JP2014192644A - Piezoelectric device and process of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To be capable of improving reliability by preventing electrode breakage and such, and to suppress an electrode being carelessly etched even when ion beam activation bonding is applied to lid bonding.SOLUTION: A piezoelectric device 100 contains a piezoelectric vibration piece 130 on which excitation electrodes 131, 132 are formed. Cap layers 141, 142 that coat the excitation electrodes 131 and such are formed on the piezoelectric vibration piece 130. Metal layers 141a, 142a are formed on the cap layer 141 and such with a metal whose sputtering rate is lower than that of the excitation electrode 131 and such. On surfaces of the metal layers, protective films 141b, 142b are formed. The protective film 141b and such are one of a metal oxide film, a mixed film of a metal oxide and another metal, and a lamination layer film of a metal and another metal.

Description

  The present invention relates to a piezoelectric device and a method for manufacturing a piezoelectric device.

  A piezoelectric vibrator (piezoelectric device) such as a quartz vibrator has a crystal vibrating piece (piezoelectric vibrating piece) mounted on a ceramic package or the like, and is hermetically sealed or vacuum sealed. However, the adoption of ceramic packages has become difficult due to the increasing market demands for electronic components that are smaller, lower in profile, and lower in price. In order to meet these requirements, a piezoelectric vibrator using a glass package has been proposed (see, for example, Patent Documents 1 and 2).

  As for the structure of the glass package, a crystal vibrating piece is mounted in a recess formed in one of a lid and a base to be bonded to each other, and a lid and a base are provided on the front and back surfaces of the crystal vibrating piece having a frame portion. There exist the structure etc. which were joined (for example, refer patent document 3). Since any structure can be manufactured at the wafer level, it is possible to realize a smaller size, a lower height, and a lower price compared to a conventional ceramic package.

  In manufacturing the glass package having the above structure, as a method for bonding glass wafers or between glass and a quartz wafer, a direct bonding method, an anodic bonding method, a metal pressure bonding method, a low melting point glass bonding method, a plasma activated bonding method, and the like. Proposal methods and ion beam activated bonding methods have been proposed. The direct bonding method requires heat treatment at a high temperature in order to obtain a sufficient bonding strength, and there remains a problem as a method for bonding a crystal resonator. The anodic bonding method is a bonding method in the case where a glass wafer containing alkali ions is used, and there is a problem that deterioration of the internal vacuum degree occurs because gas is generated during the bonding.

  In the metal pressure welding method, since bonding is performed via a metal such as AuSn eutectic metal, there is a problem in that film formation and patterning of an adhesion layer and a barrier layer are required and manufacturing cost is high. The low melting point glass bonding method involves the generation of gas from the low melting point glass paste at the time of bonding, so that there is a problem that the internal vacuum degree is deteriorated. In the plasma activated bonding method, bonding in a vacuum is considered difficult. In the ion beam activated bonding method, various materials can be bonded at room temperature by cleaning the wafer surface by irradiating the wafer with an argon beam or the like and bringing the surfaces into contact with each other.

  In this ion beam activated bonding method, generally, activation processing by ion beam irradiation and wafer bonding processing are performed in the same chamber. Therefore, immediately after the activation treatment, the supply of argon is stopped and evacuation is performed, so that bonding can be performed while maintaining the degree of vacuum required for the crystal resonator. However, since the member of the ion source body and the inner wall of the chamber are sputtered simultaneously during the ion beam irradiation, these constituent materials (stainless steel and aluminum alloy) such as iron (Fe), chromium ( Cr) and aluminum (Al) adhere (for example, refer to Patent Document 4). As described above, in ion beam activated bonding, the etching by the sputtering action of the wafer surface and the adhesion (deposition) of iron, chromium, and aluminum occur simultaneously with the irradiation of the ion beam, thereby strengthening between the glass and the quartz wafer. Is realized.

JP 2004-6525 A JP 2012-74649 A JP 2000-68780 A JP 2007-324195 A

  By the way, in the type in which the glass package includes a lid and a base, various wirings such as a through electrode and a connection electrode are formed on the surface of the base. Also in the quartz crystal resonator element mounted on the base, an excitation electrode and an extraction electrode are formed, and the extraction electrode is electrically connected to the connection electrode of the base. Also, in the type in which the lid and base are joined to the front and back surfaces of the crystal vibrating piece having the frame portion, various electrodes are formed on the base, and the excitation electrode and the extraction electrode are similarly formed on the crystal vibrating piece. Has been.

  In any type, when the ion beam activated bonding method is applied to the lid bonding, the electrode formed on the crystal vibrating piece or the base is etched by the ion beam irradiation, and the etching by the sputtering action of argon, Deposition of the metal elements that make up the inner wall of the chamber occurs. The etching amount of the crystal vibrating piece electrode and the metal adhesion amount differ depending on the mounting position of the quartz vibrating piece in the wafer or the formation position of the quartz vibrating piece. This distribution is equivalent to the in-wafer distribution of the resonance frequency variation of the quartz crystal resonator element. In the region where the electrode etching amount is larger than the metal deposition amount, the frequency variation amount shifts to the plus side. Conversely, in the region where the electrode etching amount is smaller than the metal deposition amount, the frequency variation amount shifts to the minus side. In the manufacture of a crystal resonator, the occurrence of such frequency fluctuation after wafer bonding is a problem because it decreases the manufacturing yield.

  The present invention has been made in view of the above-described problems, and improves the reliability by covering the electrode formed on the piezoelectric vibrating piece and applies an ion beam activated bonding method or the like to the bonding of the lid. The purpose of the present invention is to provide a piezoelectric device having a high manufacturing yield and a manufacturing method thereof by preventing inadvertent etching of the electrode, suppressing fluctuations in the resonance frequency of the piezoelectric vibrating piece, preventing occurrence of defective products, and the like. And

  In the present invention, a piezoelectric device including a piezoelectric vibrating piece on which an electrode is formed, the piezoelectric vibrating piece is formed with a cap layer covering the electrode, and a metal having a sputtering rate smaller than that of the electrode is used for the cap layer. In addition, a protective film is formed on the surface, and the protective film includes a metal oxide film, a film in which a metal oxide and another metal are mixed, and a laminated film of a metal oxide and another metal. One of them.

