JP2010154233A - Piezoelectric resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-reliability piezoelectric resonator in which resonance characteristics are not varied. <P>SOLUTION: A piezoelectric resonator includes: a substrate; a piezoelectric film; an upper electrode which is at least partly laminated on one surface in thickness direction of the piezoelectric film; and a lower electrode which is at least partly laminated on the other surface in the thickness direction of the piezoelectric film. The piezoelectric resonator further includes: a resonator body which is disposed on one surface in thickness direction of the substrate so as to form a void between the substrate and the resonator body; a first protecting film with which a face, on the side opposed to the face in contact with the piezoelectric film of the upper electrode, is covered; and a second protecting film which comprises the same material as the first protecting film, and covers a face on the opposite side of the face in contact with the piezoelectric film of the lower electrode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric resonator using a thickness longitudinal vibration mode.

  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, in wireless communication, microwaves in the vicinity of 2 GHz are becoming mainstream, and standards are already being developed for several GHz or more, so high performance filters corresponding to these frequencies are required. As such a filter, a filter using a piezoelectric resonator using a thickness longitudinal vibration mode of a piezoelectric film exhibiting piezoelectricity has been proposed.

  The piezoelectric resonator includes a substrate made of Si, GaAs, or the like, a resonator body formed on the substrate surface, a gap surrounded by the substrate and the resonator body, and a through-hole penetrating the resonator body and communicating with the gap. It is comprised including. The resonator body includes a piezoelectric film, and an upper electrode and a lower electrode that sandwich the piezoelectric film from both sides in the thickness direction. Here, in the piezoelectric resonator, the resonance part is formed by the inner wall surface of the part facing the air gap in the part where the piezoelectric film, the upper electrode, and the lower electrode constituting the resonator body overlap, and the air gap is formed of the piezoelectric film. The cavity is a resonance region that enables vibration.

Here, since each layer constituting the resonance part determines resonance characteristics such as a resonance frequency, it is important to suppress changes in the film quality and the like. Further, it is necessary to prevent foreign matter from adhering to the resonance part because the resonance characteristic is changed. From the above, a configuration has been proposed in which a protective film for protecting the resonance portion is provided so as to cover the upper electrode (see Patent Document 1).
JP 2008-172713 A

  However, in the piezoelectric resonator disclosed in Patent Document 1, the lower electrode side cannot be protected, and as a result, the film quality of the layer constituting the resonance part may be altered. This is particularly noticeable in a configuration in which the resonating part is disposed on the substrate via a gap.

  The present invention has been devised to solve the above-described problems, and an object of the present invention is to provide a highly reliable piezoelectric resonator in which resonance characteristics do not change.

  The piezoelectric resonator of the present invention includes a substrate, a piezoelectric film, an upper electrode at least partially laminated on one surface in the thickness direction of the piezoelectric film, and at least a portion on the other surface in the thickness direction of the piezoelectric film. A resonator body disposed on the surface in the thickness direction of the substrate so as to form a gap with the substrate, and the piezoelectric film of the upper electrode. A first protective film covering a surface opposite to the surface in contact with the first protective film; and a second protective film made of the same material as the first protective film and covering a surface of the lower electrode opposite to the surface in contact with the piezoelectric film; , Including.

  In the piezoelectric resonator according to the aspect of the invention described above, the inner wall surface of the portion facing the gap at the peripheral edge of the resonator main body is an inclined surface having an acute angle with the surface in the thickness direction of the substrate. In the inclined surface of the inner wall surface, a through hole leading to the gap is provided.

  In the piezoelectric resonator according to the aspect of the invention, in the configuration described above, the first protective film and the second protective film may be extended to a surface exposed to the through hole of the resonator body and connected to each other. It is formed integrally.

  In the piezoelectric resonator according to the aspect of the invention, in the configuration described above, the inclined surface includes a first inclined surface and a second inclined surface that are different from each other in an angle formed with one surface in the thickness direction of the substrate. .

