Droplet ejector

Abstract

A droplet ejector for a printhead comprises: a substrate having a mounting surface and an opposite nozzle surface; at least one electronic component integrated with the substrate; a nozzle-forming layer formed on at least a portion of the nozzle surface of the substrate; a fluid chamber defined at least in part by the substrate and at least in part by the nozzle-forming layer, the fluid chamber having a fluid chamber outlet defined at least in part by a nozzle portion of the said nozzle-forming layer; a piezoelectric actuator formed on at least a portion of the nozzle portion of the nozzle-forming layer; and a protective layer covering the piezoelectric actuator and the in nozzle forming layer. The piezoelectric actuator comprises a piezoelectric body provided between first and second electrodes. At least one of the said first and second electrodes is electrically connected to the at least one electronic component. The piezoelectric body comprises one or more piezoelectric materials processable at a temperature below 450 C.

Claims

1. A droplet ejector for a printhead, the droplet ejector comprising: a substrate having a mounting surface and an opposite nozzle surface; at least one electronic component integrated with the substrate; a nozzle-forming layer formed on at least a portion of the nozzle surface of the substrate; a fluid chamber defined at least in part by the substrate and at least in part by the nozzle-forming layer, the fluid chamber having a fluid chamber outlet defined at least in part by a nozzle portion of the said nozzle-forming layer; a piezoelectric actuator formed on at least a portion of the nozzle portion of the nozzle-forming layer, the piezoelectric actuator comprising a piezoelectric body provided between first and second electrodes, at least one of the said first and second electrodes being electrically connected to the at least one electronic component, and the piezoelectric body comprising one or more piezoelectric materials processable at a temperature below 450 C.; and a protective layer covering the piezoelectric actuator and the nozzle-forming layer.

2. The droplet ejector according to claim 1, wherein the one or more piezoelectric materials are depositable at a temperature below 450 C.

3. The droplet ejector according to claim 1, wherein the one or more piezoelectric materials are PVD-deposited piezoelectric materials.

4. The droplet ejector according to claim 1, wherein the one or more piezoelectric materials comprise aluminium nitride and/or zinc oxide.

5. The droplet ejector according to claim 4, wherein the aluminium nitride further comprises one or more of the following elements: scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, boron.

6. The droplet ejector according to claim 1, wherein the piezoelectric body is formed from a ceramic material comprising aluminium and nitrogen and optionally one or more elements selected from: scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, boron.

7. The droplet ejector according to claim 1, wherein the one or more piezoelectric materials are non-ferroelectric piezoelectric materials.

8. The droplet ejector according to claim 1, wherein the piezoelectric body has a piezoelectric constant d.sub.31 having a magnitude less than 10 pC/N.

9. The droplet ejector according to claim 1, wherein the at least one electronic component integrated with the substrate consists of at least one CMOS electronic component integrated with the substrate.

10. The droplet ejector according to claim 1, wherein said droplet ejector is a monolithic droplet ejector.

11. The droplet ejector according to claim 1, wherein the nozzle-forming layer comprises a nozzle-plate.

12. The droplet ejector according to claim 1, wherein the nozzle-forming layer comprises an electrical interconnect layer.

13. The droplet ejector according to claim 12, wherein the nozzle-forming layer comprises a nozzle-plate and the electrical interconnect layer is provided between the substrate and the nozzle plate.

14. The droplet ejector according to claim 12, wherein a nozzle portion of the electrical interconnect layer which forms at least a part of the nozzle portion of the nozzle-forming layer consists of dielectric material.

15. The droplet ejector according to claim 1, wherein the mounting surface of the substrate comprises a fluid inlet aperture in fluid communication with the fluid chamber.

16. The droplet ejector according to claim 1, wherein the fluid chamber is substantially cylindrical and the nozzle portion of the nozzle-forming layer is substantially annular.

