JP2015061092A - Piezoelectric device and method for manufacturing piezoelectric device - Google Patents

Abstract

The present invention provides a piezoelectric device and a method for manufacturing a piezoelectric device that can be reduced in cost by being manufactured at a wafer level and have excellent vibration characteristics. SOLUTION: A piezoelectric vibrating piece 110 having a thin vibrating portion 110b with respect to a peripheral portion 110a, an intermediate film 120 that is separated from the vibrating portion 110b and bonded to the peripheral portion 110a on the front and back surfaces of the piezoelectric vibrating piece 110, 130 and sealing films 140 and 150 stacked on the intermediate films 120 and 130. [Selection] Figure 1

Description

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

  In portable terminals, cellular phones, various information / communication devices, etc., piezoelectric devices such as crystal resonators and crystal oscillators are mounted. It is known that such a piezoelectric device is manufactured by mounting a piezoelectric vibrating piece such as a quartz vibrating piece in a package constituted by a lid and a base. Piezoelectric devices are required to be reduced in size and cost. For this reason, it has been proposed to produce a crystal resonator by wafer level packaging. (For example, refer to Patent Document 1). It has also been proposed to create a MEMS vibrator using MEMS (Micro Electro Mechanical Systems) technology. (For example, refer to Patent Document 2).

JP 2006-180169 A JP 2013-110623 A

  The vibrator package described in Patent Document 1 forms a vibrator by bonding at a wafer level. However, there is a high flatness requirement on the wafer bonding surface, and hundreds or thousands of wafers are bonded. Since the portions are bonded together, it is difficult to obtain a uniform and reliable bonding state for all the bonding portions. Further, the MEMS vibrator described in Patent Document 2 is formed using the MEMS technology, and becomes an electrostatic vibrator. However, since the MEMS vibrator is made of silicon, it is difficult to increase the Q value of resonance compared with a piezoelectric vibrating piece such as a quartz vibrating piece, and it is difficult to obtain good vibration characteristics.

  The present invention has been made in view of the above-described problems, and can be reduced in cost by being produced at the wafer level, and the vibration unit has a higher Q value than that using a MEMS structure. Therefore, an object of the present invention is to provide a piezoelectric device having excellent vibration characteristics and a method for manufacturing the piezoelectric device.

  In the present invention, the piezoelectric vibrating piece having a thin vibrating portion with respect to the peripheral portion, the intermediate film that is separated from the vibrating portion and bonded to the peripheral portion on the front and back surfaces of the piezoelectric vibrating piece, and the intermediate film are laminated. And a sealing film.

  In addition, the vibration unit may be formed in parallel with the piezoelectric vibrating piece at the center portion of the thickness of the piezoelectric vibrating piece. Further, the sealing film may be formed in a state of covering the intermediate film. Further, the same intermediate film and sealing film may be formed on the front and back surfaces of the piezoelectric vibrating piece. The piezoelectric vibrating piece may be a quartz vibrating piece.

  Furthermore, in the present invention, a vibrating part forming step for forming a vibrating part by thinning a part of the piezoelectric wafer, a sacrificial layer forming process for forming a sacrificial layer on the vibrating part, and intermediate layers on the front and back surfaces of the piezoelectric wafer An intermediate layer forming step for forming a through hole, a through hole forming step for forming a through hole in a portion of the intermediate layer corresponding to the sacrificial layer, a sacrificial layer removing step for removing the sacrificial layer through the through hole, and an intermediate layer And a sealing layer forming step of forming a sealing layer by laminating.

  The sacrificial layer forming step may include a flattening step of forming a sacrificial layer on the piezoelectric wafer and then flattening the sacrificial layer to expose a peripheral portion of the vibration part. Moreover, you may include the heating process which heats an intermediate | middle layer after a sacrificial layer removal process. Further, a cutting step of forming a plurality of vibration portions on the piezoelectric wafer and cutting out the individual after the sealing layer forming step may be included.

  According to the present invention, the piezoelectric device can be manufactured at a low cost because it can be produced at the wafer level. In addition, since the piezoelectric vibrating piece is used as the vibrating portion, the Q value can be increased as compared with the vibrating portion having the MEMS structure, and a piezoelectric device having excellent vibration characteristics can be provided.

