JP2007295306A - Bulk acoustic wave resonator, manufacturing method thereof, and filter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a BAW resonator capable of preventing generation of cracks on a piezoelectric layer, and reducing the cross sectional area of a resonation region. <P>SOLUTION: The BAW resonator is provided with a substrate 10, a lower electrode 20 formed on an upper surface 11 of the substrate 10, a piezoelectric layer 30 formed on an upper layer 21 of the lower electrode 20, an insulating layer 40 formed on an upper surface 31 of the piezoelectric layer 30, and an upper electrode 50 formed on an upper surface 41 of the insulating layer 40. The insulating layer 40 is formed on the upper surface 31 of the piezoelectric layer 30 so as to cover a side 32 as one side of the external periphery of the insulating layer 40, and the upper electrode 50 is formed on the upper surface 41 of the insulating layer 40 so as to stride on the insulating layer 40 and its tip is used as a contact part 51 contracting the upper surface 31 of the piezoelectric layer 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bulk acoustic wave resonator, a filter circuit including the bulk acoustic wave resonator, and a method for manufacturing the bulk acoustic wave resonator.

  In recent years, high-frequency bulk acoustic wave resonators with a high Q value have attracted attention due to the widespread use of high-frequency communication devices such as mobile phones and UWB (Ultra Wide Band) and the strong need for high performance and low loss in them. Yes. BAW resonance using a piezoelectric material such as aluminum nitride (AIN), zinc oxide (ZnO), or lead zirconate titanate (PZT) as such a bulk acoustic wave resonator (hereinafter referred to as “BAW resonator”). A container is known (for example, Patent Document 1). The BAW resonator has a sharp Q value at a high frequency as compared with an LC filter that has been used so far, and has an advantage of excellent pass characteristics and cutoff characteristics. In addition, there is a feature that high-frequency bandpass filters having different bandwidths can be obtained depending on the difference in the piezoelectric material used.

  This type of BAW resonator generally has the structure shown in FIG. This BAW resonator includes a lower electrode 101 provided on a substrate (not shown), a piezoelectric layer 102 formed on the upper surface of the lower electrode, and an upper electrode 103 formed on the upper surface of the piezoelectric layer 102. . Each of the lower electrode 101 and the upper electrode 103 has a strip shape having a width dimension shorter than the length of one side of the piezoelectric layer 102.

  The upper electrode 103 and the lower electrode 101 are disposed so that the longitudinal directions thereof are orthogonal to each other at a substantially central portion of the piezoelectric layer 102 in plan view. Here, a portion where the upper electrode 103 and the lower electrode 101 intersect via the piezoelectric layer 102 is a resonator, and a rectangular parallelepiped region of the piezoelectric layer 102 sandwiched between the upper electrode 103 and the lower electrode 101 is a resonance region 104. Become. Then, the resonance frequency of the resonator is designed by adjusting the dimensions of the thickness of the piezoelectric layer 102 and the area of the portion where the lower electrode 101 and the upper electrode 103 intersect (cross-sectional area of the resonance region 104). Here, the cross-sectional area of the resonance region 104 orthogonal to the vertical direction is referred to as the cross-sectional area of the resonance region 104. The protrusion 105 appearing in parallel with the lower electrode 101 appearing on the upper surface of the piezoelectric layer 102 is due to the influence of the thickness of the lower electrode 101.

  FIG. 8 shows an equivalent circuit of a BAW resonator. In FIG. 8, the electrical resistance of the upper electrode 103 and the lower electrode 101 is represented by Rx. In FIG. 8, Co represents the parallel capacitance in the resonance region, Lm represents the resonance mechanical inductance, Cm represents the resonance mechanical capacitance, and Rm represents the resonance mechanical resistance. These circuit parameters are such that the target series resonance frequency of the resonator is fs, the electromechanical coupling coefficient which is a physical property value of the piezoelectric layer 102 is keff, the Q value is Q, the dielectric constant is ε, and the resonance region 104 If the cross-sectional area of A is A and the thickness (film thickness) of the piezoelectric layer 102 is t, it can be expressed by the following equation.

