Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-06-26
2004-06-08
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000, C347S070000
Reexamination Certificate
active
06747398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer piezoelectric device and a piezoelectric actuator including such a multilayer piezoelectric device.
2. Description of the Related Art
In general, a piezoelectric actuator which makes use of a piezoelectric effect is sometimes used in a print head of an inkjet printer. As shown in
FIG. 8
, a piezoelectric actuator
1
o
has a piezoelectric property which causes it to be displaced in what is called a d
31
direction, that is, a direction that is perpendicular to the thickness direction of a piezoelectric device. A portion of the bottom surface of the piezoelectric actuator
1
o
is adhered to a fixation substrate
2
, and a pressure-generating chamber
3
is disposed in contact with the end portion of the piezoelectric actuator
1
o
that is not adhered to the fixation substrate
2
. One end of a signal-inputting flexible printed circuit board (hereinafter referred to as “FPC”)
4
is connected to the top surface of the piezoelectric actuator
1
o
. Accordingly, when a signal is input from the FPC
4
, the piezoelectric actuator
1
o
is displaced in a direction that is perpendicular to the thickness direction thereof, causing pressure to be exerted onto ink inside the pressure-generating chamber
3
, so that the ink is discharged outside the pressure-generating chamber
3
.
The structure shown in
FIGS. 9 and 10
has been known as a structure of a multilayer piezoelectric device
6
o
included in a piezoelectric actuator
1
o
. (For example, refer to Japanese Unexamined Patent Application Publication No. 11-10875.)
More specifically, the related multilayer piezoelectric device
6
o
includes a rectangular piezoelectric substrate
7
. Short internal electrodes
8
and long internal electrodes
9
, having different lengths, are arranged so that the short internal electrodes
8
extend from a side surface
7
b
towards an opposite side surface
7
c
and the long internal electrodes extend from the side surface
7
c
to the opposite side surface
7
b
. In addition, the short internal electrodes
8
and the long internal electrodes
9
are alternately stacked in the piezoelectric substrate
7
. The side surfaces
7
b
and
7
c
are opposite each other in the direction of a short side of the piezoelectric substrate
7
. In other words, in the direction of a long side (longitudinal side) of the piezoelectric substrate
7
, the electrodes
8
and
9
have lengths that are substantially equal to the overall width of the piezoelectric substrate
7
. On the other hand, in the direction of a short side of the piezoelectric substrate
7
, the short internal electrodes
8
are shorter than the long internal electrodes
9
. Active portions
10
which are displaced in a direction that is perpendicular to the lamination direction are located at the portions where the electrodes
8
and the corresponding electrodes
9
overlap. Therefore, as shown in
FIG. 10
, the active portions
10
are adjacent to the left side surface
7
b
of the two side surfaces
7
b
and
7
c
that are opposite each other in the direction of a short side of the piezoelectric substrate
7
, and have shapes that are asymmetrical in the horizontal direction.
Each of the short internal electrodes
8
is in a drawn-out state at the side surface
7
b
of the piezoelectric substrate
7
near the active portions
10
, and each of the long internal electrodes
9
is in a drawn-out state at the side surface
7
c
of the piezoelectric substrate
7
distant from the active portions
10
. A first external electrode
13
o
and a second external electrode
14
o
are electrically connected to the drawn-out short internal electrodes
8
and the drawn-out long internal electrodes
9
, respectively.
The first external electrode
13
o
extends from the side surface
7
b
of the piezoelectric substrate
7
near the active portions
10
towards the side surface
7
c
and distant from the active portions
10
by extending onto a main surface
7
a
, and terminates before reaching the side surface
7
c
. On the other hand, the second external electrode
14
o
extends from the side surface
7
c
of the piezoelectric substrate
7
and distant from the active portions
10
towards a location which opposes an end portion of the first external electrode
13
o
at a predetermined interval d therefrom by extending onto the main surface
7
a
. The certain interval d between the first and second external electrodes
13
o
and
14
o
is provided because it is necessary to electrically isolate them.
As described later, when forming the piezoelectric actuator
1
o
using the multilayer piezoelectric device
6
o
, electrical conductors on the FPC
4
need to be electrically connected to the first and second external electrodes
13
o
and
14
o
. Therefore, an area which extends a predetermined distance of L
4
from the side surface
7
c
of the piezoelectric substrate
7
and distant from the active portions
10
is provided as a predetermined soldering portion
16
o
required for soldering.
Such a multilayer piezoelectric device
6
o
and the piezoelectric actuator
1
o
including the multilayer piezoelectric device
6
o
, are formed, for example, in the following way.
In order to form the multilayer piezoelectric device
6
o
, as shown in
FIG. 11
, three types of green sheets
31
,
32
, and
33
are provided. In other words, there are provided the green sheets
31
which have electrically conductive patterns
41
, which define the short internal electrodes
8
, disposed thereon. The green sheets
32
which have electrically conductive patterns
42
, which define the long internal electrodes
9
, disposed thereon, and the green sheets
33
which do not have any electrically conductive patterns formed thereon, are also provided. These green sheets
31
,
32
, and
33
are produced by forming piezoelectric materials, such as PZT materials, into rectangular shapes in plan view. The electrically conductive patterns
41
and
42
are formed by screen printing electrically conductive paste whose main component is, for example, silver (Ag).
After alternately and sequentially placing upon each other a predetermined number of each of the green sheets
31
and
32
having the corresponding electrically conductive patterns
41
and
42
formed thereon, the green sheets
33
are disposed on the topmost and bottommost portions of the resulting layered structure. Then, all of these sheets
31
,
32
, and
33
are press-bonded all together along the lamination direction, and baked. After the baking, the first and second external electrodes
13
o
and
14
o
are formed by evaporation. Thereafter, by polarizing the piezoelectric substrate
7
, the multilayer piezoelectric device
6
o
including the active portions
10
at the portions where the short internal electrodes
8
and the corresponding long internal electrodes
9
are stacked is produced.
Next, using the multilayer piezoelectric device
6
o
, formed in the above-described manner, the piezoelectric actuator
1
o
is formed as shown in FIG.
12
. First, the multilayer piezoelectric device
6
o
is adhered to the fixing substrate
2
with an adhesive so that its active portions
10
do not overlap the fixing substrate
2
.
Then, using a dicing saw, cuts of predetermined sizes are formed at predetermined pitches along the longitudinal direction of the multilayer piezoelectric device
6
o
from the side surface
7
b
towards the side surface
7
c
in order to form slits
21
. As a result, movable portions
22
o
which can be separately driven are formed between the slits
21
. Further, cuts are formed in the first external electrode
13
o
consecutively with the corresponding slits
21
in order to form shallow grooves
23
, so that the first external electrode
13
o
is electrically isolated from each movable portion
22
o
.
Next, the FPC
4
is soldered onto the predetermined soldering portion
16
o
, so that the electrical conductors on the FPC
4
are electrically connected to each of the divided first external
Budd Mark
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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