JP2009246569A - Thin-film resonator, filter and duplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a thin-film resonator which enables spurious suppression and high-density arrangement; a filter; and a duplexer. <P>SOLUTION: The thin-film resonator includes: a resonator 20 that has a piezoelectric thin-film 15; and first and second electrodes 16 and 17 which are arranged so as to face each other with the piezoelectric thin film 15 therebetween. The plane of the resonator 20 is almost rectangular, and at least one edge of the resonator 20 is composed of a straight-line part and a notch part 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a thin film resonator including a piezoelectric thin film and a resonance part having a first electrode and a second electrode disposed so as to face each other with the piezoelectric thin film interposed therebetween, a filter, And about the duplexer.

  As the frequency of electrical signals used in wireless communication and electrical circuits is increased, filters that can be used for electrical signals that have been increased in frequency have been developed. In particular, microwaves near 2 GHz are becoming mainstream in wireless communications, and standards have already been set for several GHz or more, so an inexpensive and high-performance filter corresponding to these frequencies is required. Yes. As such a filter, a filter using a resonator using a thickness longitudinal vibration mode of a thin film exhibiting piezoelectricity has been proposed.

  A resonator using the thickness longitudinal vibration mode of a piezoelectric thin film (hereinafter referred to as a piezoelectric thin film) causes the piezoelectric thin film to vibrate in response to an input high frequency electrical signal, and the vibration Causes resonance in the thickness direction of the piezoelectric thin film to change its impedance. A resonator using such a piezoelectric thin film thickness vibration mode is called a thin film bulk acoustic resonator (abbreviated as FBAR). The FBAR has a resonance part formed by sequentially laminating a first electrode, a piezoelectric thin film, and a second electrode on one surface of a substrate by a thin film formation process. In addition, a thin film means here what is formed with a normal thin film formation process.

  The thin film resonator includes a substrate made of Si, GaAs, or the like, a piezoelectric thin film made of AlN, ZnO, or the like, and first and second electrodes that sandwich the piezoelectric thin film from both sides in the thickness direction.

  In such a thin film resonator, there is a problem that spurious is generated due to unnecessary vibration. This is because a vibration wave propagating in the transverse direction perpendicular to the thickness direction of the piezoelectric thin film (hereinafter referred to as a transverse mode) is generated, reflected by the opposing end faces of the resonance part, and the vibration wave returns to the original point. This is caused by That is, resonance occurs and spurious is generated when the change in phase during the transverse mode makes one reciprocation between the opposing end faces of the resonance part is an integral multiple of 360 degrees.

  In a thin film resonator, there are transverse modes of various wave numbers. Therefore, in a configuration like this thin film resonator, a transverse mode resonance always occurs. The resonance frequency of the transverse mode is slightly different from the resonance frequency of the thin film resonator. For this reason, an unnecessary resonance peak (spurious) is generated in the vicinity of the resonance peak of the series resonance frequency and the parallel resonance frequency.

  When a thin film resonator having spurious resonance characteristics is used for an oscillator, it may cause fluctuations in oscillation frequency and noise. Further, when such a thin film resonator is combined to constitute a filter device, ripples are generated in the filter characteristics.

  As described above, when spurious due to unnecessary vibration occurs, it becomes a large problem in practice. For this reason, the thin film resonator described in Patent Document 1 is configured such that the piezoelectric thin film or the entire sides of the first and second electrodes are formed of curves in the resonance portion to reduce the influence of the transverse mode.

JP 2003-17974 A

  In the thin film resonator, in order to connect the first and second electrodes and the common electrode, lead electrodes are provided from the first and second electrodes to the common electrode. The lead electrode is connected to one side of the first and second electrodes. However, if all the sides of the electrode are curved, it is difficult to connect the extraction electrode to one side. Further, in order to connect the extraction electrode to one side, the connected side cannot be a curve.

  In addition, when all sides of the resonance part are curved, for example, when a filter device is configured by combining thin film resonators, it is necessary to arrange them at intervals so that adjacent thin film resonators do not interfere with each other. It is difficult to downsize a device provided with a plurality of thin film resonators such as a filter device.

  An object of the present invention is to provide a thin film resonator, a filter, and a duplexer that can suppress spurious and can be arranged at high density.

The present invention is a thin film resonator including a piezoelectric thin film, and a resonance part having a first electrode and a second electrode disposed so as to face each other with the piezoelectric thin film interposed therebetween. ,
The resonance part is a thin film resonator in which a planar shape is substantially rectangular, and at least one side of the resonance part is constituted by a linear part and a notch part.

  Further, according to the present invention, the notch is provided on each side of the resonance part, and a virtual straight line perpendicular to the plane direction is provided on the other side of the straight part of each side of the resonance part. It intersects with the notch.