17. A printhead comprising a plurality of droplet ejectors according to claim 1.

18. The printhead according to claim 17, wherein the plurality of droplet ejectors share a common substrate.

19. A method of manufacturing a droplet ejector for a printhead, the method comprising: providing a substrate having a first surface and a second surface opposite the first surface; forming at least one electronic component in or on the second surface of the substrate; forming a nozzle-forming layer on the second surface of the substrate; forming a piezoelectric actuator on the nozzle-forming layer at a temperature below 450 C.; forming a protective layer covering the piezoelectric actuator and the nozzle-forming layer; and forming a fluid chamber in the substrate.

20. The method according to claim 19, wherein the step of forming the piezoelectric actuator comprises: forming a first electrode on the nozzle-forming layer; forming at least one layer of one or more piezoelectric materials on the first electrode at a temperature below 450 C.; and forming a second electrode on the at least one layer of one or more piezoelectric materials.

21. The method according to claim 20, wherein the step of forming the at least one layer of one or more piezoelectric materials comprises depositing the at least one layer of one or more piezoelectric materials by physical vapour deposition at a temperature below 450 C.

22. The method according to claim 20, wherein the one or more piezoelectric materials comprise aluminium nitride and/or zinc oxide.

23. The method according to claim 20, wherein the aluminium nitride further comprises one or more of the following elements: scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, boron.

24. The method according to claim 20, wherein the step of forming the piezoelectric actuator comprises forming a piezoelectric body from a ceramic material comprising aluminium and nitrogen and optionally one or more elements selected from: scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, boron.

25. The method according to claim 20, wherein the one or more piezoelectric materials are non-ferroelectric piezoelectric materials.

26. The method according to claim 19, wherein the step of forming at least one electronic component in or on the second surface of the substrate comprises integrally forming at least one CMOS electronic component in or on the substrate.

27. The method according to claim 19 further comprising integrally forming the substrate, the at least one electronic component, the nozzle-forming layer, the piezoelectric actuator, and the protective layer thereby forming a monolithic droplet ejector.

28. The method according to claim 19, wherein the step of forming the nozzle-forming layer comprises forming a nozzle-plate.

29. The method according to claim 19, wherein the step of forming the nozzle-forming layer comprises forming an electrical interconnect layer.

30. The method according to claim 29, wherein the method comprises: forming the electrical interconnect layer on the second surface of the substrate; and then forming the nozzle-plate on the electrical interconnect layer.

31. A method of manufacturing a printhead comprising forming a plurality of droplet ejectors on a common substrate, each droplet ejector being formed by the method according to claim 19.

Description

DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

(2) FIG. 1 is a view of a monolithic fluid droplet ejector device including integrated fluidics, electronic circuitry, nozzles and actuators according to a first embodiment;

(3) FIG. 2 is a cross sectional view of the monolithic droplet ejector device along the line F2 shown in FIG. 1;

(4) FIG. 3 is a plan view of a nozzle showing features of the monolithic droplet ejector shown in FIG. 1 with a protective coating removed;

(5) FIG. 4(a) is a schematic showing drive pulse implementations for the droplet ejector device of FIG. 1;

(6) FIG. 4(b) is a schematic showing drive pulse implementations for the droplet ejector device of FIG. 1;

(7) FIG. 5(a) is a schematic of the manufacturing process flow for manufacturing the droplet ejector device of FIG. 1;

(8) FIG. 5(b) is a schematic of the manufacturing process flow for manufacturing the droplet ejector device of FIG. 1;

(9) FIG. 5(c) is a schematic of the manufacturing process flow for manufacturing the droplet ejector device of FIG. 1;

(10) FIG. 6 is a cross sectional view showing an alternative implementation of the electrode structure according to a second example embodiment of the invention;

(11) FIG. 7 is a schematic showing an alternative drive pulse implementation for the droplet ejector device of FIG. 6;

(12) FIG. 8 is a schematic showing a cross section through an alternative implementation of the nozzle structure according to a third example embodiment of the invention; and

(13) FIG. 9 is a cross-sectional view showing an alternative implementation of bond pad structures according to a fourth example embodiment of the invention.

(14) FIG. 10 is a table listing some common piezoelectric materials and the manufacturing methods associated with them, along with typical d.sub.31 values.

