U.S. patent application number 09/231836 was filed with the patent office on 2001-08-09 for surface acoustic wave device and method for fabricating the same.
Invention is credited to MORISHIMA, KOJI.
Application Number | 20010011857 09/231836 |
Document ID | / |
Family ID | 17657441 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011857 |
Kind Code |
A1 |
MORISHIMA, KOJI |
August 9, 2001 |
SURFACE ACOUSTIC WAVE DEVICE AND METHOD FOR FABRICATING THE
SAME
Abstract
A surface acoustic wave device that is small, lightweight and
highly reliable, and protects its functional portion. The surface
acoustic wave device has surface acoustic wave elements mounted on
a circuit substrate. Each surface acoustic wave element includes a
frame-like first insulating film furnished to surround functional
portions on a chip, and a lid-like second insulating film deposited
on the first insulating film so as to cover driving electrodes and
surface wave propagation paths of the functional portions, while
securing a hollow portion over the functional portions.
Inventors: |
MORISHIMA, KOJI; (TOKYO,
JP) |
Correspondence
Address: |
VINCENT M DELUCA
ROTHWELL FIGG ERNST & KURZ
SUITE 701
555 13TH STREET N W
WASHINGTON
DC
20004
|
Family ID: |
17657441 |
Appl. No.: |
09/231836 |
Filed: |
January 15, 1999 |
Current U.S.
Class: |
310/313R ;
310/340; 310/348 |
Current CPC
Class: |
H01L 2924/16195
20130101; H01L 2224/48091 20130101; H03H 9/059 20130101; H01L
2224/16225 20130101; H03H 9/1092 20130101; H01L 2924/00014
20130101; H01L 2224/48091 20130101 |
Class at
Publication: |
310/313.00R ;
310/348; 310/340 |
International
Class: |
H01L 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 1998 |
JP |
HEI 10-282814 |
Claims
What is claimed is:
1. A surface acoustic wave device having surface acoustic wave
elements mounted on a circuit substrate, each of said surface
acoustic wave elements comprising: a piezoelectric substrate; a
functional portion which is formed on one principal plane of said
piezoelectric substrate and which has driving electrodes for
driving surface waves in a predetermined direction over a surface
of said piezoelectric substrate; a frame-like first insulating film
furnished on the one principal plane of said piezoelectric
substrate so as to surround said functional portion; and a lid-like
second insulating film for covering the driving electrodes and
surface wave propagation paths of said functional portion while
securing a predetermined space over said functional portion.
2. The surface acoustic wave device according to claim 1, wherein
surfaces of said surface acoustic wave elements are covered with an
insulating resin.
3. A surface acoustic wave device according to claim 1, further
comprising bump electrodes which are formed on either the one
principal plane or other principal plane of said piezoelectric
substrate and which constitute external connectors of said surface
acoustic wave elements, wherein said surface acoustic wave elements
are connected via said bump elements to said circuit substrate in
flip-chip bonding fashion.
4. A surface acoustic wave device having surface acoustic wave
elements mounted on a circuit substrate, each of said surface
acoustic wave elements comprising: a piezoelectric substrate; a
functional portion which is formed on one principal plane of said
piezoelectric substrate and which has driving electrodes for
driving surface waves in a predetermined direction over a surface
of said piezoelectric substrate; bump electrodes which are formed
on the one principal plane of said piezoelectric substrate and
which constitute external connectors of said functional portion;
and an first insulating film deposited on the one principal plane
of said piezoelectric substrate except where there exist at least
said functional portion and said bump electrodes; wherein said bump
electrodes of said surface acoustic wave elements are connected to
said circuit substrate in flip-chip bonding fashion, with an
anisotropic conductor interposed between said bump electrodes and
said circuit substrate.
5. The surface acoustic wave device according to claim 4, further
comprising a second insulating film deposited on said first
insulating film so as to secure a predetermined space over said
functional portion while covering the driving electrodes and
surface wave propagation paths of said functional portion except
where there exist at least said bump electrodes.