  Further, the invention is characterized in that an extraction electrode is connected to the entire linear part of one side of the first electrode constituting the resonance part.

  Further, the present invention is characterized in that the notch is not provided on one side of the first electrode to which the extraction electrode is connected.

  Further, the present invention is characterized in that the notch portion is provided so that a planar shape of the resonance portion is non-rotationally symmetric.

  The present invention is also a filter comprising a plurality of the above thin film resonators arranged on a substrate.

  Moreover, this invention is a duplexer characterized by comprising said filter.

  According to the thin film resonator of the present invention, it is possible to suppress occurrence of transverse mode resonance and prevent spurious due to unnecessary vibration. Further, the thin film resonators can be arranged with high density.

  Further, according to the filter of the present invention, the filter characteristics can be improved while being small.

  Further, according to the duplexer of the present invention, the characteristics of the duplexer can be improved while being small in size.

  FIG. 1 is a plan view showing a thin film resonator 10 according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the section line II-II in FIG.

The substrate 11 is a base member of the thin film resonator 10. A resonator body 12 is formed on the substrate 11. The substrate 11 is selected to have a thickness of about 0.05 mm to 1 mm. The substrate 11 has a substantially rectangular parallelepiped shape. The substrate 11 is made of Si (silicon), Al ₂ O ₃ (aluminum oxide), SiO ₂ (silicon oxide), glass, or the like. The longitudinal direction of the substrate 11 is the X direction, the short direction is the Y direction, and the thickness direction is the Z direction. The longitudinal direction, the lateral direction, and the thickness direction are orthogonal to each other. The longitudinal direction and the lateral direction extend in parallel or perpendicular to each side of the surface 11a of the substrate 11.

  The substrate 11 is provided with a recess 13 that opens on one surface 11 a of the substrate 11. The recess 13 is covered with the resonator body 12, and a cavity surrounded by the substrate 11 and the resonator body 12 is formed. .

  The inner peripheral surface of the recess 13 is formed in a cylindrical shape having a substantially rectangular cross section in the direction perpendicular to the Z direction. Each side of the cross section in the Z direction of the inner peripheral surface of the recess 13 extends along the Z direction or the Y direction.

An insulating layer 100 is provided on one surface 11 a of the substrate 11. The insulating layer 100 electrically insulates the substrate 11 from the first electrode 16 and the second electrode 17 constituting the resonator body 12. The insulating layer 100 is formed with a thickness of, for example, 0.1 μm or more and 1.2 μm or less, and is formed by an oxide (SiO ₂ ) film formed by thermally oxidizing the surface of the substrate 11 or a thin film forming process such as sputtering and CVD. It consists of a SiN film to be formed.

  The resonator body 12 is provided on the one surface 11 a of the substrate 11 in the Z direction via the insulating layer 100. The resonator body 12 includes a piezoelectric thin film 15, a first electrode 16 at least partially laminated on one surface 15 a in the thickness direction of the piezoelectric thin film 15, and the other surface 15 b in the thickness direction of the piezoelectric thin film 15. And a second electrode 17 on which at least a part is laminated. A part of the piezoelectric thin film 15, a part of the first electrode 16, and a part of the second electrode 17 are formed to overlap each other in the Z direction. Of the portion where the part and the part of the second electrode 17 are laminated, that is, the part where the piezoelectric thin film 15, the first electrode 16, and the second electrode 17 overlap in the Z direction when viewed from the Z direction, A resonance portion 20 is formed by a portion acoustically insulated by the recess 13. Each of the piezoelectric thin film 15 and the first and second electrodes 16 and 17 is formed in a range wider than the resonance unit 20 when viewed from the Z direction.

  The resonance part 20 is formed facing the recess 13 formed in the substrate 11. That is, the resonance part 20 is formed by a part facing the recess 13 among the parts where the piezoelectric thin film 15, the first electrode 16, and the second electrode 17 overlap in the Z direction. The side surface of the resonance unit 20 extends along the X direction or the Y direction.

  The second electrode 17 is formed on one surface 11 a in the thickness direction of the substrate 11 and is provided so as to cover the recess 13. The second electrode 17 is provided from one end portion 21 in the X direction of the substrate 11 to the central portion 22 in the X direction, and is provided apart from the peripheral edge 23 of the one surface 11 a of the substrate 11. The second electrode 17 is formed in a substantially rectangular shape when viewed from the Z direction.

  The second electrode 17 is a member having a function of applying a high-frequency voltage to the piezoelectric thin film 15, and is formed using a metal material such as W, Mo, Au, Al and Cu. The second electrode 17 also has a function of forming the resonance unit 20 at the same time as the function of the electrode. Therefore, the thickness of the second electrode 17 forms the second electrode 17 so that the thin film resonator 10 exhibits the necessary resonance characteristics. It is necessary to select precisely considering the specific acoustic impedance and density of the material, the sound velocity and wavelength of the acoustic wave propagating through the second electrode 17, and the like. The optimum thickness of the second electrode 17 varies depending on the frequency of the signal used in the electronic circuit configured using the thin film resonator 10, the design dimension of the resonance unit 20, the piezoelectric thin film material, and the electrode material, but is 0.01 μm. It is selected to be about 0.5 μm.

