U.S. patent application number 12/627028 was filed with the patent office on 2010-03-25 for piezoelectric element, droplet-ejecting head, droplet-ejecting apparatus, and method of producing a piezoelectric element.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Nanao Inoue.
Application Number | 20100071180 12/627028 |
Document ID | / |
Family ID | 37893306 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100071180 |
Kind Code |
A1 |
Inoue; Nanao |
March 25, 2010 |
PIEZOELECTRIC ELEMENT, DROPLET-EJECTING HEAD, DROPLET-EJECTING
APPARATUS, AND METHOD OF PRODUCING A PIEZOELECTRIC ELEMENT
Abstract
The present invention provides a piezoelectric element including
a piezoelectric body and top and bottom electrodes holding the
piezoelectric body therebetween, wherein an interlayer dielectric
is interposed between the piezoelectric body and the top electrode
in an area other than the active area of the piezoelectric body,
and the top electrode is layered directly on the piezoelectric body
in the active area of the piezoelectric body.
Inventors: |
Inoue; Nanao; (Kanagawa,
JP) |
Correspondence
Address: |
FILDES & OUTLAND, P.C.
20916 MACK AVENUE, SUITE 2
GROSSE POINTE WOODS
MI
48236
US
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
37893306 |
Appl. No.: |
12/627028 |
Filed: |
November 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11404648 |
Apr 14, 2006 |
7658475 |
|
|
12627028 |
|
|
|
|
Current U.S.
Class: |
29/25.35 ;
347/68 |
Current CPC
Class: |
B41J 2/1642 20130101;
B41J 2/161 20130101; B41J 2002/14459 20130101; B41J 2/1626
20130101; B41J 2202/21 20130101; Y10T 29/42 20150115; B41J
2002/14491 20130101; B41J 2/1646 20130101 |
Class at
Publication: |
29/25.35 ;
347/68 |
International
Class: |
H01L 41/22 20060101
H01L041/22 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2005 |
JP |
2005-280500 |
Claims
1. A method of producing a piezoelectric element, comprising:
forming an electro-conductive crystalline layer, forming a
deposition layer on the crystalline layer by a vapor- or
liquid-phase growth method, and patterning the crystalline layer
and the deposition layer, to thereby sequentially form a bottom
electrode made of the crystalline layer and a piezoelectric body
made of the deposition layer; forming an interlayer dielectric
layer on the bottom electrode and the piezoelectric body followed
by patterning an opening in the interlayer dielectric layer at a
position in the active area of the piezoelectric body; and forming
an electro-conductive layer on the interlayer dielectric layer as
well as on the piezoelectric body exposed at the opening of the
interlayer dielectric layer followed by patterning the
electro-conductive layer to form an top electrode made of the
electro-conductive layer.
2. A method of producing a piezoelectric element, comprising:
forming an electro-conductive crystalline layer, forming a
deposition layer on the crystalline layer by a vapor- or
liquid-phase growth method, and patterning the crystalline layer
and the deposition layer, to thereby sequentially form a bottom
electrode made of the crystalline layer and a piezoelectric body
made of the deposition layer; forming an interlayer dielectric
layer on the bottom electrode and the piezoelectric body followed
by patterning an opening in the interlayer dielectric layer at a
position in the active area of the piezoelectric body as well as an
opening in the interlayer dielectric layer at a position in an
electrical connection area where an top electrode is to be
connected to a wiring; and forming an electro-conductive layer on
the interlayer dielectric layer as well as on the piezoelectric
body exposed at the openings of the interlayer dielectric layer
followed by patterning the electro-conductive layer to form the top
electrode made of the electro-conductive layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. application Ser. No.
11/404,648 filed Apr. 14, 2006, which claims priority under 35 USC
119 from Japanese Patent Application No. 2005-280500, the
disclosure of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a droplet-ejecting
apparatus such as an inkjet-recording apparatus. It also relates to
a piezoelectric element for use in the droplet-ejecting apparatus,
a method of preparing the same, and a droplet-ejecting head using
the same.
[0004] 2. Description of the Related Art
[0005] Inkjet-recording apparatus is one of the conventional
droplet-ejecting apparatuses for printing by ejecting droplets from
multiple nozzles onto a recording medium such as paper, and has
various advantages such as smaller size, low price, and lower
noise, and is commercially available. In particular, a recording
apparatus using a piezoelectric method that ejects an ink droplet
by changing the pressure in a pressure chamber by using a
piezoelectric element, and a recording apparatus using a thermal
method that ejects an ink droplet by expanding ink by heat energy
have many advantages such as high printing speed and
high-resolution image.
[0006] Piezoelectric bodies used in the piezoelectric method occupy
a greater area relative to those of ejection elements (heating
units) used in the thermal method, and thus, it is difficult to
increase the density and the length of the recording head. For that
reason, a configuration of the piezoelectric elements arranged in a
grid pattern is now being studied. However, the piezoelectric
bodies for use in the piezoelectric method are normally composed of
sintered materials, and sintered materials conventionally used did
not have sufficiently high piezoelectric property, and as a result,
a greater element area is needed.
[0007] In contrast, piezoelectric bodies formed by deposition
methods such as vapor growth methods and liquid phase growth
methods are superior in crystallinity and orientation and have a
higher piezoelectric property compared with sintered materials, and
thus, reduction in area and increase in density and length are
expected. The formation methods of piezoelectric bodies by the
deposition methods are highly suitable for common semiconductor
processes and large-area electronic device processes, in which Si
substrates and glass substrates are used.
[0008] On the other hand, the piezoelectric element in an
inkjet-recording head demands a greater displacement of a diaphram
for increase in the ink drop volume, and thus, a thick
piezoelectric film having a thickness of 5,000 .ANG. or more is
needed.
[0009] As described, for example, in JP-A No. 2003-154646,
piezoelectric elements generally have a sandwich structure wherein
the piezoelectric body is held between a pair of top and bottom
electrodes, and have the following problems:
[0010] First, in the piezoelectric body area including the
piezoelectric body active area (active area where recording liquid
is displaced in a pressure chamber), the area other than the
piezoelectric body active area also operates and consumes wasteful
energy. When a piezoelectric body is wired as it is in the sandwich
structure wherein the piezoelectric body is held between the top
and bottom electrodes, capacitance according to the wiring length
is added, causing a problem of variation and increase in the
capacitance for each piezoelectric body. In particular, increase in
the capacitance of piezoelectric bodies that have a high dielectric
constant of several hundreds or more is significant. In addition,
the variation in the capacitance of each piezoelectric body leads
to fluctuation in the energy applied to the piezoelectric body, so
that it is difficult to maintain the uniform ink ejecting property
from the entire head. The fluctuation in the capacitance of each
bit is a serious problem, particularly in piezoelectric elements
having a two-dimensional configuration wherein piezoelectric bodies
are arranged in a grid pattern for increase in density and
length.