6. The surface acoustic wave device according to claim 1, wherein
said first and said second insulating film are composed of
photosensitive films and are formed by photolithography.
7. A method for fabricating a surface acoustic wave device, said
method comprising the steps of: forming functional portions of a
plurality of surface acoustic wave elements on one principal plane
of a piezoelectric substrate, said function portions including
driving electrodes for driving surface waves in a predetermined
direction over a surface of said piezoelectric substrate;
depositing a first insulating film on the one principal plane of
said piezoelectric substrate except where there exist at least said
functional portions and electrode pads for use by bump electrodes;
depositing a second insulating film in lid fashion over said
functional portions except where there exist at least said
electrode pads on said first insulating film so as to secure a
predetermined space while covering said driving electrodes and
surface wave propagation paths of said functional portions;
furnishing each of said functional portions with said bump
electrodes constituting external connectors of said functional
portions on the one principal plane of said piezoelectric
substrate; providing a single anisotropic conductor so as to cover
the plurality of said functional portions and each of said bump
electrodes; connecting said bump electrodes to said circuit
substrate in flip-chip bonding fashion; and separating said surface
acoustic wave elements into individual elements.
8. The method for fabricating a surface acoustic wave device
according to claim 7, wherein said first and said second insulating
film are composed of photosensitive films and are formed by
photolithography.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a surface acoustic wave
device used as a high-frequency oscillator in telecommunication
equipment as well as to a method for fabricating the device.
[0003] 2. Description of Related Art
[0004] FIG. 10 is a cross-sectional view of a conventional surface
acoustic wave device. In FIG. 10, reference numeral 1 denotes a
piezoelectric substrate (called the chip hereunder) constituting a
surface acoustic wave element. On a principal plane of the chip 1
(upper surface in FIG. 10) are a surface acoustic wave functional
portion 1a and electrode pads (the latter not shown). The
functional portion 1a comprises driving electrodes made of known
finger-shaped inter-digital transducers (called IDTs hereunder),
and propagation paths for surface waves driven in a predetermined
direction on the chip surface. The electrode pads extend from the
driving electrodes and serve as external connection terminals of
the functional portion 1a. Reference numeral 12 denotes a package
that holds the chip 1, and 12a and 12b denote package side walls
that surround the chip thereby constituting a chip holder. Part of
the side wall 12a includes a terminal portion 12c serving as
external connectors. Reference numeral 4 denotes wires for
electrically connecting the electrode pads of the functional
portion 1a to the terminal portion 12c.
[0005] Reference numeral 11 denotes a metal cover connected to a
sealing portion 12d placed on the top surface of the package side
wall 12b, whereby the functional portion 1a of the chip 1 is sealed
in an airtight and protected manner. In order to release
acoustically both the surface waves driven by the known IDTs and
the propagation paths for the waves, the surface acoustic wave
device requires that a hollow portion be secured over the surface
of the functional portion 1a and that protective measures be taken
to prevent breakdown of the functional portion 1a.
[0006] FIG. 11 is a cross-sectional view of another conventional
surface acoustic wave device disclosed in Japanese Patent
Application Laid-open No. (Hei)4-301910. In FIG. 11, those parts
with their counterparts already shown in FIG. 10 are given the same
reference numerals, and descriptions of such parts are omitted
where they are repetitive.
[0007] The device in FIG. 11 has the functional portion 1a
furnished at the bottom of the chip 1, with a hollow portion formed
between the functional portion 1a and the package 12. Bump
electrodes 6 connect the functional portion 1a with the terminal
portion 12c. That is, electrical connections between the portions
1a and 12c are secured by connecting the bump electrodes 6, formed
on electrode pads not shown, to the terminal portion 12c. The
package side wall 12a creates a stagger for a portion opposite to
the functional portion 1a and also contributes to providing the
hollow portion 9. The setup protects the functional portion 1a and
secures a clearance over its surface. As in the case of the device
in FIG. 10, the metal cover 11 on top of the chip 1 seals the
opening of the package 12 airtight with the sealing portion 12d
interposed therebetween.