An example of the piezoelectric device which concerns on 1st Embodiment is shown, (a) is the top view seen through the intermediate | middle layer and the sealing layer, (b) is sectional drawing along the AA of (a). It is. It is a flowchart explaining the manufacturing method of the piezoelectric device shown in FIG. It is a figure which shows 1 process of the manufacturing method of a piezoelectric device, Comprising: (a) is sectional drawing which shows the state which formed the vibration part, (b) is sectional drawing which shows the state which formed the sacrificial layer, (c) is intermediate | middle Sectional drawing which shows the state in which the layer was formed, (d) is sectional drawing which shows the state in which the resist film was formed. FIG. 4 is a diagram showing one step of the manufacturing method of the piezoelectric device following FIG. 3, wherein (e) is a cross-sectional view showing a state where exposure and development are performed, and (f) is a state where etching of the intermediate film is performed. Sectional view, (g) is a sectional view showing a state where a resist film is removed and an electrode is formed, and (h) is a sectional view showing a state where a sacrificial layer is etched. FIG. 5 is a diagram illustrating one step of the method for manufacturing a piezoelectric device following FIG. 4, wherein (i) is a cross-sectional view illustrating a heated state, and (j) is a cross-sectional view illustrating a state in which a sealing layer is formed. (K) is sectional drawing which shows the state in which the electrode was formed. It is a top view which shows an example of the piezoelectric device which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. Further, in the drawings, in order to describe the embodiments, the scales are schematically described, and the scales are appropriately changed and expressed by partially enlarging or emphasizing them. Further, in the case where directions are indicated in the present embodiment, directions in the drawings will be described using the XYZ coordinate system in the following drawings. In the XYZ coordinate system, a plane parallel to the surface of the piezoelectric device 100 is defined as an XZ plane. In the XZ plane, the longitudinal direction of the piezoelectric device 100 is expressed as an X direction, and a direction orthogonal to the X direction is expressed as a Z direction. A direction perpendicular to the XZ plane (thickness direction of the piezoelectric device 100) 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 FIG. FIG. 1 shows the piezoelectric device 100 according to the first embodiment, wherein (a) is a plan view when viewed through the intermediate layer 120 and the sealing layer 140 from the + Y side, and (b) is (a). It is sectional drawing in alignment with the AA of (). As shown in FIGS. 1A and 1B, the piezoelectric device 100 includes a piezoelectric vibrating piece 110, intermediate films 120 and 130, and sealing films 140 and 150, and has a five-layer structure. This is a configured piezoelectric vibrator. The piezoelectric device 100 is formed in a rectangular shape when viewed from the Y direction.

  The piezoelectric vibrating piece 110 is formed in a plate shape with the same dimensions as the piezoelectric device 100 when viewed from the Y direction. As the piezoelectric vibrating piece 110, for example, an AT-cut quartz crystal vibrating piece is used. The AT cut has an advantage that a good frequency characteristic is obtained when the piezoelectric device 100 is used at around room temperature, and the optical axis among the three crystal axes of the artificial quartz, the electrical axis, the mechanical axis, and the optical axis. This is a processing method of cutting out at an angle of 35 ° 15 ′ around the crystal axis. However, the piezoelectric vibrating piece 110 is not limited to the AT-cut crystal vibrating piece, and for example, a BT-cut crystal vibrating piece may be used. Further, the piezoelectric vibrating piece 110 is not limited to a crystal piece, and for example, lithium tantalate, lithium niobate, or the like may be used.

  A thin vibrating portion 110b is formed at the central portion of the piezoelectric vibrating piece 110 with respect to the peripheral portion 110a. The vibration part 110b is formed in a rectangular shape when viewed from the Y direction. An inclined surface 110c is formed between the vibration part 110b and the peripheral part 110a. However, it is arbitrary whether the vibration part 110b and the peripheral part 110a are connected by the inclined surface 110c. As described above, the vibrating portion 110b is made thinner than the peripheral portion 110a, thereby forming the inverted mesa type vibrating portion 110b.

  The thickness (width in the Y direction) of the vibration unit 110 b is set according to the frequency extracted from the piezoelectric device 100. In the vibration unit 110b, the depth from the surface (+ Y side surface) of the piezoelectric vibrating piece 110 and the depth from the back surface (−Y side surface) are set to be the same. However, the depth of the front surface and the back surface of the vibration unit 110b is not limited to be set to the same, and may be formed so that the front surface side is deeper than the back surface side, for example. The vibrating part 110b is formed in parallel with the piezoelectric vibrating piece 110 (in parallel with the XZ plane). However, the vibrating unit 110b is not limited to being parallel to the piezoelectric vibrating piece 110. For example, the + X side of the vibrating unit 110b is disposed on the + Y side, and the −X side of the vibrating unit 110b is disposed on the −Y side. It may be formed to be inclined with respect to the piezoelectric vibrating piece 110.