[0011] In addition, there are the following problems, in forming
such a thick piezoelectric film by a vapor- or liquid-phase growth
method:
[0012] First, when a piezoelectric body is deposited on an area
having an amorphous underlayer, the perovskite-phase
crystallization temperature needed for piezoelectric property
(temperature needed to form the perovskite crystal phase) increases
by approximately 50 to 100.degree. C.
[0013] Further, when a piezoelectric body is deposited in an area
having an amorphous underlayer, amorphous phase and mixed crystals
of perovskite and pyrochlore phases are often formed, so that this
process is not suitable for forming a uniform piezoelectric
body.
[0014] Further, the piezoelectric body layer is occasionally
separated or cracked in the area having an amorphous
underlayer.
[0015] The phenomena described above tend to become marked with
increase in thickness of the piezoelectric body.
SUMMARY OF THE INVENTION
[0016] The present invention has been made in view of the above
circumstances and provides a piezoelectric element and a method of
producing a piezoelectric element.
[0017] According to an aspect of the invention, a piezoelectric
element includes a piezoelectric body and top and bottom electrodes
holding the piezoelectric body therebetween, wherein an interlayer
dielectric is interposed between the piezoelectric body and the top
electrode in an area other than the active area of the
piezoelectric body, and the top electrode is layered directly on
the piezoelectric body in the active area of the piezoelectric
body.
[0018] According to another aspect of the invention, a method of
producing a piezoelectric element includes:
[0019] forming an electro-conductive crystalline layer, forming a
deposition layer on the crystalline layer by a vapor- or
liquid-phase growth method, and patterning the crystalline layer
and the deposition layer, to thereby sequentially form a bottom
electrode made of the crystalline layer and a piezoelectric body
made of the deposition layer;
[0020] forming an interlayer dielectric layer on the bottom
electrode and the piezoelectric body followed by patterning an
opening in the interlayer dielectric layer at a position in the
active area of the piezoelectric body; and
[0021] forming an electro-conductive layer on the interlayer
dielectric layer as well as on the piezoelectric body exposed at
the opening of the interlayer dielectric layer followed by
patterning the electro-conductive layer to form an top electrode
made of the electro-conductive layer.
[0022] According to another aspect of the invention, a method of
producing a piezoelectric element includes:
[0023] forming an electro-conductive crystalline layer, forming a
deposition layer on the crystalline layer by a vapor- or
liquid-phase growth method, and patterning the crystalline layer
and the deposition layer, to thereby sequentially form a bottom
electrode made of the crystalline layer and a piezoelectric body
made of the deposition layer;
[0024] forming an interlayer dielectric layer on the bottom
electrode and the piezoelectric body followed by patterning an
opening in the interlayer dielectric layer at a position in the
active area of the piezoelectric body as well as an opening in the
interlayer dielectric layer at a position in an electrical
connection area where an top electrode is to be connected to a
wiring; and
[0025] forming an electro-conductive layer on the interlayer
dielectric layer as well as on the piezoelectric body exposed at
the openings of the interlayer dielectric layer followed by
patterning the electro-conductive layer to form the top electrode
made of the electro-conductive layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Preferred embodiments of the present invention will be
described in detail based on the following figures, wherein:
[0027] FIG. 1 is a schematic configurational view illustrating an
inkjet-recording apparatus according to the first embodiment;
[0028] FIG. 2 is a view illustrating the print width by the
inkjet-recording unit according to the first embodiment;
[0029] FIG. 3 is a bottom view of the inkjet-recording head
according to the first embodiment;
[0030] FIG. 4 is a partial magnified top view illustrating the area
around the piezoelectric body in the inkjet-recording head
according to the first embodiment;
[0031] FIG. 5 is a cross-sectional view along the line A-A in FIG.
4;
[0032] FIG. 6 is a cross-sectional view along the line B-B in FIG.
4;
[0033] FIGS. 7A to 7G are process diagrams illustrating the
production process for the piezoelectric element shown in FIG.
5;
[0034] FIGS. 8A to 8G are process diagrams illustrating the
production process for the piezoelectric element shown in FIG.
6;
[0035] FIG. 9 is a partial magnified top view illustrating the area
around the piezoelectric body in the inkjet-recording head
according to the second embodiment;
[0036] FIG. 10 is a cross-sectional view along the line A-A in FIG.
9;
[0037] FIG. 11 is a cross-sectional view along the line B-B in FIG.
9;
[0038] FIGS. 12A to 12G are process diagrams illustrating the
production process for the piezoelectric element shown in FIG. 10;
and
[0039] FIGS. 13A to 13G are process diagrams illustrating the
production process for the piezoelectric element shown in FIG.
11.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Hereinafter, the present invention will be described with
reference to drawings. The same numbers are allocated to members
having substantially the same functions in all drawings, and
duplicated description is often omitted. In the following
embodiments, description of the configuration of ink (liquid)
channel is omitted.
First Embodiment
[0041] FIG. 1 is a schematic configurational view of an
inkjet-recording apparatus according to the first embodiment. FIG.
2 is a view illustrating the print width by the inkjet-recording
unit according to the first embodiment.
[0042] Referring to FIG. 1, an ink jet recording apparatus 10
(droplet ejecting apparatus) according to the present embodiment is
basically composed of a recording medium (paper sheet) supplying
section 12 for feeding recording media (paper sheets); a
registration adjustment section 14 for controlling the posture of
the recording media (paper sheets); a recording section 20
including a recording head section 16 for forming images on a
recording medium P by ejecting ink droplets (liquid droplets), and
a maintenance section 18 for performing maintenance of the
recording head 16; and a discharging section 22 for discharging the
recording media (paper sheets) on which the images have been formed
in the recording section 20.
[0043] The recording medium (paper sheet) supplying section 12 is
composed of a stocker 24 in which the recording media (paper
sheets) are stacked and stocked, and a transportation apparatus 26
for feeding the recording media (paper sheets) one by one from the
stocker 24 and transporting the recording media (paper sheets) to
the registration adjustment section 14.
[0044] The registration adjustment section 14 includes a loop
forming section 28 and a guide member 29 for controlling the
posture of the recording media (paper sheets). When the recording
media (paper sheets) pass through this part, the skew of the
recording media (paper sheets) is corrected by the use of the
elasticity of the recording media (paper sheets), and the recording
media (paper sheets) proceed into the recording section 20 with
control of the transportation timing.
[0045] In the discharging section 22, the recording media (paper
sheets) on which the images have been formed by the recording
section 20 are stored into a tray 25 via a medium (paper)
discharging belt 23.
