Field of Technology

The present invention relates to a piezoelectric actuator for ink jet printing heads. In particular, this invention relates to the improvement of such piezoelectric actuators and the fabrication process of a ceramic component as a multi element panel to increase the manufacturing yield and the efficiency. Thus, there is proposed a piezoelectric actuator for ink jet printing heads, the piezoelectric actuator comprising a ceramic base plate and a series of oblong, parallel orientated piezoelectric ceramic actuator cuboids bonded to a contact face of the ceramic base plate. The piezoelectric ceramic actuator cuboids comprise metallization layers at their cuboid base corners that are located on front and rear ends of each actuator cuboid . The ceramic base plate comprises on its contact face at least two contact areas that are located in approximately the distance of the actuator cuboid base corners and that are coated with a contact metallization layer. The piezoelectric ceramic actuator cuboids are contacted with the metallization layers of their base corners to the contact metallization layers of the contact face of the ceramic base plate.

Technical background

Some ceramic composites are composed of two different ceramic materials, one being a piezoelectric ceramic, the other a conventional ceramic material as a supporting element, for example Thomit 600, and include a direct electrical connection along the edge of the supporting element. Such components are predominantly printing head assemblies. However, they can be used in other applications too. In a first fabrication step the metallization on the surface and the edge of the supporting element is applied . Secondly the metalized surface is patterned with resist in the image of the desired layout, followed by protecting the metalized edges with resist. Then the metallization is etched away, the resist removed, there re- mains the desired layout on the surface of the ceramic supporting element with a patterned metallization and metalized edges. Then, one supporting element of any particular layout type with a metalized edge is assembled into a circuitry by combining one supporting element with a piezoelectric ceramic to form a composite. The composite is glued together by pressure with an adhesive to achieve bonding .

Related prior art

A typical ink jet array and method of producing the same is known from the European patent EP 0 706 887 Bl . Such an ink jet array is provided with a piezoelectric member in the form of a plate 20* opposite a duct plate 3* (see Fig. 1 that corresponds with Fig . 9 taken from EP 0 706 887 Bl and revised). The surface of the duct plate 3* that faces the piezoelectric member 20* is provided with a number of parallel elongated ink ducts 4*. The ink ducts 4* are covered with an elastic cover layer 2*. The piezoelectric member 20* is provided with a number of elongated parallel piezoelectric elements 23* that are substantially rectangular in cross section. Each piezoelectric element 23* is situated opposite an ink duct 4* such that the elastic cover layer 2* is situated between the ink ducts 4* and the piezoelectric elements 23*. When triggered by the supply of a control current, the associated piezoelectric element 23* (the middle element shown in Fig. 1) expands such that the part of the cover layer 2* that extends over this particular piezoelectric element 23* is forced into the associated ink duct 4* and a portion of the ink in this ink duct 4* is ejected in the form of a drop via a jet opening 31* at the front of the ink duct 4*. Separating strips 24* provided between the piezoelectric element 23* prevent the piezoelectric element 23* from adhering to each other.

According to EP 0 706 887 Bl (see there: column 3, lines 25-33 and 41-49), the piezoelectric actuator 18* is constructed from of a preferably ceramic support layer 19* and a plate 20* of piezoelectric material stuck to the top surface thereof, the plate 19* projecting from the plate 20* at one end. This top surface, which faces the plate 20*, is covered with a thin metal layer. The piezoelectric actuator 18* is fixed into a recess of a baseplate; then, the baseplate is fixed in a suitable processing machine for the formation of a number of slots extending parallel to one another in the longitudinal direction of the piezoelectric member. The slots extend through the plate 20* and over a short distance in the plate 19* in such a manner that the plate 20* is divided into a large number of piezoelectric elements 23* separated from one another by slots or incisions 22*.

