JP2007067788A - Piezoelectric device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin type piezoelectric device such that a package and a lid body can be sealed without the risk of environmental contamination and the frequency can precisely be adjusted. <P>SOLUTION: A piezoelectric vibration piece 32 having metal coating parts 36a and 37a for frequency adjustment by light formed on its surfaces is fixed to a package 40 as a base body. A ceramic-made lid body 48 having light transmissivity is airtightly joined to the joining surface 40a of the package 40 to include the piezoelectric vibration piece 32. A joining part 50 at least having gold-tin alloy as sealing metal 64 for joining the package 40 and lid body 48 is provided between the package 40 and lid body 48. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric device in which a piezoelectric vibrating piece made of quartz or the like housed in a base is hermetically sealed by a lid.

Piezoelectric devices such as piezoelectric vibrators and piezoelectric oscillators in small information devices such as HDDs (hard disk drives), mobile computers, IC cards, and mobile communication devices such as mobile phones, car phones, and paging systems Is widely used.
A conventional piezoelectric device is configured, for example, as shown in FIG. In the piezoelectric device 100 shown in FIG. 6, a piezoelectric vibrating piece 103 is fixed by a conductive adhesive 104 in a recess 102 of a package 101 as a base substrate. Further, the concave portion 102 of the package 101 is hermetically sealed with a lid 105 made of transparent glass so that the piezoelectric vibrating piece 103 is included in the package 101. The lid 105 is bonded to the upper surface of the package by a low melting point glass 106 having a melting point of about 320 degrees (“Centigrade”, and all temperature indications used in the following are degrees Celsius). (For example, refer to Patent Document 1).

  In the piezoelectric device 100 having such a configuration, even after the lid 105 is hermetically sealed, with respect to the frequency adjustment metal film 107 as the frequency adjustment metal coating portion formed on the piezoelectric vibrating piece 103, Frequency adjustment can be performed by irradiating laser light LB as an example of light from the outside to evaporate a part of the frequency adjustment metal film 107. In this frequency adjustment, by partially evaporating part of the frequency adjusting metal film 107, the mass of the vibrating arm of the piezoelectric vibrating piece 103 can be reduced and finely adjusted to increase the frequency. Thereby, it is possible to perform frequency adjustment corresponding to a change in frequency caused by hermetically sealing the lid 105.

JP 2002-359535 A

However, low melting point glass used as a bonding material between the package and the lid contains lead, and the use of a lead-containing sealing material is not preferable because it leads to environmental pollution.
Therefore, low-melting glass not containing lead is used. However, the melting point of such a glass is 400 ° C. or higher, which is a relatively high temperature, which may deteriorate the characteristics of the piezoelectric vibrating piece itself. In addition, lead-free low-melting glass having a relatively low melting point has been studied, but it is expensive and unsuitable.

  In addition, the glass lid has four-point bending strength (the test piece is placed on two fulcrums arranged at a fixed distance, and the load is divided into two points at equal distances from the center between the fulcrums to the left and right. Fracture strength such as maximum bending stress when folded is weak. For this reason, if stress due to dropping or the like is applied to the lid, the lid may be broken. In order to prevent the destruction of the lid, the lid strength is improved by increasing the thickness of the lid, but the overall thickness of the piezoelectric device is also increased, resulting in a thinner piezoelectric device. It is one of the causes that inhibit.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a thin piezoelectric device capable of sealing a package and a lid without fear of environmental pollution and adjusting the frequency precisely. There is to do.

  In order to solve such a problem, a piezoelectric device of the present invention includes a base substrate, a piezoelectric vibrating piece that is fixed to the base substrate and has a metal coating for adjusting frequency by light, and the piezoelectric vibrating piece. A light-transmitting ceramic lid that is hermetically bonded to the base substrate, and the base substrate and the lid formed between the base substrate and the lid are bonded to each other. And a joining portion including at least a gold-tin alloy as a sealing metal for the purpose.

