JP2007306434A - Piezoelectric vibrator, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To assure high airtightness and high bonding strength and to attain high frequency precision in a piezoelectric vibrator in which upper and lower piezoelectric substrates are bonded on both surfaces of a piezoelectric substrate formed by integrating a piezoelectric vibration chip and an outer frame. <P>SOLUTION: A crystal oscillator 1 has an intermediate crystal plate 2 to which an AT cut crystal oscillation chip 5 and the outer frame 6 are integrally coupled, upper and lower crystal substrates 3, 4. Conductive films 10, 13 are formed on a lower surface of the outer frame of the intermediate crystal plate, metal thin films 16, 18 are formed on an upper surface of the lower crystal substrate and airtightly joined together by diffused junction after being mutually sanctified and activated by plasm processing. Frequency adjustment of the crystal oscillation chip is performed before joining the intermediate crystal plate and the upper crystal substrate after joining the intermediate crystal plate and the lower crystal substrate. The upper surface of the outer frame of the intermediate crystal plate and the lower surface of the upper crystal substrate consist of crystal element surfaces and airtightly joined by surface activated bonding using the plasma processing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric vibrator in which a thickness-shear vibration mode or tuning-fork type piezoelectric vibrating piece is hermetically accommodated in a package, and a manufacturing method thereof.

  Conventionally, piezoelectric devices such as crystal resonators are required to be further reduced in size and thickness as electronic devices become smaller and thinner, and surface mount devices suitable for mounting on circuit boards and the like are often used. ing. In general, a surface-mount type piezoelectric device widely adopts a structure in which a piezoelectric vibrating piece is sealed in a package formed of an insulating material such as ceramic. In conventional package structures, the base and lid are joined by low-melting glass or seam welding, etc., so the frequency characteristics of the crystal resonator element are degraded or deteriorated due to the gas generated from the low-melting glass or the high heat of seam welding. There is a risk of causing it. Further, the low melting point glass is often not preferable because it often contains lead and may affect the environment.

  Therefore, in order to solve such a problem, a crystal resonator is proposed in which a metal layer is provided on the upper and lower surfaces of an outer frame formed integrally with the crystal resonator, and the metal layer, a lid made of glass and a case are anodically bonded. (For example, see Patent Documents 1 and 2). The crystal resonator described in Patent Document 1 connects an electrode drawn from the excitation electrode of a crystal resonator element to the base end or outer frame thereof and an external electrode on the lower surface of the case through a through hole formed in the case. is doing. In the crystal resonator described in Patent Document 2, a bonding film is provided on the upper and lower surfaces of a frame of a piezoelectric diaphragm integrally formed with a piezoelectric vibrating piece, and the bonding film on the lower surface of the frame is divided at a portion having no bonding film. At the same time, the divided bonding film is electrically connected to the bonding film on the upper surface of the frame through a contact hole, that is, a through hole, and further connected to the external electrode on the lower surface of the base through a through hole formed in the base.

  Also, the mirror-polished piezoelectric plate and the substrate are cleaned by removing moisture at the atomic level by exposure to ultraviolet rays or exposure to oxygen plasma in an oxygen-containing atmosphere, and formed by adsorption of moisture. A method of manufacturing a piezoelectric device that joins by OH group hydrogen bonding is known (see, for example, Patent Document 3). In this joining method using a hydrophilic treatment, a strong joining force can be obtained by heat-treating the joined body at 100 ° C. or higher, which is the boiling point of water.

  Furthermore, when materials having different coefficients of thermal expansion, such as a quartz crystal material and a glass material, are joined in a quartz resonator, warping may occur after joining. In order to prevent such warpage, a method of offsetting warpage by sandwiching a first substrate with a sandwich structure between second and third substrates having different thermal expansion coefficients and similar thermal expansion coefficients to each other. Is known (see, for example, Patent Document 4).

  Piezoelectric vibrations such as crystal resonators in which a piezoelectric substrate, which is a circular quartz plate with an electrode film, and a quartz protective substrate, which is the same material on both sides, are joined by joints having gold and silver A body has been proposed (see, for example, Patent Document 5). Both substrates are subjected to plasma treatment on the bonding surface of the piezoelectric substrate on which the Au film is formed and the bonding surface of the protective substrate on which the Ag film is formed, and then superposed and evenly pressurized, and heated in a vacuum furnace at a temperature of 310 ° C. for 1 hour. By doing so, it is hermetically sealed by diffusion bonding.

  Further, a metal film surrounding the IDT is formed on the main surface of the piezoelectric substrate on which the IDT and electrode pads are formed, and a metal film aligned with the metal film is formed on the main surface of the base substrate. A surface acoustic wave device in which both substrates are bonded together by bonding is known (see, for example, Patent Document 6). According to Patent Document 6, the metal films on both substrates are subjected to surface activation treatment by irradiation with an ion beam, plasma, or the like at room temperature before bonding, and are subjected to heat treatment at about 100 ° C. or less. Thus, the bonding strength can be improved by pressurizing both substrates.

JP 2000-68780 A JP 2002-76826 A JP 7-154177 A JP-A-7-86106 International Publication Number WO00 / 76066 Pamphlet JP 2004-304622 A

  However, in the above-described conventional crystal resonator package structure by anodic bonding, voltage application and heating may adversely affect the crystal substrate and the substrate bonded thereto. Therefore, it is not necessarily preferable especially when high-precision performance is required. In addition, as in the case of low melting point glass and metal bonding, outer gas is generated, which may affect or deteriorate the characteristics of the quartz crystal vibrating piece.

