U.S. patent application number 09/521167 was filed with the patent office on 2002-10-24 for single crystal thickness and width cuts for enhanced ultrasonic transducer.
Invention is credited to Beck, Heather, Chen, Jie, Gururaja, Turuvekere R., Panda, Rajesh Kumar.
Application Number | 20020153809 09/521167 |
Document ID | / |
Family ID | 24075643 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020153809 |
Kind Code |
A1 |
Chen, Jie ; et al. |
October 24, 2002 |
Single crystal thickness and width cuts for enhanced ultrasonic
transducer
Abstract
This invention is directed to a transducer comprising a
lead-based single crystal wherein the crystal is diagonally
oriented and has an effective coupling constant of at least 0.70.
In one embodiment, the lead-based crystal has the formula
Pb(B'B")O.sub.3--PbTiO.sub.3 wherein B' is Mg.sup.2+, Zn.sup.2+,
Ni.sup.2+ or Sc.sup.3+ and B" is Nb.sup.5+, Ta.sup.5+ or W.sup.6+.
Preferably, the lead-based crystal is of the formula
Pb(B'B")O.sub.3--PbTiO.sub.3 where B' is Mg.sup.2+, Zn.sup.2+,
Sc.sup.3+ and B" is Nb.sup.5+ or more specifically
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PMN-PT"),
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PZN-PT"), and
Pb(Sc.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PSN-PT"). The
invention also includes a transducer comprising a plurality of
lead-based single crystal transducers. In one embodiment the
ultrasonic probe comprising one or more piezoelectric components
having surfaces that function as transmitting and/or receiving
elements; and electrodes placed upon opposite surfaces of the
elements, and wherein each lead based piezoelectric component as
described above. In addition, the invention includes improved
materials for reduced spurious modes. Furthermore, the invention
includes diagonally oriented lead-based transducers.
Inventors: |
Chen, Jie; (North Andover,
MA) ; Panda, Rajesh Kumar; (Nashua, NH) ;
Gururaja, Turuvekere R.; (Discovery Bay, HK) ; Beck,
Heather; (Chelmsford, MA) |
Correspondence
Address: |
PHILIPS ELECTRONICS NORTH AMERICAN
580 WHITE PLAINS ROAD
TARRYTOWN
NY
10591
US
|
Family ID: |
24075643 |
Appl. No.: |
09/521167 |
Filed: |
March 8, 2000 |
Current U.S.
Class: |
310/360 |
Current CPC
Class: |
H01L 41/1875 20130101;
H01L 41/18 20130101 |
Class at
Publication: |
310/360 |
International
Class: |
H02N 002/00 |
Goverment Interests
[0001] The invention was made in part with government funds under
Office of Naval Research Grant Number N00014-98-C-0163. Therefore,
the U.S. Government has certain rights in the invention.
Claims
We claim:
1. A transducer comprising a lead-based single crystal wherein the
longitudinal or thickness direction of the crystal is diagonally
oriented and has an effective coupling constant of at least
0.70.
2. The transducer of claim 1 wherein the crystal is a face
diagonally oriented crystal.
3. The transducer of claim 1 wherein the crystal is a body
diagonally oriented crystal.
4. The transducer of claim 1 wherein the longitudinal or thickness
direction of the cut is from about 0 to about 20 degrees off the
diagonal orientation.
5. The transducer of claim 1 wherein the longitudinal or thickness
direction of the cut is from about 0 to about 10 degrees off the
diagonal orientation.
6. The transducer of claim 1 wherein the lead-based crystal is of
the formula Pb(B'B")O.sub.3--PbTiO.sub.3 wherein B' can be at least
one of the following: Mg.sup.2+, Ni.sup.2+, Sc.sup.3+, Yb.sup.3+,
Fe.sup.3+, Mn.sup.3+, In.sup.3+, Ir.sup.3+, Co.sup.3+ or Zn.sup.2+,
and B" can be at least one of the following: Nb.sup.5+, Ta.sup.5+,
Te.sup.6+ or W.sup.6+.
7. The transducer of claim 6 wherein the lead-based crystal further
comprises one or more additional metal or metal oxides wherein the
metal is Ba, Bi, Ca, Sr, La or Pt.
8. The transducer of claim 6 wherein the lead-based crystal is of
the formula Pb(B'B")O.sub.3--PbTiO.sub.3 where B' is Mg.sup.2+,
Zn.sup.2+, Sc.sup.3+ and B" is Nb.sup.5+.
9. The transducer of claim 8 wherein the lead-based crystal is of
the formula Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3,
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3, or
Pb(Sc.sub.1/3Nb.sub.2/3)- O.sub.3--PbTiO.sub.3.
10. The transducer of claim 9 wherein the lead-based crystal is of
the formula Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the
molar ratio of Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 is
from about 10:1 to about 1:1.
11. The transducer of claim 10 wherein the lead-based crystal is of
the formula Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the
molar ratio of Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 is
from about 6:1 to about 3:2.
12. The transducer of claim 11 wherein the lead-based crystal is of
the formula Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the
molar ratio of Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 is
from about 3:1 to about 5:3.
13. The transducer of claim 8 wherein the lead-based crystal is of
the formula Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the
ratio of Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 is from
about 50:1 to about 2:1.
14. The transducer of claim 13 wherein the lead-based crystal is of
the formula Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the
ratio of Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 is from
about 25:1 to about 6:1.
15. The transducer of claim 14 wherein the lead-based crystal is of
the formula Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the
ratio of Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 is about
15:1 to about 8:1.
16. The transducer of claim 1 wherein the crystal has an effective
coupling constant of at least 0.80.
17. The transducer of claim 1 wherein the crystal has an effective
coupling constant of at least 0.85.
18. A transducer comprising a lead-based single crystal wherein the
longitudinal or thickness direction of the crystal is diagonally
oriented and has an effective coupling constant of at least 0.70
wherein the ratio of the crystal length to thickness to width is
from about (300 to 15):(5 to 1):(5 to 1).
19. The transducer of claim 18 wherein the ratio of the crystal
length to thickness to width is from about (150 to 10):(3 to 1):(3
to 1).
20. The transducer of claim 19 wherein the ratio of the crystal
length to thickness to width is from about (100 to 10):(3 to
2):(2:1).
21. The transducer of claim 2 wherein the crystal has a width
orientation of about 35 to 90 degrees away from the <011>
width orientation.
22. The transducer of claim 2 wherein the crystal has a width
orientation of about 45 to 80 degrees away from the <011>
width orientation.
23. The transducer of claim 2 wherein the crystal has a width
orientation of about 50 to 70 degrees away from the <011>
width orientation.
24. The transducer of claim 3 wherein the crystal has a width
orientation of about .+-.10 degrees from the <011> width
orientation.
25. The transducer of claim 1 wherein the crystal is a one
dimensional, a quasi-one dimensional or a two dimensional
transducer.
26. A transducer comprising a plurality of lead-based single
crystal transducer elements of claim 1.
