Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2002-07-30
2004-01-27
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C252S062200
Reexamination Certificate
active
06683014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition, and more particularly, to a piezoelectric ceramic composition having improved heat resistance and piezoelectric property by replacing conventional piezoelectric ceramic components with other components, and a piezoelectric ceramic device using the same.
2. Description of the Related Art
As a result of recent developments in the information industry, almost all appliances and devices such as Hard Disc Drive (HDD), Hand-Held Phone (HHP), Compact Disc Read Only Memory (CD-ROM), CD-Recordable & Writeable (CD-RW), Digital Versatile Disc (DVD), DVD-Recordable & Writeable (DVD-RW), wireless keyboard, optical mouse or the like are provided with a SMD-type resonator producing a clock frequency, as essential parts in the digital era. Keeping pace with the performance enhancement and miniaturization trends of digital products, the resonator continues to advance toward higher frequencies and a small, light and power-efficiency. In order to manufacture more and more miniaturized resonators using a higher frequency, a piezoelectric ceramic composition having excellent piezoelectric property and thermal stability is required.
A Pb(Zr,Ti)O
3
- and a PbTiO
3
-based piezoelectric ceramic composition have been mainly used in recent years. A thickness vibration mode is a representative vibration mode in these piezoelectric ceramic compositions. The thickness vibration mode uses energy trap vibration and is divided into a fundamental vibration mode and a higher order vibration mode.
As for the Pb(Zr,Ti)O
3
-based composition, contrary to a fundamental vibration mode, piezoelectric property is relatively poor in a higher order vibration mode. For the higher order vibration mode, furthermore, because a resonance frequency constant is relatively small, there is a limitation in that it is difficult to obtain a high frequency. On the other hand, the PbTiO
3
-based composition has such characteristics as a low dielectric constant, a small grain size and a high phase transition temperature. Furthermore, due to large lattice anisotropy in the C-axis direction, it is difficult to trap energy in a fundamental vibration mode, but it is easy to trap energy in a higher order vibration mode capable of producing a high frequency. In light of these facts, the PbTiO
3
-based composition has superior piezoelectric property and thermal stability to the Pb(Zr,Ti)O
3
-based composition. Accordingly, the former has been recognized as a material suitable for a high frequency band oscillator.
Nevertheless, because the PbTiO
3
-based composition has large crystal anisotropy, there is a problem in that spontaneous phase transition stress during cooling readily causes cracks, resulting in a sintering property being poor. Recent studies have been proceeding actively with the aim of minimizing spontaneous phase transition stress during cooling and enhancing a sintering property by the substitution of A-site and/or B-site by other components or the use of other additives.
By way of a representative example, Japanese Patent Laid-Open Publication No. 7-206517 (publication date: Aug. 8, 1995, applicant: MATSUSHITA ELECTRIC IND CO LTD) discloses a piezoelectric ceramic composition comprising a (Pb,La)TiO
3
-based main component and CuO, ZrO
2
and MnO
2
as additives. The piezoelectric ceramic composition presented in the above publication has a high usable frequency and a large D/R (dynamic ratio) during resonating. In spite of these advantages, the piezoelectric ceramic composition must be sintered in an atmosphere having an oxygen partial pressure of above 80%. The composition is used as a material of a piezoelectric ceramic device with a diameter of 15-18 mm; however, the composition cannot be used as a material of a latest piezoelectric ceramic device for driving a hard disc, which has an electrode area of 2.5 mm×2.0 mm and produces a frequency of 40 MHz or more. When the device is miniaturized, there are problems in that a D/R is reduced during resonating and a spurious phenomenon occurs in third harmonic frequency.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a piezoelectric ceramic composition, which is used as a material of a piezoelectric ceramic device with an electrode area as small as 2.5 mm×2.0 mm or less.
It is another object of the present invention to provide a piezoelectric ceramic composition, which can be sintered under normal atmosphere.
It is a further object of the present invention to provide a piezoelectric ceramic composition, which has excellent electric property (D/R=above 60) and thermal property under reflow at about 250° C. or more.
It is another object of the present invention to provide a piezoelectric ceramic composition, which exhibits excellent piezoelectric property at a thickness longitudinal vibration third harmonic frequency.
It is yet another object of the present invention to provide a miniaturized piezoelectric ceramic device, which produces a high frequency and is able to be mounted in a surface mount manner at a high temperature.
In accordance with the present invention, the above and other objects can be accomplished by the provision of a piezoelectric ceramic composition represented by the general formula (1) below, which comprises essentially Pb, La, Ti, Mn and Cu:
{[Pb
(1−1.5x)±(0~0.2)
La
x
][Ti
(1−y−z)
Mn
y
Cu
z
]O
3
} Formula (1)
(wherein, 0.02<x<0.14, 0.01≦y<0.04, and 0.002≦z≦0.008.)
In accordance with another aspect of the present invention, there is provided a miniaturized piezoelectric ceramic device, which produces a high frequency and is able to be mounted in a surface mount manner at a high temperature.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A piezoelectric composition of the present invention is expressed by the general formula, [Pb
(1−1.5x)±(0~0.2)
La
x
][Ti
(1−y−z)
Mn
y
Cu
z
]O
3
. The composition is an ABO
3
composite perovskite composition, the A-site consisting of PbO and La
2
O
3
, and the B-site consisting of TiO
2
, MnO
2
and CuO. Contrary to a conventional composition, manganese (Mn) and copper (Cu) are not additives, but are substituted for titanium (Ti) as a matrix composition. As a result, charge neutrality of grains and grain boundaries, along with crystal structure and chemical stability, may be more stably adjusted.
In the above formula, lanthanum (La), an A-site component, is required to meet 0.02<x<0.14. If the x value is more than 0.014, cavities are formed in some sites occupied by Pb and thus charge neutrality is maintained. As a result, diffusion of atoms occurs to reduce internal stress due to crystal anisotropy during sintering and to prevent the formation of cracks. However, if the x value is below 0.02, such effects are not sufficiently realized, and if it exceeds 0.14, oscillation stability and thermal stability are poor.
In the above formula, Mn and Cu, B-site components, present in a small amount, serve to enhance electrical properties and thermal stability of a piezoelectric ceramic composition. Mn is required to meet 0.01≦y<0.04. If the y value is more than 0.04, because Mn acts as an electron acceptor, there are problems in that the insulation property of a sintered body is low and an amount of leakage current increases rapidly, thereby preventing polarization or lowering piezoelectric property. Cu is required to meet 0.002≦z≦0.008. Within the above range, cavities are provided, so as to lower resonance resistance and thus control an amount of leakage current. If the z value is outside the range, piezoelectric property is low and thermal stability is poor.
The piezoelectric ceramic composition of the present invention is excellent in sintering property and thus is able to be stably sintered even under normal atmosphere. Accordingly, there is
Hong Jong Kuk
Hur Kang Heon
Kwon Sang Koo
Seo Dong Hwan
Koslow C. Melissa
Lowe Hauptman & Gilman & Berner LLP
S-Cera Co., Ltd.
LandOfFree
Piezoelectric ceramic composition and piezoelectric ceramic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Piezoelectric ceramic composition and piezoelectric ceramic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Piezoelectric ceramic composition and piezoelectric ceramic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3257558