KR100515609B1 - Droplet deposition apparatus - Google Patents

Abstract

The drop-on-demand piezoelectric material printhead has a channel wall formed by piezoelectric material 10 with electrodes 26 along its length. In the portion of the channel opened by the ink supply conduit, the piezoelectric material functions locally. That is, the width of the electrode is reduced or the function is lowered by interposing a material having a low dielectric constant between the electrode and the piezoelectric material. As a result, the capacitive load is lowered.

Description

Droplet deposition apparatus {DROPLET DEPOSITION APPARATUS}

FIELD OF THE INVENTION The present invention relates to a deposition apparatus, in particular arranged by spaced apart from each other in an arrangement direction perpendicular to its length, each of which being opposed by a sidewall comprising a piezoelectric material and a bottom surface extending between the sidewalls. An inkjet printhead having a bottomsheet comprising piezoelectric material and comprising a plurality of parallel, upper open channels at least partially defined. The invention also includes a method of making such a device.

Such printheads are known, for example, from EP-A-0 277 703, EP-A-0 278 590 and EP-A-0 364 136, to change the volume of the ink chamber to eject ink droplets. Use piezoelectric materials operating in shear mode. EP-A-0 341 929 describes a method of driving such an actuator and makes it clear that each actuator has a capacitive load. In general, these capacitive loads, which affect the size and cost of the drive circuit, require current and power. Moreover, the current flowing through the circuits and the electrodes of the printhead itself can generate heat that affects the viscosity of the ink, and in many types of inkjet devices, the jetting of the ink viscosity changes in this case appears as a placement error in the printed image. The inventors have found that this causes a variation in the viscosity of the ink droplets.

The use of piezoelectric material in the printhead is limited to areas where piezoelectric activity is actually desired, i.e., the "active" (closed) portion of the channel, and by using a material having a low dielectric constant for the rest of the printhead. It is proposed to reduce the capacitive load of the printhead. This can be accomplished by inserting a piezoelectric material into the low dielectric base "letting in", which actually forms a channel through the insert and the base and deposits the electrode along the length of each channel. Only a portion of each channel wall comprising the piezoelectric material is warped in response to an electric field applied through the electrode, leaving the rest of each wall and other associated connection areas with a low capacitive load. However, this technique is expensive because the process of inserting piezoelectric materials together is complex.

1 is a perspective view showing one form of a conventional inkjet printhead to which the present invention can be applied.

2 is a cross-sectional view of the printhead of FIG. 1 taken along line A-A of FIG.

3A, 3B and 3C are cross-sectional views of the printhead portion of FIG. 1 taken along lines B-B, C-C and D-D, respectively.

4 is a cross-sectional view corresponding to FIG. 2 and including a first aspect of the invention.

5a, b and c are cross-sectional views corresponding to the cross-sections of FIGS. 3a to c, taken along lines B'-B ', C'-C' and D'-D 'of FIG.

6 is a sectional view including the second aspect of the present invention, corresponding to FIG.

FIGS. 7A, 7B and 7C are cross-sectional views corresponding to the cross sections of FIGS. 3A-C taken along lines B ″ -B ″, C ″ -C ″ and D ″ -D ″ in FIG. 6; FIG.

8 shows a cross section through a channel wall according to a second aspect of the invention;

9 is a cross-sectional view illustrating another method in accordance with the second aspect of the present invention, corresponding to FIG. 6;

10 is a cross-sectional view cut along the longitudinal axis of the channel of another printhead incorporating the present invention.

The present invention has a printhead that has a lower capacitive load than known structures and is not complicated to manufacture. Such a printhead manufacturing method is also included in the present invention.

Accordingly, the present invention is a plurality of parallel, formed by piezoelectric materials, spaced apart from each other in an arrangement direction perpendicular to the length thereof, each defined at least in part by opposing side walls and a bottom surface extending between the side walls. A lower sheet forming an upper open channel;

The side wall may include the piezoelectric material and an electrode for applying an electric field to the piezoelectric material to allow horizontal displacement of the sidewall.

An upper sheet coupled at the top of the sidewall to face the bottom surface of the channel and proximate the channel;

The channel is supplied with liquid and is in communication with a nozzle for ejecting droplets from the channel, each channel being in communication with the liquid supply means and open at a portion parallel to the channel axis and All other parts parallel to the channel axis, with other parts bound

Each sidewall comprising the piezoelectric material in the one portion of each channel does not function to prevent lateral displacement from occurring in the sidewall of the one portion of each channel.