  Furthermore, when substrates having different coefficients of thermal expansion are bonded to each other to form a multilayer sandwich structure, the substrates must be laminated simultaneously. Therefore, the alignment of each substrate having a multilayer structure is very complicated and requires a lot of labor, and there is a possibility that the actual working effect may be reduced. In addition, even when trying to absorb the difference in the coefficient of thermal expansion between the substrates with the sandwich structure, cracks due to the coefficient of thermal expansion occur in the substrate of the intermediate layer due to the heat generated during bonding and the effect of the heat treatment process, There is a risk of warping the whole. As a result, the bonding conditions of the substrates, such as the bonding temperature, are restricted, and it may be difficult to ensure sufficient bonding strength and airtightness.

  In particular, the thickness-shear vibration mode or tuning-fork type piezoelectric vibrator is sealed in a high vacuum state or inert gas atmosphere in order to secure and maintain a low CI value and to obtain high quality and high stability. It is necessary to stop. For this purpose, the packages must be sealed by bonding the substrates with high airtightness. Furthermore, excessive heating during bonding of the substrates may affect the vibration characteristics of the piezoelectric vibrating reed and prevent desired performance from being obtained.

  However, as described above, in the conventional method for directly joining metal films on the joining surfaces, a piezoelectric fork of a tuning fork type or a thickness-shear vibration mode is used for room temperature bonding from room temperature to a low temperature of 180 ° C. or lower or 100 ° C. or lower. Therefore, there is a problem that it takes a relatively long time to secure the bonding strength to such an extent that a necessary and sufficient hermeticity can be obtained. Therefore, productivity is low and it is not suitable for industrial practical use. On the other hand, when the substrates are bonded under heating at 300 ° C. as in the above-described prior art, it takes a long time to bring the inside of the package to a sufficient vacuum state, and is similarly not industrially suitable. There is.

  In addition, as described above, it is necessary to bond three conventional piezoelectric vibrators for bonding the piezoelectric substrate and the protective substrate on both upper and lower surfaces thereof by diffusion bonding between metals or room temperature bonding for the following reason. That is, when these are bonded one by one, they are formed on the surface of the piezoelectric substrate so as to pressurize them when bonding the intermediate piezoelectric substrate and one protective substrate, and to bond to the other protective substrate. The metal film is made to have a surface roughness that is insufficient for diffusion bonding by the pressurizing means, and it becomes dirty. Therefore, if the other protective substrate is pasted together in a later process, it is difficult to ensure sufficient airtightness and bonding strength necessary for the thickness-shear vibration mode crystal unit and tuning-fork type crystal unit. Produce.

  However, it is relatively difficult to obtain high alignment accuracy by simultaneously bonding the piezoelectric substrate and the protective substrate to the upper and lower surfaces thereof. In addition, the simultaneous bonding of the three substrates cannot adjust the frequency in a state where the piezoelectric vibrating piece is packaged. Therefore, a high-performance and high-quality piezoelectric vibrator having high frequency accuracy cannot be obtained.

  Accordingly, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a piezoelectric substrate integrally formed with a piezoelectric vibrating piece such as quartz and an outer frame, and an upper and lower substrate bonded to both upper and lower surfaces. In the piezoelectric vibrator that can be reduced in size and thickness, not only the conventional generation of outer gas, corrosion due to moisture, airtightness, or the problem of warping due to the difference in thermal expansion coefficient, etc. Provided is a piezoelectric vibrator capable of easily and easily aligning a piezoelectric substrate and upper and lower piezoelectric substrates, and capable of ensuring sufficient airtightness and bonding strength necessary for the piezoelectric vibrator, and a method for manufacturing the same. There is to do.

  A further object of the present invention is to provide a high-performance and high-quality piezoelectric vibrator having high frequency accuracy and a method for manufacturing the same.

  According to the present invention, in order to achieve the above object, for example, a piezoelectric vibrating piece having a thickness-shear vibration mode as a main vibration, and a piezoelectric material whose upper surface is made of a bare surface of a mirror-polished piezoelectric material and whose lower surface is mirror-polished. An intermediate piezoelectric substrate integrally bonded with an outer frame having a conductive film formed on the surface of the material, and a surface of the piezoelectric material made of the same piezoelectric material as the intermediate piezoelectric substrate and having a joint surface between the upper surface of the outer frame and mirror polished An upper piezoelectric substrate made of the same material as the intermediate piezoelectric substrate, and a lower piezoelectric substrate having a metal thin film formed on the surface of the piezoelectric material having a mirror-polished joint surface with the lower surface of the outer frame. After the surface of the upper surface of the frame and the upper piezoelectric substrate are surface-activated by, for example, plasma processing or ion beam processing, they are bonded hermetically by surface-activated bonding between the piezoelectric materials. And the bonding surfaces of the lower piezoelectric substrate are air-bonded to each other by diffusion bonding between the conductive film and the metal thin film after surface activation, for example, by plasma treatment or ion beam treatment, whereby the intermediate piezoelectric substrate and the upper and lower sides are joined together. There is provided a piezoelectric vibrator in which a piezoelectric vibrating piece is held in a floating state in a cavity defined and sealed with a piezoelectric substrate.