  The piezoelectric vibrating piece may include a lid and a base that are bonded to each other. The piezoelectric vibrating piece may be disposed in a recess formed in at least one of the lid and the base, and the lid and the base may be directly bonded. The piezoelectric vibrating piece includes a vibrating portion, a frame portion surrounding the vibrating portion, and an anchor portion that connects the vibrating portion and the frame portion, and includes a lid and a base that are respectively joined to the front surface and the back surface of the frame portion. In addition, the frame portion and the lid may be directly joined. Moreover, as a metal used for a cap layer, aluminum (Al), titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), Any of tungsten (W) is applicable.

  Furthermore, in the present invention, a method of manufacturing a piezoelectric device including a piezoelectric vibrating piece on which an electrode is formed, wherein a cap layer is formed of a metal having a sputtering rate smaller than that of the electrode so as to cover the electrode of the piezoelectric vibrating piece. A cap forming step, and a protective film forming step of forming a protective film on the surface of the cap layer, wherein the protective film is a metal oxide film, a film in which a metal oxide and another metal are mixed, and One of the laminated films of a metal oxide and another metal.

  Further, a mounting step of mounting the piezoelectric vibrating piece on the base and a lid bonding step of bonding the lid to the base using ion beam activated bonding may be included. Also, as the piezoelectric vibrating piece, a base joining step is used in which a vibrating part, a frame part surrounding the vibrating part, and an anchor part that connects the vibrating part and the frame part are used, and the base is joined to the back surface of the frame part. And a lid bonding step of bonding a lid to the surface of the frame portion using ion beam activated bonding. Further, the lid bonding step may be performed in a vacuum atmosphere.

  According to the present invention, by covering the electrode formed on the piezoelectric vibrating piece with the cap layer, the electrode can be prevented from being damaged and the reliability can be improved. Furthermore, even when an ion beam activated bonding method or the like is applied to the bonding of the lid, it is possible to prevent the electrodes from being etched carelessly and to suppress the fluctuation of the resonance frequency of the piezoelectric vibrating piece, thereby preventing the occurrence of defective products. The production yield can be improved.

The piezoelectric device which concerns on 1st Embodiment is shown, (a) is the expand | deployed perspective view, (b) is sectional drawing along the AA of (a). The piezoelectric vibrating piece shown in FIG. 1 is shown, (a) is a top view, (b) is sectional drawing along the BB line of (a). FIG. 2 shows a manufacturing process of the piezoelectric vibrating piece shown in FIG. 1, (a) shows a piezoelectric wafer, and (b) shows a lid wafer and a base wafer. It is the schematic of an ion beam activation joining apparatus. It is sectional drawing which shows the piezoelectric device which concerns on 2nd Embodiment. The piezoelectric device which concerns on 3rd Embodiment is shown, (a) is the expand | deployed perspective view, (b) is sectional drawing along CC line of (a). 6 shows the piezoelectric vibrating piece shown in FIG. 6, (a) is a plan view, and (b) is a cross-sectional view taken along the line DD in (a). FIG. It is a figure which shows the manufacturing process of the piezoelectric device shown in FIG. It is a figure which shows the relationship between the position of the crystal oscillator in a piezoelectric wafer, and frequency variation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to this. Further, in the following embodiments, in order to describe the embodiments in the drawings, the scale is appropriately changed and expressed by partially enlarging or emphasizing the description. In the following drawings, directions in the drawings will be described using an XYZ coordinate system. In this XYZ coordinate system, a plane parallel to the surface of the piezoelectric vibrating piece is defined as an XZ plane. In this XZ plane, the longitudinal direction of the piezoelectric vibrating piece is denoted as the X direction, and the direction orthogonal to the X direction is denoted as the Z direction. A direction perpendicular to the XZ plane (thickness direction of the piezoelectric vibrating piece) is expressed as a Y direction. In each of the X direction, the Y direction, and the Z direction, the direction of the arrow in the figure is the + direction, and the direction opposite to the arrow direction is the − direction.

<First Embodiment>
(Configuration of the piezoelectric device 100)
A piezoelectric device 100 according to the first embodiment will be described with reference to FIGS. 1 and 2. As illustrated in FIG. 1A, the piezoelectric device 100 is a piezoelectric vibrator including a lid 110, a base 120, and a piezoelectric vibrating piece 130. The lid 110 and the base 120 are made of borosilicate glass, but are not limited thereto. For example, in addition to soda-lime glass, non-alkali glass, quartz, and other glass, silicon, an aluminum compound such as ceramics, or the like In addition, materials including these as main components and various materials added are used. In addition, different materials may be used for the lid 110 and the base 120 instead of using the same material. However, when the same material is used, the thermal expansion coefficient becomes equal, and the generation of stress can be suppressed by temperature change.

  The lid 110 is a rectangular plate-like member in plan view, and as shown in FIG. 1A, a recess 111 is provided in the center portion on the back surface side (the surface on the −Y side). A joint surface 110a with a base 120 described later is formed so as to surround the recess 111. The bonding surface 110a has sufficient flatness suitable for bonding by ion beam activated bonding (typically, the average roughness Ra is about 1 nm).

  The base 120 is a rectangular plate-like member in plan view like the lid 110. As shown in FIG. 1B, a cavity (accommodating space) 140 that accommodates a piezoelectric vibrating piece 130 described later is formed by joining a joining surface 110a of a lid 110 to a surface 120a of the base 120 (a surface on the + Y side). It is formed. Note that the portion of the surface 120a that is to be bonded to the bonding surface 110a of the lid 110 has sufficient flatness suitable for bonding by ion beam activated bonding (typically, the average roughness Ra is 1 nm), similarly to the bonding surface 110a. Degree).

  On the −X side of the surface 120a of the base 120, rectangular connection electrodes 122 and 123 arranged in the Z direction are formed. On the back surface (the surface on the −Y side) of the base 120, rectangular external electrodes 124 and dummy electrodes 124a and 124b are formed at the four corners, respectively. In FIG. 1A, the external electrodes on the −X side and the −Z side are hidden behind the piezoelectric vibrating piece 130. The external electrode 124 is used as a pair of mounting terminals when mounted on the substrate. The dummy electrodes 124a and 124b are not electrically connected to other electrodes.

  Through holes 125 that penetrate the base 120 in the Y direction are formed at locations corresponding to the connection electrodes 122 and 123, respectively. A through electrode 126 is formed in each of the through holes 125. The connection electrode 122 and the external electrode 124 are electrically connected by the through electrode 126. Similarly, the connection electrode 123 is electrically connected to the external electrode via a through electrode (not shown).