27. The transducer of claim 26 wherein the lead-based single
crystal elements are embedded in a polymer to form a single
crystal/polymer composite.
28. A transducer comprising a lead-based single crystal orientated
slightly off the <001> orientation wherein the longitudinal
or thickness direction of the sample is cut from 2 to about 20
degrees off the <001> orientation and the coupling constant
is greater than 0.75.
29. A transducer comprising a lead-based single crystal orientated
slightly off the <001> orientation wherein the longitudinal
or thickness direction of the sample is cut from 2 to about 15
degrees off the <001> orientation and the coupling constant
is greater than 0.80.
30. A transducer comprising a lead-based single crystal orientated
in about the <001>.sub.t/<010>.sub.w orientation
wherein the sample is cut from 2 to about 15 degrees off the width
orientation and the ratio of the crystal length to thickness to
width is from about (300 to 15):(5 to 1):(5 to 1).
31. A transducer comprising a lead-based single crystal wherein the
sample is cut from 15 to about 25 degrees off the <010> width
directions and the ratio of the crystal length to thickness to
width is from (300 to 15):(5 to 3):(2 to 1).
32. An ultrasonic transducer comprising: one or more piezoelectric
components having surfaces that function as transmitting and/or
receiving elements; and electrodes placed upon opposite surfaces of
the elements, and wherein each lead based piezoelectric component
is diagonally oriented and has an effective coupling constant of at
least 0.70.
33. An ultrasonic transducer comprising: one or more piezoelectric
components having surfaces that function as transmitting and/or
receiving elements; and electrodes placed upon opposite surfaces of
the elements, and wherein each lead based piezoelectric component
is diagonally oriented and has an effective coupling constant of at
least 0.70 and the ratio of the crystal length to thickness to
width is from about (300 to 15):(5 to 1):(5 to 1).
34. An ultrasonic probe comprising: one or more piezoelectric
components having surfaces that function as transmitting and/or
receiving elements; and electrodes placed upon opposite surfaces of
the elements, and wherein each lead-based piezoelectric component
is diagonally oriented and has an effective coupling constant of at
least 0.70 and the ratio of crystal length to width is (100 to 5):
(5 to 1).
35. The ultrasonic transducer of claim 32 wherein each
piezoelectric component comprises a single crystal having the
formula Pb(B'B")O.sub.3--PbTiO.sub.3 wherein B' is Mg.sup.2+,
Zn.sup.2+, Ni.sup.2+ or Sc.sup.3+ and B" is Nb.sup.5+, Ta.sup.5+ or
W.sup.6+.
36. The ultrasonic transducer of claim 32 wherein each
piezoelectric component comprises a single crystal having the
formula Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3,
Pb(Zn.sub.1/3Nb.sub.2/3)O.s- ub.3--PbTiO.sub.3, or
Pb(Sc.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3.
37. A transducer comprising lead-based diagonally oriented
polycrystalline material.
38. The transducer of claim 37 wherein the effective coupling
constant is greater than 0.70.
39. A transducer comprising a lead-based single crystal wherein the
crystal is oriented in the <011> orientation along the
longitudinal or thickness direction.
40. The transducer of claim 39 wherein the <011> orientation
is cut from about 0 to about 20 degrees off the longitudinal or
thickness direction.
Description
FIELD OF THE INVENTION
[0002] This invention relates to improved cut orientations and
dimensions for lead based single crystal compositions including
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PMN-PT"),
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PZN-PT"), and
Pb(Sc.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PSN-PT") type
relaxor single crystal compositions. Specifically, improved
electromechanical properties of single crystals were obtained by
orienting the crystal's thickness and width along certain
directions. In addition, improved properties were also obtained by
preparing single crystals of specific dimensions. These
combinations of cut orientations and dimensions give rise to
improved crystal processibility and excellent electromechanical
properties.
BACKGROUND OF THE INVENTION
[0003] A transducer is a device that converts one form of energy to
another. For example, ultrasonic transducers convert electrical
energy to mechanical energy and vice versa. An ultrasonic
transducer includes an ultrasonic transmitting/receiving element(s)
typically consisting of piezoelectric element(s) connected to
electrodes. The electrical energy supplied to the electrodes
electrically excites the ultrasonic probe element(s) causing them
to vibrate at a given frequency. The vibrations then give rise to
acoustic waves (in this case, ultrasonic waves) which, upon
impinging on an interface representing a junction between two
media, are either reflected or transmitted. The reflected waves can
be detected by the same piezoelectric probe. This reflection and
transmission of acoustic waves at the interface between two media
is the basis of ultrasonic imaging. An ultrasonic imaging apparatus
incorporating this ultrasonic probe has been used to examine the
interior of a human body or to detect flaws in a metal welded
portion.
[0004] B-mode imaging, color flow mapping (CFM), and Doppler are
the common ultrasonic diagnostic imaging methods used on human
bodies. CFM is capable of two-dimensionally displaying in color the
blood flow velocity in organs such as the heart, liver, kidney,
spleen or carotid artery by using a Doppler shift of ultrasonic
waves caused by the bloodstream, as well as displaying tomographic
images (the so-called B-mode images where the echo signals are
represented as intensity-modulated lines in a display) of human
bodies. Diagnostic capability has been dramatically improved by
these medical diagnostic methods.
[0005] A commonly used ultrasonic probe configuration comprises an
array of a few tens to about 300 ultrasonic transmitting/receiving
elements each of which is made of a strip of piezoelectric
material. With this configuration, it is difficult to obtain
matching with a transmitting/receiving circuit because the
impedance of each piezoelectric element increases as the number of
ultrasonic transmitting/receiving elements increases. Also, for
certain applications, the surface of a phased-array probe has to be
kept as small as possible if, for example, the probe used to image
the heart through rib spacing or used internally on a live
subject.
[0006] Ultrasound as an imaging method has tradeoffs. When high
frequencies are used, the resolution is improved but the
penetration is reduced. Thus, in many cases, more than one
transducer is needed to perform a diagnosis because of the
necessary penetration depth and resolution. But good penetration
and resolution cannot be obtained at the same time. The human
tissue has strong non-linear characteristics. When it is imaged by
an ultrasonic signals, it generates harmonic signals, such as
first, second, and third harmonic signals. Recently, with the
advent of tissue harmonic imaging, it is possible to increase
penetration by transmitting at a lower fundamental frequency
(f.sub.0) and at the same time, to increase resolution by detecting
the second harmonic signal (2f.sub.0) arising from the nonlinear
response of the subject.
[0007] Another ultrasound application utilizing harmonics is the
contrast harmonic imaging. In this type of imaging, the contrast
agents used are typically gas-filled microspheres (bubbles) which
resonate at certain ultrasonic frequencies. When the contrast
agents are insonified at one frequency, they generate large
harmonic signals due to the contrast agents' nonlinear response.
The use of contrast agent significantly improves the detection of
blood-filled structures and blood flow velocity in the arterial
systems.