  Excitation electrodes 161 and 162 and extraction electrodes 163 and 164 electrically connected to the excitation electrodes 161 and 162 are formed on the front and back surfaces of the piezoelectric vibrating piece 110. The excitation electrodes 161 and 162 are formed in a rectangular shape in plan view. The excitation electrodes 161 and 162 are disposed in a state of facing each other with the vibrating portion 110b of the piezoelectric vibrating piece 110 sandwiched in the Y direction, and are formed to have substantially the same size. The vibration unit 110b vibrates at a predetermined frequency when a predetermined AC voltage is applied to the excitation electrodes 161 and 162.

  The extraction electrode 163 is formed by being extracted from the excitation electrode 161 in the + X direction on the surface of the piezoelectric vibrating piece 110. The extraction electrode 164 is formed by being extracted in the −X direction from the excitation electrode 162 on the back surface of the piezoelectric vibrating piece 100. Note that the extraction electrode 163 and the extraction electrode 164 are not electrically connected.

  The excitation electrodes 161 and 162 and the extraction electrodes 163 and 164 are formed of a conductive metal film. As the metal film, for example, chromium (Cr), titanium (Ti), nickel (Ni), nickel chromium (NiCr), nickel titanium (NiTi), nickel tungsten in order to improve adhesion to a crystal material. A two-layer structure of a base film made of (NiW) alloy or the like and a main electrode film made of gold (Au) or silver (Ag) is adopted. This metal film is formed by, for example, a photolithography technique and etching after film formation, or by sputtering deposition or vacuum deposition through a metal mask. Note that the metal film is not limited to a two-layer structure, and a structure of one or three or more conductive metal films may be used.

  In the piezoelectric vibrating piece 110, a through hole 110 d that penetrates in the Y direction corresponding to the extraction electrode 163 is formed. A through electrode 165 is formed in the through hole 110d. Further, a rectangular connection electrode 166 is formed on the back surface side of the piezoelectric vibrating piece 110 so as to cover the through electrode 165. The lead electrode 163 and the connection electrode 166 are electrically connected by the through electrode 165. The through electrode 165 is formed by, for example, copper plating or filling with a conductive paste. The connection electrode 166 is formed by, for example, sputter deposition or vacuum deposition through a metal mask.

  The intermediate films 120 and 130 are formed on the front surface and the back surface of the piezoelectric vibrating piece 110, respectively, and are disposed inside the sealing films 140 and 150. The intermediate films 120 and 130 are formed substantially the same on the front surface and the back surface of the piezoelectric vibrating piece 110 when viewed from the Y direction. The intermediate films 120 and 130 are formed to have the same thickness (width in the Y direction), but the present invention is not limited to this, and the intermediate film 120 may be formed thicker than the intermediate film 130, for example. As the intermediate films 120 and 130, for example, polysilicon, silicon dioxide or the like is used.

  As shown in FIG. 1B, the intermediate films 120 and 130 are each formed in a state of being separated from the vibration part 110b. Accordingly, a cavity K1 is formed on the front surface side of the vibration part 110b, and a cavity K2 is formed on the back surface side of the vibration part 110b. Thereby, the mechanical vibration of the vibration part 110b is permitted. The cavities K1 and K2 are set, for example, in a vacuum atmosphere, but may instead be set in an inert gas atmosphere such as nitrogen gas or argon gas. The intermediate films 120 and 130 are formed by forming films on the front and back surfaces of the piezoelectric vibrating piece 110 by, for example, vacuum deposition or sputtering deposition.

  In the intermediate film 130 on the back surface side, a through hole 130 a penetrating in the Y direction corresponding to the through electrode 165 is formed. A through electrode 167 is formed in the through hole 130a. A rectangular connection electrode 168 is formed on the back surface of the intermediate film 130 so as to cover the through electrode 167. The connection electrode 166 and the connection electrode 168 are electrically connected by the through electrode 167. The intermediate film 130 is formed with a through hole 130 b penetrating in the Y direction corresponding to the extraction electrode 164. A through electrode 169 is formed in the through hole 130b. On the back surface of the intermediate film 130, a rectangular connection electrode 170 is formed so as to cover the through electrode 169. The lead electrode 164 and the connection electrode 170 are electrically connected by the through electrode 169. The through electrodes 167 and 169 are formed by, for example, copper plating or filling with a conductive paste. The connection electrodes 168 and 170 are formed by, for example, sputter deposition or vacuum deposition through a metal mask.

  The sealing films 140 and 150 are formed so as to cover the intermediate films 120 and 130, respectively. The sealing films 140 and 150 are formed to have the same thickness (width in the Y direction), but the present invention is not limited to this. For example, the sealing film 140 may be formed thicker than the sealing film 150. As the sealing films 140 and 150, for example, silicon nitride or the like is used. The sealing films 140 and 150 are formed by being formed on the intermediate films 120 and 130, for example, by vacuum deposition or sputtering deposition.

