U.S. patent application number 10/079946 was filed with the patent office on 2002-11-28 for process for the manufacture of piezoceramic multilayer actuators.
Invention is credited to Bindig, Reiner, Schmidt, Jurgen, Schreiner, Hans-Jurgen, Simmerl, Matthias.
Application Number | 20020175591 10/079946 |
Document ID | / |
Family ID | 26008582 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020175591 |
Kind Code |
A1 |
Schreiner, Hans-Jurgen ; et
al. |
November 28, 2002 |
Process for the manufacture of piezoceramic multilayer
actuators
Abstract
For the manufacture of multilayer actuators, the laminate is
split into several actuators, which are pyrolized and then
sintered. Because lamination in the unsintered body often produces
non-homogeneity in the density, and the shrinkage during the firing
of the ceramic is not of a constant value, the final geometry of
the actuators can only be accurately obtained by the hardening of
the sintered actuators. But in this case the internal electrode
layers deposited in the actuators are thereby also processed, which
can cause electrical flashovers and leakage currents during
operation. Thus, according to the invention, a procedure is
provided in which the block of the stacked green films provided
with internal electrodes is laminated, that at least one actuator
is separated from the block, that the actuator obtains its shape by
means of a machining operation, that it is then sintered, that the
sinter skin produced by the sintering is used as an insulating
layer and that the sinter skin is abraded at the points where the
internal electrodes are connected to the external electrodes.
Inventors: |
Schreiner, Hans-Jurgen;
(Neunkirchen am Sand-Rollhofen, DE) ; Bindig, Reiner;
(Binlach, DE) ; Simmerl, Matthias; (Henfenfeld,
DE) ; Schmidt, Jurgen; (Marktredwitz, DE) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
666 FIFTH AVE
NEW YORK
NY
10103-3198
US
|
Family ID: |
26008582 |
Appl. No.: |
10/079946 |
Filed: |
February 20, 2002 |
Current U.S.
Class: |
310/311 ;
29/25.35; 310/365 |
Current CPC
Class: |
H01L 41/335 20130101;
Y10T 156/1056 20150115; Y10T 156/1057 20150115; H01L 41/0835
20130101; H01L 41/273 20130101; Y10T 29/42 20150115 |
Class at
Publication: |
310/311 ;
29/25.35; 310/365 |
International
Class: |
H04R 017/00; H01L
041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2001 |
DE |
101 08 314.9 |
Feb 12, 2002 |
DE |
102 05 928.4 |
Claims
1. Process for the manufacture of piezoelectric multilayer
actuators, in which thin layers made from a piezoceramic material,
termed green films, onto which at least one internal electrode is
placed, are stacked one above the other into a block, so that the
internal electrodes are led out alternately at opposing faces of
the actuator, where they are interconnected by an external
electrode, characterised in that the block is laminated, that at
least one actuator is separated from this block, that the actuator
obtains its shape by means of a machining operation, that it is
then sintered, that the sinter skin produced by the sintering is
used as an insulating layer and that the sinter skin is abraded at
the points where the internal electrodes are connected to the
external electrodes.
2. Process according to claim 1, characterised in that the shaping
is achieved by machining.
3. Process according to claim 1 or 2, characterised in that
multilayer actuators, which have square, polygonal, circular or
elliptical cross-sectional areas, are produced by the shaping.
4. Process according to claim 1 or 2, characterised in that
rotationally symmetric multilayer actuators are produced by the
shaping.
5. Process according to one of claims 1 to 4, characterised in that
one or more through-holes or pocket holes are introduced into the
laminated block of at least one multilayer actuator.
6. Process according to one of claims 1 to 4, characterised in that
prior to lamination, holes of the required size, shape and number
are punched in the green films and the green films provided with
the internal electrodes are then stacked one on top of the other in
the required number and arrangement, so that the boreholes or
pocket holes are produced in the desired arrangement and depth.
7. Process according to one of claims 5 or 6, characterised in that
a thread is machine-cut in the boreholes or in the pocket holes,
respectively.
8. Process according to one of claims 5 to 7, characterised in that
to increase stability and to maintain dimensional accuracy, the
borehole or the pocket holes in the multilayer actuators can be
filled prior to lamination with a filler.
9. Process according to claim 8, characterised in that a hard,
dimensionally stable and, during lamination, thermally stable
material, is used as a filler.
10. Process according to claim 8 or 9, characterised in that a
filler made from metal or ceramic or another hard, dimensionally
stable and, during lamination, thermally stable, material is
used.
11. Process according to claim 8, characterised in that a plastic
or thermoplastic material is used as a filler.
12. Process according to claim 11, characterised in that a
highly-flexible rubber or a rubber-like plastic is used.
13. Process according to one of claims 8 to 12, characterised in
that the filler is used in the form of pins or threaded pins.
14. Process according to claim 13, characterised in that following
lamination, the pins or threaded pins are withdrawn or unscrewed
from the laminate.
