Piezoelectric device and method for manufacturing the same

A piezoelectric device includes a piezoelectric vibrating piece with a pair of excitation electrodes, a base plate, and a non-conductive bonding material. The base includes a pair of castellations that are hollowed into a side face from the mounting surface to the bonding surface. The pair of castellations include a first surface and a second surface. The first surface extends outward from the mounting surface toward the bonding surface side. The second surface extends outward from the bonding surface toward the mounting surface side. The second surface has a smaller area than an area of the first surface. A wiring electrode is disposed on the first surface, the second surface, and a side face of the bonding material. The wiring electrode is of a same electrode layer as the external electrode. The wiring electrode extends from the external electrode to the extraction electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japan application serial no. 2011-171423, filed on Aug. 5, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

This disclosure relates to methods for manufacturing piezoelectric devices where wiring electrodes formed on castellations extend to extraction electrodes of piezoelectric pieces via side faces of bonding materials. The disclosure also relates to piezoelectric devices produced by the methods.

DESCRIPTION OF THE RELATED ART

A known piezoelectric device includes a piezoelectric vibrating piece that vibrates at a predetermined vibration frequency. The piezoelectric vibrating piece is sandwiched between a base plate and a lid plate. In the piezoelectric device, castellations are formed on side faces of the base plate. Wiring electrodes, which are formed on the castellations, electrically connect mounting terminals and excitation electrodes together.

For example, Japanese Unexamined Patent Application Publication No. 6-343017 discloses the following piezoelectric device. The piezoelectric device includes through-holes formed on its base plate. Electrodes are formed inside the through-holes. The electrodes electrically bond electrodes on the front side of the base plate and electrodes on the back side of the base plate together. The through-holes are etched from both the front and back sides of the base plate. This forms the through-holes to have intermediate portions that protrude to outside of the base plate. That is, the through-holes are formed to include intermediate portions with small radii. In the castellations, similarly to the through-holes, intermediate portions of the castellations are formed to protrude to outside of the base plate. Then, the castellations include a surface toward the front side direction and a surface toward the back side direction of the base plate. Accordingly, these electrodes are formed on the castellations by sputtering, vacuum-deposition or the like from both the front and back sides of the castellations.

On the other hand, it is preferred that manufacturing process of the piezoelectric device be further simplified. Since expensive metal may be used for electrode material, it is preferred that usage of the electrode material be reduced. In the case where sputtering, vacuum-deposition or the like is performed on the castellations of the base plate from one main surface, a manufacturing direction is simplified and usage of the electrode material is reduced.

SUMMARY

The present invention provides a piezoelectric device where an external electrode and a wiring electrode, which extends to an extraction electrode of a piezoelectric vibrating piece, are formed by sputtering, vacuum-deposition, or the like. The present invention also provides methods for manufacturing the piezoelectric devices.

A first aspect of invention is directed to a piezoelectric device. The piezoelectric device includes a piezoelectric vibrating piece, a base plate, and a non-conductive bonding material. The piezoelectric vibrating piece includes a pair of excitation electrodes and a pair of extraction electrodes. The pair of extraction electrodes is extracted from the pair of excitation electrode. The base plate includes a bonding surface with a pair of external electrodes and a mounting surface. The piezoelectric vibrating piece is disposed on the mounting surface. A pair of castellations is hollowed into a side face from the mounting surface to the bonding surface. The base plate includes one of glass and piezoelectric material. The non-conductive bonding material is disposed between the piezoelectric vibrating piece and the base plate. The non-conductive bonding material bonds the piezoelectric vibrating piece and the base plate together. The pair of castellations includes a first surface and a second surface. The first surface extends outward from the mounting surface toward the bonding surface side. The second surface extends outward from the bonding surface toward the mounting surface. The second surface has a smaller area than an area of the first surface. A wiring electrode is disposed on the first surface, the second surface, and a side face of the bonding material. The wiring electrode is of a same electrode layer as the external electrode. The wiring electrode extends from the external electrode to the extraction electrodes.

A second aspect of invention is directed to a method for manufacturing the piezoelectric device. The method includes: preparing a base wafer, preparing a piezoelectric wafer, and bonding the base wafer and the piezoelectric wafer together with bonding material. The base wafer includes a plurality of base plates. The base plate includes a mounting surface on which an external electrode is to be formed and a bonding surface. The bonding surface is opposite side of the mounting surface. The bonding bonds the base wafer and the piezoelectric wafer together with bonding material.

The present invention performs sputtering, vacuum-deposition or the like from one main surface. This ensures a facilitated method for manufacturing the piezoelectric devices.

DETAILED DESCRIPTION

Each embodiment of the present invention is described in detail below by referring to the accompanying drawings. It will be understood that the scope of the disclosure is not limited to the described embodiments, unless otherwise stated.

Configuration of a Piezoelectric Device100According to a First Embodiment

FIG. 1is an exploded perspective view of the piezoelectric device100. The piezoelectric device100is a surface-mount type piezoelectric device. The piezoelectric device100is used for being mounted on a printed circuit board or the like. The piezoelectric device100mainly includes a lid plate110, a base plate120a, and a piezoelectric vibrating piece130a. The lid plate110may be formed of ceramic, glass, piezoelectric material or the like. The base plate120amay be formed of piezoelectric material such as quartz-crystal material. The piezoelectric vibrating piece130aemploys, for example, an AT-cut quartz-crystal material. The AT-cut quartz-crystal material has a principal surface (in the Y-Z plane) that is tilted by 35° 15′ about the Y-axis of the crystal coordinate system (XYZ) in the direction from the Z-axis to the Y-axis around the X-axis. In the following description, the new axises tilted with reference to the axis directions of the AT-cut quartz-crystal material are denoted as the Y′ axis and the Z′ axis. Therefore, in the piezoelectric device100, the longitudinal direction of the piezoelectric device100is referred as the X axis direction, the height direction of the piezoelectric device100is referred as the Y′ axis direction, and the direction perpendicular to the X axis and the Y′ axis directions is referred to as the Z′ axis direction.

