Inkjet printhead

Abstract

A printhead for ejecting one or more printable fluids, the printhead comprising a substrate defining a plurality of MEMS droplet ejectors arranged in a grid, each droplet ejector comprising a flexible diaphragm, a piezoelectric actuator, and at least one MEMS metallization layer; the substrate further defines CMOS control circuitry comprising at least one CMOS metallization layer and one or more of: an electrically conductive connection in at least one of the metallization layers extending from the CMOS control circuitry to each piezoelectric actuator to actuate the piezoelectric actuator; an electrically conductive connection in at least one of the metallization layers extending through the grid to transmit an actuator drive waveform; and a plurality of bonding pads in the discrete regions. The printhead is compact, can be easily manufactured, and requires relatively few wired connections.

Description

Technical Field

[0001] The present invention relates to the field of inkjet print heads formed as an integral structure on a substrate. The inkjet print heads eject printable fluids, such as color inks, materials for additive printing, and the like. Background Art

[0002] Conventional piezoelectric inkjet printheads that form a high density of individual drop ejectors on the same substrate require a large number of individual wire connections, at least one per drop. For a 1200 dpi inkjet printhead, this may amount to 1200 individual wire bonds to make external off-chip connections.

[0003] It has been proposed to provide an integrated piezoelectric inkjet printhead with a CMOS drive circuit system formed on a substrate and superimposed with a MEMS layer containing nozzles and MEMS piezoelectric transducers (WO2018 / 054917, McAvoy). This allows the number of external off-chip connections to be greatly reduced. In addition, the device can be formed using conventional CMOS foundry processes without the need for additional assembly steps to join the droplet ejector components.

[0004] It is desirable to maximize drop ejector density, minimize printing artifacts, and have adjacent nozzles be subject to consistent physical parameters (temperature, pressure, etc.). As a result, on-chip wiring of individual drop ejectors presents technical problems and can limit the maximum drop ejector density. This is particularly true in devices where the nozzles are formed in the MEMS layer and the ink chamber is at least partially defined by the substrate. In this case, the resulting holes through the substrate and at least some of the surface area required for the piezoelectric transducers are not available for transmitting electrical signals, thereby limiting the drop ejector density.

[0005] The present invention addresses these problems and aims to provide a compact, monolithic printhead that can be formed with a high density of drop ejectors, typically using conventional CMOS foundry processes. Summary of the invention

[0006] A printhead for ejecting one or more printable fluids, the printhead comprising a substrate;

[0007] the substrate defining a plurality of MEMS drop ejectors arranged in a grid for ejecting droplets of the one or more printable fluids, each drop ejector comprising a flexible diaphragm and a piezoelectric actuator for ejecting a droplet of a (corresponding) printable fluid through a nozzle by moving the flexible diaphragm, each drop ejector comprising at least one MEMS metallization layer;

[0008] The substrate further defines CMOS control circuitry including at least one CMOS metallization layer.

[0009] The substrate may include conductive connections in at least one of the metallization layers (ie, at least one of the MEMS metallization layers and / or at least one of the CMOS metallization layers) extending from the CMOS control circuitry to each piezoelectric actuator to actuate the piezoelectric actuator.

[0010] The substrate may include conductive connections in at least one of the metallization layers (ie, at least one of the MEMS metallization layers and / or at least one of the CMOS metallization layers) extending through the grid to transmit actuator drive waveforms.

[0011] The substrate may include a plurality of bond pads located in discrete (eg, single) regions of the substrate (eg, along a single edge).

[0012] The substrate may include one or more of the following:

[0013] (i) conductive connections in at least one of the metallization layers (i.e., at least one of the MEMS metallization layers and / or at least one of the CMOS metallization layers) extending from the CMOS control circuitry to each piezoelectric actuator to actuate the piezoelectric actuator; and

[0014] (ii) conductive connections in at least one of said metallization layers (i.e., at least one of said MEMS metallization layers and / or at least one of said CMOS metallization layers) extending through said mesh to transmit an actuator drive waveform, optionally and / or

[0015] (iii) A plurality of bond pads located in discrete (eg, single) regions of the substrate (eg, along a single edge).

[0016] The one or more printable fluids may comprise a plurality of printable fluids, typically at least three or at least four different printable fluids. The printable fluid may be ink. The color of the ink may be different. The printhead may be a multi-channel printhead. Thus, a printhead having a plurality of different printable fluids and / or a plurality of different grids (droplet ejector zones) is referred to, typically with a separate printable fluid supply.

[0017] The grid may be a parallelogram grid. The grid may be a diamond grid, a hexagonal grid, a rectangular grid (eg, a square grid), or an equilateral triangle grid. Thus, the plurality of MEMS droplet ejectors may be arranged in a grid.

[0018] The grid of MEMS droplet ejectors typically forms a droplet ejector zone of the substrate. The droplet ejector zone typically contains at least 100 droplet ejectors. The droplet ejector zone is typically elongated. The droplet ejector zone typically has a length and a width. The droplet ejector zone may be rectangular. The droplet ejector zone may be a parallelogram. Typically, the ratio of the length to the width of the droplet ejector zone is at least 5, or at least 10, or at least 20. With respect to length and width, it is meant the length and width of a minimum area rectangle that would completely enclose the droplet ejector zone.

[0019] Typically, the grid contains multiple rows of MEMS drop ejectors extending across the width of the grid. Typically, there are more rows (extending across the width) than MEMS drop ejectors in any one row. Typically, there are 4 to 16, or more typically 8 to 12 MEMS drop ejectors in each row (which extends across the width).

[0020] Typically, the grid contains more than 50 rows (which are typically parallel to each other). The rows can be arranged parallel to the width of the droplet ejector zone. However, this is not necessary, for example in the case of a parallelogram grid, the rows will not be arranged parallel to the width of the droplet ejector zone, but at a slight angle. Typically, the rows extend at an angle of 45° to 135° relative to the length of the droplet ejector zone, or at an angle of 30° to 120° relative to the length of the droplet ejector zone, or at an angle of 15° to 105° relative to the length of the droplet ejector zone.

[0021] The substrate includes (i) conductive connections (actuation conductive connections) in at least one of the metallization layers extending from the CMOS control circuitry to each piezoelectric actuator to actuate the piezoelectric actuator.

[0022] In some embodiments, one or more separate individual conductive connections extend from the CMOS control circuitry to each piezoelectric actuator to actuate each piezoelectric actuator individually. In other embodiments, one or more conductive connections for actuating the actuators are connected to each piezoelectric actuator in a plurality of piezoelectric actuators to actuate each piezoelectric actuator, however in this case, the CMOS control circuitry is typically configured to address control signals to each piezoelectric actuator individually.