The one end portion 17c in the X direction of the second electrode 17 functions as an external connection terminal.
The piezoelectric thin film 15 is at least partially formed on one surface 17 a in the thickness direction of the second electrode 17. In the present embodiment, the piezoelectric thin film 15 is formed over one surface 17 a in the thickness direction of the second electrode 17 and one surface 11 a in the thickness direction of the substrate 11, and the other end portion of the second electrode 17 in the X direction. Extends to the other in the X direction. The piezoelectric thin film 15 is formed in a rectangular shape when viewed from the Z direction, and is formed in the central portion 22 in the X direction and the Y direction. The length L1 in the Y direction of the piezoelectric thin film 15 is selected to be greater than the length L2 in the short direction Y of the second electrode 17, and the Y direction center of the piezoelectric thin film 15 and the Y direction of the second electrode 16 are selected. Is provided on the same virtual plane perpendicular to the Y direction. The piezoelectric thin film 15 is formed larger than the recess 13 in the X direction and the Y direction.

  The piezoelectric thin film 15 is made of a piezoelectric material such as ZnO (zinc oxide), AlN (aluminum nitride), and PZT (lead zirconate titanate), and has a high frequency voltage applied by the first electrode 16 and the second electrode 17. It expands and contracts accordingly, and has a function of converting electrical signals into mechanical vibrations.

  In order for the thin film resonator 10 to exhibit the necessary resonance characteristics, the thickness of the piezoelectric thin film 15 is such that the intrinsic acoustic impedance and density of the material forming the piezoelectric thin film 15, the sound velocity of the acoustic wave propagating through the piezoelectric thin film 15, and It is necessary to select precisely considering the wavelength. The optimum thickness of the piezoelectric thin film 15 varies depending on the frequency of a signal used in an electronic circuit configured using the thin film resonator 10, the design size of the resonance unit 20, the piezoelectric thin film material, and the electrode material, but is 0.3 μm. ˜2.5 μm is selected.

  The first electrode 16 is stacked on one surface 15 a in the thickness direction of the portion of the piezoelectric thin film 15 that is stacked on the second electrode 17. In the present embodiment, the first electrode 16 is formed over one surface 15 a in the thickness direction of the piezoelectric thin film 15 and one surface 11 a in the thickness direction of the substrate 11, and the other end of the piezoelectric thin film 15 in the X direction. It extends to the other side in the X direction rather than the part. The first electrode 16 is formed in a rectangular shape when viewed from the Z direction, is formed from the central portion 22 to the other end portion 24 in the X direction of the substrate 11, and is provided apart from the peripheral edge 23 of the one surface 11 a of the substrate 11. It is done.

  The length L3 in the Y direction of the first electrode 16 is selected to be shorter than the length L1 in the Y direction of the piezoelectric thin film 15, and the center in the Y direction of the first electrode 16 and the center in the Y direction of the piezoelectric thin film 15 are selected. Are provided on the same virtual plane perpendicular to the Y direction. Of the first electrode 16, the part other than the resonance part 20 functions as the extraction electrode 16c. The part of the extraction electrode 16 c is formed on the substrate 11, and the remaining part is formed on the recess 13. That is, the length L3 of the first electrode 16 in the Y direction is selected to be less than the size of the recess 13 in the Y direction, and when viewed from the thickness direction Z, one end 16d in the X direction of the first electrode 16 is 13 so as to be separated from the edge of the substrate 11 facing 13. By forming the first electrode 16 in this way, a portion of the portion where the first electrode 16, the piezoelectric thin film 15 and the second electrode 17 overlap in the Z direction is not acoustically insulated by the recess 13. Capacitance, so-called parasitic capacitance, can be reduced. The larger the parasitic capacitance, the lower the effective electromechanical coupling coefficient of the thin film resonator. However, such a configuration has the advantage that this reduction can be minimized.

  The first electrode 16 is a member having a function of applying a high-frequency voltage to the piezoelectric thin film 15 together with the second electrode 17 and is formed using a metal material such as W, Mo, Au, Al and Cu. Further, the first electrode 16 has a function of forming the resonance unit 20 at the same time as the function of the electrode. Therefore, the thickness of the first electrode 16 is the same as that of the first electrode 16 in order to exhibit the necessary resonance characteristics. In consideration of the specific acoustic impedance and density of the material to be processed, the sound velocity and wavelength of the acoustic wave propagating through the first electrode 16, it is necessary to select precisely. The optimum thickness of the first electrode 16 varies depending on the frequency of a signal used in an electronic circuit configured using the thin film resonator 10, the design size of the resonance unit 20, the piezoelectric thin film material, and the electrode material, but is 0.01 μm. It is selected to be about 0.5 μm.