[0008] For harmonic imaging, broadband transducers must be used to
both transmit and received a bandwidth wide enough to encompass the
fundamental and harmonic frequencies. Because current PZT-type
transducers do not fulfill this bandwidth requirement, their
performance in harmonic imaging is lower than transducers that meet
the requisite bandwidth.
[0009] Nonetheless, piezoelectric materials such as PZT based
ceramics are widely used for medical ultrasound transducers. Two of
the important criteria for choosing a piezoelectric material for
ultrasound transducer applications are high values of the
longitudinal coupling constant (k.sub.33) and dielectric constant
(K). A high coupling constant is desirable because it represents
the efficiency of conversion of electrical energy to mechanical
energy and vice versa. A high dielectric constant leads to better
electrical impedance matching with the system electronics
especially for small element phased array transducers. PZT ceramics
have a typical k.sub.33 value of 0.70, but even higher coupling
constants are preferred because they would increase not only the
transmit and receive efficiency but also the bandwidth of the
transducer. The recent discovery of high coupling in lead-based
single crystal materials have generated a lot of interest in this
regard.
[0010] Lead-based ferroelectric single crystals with the general
formula Pb(B'B")O.sub.3 where B'.dbd.Mg.sup.2+, Zn.sup.2+,
Sc.sup.3+ . . . and B".dbd.Nb.sup.5+, Ta.sup.5+ . . . , and the
solid solution of these compounds with PbTiO.sub.3 have been shown
to exhibit excellent electromechanical properties near the
morphotropic phase boundary (MPB), the boundary separating the
rhombohedral phase (spontaneous polarization along <111>) and
the tetragonal phase (polarization along <001>). Some of the
important compounds include
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PMN-PT"),
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PZN-PT"), and
Pb(Sc.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 ("PSN-PT"). FIG. 1
shows the phase diagram of PZN-PT and PMN-PT.
[0011] The electromechanical properties of PZN-9% PT (ratio of PZN
to PT is .about.10 to 1) single crystals were first reported by
Yonezawa et al. in 1969 (J. Jpn. Soc. Powder Metallurgy, 16,
253-258 (1969)), then by Kuwata et al. in 1982 (Ferroelectrics, 37,
579-582 (1981); Jpn. J. Appl. Phys. 21, 1298-1302(1982)). The high
coupling constants of these single crystals make them attractive
for transducer and actuator applications. These crystals with a
composition on the rhombohedral side of the MPB and cut with the
thickness along the [001] direction showed very high coupling
(k.sub.33>0.92) and piezoelectric constants (d.sub.33>1500
pC/N). U.S. Pat. Nos. 5,295,487, 5,402,791, and 5,998,910 describe
PZN-PT and PMN-PT systems at various compositions for ultrasonic
transducer applications, the contents of which are hereby
incorporated in their entirety. Coupling constants for slivers
(k.sub.33'=0.82) and for bars (k.sub.33=0.92) have been reported
for these systems.
[0012] Previous work has focused primarily on the <001>
longitudinal orientation, and the properties, especially the
dielectric properties were found to be unstable near the MPB
compositions because the compositions undergo a phase transition
from rhombohedral to tetragonal phase. While the <111>
orientation has also been investigated for bar-shaped elements, the
electromechanical properties along this orientation have been shown
to be inferior to those along the <001> orientation. For
example, U.S. Pat. No. 5,998,910 and Kuwata et al. in Jap. J. Appl.
Phys. 21 1298-1302 (1982) report low k.sub.33 values of only about
0.35-0.68 along the <111> direction. Thus, in their materials
the electromechanical properties appear to be very sensitive to the
orientation and chemical composition of the crystal.
[0013] In addition, previous work disclosed single crystal
materials primarily having a bar shape. Very little research have
been conducted to understand the effect of the width orientation
involving quasi-one dimensional structures such as slivers (see
FIG. 2). The results were obtained for slivers that were cut with
the thickness and the width along the <001> orientation (see,
for example, U.S. Pat. No. 5,402,791). However, slivers cut at the
<001> orientation showed the presence of spurious resonance
in the frequency range of interest (see Lopath et al., Proceeding
of the Tenth IEEE International Symposium on Applications of
Ferroelectrics, East Brunswick, Aug. 18-21, 1996, pp. 543-546). For
one dimensional (1-D) and 1.5-D transducer applications, it is
critical to discover the best combination of both thickness and
width orientation cuts to optimize the electromechanical properties
of 1-D or quasi-one dimensional structures such as slivers.
[0014] Medical ultrasonic imaging applications cover a wide
frequency range spanning 1.5-40 MHz depending on the organs to be
imaged. The frequency depends on the thickness and sound velocity
of the piezoelectric and the matching layer materials (f=v/2t,
where f is the transducer frequency, v is the ultrasonic velocity
of the piezoelectric material, and t is the material thickness).
Thus, high frequency linear array applications at 8-15 MHz require
a thickness of only about 130-200 .mu.m for PZT ceramic materials.
PMN-PT or PZN-PT single crystals having a <001> orientation
have a lower velocity than PZT-type ceramics, and thus PMN-PT or
PZN-PT wafers have to be even thinner (about 100 .mu.m). Because
linear arrays have a typical wafer dimension of 40 mm.times.4
mm.times.0.2 mm, manufacturing these extremely thin crystals is
very difficult because the crystals' thinness makes them
mechanically fragile. For high frequency imaging applications
involving eye, intracardiac, and intravascular imaging, the wafer
thickness drops to 20-30 .mu.m. At this thickness range, mechanical
processing of <001> orientated single crystals is even more
challenging.
[0015] Recently, other workers have disclosed PMN-PT and PZN-PT
oriented polycrystalline materials for use as ultrasonic
transducers. (See Gentilman et al., "Processing and Application of
Solid State Converted High Strain Undersea Transmitter Materials,"
paper presented at the Piezocrystals Workshop, Arlington, Va., Jan.
18-20, 2000). They report only on the <001> orientation. No
<011> or <111> oriented polycrystalline materials are
disclosed.
SUMMARY OF THE INVENTION
[0016] This invention includes a transducer comprising a lead-based
single crystal wherein the longitudinal or thickness direction of
the crystal is diagonally oriented and has an effective coupling
constant of at least 0.70. In one embodiment, the crystal is a face
diagonally oriented crystal. Alternatively, the crystal maybe a
body diagonally oriented crystal. The longitudinal or thickness
direction of the cut may be from about 0 to about 20 degrees from
the diagonal orientation.
