WO2021262188A1

WO2021262188A1 - Fluid-ejection die with substrate layer

Info

Publication number: WO2021262188A1
Application number: PCT/US2020/039763
Authority: WO
Inventors: Chien-Hua Chen; Michael Cumbie; John L. Williams
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-06-26
Filing date: 2020-06-26
Publication date: 2021-12-30

Abstract

A fluid-ejection die is provided that has a substrate layer and a device layer at a frontside of the substrate layer. The device layer has a fluid-ejection nozzle and a chamber in which a fluid-ejection element is disposed. The substrate layer has a fluid-feed hole fluidically connected to the chamber. A panel is provided at a backside of the substrate layer. The panel has a fluid-feed slot under the fluid-feed hole. The panel forms the fluid-ejection die along with the substrate layer and the device layer. The substrate layer is backside etched through the fluid-feed slot of the panel to thin the substrate at the thin fluid-feed hole.

Description

FLUID-EJECTION DIE WITH SUBSTRATE LAYER

BACKGROUND

[0001] Printing devices, including standalone printers as well as all-in-one (AIO) printing devices that combine printing functionality with other functionality like scanning and copying, can use a variety of different printing techniques. One type of printing technology is inkjet-printing technology, which is more generally a type of fluid-ejection technology. Fluid-ejection devices have fluid-ejection dies that can selectively eject fluid like inks, binding agents, biological samples, agents, reagents, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS [0002] FIG 1 is a flowchart of an example method for fabricating a fluid- ejection cartridge including a fluid-ejection die attached to a fluid-ejection cartridge body. [0003] FIGs. 2A, 2B, 2C, 2D, 2E, and 2F are diagrams illustrating example performance of the method of FIG. 1.

[0004] FIG. 3 is a flowchart of another example method for fabricating a fluid-ejection cartridge including a fluid-ejection die attached to a fluid-ejection cartridge body. [0005] FIGs. 4A, 4B, and 4C are diagrams illustrating example performance of the method of FIG. 3.

[0006] FIG. 5 is a block diagram of an example fluid-ejection die. [0007] FIG. 6 is a block diagram of an example fluid-ejection cartridge including a fluid-ejection die.

[0008] FIG. 7 is a flowchart of an example method.

DETAILED DESCRIPTION [0009] A fluid-ejection device like an inkjet-printing device can include a fluid-ejection die that selectively ejects fluid like inks, binding agents, biological samples, agents, reagents, and so on. The fluid-ejection die may be part of a fluid-ejection die cartridge that also includes a cartridge body to which the die is fluidically attached. For instance, the cartridge may be replaceably insertable into the fluid-ejection device. The cartridge can include a reservoir to hold fluid that the die is to eject, and/or a fluidic connector to fluidically connect the cartridge to a fluid supply external to the cartridge.

[0010] The fluid-ejection die can include an array of fluid-feed holes that lead from a fluid-feed slot to firing chambers of the die. Fluid-ejection elements, such as thermal firing resistors, are disposed within the chambers. Actuation of the fluid-ejection elements causes ejection of fluid from the chambers through fluid-ejection nozzles of the fluid-ejection die. Minimizing the height of the fluid- feed holes through which fluid is supplied to the chambers from the fluid-feed slot of the die can improve fluid ejection. For example, a fluid-feed hole height of 50 micron or less can result in improved fluid ejection as compared to a height of 90 micron or more.

[0011] The fluid-ejection die may be fabricated from a wafer like a silicon wafer. One way to decrease fluid-feed hole height is to thin the wafer before forming the array of fluid-feed holes. However, thinning the wafer to a thickness of 50 micron or less may result in fabrication tools being unable to subsequently handle the wafer for further processing. That is, the fabrication tools may be unable to handle wafers that have thicknesses much less than 90 micron. This means that readily available wafers, like silicon wafers, might not be able to be used for fabricating fluid-ejection dies having fluid-feed hole arrays with heights of 50 micron or less.