[0046] A recording medium (paper sheet) transportation passageway
is formed between the recording head 16 and the maintenance section
18 for transporting the recording medium P. The recording medium P
is continuously (without stopping) transported while the recording
medium P is being sandwiched between a star wheel 17 and a
transportation roll 19. Ink droplets are ejected from the recording
head section 16 to this recording medium (paper sheet), whereby an
image is formed on the recording medium P.
[0047] The maintenance section 18 is composed of a maintenance
apparatus 21 that is disposed opposite to the ink jet recording
unit 30 (recording head 32), and can perform processes such as
capping, wiping, dummy jetting, and evacuating for the ink jet
recording unit 30 (recording head 32).
[0048] Each of the ink jet recording units 30 includes one or
plural ink jet recording heads 32. When including plural ink jet
recording heads 32 (although not shown), these heads are arranged
in a direction perpendicular to the recording medium (paper sheet)
transportation direction. By ejecting ink droplets from the nozzles
(not shown) of the recording head 32 to the recording medium P that
is transported continuously in the recording medium (paper sheet)
transportation passageway, an image is formed on the recording
medium P. Here, at least four ink jet recording units 30 are
provided, for example, corresponding to each color of yellow,
magenta, cyan, and black for recording a so-called full-color
image.
[0049] Referring to FIG. 2, the print width by each ink jet
recording unit 30 is set to be longer than the maximum recording
medium width (maximum paper sheet width PW) of the recording medium
P on which an image is assumed to be recorded by this ink jet
recording apparatus 10, whereby an image can be formed over the
total width of the recording medium P without moving the ink jet
recording unit 30 in a recording medium (paper sheet) width
direction (i.e. a so-called full width array (FWA)). Here, the
print width is basically the maximum of the recording width
obtained by subtracting a margin, where printing is not carried
out, from the both ends of the recording medium (paper sheet).
However, the print width is generally set to be larger than the
maximum width of the recording medium to be printed (maximum paper
sheet width PW). This is because there may be a case where the
recording medium (paper sheet) is transported while being tilted
(skewed) at a certain angle to the transportation direction, and
that there is a high demand for borderless prints.
[0050] Hereinafter, the inkjet-recording head 32 in the
inkjet-recording unit 30 will be described in detail. FIG. 3 is a
bottom view of the inkjet-recording head according to the first
embodiment. FIG. 4 is a partial magnified top view illustrating the
area around the piezoelectric body in the inkjet-recording head
according to the first embodiment. FIG. 5 is a cross-sectional view
along the line A-A in FIG. 4. FIG. 6 is a cross-sectional view
along the line B-B in FIG. 4. In FIG. 4, common electrode 46,
piezoelectric body 48, and signal wiring 62 are represented by
solid lines, while other members are represented by dotted lines,
for easy understanding. The same will be applied hereinafter.
[0051] As shown in FIG. 3, the inkjet-recording head 32 has
piezoelectric elements 34 (piezoelectric bodies 48) arranged in a
grid pattern, for example, of 2,560 bits (e.g., 8 lines.times.320
rows)(in the configuration wherein respective lines are phase
shifted), and respective lines are shifted with respect to each
other by 21 .mu.m along the row direction (along the recording
medium P). This configuration allows a resolution of 1,200 dpi.
[0052] At both end portions, in the width direction, of the
piezoelectric body group configured by the piezoelectric elements
34 of 2,560 bits, a plurality of drive chips 42 are provided at the
same interval along the longitudinal direction of the support
substrate 40.
[0053] An extension wiring 44 connected to the signal electrode 50
(signal wiring 62) of each piezoelectric element 34 extends in the
direction (width direction) orthogonal to the longitudinal
direction of the support substrate 40 and finally is electrically
connected while fitted to the pitch of the pad of the drive chip
42. For shortening the wire length of the extension wiring 44, it
is preferable to divide the piezoelectric elements 34 into two
groups in the width direction of the support substrate 40 and make
the extension wiring 44 extend along the width direction of the
support substrate 40.
[0054] An image with 1,200 dpi is formed on the recording medium P
by arranging the piezoelectric elements 34 in a grid pattern of
2,560 bits, shifting the piezoelectric elements 34 in each line by
21 .mu.m along the row direction, and allowing the recording medium
P to pass the inkjet-recording head 32 once; but it is not always
necessary to shift the piezoelectric elements 34 in each line along
the row direction (or to make staggered lines of the piezoelectric
elements 34).
[0055] For example, it is also possible to make the
inkjet-recording head 32 movable along the width direction of the
recording medium P being transported, and shift the relative
position of the inkjet-recording head 32 after each passage of the
recording medium P on the inkjet-recording head 32, thereby
obtaining a desirable resolution with n passages of the recording
medium P.
[0056] As shown in FIGS. 4 to 6, in the inkjet-recording heads 32,
the piezoelectric elements 34 (piezoelectric bodies 48) are
arranged in a grid pattern of 2,560 bits (8 lines.times.320 rows),
and respective lines are shifted with respect to each other, for
example by 21 .mu.m, along the row direction.
[0057] The piezoelectric elements 34 are formed on a substrate 52
having a vibrating plate (diaphragm), and a common electrode 46
(bottom electrode), a piezoelectric body 48, and a signal electrode
50 (top electrode) are laminated in this order thereon. In FIGS. 5
and 6, 52A represents a diaphragm, and 52B represents an ink
(liquid) pressure chamber.
[0058] A first interlayer dielectric layer 54 is formed on the
upper surface (signal electrode 50-side surface) of the
piezoelectric body 48 except in the active area 48A of the
piezoelectric body 48 (active area where piezoelectric body 48
displaces ink (liquid) in the pressure chamber), and the first
interlayer dielectric layer 54 is present between the piezoelectric
body 48 and signal electrode 50 except in this area. In addition,
the first interlayer dielectric layer 54 extends to and covers the
side face of the piezoelectric body, and also covers portions of
the common electrode 46 having no piezoelectric body 48 formed
thereon.
[0059] The first interlayer dielectric layer 54 has an opening in
the electrical connection area described below, where the signal
electrode 50 and the signal wiring 62 are electrically connected,
in the non-active area of the piezoelectric body 48, and the
piezoelectric body 48 and the signal electrode 50 are electrically
connected to each other through the opening. Further, the first
interlayer dielectric layer 54 has an opening for electrical
connection between the common electrode 46 and the common wiring 60
in the non-active area of the piezoelectric body 48, and the common
electrode 46 and the common wiring 60 are electrically connected
via a signal electrode 50 through the opening.