  The thickness of the resonating unit 20 is designed to be approximately λ / 2 (λ is the wavelength of the acoustic wave at the frequency of the signal used). Further, since the area of the cross section perpendicular to the Z direction of the resonance part 20 is an element that determines the impedance of the thin film resonator 10, it is necessary to design it precisely like the thickness. When the thin film resonator 10 is used in a 50Ω impedance system, the electrical capacitance of the resonance unit 20 is selected so as to have a reactance of approximately 50Ω at the frequency of the signal used. In the present embodiment, the lengths in the X direction and the Y direction of the cross section perpendicular to the Z direction of the resonance unit 20 are selected to be equal, and the area of the resonance unit 20 in the cross section is, for example, the case of the thin film resonator 10 of 2 GHz. For example, it is selected to be about 200 μm × 200 μm.

  Further, when the recess 13 is formed, an etching hole 14 (through hole) that penetrates the resonator body 12 in the stacking direction and communicates with the recess 13 is provided to etch the substrate 11 after the resonator body 12 is formed. Yes. The etching hole 14 is a hole for allowing an etching agent to enter the substrate when the concave portion 13 is etched, and the peripheral portion of the first electrode 16, that is, the peripheral portion of the resonance portion 20 when viewed from the Z direction. A plurality of locations are formed. The etching hole 14 can be formed at an arbitrary position on the peripheral portion of the resonance portion 20, but is preferably provided at the deepest bottom portion of the cutout portion 30 from the viewpoint of efficiently etching the sacrificial layer.

  The shape seen from the Z direction of the resonating unit 20, that is, the planar shape is a substantially rectangular shape, and a cutout portion 30 is provided on at least one side of the rectangular sides. By providing the notch 30, the number of parallel parts is reduced on the opposite sides of the resonance part 20, and the occurrence of transverse mode resonance can be suppressed.

  Since the resonance in the transverse mode occurs between two opposing sides of the resonance unit 20, resonance occurs when the two opposing sides are in a parallel relationship. Therefore, by providing the notch 30, it is possible to break the parallel relationship between the two opposing sides, suppress the occurrence of resonance in the transverse mode, and prevent spurious due to unnecessary vibration.

  The notch 30 may be provided on any of the piezoelectric thin film 15, the first electrode 16, and the second electrode 17. In the example illustrated in FIG. 1, the notch 30 is provided on each side of the first electrode 16. The virtual straight line perpendicular to the plane (XY plane) direction with respect to the straight line portion of each side intersects with the cutout portion 30 provided on the other side. For example, in FIG. 1, the virtual straight line AA ′ orthogonal to the straight line portion on the left side of the first electrode 16 intersects the notch portion 30 provided on the upper side of the adjacent first electrode 16, An imaginary straight line BB ′ orthogonal to the straight line portion on the left side of the first electrode 16 intersects the cutout portion 30 provided on the right side of the opposed first electrode 16. By providing the notch 30 in this way, the opposing sides of the resonance part 20 become non-parallel, or the notch 30 is interposed therebetween, thereby further suppressing the occurrence of transverse mode resonance. Can do.

  Further, by providing the cutout portion 30 so that the planar shape of the resonance portion 20 is non-rotationally symmetric, it is possible to suppress the occurrence of vibration in the rotationally symmetric mode, so that spurious generated can be reduced. Therefore, the planar shape of the resonance part 20 is preferably a shape that is non-rotationally symmetric, for example, the shape shown in FIG.

  From the viewpoint of suppressing the occurrence of transverse mode resonance, the shape of the notch 30 is such that the side facing the side where the notch 30 is provided and all sides of the notch 30 are non-parallel. It is important to be. When the notch portions 30 are provided on the opposing sides, the notch portions so that all sides are non-parallel between the opposing sides including the rectangular sides and the sides of the notch portions 30. 30 is provided.

  In other words, the resonance unit 20 has a substantially rectangular shape when viewed from the Z direction, and has a notch in a part of each side of the resonance unit 20, and is orthogonal to the linear part of each side of the rectangle. The notch is provided so that the virtual straight line that intersects the intersecting notch at an angle other than 90 degrees. By doing so, there is no portion in parallel relation on the opposite sides of the resonance part 20, so that the occurrence of resonance in the transverse mode can be suppressed.

  As described above, the notch 30 may be formed only by an arcuate curve as shown in FIG. 1, or may be combined with a straight line and a curve. Moreover, as shown in FIG. 3, the aspect comprised only by the straight line which the planar shape of the notch part 30 makes | forms substantially triangular shape may be sufficient. Moreover, there may be a plurality of notches on one side.