  In this way, the upper, middle and lower substrates made of the same piezoelectric material, such as quartz, are joined together by surface activated bonding or diffusion bonding, thereby further reducing the size compared to conventional piezoelectric vibrators. In addition to eliminating the problem of residual stress due to the difference in coefficient of thermal expansion, eliminating the generation of outer gas that deteriorates the characteristics of the piezoelectric vibrating piece and the problem of corrosion due to moisture, it is possible to improve the bonding strength. .

  In particular, since the intermediate piezoelectric substrate and the upper piezoelectric substrate and the intermediate piezoelectric substrate and the lower piezoelectric substrate are bonded under different conditions, it is practically difficult to bond three substrates at the same time. Will be joined one by one. Then, if surface activated bonding between the intermediate piezoelectric substrate and the upper piezoelectric substrate is performed in a later step, the intermediate piezoelectric substrate and the lower piezoelectric substrate can be bonded in a state where the surfaces of the conductive film and the metal thin film are suitable for diffusion bonding. Therefore, stronger bonding strength and high airtightness can be obtained.

  In one embodiment, the upper, middle and lower piezoelectric substrates are joined with their crystal plane orientations aligned so that each substrate has the same tendency to temperature changes and the temperature characteristics of the piezoelectric vibrator are further improved. Can be made.

  According to another aspect of the present invention, for example, a piezoelectric vibrating piece having a thickness-shear vibration mode as a main vibration and a piezoelectric material whose upper surface is mirror-polished and whose lower surface is mirror-polished. A step of forming an intermediate piezoelectric substrate in which the outer frame having the formed conductive film is integrally bonded, and a surface of the piezoelectric material made of the same piezoelectric material as the intermediate piezoelectric substrate and having a joint surface with the upper surface of the outer frame mirror-polished A lower piezoelectric substrate having a metal thin film formed on the surface of a piezoelectric material made of the same piezoelectric material as the intermediate piezoelectric substrate and having a joint surface with the lower surface of the outer frame mirror-polished. A step of forming, surface activating the upper and lower surfaces of the outer frame of the intermediate piezoelectric substrate, and the bonding surfaces of the upper and lower piezoelectric substrates by, for example, plasma treatment or ion beam treatment, and lower piezoelectric substrate An intermediate piezoelectric substrate is bonded to the lower piezoelectric substrate by superimposing the intermediate piezoelectric substrate thereon, and hermetically bonding the lower surface of the outer frame and the bonding surface of the lower piezoelectric substrate to each other by diffusion bonding of the conductive film and the metal thin film. The upper piezoelectric substrate is superposed on the upper surface of the outer frame, and the upper surface of the outer frame and the bonding surface of the upper piezoelectric substrate are hermetically bonded to each other by surface activation bonding of the piezoelectric materials. There is provided a method of manufacturing a piezoelectric vibrator that holds and seals a piezoelectric vibrating piece in a cavity defined between a substrate and a cavity.

  In this way, the upper, middle and lower substrates made of the same piezoelectric material, such as quartz, can be made smaller and thinner than before by surface activated bonding or diffusion bonding, and the residual due to the difference in thermal expansion coefficient. In addition to eliminating the problem of stress and the generation of outer gas and corrosion due to moisture, the upper, middle and lower substrates are divided into two stages, and surface activated bonding between the intermediate and upper piezoelectric substrates is performed later. By performing in this step, the intermediate piezoelectric substrate and the lower piezoelectric substrate can be bonded in a state where the surfaces of the conductive film and the metal thin film are suitable for diffusion bonding, so that stronger bonding strength and higher airtightness can be obtained.

  In one embodiment, after the lower piezoelectric substrate and the intermediate piezoelectric substrate are bonded, the piezoelectric vibrating piece is further adjusted in frequency before the upper piezoelectric substrate is bonded. The resonator element can be manufactured efficiently.

  In another embodiment, the upper, middle and lower piezoelectric substrates are joined with their crystal plane orientations aligned, so that the tendency of each substrate to temperature change is made the same, and the temperature characteristics of the piezoelectric vibrator are further improved. be able to.

  In another embodiment, forming an intermediate piezoelectric wafer having a plurality of intermediate piezoelectric substrates, forming an upper piezoelectric wafer having a plurality of upper substrates arranged corresponding to the intermediate piezoelectric substrates of the intermediate piezoelectric wafer, A step of forming a lower piezoelectric wafer in which a plurality of lower substrates are arranged corresponding to the intermediate piezoelectric substrate of the intermediate piezoelectric wafer, and upper and lower surfaces of the intermediate piezoelectric wafer and each bonding surface of the upper and lower piezoelectric wafers, for example, Surface activation by plasma treatment or ion beam treatment, step of superimposing an intermediate piezoelectric wafer on the lower piezoelectric wafer and bonding them together, and upper piezoelectric on the intermediate piezoelectric wafer bonded to the lower piezoelectric wafer There is provided a method of manufacturing a piezoelectric vibrator having a step of superimposing wafers and joining them together and a step of cutting a laminated body of joined piezoelectric wafers to separate the piezoelectric vibrators into individual pieces.As a result, a large number of piezoelectric vibrators can be manufactured at the same time, and productivity can be improved and costs can be reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a first embodiment of a thickness-shear vibration mode crystal resonator according to the present invention. As shown in FIGS. 1A and 1B, the crystal resonator 1 has a structure in which an upper crystal and lower crystal substrates 3 and 4 are integrally laminated on an upper surface and a lower surface of an intermediate crystal plate 2, respectively. The intermediate crystal plate 2 and the upper and lower crystal substrates 3 and 4 are each formed of an AT-cut crystal plate and are directly joined to each other in an airtight manner. These AT-cut quartz plates can be more suitably improved in frequency fluctuation, that is, temperature characteristics with respect to temperature changes of the crystal unit 1 by joining the crystal plane orientations together.