[0012] One approach, therefore, is to use silicon on insulator (SOI) wafers that have buried oxide layers. The SOI wafer may be thinned to a lesser thickness of 90 micron or more. A resist layer can then be applied to the backside of the wafer and selectively patterned in correspondence with a fluid- feed slot to be formed. The wafer is selectively etched to a target thickness of 50 micron or less, with the buried oxide layer serving as an etch stop. After removal of the resist layer, the array of fluid-feed holes can be formed. The result is that while the overall wafer thickness is still 90 micron or more, and therefore able to be handled by fabrication tools, the thickness of the wafer at the locations of the fluid-feed holes is 50 micron or less.

[0013] However, SOI wafers are more expensive than ordinary silicon wafers that do not have buried oxide layers. Furthermore, there may be manufacturing lead times associated with SOI wafers. As such, if SOI wafer specification changes between time of ordering and time of fabrication, fabrication of the fluid-ejection dies is delayed. In addition, if any problems occur during fluid-ejection die fabrication, replacement SOI wafers cannot be easily acquired if they are not already on hand. The result is that fluid-ejection dies having arrays of fluid-feed holes at minimal heights to provide optimal fluid ejection may be limited to just more expensive fluid-ejection devices.

[0014] Techniques described herein alleviate these shortcomings, providing ways to fabricate fluid-ejection dies having arrays of fluid-feed holes with heights of 50 micron or less without having to use SOI wafers. An array of fluid-feed holes may be formed within a wafer like a silicon wafer, and the wafer thinned to a thickness of 90 micron or more, sufficient for fabrication tools to subsequently handle during further processing. A panel may be molded at the backside of the wafer to form a fluid-feed slot or slots, or a preformed panel having a fluid-feed slot or slots may be affixed to the backside of the wafer. The wafer can be dry etched at its backside where the wafer is exposed through the fluid-feed slot or slots of the panel.

[0015] While overall wafer thickness is still 90 micron or more, dry etching of the wafer reduces the thickness of the wafer where exposed through the fluid- feed slot or slots of the panel to 50 micron or less. A fluid-ejection die can thus be fabricated to have an array of fluid-feed holes with a height of 50 micron or less, without having to using an SOI wafer. Furthermore, the panel itself acts or serves as the etching mask, such that a separate resist layer does not have to be applied and subsequently removed, which simplifies fabrication of the fluid- ejection die. The panel becomes a permanent part of the fluid-ejection die, defining the fluid-feed slot or slots from which fluid is supplied to the firing chambers of the die through the fluid-feed holes. [0016] FIG. 1 shows an example method 100 for fabricating a fluid-ejection cartridge including a fluid-ejection die. The method 100 includes forming fluid- feed holes, such as an array of fluid-feed holes, completely through a substrate layer of the fluid-ejection die (102). The substrate layer may be a wafer like a silicon wafer, but not an SOI wafer. The wafer may have a thickness of 400 micron or more, such as 700 micron. The fluid-feed holes may have a width of above forty micron, as one example. There may be 7,200 fluid-feed holes per fluid-ejection die, depending on the design of the die. The fluid-feed holes may be formed by machining the holes from the frontside of the substrate layer. [0017] The method 100 includes filling the fluid-feed holes with a fill material (104) to plug the holes. The fill material is removed during subsequent processing, and therefore is temporary. The fill material may be wax. The fluid- feed holes are temporarily filled with fill material so that during subsequent backside grinding of the substrate layer, no debris enters the holes. [0018] FIG. 2A shows example performance of parts 102 and 104 of the method 100. A substrate layer 202 is provided at a thickness 204, which may be a wafer thickness of 400 micron or more. Fluid-feed holes 206 are formed through the substrate layer 202, such as by machining the holes 206 from the frontside 210 of the layer 202. Two fluid-feed holes 206 are depicted in FIG. 2A. The fluid-feed holes 206 are then filled with fill material 208.

[0019] Referring back to FIG. 1, the method 100 includes then grinding the substrate layer (106). The substrate layer is ground to thin the substrate layer to a thickness, such as 90 micron or more (e.g., 100 micron), sufficient for fabrication tools to handle the layer (e.g., the wafer). The substrate layer may be ground from its backside. After grinding, the fluid-feed holes are exposed at the backside of the substrate layer, since the holes were formed completely through the layer. In another implementation, however, the fluid-feed holes may not have been formed completely through the substrate layer in part 102, but become exposed at the backside of the layer during grinding.

