U.S. patent application number 12/781218 was filed with the patent office on 2010-09-09 for inkjet head and method for manufacturing the same.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Toshihiro Ifuku, Makoto Kurotobi, Takehito Okabe, Nobuhiko Sato, Kenichi Takeda.
Application Number | 20100225712 12/781218 |
Document ID | / |
Family ID | 35995153 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100225712 |
Kind Code |
A1 |
Okabe; Takehito ; et
al. |
September 9, 2010 |
INKJET HEAD AND METHOD FOR MANUFACTURING THE SAME
Abstract
A method for manufacturing an inkjet head includes providing a
piezoelectric substrate having a porous structure, a diaphragm on
the porous structure, and a piezoelectric substance layer on the
diaphragm, and forming a cavity by etching out the porous structure
from the piezoelectric substrate.
Inventors: |
Okabe; Takehito;
(Atsugi-shi, JP) ; Sato; Nobuhiko;
(Sagamihara-shi, JP) ; Kurotobi; Makoto;
(Yokohama-shi, JP) ; Takeda; Kenichi;
(Yokohama-shi, JP) ; Ifuku; Toshihiro;
(Yokohama-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
1290 Avenue of the Americas
NEW YORK
NY
10104-3800
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
35995153 |
Appl. No.: |
12/781218 |
Filed: |
May 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11215974 |
Sep 1, 2005 |
7743503 |
|
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12781218 |
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Current U.S.
Class: |
347/71 |
Current CPC
Class: |
Y10T 29/4913 20150115;
Y10T 29/42 20150115; B41J 2/1626 20130101; Y10T 29/49401 20150115;
B41J 2/1623 20130101; Y10T 29/49126 20150115; Y10T 29/49128
20150115; B41J 2/161 20130101 |
Class at
Publication: |
347/71 |
International
Class: |
B41J 2/045 20060101
B41J002/045 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2004 |
JP |
2004-258367 |
Claims
1.-7. (canceled)
8. An inkjet head comprising: a piezoelectric substance layer; a
diaphragm provided with the piezoelectric substance layer; and a
cavity, wherein the diaphragm is made of silicon containing
5.times.10.sup.17/cm.sup.3 or less of oxygen.
9. The inkjet head according to claim 8, wherein a sidewall of the
cavity is made of silicon containing 5.times.10.sup.17/cm.sup.3 or
more of oxygen.
10. The inkjet head according to claim 8, wherein the cavity is
connected to a nozzle plate having a nozzle.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an inkjet head that sprays
drops of ink on a recording medium, such as paper, to form an ink
image, and also relates to a method for manufacturing the inkjet
head.
[0003] 2. Description of the Related Art
[0004] The following are examples of conventional technologies of
the inkjet head. [0005] (1) Japanese Patent Publication No.
2976479
[0006] Conventionally, a pressure-generating means that sprays
drops of ink from a cavity in the inkjet head has been provided to
each cavity, for example, by an adhesion process. However,
according to Japanese Patent Publication No. 2976479, the
pressure-generating means is provided on a silicon substrate by a
process other than an adhesion process. [0007] (2) Japanese Patent
Laid-Open No. 07-276636
[0008] Japanese Patent Laid-Open No. 07-276636 defines the
orientation of a crystal plane on a cavity wall in a method for
forming the cavity by etching a silicon substrate.
[0009] Problem 1: In such conventional technologies, the shape of
the cavity depends on the anisotropic etching of the single-crystal
silicon. Since the etching, in turn, depends on the crystal
structure of the single-crystal silicon, the shape of the cavity is
limited by the crystal structure of the single-crystal silicon. In
general, the cavity has a (111) face of the single-crystal silicon.
The etching rate is low on the (111) face. Thus, the etching based
on the orientation of the crystal plane produces a cavity wall that
is not perpendicular to the silicon substrate, resulting in a lower
cavity density.
[0010] The cavity wall is required to have an affinity for ink to
prevent the deposition of air bubbles.
[0011] Problem 2: Conventionally, the etching of the silicon
substrate has been performed by selective etching based on the
difference in the concentration of doped p-type impurities.