  As shown in FIGS. 2 (A) and 2 (B), the intermediate crystal plate 2 has a rectangular crystal vibrating piece 5 and an outer frame 6 integrally coupled at one end portion, that is, a base end portion 5a. Excitation electrodes 7 and 8 are formed on the upper and lower surfaces of the quartz crystal vibrating piece 5, respectively. The excitation electrode 7 on the upper surface is drawn from the base end portion 5 a to the upper surface of the outer frame 6 by the wiring film 9. Similarly, the excitation electrode 8 on the lower surface is pulled out from the base end portion 5 a and is electrically connected to the lower conductive film 10 formed over the entire circumference of the lower surface of the outer frame 6. A through hole 11 is provided at the distal end portion of the wiring film 9 at the longitudinal end portion of the outer frame 6 to which the base end portion 5 a of the crystal vibrating piece is coupled. A lead conductive film 13 separated from the lower conductive film 10 by the region 12 of the crystal element surface is formed on the lower surface of the longitudinal end portion of the outer frame 6, and the wiring film 9 is interposed through the conductive film inside the through hole 11. And are electrically connected.

  As shown in FIG. 3, the upper crystal substrate 3 has a recess 14 formed on the surface facing the intermediate crystal plate 2, that is, the lower surface. The peripheral portion surrounding the recess 14 on the lower surface of the upper crystal substrate 3 is composed of a crystal element surface, and constitutes a bonding surface 3 a with the intermediate crystal plate 2. As shown in FIG. 4, a concave portion 15 is similarly formed on the lower crystal substrate 4 on the surface facing the intermediate crystal plate 2, that is, the upper surface. A peripheral portion surrounding the concave portion 15 of the lower crystal substrate 4 constitutes a bonding surface 4a with the intermediate crystal plate 2, a metal thin film 16 corresponding to the lower conductive film 10 on the lower surface of the outer frame 6, and the metal thin film. A metal thin film 18 separated by the region 17 of the crystal face is formed. The crystal resonator element 5 is held and accommodated in a cantilevered state at the base end 5a in a cavity 19 defined by the recesses 14 and 15 when the intermediate crystal plate and the upper and lower crystal substrates are joined. Yes.

  The intermediate crystal plate 2 and the upper crystal substrate 3 are bonded to each other by surface activation bonding between crystal surfaces. The upper surface of the outer frame 6 and the upper crystal substrate bonding surface 3a are activated by a known plasma process or ion beam process, as will be described later, and then aligned and overlapped with each other, and a predetermined pressure is applied. Bonded in an airtight, good and stable state. At this time, in this embodiment, the concave portion 14 is provided so as to include the region of the wiring film so that the wiring film 9 does not contact the bonding surface 3a of the crystal face.

  On the other hand, the intermediate crystal plate 2 and the lower substrate 4 are bonded by diffusion bonding between metal thin films. Similarly, the lower surface of the outer frame 6 and the lower substrate bonding surface 4a are surface-activated by plasma processing, ion beam processing, etc., and then aligned and overlapped with each other, and by applying a predetermined pressure, Bonded in good and stable condition.

  The metal thin films 16 and 18 are preferably formed of, for example, a Cr film, a Ni / Cr film, a Ti film, or a Ni—Cr film as a base film, and an uppermost layer of an Au film. Correspondingly, the lower conductive film 10 and the lead conductive film 13 formed on the lower surface of the outer frame 6 of the intermediate crystal plate 2 are similarly formed of a Cr film, a Ni / Cr film, a Ti film, a Ni—Cr film, or the like. The uppermost layer is preferably formed of an Au film as the base film. In particular, when the film thickness of these Au films is 5000 mm or more, bonding can be performed with high airtightness in a relatively short time by diffusion bonding between the Au films. These metal thin films are easily formed by a known method such as sputtering, vapor deposition, plating, direct plating, or a combination thereof.

  On the lower surface of the lower substrate 4, as shown in FIG. 1C, external electrodes 20 and 21 are provided at each corner. Further, the lower substrate 4 has quarter circular chips 22 and 23 formed at each corner. This chipping is caused by, for example, castellations (circular through holes) formed at the intersections of the vertical and horizontal cutting lines when individual crystal plates are divided from a large crystal plate by dicing. Conductive films are formed on the inner surfaces of the notches 22 and 23, respectively, and the external electrodes 20 and 21 adjacent thereto are electrically connected to the lower conductive film 10 and the lead conductive film 13 of the intermediate crystal plate 2 viewed from the respective chips. Connected to.

