WO2021086353A1

WO2021086353A1 - A fluid ejection head fabrication method and a fluid ejection head

Info

Publication number: WO2021086353A1
Application number: PCT/US2019/058940
Authority: WO
Inventors: Donald W. Schulte; Terry Mcmahon; David R. Thomas; Tsuyoshi Yamashita
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2019-10-30
Filing date: 2019-10-30
Publication date: 2021-05-06

Abstract

A fluid ejection head may include a thin-film structure forming a fluid actuator and an electrical circuit for powering and controlling the fluid actuator. The thin-film structure may include a noble metal layer forming an electrical trace electrically connected to the fluid actuator and a tantalum layer over the electrical trace. The fluid ejection head may further include a chamber layer bonded to the tantalum layer over the electrical trace such that the tantalum layer is sandwiched between the electrical trace and the chamber layer. The chamber layer forms a fluid ejection chamber opposite the fluid actuator.

Description

A FLUID EJECTION HEAD FABRICATION METHOD AND A FLUID EJECTION HEAD

BACKGROUND

[0001] Fluid ejection heads are used to controllably eject droplets of fluid onto a target, such as a print medium. Fluid ejection heads are often formed by a thin-film structure bonded to a chamber layer. The thin-film structure provides a fluid actuator and circuitry for actuating the fluid actuator. The chamber layer provides a fluid ejection chamber from which fluid is displaced through a nozzle or orifice by the fluid actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a diagram schematically illustrating portions of an example fluid ejection head with a chamber layer bonded to a tantalum layer over a noble metal trace.

[0003] FIG. 2 is a flow diagram illustrating an example fluid ejection head fabrication method.

[0004] FIG. 3 is a flow diagram illustrating an example fluid ejection head fabrication method.

[0005] FIGS. 4A, 4B and 4C are sectional views illustrating one example method for fabricating a fluid ejection head.

[0006] FIG. 5 is a top view schematically illustrating an example fluid ejection head.

[0007] FIG. 6A is a sectional view illustrating a first portion of an example fluid ejection head. [0008] FIG. 6B is a sectional view illustrating a second portion of the example fluid ejection head of FIG. 6A.

[0009] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The FIGS are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and/or implementations consistent with the description; however, the description is not limited to the examples and/or implementations provided in the drawings.

DETAILED DESCRIPTION OF EXAMPLES

[00010] Disclosed are example fluid ejection heads and example fluid ejection head fabrication methods that may provide enhanced reliability. The example fluid ejection heads utilize a thin-film structure that provides electrical power to the fluid actuators and that grounds the fluid actuators using electrically conductive traces. The electrically conductive traces are provided by relatively wide bands or layers of a noble metal, such as gold. Because each of the electrically conductive traces is formed by a relatively wide layer of a noble metal, electrical current may be transmitted with lower electrical resistance.

[00011] The example fluid ejection heads further include a chamber layer extending over the thin-film structure and forming a fluid ejection chamber from which fluid is displaced by the fluid actuator. In one implementation, the chamber layer is formed from a photo-imageable polymer. The chamber layer is indirectly bonded to the thin-film structure, over the electrically conductive traces, by an intervening tantalum layer.

[00012] Without the intervening tantalum layer, the chamber layer may not reliably bond to the surface of the thin-film structure which would otherwise be largely covered by the noble metal material forming the electrically conductive traces. Without the intervening tantalum layer, the thin- film structure may be vulnerable to delamination from the chamber layer. Delamination of the thin-film structure from the chamber layer may lead to the fluid being ejected seeping between the chamber layer and the thin-film structure, short-circuiting the electrical circuitry.

[00013] The intermediate tantalum layer is sandwiched between the noble metal electrical trace and the photo-imageable material of the chamber layer. The intermediate tantalum layer more reliably bonds to the chamber layer as compared to the noble metal materials forming the electrically conductive traces. In one implementation, a tantalum layer is formed directly upon the noble metal electrically conductive trace, wherein the chamber layer is bonded directly to the tantalum layer. In other implementations, a tantalum layer may be formed directly upon the noble metal electrically conductive traces, wherein the chamber layer is indirectly bonded to the tantalum layer by an intervening layer of material or multiple intervening layers of other materials.

[00014] In addition to providing more reliable bonding of the chamber layer to the thin-film structure, the disclosed example methods may further reduce processing time and may facilitate the use of wet etching. Tantalum and gold may inter-diffuse when sputter deposited. The inter-diffused tantalum-gold layers may interfere with wet etching which may result in uneven subsequent etching of the bottom layers. The disclosed example methods provide a process flow where a first set of tantalum-gold layers are masked and etched before the second set of tantalum-gold layers are deposited. As a result, the etching of the lowermost gold layer after deposition of the second tantalum-gold layers may be eliminated.