According to the piezoelectric device of the present invention, the lid is made of a light-transmitting ceramic, and a gold-tin alloy is used for bonding to the substrate. This gold-tin alloy has a melting temperature of about 280 degrees. Thereby, the temperature applied at the time of sealing the lid is also about 280 degrees, and it is possible to prevent the piezoelectric vibrating piece from being adversely affected.
Furthermore, since the light-transmitting ceramic has fine particles, the strength such as four-point bending strength is strong. That is, the light-transmitting ceramic lid is stronger than the conventional glass lid, and it is possible to ensure the desired strength even if the lid is thin.
In addition, since the lid is made of a light-transmitting ceramic, frequency adjustment can be performed by irradiating laser light as an example of light from the outside after sealing with the lid. In other words, after sealing with the lid, by irradiating a laser beam from the outside, by evaporating a part of the metal coating portion for frequency adjustment formed on the piezoelectric vibrating piece fixed in the package as the base substrate, Frequency adjustment by the mass reduction method can be performed.
Thus, a thin piezoelectric device is provided in which the package and the lid are sealed without fear of environmental pollution, and the frequency can be precisely adjusted by adjusting the frequency after the frequency change caused by the sealing. be able to.

  In addition, the bonding portion includes a base substrate-side metal film including gold formed at a bonding portion of the base substrate and the lid, and a bonding portion of the lid corresponding to the base substrate-side metal film. It is desirable to include the formed lid side metal film and the gold-tin alloy formed between the base substrate side metal film and the lid side metal film.

  In this way, the molten gold-tin alloy is firmly fixed by the base substrate-side metal film and the lid-side metal film formed at the joint portions of the base substrate and the lid, and the base substrate and the lid are fixed. It becomes possible to join the body firmly.

  The lid-side metal film is preferably formed by overlapping different metal films.

In this way, a metal film having sufficient bonding strength with the lid, a metal film having sufficient bonding strength with the gold-tin alloy, and a metal film for ensuring sufficient bonding strength between the two metal films. In order to ensure the connection strength, different metal films can be used.
In this way, by using different metal films with sufficient bonding strength, it is possible to firmly bond the base substrate and the lid.

  Moreover, it is preferable that the metal film formed on the surface of the lid body among the different metal films is molybdenum (Mo) or tungsten (W).

  In this way, molybdenum (Mo) or tungsten (W) can easily enter the slight gaps in the grain boundaries of the light-transmitting ceramics forming the lid, and the so-called anchor effect causes the lid and its The bonding strength with the metal film formed on the surface can be strengthened.

  Moreover, it is desirable that the sealing metal is pre-coated at a joint portion on the upper surface of the lid-side metal film.

  In this case, since the sealing metal is pre-coated on the lid side, the troublesome work of aligning the ring-shaped sealing metal between the package and the lid at the time of sealing, for example. Can be avoided.

  Moreover, it is desirable that the sealing metal or the lid-side metal film and the sealing metal are provided in a limited region of the lid where the base substrate is joined.

  In this way, it is possible to minimize the use of the lid-side metal film and the sealing metal, and it is possible to prevent unnecessary flow of unjoined metal and waste of expensive materials including gold. it can.

  Moreover, it is desirable that the lid body has a thickness of 0.05 mm or more and 0.2 mm or less.

  In this way, it is possible to prevent the lid body from being destroyed when stress due to dropping or the like is applied, and to suppress the irregular reflection of the lid body that impedes the transmission of the laser light to a range in which the frequency can be adjusted by the laser light. Is possible.

  Furthermore, the base substrate is preferably provided with a through hole for sealing, and the through hole for sealing is preferably sealed with a filler.

  In this way, since the package has a sealing through hole, the gas in the package can be discharged from the through hole after the lid is joined, and then the through hole can be sealed. . As a result, when the lid is joined, the gas generated from the molten sealing metal or the like can be discharged, so that it is possible to prevent deterioration in oscillation characteristics due to the gas.

  1 and 2 show an embodiment of the piezoelectric device of the present invention. FIG. 1 is a schematic plan view of a state where a lid is removed, and FIG. 2 is a schematic cross-sectional view taken along line AA of FIG. FIG. In these drawings, the piezoelectric device 30 shows an example in which a piezoelectric vibrator is configured.