  FIG. 4 is a diagram illustrating another example of the planar shape of the resonance unit 20 viewed from the Z direction. In the example of the planar shape shown here, the cutout shape of the cutout portion 30 is a part of a circle or ellipse made of a curve.

  Moreover, since the effect is demonstrated if the notch part 30 is provided in at least 1 side of the side of the rectangular resonance part 20, as shown in FIG. A shape provided on only one side, a shape provided on two sides as shown in FIG. 4B, a shape provided on three sides as shown in FIG. As shown in FIG.4 (d), the shape provided in all four sides may be sufficient.

  FIG. 5 is a diagram for explaining the dimensions of the notch 30 with respect to the planar shape of the resonance part 20 viewed from the Z direction.

  The notch 30 can suppress the transverse mode resonance by breaking the parallel relationship between the two opposing sides when the resonance part 20 is rectangular, but the notch 30 is provided with a large notch. If the planar shape deviates significantly from the rectangular shape, there is a concern that the characteristics of the resonance unit 20 may be affected.

  It is preferable to provide the notch 30 so that the width of the notch 30 is 30% or more and 80% or less with respect to the length L of the side where the notch 30 is provided. By making the width of the notch 30 30% or more with respect to L, the transverse mode resonance can be sufficiently suppressed. Further, by setting the width of the cutout portion 30 to 80% or less with respect to L, a sufficiently large capacity can be secured between the first electrode 16 and the second electrode 17.

  Moreover, about the depth C of the notch part 30, the notch part 30 is provided so that it may be 0.1 to 50% with respect to the length L of the side orthogonal to the side where the notch part 30 is provided. Is preferable, and 1 to 30% is particularly preferable. By setting the depth C of the notch 30 to 0.1% or more with respect to L, the transverse mode resonance can be sufficiently suppressed. Further, the vibration mode is not greatly changed by setting the depth C of the notch 30 to 50% or less with respect to L, and the notch 30 has a sufficient size between the first electrode 16 and the second electrode 17. Capacitance can be formed.

  The first electrode 16 is provided with the extraction electrode 16c. However, when the cutout portion 30 is provided as in the present invention, the rectangular side of the resonance portion 20 provided with the extraction electrode 16c is provided with the cutout portion 30. It is connected to the extraction electrode 16c at a straight line portion other than the bent portion. Therefore, it is possible to provide the notch portion 30 while maintaining the shape of the resonance portion 20 also on one rectangular side of the resonance portion 20 of the first electrode 16 where the extraction electrode 16c is provided.

  Further, since the cutout portion 30 may be provided in any layer of the resonance portion 20, the extraction electrode 16 c is provided on the side where the extraction electrode 16 c is provided without providing the cutout portion 30 in the first electrode 16. Alternatively, a cutout portion 30 may be provided on the side of the second electrode 17 facing the thickness direction. In this way, the first electrode 16 can be connected to the lead electrode 16c over the entire side, and the wiring resistance of the first electrode 16 can be reduced.

  6A to 6C are process diagrams showing a method for manufacturing the thin film resonator 10. The production method of the present invention is roughly composed of three steps as follows.

  In the first step, an insulating layer formed on one surface 11a and having an opening, a sacrificial layer filling the opening, a resonator body 12 provided to cover the sacrificial layer, and the sacrificial layer are communicated. And a resonator-forming substrate provided with an etching hole.

  In the second step, the sacrificial layer is etched through the etching hole to form an etching space surrounded by the resonator body, the insulating layer, and a part of the exposed surface 11a of the substrate 11.

  In the third step, the substrate 11 is etched to form the recess 13 so that the etching space formed in the second step is filled with an etching agent.

First Step (a) Preparation of Substrate 11 and Formation Step of Insulating Layer 100 The substrate 11 used for the thin film resonator 10 is a plate-like member having a thickness of about 0.05 mm to 1 mm, and is made of Si (silicon), Al ₂ O _3. (Aluminum oxide), SiO ₂ (silicon oxide), glass and the like.

In the present embodiment, an example using a silicon substrate among these will be described.
An insulating layer 100 is formed over the entire surface of one surface 11 a of the substrate 11. The insulating layer 100 is formed with a thickness of 0.1 μm or more and 1.2 μm or less, and is made of an insulating film such as SiO ₂ .

The SiO ₂ insulating film can be formed by subjecting the surface of the silicon substrate 11 to heat treatment and thermal oxidation. The thickness of the SiO ₂ insulating film can be controlled by the processing conditions of the heat treatment, the heating temperature, the heating time, and the like, and is provided in the preferred range as described above.

  As an example of the heat treatment conditions, an oxide insulating film having a thickness of 0.3 μm can be formed at a heating temperature of 1050 ° C. and a heating time of 40 to 90 minutes.