[00015] In one implementation, the first set of tantalum-gold layers are masked and etched a to define the electrically conductive traces and an electrically conductive routing through a via. Following deposition of a second set of tantalum-gold layers, the second set of tantalum-gold layers are masked and etched to define a bond pad extending from the electrically conductive routing and a tantalum cavitation plate covered with a gold layer. The second set of tantalum-gold layers are subsequently masked and etched to remove the gold layer from the electrically conductive traces and the cavitation plate (when provided), wherein the tantalum layer of the second set of tantalum-gold layers remains over the gold traces for bonding to the chamber layer and over the fluid actuator to complete the cavitation plate. In some implementations, the cavitation plate over the fluid actuator may be omitted.

[00016] Disclosed is an example fluid ejection head that may include a thin-film structure forming a fluid actuator and an electrical circuit for powering and controlling the fluid actuator. The thin-film structure may include a noble metal layer forming an electrical trace electrically connected to the fluid actuator and a tantalum layer over the electrical trace. The fluid ejection head may further include a chamber layer bonded to the tantalum layer over the electrical trace such that the tantalum layer is sandwiched between the electrical trace and the chamber layer. The chamber layer forms a fluid ejection chamber opposite the fluid actuator.

[00017] Disclosed is an example fluid ejection head fabrication method. The method may include providing a thin-film structure forming a fluid actuator and electrical circuit for powering and controlling the fluid actuator, wherein the thin-film circuit comprises a noble metal electrical trace. The method may further include covering the noble metal electrical trace with a tantalum layer and bonding a chamber layer to the tantalum layer such that the tantalum layer is sandwiched between the electrical trace and the chamber layer. The chamber layer may form a fluid ejection chamber proximate the fluid actuator. [00018] Disclosed is an example fluid ejection head fabrication method. The method may include providing a portion of thin-film structure having an electrical resistor, depositing a first tantalum layer on the thin-film structure, depositing a first noble metal layer on the tantalum layer and within a via extending through the thin-film structure, wet etching the first noble metal layer and the first tantalum layer such that a first portion of the first noble metal layer forms an electrical trace and a second portion of the first noble metal layer projects from the via. The method may further include depositing a second tantalum layer, wherein the second tantalum layer comprises a first portion over electrical trace, a second portion over the second portion of the first noble metal layer and a third portion over the electrical resistor. The example fabrication method may further include depositing a second noble metal layer, wherein a first portion of the second noble metal layer extends over the first portion of the second tantalum layer, a second portion of the second noble metal layer extends over the second portion of the second tantalum layer and wherein a third portion of the second noble metal extends over the third portion of the second tantalum layer. The second portion of the second noble metal layer may form a bond pad. The example fabrication method may further include wet etching portions of the second noble metal layer to remove the first portion of the second noble metal layer and the third portion of the second noble metal layer while leaving the second portion of the second noble metal layer. Thereafter, the method includes bonding a chamber layer to the first portion of the second tantalum layer, wherein the chamber layer may form a fluid ejection chamber opposite the third portion of the second tantalum layer.

[00019] FIG. 1 is a schematic diagram illustrating portions of an example fluid ejection head 20. Fluid ejection head 20 has a construction that provides more reliable bonding of the chamber layer to a thin-film structure that powers and/or actuates a fluid actuator using noble metal electrically conductive traces. Fluid ejection head 20 facilitate such enhanced bonding by depositing a tantalum layer over the noble metal electrical trace, wherein the chamber layer is directly or indirectly bonded to the tantalum layer over the electrical traces. Fluid ejection head 20 comprises thin-film structure 24, tantalum layer 26 and chamber layer 28.

[00020] Thin-film structure 24 comprises a multitude of layers and components that form fluid actuator 30 and an electrical circuit 32, a portion of which is shown. Fluid actuator 30 comprises a device that, upon being actuated, displaces fluid within a fluid ejection chamber of chamber layer 26 through an ejection orifice or nozzle. In one implementation, fluid actuator 30 comprises a thermal resistor which, upon receiving electrical current, heats to a temperature above the nucleation temperature of the fluid so as to vaporize a portion of the adjacent fluid to create a bubble which displaces the fluid through the associated orifice. In other implementations, fluid actuator may comprise other forms of fluid actuators. In other implementations, the individual fluid actuators may be in the form of a piezo-membrane based actuator, an electrostatic membrane actuator, mechanical/impact driven membrane actuator, a magneto-strictive drive actuator, an electrochemical actuator, and external laser actuators (that form a bubble through boiling with a laser beam), other such microdevices, or any combination thereof.

[00021] Electrical circuit 32 connects fluid actuator 30 to a source of power, a voltage source, and further connects fluid actuator 30 to an electrical ground. In the example illustrated, circuit 32 further supplies electrical control signals for controlling the actuation fluid actuator 30. Electrical circuit 32 comprises electrical trace 34. Electrical trace 34 is formed from a noble metal to facilitate strong electrical conductivity. In one implementation, electrical trace 34 is formed from gold. In other implementations, electrical trace 34 is formed from platinum or other noble metals.

[00022] The noble metal electrical trace 34 is connected to fluid actuator 30. In one implementation, the noble metal electrical trace electrically connects the fluid actuator 30 to a source of power, such as a voltage source. In one implementation, noble metal electrical trace electric connects the fluid actuator 30 to a ground. In one implementation, thin-film structure 24 comprises multiple electrical traces 34, some for transmitting an electrical power to fluid actuator 30, some for connecting fluid actuator 30 to a ground and some for transmitting electrical signals to control the timing of actuation of fluid actuator 30.