  The sealing layer 150 on the back side is formed with through holes 150a and 150b penetrating in the Y direction corresponding to the through electrodes 167 and 169, respectively. Through electrodes 171 and 173 are formed in the through holes 150a and 150b, respectively. On the back surface of the sealing film 150, rectangular external electrodes 172 and 174 are formed so as to cover the through electrodes 171 and 173, respectively. The connection electrode 168 and the external electrode 172 are electrically connected by the through electrode 171. Further, the connection electrode 170 and the external electrode 174 are electrically connected by the through electrode 173. The through electrodes 171 and 173 are formed by, for example, copper plating or filling with a conductive paste. The external electrodes 172 and 174 are formed by, for example, sputter deposition or vacuum deposition through a metal mask.

  The external electrode 172 is electrically connected to the extraction electrode 163 (excitation electrode 161) through the through electrode 171, the connection electrode 168, the through electrode 167, the connection electrode 166, and the through electrode 165. On the other hand, the external electrode 174 is electrically connected to the extraction electrode 164 (excitation electrode 162) via the through electrode 173, the connection electrode 170, and the through electrode 169.

  Thus, according to the piezoelectric device 100, since the intermediate films 120 and 130 are formed on the front surface and the back surface of the vibration part 110b in a state of being separated from the thin vibration part 110b formed on the piezoelectric vibration piece 110, the vibration part The mechanical vibration of 110b is not interfered by the intermediate film 120 or the like. In addition, since a part of the piezoelectric vibrating piece 110 is used as the vibrating part 110b, the Q value can be increased as compared with the vibrating part of the MEMS structure, and the piezoelectric device 100 having excellent vibration characteristics can be provided. Further, the airtightness of the internal spaces K1, K2 in which the sealing layers 140, 150 are formed on the intermediate films 120, 130 can be maintained.

  Further, since the vibration part 110b is formed in parallel with the piezoelectric vibration piece 110 at the central portion of the thickness of the piezoelectric vibration piece 110, the vibration part 110b can be reliably separated from the intermediate films 120 and 130, and the vibration part 110b. Can be prevented from interfering with the intermediate film 120 and the like. Further, since the sealing layers 140 and 150 are formed in a state of covering the intermediate layers 120 and 130, the intermediate layers 120 and 130 can be protected by the sealing layers 140 and 150.

(Method for manufacturing piezoelectric device 100)
Next, a method for manufacturing the piezoelectric device 100 will be described with reference to FIGS. FIG. 2 is a flowchart for explaining a method of manufacturing the piezoelectric device 100 shown in FIG. 3 to 5 show steps corresponding to each of the flowcharts shown in FIG. The following description will be made with reference to FIGS. 3 to 5 as appropriate along the flowchart of FIG.

  First, as shown in FIG. 2, the piezoelectric wafer AW is processed (step S01). As the piezoelectric wafer AW, for example, an AT-cut quartz wafer is used. In the processing of the piezoelectric wafer AW, as shown in FIG. 3A, formation of the vibration part 110b, formation of the excitation electrodes 161 and 162 and extraction electrodes 163 and 164, formation of the through hole 110d, formation of the through electrode 165, The connection electrode 166 is formed. First, predetermined portions of the front surface and the back surface of the piezoelectric wafer AW are thinned by wet etching or the like, and the peripheral portion 110a and the vibration portion 110b are formed (vibration portion forming step). Note that the piezoelectric wafer AW is not limited to being thinned by wet etching, and for example, sandblasting or the like may be used.

  Next, excitation electrodes 161 and 162 are formed on the front and back surfaces of the piezoelectric wafer AW (piezoelectric vibration piece 110) with the vibration part 110b interposed therebetween, and extraction electrodes 163 and 164 extending from the excitation electrodes 161 and 162 are formed. The The excitation electrodes 161 and the like are formed by forming a conductive metal film by a photolithography method and an etching method, or vapor deposition through a metal mask.

  Next, a through hole 110d penetrating in the Y direction is formed in a portion corresponding to the extraction electrode 163 of the piezoelectric wafer AW. This through hole 110d is formed by, for example, machining such as wet etching or sand blasting. Next, the through electrode 165 is formed in the through hole 110d, for example, by filling with copper plating or conductive paste. Next, a connection electrode 166 is formed so as to cover the through electrode 165.