In addition to the transverse placement of the wall at the 'open' portion of the unwanted channel, as well as the inability of the wall at this 'open' portion, the reduction in the overall capacitive load can be achieved by forming a channel at the base comprising a uniform layer of piezoelectric material. The inventor has found that it can be achieved with a print head made substantially in accordance with the prior art. Therefore, the above complicated manufacturing method can be avoided.

According to a first preferred aspect of the invention, at least partly defined by a sidewall comprising a piezoelectric material facing each other in an arrangement direction perpendicular to its length and a bottom surface extending therebetween A lower sheet having a plurality of parallel, upper open channels and having a piezoelectric material layer having a polarity in a vertical direction; And

A top sheet facing the bottom surface of the channel and coupled to the sidewall and proximate at the top of the channel,

The channel is supplied with liquid and in communication with a nozzle for spraying droplets from the channel,

Each channel has one part open at the part parallel to the channel axis in communication with the liquid supply means and another part closed at all the parts parallel to the channel axis,

Electrodes are provided on opposite sides of the sidewall to form a shear mode actuator for ejecting droplets from the channel associated with the actuator, each electrode substantially extending the channel length,

In one portion of the channel, there is provided a droplet deposition apparatus in which a layer of material having a lower dielectric constant than the piezoelectric material is interposed between the piezoelectric material and at least one of the electrodes provided on opposite sides of the sidewall. .

Such devices achieve lower capacities than conventional designs without the complexity associated with piezoelectric inserts as described above. In said one part of the channel opened by the ink supply means, it is not necessary to lay the wall. Therefore, the electrode of this portion is separated from the piezoelectric material of the channel wall by the material layer having a lower dielectric constant than the piezoelectric material, so that the piezoelectric material portion cannot be used. In this part the capacitive load between the electrodes on the opposite side of the channel wall (in the case of other "closed" parts of the channel) is lower than that obtained only with piezoelectric material, thereby reducing the total capacitive load of the printhead. Contribute.

According to a particular embodiment, said one portion and the other portion are at least partially defined by the sidewalls having the same planar top surface and have a substantially constant height, and the height of each sidewall of said one portion and the other portion is substantially the same. . This embodiment is in particular manufacturing and there is no variation in the channel depth of processing required at least in the front of the channel. In such embodiments, other portions of the channel may extend to a constant depth, such as a nozzle. Irrespective of this, the one part and the other part may be adjacent.

Preferably, an electrode provided on the opposite side of the side wall is positioned above the respective channel sidewalls and spaced apart from the bottom surface. This arrangement is particularly useful for depositing using the known "angle application" principle. In particular, the electrode can extend approximately one half of the depth of each channel in said one part in said other part, and the electrode preferably extends around 10% of the height of each channel wall.

Where each channel comprises an additional portion having a channel wall of a height lower than the channel wall of the one or the other portion, an electrode is provided on the channel wall facing the lower portion of the additional portion of each channel, and the electrode And a material layer having a lower dielectric constant than the piezoelectric material interposed between the opposite walls and the bottom of each channel. The electrodes in this other part serve as a connection point between the electrode in the channel and the external driver chip. The low dielectric material layer between these electrodes and the reduced channel wall reduces the capacitive loading of these regions.

According to one aspect of the invention, (a) forming a plurality of parallel channels in a lower sheet comprising a layer of piezoelectric material, and (b) at least one of the sidewalls facing the first portion of each channel, the piezoelectric material Depositing a layer of material having a lower dielectric constant and maintaining opposite sidewalls of the second portion of each of the channels independent of the material; and (c) facing the first and second portions of the channel. Provided is a method of making a droplet deposition apparatus comprising depositing an electrode material on a sidewall. This method also makes it possible to produce low capacity printheads without the complexity of using known deposition methods.

Advantageously, the method masks the second portion of each channel prior to depositing the layer of material on at least one opposing sidewall of the first portion of each channel. And unmasking the second portion prior to depositing electrode material on opposite sidewalls of the second portion.

Electrode material is deposited by the metal vapor beam at an angle to the channel facing the face towards the wall.

According to a first aspect of the present invention, there is at least a space between the opposite sidewalls comprising a piezoelectric material and a lower surface extending between the sidewalls, each being spaced apart in an arrangement direction perpendicular to the length thereof. A bottom sheet comprising a plurality of parallel, upper open channels defined in part and comprising a piezoelectric material layer polarized in a vertical direction; A top sheet facing the bottom surface of the channel and coupled to the sidewall and proximate to the top of the channel, the channel being in communication with a nozzle supplied with liquid and spraying droplets from the channel, each channel being channel side Having a closed portion in all portions placed parallel to and having electrodes on opposite sides of the sidewall, forming a shear mode actuator for ejecting a liquid chamber from the channel associated with the actuator, each electrode substantially extending the channel length. And a material chamber having a dielectric constant lower than that of the piezoelectric material is interposed between at least one of the electrodes and the piezoelectric material in a region excluding the portion of each channel.