  In the piezoelectric resonator according to the aspect of the invention, in the above configuration, the through hole is formed so as to straddle a boundary portion between the first inclined surface and the second inclined surface.

  In the piezoelectric resonator of the present invention, the first protective film and the second protective film are made of silicon oxide in the above configuration.

  According to the present invention, the upper electrode and the lower electrode constituting the resonator body exposed to the external environment and the air gap are covered with the protective film, so that the alteration of the upper electrode and the lower electrode can be prevented. As a result, a highly reliable piezoelectric resonator capable of obtaining stable resonance characteristics can be provided.

  FIG. 1 is a cross-sectional view showing a configuration of a piezoelectric resonator 1 according to an embodiment of the present invention. In addition, although it is the same also in the following drawings, the same code | symbol is attached | subjected to the same location and the overlapping description is abbreviate | omitted.

  The piezoelectric resonator 1 passes through the substrate 16, the resonator body 17 formed on one surface in the thickness direction of the substrate 16, the gap 15 surrounded by the substrate 16 and the resonator body 17, and the resonator body 17, A through hole 14 communicating with the gap 15 is included. The substrate 16 is a base member of the piezoelectric resonator 1. The board | substrate 16 has a substantially rectangular parallelepiped shape, and thickness is chosen by about 0.05-1.0 mm. The substrate 16 is formed of Si (silicon), GaAs (gallium arsenide), or the like.

  The resonator body 17 includes at least a part of the piezoelectric film 11, the upper electrode 13 that is at least partially laminated on one surface in the thickness direction of the piezoelectric film 11, and the other surface in the thickness direction of the piezoelectric film 11. A laminated body including the lower electrode 12.

  In the piezoelectric resonator 1, the resonance portion 18 is formed by the inner wall surface of the portion facing the gap 15 among the portions where the piezoelectric film 11, the upper electrode 13, and the lower electrode 12 constituting the resonator body 17 overlap. The resonance characteristics of the piezoelectric resonator 1 are determined by the design of the resonance unit 18.

  Here, the first protective film 31 covers the surface of the upper electrode 13 of the resonator body 17 opposite to the surface in contact with the piezoelectric film 11, and the piezoelectric film 11 of the lower electrode 12 of the resonator body 17 covers the first protective film 31. A second protective film 32 is provided so as to cover the surface opposite to the surface in contact with. As described above, the first and second protective films 31 and 32 protect the portions of the upper electrode 13 and the lower electrode 12 that constitute the resonance portion 18 without being exposed to the external environment. As a result, the portion of the upper electrode 13 and the lower electrode 12 that constitutes the resonance portion 18 can be protected from deterioration due to external impact or moisture penetration, change in resonance characteristics due to deposits, and the like. A piezoelectric resonator having a high height can be provided.

  The first and second protective films 31 and 32 are not particularly limited as long as they are made of the same material, have stable characteristics with respect to the external environment, and can protect the electrodes 12 and 13. For example, it is preferable to use silicon oxide or the like from the viewpoint of impact resistance and chemical resistance. When silicon oxide is used, the protective film also functions as a temperature compensation film, so that a piezoelectric resonator having high reliability and excellent temperature characteristics can be provided. In addition, in order to protect from moisture, silicon nitride can be used, or various resin materials can be used in consideration of productivity. A multilayer structure may also be used.

  Next, each layer constituting the resonator body 17 will be described.

  The piezoelectric film 11 is made of a piezoelectric material such as ZnO (zinc oxide), AlN (aluminum nitride), and PZT (lead zirconate titanate), and expands and contracts according to the high-frequency voltage applied by the upper electrode 13 and the lower electrode 12. , Has the function of converting electrical signals into mechanical vibrations. In order for the piezoelectric resonator 1 to exhibit the necessary resonance characteristics, the thickness of the piezoelectric film 11 depends on the specific acoustic impedance and density of the material forming the piezoelectric film 11, the sound speed and wavelength of the acoustic wave propagating through the piezoelectric film 11, and the like. In consideration, it is necessary to select precisely. The optimum thickness of the piezoelectric film 11 varies depending on the frequency of a signal used in an electronic circuit configured using the piezoelectric resonator 1, the design dimension of the resonance unit 18 described later, the piezoelectric film material, and the electrode material. .About 2 to 3.0 μm.