Co = εA / t (1)
Co: parallel capacitance in the resonance region, ε: dielectric constant of the piezoelectric region, A: cross-sectional area of the resonance region, t: film thickness of the piezoelectric layer Cm = keff ² · Co / (1-keff ² ) (2)
Cm: resonance mechanical capacitance, keff: electromechanical coupling coefficient of piezoelectric material Lm = 1 / (4 · π ² · Cm · fs ² ) (3)
Lm: resonance mechanical inductance, fs: target series resonance frequency fp = fs / sqrt (1−keff ² ) (4)
fp: parallel resonance frequency Rm = 2 · π · fp · Lm / Q (5)
Q: Q value of the piezoelectric layer As can be seen from the above formulas (1) to (5), the BAW resonator is based on the Q value and the electromechanical coupling coefficient keff. If adjusted, the target series resonance frequency fs and parallel resonance frequency fp can be set.

According to the BAW resonator shown in FIG. 7, since the cross-sectional area of the resonance region can be determined in a region where the upper electrode 103 and the lower electrode 101 intersect in plan view, the upper electrode 103 and the lower electrode 101 It is possible to obtain a BAW resonator having a desired resonance frequency simply by adjusting the width dimension, and there is a feature that detailed alignment of the upper electrode 103 and the lower electrode 101 is unnecessary.
JP 2001-185985 A

  However, when PZT is used as the piezoelectric layer 102, in order to obtain high-quality PZT, it is necessary to use a material having high consistency with PZT crystals such as platinum (Pt) and iridium (Ir) as the lower electrode 101. However, in this case, when the piezoelectric layer 102 is formed as shown in FIG. 7, a high quality piezoelectric layer 102 can be obtained in the piezoelectric layer 102 on the lower electrode 101, but the portion not on the lower electrode 101. In this case, cracks will occur. Specifically, cracks occur during the process of crystallizing PZT on the lower electrode 101, for example, during sintering in the sol-gel method and during deposition at a high temperature in the sputtering method. And the crack which generate | occur | produced in the vicinity of the resonance area | region 104 also reaches in the resonance area | region 104, and there exists a problem that a high quality BAW resonator cannot be obtained in this case.

  Therefore, it is possible to prevent the occurrence of cracks by providing the lower electrode 101 over the entire bottom surface of the piezoelectric layer 102. However, when PZT is used as the piezoelectric layer 102, PZT is made of other piezoelectric materials such as gallium nitride. Since the dielectric constant is about five times that of the layer material, it is required to reduce the cross-sectional area of the resonance region 104 in order to obtain a desired impedance characteristic (for example, 35 to 90Ω).

  However, in the configuration shown in FIG. 7, if the lower electrode 101 is provided over the entire bottom surface of the piezoelectric layer 102, the region where the lower electrode 101 and the upper electrode 103 intersect via the piezoelectric layer 102 becomes extremely large, and the resonance region is cut off. The area cannot be reduced, and it becomes difficult to obtain a BAW resonator having desired impedance characteristics.

  An object of the present invention is to provide a BAW resonator capable of preventing the occurrence of cracks in a piezoelectric layer and reducing the cross-sectional area of a resonance region.

  A bulk acoustic wave resonator according to the present invention includes a substrate, a lower electrode formed on one surface of the substrate, a piezoelectric layer formed so that the entire lower surface is in contact with the upper surface of the lower electrode, and the upper surface of the piezoelectric layer. An insulating layer formed so as to conceal at least a part of the outer periphery thereof, and an upper electrode including a contact portion provided so as to straddle the upper surface of the insulating layer and in contact with a partial region of the upper surface of the piezoelectric layer; It is characterized by providing.

  According to this configuration, the piezoelectric layer is formed on the upper surface of the lower electrode so that the entire lower surface is in contact with the lower electrode, and the entire lower surface of the piezoelectric layer is covered with the lower electrode. In the step of forming on the upper surface, it is possible to prevent the occurrence of cracks on the lower surface of the piezoelectric layer.

