Patent Application
20130193806
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2012-014965 filed on Jan. 27, 2012, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vibration device and an oscillator in which a vibrating reed is mounted on a cavity formed between two substrates.
2. Description of the Related Art
A vibration device using a crystal unit is in common use. The vibration device using the crystal unit is small in size and has stable frequency characteristics with respect to temperature change, which is widely used as a timing source for portable information terminals such as a cellular phone and many other electronic devices. Further reduction in size and stabilization in an oscillation period are requested in recent years. Accordingly, the crystal unit is further reduced in size and mounted on a substrate by using a surface mount method.
The crystal piece 52 has a flat rectangular shape, including an excitation electrode 56 for exciting the crystal piece 52, a first lead-out portion 57a electrically connected to the excitation electrode 56 and a second lead-out portion 57b electrically connected to the first lead-out portion 57a and installed at a corner portion of the crystal piece 52 on a surface of the crystal piece 52. The excitation electrode 56 is formed on both surfaces of the crystal piece 52 so as to sandwich the crystal piece 52. The second lead-out portion 57b is formed at both corner portions of a short side of the crystal piece 52, in which the second lead-out portion 57b at one corner is electrically connected to the excitation electrode 56 formed on one surface and the second lead-out portion 57b at the other corner portion is electrically connected to the excitation electrode 56 formed on the other surface. The second lead-out portion 57b is electrically connected to a crystal terminal 54 through the conductive adhesive 58, and further connected to an external terminal 55. Therefore, the crystal piece 52 is supported in a cantilever manner so that the both corner portions of the short side are fixed to the container main body 51 by the conductive adhesive 58.
In the mount method of Patent Document 1, two points in the short side of the crystal piece 52 are fixed to the container main body 51 by the conductive adhesive 58. When the thermal expansion coefficient differs between the crystal piece 52 and the container main body 51, a stress is applied between two fixing portions when the ambient temperature changes. Accordingly, frequency characteristics are deteriorated with respect to the temperature change. Particularly, in the case where the crystal piece 52 is an AT cut crystal piece which performs thickness shear vibration, deterioration in frequency characteristics becomes conspicuous with respect to the ambient temperature change when the two points in the short side of the crystal piece 52 are fixed by the conductive adhesive 58.
Incidentally, this kind of vibration device keeps the inside of the container in a vacuum state for reducing air resistance. However, gas is generated from the conductive adhesive 58 when using the conductive adhesive 58 as in Patent Document 1, and frequency characteristics of the crystal piece 52 vary due to the generated gas. The crystal piece 52 is mounted on the container main body 51 by thermally melting the conductive adhesive 58. The conductive adhesive 58 spreads when being melted and it is difficult to control a joint area between the crystal piece 52 and the container main body 51 to be small. Furthermore, vibration characteristics of the crystal piece 52 are deteriorated when the joint area spreads. Accordingly, the reduction in size of the crystal piece 52 is limited. Additionally, as it takes time to solidify the conductive adhesive 58, the crystal piece 52 may tilt by the empty weight and touch a package while the crystal piece 52 is adhered to the container body 51, which interferes with vibration. According to the above reasons, it is difficult to apply the method of mounting the crystal piece 52 on the container main body 51 by using the conductive adhesive 58 for obtaining high-precision frequency characteristics.
The present invention has been made in view of the above problems, and an object thereof is to provide a small and high-precision vibration device which can suppress the deterioration in frequency characteristics with respect to change of ambient temperature.
A vibration device according to an embodiment of the present invention includes a base, a lid body bonded to the base to form a cavity and a vibrating reed housed in the cavity, in which the vibrating reed includes a flat main body having a rectangular shape, and an extended portion extending in a short side direction of the rectangular shape at one corner portion of the main body, the main body has two excitation electrodes for exciting vibration, the extended portion has a first terminal electrically connected to one excitation electrode, the main body has a second terminal electrically connected to the other excitation electrode and arranged in the vicinity of a short side where the extended portion is installed, and the base has a first connection portion connected to the first terminal on a surface facing the cavity and a second connection portion connected to the second terminal, thereby supporting the vibrating reed by the first and second connection portions in a cantilever manner.
The second connection portion is connected to an approximate center of a width in the short side direction of the main body.