[0020] The method 100 includes forming a device layer on the substrate layer (108). Thin film layers, a chamber layer, and a nozzle layer may constitute the device layer. The thin film layers may be formed from conductive, semiconductive, and insulative materials. The orifice plate layer may be formed from SU-8 epoxy negative photoresist, and the chamber layer may be formed from polymer. The device layer includes chambers (of the chamber layer) fluidically connected to the fluid-feed holes, fluid-ejection elements (of the thin film layers) like thermal firing resistors disposed within the chambers, and fluid- ejection nozzles (of the nozzle layer) through which the fluid-ejection elements eject fluid from the chambers.

[0021] FIG. 2B shows example performance of parts 106 and 108 of the method 100. The substrate layer 202 is ground at the backside 212 of the layer 202 to thin the substrate layer 202 to a thickness 213 that is still sufficient for fabrication tools to handle, such as 90 micron or more. A device layer 214 is formed on the frontside 210 of the layer 202. The device layer 214 includes chambers 216 fluidically connected to the fluid-feed holes 206, which are temporarily filled with fill material 208. The device layer 214 includes fluid- ejection elements 218 disposed within the chambers 216, and fluid-ejection nozzles 220 through which the elements 218 eject fluid from the chambers 216. [0022] Referring back to FIG. 1, the method 100 includes providing a panel at the backside of the substrate layer (110). The panel is provided such that it has a fluid-feed slot under the fluid-feed holes, in fluidic communication with the fluid-feeds hole in the implementation of FIG. 1. There may be one fluid- feed slot, or more than one fluid-feed slot. In the latter case, each slot may be under a different set of fluid-feed holes.

[0023] The panel may be formed from a molding material. The molding compound may be an inherently electrically insulating molding material. The molding material may be a molding compound, such as epoxy molding compound (EMC). As another example, the molding material may be a thermoplastic molding compound, such as polyphenylensulfide (PPS). The panel is thus formed from a material that is different than the material of the substrate layer.

[0024] The panel may be provided by molding the panel (e.g., EMC) directly on or at the backside of the substrate layer so that a fluid-feed slot is defined under the fluid-feed hole. The panel may instead be preformed to define a fluid-feed slot, and provided by aligning the panel so that its fluid-feed slot is under the fluid-feed hole, and affixing the preformed panel to the backside of the substrate layer, such as with adhesive. For example, the panel (e.g., PPS) may be preformed via injection molding, or the panel (e.g., EMC) may be preformed using a molded interconnect substrate (MIS) technique. [0025] FIG. 2C shows example performance of part 110 of the method 100. The substrate layer 202, with thickness 213, has the device layer 214, including chambers 216, fluid-ejection elements 218, and fluid-ejection nozzles 220, formed on the frontside 210 of the layer 202, as before. A panel 222 is provided on the backside 212 of the substrate layer 202. The panel 222 includes a fluid- feed slot 224 under both fluid-feed holes 206 of the substrate layer 202. In the example of FIG. 2C, the fluid-feed slot 224 is in fluidic communication with the fluid-feed holes 206, which are temporarily filled with fill material 208. One fluid- feed slot 224 is specifically depicted in FIG. 2C. [0026] Referring back to FIG. 1, the method 100 includes etching the substrate layer through the fluid-feed slot of the panel (112), at the backside of the layer. The substrate layer is etched to further thin the layer to a target thickness, such as 50 micron or less, corresponding to the target height of the fluid-feed holes within the layer. The panel serves as an etch mask, limiting etching of the substrate layer just where the layer is exposed through the panel. The substrate layer is thus thinned to the target thickness where the fluid-feed holes are located. Because the panel serves as an etch mask, no other masking layer, such as resist, has to be applied (and thus no such masking layer has to be subsequently removed). The substrate layer is therefore thinned to the target thickness where exposed at the fluid-feed slot, and remains at the thickness to which it was previously ground where the layer is not exposed at the fluid-feed slot. [0027] The etching may be deep reactive ion etching (DRIE), or another type of dry etching. The etching is a timed etching that does not rely on an etch stop to control the amount of the substrate layer that is removed. Rather, the substrate layer is exposed to the etchant through the panel for a length of time corresponding to the amount of the substrate layer to be removed to thin the substrate layer from the thickness to which it was previously ground to the target thickness. The substrate layer may have been initially ground to ensure that the amount of the substrate layer removed during timed etching is not too large a multiple of the target thickness, which may otherwise result in imprecise control of the target thickness.

