JP2006279777A - Surface acoustic wave device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely air-tightly seal an exciting portion and to ensure electrical insulation between a lead wire drawn to the outside of a cover and a metal bonding portion on a surface of a piezoelectric substrate, in a SAW device of a double layer structure made by bonding a SAW chip and the cover through metal bonding. <P>SOLUTION: A SAW device 1 comprises a SAW chip 2 and a cover 3. In the SAW chip 2, the exciting portion comprised of an IDT electrode 5 and a reflector 6, a metal bonding part 9 surrounding the exciting portion, an extraction electrode 8 disposed outside the metal bonding part and a lead wire 7 drawn from the IDT electrode across the metal bonding part are formed on a piezoelectric substrate 4 and in the cover 3 on which a metal bonding part 13 is formed along all the periphery in a peripheral portion of a lower surface of a glass pane. The metal bonding part of the SAW chip is comprised of an insulating layer 10 of SiO<SB>2</SB>or the like formed on the surface of the piezoelectric substrate and the lead wire and a bonding metal layer 11 laminated thereon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electronic device including functional elements such as piezoelectric elements and other various electronic components, and in particular, SAW elements using surface acoustic waves (SAW), piezoelectric elements such as piezoelectric vibrating pieces, and the like are hermetically sealed. It relates to a piezoelectric device sealed.

  Conventionally, SAW devices such as resonators, filters, and oscillators using an SAW element that includes an IDT (interdigital transducer) formed of interdigitated electrodes formed on the surface of a piezoelectric substrate and uses surface acoustic waves excited from the IDT have been used. Widely used in various electronic devices. Recently, in addition to the higher frequency and higher accuracy of SAW devices that support higher speeds of information communication, the size and thickness have been further reduced for use in small and thin information devices such as IC cards. Is required.

  Therefore, recently, a two-layer structure in which a surface acoustic wave element having an IDT electrode and an extraction electrode on the surface of a piezoelectric substrate and a cover substrate made of a glass plate are provided, and the IDT electrode is sealed by directly joining the piezoelectric substrate and the cover substrate. A surface acoustic wave device having a structure has been proposed (see, for example, Patent Document 1). With this configuration, the bonding wire for connecting the SAW element and the package side that accommodates the SAW element in the conventional structure and the base of the package for mounting the SAW element are omitted, thereby making the entire configuration simple, small and thin, The manufacturing cost is reduced and the frequency characteristics are stabilized.

  Similarly, in a surface acoustic wave device having a two-layer structure, an excitation part such as an interdigitated electrode, a bonding pad and a lead electrode are formed on a piezoelectric substrate, and a cover plate is overlaid on an insulating thin film formed around the excitation part. There is known a structure in which the excitation portion is sealed in a narrow space between the piezoelectric substrate and the cover plate, and a bonding pad is disposed on the outside thereof (see, for example, Patent Document 2). The bonding pad is connected to an external lead terminal by a bonding wire. With this configuration, it is possible to reduce the size, eliminate the possibility of hindering the operation of the excitation unit, stabilize the characteristics of the element, and the excitation unit is covered with a narrow space, so it is not necessary to seal in an inert atmosphere. .

  Further, the surface is reduced in size by forming a comb-shaped electrode, a lead electrode and an external connection pad on the surface of the insulating substrate, covering the comb-shaped electrode portion with a piezoelectric film, and sealing the comb-shaped electrode and the piezoelectric film portion with a cap. An acoustic wave element is known (see, for example, Patent Document 3). The cap controls the adhesive to be applied to a necessary amount by transferring the adhesive onto the adhesive surface with the insulating substrate, and prevents the deterioration of the characteristics due to the protrusion to the piezoelectric film portion.

  Further, in the transversal surface acoustic wave device in which the interdigital electrodes and the extraction electrode portions are formed on the piezoelectric substrate, the interdigital electrodes are covered with a simple substance or a composite film of metal or insulating material so as to provide a slight gap. A sealed structure is known (see, for example, Patent Document 4). This composite film is formed by forming a film of metal or insulating material on the photoresist covering the interdigitated electrode portion, opening a hole in this, melting and removing the internal photoresist, and then closing the hole. It is formed. With such a configuration, high reliability can be obtained and the manufacturing cost can be reduced.

Japanese Patent Laid-Open No. 8-213874 JP-A-10-163798 JP 2000-174580 A JP 2000-22488 A

  However, the surface acoustic wave elements described in Patent Documents 2 and 3 use a resin material or a resin-based adhesive in order to join a lid or a cap to a substrate on which a cross finger electrode or a comb electrode is formed. . Such a resin material or adhesive often has a hygroscopic property, and there is a possibility that the space sealed with a lid or a cap cannot sufficiently secure or maintain airtightness. In particular, in the case of a SAW resonator, accuracy higher than that of a filter is required. Therefore, if sufficient airtightness is not obtained, there arises a problem that characteristics are deteriorated and a slight change in resonance frequency occurs.