  The piezoelectric device 30 has a structure in which a lid 48 is hermetically sealed via a joint portion 50 so as to enclose a piezoelectric vibrating piece 32 in a package 40 as a base substrate. Specifically, the package 40 of the piezoelectric device 30 contains a piezoelectric vibrating piece in an airtight manner. For example, a plurality of substrates formed by molding an aluminum oxide ceramic green sheet as an insulating material are stacked. After that, it is formed by sintering. The package 40 includes a first substrate 41, a second substrate 42 stacked on the first substrate 41, and a third substrate 47 further stacked on the second substrate 42. ing.

The first substrate 41 of the package 40 constitutes the bottom surface of the package, and each end of the second substrate 42 laminated thereon, for example, the vicinity of the left end in FIGS. Electrode portions 33a and 33b are formed at the ends. On the electrode portions 33a and 33b, the portion of the extraction electrode at the base portion of the piezoelectric vibrating piece 32 is mounted and joined via the conductive adhesives 34a and 34b. The electrode portions 33a and 33b are connected to mounting terminals which are external electrodes (not shown) of the package 40 using conductive through holes (not shown).
In FIG. 2, a concave portion 42a is formed by removing the material in a concave shape below the tip of the piezoelectric vibrating piece 32 of the second substrate 42, and the tip of the piezoelectric vibrating piece 32 is caused by vibration from the outside. Even if it is swung in the vertical direction, the front end portion thereof is prevented from colliding with the inner bottom portion of the package 40 and being damaged.

  The first substrate 41 and the second substrate 42 have a through hole 43 formed approximately in the vicinity of the center thereof. In this embodiment, the through hole has a first hole 44 formed in the first substrate 41 and a second hole 45 formed in the second substrate 42 and having a smaller diameter than the first hole 44. The first hole 44 and the second hole 45 communicate with each other. The through hole 43 is a stepped hole as shown in the figure, and a conductive pattern (metal covering portion) (not shown) is formed in the step portion, and the hole is sealed by filling the metal filler 46. Has been.

  The piezoelectric vibrating piece 32 is formed of, for example, quartz, and a piezoelectric material such as lithium tantalate or lithium niobate can be used in addition to quartz. As shown in FIG. 1, the piezoelectric vibrating piece 32 includes a base portion 35 fixed to the package 40 side, and a pair of vibrations extending in parallel to be divided into two forks toward the right in the drawing with the base portion 35 as a base end. This is a so-called tuning-fork type vibration piece including arms 36 and 37. The piezoelectric vibrating piece is not limited to this, and may be an AT-cut vibrating piece obtained by cutting a quartz wafer into a rectangle.

A lead electrode is formed on the base portion 35 of the piezoelectric vibrating piece 32 and is electrically connected to the electrode portions 33a and 33b on the package 40 side. The vibrating arms 36 and 37 are preferably along the direction in which the arms extend. The long groove is formed in the same form on the front and back sides to form an excitation electrode that is a driving electrode, and can be connected to the extraction electrode.
Further, for example, near the tips of the vibrating arms 36 and 37 of the piezoelectric vibrating piece 32, metal cover portions 36a and 37a for frequency adjustment are formed. The frequency-adjusting metal cover portions 36a and 37a are made of the same metal as an excitation electrode (not shown), which is a drive electrode formed on the piezoelectric vibrating piece 32, and can be formed in the same process. Alternatively, part of the excitation electrode of the piezoelectric vibrating piece 32 may be used for the metal cover portions 36a and 37a for frequency adjustment.

The lid 48 is made of a light-transmitting ceramic (hereinafter referred to as “translucent ceramic”). The translucent ceramic is, for example, sintered with an aluminum oxide powder having a particle size of about 1 to 2 μm, and the surface is finished to a surface roughness (Ra) of about 0.003 to 0.008 μm. For example, the lid 48 can be used by cutting out from the plate-shaped material of the translucent ceramics.
The lid body 48 is provided with a lid-side metal film constituting the joint 50 and a sealing metal made of a gold-tin alloy on the joint surface. The lid side metal film and the sealing metal are formed in a region corresponding to the bonding surface 40a which is the upper end of the package 40 shown in FIG. The joint portion 50 including the lid side metal film and the sealing metal will be described in detail in a later paragraph.