Figure 2 shows diagrammatic views of a piezoelectric actuator produced according to a conventional method in the production of ink jet printing heads. In order to directly compare this prior art with the actual invention as claimed, the reference numbers assigned to the features of this prior art piezoelectric actuator are the same as for the inventive piezoelectric actuator. In more detail, Fig . 2A shows a first cross section through a piezoelectric ceramic actuator cuboid 3 of a piezoelectric actuator 1 with a number of piezoelectric ceramic actuator cuboids 3 located on a contact face 4 of a ceramic base plate 2 as known from prior art. The series of oblong, parallel orientated piezoelectric ceramic actuator cuboids 3 comprises metallization layers 5 at its front and rear ends 7,7', the metallization layers 5 reaching around the cuboid base corners 6,6'. The piezoelectric ceramic actuator cuboid 3 is bonded to the contact face 4 of the ceramic base plate 2 with an adhesive 18. The contact face 4 of the ceramic base plate 2 comprises contact areas 8,8', which are covered with contact metallization layers 9,9'. These at least two contact areas 8,8' are located in approximately the distance of the actuator cuboid base corners 6,6'. In consequence, the piezoelectric ceramic actuator cuboids 3 are contacted with the metallization layers 5 of their base corners 6,6' to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plate 2; thus, electrical contacts are provided for each individual piezoelectric ceramic actuator cuboid 3.

The method of fabricating such a composite comprises providing one supporting element (a ceramic base plate 2) with a patterned surface and a metalized edge. Also provided is one piezoelectric ceramic plate 11 with metalized edges. The composite is built by bonding the supporting element and the piezoelectric ceramic using an adhesive. When this composite is bonded and cut, the front and rear base corners 12,12' of the piezoelectric ceramic plate 11 become the cuboid base corners 6,6'. Fig . 2B shows a second cross section through a separation cut 13 between two piezoelectric ceramic actuator cuboids 3 located on a contact face 4 of a ceramic base plate 2 as known from prior art. As it can be clearly seen here, the separation cut 13 reaches through the piezoelectric ceramic actuator cuboids 3, the adhesive 18, and the ceramic base plate contact face 4 with their contact metalliza- tion layers 9,9'. At the front edge of the ceramic base plate 2, a non-cut metallization layer portion 15 is visible. This non-cut metallization layer portion 15 provides a common electrical connection for the piezoelectric ceramic cuboids 3 that are individually activatable over residual strip conductors 16 of the rear end contact metallization layer 9' on the ceramic base plate contact face 4.

Fig . 2C shows a front view of the piezoelectric actuator 1 shown in the Figs. 2A and 2B. The cross-sections according to Fig. 2A and Fig. 2B are indicated by the double arrows I and II respectively. Here, the separation cuts 13 are depicted as voids between the oblong, parallel orientated piezoelectric ceramic actuator cu- boids 3. These voids correspond with the slots or incisions 22* as disclosed in the prior art document EP 0 706 887 Bl . Here, separating strips 24*, which can be provided between the piezoelectric elements 23* to prevent the piezoelectric elements 23* (or piezoelectric ceramic actuator cuboids 3) from adhering to each other, are not shown.

By applying a corresponding manufacturing strategy, individual fingers of such a composite are achieved by sawing completely through the piezoelectric ceramic and partially into the supporting ceramic. All individual fingers of the composite will have a common connection along the edge of the supporting ceramic but are electrically isolated otherwise. However, in a single element process as just described, several problems arise:

1. Every single element must be fabricated individually. Such a process is time consuming and generates high manufacturing costs. 2. In the course of cutting supporting elements to the desired size (due to sawing or other means) sharp edges can arise. This greatly reduces the electrical conductivity over the edge or in the worst case the required common connection over the edge may not be achieved.

3. In response to this problem, edges can be smoothed away. As stated previously, in a single element process this technique must also be applied to every single element and thus produces additional manufacturing costs.

4. When a liquid photo resist is used as a mask to pattern the metalized element, due to the roughness and the high differences of the ceramic surface, the applied metallization may not be properly masked and therefore etched away by the etchant.