DETAILED DESCRIPTION OF ONE OR MORE EXAMPLE EMBODIMENTS

First Example Embodiment

(15) The first example embodiment is described with reference to FIGS. 1 to 5.

(16) FIG. 1 shows a monolithic fluid droplet ejector device 1 including integrated fluidics, electronic circuitry, nozzles and actuators according to the first example embodiment of the invention. FIG. 2 is a cross sectional view of the monolithic droplet ejector device 1 along the line F2 shown in FIG. 1.

(17) As shown in FIG. 1 and FIG. 2, the fluid droplet ejector device is a monolithic chip that includes a substrate 100 fluid inlet channels 101, electronic circuitry 200, interconnect layer 300 comprising wiring, piezoelectric actuators 400, a nozzle plate 500, a protective front surface 600, nozzles 601 and bond pads 700. FIG. 1 shows a bond pad region 104, and a nozzle region 105.

(18) The substrate 100 is typically between 20 and 1000 micrometers in thickness. The interconnect layer 300, piezoelectric actuator 400, nozzle plate 500 and protective front surface 600 are typically between 0.5 and 5 micrometers in thickness. The nozzle 601 is typically between 3 and 50 micrometers in diameter. The fluid inlet channel 103 has a characteristic dimension of between 50 and 800 micrometers.

(19) The monolithic chip shown in FIG. 1 comprises 4 rows of nozzles. Each row is offset relative to adjacent rows in an alternating pattern. Any number of nozzle rows in different configurations are possible. The arrangement of the nozzles on the chip is configured to achieve a target print density (i.e. number of dots per inch (dpi)), a target firing frequency and/or a target print speed. A range of different nozzle configurations are possible which satisfy the particular printing requirements. Different printhead nozzle configurations are effected by arranging individual nozzle and nozzle specific drive electronics 201 and 202.

(20) The substrate 100 is formed from a silicon wafer and comprises a supporting body 102, fluid inlet channels 101 and electronic circuitry 200.

(21) The fluid inlet channels 101 are formed through the thickness of the substrate 100 with an opening at one surface at a fluid inlet 103 and are terminated at the other end by the nozzle plate 500 and nozzles 601. The walls of the fluid inlet channels 101 have a similar cross section through the substrate 100 and interconnect layer 300.

(22) The fluid inlet channels 101 are substantially cylindrical (i.e. substantially circular in cross section in the plane of substrate). The corners of the fluid inlet channels 101, at the interface with the nozzle plate and at the fluid inlet interface, are rounded to minimize stress concentrations.

(23) The electronic circuitry 200 is formed on the opposite surface of the substrate 100 to the surface that includes the fluid inlets 103. The electronic circuitry 200 can include digital and/or analog circuitry. Portions of the electronic circuitry, 201 and 202, are connected directly to the piezoelectric actuators 400 by way of wiring 301 through the interconnect layer 300 and are located close to the actuators 400 to optimize the application of a drive wave form. The electrode actuator wiring interconnects 301 and 302 may be a continuous single construction or they may be constructed from multiple layers of wiring. The drive electronics may be configured to apply a set voltage or shaped voltage to the piezoelectric actuator for a set period of time.

(24) Portions of the electronic circuitry 203 are associated with the overall operation of the entire monolithic droplet ejector device and can be located separate to the actuator drive circuitry 201 and 202. The circuitry 203 associated with the general operation of the chip can perform a range of functionalities including data routing, authentication, chip monitoring (e.g. chip temperature monitoring), lifecycle management, yield information processing and/or dead nozzle monitoring. The circuitry 203 is connected to the bond pads 700 and the specific electrode drive circuitry 201 and 202 through the interconnect layer 300. The chip drive electronics 203 may include analog and/or digital circuits configured to perform different functions such as data caching, data routing, bus management, general logic, synchronization, security, authentication, power routing and/or input/output. The chip drive electronics 203 may comprise circuitry components such as timing circuitry, interface circuitry, sensors and/or clocks.

(25) There may be a number of general drive electronics areas located in different sections of the chipfor example between nozzle rows or around the periphery of the chip.

