Patent Description:
Inkjet print heads are known for example from <CIT>, <CIT>, <CIT>, or <CIT>. Such a print head comprises a plurality of a droplet jetting devices formed of a nozzle layer defining, for each droplet jetting device, a nozzle, a membrane layer carrying, on a membrane, a restrictor layer and an actuator for generating pressure waves in a liquid in a pressure chamber that is connected to the nozzle, the actuator being positioned in an actuator chamber in the restrictor layer, and a distribution layer defining a supply line for supplying the liquid to the pressure chamber. It is further known to provide the pressure chamber with an additional outlet to allow for a constant throughflow of ink through the pressure chamber, for example from <CIT>, wherein the restrictor layer comprises an inlet and an outlet restrictor positioned on opposites sides of the actuator. Said inlet and outlet restrictors however form passages which allow pressure waves generated in one pressure chamber to travel to an adjacent pressure chamber, which could affect the droplet formation there. It is known to provide a print head with so-called cross-talk dampers formed of a flexible membrane, for example from <CIT>.

It is an object of the invention to provide a space-efficient print head with cross-talk filtering and improved performance and/or lifetime.

In accordance with the present invention, an inkjet print head according to claim <NUM> and a method forming such a print head according to claim <NUM> are provided.

Said inkjet print head comprises a plurality of a droplet jetting devices formed of a nozzle layer defining, for each droplet jetting device, a nozzle, a membrane layer carrying, on a membrane, a restrictor layer and an actuator for generating pressure waves in a liquid in a pressure chamber that is connected to the nozzle, the actuator being positioned in an actuator chamber formed in the restrictor layer, and a distribution layer defining a supply line for supplying the liquid to the pressure chamber, wherein the restrictor layer comprises an inlet restrictor and an outlet restrictor positioned on opposites sides of the actuator. In the present invention, the print head is defined by that a cross-section of the inlet restrictor is different from that of the outlet restrictor. The cross-section of the inlet restrictor may be smaller than that of the outlet restrictor or vice versa, which allows one of the restrictors to have the additional functionality of acting as a particle filter and/or cross-talk filter, which prevents respectively particles and/or pressure pulses from passing through said restrictor. The other one of the restrictors then has the larger cross-section to enable a higher through-flow and/or act as a sufficiently large outlet for particles to pass through to remove said particles from the pressure chamber. The chance of particles residing in the pressure chamber and negatively affecting the performance of the droplet jetting device is thereby reduced, while preventing cross-talk between pressure chambers. The inlet and outlet restrictors are further formed in the restrictor layer, wherein also the actuator chamber is provided. This results in a compact design with a small footprint, which is advantageous for achieving a high nozzle density.

The cross-section of the inlet restrictor is smaller than that of the outlet restrictor, preferably no greater than half of the cross-section of the outlet restrictor. The cross-section or effective area of the inlet restrictor is preferably less than that of the outlet restrictor. The cross-section of the inlet restrictor may in one embodiment be sufficiently small to substantially prevent particles larger than a predetermined size as well as pressure waves originating from an actuation of the actuator from passing through it. The inlet restrictor is the narrower of the two restrictors such that it acts as a particle filter and a cross-talk damper, while the outlet restrictor is sufficiently large to allow particles to exit the pressure chamber. Thereby the chance of particles entering the pressure chamber is reduced as well as the effectiveness by which such particles may be removed from the pressure chamber. Since the restrictors are adjacent the pressure chamber, this manner of filtering and removing particles is highly effective. This improves the performance and lifetime of the droplet jetting device. Also, the chance of particles residing in and contaminating the pressure chamber is reduced.

The inlet and outlet restrictors of neighboring droplet jetting devices alternate their relative positions, such that the outlet restrictors and inlet restrictors of neighboring droplet jetting devices are respectively positioned adjacent to one another. At each separation wall between two neighboring pressure chambers either two inlet restrictors or two outlet restrictors are positioned, one at each side of the separation wall. This may be achieved by e.g. a <NUM>. pattern of the different types of restrictors. At the separation walls restrictors of the same type (i.e. inlet or outlet) are positioned in close proximity to one another, allowing these to be connected to a single line or chamber in the layer above the restrictor layer. Preferably, a single supply line is formed in the distribution layer over each pair of neighboring inlet restrictors. Both neighboring inlet restrictors may thus be supplied via said single supply line, which is formed in the distribution layer over both said inlet restrictors and the separation wall. Likewise, a single return line may be connected to neighboring pairs of outlet restrictors. A single damper element is formed in the distribution layer over each pair of neighboring restrictors, specifically outlet restrictors. Thereby the object of the present invention has been achieved.