[0028] FIG. 2D shows example performance of part 112 of the method 100. The substrate layer 202, with thickness 213, has the device layer 214, including chambers 216, fluid-ejection elements 218, and fluid-ejection nozzles 220, formed on the frontside 210 of the layer 202, as before. The panel 222 is provided on the backside 212 of the substrate layer 202, with the panel 222 having the fluid-feed slot 224 under the fluid-feed holes 206, which are temporarily filled with fill material 208, also as before.

[0029] The substrate layer 202 has been etched at its backside 212 where the layer 202 is exposed through the panel 222 (viz., where the fluid-feed holes 206 are located within the layer 202). Where exposed through the panel 222 and thus etched, the substrate layer 202 has been thinned to the target thickness 217, such as 50 micron or less. By comparison, where masked by the panel 222 and thus not etched, the substrate layer 202 remains at the thickness 213. The fluid-feed slot 224 therefore has been extended into the substrate layer 202. The fluid-feed holes 206 have a height equal to that of the target thickness 217. Stated another way, the substrate layer 202 has the target thickness 217 at the fluid-feed holes 206. [0030] Referring back to FIG. 1, the method 100 includes removing the fill material from the fluid-feed holes (114), to unplug the holes. After removal of the fill material from the fluid-feed holes, the resulting substrate layer, device layer, and panel can be considered as constituting a fluid-ejection die. The fill material, such as wax, may be removed from the fluid-feed holes via an extended soak time in a solvent remover.

[0031] FIG. 2E shows example performance of part 114 of the method 100. The substrate layer 202 has the device layer 214, including chambers 216, fluid- ejection elements 218, and fluid-ejection nozzles 220, formed on the frontside 210 of the layer 202, as before. The panel 222 is provided on the backside 212 of the substrate layer 202, with the panel 222 having the fluid-feed slot 224 under the fluid-feed holes 206 and that extends into the layer 202, also as before. The substrate layer 202 has a thickness 213, except at the holes 206, where the layer 202 instead has the target thickness 217.

[0032] The fluid-feed holes 206 have been cleared of any fill material by removal of the fill material from the holes 206. Fluid can thus be provided from the fluid-feed slot 224 to the chambers 216 through the fluid-feed holes 206.

FIG. 2E can be considered as showing a fabricated fluid-ejection die 226 including or formed by the substrate layer 202, the device layer 214, and the panel 222.

[0033] Referring back to FIG. 1, the method 100 can include attaching the fluid-ejection die to a fluid-ejection cartridge body (116), to form a fluid-ejection cartridge including the die and the body. The cartridge body can include a cavity fluidically connected to the fluid-feed slot of the die. If there is more than one fluid-feed slot, the cavity may be fluidically connected to every slot. The cavity may be a reservoir that stores a supply of fluid for the fluid-feed slot to provide to the chambers via the fluid-feed holes for ejection through the fluid-ejection nozzles by the fluid-ejection elements.

[0034] FIG. 2F shows example performance of part 116 of the method 100. The fluid-ejection die 226 includes the substrate layer 202, the device layer 214 at the frontside 210 of the layer 202, and the panel 222 at the backside 212 of the layer 202. The device layer 214 includes chambers 216, fluid-ejection elements 218, and fluid-ejection nozzles 220. The panel 222 includes the fluid- feed slot 224 under the fluid-feed holes 206 and that extends into the layer 202. The substrate layer 202 has a thickness 213, except at the holes 206, where the layer 202 instead has the target thickness 217.