[0017] Preferably, the lead-based crystal is of the formula
Pb(B'B")O.sub.3--PbTiO.sub.3 wherein B' can be at least one of the
following: Mg.sup.2+, Ni.sup.2+, Sc.sup.3+, Yb.sup.3+, Fe.sup.3+,
Mn.sup.3+, In.sup.3+, Ir.sup.3+, Co.sup.3+ or Zn.sup.2+, and B" can
be at least one of the following: Nb.sup.5+, Ta.sup.5+, Te.sup.6+
or W.sup.6+. The lead-based crystal may further comprise one or
more additional metal or metal oxides wherein the metal is Ba, Bi,
Ca, Sr, La or Pt. In one embodiment, the lead-based crystal is of
the formula Pb(B'B")O.sub.3--PbTiO.sub.3 where B' is Mg.sup.2+,
Zn.sup.2+, Sc.sup.3+ and B" is Nb.sup.5+. Specifically, the
lead-based crystal is of the formula
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3,
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3, or
Pb(Sc.sub.1/3Nb.sub.2/3)- O.sub.3--PbTiO.sub.3. The molar ratio of
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 may be from about
10:1 to about 1:1, or from about 6:1 to about 3:2 or from about 3:1
to about 5:3. For the lead-based crystal of the formula
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 and the ratio of
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 may be from about
50:1 to about 2:1; or from about 25:1 to about 6:1; or about 15:1
to about 8:1.
[0018] Preferably, the crystal has an effective coupling constant
of at least 0.80, more preferably of at least 0.85.
[0019] The invention also includes a lead-based single crystal
wherein the longitudinal or thickness direction of the crystal is
diagonally oriented and has an effective coupling constant of at
least 0.70 wherein the ratio of the crystal length to thickness to
width is from about (300 to 15):(5 to 1):(5 to 1). Preferably, the
ratio of the crystal length to thickness to width is from about
(150 to 10):(3 to 1):(3 to 1). More preferably, the ratio of the
crystal length to thickness to width is from about (100 to 10):(3
to 2):(2 to 1).
[0020] In the face diagonal orientated crystals, the crystal has a
width orientation of about 35 to 90 degrees, preferably of about 45
to 80 degrees, more preferably about 50 to 70 degrees away from the
<011> width orientation. In the body diagonal oriented
crystal, the crystal has a width orientation of about .+-.10
degrees from the <011> width orientation.
[0021] In an alternative embodiment, the transducer may comprise a
lead-based single crystal orientated slightly off the <001>
orientation wherein the longitudinal or thickness direction of the
sample is cut from 2 to about 20 degrees off the <001>
orientation and the coupling constant is greater than 0.75.
Alternatively, the sample is cut from 2 to about 15 degrees
(alternatively, 2 to 10 or 2 to 5 degrees) off the <001>
orientation and the coupling constant is greater than 0.80.
[0022] In another embodiment, a lead-based single crystal
orientated in about the <001>.sub.t/<010>.sub.w
orientation wherein the width orientation of the sample is cut from
2 to about 15 degrees (alternatively, 2 to 10 or 2 to 5 degrees)
off the <010> axis and the ratio of the crystal length to
thickness to width is from about (300 to 15):(5 to 1):(5 to 1).
Also, the sample may be cut from 15 to about 25 degrees off the
<010> width orientation and the ratio of the crystal length
to thickness to width is from (300 to 15):(5 to 3):(2 to 1).
[0023] The invention also includes a transducer comprising a
plurality of lead-based single crystal transducer elements.
Moreover, the lead-based single crystal materials may be embedded
in a polymer to form a single crystal/polymer composite. It may be
an ultrasonic transducer comprising one or more piezoelectric
components that function as transmitting and/or receiving elements;
and electrodes placed upon opposite surfaces of the elements, and
wherein each lead based piezoelectric component is diagonally
oriented and has an effective coupling constant of at least 0.70.
In addition, for sliver elements, the ratio of the crystal length
to thickness to width is from about (300 to 15):(5 to 1):(5 to 1).
For bar elements, the ratio of crystal length to width is (100 to
5): (5 to 1).
[0024] In another alternative embodiment the invention includes a
transducer comprising lead-based diagonally oriented
polycrystalline material. In the polycrystalline material the
effective coupling constant may be greater than 0.70, preferably
greater than 0.80, more preferably greater than 0.85.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 shows phase diagrams for (a) PZN-PT and (b)
PMN-PT.
[0026] FIG. 2 is a schematic showing two slivers with the thickness
oriented along the [001] and width along the [010] and [110]
directions, respectively. A [001] longitudinal oriented bar is also
shown in the graph.
[0027] FIG. 3 shows an exemplary arrangement of a plurality of
diagonally oriented one dimensional sliver-shaped elements for a
transducer.
[0028] FIG. 4 shows an exemplary arrangement of a plurality of
quasi-one dimensional (1.5D)/or two dimensional diagonally oriented
elements for a transducer.
[0029] FIG. 5 shows the stereographic projection of the
<001>.sub.t/<010>.sub.w cuts. The arrows indicate the
polarization directions (<111> orientations) and the poling
direction (<001> orientation) respectively.
[0030] FIG. 6 shows the effective coupling constant of a
<001> thickness oriented sliver cut as a function of the
width orientation away from the <010> width orientation.
0.degree.=<010>.sub.w orientation,
45.degree.=<011>.sub.w orientation.
[0031] FIG. 7 shows the stereographic projection of the
<001>.sub.t/<011>.sub.w cut. The arrows indicate the
polarization directions (<111> orientations) and the poling
direction (<001> orientation), respectively.
[0032] FIG. 8 shows a plot of the coupling constant as a function
of the width to thickness aspect ratio.
[0033] FIG. 9 shows the stereographic projections of the
<011>.sub.t/<110>.sub.w and
<011>.sub.t/<100>.sub- .w cuts.
[0034] FIG. 10 shows the stereographic projection of the
<111>.sub.t/<011>.sub.w cut.
[0035] FIG. 11 shows a schematic drawing of an orientated
polycrystalline material.
DETAILED DESCRIPTION OF THE INVENTION
[0036] This invention includes a transducer comprising a lead-based
single crystal wherein the longitudinal or thickness direction of
the crystal is diagonally oriented and has an effective coupling
constant of at least 0.70. In one embodiment, the crystal is a face
diagonally oriented crystal. Alternatively, the crystal may be a
body diagonally oriented crystal. The longitudinal or thickness
orientation of the crystal may be from about 0 to about 20 degrees
from the diagonal orientation (the <011> or <111>
axis). Alternatively, the longitudinal or thickness orientation of
the cut may be from about 0 to about 15 degrees, from about 0 to
about 10 degrees, or from about 0 to about 5 degrees from the
<011> or <111> orientation axis. Alternatively, the
diagonally oriented materials may be cut using these ranges
relative to a width orientation axis.