  Next, a process for manufacturing the crystal resonator of FIG. 1 by the method of the present invention will be described. As shown in FIG. 5, a large intermediate crystal wafer 30 is prepared in which the plurality of crystal vibrating pieces 5 and the outer frame 6 of FIG. 1 are continuously arranged in the vertical and horizontal directions. The intermediate crystal wafer 30 is mirror-polished on both surfaces so that the surface roughness is preferably about several nanometers to several tens of nanometers. The external shapes of the crystal vibrating piece 5 and the outer frame 6 are formed by etching a crystal wafer using a photolithography technique. The excitation electrode, the wiring film, and the conductive film are formed on the surfaces of the quartz crystal vibrating pieces 5 and the outer frame 6 by depositing and patterning a conductive material by vapor deposition, sputtering, or the like.

  In parallel with this, a large upper crystal wafer 31 in which a plurality of upper substrates 3 are continuously arranged in the vertical and horizontal directions is prepared. The upper crystal wafer 31 is subjected to mirror polishing so that at least the lower surface bonded to the intermediate crystal wafer 30 has a surface roughness of preferably about several nanometers to several tens of nanometers. In the upper crystal wafer 31, a plurality of recesses 14 are formed on the surface facing the intermediate crystal wafer 30 so as to correspond to the crystal vibrating pieces 5 and the outer frame 6 of the intermediate crystal wafer. These recesses can be easily formed, for example, by etching or sandblasting the quartz wafer surface.

  Similarly, a large upper crystal wafer 32 in which a plurality of lower substrates 4 are continuously arranged in the vertical and horizontal directions is prepared. The lower crystal wafer 32 is mirror-polished so that at least the upper surface bonded to the intermediate crystal wafer 30 has a surface roughness of preferably several nanometers to several tens of nanometers. In the lower crystal wafer 32, a plurality of recesses 15 are formed on the surface facing the intermediate crystal wafer 30 so as to correspond to the crystal vibrating pieces 5 and the outer frame 6 of the intermediate crystal wafer by etching or sandblasting. In addition, circular through-holes 33 are formed in the lower crystal wafer 32 at the intersections of the outlines of the lower substrate 4 orthogonal to the vertical and horizontal directions. Further, the metal thin film on the upper surface of the lower substrate 4 is formed on the upper surface of the lower crystal wafer 32 by depositing and patterning a conductive material. External electrodes 20 and 21 on the lower surface of the lower substrate 4 are formed on the lower surface of the lower crystal wafer 32 by depositing and patterning a conductive material.

Next, the respective bonding surfaces of the upper, middle and lower crystal wafers 30 to 32 are subjected to plasma treatment to be surface activated. The plasma processing is performed using a known SWP type RIE plasma processing apparatus suitable for processing a large area such as a wafer. With this plasma processing apparatus, plasma is generated using, for example, microwaves of 13.56 MHz to 2.45 GHz, the reaction gas introduced into the processing chamber is excited, and active species such as ions and excited species of the reaction gas Is generated. In this embodiment, Ar alone, CF ₄ , N ₂ alone, O ₂ alone, a mixed gas of O ₂ and N ₂ or the like is used as the reaction gas. In addition to the above-described SWP type RIE method, the plasma treatment can also be performed by an atmospheric pressure plasma method or the like.

  By this plasma treatment, the surface of each wafer is exposed to the reactive gas active species and uniformly activated. That is, the bonding surfaces of the quartz wafers 30 to 32 are removed from the surface by etching organic substances, contaminants, dust, and the like with ions contained in the plasma, and are easily bonded directly by radicals in the plasma. Reformed. The SWP-type RIE plasma processing apparatus described above can perform such two-stage plasma processing continuously in the same chamber of one apparatus.

In another embodiment, instead of plasma treatment, each of the bonding surfaces can be surface activated by irradiating with an ion beam. This ion beam treatment is performed by a known method using an inert gas such as Ar, and the bonding surface is irradiated with an Ar ⁺ ion beam in a vacuum atmosphere of about 1.33 × 10 ⁻⁶ Pa, for example.

  After the surface activation process, as shown in FIG. 6A, the intermediate crystal wafer 30 and the lower crystal wafer 32 are bonded and temporarily bonded. In this temporary bonding, these wafers may be simply bonded together, or pressure is applied with a weaker force than when the upper crystal wafer 31 is bonded in a later process. Next, as shown in FIG. 6 (B), the upper crystal wafer 31 is aligned and superposed on the upper surface of the intermediate crystal wafer 30 for temporary bonding. The temporarily bonded crystal wafer laminated body 34 applies a pressing force of up to about 20 kg uniformly to the upper and lower surfaces thereof to bond the bonded surfaces firmly and airtightly. In this embodiment, this main bonding is performed at room temperature, but in another embodiment, bonding can be performed more satisfactorily by performing heating at a relatively low temperature of about 200 ° C. Further, the temporary bonding and the main bonding of the quartz wafer can be similarly performed in an atmospheric pressure atmosphere or in a vacuum.