[0035] The fluid-ejection ejection die 226 has been attached to a fluid- ejection cartridge body 228 at the panel 222 of the die 226. The cartridge body 228 includes a cavity 230 under and fluidically connected to the fluid-feed slot 224. FIG. 2F can be considered as showing a fabricated fluid-ejection cartridge 232 including the fluid-ejection die 226 and the fluid-ejection cartridge body 228. [0036] FIG. 3 shows another example method 300 for fabricating a fluid- ejection cartridge including a fluid-ejection die. The method 300 includes forming fluid-feed holes, such as an array of fluid-feed holes, partially through a substrate layer of the fluid ejection die (302), as opposed to completely through the substrate layer as in part 102 of FIG. 1. The fluid-feed holes are formed at the frontside of the substrate layer, at a depth greater than the target height of the fluid-feed holes. As in FIG. 1 , the substrate layer may be a wafer like a silicon wafer, but not an SOI wafer, and have a thickness of 400 micron or more, such as 700 micron. The fluid-feed holes similarly may have a width of about forty micron, and there may be 7,200 holes, which can be formed via machining.

[0037] FIG. 4A shows example performance of part 302 of the method 300. A substrate layer 202 is provided at a thickness 204, which may be a wafer thickness of 400 micron or more. Fluid-feed holes 206 are partially formed through the substrate layer 202, at the frontside 210 of the layer 202. [0038] Referring back to FIG. 3, the method 300 includes grinding the substrate layer at its backside, without exposing the fluid-feed holes from the backside of the substrate layer (306). The substrate layer 306 is ground to thin the substrate layer to a thickness, such as 90 micron or more (e.g., 100 micron), sufficient for fabrication tools to handle the layer (e.g., the wafer), as in part 106 of FIG. 1.

[0039] The fluid-feed holes do have to be filled with fluid material prior to grinding in the method 300, unlike in the method 100 of FIG 1. The fluid-feed holes are temporarily filled in the method 100 to prevent them from becoming contaminated with debris during grinding. However, since the grinding does not expose the fluid-feed holes in the method 300, there is no potential for grinding debris to enter the holes. The method 300 thus simplifies fabrication by avoiding having to temporarily plug and then later unplug the fluid-feed holes. [0040] The method 300 includes forming a device layer on the substrate layer (308), as in part 108 of FIG. 1. The device layer includes chambers fluidically connected to the fluid-feed holes, fluid-ejection elements like thermal firing resistors disposed within the chambers, and fluid-ejection nozzles through which the fluid-ejection elements eject fluid from the chambers. [0041] FIG. 4B shows example performance of parts 306 and 308 of the method 300. The substrate layer 202 is ground at the backside 212 of the layer 202 to thin the layer 202 to a thickness 213 that is still sufficient for fabrication tools to handle, such as 90 micron or more. A device layer 214 is formed on the frontside 210 of the substrate layer 202. The device layer 214 includes chambers 216 fluidically connected to the fluid-feed holes 206. The device layer 214 includes fluid-ejection elements 218 disposed within the chambers 216, and fluid-ejection nozzles 220 through which the elements 218 eject fluid from the chambers 216.

[0042] Referring back to FIG. 3, the method 300 includes providing a panel at the backside of the substrate layer (310), as in part 110 of FIG. 1. The panel thus has a fluid-feed slot under the fluid-feed holes as has been described. However, because the fluid-feed holes are not exposed at the backside of the substrate layer, the fluid-feed slot is not yet in fluidic communication with the fluid-feed holes. Further, there can be more than one fluid-feed slot, as in FIG. 1. [0043] FIG. 4C shows example performance of part 310 of the method 300. The substrate layer 202, with thickness 213, has the device layer 214, including chambers 216, fluid-ejection elements 218, and fluid-ejection nozzles 220 at the frontside 210 of the layer 202, as before. A panel 222 is provided at the backside 212 of the substrate layer 202. The panel 222 includes a fluid-feed slot 224 under both fluid-feed holes 206 of the substrate layer 202. In the example of FIG. 4C, the fluid-feed slot 224 is not in fluidic communication with the fluid-feed holes 206. One fluid-feed slot 224 is specifically depicted in FIG. 4C.