(B) Insulating Layer 100 Patterning Step An opening 100a is provided by patterning on the insulating layer 100 formed over the entire surface of the one surface 11a of the substrate 11 with a suitable thickness in the step (a). The opening 100a corresponds to an etching space for etching the substrate in the second process, and the opening 100a is filled with a sacrificial layer in a subsequent process.

  The insulating layer 100 can be patterned by using a known patterning technique for an oxide insulating film in a semiconductor manufacturing process, and can be easily provided by, for example, a photolithography technique. As an example of patterning, a positive resist is applied on the insulating layer 100 by spin coating or the like, exposed and developed, and the resist is patterned to form a mask. After that, it is immersed in BHF (buffered hydrofluoric acid) having a liquid temperature of 23 ° C. to form the opening 100a.

  Since the opening 100a corresponds to the etching space as described above, the opening shape and the opening size thereof are formed in the shape and size required for the recess 13 formed by etching. Since the concave portion 13 further defines the resonant portion 20 by acoustically insulating the resonator body 12, the shape and dimensions of the concave portion 13 are used in order to exhibit the resonance characteristics required by the thin film resonator 10. It is determined by the size and material of the resonator body 12 and the frequency of the signal used in the electronic circuit configured using the thin film resonator 10.

(C) Sacrificial layer formation process The sacrificial layer 101 is formed on the insulating layer 100 in order to fill the opening 100a provided in the process (b).

As the material of the sacrificial layer 101, phosphor quartz glass (PSG), BPSG (Boron-Phosphor-
Silicate-Glass: Boron, phosphorus, silicon, glass) or other forms of glass such as spin glass can be used. Other resin materials such as polyvinyl, polypropylene, and polystyrene that can be deposited on the substrate. These sacrificial layers can be removed by organic removal materials or O ₂ plasma etching.

  In this embodiment, PSG is provided as the sacrificial layer 101 for ease of etching. The film formation method of PSG can be formed by a known film formation method such as a CVD (Chemical Vapor Deposition) method.

  Since the film thickness required for the sacrificial layer is a thickness that fills the opening 100a, the thickness is the same as the thickness of the insulating layer formed in the step (a).

  The thickness of the insulating layer, that is, the thickness of the sacrificial layer to be formed is 0.1 μm or more and 1.2 μm or less, preferably 0.3 μm or more and 0.8 μm or less.

(D) Polishing Step After forming the sacrificial layer 101 in the step (c), the unnecessary sacrificial layer 101 is removed by polishing. By the polishing process, the surface of the insulating layer 100 is exposed, and the sacrificial layer 101 is filled only in the opening 100a.

  The polishing in this step can use a polishing technique used in a semiconductor manufacturing process, and for example, CMP (Chemical Mechanical Polishing) is preferably used.

(E) Second electrode film forming step A metal film 102 to be the second electrode 17 is formed on the entire surface of the insulating layer 100 exposed by the polishing step in the step (d).

  The metal film 102 serving as the second electrode is formed using a metal material such as W, Mo, Au, Al, Pt, Ti and Cu. The metal film 102 can be formed by a film forming technique used in a semiconductor manufacturing process, and can be formed by a thin film forming process such as sputtering and CVD.

(F) Second Electrode Patterning Step In the step (e), the second electrode 17 is provided by patterning on the formed metal film 102. The second electrode 17 constitutes the resonator body 12 and is patterned so as to cover the filling portion of the sacrificial layer 101 that will later become the recess 13.

  For the patterning of the metal film 102, a known patterning technique in a semiconductor manufacturing process can be used, and for example, it can be easily provided by a photolithography technique.

  When providing the notch 30 in the 2nd electrode 17, the notch 30 of the magnitude | size and shape which are predetermined in this process is provided.

(G) Piezoelectric thin film and first electrode film forming step The piezoelectric layer 103 and the metal film 104 are formed on the entire surface of the substrate on the second electrode 17 and the insulating layer 100 obtained by patterning in the step (f). Sequentially formed.

  The piezoelectric layer 103 to be the piezoelectric thin film 15 is made of a piezoelectric material such as ZnO (zinc oxide), AlN (aluminum nitride), and PZT (lead zirconate titanate), and is formed by the first electrode 16 and the second electrode 17. It expands and contracts according to the applied high frequency voltage and has a function of converting an electrical signal into mechanical vibration.

  The piezoelectric layer 103 to be the piezoelectric thin film 15 can use a film forming technique used in a semiconductor manufacturing process. For example, one surface in the thickness direction of the second electrode 17 is formed by a thin film forming process such as sputtering and CVD. It is formed with a predetermined thickness on 17a and one surface 11a in the thickness direction of the substrate 11.