  The lower electrode 12 is at least partially laminated on the other surface in the thickness direction of the piezoelectric film 11. That is, the lower electrode 12 is the lowest layer in the resonator body 17 that is a laminate, and is formed on one surface in the thickness direction of the substrate 16. The lower electrode 12 is a member having a function of applying a high-frequency voltage to the piezoelectric film 11 and is made of a metal material such as W (tungsten), Mo (molybdenum), Au (gold), Al (aluminum), or Cu (copper). Formed using. In addition, since the lower electrode 12 has a function of forming a resonating unit 18 to be described later as well as a function as an electrode, the thickness of the lower electrode 12 forms the lower electrode 12 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 lower electrode 12, etc., it is necessary to select precisely. The optimum thickness of the lower electrode 12 varies depending on the frequency of the signal used in the electronic circuit configured using the piezoelectric resonator 1, the design dimension of the resonance unit 18, the piezoelectric film material, and the electrode material. .About.0.0 μm. The upper electrode 13 is a member having a function of applying a high frequency voltage to the piezoelectric film 11 together with the lower electrode 12, and is configured in the same manner as the lower electrode 12.

  The air gap 15 is a cavity surrounded by the substrate 16 and the resonator body 17, and is a cavity that is a resonance region that enables the piezoelectric film 11 to vibrate. The inner wall surface of the resonator body 17 constituting the air gap 15 is a air gap flat surface 15a having a space parallel to one surface in the thickness direction of the substrate 16 at the center, and the substrate 16 at the peripheral edge. The angle formed with the one surface in the thickness direction is an inclined surface 15b having an acute angle. The undulations are formed on the surfaces of the piezoelectric film 11, the upper electrode 13, and the lower electrode 12 constituting the resonator body 17 according to the shape of the inner wall surface that forms the gap 15 described above.

  The inner wall surface of the resonator body 17 that forms the air gap 15 is configured to be an inclined surface 15b having an acute angle with the surface of the substrate 16 at the peripheral edge. On the other hand, the peripheral edge portion may be configured to be perpendicular to the surface of the substrate 16. Comparing the two, the configuration of the present embodiment causes excessive stress accumulation and concentration in each of the piezoelectric film 11, the upper electrode 13, and the lower electrode 12 of the resonator body 17 corresponding to the peripheral edge. Can be reduced and the occurrence of breakage can be suppressed.

  Further, in the present embodiment, in the inner wall surface of the resonator body 17 that forms the gap 15, the gap between the gap flat surface 15 a and the one surface in the thickness direction of the substrate 16 is set to about 2.6 to 4.0 μm. The angle θ formed between the inclined surface 15b and the surface of the substrate 16 at the peripheral edge of the inner wall surface of the resonator body 17 is set to 1.14 ° to 56.3 °.

In the piezoelectric resonator 1, the resonance portion 18 is formed by the inner wall surface of the portion facing the gap 15 among the portions where the piezoelectric film 11, the upper electrode 13, and the lower electrode 12 constituting the resonator body 17 overlap. The thickness of the resonating unit 18 is designed to be approximately λ / 2 (λ is the wavelength of the acoustic wave at the frequency of the signal used). The shape seen from the thickness direction of the resonating part 18, that is, the planar shape, is a substantially rectangular shape. In order to suppress spurious, the planar shape of the resonance portion 18 may be asymmetric. In the present embodiment, the resonance part 18 is formed in a rectangular parallelepiped shape. In addition, the area of the cross section perpendicular to the thickness direction of the resonance portion 18 is an element that determines the impedance of the piezoelectric resonator 1, and therefore needs to be designed precisely like the thickness. When the piezoelectric resonator 1 is used in a 50Ω impedance system, the electrical capacitance of the resonance unit 18 is selected so as to have a reactance of approximately 50Ω at the frequency of the signal used. In the present embodiment, the area of the cross section perpendicular to the thickness direction of the resonance portion 18 is selected to be about 200 μm × 200 μm in the case of the piezoelectric resonator 1 of 2 GHz, for example.