However, the selection ratio of the selective etching is several
tens at the highest. Thus, when both a thin film portion of the
substrate and the cavity portion are made of silicon, the thickness
of the thin film portion may be poorly controlled and may vary.
Japanese Patent Laid-Open No. 2002-234156 discloses a method using
a silicon-on-insulator (SOI) substrate, in which a buried silicon
oxide layer serves as an etch stop material. In alkaline etching,
the etching rate of silicon oxide is less than one-thousandth of
that of silicon and accordingly the selectivity is excellent.
[0012] However, in alkaline etching, heat treatment during the
formation of a diaphragm or the subsequent formation of
pressure-generating means or peripheral circuitry may cause
precipitation of oxygen in the substrate. The precipitated oxide
acts as a mask during the etching because of its low etching rate
for an alkaline solution, and thus may cause nonuniform etching.
Furthermore, such an oxide deposited on the diaphragm may cause
nonuniform mechanical properties in the diaphragm, leading to
fracture or crack of the diaphragm.
[0013] Problem 3: An SOI wafer is about 4 to 10 times as expensive
as a single-crystal silicon wafer. In addition, when an SOI wafer
having a thick thin-film layer is manufactured by lamination and
polishing, variations in the thickness of the SOI layer, which are
about .+-.0.5 .mu.m, cause variations in the thickness of the thin
film portion.
SUMMARY OF THE INVENTION
[0014] To solve the problems described above, the present invention
provides a method for manufacturing an inkjet head, comprising
providing a first substrate that includes a piezoelectric substance
layer and a diaphragm formed on a porous structure, and etching out
the porous structure from the first substrate to form a cavity.
[0015] The present invention also provides an inkjet head
comprising a piezoelectric substance layer, a diaphragm provided
with the piezoelectric substance layer, and a cavity, wherein the
diaphragm is made of silicon containing 5.times.10.sup.17/cm.sup.3
or less of oxygen.
[0016] Other features and advantages of the present invention will
be apparent from the following description taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0018] FIG. 1 is a perspective view of an inkjet head according to
an embodiment of the present invention.
[0019] FIG. 2 is a transverse cross-sectional view of a portion of
the inkjet head of FIG. 1 showing piezoelectric film in greater
detail.
[0020] FIGS. 3A to 3F are schematic views illustrating a method for
manufacturing an inkjet head according to an embodiment of the
present invention.
[0021] FIGS. 4A to 4C are schematic views illustrating a process
for manufacturing a nozzle plate according to an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The best mode for carrying out the invention will be
described in detail with reference to the drawings. FIG. 1 shows
the structure of an inkjet head according to an embodiment of the
present invention. The inkjet head includes a discharge opening 1,
a communicating hole (liquid path) 2 that connects the discharge
opening 1 with a cavity 12, a common liquid chamber 4, a diaphragm
5, a lower electrode 6, a piezoelectric film (piezoelectric
substance layer) 7, and an upper electrode 8. The piezoelectric
film 7 is rectangular in FIG. 1 but may be elliptical, circular, or
parallelogrammatic.
[0023] The piezoelectric film 7 will be described in detail with
reference to FIG. 2. FIG. 2 is a transverse cross-sectional view of
a portion of the inkjet head of FIG. 1 showing the piezoelectric
film in greater detail. The piezoelectric film 7 is composed of a
first piezoelectric substance sublayer 9 and a second piezoelectric
substance sublayer 10. The diaphragm 5 and the lower electrode 6
may be separated by a buffer layer that controls crystallinity. The
lower electrode 6 and the upper electrode 8 may have a multilayer
structure. The cross section of the piezoelectric film 7 is
rectangular in FIG. 2 but may be trapezoidal or inverted
trapezoidal. The first piezoelectric substance sublayer 9 and the
second piezoelectric substance sublayer 10 may be exchanged with
each other, depending on the method of fabricating the device. Even
when the first piezoelectric substance sublayer 9 and the second
piezoelectric substance sublayer 10 are exchanged with each other,
the present invention can have the same effect.