  Patent Document 2 discloses a configuration in which an insulating thin film made of a metal thin film such as aluminum is formed as a fixing pattern around an excitation portion of a piezoelectric substrate. For this fixing pattern, a corresponding aluminum fixing pattern is formed on the surface acoustic wave element mounting substrate, and ultrasonic bonding between the aluminum and aluminum, gold metallization and thermocompression bonding, conductive adhesive, etc. It is joined by bonding with. In this configuration, the lead electrode and the fixing pattern are separately formed to prevent electrical short-circuit between them, so that the extraction electrode is defined by a recess formed on the surface acoustic wave element mounting substrate so as to surround the excitation portion. Airtightness is not ensured in the space that is used. Therefore, it is necessary to seal the entire surface acoustic wave element with a molding resin, and it is impossible to realize the demand for downsizing and thinning the apparatus.

  Therefore, the present invention has been made in view of the above-described conventional problems, and its purpose is to directly bond a SAW chip having an excitation part such as an IDT on the surface of a piezoelectric substrate and a cover by metal bonding. In a SAW device having a two-layer structure in which the excitation part is hermetically sealed and lead wires are drawn out from the inside to the outside of the cover on the piezoelectric substrate surface to be electrically connected to the outside, the size and thickness of the SAW device can be reduced. In addition to ensuring the electrical insulation between the metal joint and the lead wire intersecting with it, the airtightness of the gap sealed with the cover is secured to prevent deterioration of the characteristics, and with high accuracy. It is to realize a high-performance SAW device.

  Another object of the present invention is to provide a cover on a base provided with functional elements such as a piezoelectric fork type and piezoelectric gyro element such as a tuning fork type and thickness shear vibration mode, a piezoelectric gyro element, an IC chip, and other electronic components in addition to the SAW element. Piezoelectric device having a package structure in which the functional elements are hermetically sealed by metal bonding, and lead wires are drawn out from the inner side to the outer side of the base to be electrically connected to the outside. In the electronic device, the size and thickness of the electronic device must be reduced, and the airtightness inside the package sealed by the cover can be ensured while ensuring the electrical insulation between the metal joint and the lead wire intersecting the metal joint. It is in.

  According to a certain aspect of the present invention, in order to achieve the above object, an excitation part comprising an IDT electrode, a metal joint surrounding the excitation part, an extraction electrode disposed outside the metal joint, and an IDT electrode A surface acoustic wave (SAW) chip that is formed on the main surface of the piezoelectric substrate with lead wires that intersect with the metal junction and are connected to the extraction electrode, and is provided around the entire periphery of the lower surface of the insulating substrate. A cover having a metal joint portion, and the metal joint portion of the SAW chip is composed of an insulating layer formed on the surface of the piezoelectric substrate and the lead wire, and a joining metal layer laminated on the insulating layer. The chip and the cover are integrally formed so as to hermetically seal the excitation unit in the space defined between the SAW chip and the cover by bonding the bonding metal layer of the SAW chip and the metal bonding part of the cover. Joined surface acoustic wave device Vinegar is provided.

  As described above, the SAW chip and the cover are directly bonded to each other, so that the SAW device can be reduced in size and thickness. In addition, the insulating layer leads at the intersection between the metal bonding portion of the SAW chip and the lead wire. The electrical insulation between the wire and the metal joint can be ensured and the excitation part can be hermetically sealed, so that even when high frequency accuracy is required, the operation and the stability of the frequency characteristics can be improved. .

  In one embodiment, the thickness after joining the metal joint of the SAW chip and the metal joint of the cover is set to be greater than the thickness of the IDT electrode so that the IDT electrode does not contact the cover. Therefore, the scheduled operation can be ensured.

In another embodiment, the metal joint portion of the SAW chip is formed by an insulating layer formed of SiO ₂ and a bonding metal layer formed of a Cr / Au film and an AuSn alloy film laminated thereon, thereby The SAW chip and the cover can be easily joined together by thermocompression bonding or eutectic bonding.