More specific optional features of the invention are indicated in the dependent claims.

In an embodiment, the cross-sectional area of the inlet restrictor is between <NUM> and <NUM><NUM>, preferably between <NUM> and <NUM><NUM>. The inlet restrictor may for example have a cross-section between <NUM>×<NUM><NUM> and <NUM>×<NUM><NUM>. The outlet restrictor's diameter is larger, preferably at least twice, thrice, or more than that of the inlet restrictor, very preferably over <NUM><NUM>, for example at least <NUM>×<NUM><NUM>. The inlet restrictor's cross-section may be selected based upon the print head's application and properties of the ink to be applied to said print head.

In an embodiment, the restrictors are formed as straight passages extending perpendicular to the membrane through the full thickness of the restrictor layer. The restrictors have a substantially uniform cross-section through the full thickness of the restrictor layer. Substantially uniform is herein defined to also include minor deviations due to the restrictor formation process, for example by means of photolithographic etching. Both restrictors are further preferably parallel to a stacking direction perpendicular to the plane of the layers forming the droplet jetting device. The restrictor layer is therein bonded to the membrane, such that the restrictors are aligned with their respective openings in the membrane.

In an embodiment, the distribution layer further comprises a damper element formed of a first damper chamber and a flexible damper membrane, the damper membrane and first damper chamber being positioned over the outlet restrictor. The damper membrane seals off the first damper chamber, thereby allowing the damper membrane to deform when a pressure pulse or fluctuation reaches the damper element. Such a pressure pulse may be absorbed by the damper element and prevented from travelling into another pressure chamber. The damper element is positioned over the outlet restrictor, such that these overlap when viewed in the stacking direction. A second damper chamber is positioned between the membrane and the outlet restrictor, which second damper chamber is in fluid connection with the outlet restrictor as well as with a return line, such that ink may be removed from the pressure chamber. The cross-section of the outlet restrictor is sufficiently large to allow any particles to exit the pressure chamber. The outlet restrictor extends in the stacking direction, which is generally against the direction of gravity during use. This allows for an efficient removal of gas bubbles. Similarly, gas bubbles are less likely to pass downwards into the pressure chamber through the vertical inlet restrictor. Due to its narrow cross-section no damper element needs to be provided over the inlet restrictor. Instead a supply line is preferably positioned vertically over the inlet restrictor to create a space efficient supply structure. The damper element for example overlaps both outlet restrictors and may be formed by having the first and second damper chambers extend over both outlet restrictors. The second damper chamber therein acts as a channel connecting both outlet restrictors to the return line, preferably via an outlet channel extending facing and parallel to a plane of the membrane layer.

In an embodiment, the first damper chamber and the damper membrane extend partially over the actuator chamber. To achieve a compact design, the damper element partially overlaps the actuator chamber, when viewed in the stacking direction. In consequence, the average footprint of an individual droplet jetting device is relatively small allowing for a high nozzle density. The damper element is preferably integrated in the distribution layer and positioned between a supply line and a return line in connection to the respective pressure chamber over which the damper element extends. Between is herein preferably intended when viewed in a width direction of the actuator parallel to a plane of the membrane. The distribution layer may in an embodiment be formed of two wafers or sheets bonded together on opposite sides of a damper membrane film, wherein the first and second damper chambers are provided in different ones of the wafers or sheet at corresponding positions.

To achieve a space efficient configuration, the damper element may in an embodiment be connected to a return channel, the return channel being positioned over an actuator chamber and between a supply line and a damper element in the distribution layer. For neighboring outlet restrictors, the damper element may, at least for a major portion, be positioned over one of one of the pressure chambers corresponding to said outlet restrictors, while the return line is positioned over the other of said pressure chambers, where the return line is also located. The damper element therein extends over both outlet restrictors and with a minor portion laying over the other of said pressure chambers. In consequence, the return line is positioned over the actuator chamber of the other of the pressure chambers. The damper element does not extend over this pressure chamber as far as over the first one of the pressure chambers, such that there is space for the return line over this actuator chamber. The return line is then positioned between this latter damper element and a supply line connected to the inlet restrictor of the other of the pressure chambers. As such, the damper element, supply lines, and return lines may be positioned substantially within the footprint of the pressure chambers. This vertical overlapping configuration allows the width of the pressure chamber to effectively determine the nozzle spacing and resolution.