[0023] Typically, the length of the actuation conductive connection is consistent between the CMOS control circuitry and the piezoelectric actuators in a group of piezoelectric actuators. The actuation conductive connections have similar lengths, thicknesses, and widths so that they are affected to similar degrees by voltage drops, parasitic capacitances, antenna effects, etc.

[0024] The length of the conductive connection for actuating the piezoelectric actuator may be uniform between the CMOS control circuitry and the piezoelectric actuator within the drop ejector region.

[0025] Typically, the length of the conductive connection between the CMOS control circuitry (e.g., ejection transistor) and the piezoelectric actuator in the drop ejector region for actuating the piezoelectric actuator varies by no more than 1 cm, preferably no more than 0.1 cm. Typically, the length of the conductive connection between the CMOS control circuitry and the piezoelectric actuator in the drop ejector region for actuating the piezoelectric transducer varies by no more than 10 times the spacing between drop ejectors along a row of drop ejectors. Typically, the substrate is elongated, having a length and a width, and the length of the conductive connection between the CMOS control circuitry and the piezoelectric actuator in the drop ejector region for actuating the piezoelectric transducer varies by no more than 20% or no more than 10% of the width of the substrate. The drop ejector region typically includes at least 8 drop ejectors. The drop ejectors in the drop ejector region typically eject the same one of a plurality of printable fluids.

[0026] Typically, the conductive connections for actuating the piezoelectric actuators include metal lines extending from CMOS control circuitry in one or more CMOS metallization layers, through connections to one or more MEMS metallization layers adjacent to the corresponding piezoelectric actuator, and through one or more MEMS metallization layers to electrodes of the MEMS piezoelectric actuator.

[0027] CMOS metallization is the metallization layer that connects the CMOS devices in the substrate and is formed as part of the CMOS manufacturing process. MEMS metallization is the metallization layer that is formed (on top of the CMOS metallization layer) and is used for the purpose of operating the MEMS device. (In the present invention, the MEMS metallization layer may also contain additional conductors, such as conductive connections for transmitting actuator drive waveforms).

[0028] One or more of the piezoelectric transducer, electrodes, and MEMS metallization layers may contain gold.Gold is excluded from CMOS manufacturing facilities.

[0029] A grid of MEMS drop ejectors may form a drop ejector region of a substrate that is elongated, has a length and a width, and has relatively long sides along the length, wherein conductive connections for actuating the actuators extend into the grid from one or both of the relatively long sides of the drop ejector region.

[0030] Typically, the conductive connections extend into the grid less than 1.5 times the width of the drop ejector zone, and typically less than 1.2 times. In some embodiments, the conductive connections extend into the grid less than the width of the drop ejector zone.

[0031] The CMOS control circuitry may include a plurality of drive transistors, at least one of the plurality of drive transistors being directly connected to at least one electrode of the piezoelectric transducer of each MEMS drop ejector through the conductive connection for actuating the piezoelectric actuator without an intervening transistor, wherein the plurality of drive transistors are arranged in at least one row adjacent to the one or two opposing long sides of the drop ejector area.

[0032] The conductive connections for actuating the piezoelectric actuators may extend into the grid between rows of MEMS drop ejectors.

[0033] Typically, the conductive connections for actuating the piezoelectric actuators extend from one or both opposing long sides into the grid between rows of MEMS drop ejectors. Typically, the conductive connections for actuating the piezoelectric actuators extend laterally into the grid between rows of MEMS drop ejectors.

[0034] This arrangement ensures that MEMS drop ejectors in the same row (parallel to the width) receive control signals from the control circuitry at very similar times. This improves print quality and / or reduces control complexity.

[0035] Typically, the aspect ratio of length to width (of the grid / droplet ejector zone) is at least 5, or at least 10, or at least 20.

[0036] The conductive connections for actuating the piezoelectric actuators may extend from one or both long sides into the grid, wherein the conductive connections for actuating the piezoelectric actuators extend from both long sides into the grid along the width.

[0037] The conductive connections for actuating the piezoelectric transducers may extend between rows of piezoelectric actuators that are aligned at an angle of at least 45° to the length of the drop ejector zone, and typically at least 60° or at least 75°.

[0038] The actuator drive waveform may contain a pulse with each polarity portion. Thus, the direction of the potential difference across each piezoelectric actuator reverses twice in each drop ejection.

[0039] The CMOS control circuitry can be configured to determine, for each MEMS droplet ejector, for each of a plurality of ejection cycles, whether the MEMS droplet ejector should eject a droplet, wherein a conductive connection for actuating the actuator is connected to an ejector switch (typically a latch) associated with each MEMS droplet ejector to thereby control whether each individual MEMS droplet ejector ejects a droplet.

[0040] Thus, a determination is made in the CMOS control circuitry as to whether each MEMS droplet ejector should eject a droplet (typically in response to digital image data received via a digital interface, typically one or more bond pads). This avoids the requirement for a large number of separate conductive connections to the control circuitry external to the substrate, thereby reducing the difficulty of connecting to the substrate. Typically, a determination is made for each MEMS droplet ejector for each of a plurality of ejection cycles. An ejection cycle may contain a plurality of phases, during each phase, if selected, a different subset of the MEMS droplet ejectors ejects printable fluid.

[0041] The substrate may include (ii) conductive connections extending through the grid in at least one of the metallization layers to transmit actuator drive waveforms to connect the MEMS drop ejector to one or more actuator drive waveform sources.

[0042] The conductive connections may connect different groups of MEMS drop ejectors to different ones of a plurality of actuator drive waveform sources to thereby deliver different actuator drive waveforms to the different groups of MEMS drop ejectors.

[0043] Typically, the MEMS droplet ejector comprises a plurality of spatially separated MEMS droplet ejector zones, each zone comprising a grid of MEMS droplet ejectors, and each MEMS droplet ejector in the same droplet ejector zone receives the same actuator drive waveform. Typically, for at least two or at least four different droplet ejector zones, the droplet ejectors in each zone receive different actuator drive waveforms. Typically, the droplet ejectors in each zone receive printable fluids from the same source. Thus, droplet ejectors ejecting different printable fluids may receive different actuator drive waveforms, while those droplet ejectors ejecting the same printable fluid may be located in the same droplet ejector zone and receive the same actuator drive waveform. Thus, the actuator drive waveform may be customized according to the physical properties of each printable fluid.

[0044] The source of the actuator drive waveform may include one or more actuator drive waveform generators. The source of the actuator drive waveform may include one or more interfaces, such as bonding pads of the print head substrate, typically the plurality of bonding pads, for receiving the actuator drive waveform from a source external to the substrate. The external source may be, for example, one or more actuator drive waveform generators that are not formed on the substrate and are typically separate from the print head, but are located within a printing device (such as a printer that also includes a print head).

