a cross-sectional view taken along the line XX in FIG.

  Referring to FIGS. 5A and 5B, a lower electrode 12 is provided on a substrate 10 made of silicon. A piezoelectric film 14 is provided on the lower electrode 12. An upper electrode 16 is provided on the piezoelectric film 14 so as to have a portion facing the lower electrode 12 with the piezoelectric film 14 interposed therebetween. Thereby, a laminated film 17 including the lower electrode 12, the piezoelectric film 14, and the upper electrode 16 is formed. The portion where the lower electrode 12 and the upper electrode 16 face each other across the piezoelectric film 14 (resonance unit 20) is connected by two ellipses (P and Q) having different axis length ratios sharing one axis. The lower electrode 12 has an ellipse Q, and the upper electrode 16 has an ellipse P. Here, the length of the axis shared by the two ellipses (P and Q) is A, the length of the other axis of the ellipse P is B, and the length of the other axis of the ellipse Q is C. The ratio of the lengths of A, B, and C is a: b: c. A space 18 is provided in the substrate 10 below the resonance portion 20, and the resonance portion 20 is included in the space 18. The piezoelectric film 14 is provided with an opening 22 for electrical connection to the lower electrode 12.

  When the air gap 18 is formed under the resonating portion 20, the laminated film 17 is deformed to a height h as shown by the broken line in FIG. Here, FIG. 6 shows a simulation result calculated for the relationship between the shape of the resonance part 20 and the deformation height h of the laminated film 17. The horizontal axis of FIG. 6 shows the ratio of b when the ratio of the lengths a: b: c of the two ellipses (P and Q) is fixed at 7: 5, and the vertical axis indicates the laminated film. 17 shows a deformation height h. Moreover, the calculation result about each case where the film | membrane stress at the time of film-forming of the piezoelectric film 14 is 500 MPa, 250 MPa, and 100 MPa is shown. According to FIG. 6, when the ratio of b is 9, that is, when a: b: c is 7: 9: 5, the deformation of the laminated film 17 is the largest. The greatest deformation of the laminated film 17 means that the film stress when the piezoelectric film 14 is formed is most released.

  Next, FIG. 7A to FIG. 7C show simulation results for calculating the residual stress distribution of the piezoelectric film 14 after the stack film 17 is deformed to the height h. 7A shows a case where the shaft length ratio a: b: c is 7: 3: 5, FIG. 7B shows a case where 7: 9: 5, and FIG. 7C shows a case where 7: 15: 5. 7A to 7C show the results when the film stress during the formation of the piezoelectric film 14 is 500 MPa. With reference to FIG. 7A to FIG. 7C, changing the ratio of b causes a change in the residual stress distribution of the piezoelectric film 14, and the shaft length ratio a: b: c is 7: 9. : 5, the ratio of the area where the residual stress is as small as 162.5 MPa (the hatched area in FIG. 7 (a) to FIG. 7 (c)) is the largest with respect to the area of the resonance part 20. . From this, it can be confirmed that when the deformation of the laminated film 17 is large, the region where the residual stress of the piezoelectric film 14 is small is the largest.

  From these results, the film stress at the time of forming the piezoelectric film 14 can be partially relieved by the bending deformation of the laminated film 17. Since the magnitude of this deflection deformation varies depending on the shape of the resonance part 20, the piezoelectric film is optimized by optimizing the shape of the resonance part 20, that is, by setting the shaft length ratio a: b: c to 7: 9: 5. The area | region with small 14 residual stress can be enlarged most.