  The through hole 14 provided in the piezoelectric resonator 1 is formed by penetrating the resonator body 17 in a direction perpendicular to the surface of the substrate 16 and opening on the inclined surface 15 b of the resonator body 17 forming the air gap 15. And in this Embodiment, the hole diameter of the through-hole 14 is about 10 micrometers, for example. Thus, since the through hole 14 is provided so as to open to the inclined surface 15b of the resonator body 17, the through hole 14 is provided with the resonance portion 18 as compared with the case where the through hole 14 is provided to open to the air gap flat surface 15a. Has little effect on Therefore, the piezoelectric resonator 1 having excellent resonance characteristics can be obtained. In addition, compared to the case where the resonator body 17 is provided so as to open to the flat air gap surface 15a, the opening area on the air gap 15 side of the through hole 14 is large even though the hole diameter is the same. Although details will be described later, the piezoelectric resonator 1 is manufactured by removing a sacrificial layer formed in a portion corresponding to the gap 15 with an etchant through the through hole 14. The piezoelectric resonator 1 of the present embodiment has a large opening area on the side of the gap 15 of the through hole 14, so that the sacrificial layer removal efficiency by the etching agent is improved, and a part of the sacrificial layer remains in the gap 15. Will be. Therefore, it is suppressed that the resonance characteristic as the piezoelectric resonator 1 is impaired, and the piezoelectric resonator 1 having excellent resonance characteristics is obtained. In particular, the lower electrode 12 exposed in the gap 15 is more likely to be deteriorated due to the influence of an etching agent residue or the like than the film constituting the other resonator body 17. On the other hand, in the present embodiment, by increasing the opening area of the through hole 14, it is possible to significantly suppress the residue of etching residues and the like, and to protect the lower electrode 12 by the second protective film 32. The deterioration of the lower electrode 12 is significantly suppressed, and the piezoelectric resonator 1 is highly reliable.

  Next, FIG. 2 is a cross-sectional view showing another example of the embodiment of the piezoelectric resonator of the present invention. The piezoelectric resonator 2 shown in FIG. 2 is formed integrally with the piezoelectric resonator 1 shown in FIG. 1 so as to cover the surface where the first and second protective films 31 and 32 are exposed to the through hole 14 of the resonance portion 18. Different in that it is.

  Thus, since the first and second protective films 31 and 32 cover the surface exposed to the through hole 14 of the resonance part 18 and are integrally formed, only the surfaces of the upper and lower electrodes 12 and 13 are formed. In addition, the side surfaces of the piezoelectric film 11 exposed to the external environment can be covered. That is, since the entire resonance portion 18 that determines the resonance characteristics of the piezoelectric resonator 2 can be covered, a more reliable piezoelectric resonator can be provided.

  Next, FIG. 3 is an enlarged cross-sectional view of a main part showing still another example of the embodiment of the piezoelectric resonator of the present invention. Specifically, a portion corresponding to a portion surrounded by a broken line in FIG. 1 is shown. The piezoelectric resonator shown in FIG. 3 is different from the piezoelectric resonator 1 shown in FIG. 1 in the shape of the inclined surface of the resonator body 17.