[0044] Referring back to FIG. 3, the method 300 includes etching the substrate layer through the fluid-feed slot of the panel (312), at the backside of the layer. The substrate layer is etched to further thin the layer to a target thickness, such as 50 micron or less, corresponding to the target height of the fluid-feed holes within the layer. Because the fluid-feed holes were formed in the substrate layer at a depth greater than this target height, the etching exposes the holes at the backside of the layer. But for resulting in the exposure of the fluid- feed holes at the backside layer, etching can be performed in part 312 as in part 112 of FIG. 1. Furthermore, in part 312, the fluid-feed holes are not plugged when backside etching is performed.

[0045] After etching of the substrate layer, the resulting substrate layer, device layer, and panel can be considered as constituting a fluid-ejection die. The result of example performance of part 312 is depicted in the FIG. 2E that has been described in relation to the method of FIG. 1.

[0046] The method 300 can include attaching the fluid-ejection die to a fluid-ejection cartridge body (316), to form a fluid-ejection ejection cartridge including the die and the body, as in part 116 of FIG. 1. The result of example performance of part 316 is depicted in FIG. 2F that has been described in relation to the method of FIG. 1.

[0047] FIG. 5 shows a block diagram of an example fluid-ejection die 226. The fluid-ejection die 226 includes a substrate layer 202 having a fluid-feed hole 206. The fluid-ejection die 226 includes a device layer 214 at a frontside of the substrate layer 202. The device layer 214 has a fluid-ejection nozzle 220 and a chamber 216 in which a fluid-ejection element 218 is disposed and that is fluidically connected to the fluid-feed hole 206. The fluid-ejection die 226 includes a panel 222 at a backside of the substrate layer 202. The panel 222 has a fluid-feed slot 224 fluidically connected to the fluid-feed hole 206.

[0048] FIG. 6 shows a block diagram of an example fluid-ejection cartridge 232. The fluid-ejection cartridge 232 includes a fluid-ejection cartridge body 228 and a fluid-ejection die 226 attached to the fluid-ejection cartridge body 228. The fluid-ejection die 226 includes a substrate layer 202 having an array of fluid-feed holes 206. The fluid-ejection die 226 includes a device layer 214 at a frontside of the substrate layer 202. The device layer 226 has fluid-ejection nozzles 220 and chambers 216 in which fluid-ejection elements 218 are disposed and that are fluidically connected to the fluid-feed holes 206. The fluid-ejection die 226 includes a panel 222 at a backside of the substrate layer 202. The panel 222 has a fluid-feed slot 224 fluidically connected to the fluid-feed holes 206.

[0049] FIG. 7 shows an example method 700. The method 700 includes providing a fluid-ejection die having a substrate layer and a device layer at a frontside of the substrate layer (702). The device layer has a fluid-ejection nozzle and a chamber in which a fluid-ejection element is disposed, and the substrate layer has a fluid-feed hole fluidically connected to the chamber. Part 702 may be implemented by performing parts 102, 104, 106, and 108 of FIG. 1 or parts 302 and 306 of, and 308 of FIG. 3, for instance. [0050] The method 700 includes providing a panel at a backside of the substrate layer (704). The panel has a fluid-feed slot under the fluid-feed hole, and along with the substrate layer and the device layer, constitutes or forms the fluid-ejection die. Part 704 may be implemented by performing part 110 of FIG. 1 or part 310 of FIG. 3. The method 700 includes backside etching the substrate layer through the fluid-feed slot of the panel to thin the substrate layer at the fluid- feed hole (706). Part 706 may be implemented by performing part 112 of FIG. 1 or part 312 of FIG. 3.

[0051] Techniques have been described herein for fabricating a fluid- ejection die having a fluid-feed hole height at a minimal thickness without having to use SOI wafers. The techniques instead employ a panel that can be molded onto the backside of a substrate layer like a ground silicon wafer, or preformed and affixed to the backside of the layer. The panel defines a fluid-feed slot in fluidic communication with the fluid-feed hole, and serves as an etch mask when the substrate layer is etched to thin the layer to a target thickness at the fluid- feed hole of the layer. The described techniques permit fabrication of fluid- ejections dies having minimal height fluid-feed holes in a less costly and more efficient manner.