The base plate120amay be formed in a rectangular shape that has long sides extending in the X axis direction and short sides extending in the Z′ axis direction. The base plate120ahas a surface at the −Y′ axis side that is a mounting surface on which external electrodes125and grounding terminals126are to be formed. The external electrodes125are electrodes for soldering and electrically connecting the piezoelectric device100to a printed circuit board or the like. The grounding terminals126are terminals for discharging static electricity and the like, which are charged on the piezoelectric device100. In the base plate120a, non-conductive bonding material140(seeFIGS. 2A to 2C) is applied over a bonding surface122on a surface at the +Y′ axis side. The base plate120ais then bonded to the piezoelectric vibrating piece130a. Further, the base plate120aincludes a recess123, which is formed to be hollowed into the bonding surface122in the −Y′ axis direction. The base plate120aincludes a side face of a corner portion at the −X axis side and the +Z′ axis side, and a side face of a corner portion at the +X axis side and the −Z′ axis side. On these side faces, respective castellations127are formed to be recessed inward the base plate120a. Each of the castellations127includes a wiring electrode128, which is electrically connected to the external electrode125.

The lid plate110is formed in a rectangular shape that has long sides extending in the X axis direction and short sides extending in the Z′ axis direction. The lid plate110includes a bonding surface112, which is to be bonded to the piezoelectric vibrating piece130avia the bonding material140(seeFIGS. 2A to 2C) on its surface at the −Y′ axis side. The lid plate110includes a recess111, which is formed to be hollowed into the bonding surface112in the +Y′ axis direction.

The piezoelectric vibrating piece130aincludes an excitation unit133, a framing portion134, and connecting portions135. The excitation unit133vibrates at a predetermined vibration frequency. The framing portion134is formed to surround a peripheral area of the excitation unit133. The connecting portions135connect the excitation unit133and the framing portion134together. In regions other than the connecting portions135between the excitation unit133and the framing portion134, through grooves136are formed to pass through the piezoelectric vibrating piece130ain the Y′ axis direction. Further, respective excitation electrodes131are formed on surfaces at the +Y′ axis side and the −Y′ axis side of the excitation unit133. From the excitation electrode131formed at the +Y′ axis side, an extraction electrode132is extracted via the connecting portion135formed at the −X axis side and via side faces at the −X axis side and the +Z′ axis side of the through groove136. The extraction electrode132is extracted to a corner portion at the −X axis side and the +Z′ axis side on a surface at the −Y′ axis side of the framing portion134. From the excitation electrode131formed at the −Y′ axis side, an extraction electrode132is extracted via the connecting portion135formed at the +X axis side. The extraction electrode132is extracted to a corner portion at the +X axis side and the −Z′ axis side on a surface at the −Y′ axis side of the framing portion134.

FIG. 2Ais a cross-sectional view taken along the line A-A ofFIG. 1. The piezoelectric device100is formed as follows. The bonding surface122of the base plate120aand the surface at the −Y′ axis side of the framing portion134in the piezoelectric vibrating piece130aare bonded together via the non-conductive bonding material140. The bonding surface112of the lid plate110and the surface at the +Y′ axis side of the framing portion134in the piezoelectric vibrating piece130aare bonded via the non-conductive bonding material140. The bonding material140employs, for example, low-melting-point glass, which is a glass bonding material with a melting point equal to or lower than 500 degrees, or resin bonding material such as polyimide resin. Each of the castellations127of the base plate120aincludes a first surface127aand a second surface127b. The first surface127aextends outward from a surface at the −Y′ axis side of the base plate120atoward the bonding surface122side of the base plate120a. The second surface127bextends outward from the bonding surface122toward the surface at the −Y′ axis side of the base plate120a. The second surface127bhas a smaller area than that of the first surface127a. That is, a normal vector of the first surface127ahas a component in the −Y′ axis direction, while a normal vector of the second surface127bhas a component in the +Y′ axis direction. On the surface at the −Y′ axis side of the base plate120a, the external electrodes125are formed. Wiring electrodes128are formed on the first surface127aand the second surface127bin each castellations127, and on a side face of the bonding material140. The external electrodes125and the wiring electrodes128may be formed of the same electrode layer. The external electrodes125and the extraction electrodes132of the piezoelectric vibrating piece130aare electrically connected together via the wiring electrode128.

FIG. 2Bis a plan view of the base plate120a. Electrodes are not formed on the bonding surface122at the +Y′ axis side of the base plate120a. In the castellations127, the wiring electrodes128are formed after the base plate120ais bonded to the piezoelectric vibrating piece130a.

FIG. 2Cis a plan view of the base plate120aillustrating the external electrodes125and the grounding terminals126.FIG. 2Cis a transparent view of the base plate120afrom the +Y′ axis side of the base plate120aillustrating the external electrodes125and the grounding terminals126, which are formed on the surface at the −Y′ axis side of the base plate120a. The external electrodes125are formed to contact the castellation127. The grounding terminals126are formed to include respective corner portions, which do not have the castellations127, of the base plate120a. The external electrodes125and the grounding terminals126are formed to contact the short sides and the long sides of the base plate120awithout spaces.

The bonding material used in the piezoelectric device is affected by heat of, for example, solder when mounted on a printed circuit board or the like. This may break sealing inside the piezoelectric device. In the piezoelectric device100, the first surface127a, which has the normal vector with a component in the −Y′ axis direction, is formed larger than the second surface127b. This prevents solder from reaching a portion between the piezoelectric vibrating piece130aand the base plate120a. Therefore, this reduces an influence of the solder on the bonding material140, which is formed between the piezoelectric vibrating piece130aand the base plate120a.

A Method for Manufacturing the Piezoelectric Device100

FIG. 3is a flowchart illustrating a method for manufacturing the piezoelectric device100. Hereinafter, the method for manufacturing the piezoelectric device100will be described by referring toFIG. 3.

In step S101, a piezoelectric wafer W130is prepared. The piezoelectric wafer W130is a wafer formed of piezoelectric material, and includes a plurality of piezoelectric vibrating pieces described below.