  Specifically, in the present embodiment, the first gap inclined surface 15c and the second gap inclined surface 15d, which are two inclined surfaces, are provided. The first air gap inclined surface 15c is located on the one surface side in the thickness direction of the substrate 16 with respect to the second air gap inclined surface 15d, and the angle θ1 between the first air gap inclined surface 15c and the substrate 16 surface is the second air gap inclined surface 15d. Is set smaller than the angle θ2 formed by the surface of the substrate 16. Thus, from the viewpoint of reducing stress concentration on the constituent members of the resonator body 17 and suppressing the occurrence of breakage, the inclined surface at the peripheral edge of the inner wall surface of the resonator body 17 is in the thickness direction of the substrate 16. It is preferable to have a plurality of inclined surfaces having different angles with respect to one surface. The angle θ1 formed between the first gap inclined surface 15c and the surface of the substrate 16 is set to 1.14 ° or more and less than 26.5 °, and the angle θ2 formed between the second gap inclined surface 15d and the surface of the substrate 16 is It is set to 26.5 ° or more and 56.3 ° or less.

  Moreover, although a reason is mentioned later, it is preferable that the through-hole 14 is formed so that the boundary part of the 1st space | gap inclined surface 15c and the 2nd space | gap inclined surface 15d may be straddled.

  Next, an example of a method for manufacturing a piezoelectric resonator according to the present invention will be described. FIG. 4 is a process diagram showing a manufacturing method of the piezoelectric resonator 2 according to the embodiment of the present invention shown in FIG. The manufacturing method of the piezoelectric resonator 2 uses a semiconductor manufacturing technique, and mainly includes four steps as follows.

[Board preparation process]
In the substrate preparation step, a resonator forming substrate is prepared. The prepared resonator forming substrate is obtained by laminating a sacrificial layer and the resonator body 17 on the surface of the substrate 16.

(A) Preparation of substrate 16 and formation process of sacrificial layer The substrate 16 used in the piezoelectric resonator 1 is a plate-like member made of Si (silicon), GaAs (gallium arsenide), etc. In this embodiment, silicon An example using a substrate will be described. The sacrificial layer is a portion corresponding to the gap 15 of the piezoelectric resonator 2 to be manufactured. In this embodiment, the sacrificial layer is surrounded by the gap flat surface 15a, the inclined surface 15b, and the substrate 16 which are the inner wall surfaces of the resonator body 17. A sacrificial layer 21 is formed on the surface of the substrate 16 corresponding to the voids 15 formed in this way.

First, as shown in FIG. 4A, the sacrificial layer 21 is formed over the entire surface of the substrate 16 in the thickness direction. The sacrificial layer 21 is made of SiO ₂ (silicon dioxide) or PSG (phosphorus-doped glass), and may be a single layer or a laminate of these in order. The sacrificial layer 21 made of SiO ₂ can be formed by subjecting the surface of the silicon substrate 16 to heat treatment and thermal oxidation, and its thickness is controlled by the heat treatment treatment conditions, the heating temperature, the heating time, and the like. For example, it is set to 0.1 to 1.0 μm. The sacrificial layer 21 made of PSG can be formed by a CVD (Chemical Vapor deposition) method, and its thickness can be controlled by processing conditions such as temperature and time during CVD processing. Set to 5 to 3.0 μm. Even if it is formed to be relatively thick in this way, PSG can be etched in a relatively short time in the sacrificial layer etching step described later because PSG has a high etching rate. The surface of the sacrificial layer 21 may be smoothed using a CMP (Chemical Mechanical Polishing) apparatus.

(B) Sacrificial Layer Patterning Step As shown in FIG. 4B, the sacrificial layer 21 formed over the entire surface of one surface of the substrate 16 is formed into a shape corresponding to the gap 15 by patterning.

  For the patterning of the sacrificial layer 21, a known patterning technique for an oxide insulating film in a semiconductor manufacturing process can be used, and can be easily provided by, for example, a photolithography technique. As an example of patterning, a positive resist is applied onto the sacrificial layer 21 by spin coating or the like, exposed and developed, and the resist is patterned to form a mask. After that, the sacrificial layer 21 having a shape corresponding to the gap 15 is obtained by dipping in a hydrofluoric acid aqueous solution.