  According to another aspect of the present invention, a base, a functional element provided on the base, a metal joint provided on the surface of the base so as to surround the functional element, and an outer side of the metal joint on the surface of the base The lead electrode placed on the base, the lead wire that crosses the metal joint from the functional element on the surface of the base and connects to the lead electrode, and the metal that is provided along the entire periphery of the lower surface of the insulating substrate. A cover having a joint portion, wherein the metal joint portion of the base includes an insulating layer formed on the surface of the base and the lead wire, and a joint metal layer laminated on the insulating layer, the base and the cover, Bonding the bonding metal layer of the base and the metal bonding portion of the cover provides an electronic device that is integrally bonded to hermetically seal the functional element in a space defined between the base and the cover. .

  Here, the functional element includes not only the SAW element described above but also a piezoelectric element such as a tuning fork-type or thickness-shear vibration mode piezoelectric vibrating piece or a piezoelectric gyro element, an IC chip, and various electronic components. With such a configuration, the functional element can be hermetically sealed while ensuring electrical insulation between the lead wire and the metal joint portion by the insulating layer at the intersection between the metal joint portion of the base and the lead wire. , The stability of the operation can be improved.

In one embodiment, the base metal joint is formed by an insulating layer formed of SiO ₂ and a joint metal layer formed of a Cr / Au film and an AuSn alloy film laminated thereon, thereby forming the base. And the cover can be easily joined together by thermocompression bonding or eutectic bonding.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1A to 1C show a configuration of a preferred embodiment of a SAW resonator to which the present invention is applied. The SAW resonator 1 has a structure in which a SAW chip 2 and a cover 3 are directly joined. The SAW chip 2 is formed of a rectangular piezoelectric substrate 4 as shown in FIGS. 1A and 1B, and an IDT 5 including a pair of crossed finger electrodes is formed at the center of the upper surface, and reflectors are formed on both sides in the longitudinal direction. 6,6 are formed. The interdigitated electrodes have lead wires 7 and 7 drawn out from the bus bar in opposite directions along the longitudinal edges of the piezoelectric substrate 4, respectively, and take-out electrodes 8 formed near the corners in the diagonal direction of the piezoelectric substrate. , 8 are connected.

  The piezoelectric substrate 4 of this embodiment is made of quartz. In other embodiments, other piezoelectric materials such as lithium tantalate and lithium niobate can be used. The crossed finger electrode, the reflector and the lead wire are formed of an Al film from the viewpoint of characteristics, workability and cost. The crossed finger electrode or the like may be made of a conductive metal material such as an aluminum alloy generally used in addition to Al. The extraction electrodes 8, 8 are made of, for example, a Cr / Au film, a Cr / Ni / Au film, or an Al or Al alloy film.

A rectangular frame-shaped metal joint 9 is provided on the upper surface of the piezoelectric substrate 4. The metal joint portion 9 is formed so as to straddle the lead wires 7 and 7 so as to completely surround the excitation portion composed of the IDT 5 and the reflectors 6 and 6 and so that the extraction electrodes 8 and 8 are positioned on the outer side. The metal bonding portion 9 includes an insulating layer 10 formed on the upper surface of the piezoelectric substrate 4 and lead wires 7 formed on the upper surface, and a bonding metal layer 11 laminated thereon. The insulating layer 10 is formed of a hard thin film formed by sputtering, vapor deposition, or CVD using an insulating material such as SiO ₂ . The thickness of the insulating layer 10 is set so that electrical insulation between the lead wire and the bonding metal layer 11 can be secured at the intersection with the lead wires 7 and 7. As the insulating material for forming the insulating layer, a material that can ensure airtightness and does not have hygroscopicity or moisture permeability is preferable. In addition to SiO ₂ , for example, Al ₂ O ₃ or DLC (diamond-like carbon) is used. A diamond film or the like can be used.

  As shown in FIGS. 1A and 1B, the bonding metal layer 11 is more than the insulating layer 10 in order to ensure electrical insulation with the lead wires at the intersections with the lead wires 7 and 7. Narrow and slightly spaced inward from both edges. As shown well in FIG. 1C, the bonding metal layer 11 of the present example includes a Cr film 12 formed on the insulating layer 10 as a base layer, an Au film 13 formed thereon, and It comprises an AuSn alloy layer 14 laminated thereon. For the AuSn alloy layer 14, various conventionally known metals or alloy materials suitable for metal bonding can be used. In another embodiment, the Cr film 12 can be formed of a Cr / Ni film and / or the Au film 13 can be formed of an Au / Ni film.