Subsequently, sacrificial layers 175 and 176 are formed (step S02). As shown in FIG. 3B, sacrificial layers 175 and 176 are formed on the front side and the back side of the vibration part 110b (sacrificial layer forming step). As the sacrificial layers 175 and 176, for example, silicon dioxide (SiO ₂ ), amorphous silicon, a photoresist, and other polymer materials can be appropriately selected. In the case where silicon dioxide is used as the sacrificial layers 175 and 176, for example, the sacrificial layers 175 and 176 are formed by a vacuum process such as a plasma CVD method using a predetermined gas or a sputtering method. For etching silicon dioxide, for example, etching using hydrofluoric acid vapor is used in the dry etching method, and for example, a technique such as immersion in buffer hydrofluoric acid can be used in the wet etching method.

When amorphous silicon is used for the sacrificial layers 175 and 176, the sacrificial layers 175 and 176 are formed by, for example, a plasma CVD method using a gas such as H ₂ or SiH ₄ or a vacuum process such as a sputtering method. Note that dry etching or wet etching is used for etching the amorphous silicon. In the dry etching method, for example, XeF ₂ (xenon fluoride) gas or the like is used, and in the wet etching method, for example, hydrofluoric acid or the like is used.

  Subsequently, the sacrificial layers 175 and 176 are planarized (step S03). When the sacrificial layers 175 and 176 are formed in step S02, the sacrificial layer 175 and the like are formed on the entire front and back surfaces of the piezoelectric vibrating piece 110. By flattening this film, the peripheral portion 110a of the piezoelectric vibrating piece 110 is exposed (flattening step). For example, CMP (Chemical Mechanical Polishing) is used for the planarization step. By the planarization process, the sacrificial layers 175 and 176 on the front surface and the back surface of the vibration part 110b remain, and the sacrificial layer on the peripheral part 110a is removed. Thereby, the sacrificial layers 175 and 176 are formed on the same surface with respect to the peripheral portion 110a.

  However, the sacrificial layers 175 and 176 are not limited to the same surface as the peripheral portion 110a. For example, the sacrificial layers 175 and 176 are formed in a state of being recessed or raised in the Y direction with respect to the peripheral portion 110a. Also good. Further, the sacrificial layers 175 and 176 are not limited to being formed on the entire surface of the piezoelectric vibrating piece 110 by the plasma CVD method or the like as described above. For example, the sacrificial layers 175 and 176 are locally formed on the vibrating portion 110b by using the ink jet method or the like. You may make it form. As described above, in the case where the sacrificial layers 175 and 176 can be locally formed, the planarization process in step S03 described above may not be performed.

  Subsequently, the intermediate films 120 and 130 are formed (step S04). As shown in FIG. 3C, intermediate films 120 and 130 are formed on the front surface and the back surface of the piezoelectric wafer AW after the planarization process (intermediate film forming process). For the intermediate films 120 and 130, for example, polysilicon or silicon dioxide is used. For the intermediate film forming step, for example, vacuum deposition, sputter deposition, low-pressure CVD, or the like is used.

  The film thickness of the intermediate films 120 and 130 can be set arbitrarily. However, when the cavities K1 and K2 (see FIG. 1) are formed, the film thickness is set such that the intermediate films 120 and 130 are strong enough to maintain a state where they are separated from the vibration part 110b. The intermediate films 120 and 130 are formed with the same film thickness, but may be different. In addition, the intermediate films 120 and 130 are not limited to be formed to have a uniform film thickness. For example, the film thickness of a portion facing the vibrating portion 110b is made larger than others, and the film thickness is partially changed. Also good. Further, the intermediate films 120 and 130 are not limited to being formed of the same material, and may be formed of different materials.

  Subsequently, resist films 178 and 179 are formed (step S05). As shown in FIG. 3D, resist films 178 and 179 are formed on the entire front and back surfaces of the intermediate films 120 and 130. As the resist films 178 and 179, for example, a negative photoresist made of novolak resin or the like is used. For example, a spin coater or a slit coater is used to form the resist film.

  Subsequently, exposure and development are performed (step S06). As shown in FIG. 4E, the resist films 178 and 179 are subjected to an exposure process using a predetermined mask and then developed, whereby a plurality of resist patterns penetrating in the Y direction are obtained. Through holes 178a and 179a are formed. The through holes 178 a and 179 a are formed at locations corresponding to the sacrificial layers 175 and 176. The resist film 179 on the back side is formed with a through hole 179 b that penetrates in the Y direction corresponding to the through electrode 165 and a through hole 179 c that penetrates in the Y direction corresponding to the lead electrode 164. The

  Subsequently, the intermediate films 120 and 130 are etched (step S07). As shown in FIG. 4F, the intermediate films 120 and 130 are etched through the resist pattern, so that the intermediate films 120 and 130 penetrate through the through holes 178a and 179a of the resist films 178 and 179. Holes 120a and 130c are formed. In this way, through holes 120a and 130c are formed in the intermediate films 120 and 130 by the series of steps shown in steps S05 to S07 described above (through hole forming step). The number of through holes 120a and 130c and the opening diameter can be arbitrarily set.