[0045] The drop ejector zone may have a length and a width and have relatively long sides along the length, wherein the conductive connections for transmitting actuator drive waveforms extend from one or both of the relatively long sides of the drop ejector zone into the grid.

[0046] Conductive connections for transmitting actuator drive waveforms may extend from one or both relatively long sides into the grid. Conductive connections for transmitting actuator drive waveforms may extend from one or both relatively long sides into the grid between MEMS drop ejector rows. Conductive connections for transmitting actuator drive waveforms may extend laterally into the grid between MEMS drop ejector rows.

[0047] Conductive connections for conveying actuator drive waveforms may extend between rows of piezoelectric actuators that are aligned at an angle of at least 45° to the length of the drop ejector zone, and typically at least 60° or at least 75°.

[0048] The substrate may define a plurality of elongated drop ejector zones, and the conductive connections for conducting the actuator drive waveform comprise a plurality of separate busses, wherein for one or more elongated drop ejector zones, a conductor that is part of the bus to conduct the actuator drive waveform to that zone extends across the width of one or more additional drop ejector zones.

[0049] Thus, the conductive connections used to transmit the actuator drive waveforms need not extend around the (short) edge of each drop ejector zone, reducing their length and enabling the use of more substrate surface area than if they extended around the (short) edge of each drop ejector zone.

[0050] The substrate may include (iii) a plurality of bond pads in a single discrete region of the substrate.

[0051] The substrate may include a bonding pad area, the bonding pad area including a plurality of bonding pads, the bonding pad area being spatially separated from a plurality of MEMS droplet ejectors and typically also being spatially separated from the CMOS control circuitry. There may be only a single bonding pad area. The bonding pad area may be elongated and arranged along a single edge of the substrate. Typically, the substrate is elongated with opposing long edges with a short edge therebetween, and the bonding pad area is arranged along the long edge. However, in some embodiments, the bonding pad area may be on the short edge. There may be two bonding pad areas, the bonding pad areas being elongated and also typically arranged along opposing long sides of the substrate. The bonding pad area or the bonding pads within the bonding pad area may be spaced apart along a straight line.

[0052] The substrate may contain fewer than 75 or even fewer than 50 external electrical connections in total. The ratio of individually controllable MEMS drop ejectors to external electrical connections may be greater than 1, greater than 10, or in some embodiments greater than 100. This is accomplished by the CMOS control circuitry and reduces the complexity of the wiring connections to the substrate compared to a printing device that requires a separate electrical connection for each individually controllable MEMS drop ejector on the substrate.

[0053] One or more conductive connections for the actuator drive signal may be configured to provide potentials to 100 or more, or even 1000 or more drop ejectors in a switched manner. The conductive connections extending from the CMOS drive circuitry to the piezoelectric actuator to actuate the piezoelectric actuator may each provide potentials to 10 or fewer, 4 or fewer, or only one piezoelectric actuator. Therefore, they may require a much lower conductive metal cross-section than the conductive connections for the actuator drive signal.

[0054] There may be no transistors in the grid of a MEMS drop ejector.

[0055] However, for at least a majority of the plurality of MEMS drop ejectors, an ejector switch comprising one or more CMOS transistors formed on the substrate may be located within a grid in electronic communication with one or more of the conductive connections (the conductive connections for actuating the piezoelectric actuators and / or the conductive connections for transmitting the actuator drive waveforms and / or the conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages) to controllably cause a potential difference to be applied to electrodes of the piezoelectric actuators of the corresponding MEMS drop ejectors and cause the MEMS drop ejectors to eject printable fluid. The ejector switch typically includes a latch.

[0056] The injector switch may be configured to selectively communicate an actuator drive waveform (voltage and / or current) to a corresponding piezoelectric transducer, the actuator drive waveform being received via one or more of the conductive connections in at least one metallization layer.

[0057] Thus, the power electronics required to generate current for the piezoelectric converter can be located elsewhere, and the associated heat generated elsewhere. In some embodiments, the injector switch only needs to switch the actuator drive waveform, thereby reducing power consumption on the in-grid substrate.

[0058] Typically, the CMOS control circuitry is located in one or more discrete areas of the substrate, separate from the bond pads and MEMS drop ejector.

[0059] However, in some embodiments, for at least a majority of the plurality of MEMS drop ejectors, the ejector switch may be located within the grid. In other embodiments, one or more transistors are located within the CMOS control circuitry, the one or more transistors being used as ejector switches for individual corresponding MEMS drop ejectors. Thus, within a grid of MEMS drop ejectors, there may be no transistors, or at least fewer transistors than MEMS drop ejectors.

[0060] Each MEMS drop ejector may include an orifice through the substrate to eject a printable fluid.

[0061] Thus, the substrate comprises a plurality of holes, each hole being associated with a corresponding drop ejector in the MEMS drop ejector. The holes typically form a grid. The holes are typically nozzles of the MEMS drop ejector. Typically, each nozzle is in fluid communication with a printable fluid chamber at least partially defined by the substrate.

[0062] Because each MEMS drop ejector includes a hole through the substrate, the substrate surface area available for conductive connections is limited. Typically, the conductive connections extend between rows of holes.

[0063] Typically, each flexible membrane extends around a corresponding aperture. The conductive connection may extend between the flexible membranes without overlapping the flexible membranes. The conductive connection may extend between the apertures without overlapping the central 50% of the surface area of ​​the flexible membranes.

[0064] It is possible that in at least one region of the substrate (typically at least one region of the substrate within a grid of drop ejectors, eg adjacent to each drop ejector), one or more MEMS metallization layers overlie one or more CMOS metallization layers.

[0065] One or more MEMS metallization layers may be formed directly over one or more CMOS metallization layers.

[0066] For example, at the interface of the CMOS control circuitry, one or more CMOS metallization layers may be integrated with one or more MEMS metallization layers. Thus, one or more CMOS metallization layers and one or more metallization layers may be formed simultaneously.

[0067] One or more CMOS metallization layers may be electrically connected to one or more MEMS metallization layers.

[0068] One or more insulating layers may be formed between one or more CMOS metallization layers and one or more MEMS metallization layers. Typically, the one or more insulating layers are thicker than the insulating layers between the CMOS metallization layers. This provides additional electrical insulation and reduces parasitic capacitance between metal wiring layers.

[0069] The substrate may further include conductive connections extending through the grid in at least one metallization layer to connect each of the MEMS drop ejectors (typically, an ejector switch of each MEMS drop ejector) to two or more different fixed voltages, wherein the CMOS control circuitry (typically, an ejector switch associated with each MEMS drop ejector) is configured to selectively connect at least one electrode of the piezoelectric actuator of the corresponding drop ejector to each of a plurality of the two or more different fixed voltages in turn in response to a control signal from the CMOS control circuitry.