[0037] Preferably, the lead-based crystal is of the formula
Pb(B'B")O.sub.3--PbTiO.sub.3 wherein B' can be at least one of the
following: Mg.sup.2+, Ni.sup.2+, Sc.sup.3+, Yb.sup.3+, Fe.sup.3+,
Mn.sup.3+, In.sup.3+, Ir.sup.3+, Co.sup.3+, or Zn.sup.2+, and B"
can be at least one of the following: Nb.sup.5+, Ta.sup.5+,
Te.sup.6+ or W.sup.6+. The lead-based crystal may further comprise
one or more additional metal or metal oxides wherein the metal is
Ba, Bi, Sr, Ca, La or Pt. In one embodiment, the lead-based crystal
is of the formula Pb(B'B")O.sub.3--PbTiO.sub.3 where B' is
Mg.sup.2+, Zn.sup.2+, Sc.sup.3+ and B" is Nb.sup.5+. Specifically,
the lead-based crystal is of the formula
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3,
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3, or
Pb(Sc.sub.1/3Nb.sub.2/3)- O.sub.3--PbTiO.sub.3. The molar ratio of
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 may be from about
10:1 to about 1:1, or from about 6:1 to about 3:2 or from about 3:1
to about 5:3. For the lead-based crystal of the formula
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3--PbTiO.sub.3, the ratio of
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 to PbTiO.sub.3 may be from about
50:1 to about 2:1; or from about 25:1 to about 6:1; or about 15:1
to about 8:1.
[0038] Preferably, the crystal has an effective coupling constant
of at least 0.80, more preferably of at least 0.85.
[0039] The invention also includes a lead-based single crystal
wherein the longitudinal or thickness direction of the crystal is
diagonally oriented and has an effective coupling constant of at
least 0.70 wherein the ratio of the crystal length to thickness to
width is from about (300 to 15):(5 to 1):(5 to 1). Preferably, the
ratio of the crystal length to thickness to width is from about
(150 to 10):(3 to 1):(3 to 1). More preferably, the ratio of the
crystal length to thickness to width is from about (100 to 10):(3
to 2):(2 to 1).
[0040] In the face diagonal orientated crystals, the crystal has a
width orientation of about 35 to 90 degrees, preferably of about 45
to 80 degrees, more preferably about 50 to 70 degrees away from the
<011> orientation. In the body diagonal oriented crystal, the
crystal has a width orientation of about .+-.20 degrees or .+-.10
degrees from the <011> width orientation.
[0041] In an alternative embodiment, the transducer may comprise a
lead-based single crystal orientated slightly off the <001>
orientation wherein the longitudinal or thickness direction of the
sample is cut from 2 to about 20 degrees off the <001>
orientation and the coupling constant is greater than 0.75.
Alternatively, the longitudinal or thickness orientation of the
sample is cut from 2 to about 15 degrees off the <001>
orientation and the coupling constant is greater than 0.80. In this
case, the cut may also be from about 2 to about 10 degrees or about
2 to about 5 degrees off the <001> axis.
[0042] In another embodiment, a lead-based single crystal
orientated in about the <001>.sub.t/<010>.sub.w
orientation wherein the sample is cut from 2 to about 15 degrees
(alternatively, 2 to 10 or 2 to 5 degrees) off the width
orientation and the ratio of the crystal length to thickness to
width is from about (300 to 15):(5 to 3):(3 to 1). Also, the sample
may be cut from 15 to about 25 degrees off the <010> width
orientation and the ratio of the crystal length to thickness to
width is from (300 to 15):(5 to 3):(2 to 1).
[0043] The invention also includes a transducer comprising a
plurality of lead-based single crystal transducer elements.
Moreover, the lead-based single crystal elements may be embedded in
a polymer to form a single crystal/polymer composite. It may be an
ultrasonic transducer comprising one or more piezoelectric
components that function as transmitting and/or receiving elements;
and electrodes placed upon opposite surfaces of the elements, and
wherein each lead based piezoelectric component is diagonally
oriented and has an effective coupling constant of at least 0.70.
In addition, for sliver elements, the ratio of the crystal length
to thickness to width is from about (300 to 15):(5 to 1):(5 to 1).
For bar elements, the ratio of crystal length to width is (100 to
5): (5 to 1).
[0044] In another alternative embodiment the invention includes a
transducer comprising lead-based diagonally oriented
polycrystalline material. In the polycrystalline material the
effective coupling constant may be greater than 0.70, preferably
greater than 0.80, more preferably greater than 0.85.
[0045] As used herein, the term diagonally oriented describes a
piezoelectric element or a single crystal element having a
longitudinal or thickness direction along an orientation such as
<011> or <111>, which are at an angle relative to the
<001> orientation. The term diagonally oriented includes face
diagonally oriented, e.g., <011> orientations or all twelve
face diagonal orientations. In one embodiment, samples may be cut
about .+-.20 degrees from the <011> orientation.
Alternatively, samples may be cut about .+-.15 degrees from the
<011> orientation. Alternatively, samples may be cut about
.+-.10 degrees or .+-.5 degrees from the <011> orientation.
The term diagonally oriented also includes body diagonally oriented
samples, e.g., <111> oriented samples or all eight body
diagonal orientations. In one embodiment, samples may be cut about
.+-.20 degrees or .+-.15 degrees from the <111> orientation.
Alternatively, samples may be cut about .+-.10 degrees or .+-.5
degrees from the <111>.
[0046] As used herein, the term effective coupling constant
(k.sub.33') designates the coupling constant corresponding to the
k.sub.33 mode of an oriented piezoelectric element.
[0047] For one dimensional transducer applications, the single
crystal elements are normally diced into sliver shape where the
length > thickness > width. For this particular single
crystal element shape, both the thickness and width orientations
significantly affect the electromechanical properties of the
slivers. Here the effective coupling constant (k.sub.33' for
slivers or for bars with low longitudinal length to width ratio)
replaces the longitudinal coupling constant (k.sub.33 for bars)
because of the clamping effect along the sliver length. FIG. 2 is a
schematic showing the thickness ([001]) and width ([010], [110])
orientations of single crystal elements in the form of slivers. A
[001] longitudinal oriented bar is also shown for comparison.
[0048] Aside from the coupling constant, the longitudinal velocity
and clamped dielectric constant are also important parameters in
designing ultrasound transducers. Both velocity and dielectric
constant are a strong function of crystal orientations. By
exploiting the difference in material properties at various
orientations, better ultrasonic transducers can be designed. For
example, high frequency devices (7-40 MHz center frequency) require
very thin crystals which give rise to substantial manufacturing
defects because of their mechanical fragility. An orientation cut
with high longitudinal velocity allows the use of relatively thick
crystal for the same center frequency thus minimizing mechanical
defects during the manufacturing and processing stages.
[0049] This invention includes engineering of PMN-PT and PZN-PT
single crystals to obtain improved coupling, higher velocities and
dielectric constants. These improvements are accomplished by a
range of novel thickness and width cuts which include the
<011> and <111> orientations.
[0050] Among others, the present invention includes the discovery
of: (1) a new orientation cut with longitudinal or thickness
orientation at or near <011> orientation with excellent
electromechanical properties; (2) the <011> thickness
orientated sliver cuts that exhibit very high k.sub.33' values with
crystal width orientations between 35 to 90 degrees away from the
<110> orientation; (3) <001> orientation cuts with
longitudinal or thickness orientation slightly off the <001>
orientation by about 2 to about 20 degrees; (4)
<001>.sub.t/<010>.sub.w sliver cuts with width
orientation off the <010> orientation by about 2 to about 25
degrees, more preferably from about 2 to about 15 degrees, which
gives high coupling constants; and (5) cuts having thickness
orientation at or near <111> that have high velocities and
high dielectric constants. These <111> oriented materials
allow fabrication of transducer elements using thicker crystals
with improved mechanical durability and processing properties.
