Ferroelectric element and process for producing the same

Details Ferroelectric element and process for producing the same Ferroelectric element and process for producing the same

1998-07-29

2001-07-03

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C029S253000

Reexamination Certificate

active

06255762

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a ferroelectric element and more particularly to a ferroelectric element particularly in the form of a thin layer, which is advantageously usable as a piezoelectric element in ink jet printers and other devices. The present invention also relates to a process for producing the ferroelectric element and a ferroelectric precursor which can be advantageously used in the production of the ferroelectric element. Further, the present invention relates to a piezoelectric ink jet head using the above ferroelectric element as a piezoelectric element. The term “piezoelectric” and the term “ferroelectric” used herein are defined as follows. Materials, which, when an external force (a stress from the outside) is applied to a crystal thereof, develop polarization, are called piezoelectrics, and, among the piezoelectrics, those wherein the polarization can be reversed by an external electric field are expressly called ferroelectrics.
BACKGROUND ART
In recent years, in office automation equipment, such as word processors, personal computers, facsimile machines, various measuring instruments, such as medical measuring instruments, and other devices, ink jet printers have been extensively used for printing information from these devices at high density. As is well known in the art, in the ink jet printer, an ink droplet is ejected from a head section of the printer and deposited directly onto a recording medium, such as recording paper, to perform monochrome or color printing. The ink jet printer has many advantages including that printing can be performed on even a three-dimensional recording medium, running cost is low since plain paper can be used as the recording medium, the head can be easily mounted in the printer, the need to provide the step of transfer, fixation and the like can be eliminated, color printing is easily performed, and a sharp color printed image can be provided. The head section of the ink jet printer can be classified into several types according to the drive system for ejecting ink droplets from the head section. Among them, a typically and advantageously used one is a piezoelectric ink jet head.
The piezoelectric ink jet head generally comprises: a plurality of ink chambers which are disposed at equidistant spaces and function as an ink flow passage and a pressurizing chamber for ejecting an ink; and a nozzle plate mounted on the front end of the ink chambers and equipped with nozzles, for ejecting an ink, corresponding respectively to the ink chambers; and pressing means for pressurizing an ink within the ink chamber in response to the demand for printing. The pressing means comprises a piezoelectric element (known also as “piezo element”), and electrostrictive effect attained by this piezoelectric element is utilized to create a pressure wave within an ink chamber, filled with ink, in the head section, permitting the ink to be ejected through the nozzle in the head section.
The structure of the piezoelectric ink jet head will be described in more detail with reference to FIG.
1
. An ink jet head
10
, a part of which is shown in the drawing, has an ink chamber member
11
comprising a plurality of ink chambers
12
serving as an ink flow passage and a pressurizing chamber for ejecting ink. A nozzle plate (not shown) equipped with nozzles disposed so as to correspond respectively to the ink chambers
12
is mounted on the front end of the ink chamber
11
. The ink pressurized within the ink chamber
12
can be ejected as a droplet through the bore of the nozzle. In the ink chamber member
11
shown in the drawing, pressing means is mounted on the open face of the ink chamber
12
. In the example shown in the drawing, the pressing means comprises: a diaphragm
15
for creating a change in volume of the ink chamber
12
; a piezoelectric element
17
as a driving element for distorting the diaphragm
15
; and an upper electrode
16
and a lower electrode
18
which can apply voltage according to need, the piezoelectric element
17
being sandwiched between the upper electrode
16
and the lower electrode
18
.
Ferroelectric elements have been extensively used as the piezoelectric element for the ink jet head or as an element, for example, for capacitors, actuators, memories and other elements. The ferroelectric element consists essentially of a ferroelectric or a ferroelectric material. Typical ferroelectric materials include an oxide ceramic represented by the general formula ABO
3
and having a simple perovskite structure as shown in FIG.
2
and an oxide ceramic having a composite perovskite structure represented by the general formula (A
1
, A
2
, . . . ) (B
1
, B
2
, . . . ) O
3
. The term “perovskite structure” used herein refers to both a simple perovskite structure and a composite perovskite structure unless otherwise specified. As shown in the drawing, a ceramic having the above perovskite structure contains metallic ions A and B in the structure. Examples of more specific ferroelectric materials having the above structure include lead zirconate titanate (PZT) represented by the general formula Pb(Zr, Ti)O
3
. In particular, ferroelectrics, containing lead (Pb) as one metal component, including PZT are generally known to have large remanence, specific permittivity, and piezoelectric constant and possesses excellent piezoelectricity and ferroelectricity. In the present specification, the ferroelectric material will be described particularly with reference to PZT.
A sol-gel process has hitherto been well known as a technique for the production of PZT, particularly PZT in a thin layer form. Use of the sol-gel process in the production of PZT is advantageous in that a high-purity thin layer of PZT can be formed, the composition of the formed thin layer of PZT can reflect the composition of the starting material used, which facilitates the control of the composition and can provide a thin layer of PZT having high surface smoothness by repetition of spin coating and firing.
The production of a thin layer of PZT by the sol-gel process and use of the thin layer of PZT as a piezoelectric element will be described in more detail. For example, as described in Japanese Unexamined Patent Publication (Kokai) No. 6-112550, lead acetate is dissolved in acetic acid, and the solution is heated under reflux for 30 min. Zirconium tetrabutoxide and titanium tetraisopropoxide are then dissolved in the solution, water and diethylene glycol are added dropwise thereto, and the mixture is satisfactorily stirred to conduct hydrolysis. To the resultant alcohol solution of a PZT precursor is added polyethylene glycol monomethyl ether in an amount of 10% by weight based on the PZT precursor, followed by satisfactory stirring. Thus, a homogeneous sol is prepared. A platinum electrode is formed on a silicon substrate, the sol is then spin-coated onto the electrode, and the coating is heated at about 350° C. Thus, a 2.5 &mgr;m-thick, thin, crack-free porous gel layer can be formed.
Subsequently, the same starting material as the above PZT material is hydrolyzed to form a sol. In this case, however, no polyethylene glycol monomethyl ether is added. The sol is spin-coated onto the above thin, porous gel layer to form a coating which is then dried by heating at 400° C. The thin layer thus formed is fired in an oxygen atmosphere for 15 hr. The firing temperature is generally 600 to 700° C. Thus, a thin layer of PZT having a perovskite structure can be formed through the above series of steps. The above sol-gel reaction may be represented by a general formula as shown in
FIG. 3
wherein R represents an alkyl group.
Further, hydrothermal synthesis has hitherto been well known as a method for the formation of a thin layer of PZT from an aqueous solution of a main starting compound. The formation of the thin layer of PZT by hydrothermal synthesis will be described. For example, as described in Japanese Unexamined Patent Publication (Kokai) No. 6-112543, 0.2 mol of lead nitrate, 0.104 mol of zirconium oxychloride, and 0.096 mol of titanium tetrachlor

Affiliated with

Also associated with

Rating

Ferroelectric element and process for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ferroelectric element and process for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ferroelectric element and process for producing the same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2533658