According to a first aspect of the present invention, there is at least partially spaced apart from each other in the direction of placement perpendicular to its length, each of which has an opposite sidewall having a height and a bottom surface extending between said sidewalls. A lower sheet consisting of a plurality of parallel, upper open channels defined by the piezoelectric material; An upper sheet coupled to the sidewall facing the lower surface of the channel and proximate at the top of the channel, the channel being supplied with liquid and in communication with a nozzle for ejecting droplets from the channel, each channel being A layer of material having a closed portion in all portions parallel to the channel axis, an electrode applying an electric field to the piezoelectric material of the sidewalls, and having a dielectric constant lower than that of the piezoelectric material in the region excluding the portion of each channel The droplet deposition apparatus is provided between at least one of the electrodes and the piezoelectric material of the side wall.

Similar advantages are also provided by the second preferred aspect of the present invention, which extends between the sidewalls and the sidewalls comprising opposing piezoelectric materials, each having a flat top surface, spaced from each other in a direction perpendicular to the length thereof. A lower sheet consisting of a plurality of parallel, upper open channels defined at least in part by a lower surface being formed and having a piezoelectric material layer polarized in a vertical direction; A top sheet facing the bottom surface of the channel and coupled to the sidewall to proximate at the top of the channel, the channel being in communication with a nozzle supplied with liquid and spraying droplets from the channel, each channel being liquid It has one part open at the part parallel to the channel side communicating with the drop supply means, and another part closed at all the parts parallel to the channel axis, and an electrode is installed on the opposite side of the side wall to the actuator. A droplet deposition apparatus that forms a shear mode actuator for injecting droplets from associated channels, wherein an electrode provided in said one portion of each channel extends a smaller proportion of the height of each sidewall than an electrode provided in the other portion of each channel. It is about.

Such a device achieves a lower capacity than a conventional design in a simple manner. In one part of the channel that is open to the ink supply means, these walls do not have to be replaced so that the electrode of this part is sufficient to move the active voltage to the electrode in the closed part of the channel but in the open part the piezoelectric material It is necessary to extend the (smaller) ratio of the channel wall height that is insufficient to drive it, so it cannot be used locally. In the closed part, the electrode extends at a rate large enough for the wall to move the channel wall downward. In this method, the capacitive load of the channel wall in the one (open) portion is reduced compared to the conventional design, resulting in a reduction in the capacity of the printhead as a whole.

According to a particular embodiment, the one and the other part are at least partially defined by sidewalls of substantially constant height such that the height of each sidewall of the one and the other part is substantially the same. This embodiment is particularly suitable for manufacturing and there is no variation in the channel processing depth required at the front of the channel. In such embodiments, the other portion of the channel may extend to a constant depth, such as a nozzle. Regardless, the one and the other part is continuous.

Preferably an electrode provided on the opposite side of the side wall is located on top of each channel side wall, spaced apart from the bottom surface. This arrangement is very useful for depositing using the known "angle application" principle. In particular, in one such part, the electrode preferably extends around 10% of the height of each channel wall.

According to a second aspect the invention is particularly advantageous in embodiments in which the length ratio of the one and the other channel portion is approximately two or more.

(A) forming a plurality of parallel channels separated by a channel wall having a planar top surface in a lower sheet comprising a layer of piezoelectric material, (b) said angle at a first ratio of each sidewall height Depositing electrode material on opposite sidewalls of the first portion of the channel; (c) depositing electrode material on opposite sidewalls of the second portion of each channel at a second ratio different from the first ratio of the height of each sidewall. A method of manufacture comprising the step of depositing.

In addition, improvements in known deposition methods allow the manufacture of low volume heads without complexity.

According to a preferred embodiment, the method comprises: masking a second portion of each channel prior to depositing electrode material on opposite walls of the first portion of each channel at a first ratio of each sidewall height; Unmasking the second portion prior to depositing electrode material on opposite sidewalls of the first and second portions of each channel. This procedure is simple to realize and does not require breaking of the vacuum between deposition steps. Advantageously, the first ratio is greater than the second ratio, and the second ratio is preferably no greater than 10% of the wall height. This can be achieved with an improvement in the material deposition technique by means of a metal vapor beam directed at the channel angle facing the wall and its surface, the deposition angle in the first part being inclined than the deposition angle in the second part. Urgent.

The invention is described by way of example only with reference to the drawings.