  Here, the thickness of the translucent ceramic as the lid 48 will be described with reference to FIG. FIG. 4 is a graph showing the correlation between the thickness of the translucent ceramic, the light transmittance, and the strength.

The light transmissivity of the translucent ceramic is adjusted by transmitting laser light from the outside to the metal cover portions 36a and 37a for frequency adjustment provided on the piezoelectric vibrating piece 32 after the lid 48 is bonded to the package 40. Used to do. As shown in FIG. 4, the transmittance through which laser light as light passes through the translucent ceramic increases as the thickness of the translucent ceramic decreases. This is because the occurrence of refraction, irregular reflection, and the like of laser light by the translucent ceramic is less likely to occur as the thickness is smaller. Therefore, the laser beam is more easily transmitted as the thickness of the translucent ceramic is reduced.
In general, a transmittance of 50% or more is required for transpiring the metal coating portions 36a and 37a for frequency adjustment without problems by laser light having an output (about 20 to 30 mW) generally used for frequency adjustment. ing. It can be seen that the thickness of the translucent ceramic that can secure the transmittance of 45% or more is within the transmittance usable region shown in FIG.

On the other hand, the strength of translucent ceramics decreases as the thickness decreases. When this strength reaches a specified value, the lid 48 may break due to impact such as dropping or bending stress. As an example, the strength of the translucent ceramic is measured by the measuring method as shown in FIG. 5 (the test piece is placed on two fulcrums arranged at a fixed distance, and divided into two points at equal distances from the center between the fulcrums. The maximum bending stress when a load is applied and it is bent. The strength of the translucent ceramic is desirably 570 megapascals (MPa) or more, and the thickness of the translucent ceramic as the strength usable region is 0.05 mm or more as shown in FIG. It can be seen that it is.
As a result, the thickness of the translucent ceramic that can be used is 0.07 mm or more, which corresponds to the practical usable area shown in FIG. 4, which is an area where the above-described transmittance usable area and strength usable area overlap. It is desirable to be in the range of 15 mm or less.

  The light transmittance of the lid body 48 may be in a region corresponding to the frequency-adjusting metal coating portions 36 a and 37 a provided in the piezoelectric vibrating piece 32 after the lid body 48 is joined to the package 40. . Therefore, if the lid-side metal film and the sealing metal are regions other than the region corresponding to the frequency-adjusting metal coatings 36a and 37a, the region beyond the region corresponding to the joint surface 40a that is the upper end of the package 40. May be formed.

Next, the joint part 50 including the lid-side metal film and the sealing metal will be described with reference to FIG. FIG. 3 is an enlarged partial cross-sectional view showing a joint portion between the package 40 and the lid 48. In addition, each metal layer shown in the figure is shown thicker than the actual thickness for convenience of understanding.
In FIG. 3, the bonding portion 50 includes a base substrate side metal film 54, a sealing metal 64, and a lid side metal film 65. A base substrate side metal film 54 is formed on the bonding surface 40 a which is the upper end of the package 40. The base-substrate-side metal film 54 is formed, for example, by coating a nickel (Ni) layer 52 on a tungsten (W) layer 51 which is a base for ceramics, and coating a gold (Au) layer 53 thereon. is there.

  On the other hand, a lid-side metal film 65 is formed on the bonding surface 48 a that is one surface of the lid 48. The lid-side metal film 65 is formed, for example, by forming a tungsten (W) layer 61 on the surface of the light-transmitting ceramic, preferably forming a nickel (Ni) layer 62 on the surface, and further forming a gold (Au) layer on the surface. 63 is formed. The nickel layer 62 is provided to prevent tungsten from diffusing from the tungsten layer 61 to the gold layer 63.

  The tungsten (W) layer 61 can be formed, for example, by baking a paste-like material applied to the surface of the light-transmitting ceramic at a high temperature of about 1000 degrees. Further, the nickel (Ni) layer 62 and the gold (Au) layer 63 can be formed, for example, by performing an electrolytic plating process for each layer. More preferably, a sealing metal 64 is precoated on the surface side of the lid-side metal film 65.