(26) The electronic drive circuitry includes 200 CMOS drive circuitry.

(27) The interconnect layer 300 is formed directly on top of the electronics circuitry 200 and the substrate 100 and comprises electrical insulator and wiring. Wiring in the interconnect layer 300 connects chip electronic circuitry 203 to both the bond pads 700 and to the actuator electrode drive circuitry 201 and 202. The interconnect layer 300 includes power and data routing wiring which is routed between nozzles, around the periphery of the chip and/or over drive electronics. The interconnect layer 300 typically comprises multiple layers having different wiring paths.

(28) A nozzle plate 500 is formed on top of the interconnect layer 300. The nozzle plate 500 is formed from either a single material or a laminate of multiple materials. The nozzle plate 500 is continuous across the front surface of the chip with electrical openings for wiring between the interconnect layer 300 below and actuator electrodes 401 above.

(29) The nozzle plate 500 is formed from one or more materials which must be manufacturable with the CMOS electronic drive circuitry 200 in terms of deposition temperatures, compositions, and chemical processing steps. The nozzle plate materials must also be chemically stable and impervious to the jetted fluids. The nozzle plate materials must also be compatible with the functioning of the piezoelectric actuator. For example, the Young's modulus of suitable materials lies in the range of 70 GPa to 300 GPa. However, variations in Young's modulus can be accommodated for by changing the thickness of the nozzle plate 500. Example nozzle plate materials include one or more of (e.g. including combinations and/or laminates of) silicon dioxide (SiO.sub.2), silicon nitride (Si.sub.3N.sub.4), silicon carbide (SiC) and silicon oxynitride (SiO.sub.xN.sub.y).

(30) Each piezoelectric actuator 400 comprises a laminate of a first electrode 401, a piezoelectric layer 402 and a second electrode 403. The first electrode 401 is attached to the nozzle plate 500. The piezoelectric actuator 402 is attached to the first electrode 401. The second electrode 403 is attached to the piezoelectric actuator surface opposite the first electrode attachment surface.

(31) The first electrode 401 is electrically connected to a wiring connection 301 in the interconnect layer 300. The second electrode 403 is electrically connected to a wiring connection 302 in the interconnect layer 300. The first electrode 401 and second electrode 403 are electrically isolated from each other. The electrode materials are electrically conductive and are typically formed from metals or intermetallic compounds such as titanium (Ti), aluminium (Al), titanium-aluminide (TiAL), tungsten (W) or platinum (Pt), or alloys thereof. These materials are manufacturable (in terms of deposition temperature and chemical process compatibility) with CMOS drive circuitry and the piezoelectric layer.

(32) The piezoelectric actuator 402 is formed from material chosen for compatibility with the manufacture of CMOS and interconnect circuitry. CMOS drive circuitry can typically survive a temperature of up to about 450 C. However, high yield manufacturing requires a much lower peak manufacturing temperature, typically 300 C. Deposition methods that subject the CMOS drive electronics to temperatures over a duration can degrade performance, typically affecting dopant mobility and the degradation of wiring within the interconnect layer. The temperature limit restricts deposition methods for the piezoelectric layers. Suitable piezoelectric materials include aluminium nitride (AlN), aluminium nitride compounds (in particular scandium aluminium nitride (ScAlN)) and zinc oxide (ZnO), which are compatible with CMOS electronics. The composition of the piezoelectric material is chosen to optimise the piezoelectric properties. For example, the concentrations of any additional elements in aluminium nitride compounds (such as the concentration of scandium in scandium aluminium nitride) are typically chosen to optimise the magnitude of the d.sub.31 piezoelectric constant. The higher the concentration of scandium in scandium aluminium nitride, the typically larger the value of d.sub.31. The mass percentage of scandium in scandium aluminium nitride may be as high as 50%.

(33) The piezoelectric actuator material is not continuous over the surface of the nozzle plate 500. The piezoelectric material is located primarily over the nozzle plate and includes a number of openings including electrode openings 404 and a region around the nozzle 405.