  The connection electrodes 122 and 123 and the external electrode 124 are made of conductive metal films. As the metal film, for example, chromium (Cr), titanium (Ti), nickel (Ni), nickel chromium (NiCr), nickel titanium (NiTi), nickel tungsten (NiW) alloy is formed as an underlayer. A laminated structure in which gold (Au) or silver (Ag) is formed thereon is employed. The through electrode 126 is formed by filling the through hole 125 of the base 120 with copper plating or the like.

  As shown in FIG. 2A, the piezoelectric vibrating piece 130 is formed of a rectangular plate-like member having a long side in the X direction and a short side in the Z direction. As the piezoelectric vibrating piece 130, for example, an AT-cut crystal vibrating piece is used. The AT cut has an advantage that a good frequency characteristic can be obtained when a piezoelectric device such as a crystal resonator or a crystal oscillator is used near room temperature, and includes three crystal axes of an artificial crystal, an electric axis, a mechanical axis, This is a processing method of cutting at an angle of 35 ° 15 ′ around the crystal axis with respect to the optical axis.

  A rectangular excitation electrode 131 is formed on the front surface (+ Y side surface) of the piezoelectric vibrating piece 130, and a rectangular excitation electrode 132 is also formed on the back surface (−Y side surface). The excitation electrodes 131 and 132 are arranged in a state of being opposed to each other with the piezoelectric vibrating piece 130 sandwiched in the Y direction, and are formed to have substantially the same size. When a predetermined alternating voltage is applied to the excitation electrodes 131 and 132, the piezoelectric vibrating piece 130 vibrates at a predetermined frequency. Note that a mesa whose middle layer is thicker than the peripheral portion may be formed on at least one of the front and back surfaces of the piezoelectric vibrating piece 130, and when this mesa is formed, the excitation electrodes 131 and 132 are formed on the mesa. Correspondingly formed.

  Lead electrodes 133 and 134 that are electrically connected to the excitation electrodes 131 and 132, respectively, are formed on the front and back surfaces of the piezoelectric vibrating piece 130. The extraction electrode 133 is formed by being extracted from the excitation electrode 131 in the −X direction on the surface of the piezoelectric vibrating piece 130. The extraction electrode 134 is formed by being extracted in the −X direction from the excitation electrode 132 on the back surface of the piezoelectric vibrating piece 130. Note that the extraction electrode 133 and the extraction electrode 134 are not electrically connected. Further, the extraction electrode 133 may be extracted from the end portion on the −X side of the piezoelectric vibrating piece 130 so as to go around to the back surface side.

  Excitation electrodes 131 and 132 and extraction electrodes 133 and 134 are formed of a conductive metal film. As this metal film, as shown in FIG. 2B, chromium (Cr), titanium (Ti), nickel (Ni), nickel chromium (NiCr), A two-layer structure of a base layer 131a, 132a made of nickel titanium (NiTi), nickel tungsten (NiW) alloy or the like and a main electrode layer 131b, 132b made of gold (Au), silver (Ag) or the like is adopted.

  Further, as shown in FIG. 2B, cap layers 141 and 142 are formed on the excitation electrodes 131 and 132 so as to cover the excitation electrodes 131 and 132, respectively. The cap layers 141 and 142 are formed to have approximately the same size as the excitation electrodes 131 and 132, but may be formed in a slightly larger region so as to cover the side surfaces of the excitation electrodes 131 and 132. Further, the cap layers 141 and 142 may be formed on the extraction electrodes 133 and 134. In this case, the cap layers 141 and 142 are not formed in regions of the extraction electrodes 133 and 134 where conductive adhesives 150 and 151 described later are applied. The film thickness of the cap layers 141 and 142 is not particularly limited, but is set to several nm to several tens of nm.

  As shown in FIG. 2B, the cap layers 141 and 142 include metal layers 141a and 142a and protective films 141b and 142b formed on the metal layers 141a and 142a. For the metal layers 141a and 142a, a metal having a sputtering rate smaller than that of the metal used in the main electrode layers 131b and 132b of the excitation electrodes 131 and 132 is used. Examples of the metal used for the metal layers 141a and 142a include aluminum (Al), titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), and tantalum. (Ta) and tungsten (W).

  The sputter etching action by irradiation with an argon ion beam (argon beam) is as follows. When the ion beam is irradiated from the vertical direction, assuming that the sputtering rate of silver is 1, that of gold is 0.71, aluminum is 0.36, titanium is 0.17, vanadium is 0.21, and zirconium is 0. .22, niobium is 0.19, molybdenum is 0.19, hafnium is 0.24, tantalum is 0.18, and tungsten is 0.18. Both metals have a sputtering rate smaller than that of gold or silver of the main electrode layers 131b and 132b. Since the frequency fluctuation amount due to sputtering of the excitation electrodes 131 and 132 is proportional to the mass etched by sputtering, for example, a metal having a low product of the sputtering rate and density such as aluminum or titanium having a low density is used as the metal layer. By using it as 141a and 142a, there is an advantage that the amount of frequency fluctuation can be made smaller.

  The protective films 141b and 142b are formed of a metal oxide film used for the metal layers 141a and 142a, a film in which the metal oxide is mixed with another metal, or the metal oxide and another metal. And a laminated film. The other metal is, for example, iron (Fe), chromium (Cr), or aluminum (Al), and is used as a member of an ion source main body or a constituent material of a bonding chamber of an ion beam activated bonding apparatus 10 to be described later. Yes. The oxide film or the like has a lower sputtering rate than the metal (gold or silver) used in the main electrode layers 131b and 132b, and further has a lower sputtering rate than the metal used in the cap layers 141 and 142. Note that the oxide film is, for example, a natural oxide film formed by oxidizing the metal of the metal layers 141a and 142a with oxygen in the atmosphere.

  As shown in FIG. 1, the piezoelectric vibrating piece 130 is supported on the surface 120 a of the base 120 by conductive adhesives 150 and 151. The lead electrode 134 and the connection electrode 122 are electrically connected via the conductive adhesive 150, and the lead electrode 133 and the connection electrode 123 are electrically connected via the conductive adhesive 151. Then, when the lid 110 and the base 120 are joined, the piezoelectric vibrating piece 130 is accommodated in the cavity 140. The cavity 140 is sealed in a vacuum atmosphere or an inert gas atmosphere such as nitrogen gas. Note that the bonding surface 110a of the lid 110 and the surface 120a of the base 120 are directly bonded without using a bonding material or the like.