  In the present embodiment, the frequency of each crystal vibrating piece can be adjusted in the state of FIG. 6A in which two crystal wafers are bonded. In that case, the intermediate crystal wafer 30 is previously removed from the conductive material that forms the lower conductive film 10 and the lead conductive film 13 of each crystal resonator by the line width that is diced along the outline 35 of the crystal resonator. To pattern. The lower crystal wafer 32 is patterned so that the conductive material forming the metal thin films 16 and 18 of each crystal resonator is similarly removed by the line width that is diced along the outline 35 of the crystal resonator. Since the excitation electrode of each crystal resonator 1 is electrically separated and independent from the excitation electrode of the adjacent crystal resonator in the state of the wafer, the characteristic test and the frequency measurement / Adjustments can be made. The frequency adjustment can be performed by irradiation with a laser beam or the like, or can be performed simultaneously with the plasma processing of the bonding surface on the upper surface of the intermediate crystal wafer 30 by the plasma processing using the plasma processing apparatus described above.

  Finally, as shown in FIG. 6C, the crystal wafer laminate 34 is cut and divided by dicing or the like along the outline 35 of the crystal resonator orthogonal to the vertical and horizontal directions. Thereby, the crystal unit 1 shown in FIG. 1 is completed. In another embodiment, the external electrodes on the bottom surface of the lower substrate 4 can be formed by sputtering or the like in a wafer laminated body state before dicing, thereby simplifying the process.

  FIG. 7 shows a second embodiment of a crystal resonator according to the present invention. As in the first embodiment of FIG. 1, in the crystal resonator 41 of the present embodiment, upper and lower crystal substrates 43 and 44 are integrally laminated with an intermediate crystal plate 42 interposed therebetween. As shown in FIGS. 8A and 8B, the intermediate crystal plate 42 is formed by integrally forming an AT-cut crystal vibrating piece 45 and an outer frame 46, and excitation electrodes 47, 48 is formed, but differs from the first embodiment in the following points.

  In the present embodiment, the plate thickness of the outer frame 46 is formed to be equal to both the upper and lower sides in the thickness direction and thicker than the crystal vibrating piece 45, and the crystal vibrating piece 45 and the outer frame 46 are respectively provided on the upper and lower surfaces via steps 49 and 50. Are combined. In particular, in the case of this embodiment, the step 49 is provided on the upper surface of the outer frame 46 on the inner side of the boundary with the crystal vibrating piece base end portion 45 a, and the wiring film 51 drawn out from the excitation electrode 47 has the step 49. It is formed in a region that is flush with the inner quartz crystal vibrating piece 45. The lower surface of the outer frame 46 is provided with a step 50 at the boundary with the crystal vibrating piece base end 45 a, and the lower conductive film 52 formed over the entire circumference of the outer frame is drawn through the step 50. The excitation electrode 48 is electrically connected.

  As in the first embodiment of FIG. 1, a through hole 53 is formed at the distal end portion of the wiring film 51 at the longitudinal end portion of the outer frame 46 coupled to the crystal vibrating piece base end portion 45a. A lead conductive film 55 separated from the lower conductive film 52 by a crystal element surface region 54 is formed on the lower surface of the outer edge 46 in the longitudinal direction. The lead conductive film 55 is separated from the wiring film 51 via the conductive film inside the through hole 53. Electrically connected.

  Further, the present embodiment is different from the first embodiment in that the upper and lower crystal substrates 43 and 44 are flat plates each having a flat surface facing the intermediate crystal plate 42. The entire lower surface of the upper crystal substrate 43 is made of a crystal element surface. On the other hand, on the upper surface of the lower crystal substrate 44, as shown in FIG. 9, the metal thin film 56 and the lower conductive film 52 and the lead conductive film 55 on the lower surface of the outer frame 46 of the intermediate crystal plate 42 are formed. A metal thin film 58 is formed which is electrically separated by the region 57 of the crystal face.

  The intermediate crystal plate 42 and the upper crystal substrate 43 are bonded to each other after the surface of the joint is activated by, for example, a known plasma treatment or ion beam treatment, and are superposed in alignment with each other. It is airtightly and satisfactorily joined by surface activated joining. Similarly, the intermediate crystal plate 42 and the lower crystal substrate 44 are each made of a metal thin film by applying a predetermined pressure after aligning and joining each other after surface activation by plasma treatment or ion beam treatment. It is joined airtightly and satisfactorily by diffusion bonding between them. The crystal vibrating piece 45 floats in a cantilever manner at the base end portion 45a in the cavity 59 defined inside the crystal resonator 41 by making the outer frame 46 of the intermediate crystal plate 42 thicker than the crystal vibrating piece 45. It is held in the state.

  Similarly, the crystal resonator 41 of the second embodiment can be manufactured by the method of the present invention according to the steps shown in FIG. At this time, the upper and lower crystal wafers constituting the large number of upper and lower crystal substrates 43 and 44 can be advantageously formed of wafers that are flat on both sides.

  FIG. 10 shows a third embodiment of a crystal resonator according to the present invention. As in the first embodiment of FIG. 1, in the crystal resonator 61 of this embodiment, upper and lower substrates 63 and 64 are integrally laminated with an intermediate crystal plate 62 interposed therebetween. As shown in FIGS. 11A and 11B, the intermediate crystal plate 62 has an AT-cut crystal vibrating piece 65 and an outer frame 66 integrally formed, and excitation electrodes 67, 68 is formed, but differs from the first embodiment in the following points.