FIG. 4is a plan view of the piezoelectric wafer W130. In the piezoelectric wafer W130, the piezoelectric vibrating pieces130aand the piezoelectric vibrating pieces130bare alternately formed in the X axis direction and the Z′ axis direction. InFIG. 4, scribe lines142are illustrated by two-dot chain lines at boundaries of the respective piezoelectric vibrating pieces130aand130bnext to one another. The scribe lines142are lines to be used for dicing the wafer in step S107described later. The piezoelectric vibrating piece130ais connected to the connecting portion135at the +X axis side and the −Z′ axis side of the excitation unit133, and is also connected to the connecting portion135at the −X axis side and the +Z′ axis side of the excitation unit133. The piezoelectric vibrating piece130bis connected to the connecting portion135at the +X axis side and the +Z′ axis side of the excitation unit133, and is also connected to the connecting portion135at the −X axis side and the −Z′ axis side of the excitation unit133. Accordingly, each piezoelectric vibrating piece130aincludes the extraction electrode132that is extracted to a corner portion at the +X axis side and the −Z′ axis side and the extraction electrode132that is extracted to a corner portion at the −X axis side and the +Z′ axis side, on the surface at the −Y′ axis side of the framing portion134. Each piezoelectric vibrating piece130bincludes the extraction electrode132that is extracted to a corner portion at the +X axis side and the +Z′ axis side and the extraction electrode132that is extracted to a corner portion at the −X axis side and the −Z′ axis side, on the surface at the −Y′ axis side of the framing portion134. The piezoelectric vibrating pieces130aand the piezoelectric vibrating pieces130bare only different in positions of the connecting portion135, extracting direction of the extraction electrode132, and the like. The piezoelectric vibrating pieces130aand the piezoelectric vibrating pieces130bhave the same electrical characteristics.

In step S102, a base wafer W120is prepared. The base wafer W120includes the recesses123and through-holes143, which pass through the base wafer W120in the Y′ axis direction. This forms a plurality of base plates described below on the base wafer W120.

FIG. 5is a plan view of the base wafer W120. In the base wafer W120, the base plates120aand base plates120bare alternately formed in the X axis direction and the Z′ axis direction.FIG. 5illustrates the scribe lines142with the two-dot chain lines at boundaries of the respective base plates120aand120bnext to one another. The scribe lines142are lines to be used for dicing the wafer in step S107described later. At intersection points of the scribe lines142that extend in the X axis direction and the Z′ axis direction, the through-holes143, which pass through the base wafer W120in the Y′ axis direction, are formed at every other intersection point in the X axis direction and the Z′ axis direction. In each base plate120a, the through-holes143are formed at the +X axis side and the −Z′ axis side, and formed at the −X axis side and the +Z′ axis side. In each base plate120b, the through-holes143are formed at the +X axis side and the +Z′ axis side, and formed at the −X axis side and the −Z′ axis side. The through-holes143make the castellations127after the wafer is diced in step S107described later.

FIGS. 6A to 6Dand7A to7D are diagrams illustrating respective steps of a flowchart of a method for manufacturing the base wafer W120inFIG. 5. In the right side of respective steps inFIGS. 6A to 6Dand7A to7D, diagrams to describe the respective steps are illustrated. These diagrams, which describe the respective steps inFIGS. 6A to 6Dand7A to7D, are cross-sectional views corresponding to cross-sectional surfaces of the base wafer W120taken along the line B-B ofFIG. 5. The method for manufacturing the base wafer W120will be described below by referring toFIGS. 6A to 6Dand7A to7D.

In step S201ofFIGS. 6A to 6D, a wafer formed of piezoelectric material is prepared.FIG. 6Aillustrates a partial cross-sectional view of the base wafer W120, which is formed of piezoelectric material such as quartz crystal. The base wafer W120, which is prepared in step S201, has surfaces at the +Y′ axis side and the −Y′ axis side, which are formed to be planar surfaces as illustrated inFIG. 6A.

In step S202, anticorrosion films150and photoresists151are formed on both the surfaces at the +Y′ axis side and the −Y′ axis side of the base wafer W120.FIG. 6Bis a partial cross-sectional view of the base wafer W120with the anticorrosion films150and the photoresists151on both surfaces at the +Y′ axis side and the −Y′ axis side. First, the anticorrosion films150are formed on the surfaces at the +Y′ axis side and the −Y′ axis side of the base wafer W120. Further, the photoresists151are formed on surfaces of the anticorrosion films150. The anticorrosion films150are formed by sputtering, evaporation, or the like of metal films on the base wafer W120. For example, the anticorrosion films150are formed as follows. On the base wafer W220, a film of Nickel (Ni), Chromium (Cr), Titanium (Ti), Nickel-Tungsten (NiW), or the like is formed as a foundation. On the foundation, a film of gold (Au), silver (Ag), or the like is then formed. The photoresists151are uniformly applied over the surfaces of the anticorrosion films150by a technique of spin coat or the like.

In step S203, the photoresists151are exposed and developed, and the anticorrosion films150are etched.FIG. 6Cis a partial cross-sectional view of the base wafer W120where the photoresists151and the anticorrosion films150are partially removed on the surface at the −Y′ axis side. Regions where the photoresists151and the anticorrosion films150are removed in step S203are regions144. In the regions144, the through-holes143are formed on the surface at the −Y′ axis side of the base wafer W120. The regions144are formed in a circular shape, and their diameters are formed to be a length WX1.

In step S204, the base wafer W120is etched by wet etching. This partially forms the through-holes143.FIG. 6Dis a partial cross-sectional view of the base wafer W120where the through-holes143are partially etched by wet etching. In step S204, a piezoelectric material, which is exposed in the regions144in step S203, is etched by wet etching. This forms first through-holes143a, which are each a part of the through-hole143, on a surface at the −Y′ axis side of the base wafer W120. The piezoelectric material may have an anisotropic nature in etching. It is difficult for etchant to circulate deep into the first through-holes143ain the base wafer W120. Thus, the first through-holes143aare formed to have smaller opening diameters as the first through-hole143abecomes deeper in the +Y′ axis direction. Assume that the diameter of the first through-hole143ais a length WX2, and the length WX1is larger than the length WX2. Depth of the first through-hole143ain the Y′ axis direction is formed to be a first distance HY1. The first through-hole143aforms the first surfaces127aof the castellations127in the base plate (seeFIGS. 2A to 2C).

In step S205ofFIG. 7A, the anticorrosion films150and the photoresists151are formed on both main surfaces that are surfaces at the +Y′ axis side and the −Y′ axis side of the base wafer W120. Step S205inFIG. 7Ais a step which is sequentially performed after step S204inFIG. 6D.FIG. 7Ais a partial cross-sectional view of the base wafer W120where the anticorrosion films150and the photoresists151are formed on surfaces at the +Y′ axis side and the −Y′ axis side. After step S204, the anticorrosion films150and the photoresists151on the base wafer W120are all removed. The anticorrosion films150and the photoresists151are again formed on whole surfaces at the +Y′ axis side and the −Y′ axis side of the base wafer W120.

