Method for manufacturing piezoelectric oscillator

[0002] The present invention relates to a manufacturing method of a piezoelectric vibrator having a piezoelectric vibration piece hermetically sealed by lid members, and more particularly to a manufacturing method of a piezoelectric vibrator using anodic bonding.

[0003] As shown in FIG. 7, a conventional surface-mount type piezoelectric vibrator 50 is comprised of a piezoelectric vibrator piece 51, a container 52 fixing one end of the piezoelectric vibration piece 51, and a lid member 56 for sealing the container 52.

[0004] The container 52 fixed with the piezoelectric vibration piece 51 has a concave portion 53 defining a space sufficiently large to an extent not interfering with vibration of the piezoelectric vibration piece 51. In this concave portion 53 a step portion 54 is provided having a smaller depth than other portions. The piezoelectric vibration piece 51 is fixed on a top surface of the step portion 54 of the container 52 through an adhesive layer 55, such as a solder material or conductive adhesive. The container 52 is bonded thereon with the lid member 56 through a similar adhesive layer 55 used for fixing of the piezoelectric vibration piece 51, thus hermetically sealing the piezoelectric vibration piece 51 within the concave portion 53 of the container 52.

[0005] However, where a solder material is used as an adhesive layer 55 to bond the piezoelectric vibration piece 51 and the lid member 56, bonding is made by thermally fusing the solder member and accordingly gas is produced due to the fusing. Because the gas will be filled within the hermetically-sealed concave recess 53 of the container 52, there is the problem that an electrode film of the piezoelectric vibration piece 51 causes chemical change such as oxidation thus having an effect upon reliability of the piezoelectric vibrator.

[0006] Meanwhile, where a conductive adhesive is used as an adhesive layer 55, gas is produced due to an epoxy resin upon thermosetting thus resulting in a problem having a bad effect upon the piezoelectric vibration piece similarly to the solder material.

[0007] Furthermore, there is a possibility that such a gas occurs to heating in mounting process, particularly in a reflow process or during environmental testing, after completing production of a piezoelectric vibrator.

[0008] The present invention has been made in view of such a circumstance, and it is an object to provide a manufacturing method of a piezoelectric vibrator which is free from lowering of piezoelectric vibrator characteristic.

[0009] A first aspect of the present invention for solving the above problem lies in, in a manufacturing method of a piezoelectric vibrator having a piezoelectric vibration plate having a piezoelectric vibration piece and a frame portion integrally connected with a base portion thereof and surrounding the piezoelectric vibration piece, on respective sides of which a pair of lid members are bonded to hermetically seal the piezoelectric vibration piece without interfering with vibration of the piezoelectric vibration piece, the manufacturing method of the piezoelectric vibrator comprising a step of: forming a metal film generally over an entire surfaces of respective surfaces of the piezoelectric vibration plate; patterning the metal film to form oscillation electrode films on both surfaces of the piezoelectric vibration piece and forming bonding films to be bonded to the pair of lid members in a corresponding area to the both surfaces of the frame portion; and laminating the piezoelectric vibration plate and the pair of lid members through the bonding films on both surfaces of the frame portion of the piezoelectric vibration plate by applying a temperature of 100-200° C. and applying a voltage of 0.5-5.0 kV to the lid members and the bonding films with the piezoelectric vibration plate side rendered as an anode.

[0010] A second aspect of the invention lies, in that in the first aspect, the lid members are formed of soda-lime glass and the metal film is formed of an aluminum alloy.

[0011] In the above invention, it is possible to form a piezoelectric vibration plate and lid members through a bonding film positively and easily.

[0012] FIG. 1 is an exploded perspective view of a piezoelectric vibrator according to one embodiment of the present invention;

[0013] FIG. 2 is a sectional view of a piezoelectric vibrator according to the one embodiment of the invention;

[0014] FIG. 3 is a sectional view showing a manufacturing process for a piezoelectric vibrator of the invention;

[0015] FIG. 4 is a schematic view showing a manufacture process for a piezoelectric element of the invention;

[0016] FIG. 5 is a sectional view showing another example of a piezoelectric vibrator according to the invention;

[0017] FIG. 6 is a sectional view showing another example of a piezoelectric vibrator according to the invention; and

[0018] FIG. 7 is a sectional view of a piezoelectric element according to a prior art.