[0051] The present invention discloses a combination of particular
thickness and width orientations for compositions near the MPB that
exhibit extremely high and stable electromechanical properties for
sliver or bar-shaped transducer elements. The experimental examples
described below highlight the domain engineering of relaxor single
crystals to obtain high coupling and improved sliver velocities and
dielectric constants. The results were accomplished by selection of
improved single crystal thickness and width cuts.
[0052] The present invention also includes improved sliver
dimensions that eliminate the presence of spurious resonances. The
magnitude of these spurious resonances greatly depends on the
aspect ratio of the slivers and the angular orientation of the
sliver's width. Also, these spurious resonances are related to the
highly directional nature of the velocities in the single crystals.
The present invention describes the existence of a critical aspect
ratio (width/height) and the width orientation which would provide
high coupling constant and clean resonance mode.
[0053] There are many ways of growing the single crystals of PMN-PT
and PZN-PT. Some of the techniques successfully employed include
flux growth (Kobayashi et al. Jpn. J. Appl. Phys, 36, 6035 (1997);
Mulvihill et al. Jpn. J. Appl. Phys, 35, 51 (1996); Park et al.
Jpn. J. Appl. Phys, 36, 1154 (1997)) and the vertical Bridgeman
method (Kobayashi et al. Jpn. J. Appl. Phys, 37, 3382 (1998);
Harada et al. Key Eng. Matls., 157-158, 95 (1999)), the contents of
which are hereby incorporated in their entirety. One of the
problems of growing the relaxor single crystals using the flux
method is the inability to obtain large crystal sizes suitable for
ultrasound transducers. Also, the crystals produced by this method
are prone to defects such as inclusions that arise during the
growth process. Using the Bridgeman technique, vendors have shown
the ability to grow large crystals (diameter <25 mm) with
uniform properties within the plates. Several lead-based single
crystals have been studied previously. See U.S. Pat. Nos.
5,295,487, 5,402,791, and 5,998,910 which describe PZN-PT and
PMN-PT systems at various compositions for ultrasonic transducer
applications, the contents of which are hereby incorporated in
their entirety.
[0054] Recently, workers have reported the fabrication details of
40-channel single crystal phased-array transducer (Saitoh et al.
IEEE Trans. on UFFC, 46, 152 (1999)) and a 5 MHz PMN-PT phased
array single crystal transducer (Panda et al. Proceeding of the 9th
US-Japan Seminar on Dielectric and Piezoelectric Ceramics, Okinawa,
November 2-5, P143-146, 1999), the contents of which are hereby
incorporated in their entirety. Significant improvements are
observed by replacing a PZT ceramic with a PZN-8% PT and PMN-PT
single crystals. Accordingly, the lead-based single crystal
transducers of this invention may be incorporated into phase array
or composite transducers; see also U.S. Pat. No. 5,998,910, the
contents of which are incorporated herein in their entirety. Two
possible designs with diagonally orientated single crystals for
multi-element or phase array transducers are shown in FIGS. 3 and
4. FIG. 3 shows a transducer with a plurality of silver type
crystals. FIG. 4 shows a transducer with a plurality of
quasi-1dimensional (1.5D) or 2D single crystals. In these designs,
the lead-based single crystal materials may also be embedded in a
polymer to form a single crystal/polymer composite.
[0055] This invention also includes oriented polycrystalline
materials. Both the composition and the various orientations and
dimensions disclosed above for single crystals may be similarly
applied to oriented polycrystalline materials. These materials are
also known as polycrystals or oriented piezoelectric materials.
EXAMPLE A
Crystal Cultivation
[0056] Chemical grade PbO, MgO, Nb.sub.2O.sub.5, ZnO, and TiO.sub.2
were used to form PMN-PT and PZN-PT compositions. The PMN-PT
contained 26% to 40% of PT (40 mm (length).times.25 mm (diameter))
and the PZN-PT had compositions of 4.5% and 8% (20 mm
(length).times.15 mm (thickness).times.15 mm (width)) of PT.
Bridgman and flux growing techniques were used to grow PMN-PT and
PZN-PT single crystals. The single crystals were oriented using the
Laue back reflection method and sliced using an ID saw parallel to
the (001), (011), and (111) planes to approximately 1 mm in
thickness. After the wafers were lapped and polished, gold coating
was deposited on opposite surfaces to form the electrodes. The
single crystal wafers with <001>, <011>, and
<111> thickness orientations were then diced using a dicing
saw typically into 10-15 mm.times.0.3-0.5 mm.times.0.15-0.3 mm
slivers having various width orientation cuts. The longitudinal
orientated bars at or near the <001> and <011>
orientations were also cut. The length to width aspect ratio of
these bars are in the range of 3:1 to about 7:1. The slivers and
bars were poled at room temperature in air or in oil and the
electromechanical and dielectric properties were measured using an
HP 4194A impedance gain phase analyzer.
EXAMPLE B
<001>.sub.t/<010>.sub.w Cuts
[0057] FIG. 5 shows the stereographic projection of the
<001>.sub.t/<010>.sub.w cut, where the sliver thickness
orientation lies along <001> and the width orientation along
<010>. In the rhombohedral phase, there are four <111>
polarization directions along the (001) plane. Each of the
polarization direction is 54.7 degree away from the poling
direction of <001>. The PMN-PT and PZN-PT slivers, with
thickness orientation along <001> and width orientation along
<010>, were characterized as a function of PT compositions
encompassing rhombohedral and tetragonal phases.
[0058] Table 1 lists piezoelectric and dielectric properties of
these slivers. As shown in the table, very high effective coupling
constant (k.sub.33' close to 0.90) can be obtained for the
<001>.sub.t/<0- 10>.sub.w slivers at the rhombohedral
phase composition near the MPB. The properties, especially the
dielectric constant, are a strong function of PT composition. When
the PMN-PT composition undergoes a transition from rhombohedral
phase (<33% PT in PMN-PT system) to a tetragonal phase (>35%
of PT in PMN-PT system), the dielectric constant decreases by more
than 40%. The properties of the <001>.sub.t/<010>.sub-
.w cut would thus appear to be sensitive at the MPB compositions
even to slight perturbations such as a minor change in
composition.