  Next, when the shape of the resonance part 20 is changed, the result about the change of the Q value of the antiresonance frequency is shown. FIG. 8A shows the measurement result of the Q value of the anti-resonance frequency of the piezoelectric thin film resonator of the 2.0 GHz band, and FIG. 8B shows the anti resonance frequency of the piezoelectric thin film resonator of the 2.5 GHz band. The configuration of the piezoelectric thin film resonator used for the measurement is the same as that shown in FIGS. 5 (a) and 5 (b). The substrate 10 is made of Si, the lower electrode 12 is made of a 250 nm thick Ru film, and the upper electrode 16 is made of a 250 nm thick Ru film. The piezoelectric film 14 is made of an AlN film having an orientation with the (002) direction as the main axis, and has a thickness of 1150 nm for a 2.0 GHz band piezoelectric thin film resonator and a thickness of 1000 nm for a 2.5 GHz band piezoelectric thin film resonator. It is.

  Referring to FIGS. 8A and 8B, the horizontal axis is the same as the horizontal axis in FIG. 6, and the vertical axis indicates the Q value of the antiresonance frequency. The solid line indicates an approximate expression obtained by approximating the measurement result with a cubic curve. According to FIGS. 8A and 8B, the Q value of the antiresonance frequency is improved when the ratio of b is 7 or more, and in particular, the Q value of the antiresonance frequency is more when the ratio of b is 8 to 10. Improved. From this result, it can be confirmed that the Q value of the antiresonance frequency is also improved in accordance with the improvement of the residual stress of the piezoelectric film 14.

  Next, the results of changes in the Q value of the resonance frequency when the shape of the resonance unit 20 is changed will be shown. FIG. 9A shows the measurement result of the Q value of the resonance frequency of the piezoelectric thin film resonator of the 2.0 GHz band, and FIG. 9B shows the resonance frequency of the piezoelectric thin film resonator of the 2.5 GHz band.

  Referring to FIGS. 9A and 9B, the horizontal axis is the same as the horizontal axis in FIGS. 8A and 8B, and the vertical axis indicates the Q value of the resonance frequency. In addition, the solid line indicates an approximate expression obtained by approximating the measurement result with a cubic curve, as in FIGS. 8A and 8B. According to FIG. 9A and FIG. 9B, it can be confirmed that the Q value of the resonance frequency simply decreases as the ratio of b increases. This is because the electrical resistance of the upper electrode 16 increases as the ratio of b increases, that is, as the length of the upper electrode 16 increases.

  From the results shown in FIGS. 8A to 9B, by improving the residual stress of the piezoelectric film 14, in particular, the lengths of the axes of the two ellipses (P and Q) constituting the shape of the resonance part 20 are improved. By setting the ratio a: b: c to 7: 8 to 10: 5, a piezoelectric thin film resonator having an improved antiresonance frequency Q value can be obtained. Further, by reducing the ratio of b, it is possible to obtain a piezoelectric thin film resonator having an improved Q value of the resonance frequency. Thus, by controlling the shaft length ratio a: b: c, that is, by controlling the shape of the resonance part 20, the Q value of the antiresonance frequency and the Q value of the resonance frequency can be controlled. Therefore, based on these results, a filter capable of realizing low loss will be described in the first embodiment.

  FIG. 10 is a circuit diagram of a ladder filter according to the first embodiment. Referring to FIG. 10, series resonators S1, S2, and S3 are connected in series between an input terminal Tin and an output terminal Tout. A parallel resonator P1 is connected between the node between the series resonators S1 and S2 and the ground, and a parallel resonator P2 is connected between the node between the series resonators S2 and S3 and the ground. Yes. The series resonator S and the parallel resonator P have different structures as will be described later.

  First, the structure of the series resonator S will be described. FIG. 11A is a top view of the series resonator S, and FIG. 11B is a cross-sectional view taken along the line XX in FIG. Referring to FIGS. 11A and 11B, a portion (resonating portion 20) where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 interposed therebetween has a shape composed of one ellipse. The major axis of the ellipse is 157 μm and the minor axis is 112 μm. That is, the ratio of the length of the major axis to the minor axis of the ellipse is 7: 5. Since other configurations are the same as those of the piezoelectric thin film resonator shown in FIGS. 5A and 5B, the description thereof is omitted. The substrate 10 is made of Si, the lower electrode 12 is made of a Ru film having a thickness of 250 nm, the piezoelectric film 14 is made of an AlN film having an orientation with the main axis in the (002) direction having a thickness of 1150 nm, and the upper electrode 16 Consists of a 250 nm thick Ru film.