[0060] On the other hand, a second interlayer dielectric layer 56
is formed on the surface (at the opposite side to piezoelectric
body 48) of the signal electrode 50 and on the surface of the
common wiring 60 electrically connected to the common electrode 46
described below. In addition, a protective layer 58 is formed on
the surface of the signal wiring 62 electrically connected to the
signal electrode 50 described below. However, the protective layer
58 is formed only on the area other than the active area 48A of the
piezoelectric body 48 and covers only the signal wiring 62.
[0061] Hereinafter, the common electrode 46 and the signal
electrode 50 will be described. The common electrodes 46 are
respectively formed in each line of the piezoelectric bodies 48,
and are common in each 320 bits of the piezoelectric bodies 48. The
common electrode 46 is connected to common wirings 60, which are
formed at a layer position different therefrom, in the non-active
area of the piezoelectric body 48. The common wiring 60 reduces the
electric current density in the common electrode and prevents
deterioration of the electrode material. The common wiring 60 may
be formed separately from the common electrode 46, and it is
possible to reduce the wiring resistance sufficiently by using a
material having a resistivity of 10 .mu..OMEGA.cm or less such as
Al, Cu, or Ag as the electrode material.
[0062] On the other hand, a signal electrode 50 is formed for each
piezoelectric body 48, and is connected to the signal wiring 62,
which is formed at a layer position different therefrom, in the
non-active area of the piezoelectric body 48. The signal wiring 62
may be formed separately from the common electrode 46, and it is
possible to reduce the wiring resistance sufficiently by using a
material having a resistivity of 10 .mu..OMEGA.cm or less such as
Al, Cu, or Ag as the electrode material.
[0063] Although not shown in the figures, the common wiring 60 and
the signal wiring 62 are extended and respectively connected to the
extension wirings 44 (refer to FIG. 3) through the pads provided in
the openings formed in the first interlayer dielectric layer 54 and
the second interlayer dielectric layer 56, and to the drive chip 42
via the wirings.
[0064] The common electrode 46, the common wiring 60 and the signal
wiring 62 are laminated respectively via an adsorption layer (e.g.,
Ti 100 .ANG.), although not shown in the figures.
[0065] In addition, the common wiring 60 and the signal wiring 62
are formed at layer positions different from each other (laminated
via the second interlayer dielectric layer 56), which allows
arrangement of the piezoelectric bodies 48 in a grid pattern (in
the configuration wherein respective lines are phase shifted,
however) for high pixel density. Although not shown in the figures,
the signal wirings 62 for respective lines of the piezoelectric
bodies 48 may be formed at different layer positions, for high
pixel density and for reduction in wiring resistance.
[0066] The common electrode 46 is made of a crystalline layer.
Examples of the crystalline layers include crystalline metal layers
and crystalline electro-conductive metal-oxide layers (crystalline
oriented layers). The crystalline layer means a thin film layer of
a crystalline material in the cubic system such as simple cubic
system, body-centered cubic system, and face-centered cubic system;
in the tetragonal crystalline system such as simple tetragonal
system and body-centered tetragonal system; in the orthorhombic
system such as simple orthorhombinc system, body-centered
orthorhombic system, one-face-centered orthorhombic system, and
face-centered orthorhombic system; in the rhombohedral system; in
the hexagonal system; in the monoclinic system such as simple
monoclinic system and one-face-centered monoclinic system; or in
the triclinic system. The crystalline metal layer is a layer of a
metal, metal nitride, metal silicide, or metal boride, which forms
any one of the crystal systems above. The crystalline
electro-conductive metal-oxide layer is a layer of an
electro-conductive oxide having any one of the crystal systems
above.
[0067] Typical examples of the materials for the crystalline layer
are listed below.
Crystalline Metal Layer
[0068] Noble metals (e.g., Au, Ag, Ru, Rh, Pd, Os, Ir, Pt, etc.)
[0069] Noble metal oxides (e.g., IrO.sub.2, RuO.sub.2, etc.),
high-melting point metals (e.g., .alpha.-Ta (bcc-Ta), bcc-V,
bcc-Nb, bcc-Mo, bcc-W, hcp-Ti, hcp-Zr, hcp-Hf, TaMo, TaTi, TiAl,
.beta.-Ta, bcc-Ti, bcc-Zr, bcc-Ti, bcc-Zr, etc.), and [0070] Metal
nitrides, metal silicides, and metal borides (e.g., Ta.sub.2N,
TaN.sub.0.1, TaN.sub.0.8, TaN, Ta.sub.6 N.sub.2.57, Ta.sub.4N,
[0071] TaB.sub.2, TaB,
[0072] TaSi.sub.2, Ta.sub.5Si, .beta.-Ta.sub.5Si.sub.3,
.alpha.-Ta.sub.5Si.sub.3, Ta.sub.2Si, Ta.sub.3Si, Ta.sub.4Si,
Ta.sub.3.28Si.sub.0.72,
[0073] VN, V.sub.2N, V.sub.6 N.sub.2.7, VN.sub.0.2, VN.sub.0.35,
VB.sub.2, V.sub.1.54B.sub.50,
[0074] VSi.sub.2, V.sub.3Si, V.sub.5Si.sub.3,
[0075] Nb.sub.2N, NbN, NbN.sub.0.95, Nb.sub.4.62N.sub.2.14,
Nb.sub.4N.sub.3.92, Nb.sub.4N.sub.3,
[0076] NbSi.sub.2, Nb.sub.3Si,
[0077] MoN, Mo.sub.2N,
[0078] MoB.sub.4, Mo.sub.0.8B.sub.3, Mo.sub.2B,
[0079] MoSi.sub.2, Mo.sub.5Si.sub.3,
[0080] WN, W.sub.2N,
[0081] WB.sub.4, W.sub.2B.sub.5,
[0082] WSi.sub.2, W.sub.5Si.sub.3, W.sub.3Si,
[0083] TiN, Ti.sub.2N, TiN.sub.0.26, TiN.sub.0.30,
[0084] TiB.sub.2,
[0085] TiSi.sub.2, TiSi, Ti.sub.5Si.sub.4, Ti.sub.5Si.sub.3,
[0086] ZrN.sub.0.28, ZrN,
[0087] ZrB.sub.2,
[0088] ZrSi.sub.2, ZrSi, Zr.sub.5Si.sub.3,
[0089] HfB.sub.2, HfN.sub.0.40, HfN,
[0090] HfB,
[0091] HfSi.sub.2, Hf.sub.5Si.sub.4, Hf.sub.2Si, Hf.sub.5Si.sub.3,
etc.)