[0024] The lower electrode 6 extends longer than the piezoelectric
film 7. The upper electrode 8 extends in the direction opposite to
the lower electrode 6 and is connected to a power supply (not
shown). In FIGS. 1 and 2, the patterned lower electrode 6 may be
formed independently of the piezoelectric film 7.
[0025] The thickness of the diaphragm 5 in the inkjet head
according to the present invention is in the range of 0.1 to 50
.mu.m, and can be in the range of 0.5 to 10 .mu.m, or in the range
of 1.0 to 6.0 .mu.m. When a buffer layer is disposed between the
diaphragm 5 and the lower electrode 6, the total thickness of the
diaphragm 5 and the buffer layer is in the range described above.
The thicknesses of the lower electrode 6 and the upper electrode 8
are in the range of 0.05 to 0.4 .mu.m and can be in the range of
0.08 to 0.2 .mu.m. The width of a cavity 12 in a silicon substrate
11 is in the range of 30 to 180 .mu.m. The length of the cavity 12
depends on the number of drops of ink to be sprayed and is
generally in the range of 0.3 to 6.0 mm. The discharge opening 1
may be circular or star-shaped and can have a diameter of 7 to 30
.mu.m.
[0026] The discharge opening 1 can taper down to a narrow tip. The
length of the communicating hole 2 can be in the range of 0.05 to
0.5 mm. When the communicating hole 2 has a length greater than 0.5
mm, the discharge speed of the drops of ink may be decreased. On
the other hand, when the communicating hole 2 has a length smaller
than 0.05 mm, the discharge speed of the drops of ink from each
discharge opening may vary greatly.
[0027] The lower electrode 6 and the upper electrode 8 may be made
of a metallic material or an oxide material. Examples of the
metallic material include Au, Pt, Ni, Cr, and Ir. The metallic
material may be laminated on Ti or Pb. Examples of the oxide
material include a strontium titanium oxide (STO), a strontium
ruthenium oxide (SRO), IrO.sub.2, RuO.sub.2, and
Pb.sub.2Ir.sub.2O.sub.7, each doped with La or Nb. Desirably, the
lower electrode 6 and/or the upper electrode 8 has a crystal
structure of the metallic material or the oxide material. The lower
electrode 6 and the upper electrode 8 may or may not be made of the
same material and may or may not have the same structure. One of
the lower electrode 6 and the upper electrode 8 acts as a common
electrode and the other acts as a drive electrode.
[0028] A method for manufacturing the inkjet head according to the
present invention will be described below with reference to FIG. 3.
In the method for manufacturing the inkjet head according to the
present invention, the production of a piezoelectric substrate Al
mainly involves a process for producing a nozzle pattern on the
backside of the substrate, an anodization process, a process for
forming a diaphragm, a process for forming a piezoelectric
substance, and an etching process. Then, the piezoelectric
substrate A1 is laminated to a nozzle plate A2 in a lamination
process.
[0029] In FIGS. 3A to 3F, the piezoelectric substrate A1 includes
cavities 30 and a diaphragm 18. The nozzle plate A2 includes a
communicating hole, a discharge opening, and a common liquid
chamber.
1. Formation of Cavity
(1) Patterning of Anodization Area
[0030] As shown in FIG. 3A, a film resistant to anodization 16 is
formed on a principal surface of a single-crystal silicon substrate
15 that has top and bottom polished surfaces and has a thickness of
625 .mu.m, except on surface areas where porous silicon layers 17
are to be formed.
[0031] The anodization-resistant film 16 may be formed by any
method and may be formed by a patterning technique that is widely
used in the semiconductor process. The material and the thickness
of the anodization-resistant film 16 are determined such that the
anodization-resistant film 16 is not detached and does not dissolve
during the formation of the porous silicon layers 17. For example,
the anodization-resistant film 16 is made of silicon nitride,
silicon oxide, a resist, a resin (acryl resin or epoxy resin), or
wax (for example, Apiezon Wax (trade name) or Electron Wax (trade
name)). Alternatively, the areas where the porous silicon layers 17
are to be formed may be of a p-type or a p+-type, and the area
where the porous silicon layers 17 are not to be formed may be of a
p.sup.--type or an n-type.