[0070] The drop ejector region may have a length and a width and have relatively long sides along the length, wherein conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages extend into the grid from one or both relatively long sides of the drop ejector region.

[0071] Conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages may extend from one or both relatively long sides into the grid. Conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages may extend from one or both relatively long sides into the grid between rows of MEMS drop ejectors. Conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages may extend laterally into the grid between rows of MEMS drop ejectors.

[0072] Conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages extend between the rows of piezoelectric actuators, which may be aligned at an angle of at least 45° to the length of the drop ejector zone, and typically at least 60° or at least 75°.

[0073] The substrate may define a plurality of elongated drop ejector zones, and the conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages comprise a plurality of separate busses, wherein for one or more elongated drop ejector zones, a conductor that is part of the bus to conduct the actuator drive waveform to the zone extends across the width of one or more additional drop ejector zones.

[0074] Thus, the conductive connections used to connect each MEMS droplet ejector to two or more different fixed voltages do not need to extend around the (short) edge of each droplet ejector zone, reducing their length and enabling the use of more substrate surface area than if they extended around the (short) edge of each droplet ejector zone.

[0075] One or more conductive connections for connecting each MEMS drop ejector to two or more different fixed voltages can be configured to provide electrical potentials to 100 or more, or even 1000 or more drop ejectors in a switched manner.

[0076] The ejector switch may be configured to selectively connect the corresponding piezoelectric transducer to two or more (or three or more) different fixed voltages in sequence to actuate droplet ejection, the piezoelectric transducer being connected to the different fixed voltages via one or more of the conductive connections in at least one metallization layer.

[0077] The print head may include a first plurality of conductive connections and a second plurality of conductive connections, wherein one of the first plurality of conductive connections and the second plurality of conductive connections includes the conductive connections for actuating the piezoelectric actuator, and the other of the first plurality of conductive connections and the second plurality of conductive connections includes conductive connections for conducting a drop ejector waveform or a plurality of different potentials, and wherein at one or more locations within the grid, at least one first conductive connection and at least one second conductive connection both extend. Typically, they extend in different metallization layers.

[0078] The at least one first and at least one second conductive connection may be parallel.The at least one first and at least one second conductive connection may cross each other.

[0079] Typically, at least one conductive connection for conducting the drop ejector waveform is located within a MEMS metallization layer, and at least one conductive connection for actuating the piezoelectric actuator is located within a CMOS metallization layer.

[0080] Typically, one of the first plurality of conductive connections and the second plurality of conductive connections extends through one or more MEMS metallization layers, and the other of the first plurality of conductive connections and the second plurality of conductive connections extends through one or more CMOS metallization layers.

[0081] Conductors for transmitting activation signals to the drop ejectors can extend between drop ejector rows so that they overlap but are located in different metallization layers (e.g., different CMOS metallization layers). This enables a large number of drop ejectors to be individually addressed from one side of the drop ejector area.

[0082] At one or more locations within the grid, at least one conductive connection for actuating the piezoelectric actuator and at least one conductive connection for conducting a drop ejector waveform may extend (typically in parallel) between the same adjacent drop ejector rows.

[0083] The grid can include at least first, second, and third rows of MEMS drop ejectors (typically without further rows in between), wherein a plurality (typically at least four) of conductive connections extend between drop ejectors in the first and second rows to different respective drop ejectors along the length of the second row, typically wherein a plurality (typically at least four) of conductive connections extend between drop ejectors in the second and third rows to different respective drop ejectors along the length of the second row.

[0084] Multiple (typically at least four) conductive connections extending between drop ejector rows to different respective drop ejectors can extend through the same or different metallization layers.

[0085] The CMOS control circuit system may include one or more first regions and one or more second regions, wherein the substrate includes one or more isolation features separating the first region and the second region, wherein the one or more first regions include transistors for processing digital signals, and the one or more second regions include drive transistors for directly providing an electrical potential to electrodes of a piezoelectric actuator, wherein the second region operates at least twice the maximum electrical potential of the first region.

[0086] The CMOS control circuitry may be formed on a first surface of the substrate, and wherein the flexible diaphragm, the piezoelectric actuator, and the MEMS metallization layer are also formed on the first surface of the substrate.

[0087] The first surface of the substrate typically includes a nozzle-forming layer including a flexible diaphragm and a piezoelectric actuator.

[0088] The substrate may define a plurality of adjacent drop ejector regions, the plurality of drop ejector regions being elongated, having a length and a width, and being spaced apart orthogonally to their lengths, wherein between each adjacent drop ejector region, at least one CMOS circuitry region is provided, the CMOS circuitry region also being elongated and aligned in the same orientation as the drop ejector region, the CMOS circuitry region comprising at least one CMOS metallization layer, wherein a conductive connection extends from the CMOS circuitry into the adjacent drop ejector region to actuate a piezoelectric actuator.

[0089] Typically, the substrate is elongated (usually rectangular) and the length and width of the drop ejector zone are aligned with the length and width of the substrate.

[0090] At least one CMOS circuitry region may include a higher voltage region including one or more digital logic gates and a lower voltage region including an ejection transistor directly connected to a piezoelectric transducer of a corresponding drop ejector.

[0091] Typically, the higher voltage region and the lower voltage region are separated by isolation features in the substrate.

[0092] For higher voltage region and lower voltage region, it refers to the relative voltage during operation.

[0093] One or more conductive connections for the actuator drive waveform may extend laterally across one or more drop ejector regions and connect to higher voltage areas of the CMOS circuitry region.

[0094] The invention extends in a second aspect to a printing apparatus comprising a print head according to the first aspect of the invention.

[0095] According to a third aspect of the present invention there is provided a method of forming a print head according to any preceding claim, the method comprising the steps of:

[0096] forming a grid of apertures through the substrate, each aperture at least partially defining a fluid chamber of the drop ejector;

[0097] forming the CMOS control circuitry including at least one CMOS metallization layer on a first surface of the substrate;

[0098] forming a MEMS layer on a first of the substrates to thereby form the plurality of drop ejectors, the MEMS layer comprising a flexible diaphragm, a piezoelectric actuator, and at least one MEMS metallization layer;

[0099] Each drop ejector is thereby conductively connected to the CMOS control circuitry via at least one of the metallization layers.

[0100] The method may include forming an insulating layer on the CMOS control circuitry prior to the step of forming at least one MEMS metallization layer.