[00023] Electrical trace 34 may be in the form of a wide band or layer of the noble metal material to provide high electrical conductivity and low resistance. Electrical trace 34 forms an exterior of thin-film structure 24, extending across those exterior surfaces of thin-film structure that extend opposite to and, but for tantalum 26, would otherwise be directly bonded to chamber layer 28. The wide band of noble metal forming electrical trace 34 results in electrical trace 34 covering a large percentage of the exterior surface of thin-film structure 24 that is to be bonded to chamber layer 28. In one implementation, noble metal electrical trace 34, alone or in combination with other noble metal electrical traces 34, covers or forms at least 25% of the surface of thin-film structure 24 that extends adjacent and opposite to chamber layer 28.

[00024] Tantalum layer 26 extends over and covers noble metal electrical trace 34. In one implementation, tantalum layer 26 covers an entirety of an outermost surface of electrical trace 34 and may include other separate or spaced portions that cover the outermost surfaces of all other electrical traces 34 forming the exterior of thin-film structure 24. In yet another implementation, tantalum layer 26 covers 50% of the outer surface area of the electrical traces, including electrical trace 34, that form the exterior thin-film structure 24. In another implementation, tantalum layer 26 covers 75%, 90% or 100 % of the outer surface area of the electrical traces, including electrical trace 34. Tantalum 26 has a greater adhesive strength for adhering to the material of chamber layer 28, or to an intermediate layer between tantalum layer 26 and the material chamber layer 28, as compared to the noble metal forming electrical trace 34.

[00025] Chamber layer 28 extends over thin-film structure 24 and forms a fluid ejection chamber 38. Fluid ejection chamber 38 extends opposite to fluid actuator 30. In one implementation, fluid actuator 30 is spaced from fluid ejection chamber 38 by additional layers of thin-film structure 24. In another implementation, fluid actuator 30 is exposed within fluid ejection chamber 38.

[00026] In one implementation, chamber layer 28 additionally forms a smaller ejection orifice (not shown) extending from fluid ejection chamber 38. In other implementations, chamber layer 28 is capped by an orifice plate providing the ejection orifice. Chamber layer 28 comprises a single layer of material or multiple constituent sub layers of material.

[00027] Chamber layer 28 is directly or indirectly bonded to tantalum layer 26 such that tantalum layer 26 is sandwiched between trace 34 and chamber layer 28. In implementations where chamber layer 28 is directly bonded to tantalum layer 26, tantalum layer 26 better adheres to the material or materials of chamber layer 28 as compared to the noble metal forming trace 34. In implementations where chamber layer 28 is indirectly bonded to tantalum layer 26 by an intermediate layer that is in direct contact with tantalum layer 26 and that is bonded to chamber layer 28, tantalum layer 26 better adheres to the intermediate layer as compared to the noble metal forming trace 34. In one implementation, chamber layer 28 is formed from a photo-imageable or photo definable polymer material which polymerizes with exposure to light or similar electromagnetic radiation. Materials of this type are available from E.l. DuPont deNemoirs Company of Wilimington Del. or Chicrochem Corp. of Newton Mass. Examples of photo-imageable polymer materials include, but are not limited to, Parad ™, Vacrel™, SU8™ and IJ5000™. [00028] FIG. 2 is a flow diagram of portions of an example fluid ejection head fabrication method 100. Method 100 may be utilized to form fluid ejection head 20 described above. As indicated by block 104, a thin-film structure, such as structure 24, is provided. The thin-film structure forms a fluid actuator, such as fluid actuator 30, and an electrical circuit for powering and controlling the fluid actuator. The electrical circuit comprises a noble metal electrical trace, such as trace 34.

[00029] As indicated by block 108, the noble metal electrical trace is covered with a tantalum layer, such as tantalum layer 26. As indicated by block 112, a chamber layer, such a chamber layer 28, is bonded (directly or indirectly) to the tantalum layer such that the tantalum layer is sandwiched between the electrical trace and the chamber layer, wherein the chamber layer forms a fluid ejection chamber proximate the fluid actuator.

[00030] FIG. 3 is a flow diagram illustrating portions of an example fluid ejection head fabrication method 200 for forming certain components of a fluid ejection head. FIGS. 4A, 4B and 4C are sectional views illustrating the forming of selected components the fluid ejection head per method 200. FIG. 3 and FIGS. 4A-4C illustrate the fabrication of portions of an example thin-film structure having an example electrically conductive via routing within a via, an example bond pad, an example electrically conductive trace and an example fluid actuator in the form of a resistor having an overlying cavitation plate.

FIG. 3 and FIGS. 4A-4C further illustrate the covering of the electrically conductive trace with a layer of tantalum and the bonding of a chamber layer and orifice plate over the thin-film structure and over the tantalum layer.