15. Process according to claim 8, characterised in that a filler is
used that remains dimensionally stable approximately up to the
lamination temperature and is thermally removed.
16. Process according to claim 15, characterised in that a wax or a
low-melting-point polymer is used as a filler, and that these
fillers smelt during lamination or sintering.
17. Process according to claim 15, characterised in that a suitable
organic material that pyrolizes without residues during lamination
or sintering is used as a filler.
18. Process according to claim 15, characterised in that the
thermal removal is achieved by smelting and/or thermal
decomposition in a thermal process preceding sintering, for example
an appropriate debonding process.
Description
[0001] The invention concerns a process for the manufacture of
piezoceramic multilayer actuators according to the preamble of the
first claim.
[0002] A piezoceramic multilayer actuator 1 is shown schematically
in FIG. 1. The actuator consists of stacked thin layers 2 of
piezoelectrically active material, for example lead zirconate
titanate (PZT), with conductive internal electrodes 3, which are
led out alternately to the surface of the actuator, disposed
between said layers. External electrodes 4, 5 interconnect the
internal electrodes 3. As a result, the internal electrodes 3 are
electrically connected in parallel and combined into two groups.
The two external electrodes 4, 5 are the connecting poles of the
actuator 1. They are connected via the connections 6 to a voltage
source, not shown here. If an electrical voltage is applied via the
connections 6 to the external electrodes 4, 5, this electrical
voltage is transmitted in parallel to all internal electrodes 3 and
produces an electric field in all layers 2 of the active material,
which is consequently mechanically deformed. The sum of all of
these mechanical deformations is available at the end faces of the
head region 7 and the foot region 8 of the actuator 1 as a useable
expansion 9 and/or force.
[0003] Piezoceramic multilayer actuators are fabricated according
to the prior art as monoliths, that is to say the active material
onto which internal electrodes are deposited by a silk screen
process prior to sintering, is disposed as a so-called green film
in successive layers as a stack that is compressed into a green
body. The compression of the green body is usually carried out by
lamination under the action of pressure and temperature in
laminating moulds. Depending on the lamination tool used, this
process determines to a large extent the external shape of the
actuators. The laminate is separated into several actuators, which
are pyrolized and then sintered. Since lamination in the unsintered
body often produces non-homogeneity in the density, and the
shrinkage during the firing of the ceramic is not of a constant
value, the final required geometry of the actuators can only be
accurately obtained by the hardening of the sintered actuators.
However, in this case the internal electrode layers deposited in
the actuators are thereby also processed. If the processed surfaces
are not subsequently electrically insulated, then when these
piezoceramic multilayer actuators are actively operated, there is a
risk of an electrical flashover at the actuator surface because the
dielectric field strength in air, which amounts to approximately
1000 V/mm, is exceeded by the operating field strengths of over
2000 V/mm. At the same time the smearing of the electrodes caused
by the hardening additionally leads to reduced dielectric strength
and/or leakage currents.
[0004] The object of the present invention is to present a process
that simplifies the manufacture of multilayer actuators and by
which the demonstrated disadvantages are avoided.
[0005] This object is achieved by means of the characterising
features of the first claim. Advantageous developments of the
invention are claimed in the sub-claims.
[0006] By stacking green films made of piezoceramic material, which
are printed with the corresponding patterns of the internal
electrodes for at least one piezoceramic multilayer actuator and by
corresponding lamination under pressure of around 100 bar at a
temperature of approximately 120.degree. C., a green body is
obtained with high mechanical strength, good adhesion between film
layers, good mechanical machinability and homogeneous density.
According to the invention, it is therefore possible to easily
detach the multilayer actuators from such a green body as a
laminate and subsequently by machining to yield their shape, which
is usually already the final shape, so that after sintering the
actuators require no further finishing. The insulating sinter skin
needs only to be removed at the connecting faces where the internal
electrodes have to be connected to the respective external
electrode, for example by grinding. Due to the high mechanical
strength of the laminate blocks, all machining operations, such as
turning, milling, sawing, drilling or grinding are possible. In
this case the bodies are neither damaged nor deformed. Due to the
lower hardness of the material compared to the sintered state, tool
wear is considerably reduced, thus making low-cost production
possible.
[0007] Due to sintering, a so-called sinter skin forms all over the
surface of the piezoceramic multilayer actuator, which sinter skin
has such a high electrical insulating capability, even in the
region where the internal electrodes emerge at the surface of the
actuator, that subsequent insulation of the surfaces of the
piezoceramic multilayer actuator can usually be omitted.
[0008] Through suitable choice and/or combination of machining
methods, the good machinability of the laminate enables
piezoceramic multilayer actuators to be manufactured with different
shapes. The cross-sectional areas can be circular, elliptical,
square or polygonal. All edges of the green bodies can be broken,
chamfered or rounded off prior to sintering. The ease of machining
of the ceramic material in the green phase also enables
rotationally symmetric mouldings to be produced.