  By forming the through holes 120a and 130c, the sacrificial layers 175 and 176 are exposed to the outside through the through holes 178a and 179a and the through holes 120a and 130c. Further, in the intermediate film 130 on the back surface, through holes 130a and 130b penetrating in the Y direction corresponding to the through holes 179b and 179c are formed.

  Subsequently, the resist films 178 and 179 are removed and electrodes are formed (step S08). As shown in FIG. 4G, first, the resist films 178 and 179 are removed with a predetermined stripping solution or the like. Next, through electrodes 167 and 169 are formed in the through holes 130a and 130b of the intermediate film 130 by copper plating, filling with a conductive paste, or the like. Next, rectangular connection electrodes 168 and 170 are formed so as to cover the through electrodes 167 and 169. The connection electrodes 168 and 170 are formed by forming a conductive metal film by, for example, photolithography and etching, or sputtering deposition or vacuum deposition through a metal mask. Note that the connection electrode 166 and the connection electrode 168 are electrically connected through the through electrode 167, and the extraction electrode 164 and the connection electrode 170 are electrically connected through the through electrode 169.

  Subsequently, the sacrificial layers 175 and 176 are etched (step S09). As shown in FIG. 4H, the sacrificial layers 175 and 176 are removed by a process such as dry etching or dissolution through the through holes 120a and 130c of the intermediate films 120 and 130 (sacrificial layer removing step). ). Simultaneously with the removal of the sacrificial layers 175 and 176, the impurities remaining in the vibration part 110b are also removed through the through holes 120a and 130c. By removing the sacrificial layers 175 and 176, a cavity K1 is formed on the front surface side of the vibration part 110b, and a cavity K2 is formed on the back surface side of the vibration part 110b.

  In addition, after removing the sacrificial layers 175 and 176, the frequency of the vibration unit 110b may be adjusted. The frequency is adjusted by etching the excitation electrodes 161 and 162 on the front surface and the back surface of the vibration part 110b. Therefore, the excitation electrodes 161 and 162 may be formed to have a slightly thicker thickness so as to be lower than the desired frequency in advance, and etching may be performed after the formation of the cavities K1 and K2 to match the desired frequency.

  Subsequently, high temperature annealing is performed (step S10). As shown in FIG. 5I, after the sacrificial layers 175 and 176 are removed, the intermediate films 120 and 130 are heated (heating step). This high temperature annealing is performed, for example, by putting the piezoelectric wafer AW in a heating furnace and heating it to a predetermined temperature. By this heating step, the intermediate films 120 and 130 are heated to close the through holes 120a and 130c. In the heating process, by setting the inside of the heating furnace to a vacuum, when the through holes 120a and 130c are closed, the inside of the cavities K1 and K2 can be set to a vacuum atmosphere.

  Note that whether or not to perform the heating process of step S10 is arbitrary, and the subsequent step S11 may be performed without this heating process. Further, in the heating process, the through holes 120a and 130a of the intermediate films 120 and 130 are not completely closed, and the opening diameters of the through holes 120a and 130a may be reduced.

  Subsequently, the sealing films 140 and 150 are formed (step S11). As shown in FIG. 5J, sealing films 140 and 150 are formed so as to cover the entire surfaces of the intermediate films 120 and 130 (sealing film forming step). As the sealing films 140 and 150, for example, silicon nitride or the like is used. The sealing films 140 and 150 are formed by, for example, vacuum deposition or sputter deposition. In addition, when the through hole 120a and the like are still opened after the heating process in step S10 described above, the inside of the cavities K1 and K2 is formed in a vacuum atmosphere by performing this sealing film forming process in a vacuum atmosphere. Can do.

  The film thickness of the sealing films 140 and 150 can be set arbitrarily. However, the film thickness is set so as to have a strength capable of maintaining the state separated from the vibrating portion 110b together with the intermediate films 120 and 130. The sealing films 140 and 150 are formed with the same film thickness, but may be different. Further, the sealing films 140 and 150 are not limited to be formed with a uniform film thickness. For example, the film thickness of a part corresponding to the vibration part 110b is made larger than others, and the film thickness is partially changed. May be. Further, the sealing films 140 and 150 are not limited to being formed of the same material, and may be formed of different materials.