In an embodiment, the distribution layer is provided on the restrictor layer. The distribution layer is preferably bonded directly on the restrictor layer, e.g. by an adhesive or other type of chemical bonding. Preferably, the distribution layer is formed of two wafers bonded on opposite sides of a damper membrane film. This allows for a relatively simple construction of the restrictor layer and distribution layers, as these can be formed of no more than four layers (ignoring adhesive or bonding layers), specifically three wafers and a membrane film. For example, the distribution layer may be formed of two etched silicon wafers bonded on opposite sides of a damper membrane film. Both said wafers can be etched to form the passages for supply and return lines as well as the first and second actuator chambers including an outlet channel between the second damper chamber and the return line. The distribution layer is bonded onto the restrictor layer which may be formed of a single wafer provided with passages for inlet and outlet restrictors as well as an actuator chamber. The passages are formed as through-holes, while the actuator may be formed as a recess or as a through-hole. The restrictor layer in turn is bonded onto the membrane, such that the actuator is sealed by the membrane in the actuator chamber and positioned over the pressure chamber, which is formed on an opposite side of the membrane. The pressure chamber is completed by adhering the nozzle layer to the membrane layer.

In an embodiment, the print head according to the present invention comprises four droplet jetting devices positioned in a row, wherein the inlet restrictors of the central droplet jetting devices are positioned besides one another with a single supply channel extending over both inlet restrictors, and wherein each pair of an outer droplet jetting device and its neighbor comprise a damper element positioned over both outlet restrictors and at least one of the actuator chambers of said droplet jetting devices and an outlet channel connected to a second damper chamber of the damper element and to both outlet restrictors, which outlet channel extends over only one of the actuator chambers of said droplet jetting devices. With the exception of the outer ends of the row, respectively the inlet restrictors and outlet restrictors are spatially grouped together, in close proximity to one another on opposite sides of a separation wall between pressure chambers. Effectively, along the direction of the row in the restrictor layer, one finds in order, an inlet restrictor, an actuator chamber, a pair of outlet restrictors, an actuator chamber, a pair of inlet restrictors, an actuator chamber, a pair of outlet restrictors, an actuator chamber, and an inlet restrictor. A single damper element is provided over neighboring outlet restrictors, which outlet restrictors are connected to the same return line. Neighboring inlet restrictors are supplied via the same supply line. The inlet restrictors at the outer ends of the row are provided with an individual supply line. Consequently, the row structure of the distribution layer there provides in order a supply line, a damper element, a return line, a supply line, a damper element, a return line, and a supply line. The pairs of respective restrictors are each connected to their respective supply or return line. This structure may be repeated perpendicular to the row direction to create a large array of nozzles.

The present invention further relates to a method of forming an inkjet print head, comprising the steps of:.

The restrictor layer may be formed of a single wafer by etching through-holes for the passages. The passages preferably have a uniform cross-section, wherein the cross-section of the inlet passages is different, specifically smaller, than that of the outlet passages. The actuator chamber recess is formed by partially etching the wafer in between inlet and outlet restrictor passages. The membrane layer comprises a flexible membrane with multiple actuators on it. The flexible membrane is provided with openings aligned with the inlet and outlet passages in the restrictor layer, such that when bonded together the passages are in fluid connection to the pressure chamber, which is formed by mounting the nozzle layer on the membrane layer. The membrane or nozzle layer may comprise the side or separation walls of the pressure chambers. In the stacking direction, the inlet and outlet passages as well as the actuator chamber recesses are within the footprint or circumference of each respective pressure chamber. This allows for a high nozzle density.

In an embodiment, the method according to the present invention further comprises the steps of:.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the scope of the present invention will become apparent to those skilled in the art from this detailed description.

<FIG> shows a cross-section of a MEMS chip as part of an inkjet print head <NUM>. <FIG> shows an enlarged view of a single droplet jetting device <NUM>, specifically the left most droplet jetting device which was integrated into the MEMS chip in <FIG>. The MEMS chip may be used in an ink jet print head <NUM> for various applications, such as the printing as images or other 2D or 3D structures, like components or electronics. The MEMS chip and, accordingly, the jetting devices <NUM> have a layered structure comprising as main layers a distribution layer <NUM>, a restrictor layer <NUM>, a membrane layer <NUM>, and a nozzle layer <NUM>.