5. Polishing the surfaces of the elements is not possible, because a certain roughness is necessary for a good electrical and mechanical contact between the two elements bonded together.

Objects and summary of the present invention

It is an object of the present invention to provide a piezoelectric actuator for ink jet printing heads and a respective manufacturing method that reduce the drawbacks known from prior art and allows for an improvement of the fabrication proc- ess of a ceramic component as a multi element panel with increased manufacturing yield and efficiency.

This object is achieved according to a first aspect in that a piezoelectric actuator for ink jet printing heads is provided . The piezoelectric actuator comprises:

(a) a ceramic base plate, the ceramic base plate comprising on a contact face at least two contact areas that are located in approximately the distance of actuator cuboid base corners and that are coated with a contact metallization layer;

(b) a series of oblong, parallel orientated piezoelectric ceramic actuator cuboids that are located on the contact face of the ceramic base plate; the piezoelectric ceramic actuator cuboids:

- comprising metallization layers at their cuboid base corners that are located on front and rear ends of each actuator cuboid; - being separates, divided by separation cuts from a piezoelectric ceramic plate that is bonded to the ceramic base plate contact face; and

- being contacted with the metallization layers at their base corners to the contact metallization layers of the contact face of the ceramic base plate.

The piezoelectric actuator according to the present invention is characterized :

- in that the ceramic base plate comprises in its contact face a groove with a bottom; the groove, which extends below the piezoelectric ceramic actuator cuboids and over the entire length of the piezoelectric actuator, and at least one adjacent base plate contact face being coated with that one of the contact metallization layers to which the front actuator cuboid base corners are contacted;

- and in that each separation cut reaches through the piezoelectric ceramic actuator cuboids and the ceramic base plate contact face with their contact metallization layers, but without reaching the bottom of the groove, leaving therefore in the groove a non-cut contact metallization layer portion that provides a common electrical connection for the piezoelectric ceramic cuboids, which are individually activatable over residual strip conductors of the rear end contact metallization layer on the ceramic base plate contact face. This object is achieved according to a second aspect in that a method of producing piezoelectric actuators for ink jet printing heads is proposed. The piezoelectric actuator comprises a ceramic base plate and a series of oblong, parallel orientated piezoelectric ceramic actuator cuboids that are located on a contact face of the ceramic base plate. The piezoelectric ceramic actuator cuboids comprise metalliza- tion layers at their cuboid base corners that are located on font and rear ends of each actuator cuboid. The ceramic base plate comprises on its contact face at least two contact areas that are located in approximately the distance of the actuator cuboid base corners and that are coated with a contact metallization layer. The piezoelectric ceramic actuator cuboids are contacted with the metallization layers of their base corners to the contact metallization layers of the contact face of the ceramic base plate.

The method of producing piezoelectric actuators according to the present invention is characterized in that the method comprises the steps of: (a) forming in the contact face of the ceramic base plate a groove with a bottom, which groove extends below the piezoelectric ceramic actuator cuboids and over the entire length of the piezoelectric actuator;

(b) coating the groove and at least one adjacent base plate contact face with

that one of the contact metallization layers to which the front actuator cuboid base corners are to be contacted;

(c) dividing by separation cuts the piezoelectric ceramic actuator cuboids from a piezoelectric ceramic plate that is bonded to the ceramic base plate contact face; each separation cut reaching through the piezoelectric ceramic actuator cuboids and the ceramic base plate contact face with their contact metallization layers, but without reaching the bottom of the groove; and

(d) providing a common electrical connection for the piezoelectric ceramic cuboids that are individually activatable over residual strip conductors of the rear end contact metallization layer on the ceramic base plate contact face by leaving a non-cut contact metallization layer portion in the groove.

Additional and inventive elements are defined in and result from the dependent claims. Advantages of the present invention include :

The provision of a groove or "blind channel" for establishing a common electrical connection for the piezoelectric ceramic cuboids allows for the multi component production of piezoelectric actuators, because all contact metallization layers on the ceramic base plate are located on or in its contact face. Using a multi element process, a fabrication method with better yield and improved efficiency is provided; the average yield has been increased from 65% to 95%.

