Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-04-28
2001-11-27
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S330000, C310S359000, C310S365000, C310S366000, C310S334000
Reexamination Certificate
active
06323580
ABSTRACT:
FIELD OF INVENTION
This invention relates to an improved ferroic transducer, and more particularly to such a transducer with interdigitated electrodes.
BACKGROUND OF INVENTION
Conventional ferroic transducers employ the ferroic material between a pair of electrodes on opposite sides of the transducer which use the electric field across the thickness of the transducer to convert the acoustic signals into electrical signals and vice versa for underwater or medical sonar use. The term ferroic when used herein includes ferroelectric, pyroelectric and electrostrictive materials. Another application is as a bolometer array for IR imaging using the pyroelectric coefficient of the material. Typically these devices at least in thin film form have low sensitivity. In addition they have high capacitance in the neighborhood of 10-100 pf which is not well matched with present CMOS technology that has input capacitances as low as 0. 1 pf or even less. One attempt to increase sensitivity and decrease capacitance partitions the transducer into many small elements and connects them in series. However, this introduces a number of problems including wasted space, complicated fabrication and increased stray capacitance: the individual elements must be spaced from each other, interlayer connections must be provided and the multitude of individual elements increases stray capacitance.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an improved ferroic transducer.
It is a further object of this invention to provide such a ferroic transducer with higher sensitivity and lower capacitance.
It is a further object of this invention to provide such a ferroic transducer which requires only a single metal layer.
It is a further object of this invention to provide such a ferroic transducer which requires no multilayer or through-layer electrical connections.
It is a further object of this invention to provide such a ferroic transducer in which all the electrodes are on the same side.
It is a further object of this invention to provide such a ferroic transducer in which the sensitivity can be varied by varying the electrode spacing independent of the thickness of the transducer film.
The invention results from the realization that a ferroic transducer which is simpler and much more sensitive can be achieved by placing all the electrodes on the same side of the ferroic material such as ferroelectric, pyroelectric or electrostrictive material and utilizing the in-plane electric field instead of the cross-plane electric field thereby doubling the ferroelectric receive coefficient and enabling the sensitivity to be increased by increasing the electrode spacing independent of the thickness of the transducer film.
This invention features an interdigitated electrode ferroic transducer including a film of ferroic material electrically polarized substantially in the plane of the film, and a set of interdigitated electrodes including at least two electrodes spaced from one another on the same side of the film and disposed at the termini of the polarization field.
In a preferred embodiment the ferroic material may be a ferroelectric material, a pyroelectric material or an electrostrictive material. There may be more than two electrodes, each one disposed at a terminus of the polarization field. The electrodes may be connected with a drive circuit for generating an acoustic wave output or with a sensing output for sensing an acoustic wave input, or may be connected to both types of circuits to act as both a transmitter and a receiver. The film may be thin film layer, for example, between 0.1 and 10 microns. The electrodes may be straight and parallel to each other or circular and concentric. The transducer may include an insulating layer on the side of the film opposite the electrodes. The insulating layer may be Al
2
O
3
The transducer may include a structural layer on the side of the insulating layer opposite the film. The structural layer may be made of a material from the group including silicon and polysilicon. There may be a substrate on the side of the structural layer opposite the electrodes. The substrate may be made of silicon. The substrate may include a well on the side opposite the electrode for receiving and/or transmitting acoustic energy to and/or from the film. The substrate may include a closed cavity for providing compliance for receiving and/or transmitting acoustic energy to and from the film. The ferroelectric material may be PZT. The film may include a pyroelectric material. The transducer may include a dielectric layer on the side of the film opposite the electrodes. It may include a conductor ground plane on the side of the dielectric layer opposite the electrodes. It may include a substrate on the side of the ground plane opposite the electrodes. The substrate may be silicon. The substrate may include a well on the side opposite the electrodes for receiving infrared radiation. The transducer may include an infrared absorbing layer in the well. The electrodes may be equally spaced or spaced to provide equal integrals of the electric field and voltage between said electrodes.
The invention also features an imaging array of interdigitated electrode ferroic transducers, each transducer including a film of ferroic material electrically polarized substantially in the plane of the film. There is a set of interdigitated electrodes including at least two electrodes spaced from each other on the same side of the film and disposed at the termini of the polarization field.
REFERENCES:
patent: 2540194 (1951-02-01), Ellett
patent: 2540412 (1951-02-01), Adler
patent: 3114849 (1963-12-01), Poschenrieder
patent: 4638206 (1987-01-01), Tsunooka et al.
patent: 5209119 (1993-05-01), Polla et al.
patent: 5315205 (1994-05-01), Ohno et al.
patent: 5488954 (1996-02-01), Sleva et al.
patent: 5786655 (1998-07-01), Okumura et al.
patent: 5825119 (1998-10-01), Shibata et al.
patent: 5852337 (1998-12-01), Takeuchi et al.
patent: 5862275 (1999-01-01), Takeuchi et al.
patent: 5956292 (1999-09-01), Bernstein
patent: 6043587 (2000-03-01), Jaenker
Budd Mark O.
Iandiorio & Teska
The Charles Stark Draper Laboratory Inc.
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