  The insulating layer is formed on the upper surface of the piezoelectric layer so as to conceal at least a part of the outer periphery of the upper surface of the piezoelectric layer. The upper electrode is provided so that the contact portion contacts the upper surface of the piezoelectric layer so as to straddle the upper surface of the piezoelectric layer. Therefore, the region sandwiched between the upper electrode and the lower electrode via the insulating layer and the piezoelectric layer is not a resonance region, and the cross-sectional area of the resonance region can be set only by the area of the contact portion in contact with the piezoelectric layer. The cross-sectional area of the resonance region can be reduced.

  Furthermore, since the insulating layer hides at least a part of the outer periphery of the upper surface of the piezoelectric layer, a region other than the outer periphery of the piezoelectric layer can be used as a resonance region. As a result, a region other than the outer periphery of the upper surface of the piezoelectric layer having poor resonance characteristics can be made a resonance region, and a high-quality bulk acoustic wave resonator can be obtained.

  In the above configuration, it is preferable that the insulating layer includes an opening that exposes a partial region of the upper surface of the piezoelectric layer, and covers the entire outer periphery of the upper surface of the piezoelectric layer.

  According to this configuration, since the insulating layer is provided over the entire outer periphery of the piezoelectric layer, when the upper electrode is formed so as to straddle the insulating layer, the outer peripheral portion of the piezoelectric layer having poor piezoelectric characteristics does not become the resonance region. A highly accurate bulk acoustic wave resonator can be obtained. In addition, since the outer periphery of the piezoelectric layer is covered with an insulating layer, the degree of freedom in arranging the upper electrode can be increased.

  Further, in the above configuration, the upper electrode is provided so as to cover the opening by setting the area of the opening to the same area as the cross-sectional area of the resonance region, and the entire area of the opening serves as the contact portion. It is preferable.

  According to this configuration, since the cross-sectional area of the resonance region of the opening can be adjusted only by the area of the opening, attention should be paid to the alignment accuracy between the insulating layer and the upper electrode and the processing accuracy of the upper electrode. In addition, the manufacturing process can be facilitated.

  In the above configuration, it is preferable that the opening has a strip shape, the upper electrode is formed so as to intersect with a long side of the opening, and the intersecting portion serves as the contact portion.

  According to this configuration, the cross-sectional area of the resonance region can be set by adjusting the short side dimension of the strip-shaped opening and the width dimension of the upper electrode. Even if a difficult lift-off process or the like is used, it is only necessary to form the opening portion while paying attention to the dimension of the short side. As a result, the resonator can be configured with high accuracy by an easy process.

  In the above structure, the sidewall of the insulating layer preferably has a tapered shape extending in the direction of the upper electrode.

  According to this configuration, since the angle between the side wall of the insulating layer and the upper surface of the piezoelectric layer is greater than 90 degrees, the thickness of the upper electrode is reduced at the edge between the side wall of the opening and the upper surface of the piezoelectric layer. Thus, it is possible to prevent disconnection due to increase in resistance value or disconnection of the upper electrode.

  Moreover, the filter circuit by this invention is provided with the bulk acoustic wave resonator in any one of Claims 1-5.

  According to this configuration, it is possible to provide a filter circuit including a bulk acoustic wave resonator capable of preventing the occurrence of cracks in the piezoelectric layer and reducing the cross-sectional area of the resonance region.

  The method for manufacturing a bulk acoustic wave resonator according to the present invention includes a step of forming a lower electrode on an upper surface of a substrate, a step of forming a piezoelectric layer so that the entire lower surface is in contact with the upper surface of the lower electrode, and the piezoelectric layer Forming an insulating layer so that at least a part of the outer periphery of the upper surface of the piezoelectric layer is concealed; and a contact portion in contact with a partial region of the upper surface of the piezoelectric layer, the upper electrode straddling the upper surface of the insulating layer Providing a step.

  According to this configuration, it is possible to manufacture a bulk acoustic wave resonator capable of preventing the occurrence of cracks in the piezoelectric layer and reducing the cross-sectional area of the resonance region.

  According to the present invention, the piezoelectric layer is formed on the upper surface of the lower electrode so that the entire lower surface is in contact with the lower electrode, and the entire lower surface of the lower electrode is not exposed, so the piezoelectric layer is formed on the upper surface of the lower electrode. In the step, the cracks generated on the lower surface of the piezoelectric layer can be prevented.