In step S206, the photoresists151are exposed and developed, and the anticorrosion films150are etched.FIG. 7Bis a partial cross-sectional view of the base wafer W120where the photoresists151are exposed and developed, and the anticorrosion films150are etched. The anticorrosion films150and the photoresists151to be removed are located in regions145and regions146. The region145is region where the through-hole143on the surface at the +Y′ axis side of the base wafer W120is formed. The region146is a region where the recess123is formed. The regions145are each formed to be in a circular shape with a diameter of a length WX3, which is longer than the length WX2.

In step S207, the base wafer W120is etched by wet etching. This partially forms the recesses123and the through-holes143.FIG. 7Cis a partial cross-sectional view of the base wafer W120where parts of the through-holes143and the recesses123are formed by wet etching. In step S207, the piezoelectric material exposed at the regions145and the regions146in step S206are etched by wet etching. This forms second through-holes143bthat are the parts of the through-holes143and the recesses123on the surface at the +Y′ axis side of the base wafer W120. The second through-holes143bare formed to have smaller opening diameters as the second through-holes143bbecomes deeper in the −Y′ axis direction. Depths of the second through-holes143bin the Y′ axis direction are each formed to be a second distance HY2, which is shorter than the first distance HY1. Forming the second through-holes143bforms the second surfaces127b(seeFIGS. 2A to 2C) of the castellations127in the base plate.

In step S208, the photoresists151and the anticorrosion films150are removed.FIG. 7Dis a partial cross-sectional view of the base wafer W120where the photoresists151and the anticorrosion films150are removed.FIG. 7Dis a cross-sectional view taken along the line B-B ofFIG. 5. In step S208, the photoresists151and the anticorrosion films150are removed. This prepares the base wafer W120including the recesses123and the through-holes143. The through-holes143each include the first surface127aand the second surface127b, and also include an intermediate portion127cbetween the first surface127aand the second surface127b. The through-holes143are each formed to have the intermediate portion127cwith a diameter of the length WX2.

Returning toFIG. 3, in step S103, a lid wafer W110is prepared. In the lid wafer W110, the recesses111are formed on the surface at the −Y′ axis side. This forms a plurality of lid plates110in the lid wafer W110.

In step S104, the base wafer W120and the piezoelectric wafer W130are bonded together. Step S104is a bonding step.FIG. 8Ais a partial cross-sectional view of a wafer where the piezoelectric wafer W130and the base wafer W120are bonded together.FIG. 8Aillustrates a cross-sectional view taken along the line B-B ofFIG. 5. The base wafer W120and the piezoelectric wafer W130are bonded such that the bonding surface122of the base wafer W120is bonded to the surface at the −Y′ axis side of the framing portion134in the piezoelectric wafer W130via the bonding material140. At this time, the bonding material140is not formed on the extraction electrodes132, which face the through-holes143. The base wafer W120and the piezoelectric wafer W130are bonded together such that the piezoelectric vibrating piece130aoverlaps with the base plate120a, while the piezoelectric vibrating piece130boverlaps with the base plate120b.

In step S105, the piezoelectric wafer W130and the lid wafer W110are bonded together.FIG. 8Bis a partial cross-sectional view of a wafer where the piezoelectric wafer W130and the lid wafer W110are bonded together. The lid wafer W110and the piezoelectric wafer W130are bonded such that the bonding surface112of the lid wafer W110is bonded to the surface at the +Y′ axis side of the framing portion134in the piezoelectric wafer W130via the bonding material140.

In step S106, electrodes are formed on the base wafer W120.FIG. 8Cis a partial cross-sectional view of a wafer where the electrodes are formed on the base wafer W120. Step S106is a wiring forming step. A metal film is formed on a surface at the −Y′ axis side of the base wafer W120by sputtering, vacuum-deposition, or the like. This forms the grounding terminals126, the external electrodes125, and the wiring electrodes128on the base wafer W120. For example, the metal film is formed by forming a chromium (Cr) film and further forming a gold (Au) film on the chromium film on the base wafer W120through a mask147. The external electrodes125and the wiring electrodes128are formed in the same step. Thus, the external electrodes125and the wiring electrodes128may be formed of the same metal films that are continuously connected together. The openings at the +Y′ axis side of the through-holes143are closed by the framing portion134of the piezoelectric wafer W130. This forms the metal film over all the through-holes143. Further, the metal film is also formed on the surfaces, which are exposed toward the through-holes143, of the bonding material140and the extraction electrodes132. Accordingly, step S106electrically connects the external electrodes125, the wiring electrodes128, and the extraction electrodes132together.

In step S107, the wafer with the electrodes formed in step S106is cut by dicing. In the step S107, the wafer is diced using a dicing saw (not shown) or the like along the scribe lines142inFIG. 4,FIG. 5, andFIG. 8AtoFIG. 8C. This cuts the wafer into the individual piezoelectric devices100.

In the method for manufacturing the piezoelectric device100, sputtering or vacuum-deposition is not performed on the surface at the +Y′ axis side of the base wafer W120. This preferably facilitates the manufacturing process. Sputtering or vacuum-deposition is not performed on the surface at the +Y′ axis side of the base wafer W120. This preferably reduces usage of the electrode material. Further, in the through-holes143of the base plate, the first surfaces127a, which each have the normal vector with a component in the −Y′ axis direction, are formed to have larger area than those of the second surfaces127b. This facilitates performing evaporation of the metal film on the through-holes143with the large first surfaces127afrom the −Y′ axis side of the base wafer W120. The second surfaces127bare each formed to have a small area and have the opening at the +Y′ axis side of the through-hole143closed by the framing portion134of each piezoelectric vibrating piece. This facilitates forming the metal film also on the second surface127b. That is, in the piezoelectric device100, forming the electrodes on the through-holes143is facilitated.

Second Embodiment

The base plate may employ glass as base material. Glass does not have an anisotropic nature in wet etching. Thus, in the case where the base plate employs glass as base material, the castellations have different shapes from those of the castellations in the first embodiment. A piezoelectric device where the base plate that employs glass as base material is used will be described below. In the following description, like reference numerals designate corresponding or identical elements of the piezoelectric vibrating piece in the first the embodiment, and therefore such elements will not be further elaborated here.