1-3 show piezoelectric wall actuators operating in a shear mode, and show, for example, a typical inkjet printhead 8 known from US-A-5 016 028. It comprises a base 10 of piezoelectric material mounted on a circuit board 12 where only the part showing the connecting track 14 is illustrated.

As described, for example, in US-A-5016028, a number of parallel grooves are formed in the base 10 extending into the piezoelectric material layer. Each groove comprises a relatively deep front portion to provide an ink channel 20 separated by opposing actuator walls 22 having an upper surface and a relatively shallow rear portion to provide a connection track at position 23. do. The front part and the rear part are connected by the "runout" part R of the channel, the radius of which is determined by the radius of the cutting disc used to form the channel (for example in EP-A-0 364 136 described above). Is disclosed).

As illustrated in FIG. 3, after forming the grooves, metal plating is deposited to provide to the front electrode 26 on the opposite side of the ink channel 20, which extends by approximately half of the channel height at the top of the wall. 3a and b, the rear part is deposited to provide a connecting track 24 connected to the electrodes of each channel 20 (Fig. 3c). The top of the wall is not metal plated so that the tracks 24 and the electrodes 26 form active separation electrodes for each channel. Such metallization techniques are known, for example, from EP-A-0 364 136, supra.

After depositing and selectively coating the base 10 with a passivant layer for electrical separation of the electrode portion from the ink, the base 10 is mounted on the circuit board 12 as shown in FIG. A wire bonding connection 28 is made which connects the connecting track 24 of the base 10 to the connecting track 14 of the circuit board 12.

Bonding on top of the actuator wall 22 secures the cover 16 to form a plurality of "closed" channels 20. At one end, each channel has access to the supply of replenishment ink, which in the example shown passes through the window 27 of the cover 16. At the other end of each channel is located a nozzle 30 which can be formed (advantageously by UV excimer laser ablation) on the nozzle plate 17 coupled to the printhead.

In this example, the printhead is operated to deliver ink from the ink supply to the nozzle 30 past the window 27, which is drawn into the ink channel 20. As known, for example, from EP-A-0 277 703, the application of an appropriate voltage waveform to the electrode on the side of the channel wall is transverse to the respective channels and walls which in turn deform the polar piezoelectric material of the channel wall in shear mode. Causes a potential difference that is set across the wall for deflection. Thus, one or both of the walls constraining the ink channel can be deflected.

The movement of the wall into the channel reduces the channel capacity and sets the pressure of the ink along the channel length, which is closed at the top and bottom by the base and cover, respectively, and closed at both sides by each channel wall. Known as the "active" length and referred to as "L" in FIGS. 1 and 2. Loss of pressure causes ink droplets to eject from the nozzle.

As described above, the printhead of the type described provides a capacitive load, and in the front part (corresponding to FIGS. 3A and B), the capacitor is formed by channel walls and electrodes located on both sides, It will be appreciated that at the rear of the channel, the piezoelectric base as well as the (reduced) wall contributes to the capacitive effect in conjunction with the connecting track 24.

4 illustrates a printhead according to the first aspect of the invention as a cross-sectional view corresponding to FIG. 2. 5 shows a corresponding cross section. The "active" length structure of the printhead of Figure 4 is like a conventional head, with electrodes 26 'extending approximately half way down the wall.

However, at one side open to the ink supply window 27 so that in the full-depth channel (referred to as "N") rather than the "active" length of the channel, the electrode 26 "extends only along the very top of the wall. This delivers an actuation signal from the connecting track 24 of the active channel portion to the electrode 26 'and significantly reduces the capacitive load of the channel portion by reducing the area of piezoelectric material located between the channel electrodes as is apparent in FIG. Is sufficient to reduce (this follows the principle that the capacity C of a parallel plate capacitor with a plate of region A separated by the thickness L of the material having a relative dielectric constant K is given by C = K.eo> A / L, where eo is the permittivity of free space)

The reduced depth electrode 26 " is advantageously used in the " runout " portion R and thus is coupled with the connecting track 24 formed in a conventional manner.

With regard to the production of the tracks 26 ', 26 "of different heights, this is not entirely but advantageously achieved by metal vapor deposition. The principle of this technique is well described in EP-A-0 364 136. The channel-like piezoelectric body is exposed to the metal vapor beam facing perpendicular to the plane of the body, ie substantially parallel to the channel sidewalls, but the rear portion “C” of the groove is shielded. As indicated by dashed line 60 in FIG. 6, the metal is deposited to form a connecting track 24 of thickness, typically 2-4 μm, sufficient to withstand the wire bonding process.

