Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-01-15
2001-10-30
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S340000, C310S348000
Reexamination Certificate
active
06310421
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of Related Art
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 la and electrode pads (the latter not shown). The functional portion
1
a
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
1
a.
Reference numeral
12
denotes a package that holds the chip
1
, and
12
a
and
12
b
denote package side walls that surround the chip thereby constituting a chip holder. Part of the side wall
12
a
includes a terminal portion
12
c
serving as external connectors. Reference numeral
4
denotes wires for electrically connecting the electrode pads of the functional portion
1
a
to the terminal portion
12
c.
Reference numeral
11
denotes a metal cover connected to a sealing portion
12
d
placed on the top surface of the package side wall
12
b
, whereby the functional portion
1
a
of the chip
1
is sealed in an airtight and protected
30
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
1
a
and that protective measures be taken to prevent breakdown of the functional portion
1
a.
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.
The device in
FIG. 11
has the functional portion
1
a
furnished at the bottom of the chip
1
, with a hollow portion formed between the functional portion
1
a
and the package
12
. Bump electrodes
6
connect the functional portion
1
a
with the terminal portion
12
c.
That is, electrical connections between the portions
1
a
and
12
c
are secured by connecting the bump electrodes
6
, formed on electrode pads not shown, to the terminal portion
12
c
. The package side wall
12
a
creates a staggered portion opposite to the functional portion
1
a
and also contributes to providing the hollow portion
9
. The setup protects the functional portion
1
a
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
12
d
interposed therebetween.
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
1
a.
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.
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.
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
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.
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.
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 a 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.
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.
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 sub
Budd Mark O.
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figgs Ernst & Manbeck
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