  In addition, the metal film 104 to be the first electrode 16 is formed using a metal material such as W, Mo, Au, Al, Pt, Ti, and Cu, similarly to the metal film 102. The metal film 104 can be formed by a film forming technique used in a semiconductor manufacturing process, for example, by a thin film forming process such as sputtering and CVD.

(H) Piezoelectric thin film and first electrode patterning step In the step (g), the piezoelectric thin film 15 and the first electrode 16 are provided by patterning on the formed piezoelectric layer 103 and the metal film 104. The piezoelectric thin film 15 and the first electrode 16 constitute the resonator body 12 and are patterned on the second electrode 17.

  For the patterning of the piezoelectric layer 103 and the metal film 104, a known patterning technique in a semiconductor manufacturing process can be used, and can be easily provided by, for example, a photolithography technique.

  When the notch 30 is provided in the piezoelectric thin film 15 and the first electrode 16, the notch 30 having a predetermined size and shape is provided in the piezoelectric thin film 15 and the first electrode 16 in this step.

  Further, in this step, an etching hole 14 is formed in the resonator body 12. The etching hole 14 is a through-hole penetrating the resonator body 12 in the stacking direction (Z direction), and is provided so as to communicate with the sacrificial layer 101 above the sacrificial layer 101.

  Due to the etching hole 14, a part of the surface of the sacrificial layer 101 is exposed to the outside through the etching hole 14. In the second step, which is a subsequent step, the sacrificial layer 101 can be removed by etching by allowing an etchant to enter the etching hole 14.

  As a method of forming the etching hole 14, a via formation technique in a semiconductor manufacturing process can be used, and for example, it can be easily provided by a photolithography technique.

  The etching hole 14 is formed as, for example, a substantially cylindrical through hole, and the diameter thereof is set to 5 μm to 30 μm. Further, about 4 to 8 etching holes 14 are formed along the outer peripheral portion of the sacrificial layer 101 when viewed in plan from the Z direction. Further, the etching hole 14 is preferably disposed at least in a portion located at the shortest distance from the center of the sacrificial layer 101 in the outer peripheral portion of the sacrificial layer 101, for example, at the deepest bottom of the notch 30. It is preferable to provide it.

  By the steps (a) to (h) as described above, a resonator forming substrate that is a precursor of the thin film resonator 10 is formed.

Second Step (i) Sacrificial Layer Etching Step By removing the sacrificial layer 101 by etching through the etching hole 14 formed in the step (h), the second electrode 17 and the insulating layer 100 of the resonator body 12 are removed. And an etching space 105 for substrate etching surrounded by one surface 11a of the substrate 11 is formed. The etching space 105 corresponds to the opening 100 a provided in the insulating layer 100.

  The etching space 105 is a cavity having the same height as the thickness of the insulating layer 100 and the same bottom area as the opening area of the opening 100a.

  Etching of the sacrificial layer 101 can be performed using an etching technique in a semiconductor manufacturing process, and can be easily performed using an etchant corresponding to the material of the sacrificial layer. The etching agent may be an etching solution or an etching gas, and may be selected from wet etching and dry etching according to various etching conditions.

  In the present embodiment, PSG that is a sacrificial layer is removed by wet etching. Etching is performed using a hydrofluoric acid aqueous solution as an etchant at a temperature of 23 ° C.

  In this way, the sacrificial layer 101 is removed by etching to form an etching space 105, and a part of one surface 11 a of the substrate 11 is exposed so as to face the etching space 105.

Third Step (j) Substrate Etching Step Etching agent enters the etching space 105 formed in step (i) through the etching hole 14 so that the etching space 15 is filled with the etching agent. The recess 13 is formed by etching in the thickness direction (Z direction) from the surface facing the etching space 105.

  Etching of the substrate 11 can utilize an etching technique in a semiconductor manufacturing process, and can be easily performed using an etching agent according to the material of the substrate. The etching agent may be an etching solution or an etching gas, and may be selected from wet etching and dry etching according to various etching conditions.

  In the present embodiment, the substrate 11 is partially removed by wet etching to form the recess 13.

By forming the recess 13 in this way, the thin film resonator 10 is obtained.
Next, an embodiment of a filter according to the present invention in which a plurality of the above thin film resonators 10 are arranged on a substrate will be described.

  FIG. 7 is a plan view showing a configuration of a filter according to another embodiment of the present invention, and is configured by arranging a plurality of the above-described thin film resonators 10 on a substrate 43.

  In arranging a plurality of thin film resonators 10, the planar shape of the resonance part 20 is substantially rectangular, and at least one side of the resonance part 20 is constituted by a straight part and a notch part 30. There is no portion protruding outward, the distance between the thin film resonators 10 can be reduced, and a high-density arrangement is possible. Since the occurrence of spurious in each thin film resonator 10 is suppressed, the filter characteristics can be improved while being small.