  The insulating layer is formed on the upper surface of the piezoelectric layer so as to conceal at least a part of the outer periphery of the upper surface of the piezoelectric layer. The upper electrode is provided so that the contact portion contacts the upper surface of the piezoelectric layer so as to straddle the upper surface of the piezoelectric layer. Therefore, the region sandwiched between the upper electrode and the lower electrode via the insulating layer and the piezoelectric layer is not a resonance region, and the cross-sectional area of the resonance region can be set only by the area of the contact portion that is in direct contact with the piezoelectric layer. The occurrence of cracks can be prevented, and the cross-sectional area of the resonance region can be reduced.

  Furthermore, since the insulating layer hides at least a part of the outer periphery of the upper surface of the piezoelectric layer, a region other than the outer periphery of the piezoelectric layer having poor resonance characteristics can be used as the resonance region. As a result, a high-quality bulk acoustic wave resonator can be obtained.

(Embodiment 1)
FIG. 1 is a view showing a bulk acoustic wave resonator (hereinafter referred to as a “BAW (Bulk Acoustic Wave) resonator”) 1 according to Embodiment 1 of the present invention, and FIG. b) shows a 1b-1b cross-sectional view. In FIGS. 1A and 1B, the upper electrode 50 side is the upward direction and the lower electrode 20 side is the downward direction. In FIG. 1A, the substrate 10 is omitted.

  As shown in FIGS. 1A and 1B, the BAW resonator 1 includes a substrate 10, a lower electrode 20 formed on the upper surface 11 of the substrate 10, and a piezoelectric layer formed on the upper surface 21 of the lower electrode 20. 30, an insulating layer 40 formed on the upper surface 31 of the piezoelectric layer 30, and an upper electrode 50 formed on the upper surface 41 of the insulating layer 40.

Here, the substrate 10 is made of a layer formed of a material having a high acoustic impedance such as zinc oxide (ZnO), molybdenum (Mo) or tungsten (W), and a material having a low acoustic impedance such as (silicon dioxide) SiO _2. An acoustic mirror in which the formed layers are alternately stacked is provided. However, the substrate 10 may be made of a material that does not lose the resonance energy of the piezoelectric layer 30 so that the bottom portion of the resonance region becomes a void, such as F-BAR.

The lower electrode 20 has a flat plate shape and is formed on the upper surface 11 of the substrate 10 so as to cover almost the entire area of the upper surface 11 of the substrate 10. The lower electrode 20 is made of platinum (Pt) having high consistency with PZT constituting the piezoelectric layer 30. However, if the material is highly compatible with PZT constituting the piezoelectric layer 30, a material such as iridium (Ir), lanthanum nickel oxide (LaNiO ₃ ), or strontium ruthenium oxide (SrRuO ₃ ) is used instead of platinum (Pt). May be adopted.

  The piezoelectric layer 30 is made of PZT, has a rectangular parallelepiped shape, and is formed on the upper surface 21 of the lower electrode 20.

  The insulating layer 40 is formed on the upper surface 31 so as to hide the side 32 that is one of the four sides constituting the outer periphery of the upper surface 31 of the piezoelectric layer 30. Here, the width x of the rectangular region D <b> 1 where the upper surface 31 and the insulating layer 40 are in contact is slightly smaller than half the length of the side 34 orthogonal to the side 32. Accordingly, a contact portion 51 described later is positioned at the center of the piezoelectric layer 30, and the resonance region 60 can be formed at the center of the piezoelectric layer 30. That is, the vicinity of the outer periphery of the upper surface 31 of the piezoelectric layer 30 is more likely to be scratched or the like than the central portion, and if the resonance region 60 is formed in the region near the outer periphery, it becomes difficult to obtain a high-quality BAW resonator. For this reason, the resonance region 60 is preferably formed in the center of the upper surface 31 of the piezoelectric layer 30. As shown in FIG. 1A, the insulating layer 40 is formed on the upper surface 31 of the piezoelectric layer 30 so as to cover a region slightly smaller than the right half region of the substrate 10, the lower electrode 20, and the piezoelectric layer 30. Has been. The area of the cross section of the resonance region 60 orthogonal to the vertical direction is referred to as the cross sectional area of the resonance region 60.

