Patent Application
20110193642
This application claims priority under 35 U.S.C. ยง119 to Japanese Patent Application No. 2010-024657 filed on Feb. 5, 2010, the entire content of which is hereby incorporated by reference.
The present invention relates to a piezoelectric vibrator which encloses a piezoelectric vibrating reed in a cavity formed between substrates and an oscillator using the same, and more particularly, to a small-sized piezoelectric vibrator.
In recent years, piezoelectric vibrators using crystals or the like have been used as time sources or timing sources for portable phones or portable information terminal devices. Various types of piezoelectric vibrators are known, and as an example, a surface-mounted piezoelectric vibrator is known. As the surface-mounted piezoelectric vibrator, there is one known having a three-layer structure type in which a piezoelectric substrate provided with a piezoelectric vibrating reed is interposed between a base substrate and a lid substrate in the vertical direction. The piezoelectric vibrating reed is accommodated in a cavity formed between the base substrate and the lid substrate. Recently, a piezoelectric vibrator with a two-layer structure type has been developed. In this type, a cavity is formed of a concave portion provided on an inner surface of the base substrate or the lid substrate, a piezoelectric vibrating reed is mounted on a surface of the base substrate, and the lid substrate is directly bonded to a periphery of the base substrate to accommodate the piezoelectric vibrating reed in the corresponding cavity. The piezoelectric vibrator with the two-layer structure type is excellent because it can achieve a reduction in thickness compared to the three-layer structure type (for example, refer to JP-A-2009-232449).
As illustrated in
A crystal plate is used for the piezoelectric vibrating reed 103. Through-electrodes 104a and 104b are implanted in the base substrate 101, and outer electrodes 105a and 105b and lead-out electrodes 107a and 107b are respectively connected to an outer surface and an inner surface of the base substrate 101. The piezoelectric vibrating reed 103 is mounted on the lead-out electrodes 107a and 107b.
As illustrated in
Excitation electrodes 109a and 109b are provided on both surfaces of the piezoelectric vibrating reed 103 to be opposite to each other, are electrically connected to terminal electrodes 111a and 111b provided under end portions of a lower side of the piezoelectric vibrating reed 103, and are respectively connected to the lead-out electrodes 107a and 107b via the mounting member 108. Therefore, the outer electrode 105a is electrically connected to the excitation electrode 109a via the through-electrode 104a, the lead-out electrode 107a, the mounting member 108, and the terminal electrode 111a. In addition, the outer electrode 105b is electrically connected to the excitation electrode 109b via the through-electrode 104b, the lead-out electrode 107b, the mounting member 108, and the terminal electrode 111b. That is, drive power is applied to the excitation electrodes 109a and 109b from the outer electrodes 105a and 105b to excite the piezoelectric vibrating reed 103, thereby generating a signal having a predetermined period.
In recent years, reduction in the sizes of portable devices and portable terminals has been progressing. With this, a reduction in the size of the piezoelectric vibrator 100 is also required. When the size of the piezoelectric vibrator 100 is reduced, the sizes of the piezoelectric vibrating reed 103 and the lead-out electrode 107 and areas of the bonding material 106 need to be reduced. However, for example, in a case where the crystal plate is used for the piezoelectric vibrating reed 103, if the size of the piezoelectric vibrating reed 103 is reduced, the CI value (crystal impedance value) is increased, and thus vibration characteristics are deteriorated. In addition, in order to stabilize the vibrations of the piezoelectric vibrating reed 103, the inside of the cavity 110 has to be blocked from the air. For example, the cavity 110 is maintained in a vacuum state. Accordingly, the bonding material 106 needs to have a certain degree of width.
In addition, when a parasitic capacitance occurs between the lead-out electrode 107b and the excitation electrode 109, the vibration characteristics are deteriorated. Accordingly, the lead-out electrodes 107b and the excitation electrode 109 need not to be overlapped with each other in a plan view. In addition, the base substrate 101 and the lid substrate 102 are heated when bonded to each other via the bonding material 106. Then, there may be a case where wiring resistance of the lead-out electrodes 107a and 107b is increased. In this point of view, in a case where the size of the piezoelectric vibrator 100 is reduced, the size of the piezoelectric vibrating reed 103 or the width of the bonding material 106 cannot be reduced by a necessary amount or greater, and consequently, the width of the lead-out electrode 107b is reduced and thus the resistance is increased, also resulting in deterioration of the vibration characteristics.
In order to solve the above problems, an object of the invention is to provide a piezoelectric vibrator capable of achieving a reduction in the size without deterioration of vibration characteristics.