And shielding of the channel portion to form the active length L of the printhead is removed and the channeled body and the metal vapor beam rotate to each other in the position shown in FIG. 5A so that the electrode provides a rise in typical plating depth of 125 [mu] m. To the channel wall of the portion L to approximately half of the height of the wall, typically deposited at a thickness equal to 1 μm in the plane perpendicular to the metal vapor beam. It will be appreciated that relative rotation needs to be performed twice so that the two sidewalls of each channel are coated. This process corresponds to the electrode deposition method disclosed in EP-A-0 364 136.

Finally, the remainder of the channel, i.e. the N and R portions, is removed and the channeled body and the metal vapor beam are rotated back to each other at the shallow angle shown in FIG. 5B, whereby the electrode deposited on the active permanent in the previous step. A shallow electrode 26 "(typically 25 [mu] m deep) is deposited in the R and N portions along the top of 26 '. In the active region of the channel, the shallow electrode helps to challenge along the length of the active region. This is particularly advantageous when electrode materials with high resistivity are used, and further rotation is required to be deposited along the top of the other walls.

The method described above has the advantage that in each deposition process the deposition parameters are tailored to obtain optimum electrode properties in the particular area to be plated. Thus, the first step of deposition can be performed with high speed deposition to place a sufficient amount of metal layer to form a connection track that remains attached to the ceramic substrate during the wire bonding process. On the other hand, the second step of electrode deposition at the active length of the channel can be performed at a low deposition rate such that the electrode deposited on the wall of the active portion of the channel exhibits electrical ductility. The final step in which the shallow electrode 26 "is settled may be performed with a high degree of deposition which reflects that the electrode is deposited at an angle lying close to the vertical.

It can be achieved by a physical mask located between the channel base 10 and the metal vapor source, preferably adjacent the channel element 10, in order to obtain good edges in the plating. The mask is ideally made from metals suitable for use in vacuum systems, for example metals such as polyimide. Each mask has holes formed in areas corresponding to the areas to be applied, and according to the method described above, they are opened in turn after the appropriate deposition step by pulling or sliding them off or moving them in the channeled base. Preferably each mask is removed without opening the vacuum chamber, which causes an oxide film to be formed between the successively formed electrode layers.

Alternating electrode deposition methods include depositing shallow electrodes along the entire length of the channel. In the conventional manner known from EP-A-0 364 136, the mask shielding the inactive portion "N" of the channel is an electrode half the depth of the wall in the active portion "L" of the channel and the shallow rear portion "C" of the channel. Connection tracks are introduced into the chamber prior to deposition.

Undesired metal deposition on the walls can be avoided, for example, by thermoplastic "lift off" films as known in EP-A-0 397 441 or by lapping after deposition such as EP-A-0 364 136. . Further arrangements in areas such as connecting tracks, for example in the course of subsequent arrangements of electrodes 26 'or 26 ", are advantageously taken into account when calculating the required initial placement thickness of the connecting tracks (e.g., behind the grooves). 2 μm of electrode material that needs to be applied for the first time in part (“C”) and electrode material that is applied in the rear part in a continuous application step is calculated only when calculating the required initial application thickness of the connecting track. Good.

Figures 4 and 5 illustrate aspects of the invention as applied to a printhead (so-called "cantilever structure" disclosed in EP-A-0 354 136, having a wall of piezoelectric material perpendicular to the piezoelectric material layer and perpendicular to a single direction). However, the present invention is not limited to these means and, for example, as disclosed in EP-A-0 277 703, a "Cheveron" structure is polarized in two opposite directions in which the piezoelectric material is opposed. The latter structure has the advantage of requiring a lower operating voltage than the " cantilever " structure, while having the disadvantage of having a high capacitive load. As can be seen from EP-A-0 277 703 above, this structure requires an electrode in the active portion L of the channel to extend the entire length of the wall. The height of the silver electrode is not the same as that used in the cantilever, ie typically not more than 25 μm and / or 20% of the wall height. Laminates are described that can produce "chevron" structures.

6 illustrates a printhead according to another aspect of the present invention as a cross-sectional view corresponding to FIG. 2, and FIG. 7 shows a corresponding cross-sectional view. In the previous aspect, the "active" length structure of the printhead is the same as a conventional head, extending about half of the wall of piezoelectric material in the case of a "cantilever" actuator.

In contrast, the full depth channel portion N, which is open at one side with the ink supply window 27 and is not part of the "active" length, has a dielectric layer lower than that of the piezoelectric material. And the piezoelectric material of the channel wall 22 are different from the conventional structure. This is illustrated in the cross-sectional view of FIG. 7B.

