U.S. patent application number 09/911227 was filed with the patent office on 2003-01-23 for co-fired piezo driver and method of making for a ring laser gyroscope.
Invention is credited to Mortenson, Douglas P., Schober, Christina M., Sittler, Daniel L..
Application Number | 20030015944 09/911227 |
Document ID | / |
Family ID | 25429935 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030015944 |
Kind Code |
A1 |
Schober, Christina M. ; et
al. |
January 23, 2003 |
CO-FIRED PIEZO DRIVER AND METHOD OF MAKING FOR A RING LASER
GYROSCOPE
Abstract
A multi-layer PZT comprises a plurality of stacked ceramic
layers. The stack of ceramic layers includes a top ceramic layer on
which negative and positive contacts for electrically coupling the
PZT to external circuitry are formed. The stack of ceramic layers
also includes at least one negatively poled ceramic layer having a
negative conductive pattern formed thereon and at least one
positively poled ceramic layer having a positive conductive pattern
formed thereon. The PZT also includes a negative pattern
interconnect for electrically connecting the negative contact and
the negative conductive pattern and a positive pattern interconnect
for electrically connecting the positive contact and the positive
conductive pattern. The multi-layer PZT can be fabricated using a
ceramic co-firing process.
Inventors: |
Schober, Christina M.; (St.
Anthony, MN) ; Mortenson, Douglas P.; (Maple Grove,
MN) ; Sittler, Daniel L.; (Hugo, MN) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
25429935 |
Appl. No.: |
09/911227 |
Filed: |
July 23, 2001 |
Current U.S.
Class: |
310/366 |
Current CPC
Class: |
H01L 41/0833 20130101;
H01L 41/0471 20130101 |
Class at
Publication: |
310/366 |
International
Class: |
H01L 041/083 |
Claims
The embodiments of the invention in which an exclusive property or
right is claimed are defined as follows:
1. A multi-layer piezoelectric transducer that can be used as a
path length control apparatus of an optical device, comprising: a
plurality of ceramic layers stacked so as to form a stack, each
ceramic layer having first and second opposing surfaces, said
plurality of ceramic layers including: a top layer at a first end
of the stack having a top conductive pattern formed on the first
surface thereof that comprises a polarity contact and an opposing
polarity contact; at least one poled ceramic layer having a
polarity conductive pattern formed on the first surface thereof; at
least one oppositely poled ceramic layer having a opposing polarity
conductive pattern formed on the first surface thereof; and a
polarity pattern interconnect for electrically connecting each said
polarity conductive pattern and the said polarity contact; and an
opposing polarity pattern interconnect for electrically connecting
the opposing polarity conductive pattern and the opposing polarity
contact.
2. The multi-layer piezoelectric transducer of claim 1, wherein the
plurality of ceramic layers further includes a bottom ceramic layer
at a second end of the stack opposite the first end and having a
conductive pattern formed on the first surface thereof.
3. The multi-layer piezoelectric transducer of claim 1, wherein the
polarity is negative and the opposing polarity is positive and the
poled ceramic layer is negatively poled and the oppositely poled
ceramic layer is positively poled.
4. The multi-layer piezoelectric transducer of claim 3, wherein:
the plurality of ceramic layers includes a plurality of negatively
poled ceramic layers, each of which has a negative conductive
pattern formed on the first surface thereof, and a plurality of
positively poled ceramic layers, each of which has a positive
conductive pattern formed on the first surface thereof; the
plurality of negatively poled ceramic layers and the plurality of
positive ceramic layers are arranged within the stack in an
alternating sequence; the negative pattern interconnect
electrically connects the negative conductive patterns to one
another and to the negative contact; and the positive pattern
interconnect electrically connects the positive conductive patterns
to one another and to the positive contact.
5. The multi-layer piezoelectric transducer of claim 4, wherein the
plurality of ceramic layers includes a same number of negatively
poled ceramic layers as positively poled ceramic layers.