  The cover 3 is formed of a rectangular glass thin plate corresponding to the outer shape and dimensions of the metal joint portion 9 of the piezoelectric substrate 4. On the lower surface of the cover 3, as shown in FIG. 2, a metal joint 15 is formed around the entire periphery of the cover 3. The metal joint 15 of the cover 3 has a frame shape and dimensions corresponding to the joint metal layer 11 of the metal joint 9 of the piezoelectric substrate 4. As shown in FIG. 1C, the metal bonding portion 15 is formed by laminating a Cr film 16 formed on the surface of the glass thin plate as an underlayer, an Au film 17 formed thereon, and further thereon. AuSn alloy layer 18. Similarly, various conventionally known metals or alloy materials suitable for bonding with the bonding metal layer 11 of the piezoelectric substrate 4 can be used for the AuSn alloy layer 18. In another embodiment, the Cr film 16 can be formed of a Cr / Ni film and / or the Au film 17 can be formed of an Au / Ni film.

  In this embodiment, soda glass having a thermal expansion coefficient close to that of the crystal of the piezoelectric substrate 4 is used for the glass thin plate constituting the cover 3. In another embodiment, the cover 3 can be formed of another glass material or insulating material having a thermal expansion coefficient comparable or close to that of quartz, or of course, the same quartz as the piezoelectric substrate 4. Further, when the piezoelectric substrate 4 is formed of a piezoelectric material other than quartz, the cover 3 can be formed of a thin plate of an insulating material having a thermal expansion coefficient comparable or approximate to that.

  The SAW chip 2 and the cover 3 are integrally joined to each other by thermocompression bonding or eutectic bonding between the metal joint 9 and the metal joint 15. Accordingly, the IDT 5 and the reflectors 6 and 6 are hermetically sealed in a narrow gap defined between the SAW chip 2 and the cover 3. Therefore, the thicknesses of the metal joint 9 and the metal joint 15 are determined so that the gap can be sufficiently defined between the SAW chip 2 and the cover 3 when they are joined. In this embodiment, as shown in the drawing, the thickness in the state where the two metal joints are joined is set to be thicker than the Al film forming the IDT 5 and the reflectors 6 and 6. In another embodiment, when the SAW chip 2 and the cover 3 are joined together, the thickness of each metal joint is set so that the lower surface of the cover 3 is in contact with the upper ends of the IDT 5 and the reflectors 6, 6. Thinning can also be achieved.

  Further, in the metal joint portion 9 of the piezoelectric substrate 4, steps are generated in the insulating layer 10, the Cr film 12, and the Au film 13 at the intersections with the lead wires 7 and 7 as shown in FIG. Since the film thickness of the lead wire is relatively small, this step is absorbed when the AuSn alloy layers 14 and 18 of the metal joints 9 and 15 are sufficiently thick so that they are bonded by thermocompression bonding or eutectic bonding. can do. Therefore, sufficient airtightness and bonding strength can be ensured over the entire circumference of the metal bonding portion.

  FIG. 3 shows a connection state with the outside when the SAW resonator 1 of this embodiment is used. Since the SAW resonator 1 has extraction electrodes 8 and 8 provided on the upper surface of the piezoelectric substrate 4, the SAW resonator 1 can be connected to the outside by a bonding wire 19 after being fixed at a predetermined position. Further, it is possible to connect with a lead frame instead of wire bonding. Thus, the SAW resonator 1 of the present embodiment can be mounted on a bare chip.

  4A and 4B show a modification of the SAW resonator 1 shown in FIG. The SAW resonator 1 of this modification is provided with connection terminals 20a and 20b for external connection at each corner of the bottom surface of the piezoelectric substrate 4. The ends of the lead wires 7 drawn out to the outside of the cover 3 are electrically connected to the corresponding connection terminals 20a through the through holes 21 formed in the piezoelectric substrate 4, respectively. Thus, the SAW resonator 1 can be directly surface mounted on an external device such as a circuit board. The terminal 20b that is not connected to any of the lead wires 7 is a so-called dummy terminal.

  5A and 5B show another modification of the SAW resonator 1 shown in FIG. In the SAW resonator 1 of this modified example, external connection terminals 20a and 20b are provided at each corner of the bottom surface of the piezoelectric substrate 4 as in the modified example of FIG. The end portions of the lead wires 7 drawn out to the outside of the cover 3 are extended to the peripheral edge of the piezoelectric substrate 4, and the corresponding connection terminals 20 a are formed through the electrode films 22 formed on the side surfaces of the piezoelectric substrate 4. And are electrically connected. Thus, the SAW resonator 1 can be directly surface mounted on an external device such as a circuit board. Similarly, the terminal 20b that is not connected to any of the lead wires 7 is a so-called dummy terminal.