The capacitive load of the channel wall in this channel portion can be represented by three capacitors connected in series rather than a single capacitor of a conventional design. As illustrated in FIG. 8, the capacitor C1 is formed via the layer 40 on the side of the wall in addition to the capacitor C2 formed by the piezoelectric material of the wall 22 itself. By selecting a material having a lower dielectric constant than the piezoelectric material, the total capacity of the series capacitors C1 and C2 can be made less than that of the piezoelectric material alone. (Approximately the total capacity is given by _{1 / C total = 1 / C} 2 + 2 / C 1, a low value of C ₁ can be seen that given a low value of _total C).

As shown in FIG. 7C, this technique can be advantageously applied to the runout area R as well as the area C of the connecting track.

With respect to the previous aspect of the invention, this aspect can be achieved using a deposition technique known as the vehicle body. As a material having a lower dielectric constant than the piezoelectric material, silicon nitride may be used. It has a relative dielectric constant of about 8 (compared to a value of about 3600 for a piezoelectric material such as lead zirconium titanate (PZT)) and is commonly used in inkjet printheads as a protective floating coating for channel electrodes.

Such materials can be deposited on the channel walls using the technique known from WO 95/07820 and retain the active portion L of the masked channel. The silicon nitride layer typically has a thickness of 0.3 to 0.5 mu m. The deposition process requires only a single mask arranged so that the low-k material that is introduced does not protect the active length of the channel. As shown in FIG. 9, the mask 70 is in the active region L because the deposition technique is used to bring it close to the top of the wall 22 and to penetrate the low dielectric material that enters under the entrained region 72. It should extend below L. In addition, the mask 70 must have a practical thickness and must be thermally conductive to avoid overheating and warping during the application process. It is therefore made of aluminum of 2-3 mm thickness.

The electrodes are applied continuously over the entire length of the channel in a conventional manner as described above. In fact, the applicator is believed to provide a smoother surface for the application of the electrodes than the visible surface of the channel wall, as a result of which the inactive portions of the channel are less fatigued.

For the previous aspects of the present invention, it has been found that the use of thermoplastic "lift off" films or lappings is satisfactory for removing electrodes and low dielectric materials deposited on top of the channel walls. Further, the present invention is equally applicable to printhead structures such as "cantilevers" and "chevrons" when the piezoelectric material is polar in the direction perpendicular to the piezoelectric material layer.

Many other insulating materials and / or other application techniques may be used instead of silicon nitride for low dielectric layers; Oxides, in particular silicon oxide, aluminum oxide, aluminum nitride and diamond type carbon can be used. Choosing the right material allows channel electrodes to be applied using a low dielectric layer and a single applicator, and has very beneficial results in terms of manufacturing time (no need to move elements with channels from one machine to another) and in main equipment. Gives birth For example, a low dielectric layer of aluminum nitride can be deposited in the channel element in the chamber by depositing with aluminum or by applying nitrogen ions or free radicals to the channeled component. Continuous discharge of the channel allows vaporizing the aluminum to be applied as an electrode on the channel wall in the same chamber in a manner known from EP-A-0 364 136 above.

Many modifications of the above embodiments are possible within the scope of the invention. For example, the above embodiment may use a combination of the low dielectric material layer interposed between the electrode and the channel sidewall and the inactive portion " N " of the channel with the thin electrode. Alternatively, one or both aspects of the invention may be used in combination with other dose-reducing means.

The relative dimensions of the active and inactive lengths of the channels may be varied from those shown in the figures: of the kind described in EP-A-0 422 870 (low capacitive loads are particularly important in view of particularly high drive frequencies). High frequency operation requires an active channel length (L) in the low end of the range of 1 to 10 mm, for example 4 mm, while the dimensions of the manifold apertures in the longitudinal direction of the channel are excessively pressured to conform to existing ink supply structures and the like. It is necessary to keep it substantially constant, for example 10 mm, so that sufficient ink flows without dropping. In summary, the present invention is particularly preferred for printheads having a ratio of inactive full length to active full length of about 2 or more.

Other important dimensions of this printhead are: 300 μm full channel depth, 150 μm electrode depth of active portion of the channel, 62 μm channel wall width of full depth portions (L, N), length of connecting track (C) Is 7.4 mm, the channel wall width of the connecting track portion is 47 μm, the overall length of the actuator (C + R + N + L) is 11.5 mm, and the active length (L) is 1.5 mm.