A piezoelectric vibrator according to the invention includes: a base substrate; a piezoelectric vibrating reed which is held on a mounting portion formed on a surface of the base substrate in a cantilevered state; and a lid substrate which is bonded to the base substrate and covers and accommodates the piezoelectric vibrating reed, wherein the piezoelectric vibrating reed has first and second excitation electrodes on outer surfaces thereof for driving, the base substrate has first and second through-electrodes which penetrate from the surface thereof to the rear surface on the reverse side, a first lead-out electrode which is formed on the surface thereof and has one end connected to the first through-electrode and the other end connected to the mounting portion, and a first connection portion and a second connection portion which are electrically connected to the first lead-out electrode, the first connection portion being positioned in the vicinity of the mounting portion and the second connection portion being positioned in the vicinity of the first through-electrode, a conductor film is formed on a bonding surface where the base substrate and the lid substrate are bonded to each other, and the first lead-out electrode and the conductor film are electrically connected via the first and second connection portions, and the first excitation electrode is electrically connected to the first through-electrode via the mounting portion, and the first lead-out electrode, and the conductor film, and the second excitation electrode is electrically connected to the second through-electrode via the mounting portion.
In addition, the piezoelectric vibrating reed has a flat plate shape, and the first and second excitation electrodes are formed on the front and the rear surface of the flat panel shape to be opposite to each other, and the first lead-out electrode is installed at a position so as not to overlap with the first and second excitation electrodes as viewed in a direction normal to the surface of the base substrate.
In addition, the lid substrate has a concave portion for accommodating the piezoelectric vibrating reed, an upper surface of a side wall of the concave portion is bonded to the base substrate, first and second stepped portions are formed between the upper surface of the side wall and a bottom surface of the concave portion, first and second stepped electrodes are respectively formed from an inner surface of the side wall to upper surfaces of the first and second stepped portions, and the first stepped electrode electrically connects the conductor film to the first connection portion, and the second stepped electrode electrically connects the conductor film to the second connection portion.
An oscillator according to the invention includes: the piezoelectric vibrator according to any of the above descriptions; and a drive circuit for supplying a drive signal to the piezoelectric vibrator.
According to the invention, with regard to wires between the mounting portion and the first through-electrode, the first lead-out electrode formed on the base substrate is connected to the conductor film formed on the bonding surface where the lid substrate and the base substrate are bonded to each other in parallel, so that the resistance of the wires is reduced, thereby providing a small-sized piezoelectric vibrator which prevents degradation of vibration characteristics.
A piezoelectric vibrator according to the invention includes: a base substrate; a piezoelectric vibrating reed which is held on a mounting portion formed on a surface of the base substrate in a cantilevered state; and a lid substrate which accommodates and covers the piezoelectric vibrating reed and is bonded to a bonding portion on a peripheral portion of the base substrate. The piezoelectric vibrating reed has first and second excitation electrodes on its surface and the rear surface for causing excitation of the piezoelectric vibrating reed. The base substrate has first and second through-electrodes which penetrate from the surface thereof to the rear surface on the reverse side, a first lead-out electrode which is formed on the surface thereof and has one end connected to the first through-electrode and the other end connected to the mounting portion, and a first connection portion positioned in the vicinity of the mounting portion and a second connection portion positioned in the vicinity of the first through-electrode, which are electrically connected to the first lead-out electrode. A conductor film is formed on a bonding surface where the base substrate and the lid substrate are bonded to each other, and the first lead-out electrode and the conductor film are electrically connected via the first and second connection portions. As a result, the first excitation electrode is electrically connected to the first through-electrode via the mounting portion, the first lead-out electrode, and the conductor film, and the second excitation electrode is electrically connected to the second through-electrode via the mounting portion.
When the outer shape of the piezoelectric vibrator is reduced, it becomes difficult to form the first and second through-electrodes to be close in one side of the base substrate. Here, the first and second through-electrodes are formed at positions on the surface of the base substrate as far apart as possible. On the other hand, the piezoelectric vibrating reed needs to be installed on the mounting portion in the cantilevered state. Accordingly, when the lead-out electrode is formed on the base substrate, and the lead-out electrode needs to be drawn from any one of or both of the first and second through-electrodes which are separated from each other so as to be connected to the mounting portion. According to the invention, the first lead-out electrode is formed on the base substrate, the conductor film formed on the bonding portion where the base substrate and the lid substrate are bonded to each other and the first lead-out electrode are electrically connected via the first and second connection portions, and the conductor film formed on the bonding portion is used as the lead-out electrode. That is, between the mounting portion and the first through-electrode, the first lead-out electrode formed on the base substrate and the conductor film formed on the bonding portion are connected in parallel, thereby reducing the resistance between the mounting portion and the first through-electrode.