Claims

We claim:

1. A method comprising: providing a fluid-ejection die having a substrate layer and a device layer at a frontside of the substrate layer, the device layer having a fluid-ejection nozzle and a chamber in which a fluid-ejection element is disposed, the substrate layer having a fluid-feed hole fluidically connected to the chamber; providing a panel at a backside of the substrate layer, the panel having a fluid-feed slot under the fluid-feed hole, the panel forming the fluid-ejection die along with the substrate layer and the device layer; and backside etching the substrate layer through the fluid-feed slot of the panel to thin the substrate layer at the fluid-feed hole.

2. The method of claim 1 , wherein the panel having the fluid-feed slot serves as a mask during backside etching such that no separate mask is provided on the panel when backside etching is performed.

3. The method of claim 1 , wherein providing the panel at the backside of the substrate layer comprises molding the panel at the backside of the substrate layer.

4. The method of claim 1 , wherein providing the panel at the backside of the substrate layer comprises affixing a preformed panel at the backside of the substrate layer.

5. The method of claim 1 , wherein providing the fluid-ejection die having the substrate layer and the device layer comprises: frontside forming the fluid-feed hole through the substrate layer; backside grinding the substrate layer to thin the substrate layer from a wafer thickness to a first thickness; and forming the device layer on the substrate layer, wherein backside etching the substrate layer thins the substrate layer where the substrate layer is exposed at the fluid-feed slot from the first thickness to a second thickness, the substrate layer remaining at the first thickness where the substrate layer is not exposed at the fluid-feed slot.

6. The method of claim 5, wherein the wafer thickness is 400 micron or more, the first thickness is 90 micron or more, and the second thickness is 50 micron or less.

7. The method of claim 5, wherein providing the fluid-ejection die having the substrate layer and the device layer further comprises filling the fluid-feed hole with a fill material to plug the fluid-feed hole before backside grinding the substrate layer, wherein the fluid-feed hole is exposed at the backside of the substrate layer when backside grinding is finished, and wherein the method further comprises removing the fill material from the from the fluid-feed hole to unplug the fluid-feed hole.

8. The method of claim 5, wherein the fluid-feed hole is not exposed at the backside of the substrate layer when backside grinding is finished, wherein the substrate layer is backside ground without exposing the fluid- feed hole, to thin the substrate layer, wherein the fluid-feed hole is not plugged when backside etching is performed and is exposed at the backside of the substrate layer during backside etching.

9. The method of claim 1 , further comprising attaching the fluid-ejection die to a fluid-ejection cartridge body to form a fluid-ejection cartridge including the fluid-ejection die and the fluid-ejection cartridge body.

10. A fluid-ejection die comprising: a substrate layer having a fluid-feed hole; a device layer at a frontside of the substrate layer, the device layer having a fluid-ejection nozzle and a chamber in which a fluid-ejection element is disposed and that is fluidically connected to the fluid-feed hole; and a panel at a backside of the substrate layer, the panel having a fluid-feed slot fluidically connected to the fluid-feed hole.

11. The fluid-ejection die of claim 10, wherein the substrate layer and the panel are formed from different materials.

12. The fluid-ejection die of claim 10, wherein the substrate layer has a first thickness where the substrate layer is not exposed at the fluid-feed slot and has a lesser, second thickness where the substrate layer is exposed at the fluid-feed slot.

13. The fluid-ejection die of claim 12, wherein the first thickness is 90 micron or more, and the second thickness is 50 micron or less.

14. A fluid-ejection cartridge comprising: a fluid-ejection cartridge body; a fluid-ejection die attached to the fluid-ejection cartridge body and comprising: a substrate layer having an array of fluid-feed holes; a device layer at a frontside of the substrate layer, the device layer having a plurality of fluid-ejection nozzles and a plurality of chambers in which a plurality of fluid-ejection elements are disposed and that are fluidically connected to the fluid-feed holes; and a panel at a backside of the substrate layer, the panel having a fluid-feed slot fluidically connected to the fluid-feed holes.

15. The fluid-ejection cartridge of claim 14, wherein the substrate layer has a first thickness where the substrate layer is not exposed at the fluid-feed slot and has a lesser, second thickness where the substrate layer is exposed at the fluid- feed slot.