[00031] As indicated by block 204, a portion of a thin-film structure 324 having a fluid actuator in the form of an electrical resistor 330 is provided. In one implementation, the resistor may comprise a layer of an electrically resistant material such as Tantalum Aluminum (TaAI), a single layer of Ta and Al atoms co-sputtered together deposited upon a silicon substrate. In other implementations, resistor 330 may be formed from other materials. The electrical resistor 330 may be connected to an electrical circuit that supplies power to the electrical resistor. The electrical circuit may include the electrically conductive via routing, the bond pad, and the electrically conductive trace formed as described below.

[00032] As indicated by block 208, a first tantalum layer 432 is deposited upon the thin-film structure 324. A portion of the tantalum layer is deposited within a via 434 that extends into thin-film structure 324. As indicated by block 212, the first noble metal layer 436 is deposited on the tantalum layer 432 and within the via 434. Once the layers have been formed, as indicated by block 216, the layers 432 and 436 are concurrently subjected to a mask and wet etch such that a first portion 440 of the first noble metal layer 436 forms the electrically conductive trace 334 and such that a second portion 442 of the first noble metal layer 436 projects from the via 434 to form portions of an electrically conductive routing 444 within via 434 and portions of a bond pad 446 as shown in FIG. 4A.

[00033] As indicated by block 220 and as shown in FIG. 4B, a second tantalum layer 452 is deposited and subsequently masked and wet etched. A first portion 454 of the etched second tantalum layer 452 extends over and on the electrically conductive trace 334. A second portion 455 of the second tantalum layer 452 extends on the second portion 442 of the first noble metal layer 440 and a third portion 456 of the second tantalum layer 452 extends over the electrical resistor 330.

[00034] As indicated by block 224 and further shown by FIG. 4B, a second noble metal layer 460 is deposited. The second noble metal layer 460 is subsequently masked and wet etched such that a first portion 462 of the second noble metal layer 460 extends over the first portion 454 of the second tantalum layer 452, a second portion 464 of the second noble metal layer 460 extends over the second portion 455 of the second tantalum layer 452 and such that a third portion 466 of the second noble metal layer 460 extends over the third portion 456 of the second tantalum layer 452. The second portion 464 of the second noble metal layer 460 forms the completed bond pad 446 and the completed electrically conductive via routing 444.

[00035] As indicated by block 228, and as indicated by broken lines in FIG. 4B, a wet etch is carried out to remove the first portion 462 and the third portion 466 of the noble metal layer 460 while leaving the second portion 464 of the noble metal layer 460. As a result, portions 454 and 456 of the second tantalum layer 452 are exposed.

[00036] As indicated by block 232, and as shown by FIG. 4C, chamber layer 328, similar to chamber layer 28 described above, is bonded to the first portion 454 of the second tantalum layer 452. As described above, the tantalum layer provides better adhesion of the thin-film structure 324 to chamber layer 328 as compared to the noble metal material of layer 436. As further shown by FIG. 4C, the chamber layer 328 forms a fluid ejection chamber 470 opposite to the third portion 456 of the second tantalum layer 452. Portion 456 forms a cavitation plate 331 over the resistor 330. In other implementations, portion 456 and the formed cavitation plate may be omitted.

[00037] In the example illustrated, chamber layer 328 is capped by an orifice plate 480 which forms a nozzle or fluid ejection orifice 482 extending from ejection chamber 470. In other implementations, orifice plate 480 may be omitted such as where chamber layer 328 additionally provides orifice 482.

[00038] In addition to providing more reliable bonding of the chamber layer 328 to the thin-film structure 324, method 200 may further reduce processing time and may facilitate the use of wet etching. Tantalum and gold may inter-diffuse when sputter deposited. The inter-diffused tantalum-gold layers may interfere with wet etching which may result in uneven subsequent etching of the bottom layers. Method 200 provides a process flow where a first set of tantalum-gold layers 432, 436 are masked and etched before the second set of tantalum-gold layers 452, 460 are deposited. As a result, the etching of the lowermost gold layer after deposition of the second tantalum- gold layers may be eliminated.

[00039] FIG. 5 is a top view illustrating portions of an example fluid ejection head 520. FIG. 5 illustrates an example electrical circuit provided in part by the contact pads, vias, and electrically conductive traces that may be formed by method 200. Fluid ejection head 520 comprises thin-film structure 524, tantalum layers 526-1 , 526-2 and 526-3 (collectively referred to as tantalum layers 526) and chamber layer 528. Thin-film structure 524 comprises a fluid actuator in the form of a resistor 330, an overlying cavitation plate 331, contact pads 541-1 , 541-2, 541-3 (collectively referred to as contact pads 541), electrically conductive via routings 544-1, 544-2, 544-3 (collectively referred to as via routings 544), electrically conductive noble metal traces 546-1, 546-2 and 546-3 (collectively referred to as noble metal traces 546), electrically conductive via routings 548-1, 548-2, 548-3, 548-4, 548-5 and 548-6 (collectively referred to as via routings 548) and a switch in the form of a field-effect transistor (FET) 550.