  Next, the structure of the parallel resonator P will be described. 12A is a top view of the parallel resonator P, and FIG. 12B is a cross-sectional view taken along the line XX in FIG. 12A. Referring to FIGS. 12A and 12B, a portion where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 therebetween (resonating portion 20) has two ellipses with different axial length ratios (resonance portion 20). P and Q) are connected by sharing one axis. The length A of the shared axis is 133 μm, the length B of the other axis of the ellipse P is 171 μm, and the length C of the other axis of the ellipse Q is 95 μm. That is, the length ratio a: b: c of A, B, and C is 7: 9: 5. A mass load film 24 made of a Ti film and having a thickness of about 100 nm is provided on the upper electrode 16 of the resonance unit 20. By providing the mass load film 24, the resonance frequency of the series resonator S and the antiresonance frequency of the parallel resonator P can be set to substantially the same frequency. Thereby, the characteristics of the bandpass filter can be obtained. The other configuration is the same as that of the series resonator S and is shown in FIG. 11A and FIG.

  A method for manufacturing the series resonator S and the parallel resonator P will be described with reference to FIGS. FIGS. 13 (a) to 13 (c) show sectional views corresponding to the line XX in FIG. 11 (a) with respect to the series resonator S, and FIGS. 13 (d) to 13 (f) show parallel resonance. FIG. 12 is a cross-sectional view corresponding to the section XX in FIG. Referring to FIGS. 13A and 13D, a Ru film is sputtered as a lower electrode 12 in an Ar gas atmosphere under a pressure of 0.6 to 1.2 Pa on a substrate 10 made of Si. Use to form. Thereafter, the lower electrode 12 is formed into a predetermined shape using an exposure technique and an etching technique.

13B and 13E, an AlN film is formed on the substrate 10 and the lower electrode 12 as a piezoelectric film 14 in an Ar / N ₂ mixed gas atmosphere under a pressure of about 0.3 Pa. It is formed using a sputtering method. A Ru film is formed on the piezoelectric film 14 as the upper electrode 16 by sputtering in an Ar gas atmosphere under a pressure of 0.6 to 1.2 Pa. In the parallel resonator P, a Ti film is formed as the mass load film 24 on the upper electrode 16 by using a sputtering method. Thereafter, the piezoelectric film 14, the upper electrode 16, and the mass load film 24 are formed into a predetermined shape using an exposure technique and an etching technique.

  13C and 13F, a deep-RIE (reactive dry etching) method is used and etching is performed from the back surface of the substrate 10 to sandwich the piezoelectric film 14 with the lower electrode 12 and the upper electrode 16. A gap 18 is formed in the substrate 10 under the portion facing each other. As described above, the series resonator S and the parallel resonator P are completed.

  FIG. 14 shows the pass characteristics of the ladder filter according to the first embodiment and the pass characteristics of the ladder filter according to the first comparative example. The ladder type filter according to Comparative Example 1 uses a piezoelectric thin film resonator shown in FIG. 11A and FIG. A piezoelectric thin film resonator shown in FIG. 11A and FIG. 11B is provided on the parallel resonator P, and a mass load film 24 made of a Ti film and having a thickness of about 100 nm is provided on the upper electrode 16 of the resonance section 20. A thin film resonator is used.

  Referring to FIG. 14, the ladder type filter according to Example 1 has a loss improved by about 0.1 dB in the pass band as compared with the ladder type filter according to Comparative Example 1. Thus, in the first embodiment, the loss in the passband is improved, and a low-loss filter can be obtained.