1TABLE 1 The clamped dielectric and electromechanical properties of
PMN-PT and PZN-PT slivers with <001>.sub.t/<010>.sub.w
orientation cut. Clamped Dielectric Effective Coupling Velocity: v
Constant: Constant: k.sub.33'(Sliver) (mm/.mu.sec) K(1 MHz) PMN-PT
<0001>.sub.t/<010>.sub.w cuts 26-27% of PT (rhom)
0.77-0.85 3.2-3.4 1400 29-30% of PT (rhom) 0.86-0.90 3.1-3.3 1400
32% of PT (rhom) 0.86-0.89 3.1-3.3 1400 34% of PT (MPB) 0.77-0.80
3.3 1300 35-36% of PT (tetra) 0.73-0.77 3.8 800 PZN-PT
<001>.sub.t/<010>.sub.w cuts 4.5% of PT (rhom)
0.84-0.87 2.5-2.6 1100 8% of PT (rhom) 0.85-0.88 2.4-2.6 900
EXAMPLE C
<001>.sub.t/<011>.sub.w Cuts and Cuts Between
<001>.sub.t/<010>.sub.w and
<001>.sub.t/<011>.sub- .w
[0059] The slivers with thickness orientation along <001> and
width orientation along <011> were measured at rhombohedral
phase compositions. Compared to the
<001>.sub.t/<010>.sub.w cut, the
<001>.sub.t/<011>.sub.w cut's velocity is much higher
but its coupling constant is relatively lower
(v.sub.<001>/<011>=- 3.8 mm/.mu.sec and
k.sub.33'.sub.<001>/<011>=0.78 vs.
v.sub.<001>/<010>=3.2 mm/.mu.sec and
k.sub.33'.sub.<001>- ;/<010>=0.87). When compared
with the <001>.sub.t/<010>.- sub.w cut, the
<001>.sub.t/<011>.sub.w cut is very sensitive to the
width orientation. For instance, when one moves just a few degrees
away from the <011> width orientation, additional resonance
peak appears.
[0060] FIG. 6 shows the coupling constant as a function of cutting
angle relative to the <010> width orientation. Because the
<111> polarization directions in the rhombohedral phase are
not clamped along the length direction of the
<001>.sub.t/<010>.sub.w cut (see FIG. 5), the coupling
constant at this orientation is not very sensitive to the width
orientation as shown in FIG. 6. When the cutting angle of the width
orientation is more than 15 degrees away from the <010>
orientation, an additional resonant mode appears and the effective
coupling constant (k.sub.33') starts to decrease as the width
orientation angle increase.
[0061] When the width orientation is along the <011>
orientation (the <001>.sub.t/<011>.sub.w cut, which is
45 degrees away from the <001>.sub.t/<010>.sub.w cut),
the original main resonance peak disappears and the additional
resonance peak becomes the main peak. Because two of the four
<111> polarization directions are clamped along the sliver
length direction as shown in FIG. 7, this cut is sensitive to the
width orientation.
[0062] The above findings indicate that the
<001>.sub.t/<010>.- sub.w.+-.15 degree cut offers
flexibility in designing transducers because they allow processing
within more than a 30 degree range of width orientations without a
change in their electromechanical properties.
EXAMPLE D
Aspect Ratios with Clean Resonance Modes
[0063] All the specimens described in this work were oriented along
the <001> thickness direction with a thickness of 285 .mu.m
and lengths greater than ten times the thickness.
[0064] Slivers with an aspect ratio of 0.67-0.32 (width/height)
were cut with the width oriented 23.degree. away from the
<010> orientation. The slivers showed two major resonance
peaks in the frequency range of interest. An interesting phenomenon
was discovered upon decreasing the aspect ratio (width/height) of
these slivers. The intensity of the spurious mode became weaker
with decreasing aspect ratio. As shown in FIG. 8, this mode finally
disappeared completely for aspect ratios less than 0.43. Thus, the
fabrication of low aspect ratio slivers with <001>
orientation along the thickness should provide a single clean
resonance peak with high coupling, up to 25 degrees from the
<010> width orientation.
EXAMPLE E
<001> and <011> Longitudinal Orientated Bar Samples
[0065] Bar-shaped samples were also characterized. The bars, having
a PMN-31% PT composition and a length-to-width aspect ratio of 7:1
and 3:1, were oriented longitudinally along the <001> and the
<011> orientations. Coupling constants of k'.sub.33 higher
than 0.90 were obtained on both <001> and <011>
orientation (See Table 2A and 2B). This data indicates that not
only the <001> orientation cut offers excellent coupling
constants, but also the <011> orientation. Very little
differences were observed in these two orientations. Table 2B show
that even if the orientation cuts were shifted slightly off the
<001> and <011> orientations, up to 15 degrees, the
coupling constants remained very high and relatively unchanged.
2TABLE 2A The effective coupling constants of PMN-PT 31% cuts at
<001>, <011> and <111> orientations. (Sample
geometry: 6.0 mm .times. 0.9 mm .times. 0.9 mm PMN-PT 31% Effective
Coupling Velocity (bar, L:W = 7:1) Constant k'.sub.33 (mm/.mu.sec)
<001> 0.93 3.5 <011> 0.91 3.8
[0066]
3TABLE 2B The effective coupling constants of PMN-PT 31% cuts at or
near <001>, <011> orientations (Sample geometry: 2.4 mm
.times. 0.8 mm .times. 0.8 mm) PMN-PT 31% Effective Coupling (bar,
L:W = 3:1) Constant k'.sub.33 <001> 0 degree 0.89 <001>
2.5 degree 0.87 <001> 5 degree 0.88 <001> 10 degree
0.87 <011> 15 degree 0.85 <011> 0 degree 0.88
<011> 2.5 degree 0.87 <011> 5 degree 0.86 <011>
10 degree 0.85 <011> 15 degree 0.83
EXAMPLE F
<011>.sub.t/<010>.sub.w,
<011>.sub.t/<110>.sub.w cuts
[0067] PMN-PT single crystals with thickness orientation along
<011> were investigated for the existence of orientation cuts
having favorable electromechanical properties. FIG. 9 shows the
stereographic plots of both <011>.sub.t/<110>.sub.w and
<011>.sub.t/<010>- ;.sub.w cuts. As shown in the
<011> stereographic projection of the figure, there are two
<111> and two <001> polarization directions along the
(011) plane. Each of them is 35.3.degree. or 45.degree. away from
the <011> poling direction (also the thickness orientation).
Unlike the <001> thickness orientation, none of the
polarization directions in rhombohedral and tetragonal phases is
parallel to the <011> thickness orientation (or poling
direction). It is expected that the dielectric and
electromechanical properties of this cut will be less sensitive to
the rhombohedral-tetragonal phase transition compared to the
<001> orientation cut.
[0068] Due to the clamping effect, the k.sub.33' for the
rhombohedral <011>.sub.t/<110>.sub.w cut is very low
but the velocity is very high. On the other hand, the clamping
effect for the <011>.sub.t/<010>.sub.w cut is very
small for rhombohedral phase, so the
<011>.sub.t/<010>.sub.w gives relatively high k.sub.33'
and moderate velocity. Table 3 lists the effective coupling
constant and longitudinal velocity of
<011>.sub.t/<110>.sub.w and
<011>.sub.t/<010>.sub.w orientation cuts.