Moreover, the base substrate and the lid substrate may be made of a glass substrate. When the glass substrate is used, a molding process can be easily performed compared to a case where a ceramic substrate is used. In addition, since the glass material has a low thermal conductivity, an external temperature change is less likely to be transmitted to the piezoelectric vibrating reed, and a rapid temperature change is less likely to be influenced thereon. In addition, since the glass substrate is transparent, trimming can be performed using laser light after a package is assembled. In addition, the base substrate and the lid substrate can be bonded via the conductor film by anodic bonding, so that airtightness of the package can be maintained for a long time. In addition, a conductive adhesive may be used instead of the anodic bonding.
A crystal substrate in an AT mode can be used for the piezoelectric vibrating reed. A conductive adhesive material or a metal bump can be used for the mounting portion. When the metal bump is used, the piezoelectric vibrating reed can be mounted within a short time, so that adhesion of the piezoelectric vibration in the cantilevered state can be easily performed. The conductor film formed during the anodic bonding or the first lead-out electrode extending to the bonding surface may be used for the first and second connection portions. In addition, in the case where the base substrate and the lid substrate are bonded by the conductive adhesive, the conductive adhesive may be used. The metal bump or the conductive adhesive may be used for the first and second mounting portions.
In addition, the first and second excitation electrodes can be formed to be opposite to each other with the piezoelectric vibrating reed interposed therebetween, and the first lead-out electrode can be installed at a position so as not to overlap with the first and second excitation electrodes as viewed in a direction normal to the surface of the base substrate. Accordingly, parasitic capacitance that occurs between the first and second lead-out electrodes and the first and second excitation electrodes can be reduced, thereby stabilizing vibrations of the piezoelectric vibrating reed.
In addition, the concave portion for accommodating the piezoelectric vibrating reed in the lid substrate can be formed. The upper surface of the side wall of the concave portion is bonded to the peripheral portion of the base substrate. In this case, first and second stepped portions are formed between the bottom surface of the concave portion and the upper surface of the side wall thereof, and first and second stepped electrodes are formed from an inner surface of the side wall to upper surfaces of the first and second stepped portions. In addition, the first stepped electrode electrically connects the conductor film to the first connection portion, and the second stepped electrode electrically connects the conductor film to the second connection portion.
As such, the first and second stepped portions are formed at positions where the first and second connection portions are installed, and when the conductor film is connected via the first and second stepped electrodes, heights of the first and second connection portions can be reduced. For example, when distances of upper surfaces of the first and second stepped portions from the surface of the base substrate are set to be substantially the same as a distance of the surface of the piezoelectric vibrating reed on the mounting portion side therefrom, the mounting portion and the first and second connection portions can be simultaneously formed in the same step. For example, in a case where the mounting portion and the first and second connection portions are formed of metal bumps, bumps of the same metal are placed in the same step and are connected (flip tip connection) in the same step. Hereinafter, detailed description will be provided with reference to the accompanying drawings.
A piezoelectric vibrator 1 according to a first embodiment of the invention will be described with reference to
As illustrated in
The base substrate 2 has a rectangular shape. The base substrate 2 includes two through-electrodes 10a and 10b which penetrate from a surface H to a rear surface R in its diagonal region, and the bonding member 13 is provided on a peripheral portion of the surface H. The base substrate 2 includes first and second lead-out electrodes 5a and 5b on an inner peripheral side of the bonding member 13 in the vicinity of one short side of the surface H, and first and second mounting portions 9a and 9b formed on the first and second lead-out electrodes 5a and 5b. The base substrate 2 includes the first lead-out electrode 5a extending from the vicinity of the one short side on the inner peripheral side of the bonding member 13 in the vicinity of the other short side of the surface H. The bonding member 13 is formed of a conductor film such as aluminum or silicon.
The base substrate 2 further includes a first connection portion 7a and a second connection portion 7b which respectively extend from the bonding member 13 in the vicinity of the first mounting portion 9a and in the vicinity of the first through-electrode 10a. The first connection portion 7a electrically connects the first lead-out electrode 5a to the bonding member 13 in the vicinity of the first mounting portion 9a, and the second connection portion 7b electrically connects the first lead-out electrode 5a to the bonding member 13 in the vicinity of the first through-electrode 10a. Therefore, the resistance between the first mounting portion 9a and the first through-electrode 10a is reduced as a current path due to the bonding member 13 is increased. The base substrate 2 includes a second outer electrode 11b formed at the other angular portion of the one short side of the rear surface R, a first outer electrode 11a formed at the one angular portion of the other short side thereof, and a dummy electrode 11c formed at another angular portion. The second outer electrode 11b and the first outer electrode 11a are electrically connected to the second through-electrode 10b and the first through-electrode 10a, respectively.