6. The multi-layer piezoelectric transducer of claim 4, wherein:
the stack of ceramic layers has a negative electrode surface and a
positive electrode surface; the negative contact is located
adjacent to the negative electrode surface; each negative
conductive pattern includes a negative electrode located adjacent
to the negative electrode surface; the negative pattern
interconnect includes a first conductive coating formed on at least
a portion of the negative electrode surface so as to electrically
connect the negative contact and the negative electrodes to one
another; the positive contact is located adjacent to the positive
electrode surface; each positive conductive pattern includes a
positive electrode located adjacent to the positive electrode
surface; and the positive pattern interconnect includes a second
conductive coating formed on at least a portion of the positive
electrode surface so as to electrically connect the positive
contact and the positive electrodes to one another.
7. The multi-layer piezoelectric transducer of claim 4, wherein:
the negative pattern interconnect includes: a negative via formed
in the stack so that the negative via passes through the negative
contact and each negative conductive pattern; a negative via
conductor formed on an interior surface of the negative via that
electrically connects the negative contact and each negative
conductive pattern to one another; and the positive pattern
interconnect includes: a positive via formed in the stack so that
the positive via passes through the positive contact and each
positive conductive pattern; a positive via conductor formed on an
interior surface of the positive via that electrically connects the
positive contact and each positive conductive pattern to one
another.
8. The multi-layer piezoelectric transducer of claim 3, wherein
each negative conductive pattern has a shape that is substantially
symmetrical to the shape of each positive conductive pattern.
9. The multi-layer piezoelectric transducer of claim 3, wherein the
top conductive pattern further comprises a floating portion that is
electrically isolated from the negative contact and the positive
contact.
10. The multi-layer piezoelectric transducer of claim 9, wherein
the top conductive pattern has an isolation channel for
electrically isolating the negative contact, the positive contact,
and the floating portion from one another.
Description
TECHNICAL FIELD
[0001] The present invention relates to path length control
apparatus (PLC) for optical devices and in particular to a co-fired
piezoelectric transducer that can be used in a PLC for a ring laser
gyroscope and method of making the same.
BACKGROUND OF THE INVENTION
[0002] A ring laser gyroscope (RLG) is commonly used to measure the
angular rotation of an object, such as an aircraft. Such a
gyroscope has two counter-rotating laser light beams that move
within a closed loop optical path or "ring" with the aid of
successive reflections from multiple mirrors. The closed path is
defined by an optical cavity that is interior to a gyroscope frame
or "block." In one type of RLG, the block includes planar top and
bottom surfaces that are bordered by six planar sides that form a
hexagon-shaped perimeter. Three planar non-adjacent sides of the
block form the mirror mounting surfaces for three mirrors at the
corners of the optical path, which is triangular in shape.
[0003] Operationally, upon rotation of the RLG about its input axis
(which is perpendicular to and at the center of the planar top and
bottom surfaces of the block), the effective path length of each
counter-rotating laser light beam changes and a frequency
differential is produced between the beams that is nominally
proportional to angular rotation. This differential is then
optically detected and measured by signal processing electronics to
determine the angular rotation of the vehicle. To maximize the
signal out of the RLG, the path length of the counter-rotating
laser light beams within the cavity must be adjusted. Thus, RLGs
typically include a path length control apparatus (PLC), the
purpose of which is to control the path length for the
counter-rotating laser light beams for maximum signal.
[0004] One such known PLC 10 for a block 12 of a RLG 14 is
illustrated in FIGS. 1-2. The PLC 10 includes a piezoelectric
transducer (PZT) 16 which is secured to a mirror 18 via an
epoxy-based adhesive 20. The epoxy adhesive 20 completely covers
the interface (defined by a lower surface 22 of the PZT 16 and an
upper surface 24 of the mirror 18) between the PZT 16 and the
mirror 18. The mirror 18 is secured to a mirror mounting surface 26
of the optical block 12. The mirror 18 communicates with laser
bores 32 (only partially shown) of an optical cavity 34 (only
partially shown) of the block 12. The bores 32 partially form a
portion of the closed loop optical path 38 defined by the optical
cavity 34. As seen in FIG. 1, the mirror 18 reflects
counter-rotating laser light beams 40 at its respective corner of
the closed loop optical path 38.
[0005] Conventional PZT 16 (perhaps shown best in FIG. 2) is
defined by a pair of piezoelectric elements 42 and 44. A conductive
tab 45 is sandwiched between the elements 42 and 44, which are
bonded to the conductive tab 45 by thin layers of conductive epoxy.