Configuration of a Piezoelectric Device200

FIG. 9is an exploded perspective view of the piezoelectric device200. The piezoelectric device200mainly includes the lid plate110, a base plate220, and the piezoelectric vibrating piece130a. In the piezoelectric device200, the base plate220employs glass as base material.

The base plate220is formed in a rectangular that has long sides extending in the X axis direction and short sides extending in the Z′ axis direction. The base plate220has a surface at the −Y′ axis side that is a mounting surface on which the external electrodes225(seeFIG. 10A) and the grounding terminals226(seeFIG. 10C) are to be formed. The external electrodes225are electrodes for soldering and electrically connecting the piezoelectric device200to a printed circuit board or the like. The grounding terminals226are terminals for discharging static electricity and the like, which are charged on the piezoelectric device200. The bonding material140is applied over a bonding surface222at the +Y′ axis side of the base plate220. Then, the base plate220is bonded to the piezoelectric vibrating piece130a. Further, the base plate220includes a recess223, which is formed to be hollowed into the bonding surface222in the −Y′ axis direction. On side faces of corner portions at four corners of the base plate220, castellations227are formed to be recessed inward the base plate220. The castellations227are formed to extend to the long sides and the short sides of the base plate220. Each of the castellations227includes a first surface271, a second surface272, and a protruding surface273. The first surface271extends outward from the mounting surface toward the bonding surface222side. The second surface272extends outward from the bonding surface222toward the mounting surface. The second surface272has a smaller area than that of the first surface271. The protruding surface273is disposed between the first surface271and the second surface272. The protruding surface273protrudes outside of the base plate220farther than the first surfaces271and the second surfaces27. On the respective castellations227, wiring electrodes228are formed. The wiring electrodes228are electrically connected to the external electrodes225.

FIG. 10Ais a cross-sectional view taken along the line C-C ofFIG. 9. The piezoelectric device200is formed as follows. The bonding surface222of the base plate220and the surface at the −Y′ axis side of the framing portion134in the piezoelectric vibrating piece130aare bonded via the bonding material140. The bonding surface112of the lid plate110and the surface at the +Y′ axis side of the framing portion134in the piezoelectric vibrating piece130aare bonded via the bonding material140. Each of the castellations227of the base plate220includes the first surface271, the second surface272, and the protruding surface273. The first surfaces271and the second surfaces272are formed as curved surfaces that are hollowed into the base plate220. The protruding surface273is formed to protrude outside the base plate220. On the surface at the −Y′ axis side of the base plate220, grounding terminals226(seeFIG. 10C) and the external electrodes225are formed. On the castellations227, the wiring electrodes228are formed. The wiring electrodes228and the external electrodes225may be formed of the same electrode layer that are continuously connected together. The wiring electrode228electrically connects the external electrode225and the extraction electrode132, which is formed on the framing portion134of the piezoelectric vibrating piece130a, together.

FIG. 10Bis a plan view of the base plate220. The surface at the +Y′ axis side of the base plate220does not have any electrode. On the castellations227at the +X axis side and the −Z′ axis side and castellations227at the −X axis side and the +Z′ axis side of the base plate220, the wiring electrodes228are formed after the base plate220is bonded to the piezoelectric vibrating piece130a. The wiring electrode228formed on the castellations227are formed not to contact short sides parallel to the Z′ axis of the base plate220or long sides parallel to the X axis. That is, in the X-Z′ plane, the wiring electrodes228are not formed on end portions227a, which are in contact with the short sides or long sides in the base plate220, of the castellations227. At the end portions227aof the castellations227, the glass is exposed outside.

FIG. 10Cis a plan view of the base plate220illustrating the external electrodes225and the grounding terminals226.FIG. 10Cis a transparent view of the base plate220from the +Y′ axis side of the base plate220illustrating the external electrodes225and the grounding terminals226, which are formed on the surface at the −Y′ axis side of the base plate220. The external electrodes225are formed to contact the castellations227but not to contact the short sides or the long sides of the base plate220. The grounding terminals226are formed not to contact the short sides of the base plate220, the long sides of the base plate220, or the castellations227.

The piezoelectric device200includes the first surfaces271of the castellations227in the base plate220. The first surfaces271have the curved surfaces hollowed into the base plate220. This prevents solder from reaching the bonding surface222in the case where the piezoelectric device200is mounted on a printed circuit board or the like, thus appropriately reducing an influence of the solder on the bonding material140. In the piezoelectric device200, the second surfaces272are each formed to have a small area. This forms the bonding surfaces222with a large area in the base plate220. Accordingly, the bonding material140preferably has a large forming area.

A Method for Manufacturing the Piezoelectric Device200

The piezoelectric device200is formed in accordance with the flowchart ofFIG. 3, similarly to the piezoelectric device100. The method for manufacturing the piezoelectric device200will be described below by referring toFIG. 3.

In step S101, a piezoelectric wafer W230is prepared. The piezoelectric wafer W230is a wafer formed of glass, and includes a plurality of piezoelectric vibrating pieces130a.

FIG. 11is a plan view of the piezoelectric wafer W230. In the piezoelectric wafer W230, the piezoelectric vibrating pieces130aare arranged in the X axis direction and the Z′ axis direction.FIG. 11illustrates the scribe lines142by two-dot chain lines at boundaries of the respective piezoelectric vibrating pieces130anext to one another. The extraction electrodes132of each piezoelectric vibrating piece130ainFIG. 11are not electrically connected to the extraction electrodes132of another piezoelectric vibrating piece130a.

In step S102, the base wafer W220is prepared. The base wafer W220includes the recesses223and through-holes243, which pass through the base wafer W220in the Y′ axis direction. This forms a plurality of base plates220in the base wafer W220.

FIG. 12is a plan view of the base wafer W220. The base wafer W220includes the base plates220that are arranged in the X axis direction and the Z′ axis direction.FIG. 12illustrates the scribe lines142by two-dot chain lines at boundaries of the respective the base plates220next to one another. At intersection points of the scribe lines142that extend in the X axis direction and the Z′ axis direction, the through-holes243are formed. The through-holes243pass through the base wafer W220in the Y′ axis direction, and extend in the X axis direction and the Z′ axis direction along the scribe lines142. Thus, the through-holes243are formed in the four corners of the respective the base plates220. The through-holes243make the castellations227after the wafer is diced in step S107described later.