  Thus, according to the piezoelectric device 100, since the cap layers 141 and 142 are formed on the excitation electrodes 131 and 132, the excitation electrodes 131 and 132 are covered with the cap layers 141 and 142 having a low sputtering rate. Damage or the like can be prevented and reliability can be improved.

(Method for Manufacturing Piezoelectric Device 100)
Next, a method for manufacturing the piezoelectric device 100 will be described with reference to FIG. The piezoelectric device 100 is manufactured by a so-called wafer level packaging method. When manufacturing the piezoelectric vibrating piece 130, multi-chamfering is performed by cutting individual pieces from the piezoelectric wafer AW1. First, as shown in FIG. 3A, a piezoelectric wafer AW1 is prepared. The piezoelectric wafer AW1 is cut out from the quartz crystal body by AT cut.

  Next, the piezoelectric wafer AW1 is formed so as to have a small thickness (width in the Y-axis direction) by etching, cutting, or the like, and is adjusted to have a desired frequency characteristic. Note that a mesa having a thick central portion with respect to the peripheral portion may be formed by photolithography, etching, or the like. Next, excitation electrodes 131 and 132 are formed on the front and back surfaces of the piezoelectric wafer AW1 (piezoelectric vibrating piece 130).

  Excitation electrodes 131 and 132 are formed by forming base layers 131a and 132a such as nickel chrome by sputtering using a metal mask or vacuum deposition, and then forming main electrode layers 131b and 132b such as gold. . Instead of using a metal mask or the like, the excitation electrodes 131 and 132 may be patterned by photolithography and etching. The extraction electrodes 133 and 134 are formed simultaneously with the excitation electrodes 131 and 132, but may be formed separately from the excitation electrodes 131 and 132.

  Next, cap layers 141 and 142 are formed on the excitation electrodes 131 and 132. For the cap layers 141 and 142, first, metal layers 141a and 142a such as aluminum are formed by sputtering or vacuum deposition using a metal mask, photolithography, etching, or the like (cap forming step), and then the metal layer 141a. , 142a is exposed to the atmosphere to form a natural oxide film. This natural oxide film becomes the protective films 141b and 142b (protective film forming step). Note that the protective film 141b and the like are not limited to being formed by exposure to the air, and may be formed by vapor deposition or the like. After the formation of the cap layers 141 and 142, each piezoelectric vibrating piece 130 is completed by dicing the piezoelectric wafer AW1 along the scribe line.

  Similarly to the piezoelectric vibrating piece 130, the lid 110 and the base 120 are subjected to multiple chamfering for cutting out the individual from the lid wafer LW1 and the base wafer BW1. As the lid wafer LW1 and the base wafer BW1, for example, borosilicate glass is used. In the lid wafer LW1, the concave portion 111 for forming the cavity 140 is formed by sandblasting or wet etching. On the other hand, through holes 125 and the like are formed in the base wafer BW1 by sandblasting or wet etching.

  The base wafer BW1 is filled with the through holes 125 and the like by, for example, copper plating, etc., and the through electrodes 126 and the like are formed. Connection electrodes 122 and 123 are formed on the front surface of the base wafer BW1 and an external electrode 124 is formed on the back surface so as to be electrically connected to the through electrode 126 and the like. At the same time, dummy electrodes 124a and 124b are also formed. The connection electrodes 122 and 123 and the external electrode 124 are formed by depositing gold or silver on a base layer such as nickel tungsten by sputtering or vacuum deposition using, for example, a metal mask.

  Next, the individual piezoelectric vibrating pieces 130 are mounted on the base wafer BW1 with the conductive adhesives 150 and 151 (placement step). By the conductive adhesives 150 and 151, the excitation electrodes 131 and 132 of the piezoelectric vibrating piece 130 and the external electrode 124 are electrically connected. Next, the lid wafer LW1 is bonded to the base wafer BW1 by ion beam activated bonding (lid bonding step). A specific joining method will be described below.

  In the ion beam activated bonding, an ion beam activated bonding apparatus 10 is used as shown in FIG. As shown in FIG. 4, the ion beam activated bonding apparatus 10 irradiates an ion beam toward the bonding surface, a vacuum chamber 20, an alignment stage 30 having a wafer holder, a pressure mechanism 40 having a wafer holder, and a bonding surface. An ion source 50 and a neutralized electron source 60 are provided. The vacuum chamber 20 is evacuated by a vacuum exhaust pump (for example, a turbo molecular pump) (not shown) and set in a vacuum atmosphere. Argon gas is supplied to the ion source 50 and the neutralized electron source 60 via a mass flow meter.

  The lid wafer LW1 is held on the wafer holder of the pressurizing mechanism 40 by an electrostatic chuck or the like, and the base wafer BW1 is held on the wafer holder of the alignment stage 30. As a result, the lid wafer LW1 and the base wafer BW1 are arranged so that their bonding surfaces face each other. Next, after the chamber 20 is evacuated until a predetermined degree of vacuum is reached, an argon beam (ion beam) IB is irradiated from the ion source 50 toward both wafers. The argon beam IB is neutralized by the neutralizing electron source 60.

  By this argon beam IB, the surfaces of the lid wafer LW1 and the base wafer BW1 are sputter-etched to clean the surfaces. At this time, a member such as an anode constituting the ion source 50 is sputtered to be exposed to the argon plasma, and the argon beam IB irradiated from the ion source 50 is made of stainless steel which is a constituent member of the ion source 50. Contains iron and chromium as ingredients. Further, since the argon beam IB irradiated from the ion source 50 has a large divergence angle, not only the lid wafer LW1 and the like, but also the parts made of stainless steel or aluminum alloy on the inner wall of the vacuum chamber 20 are sputtered. Thereby, iron, chromium, aluminum or the like is deposited on the lid wafer LW1 or the like. That is, on the surfaces of the lid wafer LW1 and the base wafer BW1, the etching action and the deposition action proceed simultaneously. Therefore, the protective films 141b and 142b include, in addition to the metal oxide film used for the metal layers 141a and 142a, a film in which this oxide and iron, chromium, aluminum, or the like are mixed, or the oxide and iron, It is in the form of a laminated film with chromium, aluminum or the like.

  As described above, the cap layers 141 and 142 (protective films 141b and 142b) formed on the excitation electrodes 131 and 132 of the piezoelectric vibrating piece 130 have a sputtering rate compared to gold and silver used for the excitation electrode 131 and the like. small. Therefore, since the excitation electrodes 131 and 132 are covered with the cap layers 141 and 142 (protective films 141b and 142b), they are not inadvertently etched by the irradiation with the argon beam IB.