[00040] Resistor 330 and cavitation plate 331 are described above. Resistor 330 comprises a layer of electrically resistant material such as Tantalum Aluminum (TaAI), a single layer of Ta and Al atoms co-sputtered together. Cavitation plate 331 overlies resistor 330 between resistor 330 in a corresponding fluid ejection chamber. In some implementations, cavitation plate 331 may be omitted.

[00041] Contact pads 541 extend along the surface of thin-film structure 524. Each of contact pads 541 may be formed in a fashion similar to that described above with respect to method 200 and as shown in FIGS. 4A-4C. Each of contact pads 541 has a noble metal electrically conductive surface, such as gold, facilitating electrical connection to head 520. In the example illustrated, contact pad 541-1 is connected to a voltage source 540. Contact pad 541-2 is connected to ground 542. Contact pad 541-3 is electrically connected to an addressing line from control circuitry 543.

[00042] Electrically conductive via routings 544-1 , 544-2 and 544-3 comprise layers of electrically conductive material extending into and below the surface of thin-film structure 524 within corresponding vias to provide electrical connection to subsurface electrically conductive layers 522-1, 522-2 and 522-3, respectively.

[00043] FIG. 5 illustrates portions of tantalum layers 526 removed or broken away to illustrate the underlying noble metal electrically conductive traces 546. Noble metal electrically conductive traces 546 comprise wide layers of a noble metal material, such as gold, across the surface of thin-film structure 524. Each of traces 546 may be similar to the trace 34 described above. The wide band of noble metal forming electrical traces 546 results in electrical traces 546 covering a large percentage of the exterior surface of thin-film structure 524 that is to be bonded to chamber layer 528. In one implementation, noble metal electrically conductive traces 546 collectively cover or form 25% or more of the surface of thin-film structure 524 that extends adjacent and opposite to chamber layer 528. In one implementation, the noble metal electrically conductive traces cover or form 50% or more of the surface of thin-film structure 524 that extends adjacent and opposite to chamber layer 528. In the example illustrated, the noble metal electrically conductive traces cover or form 75 % or more of the surface of thin-film structure 524 that extends adjacent and opposite to chamber layer 528. [00044] Electrically conductive via routings 548 comprise layers of electrically conductive material extending from the noble metal electrically conductive traces 546 on the surface of thin-film structure 524 through corresponding vias to subsurface structures or layers of thin-film structure 524. In the example illustrated, routing 548-1 extends from the subsurface electrically conductive layer 522-1 to noble metal electrically conductive trace 546-1 on the surface of structure 524. Routing 548-2 extends from the subsurface electrically conductive layer 522-2 to noble metal electrically conductive trace 546-2 on the surface of structure 524. Routing 548-3 extends from the subsurface electrically conductive layer 522-3 to the noble metal electrically conductive trace 546-3 on the surface of structure 524. Routing 548-4 extends from the electrically conductive noble metal trace 546- 1 to a subsurface electrically conductive layer 522-4 which is electrically connected to a first end of resistor 330. Routing 548-5 extends from the source S of transistor 550 below the surface of structure 524 to electrically conductive noble metal trace 546-2. Routing 548-6 extends from the gate G of transistor 550 to the noble metal electrically conductive trace 526-3. As further shown by FIG. 5, a second end of resistor 330 is electrically connected to the drain D of transistor 550 by a subsurface electrically conductive layer 522-5.

[00045] During use of fluid ejection head 520, the fluid actuator, in the form of resistor 330, is actuated by control circuitry 543 outputting electrical signal voltage which is transmitted by contact pad 541-3, down to subsurface layer 522-3 by via routing 544-3, across subsurface layer 522-3, up through via routing 548-3, across noble metal electrical trace 546-3, down through electrically conductive via routing 548-6 and across electrically conductive subsurface layer 522-6 to the gate G of transistor 550, closing the electrical circuit. As a result, voltage source 540 transmits electrical power through contact pad 541-1, down through via routing 544-1 to subsurface electrically conductive layer 522-1 , across subsurface electrically conductive layer 522-1 , up through via routing 548-1 to noble metal electrically conductive trace 546- 1, down through electrically conductive via 548-4 to subsurface electrically conductive layer 522-4 electrically connected to a first end of resistor 330.

The electrical current passing through resistor 330 further flows through subsurface electrically conductive layer 522-5 to the drain D of transistor 550. Because the transistor 550 is actuated by the electrical signal voltage, electrical current is transmitted across transistor 552 source S, where the electrical current is further transmitted across subsurface electrically conductive layer 522-7 to via routing 548-5, up through via routing 548-5 to noble metal electrically conductive trace 546-2, down through electrically conductive via routing 548-2, across subsurface electrically conductive layer 522-2, up through electrically conductive via routing 544-2, and across contact pad 541-2 to ground 542.

[00046] Tantalum layers 526 comprise layers of tantalum overlying traces 546. Tantalum layers 526-1 , 526-2 and 526-3 have surface areas corresponding to the areas of traces 546-1 , 546-2 and 546-3, respectively. In other implementations, tantalum layers 526 may partially cover the respective traces 546. In some implementations, tantalum layers 526 have surface areas greater than the underlying portions of the respective traces 546. Tantalum layers 526 are electrically spaced or insulated from one another to avoid short-circuiting between the underlying traces 546. Tantalum layers 526 facilitate more reliable bonding of thin-film structure 524 to chamber layer 528.