  According to the first embodiment, as illustrated in FIGS. 12A and 12B, the parallel resonator P includes a portion where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 interposed therebetween (resonance unit 20). ) Have a shape in which two ellipses (P and Q) having different axis length ratios are connected by sharing one axis. Further, since the length ratio a: b: c of the axes of the two ellipses (P and Q) is 7: 9: 5, the ellipse P is an ellipse having one shared axis as a short axis, and the ellipse Q Is an ellipse whose major axis is one shared axis. Thereby, as shown to Fig.8 (a) and FIG.8 (b), the parallel resonator P can improve the Q value of an antiresonance frequency. As described in FIG. 3C, the amount of passage through the parallel resonator P has a maximum value at the antiresonance frequency. For this reason, when the Q value of the antiresonance frequency of the parallel resonator P is improved, the passing amount increases. Therefore, according to the first embodiment, the loss in the passband is improved, and a low-loss filter can be obtained.

  Further, as described in FIG. 3C, the passing amount of the series resonator S has a maximum value at the resonance frequency. As shown in FIGS. 9A and 9B, the Q value of the resonance frequency monotonously decreases as the ratio of b in the shaft length ratio a: b: c increases. That is, in the case of the resonating unit 20 in which b and c are shorter than a, the Q value of the resonance frequency can be improved. According to the first embodiment, as shown in FIGS. 11 (a) and 11 (b), the shape of the resonance unit 20 of the series resonator S has a ratio of the length of the major axis to the length of the minor axis of 7: 5. For this reason, the Q value of the resonance frequency of the series resonator S can be improved. Therefore, according to the first embodiment, the loss in the passband is improved, and a low-loss filter can be obtained.

  Further, as shown in FIGS. 12A and 12B, the resonance unit 20 of the parallel resonator P has a ratio of the lengths of the axes of two ellipses (P and Q) a: b: c of 7 : 9: 5 was shown, but the present invention is not limited to this, and any ratio that can improve the Q value of the anti-resonance frequency may be used. In particular, as shown in FIGS. 8A and 8B, the Q value of the anti-resonance frequency can be improved, even when the shaft length ratio a: b: c is 7: 8 to 10: 5. Good. In other words, the ellipse P having the short axis as one shared axis may have a ratio of the short axis length to the long axis length of 7: 8-10.

  Further, as shown in FIGS. 11A and 11B, the resonance unit 20 of the series resonator S is an ellipse in which the ratio of the length of the major axis to the length of the minor axis is 7: 5. Although shown, the present invention is not limited to this and may be an ellipse of other sizes. Moreover, the shape where two ellipses like the parallel resonator P were connected by sharing one axis | shaft may be sufficient. In particular, it is preferable that the Q value of the resonance frequency can be improved.

  Furthermore, according to the first embodiment, as shown in FIGS. 12A and 12B, the lower electrode 12 has an ellipse Q whose major axis is one shared axis, and the upper electrode 16 is shared. And an ellipse P having a short axis as one axis. According to this, when the piezoelectric film 14 shown in FIGS. 13B and 13E is etched into a predetermined shape, a region for etching the piezoelectric film 14 is made larger than the circumference of the resonance unit 20. be able to. For this reason, the stress concerning the piezoelectric film 14 of the resonance part 20 can be suppressed. Therefore, the Q value of the antiresonance frequency can be improved, and a filter with improved passband loss can be obtained.

  Furthermore, in the series resonator S and the parallel resonator P, a portion (resonant portion 20) where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 interposed therebetween is provided on the gap 18 provided in the substrate 10. Yes. In addition, a portion (resonance unit 20) where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 interposed therebetween is included in the gap 18 provided in the substrate 10. Accordingly, a piezoelectric thin film resonator having excellent resonance characteristics can be obtained.

  Furthermore, by using aluminum nitride or zinc oxide exhibiting orientation with the (002) direction as the main axis as the piezoelectric film 14, a piezoelectric thin film resonator having good resonance characteristics can be obtained.