(2) Formation of Porous Silicon Layer (FIG. 3A)
[0032] The porous silicon layers 17 may be formed by the
anodization of the single-crystal silicon substrate 15. In the
anodization, an electric current is applied to the substrate in an
aqueous solution containing hydrofluoric acid. The principal
surface of the single-crystal silicon substrate 15 serves as a
cathode.
[0033] The anodization proceeds only in the area where the
anodization-resistant film 16 is not formed. The thickness of the
porous silicon layers 17 is controlled, for example, by the
duration of the anodization. The thickness of the porous silicon
layers 17 is determined in view of the fact that the porous silicon
layers 17 are eventually to be converted into the cavities 30. The
porous silicon layers 17 may be formed from the top surface to the
bottom surface of the single-crystal silicon substrate 15.
(3) Formation of Diaphragm (FIG. 3B)
[0034] The anodization-resistant film 16 is removed. Then, a
non-porous single crystal diaphragm 18 is formed, for example, by
thermal CVD, plasma CVD, molecular beam epitaxy (MBE), or
liquid-phase epitaxy. The non-porous single crystal diaphragm 18
can be made of silicon.
[0035] When the anodization-resistant film 16 is made of
single-crystal silicon, it need not to be removed. The porous
silicon layers 17 may be selectively oxidized before the formation
of the non-porous single crystal diaphragm 18.
(4) Formation of Pressure-Generating Means (FIG. 3C)
[0036] A PZT piezoelectric substance layer 20 and accompanying
electrode layers 21 and 22 may be formed on the non-porous single
crystal diaphragm 18 formed on the porous silicon layer 17 in the
following manner.
[0037] A common electrode layer 21, which is made of Pt, Cr and/or
Ni and has a thickness of 1 .mu.m, the piezoelectric substance
layer 20, which is made of PZT and has a thickness of 10 .mu.m, and
an individual electrode layer 22, which is made of Pt, Cr and/or
Ni, are formed on the non-porous single crystal diaphragm 18 by
sputtering or ion plating. Then, a resist pattern serving as a mask
is formed on the individual electrode layer 22. Then, ion etching
or reactive ion etching of the common electrode layer 21, the
individual electrode layer 22, and the piezoelectric substance
layer 20 produces a common electrode 21', an individual electrode
22', and a piezoelectric substance 20'. At the same time, an
oscillator and a wiring are formed.
(5) Removal of Porous Layer (FIGS. 3D and 3E)
[0038] The porous silicon layers 17 are removed from the backside
of the single-crystal silicon substrate 15. If the porous silicon
layers 17 are exposed at the backside after the formation of the
porous silicon layers 17, an exposure process will not be required.
If the porous silicon layers 17 are not exposed at the backside,
the single-crystal silicon substrate 15 is lapped, ground,
polished, or etched to expose the porous silicon layers 17.
[0039] Then, the porous silicon layers 17 in the single-crystal
silicon substrate 15 are etched, for example, with a solution
containing hydrofluoric acid. A solution containing hydrofluoric
acid is suitable for an etchant, in particular when the porous
silicon layers 17 have previously been oxidized. However, the
etchant is not limited to a solution containing hydrofluoric acid.
If an oxide is not found on the porous wall of the porous silicon
layers 17 or has previously been removed from the porous wall, an
aqueous alkaline solution may also be used as an etchant.
[0040] The etching produces the cavities 30, an ink feed channel,
and a common ink channel. At the same time, a thin film portion 19
made of a silicon single crystal is formed.
[0041] In the process (5), the single-crystal silicon substrate 15
is reduced in thickness and therefore is liable to break. Thus, it
is desirable that, before the process (5), the single-crystal
silicon substrate 15 be fixed on a supporting substrate, for
example, with a resin, such as an adhesive or wax, or a
double-faced adhesive tape.