[00047] Chamber layer 528 is similar to chamber layer 28 and/or chamber layer 328 described above. Chamber layer 528 is directly or indirectly bonded to tantalum layers 526 such that tantalum layers 526 are sandwiched between traces 546 and chamber layer 528. In implementations where chamber layer 528 is directly bonded to tantalum layers 526, tantalum layers 526 better adhere to the material or materials of chamber layer 528 as compared to the noble metal forming traces 546. In implementations where chamber layer 528 is indirectly bonded to tantalum layers 526 by an intermediate layer that is in direct contact with tantalum layers 526 and that is bonded to chamber layer 528, tantalum layers 526 better adhere to the intermediate layer as compared to the noble metal forming traces 546. In one implementation, chamber layer 528 is formed from a photo-imageable or photo definable polymer material which polymerizes with exposure to light or similar electromagnetic radiation. Materials of this type are available from E.l. DuPont deNemoirs company of Wilimington Del. Or Chicrochem Corp. of Newton Mass.. Examples of photo-imageable polymer materials include, but are not limited to, Parad ™, Vacrel™, SU8™ and IJ5000™.

[00048] As further shown by FIG. 5, chamber layer 528 (the outline of which is shown by broken lines) forms a fluid ejection chamber 570 generally opposite to resistor 330 and cavitation layer 331. In one implementation, chamber layer 528 additionally forms a fluid ejection orifice 582 through which fluid is ejected from chamber 570. In other implementations, chamber layer 528 may be capped by a separate orifice plate 480 (shown in FIG. 4C) providing fluid ejection orifice 582.

[00049] FIGS. 6A and 6B are sectional views illustrating different portions of an example fluid ejection head 620. Fluid ejection head 620 comprises thin-film structure 624, tantalum layer 626, chamber layer 628 and layer 629, sometimes referred to as an orifice plate. Thin-film structure 624 comprises substrate 664, dielectric layer 700, conductive layers 102, silicate glass layer 706, electrical resistive layer 708, conductive layer 710, dielectric layer 712, tantalum layer 714, gold layer 716, tantalum layer 626 and gold layer 719.

[00050] Substrate 641 comprises a layer or multiple layers of materials that are to be selectively doped such that portions of the substrate 641 may be made more electrically conductive while other portions are left with higher resistivity in order to form a transistor 650. According to one example implementation, substrate 641 comprises silicon, wherein the entire silicon substrate is lightly doped to have a moderate resistivity within tightly controlled specifications and wherein selected regions are more heavily doped so as to be more electrically conductive. In other implementations, substrate 641 may be formed from other semiconductor or semi-conductive materials.

[00051] In the example illustrated, substrate 641 has doped regions 720, 722 which are electrically conductive and lightly doped regions 724 between such doped regions 720, 722. Doped regions 720 serve as a source; doped regions 722 (enclosed by the gate structure of layer 702 in the form of a ring) serve as a drain and lightly doped regions 724 serve as channels in a transistor 650 used to provide power to the fluid actuator provided by electrically resistive layer 708.

[00052] Dielectric layer 700 comprises one or more layers of dielectric material patterned over substrate 641. In one implementation, layer 700 is formed in two stages. During the first stage, layer 700 is patterned such that layer 700 blocks subsequent heavier doping of underlying regions of substrate 641 such that layer 700 overlies and defines lightly doped regions 724. These regions of layer 700 further serve to locate and align subsequent formation of a single layer which provides layers 702 and 704. During the second stage, after formation of layers 702 and 704, and after doping to form regions 720 and 722, substrate 641 is oxidized to passivate surfaces of regions 720 and 722 to grow additional portions of layer 700.

[00053] Dielectric layer 700 electrically separates lightly doped regions 724, which serve as transistor channels, from the overlying gate of the transistors provided by conductive layer 702. The dielectric layer 700 is sufficiently thin such that electrical fields emitted from the gate provided by layer 702 make lightly doped regions 724 more electrically conductive. In the example illustrated, dielectric layer 700 comprises an oxidized surface of substrate 641. In the implementation illustrated wherein substrate 641 comprises silicon, layer 700 comprises S1O2. In another implementation, layer 700 may be formed in other fashions or from other dielectric materials.

[00054] Conductive layer 702 comprises a layer of electrically conductive material. Layer 702 self aligns with portions of underlying layer 700 and inhibits or prevents subsequent etching away of the underlying portions of layer 700. Layer 702 overlies dielectric layer 700 and lightly doped regions 724 and serves as a gate of a transistor. In the example implementation illustrated, layer 702 comprise polysilicon (also known as polycrystalline silicon, poly-Si or poly). Layer 702 is doped to a low conductivity while simultaneously preventing dopants from entering the channel regions 724.

[00055] In other implementations, layer 702 may be formed from other materials that inhibit doping of underlying portions of substrate 641 that are also electrically conductive. In yet another implementation, layer 702 may be merely electrically conductive, wherein dielectric layer 700 is formed from one or more layers that inhibit doping of substrate 641 when regions 720 are doped.