(34) The protective front surface 600 is formed on the outer surface of the droplet ejector device 100 and covers the piezoelectric actuator 402, the electrodes 401 and 403, and the nozzle plate 500. The protective front surface has openings for the nozzles 601 and for the bond pads 700. The protective front surface material is chemically inert and impermeable. The protective front surface material may also be repellent to the fluid to be ejected. The mechanical properties of the protective front surface material are chosen carefully to minimize the effect on the forcing action of the piezoelectric actuator 400 and nozzle plate 500. The protective front surface material is chosen to be manufacturable with a CMOS compatible process flow, for example in terms of processing temperature and chemical process compatibility. The protective front surface 600 prevents contact of fluid with any of the electrodes 401 and 403 and piezoelectric actuator 402. Suitable protective front surface materials include polyimides, polytetrafluoroethylene (PTFE), diamond-like carbon (DLC) or related materials.

(35) FIG. 3 is a plan view of a nozzle showing features of the monolithic droplet ejector structure 1 with the protective coating 600 removed according to the first embodiment. The dashed line shows the underlying position of the fluid inlet 103 in relation to the piezoelectric actuator 400.

(36) In use, the fluid droplet ejector device 1 is mounted on a substrate that can supply fluid to the fluid inlet 103. Fluid pressure is typically slightly negative at the fluid inlet 103 and the fluid inlet channels 101 typically prime or fill with fluid by surface tension driven capillary action. The nozzles 601 prime up to the outer surface of the protective front surface 600 due to capillary action once the fluid inlets 103 are primed. The fluid does not move onto the outer surface of the protective surface 600 past the nozzles 601 due to the combination of negative fluid pressure and the geometry of the nozzle 601.

(37) The actuator drive circuitry 201 and 202 controls the application of a voltage pulse to the drive electrodes 401 and 403 according to a timing signal from the overall drive circuitry 203. The application of electrode voltage across the piezoelectric material 402 creates an electric field. The application of this field causes a deformation of the piezoelectric material 402. The deformation can either be tensile or compressive strain depending on the orientation of the electric field with respect to the direction of polarization in the material. The induced strain caused by the expansion or contraction of the piezoelectric materials 402 induces a strain gradient through the thickness of the nozzle plate 500, piezoelectric actuator 400 and the protective front layer 600 causing a movement or displacement perpendicular to the fluid inlet channel.

(38) The piezoelectric properties of the piezoelectric material can be characterized in part by the transverse piezoelectric constant d.sub.31. d.sub.31 is the particular component of the piezoelectric coefficient tensor which relates the electric field applied across the piezoelectric material in a first direction to the strain induced in the piezoelectric material along a second direction perpendicular to said first direction. The piezoelectric actuator 400 shown is configured such that the applied electric field induces a strain in the material in a direction perpendicular to the direction in which the field is applied, and is therefore characterized by the d.sub.31 constant.

(39) The application of a DC or constant electric field can cause a net positive or negative displacement of the nozzle plate 500. A positive displacement of the nozzle plate is shown in FIG. 4(a).

(40) The application of a pulsed electric field can cause an oscillation of the nozzle plate 500. This oscillation of the nozzle plate induces a pressure in the fluid inlet 103 under the nozzle plate 500 which causes droplet ejection out of the nozzle 601. The frequency and amplitude of the nozzle plate oscillation is primarily a function of the mass and stiffness characteristics of the nozzle plate 500, piezoelectric actuator 400, the protective layer 600, the fluid properties (for example, the fluid density, fluid viscosity (either Newtonian or non-Newtonian) and surface tension), nozzle and fluid inlet geometries and the configuration of both drive pulses.

(41) FIGS. 4(a)-4(b) show a drive pulse implementation. Voltage pulses across electrode 401 and 403 are shown. The electric field direction is labelled as E and the deflection is labelled as x.

(42) The application of a steady state or DC electric field across the electrodes causes a contraction in the piezoelectric layer 402 and a steady state deflection of the nozzle plate away from the fluid inlet as shown in FIG. 4 (a). The fluid pressure under the nozzle plate is the same as the fluid inlet supply pressure. Strain energy is stored in the nozzle plate 500, the piezoelectric actuator 400 and the protective layer 600.