It will be appreciated that using the present invention in such a structure there is a proportionately large reduction in the capacitive load of the printhead over printheads of the kind shown in the figures. For example, in accordance with one aspect of the present invention, the use of a thin electrode of 25 μm depth in the inactive portion of a single channel wall having the above dimensions may be used for a same wall using an electrode of constant height 150 μm for 540 pF. This results in a wall with a total capacity of 354pF compared with the value of. The use of a low dielectric application film according to another aspect of the present invention will have a total wall capacity of 190 pF while the use of both embodiments will have a wall capacity of 140 pF. This value is very similar to that shown by the active portion of the wall alone (129pF).

The invention is not limited only to the structure of the printhead shown in the figures: the coating liquid is directed to the holes in the channel base as shown in EP-A-0 364 136, i.e. all channel sides lying parallel to the channel axis. It can also be supplied through. Similarly, nozzles that do not need to be located on the channel axis as shown in the figures may be located on a cover or foundation (so-called "top-shooter" and "bottom-shooter" structures) or elsewhere known in the art. . The device according to the invention need not be limited to the method described herein and, for example, selective application of the electrode and / or low dielectric layer may be considered after coupling to the base with the top cover channel. In addition, the base with the channel and the top layer may be incorporated into a separation assembly, each of which is subjected to a manufacturing step separately.

The invention is, of course, applicable to the "wafer scale" manufacturing method and structure described in WO 95/18717, of course. Application and electrode application masks need to be applied. In these structures the ink is supplied from the end rather than from the side of the channel and from, for example, manifold 100 lying perpendicular to the channel longitudinal axis as shown in FIG. Within these regions 120 lying outside of the portion (“active” 130) it is simply arranged between the element material having a channel 110 and the electrode material 105.

The present invention is applicable to a structure having piezoelectric material polarized in a different manner to the above structure and has another device corresponding to the working electrode. An example of such a device is described in US-A-5 235 352, which has a channel-separating wall containing piezoelectric material polarized parallel to the array direction of the channel and is positioned by electrodes located in their walls perpendicular to the polarization direction. Receives an electric field. The low dielectric layer is applied between the electrode and the piezoelectric material in these portions of the wall corresponding to the inactive, non-closed portions of the channel. Each feature illustrated in this specification (including the claims) and / or in the figures may be independently incorporated into other disclosures and / or illustrated features.

The abstract appended hereto summarizes the specification of the present invention.

The drop-on-demand piezoelectric printhead has a channel wall formed by piezoelectric material 10 with electrodes 26 along its length. The portion of the channel opened into the ink supply conduit is achieved by interposing a material 40 of low dielectric constant between the electrode and the piezoelectric material locally or by reducing the width of the electrode. The result is a low capacitive load.

Claims (23)