[00056] Silicate glass layer 706 comprises a layer of dielectric material overlying regions 720 of substrate 641 and layers 702. Layer 706 has a relatively large thickness and electrically insulates regions 720 of substrate 641 from layer 702 and from resistive layer 708 and conductive layer 710. Because layer 706 is silicate glass, layer 706 may be more easily deposited and blanket coated across substrate 641 and layers 702. In particular, the addition of phosphorus enhances the fluidity of the silicate glass forming layer 706 for enhanced coverage. In the example implementation illustrated, silicate glass layer 706 is formed from polysilicate glass (PSG). In another implementation, layer 706 may be formed from other forms of silicate glass such as borophosphosilicate glass (BPSG).

[00057] Resistive layer 708 comprises a layer of electrically resistant material deposited upon layer 706 within the area of firing or fluid ejection chamber 770. Layer 708 serves as a resistor which emits heat upon transmitting electrical current from firing voltage source 640. This heat emitted by layer 708 within the area of fluid ejection chamber 778 vaporizes a portion of fluid within the fluid ejection chamber 778, forcefully ejecting a remaining portion of fluid within fluid ejection chamber 778. In the example illustrated, layer 708 comprises a layer of Tantalum Aluminum (TaAI), a single layer of Ta and Al atoms co-sputtered together. In other implementations, layer 708 may be formed from other resistant materials.

[00058] Conductive layer 710 (sometimes referred to as the metal 1 layer or metal 1 bus) comprise a layer of electrically conductive material including a first portion 726 which electrically connects portions of layer 708 to firing voltage source 640, a second portion 728 which electrically connects a second spaced portion of layer 708 to regions 722 which serve as a drain of the transistor 650, a third portion 729 which is in contact with layer 702 and electrically connects layer 702 to address line voltage source 632, and a fourth portion 730 which electrically connects the bond pad 741 and electrically conductive via routing 644 to a gold trace layer formed by gold layer 716 on tantalum layer 714 extending between chamber layer 628 and the remainder of thin film structure 624.

[00059] Dielectric layer 712, sometimes referred to as a passivation layer, comprises a layer of dielectric material extending over layer 710 and electrically insulating or isolating portions of layer 710. In the example illustrated, layer 712 includes regions 740, 742 and 744. Region 740 extends through layer 710 into contact with layer 708, electrically separating portions 726 and 728 of layer 710. Region 742 extends through layer 710 to layer 706, electrically separating region 728 from region 729 of layer 710. Region 744 extends through layers 710 to layer 706, separating region 729 from region 730 of layer 710. According to one example implementation, dielectric layer 712 may comprise consecutive layers of SiC and SiN. In other implementations, dielectric layer 712 may include other materials and have greater or fewer dielectric layers.

[00060] Tantalum layer 714 and gold layer 716 form a portion of bond pad 741 , electrically conductive trace 646-1 and electrically conductive via routings 648-1 , 648-2. Electrically conductive trace 646 extends beneath chamber layer 628, around fluid ejection chamber 770, between electrically conductive routing 648-1 and electrically conductive routing 648-2.

Electrically conductive trace 646-1 comprises a relatively wide layer band of gold provide low resistance electrical conduction.

[00061] Tantalum layer 626 extends over those portions of 716 forming bond pad 741 , electrically conductive via routing 644 and trace 646-1 , enhancing the bonding of chamber layer 628 to thin film structure 624. In the example illustrated, tantalum layer 626 further extends over resistor 630 to form cavitation plate 631 . Gold layer 719 extends over those portions of tantalum layer 626 in the regions of bond pad 741 and electrically conductive via routing 644 to provide an enhanced electrically conductive surface for electrical contacts.

[00062] Chamber layer 628, sometimes referred to as a barrier layer, comprises a layer of material which are patterned so as to form fluid ejection chamber 770 about resistor 630. Layer 629, sometimes referred to as an orifice plate, comprises a layer of multiple layers extending over chamber layer 118 and forming nozzle openings 682 of fluid ejection chamber 770. Layers 118 and 120, together, form orifice structure 852. Although orifice structure 852 is illustrated as being formed from two layers, orifice structure 852 may alternatively be formed from a single layer or from greater than two layers. Orifice structure 852 may be formed from various polymers, epoxy materials, metals and the like.

[00063] FIG. 6B is a sectional view through a different portion of fluid ejection head 620, illustrating the electrical connection from the transistor 650 back to a ground 800. As shown by FIG. 6B, layers 708 and 710 are electrically connected to a bond pad 841 through an electrically conductive via routing 844 formed by layers 714, 716, 626 and 720. The bond pad 841 is to be connected to ground 800. Layers 708 and 710 extend below dielectric layer 712 until making electronic contact with an electrically conductive via 846 formed by layers 714 and 716 which also form an electrically conductive trace 646-2 extending below chamber layer 628. The electrically conductive trace 646-2 extends below chamber layer 628 to an electrically conductive via routing 848 which is electrically connected to a second portion of layers 708 and 710 which are in electrical connection with region 720.