The extended portion is formed in a shape of an L-shaped arm in plan view of a surface of the flat main body seen from a vertical direction, in which one end of the L-shaped arm is connected to the main body and the first connection portion is connected in the vicinity of the other end of the L-shaped arm.
One side of the L-shaped arm is extended in the short side direction of the main body and the other side of the L-shaped arm is in parallel to a longitudinal direction of the main body toward a direction of an opposite side of the short side where the extended portion is installed.
The extended portion has a concave shape or a spiral shape in plan view of a surface of the flat main body seen from a vertical direction, one end of the concave shape or the spiral shape is connected to the main body and the first connection portion is connected in the vicinity of the other end thereof.
The vibrating reed is an AT cut crystal vibrating reed.
The first and second connection portions are formed by using metal bumps.
The metal bumps are gold bumps.
The base includes a first wiring electrically connected to the first connection portion, a second wiring electrically connected to the second connection portion and first and second through electrodes piercing through the base as well as electrically connected to the first and second wirings respectively.
An oscillator according to an embodiment of the present invention includes the vibration device described in any of the above and a drive circuit supplying drive signals to the vibration device.
The vibration device according to the embodiment of the present invention includes the base, the lid body bonded to the base to form the cavity and the vibrating reed housed in the cavity, in which the vibrating reed includes the flat main body having the rectangular shape, and an extended portion extending in the short side direction of the rectangular shape at one corner portion of the main body, the main body has two excitation electrodes for exciting vibration, the extended portion has the first terminal electrically connected to one excitation electrode, the main body has the second terminal electrically connected to the other excitation electrode and arranged in the vicinity of a short side where the extended portion is installed, and the base has the first connection portion connected to the first terminal on the surface facing the cavity and the second connection portion connected to the second terminal, thereby supporting the vibrating reed by the first and second connection portions in a cantilever manner. Accordingly, the vibration device in which deterioration in frequency characteristics is reduced if ambient temperature changes.
As shown in
As described above, as the vibrating reed 6 is supported by two points in the main body 7 and the extended portion 8, the vibrating reed 6 can be supported more elastically than in the case of supporting the vibrating reed 6 by two points in the main body 7. That is, when ambient temperature changes and a stress is applied between two points in the main body 7 and the extended portion 8 due to difference in the thermal expansion coefficient in the case where the thermal expansion coefficient differs between the base 3 and the vibrating reed 6, the stress is alleviated by the extended portion 8 to thereby reduce effects on vibration characteristics.
Hereinafter, explanation will be specifically made. As shown in
The extended portion 8 having a shape of an L-shaped arm in plan view of the front surface H of the flat main body 7 seen from a vertical direction, in which one end thereof is connected to the main body 7 and the other end is supported by the first connection portion 12a. The extended portion 8 includes the first terminal 10a on the front surface H and the rear surface R, in which the first terminal 10a is electrically connected to the excitation electrodes 9a on the front surface H through a wiring 11 a as well as electrically connected to the first connection portion 12a. Accordingly, the first connection portion 12a is electrically connected to the excitation electrodes 9a installed on the front surface H of the main body 7.
The main body 7 includes the second terminal 10b on the front surface H and the rear surface R from the center of the left side where the extended portion 8 is installed toward an upper side, and the second terminal 10b is electrically connected to the excitation electrode 9b on the rear surface R through a wiring 11b. The main body 7 is supported by the second connection portion 12b connected to an approximate center of a width in the short side direction (y direction) of the main body 7 and the second connection portion 12b is electrically connected to the second terminal 10b. Therefore, the second connection portion 12b is electrically connected to the excitation electrode 9b installed on the rear surface R of the main body 7.
The extended portion 8 is connected so that one shorter side of the L-shaped arm extends from the short side direction (-y direction) of the main body 7 and so that the other longer side of the L-shaped arm extends along a longitudinal direction (x direction) of the main body 7. In the vibrating reed 6, an end portion of the L-shaped arm on the opposite side of the connection portion with respect to the main body 7 is supported by the first connection portion 12a, and a portion in the vicinity of the left side of the main body 7 as well as the approximate center of the width in the short side direction of the main body 7 is supported by the second connection portion 12b. If the ambient temperature changes and a portion between the vibrating reed 6 and the base 3 expands and contracts due the difference in thermal expansion coefficient, the expansion and contraction are absorbed by the L-shaped arm of the extended portion 8. Therefore, the stress applied on the main body 7 is alleviated and the deterioration in frequency characteristics due to temperature change can be reduced. Additionally, the second connection portion 12b supports the approximate center of the width in the short side direction of the main body 7, therefore, effects on the vibration of the main body 7 are reduced.