  Subsequently, an electrode is formed (step S12). As shown in FIG. 5K, first, through holes 150a and 150b penetrating in the Y direction are formed in the sealing film 150 on the back surface side. The through holes 150 a and 150 b are formed at positions corresponding to the connection electrodes 168 and 170 formed in the intermediate film 130. The through holes 150a and 150b are formed by, for example, exposing and developing a resist film to form a resist pattern and etching the sealing film 150 through the resist pattern, as in step S07 described above. Next, through electrodes 171 and 173 are formed in the through holes 150a and 150b, respectively. The through electrodes 171 and 173 are formed by, for example, copper plating or filling with a conductive paste.

  Next, rectangular external electrodes 172 and 174 are formed so as to cover the through electrodes 171 and 173. The external electrodes 172 and 174 are formed by forming a conductive metal film by, for example, photolithography and etching, sputtering deposition or vacuum deposition through a metal mask, or application of a conductive paste. The connection electrode 168 and the external electrode 174 are electrically connected via the through electrode 171, and the connection electrode 170 and the external electrode 173 are electrically connected via the through electrode 173.

  Subsequently, the piezoelectric wafer AW is cut (step S13). The piezoelectric wafer AW is cut along a preset scribe line (cutting process). In this cutting step, for example, a dicing apparatus using a laser or a dicing saw is used. By this cutting process, the individualized piezoelectric device 100 is completed.

  5 (k), the side surfaces of the intermediate films 120 and 130 are left exposed, and the side surfaces of the intermediate films 120 and 130 are not exposed as in the piezoelectric device 100 of FIG. 1 (b). The sealing films 140 and 150 are not covered. In order to create a configuration as shown in FIG. 1, first, after the intermediate films 120 and 130 are formed, the intermediate films 120 and 130 are patterned to form island shapes. Next, sealing films 140 and 150 are formed thereon. Next, it is possible to create a form in which the side surfaces of the intermediate films 120 and 130 are covered with the sealing films 140 and 150 by cutting along portions where the intermediate films 120 and 130 are not present.

  As described above, according to the method for manufacturing the piezoelectric device 100, the cavities K1 and K2 are held in the predetermined atmosphere by the intermediate films 120 and 130 and the sealing films 140 and 150. Compared with sealing, the piezoelectric device 100 can be manufactured easily. Further, by using the piezoelectric wafer AW, the piezoelectric device 100 having excellent vibration characteristics can be manufactured at a wafer level at a low cost.

  Further, by performing a planarization step after the formation of the sacrificial layers 175 and 176, the sacrificial layers 175 and 176 can be surely formed on the front and back surfaces of the vibration unit 110b except for the peripheral portion 110a. Further, by performing a heating process for heating the intermediate films 120 and 130 after the sacrificial layer removing process, the through holes 120a and 130a can be closed or the opening diameter can be reduced, and the sealing films 140 and 150 thereafter. The film can be easily formed.

Second Embodiment
Next, a second embodiment will be described with reference to FIG. FIG. 6 is a plan view illustrating an example of the piezoelectric device 200 according to the second embodiment. In FIG. 6, it has shown in the state which permeate | transmitted the intermediate film and the sealing film (refer FIG. 1). 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. As shown in FIG. 6, the piezoelectric device 200 includes a piezoelectric vibrating piece 210, and has an intermediate film and a sealing film on the front and back surfaces of the piezoelectric vibrating piece 210, respectively, as in the piezoelectric device 100 of the first embodiment. The piezoelectric vibrator has a five-layer structure. The piezoelectric device 200 is formed in a rectangular shape when viewed from the Y direction.

  The piezoelectric vibrating piece 210 is formed in a plate shape with the same dimensions as the piezoelectric device 200 when viewed from the Y direction. As in the first embodiment, for example, an AT-cut crystal vibrating piece is used for the piezoelectric vibrating piece 210. However, the piezoelectric vibrating piece 210 is not limited to the AT-cut crystal vibrating piece, and for example, a BT-cut crystal vibrating piece may be used. Further, the piezoelectric vibrating piece 210 is not limited to a crystal piece, and for example, lithium tantalate, lithium niobate, or the like may be used.

  A thin vibrating portion 210b is formed at the central portion of the piezoelectric vibrating piece 210 with respect to the peripheral portion 210a. The vibration part 210b is formed in a circular shape when viewed from the Y direction. An inclined surface 210c is formed between the vibration part 210b and the peripheral part 210a. However, the vibrating portion 210b is not limited to a circular shape, and may be formed in an elliptical shape, an oval shape, or a polygonal shape (excluding a square shape), for example. Further, whether or not the inclined surface 210c is formed is arbitrary.