Using the multi element process, dry film resists can be used for masking the applied metallization of the panel by hot roll lamination. Dry films generally have increased film thickness and mask the peaks in the ceramic material much better than liquid resists. Brief description of the drawings

The present invention is described in more details with the help of the attached schematic drawings, which show preferred exemplary embodiments of the present invention without limiting its scope. It is shown in :

Fig . l a revised Fig . 9 of the prior art document EP 0 706 887 Bl, explaining the construction and function principle of a piezoelectric actuator for ink jet printing heads; diagrammatic views of a piezoelectric actuator produced according a conventional method, wherein :

Fig . 2A shows a first cross section through a piezoelectric ceramic actuator cuboid located on a contact face of a ceramic base plate as known from prior art;

Fig . 2B shows a second cross section through a separation cut between two piezoelectric ceramic actuator cuboids located on a contact face of a ceramic base plate as known from prior art; and

Fig . 2C shows a front view of the piezoelectric actuator shown in the

Figs. 2A and 2B; diagrammatic views of a piezoelectric actuator produced according to the method of the present invention, wherein :

Fig . 3A shows a first cross section through a piezoelectric ceramic actuator cuboid located on a contact face of a ceramic base plate;

Fig . 3B shows a second cross section through a separation cut between two piezoelectric ceramic actuator cuboids located on a contact face of a ceramic base plate;

Fig . 3C shows a third cross section through a common contact line at one extreme of a confectioned piezoelectric actuator; and

Fig . 3D shows a front view of the confectioned piezoelectric actuator shown in the Figs. 3A to 3C; Fig . 4 overviews over a larger ceramic supporting substrate (panel) comprising several single supporting elements for the multi component production of piezoelectric actuators according to the present invention, wherein : Fig . 4A shows intended unit cuts for selecting a certain intermediate assembly size, intended confection cuts for the piezoelectric actuators, and intended grooves in the contact face of the panel; Fig . 4B shows an intermediate assembly with grooves, contact metallization layers, common contact layer portions, and portions of epoxy resin glue deposited on the contact face of the panel; Fig . 4C shows the intermediate assembly of Fig. 4B with piezoelectric ceramic plates bonded to the contact face of the panel; and Fig . 4D shows a number of applied separation cuts for separating piezoelectric ceramic actuator cuboids and their arrangement on the confectioned piezoelectric actuators.

Detailed description of the present invention

Figure 3 shows diagrammatic views of a piezoelectric actuator produced according to the method of the present invention. As already pointed out, the reference numbers assigned to the features of the actual invention as claimed are the same as for the prior art piezoelectric actuator according to Fig. 2, in order to directly compare this invention with the existing prior art.

Fig . 3A shows a first cross section through a piezoelectric ceramic actuator cuboid of a piezoelectric actuator, the piezoelectric ceramic actuator cuboid being located on a contact face of a ceramic base plate. This piezoelectric actuator 1 for ink jet printing heads comprises a ceramic base plate 2 and a series of oblong, parallel orientated piezoelectric ceramic actuator cuboids 3 that are located on a contact face 4 of the ceramic base plate 2. The piezoelectric ceramic actuator cuboids 3 comprise metallization layers 5 around their cuboid base corners 6,6', which cu- boid base corners 6,6' are located on front and rear ends 7,7' of each actuator cuboid 3. The ceramic base plate 2 comprises on its contact face 4 at least two contact areas 8,8' that are located in approximately the distance of the actuator cuboid base corners 6,6' and that are coated with a contact metallization layer 9,9'. The piezoelectric ceramic actuator cuboids 3 are bonded to the ceramic base plate contact face 4. Such bonding preferably is carried out by the application of an adhesive and by heating and pressing the piezoelectric ceramic plate 11 (see Figs. 4B and 4C) against the ceramic base plate 2. The piezoelectric ceramic actuator cuboids 3 are contacted at least at their front and rear base corners 6,6' with the metallization layers 5 of their base corners 6,6' to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plate 2. The piezoelectric ceramic actuator cuboids 3 are separates, which are cut from a piezoelectric ceramic plate 11 that is bonded to the ceramic base plate 2. The ceramic base plate 2 comprises in its contact face 4 a groove 10 with a bottom 14. This groove 10 preferably extends at an essentially perpendicular direction to the piezoelectric ceramic actuator cuboids 3. This is groove 10 preferably is located close to the actuator cuboid front ends 7. In any case, the groove 10 extends below the piezoelectric ceramic actuator cuboids 3 and over the entire length of the piezoelectric actuator 1. The groove 10 and at least one of the adjacent base plate contact face 4 are coated with that one of the contact metallization layers 9 to which the front actuator cuboid base corners 6 are contacted later. Here, both adjacent base plate contact faces 4 are coated with the contact metallization layer 9.