Opposite polarity conductive tabs 41 and 43 are adhered to the
outer major surfaces of elements 42 and 44, respectively, also by
thin layers of conductive epoxy. The opposite polarity leads 47 and
49 extend from the positive conductive tabs 41 and 43,
respectively. Another lead 48 extends from the negative conductive
tab 45. As shown in FIG. 1, the opposite polarity leads 47 and 49
are electrically connected to form a single lead 46, and the leads
46 and 48 extend from the PZT 16 and are connected to terminals 50
and 52 of a wireboard element 54. Leads 58 and 59 extend from the
terminals 50 and 52, respectively, of the wireboard element 54 and
are coupled to a regulated voltage source (not shown) which is in
turn coupled to a detector (not shown) which monitors the intensity
of the light beams 40. The PZT 16 takes an applied voltage
delivered by the regulated voltage source, in response to a signal
provided by the detector, and turns this voltage into small but
precisely controlled mechanical movement. This mechanical movement
of the PZT 16 affects translational movement (as represented by
double-headed arrow 60) of the mirror 18, and thereby controls the
laser light beam path length.
SUMMARY OF THE INVENTION
[0006] The present invention is a multi-layer PZT fabricated as a
multi-layer ceramic assembly. The multi-layer PZT of the present
invention has contacts, which are electrically connected to other
layers within the multi-layer PZT, formed directly on the top layer
of the PZT, and the regulated voltage source can be coupled
directly to the PZT at the top layer contacts. The present
invention is a multi-layer piezoelectric transducer that can be
used as a path length control apparatus of an optical device. The
multi-layer piezoelectric transducer includes a plurality of
ceramic layers so as to form a stack, wherein each ceramic layer
has first and second opposing surfaces. The plurality of ceramic
layers includes a top layer at a first end of the stack having a
top conductive pattern formed on the first surface thereof. The top
conductive pattern includes a negative contact and a positive
contact. The plurality of ceramic layers also includes at least one
poled ceramic layer having a conductive pattern formed on the first
surface thereof. The plurality of ceramic layers include additional
poled ceramic layers having alternating conductive patterns formed
on the first surface thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a sectional view of a portion of a prior art path
length control apparatus for a ring laser gyroscope incorporating a
prior art piezoelectric transducer.
[0008] FIG. 2 is an isometric view of the prior art piezoelectric
transducer shown in FIG. 1.
[0009] FIG. 3 is an isometric view of a second embodiment of a
multi-layer piezoelectric transducer according to the present
invention.
[0010] FIG. 4 is a cross-sectional view of the multi-layer
piezoelectric transducer of FIG. 3 taken along the line 8-8.
[0011] FIG. 5 is a top, plan view of the top conductive pattern of
the multi-layer piezoelectric transducer of FIG. 3.
[0012] FIG. 6 is a top, plan view of the negative conductive
pattern of the multilayer piezoelectric transducer of FIG. 3.
[0013] FIG. 7 is a top, plan view of the positive conductive
pattern of the multilayer piezoelectric transducer of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0014] A multi-layer PZT 200 is shown in FIGS. 3-4 and can be used
as a path length control apparatus of an optical device. PZT 200
comprises a stack 202 of circular ceramic layers that includes a
top ceramic layer 204 at a first end of the stack 202 and
alternating negative ceramic layers 206 and positive ceramic layers
208. At the second end of the stack 202 opposite the first end is a
bottom ceramic layer 209, which, as described below, may be a
negative ceramic layer, a positive ceramic layer, or a
substantially unpoled ceramic layer. Although the PZT 200 is shown
in FIGS. 3-4 as having two negative ceramic layers 206 and one
positive ceramic layers 208, it is to be understood that the PZT
200 can be fabricated with any number of negative ceramic layers
206 and positive ceramic layers 208. The ceramic layers of the
stack 202 typically have dimensions that are similar to the
dimensions of the ceramic layers of PZT 100 described above.
[0015] The top ceramic layer 204 has a top conductive pattern 210
(perhaps shown best in FIG. 5) formed on an upper surface thereof,
each negative ceramic layer 206 has a negative conductive pattern
212 (shown in FIG. 6) formed on an upper surface thereof, and each
positive ceramic layer 208 has a positive conductive pattern 214
(shown in FIG. 7) formed on an upper surface thereof. As explained
in detail below, the bottom ceramic layer 209 has either a negative
conductive pattern 212 or a positive conductive pattern 214 formed
on an upper surface thereof.