[0009] The laminated block with the at least one multilayer
actuator has a high strength and a high dimensional stability. It
is thus possible, prior to sintering, to place several boreholes or
pocket holes in the block and/or the unsintered piezoceramic
multilayer actuator, which can additionally be provided with a
thread. Such an arrangement can be advantageous for subsequent
applications, such as fixings or connections. Since the layers of
the internal electrodes are penetrated by the boreholes or pocket
holes as well as by the mahine-cut thread, in this case the sinter
skin produced by sintering can also be advantageously used as an
insulating layer.
[0010] A further option for shaping the multilayer actuators
consists in punching holes of the required size, shape and number
in the green films in the same operating cycle, prior to
lamination, in which the green films are suitably punched out for
the laminating mould. The green films with the printed internal
electrodes thereon are then stacked one on top of the other in the
required number and arrangement, so that the boreholes or pocket
holes are produced in the desired arrangement and depth. Here
again, threads can be machine-cut in the holes following
lamination.
[0011] To increase stability and to maintain dimensional accuracy,
the boreholes, through-holes or pocket holes can be filled prior to
lamination with a filler which prevents any plastic deformation of
the recesses which otherwise may occur during lamination. This
filler is chosen so that under lamination conditions it is not more
plastic or cannot be deformed to a greater degree than the
piezoceramic material of the green films.
[0012] A filler may consist of a hard, dimensionally stable and,
during lamination, thermally stable material, for example metal or
ceramic. According to the shaping, pins or threaded pins can be
inserted into the boreholes or pocket holes.
[0013] Furthermore, plastic or thermoplastic fillers, in particular
a highly-flexible rubber or rubber-like plastic, are suitable. Here
too the filler can have the form of a pin or threaded pin.
[0014] Following lamination, the pins or threaded pins are
withdrawn or unscrewed from the laminate.
[0015] Fillers which remain dimensionally stable up to the
lamination temperature are also suitable. During lamination or
sintering these fillers smelt or pyrolize. For example, wax or
low-melting-point polymers can be removed from the laminate by
heating. A suitable organic material can also be used as a filler,
such as is known from the prior art for forming porous ceramics,
for example carbon black or a polymer that pyrolizes without
residues during lamination or sintering at temperatures up to
700.degree. C.
[0016] The thermal removal may also be achieved by melting out
and/or thermal decomposition in a thermal process preceding
sintering, for example an appropriate debonding process.
[0017] The invention is explained in further detail with the aid of
an exemplifying embodiment in which:
[0018] FIG. 2 shows a green film with several internal electrodes,
and
[0019] FIG. 3 shows a multilayer actuator manufactured according to
the process according to the invention.
[0020] FIG. 2 shows a green film 10 made of piezoceramic material
already punched out for the laminating mould. Six internal
electrodes 11 are each placed on this green film, this application
usually being achieved by the silk screen process. The assignment
of several internal electrodes to one green film allows the
efficient manufacture of several multilayer actuators at the same
time. On one side of the circular cross-sectional area 12, a
circular section is cut out so that the area is limited by a secant
13. A hole 15 is punched out concentrically to the mid-point
14.
[0021] The required numbers of green films are stacked one above
the other to form a block, so that the internal electrodes lie one
above the other. The number of films depends on the size of the
multilayer actuator. In the present exemplifying embodiment, the
block has six multilayer actuators. Due to the ease of separation,
following lamination, the multilayer actuators, still in the green
state, are separated from each other around the internal
electrodes. Likewise still in the green state, the final machining
of the multilayer actuators can then take place until the specified
basic diameter of the multilayer actuator is obtained. Only after
this are the multilayer actuators sintered.
[0022] The arrangement of the internal electrodes 11 on the green
film 10 always has the same orientation. These are internal
electrodes of the same polarity. The internal electrodes of the
opposite polarity can be fabricated in the same way. In this case,
however, their orientation is opposite to the orientation of the
internal electrodes of opposite polarity assigned to them, that is
to say rotated by 180 degrees on the subsequent green film. The
electrode layers with the opposite polarity therefore alternate. In
a block which shows the contour of a multilayer actuator, the holes
15 lying one above the other form a continuous recess.
[0023] A multilayer actuator 16 that has been manufactured
according to the process according to the invention is shown in a
schematic, much enlarged representation in FIG. 3. It has a
circular cross-section 12 and is fully coated by a sinter skin 17.
The internal electrodes 11 of the same polarity are fully exposed
on the peripheral face, whereas in the case of the internal
electrodes of opposite polarity the circumference is broken because
of the missing circular section. This design is advantageously
utilised to connect the internal electrodes of the same polarity to
the respective external electrode 18, at the opposite sides of the
multilayer actuator where the internal electrodes of the same
polarity can now be seen at the periphery. The sinter skin 17 is
removed in this region by grinding, and the internal electrodes 11
are exposed at their peripheral face. A continuous recess 20,
formed from the holes 15 lying one above the other in the green
films 10, which can be used for fixing purposes, runs
concentrically to the axis 19 of the multilayer actuator 16.
* * * * *