The distribution layer <NUM> is formed of multiple single silicon layers, which together have a relatively large thickness as compared to the other layers <NUM>, <NUM>, <NUM>. The distribution layer <NUM> defines an ink supply line <NUM> through which liquid ink may be supplied from an ink reservoir (not shown) to a pressure chamber <NUM>-<NUM>‴ that is formed on the bottom side of the membrane layer <NUM>. The ink reservoir is common to a plurality of jetting devices and is formed separately from the distribution layer <NUM> on the top side of the distribution layer, i.e. on the side opposite to the membrane layer <NUM>. As shown in <FIG>, the distribution layer <NUM> is further provided with a return line <NUM>-<NUM>' for transporting ink out of the pressure chamber <NUM>-<NUM>"', for example back to the ink reservoir. This allows for a continuous flow of ink through the pressure chamber <NUM>-<NUM>"', even when the actuator <NUM>-<NUM>‴ is inactive. This constant throughflow prevents ink from stagnating in the pressure chamber <NUM>-<NUM>"' and allows particles such as dirt or gas bubbles to be removed from the pressure chamber <NUM>-<NUM>"', thereby improving the performance and lifetime of the droplet jetting device <NUM>-<NUM>"'. A damper element <NUM>-<NUM>' is also formed in the distribution layer <NUM> by means of a first damper chamber <NUM>-<NUM>' and a deformable damper membrane <NUM>-<NUM>'.

The membrane layer <NUM> is obtained from a SOI wafer having an insulator layer <NUM> and silicon layers <NUM> and <NUM> formed on both sides thereof. The pressure chamber <NUM>-<NUM>"' is formed in the bottom silicon layer <NUM>. The top silicon layer <NUM> and the insulator layer <NUM> form a continuous flexible membrane <NUM> with uniform thickness which extends over the entire area of the MEMS chip and is pierced by openings <NUM>, <NUM> at the positions of the inlet restrictors <NUM>-<NUM>‴ and the outlet restrictors <NUM>-<NUM>‴ respectively, so as to connect the ink supply line <NUM> to the pressure chamber <NUM>-<NUM>‴ and the pressure chamber <NUM>-<NUM>‴ to the return line <NUM>-<NUM>'. A piezoelectric actuator <NUM>-<NUM>‴ is formed on the top side of the part of the membrane <NUM> that covers the pressure chamber <NUM>-<NUM>"'. The actuator <NUM>-<NUM>‴ is accommodated in an actuator chamber <NUM>-<NUM>‴ formed at the bottom side of the restrictor layer <NUM>. The restrictor layer <NUM> is positioned between the membrane layer <NUM> and the distribution layer <NUM>. Aside from the actuator chamber <NUM>-<NUM>"', the restrictor layer <NUM> defines an inlet restrictor <NUM>-<NUM>‴ and an outlet restrictor <NUM>-<NUM>"', connected respectively to the supply line <NUM>-<NUM>" and the return line <NUM>-<NUM>'. The actuator chamber <NUM>-<NUM>‴ is formed as a recess having a height less than the thickness of the restrictor layer <NUM>. The actuator chamber <NUM>-<NUM>‴ in the cross-sectional view in <FIG> is positioned between the inlet restrictor <NUM>-<NUM>‴ and the outlet restrictor <NUM>-<NUM>"'.

An electrically insulating silicon oxide layer <NUM> insulates the actuator <NUM>-<NUM>‴ and its electrodes from the silicon layer <NUM> and carries electric leads <NUM> arranged to contact the electrodes on the top and bottom sides of the actuator <NUM>-<NUM>"'. The leads <NUM> are partially exposed and extend towards a contact region (not shown) where the distribution layer <NUM> has been locally removed. The inlet restrictor <NUM>-<NUM>‴ and the outlet restrictor <NUM>-<NUM>‴ are formed as a passage with a constant or uniform cross-section and extend through the full thickness of the restrictor layer <NUM> in the stacking direction Z. The width and/or cross-section of the inlet restrictor <NUM>-<NUM>‴ is significantly smaller than that of the trench <NUM> forming the supply line <NUM>-<NUM>". The outlet restrictor's effective diameter in turn is substantially smaller than that of the return line <NUM>. Narrow restrictors <NUM>-<NUM>"', <NUM>-<NUM>‴ improve the control over the pressure wave in the pressure chamber <NUM>-<NUM>‴.