Crystalline Electro-Conductive Metal-Oxide Layer
[0092] BaRuO.sub.3, SrRuO.sub.3, (Ba,Sr)RuO.sub.3, BaPbO.sub.3,
LaCuO.sub.3, LaNiO.sub.3, LaCoO.sub.3, LaTiO.sub.3,
(La,Sr)CoO.sub.3, (La,Sr)VO.sub.3, (La,Sr)MnO.sub.3, LuNiO.sub.3,
CaVO.sub.3, CaIrO.sub.3, CaRuO.sub.3, CaFeO.sub.3, SrVO.sub.3,
SrCrO.sub.3, SrIrO.sub.3, SrFeO.sub.3, ReO.sub.3, and the like.
[0093] Among the materials listed above, ruthenium oxides (e.g.,
RuO.sub.2, BaRuO.sub.3, SrRuO.sub.3, and (Ba,Sr)RuO.sub.3) are
particularly preferable, from the viewpoints of low electric
conductivity, easiness in handling, and high stability in
properties.
[0094] A configuration using a common electrode 46 as a bottom
electrode and a signal electrode 50 as an top electrode is
described in this embodiment, but the configuration is not limited
thereto. Thus, a configuration using a signal electrode 50 as a
bottom electrode and a common electrode 46 as an top electrode is
also possible. The top electrode may have a known electrode
configuration.
[0095] Hereinafter, the piezoelectric body will be described. The
piezoelectric body 48 is preferably formed by a vapor- or
liquid-phase growth method such as sputtering method, MOCVD
(Metal-Organic Chemical Vapor Deposition) method, sol-gel method,
or hydrothermal method. The vapor- or liquid-phase growth method
enables the formation of piezoelectric bodies with higher density,
higher accuracy, and lower cost compared with conventional
mechanical formation methods of polishing and adhering a
piezoelectric body after sintering.
[0096] The sputtering method is a method of forming a thin film on
the surface of an object by sputtering atoms or molecules from the
surface of a film-forming source (target) by ion bombardment and
depositing the atoms or molecules on the object placed around the
target. Alternatively, the CVD method is a method of
vapor-depositing a thermally decomposed product of a vapor-phase
molecule flowing over a heated substrate.
[0097] The sol-gel method is a method of forming a film by using
the conversion from the sol state wherein solid fine particles are
dispersed uniformly in liquid into the gel state wherein the fine
particles form a three dimensional network structure by the
attractive interaction generated among them.
[0098] The vapor- or liquid-phase growth methods include a method
of crystallizing a piezoelectric body 48 during deposition
(vapor-phase or liquid-phase growth) and a method of depositing the
precursor of a piezoelectric body 48 (in the vapor or liquid phase)
and then thermally crystallizing the piezoelectric body 48. In the
former method, the crystalline material for piezoelectric body 48
is formed in a high-temperature atmosphere, for example, at a
temperature of 500.degree. C. or higher, while in the latter
method, the precursor for the piezoelectric body 48 is formed in a
low-temperature atmosphere, for example, at a temperature of
500.degree. C. or lower. In particular, the sputtering and MOCVD
methods permit crystal growth in a high-temperature atmosphere. On
the other hand, in the sol-gel and aero-sol methods it is necessary
to use a method of forming a precursor under a low-temperature
atmosphere and then carrying out the crystallization.
[0099] The piezoelectric body 48 is formed on the common electrode
46 (bottom electrode) made of the crystalline layer described above
by a vapor- or liquid-phase growth method.
[0100] The material for the piezoelectric body 48 is not
particularly limited as far as it is known as a material for a
piezoelectric body that can be deformed by voltage application. For
example, a lead zirconate titanate (PZT)-based piezoelectric body
having a relatively greater piezoelectric constant is preferably
used for ejecting droplets from the viewpoint of desirable
properties.
[0101] Hereinafter, as dielectric layers, the first interlayer
dielectric layer 54, second interlayer dielectric layer 56, and
protective layer 58 will be described. The dielectric material for
these dielectric layers is not particularly limited as long as it
has dielectric property, gas (oxygen) permeation resistance, and
liquid resistance; but particularly when the dielectric layer is in
contact with the piezoelectric body 48, the dielectric layer may
increase the capacitance of the piezoelectric element 34; and thus,
use of an dielectric material having a low dielectric constant, for
example, a dielectric constant of 1/10 or less of that of the
piezoelectric body, is preferable (the dielectric constant of the
dielectric material is preferably 1 to 70, and more preferably 1 to
10). Specifically, the dielectric constant of the piezoelectric
body 48 is, for example, 500 or more, and the dielectric constant
of the dielectric layer should be 100 or less. Examples of the
dielectric materials include inorganic dielectric materials such as
silicon oxide (USG: undoped silicate glass), silicon nitride, BPSG
(boro-phospho-silicate glass), FSG (fluorinated silicate glass),
black diamond, FDLC (fluorinated diamond-like carbon), silicon
oxide nitride, SiCO (C-doped USG), silicon carbide, tantalum oxide,
aluminum oxide, zirconia oxide, titanium oxide, and the like.
[0102] A typical example of the method of producing the
piezoelectric element according to the present embodiment will be
described below. FIGS. 7A to 7G are process diagrams illustrating
the production process for the piezoelectric element shown in FIG.
5. FIGS. 8A to 8G are process diagrams illustrating the production
process for the piezoelectric element shown in FIG. 6.
[0103] As shown in FIGS. 7A and 8A, a crystalline layer 46A made of
Ir is first formed on one side of a substrate 52 made of single
crystal silicon having a thickness of 300 .mu.m, which is doped
with boron to a depth of 4.0 .mu.m, by depositing Ti 100 .ANG. (not
shown in the figures) and Ir 2500 .ANG. by sputtering; and then, a
deposition layer 48B made of PZT (lead zirconate titanate:
dielectric constant: 700) is formed by sputtering in an atmosphere
at 550.degree. C.
[0104] As shown in FIGS. 7B and 8B, the crystalline layer 46A and
the deposition layer 48B (Ir/PZT) are then patterned by reactive
ion etching (RIE) together with the deposited Ti layer not shown in
the figures, to give a common electrode 46 made of the crystalline
layer 46A and a piezoelectric body 48 made of the deposition layer
48B. In this embodiment, the lower-layer common electrode 46
(including the Ti layer) is patterned in a size that is larger by
approximately 1 .mu.m than the upper-layer piezoelectric body 48 by
using different photomasks. Of course, the piezoelectric body 48
and the common electrode 46 may be the same in size.
[0105] The Ti layer not shown in the figures is an adsorption layer
that is adsorbed to the substrate. In the figures, the common
electrode 46 is patterned in a belt-shaped pattern including the
active area 48A of the piezoelectric body 48, but the pattern is
not limited thereto.