[0101] The MEMS layer may have holes in it. The holes may serve as nozzles for the droplet ejectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0102] Example embodiments of the present invention will now be described with reference to the following drawings, in which:

[0103] Figure 1 is a plan view of an integrated inkjet print head;

[0104] Figure 2 is a schematic diagram of the control circuit system inside and outside the print head;

[0105] Figure 3 is a plan view of an electrode drive conductor extending through a droplet ejector grid;

[0106] Figure 4 is a cross section through the region of the integrated inkjet print head;

[0107] Figure 5 is a plan view of rows of eight actuators connected to respective drive circuitry on either side of the rows by electrode drive conductors extending into the grid from opposite long sides;

[0108] Figure 6 is a plan view of an embodiment in which a row of eight actuators is connected to drive circuitry arranged along a single side of the row;

[0109] Figure 7 is from Figure 1 A plan view of selected components of a portion of a print head on the left;

[0110] Figure 8 and 9 is a plan view of electrical connections extending across a droplet ejector grid;

[0111] Fig.10 is a plan view of a conductor extending across a grid of multiple droplet ejectors in different channels;

[0112] Fig.11 is a cross-section of a print head substrate according to the present invention;

[0113] Fig.12 is a longitudinal cross section extending between two actuator drive waveform conductors through the Figure 3 A cross section of a print head substrate;

[0114] Fig.13 and 14 Corresponds to Figure 3 and 11 , is an alternative cross section through the substrate;

[0115] Fig.15 is a flow chart of a method of manufacturing a print head module. DETAILED DESCRIPTION

[0116] Figure 1 1 is a plan view showing the layout of an integrated inkjet printhead 100. The printhead is formed on a single semiconductor substrate 102 and is elongated with a relatively long edge 104 parallel to its length 106 and a relatively short edge 103 parallel to its width 108. A bonding pad area 110 containing a plurality of bonding pads 112 is arranged along a portion of a single long edge. The substrate has a plurality of elongated areas of integrated droplet ejectors 114A, 114B, 114C, 114D, each area being associated with a different channel and aligned with the long edge of the substrate and thus extending longitudinally. Each area contains a droplet ejector having the same printable fluid supply. In this example, each area of ​​the integrated droplet ejector has a different color printable fluid supply, although the present invention is applicable to multi-channel devices having a monochrome or single type printable fluid supply. Within each area, the droplet ejector is arranged in a grid (a repeated array of dots, such as a diamond grid, a square grid, a hexagonal grid, a rectangular grid, a parallelogram grid, an equilateral triangle grid). In this example, the drop ejectors are arranged in a parallelogram grid having columns extending parallel to the length (longitudinal) of the substrate and rows extending across the width of the grid at a slight angle to the width (lateral) of the grid. The drop ejector rows extend laterally across each drop ejector zone at a slight angle to the long edge and the length of the drop ejector zone. This parallelogram arrangement provides drop ejectors in a wide range of longitudinal positions, increasing the maximum print density.

[0117] The substrate is a semiconductor substrate on which CMOS control circuitry is formed. The CMOS control circuitry includes central control circuitry 120 (main data path circuitry) that performs calculations and determines signal transmission, and also includes drive circuitry 122 that includes at least one CMOS drive transistor for each drop ejector. The drive circuitry acts as a latch and provides wired connections for electrodes of the piezoelectric actuator in each drop ejector. The elongated regions of the drive circuitry 122 are arranged along the relatively long sides of each region of drop ejectors and are also interposed between the relatively long sides and are configured to controllably actuate the drop ejectors in each drop ejector region such that individual rows of drop ejectors are actuated by drive transistors at either end of the row using conductive connections 240 extending from the relatively long sides into the grid of drop ejectors.

[0118] Figure 2 Schematic diagram of control circuitry for a printhead assembly. In this example, control of the printhead is distributed between a machine controller 220 separate from the substrate and control circuitry (e.g., CMOS circuits) 120, 122A-D on substrate 102. They are connected in part by conductors extending through a single or multiple flexible cable interconnects 218.

[0119] Individual piezoelectric actuators 320 within the drop ejector are controlled by applying electrical potentials to their electrodes 340, 342. These potentials are typically time varying in the form of actuator drive waveforms that are typically repeated in each drop ejection cycle. The machine controller includes at least a processor 200, such as a microprocessor or microcontroller, having a memory 202 storing relevant data and program code. A wired or wireless electronic interface 204 receives input data from an external device driver. It will be appreciated by those skilled in the art that the machine controller may be distributed among several separate components or functional modules, such as one component that converts an image into a pixelated pattern for printing using, for example, a dither matrix, and a separate component that converts the pixelated pattern into a print pattern for a different nozzle.

[0120] The machine controller may include at least one waveform generator and voltage amplifier 208 that provides a continuous pattern of actuator control pulses to the print head via one or more drive signal conductors 210. A ground conductor 212 also extends from the machine controller to the substrate. (The ground connection on the substrate is not shown for clarity). The processor 200 typically generates digital control signals 214 as a serial bus and also transmits a clock signal 216 to the print head that is used to synchronize printing with movement of the print head. The connector also provides voltage levels associated with the operating voltages of the CMOS control electronics.

[0121] On substrate 100, bond pads 112 are connected to conductors of a flexible connector, and signals are transmitted from the bond pads through metallization layers to CMOS control circuitry 120, and from the CMOS control circuitry to electrodes 320, 340, thereby actuating individual piezoelectrics 342 within corresponding drop ejectors. The received signals include digital control signals encoding image information and analog actuator control pulses conducted through actuator drive waveform conductors 250.

[0122] The control circuit 120 on the substrate 102 extends to a drive circuit system 122, which includes a jet switch circuit 220, which includes a jet transistor having an output, which is directly electrically connected to the electrodes 340, 342 through an electrode drive conductor 240 (i.e., without additional intervening switching semiconductor junctions). The jet switch circuit selectively switches actuator control pulse signals received through conductors 250 to apply these pulse signals to the corresponding electrodes through the electrode drive conductors 240. If one electrode is maintained at ground, the jet switch circuit can be as simple as a single transistor per actuator, or a single transistor per electrode, to switch the signal applied to the electrode, and there can be a single electrode drive conductor 240 extending to a single piezoelectric actuator, although in the example shown there are two conductors extending to each single piezoelectric actuator, one for each electrode.

[0123] The jet switch circuit does not perform power amplification. Instead, it switches the actuator control pulses, thereby determining for each pulse whether each pulse is relayed to the corresponding actuator. Voltage amplification is performed in the machine controller by amplifier 208.

[0124] The jet switching circuit is controlled by a latch and shift transistor 222, which receives and stores digital data from a control circuit 224, which processes the received data, for example, converts the received serial data, stores the data in a register 226, and uses the received data to determine which actuators to actuate during each consecutive actuator activation event. The control circuit 228 also stores fine-tuning data for customizing the precise timing of the voltage switches for each actuator, which is typically determined during a calibration step at setup, and may store configuration data 230 indicating the physical layout of the nozzles, safety information, and or nozzle actuation count history information. The control circuit 224 also receives data from sensors 232, 234, 236, some of which are associated with individual actuators, such as nozzle fill level sensors, and some of which sense parameters related to the function of the entire print head, such as temperature sensors.