FIGS. 13A to 13D,14A to14D, and15A to15C are diagrams illustrating respective steps of a flowchart of a method for manufacturing the base wafer W220inFIG. 12. In the right side of respective steps inFIGS. 13A to 13D,14A to14D, and15A to15C, diagrams to describe the respective steps are illustrated. These diagrams, which describe the respective steps inFIGS. 13A to 13D,14A to14D, and15A to15C, are cross-sectional views corresponding to cross-sectional surfaces of the base wafer W220taken along the line D-D ofFIG. 12. The method for manufacturing the base wafer W220will be described below by referring toFIGS. 13A to 13D,14A to14D, and15A to15C.

In step S211ofFIG. 13A, a wafer formed of glass is prepared.FIG. 13Aillustrates a partial cross-sectional view of the base wafer W220formed of glass. The wafer prepared in step S211has planar surfaces at the +Y′ axis side and the −Y′ axis side as illustrated inFIG. 13A.

In step S212, the anticorrosion films150and the photoresists151are formed on both the surfaces at the +Y′ axis side and the −Y′ axis side of the base wafer W220.FIG. 13Billustrates a partial cross-sectional view of the base wafer W220with the anticorrosion films150and the photoresists151. As illustrated inFIG. 13B, the anticorrosion films150are formed on the surfaces at the +Y′ axis side and the −Y′ axis side of the base wafer W220. Further, the photoresists151are formed on surfaces of the anticorrosion films150. The anticorrosion films150are formed by sputtering, vacuum-deposition, or the like of metal films on the base wafer W220. For example, the anticorrosion films150are formed as follows. On the base wafer W220, a film of Nickel (Ni), Chromium (Cr), Titanium (Ti), Nickel-Tungsten (NiW), or the like is formed as a foundation. On the foundation, a film of gold (Au), silver (Ag), or the like is then formed. The photoresists151are uniformly applied over the surfaces of the anticorrosion films150by a technique of spin coat or the like.

In step S213, the photoresists151are exposed and developed.FIG. 13Cillustrates a partial cross-sectional view of the base wafer W220where the photoresists151are exposed and developed. Portions where the photoresists151are exposed and developed in step S213form recessed regions160and penetration regions161. The recessed regions160are regions that correspond to the recesses223(seeFIG. 9) on the surface at the +Y′ axis side of the base wafer W220. The penetration regions161are regions that correspond to the through-holes243on the surface at the −Y′ axis side of the base wafer W220. In the case where the base material of the base wafer W220is glass, regions that are etched by wet etching in the base wafer W220are expanded. Thus, the recessed regions160and the penetration regions161are formed to be smaller than the respective regions of the recesses223and the through-holes243. Assume that a width in the X axis direction of the penetration region161is a width WA1, it is preferred that the width WA1be formed to ensure the small through-holes243, so as not to make the through-holes243excessively large.

In step S214, the anticorrosion films150are etched.FIG. 13Dillustrates a partial cross-sectional view of the base wafer W220with the etched anticorrosion films150. In step S214, the anticorrosion films150in the recessed regions160, where the photoresists151are exposed and developed in step S213, and in the penetration regions161are removed by etching.

In step S215ofFIG. 14A, the base wafer W220is etched by wet etching.FIG. 14Aillustrates a partial cross-sectional view of the base wafer W220with etched glass. In step S215, the glass in the recessed regions160and the penetration regions161are dipped in etchant. This performs wet etching on the recessed regions160and the penetration regions161so as to each have a depth HA1. In the wet etching on the glass, a portion below the anticorrosion film150is also etched. Accordingly, for example, a width WA2of glass in X axis direction, which is etched in the penetration region161becomes larger than the width WA1(seeFIG. 13C) of the penetration region161in the X axis direction.

In step S216, the anticorrosion films150and the photoresists151on the surface at the +Y′ axis side of the base wafer W220are removed. Subsequently, the anticorrosion film150is again formed on the surface at the +Y′ axis side of the base wafer W220, and the photoresist151is then formed on the surface of the anticorrosion film150.FIG. 14Billustrates a partial cross-sectional view of the base wafer W220where the anticorrosion film150and the photoresist151are formed on the surface at the +Y′ axis side. The anticorrosion films150and the photoresists151are formed on the whole surface at the +Y′ axis side of the base wafer W220.

In step S217, the photoresist151is exposed and developed.FIG. 14Cillustrates a partial cross-sectional view of the base wafer W220where the photoresist151on the surface at the +Y′ axis side is exposed and developed. Portions where the photoresist151is exposed and developed in step S217are the penetration regions162corresponding to the through-holes243on the surface at the +Y′ axis side. Similarly to the recessed regions160and the penetration regions161, the base wafer W220has expanded etched regions by wet etching. Accordingly, the penetration regions162are formed to be smaller than regions of the through-holes243on the surface at the +Y′ axis side. A width of the penetration region162in the X axis direction is assumed to be a width WA3.

In step S218, the anticorrosion films150is etched.FIG. 14Dillustrates a partial cross-sectional view of the base wafer W220with etched anticorrosion films150. In step S218, the anticorrosion film150on the penetration regions162are etched to be removed.

In step S219ofFIG. 15A, the base wafer W220is etched by wet etching.FIG. 15Aillustrates a partial cross-sectional view of the base wafer W220with etched glass. In step S219, the glass exposed in the penetration regions161and the penetration regions162are dipped in etchant for wet etching. This forms the penetration region161to have a depth of a depth HA3, and forms the penetration region162to have a depth of a depth HA2. A size of the depth HA3of the penetration region161is a sum of the depth HA1(seeFIG. 14A) and the depth HA2. As a result of the wet etching, a width of the glass in the X axis direction, which is etched by wet etching in each penetration region162, becomes a width WA5, while a width of the glass in the X axis direction, which is etched by wet etching in each penetration region161, becomes a width WA4. The width WA5is larger than the width WA3(seeFIG. 14C), the width WA4is larger than the width WA2(seeFIG. 14A), and the width WA4is larger than the width WA5.

In step S220, the anticorrosion films150and the photoresists151are removed.FIG. 15Billustrates a partial cross-sectional view of the base wafer W220where the anticorrosion films150and the photoresists151are removed. In the base wafer W220ofFIG. 15B, the recesses223are formed on the respective base plates220. The glass in a position of each through-hole243has a thickness HA4.