[0106] It is preferable that the area boundary (end face) of the
piezoelectric body 48 is obliquely formed at an angle of 10 to
80.degree. with respect to the substrate face. If the angle is
80.degree. or more, sufficient step coverage may not be obtained,
which leads to disconnection of the signal wiring 62 electrically
connected to the signal electrode 50. If the angle is 10.degree. or
less, the distance between the piezoelectric bodies 48 and the
distance between the piezoelectric body and the common wiring 60
may be extended, which makes it difficult to carry out high-density
arrangement of the piezoelectric bodies 48.
[0107] A SiO.sub.2 (dielectric constant: 1.3) layer with 5,000
.ANG. thickness is then formed as the first interlayer dielectric
layer 54 by CVD on the exposed surface (surface and side faces) of
the piezoelectric body 48, the exposed surface of the common
electrode 46, and the exposed surface of the substrate 52. An
opening 54A for defining the active area 48A of the piezoelectric
body 48 and an opening 54B as the Via area for electrical
connection between the piezoelectric body 48 and the signal
electrode 50 in the electrical connection area, where the signal
electrode 50 and the signal wiring 62 are connected, are then
formed by photolithography and etching. At the same time, an
opening 54C is formed in the non-active area of the piezoelectric
body 48 by etching the first interlayer dielectric layer 54 to
expose the common electrode 46. A signal electrode 50 and a common
wiring 60 will sequentially be deposited and patterned later on the
opening 54C (exposed area of the common electrode 46). In this
manner, it is possible to reduce the wiring resistance of the
common electrode 46. The openings 54A and 54B are formed separately
in the description above, but they may be formed as a common
opening.
[0108] As shown in FIGS. 7C and 8C, an Ir layer with 2500 .ANG.
thickness is then deposited on the entire surface over the
substrate 52, and the Ir layer is patterned by reactive ion etching
to form an signal electrode 50 made of Ir. In this manner, the
signal electrode 50 is connected electrically to the piezoelectric
body 48 through the opening 54A (active area 48A of the
piezoelectric body 48) as well as through the opening 54B. A signal
electrode 50 is formed also on the common electrode 46 exposed at
the opening 54C.
[0109] As shown in FIGS. 7D and 8D, a common wiring 60 is then
formed by depositing TiNx 100 .ANG./Ti 100 .ANG./Al 5,000 .ANG./Ti
100 .ANG./TiNx 200 .ANG. layers followed by patterning by etching
to be electrically connected to the common electrode 46 via the
signal electrode 50.
[0110] As shown in FIGS. 7E and 8E, a silicon oxide nitride SiOxNy
layer with 5,000 .ANG. thickness is then deposited as the second
interlayer dielectric layer 56 by plasma CVD to cover the exposed
signal electrode 50 and common wiring 60. Further, for electrical
connection between the signal electrode 50 and the signal wiring
62, an opening 56A is formed by etching the second interlayer
dielectric layer 56 in the non-active area of the piezoelectric
body 48 to expose the signal electrode 50. The electrical
connection area (opening 56A), where the signal electrode 50 and
signal wiring 62 are connected, is located in the electrical
connection area (opening 54B), where the piezoelectric body 48 and
signal electrode 50 are connected, in the non-active area of the
piezoelectric body 48.
[0111] As shown in FIGS. 7F and 8F, a signal wiring 62 is then
formed on the signal electrode 50 exposed at the opening 56A by
depositing and patterning Ti 100 .ANG./Al 7000 .ANG. layers to be
connected electrically to the signal electrode 50.
[0112] The signal electrode 50 and the signal wiring 62 are
electrically connected to each other in the vicinity of the active
area 48A of the piezoelectric body 48. In addition, the second
interlayer dielectric layer 56 is formed for interlayer separation
of the common wiring 60 from the signal wiring 62 and for providing
these layers respectively at different layer positions.
[0113] As shown in FIGS. 7G and 8G, a silicon nitride SiNx layer
with 5,000 .ANG. thickness is then deposited and patterned as a
protective layer 58 by plasma CVD to cover the area of the signal
wiring 62.
[0114] Films deposited in the active area 48A of the piezoelectric
body 48 may constrain displacement of the piezoelectric body. Thus,
the protective layer 58 covers only the area of the signal wiring
62, but not the active area 48A of the piezoelectric body 48.
However, the protective layer 58 may be formed on the entire
surface including the active area 48A of the piezoelectric body
48.
[0115] An ink (liquid) pressure chamber 52B and a boron-diffused
diaphragm 52A having a thickness of 4 .mu.m are formed by etching
the active area 48A of the piezoelectric body 48 from the rear face
of the substrate 52.
[0116] In this manner, it is possible to prepare the piezoelectric
element 34.
[0117] In the inkjet-recording apparatus according to the
embodiment described above, the piezoelectric element 34 has a
configuration wherein a first interlayer dielectric layer 54
mediates between the piezoelectric body 48 and the signal electrode
50 in the area except the active area 48A of the piezoelectric body
48, and the piezoelectric body 48 and the signal electrode 50 are
connected to each other directly only in the active area 48A of the
piezoelectric body 48. Thus, the active area 48A of the
piezoelectric body 48 is defined accurately by the first interlayer
dielectric layer 54, i.e., by the boundary of the opening 54A.
Accordingly, operation of the piezoelectric body is prohibited in
the area other than the active area 48A of the piezoelectric body
48. In addition, the capacitance in the area having the first
interlayer dielectric layer 54 surrounding the active area 48A of
the piezoelectric body 48 is smaller than the capacitance of the
active area 48A having only the piezoelectric body 48 between the
common electrode 46 and the signal electrode 50, whereby wasteful
energy consumption can be reduced.
[0118] Further, coverage of the side face of the piezoelectric body
48 with the first interlayer dielectric layer 54 enables sufficient
electrical insulation between the side face of the piezoelectric
body 48 and the signal electrode 50, and prevention of discharge
and short circuiting at the side face of the piezoelectric body 48,
and can make the electric field applied to the piezoelectric body
48 uniform. In particular in the preparation, when a common
electrode 46 (bottom electrode) and a piezoelectric body are
sequentially deposited and patterned, and a signal electrode 50
(top electrode) is deposited and patterned without deposition of a
first interlayer dielectric layer 54, it is difficult to etch the
signal electrode 50 (top electrode) near the boundary with the
piezoelectric body 48 having a thickness of about 5,000 .ANG. to
several .mu.m. Therefore, it is effective to provide a first
interlayer dielectric layer 54 between the piezoelectric body 48
and the signal electrode 50 in the area except the active area 48A
of the piezoelectric body 48 and cover the side face of the
piezoelectric body 48 with the first interlayer dielectric layer
54.