The base 3 includes a first wiring 14a electrically connected to the first connection portion 12a, a second wiring 14b electrically connected to the second connection portion 12b and first and second through electrodes 15a, 15b piercing through the base 3 and electrically connected to the first and second wirings 14a and 14b respectively. On a surface of the base 3 on the opposite side of the cavity 5, an external terminal 16a electrically connected to the first through electrode 15a and an external terminal 16b electrically connected to the second through electrode 15b are provided. Drive signals are inputted to the external terminals 16a and 16b from a control circuit and the like. In
Here, an AT cut crystal piece can be used as the vibrating reed 6. The vibration device can be miniaturized by using the AT cut crystal piece. The AT cut crystal piece can be cut out individually from an AT cut crystal plate by photolithography and an etching method. Therefore, the extended portion 8 extending from one corner of the main body 7 can be easily formed by photolithography and the etching method at the time of cutout. As the base 3 and the lid body 4, ceramic materials such as alumina ceramics can be used. Glass materials can be also used instead of ceramic materials. When using glass materials, the thermal expansion coefficient can be approximately the same as the coefficient of the vibrating reed 6, which can further reduce the deterioration in frequency characteristics due to temperature change.
As the first and second connection portions 12a and 12b, metal bumps such as gold bumps can be used. Additionally, an electrode having a stacked structure of gold (Au) and Cr is formed in the main body 7 and the extended portion 8, and the electrode is patterned to thereby form the excitation electrodes 9a, 9b, the wirings 11a, 11b, the first and second terminals 10a, 10b. Then, the vibrating reed 6 is mounted on the first and second connection portions 12a and 12b of the base 3 by flip-chip bonding. When using the metal bumps as the first and second connection portions 12a and 12b, an area of a holding portion holding the vibrating reed 6 can be smaller than in the case of using adhesive.
When using metal bumps as the first and second connection portions 12a and 12b, gas is not generated such as in the case of the conductive adhesive, therefore, frequency characteristics do not change due to the generated gas. When the vibrating reed 6 is mounted by using the metal bumps, the first and second connection portions 12a and 12b are solidified in a shorter time than in the case of using the conductive adhesive, therefore, it is possible to prevent the vibrating reed 6 from tilting by the empty weight and touching the base 3 to interfere with vibration. The lid body 4 can be bonded to the base 3 by an anodic bonding through a bonding material 13 made of, for example, an aluminum film. The anodic bonding can be performed in a vacuum, and the vacuum can be maintained inside the cavity 5 after the bonding.
In the present embodiment, the vibrating reed 6 is mounted on the base 3 by flip-chip bonding, therefore, an outline of the vibration device 1 can be formed to be small. The base 3 can be formed so that a width in the short side direction (y direction) is 2.5 mm to 1.2 mm, a width in the longitudinal direction (x direction) is 3.2 mm to 1.6 mm.
In any case of
The second connection portion 12b may support an upper position of the width than the approximate center or may support a lower position of the width than the approximate the center instead of supporting the approximate center of the width in the short side direction of the main body 7. However, vibration is stabilized more effectively when supporting the approximate center of the width in the short side direction of the main body 7 as compared with the case of supporting the lower position or the upper position of the width.
Accordingly, the different points will be chiefly explained and explanation about the equivalent points is omitted.
As shown in
The present invention is not limited to the layout of the second embodiment, and for example, the first and second through electrodes 15a and 15b may be arranged in the vicinity of a corner portion made by the left side and the upper side of the cavity 5 and in the vicinity of a corner portion made by the right side and the lower side. In this case, a layout obtained by vertically inverting the vibrating reed 6, the second connection portion 12b and the first and second wirings 14a, 14b shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-014965 | Jan 2012 | JP | national |