  Next, after irradiating the argon beam IB for a predetermined time, the lid wafer LW1 and the base wafer BW1 are aligned, and then the two wafers are bonded by the pressurizing mechanism 40 under a predetermined load and pressure contact time condition. To do. Thereafter, the bonded wafer is taken out from the ion beam activated bonding apparatus 10 and diced along a scribe line to complete each piezoelectric device 100. Note that the external electrode 124 on the back surface of the base wafer BW1 may be formed after the lid wafer LW1 and the base wafer BW1 are bonded.

  By the way, since gold or silver as the main electrode material is a metal having a high density and a high sputtering rate, when the ion beam is irradiated and sputtered during the ion beam activated bonding, the piezoelectric vibrating piece 130 is used. The frequency of is greatly shifted to the plus side (the resonance frequency is increased). In addition, since the etching amount is sensitive to the beam intensity in the wafer surface, a large distribution occurs in the frequency shift amount in the wafer surface. On the other hand, when the member of the ion source 50 and the inner wall of the vacuum chamber 20 are sputtered, these constituent materials such as iron, chromium, and aluminum are deposited on the excitation electrode 131 and the like. The density of these metals is Since it is smaller than gold or silver and has a film thickness of several nanometers, the frequency of the piezoelectric vibrating piece 130 is slightly shifted to the minus side (resonance frequency is lowered).

  On the other hand, the cap layer 141 and the like (protective film 141b and the like) have a low sputtering rate and, as shown in FIG. 4, the direction in which the irradiation direction of the argon beam IB is inclined by approximately 90 ° from the vertical direction of the lid wafer LW or the like. Therefore, the substantial sputtering rate is remarkably reduced. As a result, the cap layers 141 and 142 (protective films 141b and 142b) are hardly etched, and only metal deposition such as iron, chromium, and aluminum occurs on the cap layer 141 and the like.

  Since this metal adhesion amount is as small as several nm as a film thickness and can be made constant without having a distribution in the wafer surface by optimizing the irradiation conditions, the resonance frequency of the piezoelectric device 100 after bonding is In the wafer plane, the fluctuation is uniformly negative. If the resonance frequency is adjusted in the frequency adjustment step performed before bonding in consideration of this variation, the piezoelectric device 100 having a desired resonance frequency is bonded to the glass substrate by a wafer level packaging method after the bonding. Can be manufactured.

  Thus, according to the method for manufacturing the piezoelectric device 100, the excitation electrode 131 of the piezoelectric vibrating piece 130 and the like are prevented from being inadvertently etched, and fluctuations in the resonance frequency of the piezoelectric vibrating piece 130 are suppressed. Can be prevented. Further, when the protective film 141b or the like such as the cap layer 141 is a natural oxide film, it is formed only by being exposed to the atmosphere during the manufacturing process, so there is no need to add a special process.

Second Embodiment
Next, the second embodiment will be described. In the following description, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified. FIG. 5 shows a piezoelectric device 200 according to the second embodiment. FIG. 5 shows a cross-sectional view along a line corresponding to the line AA in FIG. The piezoelectric device 200 uses a piezoelectric vibrating piece 130 similar to that of the first embodiment.

  The piezoelectric device 200 has a lid 210 and a base 220. The lid 210 is a rectangular plate-like member in plan view, and as shown in FIG. 5, of the back surface (the surface on the −Y side) 210 a, the bonding portion with the base 220 is bonded by ion beam activated bonding. Sufficient flatness (typically, the average roughness Ra is about 1 nm).

  The base 220 is a rectangular plate-like member in plan view, and as shown in FIG. 5, a concave portion 221 is provided in a central portion on the front surface side (+ Y side surface). A joint surface 220 a with the lid 210 is formed so as to surround the recess 221. By joining the lid 210 and the base 220, a cavity (accommodating space) 240 for accommodating the piezoelectric vibrating piece 130 is formed. The bonding surface 220a has sufficient flatness suitable for bonding by ion beam activated bonding (typically, the average roughness Ra is about 1 nm).

  A connection electrode 222 is formed in the recess 221 of the base 220, and an external electrode 224 is formed on the back surface of the base 220. A through-hole 225 that penetrates the base 220 in the Y direction is provided, and a through-electrode 226 that electrically connects the connection electrode 222 and the external electrode 224 is formed in the through-hole 225. A dummy electrode 224 a is formed on the back surface of the base 220. The connection electrode 222, the external electrode 224, and the through electrode 226 are substantially the same as the piezoelectric device 100 of the first embodiment.

  As described above, according to the piezoelectric device 200, since the piezoelectric vibrating piece 130 is used as in the first embodiment, the excitation electrodes 131 and 132 are covered with the cap layers 141 and 142, so that damage or the like is prevented. Reliability can be improved. The manufacturing method of the piezoelectric device 200 is substantially the same as the manufacturing method of the piezoelectric device 100 except that the recess 210 is not formed on the lid 210 and the recess 221 is formed on the base 220. Inadvertent etching can be prevented, and fluctuations in the resonance frequency of the piezoelectric vibrating piece 130 can be suppressed to prevent generation of defective products.

<Third Embodiment>
(Configuration of piezoelectric device 300)
A piezoelectric device 300 according to the third embodiment will be described with reference to FIGS. 6 and 7. In this piezoelectric device 300, as shown in FIG. 6A, a lid 310 is joined to the + Y side of the piezoelectric vibrating piece 330 and a base 320 is joined to the -Y side so as to sandwich the piezoelectric vibrating piece 330. The For the lid 310 and the base 320, for example, borosilicate glass or the like is used as in the first and second embodiments.

  As shown in FIGS. 6A and 6B, the lid 310 is formed in a rectangular plate shape, and has a recess 311 formed on the back surface (surface on the −Y side) and a joint surface surrounding the recess 311. 310a. The joining surface 310a is joined to the surface (+ Y side surface) 332a of a frame portion 332 of the piezoelectric vibrating piece 330 described later. The bonding surface 310a and the surface 332a are directly bonded. Note that the bonding surface 310a and the surface 332a have sufficient flatness suitable for bonding by ion beam activation bonding (typically, the average roughness Ra is about 1 nm).