[0125] Figure 3 1 is a cross-section of a region of an integrated inkjet printhead 100 comprising a silicon substrate 102 with an insulating layer 302 (thus a silicon-on-insulator or silicon-on-insulator-on-silicon substrate). Integrated CMOS circuitry 120, 122 is formed in a first surface 304 of the silicon substrate, superimposed thereon with a CMOS metallization layer 306 and an intervening passivation layer 308, such as SiO 2, SiN, SiON. Those skilled in the art will appreciate that a CMOS circuit includes both doped regions of a substrate and metallization layers within interconnects formed on a first surface of the substrate. The number of CMOS metallization layers is variable, but is typically at least three layers.

[0126] The CMOS circuit system is divided into a central control circuit system 120 and a drive circuit system 122, wherein the central control circuit system is digital and operates at a standard CMOS digital logic voltage (such as 5V), and the drive circuit system processes digital logic signals and switches analog signals, particularly actuator control pulse signals, and therefore operates at a higher voltage than the central control circuit system. The CMOS circuits operating at two different voltage levels are separated by a deep trench isolation (DTI) barrier layer 310. A cross connector 312 extends across the DTI barrier to connect the ejection transistors in the drive circuit system 112 to the electrode drive conductor 240, which extends into the grid of the droplet ejector. The bonding pads 112 are formed on the substrate and communicate with the central control circuit system primarily through paths in the CMOS metallization layers to process digital signals, however, one or more bonding pads conduct analog actuator control pulse signals to the drive circuit system.

[0127] The print head further includes a piezoelectric actuator, which includes a piezoelectric body 320, which is formed of AlN or ScAlN in this example, but can be formed of another suitable piezoelectric material that can be processed at a temperature below 450°C so that it can be deposited without causing damage to the underlying CMOS structure. The piezoelectric actuator 320 forms a diaphragm with a material layer such as silicon, silicon oxide, silicon nitride or a derivative thereof, and has a passivation layer 322 (sometimes referred to as a nozzle defining layer 322) that prevents the applied potential from contacting the fluid. Therefore, the MEMS layers 320, 322, 323, 340, 342, 350, 352, 362 are superimposed on the CMOS layers 120, 122, 306, 307, 312, wherein the MEMS layers and the CMOS layers are formed integrally.

[0128] CMOS metallization layer 306 includes interconnects that conduct external signals, signals to central control circuitry, and signals within drive circuitry. The drive circuitry is configured to apply a potential difference to piezoelectric actuator electrodes 340 and 342 through CMOS metallization layer 306 and connections to adjacent drop ejectors of one or more MEMS metallization layers 350 in use. In this example, the MEMS metallization layer is shown connected to the CMOS metallization layer by vias 352 extending through a passivation layer 354 between the MEMS structure and the CMOS metallization layer. Extending to Figure 4The electrode drive conductor 240 of one of the electrodes 342 is shown formed in part by a conductive trace 307 in a MEMS metallization layer 350 and a CMOS metallization layer.

[0129] The piezoelectric actuator 320 and the passivation layers 322, 323, 354 define the walls of a fluid chamber 360, which receives a printing agent, such as ink (in the case of an inkjet printer) or another printable fluid (e.g., in the case of an additive manufacturing printer) through a conduit (not shown). In operation, when a drop ejection voltage waveform is applied, the piezoelectric actuator bends and ejects fluid through a corresponding nozzle 344.

[0130] As can be seen, the semiconductor cross section contains different regions. Region 370 contains both CMOS and MEMS metallization (and metal wiring) and CMOS transistors. Region 372 contains only MEMS metallization, no CMOS metallization or transistors. Region 374 contains CMOS and MEMS metallization (and metal wiring), but no CMOS transistors.

[0131] This actuator configuration is compact and energy efficient, but the presence of the aperture (chamber and nozzle) and the flexible region (piezoelectric actuator) limits the surface area available for routing conductive connections and thus can limit nozzle density.

[0132] Reference again Figure 1 , the ejection switching circuitry extends along the long sides of the elongated grid of drop ejectors, and the electrode drive conductors from the ejection transistors to the electrodes extend into the grid of drop ejectors from either side such that the connections from the ejection transistors to the electrodes are short (less than the width of the elongated grid) and of similar length to each other.

[0133] refer to Figure 4 , the electrode drive conductors 240 extend from the drive transistors between the piezoelectric actuators 320 into the grid of drop ejectors along the rows. (Note that Figure 4 Relative to Figure 1 Rotated 90°, width 108 is shown for reference). Figure 4 It can be seen that if the density of drop ejectors is as high as possible, due to the presence of nozzles 344 (which are essentially holes through the substrate) and due to the desire to avoid piezoelectric actuators 320, the available space for electrode drive conductors 240 in a single two-dimensional plane is very limited, although in practice the amount of overlap with the actuators may be limited.

[0134] Figure 5 is a plan view of rows of eight actuators connected to respective drive circuitry 122 on either side of the rows by electrode drive conductors 240 extending into the grid from opposite long sides.

[0135] Figure 6 is a plan view of an embodiment in which a row of eight actuators is connected to the drive circuitry 122 arranged along a single side of the row. Different regions of the electrode drive conductors 240, 240' are arranged in two different CMOS metallization layers (e.g., M3 and M1). In this plan view, the electrode drive conductors in the layer away from the substrate 240 are superimposed on the conductors close to the substrate 240' and thus partially shield the conductors.

[0136] In these arrangements, the electrode drive conductors (conductive connections for actuating the piezoelectric actuators) are relatively short and of consistent length. Therefore, they actuate the piezoelectric actuators at consistent times. Each electrode drive conductor can be shorter than 1.5 times the width of the droplet ejector zone, or even shorter than the width of the droplet ejector zone. It is not necessary for the electrode drive conductors to extend around the edges of the droplet ejector zone, which would take up space on the substrate, reduce the overall nozzle density and cause variability in the timing of the actuation signals.

[0137] Figure 7 is from Figure 1 A plan view of selected components of a portion of the printhead on the left. The long edge of the substrate contains bonding pads 112 and a main CMOS control circuit area 120 for timing control, decoding and distributing data, etc. A first nozzle area 114 containing a grid of drop ejectors is located between elongated areas of drive circuitry 122, which contains high voltage transistor circuits surrounded by DTI isolation pockets 310. Strips of CMOS digital control logic 121, which is part of the CMOS control circuit area, extend between the strips of drive circuitry.