[0008] Conventional surface acoustic wave devices are typically
constituted as outlined above. In such devices, the cover 11 made
of metal has been used for airtight sealing. When an alternative
insulating resin, although less expensive, is used to surround the
chip 1 periphery, the resin adheres on the chip 1 and makes it
impossible to secure a hollow portion over the surface of the
functional portion 1a. Meanwhile, the use of the metal cover pushed
up manufacturing costs of the surface acoustic wave device, a
disadvantage that has plagued the prior art.
[0009] It is therefore an object of the present invention to
overcome the above and other deficiencies of the prior art and to
provide a surface acoustic wave device that is small, lightweight,
highly reliable, and is protected against breakdown of its
functional portion with a hollow segment secured over the surface
of that functional portion.
[0010] It is another object of the present invention to provide a
method for fabricating a surface acoustic wave device in ways that
are simpler, more efficient, more accurate and less expensive than
before.
SUMMARY OF THE INVENTION
[0011] According to a first aspect of the present invention, there
is provided a surface acoustic wave device having surface acoustic
wave elements mounted on a circuit substrate, each of the surface
acoustic wave elements comprises a piezoelectric substrate, a
functional portion which is formed on one principal plane of the
piezoelectric substrate and which has driving electrodes for
driving surface waves in a predetermined direction over a surface
of the piezoelectric substrate, a frame-like first insulating film
furnished on the one principal plane of the piezoelectric substrate
so as to surround the functional portion and a lid-like second
insulating film for covering the driving electrodes and surface
wave propagation paths of the functional portion while securing a
predetermined space over the functional portion.
[0012] Here, the surface acoustic wave device may further comprise
bump electrodes which are formed on either the one principal plane
or other principal plane of the piezoelectric substrate and which
constitute external connectors of the surface acoustic wave
elements, wherein the surface acoustic wave elements are connected
via the bump elements to the circuit substrate in flip-chip bonding
fashion.
[0013] According to a second aspect of the present invention, there
is provided a surface acoustic wave device having surface acoustic
wave elements mounted on a circuit substrate, each of the surface
acoustic wave elements comprises a piezoelectric substrate, a
functional portion which is formed on one principal plane of the
piezoelectric substrate and which has driving electrodes for
driving surface waves in a predetermined direction over a surface
of the piezoelectric substrate, bump electrodes which are formed on
the one principal plane of the piezoelectric substrate and which
constitute external connectors of the functional portion and an
first insulating film deposited on the one principal plane of the
piezoelectric substrate except where there exist at least the
functional portion and the bump electrodes, wherein the bump
electrodes of the surface acoustic wave elements are connected to
the circuit substrate in flip-chip bonding fashion, with an
anisotropic conductor interposed between the bump electrodes and
the circuit substrate.
[0014] Here, the surface acoustic wave device may further comprise
a second insulating film deposited on the first insulating film so
as to secure a predetermined space over the functional portion
while covering the driving electrodes and surface wave propagation
paths of the functional portion except where there exist at least
the bump electrodes.
[0015] According to a third aspect of the present invention, there
is provided a method for fabricating a surface acoustic wave
device, the method comprises the steps of forming functional
portions of a plurality of surface acoustic wave elements on one
principal plane of a piezoelectric substrate, the function portions
including driving electrodes for driving surface waves in a
predetermined direction over a surface of the piezoelectric
substrate, depositing a first insulating film on the one principal
plane of the piezoelectric substrate except where there exist at
least the functional portions and electrode pads for use by bump
electrodes, depositing a second insulating film in lid fashion over
the functional portions except where there exist at least the
electrode pads on the first insulating film so as to secure a
predetermined space while covering the driving electrodes and
surface wave propagation paths of the functional portions,
furnishing each of the functional portions with the bump electrodes
constituting external connectors of the functional portions on the
one principal plane of the piezoelectric substrate, providing a
single anisotropic conductor so as to cover the plurality of the
functional portions and each of the bump electrodes, connecting the
bump electrodes to the circuit substrate in flip-chip bonding
fashion and separating the surface acoustic wave elements into
individual elements.
