Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-06-27
2003-04-22
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06552475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to surface acoustic wave devices used in resonators, piezoelectric filters, and other devices, and more specifically, the present invention relates to improvements to surface acoustic wave devices having a construction such that electrodes are externally connected via Au bumps.
2. Description of the Related Art
In conventional surface acoustic wave devices, bumps formed of Au or other materials, are often used for externally connecting the surface acoustic wave devices. Constructions of an electrical connection between conventional surface acoustic wave devices and the external environment will be described below with reference to
FIGS. 10 and 11
.
As shown in
FIG. 10A
, a surface acoustic wave device
51
includes a surface acoustic wave substrate
52
made of a piezoelectric material. The surface acoustic wave substrate
52
is provided with interdigital electrodes (IDT electrodes)
53
and
54
on the top surface
52
a
thereof. The IDT electrodes
53
and
54
are defined by aluminum patterns. The IDT electrode
53
includes first and second comb-like electrode portions
53
a
and
53
b
, which have a construction such that a plurality of electrode fingers are electrically connected to each other at one end thereof. The first and the second comb-like electrode portions
53
a
and
53
b
are connected to wiring electrode portions
53
c
and
53
d
, respectively.
Similarly, the IDT electrode
54
includes first and second comb-like electrode portions
54
a
and
54
d
and first and second wiring electrode portions
54
c
and
54
d.
The wiring electrode portions
53
c
,
53
d
,
54
c
, and
54
d
are used to connect the surface acoustic wave device
51
to external elements, and bumps
55
formed of Au are provided thereon to achieve such connection. More specifically, the wiring electrode portions
53
c
,
53
d
,
54
c
, and
54
d
are electrically connected to electrode bonding pads, which are provided on a substrate disposed outside of the surface acoustic wave device
51
, via the bumps
55
.
FIG. 10B
shows an enlarged view of a portion located around the wiring electrode portion
53
c
as an example of a portion around the bump
55
. As shown in
FIG. 10B
, the surface acoustic wave substrate
52
is provided with the wiring electrode portion
53
c
made of aluminum on the top surface thereof, and the bump
55
is disposed on the wiring electrode portion
53
c.
In addition, in order to reduce a conductor resistance, a wiring electrode portion having a two-layer construction as shown in
FIG. 11
has been suggested. With reference to
FIG. 11
, the wiring electrode portion
53
c
is constructed by laminating wiring electrode layers
53
c
1
and
53
c
2
formed of aluminum on the surface acoustic wave substrate
52
.
The bumps
55
are formed by a wire bump-bonding method, and by heating the surface acoustic wave substrate
52
to a temperature of 100° C. to 300° C.
However, the surface acoustic wave substrate included in the surface acoustic wave device is often made of a highly pyroelectric material such as lithium tantalate (LiTaO
3
), lithium niobate (LiNbO
3
), or other such materials. When such highly pyroelectric materials are heated, electric charges are generated on the surfaces thereof. In such a case, in the surface acoustic wave device
51
, for example, since the comb-like electrode portions
53
a
,
53
b
,
54
a
, and
54
b
are separated from each other, an electric discharge may occur between the electrode fingers which are located close to each other. Thus, the electrode fingers may melt, be broken or otherwise damaged. Especially in the IDT electrodes
53
and
54
, the size of a gap between the adjacent electrode fingers is several micrometers, and failures due to pyroelectricity as described above easily occur.
Thus, in order to prevent this, the following two methods have been conventionally used. According to a first method, all the electrodes provided on a mother substrate are first short circuited and connected to a ground potential, and then the bumps are formed. The electrodes that are short circuited are cut at a time when the surface acoustic wave devices are separated from the mother substrate during a dicing process. In addition, according to a second method, temperature gradients with which the surface acoustic wave devices are heated or cooled are made extremely small, so that the above-described failures caused by pyroelectricity are prevented.
However, in the first method, it is difficult to reliably prevent failures due to pyroelectricity. In addition, in the second method, there is a problem in that the time for processing is considerably increased. Instead of the first and the second methods, a method in which the bumps are formed at room temperature may also be applied in order to prevent failures due to pyroelectricity. However, when the bumps are formed at such a low temperature, the bonding strength may be considerably reduced.
In addition, the following method is disclosed in the Japanese Unexamined Patent Application Publication No. 8-307192. That is, all regions of the IDT electrodes including the comb-like electrode portions and the wiring electrode portions are first formed by an aluminum film, and are covered by a Pd film or a Pt film. Then, the Au bumps are formed. In this method, however, it is extremely difficult to cover the side surfaces of the aluminum film by the Pd film or the Pt film. Thus, this method is not practical.
SUMMARY OF THE INVENTION
In order to solve the problems described above, preferred embodiments of the present invention provide a surface acoustic wave device which greatly reduces the time required for forming the bumps, which prevents melting or the breakage of the electrodes, and which has very high bonding strength between the bump and the electrodes.
According to a preferred embodiment of the present invention, a surface acoustic wave device includes a surface acoustic wave substrate, at least one interdigital electrode disposed on the surface acoustic wave substrate, the interdigital electrode including a first comb-like electrode portion in which a plurality of electrode fingers are connected to each other at one end thereof, a second comb-like electrode portion in which a plurality of electrode fingers are connected to each other at one end thereof, and first and second wiring electrode portions which include lead electrodes which are electrically connected to the first and the second comb-like electrode portions, respectively, and bonding pads which are connected to an external environment via bumps, the electrode fingers of the first and the second comb-like electrode portions being interdigitated with each other, the first and the second comb-like electrode portions and the first and the second wiring electrode portions including an aluminum film, and first, second and third metal films which are laminated on each of the first and the second wiring electrode portions including the aluminum film in the order of the first metal film, the second metal film, and the third metal film, the first metal film being more bondable to aluminum than the second metal film, the third metal film being more bondable to the bumps than the first metal film, and the second metal film having an ability to suppress the diffusion of metals used to form the first and third metal films.
As described above, each of the wiring electrode portions including the lead electrodes and the bonding pads is preferably provided with a laminate including the first, second and third metal films. The laminate is tightly connected to the wiring electrode portion due to the first metal film, and the third metal film is tightly fixed to the bump.
In addition, since the third metal film is made from a metal being more bondable to the bumps, it is not necessary to apply heat during the process of forming the bumps. Thus, even when the surface acoustic wave substrate is constructed of a highly pyroelectric material, failures due to pyroelectricity
Fuyutsume Toshiyuki
Hori Yoshitsugu
Kimura Yuji
Shimoe Kazunobu
Taga Shigeto
Budd Mark O.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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