[0016] Negative castilation 226 that covers the side of the stack
202 is formed nearside edge 228. A negative contact 216 (described
below) that is formed in the top conductive pattern 210, the
negative conductive patterns 212, and the negative castilation 226
are shaped and located so that the negative castilation 226
intercontacts the negative contact 216 of the top conductive
pattern 210 and each of the negative conductive patterns 212.
Positive castilation 230 that connects to each layer of the stack
202 are formed on a second side edge 232. A positive contact 218
(described below) that is formed in the top conductive pattern 210,
the positive conductive patterns 214, and the positive castilation
230 are shaped and located so that the positive castilation 230
interconnects the positive contact 218 of the top conductive
pattern 210 and each of the positive conductive patterns 214.
[0017] The top conductive pattern 210 (perhaps shown best in FIG.
5) includes a negative contact 216 and a positive contact 218. In
the embodiment shown, the negative contact 216 has a generally
semicircular shape with the circular periphery near the first side
edge 228. The positive contact 218 is generally cresent-shaped. The
negative contact 216 and the positive contact 218 are separated and
electrically isolated from each other by a channel 224 formed in
the top conductive pattern 210 in which no conductive material is
applied. The negative and positive contacts 216 and 218 serve as
terminals to which a regulated voltage source (not shown) of an
optical device such as a RLG can be coupled to the PZT 200
[0018] The negative conductive pattern 212, shown in FIG. 6, is
generally circular except for a crescent-shaped cutout portion 238
near the second side edge 232 in which no conductive material is
present. The negative castilation 226 connects to the negative
conductive pattern 212 so that the conductive coatings of the
negative pattern castilation (shown in FIG. 4) formed on the
surfaces of the stack 202 near side 228 can electrically connect
the negative conductive pattern 212 to the other negative
conductive patterns 212 and the negative contact 216. The positive
castilation 230 connects to the positive conductive pattern 214 so
that the conductive coatings of the positive pattern castilation
(shown in FIG. 4) formed on the surfaces of the stack 202 near side
232 can electrically connect the positive conductive pattern 214 to
the other positive conductive patterns 214 and the positive contact
218. The negative conductive pattern 212 does not extend to the
peripheral edge of the negative ceramic layer 206 and instead a
channel 240 separates and electrically isolates the rest of the
negative conductive pattern 212 from the peripheral edge of the
negative ceramic layer 206. Preferably, all the negative conductive
patterns 212 formed on ceramic layers of the stack 202 have
substantially the same shape.
[0019] The positive conductive pattern 214, shown in FIG. 7, is
generally circular except for a crescent-shaped cutout portion 242
near the first side edge 228 in which no conductive material is
present. The positive castilation 230 connects to the positive
conductive pattern 214 so that the conductive coatings of the
positive pattern castilation (shown in FIG. 4) formed on the
surfaces of the stack 202 near side 232 can electrically connect
the positive conductive pattern 214 to the other positive
conductive patterns 214 and the positive contact 218. The negative
castilation 226 connects to the negative conductive pattern 212 so
that the conductive coatings of the negative pattern castilation
(shown in FIG. 4) formed on the surfaces of the stack 202 near side
228 can electrically connect the negative conductive pattern 212 to
the other negative conductive patterns 212 and the negative contact
216. The positive conductive pattern 214 does not extend to the
peripheral edge of the positive ceramic layer 208 and instead a
channel 244 separates and electrically isolates the rest of the
positive conductive pattern 214 from the peripheral edge of the
positive ceramic layer 208. Preferably, the positive conductive
patterns 214 formed on ceramic layers of the stack 202 are all
substantially the same. Also, it is preferable that the positive
conductive patterns 214 are mirror images of, and have
substantially the same shape as, the negative conductive patterns
212 so that the bending imparted to the PZT 200 by each of the
positive ceramic layers 208 is symmetrical to the bending imparted
to the PZT 200 by each of the negative ceramic layers 206.