[0016] The above and other objects, effects, features and
advantages of the present invention will become more apparent from
the following description of the embodiments thereof taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional view of a surface acoustic wave
device according to embodiment 1 of the present invention.
[0018] FIG. 2 is a cross-sectional view of a surface acoustic wave
device according to embodiment 2 of the present invention.
[0019] FIGS. 3A to 3F are schematic views showing steps to
fabricate a chip for use by a surface acoustic wave device
according to embodiment 3 of the present invention.
[0020] FIGS. 4A and 4B are perspective views illustrating
respectively typical states of the chips in FIGS. 3D and 3F as they
are being fabricated.
[0021] FIG. 5 is a cross-sectional view of a surface acoustic wave
device according to embodiment 4 of the present invention.
[0022] FIG. 6 is a cross-sectional view of a surface acoustic wave
device according to embodiment 5 of the present invention.
[0023] FIG. 7 is a plan view of a chip 1 used by the embodiment 5
of the present invention.
[0024] FIG. 8 is a cross-sectional view of a surface acoustic wave
device according to embodiment 6 of the present invention.
[0025] FIGS. 9A to 9F are schematic views showing steps to
fabricate a chip for use by a surface acoustic wave device, the
steps constituting a method according to embodiment 7 of the
present invention.
[0026] FIG. 10 is a cross-sectional view of a conventional surface
acoustic wave device.
[0027] FIG. 11 is a cross-sectional view of another conventional
surface acoustic wave device disclosed in Japanese Patent
Application Laid-open No. (Hei) 4-301910.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Embodiments of the present invention will be described below
with reference to the accompanying drawings. It is noted that the
same reference symbols in the drawings denote the same or
corresponding components.
[0029] Embodiment 1
[0030] An embodiment 1 of this invention will now be described with
reference to FIG. 1. FIG. 1 is a cross-sectional view of a surface
acoustic wave device according to embodiment 1.
[0031] In FIG. 1, reference numeral 1 denotes a piezoelectric
substrate chip constituting a surface acoustic wave element. On a
principal plane of the chip 1 (upper surface in FIG. 1) are a
surface acoustic wave functional portion 1a and electrode pads. The
functional portion 1a comprises driving electrodes made of known
IDTs, and propagation paths for surface waves driven in a
predetermined direction on the chip surface. The electrode pads,
not shown, extend from the driving electrodes and serve as external
connection terminals of the functional portion 1a.
[0032] Reference numeral 3 denotes a circuit substrate on which to
mount the chip; 3c for a terminal portion formed on a part of the
circuit substrate 3; 4 for wires that connect the electrode pads of
the functional portion 1a electrically to the terminal portion 3c;
2a for a frame-like first insulating film deposited on the upper
surface of the chip 1 surrounding the functional portion 1a on the
chip 1; and 2b for a lid-like second insulating film attached to
the first insulating film 2a in covering relation therewith. The
second insulating film 2b ensures a suitable hollow portion 9 over
the functional portion 1a and protectively envelopes the driving
electrodes and surface acoustic wave propagation paths of the
functional portion 1a.
[0033] In the surface acoustic wave device of the above
constitution, the crucially important functional portion 1a is
protected by the first and the second insulating film 2a and 2b
with the hollow portion 9 interposed therebetween. The makeup
allows the chip 1 to be fabricated in a secure manner with little
risk of getting the functional portion 1a inadvertently damaged
during the process.