4TABLE 3 Electromechanical properties of
<011>.sub.t/<110>.sub.w and
<011>.sub.t/<010>.sub- .w. Effective Coupling Velocity
PMN-PT 32% Constant k.sub.33' (sliver) (mm/.mu.sec)
<011>.sub.t/<110&- gt;.sub.w Cut 0.46 5.0
<011>.sub.t/<010>.sub.w Cut 0.82 3.9
EXAMPLE G
<011>.sub.t/<211>.sub.w,
<011>.sub.t/<522>.sub.w,
<011>.sub.t/<311>.sub.w Cuts and Variable Angle Cuts
from <110> to <010> Orientations
[0069] Table 4 shows the effective coupling constants of PMN-PT
slivers with thickness orientation along <011> and width
orientations between the <110> and <010> orientations.
When both <111> and <001> polarization directions are
not clamped along the width direction, very high coupling constants
can be obtained from these slivers. As shown in Table 4, k.sub.33'
as high as 0.90 can be obtained for slivers with width orientations
from 50 to 70 degrees away from <110>. These
<011>.sub.t/<110>.sub.w 50-70 degree cuts include the
<011>.sub.t/<211>.sub.w (55.4.degree.),
<011>.sub.t/<522>.sub.w (60.4.degree.), and
<011>.sub.t/<311>.sub.w (65.4.degree.) cuts. Not only
do the <011>.sub.t/<110>.sub.w 50-70 degree cuts
exhibit very high values of k.sub.33', but their properties also
show little sensitivity to the width orientation over a wide range
of angles which enables easier transducer fabrication. These
results demonstrate that the <011> orientation offers a range
of useful thickness cuts with excellent coupling properties for
transducer applications.
5TABLE 4 The effective coupling constant and longitudinal velocity
of PMN-PT slivers with <011>.sub.t/<110>.sub.w 0-90
degree orientation cuts. Effective Coupling Velocity PMN-PT 32%
Constant k.sub.33' (sliver) (mm/.mu.sec)
<011>.sub.t/<110>.sub- .w 0 degree 0.46 5.0
<011>.sub.t/<110>.sub.w 35 degree 0.72 3.4
<011>.sub.t/<110>.sub.w 40 degree 0.79 3.3
<011>.sub.t/<110>.sub.w 50 degree 0.88 3.1
<011>.sub.t/<110>.sub.w 55 degree 0.90 3.1
(<011>.sub.t/<211>.sub.w cut)
<011>.sub.t/<110>.sub.w 60 degree 0.90 3.1
<011>.sub.t/<522>.sub.w cut) <011>.sub.t/<1-
10>.sub.w 65 degree 0.90 3.2 (<011>.sub.t/<311>.sub-
.w cut) <011>.sub.t/<110>.sub.w 70 degree 0.88 3.3
<011>.sub.t/<110>.sub.w 75 degree 0.86 3.5
<011>.sub.t/<110>.sub.w 80 degree 0.85 3.6
<011>.sub.t/<110>.sub.w 90 degree 0.82 3.9
<011>.sub.t/<010>.sub.w cut)
EXAMPLE H
<111>.sub.t/<011>.sub.w Cut
[0070] FIG. 10 depicts the stereographic projection of the
<111>.sub.t/<011>.sub.w cut. Table 5 shows the
electromechanical properties of PMN-PT slivers with thickness
orientation along <111> and width orientations at and near
the <011> orientation. While their coupling constants are
slightly lower than those of the
<001>.sub.t/<010>.sub.w .+-.15 degree and
<011>.sub.t/<110>.sub.w 50-70 degree cuts, the
<111>.sub.t/<011>.sub.w cut's dielectric constants are
2-3 times greater and its velocities are 50% higher than those of
the <001>.sub.t/<010>.sub.w cut. Also, the acoustic
properties of this orientation cut are less sensitive to the width
orientation as shown in Table 5.
[0071] The <111>.sub.t/<011>.sub.w cut offers a much
higher velocity coupled with excellent dielectric properties
compared to those of the PZT-type ceramics or other orientation
cuts of PMN-PT and PZN-PT single crystals. The high velocity (50%
higher for the <111> orientation than in the <001>
orientation) allows the use of thicker crystals which in turn
improves the manufacturability of transducers for high frequency
applications. The high dielectric constant, on the other hand,
permits a design with low electrical impedance which enhances
electrical impedance matching between the transducers and the
electronic circuits.
6TABLE 5 Electromechanical properties of
<111>.sub.t/<011>.sub.w cuts. Clamped Effective
Coupling Dielectric PMN-PT 34% Constant: Velocity: v Constant:
<111>.sub.t/<011>.sub.w cuts k.sub.33' (Sliver)
(mm/.mu.sec) K (1 MHz) <111>.sub.t/<011&- gt;.sub.w 0
degree 0.76 5.0 3050 <111>.sub.t/<011>.sub.- w .+-. 5
degree 0.76 4.9 3050 <111>.sub.t/<011>.sub.w .+-. 10
degree 0.75 4.9 3050
EXAMPLE I
Diagonally Oriented Lead-Based Polycrystalline Materials
[0072] Gentilman disclosed the injection molding method to
fabricate oriented polycrystal PMN-PT and PZN-PT materials from the
<001> oriented single crystal seeds (see Gentilman,
"Processing and Application of Solid State Converted High Strain
Undersea Transmitter Materials," paper presented at the
Piezocrystals Workshop, Arlington, Va., Jan. 18-20, 2000). As with
single crystal materials, polycrystalline-based materials may also
exhibit favorable properties that are determined by their thickness
or width orientations. Using similar methods, polycrystalline
PMN-PT or PZN-PT are partially aligned along the <011> and
<111> directions. Because the single crystals described in
this application which are also oriented along the <011> and
<111> directions possess improved electromechanical
properties over a wide range of angles (up to 15 degrees), the
aligned polycrystalline ceramics may likewise achieve improved
properties comparable to those of similarly oriented single
crystals. Because processing polycrystalline ceramics is cheaper
than growing single crystals, the use of oriented polycrystalline
PMN-PT and PZN-PT, instead of their single-crystal counterparts,
would allow fabrication of transducers at significantly lower cost.
This makes polycrystalline materials attractive for transducer
applications.
[0073] The oriented polycrystalline ceramic is fabricated by mixing
long rods of diagonal oriented single crystal seeds (prepared as
described above using chemical grade PbO, MgO, Nb.sub.2O.sub.5,
ZnO, and TiO.sub.2) with ceramic powder and applying a shear
pressure to align the seeds. The following fabrication methods are
used to align the single crystal seeds: extrusion, injection
molding, tape casting, etc. The sintering process allows the single
crystal seeds to grow into a ceramic matrix that is partially
oriented due to and according to the alignment of the seeds see
FIG. 11. The sintered polycrystalline materials are cut into
<011> or <111> orientations and expected to have
properties similar to those of single crystals. For a reference on
the preparation of a textured polycrystalline material,
specifically Sr.sub.2Nb.sub.2O.sub.7, see Braharmaroutu et al.
Proceedings of the Tenth IEEE International Symposium on
Applications of Ferroelectrics, East Brunswick, N.J., Aug. 18-21,
1996, page 883-886, the contents of which is incorporated in its
entirety into the present application.
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