(C) Formation Process of Resonator Main Body 17 that is a Laminated Body As shown in FIG. 4C, the lower electrode 12, the piezoelectric film 11, and the upper electrode 13 are formed on the sacrificial layer 21 having a shape corresponding to the gap 15. A resonator body 17 is formed.

  First, the lower electrode 12 is formed on at least a part of the surface of the substrate 16 and the surface of the sacrificial layer 21. The lower electrode 12 can be formed by a sputtering method, a CVD method, or the like. Next, when viewed in plan from the thickness direction of the substrate 16, that is, the surface of the lower electrode 12, the surface of the sacrificial layer 21 in which the lower electrode 12 is not stacked, and the surface of the substrate 16 in which the lower electrode 12 and the sacrificial layer 21 are not stacked. A piezoelectric film 11 is formed so as to cover each of the above. The piezoelectric film 11 can be formed by a sputtering method, a CVD method, or the like. Next, the upper electrode 13 is formed on at least a part of the surface of the piezoelectric film 11. At this time, the upper electrode 13 is formed so that at least a part thereof faces the sacrificial layer 21 with the piezoelectric film 11 and the lower electrode 12 interposed therebetween.

  As described above, in the substrate preparation step, a resonator forming substrate in which the sacrificial layer 21, the lower electrode 12, the piezoelectric film 11, and the upper electrode 13 are laminated on the surface of the substrate 16 is prepared.

[Through hole forming step]
In the through hole forming step, as shown in FIG. 4D, the resonator body 17 constituting the resonator forming substrate prepared in the substrate preparing step is tilted in a direction perpendicular to the surface of the substrate 16. A through hole 14 reaching the surface is formed. The through hole 14 can be formed by using a via formation technique in a semiconductor manufacturing process, and can be easily provided by, for example, a photolithography technique. For example, when the planar shape of the sacrificial layer 21 is substantially square, four through holes 14 may be provided in the vicinity of each vertex of the square.

  At this time, since the through hole 14 reaching the inclined surface of the sacrificial layer 21 is formed, the formed through hole 14 has a hole diameter larger than that formed so as to penetrate to the flat surface of the second sacrificial layer 22. Even if it is the same, the opening area on the sacrificial layer side of the through hole 14 becomes large.

[Sacrificial layer etching process]
In the sacrificial layer etching step, as shown in FIG. 4E, the sacrificial layer 21 is removed by an etching agent through the through hole 14 to form a void 15 surrounded by the substrate 16 and the resonator body 17. Etching removal of the sacrificial layer 21 can be performed using an etching technique in a semiconductor manufacturing process, and can be easily performed using an etching agent according 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, the sacrificial layer 21 is removed by wet etching. Etching is performed under a predetermined temperature condition using a hydrofluoric acid aqueous solution as an etchant as an etchant.

  At this time, as described above, the opening area on the sacrificial layer side of the through-hole 14 formed so as to penetrate to the inclined surface of the sacrificial layer 21 is larger than that formed when penetrating to the flat surface. However, the sacrificial layer removal efficiency when the one sacrificial layer 21 is removed by the etchant through the through hole 14 is improved. Therefore, the sacrificial layer 21 can be efficiently and completely removed by etching, and a part of the sacrificial layer can be prevented from remaining in the gap 15 to be formed. Further, since the through hole 14 is formed on the peripheral edge side of the resonator body 17, a flow is generated in the etching agent that has flowed through the through hole 14 and entered the gap 15. The flow of the etching agent in the gap 15 also improves the etching rate.