  Although the above embodiments have been described with respect to the SAW resonator, the present invention can be similarly applied to other SAW devices such as a filter and an oscillator using a SAW element. In the above-described embodiment, the SAW chip itself having a SAW element formed on the piezoelectric substrate is used as the base of the package, and a cover is metal-bonded to the SAW chip for airtight sealing. In the present invention, even when the SAW chip is accommodated in a separate base and hermetically sealed with a cover, the same applies as long as the lead wire is drawn out from the inside of the cover beyond the joint portion on the base. Can be applied to.

  Therefore, the present invention is not limited to the SAW device, and in addition to the SAW element, a piezoelectric element such as a tuning fork type or thickness-shear vibration mode piezoelectric vibrating piece or a piezoelectric gyro element is hermetically sealed in the package. Similarly, the present invention can be applied to other piezoelectric devices as long as the lead wire is drawn across the joint with the cover on the base of the package. Furthermore, it is clear that the present invention is not limited to piezoelectric devices. That is, when functional elements such as an IC chip and various electronic components are hermetically sealed in the package in addition to the piezoelectric element, the lead wire is drawn across the joint portion with the cover on the base of the package and externally connected. The present invention can be similarly applied to electronic devices to be connected.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention can be implemented by adding various modifications and changes to the above embodiments. For example, the cover bonded to the piezoelectric substrate may be provided with a dent on the lower surface inside the metal bonding portion in order to define a gap for sealing the excitation portion. Further, the piezoelectric substrate is not limited to a substrate formed of a piezoelectric material such as quartz, but may be a substrate of silicon or the like laminated with a diamond thin film and a piezoelectric film.

(A) is a plan view showing a preferred embodiment of a SAW resonator according to the present invention with its cover omitted, (B) is a sectional view taken along line IB-IB, and (C) is a line taken along IC-IC. FIG. The bottom view of the cover shown in FIG. The side view which shows the state which connected the SAW resonator of FIG. 1 by wire bonding. (A) is a side view of a SAW resonator according to a modification of FIG. 1, and (B) is a bottom view thereof. (A) is a side view of a SAW resonator according to another modification of FIG. 1, and (B) is a bottom view thereof.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... SAW resonator, 2 ... SAW chip, 3 ... Cover, 4 ... Piezoelectric substrate, 5 ... IDT, 6 ... Reflector, 7 ... Lead wire, 8 ... Extraction electrode, 9, 15 ... Metal junction part, 10 ... Insulation 11, bonding metal layer, 12, 16, Cr film, 13, 17, Au film, 14, 18, AuSn alloy layer, 19, bonding wire, 20 a, 20 b, connection terminal, 21 through-hole, 22, electrode film .

Claims (5)

An excitation part composed of an IDT electrode, a metal joint that surrounds the excitation part, an extraction electrode arranged outside the metal joint, and an electrode that is drawn from the IDT electrode so as to cross the metal junction and is connected to the extraction electrode A surface acoustic wave (SAW) chip having a lead wire to be formed on the main surface of the piezoelectric substrate;
A cover having a metal joint provided along the entire circumference on the lower surface periphery of the insulating substrate,
The metal joint portion of the SAW chip comprises an insulating layer formed on the surface of the piezoelectric substrate and the lead wire, and a joining metal layer laminated on the insulating layer,
The SAW chip and the cover join the joining metal layer of the SAW chip and the metal joint part of the cover, so that the excitation part is placed in a space defined between the SAW chip and the cover. A surface acoustic wave device which is integrally bonded so as to be hermetically sealed.   2. The surface acoustic wave device according to claim 1, wherein a thickness of the SAW chip after joining the metal joint portion and the metal joint portion of the cover is larger than a thickness of the IDT electrode. The metal joint portion of the SAW chip is formed by the insulating layer formed of SiO ₂ and the joint metal layer formed of a Cr / Au film and an AuSn alloy film laminated thereon. The surface acoustic wave device according to claim 1 or 2. A base, a functional element provided on the base, a metal joint provided on the surface of the base so as to surround the functional element, and an extraction electrode disposed outside the metal joint on the surface of the base; And a lead wire that is drawn from the functional element so as to intersect the metal joint portion and is connected to the extraction electrode, and a metal joint portion that is provided along the entire periphery of the lower surface of the insulating substrate. And a cover having
The metal bonding portion of the base is composed of an insulating layer formed on the surface of the base and the lead wire, and a bonding metal layer laminated on the insulating layer,
The base and the cover seal the functional element in a space defined between the base and the cover by joining the joining metal layer of the base and the metal joint of the cover. An electronic device characterized by being integrally joined so as to stop. The metal bonding portion of the base is formed by the insulating layer formed of SiO ₂ and the bonding metal layer formed of a Cr / Au film and an AuSn alloy film laminated thereon. The electronic device according to claim 4.

Images