The nozzle layer <NUM> is obtained from an SOI wafer and has a thin silicon layer <NUM> interposed between two insulator layers <NUM> and <NUM>. By etching a channel <NUM>, a nozzle <NUM>-<NUM>‴ is formed in the two insulator layers <NUM> and <NUM> and in the silicon layer <NUM> intervening between them, so that the thickness of these three layers defines the length of the nozzle <NUM>-<NUM>"'. The nozzle <NUM>-<NUM>‴ is positioned at a middle or central portion of the pressure chamber <NUM>-<NUM>"', between in the inlet restrictor <NUM>-<NUM>‴ and the outlet restrictor <NUM>-<NUM>‴, in the cross-sectional view of <FIG> and <FIG>.

It will be understood that the droplet jetting devices <NUM>-<NUM>‴ of the MEMS chip are arranged such that their nozzles <NUM>-<NUM>‴ define a nozzle array consisting for example of four or even more parallel nozzle lines with uniform nozzle-to-nozzle spacings which will determine the spatial resolution of the print head. Within the contact region, each of the leads <NUM> can be contacted, e.g. via bumps or contact pads, so that energizing signals in the form of electric voltage pulses may be applied individually to each actuator <NUM>-<NUM>"'.

When a voltage is applied to the electrodes of the actuator <NUM>-<NUM>"', the piezoelectric material of the actuator is caused to deform in a bending mode, thereby flexing the membrane <NUM> and consequently changing the volume of the pressure chamber <NUM>-<NUM>"'. Typically, a voltage pulse is applied to the actuator to cause a deformation that increases the volume of the pressure chamber <NUM>-<NUM>‴, so that ink is sucked-in from the supply line <NUM>. Then, when the voltage pulse drops off or changes into a pulse with opposite polarity, the volume of the pressure chamber <NUM>-<NUM>"' is decreased abruptly, so that an acoustic pressure wave is generated which propagates through the pressure chamber <NUM>-<NUM>"' and through the nozzle <NUM>-<NUM>"', with the result that a droplet of ink is jetted-out from the nozzle <NUM>-<NUM>"'.

The print head MEMS chip in <FIG> comprises four neighboring droplet jetting devices <NUM>-<NUM>"', the pressure chambers <NUM>-<NUM>‴ of which are identically in size. Each pressure chamber <NUM>-<NUM>"' has three openings: the nozzle <NUM>-<NUM>"', the inlet restrictor <NUM>-<NUM>"', and the outlet restrictor <NUM>-<NUM>"'. For each of the four droplet jetting devices <NUM>-10ʺʺ the nozzle <NUM>-<NUM>‴ is in the same central position with respect to the pressure chamber <NUM>-<NUM>"'. The inlet restrictors <NUM>-<NUM>‴ and outlet restrictors <NUM>-<NUM>‴ alternate in their relative positions from one four droplet jetting device <NUM>-<NUM>‴ to the next. In consequence, on the respective sides of neighboring four droplet jetting devices <NUM>-<NUM>‴ either the restrictors <NUM>-<NUM>‴ or outlet restrictors <NUM>-<NUM>‴ positioned adjacently at the separation walls between the pressure chambers <NUM>-<NUM>‴ neighboring droplet jetting devices <NUM>-<NUM>‴.

Each inlet restrictor <NUM>-<NUM>‴ has a substantially smaller cross-section than its respective outlet restrictor <NUM>-<NUM>"'. The inlet restrictor <NUM>-<NUM>‴ is formed as a passage with a uniform cross-section over the full length of the passage, which passage extends through the entire restrictor layer <NUM>. The outlet restrictor <NUM>-<NUM>‴ is formed in a similar manner on an opposite of the actuator chamber <NUM>-<NUM>‴ and width a larger cross-section. The narrow cross-section of the inlet restrictor <NUM>-<NUM>‴ allows the inlet restrictor <NUM>-<NUM>‴ to act as a filter, preventing dirt particles and gas bubbles from passing into the pressure chamber <NUM>. Since the inlet restrictor <NUM>-<NUM>‴ is positioned at the pressure chamber <NUM>-<NUM>"' itself, this filter is highly effective. A narrow cross-section of the inlet restrictor <NUM>-<NUM>‴ provides the additional advantage of so-called "cross-talk filtering". Pressure waves generated in one pressure chamber <NUM>-<NUM>"' are prevented from travelling through the narrow inlet restrictor <NUM>-<NUM>‴ into a neighboring pressure chamber <NUM>-<NUM>"'.