  The base 320 is also formed in the shape of a rectangular plate, and has a recess 321 formed on the surface (+ Y side surface) and a joint surface 320a surrounding the recess 321. The bonding surface 320 a faces the back surface (the surface on the −Y side) 332 b of the frame portion 332 of the piezoelectric vibrating piece 330. As shown in FIG. 8, the base 320 is bonded to the back surface side (the surface side on the −Y side) of the piezoelectric vibrating piece 130 by the bonding material 150 disposed between the bonding surface 122 and the back surface 132 b of the frame portion 132. Is done. In addition to being directly bonded to the bonding surface 320a and the surface 332b, a bonding material such as low melting glass or polyimide may be used.

  As shown in FIG. 6, connection electrodes 322 and 323 are formed on the −X side region of the surface of the base 320, and external electrodes 324 and 325 are formed on the −X side region of the back surface of the base 320. The The base 320 is formed with through electrodes 326 and 327 that penetrate in the Y direction. The connection electrode 322 and the external electrode 324 are electrically connected by the through electrode 326, and the connection electrode 323 and the external electrode 325 are electrically connected by the through electrode 327. As shown in FIG. 6B, a dummy electrode 324a is formed in the + X side region of the back surface of the base 320.

  The connection electrodes 322, the external electrodes 324, the through electrodes 326, and the like are made of the same metal as in the first and second embodiments. Further, the through electrodes 326 and 327 are not limited to being used for connection between the connection electrodes 322 and 323 and the external electrodes 324 and 325. For example, notches (castellation) may be formed in corners or sides of the base 320, and electrodes may be formed in the notches to connect the connection electrodes 322 and 323 to the external electrodes 324 and 325.

  For example, an AT-cut quartz material is used for the piezoelectric vibrating piece 330 as in the first and second embodiments. As shown in FIG. 7A, the piezoelectric vibrating piece 330 connects the vibration part 331 that vibrates at a predetermined frequency, the frame part 332 that surrounds the vibration part 331, and the vibration part 331 and the frame part 332. It is comprised by the anchor part 333. A through-hole 334 that penetrates in the Y-axis direction is formed between the vibration part 331 and the frame part 332 except for the anchor part 333.

  The vibration part 331 is formed in a rectangular shape and has the same thickness in the Y-axis direction as the frame part 332, but may be formed thinner than the frame part 332. Further, a mesa having a thick central portion with respect to the peripheral portion of the vibration portion 331 may be formed. The frame portion 332 is formed in a rectangular shape surrounding the vibration portion 331, and the front surface 332a and the back surface 332b are bonded to the bonding surface 310a of the lid 310 and the bonding surface 320a of the base 320, respectively.

  An excitation electrode 335 is formed on the surface of the vibration part 331, and an extraction electrode 337 is formed from the excitation electrode 335 to the surfaces of the anchor part 333 and the frame part 332 in the −X direction. Furthermore, the extraction electrode 337 is connected to the extraction electrode 337a on the back surface of the frame portion 332 through a through electrode 339 that penetrates the frame portion 332 in the Y direction. An excitation electrode 336 is formed on the back surface of the vibration portion 331, and an extraction electrode 338 is formed from the excitation electrode 336 toward the −X direction to the back surface of the anchor portion 333 and the frame portion 332.

  As shown in FIG. 7B, the excitation electrodes 335 and 336, the extraction electrodes 337 and 338, and the like include a base layer 335a and 336a such as nickel tungsten and a main electrode such as gold in order to improve adhesion to the crystal material. A two-layer structure with layers 335b and 336b is employed. The metal used for the base layer 335a and the like, the main electrode layer 335b and the like is the same as in the first and second embodiments.

  As shown in FIG. 7B, cap layers 341 and 342 are formed on the excitation electrodes 335 and 336 so as to cover the excitation electrodes 335 and 336, respectively. The cap layers 341 and 342 are formed to have substantially the same size as the excitation electrodes 335 and 336, but may be formed in a slightly larger region so as to cover the side surfaces of the excitation electrodes 335 and 336. Further, the cap layers 341 and 342 may be formed on the extraction electrodes 337 and 338. In this case, the cap layers 341 and 342 are not formed in regions of the extraction electrodes 337 and 338 that are connected to the connection electrodes 322 and 323 of the base 320. The film thickness of the cap layers 341 and 342 is not particularly limited, but is set to several nm to several tens of nm.

  As shown in FIG. 7B, the cap layers 341 and 342 include metal layers 341a and 342a and protective films 341b and 342b formed on the metal layers 341a and 342a. For the metal layers 341a and 342a, a metal having a sputtering rate smaller than that of the metal used in the main electrode layers 335b and 336b of the excitation electrodes 335 and 336 is used. As a metal used for the metal layers 341a and 342a, for example, the same metal as in the first and second embodiments such as aluminum is used.

  The protective films 341b and 342b are a film of a metal oxide used for the metal layers 341a and 342a, a film in which the metal oxide is mixed with another metal, or a metal oxide and another metal. And a laminated film. Since the protective films 341b and 342b are the same as those in the first and second embodiments, description thereof is omitted.

  As shown in FIG. 6, the connection surface 310 a of the lid 310 is directly joined to the surface 332 a of the frame portion 332 of the piezoelectric vibration piece 330. Further, the connection surface 320 a of the base 320 is joined to the back surface 332 b of the frame portion 332 of the piezoelectric vibrating piece 330. In addition to direct bonding, a bonding material may be used for bonding the back surface 332b and the connection surface 320a. By joining the piezoelectric vibrating piece 330 and the base 320, the extraction electrodes 337 a and 338 and the connection electrodes 322 and 323 are electrically connected. A conductive adhesive may be interposed between the extraction electrodes 337a and 338 and the connection electrodes 322 and 323. Then, when the lid 310 and the base 320 are joined to the piezoelectric vibrating piece 330, the vibrating portion 331 of the piezoelectric vibrating piece 330 is housed in the cavity 340. The cavity 340 is sealed in a vacuum atmosphere or an inert gas atmosphere such as nitrogen gas.

  Thus, according to the piezoelectric device 300, since the cap layers 341 and 342 are formed on the excitation electrodes 335 and 336, the excitation electrodes 335 and 336 are covered with the cap layers 341 and 342 having a low sputtering rate. Damage or the like can be prevented and reliability can be improved.

(Method for Manufacturing Piezoelectric Device 300)
Next, a method for manufacturing the piezoelectric device 300 will be described with reference to FIG. The piezoelectric device 300 is manufactured by a wafer level packaging method, similar to the piezoelectric device 100 described above. All of the lid 310, the base 320, and the piezoelectric vibrating piece 330 are subjected to multiple chamfering for cutting out individual wafers. For example, borosilicate glass is used as the lid wafer LW2 and the base wafer BW2. As the piezoelectric wafer AW2, a crystal piece cut out from a crystal crystal body by AT cut is used.