[0034] Because the first and the second insulating film 2a and 2b
seal the functional portion 1a in a simplified fashion, it is not
mandatory, as with conventional surface acoustic wave devices, to
provide costly airtight sealing on the functional portion. The
result is an inexpensively manufactured surface acoustic wave
device.
[0035] Embodiment 2
[0036] An embodiment 2 of the invention will now be described with
reference to FIG. 2. FIG. 2 is a cross-sectional view of a surface
acoustic wave device according to embodiment 2. In FIG. 2, those
parts with their counterparts already shown in FIG. 1 are given the
same reference numerals, and descriptions of such parts are omitted
where they are repetitive.
[0037] In FIG. 2, reference numeral 5 represents an insulating
resin. The chip 1, with its functional portion 1a capped by the
first and the second insulating film 2a and 2b, is mounted on the
circuit substrate 3. Metal wires 4 are used to connect the
functional portion 1a electrically to the terminal portion 3c. The
insulating resin 5 is deposited so as to cover the chip 1 and metal
wires 4. This makeup ensures the same effects as the embodiment 1
and provides a surface acoustic wave device still more reliable
than the embodiment 1.
[0038] Embodiment 3
[0039] An embodiment 3 of this invention will now be described with
reference to FIGS. 3A to 3F, and FIGS. 4A and 4B. FIGS. 3A to 3F
are schematic views showing steps to fabricate a chip for use by a
surface acoustic wave device according to the embodiment 3. FIGS.
4A and 4B are perspective views illustrating respectively typical
states of the chips in FIGS. 3D and 3F as they are being
fabricated.
[0040] FIG. 3A shows a wafer 30. On the wafer 30, a plurality of
functional portions 1a are formed through conductor patterning at
suitable intervals as indicated in FIG. 3B.
[0041] A photosensitive film 40 is then deposited on all functional
portions 1a on the wafer 30 as illustrated in FIG. 3C. With the
film 40 in place, a frame-like first insulating film 2a is formed
by photolithography so as to surround each functional portion as
shown in FIGS. 3D and 4A. FIG. 4A depicts a case in which two
functional portions 1a are surrounded by the first insulating film
2a.
[0042] Thereafter, a single photosensitive film 50 is deposited on
the first insulating film 2a over the wafer as illustrated in FIG.
3E. The process creates a suitable hollow portion 9 between each
functional part 1a and the photosensitive film 50. With the hollow
portions thus provided, a lid-like second insulating film 2b is
formed also by photolithography (as in FIGS. 3D and 4A) to cover
each of the first insulating films 2a as depicted in FIG. 3F and
4B.
[0043] After that, the wafer is diced up along separation lines 60
separating chips as shown in FIGS. 4A and 4B, whereby the
individual chips are formed.
[0044] As described, the embodiment 3 of the invention has its
first and second insulating films fabricated finely, precisely and
efficiently, the films offering the same effects as those of the
first and the embodiment 2.
[0045] Embodiment 4
[0046] An embodiment 4 of this invention will now be described with
reference to FIG. 5. FIG. 5 is a cross-sectional view of a surface
acoustic wave device according to embodiment 4. In FIG. 5, those
parts with their counterparts already shown in FIG. 1 are given the
same reference numerals, and descriptions of such parts are omitted
where they are repetitive.
[0047] In FIG. 5, reference numeral 6 denotes bump electrodes
constituting external connectors of the functional portion 1a. The
chip 1, with its functional portion 1a capped by the first and the
second insulating film 2a and 2b, is connected by the bump
electrodes 6 to suitable connectors 3c on the circuit substrate 3
in flip-chip bonding fashion.
[0048] The makeup above allows the embodiment 4 to be a smaller
surface acoustic wave device than the embodiment 1 while offering
the same effects as those of the latter.