  In the first embodiment, the case of a ladder type filter using an FBAR type piezoelectric thin film resonator has been described as an example. However, a ladder type filter using an SMR type piezoelectric thin film resonator may be used. Further, the substrate 10 can be a quartz substrate, a glass substrate, or the like. Although the lower electrode 12 and the upper electrode 16 have been described using the Ru film as an example, the materials described in the background art can be used.

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

FIG. 1 is a cross-sectional view of a piezoelectric thin film resonator having a via hole type gap. FIG. 2 is a cross-sectional view of a piezoelectric thin film resonator having a cavity-type gap. FIGS. 3A and 3B are equivalent circuit diagrams of the series resonator and the parallel resonator, respectively, and FIG. 3C is a frequency characteristic of the series resonator and the parallel resonator. FIG. 4A is an equivalent circuit diagram of a one-stage ladder type filter, and FIG. 4B is a pass characteristic of the ladder type filter. FIG. 5A is a top view of the piezoelectric thin film resonator used in the simulation, and FIG. 5B is a cross-sectional view taken along the line XX in FIG. FIG. 6 shows simulation results calculated for the shape of the resonance part and the deformation height of the laminated film. FIG. 7A to FIG. 7C show simulation results for calculating the residual stress distribution applied to the piezoelectric film for each shape of the resonance part. FIGS. 8A and 8B show simulation results calculated for the Q value of the antiresonance frequency. FIG. 9A and FIG. 9B are simulation results calculated for the Q value of the resonance frequency. FIG. 10 is an equivalent circuit diagram of the ladder filter according to the first embodiment. FIG. 11A is a top view of the series resonator S constituting the ladder filter according to the first embodiment, and FIG. 11B is a cross-sectional view taken along the line XX in FIG. 12A is a top view of the parallel resonator P constituting the ladder filter according to the first embodiment, and FIG. 12B is a cross-sectional view taken along the line XX in FIG. 13 (a) to 13 (c) are cross-sectional views showing a method for manufacturing the series resonator S, and FIGS. 13 (d) to 13 (f) are cross-sectional views showing a method for manufacturing the parallel resonator P. is there. FIG. 14 is a diagram illustrating pass characteristics of the ladder filter according to the first embodiment.

Explanation of symbols

10 substrate 11 SiO ₂ film 12 lower electrode 14 piezoelectric film 16 upper electrode 17 stacked film 18 gap 20 resonating portion 22 opening 24 mass load film

Claims (7)

Provided on the piezoelectric film so as to have a substrate, a lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode, and a portion facing the lower electrode across the piezoelectric film A plurality of piezoelectric thin film resonators having an upper electrode;
The plurality of piezoelectric thin film resonators are provided in a ladder shape, and the piezoelectric thin film resonator provided on a parallel arm among the plurality of piezoelectric thin film resonators includes the lower electrode and the upper electrode sandwiching the piezoelectric film. 2. A filter characterized in that opposing portions have a shape in which two ellipses having different axis length ratios are connected by sharing one axis.   2. The filter according to claim 1, wherein one of the two ellipses is an ellipse having the one axis as a minor axis, and the other ellipse is an ellipse having the one axis as a major axis. .   3. The filter according to claim 2, wherein the lower electrode has an ellipse whose major axis is the one axis, and the upper electrode has an ellipse whose minor axis is the one axis.   4. The filter according to claim 2, wherein the ellipse having one axis as a short axis has a ratio of the length of the short axis to the length of the long axis of 7: 8-10. 5.   5. The filter according to claim 1, wherein a portion where the lower electrode and the upper electrode face each other with the piezoelectric film interposed therebetween is provided in a gap provided in the substrate. .   6. The filter according to claim 1, wherein a portion where the lower electrode and the upper electrode face each other with the piezoelectric film interposed therebetween is included in the gap.   The filter according to any one of claims 1 to 6, wherein the piezoelectric film is made of aluminum nitride or zinc oxide exhibiting orientation with a (002) direction as a main axis.

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