  Excitation electrodes 261 and 262 and extraction electrodes 263 and 264 electrically connected to the excitation electrodes 261 and 262 are formed on the front and back surfaces of the piezoelectric vibrating piece 210. The excitation electrodes 261 and 262 are formed in a circular shape in plan view. The excitation electrodes 261 and 262 are arranged in a state of being opposed to each other with the vibrating portion 210b of the piezoelectric vibrating piece 210 sandwiched in the Y direction, and are formed to have substantially the same size. The vibration part 210b vibrates at a predetermined frequency when a predetermined AC voltage is applied to the excitation electrodes 261 and 262.

  The extraction electrode 263 is formed by being extracted from the excitation electrode 261 in the + X direction on the surface of the piezoelectric vibrating piece 210. The extraction electrode 264 is formed by being extracted from the excitation electrode 262 in the −X direction on the back surface of the piezoelectric vibrating piece 210. Note that the extraction electrode 263 and the extraction electrode 264 are not electrically connected. The electrical connection from the extraction electrodes 263 and 264 to the external electrodes 172 and 174 (see FIG. 1B) is the same as that of the piezoelectric device 100 shown in FIG.

  As described above, according to the piezoelectric device 200, similarly to the piezoelectric device 100 of the first embodiment, the mechanical vibration of the vibration unit 210b is not interfered by the intermediate film or the like. Further, since a part of the piezoelectric vibrating piece 210 is used for the vibrating part 210b, the Q value can be increased and the piezoelectric device 200 having excellent vibration characteristics can be provided. The method for manufacturing the piezoelectric device 200 is the same as the method for manufacturing the piezoelectric device 100 described above.

  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, in each of the embodiments described above, the electrical connection from the extraction electrodes 163 and 164 (263 and 264) to the external electrodes 172 and 174 is not limited to the illustrated form. For example, the lead electrodes 163 and 164 may be connected to the external electrodes 172 and 174 via the side surfaces of the piezoelectric device 100 without using the through electrode 167 and the like.

  Further, in the piezoelectric vibrating reeds 110 and 210 of the above-described embodiments, a penetrating portion penetrating in the Y direction may be formed between the peripheral portions 110a and 210a and the vibrating portions 110b and 210b. In this case, for example, a penetrating part may be formed so as to surround the vibrating parts 110b and 210b while leaving a portion on the −X side, and the vibrating parts 110b and 210b may be held in a cantilever state. When forming such a penetration part, extraction electrode 163, 164, 263, 264 is arranged avoiding a penetration part.

DESCRIPTION OF SYMBOLS 100, 200 ... Piezoelectric device 110, 210 ... Piezoelectric vibrating piece 110a, 210a ... Peripheral part 110b, 210b ... Vibrating part 120, 130 ... Intermediate film 120a, 130c ... Through-hole 140 150 ... Sealing film 175, 176 ... Sacrificial layer AW ... Piezoelectric wafer

Claims (9)

A piezoelectric vibrating piece having a thin vibrating portion with respect to the peripheral portion;
On the front and back surfaces of the piezoelectric vibrating piece, an intermediate film that is separated from the vibrating portion and joined to the peripheral portion,
And a sealing film laminated on the intermediate film.   The piezoelectric device according to claim 1, wherein the vibrating portion is formed in parallel with the piezoelectric vibrating piece at a central portion of the thickness of the piezoelectric vibrating piece.   The piezoelectric device according to claim 1, wherein the sealing film is formed in a state of covering the intermediate film.   The piezoelectric device according to any one of claims 1 to 3, wherein the same intermediate film and the same sealing film are formed on the front surface and the back surface of the piezoelectric vibrating piece.   The piezoelectric device according to claim 1, wherein the piezoelectric vibrating piece is a crystal vibrating piece. A vibrating part forming step of forming a vibrating part by thinning a part of the piezoelectric wafer;
A sacrificial layer forming step of forming a sacrificial layer on the vibrating portion;
An intermediate layer forming step of forming an intermediate film on the front and back surfaces of the piezoelectric wafer;
A through hole forming step of forming a through hole at a location corresponding to the sacrificial layer of the intermediate film;
A sacrificial layer removing step of removing the sacrificial layer through the through hole;
And a sealing film forming step of forming a sealing film by laminating on the intermediate film.   The method of manufacturing a piezoelectric device according to claim 6, wherein the sacrificial layer forming step includes a flattening step of forming the sacrificial layer on the piezoelectric wafer, and then flattening the sacrificial layer to expose a peripheral portion of the vibrating portion. Method.   8. The method for manufacturing a piezoelectric device according to claim 6, further comprising a heating step of heating the intermediate film after the sacrificial layer removing step.   9. The method for manufacturing a piezoelectric device according to claim 6, further comprising a cutting step of forming a plurality of the vibrating portions on the piezoelectric wafer and cutting out the individual after the sealing film forming step.

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