[0138] The actuator drive waveform conductors 250 are arranged in a two-dimensional grid, extending up each elongated region of the drive circuit system and across the drop ejector area. These drive waveform conductors require a relatively large surface area, since current may pass through them in operation, and the grid of multiple parallel drive waveform conductors effectively distributes the waveform signal. It can be seen that some of the actuator drive waveform conductors 250 extend (laterally) across the grid of the drop ejector in parallel with the electrode drive conductors 240 (for clarity, only connections to three rows are shown), but in different metallization layers.

[0139] Figure 8 and 9250C, 250D. In this example, conductor 250A conducts a first actuator drive waveform for a magenta ink ejector, conductor 250B conducts a second actuator drive waveform for a blue ink ejector, and conductors 250C, 250D conduct a third actuator drive waveform and a fourth actuator drive waveform for yellow and black ink ejectors, respectively. Each is part of a bus to which a corresponding actuator drive waveform is assigned. The actuator drive waveform conductors can be wider than the electrode drive conductors and, in this example, are located above the electrode drive conductors (i.e., farther from the first surface of the substrate). In FIG. Fig. 9 , only the magenta drive waveform transverse conductor 250A is shown connected to the longitudinal conductors extending along the drive circuitry 122. Fig.10 As shown in the plan view of FIG. 1 , conductors for other channels / inks extend across the grid of drop ejectors, with conductors for each channel connected to drive circuitry on either side of the ejector for that channel.

[0140] Fig.11 is along with Figure 3 Different cross sections through a printhead substrate according to the invention. In the middle of the image, the MEMS metallization layer 250 is an actuator drive waveform conductor 250 (or one of 250A, 250B, 250C, 250D) superimposed on two electrode drive conductors 240, 240' located in M3 and M1 of the CMOS metallization layer.

[0141] Fig.12 is a longitudinal cross section extending between the two actuator drive waveform conductors 250C, 250D through the Figure 3 A cross section of a print head substrate (through Figure 8 Below the MEMS layers 354, 322 and the actuator drive waveform conductors 250C, 250D, there are a plurality of smaller electrode drive conductors 240, 240' located in M3 and M1 of the CMOS metallization layer 306.

[0142] Fig.13 and 14 Corresponds to Figure 3 and 11 , except showing an electrode drive conductor 240 connected to the lower (closer to the substrate) electrode 342 of the drop ejector, and having an alternative cross section of an actuator drive waveform conductor 250 superimposed on the electrode drive conductors 240, 240'.

[0143] Thus, the electrode drive conductors 240 extend only a short distance from the ejection transistor, and each electrode drive conductor drives only a single drop ejector. The actuator drive waveform conductors each drive one or more complete drop ejector zones. They may need to drive more than 100 or even more than 1000 drop ejectors. Therefore, they need to have a much larger cross-section than the electrode drive conductors. They are housed in the MEMS metallization layer and are wider than the electrode drive conductors in the CMOS metallization layer. Therefore, the actuator drive waveform conductors extend in a grid, across the drop ejector zones, and along the CMOS drive circuit system, which extends longitudinally between the drop ejector zones. Therefore, the transmission of signals around the ends of the drop ejector zones (i.e., along the short sides 103 of the substrate), and in particular the actuator drive waveform conductors, can be minimized or avoided.

[0144] Fig.15 A flow chart illustrating a method of manufacturing a printhead module is shown. The method 400 of manufacturing a printhead module includes forming 410 an integrated circuit (e.g., CMOS control circuit 224 and metal interconnect layer 306) on substrate 102. The CMOS circuit is formed by standard CMOS processing methods including ion implantation on a p-type or n-type substrate, and interconnects are later formed by standard processes such as ion implantation, chemical vapor deposition, physical vapor deposition, etching, chemical mechanical planarization, and / or electroplating.

[0145] Thereafter, the substrate with the integrated CMOS circuitry is transferred 420 from the CMOS foundry to the MEMS foundry. Additional material layers are formed on the substrate using continuous thin film deposition techniques to form a MEMS device, including electrodes 340 and 342 with intervening piezoelectrics 320. Thus, the method further comprises forming 430 a plurality of actuators (typically piezoelectric actuators), each actuator being electrically connected to the integrated circuit. Each step must avoid damage to the CMOS control circuitry. The piezoelectrics are formed of materials such as AlN or ScAlN, which can be deposited by PVD (including low temperature sputtering) at a temperature below 450°C. The electrodes are formed of, for example, titanium, platinum, aluminum, tungsten, or alloys thereof.

[0146] The method further comprises forming 440 a nozzle outlet 344 associated with each actuator. In other words, a plurality of nozzle outlets are formed. Each nozzle outlet is associated with a corresponding actuator in the plurality of actuators. Each nozzle outlet extends through the substrate. Typically, each nozzle outlet further extends through one or more additional layers on the substrate. The method further comprises forming 450 a print agent manifold for conveying print agent through it toward the plurality of nozzle outlets. The print agent manifold may be formed before or after forming the nozzle outlets. The print agent manifold may be formed before or after forming the plurality of actuators. The print agent manifold is a fluid channel defining a fluid communication path between a print agent inlet of a printhead module and a plurality of nozzle outlets. An etching procedure such as DRIE may be used to form fluid channels and orifices through the substrate. A channel defining layer may be formed using DRIE etching and wafer bonding of a silicon MEMS substrate. The nozzle defining layer may be formed by depositing or bonding a metal, a silicon MEMS wafer, or a plastic material onto the subsequently defined channel. Each drop ejector chip is connected to the machine controller through a flexible interconnect 218 that contains a limited number of conductors, typically less than 75 or less than 50, and possibly less than 25.

[0147] Due to the requirement to avoid damaging the CMOS control circuit on which the piezoelectric actuator including the piezoelectric body is formed, the material forming the piezoelectric body cannot be and is not PZT. Therefore, depending on its precise composition, the piezoelectric actuator has a much lower piezoelectric constant d than PZT. 31 , typically by at least one and possibly two orders of magnitude.

[0148] In the above embodiment, one or more analog actuator drive waveforms (e.g., one for each printable fluid type or ink color) are generated off-chip and conducted to the substrate where they are distributed via the drive waveform conductors 250. In an alternative embodiment, multiple voltage rails at different potentials are instead provided, such as at least three different potentials, and these voltage rails extend through the substrate rather than the drive waveform conductors to the drive circuitry, and the drive circuitry includes multiple transistors per drop ejector that switch over time which voltage rail is connected to each electrode of each drop ejector during each ejection cycle that selects the drop ejector. For example, there may be a positive voltage, a negative voltage, and a ground that are switched in sequence to provide a drop ejection waveform.