[0019] Embodiments of the present invention will now be described with reference to the drawings.

[0020] FIG. 1 is an exploded perspective view showing one embodiment of a piezoelectric vibrator, and FIG. 2 is a sectional view thereof.

[0021] A piezoelectric vibrator of this embodiment is, for example, a quartz crystal vibrator having a tuning fork type quartz crystal vibration piece formed of quartz (SiO₂). As shown in the FIG. 1, the piezoelectric vibrator is made up by a quartz crystal plate 12 having a quartz crystal vibration piece 11, and a pair of lid members 14 to be bonded onto respective surfaces of the quartz crystal plate 12 to hermetically seal the quartz crystal vibration piece 11 for vibration.

[0022] The quartz crystal plate 12 of this embodiment has the tuning fork type quartz crystal vibration piece or tine 11 and a frame portion 15 connected integrally with a base portion thereof in a manner surrounding the quartz crystal vibration piece 11.

[0023] The pair of lid members 14 are each formed, for example, of soda-lime glass or the like and have a concave portion or recess 13 to define a space large enough to an extent so as not to prevent vibration of the quartz crystal vibration plate 11 and formed an area in corresponding to the quartz crystal vibration piece 11.

[0024] Also, as shown in FIG. 2, the quartz crystal plate 12 has oscillation electrode films 16 formed on its top and bottom both surfaces and side surfaces thereof to vibrate the quartz crystal vibration piece 11, and also has bonding films 17 formed of the same material as the oscillation electrode films 16 in corresponding areas to both surfaces of the frame 15 to provide actual bonding to the lid members 14. This bonding films 17 and the lid members 14 are bonded by so-called anodic bonding, as hereinafter described in greater detail, thereby providing bonding between the quartz crystal plate 12 and the lid members 14.

[0025] Also, the oscillation electrode film 16 extends to an end of the quartz crystal plate 12 and is connected with the bonding film 17. In this embodiment, the oscillation electrode films 16 have one pole electrode 16aconnected to a lead electrode 18athrough a terminal connection bonding film 17a. Also, the other electrode 16bextends to a terminal connection bonding film 17bthrough an electrode provided for connection on the side surface of the quartz vibration piece 11, and is connected to a lead electrode 18b.

[0026] Incidentally, at least part of the bonding films 17 formed on the respective surfaces of the quartz crystal plate 12 are formed respectively to surround the concave portions 13 on both surface. This, after bonding, provides hermetic seal to the concave portions 13.

[0027] Hereunder, an explanation is made of a manufacturing, process for the quartz crystal resonator constructed as described above. Incidentally, FIG. 3 is a perspective view illustrating a manufacturing process for the piezoelectric vibrator according to the embodiment.

[0028] First, as shown FIG. 3A, a quartz wafer to be formed into a quartz crystal plate 12 is etched to form a quartz crystal vibration piece 11 as an actual driving portion and a frame 15 surrounding the same.

[0029] Next, as shown in FIG. 3B, a metal film 20 is formed by sputtering or the like over almost the entire area of the respective surfaces of the quartz crystal plate 12. This metal film 20 is a film serving as an oscillation electrode film 16 for vibrating the quartz crystal vibration piece 11 and bonding films 17 used as actual bonding portions for bonding the frame to the lid members 14. The material of the metal film is not especially limited but preferably uses, for example, an aluminum alloy or the like.

[0030] Next, as shown in FIG. 3C, the metal film 20 is patterned to form oscillation electrode films 16 and a surrounding bonding film 17 in an entire peripheral area corresponding to the frame 15.