(43) The electric field is removed and a reverse electric field pulse is applied as shown in FIG. 4 (b). This causes both a release of the stored strain energy and the application of additional expansion of the piezoelectric material 402. The actuator moves towards the fluid inlet as shown in FIG. 4 (b). This causes a positive pressure in the fluid inlet and nozzle region which causes droplet ejection out of the nozzle 601. The reverse electric field pulse may come immediately after the removal of the DC pulse or at a slightly delayed duration.

(44) The final removal of the electric field across the piezoelectric material 402 causes the nozzle plate 500 to return to a position with no induced strain.

(45) The control of two electrodes for any nozzle-actuator-nozzle plate in the device facilitates directional switching of the applied electric fields in relation to the inherent polarization of the piezoelectric material. This allows the device to incorporate stored strain energy into the nozzle plate 500 and actuator 400 structure. The release and integration of this stored strain energy augments volumetric displacements during a nozzle plate droplet ejection oscillation. The increased volumetric displacement is achieved without having to increase applied voltages and electric fields.

(46) It is also possible to replace the DC electric field configuration described in FIG. 4(a) with a pulse field configuration as shown in FIG. 4(b). This has the advantage of minimizing any applied strain effects over longer durations. An additional advantage of the dual pulsed approach is enabled by the timing of the field pulse switching application. The application of the first pulse will induce an oscillation with an initial nozzle plate movement away from the fluid inlet as shown in FIG. 4(b). This oscillation will introduce a negative fluid pressure under the nozzle plate which introduces a net fluid flow towards the nozzle which can additionally augment the fluid ejection flows through the nozzle.

(47) FIGS. 5(a)-5(c) is a schematic showing the manufacturing process flow for the droplet ejector device. The first manufacturing step, as shown in FIG. 5(a), is to create drive circuitry and the interconnect layer 300, for example CMOS drive circuitry and interconnects, on a surface of a silicon wafer substrate. CMOS drive circuitry is formed by standard processesfor example ion implantation on p-type or n-type substrates followed by the creation of a wiring interconnect layer by standard CMOS fabrication processes (e.g. ion implantation, chemical vapour deposition (CVD), physical vapour deposition (PVD), etching, chemical-mechanical planarization (CMP) and/or electroplating).

(48) Subsequent manufacturing steps are implemented to define features and structures of the monolithic droplet ejector device. Subsequent steps are chosen not to damage structures formed in previous steps. A key manufacturing parameter is the peak processing temperature. Problems associated with processing CMOS at high temperatures include the degradation of dopant mobility and interconnect wiring schemes. CMOS electronics are known to survive temperatures of 450 C. However, a much lower temperature (i.e. below 300 C.) is desirable for high yield.

(49) The nozzle plate 500, the piezoelectric actuator 400, the protective layer 600 and the bond pads 700 are formed on top of the interconnect layer as shown in FIG. 5(b).

(50) The nozzle plate 500 is deposited using a CVD or PVD process.

(51) The formation of a CMOS compatible piezoelectric material 402 is of particular interest as this is the key driving element of the actuator. Table 10 shows a table listing some common piezoelectric materials and the manufacturing methods associated with them, along with typical d.sub.31 values. It can be seen that materials with the highest d.sub.31 values are incompatible with manufacture of monolithic CMOS structures. Materials that are compatible with CMOS structures have low d.sub.31 values and hence a much lower forcing capability.

(52) As can be seen from the table, although lead zirconate titanate (PZT) can be deposited by PVD (including sputtering) at low temperatures, it subsequently requires a post process anneal at a temperature above the allowable temperature for CMOS. PZT can also be deposited by sol gel methods, but this again requires a high temperature anneal above the CMOS limit. PZT also has a very slow rate of deposition that is not viable commercially. PZT additionally contains lead, which is undesirable environmentally.

(53) ZnO, AlN and AlN compounds (such as ScAlN) materials can be deposited using low-temperature PVD (e.g. sputtering) processes that do not require post processing such as annealing. These materials also do not require poling. A poling step is required for PZT, wherein the material is subjected to a very high electric field which orients all the electric dipoles in the direction of the field.