Departing from the Fig . 3A, but still within the gist of the present invention and for contacting the piezoelectric ceramic actuator cuboids 3 with their metallization layers 5 to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plate 2, alternative metallization layers (not shown) are only applied to the surface at the base corners 6,6' of the piezoelectric ceramic actuator cuboids 3 which faces the contact face 4 of the ceramic base plate 2. Such one-sided application of metallization layers 5 to the underside allows for a multi component production of piezoelectric ceramic plates 11, because all metallization layers 5 on the piezoelectric ceramic plates 11 are located on its surface that later faces the con- tact face 4 of the ceramic base plate 2.

As indicated in Figs. 3A to 3D, each separation cut 13 reaches through the piezoelectric ceramic actuator cuboids 3, the adhesive 18, and the ceramic base plate contact face 4 with their contact metallization layers 9,9. However and according to the present invention, the separation cuts 13 do not reach the bottom 14 of the groove 10 (see Fig . 3B). Thus, a non-cut contact metallization layer portion 15 is left in the groove 10. This non-cut contact metallization layer portion 15 provides a common electrical connection for the piezoelectric ceramic cuboids 3 that are in- dividually activatable over residual strip conductors 16 of the rear end contact metallization layer 9' on the ceramic base plate contact face 4.

This groove 10 in the contact face 4 of the ceramic base plate 2 preferably is performed up to half of the thickness of the ceramic base plate 2. On the one hand, this layout results in a good electrical contact between the piezoelectric ceramic actuator cuboids 3. On the other hand, this layout guarantees a high mechanical stability of the ceramic base plate 2. The minimum depth of the groove 10 is variable according to the requirements of the subsequent production processes. A larger groove depth is also possible, but dictated by the requirement of the mechanical stability of the elements. The preferred shape of the groove cross-section as shown is half-lentoid or half-circular; it can also be chosen as a three-center arch or any other depression in the contact face 4 of the ceramic base plate 2. In the case of a half-lentoid or three-center arch cross-section of the groove 10, the non- cut contact metallization layer portion 15 is wider; thus providing better electrical connection. It is preferred that the borders of the groove 10 are beveled such that no sharp edges occur between the groove surface and the adjacent contact face 4. Optionally, one or more additional metallization portions can be deposited on the contact face 4 of the ceramic base plate 2 (not shown). Figure 3C shows a third cross section through a common contact line 22 that is located at at least one extreme of a confectioned piezoelectric actuator 1. In addition to the contact metallization layers 9,9' that extend in the direction of the dashed arrow "m" in Fig . 4A, a coating for the common contact lines 22 is applied (compare with Fig . 4B). This coating for the common contact lines 22 includes a portion 23 which extends in the direction of the dashed arrow "n" in Fig . 4A. This portion 23 connects both contact metallization layers 9,9' to each other. For each one of the future piezoelectric actuators 1, preferably two such portions 23 are provided on both extremes of the piezoelectric actuators 1 (see Fig . 4D). Thus, all piezoelectric ceramic cuboids 3 can individually be energized by applying electrical tension to a residual strip conductor 16 and to one or both common contact lines 22 of a piezoelectric actuator 1.