  In the present embodiment, the lower surface of the outer frame 66 is arranged in the same plane as the lower surface of the crystal vibrating piece 65, and the thickness thereof is increased only upward in the thickness direction, and the outer frame 66 is coupled to the crystal vibrating piece base end 65a. A step 69 with respect to the crystal vibrating piece 65 is formed on the upper surface side of the end portion in the longitudinal direction of the frame 66. Similar to the second embodiment, the step 69 is provided on the inner side of the boundary with the crystal vibrating piece base end portion 65 a, and the wiring film 70 drawn out from the excitation electrode 67 is disposed inside the step 69. It is formed in a region that is flush with the piece 65. A lower conductive film 71 formed over the entire circumference of the lower surface of the outer frame 66 is electrically connected to the excitation electrode 68 drawn from the base end portion 65a.

  As in the first embodiment of FIG. 1, a through hole 72 is formed at the distal end portion of the wiring film 70 at the longitudinal end portion of the outer frame 66 coupled to the crystal vibrating piece base end portion 65a. A lead conductive film 74 separated from the lower conductive film 71 by a crystal element surface region 73 is formed on the lower surface of the end portion in the longitudinal direction of the outer frame 66, and the wiring film 70 and the conductive film inside the through hole 72 are interposed therebetween. Electrically connected.

  Further, the present embodiment is different from the first embodiment in that the upper crystal substrate 63 is a flat plate having a flat surface facing the intermediate crystal plate 62. The lower crystal substrate 64 has the same configuration as the lower crystal substrate 4 of the first embodiment. That is, as shown in FIG. 12, the lower crystal substrate 64 has a recess 75 formed on the surface facing the intermediate crystal plate 62, that is, the upper surface. A peripheral portion surrounding the concave portion 75 of the lower crystal substrate 4 constitutes a bonding surface with the intermediate crystal plate 2, a metal thin film 76 corresponding to the lower conductive film 71 on the lower surface of the outer frame 66, and a crystal formed from the metal thin film. A metal thin film 78 separated by a bare surface region 77 is formed.

  The intermediate crystal plate 62 and the upper crystal substrate 63 are obtained by crystallizing the crystal surfaces by applying a predetermined pressure to each other after the surface of each of the intermediate crystal plates 62 and the upper crystal substrate 63 is surface-activated by, for example, known plasma processing or ion beam processing. It is airtightly and satisfactorily joined by surface activated joining. Similarly, the intermediate crystal plate 62 and the lower crystal substrate 64 are obtained by subjecting the joint surfaces to surface activation by plasma processing or ion beam processing, aligning them with each other, and applying a predetermined pressure. It is joined airtightly and satisfactorily by diffusion bonding between them. The crystal vibrating piece 65 floats in a cantilever manner at the base end portion 65a in the cavity 79 defined inside the crystal resonator 61 by making the outer frame 66 of the intermediate crystal plate 62 thicker than the crystal vibrating piece 65. It is held in the state.

  The preferred embodiments of the present invention have been described in detail above. However, as will be apparent to those skilled in the art, the present invention can be carried out with various modifications and changes made to the above embodiments within the technical scope thereof. . For example, the intermediate crystal plate, the upper crystal substrate, and the lower crystal substrate can be formed of various other known piezoelectric materials such as lithium tantalate and lithium niobate. Even in that case, the temperature characteristics of the piezoelectric vibrator can be improved more favorably by forming each piezoelectric plate with the same piezoelectric material and bonding the crystal plane orientations. Further, the present invention can be similarly applied to a tuning fork type piezoelectric vibrator.

(A) is a side view of a first embodiment of a crystal resonator according to the present invention, (B) is a longitudinal sectional view thereof, and (C) is a bottom view thereof. (A) is a top view of the intermediate crystal plate shown in FIG. 1, and (B) is a bottom view thereof. The bottom view of the upper side crystal substrate shown in FIG. FIG. 2 is a top view of the lower crystal substrate shown in FIG. 1. 4 is a schematic perspective view showing three crystal wafers bonded together in the manufacturing process of the crystal resonator according to the method of the present invention. FIG. (A) is an explanatory view showing the procedure for bonding the middle and lower crystal wafers, (B) is an explanatory diagram showing the procedure for bonding the upper crystal wafer, and (C) is a bond of three crystal wafers. The schematic perspective view which shows a body. The longitudinal cross-sectional view of 2nd Example of the crystal oscillator by this invention. (A) is a top view of the intermediate crystal plate shown in FIG. 7, and (B) is a bottom view thereof. FIG. 8 is a top view of the lower crystal substrate shown in FIG. 7. The longitudinal cross-sectional view of 3rd Example of the crystal oscillator by this invention. (A) is a top view of the intermediate crystal plate shown in FIG. 10, and (B) is a bottom view thereof. FIG. 11 is a top view of the lower crystal substrate shown in FIG. 10.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41,61 ... Crystal oscillator, 2, 42, 62 ... Intermediate crystal plate, 3, 43, 63 ... Upper crystal substrate, 3a, 4a ... Bonding surface, 4, 44, 64 ... Lower crystal substrate, 5, 45, 65 ... crystal resonator element, 5a, 45a, 65a ... base end, 6, 46, 66 ... outer frame, 7, 8, 47, 48, 67, 68 ... excitation electrode, 9, 51, 70 ... wiring film DESCRIPTION OF SYMBOLS 10,52,71 ... Lower conductive film 11, 53, 72 ... Through hole, 12, 17, 54, 57, 73, 77 ... Area, 13, 55, 74 ... Lead conductive film, 14, 15, 75 Recess, 16, 18, 56, 58, 76, 78 ... Metal thin film, 19, 59, 79 ... Cavity, 20, 21 ... External electrode, 22, 23 ... Chip, 30 ... Intermediate crystal wafer, 31 ... Upper crystal wafer 32 ... Lower crystal wafer, 33 ... Through hole, 34 ... Wafer stack, 35 ... Outer shell , 49,50,69 ... step.