[Etching agent removal process]
In the etching agent removing step, the etching agent remaining in the gap 15 formed in the sacrificial layer etching step is removed through the through hole 14. First, a rinsing solvent such as pure water or IPA (isopropanol) is filled into the gap 15 where the etching agent remains through the through-hole 14, and the inside of the gap 15 is cleaned with these rinsing solvents. When the cleaning in the gap 15 is completed, the rinse solvent is volatilized using a dryer.

  In the sacrificial layer etching process, when the sacrificial layer is removed by dry etching, the vacuum evacuation may be repeated so that the etching gas as the etching agent is completely exhausted from the gap 15. .

[Protective film formation process]
In the protective film forming step, as shown in FIG. 2 (f), the first and second protective films 31 and 32 are formed so as to cover the resonance part 18. Specifically, the upper surface and the side surface of the upper electrode 13, the lower surface and the side surface of the lower electrode 12, and the side surface of the resonance part 18 exposed in the through hole 14 are integrally formed by CVD or the like. Here, since the through hole 14 is formed on the peripheral edge side of the resonator body 17, a flow is generated in the carrier gas that has flowed through the through hole 14 and entered the gap 15. By the flow of the carrier gas in the gap 15, the film can be efficiently formed on the lower surface side of the lower electrode 12, the side surface of the through hole 14, and the like.

  As described above, the resonator forming substrate in which the sacrificial layer 21 and the resonator body 17 are laminated on the surface of the substrate 16 in the substrate preparing step is prepared, and the resonator forming the resonator forming substrate in the through hole forming step. A through hole 14 is formed through the main body 17 in a direction perpendicular to the surface of the substrate 16 up to the inclined surface of the sacrificial layer 21. (2) The sacrificial layer 22 is removed to form the void 15, and the etching agent remaining in the void 15 in the etching agent removing step is removed by the rinsing solvent through the through hole 14, and the rinsing solvent is volatilized and dried to protect it. The piezoelectric resonator 2 can be manufactured by forming the first and second protective films 31 and 32 that cover the resonance portion 18 in the film forming process.

  As shown in FIG. 3, in the case where the inclined surface of the resonator body 17 has a plurality of inclined surfaces, the sacrificial layer 21 is laminated with two or more different layers in the substrate preparation step. In the patterning step, the angle of the inclined surface on the side surface of each layer may be varied using the difference in the etching rate depending on the material.

  Further, as shown in FIG. 3, it is preferable to form the through hole 14 so as to straddle the first and second inclined surfaces 15 c and d because there are the following advantages.

  Interference fringes can be visually recognized at the boundary portion from the through hole 14 formed so as to penetrate to the region including the boundary portion of the inclined surface of the sacrificial layer 21 which is an inclined surface having a different angle with the surface of the substrate 16. . That is, when the through hole 14 reaches the sacrificial layer 21, the interference fringe becomes obvious. Accordingly, it is possible to easily confirm that the through hole 14 has reached the sacrificial layer 21 by confirming the interference fringes appearing on the bottom surface of the through hole 14. When the through-hole 14 is provided in the flat portion as in the prior art, the sacrificial layer does not have inclined surfaces with different angles, so interference fringes do not appear, or even if they appear, the through-holes are visually observed or a metal microscope or the like. However, the state hardly changes before and after the through hole 14 reaches the sacrifice layer. Therefore, conventionally, in order to confirm that the through-hole 14 has reached the sacrificial layer, it is necessary to use a large-scale device or to determine the conditions when the through-hole 14 reaches the sacrificial layer. The manufacturing process was complicated and hindered productivity improvement. Further, when the confirmation work of whether or not the through hole 14 has reached the sacrificial layer is omitted, or when the conditions for forming the through hole are changed, the through hole 14 does not reach the sacrificial layer. In some cases, the sacrificial layer is subsequently etched. In this case, there arises a problem that the sacrificial layer is not removed well, and that it takes a very long time to completely remove the sacrificial layer.