  The lid wafer LW2 has a recess 311 formed by sandblasting or wet etching. On the other hand, the base wafer BW2 is formed with a recess 321 and a through hole by sandblasting or wet etching. In the base wafer BW2, through electrodes 326 and 327 are formed by, for example, copper plating. Connection electrodes 322 and 323 are formed on the front surface of the base wafer BW2 and external electrodes 324 and 325 are formed on the back surface so as to be electrically connected to the through electrodes 326 and 327. At the same time, a dummy electrode 324a is also formed. The connection electrodes 322 and 323 and the external electrodes 324 and 325 are formed by depositing gold or silver on a base layer such as nickel tungsten by sputtering or vacuum deposition using, for example, a metal mask.

  The piezoelectric wafer AW2 is adjusted so that the thickness (width in the Y-axis direction) is reduced by etching, cutting, or the like. Note that a mesa having a thick central portion with respect to the peripheral portion of the vibration portion 331 may be formed by a photolithography method, etching, or the like. Next, excitation electrodes 335 and 336 are formed on the front and back surfaces of the vibration part 331. Excitation electrodes 335 and 336 are formed by forming base layers 335a and 336a of nickel chrome or the like by sputtering using a metal mask or vacuum deposition, and then forming main electrode layers 335b and 336b of gold or the like. . Instead of using a metal mask or the like, the excitation electrodes 335 and 336 may be patterned by a photolithography method, etching, or the like.

  The extraction electrodes 337, 337a, 338 are formed simultaneously with the excitation electrodes 335, 336. The through electrode 339 is formed by filling with copper plating or the like prior to the formation of the extraction electrodes 337, 337a, 338. However, it is not limited to being filled as the through electrode 339, and a conductive metal film may be formed on the wall surface of the through hole.

  Next, cap layers 341 and 342 are formed on the excitation electrodes 335 and 336. As in the first embodiment, the cap layers 341 and 342 are formed by first forming metal layers 341a and 342a such as aluminum (cap formation step), and then exposing the film formation surfaces of the metal layers 341a and 342a to the atmosphere. As a result, a natural oxide film is formed. The natural oxide films become protective films 341b and 342b (protective film forming step). Note that the protective film 341b and the like are not limited to being formed by exposure to the air, and may be formed by vapor deposition or the like.

  Next, the base wafer BW2 is bonded to the back surface of the piezoelectric wafer AW2. At this time, the joining surface 320a of the base 320 is joined to the back side of the portion that will later become the frame portion 332 of the piezoelectric vibrating piece 330 (base joining step). Note that the bonding between the two is not limited to the ion beam activated bonding using the ion beam activated bonding apparatus 10 shown in FIG. 4, but also various bondings such as bonding using a bonding material such as low melting point glass or polyimide. The method is used. When the base wafer BW2 is bonded to the piezoelectric wafer AW2, the extraction electrodes 337a and 338 and the connection electrodes 322 and 323 are electrically connected.

  Next, a through hole 334 is formed by penetrating a part of the piezoelectric wafer AW2 in the Y direction by wet etching or the like. As a result, the piezoelectric vibrating piece 330 including the vibrating portion 331, the frame portion 332 surrounding the vibrating portion 331, and the anchor portion 333 that connects the vibrating portion 331 and the frame portion 332 is formed on the piezoelectric wafer AW2. The The through hole 334 is formed after the base wafer BW2 is bonded, but may be formed before the bonding.

  Next, the lid wafer LW2 is bonded to the surface of the piezoelectric wafer AW2 by ion beam activated bonding (lid bonding step). As in the first embodiment, ion beam activated bonding apparatus 10 shown in FIG. 4 is used for ion beam activated bonding. The lid wafer LW2 is held by the wafer holder of the pressurizing mechanism 40, and the piezoelectric wafer AW2 (the base wafer BW2 is bonded to the back surface) is held by the wafer holder of the alignment stage 30. The lid wafer LW2 and the piezoelectric wafer AW2 are in a state of being opposed to each other. Next, after the inside of the chamber 20 is evacuated, an argon beam IB is irradiated from the ion source 50 toward both wafers.

  The surfaces of the lid wafer LW2 and the piezoelectric wafer AW2 are sputter etched by the argon beam IB to clean the surfaces. Note that iron, chromium, aluminum, and the like are deposited on the piezoelectric wafer AW2 and the like as in the first embodiment. Therefore, the protective films 341b and 342b include, in addition to the metal oxide film used for the metal layers 341a and 342a, a film in which the oxide and iron, chromium, aluminum, or the like are mixed, or the oxide and iron, It is in the form of a laminated film with chromium, aluminum or the like. Similarly to the first embodiment, since the cap layers 341 and 342 (protective films 341b and 342b) have a smaller sputtering rate than the excitation electrode 335 and the like, the excitation electrodes 335 and 336 are irradiated with the argon beam IB. Will not be inadvertently etched.

  Next, after irradiating the argon beam IB for a predetermined time, the lid wafer LW2 and the piezoelectric wafer AW2 are aligned, and then both wafers are bonded by the pressurizing mechanism 40 under a predetermined load and pressure contact time condition. To do. Thereafter, the bonded wafer is taken out from the ion beam activated bonding apparatus 10 and diced along a scribe line to complete individual piezoelectric devices 300.

  As described above, according to the method for manufacturing the piezoelectric device 300, as in the first embodiment, the excitation electrode 335 and the like are prevented from being inadvertently etched, and the fluctuation of the resonance frequency of the piezoelectric vibrating piece 330 is suppressed. Generation of defective products. Similarly to the first embodiment, if the resonance frequency is adjusted in consideration of the amount of metal adhesion at the time of ion beam activated bonding, the piezoelectric device 300 having a desired resonance frequency is bonded to a wafer level package made of glass after bonding. Can be manufactured at a high yield by using the method of wrapping.

