Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-09-06
2002-12-17
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000, C310S358000
Reexamination Certificate
active
06495945
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to piezoelectric/electrostrictive elements, and in particular to piezoelectric/electrostrictive elements employed as actuators utilizing flexural displacement and sensors for detecting fluid properties, sound pressure, minute weights and accelerations, etc., as for example, in microphones or viscosity sensors.
BACKGROUND OF THE INVENTION
Piezoelectric/electrostrictive film elements are utilized in various types of actuators and sensor devices. The various applications of piezoelectric/electrostrictive film elements include the measuring of various properties of fluids, such as the measuring of the properties of density, concentration and viscosity, etc., as disclosed, for example, in Japanese Patent publication No. 8-201265A. Such elements are conveniently employed as sensors because there is a correlation between the amplification of a piezoelectric/electrostrictive oscillator and the viscosity resistance of a fluid in contact with the oscillator. To quantify this correlation, piezoelectric/electrostrictive elements exploit the principal that the form of oscillation in a mechanical system like the oscillation of an oscillator can be converted to an equivalent circuit in an electrical system. For example, a piezoelectric/electrostrictive film oscillates in a fluid and receives a mechanical resistance based on the viscosity resistance of the fluid. Based on the above-mentioned principle, the oscillator thereby senses the variation of an electrical constant of an equivalent electrical circuit of the piezoelectric/electrostrictive element configuring the oscillator. As a result, it becomes possible to measure various parameters, which include the viscosity, density and concentration of the fluid.
A piezoelectric/electrostrictive film oscillator has the capability to measure fluids in both the liquid and gas phases. Moreover, the above oscillator is capable of not only measuring liquids consisting of a single constituent element (i.e., water, alcohol, or oils, etc.) but may also measure fluids composed of slurries and pastes into which a soluble or insoluble medium is dissolved, mixed or suspended.
Examples of the electrical constants that a piezoelectric/electrostrictive oscillator is capable of detecting include loss factor, phase, resistance, reactance, conductance, susceptance, inductance and capacitance. Particularly preferred electrical constants are phase and loss factors because they have a single maximum or minimum point of variation near the resonance frequency of an equivalent circuit. Consequently, not only can the viscosity of a fluid be measured, but its density and concentration are capable of being quantified as well. For example, the concentration of sulfuric acid in an aqueous solution of sulfuric acid can be measured through the use of the above electrical constants. Furthermore, in addition to the use of electrical constants, the variation in resonance frequency may also be utilized as an index for sensing variations in the form of oscillation insofar as there are no specific problems from the standpoint of precision of measurement and durability.
FIG. 2
illustrates a conventional piezoelectric/electrostrictive film element as disclosed in Japanese Patent publication No. 5-267742A. An auxiliary electrode
8
is formed at a position independent of a lower electrode
4
, which is laminated on a ceramic substrate
1
having a thin diaphragm
3
and a thicker portion
2
. The fluid to be analyzed is introduced into a hollow portion
10
via through-hole
9
. A portion of the auxiliary electrode is positioned beneath a piezoelectric/electrostrictive film
5
. As a result of this configuration, it is possible to improve the reliability of the connection of an upper electrode
6
through the continuous formation (i.e., without a break in the connection) of the upper electrode on the face of the auxiliary electrode
8
and the piezoelectric/electrostrictive film
5
.
A piezoelectric/electrostrictive film element is also disclosed in Japanese Patent publication No. 6-260694A. As shown in
FIG. 2
, a piezoelectric/electrostrictive film
5
is positioned on a lower electrode
4
and is of a size that the surrounding portion of the piezoelectric/electrostrictive film
5
extends beyond the electrode
4
. As a consequence, it is not necessary to precisely position the lower electrode
4
and the piezoelectric/electrostrictive film
5
, and thus short circuits between the upper and the lower electrodes are easily prevented. Additionally, an extending portion
11
of the piezoelectric/electrostrictive film can manifest more than sufficient flexural displacement, generation and oscillation because it is in an incompletely bonded state with the substrate
1
(i.e., the extended portion
11
is not bonded with the substrate due to the purpose of incompletely bonded portions
7
A). An “incompletely bonded state” means that a portion of the extending portion
11
is either partially bonded to the ceramic substrate or that an unbonded region without any bonded portion is in existance. More specifically, “incompletely bonded state” is defined to mean that the peeling (tear-off) strength of the film
5
to the substrate
1
is 0.5 kg/mm
2
or less.
With respective to the formation of an unbonded state as described above, there are instances when it is necessary to have a low reactivity between the materials selected for the substrate and the piezoelectric/electrostrictive film. In this regard, it is also possible to form a dummy layer between the piezoelectric/electrostrictive film and the substrate so as to prevent their direct contact. Ideally, the dummy layer is formed by a stamping method, a screen printing method or an ink jet method. The incompletely bonded portion
7
A is formed when the dummy layer is subsequently dissolved. For example, the dummy layer is fabricated with combustible/removable materials (i.e., resin materials, etc.,) that are dissolved away to form the incompletely bonded portions
7
A when the piezoelectric/electrostrictive film
5
is heat treated. Alternatively, in the case where the piezoelectric/electrostrictive film and the upper electrode are not heat treated, the dummy layer is formed with a resin material to be dissolved in a composition such as water or organic solvents, etc. Accordingly, after the formation of either the piezoelectric/electrostrictive film
5
alone or in conjunction with the upper electrode
6
, the incompletely bonded portion
7
A is formed by dissolving or removing the dummy layer (i.e., water or organic solvents, etc.).
In the above-described prior art piezoelectric/electrostrictive oscillators, the electrical constants between the individual sensor elements tend to vary in both the initial phase with the subsequent passage of time. In such cases, a bothersome fine-tuning process is required to insure the proper performance of the oscillator. In such prior art piezoelectric/electrostrictive oscillators employed as sensor elements utilizing electrical constants, an incompletely bonded portion
7
B, which is in the same incompletely bonded state as the incompletely bonded state
7
A of the extending portion
11
, is formed between the lower electrode
4
and auxiliary electrode
8
. Variations and alterations in the incompletely bonded state of this incompletely bonded portion
7
B are the principal cause of changes in the oscillation of the sensor elements, which, in turn, yields alterations in the electrical constants of prior art piezoelectric/electrostrictive oscillators. That is to say that the incompletely bonded state of prior art devices is a drawback because the incompletely bonded state
7
B is not reliably replicated. For example, since the thin diaphragm oscillates or is displaced, partial destruction of the bond or microscopic cracking at the portion of
7
B is likely to occur when the oscillator is in operation.
SUMMARY OF THE INVENTION
The present invention relates a piezoelectric/electrostrictive element comprising successively laminated layers. A lower electr
Takahashi Nobuo
Yamaguchi Hirofumi
Burr & Brown
Dougherty Thomas M.
NGK Insulators Ltd.
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