  On the other hand, when the through hole 14 is formed so as to straddle the first and second inclined surfaces 15c, d, the through hole 14 is provided at a position straddling the boundary portion of the inclined surface of the sacrificial layer 21 having different angles. Thus, when the through-hole 14 reaches the sacrificial layer, an interference fringe can be generated. By using this interference fringe, the through-hole 14 can reach the second sacrificial layer 21 easily and reliably. Become.

  Furthermore, the interference fringes that appear at the boundary can be used as an index for monitoring the sacrificial layer etching end point in the sacrificial layer etching step. As a method of detecting such interference fringes 32, visual observation may be used, or detection may be performed using an optical detection device such as a metal microscope.

  The piezoelectric resonator of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in FIGS. 1 to 3, the case where the through hole 14 is formed in the inclined surface 15 b of the resonator body 17 is described as an example, but the through hole 14 may be provided in the flat air surface 15 a. Further, the case has been described in which the gap 15 is formed by forming the cavity main body 17 with a convex shape with respect to the substrate 16 by supporting the gap flat surface 15a so that the inclined surface 15b lifts up. However, it may be formed by providing a concave portion in the substrate 16 and disposing the flat resonator body 17 so as to close it, or disposing the flat resonator body 17 on the substrate 16 via a spacer or the like. You may form by.

  1, 2, and 4, the through hole 14 has been described using an example in which the through hole 14 is formed in a direction orthogonal to the surface of the substrate 16, but the through hole 14 has the air gap 15 and the upper surface of the resonator body 17. And the shape and angle of the through-hole 14 can be freely set as appropriate.

  In FIG. 4, a base layer for forming the lower electrode 12 may be provided on the sacrificial layer 21. In that case, an underlayer may be interposed between the second protective film 32 and the lower electrode 12.

It is sectional drawing which shows the structure of the piezoelectric resonator which is one Embodiment of this invention. It is sectional drawing which shows the structure of the piezoelectric resonator which is the other form of implementation of this invention. It is a principal part expanded sectional view which shows the structure of the piezoelectric resonator which is other form of implementation of this invention. It is process drawing which shows the manufacturing method of the piezoelectric resonator 1 which is one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric resonator 11 Piezoelectric film 12 Lower electrode 13 Upper electrode 14 Through-hole 15 Air gap 15a Air gap flat surface 15b Inclined surface 15c First air gap inclined surface 15d Second air gap inclined surface 16 Substrate 17 Resonator body 18 Resonator 21 Sacrificial layer 31 First protective film 32 Second protective film

Claims (6)

A substrate,
A piezoelectric film; an upper electrode at least partially laminated on one surface in the thickness direction of the piezoelectric film; and a lower electrode laminated at least partially on the other surface in the thickness direction of the piezoelectric film. A resonator body disposed on the surface in the thickness direction of the substrate so as to form a gap with the substrate;
A first protective film covering a surface of the upper electrode opposite to the surface in contact with the piezoelectric film;
A second protective film made of the same material as the first protective film and covering the surface of the lower electrode opposite to the surface in contact with the piezoelectric film;
A piezoelectric resonator comprising: The inner wall surface of the portion facing the gap at the peripheral edge of the resonator body is an inclined surface with an acute angle formed with the surface in the thickness direction of the substrate,
2. The piezoelectric resonator according to claim 1, wherein the inclined surface of the inner wall surface is provided with a through hole leading to the gap.   3. The piezoelectric device according to claim 2, wherein the first protective film and the second protective film are integrally formed by extending to a surface exposed to the through hole of the resonator main body and being connected to each other. Resonator.   4. The piezoelectric resonator according to claim 2, wherein the inclined surface has a first inclined surface and a second inclined surface having different angles with respect to one surface in the thickness direction of the substrate.   The piezoelectric resonator according to claim 4, wherein the through-hole is formed so as to straddle a boundary portion between the first inclined surface and the second inclined surface.   The piezoelectric resonator according to claim 1, wherein the first protective film and the second protective film are made of silicon oxide.

Images