  The sealing metal 64 is made of a gold-tin alloy (AuSn). The gold-tin alloy constituting the sealing metal 64 can be bonded by punching an alloy plate prepared in advance into a shape corresponding to the bonding surface 40a, and heating and melting it. Alternatively, gold and tin may be sequentially formed on the surface side of the lid-side metal film 65 by vapor deposition or sputtering, and heated and melted to form an alloy.

  The present embodiment is configured as described above. The manufacturing process thereof will be briefly described. First, as a previous process, the package 40 and the lid 48 are separately formed. The package 40 performs the bonding process of the piezoelectric vibrating piece 32 in a state where the through hole 43 is not blocked. That is, by applying the conductive adhesives 34a and 34b on the electrode portions 33a and 33b exposed on the inner surface of the package 40, mounting the piezoelectric vibrating piece 32 thereon, and drying and curing it, the piezoelectric vibrating piece 32 is obtained. Is fixed in the package 40.

Next, for example, the package 40 is placed in a vacuum chamber, and a sealing process is performed.
In this case, the base substrate side metal film 54 described in FIG. 3 is formed on the package 40, the lid body 48 is formed with the lid side metal film 65, and the sealing metal 64 is precoated. Therefore, the lid 48 can be bonded and sealed to the package 40 simply by placing the lid 48 on the package 40 and performing predetermined heating.

  In this case, since the sealing metal 64 is a gold-tin alloy, the sealing metal 64 can be melted and sealed at about 280 degrees which is not high enough to adversely affect the piezoelectric vibrating piece 32. Further, since the sealing metal 64 (gold-tin alloy) melts at about 280 degrees, heating in a reflow process (about 250 degrees) when mounting the piezoelectric device 30 on a substrate such as a device that uses the piezoelectric device 30. ) Will not melt and flow out. During this heating, the conductive adhesive bonded to the piezoelectric vibrating piece 32 and the moisture inside the package 40 are generated as gas, and the generated gas is released to the outside from the through hole 43 (degassing). Thereafter, for example, a spherical AuGe alloy is disposed on the inner step portion of the through hole 43 and melted by a laser beam or the like to form a filled metal (metal filler) 46, and the through hole 43 can be sealed.

Finally, as shown in FIG. 2, when the laser beam LB as an example of light is irradiated from the outside, the laser beam LB is transmitted through the light-transmitting ceramic lid 48 and the laser beam LB is used for adjusting the frequency of the piezoelectric vibrating piece 32. The frequency adjustment by the mass reduction method is performed by evaporating part of the metal coating portions 36a and 37a.
Thus, the piezoelectric device 30 is completed.

  Thus, in this embodiment, since the lid 48 is made of translucent ceramics, the laser beam LB is transmitted. Therefore, after sealing with the lid 48, the laser beam LB is irradiated from the outside to evaporate the metal coating portions 36 a and 37 a for frequency adjustment of the piezoelectric vibrating piece 32 in the package 40, thereby adjusting the frequency by the mass reduction method. Can do.

  In addition, the translucent ceramic has a 4-point bending strength at room temperature of 600 MPa, which is 6 times stronger than that of the conventional borosilicate glass due to the fine particles. For this reason, even if the lid body 48 is made thinner than the conventional glass lid body, it is possible to ensure a desired strength. Thereby, the thin piezoelectric device 30 can be provided.

  Further, since the sealing metal 64 made of a gold-tin alloy is used for joining the light-transmitting ceramic lid 48, it can withstand heat during reflow when the piezoelectric device 30 is mounted, and the lid 48 An adverse effect on the piezoelectric vibrating piece 32 at the time of sealing the body 48 is also prevented.

Further, since the package 40 includes the through-hole 43 for sealing, the gas in the package 40 can be discharged from the through-hole 43 when the lid body 48 is sealed, and then the hole can be sealed. . For this reason, the CI value does not increase due to the gas component adhering to the piezoelectric vibrating piece 32.
Thus, the package 40 and the lid 48 can be sealed without fear of environmental pollution, and the frequency can be precisely adjusted, so that the thin piezoelectric device 30 can be provided.