  Further, the side wall 43 has an inclined tapered shape so that the angle θ between the side wall 43 of the insulating layer 40 on the central side of the piezoelectric layer 30 and the upper surface 31 of the piezoelectric layer 30 is larger than 90 degrees. .

  The upper electrode 50 is formed on the upper surface 41 of the insulating layer 40, and has a tapered shape such that the shape becomes narrower toward the tip, and the tip portion becomes a contact portion 51 in contact with the upper surface 31 of the piezoelectric layer 30. ing. The contact portion 51 has a rectangular shape such as a rectangle or a square. A rectangular parallelepiped region of the piezoelectric layer 30 sandwiched between the contact portion 51 and the lower electrode 20 becomes a resonance region 60. Here, by forming the upper electrode 50 in a tapered shape, the resistance of the upper electrode 50 can be reduced even if the area of the contact portion 51 is reduced in order to obtain desired impedance characteristics.

  FIG. 2 is a diagram illustrating a manufacturing process of the BAW resonator 1. First, as shown to (a), the board | substrate 10 is prepared. Next, as shown in (b), a metal layer to be the lower electrode 20 is formed on the upper surface 11 of the substrate 10 using a technique such as sputtering or vapor deposition. Next, as shown in (c), a PZT layer to be the piezoelectric layer 30 is formed using a technique such as sputtering or sol-gel, and sintered.

  Next, as shown in FIG. 4D, the sintered piezoelectric layer 30 is patterned to remove the right side portion of the piezoelectric layer 30 and the left side portion of the piezoelectric layer 30. Next, as shown in (e), the lower electrode 20 is subjected to patterning, and the right portion of the lower electrode 20 is removed.

Next, as shown in (f), a photoresist 70 is applied to the upper surface 21 of the lower electrode 20 and the upper surface 31 of the piezoelectric layer 30 and irradiated with light to form a photoresist in a region other than the region where the insulating layer 40 is formed. 70 is removed. Next, as shown in (g), the insulating layer 40 is formed. Next, as shown in (h), the photoresist 70 is removed to remove the left portion of the insulating layer 40 and form an opening that exposes the left portion of the piezoelectric layer 30. That is, in (f) to (h), silicon dioxide (SiO ₂ ), silicon nitride (SiN), or the like is used as the insulating layer 40, and after the insulating layer 40 is formed by the CVD method, the insulating layer 40 is patterned. The insulating layer 40 is formed by a lift-off method.

  Next, as shown in (i), after the upper electrode 50 is formed using a technique such as sputtering or vapor deposition, the area of the contact portion 51 is large enough to obtain a desired resonance frequency. In addition, the upper electrode 50 is patterned so that the width of the upper electrode 50 becomes narrower toward the contact portion 51.

  In the BAW resonator 1 formed as described above, the film thickness t of the piezoelectric layer 30 and the area of the contact portion 51 (cross-sectional area of the resonance region 60) are set to values that can obtain a desired resonance frequency. By designing, it is possible to obtain the BAW resonator 1 having parameters as expressed by the equations (1) to (4) shown in the background art.

  Further, as shown in FIGS. 2C to 2E, the piezoelectric layer 30 is formed after the Pt layer as the lower electrode 20 is formed and before the lower electrode 20 is patterned. When a manufacturing method such as a sol-gel method in which a solution is applied and coded is employed, film thickness having high thickness accuracy can be obtained without causing thickness unevenness due to a base step. Further, since the lower electrode 20 is formed over the entire bottom surface of the piezoelectric layer 30, cracks generated in the piezoelectric layer 30 when the piezoelectric layer 30 is sintered can be prevented, and a high-quality BAW resonator. 1 can be manufactured.

  Further, the contact portion 51 is provided in the vicinity of the central portion of the piezoelectric layer 30, and the region near the outer periphery of the piezoelectric layer 30 with poor processing accuracy and poor piezoelectric characteristics is not defined as the resonance region 60. Resonance characteristics can be improved.