[0031] Next, as shown in FIG. 4, lid members 14 are bonded onto the opposite surfaces of the quartz crystal resonator 10 through the bonding films 17 by anodic bonding in an inert gas or vacuum, hermetically sealing the quartz crystal vibration piece 11 within the respective concave portions 13 of the lid members 14. At this time, it is preferred that the members are heated within the range 100 to 200° C. and a direct current voltage of 0.5 to 5.0 kV is applied to the bonding films 17 on the respective surfaces of the quartz crystal plate 12 and the lid members 14 by a direct current power source 30 such that an anode electrode is on the bonding films 17 side. For example, in this embodiment, the members were heated up to approximately 120° C. and a direct current voltage of about 3.5 kv was applied.

[0032] In this manner, the bonding films 17 and the lid members 14 are well bonded by anodically bonding between the quartz crystal plate 12 and the lid members 14 through the bonding films 17 under the conditions as described above. That is, the quartz crystal plate 12 and the lid members 14 are well bonded through the bonding films 17 without causing cracks or the like.

[0033] Here, quartz as a material of the quartz crystal plate 12 has a thermal expansion coefficient of 13.7 ppm/° C. while soda-lime glass used for the lid members 14 has a thermal expansion coefficient of 8.5 ppm/° C. That is, these materials have a comparatively great difference in thermal expansion coefficient, i.e. 5.2 ppm/° C., and are difficult to anodically bond under the conventionally-known condition. However, in the present embodiment anodic bonding is made at a low bonding temperature of approximately 100 to 200° C. and by applying a comparatively high direct current voltage of about 0.5 to 5.0 kV. This reduces the effect of thermal expansion coefficient to an extremely small amount, thus preferred bonding is possible even for members that are comparatively large in thermal expansion coefficient.

[0034] Incidentally, in an actual process, bonding is made between a quartz wafer formed with a plurality of quartz crystal vibration pieces 11 and lid forming members formed with a plurality of lid members 14 having concave portions or recesses 13 in the corresponding area to the quartz crystal vibration piece 11 and thereafter cutting is performed at predetermined positions into individual quartz crystal resonators.

[0035] As described above, in the present embodiment anodic bonding is made between the quartz crystal plate 12 and the lid members 14 through the bonding films to seal the quartz crystal vibration piece 11. Accordingly, degassing or the like does not occur and there is no fear of lowering in vacuum. Meanwhile, because the oscillation electrode films 16 and the bonding films 17 are formed in the same material, they can be formed at the same time thereby simplifying the manufacturing process.

[0036] Incidentally, although in the above embodiment the oscillation electrode films 16 were extended to the end of the quartz crystal plate 12 and connected to the lead terminals 18aand 18bthe invention is not limited to this structure. For example, as shown in FIG. 5, a formed in the hole 19 through thickness direction for example may be formed in the lid member 14 in a corresponding area to the, frame portion 15 of the quartz crystal plate 12 so that connection can be made between the electrode film 16 and the lead electrode 18A through the through-hole 19.

[0037] Also, although in the above embodiment a space was defined by the concave portion 13 of the lid member 14 such that the quartz crystal vibration piece 11 is not interfered in vibration, the invention is not limited to this structure. For example, as shown in FIG. 6, the quartz crystal plate 12 for example may be reduced in thickness in an area to be formed into a quartz crystal vibration piece 11A without providing a concave portion in the lid member 14A.

[0038] Furthermore, although in the above embodiment the piezoelectric vibration plate was formed of quartz, the invention is not limited to this. Alternatively, it may be formed of ceramic or the like.

[0039] With any of these structures, certain and easy bonding is possible between the piezoelectric vibrator and the lid members in a manner as described above.

[0040] As explained above, in the present invention, the bonding films of a same material as oscillation electrode films are formed on the top and bottom both surfaces of the piezoelectric vibration plate so that the piezoelectric vibration plate and lid members are anodically bonded through the bonding film. Due to this, the piezoelectric vibration piece can be positively hermetically sealed. Also, the bonding film can be formed in a same process as the oscillation electrode film, providing an effect of simplifying the manufacture process.