Claims (10)

An intermediate piezoelectric substrate in which a piezoelectric vibrating piece and an outer frame having a conductive film formed on the surface of the piezoelectric material whose upper surface is made of a mirror-polished piezoelectric material and whose lower surface is mirror-polished are integrally coupled;
An upper piezoelectric substrate made of the same piezoelectric material as the intermediate piezoelectric substrate, and a bonding surface with the upper surface of the outer frame made of a material surface of the piezoelectric material that has been mirror-polished;
A lower piezoelectric substrate made of the same piezoelectric material as the intermediate piezoelectric substrate, and having a metal thin film formed on the surface of the piezoelectric material having a mirror-polished joint surface with the lower surface of the outer frame,
After the surface of the outer frame upper surface and the bonding surface of the upper piezoelectric substrate are each surface activated, they are bonded airtight by surface activated bonding between the piezoelectric materials,
The joint surfaces of the outer frame lower surface and the lower piezoelectric substrate are each surface-activated, and then are airtightly bonded to each other by diffusion bonding of the conductive film and the metal thin film,
Accordingly, the piezoelectric vibrator is held in a state of being floated in a cavity defined and sealed between the intermediate piezoelectric substrate and the upper and lower piezoelectric substrates.   The piezoelectric vibrator according to claim 1, wherein the piezoelectric vibrating piece has a thickness-shear vibration mode as a main vibration.   The piezoelectric vibrator according to claim 1 or 2, wherein the upper, middle and lower piezoelectric substrates are bonded with their crystal plane orientations aligned.   The piezoelectric vibrator according to claim 1, wherein the piezoelectric material is quartz. An intermediate piezoelectric substrate is formed by integrally bonding a piezoelectric vibrating piece and an outer frame having a conductive film formed on the surface of the piezoelectric material whose upper surface is made of a mirror-polished piezoelectric material and whose lower surface is mirror-polished. And a process of
Forming an upper piezoelectric substrate made of the same piezoelectric material as that of the intermediate piezoelectric substrate and made of a material surface of the piezoelectric material having a mirror-polished joint surface with the outer frame upper surface;
Forming a lower piezoelectric substrate made of the same piezoelectric material as the intermediate piezoelectric substrate and having a metal thin film formed on the surface of the piezoelectric material having a mirror-polished bonding surface with the lower surface of the outer frame;
Surface activation of the upper and lower surfaces of the outer frame of the intermediate piezoelectric substrate and the bonding surfaces of the upper and lower piezoelectric substrates;
Overlaying the intermediate piezoelectric substrate on the lower piezoelectric substrate, and bonding the lower surface of the outer frame and the bonding surface of the lower piezoelectric substrate in an airtight manner by diffusion bonding of the conductive film and the metal thin film; ,
The upper piezoelectric substrate is superimposed on the upper surface of the intermediate piezoelectric substrate bonded to the lower piezoelectric substrate, and the upper surface of the outer frame and the bonding surface of the upper piezoelectric substrate are hermetically sealed by surface activated bonding between the piezoelectric materials. And a step of bonding to
A method for manufacturing a piezoelectric vibrator, comprising: holding and sealing the piezoelectric vibrating piece in a floating state in a cavity defined between the intermediate piezoelectric substrate and the upper and lower piezoelectric substrates.   6. The piezoelectric device according to claim 5, further comprising a step of adjusting a frequency of the piezoelectric vibrating piece after joining the lower piezoelectric substrate and the intermediate piezoelectric substrate and before joining the upper piezoelectric substrate. A method for manufacturing a vibrator.   Forming an intermediate piezoelectric wafer having a plurality of the intermediate piezoelectric substrates, forming an upper piezoelectric wafer having the plurality of upper substrates arranged corresponding to the intermediate piezoelectric substrates of the intermediate piezoelectric wafer, and a plurality of the above Forming a lower piezoelectric wafer in which a lower substrate is disposed in correspondence with the intermediate piezoelectric substrate of the intermediate piezoelectric wafer; and upper and lower surfaces of the intermediate piezoelectric wafer and bonding surfaces of the upper and lower piezoelectric wafers. A step of surface activation, a step of superimposing the intermediate piezoelectric wafer on the lower piezoelectric wafer and integrally bonding the upper piezoelectric wafer, and an upper piezoelectric wafer on the intermediate piezoelectric wafer bonded to the lower piezoelectric wafer. 7. The method according to claim 5, further comprising a step of superimposing and integrally bonding, and a step of cutting the laminated body of the bonded piezoelectric wafers to divide the piezoelectric vibrator into individual pieces. Method of manufacturing the electric vibrator.   The piezoelectric vibrator according to claim 5, wherein the piezoelectric vibrating piece has a thickness-shear vibration mode as a main vibration.   9. The piezoelectric vibrator according to claim 5, wherein the upper, middle and lower piezoelectric substrates are joined with their crystal plane orientations aligned.   The method for manufacturing a piezoelectric vibrator according to claim 5, wherein the piezoelectric material is quartz.

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