  In order to eliminate unnecessary reflection at a high frequency, the BAW resonator 1 must be designed so that the impedance characteristic becomes a desired value. In particular, when a material having a large dielectric constant such as PZT is adopted as the piezoelectric layer 30, it is required to reduce the cross-sectional area of the resonance region 60. In this case, when a resonance region is provided in the region of the outer peripheral portion of the piezoelectric layer 30, a region having poor piezoelectric characteristics dominates most of the resonance region. Therefore, the effect of setting the resonance region 60 in the central portion of the piezoelectric layer 30 is great.

  The reason why the opening was formed by lift-off processing is that when the opening is processed by etching, the surface of the piezoelectric layer 30 corresponding to the resonance region 60 is also ground during etching, resulting in surface roughness and deterioration of the resonance characteristics. is there.

  Further, since the side wall 43 of the insulating layer 40 has a tapered shape that is inclined so that the opening becomes wider toward the upper side, the side wall 43 and the upper surface 31 of the piezoelectric layer 30 intersect with each other. It is possible to prevent the upper electrode 50 from being disconnected due to disconnection or the upper electrode 50 from being thinned to increase the resistance of the upper electrode 50.

(Embodiment 2)
3A and 3B are diagrams showing a BAW resonator 1a according to the second embodiment. FIG. 3A is an external perspective view, and FIG. 3B is a 3b-3b cross-sectional view. In the BAW resonator 1a according to the second embodiment, the insulating layer 40a is formed on the upper surface 31 of the piezoelectric layer 30 so as to conceal the four sides on the outer periphery of the piezoelectric layer 30, and the opening 42a is formed in the central portion of the insulating layer 40a. The contact portion 51 is formed in the opening 42a by exposing the central portion of the piezoelectric layer 30.

  Specifically, the insulating layer 40 a is formed on the upper surface 31 of the piezoelectric layer 30 so as to conceal the four sides constituting the outer periphery of the piezoelectric layer 30, and is also formed on the upper surface 11 on the right side of the substrate 10. The opening 42 a is provided in the central portion of the piezoelectric layer 30, has a square or rectangular shape when viewed from above, and exposes the upper surface 31 of the piezoelectric layer 30. Note that the shape of the opening 42a in a top view is not limited to a rectangular shape, and other shapes such as a circle, an ellipse, and a triangle may be adopted. Further, the four side walls 43a of the opening 42a have a tapered shape that is inclined so that the cross-sectional area of the opening increases toward the top. The cross-sectional area of the opening 42 a is larger than the area of the contact part 51.

  Similar to the first embodiment, the upper electrode 50 is formed so as to straddle the upper surface 41a on the right side of the insulating layer 40a, and the contact portion 51 at the tip is in contact with the upper surface 31 of the piezoelectric layer 30. Therefore, even if the upper electrode 50 and the lower electrode 20 face each other, the region where the insulating layer 40 exists is not the resonance region 60, but a rectangular parallelepiped of the piezoelectric layer 30 where the lower electrode 20 and the contact portion 51 face each other. Only the region can be the resonance region 60.

  Thus, according to the BAW resonator 1a according to the second embodiment, since the opening 42a is provided in the central portion of the insulating layer 40a, the degree of freedom in disposing the upper electrode 50 on the insulating layer 40a is increased. be able to. In addition, since the cross-sectional area of the resonance region can be determined by the cross-sectional area of the contact portion 51, the cross-sectional area of the opening 42a can be increased, and the opening 42a can be accurately formed even when lift-off processing is used. Therefore, a highly accurate BAW resonator 1a can be obtained.

(Embodiment 3)
4A and 4B are diagrams showing a BAW resonator 1b according to Embodiment 3, wherein FIG. 4A is an external perspective view, and FIG. 4B is a 4b-4b cross-sectional view. The BAW resonator 1b according to the third embodiment processes the upper electrode 50b with an insulating layer so that the cross-sectional area of the opening 42b is the same as the cross-sectional area of the resonance region 60 and covers the entire area of the opening 42b. It is formed on the upper surface 41b of 40b.

  Specifically, a rectangular opening 42b such as a square or a rectangle is formed in the central portion of the insulating layer 40b to expose the upper surface of the piezoelectric layer 30, and then a strip shape is formed so as to cover the opening 42b. The upper electrode 50b is formed on the upper surface 41b of the insulating layer 40b. Accordingly, the entire area of the bottom surface of the opening 42b is covered with the upper electrode 50b to form the contact portion 51b. For this reason, the area of the bottom surface of the opening 42 b is approximately the same as the cross-sectional area of the resonance region 60. The side wall 43b of the opening 42b has a tapered shape as in the first and second embodiments.