In step S221, the through-holes243are formed by sand-blasting.FIG. 15Cillustrates a partial cross-sectional view of the base wafer W220where the through-holes243are formed by sand-blasting. In step S221, sand-blasting is performed to spray polishing material onto the surface at the −Y′ axis side of the base wafer W220. This passes through the through-holes243, thus forming the protruding surfaces273.FIG. 15Cis a cross-sectional view taken along the line D-D ofFIG. 12.

Returning toFIG. 3, in step S103, the lid wafer W110is prepared. In the lid wafer W110, the recesses111are formed on the surface at the −Y′ axis side. This forms the plurality of lid plates110in the lid wafer W110.

In step S104, the base wafer W220and the piezoelectric wafer W230are bonded together. Step S104is a bonding step.FIG. 16Ais a partial cross-sectional view of a wafer where the piezoelectric wafer W230and the base wafer W220are bonded together.FIG. 16Aillustrates a cross-sectional view taken along the line D-D ofFIG. 12. The base wafer W220and the piezoelectric wafer W230are bonded such that the bonding surface222of the base wafer W220is bonded to the surface at the −Y′axis side of the framing portion134in the piezoelectric wafer W230via the bonding material140. At this time, the bonding material140is not formed on the extraction electrodes132, which face the through-holes243.FIG. 16Aillustrates that the extraction electrodes132are not formed on the scribe lines142.

In step S105, the piezoelectric wafer W230and the lid wafer W110are bonded together.FIG. 16Bis a partial cross-sectional view of a wafer where the piezoelectric wafer W230and the lid wafer W110are bonded together. The lid wafer W110and the piezoelectric wafer W230are bonded such that the bonding surface112of the lid wafer W110is bonded to the surface at the +Y′ axis side of the framing portion134in the piezoelectric wafer W230via the bonding material140.

In step S106, electrodes are formed on the base wafer W220.FIG. 16Cis a partial cross-sectional view of a wafer where the electrodes are formed on the base wafer W220. Step S106is a wiring forming step. A metal film is formed on the surface at the −Y′ axis side of the base wafer W220by sputtering, vacuum-deposition or the like. This forms the grounding terminals226, the external electrodes225, and the wiring electrodes228on the base wafer W220. For example, the metal film is formed by forming a chromium (Cr) film and further forming a gold (Au) film on the chromium film on the base wafer W220through a mask148. The external electrodes225and the wiring electrodes228are formed in the same step. Thus, the external electrodes225and the wiring electrodes228are formed of the same metal film that are continuously connected together. The openings at the +Y′ axis side of the through-holes243are closed by the framing portion134of the piezoelectric wafer W230. This forms the metal film over all the through-holes243. Further, the metal film is also formed on the surfaces of the bonding material140and the extraction electrodes132, which are both exposed to the through-holes243. Accordingly, this step S106electrically connects the external electrodes225, the wiring electrodes228, and the extraction electrodes132together. This forms a plurality of piezoelectric devices200on the wafer. InFIG. 16C, the mask148is also arranged on the scribe lines142. The piezoelectric device200includes the adjacent wiring electrodes228in the respective through-holes243. The adjacent wiring electrodes228are not electrically connected together.

FIG. 17Ais a plan view of the base wafer W220illustrating the surface with electrodes at the −Y′ axis side. The electrodes on the base wafer W220are not formed on the scribe lines142as illustrated inFIG. 17A. Thus, the grounding terminals226and the external electrodes225on each base plate220are not electrically connected to the grounding terminals226or the external electrodes225on an adjacent base plate220. As illustrated inFIG. 16C, the wiring electrodes228and the extraction electrodes132of the piezoelectric device200are not electrically connected to those of an adjacent piezoelectric device200. Thus, each of the piezoelectric devices200on the wafer is not electrically connected to another piezoelectric device200. Accordingly, as illustrated inFIG. 17A, a pair of probes149are brought in contact with a pair of external electrodes225on each piezoelectric device200after forming the electrodes on the base wafer W220. This allows to check the vibration frequency of each piezoelectric device200.

FIG. 17Bis an enlarged plan view of the region171inFIG. 17A.FIG. 17Billustrates a part of the mask148used in step S106. The mask148includes first openings and second openings. The first openings are openings used to form the external electrodes225. The second openings are openings used to form the wiring electrodes228on the through-hole243. The first openings are connected to the respective second openings. The first openings each have approximately the same shape as a planar shape of each external electrode225. The second openings each have a planar shape that is slightly larger toward the through-hole243side than a shape of each wiring electrode228in the X-Z′ plane on the through-holes243. As illustrated inFIG. 17B, the wiring electrodes228are formed on only a part of the through-holes243. Accordingly, the second opening to form the wiring electrodes228has a smaller area than that of the through-hole243. The mask148also has openings to form the grounding terminals226.

In step S107ofFIG. 3, the wafer on which the electrodes are formed in step S106is cut by dicing. The dicing is performed using a dicing saw along the scribe lines142, thus cutting the wafer into the individual piezoelectric devices200.

In the manufacturing process of the piezoelectric device, while dicing the wafer, the dicing saw possibly catches the electrodes on the piezoelectric device, thus causing delamination of the electrodes. In the case where the dicing saw cuts the electrodes along with the wafer, areas of the electrodes in the respective piezoelectric devices are different in each of the piezoelectric devices due to misalignment of the dicing. This causes a problem in that crystal impedance (CI) value varies among the piezoelectric devices. In the method for manufacturing the piezoelectric device200, as illustrated inFIGS. 16C and 17B, the wiring electrodes228are not formed on the scribe lines142. This prevents the dicing of wafer from affecting the wiring electrodes228of the piezoelectric device200. This avoids the variation in crystal impedance (CI) value of each piezoelectric device due to uniformity in size of the area of electrodes on each piezoelectric device.

Various shapes of castellations formed on a base plate have been contrived. As modifications of castellations formed on base plates, a base plate320and a base plate420will be described below. The base plate320has castellations that extend from respective corner portions of the base plate in the short side direction. The base plate420has castellations that are formed at the short sides of the base plate so as not to include a corner portion of the base plate.