Since the outlet restrictor <NUM>-<NUM>‴ is intended for removing dirt particles and gas bubbles from the pressure chamber <NUM>-<NUM>"', a wider cross-section is provided for the outlet restrictor <NUM>-<NUM>"'. Particles are then allowed to be flushed from the pressure chamber <NUM>-<NUM>"' on an ink flow between the inlet and outlet restrictors <NUM>-<NUM>‴, <NUM>-<NUM>‴. The larger cross-section however also increases the risk of cross-talk, since larger cross-section of the outlet restrictor <NUM>-<NUM>‴ may allow pressure waves to travel from one pressure chamber <NUM>-<NUM>"' to the other. The damper element <NUM>-<NUM>' is positioned over the outlet restrictors <NUM>-<NUM>‴ to absorb any pressure waves exiting the pressure chamber <NUM>-<NUM>"' there. The damper element <NUM> is formed by a flexible damper membrane <NUM> which seals off the first damper chamber <NUM>. The second damper chamber <NUM> is positioned on the opposite side of the damper membrane <NUM> and over the outlet restrictors <NUM>-<NUM>‴ for receiving ink from the pressure chambers <NUM>-<NUM>"'. Pressure waves or pulses exiting the outlet restrictor <NUM>-<NUM>‴ are absorbed by the damper membrane <NUM>, preventing them from reaching another pressure chamber <NUM>-<NUM>‴.

The damper element <NUM> in <FIG> is formed in the distribution layer <NUM> by separating the first and second damper chambers <NUM>-<NUM>', <NUM>-<NUM>' from on another by means of the damper membrane film <NUM>. The damper element <NUM> in <FIG> extends over the pair of neighboring outlet restrictors <NUM>-<NUM>'. The majority of this damper element <NUM> is positioned over the actuator <NUM> of the left one of this pair of neighboring droplet forming devices <NUM>, <NUM>' in <FIG>. From the second damper chamber <NUM> an outlet passage <NUM> extends parallel to the plane of the layers <NUM>-<NUM> into the return line <NUM>. The return line <NUM> is formed as a trench <NUM> in the distribution layer <NUM>. The return line <NUM> is positioned over the actuator <NUM>' of other of the pair of droplet jetting devices <NUM>, <NUM>'. Similarly and as shown in <FIG>, the damper element <NUM>' extends over the outlet restrictors <NUM>", <NUM>‴ of the other pair of droplet jetting devices <NUM>", <NUM>"'. For each pair of neighboring droplet jetting devices <NUM>-<NUM>‴ a single damper element <NUM>, <NUM>' and a single return line <NUM>, <NUM>' is provided. In <FIG>, each damper element <NUM>, <NUM>' and respective return line <NUM>, <NUM>' lie in between the remote ends of the respective pressure chambers <NUM>-<NUM>"', where the inlet restrictors <NUM>-<NUM>‴ are located. This results in a small footprint of each droplet jetting device <NUM>-<NUM>‴, which allows for a high nozzle resolution.

In between pairs of adjacent outlet restrictors <NUM>-<NUM>‴ in <FIG>, adjacent pairs of inlet restrictors <NUM>', <NUM>" are arranged on opposing sides of the separation wall between the pressure chambers <NUM>', <NUM>" of the central droplet jetting devices <NUM>', <NUM>" in <FIG>. Said inlet restrictors <NUM>', <NUM>" are connected to a single supply line <NUM>', which is formed as trench <NUM>' in the distribution layer <NUM> over both said inlet restrictors <NUM>', <NUM>". The cross-section of said central supply line <NUM>' is larger than that of the supply lines <NUM>, <NUM>" which each supply an individual droplet jetting device <NUM>, <NUM>"'.