The embodiment has been described above, but the present invention is not limited to the above description, and various modifications can be made without departing from the gist of the present invention. For example, a tuning fork type piezoelectric vibrating piece (crystal vibrating piece) may be used instead of the piezoelectric vibrating piece 130 or the like. Further, the piezoelectric vibrating piece 130 and the like are not limited to the quartz vibrating piece, and other piezoelectric materials such as lithium tantalate and lithium niobate may be used. Further, instead of the piezoelectric vibrating piece 130 and the like, a MEMS (Micro Microscope) using a silicon wafer is used.
Electro Mechanical Systems) devices may be used. Further, the piezoelectric device is not limited to a piezoelectric vibrator (quartz crystal vibrator), and may be an oscillator. In the case of an oscillator, an IC or the like is mounted and electrically connected to the piezoelectric vibrating piece 130 or the like. Furthermore, crystal pieces such as AT cuts may be used as the lid wafers LW1 and LW2 and the base wafers BW1 and BW2.

  Examples will be described below. As an example, a 26 MHz crystal resonator (piezoelectric device 100) having the glass package structure shown in FIG. 1B was used. An AT-cut quartz crystal vibrating piece was used as the piezoelectric vibrating piece, and the excitation electrodes 131 and 132 were formed with chromium: 30 nm as the base layers 131a and 132a and silver: 150 nm as the main electrode layers 131b and 132b. The cap layers 141 and 142 were formed of aluminum: 3 nm as the metal layers 141a and 142a. As shown in FIG. 3, after this crystal vibrating piece is mounted on a 6-inch base wafer BW1 with a conductive paste, the base wafer BW1 and the 6-inch lid wafer LW1 are bonded to the ion beam activated bonding shown in FIG. Bonding was performed by the apparatus 10 to produce a 26 MHz crystal resonator. Note that the protective films 141b and the like of the cap layers 141 and 142 are formed as oxide films by being exposed to the atmosphere after the aluminum film is formed.

  As a comparative example, a 26 MHz AT-cut quartz crystal resonator having an excitation electrode made of chromium: 30 nm (underlayer) / silver: 150 nm (main electrode layer) without a cap layer is manufactured through the same process as the embodiment. did. The electrode material was formed by electron beam evaporation.

  The amount of frequency fluctuation before and after bonding the base wafer BW1 and the lid wafer LW1 was measured, and the in-plane distribution of the frequency fluctuation amount was compared between the example and the comparative example. In both cases, the frequency is adjusted when the crystal vibrating piece is mounted on the base wafer BW1, and the in-plane frequency is set to 26 MHz. FIG. 9 is a diagram in which changes in the amount of frequency fluctuation are plotted in the 6-inch wafer along the direction parallel to the central axis of the ion source 50 for the example and the comparative example. In FIG. 9, the plus direction of the horizontal axis is the ion source 50 side.

  The embodiment has a constant frequency fluctuation of about −30 ppm at the wafer in-plane position, while the comparative example has a large frequency fluctuation amount of +250 ppm in the positive direction of the horizontal axis (side closer to the ion source 50). It decreases toward the center and gradually approaches −30 ppm from the wafer center toward the end opposite to the ion source 50. On the side close to the ion source 50, etching with an argon beam is stronger than metal deposition, and thus silver etching proceeds. Since silver has a high sputtering rate and a high density, frequency fluctuation is significant. As the distance from the ion source 50 increases (in FIG. 9, toward the negative side of the horizontal axis), the contribution of etching gradually decreases, and the contribution of frequency fluctuation due to metal adhesion becomes visible.

  In this embodiment, thanks to the aluminum cap layer 141 and the like, the etching effect on the cap layer 141 and the like as well as the silver main electrode layer 131b and the like is extremely small. Only fluctuations are observed. In this embodiment, if the frequency is adjusted to +30 ppm of the target frequency in the frequency adjustment step before bonding the lid wafer LW1 and the base wafer BW1, a crystal resonator having a frequency of 26 MHz can be manufactured after bonding. . In this example, aluminum was used for the cap layer 141 and the like, but similar results were obtained for titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten.

DESCRIPTION OF SYMBOLS 10 ... Ion beam activation joining apparatus 100, 200, 300 ... Piezoelectric device 110, 210, 310 ... Lid 120, 220, 320 ... Base 130, 330 ... Piezoelectric vibrating piece 131, 132, 335, 336 ... Excitation electrode (electrode)
141, 142, 341, 342 ... cap layer 141a, 142a, 341a, 342a ... metal layer 141b, 142b, 341b, 342b ... protective layer 331 ... vibrating part 332 ... frame part 333 ... anchor part

Claims (8)

A piezoelectric device including a piezoelectric vibrating piece on which an electrode is formed,
The piezoelectric vibrating piece has a cap layer that covers the electrode,
As the cap layer, a metal having a smaller sputtering rate than the electrode is used, and a protective film is formed on the surface thereof.
The protective film is any one of a film of the metal oxide, a film in which the metal oxide is mixed with another metal, and a laminated film of the metal oxide and another metal. A piezoelectric device. Including a lid and a base joined together,
The piezoelectric vibrating piece is disposed in a recess formed in at least one of the lid and the base,
The piezoelectric device according to claim 1, wherein the lid and the base are directly bonded. The piezoelectric vibrating piece includes a vibrating portion, a frame portion surrounding the vibrating portion, and an anchor portion that connects the vibrating portion and the frame portion,
Including a lid and a base respectively joined to the front surface and the back surface of the frame portion;
The piezoelectric device according to claim 1, wherein the frame portion and the lid are directly joined.   As the metal used for the cap layer, aluminum (Al), titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten The piezoelectric device according to any one of claims 1 to 3, wherein the piezoelectric device is any one of (W). A method of manufacturing a piezoelectric device including a piezoelectric vibrating piece having electrodes formed thereon,
A cap forming step of forming a cap layer with a metal having a smaller sputtering rate than the electrode so as to cover the electrode of the piezoelectric vibrating piece;
A protective film forming step of forming a protective film on the surface of the cap layer,
The protective film is any one of a film of the metal oxide, a film in which the metal oxide is mixed with another metal, and a laminated film of the metal oxide and another metal. A method of manufacturing a piezoelectric device. A placing step of placing the piezoelectric vibrating piece on a base;
6. A method of manufacturing a piezoelectric device according to claim 5, further comprising a lid bonding step of bonding a lid to the base using ion beam activated bonding. As the piezoelectric vibrating piece, one having a vibrating part, a frame part surrounding the vibrating part, and an anchor part that connects the vibrating part and the frame part is used,
A base joining step for joining a base to the back surface of the frame part;
A method for manufacturing a piezoelectric device according to claim 5, further comprising: a lid bonding step of bonding a lid to the surface of the frame portion using ion beam activated bonding.   The method for manufacturing a piezoelectric device according to claim 6, wherein the lid bonding step is performed in a vacuum atmosphere.

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