The piezoelectric vibrating reed 4 is made of a rectangular thin plate and includes first and second excitation electrodes 6a and 6b (see
Detailed description will be provided with reference to
The first and second lead-out electrodes 5a and 5b are separated from each other on the inner peripheral side of the bonding member 13 and on the surface H of the base substrate 2. The first lead-out electrode 5a is formed to extend from an angular region between the lower side and the left side on the inner peripheral side of the bonding member 13 to the other short side (hereinafter, referred to as the upper side), covers an upper surface of the first through-electrode 10a, and is electrically connected to the first through-electrode 10a. The second lead-out electrode 5b covers an upper surface of the second through-electrode 10b in an angular region between the lower side and the left side on the inner peripheral side of the bonding member 13 and is electrically connected to the second through-electrode 10b. In addition, the concave portion 16 is formed on the surface of the lid substrate 3 on the piezoelectric vibrating reed 4 side, and the upper surface of the side wall of the concave portion 16 and the periphery of the base substrate 2 are bonded by anodic bonding via the bonding member 13. A metal film, for example, Au/Cr may be used for the first and second lead-out electrodes 5a and 5b.
The first and second mounting portions 9a and 9b (see
The first mounting portion 9a is electrically connected to the first terminal electrode 12a formed on the lower side of the piezoelectric vibrating reed 4, and the second mounting portion 9b is electrically connected to the second terminal electrode 12b formed on the lower side of the piezoelectric vibrating reed 4. In addition, the first lead-out electrode 5a and the bonding member 13 conduct with the first and second connection portions 7a and 7b. Moreover, as viewed in a direction normal to the surface H of the base substrate 2, the first and second excitation electrodes 6a and 6b provided in the piezoelectric vibrating reed 4 are installed so as not to overlap with the first and second lead-out electrodes 5a and 5b.
As a result, the first excitation electrode 6a is electrically connected to the first outer electrode 11a via the first terminal electrode 12a, the first mounting portion 9a, the first lead-out electrode 5a, the bonding member 13, and the first through-electrode 10a. The second excitation electrode 6b is electrically connected to the second outer electrode 11b via the second terminal electrode 12b, the second mounting portion 9b, the third lead-out electrode 5c, and the second through-electrode 10b. Therefore, as a drive power is applied to the first and second outer electrodes 11a and 11b to vibrate the piezoelectric vibrating reed 4, a frequency signal can be obtained by the first and second outer electrodes 11a and 11b.
The first lead-out electrode 5a and the bonding member 13 are electrically connected to the first and second connection portions 7a and 7b and thus implement a parallel connection, so that lead-out resistance can be reduced. In addition, since the first and second lead-out electrodes 5a and 5b do not overlap with the first and second excitation electrodes 6a and 6b in the plan view, parasitic capacitance of the lead-out electrode can be reduced, thereby stabilizing vibration. Moreover, in the first embodiment, the concave portion is provided in the lid substrate 3. However, instead of this, the concave portion may be provided in the base substrate 2. In this case, the first lead-out electrode 5a and the first and second mounting portions 9a and 9b may be formed on a bottom surface of the concave portion, and the first and second connection portions 7a and 7b may be formed on the bottom surface of the concave portion from an upper surface of the concave portion via its inner side surface.
As illustrated in
Distances of the first and second stepped portions 17a and 17b from their stepped upper surfaces to the surface H of the base substrate 2 are set to be substantially the same as a distance from the surface of the piezoelectric vibrating reed 4 on the base substrate 2 side to the surface H. Accordingly, the piezoelectric vibrating reed 4 can be simultaneously performed in a flip chip bonding by forming the first and second connection portions 7a and 7b of the same mounting members as the first and second mounting portions 9a and 9b, for example, metal bumps. The first and second lead-out electrodes 5a and 5b are formed so as not be overlap with the first and second excitation electrodes 6a and 6b formed on both surfaces of the piezoelectric vibrating reed 4.
Moreover, the first and second stepped portions 17a and 17b may be formed over the entire inner wall of the left side or over the entire inner wall of the concave portion 16 instead of at the angular portion between the lower side and the left side and at the angular portion between the upper side and the left side. In addition, according to the first or second embodiment, the first and second through-electrodes 10a and 10b are installed in the diagonal region of the rectangular base substrate 2. However, the invention is not limited to this, and the first and second through-electrodes 10a and 10b may be installed on the opposite sides to each other or on one of the sides.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-024657 | Feb 2010 | JP | national |
