Compositions – Piezoelectric
Reexamination Certificate
2000-04-19
2002-03-12
Koslow, C. Melissa (Department: 1755)
Compositions
Piezoelectric
C252S06290R, C501S017000, C501S032000, C501S134000, C427S100000
Reexamination Certificate
active
06355185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric paste, and particularly to a piezoelectric paste advantageously used for forming a piezoelectric film provided as a thick film in a piezoelectric part such as a piezoelectric actuator, a oscillator, a piezoelectric sensor, or the like.
The present invention also relates to a piezoelectric film formed by using the above piezoelectric paste, and a piezoelectric part comprising the piezoelectric film.
2. Description of the Related Art
Typical examples of known perovskite oxides exhibiting ferroelectricity and high piezoelectricity include Pb(Zr, Ti)O
3
system ceramics, i.e., PZT ceramic crystals. PZT ceramic crystals can be obtained by, for example, mixing Pb
3
O
4
, TiO
2
and ZrO
3
raw material powders using a ball mill and then effecting a solid solution reaction by calcination.
In using such PZT crystals for forming the piezoelectric portion of a piezoelectric part such as a piezoelectric actuator, oscillator, piezoelectric sensor, or the like, the piezoelectric film is formed in the shape of a thick film in some cases. In order to form such a piezoelectric film, the PZT crystals are prepared in a powder state, and a glass powder and an organic vehicle are added to the PZT crystal powder to form a piezoelectric paste, which is coated and burned to form a thick film.
Since the sintering temperature of the PZT crystal grains exceeds 1000° C., evaporation of lead is not negligible in the burning step, and thus the sintering temperature is desired to be decreased as much as possible. Therefore, a powder containing as a main component amorphous stable glass having a low softening point and causing viscous flow in the burning step, for example, such as borosilicate glass, alkali-added glass, or the like, is used as the glass powder to be added to the piezoelectric paste, for causing the glass powder to also function as a sintering additive.
However, a piezoelectric film after burning the piezoelectric paste containing the above-described amorphous glass having a low softening point has a state in which the PZT crystal grains are covered with an amorphous glass phase having a low dielectric constant, deteriorating the ferroelectricity of the piezoelectric film. This causes difficulties in rotation of dipoles, and thus causes the problem of deteriorating the performance of a polarization treatment by application of a DC electric field.
In the piezoelectric film formed by the above-mentioned thick film forming technique, a piezoelectric constant d
ij
which is an important piezoelectric property, is decreased due to a decrease in polarizability, decreasing the piezoelectric strain value in application of an external electric field. Therefore, the construction of a piezoelectric actuator using such as piezoelectric film has the problem of decreasing flexure caused by element bending during drive.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide piezoelectric paste maintaining the ferroelectricity of piezoelectric crystals such as PZT ceramic crystals, and thus causing no decrease in polarizability and permitting the achievement of high piezoelectricity and the formation of a piezoelectric film, and to provide a piezoelectric film formed by using the piezoelectric paste and a piezoelectric part comprising the piezoelectric film.
In order to solve the above-described technical problems, the present invention is characterized in brief by using, as the glass powder contained in piezoelectric paste, a powder comprising crystallized glass which precipitates a solid solution phase such as a PZT solid solution phase having ferroelectricity and high piezoelectricity by heat treatment such as burning.
In more detail, the piezoelectric paste of the present invention comprises a piezoelectric crystal powder, a crystallized glass powder precipitating a solid solution phase by heat treatment and an organic vehicle.
In a preferred embodiment, the piezoelectric paste of the present invention comprises a piezoelectric crystal powder containing a Pb(Zr, Ti)O
3
system ceramic, a crystallized glass powder precipitating a Pb(Zr, Ti)O
3
system solid solution phase by heat treatment and an organic vehicle.
The piezoelectric crystal powder preferably has a composition represented by the formula Pb(Z
rx
Ti
1−x
)O
3
wherein x is in the range of about 0.49 to 0.56.
The piezoelectric crystal powder more preferably comprises a compound perovskite oxide containing a first component having a composition represented by the formula Pb(Zr
x
Ti
1−x
)O
3
wherein x is in the range of about 0.49 to 0.56, and a second component having a composition represented by the formula Pb(Zn
⅓
Nb
⅔
)O
3
, Pb(Mg
⅓
Nb
⅔
)O
3
or Pb(Ni
⅓
Nb
⅔
)O
3
, wherein the content of the second component is in the range of about 10% to 40% by weight based on the total of the first and second components.
The compound perovskite oxide is obtained by calcining a mixture of a crystal powder of the first component and a crystal powder of the second component.
The second component preferably further contains BaTiO
3
. The second component containing BaTiO
3
is preferably obtained by adding a BaTiO
3
crystal powder having an average grain diameter of about 0.5 &mgr;m or less to a raw material of Pb(Zn
⅓
Nb
⅔
)O
3
, Pb(Mg
⅓
Nb
⅔
)O
3
or Pb(Ni
⅓
Nb
⅔
)O
3
, followed by heat treatment.
In an embodiment, the crystallized glass powder preferably contains a main component represented by the formula iPbO—jTiO
2
—kZrO
2
—mSiO
2
wherein i is in the range of about 62 to 70 mol %, j is in the range of about 7 to 19 mol %, k is in the range of about 7 to 19 mol %, and m is in the range of about 8 to 9 mol %, and an additive component composed of Bi
2
O
3
or MnO
2
and having a content of about 3 parts by weight based on 100 parts by weight of main component.
The present invention also provides a piezoelectric film obtained by coating the above-described piezoelectric paste on a substrate, and burning it.
In the piezoelectric film of the present invention, the burning temperature is preferably selected in the range of about 800 to 950° C.
The present invention further provides a piezoelectric part comprising an insulating substrate, a lower first layer electrode formed on the insulating substrate, a piezoelectric film formed on the lower layer electrode, and an upper second layer electrode formed on the piezoelectric film. In this piezoelectric part, the piezoelectric film comprises the above-described piezoelectric film.
REFERENCES:
patent: 5403788 (1995-04-01), Nishida et al.
patent: 0376670 (1989-12-01), None
patent: 1466704 (1977-03-01), None
patent: 2161647 (1986-01-01), None
patent: 98/43925 (1998-10-01), None
Koslow C. Melissa
Murata Manufacturing Co. Ltd.
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