[0020] If the ceramic layer immediately adjacent the bottom ceramic
layer 209 is a negative ceramic layer 206 having a negative
conductive pattern 212 formed thereon (as shown in FIGS. 3-4), then
preferably the bottom ceramic layer 209 has a positive conductive
pattern 214 formed on an upper surface thereof so that a voltage
can be developed across the immediately adjacent negative ceramic
layer 206 when a volt age is developed across the negative and
positive contacts 216 and 218. Likewise, if the ceramic layer
immediately adjacent the bottom ceramic layer 209 is a positive
ceramic layer 208 having a positive conductive pattern 214 formed
thereon, then preferably the bottom ceramic layer has a negative
conductive pattern 212 formed on an upper surface thereof so that a
voltage can be developed across the immediately adjacent positive
ceramic layer 208 when a voltage is developed across the negative
and positive contacts 216 and 218.
[0021] The bottom ceramic layer 209 can be formed as an unpoled
ceramic layer (as shown in FIGS. 3-7). The bottom surface 211 of
such an unpoled bottom ceramic layer 209 need not have a conductive
pattern formed thereon. This allows a better epoxy bond to be
formed between the bottom surface 211 of the PZT 200 and the
optical device to which the PZT 200 is being attached. But, such an
unpoled ceramic layer 209 that does not have a conductive pattern
formed on its bottom surface 211 will not apply a bending force to
the PZT 200 upon application of a voltage to the negative and
positive contacts 216 and 218 and instead will resist the bending
force provided by the negative and positive ceramic layers 206 and
208.
[0022] Alternatively, the bottom ceramic layer 209 can be formed as
a poled ceramic layer. If the poled bottom ceramic layer 209 in
such an embodiment has a positive conductive pattern 214 formed on
the upper surface thereof, preferably the bottom surface 211 of
such a poled bottom ceramic layer 209 would have a negative
conductive pattern 212 (connected to the other negative conductive
patterns 212) formed thereon so that a voltage can be developed
across the bottom ceramic layer 209 during the poling step.
Likewise, if the poled bottom ceramic layer 209 has a negative
conductive pattern 212 formed on the upper surface thereof,
preferably the bottom surface 211 of such a poled bottom ceramic
layer 209 would have a positive conductive pattern 214 (connected
to the other positive conductive patterns 214) formed thereon so
that a voltage can be developed across the bottom ceramic layer 209
during the poling step. In operation, a poled bottom ceramic layer
209 will apply a bending force to the PZT 200 upon application of a
voltage to the negative and positive contacts 216 and 218 and will
not resist the bending force provided by the negative and positive
ceramic layers 206 and 208. However, the epoxy bond that would be
formed between the conductive pattern formed on the bottom surface
211 of the bottom ceramic layer 209 and the optical device would be
less secure.
[0023] The negative and positive ceramic layers 206 and 208 (along
with the bottom ceramic layer 209 if the bottom ceramic layer 209
is to be poled) can be poled at the same time by applying an
appropriate voltage across the negative castilation 226 (which is
in electrical contact with the negative conductive patterns 212)
and the positive castilation 230 (which is in electrical contact
with the positive conductive patterns 214) in the same manner that
the ceramic layers of PZT 100 are poled. Also, as with PZT 100, to
improve the bending symmetry of PZT 200, it is preferred that the
amount of the top ceramic layer 204 that is poled during the poling
step is reduced.
[0024] Negative and positive leads from external circuitry such as
a regulated voltage source (not shown in FIGS. 3-7) can be
connected to the negative and positive contacts 216 and 218,
respectively.
[0025] The PZT 200 shown in FIGS. 3-7 can be used as a PLC in an
optical device such as a RLG. A regulated voltage source and/or
other circuitry can be coupled to the contacts 120 and 122 of PZT
100 and the contacts 216 and 218 of PZT 200. Thus, a wireboard
element need not be attached to a PZT according to the present
invention in order to provide a point at which a regulated voltage
source or other circuitry can be coupled to the PZT. The regulated
voltage source can be used to apply a voltage to the multi-layer
PZT, which turns this voltage into small but precisely controlled
mechanical movement in order to maintain a constant light path
length in an optical device such as a RLG.
[0026] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the scope of the invention. For example, the number
of layers used and the shape of the final PZT can be varied to suit
the particular application for which the PZT is fabricated.
* * * * *