The distribution layer <NUM> is formed of a pair of sub-layers 12A, 12C, for example silicon wafers, which are bonded to opposite sides of a membrane film 12B. The upper sub-layer 12A has been provided with through-holes to form the upper portions of the supply and return trenches <NUM>-<NUM>", <NUM>-<NUM>'. The first damper chambers <NUM>, <NUM>' are formed as recesses. The second sub-layer 12C is provided with corresponding openings for the trenches <NUM>-<NUM>", <NUM>-<NUM>' as well a second damper chamber <NUM>, <NUM>' aligned with the position of the first damper chamber <NUM>, <NUM>'. Additionally, outlet channels <NUM>, <NUM>' are provided to connect the second damper chambers <NUM>, <NUM>' to their respective outlet trenches <NUM>, <NUM>' in the sub-layer 12C. The sub-layers 12A, 12C are then adhered to the membrane film 12B, aligning the respective openings to form the trenches <NUM>-<NUM>", <NUM>-<NUM>' and sealing off the first damper chamber <NUM>, <NUM>'.

When forming rows of large numbers of nozzles <NUM>-<NUM>"', a single trench <NUM>-<NUM>" can be used to supply ink to all nozzles <NUM>-<NUM>‴ in a row. This is shown in <FIG>, wherein the nozzle rows extend in the direction X. For the sake of illustration four different groups of droplet jetting devices <NUM>-<NUM>‴ in the direction X are illustrated, though in practice this number will be significantly greater, for example <NUM> or <NUM> of such units per cm (<NUM> or <NUM> of such units per inch). The droplet jetting devices <NUM>-<NUM>‴ as discussed for <FIG> and <FIG> are provided in a repeating manner in the direction X. The droplet jetting devices <NUM>-<NUM>‴ are aligned along the direction X. In consequence the restrictors <NUM>-<NUM>"', <NUM>-<NUM>'" in <FIG> extend in parallel rows in direction X. A single trench <NUM>-<NUM>" extending in the direction X is then sufficient to supply ink to the respectively aligned restrictors <NUM>-<NUM>"'. Similarly, a single membrane <NUM>-<NUM>' is provided for forming the damper element <NUM>-<NUM>' over the respective neighboring rows of outlet restrictors <NUM>-<NUM>‴.

The present invention further relates to a process of manufacturing a large number of MEMS chips each of which includes a plurality of droplet jetting devices <NUM>-<NUM>"'.

The membrane layer is formed by etching a doubled sided SOI wafer. On one side of the insulator layer <NUM> one silicon layer <NUM> is etched to form recesses for the rectangular pressure chambers <NUM>-<NUM>"'. In the length direction X the pressure chambers <NUM>-<NUM>‴ are separated by separation walls of non-etched silicon. The other silicon layer <NUM> along with the insulator layer <NUM> is etched to provide the openings <NUM>, <NUM> for connecting the outlet restrictor <NUM>-<NUM>‴ and inlet restrictors <NUM>-<NUM>‴ to the pressure chamber <NUM>-<NUM>"'. An insulating silicon oxide layer <NUM> is the provided on the other silicon layer <NUM> on a side opposite the insulator layer <NUM>. Subsequently, bottom electrodes and leads connected thereto for the actuator <NUM>-<NUM>‴ are deposited on the insulating silicon oxide layer <NUM>. A piezo-electric material is then deposited onto the bottom electrode, followed by top electrodes, leads, an additional insulating and moisture protection layers to form a functioning actuator <NUM>-<NUM>"'.

The nozzle layer <NUM> is obtained from a SOI wafer with a top silicon layer <NUM> and a thinner silicon layer <NUM> in between two insulator layers <NUM> and <NUM>. A passage <NUM> for the nozzle <NUM>-<NUM>‴ is etched through the two insulator layers <NUM> and <NUM> and the silicon layer <NUM>. The nozzle layer <NUM> is bonded to the membrane layer <NUM> via an adhesive layer <NUM>.

The restrictor layer <NUM> is formed of single silicon wafer. Inlet and outlet passages for the inlet and outlet restrictors <NUM>-<NUM>‴, <NUM>-<NUM>‴ are etched through this silicon wafer in corresponding positions and cross-sections with the openings <NUM>, <NUM> in the top silicon layer <NUM> of the membrane layer <NUM>. In an exaggerated view in <FIG> the cross-sections of the opening <NUM> is shown as slightly smaller than that of the outlet restrictor <NUM>-<NUM>‴ to prevent the adhesive <NUM> from flowing into the opening <NUM>. This may also be applied to the opening <NUM>. Between the inlet and outlet passages for the restrictors <NUM>-<NUM>‴, <NUM>-<NUM>"', a recess is etched to form the actuator chamber <NUM>-<NUM>‴. The restrictor layer <NUM> is then bonded onto the membrane layer <NUM> opposite to the pressure chambers <NUM>-<NUM>"' by means of adhesive layer <NUM>. Thereby, each actuator <NUM>-<NUM>‴ is sealed in its actuator chamber <NUM>-<NUM>‴ by the membrane layer <NUM>. The inlet and outlet passages for the restrictors <NUM>-<NUM>"', <NUM>-<NUM>‴ as well as the actuator chamber <NUM>-<NUM>‴ are positioned over its respective pressure chamber <NUM>-<NUM>"', i.e. within the footprint or area of said pressure chamber <NUM>-<NUM>‴ when viewed in the stacking direction Z.