Figure 3D shows a front view of the confectioned piezoelectric actuator shown in the Figs. 3A to 3C. The cross-sections according to the Figs. 3A, 3B, and 3C are indicated by the double arrows I, II, and III respectively.

Figure 4 shows overviews over a larger ceramic supporting substrate (panel) 17 comprising several single supporting elements or ceramic base plates 2 for the multi component production of m x n (3 x 2 = 6) piezoelectric actuators 1 according to the present invention and according to selected steps of the inventive method . The exemplary layout for the production of six piezoelectric actuators 1 for ink jet printing heads is shown. In the contact face 4 of the ceramic panel 17 that comprises the size of six ceramic base plates 2, two grooves 10, each with a bottom 14, are formed . These grooves 10 (additionally indicated by arrows) preferably extend at an essentially perpendicular direction to the piezoelectric ceramic actuator cuboids 3, and these grooves 10 preferably are located close to the actuator cuboid front ends 7 of the respective piezoelectric actuators 1. In any case, these grooves 10 extend below the piezoelectric ceramic actuator cuboids 3 and over the entire length of the piezoelectric actuator 1.

Figure 4A shows intended unit cuts 19,19' for selecting a certain size of one ore more intermediate assemblies 24. Such intermediate assemblies 24 can e.g. be selected to comprise m = 1 column of n =2 ceramic base plates 2 (see left por- tion) or m =2 columns of n =2 ceramic base plates 2 (see right portion). In this case, one unit cut 19 will be carried out. If the panel 17 is to be divided into m =3 columns of n ceramic base plates 2, the eventual unit cut 19' is also carried out. The intended confection cuts 20,21 for the piezoelectric actuators are also shown here. With the first confection cuts 20 a column of piezoelectric actuators 1 is cut out of the panel 17. With the second confection cuts 21, the individual piezoelectric actuators 1 are separated from the column. The intended grooves 10 in the contact face 4 of the panel 17 are also visualized. Prior to depositing the metallization layers or portions 9,9',23 on the contact face 4 of the panel 17, these grooves 10 are produced, e.g . by milling . Figure 4B shows an intermediate assembly 24 with grooves 10, contact metallization layers 9,9', common contact layer portions 23, and portions of an adhesive 18 deposited on the contact face 4 of the panel 17. Preferred adhesives are selected for a group that comprises adhesive tapes, polycarbonates, acrylic adhesives and epoxy resins; most preferred are epoxy resins. These portions of adhesives 18 preferably are exactly chosen so that no adhesive 18 covers the contact metallization layers 9,9' during bonding; alternatively, other precautions can be taken (such as leading away superfluous glue form the sensitive areas). This is of particular importance because the preferred glue, an epoxy resin, is electrically non- conductive and would impair the electrical contact between the metallization layers 5 of the piezoelectric ceramic actuator cuboids 3 and the contact metallization layers 9,9' of the ceramic base plate 2. In fact, this electrical contact is merely based on physical touch between the surfaces of the layers 9, 9',5. Contacting the metallization layers 5 at the base corners 6,6' of the piezoelectric ceramic actuator cuboids 3 to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plate 2 is established by physical contact of at least peaks on the surfaces of the metallization layers 5,9,9'.

On the contact face 4 of the ceramic panel 17, two series of contact metallization layers 9,9' are deposited on contact areas 8,8' that are located in approximately the distance of the actuator cuboid base corners 6,6'. Each contact area 8 comprises a groove 10 and at least one (preferably both) adjacent base plate contact face 4 portions. Coating of the grooves 10 is made with that ones of the contact metallization layers 9 to which the front actuator cuboid base corners 6 are to be bonded.