[0049] If part or all of the chip is covered with an appropriate
insulating resin as is the case with the embodiment 2, the
embodiment 4 may be fabricated as a surface acoustic wave device
with significantly enhanced reliability.
[0050] Embodiment 5
[0051] An embodiment 5 of this invention will now be described with
reference to FIGS. 6 and 7. FIG. 6 is a cross-sectional view of a
surface acoustic wave device according to the embodiment 5. FIG. 7
is a plan view of a chip 1 used by the embodiment 5.
[0052] In FIGS. 6 and 7, those parts with their counterparts
already shown in FIG. 1 are given the same reference numerals, and
descriptions of such parts are omitted where they are
repetitive.
[0053] As shown in FIGS. 6 and 7, an insulating film 7 is formed
over the chip 1 except where there are at least the functional
portion 1a and the electrode pads 10 constituting external
connectors of the functional portion 1a. The thickness of the
insulating film 7 should preferably be made equal to or slightly
less than that of the bump electrodes 6 as depicted in FIG. 6.
[0054] The chip 1 is mounted on the bump electrodes 6 so that a
hollow portion 9 is secured over its functional portion 1a as shown
in FIG. 6. The chip 1 is then connected to suitable connectors 3c
on the circuit substrate 3 in flip-chip bonding fashion, with an
anisotropic conductor 8 interposed between the bump electrodes 6
and the connectors 3c.
[0055] In the embodiment 5 of the above constitution, the chip 1 is
bonded to the circuit substrate 3 not only via the bump electrodes
6 but also through the insulating film 7. This setup prevents
junction stress from getting concentrated locally, thereby
implementing a surface acoustic wave device with its bump
electrodes 6 offering high connection reliability.
[0056] If part or all of the chip is covered with an appropriate
insulating resin as is the case with the embodiment 2, the
embodiment 5 may also be fabricated as a surface acoustic wave
device with significantly enhanced reliability.
[0057] Furthermore, if the insulating film 7 is formed by
photolithography using a photosensitive material as with the
embodiment 3, the embodiment 5 will have its insulating film 7
fabricated finely, precisely and efficiently.
[0058] Embodiment 6
[0059] An embodiment 6 of this invention will now be described with
reference to FIG. 8. FIG. 8 is a cross-sectional view of a surface
acoustic wave device according to embodiment 6. In FIG. 8, those
parts with their counterparts already shown in FIG. 1 are given the
same reference numerals, and descriptions of such parts are omitted
where they are repetitive.
[0060] As shown in FIG. 8, a first insulating film 7a is formed
over the chip 1 except where there are at least the functional
portion 1a and bump electrode pads 10. A second insulating film 7b
is deposited on the first insulating film 7a. The functional
portion 1a of the chip 1 is covered with the first and the second
insulating film 7a and 7b in such a manner that a hollow portion 9
is secured over the surface of the functional part 1a. Those parts
of the films 7a and 7b which correspond to the electrode pads 10
are removed so that the bump electrodes 6 are exposed. The combined
thickness of the first and the second insulating film 7a and 7b
should preferably be made identical to or slightly less than the
height of the bump electrodes 6.
[0061] The chip 1 is connected by the bump electrodes 6 to suitable
connectors 3c on the circuit substrate 3 in flip-chip bonding
fashion, with the anisotropic conductor 8 interposed between the
bump electrodes 6 and the connectors 3c.
[0062] The embodiment 6 of the above constitution provides the same
effects as the embodiment 5. Because the crucially important
functional portion 1a is protected by the first and the second
insulating film 7a and 7b with the hollow portion interposed
therebetween, the above makeup allows the chip 1 to be fabricated
in a secure manner with little risk of getting the functional
portion 1a inadvertently damaged during the process.
[0063] Because the first and the second insulating film 7a and 7b
seal the functional portion 1a in a simplified fashion, it is not
mandatory, as with conventional surface acoustic wave devices, to
provide costly airtight sealing on the functional portion. This
makes it possible to manufacture an inexpensive yet viable surface
acoustic wave device.