(6) Formation of Nozzle Plate (FIGS. 4A to 4C)
[0042] A manufacturing process and the structure of the nozzle
plate A2 will be described below with reference to FIGS. 4A to 4C.
The nozzle plate A2 may be made of any material that can form the
nozzle. Examples of such a material include glass, a resin, and a
single-crystal silicon substrate. A stable single-crystal silicon
substrate that has the same coefficient of thermal expansion as
that of the piezoelectric substrate A1 is suitable for the
material. The nozzle may be formed in the following manner.
[0043] In FIGS. 4A to 4C, SiO.sub.2 films 61 having a thickness of
0.1 .mu.m are formed on the top surface and the bottom surface of a
double-sided polished single-crystal silicon substrate 60 having a
thickness of 100 .mu.m by thermal oxidation. Then, a resist layer
63 is formed over the entire surface of the upper SiO.sub.2 film
61. Another resist layer 63 is formed on the lower SiO.sub.2 film
61, except the areas 64 corresponding to the openings of the
cavities 30 in the piezoelectric substrate A1, so as to have a
crystal edge in the [110] direction (FIG. 4A).
[0044] The SiO.sub.2 film 61 at the areas 64 is removed by etching
and then the resist layers 63 are removed. Then, the single-crystal
silicon substrate 60 is anisotropically etched with a mixture of
pyrocatechol, ethylenediamine, and water (FIG. 4B). Then, the
SiO.sub.2 films 61 are removed. In this way, nozzles 70 having an
outlet 71, which is smaller in diameter than the openings of the
cavities 30, are formed (FIG. 4C). The positions of the nozzles 70
coincide with the positions of the cavities 30.
(7) Bonding of Piezoelectric Substrate A1 and Nozzle Plate A2 (FIG.
3F)
[0045] The piezoelectric substrate A1 is bonded to the nozzle plate
A2 with the piezoelectric substance layer 20 and the nozzle outlet
71 facing outward. A voltage of 1000 V is applied between the
negatively charged piezoelectric substrate A1 and the positively
charged nozzle plate A2 at 400.degree. C. to bond them
anodically.
[0046] In the present invention, at least part of the side wall of
the cavity 30 and the non-porous single crystal diaphragm (thin
film portion) 18 are made of a silicon single crystal in one piece.
The sidewall of the cavity 30 is perpendicular to the non-porous
single crystal diaphragm 18 or tapers down to the nozzle outlet 71.
The surface of the thin film portion 18 in the cavity 30 has bumps
and dips having a height of at least 5 nm at intervals less than 50
nm (bumps and dips are also formed on the sidewall of the cavity 30
in FIG. 3E).
[0047] According to the present invention, the shape of the cavity
is principally defined by the anodization from the diaphragm side.
The shape of the anodized portion is uniform along the electric
line of force. Thus, there are no hollows in the corners, unlike in
the method using an SOI substrate. Furthermore, the sidewall of the
cavity and the surface of the thin film portion in the cavity have
bumps and dips, which have been formed by the etching of the porous
silicon layer and have a height of at least 5 nm at intervals less
than 50 nm. This improves the wettability of these surfaces by
ink.
[0048] The thin film portion is made of a single-crystal silicon
containing 5.times.10.sup.17/cm.sup.3 or less of oxygen. According
to the present invention, the cavity is formed by selective etching
of the porous silicon. Thus, for example, a mixture of hydrofluoric
acid and nitric acid or oxygenated water is used instead of an
alkaline solution. When the concentration of oxygen in the thin
film portion is high, an oxygen precipitate is formed in the
single-crystal silicon substrate by heat treatment. Thus, the
oxygen precipitate in the thin film portion may be etched, causing
damage to the thin film portion. When the concentration of oxygen
in the thin film portion is 5.times.10.sup.17/cm.sup.3 or less,
however, oxygen precipitation hardly occurs as compared with a
typical CZ substrate, and therefore the thin film portion is rarely
etched during the removal of the porous silicon layer. Widely
commercialized silicon substrates made by the crystal pulling
method (CZ method) contain over 1.times.10.sup.18/cm.sup.3 of
oxygen, and the heat treatment thereof causes oxygen precipitation.