[0119] Also, the common electrode 46 (bottom electrode) and the
signal electrode 50 (top electrode) are electrically insulated from
each other by the first interlayer dielectric layer 54 to enable
the piezoelectric element to function as a piezoelectric element
with sufficient reliability. At the same time, the first interlayer
dielectric layer 54 functions as a protective layer for the
piezoelectric body 48, particularly for the side face thereof, to
prevent diffusion of the constituent materials of the piezoelectric
body 48 and penetration of oxygen, whereby the reliability of the
piezoelectric element is drastically improved. Further, the
capacitance is reduced in the area having the first interlayer
dielectric layer 54 other than the active area 48A of the
piezoelectric body 48, whereby the capacitance of the entire
element is reduced.
[0120] The electrical connection area (opening 56A), where the
signal electrode 50 and signal wiring 62 are connected, overlaps
the electrical connection area (opening 54B), where the
piezoelectric body 48 and signal electrode 50 are connected, in the
non-active area of the piezoelectric body 48; thus, the
piezoelectric body, the signal electrode, and the signal wiring
have a layered structure in this area; and such a configuration
allows ohmic contact and reliable electrical connection among
them.
[0121] With respect to the inkjet-recording apparatus according to
this embodiment, in the preparation of the piezoelectric element
34, a deposition layer 48B for the piezoelectric body 48 is formed
on a crystalline layer 46A for common electrode 46 by a vapor- or
liquid-phase growth method, and a common electrode 46 and a
piezoelectric body 48 are formed by pattering these layers; and
thus, the perovskite-phase crystallization temperature needed for
piezoelectric property, i.e., the temperature needed to form the
perovskite crystal phase is not raised, and also a mixed crystal of
perovskite and pyrochlore phases is not formed. Further,
exfoliation and cracking of the piezoelectric body do not take
place. Thus, it is possible to produce the piezoelectric element 34
by deposition at low temperature without deteriorating the
crystallinity and orientation of the piezoelectric body and without
cracking and exfoliation thereof.
[0122] For example, when a piezoelectric body is formed by
depositing a PZT (PbZr.sub.(1-x)Ti.sub.xO.sub.3) material with a
thickness of 5.0 .mu.m by sputtering on an undercoat layer of
face-centered cubic crystal Ir, it is possible to form a perovskite
crystal phase in the tetragonal crystalline system at an
atmospheric temperature of 550.degree. C., but in contrast, an
amorphous phase or a mixed crystal system of the perovskite and
amorphous phases or of the perovskite and pyrochlore phases is
formed on an undercoat layer of amorphous SiO.sub.2 at the same
atmospheric temperature, and in this case an atmospheric
temperature of 620.degree. C. is needed for growth of a single
perovskite phase. This fact indicates that it is possible to
produce a piezoelectric body without deteriorating the
crystallinity and orientation of the piezoelectric body and also at
low temperature by forming a piezoelectric body on a crystalline
layer by deposition.
[0123] Similarly, when a thick piezoelectric body having a
thickness of 5,000 .ANG. or more is deposited on an amorphous
SiO.sub.2 layer, cracks of approximately 1.0 .mu.m and exfoliation
are generated. On the other hand, no cracks or exfoliation are
generated when a crystalline layer of Ir with a thickness of 2,000
.ANG. is previously formed on an amorphous SiO.sub.2 underlayer and
a thick piezoelectric body having a thickness of 5,000 .ANG. or
more is deposited similarly on the crystalline layer. This fact
indicates that it is possible to prevent cracking and exfoliation
by forming a piezoelectric body on a crystalline layer by
deposition.
[0124] Alternatively, when a PZT (PbZr.sub.(1-x)Ti.sub.xO.sub.3)
material with a thickness of 5.0 .mu.m is deposited by sputtering
on the crystalline layer of ruthenium oxide (BaRuO.sub.3,
(Ba,Sr)RuO.sub.3, or SrRuO.sub.3) as an undercoat layer having a
thickness of 2,000 .ANG. at an atmospheric temperature of
550.degree. C. similarly to the above, it is possible to form a
piezoelectric body in the tetragonal perovskite crystal phase and
there is no cracking or exfoliation of the layer. In addition, it
is found that ruthenium oxide used as the underlayer has high
chemical stability, superior handling property, and high electric
conductivity of several m.OMEGA.cm to several 10 m.OMEGA.cm, and
thus, has optimum properties as the electrode for driving the
piezoelectric body.
[0125] As is apparent from the findings above, it is possible to
produce a piezoelectric element at low temperature without
deteriorating the crystallinity and orientation of the
piezoelectric body and without cracking and exfoliation, by forming
a piezoelectric body on a crystalline layer by deposition.
[0126] In the first embodiment, the common electrode, the
piezoelectric body, and the signal electrode are formed
successively by deposition, but of course, they may be formed by
laminating the constituent layers.
Second Embodiment
[0127] FIG. 9 is a partial magnified top view illustrating the area
around the piezoelectric body in the inkjet-recording head
according to the second embodiment. FIG. 10 is a cross-sectional
view along the line A-A in FIG. 9. FIG. 11 is a cross-sectional
view along the line B-B in FIG. 9.
[0128] As shown in FIGS. 9 to 11, the inkjet-recording apparatus
according to this embodiment has a configuration wherein, in the
piezoelectric element 34 according to the first embodiment, no
opening in the first interlayer dielectric layer 54 is formed in
the electrical connection area, where the signal electrode 50 and
signal wiring 62 are connected, in the non-active area of the
piezoelectric body, i.e., the piezoelectric body 48 and the signal
electrode 50 are not electrically connected to each other and have
the first interlayer dielectric layer therebetween in the
electrical connection area.
[0129] The other components are the same as those in the first
embodiment, and description thereof is omitted.
[0130] Hereinafter, an example of the method of producing the
piezoelectric element according to this embodiment will be
described. FIGS. 12A to 12G are process diagrams showing the
production process for the piezoelectric element shown in FIG. 10.
FIGS. 13A to 13G are process diagrams showing the production
process for the piezoelectric element shown in FIG. 11.
[0131] As shown in FIGS. 12 and 13, in the method of producing the
piezoelectric element according to this embodiment, in FIGS. 12B
and 13B, no opening in the first interlayer dielectric layer 54 is
formed in the electrical connection area, where the signal
electrode 50 and signal wiring 62 are connected, in the non-active
area of the piezoelectric body, i.e., the method is the same as
that in the first embodiment except that no opening is formed in
the electrical connection area, where the signal electrode 50 and
signal wiring 62 are connected, in the first embodiment (FIGS. 7B
and 8B).
[0132] In this embodiment, the piezoelectric body 48 and the signal
electrode 50 are not electrically connected to each other in the
electrical connection area, where the signal electrode 50 and
signal wiring 62 are connected, in the non-active area of the
piezoelectric body 48, and a first interlayer dielectric layer is
interposed, and thus, the capacitance is decreased due to the
increase in the interposition area of the first interlayer
dielectric layer 54 compared with the first embodiment, whereby
wasteful energy consumption is reduced.
