Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-10
2001-07-24
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000, C310S331000
Reexamination Certificate
active
06265811
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an element for converting electric energy into mechanical energy to be used, for example, for actuators, various vibrators, displays, and relays, or a capacitor element to be used, for example, for filters and resonance circuits. In particular, the present invention relates to a ceramic element based on the use of the phase transition between the anti-ferroelectric phase and the ferroelectric phase, a display device based on the ceramic element to be used for driving a picture element (image pixel) to perform display, a relay device based on the ceramic element to be used for driving a relay to perform switching, and a capacitor based on the ceramic element to be used for varying the capacitance.
Recently, it has been demanded, for example, in the fields of optics and precision manufacturing, to use a displacement element for adjusting the optical path length or the position on the order of submicron.
In order to respond to such a demand, development is being advanced for actuators which utilize occurrence of displacement based on the inverse piezoelectric effect caused when an electric field is applied to a piezoelectric material such as a ferroelectric substance.
In such a trend, the present applicant has also previously proposed piezoelectric/electrostrictive film-type elements made of ceramics, which can be preferably used for various applications, as described, for example, in Japanese Laid-Open Patent Publication Nos. 3-128681 and 5-49270.
The previously proposed piezoelectric/electrostrictive film-type element has such excellent features that it serves as a compact and inexpensive electromechanical conversion element with high reliability to provide a large displacement at a low driving voltage, in which the response speed is quick, and the generated force is large. The piezoelectric/electrostrictive film-type element is useful to be used, for example, as a constituting component of actuators, displays, and relays.
The piezoelectric/electrostrictive film-type element described above is operated such that the mechanical displacement is obtained in accordance with the inverse piezoelectric effect or the electrostrictive effect by applying a voltage to the piezoelectric/electrostrictive operating section (actuator element). Therefore, the piezoelectric/electrostrictive film-type element is advantageous in that the magnitude of the displacement amount can be precisely controlled with respect to the applied voltage, while it is disadvantageous in that it is difficult to obtain a large displacement-generating force when a minute element is used.
In the case of the piezoelectric/electrostrictive film-type element, when it is required to maintain a state of displacement in one direction for a certain period of time, it is necessary to continuously apply the voltage to the piezoelectric/electrostrictive film operating section.
For this reason, for example, when the piezoelectric/electrostrictive film-type element is applied to a display device as disclosed by the present inventors in Japanese Laid-Open Patent Publication No. 7-287176, it is necessary to continuously apply the voltage to the piezoelectric/electrostrictive film operating section throughout the period in which the light emission state should be maintained.
In this case, for example, when a display device, which comprises a large number of light-emitting elements disposed two-dimensionally, is produced, it is necessary to arrange electric wiring for driving each of the elements one by one. Such an arrangement involves large restriction in view of design and production.
SUMMARY OF THE INVENTION
The present invention has been made considering the problems as described above, an object of which is to provide a ceramic element which makes it possible to precisely control the magnitude of displacement amount with respect to an applied voltage, and obtain a large displacement-generating force exceeding those obtained by the piezoelectric/electrostrictive film-type element even when a minute element is used.
Another object of the present invention is to provide a ceramic element which makes it possible to maintain a displacement amount approximately equivalent to that obtained when a driving voltage is applied, in the no voltage-loaded state or in a low voltage-loaded state after completion of application of the driving voltage, in addition to the condition described above.
Still another object of the present invention is to provide a ceramic element which makes it possible to simplify electric wiring for driving the element and effectively reduce the production cost when a variety of applications (for example, display devices and filters) are constructed, in addition to the condition described above.
Still another object of the present invention is to provide a display device which consumes less electric power and which makes it possible to simplify electric wiring for driving the display device and effectively reduce the production cost and the running cost.
Still another object of the present invention is to provide a relay device which consumes less electric power and which makes it possible to simplify electric wiring for driving the relay device, effectively reduce the production cost and the running cost, and realize various types of switching operations.
Still another object of the present invention is to provide a capacitor which makes it possible to easily construct a thin-type capacitance-variable capacitor with its capacitance changeable in an analog manner, and facilitate miniaturization of, for example, parametric amplifiers incorporated with the variable capacitor, automatic frequency control circuits (AFC), and various types of communication instruments.
According to the present invention, there is provided a ceramic element comprising an operating section having an anti-ferroelectric film and at least a pair of electrodes formed on the anti-ferroelectric film, a vibrating section for supporting the operating section, and a fixed section for supporting the vibrating section in a vibrating manner.
The principle of operation of the anti-ferroelectric film will now be explained. When the ferroelectric phase is induced in the anti-ferroelectric film in accordance with the change in, for example, the temperature, the stress, and the electric field, then the strain x
F
is given by the following expression:
X
F
=Q
(1+&OHgr;)
P
F
2
wherein P
F
represents the ferroelectric polarization, and it satisfies P
F
=(Pa+Pb)/2, and wherein Pa and Pb represent the sub-lattice polarization.
In the case of the perovskite type crystal, the electrostrictive constant Qh (=Q
11
+2Q
12
) has a positive value. Therefore, the spontaneous volume strain of an ordinary ferroelectric is always positive, while in the case of the anti-ferroelectric, its spontaneous strain x
A
may be positive or negative depending on the value of &OHgr;. In the case of lead zirconate (PbZrO
3
), there is given &OHgr;=1.8.
It is assumed that the absolute values |Pa|, |Pb| of the sub-lattice polarization are not changed so much before and after the anti-ferroelectric phase-ferroelectric phase transition. On this assumption, the amount of strain change &Dgr;x involved in the transition is represented as follows:
&Dgr;
x=x
F
−x
A
=2
Q&OHgr;P
F
2
Further, it is known that large displacement is obtained when the anti-ferroelectric phase-ferroelectric phase transition is utilized, rather than when the paraelectric phase-anti-ferroelectric phase transition is used.
It is known, for example, that a ceramic (polycrystal) derived from lead zirconate titanate (PZT) successively causes transition to the pseudo-tetragonal anti-ferroelectric phase and the orthorhombic ferroelectric phase in accordance with the decrease in temperature from the cubic paraelectric phase which is the phase at a high temperature. Therefore, when a composition, in which the anti-ferroelectric phase is stable at room temperature, is selected,
Kashiwaya Toshikatsu
Takahashi Nobuo
Takeuchi Yukihisa
Budd Mark O.
Burr & Brown
NGK Insulators Ltd.
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