Configuration of the Base Plate320

FIG. 18Ais a perspective view of the base plate320. The base plate320is formed in a rectangular shape that has long sides extending in the X axis direction and short sides extending in the Z′ axis direction. The base plate320has a surface at the −Y′ axis side that is a mounting surface on which external electrodes325(seeFIG. 18B) and grounding terminals326(seeFIG. 18B) are to be formed. The bonding material140is applied over a bonding surface322at the +Y′ axis side of the base plate320. The base plate320is then bonded to the piezoelectric vibrating piece130a. Further, a recess323is formed to be hollowed into the bonding surface322in the −Y′ axis direction in the base plate320. On side faces of corner portions at four corners of the base plate320, castellations327are recessed inwardly into the base plate320. The castellations327extend from the respective corner portions of the base plate320in the short side direction. The castellation327includes a first surface371, a second surface372, and a protruding surface373. The first surface371extends outward from the mounting surface toward the bonding surface322side. The second surface372extends outward from the bonding surface322to the mounting surface. The second surface372has a smaller area than that of the first surfaces371. The protruding surface373is disposed between the first surfaces371and the second surfaces372. The protruding surface373protrudes outside of the base plate320farther than the first surfaces371and the second surfaces372. In the case where the base plate320constitutes a part of the piezoelectric device, a wiring electrode328is formed on each of the castellations327of the base plate320. The wiring electrodes328are electrically connected to the external electrodes325and the extraction electrodes132of the piezoelectric vibrating piece130a.

FIG. 18Bis a plan view of the base plate320illustrating the external electrodes325and the grounding terminals326.FIG. 18Bis a transparent view of the base plate320from the +Y′ axis side of the base plate320, illustrating the external electrodes325and the grounding terminals326, which are formed on the surface at the −Y′ axis side of the base plate320. The external electrodes325are formed to contact the castellations327. The grounding terminals326are formed not to contact the castellations327. The external electrode325is electrically connected to the wiring electrode328.

FIG. 18Cis a partial plan view of the surface at the −Y′ axis side of the base wafer where the base plates320are formed.FIG. 18Cis a diagram illustrating a region similar to that ofFIG. 17B.FIG. 18CandFIG. 17Bare different in shape of the through-holes.FIG. 18Cillustrates a through-hole343that is formed at an intersection point of the scribe lines142. The through-hole343has a rectangular shape that extends in the Z′ axis direction. The through-hole343extends in the Z′ axis direction. This separates a pair of wiring electrodes328, which are formed on one through-hole343, from one another. Accordingly, this prevents the pair of wiring electrodes328from being electrically connected to one another.

Configuration of the Base Plate420

FIG. 19Ais a perspective view of the base plate420. The base plate420is formed in a rectangular shape that has long sides extending in the X axis direction and short sides extending in the Z′ axis direction. The base plate420has a mounting surface at the −Y′ axis side on which external electrodes425(seeFIG. 19B) and grounding terminals426(seeFIG. 19B) are formed. The bonding material140is applied over a bonding surface422at the +Y′ axis side of the base plate420. The base plate420is then bonded to the piezoelectric vibrating piece130a. Further, a recess423is formed to be hollowed into the bonding surface422in the −Y′ axis direction in the base plate420. On side faces of the short sides that do not include corner portions at four corners of the base plate420, castellations427are recessed inwardly into the base plate420. The castellation427includes a first surface471, a second surface472, and a protruding surface473. The first surface471extends outward from the mounting surface toward the bonding surface422side. The second surface472extends outward from the bonding surface422toward the mounting surface. The second surface472has a smaller area than that of the first surface471. The protruding surface473is disposed between the first surfaces471and the second surfaces472. The protruding surface473protrudes outside of the base plate420farther than the first surfaces471and the second surfaces472. In the case where the base plate420constitutes a part of the piezoelectric device, a wiring electrode428is formed on each of the castellations427of the base plate420. The wiring electrode428is electrically connected to the external electrodes425and the extraction electrodes132of the piezoelectric vibrating piece130a.

FIG. 19Bis a plan view of the base plate420illustrating the external electrodes425and the grounding terminals426.FIG. 19Bis a transparent view of the base plate420from the +Y′ axis side of the base plate420, illustrating the external electrodes425and the grounding terminals426, which are formed on the surface at the −Y′ axis side of the base plate420. The external electrode425is formed to contact the castellation427. The grounding terminal426is formed not to contact the castellation427. The external electrode425and the grounding terminal426are not in contact with the short sides or the long sides of the base plate420. The external electrode425is electrically connected to the wiring electrode428.

FIG. 19Cis a partial plan view of the surface at the −Y′ axis side of the base wafer where the base plates420are formed.FIG. 19Cillustrates a half of the base plate420at the −X axis side and a half of the other base plate420at the +X axis side. These two base plates420are in contact with one another on the base wafer. The scribe line142that extends in the Z′ axis direction is illustrated between the two base plates420.FIG. 19Cillustrates the through-holes443that has a rectangular shape and extends in the Z′ axis direction. The through-hole443is formed on the scribe line142that extends in the Z′ axis direction. The through-hole443is not formed on the scribe line142that extends in the X axis direction. The through-hole443extends in the Z′ axis direction. This separates a pair of wiring electrodes428, which are formed on one through-hole443, from one another. Accordingly, this prevents the pair of wiring electrodes428from being electrically connected to one another.

Representative embodiments have been described in detail above. As evident to those skilled in the art, the present invention may be changed or modified in various ways within the technical scope of the invention.

For example, in the manufacturing process of the piezoelectric device100inFIG. 3, step S106of forming electrodes may be performed before step S105. In this case, while contacting probes on the external electrodes to measure a frequency of the piezoelectric vibrating piece, a metal may be added onto or removed from the excitation electrodes131on the surface at the +Y′ axis side of the piezoelectric vibrating piece. This ensures a facilitated frequency adjustment of the piezoelectric vibrating piece. The base plate that is made of glass as the base material in the second embodiment may be formed using the method inFIGS. 6A to 6Dand7A to7D. This method may form castellations without the protruding surface by forming the first surface and the second surface alone.

Further, while in the embodiments, the piezoelectric vibrating pieces are AT-cut quartz-crystal vibrating pieces, for example, a BT-cut or tuning-fork type quartz-crystal vibrating piece that vibrates in a thickness-shear vibration mode may also be used, similarly to the AT-cut quartz-crystal vibrating pieces. Further, the piezoelectric vibrating pieces are basically applied to piezoelectric material including not only quartz-crystal material but also lithium tantalite, lithium niobate, and piezoelectric ceramic.