The distribution layer <NUM> is formed by bonding two silicon wafers 12A, 12C together on opposite sides of the damper membrane film 12B. One silicon wafer 12A is etched to provide passages for the supply and return lines <NUM>-<NUM>", <NUM>-<NUM>' as well as recesses for forming the first damper chambers <NUM>-<NUM>', which are sealed by the damper membrane film 12B. The other silicon wafer 12C is provided with corresponding channels supply and return lines <NUM>-<NUM>", <NUM>-<NUM>' as well as a channel for the second damper chambers <NUM>-<NUM>' positioned in alignment with and opposite to the first damper chambers <NUM>-<NUM>' with respect to the damper membrane film 12B. Additionally, outlet channels <NUM>-<NUM>' are etched in the second silicon layer 12C to provide a connection between each second damper chamber <NUM>-<NUM>' and its adjacent return line <NUM>-<NUM>'. The supply lines <NUM>-<NUM>" are positioned over the inlet restrictors <NUM>-<NUM>‴, while the damper chambers <NUM>-<NUM>', <NUM>-<NUM>' and the return lines <NUM>-<NUM>' are positioned as neighboring pairs between inlet restrictors <NUM>-<NUM>"'. The damper chambers <NUM>-<NUM>', <NUM>-<NUM>' are positioned for a major part over a respective pressure chamber <NUM>-<NUM>‴, while the return line <NUM>-<NUM>' in fluid connection with said damper chambers <NUM>-<NUM>' is positioned over a neighboring pressure chamber <NUM>-<NUM>"". The distribution layer <NUM> is bonded to the restrictor <NUM> by means of an adhesive.

It will also be appreciated that in this document the terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.

Claim 1:
An inkjet print head (<NUM>) comprising a plurality of a droplet jetting devices (<NUM>-<NUM>‴) formed of a nozzle layer (<NUM>) defining, for each droplet jetting device, a nozzle (<NUM>-<NUM>"'), a membrane layer (<NUM>) carrying, on a membrane (<NUM>), a restrictor layer (<NUM>) and an actuator (<NUM>-<NUM>‴) for generating pressure waves in a liquid in a pressure chamber (<NUM>-<NUM>‴) that is connected to the nozzle (<NUM>-<NUM>‴), the actuator (<NUM>-<NUM>‴) being positioned in an actuator chamber (<NUM>-<NUM>‴) in the restrictor layer (<NUM>), and a distribution layer (<NUM>) defining a supply line (<NUM>-<NUM>") for supplying the liquid to the pressure chamber (<NUM>-<NUM>"'), wherein the restrictor layer (<NUM>) comprises an inlet restrictor (<NUM>-<NUM>‴) and an outlet restrictor (<NUM>-<NUM>‴) positioned on opposites sides of the actuator (<NUM>-<NUM>‴), characterized in that a cross-section of the inlet restrictor (<NUM>-<NUM>‴) is different from that of the outlet restrictor (<NUM>-<NUM>"'), wherein the cross-section of the inlet restrictor (<NUM>-<NUM>‴) is smaller than that of the outlet restrictor (<NUM>-<NUM>‴), preferably no greater than half of the cross-section of the outlet restrictor (<NUM>-<NUM>"'), characterised in that the inlet and outlet restrictors (<NUM>-<NUM>", <NUM>-<NUM>') of neighboring droplet jetting devices (<NUM>-<NUM>‴) alternate in position, such that the outlet restrictors (<NUM>-<NUM>‴) and inlet restrictors (<NUM>-<NUM>‴) of neighboring droplet jetting devices (<NUM>-<NUM>‴) are respectively positioned adjacent one another, and wherein a single damper element (<NUM>-<NUM>') is formed in the distribution layer (<NUM>) over each pair of neighboring outlet restrictors (<NUM>-<NUM>‴).