[0064] If part or all of the chip is covered with an appropriate
insulating resin as is the case with the embodiment 2, the
embodiment 6 may also be fabricated as a surface acoustic wave
device with significantly enhanced reliability.
[0065] Furthermore, if the first and the second insulating film 7a
and 7b are formed by photolithography using a photosensitive
material as with the embodiment 3, the embodiment 6 will have its
first and second insulating films 7a and 7b fabricated finely,
precisely and efficiently.
[0066] Embodiment 7
[0067] An embodiment 7 of this invention will now be described with
reference to FIGS. 9A to 9F. FIGS. 9A to 9F are schematic views
showing steps to fabricate a chip for use by a surface acoustic
wave device, the steps constituting a method according to
embodiment 7.
[0068] FIG. 9A shows a wafer 30. On the wafer 30, a plurality of
functional portions 1a are formed through conductor patterning at
suitable intervals as depicted in FIG. 9B.
[0069] A first insulating film 7a made illustratively of a
photosensitive material is then deposited on the wafer surface
comprising the functional portions 1a. The first insulating film 7a
is shaped as shown in FIG. 9C by photolithography, with the
functional portions 1a and electrode pads for bump electrodes
excluded.
[0070] In the state above, a second insulating film 7b composed of
a photosensitive material is further deposited on the first
insulating film 7a. A lid covering the functional portions 1a is
formed by similar photolithography. With the electrode pads for
bump electrodes excluded, the second insulating film 7b is then
formed as shown in FIG. 9C.
[0071] The bump electrodes 6 corresponding to each of the
functional portions are furnished as illustrated in FIG. 9D. At
this point, the combined thickness of the first and the second
insulating film 7a and 7b should preferably be made identical to or
slightly less than the height of the bump electrodes 6.
[0072] Thereafter, as shown in FIG. 9E, a single anisotropic
conductor 8 is furnished so as to cover all functional portions and
their bump electrodes 6, the conductor being in contact with the
bump electrodes.
[0073] In this state, the wafer is diced up along separation lines
60 separating chips as shown in FIG. 9F, whereby the individual
chips are formed.
[0074] By use of the above method according to embodiment 7, it is
possible to fabricate efficiently a surface acoustic wave device
offering the same effects as those of the fifth and the embodiment
6.
[0075] The surface acoustic wave device of the present invention
has surface acoustic wave elements mounted on a circuit substrate,
each of the surface acoustic wave elements comprises a
piezoelectric substrate, a functional portion which is formed on a
principal plane of the piezoelectric substrate and which has
driving electrodes for driving surface waves in a predetermined
direction over a surface of the piezoelectric substrate, a
frame-like first insulating film furnished on the principal plane
of the piezoelectric substrate so as to surround the functional
portion and a lid-like second insulating film for covering the
driving electrodes and surface wave propagation paths of the
functional portion while securing a predetermined space over the
functional portion. This structure provides a hollow portion over
the surface of the functional portions so that the device is
fabricated in secure, damage-free fashion.
[0076] In the surface acoustic wave device of the present
invention, the surfaces of the surface acoustic wave elements may
be covered with an insulating resin. This makes it possible to
fabricate a more reliable surface acoustic wave device than
before.
[0077] The surface acoustic wave device of the present invention
may further comprise bump electrodes which are formed on either one
principal plane or another principal plane of the piezoelectric
substrate and which constitute external connectors of the surface
acoustic wave elements, wherein the surface acoustic wave elements
are connected via the bump elements to the circuit substrate in
flip-chip bonding fashion. This preferred structure helps reduce
the size of the surface acoustic wave device.