  Thus, according to the BAW resonator 1b according to the third embodiment, the cross-sectional area of the opening 42b is set to be approximately the same as the cross-sectional area of the resonance region 60, and the opening 42b is covered with the upper electrode 50b. Therefore, by accurately processing only the cross-sectional area of the opening 42b, it becomes possible to obtain the resonance region 60 having a desired cross-sectional area, and it is not necessary to position the upper electrode 50b with high accuracy in the opening 42b. Even if the processing accuracy of the upper electrode 50b is lowered, the resonance region 60 can be formed with high accuracy.

  Furthermore, since the resonance region 60 is formed in the central portion of the piezoelectric layer 30 as in the first and second embodiments, the resonance characteristics such as the Q value can be improved. In addition, since the opening 42b has a tapered shape, it is possible to prevent the upper electrode 50b from being disconnected and having a high resistance due to a thin film.

(Embodiment 4)
5A and 5B are diagrams showing a BAW resonator 1c according to the fourth embodiment. FIG. 5A is an external perspective view, and FIG. 5B is a cross-sectional view of 5b-5b. The BAW resonator 1b according to the fourth embodiment is characterized in that a strip-shaped opening 42c is formed, and the upper electrode 50c is formed so as to intersect the longitudinal direction of the opening 42c.

  Specifically, the opening 42 c has a strip shape and is formed in the central portion of the piezoelectric layer 30. The upper electrode 50c is disposed along the upper surface 41c of the insulating layer 40c so that the longitudinal direction is parallel to the direction of the short side S1 of the opening 42c and the tip 52c is located above the insulating layer 40c. Yes. The upper electrode 50c covers a part of the upper surface 31 of the piezoelectric layer 30 in the opening 42c, and the covered portion serves as a contact portion 51c. The width of the upper electrode 50c is reduced toward the tip 52c to reduce the resistance. The side wall 43c of the opening 42c has a tapered shape that is inclined so that the cross-sectional area of the opening 42c increases as it goes upward.

  Therefore, the cross-sectional area of the resonance region 60 is determined by the dimension of the short side S1 of the opening 42c and the dimension of the width S2 at the opening 42c of the upper electrode 50c. Therefore, even if the contact portion 51c is not positioned with high accuracy in the opening 42c, only the dimension of the short side S1 of the opening 42c and the dimension of the width S2 at the opening 42c of the upper electrode 50c are set. The cross-sectional area of the resonance region 60 can be set to a desired size. Thereby, the freedom degree of the dimension of the long side of the opening part 42c can be raised.

  As described above, according to the BAW resonator 1c according to the fourth embodiment, the resonance region 60 having a desired cross-sectional area can be obtained without positioning the contact portion 51c with high accuracy in the opening 42c. In addition, since the long side of the opening 42c can be enlarged and the cross-sectional area of the opening 42c can be made relatively large, the opening 42c can be formed with high accuracy by lift-off processing.

  Further, since the opening 42c is provided in the central portion of the piezoelectric layer 30 as in the first to third embodiments, the resonance characteristics of the BAW resonator 1c can be enhanced, and the side wall 43c of the opening 42c is opened. Since the cross-sectional area of the portion 42c has a tapered shape that increases so as to increase upward, it is possible to prevent the upper electrode 50c from being increased in resistance due to disconnection or thinning.

  FIG. 6 shows a circuit diagram of a filter circuit 2 configured using any of the BAW resonators 1 to 1c of the first to fourth embodiments. FIG. 6A shows a one-stage filter circuit, and FIG. 6B shows a three-stage filter circuit.

  As shown in FIG. 6A, the filter circuit 2 includes a pair of input terminals T1, T2, two BAW resonators C1, C2, and a pair of output terminals T3, T4.

  The BAW resonators C1 and C2 are each configured by any one of the BAW resonators 1 to 1c of the first to fourth embodiments. One end of the BAW resonator C1 is connected to the input terminal T1, and the other end is connected to the output terminal T3 and the BAW resonator C2. One end of the BAW resonator C2 is connected to the input terminal T2 and the output terminal T4.