(54) ZnO, AlN and AlN compounds (e.g. ScAlN) materials are therefore commercially viable materials for the fabrication of a monolithic droplet ejector device. However, the value of d.sub.31 for these materials is significantly lower than that of PZT. The particular configuration of the nozzle (i.e. the actuatable nozzle plate), which improves ejection efficiency, and the use of two control electrodes, which improves actuation efficiency (as shown in FIGS. 4(a)-4(b)), counter the lower d.sub.31 value associated with these materials.

(55) Piezoelectric electrode materials are deposited using a CMOS compatible process such as PVD (including low-temperature sputtering). Typical electrode materials may include titanium (Ti), platinum (Pt), aluminium (Al), tungsten (W) or alloys thereof. The electrodes are defined by standard patterning and etch methods.

(56) Protective materials can be deposited and patterned using a spin on and cure method (suitable for polyimides or other polymeric materials). Some materials, such as PTFE, may require more specific deposition and patterning approaches.

(57) Bond pads are deposited using methods such as CVD or PVD (e.g. sputtering).

(58) The fluid inlet channels are defined using high aspect ratio Deep Reactive Ion Etching (DRIE) methodologies as shown in FIG. 5(c). The fluid inlets are aligned to the nozzle structures using a wafer front-back side alignment tool. The wafer may be mounted on a handle wafer during the front-back alignment and etch steps.

(59) The DRIE approach may also be used to singulate the die, however, other approaches may be used such as a wafer saw.

Second Example Embodiment

(60) FIG. 6 is a cross sectional view showing an alternative implementation of the electrode structure. In this embodiment, the electrode 403, is connected by wiring, 302, to a ground line 204 rather than drive circuitry. The ground line 204 is located within the interconnect layer 300 and is connected to the drive circuitry region 203 or directly to grounded bond pads 700.

Third Example Embodiment

(61) FIG. 7 is a schematic showing an alternative drive pulse implementation compatible with this droplet ejector device. A voltage pulse, as shown in FIG. 7, is applied to only one of the electrodes, for example 401. This creates an electric field through the piezoelectric actuator 400 that creates a downward displacement of the nozzle plate 500. It is also possible to configure the device with a drive pulse applied to electrode 403 and a ground voltage applied to electrode 401.

Fourth Example Embodiment

(62) FIG. 8 is a schematic showing a cross section of an alternative implementation of the nozzle structure and shows the extension of the interconnect layer 304 attached to the nozzle plate layer 500 in the vicinity of the fluid inlet 101. The interconnect layer extension 304 may comprise solely dielectric material without any wiring. In another variation, the device has no nozzle plate layer and only an interconnect layer attached to the piezoelectric actuator.

Fifth Example Embodiment

(63) FIG. 9 is a cross-sectional view showing an alternative implantation of the bond pad structures. The protective front surface has been removed in the vicinity of the bond pads 701. This geometry improves accessibility of external wiring schemes and reduces the overall height of wire bonding above the height of the chip.

(64) Further variations and modifications may be made within the scope of the invention herein disclosed.

(65) The device may be formed on a silicon wafer substrate. Alternatively, the substrate may comprise a silicon-on-insulator wafer or III-V semiconductor wafer.

(66) The fluid inlet channels may be substantially cylindrical and therefore have substantially circular cross-sections in the plane of the substrate. Alternatively, the fluid inlet channels may take a variety of other cross-sections including multiple-sided, regular or irregular shapes. The shape of the fluid inlet channels is typically dependent on other aspects of the monolithic chip design such as the layout of nozzles, the drive electronics placement and the wiring routing in the interconnect layer 300.

(67) The cross sectional shapes may also be selected to minimize the width of the printhead chip without introducing failure mechanisms. Failure mechanisms may be structural (for example, too many fluid inlets may reduce the robustness of the chip) or they may be operational (for example, interconnect wires may be insufficient to carry the appropriate current). A reduced printhead width is desirable because it increases the number of chips which can be manufactured on a single wafer.