In addition to the contact metallization layers 9,9' that extend in the direction of the arrow "m" in Fig. 4A, a coating for the common contact lines 22 is applied. This coating for the common contact lines 22 (see Fig . 4D) includes a portion 23, which extends in the direction of the "n" arrow in Fig . 4A, and which connects both contact metallization layers 9,9' to each other. For each one of the future piezoelectric actuators, preferably two such portions 23 are provided on both extremes of the piezoelectric actuators 1. Thus, all piezoelectric ceramic cuboids 3 can indi- vidually be energized by applying electrical tension to a residual strip conductor 16 and to one or both common contact lines 22 of a piezoelectric actuator 1.

Figure 4C shows the intermediate assembly of Fig . 4B with six piezoelectric ce- ramie plates 11 bonded to the contact face 4 of the panel 17. All piezoelectric ceramic plates 11 are bonded to the contact face 4 of the ceramic panel 17, preferably by heat adhesive bonding (i.e. using an electrically non-conducting epoxy resin). Preferably (as shown), the individual piezoelectric ceramic plates 11 are bonded separately to the ceramic base plate 2; thus, more precise bonding is pos- sible. These piezoelectric ceramic plates 11 comprise metallization layers 5 at or around their front and rear base corners 12,12' that are located on font and rear ends 7,7' of each future actuator cuboid 3.

Preferably before separating the oblong, parallel orientated piezoelectric ceramic actuator cuboids 3 from the piezoelectric ceramic plates 11, a series of unit cuts 19 is applied in the "n" direction according to Fig. 4A. In consequence, intermediate assemblies 24 are cut out. These intermediate assemblies 24 all comprise a ceramic base plate 2 with e.g . n = 2 contact metallization layers 9,9', and n = 2 piezoelectric ceramic plates 11 bonded to the contact face 4 of the ceramic base plate 2.

It is a preferred embodiment to create intermediate assemblies 24 with the parameters m = 1 and n = 7; in this case, there is located a common contact line portion 23 on both sides of the preferred intermediate assembly 24, these com- mon contact line portions 23 running in the "n" direction according to Fig . 4A (see Fig . 4D).

Figure 4D shows a number of applied separation cuts 13 for separating piezoelectric ceramic actuator cuboids 3 and the arrangement of these piezoelectric ceramic actuator cuboids 3 on the confectioned piezoelectric actuators 1. For producing the series or arrays of oblong, parallel orientated piezoelectric ceramic actuator cuboids 3, each separation cut 13 reaches through the piezoelectric ceramic actuator cuboids 3, the adhesive 18, and the ceramic base plate contact face 4 with their contact metallization layers 9,9', but not the bottom 14 of the groove 10. Despite these separation cuts 13, the piezoelectric ceramic actuator cuboids 3 remain bonded to the contact face 4 of the ceramic base plate 2 and remain in electrical contact with the metallization layers 5 of their base corners 6,6' to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plates 2. A common electrical connection for the piezoelectric ceramic cuboids 3 is provided by leaving a non-cut contact metallization layer portion 15 in the groove 10.

Therefore, all piezoelectric ceramic cuboids 3 are individually activatable over residual strip conductors 16 of the rear end contact metallization layer 9' on the ceramic base plate contact face 4 and to one or both common contact lines 22 of a piezoelectric actuator 1.

In Fig. 4D, only the first and last four separation cuts 13 are drawn for each piezoelectric actuator 1. At both extremes of these piezoelectric actuators 1, a portion will be cut away by first confection cuts 20; thus, these portions do not show separation cuts 13. Preferably at both extremes of these piezoelectric actuators 1, another portion does not show separation cuts 13 as well; these other portions constitute common contact lines 22 with common contact line portions 23.