  FIG. 8 is an equivalent circuit diagram showing an embodiment of the duplexer according to the present invention. Two filters having the configuration as shown in FIG. 7 are mounted on a substrate (transmitting filter 41 and receiving filter 42). It is constituted by.

  As shown in FIG. 8, the duplexer is called an antenna duplexer or duplexer, and is connected to one antenna, and includes a branch circuit, a transmission filter, and a reception filter.

  The duplexer 50 includes, as input / output ports, an antenna port P1 connected to the antenna, a transmission port P2 connected to the transmitter, and a reception port P3 connected to the receiver. The duplexer 50 is provided between the antenna port P1 and the transmission port P2. The transmission Tx filter 41 is connected, and the reception Rx filter 42 is connected between the antenna port P1 and the reception port P3.

  As described above, the transmission Tx filter 41 and the reception Rx filter 42 can be miniaturized by arranging the thin film resonators 10 at a high density, and the duplexer 50 obtained by mounting these filters. Can also be miniaturized. Since spurious generation is suppressed in the thin film resonator 10 provided in each filter, the characteristics of the duplexer 50 can be improved while being small.

  As shown in FIG. 1, the thin film resonator 10 was manufactured with a configuration in which a curved notch 30 was provided on all sides of the second electrode 16.

  The first electrode 16 and the second electrode 17 were patterned by providing a metal film made of Mo having a thickness of 0.3 μm. The piezoelectric thin film 15 was patterned by providing a piezoelectric layer made of AlN having a thickness of 1.4 μm.

  The resonance unit 20 is a square having a side length L of 100 μm, and the width of the cutout 30 is set such that A = B = 50 μm, that is, A + B is 100% of the side length L. The depth C of the notch 30 was 12.5 μm, and C was 12.5% of the side length L.

  Further, as a comparative example, a thin film resonator in which a notched portion 30 was not provided in the resonance portion but a square first electrode was provided was manufactured. The first electrode was provided so that the area of the first electrode of the comparative example was the same as that of the first electrode 16 of the example.

  The resonance characteristics of the thin film resonators of Examples and Comparative Examples were measured with a network analyzer.

  The measuring apparatus used the network analyzer 8753D by Agilent, and measured with the port number 1 using the high frequency probe.

  FIG. 9 is a graph showing measurement results of Examples and Comparative Examples. FIG. 9A shows the measurement result of the example, and FIG. 9B shows the measurement result of the comparative example. The vertical axis represents the impedance, and the horizontal axis represents the frequency of the input signal. The input signal is a voltage signal.

  As can be seen from the measurement results, in the comparative example, the waveform was disturbed by spurious near the antiresonance point. On the other hand, in the example, spurious was suppressed and a smooth waveform was obtained.

1 is a plan view showing a thin film resonator 10 according to an embodiment of the present invention. It is sectional drawing seen from the cut surface line II-II of FIG. It is a figure which shows the example of the planar shape seen from the Z direction of the resonance part. It is a figure which shows the other example of the planar shape seen from the Z direction of the resonance part. It is a figure for demonstrating the dimension of the notch part 30 about the planar shape seen from the Z direction of the resonance part. FIG. 4 is a process diagram illustrating a method for manufacturing the thin film resonator 10. FIG. 4 is a process diagram illustrating a method for manufacturing the thin film resonator 10. FIG. 4 is a process diagram illustrating a method for manufacturing the thin film resonator 10. It is a top view which shows the structure of the filter which is other embodiment of this invention. It is an equivalent circuit diagram which shows the structure of the duplexer 50 which is further another embodiment of this invention. It is a graph which shows the measurement result of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Thin film resonator 11 Substrate 14 Etching hole 15 Piezoelectric thin film 16 1st electrode 17 2nd electrode 20 Resonance part 30 Notch

Claims (7)

A thin film resonator including a piezoelectric thin film, and a resonance part having a first electrode and a second electrode disposed so as to face each other with the piezoelectric thin film interposed therebetween,
The resonance part has a substantially rectangular planar shape, and at least one side of the resonance part is constituted by a straight part and a notch part.   The notch is provided on each side of the resonance part, and a virtual straight line perpendicular to the plane direction with respect to the straight part of each side of the resonance part is provided with the notch part provided on the other side. The thin film resonator according to claim 1, which intersects.   3. The thin film resonator according to claim 1, wherein an extraction electrode is connected to an entire linear portion of one side of the first electrode constituting the resonance portion.   The thin film resonator according to claim 3, wherein the notch is not provided on one side of the first electrode to which the extraction electrode is connected.   The thin film resonator according to claim 1, wherein the cutout portion is provided so that a planar shape of the resonance portion is non-rotationally symmetric.   A filter comprising a plurality of thin film resonators according to claim 1 arranged on a substrate.   A duplexer comprising the filter according to claim 6.

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