[0133] Although a common electrode 46 (bottom electrode) having a
single-layered structure of crystalline layer is described in the
embodiments, the common electrode 46 (bottom electrode) may have a
multi-layered structure including an amorphous layer and a
crystalline layer (in this case, the piezoelectric body is
deposited on the crystalline layer).
[0134] In the embodiments, an example of FWA for medium (paper)
width is described, but the inkjet-recording head according to the
invention is not limited thereto, and may be applied to apparatuses
for the partial width array (PWA) using main- and sub-scanning
mechanisms.
[0135] Also in the embodiments, an image (including character) is
formed on a recording medium P, but the droplet-ejecting head and
the droplet-ejecting apparatus according to the invention are not
limited thereto. Thus, the recording medium is not limited to
paper. The liquid to be ejected is also not limited to ink. For
example, the droplet-ejecting head and the droplet-ejecting
apparatus according to the invention may be used as a
droplet-ejecting head and a droplet-ejecting apparatus for various
industries and, for example, may be used for producing color
filters for display by ejecting ink onto a polymer film or glass
and for producing bumps for mounting by ejecting solder in the
welding state onto a substrate.
[0136] As described above, the piezoelectric element according to
the invention is a piezoelectric element including a piezoelectric
body and top and bottom electrodes holding the piezoelectric body
therebetween, wherein an interlayer dielectric is interposed
between the piezoelectric body and the top electrode in an area
other than the active area of the piezoelectric body, and the top
electrode is layered directly on the piezoelectric body in the
active area of the piezoelectric body.
[0137] In the piezoelectric element according to the invention, an
interlayer dielectric is interposed between the piezoelectric body
and the top electrode in an area other than the active area of the
piezoelectric body, and the top electrode is connected directly to
the piezoelectric body 48 only in the active area of the
piezoelectric body. Thus, the active area of the piezoelectric body
is defined accurately by the interlayer dielectric layer to thereby
prevent operation of the piezoelectric body in the area other than
the active area of the piezoelectric body. The capacitance in the
area around the active area of the piezoelectric body, where an
interlayer dielectric layer is interposed, is smaller than the
capacitance in the active area where only the piezoelectric body
are held between the top and bottom electrodes, whereby wasteful
energy consumption can be reduced.
[0138] The piezoelectric element according to the invention can
further include an upper wiring electrically connected to the top
electrode, wherein an opening is provided in the interlayer
dielectric at a position in the electrical connection area, where
the top electrode and the upper wiring are connected, and the
piezoelectric body and the top electrode are electrically connected
to each other at the opening as well as in the active area of the
piezoelectric body.
[0139] Alternatively, the piezoelectric element according to the
invention can further include an upper wiring electrically
connected to the top electrode, wherein the interlayer dielectric
is interposed between the top electrode and the piezoelectric body
at a position in the electrical connection area, where the top
electrode and the upper wiring are connected.
[0140] In the piezoelectric element according to the invention, the
interlayer dielectric is preferably formed so as to cover the side
face of the piezoelectric body.
[0141] In the piezoelectric element according to the invention, the
dielectric constant of the interlayer dielectric is preferably 1/10
or less of that of the piezoelectric body. With such a dielectric
constant, it is possible to reduce the increase in capacitance.
[0142] The piezoelectric element according to the invention
preferably further includes upper and lower wirings separately
which are electrically connected respectively to the top and bottom
electrodes in an area other than the active area of the
piezoelectric body. In this case, the upper and lower wirings are
preferably provided at layer positions that are different from each
other.
[0143] In the piezoelectric element according to the invention, the
bottom electrode preferably includes a crystalline layer. In
addition, the crystalline layer is preferably made of a ruthenium
oxide. Further, the piezoelectric body is preferably formed by a
vapor- or liquid-phase growth method.
[0144] The droplet-ejecting head according to the invention
includes the piezoelectric element according to the invention. In
the droplet-ejecting head according to the invention, a plurality
of the piezoelectric elements may be arranged in a grid
pattern.
[0145] The droplet-ejecting apparatus according to the invention
includes the droplet-ejecting head according to the invention.
[0146] The first method of producing a piezoelectric element
according to the invention includes: forming an electro-conductive
crystalline layer, forming a deposition layer on the crystalline
layer by a vapor- or liquid-phase growth method, and patterning the
crystalline layer and the deposition layer, to thereby sequentially
form a bottom electrode made of the crystalline layer and a
piezoelectric body made of the deposition layer; forming an
interlayer dielectric layer on the bottom electrode and the
piezoelectric body followed by patterning an opening in the
interlayer dielectric layer at a position in the active area of the
piezoelectric body; and forming an electro-conductive layer on the
interlayer dielectric layer as well as on the piezoelectric body
exposed at the opening of the interlayer dielectric layer followed
by patterning the electro-conductive layer to form an top electrode
made of the electro-conductive layer.
[0147] Alternatively, the second method of producing a
piezoelectric element according to the invention includes: forming
an electro-conductive crystalline layer, forming a deposition layer
on the crystalline layer by a vapor- or liquid-phase growth method,
and patterning the crystalline layer and the deposition layer, to
thereby sequentially form a bottom electrode made of the
crystalline layer and a piezoelectric body made of the deposition
layer; forming an interlayer dielectric layer on the bottom
electrode and the piezoelectric body followed by patterning an
opening in the interlayer dielectric layer at a position in the
active area of the piezoelectric body as well as an opening in the
interlayer dielectric layer at a position in an electrical
connection area where an top electrode is to be connected to a
wiring; and forming an electro-conductive layer on the interlayer
dielectric layer as well as on the piezoelectric body exposed at
the openings of the interlayer dielectric layer followed by
patterning the electro-conductive layer to form the top electrode
made of the electro-conductive layer.
[0148] In the first and second methods of producing a piezoelectric
element, a deposition layer is formed on a crystalline layer by a
vapor- or liquid-phase growth method, and a piezoelectric body is
formed by pattering the deposition layer. Therefore, the
perovskite-phase crystallization temperature needed for
piezoelectric property, i.e., the temperature needed to form the
perovskite crystal phase is not raised, and also a mixed crystal of
perovskite and pyrochlore phases is not generated. Further,
exfoliation and cracking of the piezoelectric body do not take
place.
[0149] Therefore, the invention can provide a piezoelectric element
which reduces wasteful energy consumption. Also, the invention can
provide a method of producing a piezoelectric element, which allows
formation of a uniform piezoelectric body by deposition at low
temperature without exfoliation or cracking.
* * * * *