But oxygen precipitation hardly occurs when the oxygen
concentration is less than 5.times.10.sup.17/cm.sup.3.
[0049] The concentration of oxygen in the single-crystal silicon of
the sidewall of the cavity is 5.times.10.sup.17/cm.sup.3 or more.
The sidewall is often formed by alkaline etching. A higher oxygen
concentration causes oxygen precipitation during the formation of a
thin film, a PZT film, or peripheral circuitry. The oxygen
precipitate is not etched during alkaline etching and acts as a
mask when a cavity or an ink feed channel is formed, causing a
problem that a desired shape cannot be obtained by the etching.
[0050] According to the present invention, the cavity is formed by
selective etching of the porous silicon, for example, using a
mixture of hydrofluoric acid and nitric acid or oxygenated water,
instead of an alkaline solution. Thus, the problem described above
does not occur.
[0051] Furthermore, the single-crystal silicon in the thin film
portion is of a p-type or an n-type, and the single-crystal silicon
constituting the sidewall of the cavity is of a p-type. The
concentration of p-type carriers in the sidewall of the cavity is
higher than that in the thin film portion.
[0052] The single-crystal silicon constituting the sidewall of the
cavity is of a p.sup.+-type. In addition to the selective etching
of the porous silicon layer for the formation of the cavity, when
etching is required to form the ink feed channel or the like, the
p.sup.+-type single-crystal silicon can be predominantly etched
over a p.sup.--type or n-type single crystal epitaxial silicon of
the thin film portion using a mixture of hydrofluoric acid, nitric
acid, and acetic acid (J. Electrochem. Soc. 144 (1997) p. 2242). A
1:3:8 mixture of hydrofluoric acid, nitric acid, and acetic acid is
recommended as an etchant. Such a hydrofluoric acid-based etchant
can etch silicon oxide. Thus, the problem of the oxygen precipitate
does not occur.
[0053] A hydrofluoric acid-based etchant cannot be used in
selective etching of the conventional SOI wafer using silicon oxide
as an etch stop layer. However, when an epitaxial silicon layer
that is not of the p.sup.+-type is used as the etch stop layer, as
in the present invention, a hydrofluoric acid-based etchant can be
suitably used.
[0054] Furthermore, since the thin film portion is made of
epitaxial single-crystal silicon, it is free from
crystal-originated particles (COP), which can form a through-hole
in a thin film having a thickness less than 1 micron.
[0055] The method according to the present invention comprises a
process for removing the porous silicon to form the cavity.
According to the method of the present invention, unlike the
conventional method, the shape of the cavity is principally defined
by the anodization from the diaphragm side. The selection ratio of
the selective etching of the porous silicon is at least 1000. Thus,
the thin film portion maintains a uniform thickness during the
removal of the porous silicon.
[0056] According to the present invention, the thickness of the
single-crystal silicon thin film portion constituting the diaphragm
can be reduced to about 0.1 to 50 .mu.m. In addition, the diaphragm
can be accurately formed in one piece since no adhesion process is
required to be employed. Since the nozzle plate is made of the same
material as the piezoelectric substrate, deformation due to a
difference in the coefficient of thermal expansion between the
nozzle plate and the piezoelectric substrate does not occur during
or after their bonding. This also ensures high dimensional accuracy
of the inkjet head. The reduced thickness of the oscillator allows
a small cavity to generate a sufficient displacement at low
voltage. Thus, a small, highly integrated, reliable inkjet head
operable at low voltage can be provided at low cost. In addition, a
shortened ink feed channel allows the inkjet head to remove air
bubbles consistently.
[0057] As many apparently widely different embodiments of the
present invention can be made without departing from the spirit and
scope thereof, it is to be understood that the invention is not
limited to the specific embodiments thereof except as defined in
the claims.
[0058] This application claims the benefit of Japanese Application
No. 2004-258367 filed Sep. 6, 2004, which is hereby incorporated by
reference herein in its entirety.
* * * * *