Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2000-03-09
2002-04-23
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S195000, C310S31300R
Reexamination Certificate
active
06377139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave device for use as a resonator or a band filter in communication devices or other apparatuses, and more particularly, the present invention relates to an edge reflection type surface acoustic wave device which utilizes an SH type surface acoustic wave.
2. Description of the Related Art
Edge reflection type surface acoustic wave devices which utilize an SH type surface acoustic wave such as a BGS (Bleustein-Gulyaev-Shimizu) wave, a Love wave, or other such waves are known. In an edge reflection type surface acoustic wave device, edges are formed which are on the opposite ends in the surface acoustic wave propagation direction of the area where an interdigital transducer (IDT) is provided, and the edges are perpendicular to the surface acoustic wave propagation direction. A surface acoustic wave is reflected by the edges. Accordingly, reflectors are not necessary and as a result, the surface acoustic wave device can be miniaturized.
Japanese Unexamined Patent Publication No. 7-263998 discloses an edge reflection type surface acoustic wave resonator in which grooves are formed on a surface acoustic wave substrate, and the inner side walls of the grooves constitute the reflection edges. As shown in
FIG. 7
, in an edge reflection type surface acoustic wave resonator
51
, an IDT
53
is formed on a surface acoustic wave substrate
52
. On the opposite ends in the surface acoustic wave propagation direction of the IDT
53
, grooves
52
a
and
52
b
are formed. The inner side walls
52
a
1
and
52
b
1
of the grooves
52
a
and
52
b
constitute the reflection edges.
The inner side walls
52
a
1
and
52
b
1
of the grooves
52
a
and
52
b
are used as the reflection edges because the stability of mounting is improved. In the edge reflection type surface acoustic wave resonator
51
, only one IDT
53
is provided. When the number of pairs of the electrode fingers of the IDT
53
is small, the chip size in the surface acoustic wave propagation direction is very small, so that the mounting stability is deteriorated. Accordingly, substrate portions
52
c
and
52
d
are formed on the outer sides of the inner side walls
52
a
1
and
52
b
1
constituting the reflection edges, and thereby, the chip size is increased in the surface acoustic wave propagation direction, so that the mounting stability is improved.
On the other hand, there are some edge reflection type surface acoustic wave devices which have a relatively large number of electrode finger pairs such as an edge reflection type longitudinally coupled SAW resonator filter having a plurality of IDTs. For example, as shown in
FIG.8
, in an edge reflection type longitudinally coupled SAW resonator filter
61
, two IDTs
63
and
64
are formed on a surface acoustic wave substrate
62
. In this case, since the IDTs
63
and
64
are provided, the number of electrode fingers is relatively large, and thereby, the distance between the side surfaces
62
a
and
62
b
of the surface acoustic wave substrate
62
is relatively large. Thus, the chip size measured in the surface acoustic wave propagation direction is sufficiently large, and thereby, the mounting stability is high.
That is, for an edge reflection type longitudinally coupled SAW resonator filter, it is not necessary to form the substrate portions
52
c
and
52
d
on the outer sides of the grooves
52
a
and
52
b
, respectively, in contrast to the surface acoustic wave resonator
51
shown in FIG.
7
. If the substrate portions
52
c
and
52
d
are provided, they will prevent miniaturization without serving any useful purpose.
In the edge reflection type surface acoustic wave device, the electrode fingers of the IDTs
63
and
64
are located near the side surfaces
62
a
and
62
b
, similarly to the edge reflection type longitudinally coupled SAW resonator filter
61
. That is, the electrode fingers
65
a
and
65
b
located at the outermost ends in the surface acoustic wave propagation direction are formed along the edges defined by the side surfaces
62
a
,
62
b
and the upper surface
62
c
, respectively.
Referring to the production of the SAW resonator filter
61
, the IDTs
63
and
64
are formed on a mother surface acoustic wave substrate, and thereafter, the surface acoustic wave substrate is cut in the thickness direction to form the side surfaces
62
a
and
62
b
. The side surfaces
62
a
and
62
b
should be formed with high precision, since the edges defined by the side surfaces
62
a
,
62
b
reflect a surface acoustic wave. In addition, since the electrode fingers
65
a
and
65
b
are located near the edges
62
a
and
62
b
, respectively, chipping at the surface of the surface acoustic wave substrate
62
which is caused during cutting of the substrate
62
should be prevented as much as possible. If the chipping and the breaking of a substrate material is increased, the electrode fingers
65
a
and
65
b
will be disconnected, which will considerably affect the filter characteristics.
Such problems as described above arise not only in the edge reflection type longitudinally coupled type SAW resonator filter
61
but also in other edge reflection type surface acoustic wave devices such as an edge reflection type surface acoustic wave resonator.
On the other hand, Japanese Unexamined Patent Publication No. 9-326373 discloses a method of preventing the chipping of a substrate, which occurs during cutting of a semiconductor wafer or other such component. In particular, as the method of cutting a substrate, a bevel cutting method illustrated in
FIG. 9A
, and a step cutting method shown in
FIG. 9B
are described.
As shown in
FIG. 9A
, according to the bevel cutting method, first, a V-shaped groove
71
a
is formed on a substrate
71
via a blade
72
having a V-shaped cross-section. Next, the portion of the substrate
71
where the V-shaped groove
71
a
is formed is cut via another cutting blade
73
so that the groove extends to and reaches the lower major surface
71
b
of the substrate
71
. According to this method, when the cutting is performed via the blade
73
, chipping at the edge defined by the upper surface
71
d
and the side
71
c
of the substrate
71
is prevented, since the V-shaped groove
71
a
is previously formed.
Further, according to the step cutting method shown in
FIG. 9B
, first, the substrate
71
is imperfectly cut via a cutting blade
74
having a relatively wide cutting width to form a groove
71
e
such that a small cutting margin is left. Next, cutting is performed in the groove
71
e
with a blade
75
having a relative narrow cutting width, so that the groove extends to and reaches the lower surface of the substrate
71
. In this case, the second cutting step can be easily performed, since the cutting is carried out from the bottom of the groove
71
e
to the lower surface
71
b
of the substrate
71
via the blade
75
. Thus, chipping at the lower surface
71
b
of the substrate
71
can be prevented.
However, in an edge reflection type surface acoustic wave device, when reflection edges are formed by cutting, it is necessary not only to prevent the above-described chipping but also to form the reflection edges which are as vertical relative to the substrate as possible. Thus, according to the bevel cutting method, an inclined-surface portion is formed between the upper surface
71
d
of the substrate
71
where the IDT is formed and the side surface
71
c
thereof, which is caused by the V-shaped groove
71
a
. Therefore, the verticality of the upper portion of the side is deteriorated.
On the other hand, the step cutting method is effective in preventing chipping at the lower surface of a substrate, but is not effective in preventing chipping at the upper surface of a substrate.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an edge reflection type surface acoustic wave device and a method of manufacturing thereof, in which reflection
Ago Junya
Horiuchi Hideya
Kadota Michio
Mukai Takao
Keating & Bennett LLP
Murata Manufacturing Co. Ltd
Pascal Robert
Summons Barbara
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