Claims

1. A printhead for ejecting one or more printable fluids, the printhead comprising a substrate; The substrate defines a plurality of MEMS drop ejectors arranged in a grid for ejecting droplets of the one or more printable fluids, each drop ejector comprising a flexible diaphragm and a piezoelectric actuator to eject a drop of the printable fluid through a nozzle by moving the flexible diaphragm, each drop ejector comprising at least one MEMS metallization layer; The substrate further defines CMOS control circuitry including at least one CMOS metallization layer; The substrate further comprises one or more of the following: (i) conductive connections in at least one of the metallization layers extending from the CMOS control circuitry to each piezoelectric actuator to actuate the piezoelectric actuator; and (ii) conductive connections in at least one of the metallization layers extending through the grid to transmit actuator drive waveforms.

2. The printhead of claim 1 , wherein the substrate comprises (i) conductive connections in at least one of the metallization layers extending from the CMOS control circuitry to each piezoelectric actuator to actuate the piezoelectric actuator.

3. The printhead of claim 2, wherein the length of the conductive connections for actuating the piezoelectric actuators is consistent between the CMOS control circuitry and the piezoelectric actuators within a set of drop ejectors.

4. A printhead according to claim 2 or claim 3, wherein the grid of MEMS drop ejectors forms a drop ejector area of ​​the substrate, the drop ejector area being elongated, having a length and a width, and having opposing long sides along the length, wherein the conductive connections for actuating the actuators extend into the grid from one or both of the opposing long sides of the drop ejector area, typically wherein the CMOS control circuitry comprises a plurality of drive transistors, at least one of the plurality of drive transistors being directly connected to at least one electrode of a piezoelectric transducer of each MEMS drop ejector via the conductive connections for actuating the piezoelectric actuators without intervening transistors, wherein the plurality of drive transistors are arranged in at least one row adjacent to the one or both opposing long sides of the drop ejector area.

5. The printhead of claim 4, wherein the conductive connections for actuating the piezoelectric actuators extend into the grid between rows of MEMS drop ejectors.

6. A printhead according to any preceding claim, wherein (ii) conductive connections extend through the grid in at least one of the metallization layers to transmit actuator drive waveforms to connect the MEMS drop ejector to one or more actuator drive waveform sources.

7. The printhead of claim 6, wherein the conductive connections connect different groups of MEMS drop ejectors to different ones of a plurality of actuator drive waveform sources to thereby deliver different actuator drive waveforms to the different groups of MEMS drop ejectors.

8. A print head according to claim 6 or claim 7, wherein the droplet ejector area has a length and a width and has relatively long sides along the length, and wherein the conductive connection for transmitting the actuator drive waveform extends from one or both of the relatively long sides of the droplet ejector area into the grid.

9. A printhead according to any preceding claim, wherein each MEMS drop ejector comprises an orifice through the substrate to eject a printable fluid.

10. A printhead according to any preceding claim, wherein the substrate further comprises conductive connections extending through the grid in at least one metallization layer to connect each of the MEMS drop ejectors to two or more different fixed voltages, wherein the CMOS control circuitry is configured to selectively connect at least one electrode of the piezoelectric actuator of a corresponding drop ejector to each of a plurality of the two or more different fixed voltages in turn in response to a control signal from the CMOS control circuitry.

11. A printhead according to any preceding claim, wherein in at least one region of the substrate the one or more MEMS metallisation layers overlie the one or more CMOS metallisation layers.

12. A print head according to any preceding claim, comprising a first plurality of conductive connections and a second plurality of conductive connections, wherein one of the first plurality of conductive connections and the second plurality of conductive connections comprises the conductive connection for actuating the piezoelectric actuator, and the other of the first plurality of conductive connections and the second plurality of conductive connections comprises a conductive connection for conducting a droplet ejector waveform or a plurality of different electrical potentials, and wherein at one or more locations within the grid, at least one first conductive connection and at least one second conductive connection both extend but in different metallization layers.

13. A printhead according to any preceding claim, wherein at one or more locations within the grid, at least one conductive connection for actuating the piezoelectric actuator and at least one conductive connection for conducting a drop ejector waveform extend in parallel between the same adjacent drop ejector rows.

14. A printhead according to any preceding claim, wherein the grid comprises at least first, second and third rows of MEMS drop ejectors, wherein a plurality of conductive connections extend between drop ejectors in the first and second rows to different respective drop ejectors along the length of the second row.

15. The printhead of claim 14, wherein a plurality of conductive connections extend between the second and third rows of drop ejectors to different respective drop ejectors along the length of the second row.

16. A print head according to any preceding claim, wherein the CMOS control circuit system comprises one or more first regions and one or more second regions, wherein the substrate comprises one or more isolation features separating the first regions and the second regions, wherein the one or more first regions comprise transistors for processing digital signals, and the one or more second regions comprise drive transistors for directly providing an electrical potential to electrodes of a piezoelectric actuator, wherein the second regions operate at least at twice the maximum electrical potential of the first regions.

17. A printhead according to any one of claims 1 to 4, wherein the substrate defines a plurality of adjacent drop ejector zones, the plurality of drop ejector zones being elongated, having a length and a width, and being spaced apart orthogonally to their lengths, wherein between each adjacent drop ejector zone, at least one CMOS circuitry zone is provided, the CMOS circuitry zone also being elongated and aligned in the same orientation as the drop ejector zone, the CMOS circuitry zone comprising at least one CMOS metallization layer, wherein a conductive connection extends from the CMOS circuitry into an adjacent drop ejector zone to actuate a piezoelectric actuator.

18. A printhead according to claim 17, wherein the at least one CMOS circuitry area includes both a higher voltage region and a lower voltage region, the lower voltage region including one or more digital logic gates, the higher voltage region including an ejection transistor, the ejection transistor being directly connected to a piezoelectric transducer of a corresponding drop ejector, and wherein the higher voltage region and the lower voltage region are separated by isolation features in the substrate, typically wherein one or more conductive connections for actuator drive waveforms extend laterally across one or more drop ejector regions and connect to the higher voltage region of the CMOS circuitry area.

19. A printhead according to any preceding claim, comprising a plurality of bonding pads located in discrete areas of the substrate.

20. A printing apparatus comprising a print head according to any preceding claim.

21. A method of forming a print head or printing apparatus according to any preceding claim, the method comprising the steps of: forming a grid of apertures through the substrate, each aperture at least partially defining a fluid chamber of the drop ejector; forming the CMOS control circuitry including at least one CMOS metallization layer on a first surface of the substrate; forming a MEMS layer on a first of the substrates to thereby form the plurality of drop ejectors, the MEMS layer comprising a flexible diaphragm, a piezoelectric actuator, and at least one MEMS metallization layer; Each drop ejector is thereby conductively connected to the CMOS control circuitry via at least one of the metallization layers.

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