  The filter circuit 3 shown in FIG. 6B includes three filter circuits 201 to 203 connected in cascade. Each of the filter circuits 201 to 203 is configured by the filter circuit 2 shown in FIG. In the filter circuit 3, the output terminals T3 and T4 of the filter circuit 201 are respectively connected to the input terminals T1 and T2 of the filter circuit 202, and the output terminals T3 and T4 of the filter circuit 202 are respectively input to the filter circuit 203. Connected to T1 and T2.

  According to the filter circuits 2 and 3 having such a configuration, since any one of the BAW resonators 1 to 1c according to the first to fourth embodiments is employed, a filter circuit having high resonance characteristics can be provided.

It is a figure which shows the BAW resonator by Embodiment 1 of this invention, (a) shows the external appearance perspective view, (b) has shown sectional drawing. It is a figure which shows the manufacturing process of a BAW resonator. It is a figure which shows the BAW resonator by Embodiment 2 of this invention, (a) shows the external appearance perspective view, (b) has shown 3b-3b sectional drawing. It is a figure which shows the BAW resonator by Embodiment 3 of this invention, (a) shows the external appearance perspective view, (b) has shown 4b-4b sectional drawing. It is a figure which shows the BAW resonator by Embodiment 4 of this invention, (a) shows an external appearance perspective view, (b) has shown 5b-5b sectional drawing. 1 shows a circuit diagram of a filter circuit according to the invention. FIG. 6A shows a one-stage filter circuit, and FIG. 6B shows a three-stage filter circuit. It is a figure which shows background art. It is a figure which shows background art.

Explanation of symbols

1, 1a, 1b, 1c BAW resonator 2, 3 Filter circuit 10 Substrate 11 Upper surface 20 Lower electrode 21 Upper surface 201, 202, 203 Filter circuit 30 Piezoelectric layer 31 Upper surface 40 40a, 40b, 40c Insulating layers 41, 41a, 41b, 41c upper surface 42a, 42b, 42c opening 43, 43a, 43b, 43c side wall 50, 50b, 50c upper electrode 51, 51b, 51c contact part 52c tip 60 resonance region C1, C2 BAW resonator D1 region S1 short side S2 width t Film thickness T1, T2 Input terminal T3, T4 Output terminal x Width dimension θ Angle

Claims (7)

A substrate,
A lower electrode formed on one side of the substrate;
A piezoelectric layer formed such that the entire lower surface is in contact with the upper surface of the lower electrode;
An insulating layer formed such that at least a part of the outer periphery of the upper surface of the piezoelectric layer is concealed;
A bulk acoustic wave resonator comprising: an upper electrode that is provided so as to straddle an upper surface of the insulating layer and includes a contact portion that contacts a partial region of the upper surface of the piezoelectric layer.   2. The bulk acoustic wave resonator according to claim 1, wherein the insulating layer includes an opening that exposes a partial region of the upper surface of the piezoelectric layer, and covers the entire outer periphery of the upper surface of the piezoelectric layer. .   The bulk acoustic wave resonator according to claim 2, wherein the upper electrode is provided so as to cover the entire area of the opening, and the entire area of the opening serves as the contact portion. The opening is strip-shaped,
The bulk acoustic wave resonator according to claim 2, wherein the upper electrode is formed so as to intersect with a long side of the opening, and the intersecting portion serves as the contact portion.   The bulk acoustic wave resonator according to claim 1, wherein a side wall of the insulating layer has a taper shape extending in the direction of the upper electrode.   A filter circuit comprising the bulk acoustic wave resonator according to claim 1. Forming a lower electrode on the upper surface of the substrate;
Forming a piezoelectric layer so that the entire lower surface is in contact with the upper surface of the lower electrode;
Forming an insulating layer such that at least a portion of the outer periphery of the upper surface of the piezoelectric layer is concealed;
And a step of providing an upper electrode so as to straddle the upper surface of the insulating layer. The method further includes a step of providing a contact portion in contact with a part of the upper surface of the piezoelectric layer.

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