Formed by piezoelectric materials and spaced apart from each other in a direction perpendicular to the length, each forming a plurality of parallel, upper open channels defined at least in part by opposing sidewalls and a bottom surface extending between the sidewalls; A lower sheet; And In a portion lying parallel to the channel axis, facing the bottom surface of the channel and in communication with the droplet supply means and the closure portion bound to all of the portions lying parallel to the channel axis in the channel. A topsheet providing an open opening, The sidewalls are formed by the piezoelectric material and include electrodes for applying an electric field to the piezoelectric material to cause lateral displacement of the sidewalls, the electrodes extending the channel length, The channel is supplied with liquid and is in communication with a nozzle for ejecting droplets from the channel, And the side wall portion of the opening portion does not function so that no lateral displacement occurs in the side wall of the opening portion of each channel. The piezoelectric material of claim 1, wherein in the opening of each channel, a layer of material having a dielectric constant lower than that of the piezoelectric material is disposed between the piezoelectric material and at least one electrode provided on an opposite side of the wall. Droplet deposition apparatus that prevents the piezoelectric material from functioning. The method of claim 1, wherein the electrode provided in the opening of each channel extends at a rate less than the ratio of the height of each side wall of the electrode provided in the closure of each channel to disable the driving of the piezoelectric material of the opening. A droplet deposition device that can no longer function. Spaced apart from each other in a direction perpendicular to the length, each consisting of a plurality of parallel, upper open channels at least partially defined by opposing sidewalls and a bottom surface extending between the sidewalls and perpendicular to the layer. A lower sheet having a piezoelectric material layer having a polarity in a direction; And A liquid chamber and a closing portion which are coupled to the side wall facing the lower surface of the channel and closed at all portions lying parallel to the channel axis in the channel, in communication with the supply means and in parallel with the channel axis. A topsheet providing an opening that is open at the portion, The channel is supplied with liquid and is in communication with a nozzle for ejecting droplets from the channel, Electrodes are provided on the opposite side of the side wall to form a shear mode actuator for injecting droplets from the channel associated with the actuator, Each electrode extends the channel length, And a material layer having a lower dielectric constant of the piezoelectric material in the opening of the channel is interposed between the piezoelectric material and at least one of the electrodes provided on the opposite side of the sidewall. 5. The apparatus of claim 4, wherein each channel comprises: an additional portion having a channel wall of a height smaller than the channel wall of the open or closed portion, an electrode provided on the opposite channel wall, and the additional portion of each channel. And a material layer having a lower dielectric constant than a piezoelectric material between the electrode of each channel and the opposing wall and the bottom of each channel. A method of manufacturing the droplet deposition apparatus of claim 4, (a) forming a plurality of parallel channels in a lower sheet with a piezoelectric material charge; (b) the material has a lower dielectric constant than the piezoelectric material, and opposing sidewalls of the second portion of each channel remain without the material, and a layer of material on at least one opposing sidewall of the first portion of each channel Applying; (c) applying an electrode material on opposite sidewalls of said first and second portions of said channel. The method of claim 6, (d) masking said second portion of each channel prior to applying said layer of material on at least one opposing side wall of said first portion of each channel; (e) unmasking said second portion before applying electrode material on opposite sidewalls of said first and second portions of said channel. 7. The method of claim 6, wherein the electrode material is deposited by a metal vapor beam at an angle with the channel facing the face towards the wall. Each consisting of a plurality of parallel, upper open channels spaced apart from each other in a direction perpendicular to the length thereof, each at least partially defined by opposing sidewalls having parallel upper surfaces and a lower surface extending between the sidewalls; A lower sheet including a piezoelectric material layer having a polarity in a direction perpendicular to the layer; An upper sheet coupled to the sidewall facing the lower surface of the channel and proximate the upper portion of the channel, the channel being in fluid communication with a nozzle for injecting droplets from the channel, each The channel has a closed portion closed at all portions parallel to the channel side and an open portion in communication with the droplet supply means and open at the portion parallel to the channel axis and having an electrode on the opposite side of the side wall. Is installed to form a shear mode actuator for injecting droplets from a channel associated with the actuator, each electrode extending the channel length, and an electrode provided at the opening of each channel is installed at the closure of each channel. A droplet deposition apparatus in which a height ratio of each sidewall extends smaller than an electrode. 10. The droplet deposition apparatus of claim 4 or 9, wherein the one portion and the other portion are at least partially defined by sidewalls of constant height such that the height of each sidewall of the opening portion and the closure portion is the same. 10. The droplet deposition apparatus of claim 4 or 9, wherein for each channel a nozzle is placed adjacent the closed portion of the channel. 10. A droplet deposition apparatus according to claim 4 or 9, wherein for each channel, the openings and closures are continuous. 7. The droplet deposition apparatus of claim 6, wherein the electrode preferably extends around 10% of the height of each channel of the opening. 7. The droplet deposition apparatus of claim 6, wherein the electrode extending from the closure extends to approximately half or the entire depth of each channel wall. 10. A droplet deposition apparatus according to claim 4 or 9, wherein the ratio of the lengths of the open and closed channel portions is approximately two or more. A method of manufacturing the droplet deposition apparatus of claim 9, (a) forming a plurality of parallel channels separated by channel walls having a coplanar top in a lower sheet with a layer of piezoelectric material; (b) applying electrode material on opposite sidewalls of the first portion of each channel over a first portion of each sidewall height; (c) the first and second portions are different, and the droplet deposition apparatus comprises applying an electrode material on opposite walls of the second portion of each channel over a second portion of each sidewall height. How to prepare. The method of claim 16, (d) masking said second portion of each channel prior to applying electrode material onto the opposing wall of the first portion of each channel over a first portion of each side wall height; (e) unmasking said second portion prior to applying electrode material on opposing sidewalls of said first and second portions of each channel. 17. The electrode material of claim 16, wherein the electrode material is deposited by means of a metal vapor beam at an angle in a channel facing the face towards the wall, the deposition angle in the first portion being inclined than the deposition angle in the second portion. Urgent way. A method of coating the surface of a piezoelectric element, Positioning the element in a chamber, exposing the surface to a metal vapor beam, and switching the state in which the chamber contains a vacuum and the state in which free radical ions are applied to the surface of the element. Way. 20. The method of claim 19, wherein the ion or free group is oxygen or nitrogen. 21. The method of claim 20, wherein the metal vapor beam is vaporized aluminum. 20. The method of claim 19, wherein the element is formed in a channel, each having a foundation and two opposite sidewalls therebetween, wherein a coating is applied on the sidewalls. 23. The method of claim 22, wherein with the chamber in vacuum, the metal vapor beam is opposed at an angle other than zero with respect to the channel wall.