Following to applying the separation cuts 13 to an intermediate assembly, first confection cuts 20 (in the "n" direction) and second confection cuts 21 (in the "m" direction") are applied to this intermediate assembly 24. In consequence, m x n (e.g . 7) piezoelectric actuators 1 for ink jet printing heads can be cut out from one intermediate assembly. The inventive method relates to the production of piezoelectric actuators 1 for ink jet printing heads, which piezoelectric actuator 1 comprises a ceramic base plate 2 and a series of oblong, parallel orientated piezoelectric ceramic actuator cuboids 3 located on a contact face 4 of the ceramic base plate 2. The piezoelectric ceramic actuator cuboids 3 comprise metallization layers at or around their cuboid base corners 6,6' that are located on font and rear ends 7,7' of each actuator cuboid 3. The ceramic base plate 2 comprises on its contact face 4 at least two contact areas 8,8' that are located in approximately the distance of the actuator cuboid base corners 6,6' and that are coated with a contact metallization layer 9,9'. The piezoelectric ceramic actuator cuboids 3 are contacted with the metallization layers 5 of their base corners 6,6' to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plate 2.

The inventive method comprises the steps of:

(a) forming in the contact face 4 of the ceramic base plate 2 at last one groove

10 with a bottom 14, the groove 10 extending below the piezoelectric ceramic actuator cuboids 3 and over the entire length of the piezoelectric actuator 1;

(b) coating the groove 10 and at least one adjacent base plate contact face 4 with that one of the contact metallization layers 9 to which the front actuator cuboid base corners 6 are to be contacted;

(c) bonding with an adhesive 18 individual piezoelectric ceramic plates 11 to the ceramic base plate contact face 4;

(d) contacting the piezoelectric ceramic actuator cuboids 3 with the metallization layers 5 at their base corners 6,6' to the contact metallization layers 9,9' of the contact face 4 of the ceramic base plate 2;

(e) dividing by separation cuts 13 the piezoelectric ceramic actuator cuboids 3 from the piezoelectric ceramic plate 11; each separation cut 13 reaching through the piezoelectric ceramic actuator cuboids 3 and the ceramic base plate contact face 4 with their contact metallization layers 9,9', but without reaching the bottom 14 of the groove 10; and

(f) providing a common electrical connection for the piezoelectric ceramic cuboids 3 that are individually activatable over residual strip conductors 16 of the rear end contact metallization layer 9' on the ceramic base plate contact face 4 by leaving a non-cut contact metallization layer portion 15 in the groove 10.

This method may include the step of using a larger ceramic supporting substrate (panel 17) comprising several (m x n) single supporting elements (ceramic base plates 2). Various methods may be used to fabricate the electrical structure. The best metallization scheme is sputtering at high pressure (e.g . at a pressure of 5 x 10 ^"3 mbar Ar), thus producing good adhesion and good wetting inside the grooves with sputtered materials (see table 1). Optionally, manual repairing defects in the dry resist may be applied giving an even higher throughput rate. The process is particularly suited for metallization systems which are very sensitive to any kind of chemicals used during the fabrication process.

The new fabrication process is particularly suited, but not limited to ceramic substrates with a high peak roughness (i.e. see rms roughness in table 1).

The same reference numbers refer to similar elements in the Figures, even if they are not described in detail in each case.

Actuating of the piezoelectric actuator 1 produced according to the present invention may be carried out with an actuating device as known from EP 1 291 181 Bl, for example. The method of the present invention is illustrated by the following example of a piezoelectric actuator 1 produced according to the present invention :

Table 1 :

Reference numbers

1 Piezoelectric actuator

2 ceramic base plate

3 piezoelectric ceramic actuator cuboids

4 contact face

5 metallization layer

6,6' cuboid base corners

7 front end of 3

7' rear end of 3

8,8' contact areas

9,9' contact metallization layers

10 groove

11 piezoelectric ceramic plate

12 front base corner of 11

12' rear base corner of 11

13 separation cut

14 bottom of 10

15 non-cut contact metallization layer portion 16 residual strip conductor

17 panel

18 adhesive

19 unit cut

19' eventual unit cut

20 first confection cuts

21 second confection cuts

22 common contact line

23 common contact line portion

24 intermediate assembly