[00064] As with electrically conductive trace 646-1 , electrically conductive trace 646-2 is covered with tantalum layer 626 which enhances bonding of chamber layer 628 to thin film structure 624.

[00065] Although the present disclosure has been described with reference to example implementations, workers skilled in the art will recognize that changes may be made in form and detail without departing from disclosure. For example, although different example implementations may have been described as including features providing various benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example implementations or in other alternative implementations. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example implementations and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements. The terms “first”, “second”, “third” and so on in the claims merely distinguish different elements and, unless otherwise stated, are not to be specifically associated with a particular order or particular numbering of elements in the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A fluid ejection head comprising: a thin-film structure forming a fluid actuator and an electrical circuit for powering and controlling the fluid actuator, the thin-film structure comprising a noble metal layer forming an electrical trace electrically connected to the fluid actuator; a tantalum layer over the electrical trace; and a chamber layer bonded to the tantalum layer over the electrical trace such that the tantalum layer is sandwiched between the electrical trace and the chamber layer, wherein the chamber layer forms a fluid ejection chamber opposite the fluid actuator.

2. The fluid ejection head of claim 1 further comprising a via through the thin-film structure, wherein a first portion of the noble metal layer forms the trace and wherein a second portion of the noble metal layer extends in the via.

3. The fluid ejection head of claim 2, wherein a first portion of the tantalum layer extends over the electrical trace and a second portion of the tantalum layer extends over the via, the fluid ejection head further comprising: a second noble metal layer over the second portion of the tantalum layer to form a bond pad electrically connected to the second portion of the noble metal layer within the via by the second portion of the tantalum layer.

4. The fluid ejection head of claim 3, wherein the thin-film structure further comprises a second tantalum layer, wherein the electrical trace is sandwiched between the first portion of the tantalum layer and a first portion of the second tantalum layer and wherein the second portion of the noble metal layer is sandwiched between the second portion of the tantalum layer and a second portion of the second tantalum layer.

5. The fluid ejection head of claim 3, wherein the fluid actuator comprises an electrical resistor.

6. The fluid ejection head of claim 5, wherein a third portion of the tantalum layer extends over the electrical resistor to form a cavitation plate.

7. The fluid ejection head of claim 1 further comprising an orifice plate bonded to the chamber layer and forming an ejection orifice extending from the fluid ejection chamber.

8. The fluid ejection head of claim 1 further comprising a second tantalum layer such that the electrical trace is sandwiched between the tantalum layer and the second tantalum layer.

9. The fluid ejection head of claim 8, wherein the chamber layer comprises a photo-imageable polymer.

10. The fluid ejection head of claim 1 , wherein the noble metal layer comprises gold.

11. The fluid ejection head of claim 1 , wherein the chamber layer is directly bonded to the tantalum layer.

12. A fluid ejection head fabrication method comprising: providing a thin-film structure forming a fluid actuator and electrical circuit for powering and controlling the fluid actuator, the electrical circuit comprising a noble metal electrical trace; covering the noble metal electrical trace with a tantalum layer; and bonding a chamber layer to the tantalum layer such that the tantalum layer is sandwiched between the electrical trace and the chamber layer, the chamber layer forming a fluid ejection chamber proximate the fluid actuator.

13. The fluid ejection head fabrication method of claim 12 further comprising: forming a noble metal layer over the thin-film structure, the noble metal layer having a first portion forming the electrical trace and a second portion extending within a via through the thin-film structure, wherein the tantalum layer has a first portion over the electrical trace and a second portion over the via, the method further comprising forming a second noble metal layer over the second portion of the tantalum layer to form a bond pad electrically connected to the second portion of the noble metal layer within the via by the second portion of the tantalum layer.

14. The method of claim 13, wherein the fluid actuator comprises an electrical resistor and wherein tantalum layer comprises a third portion forming a cavitation plate over the electrical resistor.

15. A method comprising: providing a portion of thin-film structure having an electrical resistor; depositing a first tantalum layer on the thin-film structure; depositing a first noble metal layer on the first tantalum layer and within a via extending through the thin-film structure; wet etching the first noble metal layer and the first tantalum layer such that a first portion of the first noble metal layer forms an electrical trace and a second portion of the first noble metal layer projects from the via; depositing a second tantalum layer, the second tantalum layer comprising a first portion on electrical trace, a second portion on the second portion of the first noble metal layer and a third portion over the electrical resistor; depositing a second noble metal layer, a first portion of the second noble metal layer extending over the first portion of the second tantalum layer, a second portion of the second noble metal layer extending over the second portion of the second tantalum layer, the second portion of the second noble metal layer forming a bond pad, and a third portion on the third portion of the second tantalum layer; wet etching portions of the second noble metal layer to remove the first portion of the second noble metal layer and the third portion of the second noble metal layer while leaving the second portion of the second noble metal layer; and bonding a chamber layer to the first portion of the second tantalum layer, the chamber layer forming a fluid ejection chamber opposite the third portion of the second tantalum layer.