[0078] The surface acoustic wave device of the present invention
has surface acoustic wave elements mounted on a circuit substrate,
each of the surface acoustic wave elements comprises a
piezoelectric substrate, a functional portion which is formed on a
principal plane of the piezoelectric substrate and which has
driving electrodes for driving surface waves in a predetermined
direction over a surface of the piezoelectric substrate, bump
electrodes which are formed on the principal plane of the
piezoelectric substrate and which constitute external connectors of
the functional portion and an insulating film deposited on the
principal plane of the piezoelectric substrate except where there
exist at least the functional portion and the bump electrodes,
wherein the surface acoustic wave elements are connected via the
bump electrodes to the circuit substrate in flip-chip bonding
fashion, with an anisotropic conductor interposed between the bump
electrodes and the circuit substrate. This structure prevents
junction stress from getting concentrated locally on the chip,
allowing the bump electrodes to offer high connection
reliability.
[0079] The surface acoustic wave device of the present invention
has surface acoustic wave elements mounted on a circuit substrate,
each of the surface acoustic wave elements comprises a
piezoelectric substrate, a functional portion which is formed on a
principal plane of the piezoelectric substrate and which has
driving electrodes for driving surface waves in a predetermined
direction over a surface of the piezoelectric substrate, a first
insulating film deposited on the principal plane of the
piezoelectric substrate except where there exist at least the
functional portion and bump electrodes and a second insulating film
deposited on the first insulating film so as to secure a
predetermined space over the functional portion while covering the
driving electrodes and surface wave propagation paths of the
functional portion except where there exist at least the bump
electrodes, wherein the surface acoustic wave elements are
connected via the bump electrodes to the circuit substrate in
flip-chip bonding fashion, with an anisotropic conductor interposed
between the bump electrodes and the circuit substrate. This
structure reinforces protection of the functional portions and
eliminates the need for providing their airtight sealing. The
resulting device is inexpensive and, with junction stress dispersed
over the chip, fabricated in a way that allows its bump electrodes
to offer high connection reliability.
[0080] In the surface acoustic wave device of the present
invention, the first and the second insulating film of the surface
acoustic wave device may be composed of photosensitive films and
formed by photolithography. This structure allows the insulating
films to be fabricated finely, precisely and efficiently.
[0081] A method for fabricating a surface acoustic wave device of
the present invention comprises the steps of forming functional
portions of a plurality of surface acoustic wave elements on one
principal plane of a piezoelectric substrate, the function portions
including driving electrodes for driving surface waves in a
predetermined direction over a surface of the piezoelectric
substrate, depositing a first insulating film on the principal
plane of the piezoelectric substrate except where there exist at
least the functional portions and electrode pads for use by bump
electrodes, depositing on the first insulating film a second
insulating film in lid fashion covering each of the functional
portions except each of the electrode pads so as to secure a
predetermined space over the functional portions while covering the
driving electrodes and surface wave propagation paths of the
functional portions, furnishing each of the functional portions
with the bump electrodes constituting external connectors of the
functional portions on the principal plane of the piezoelectric
substrate, providing a single anisotropic conductor so as to cover
the plurality of functional portions and each of the bump
electrodes, connecting the bump electrodes to the circuit substrate
in flip-chip bonding fashion and separating the surface acoustic
wave elements into individual elements. This method fabricates the
inventive surface acoustic wave device efficiently.
[0082] Preferably, the inventive method may further comprise the
steps of having the first and the second insulating film composed
of photosensitive films and formed by photolithography. The
additional steps make it possible to fabricate the insulating films
finely, precisely and efficiently.
[0083] The present invention has been described in detail with
respect to various embodiments, and it will now be apparent from
the foregoing to those skilled in the art that changes and
modifications may be made without departing from the invention in
its broader aspects, and it is the invention, therefore, in the
appended claims to cover all such changes and modifications as fall
within the true spirit of the invention.
[0084] The entire disclosure of Japanese Patent Application No.
10-282814 filed on Oct. 5, 1998 including specification, claims,
drawings and summary are incorporated herein by reference in its
entirety.
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