  Note that a molybdenum (Mo) layer using molybdenum (Mo) may be used instead of the tungsten (W) layer 61 among the metal layers constituting the lid-side metal film 65.

  The sealing metal 64 may be precoated on the surface of the base substrate side metal film 54 on the package 40 side. Further, the sealing metal 64 can be formed on the lid 48 side or the package 40 side only in a region corresponding to the bonding surface 40a in FIG. Thereby, it is possible to prevent the gold-tin alloy as the sealing metal 64 from flowing out unnecessarily at the time of sealing, and waste of expensive materials.

The present invention is not limited to the above-described embodiment. Each configuration of the embodiment may be omitted as appropriate and combined with other configurations not shown.
In addition, the present invention can be applied to all piezoelectric devices regardless of the names of piezoelectric vibrators, piezoelectric oscillators, etc., as long as they are covered with a package and accommodate a piezoelectric vibrating piece inside. .

The schematic plan view except the cover which shows embodiment of the piezoelectric device of this invention. AA schematic sectional drawing of FIG. The expanded sectional view of the junction part of the cover body and package of the piezoelectric device of FIG. The graph which shows the correlation of the thickness of translucent ceramics, light transmittance, and intensity | strength. The schematic front sectional view which shows the measuring method of the intensity | strength of translucent ceramics. FIG. 6 is a schematic cross-sectional view showing an example of a conventional piezoelectric device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 ... Piezoelectric device, 32 ... Piezoelectric vibration piece, 33a, 33b ... Electrode part, 34a, 34b ... Conductive adhesive, 35 ... Base part, 36, 37 ... Vibrating arm, 36a, 37a ... Metal coating part, 40 ... Base base | substrate 40a ... joining surface, 41 ... first substrate, 42 ... second substrate, 42a ... concave, 43 ... through hole, 44 ... first hole, 45 ... second hole, 46 ... metal filling Material 47... Third substrate 48. Lid 48 a Bonding surface 50 Bonding portion 51 Tungsten (W) layer 52 Nickel (Ni) layer 53 Gold (Au) layer 54 Base substrate side metal film, 61 ... tungsten (W) layer, 62 ... nickel (Ni) layer, 63 ... gold (Au) layer, 64 ... metal for sealing, 65 ... metal film on the lid side.

Claims (8)

A base substrate;
A piezoelectric vibrating piece fixed to the base substrate and having a metal coating for adjusting the frequency by light formed on the surface;
A lid made of a ceramic material that includes the piezoelectric vibrating piece and is light-tightly bonded to the base substrate;
A bonding portion including at least a gold-tin alloy as a sealing metal for bonding the base substrate and the lid formed between the base substrate and the lid. A characteristic piezoelectric device. The piezoelectric device according to claim 1.
The joint is
A base substrate-side metal film containing gold formed at a joint portion of the base substrate with the lid;
A lid-side metal film formed at a joint corresponding to the base substrate-side metal film of the lid;
A piezoelectric device comprising: the gold-tin alloy formed between the base substrate side metal film and the lid side metal film. The piezoelectric device according to claim 1 or 2,
The lid-side metal film is formed by stacking different metal films. The piezoelectric device according to claim 2 or 3,
Of the different metal films, the metal film formed on the surface of the lid is molybdenum (Mo) or tungsten (W). The piezoelectric device according to any one of claims 1 to 4,
The piezoelectric device according to claim 1, wherein the sealing metal is pre-coated at a joint portion on the upper surface of the lid-side metal film. The piezoelectric device according to any one of claims 1 to 5,
The piezoelectric device according to claim 1, wherein the sealing metal or the lid-side metal film and the sealing metal are provided in a limited region of a joint portion of the base body of the lid. The piezoelectric device according to any one of claims 1 to 6,
The said cover has a thickness of 0.05 mm or more and 0.2 mm or less, The piezoelectric device characterized by the above-mentioned. The piezoelectric device according to any one of claims 1 to 7,
Furthermore, the base substrate includes a through hole for sealing, and the through hole for sealing is sealed with a filler.

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