Fluid ejection device

According to an example, a fluid ejection device may include a substrate, a resistor positioned on the substrate, an overcoat layer positioned over the resistor, a fluidics layer having surfaces that form a firing chamber about the resistor, in which the overcoat layer is positioned between the resistor and the firing chamber, and a thin film membrane covering the surfaces of the fluidics layer that form the firing chamber and a portion of the overcoat layer that is in the firing chamber.

BACKGROUND

Thermal inkjet printheads eject fluid ink drops from nozzles by passing electrical current through resistor elements contained in a firing chamber. Heat from a resistor element creates a rapidly expanding vapor bubble that forces a small ink drop out of a nozzle of the firing chamber. When the resistor element cools, the vapor bubble quickly collapses and draws more fluid ink into the firing chamber in preparation for ejecting another drop through the nozzle. Fluid ink is drawn from a reservoir via a fluid slot that extends through the substrate on which the resistor element and the firing chamber are formed.

DETAILED DESCRIPTION

Additionally, It should be understood that the elements depicted in the accompanying figures may include additional components and that some of the components described in those figures may be removed and/or modified without departing from scopes of the elements disclosed herein. It should also be understood that the elements depicted in the figures may not be drawn to scale and thus, the elements may have different sizes and/or configurations other than as shown in the figures.

Disclosed herein are fluid ejection devices and methods of fabricating the fluid ejection devices. The fluid ejection devices may include a fluidics layer that includes surfaces that form a firing chamber about, e.g., around, a resistor. According to an example of the present disclosure, a thin film membrane may be formed to cover the surfaces of the fluidics layer that form the firing chamber. The thin film membrane may thus form a barrier between the fluidics layer and the firing chamber. In this regard, the thin film membrane may protect the fluidics layer from delamination and decomposition that may be caused by the fluid contained in the firing chamber, particularly when the fluid contains aggressive ink chemistries.

According to an example, by protecting the fluidics layer in the fluid ejection devices, the fluid ejection devices may be made with relatively larger firing chambers, may have greater durability, and may be able to print with improved optical density as compared with conventional fluid ejection devices. The thin film membrane may also form a wettable coating over the walls of the firing chamber, which may facilitate filling of the firing chamber with fluid. As disclosed herein, the thin film membrane may be applied at any of a number of stages during the manufacture of a fluid ejection device following formation of the fluidic layer. In addition, the thin film membrane may be formed through a deposition technique that may be performed at relatively low temperatures, such as atomic layer deposition.

With reference first toFIG. 1, there is shown a simplified block diagram of a fluid ejection system100having a thin film membrane covering the walls (or surfaces) of a firing chamber, according to an example of the present disclosure. The fluid ejection system100may be an inkjet printing system100that includes a print engine102having an electronic controller104, a mounting assembly106, a replaceable fluid supply device108or fluid supply devices (e.g., as shown inFIG. 2), a media transport assembly110, and a power supply112that provides power to the various electrical components of inkjet printing system100. The inkjet printing system100further includes fluid ejection devices114implemented as printheads114that eject drops of ink or other fluid through a plurality of nozzles116(also referred to as orifices or bores herein) toward print media118so as to print onto the print media118.

In some examples, a printhead114may be an integral part of a supply device108, while in other examples, a printhead114may be mounted on a print bar (not shown) of the mounting assembly106and coupled to a supply device108(e.g., via a tube). The print media118may be any type of suitable sheet or roll material, such as paper, card stock, transparencies, Mylar, polyester, plywood, foam board, fabric, canvas, and the like.

The printhead114inFIG. 1is depicted as a thermal-inkjet (TIJ) printhead114. In TIJ printheads114, electric current is passed through a resistor element to generate heat in an ink-filled chamber. The heat vaporizes a small quantity of ink or other fluid, creating a rapidly expanding vapor bubble that forces a fluid drop out of a nozzle116. As the resistor element cools the vapor bubble collapses, drawing more fluid from a reservoir into the chamber in preparation for ejecting another drop through the nozzle116. The nozzles116are typically arranged in one or more columns or arrays along printhead114such that properly sequenced ejection of ink from the nozzles116causes characters, symbols, and/or other graphics or images to be printed on the print media118as the printhead114and the print media118are moved relative to each other.

The mounting assembly106positions the printhead114relative to the media transport assembly110, and the media transport assembly110positions the print media118relative to the printhead114. Thus, a print zone120may be defined adjacent to the nozzles116in an area between the printhead114and the print media118. In one example, the print engine102is a scanning type print engine. In this example, the mounting assembly106includes a carriage for moving the printhead114relative to the media transport assembly110to scan the print media118. In another example, the print engine102is a non-scanning type print engine. In this example, the mounting assembly106fixes the printhead114at a prescribed position relative to the media transport assembly110while the media transport assembly110positions the print media118relative to the printhead114.

The electronic controller104may include components such as a processor, memory, firmware, and other printer electronics for communicating with and controlling the supply device108, the printhead114, the mounting assembly106, and the media transport assembly110. The electronic controller104may receive data122from a host system, such as a computer, and may temporarily store the data122in a memory. The data122may represent, for example, a document and/or file to be printed. Thus, the data122may form a print job for the inkjet printing system100that includes print job commands and/or command parameters. Using the data122, the electronic controller104may control the printhead114to eject ink drops from the nozzles116in a defined pattern that forms characters, symbols, and/or other graphics or images on the print medium118.

Turning now toFIG. 2, there is shown a fluid supply device108implemented as an ink cartridge108, according to an example of the present disclosure. The ink cartridge supply device108generally includes a cartridge body200, a printhead114, and electrical contacts202. Individual fluid drop generators within the printhead114may be energized by electrical signals provided at the contacts202to eject fluid drops from selected nozzles116. The fluid may be any suitable fluid used in a printing process, such as various printable fluids, inks, pre-treatment compositions, fixers, and the like. In some examples, the fluid may be a fluid other than a printing fluid. The supply device108may contain its own fluid supply within cartridge body200, or the supply device108may receive fluid from an external supply (not shown) such as a fluid reservoir connected to the device108through a tube, for example.

With reference now toFIG. 3, there is shown a partial cross-sectional view of a fluid ejection device (or printhead)114that employs a thin film membrane322over the components of the fluid ejection device114to protect, for instance, a fluidics layer from damage caused by ink in a firing chamber, according to an example of the present disclosure. The fluid ejection device114is depicted as including a substrate300, which may be made of silicon (Si), or another appropriate material such as glass, a semiconductive material, various composites, and so on. A stack of thin film materials on the substrate300and the formation of a fluid slot through the substrate300and the thin film stack may provide functionality to the fluid ejection device114.

The thin film stack may include a sealant or capping layer (not shown) over the substrate300such as a thermally grown field oxide and an insulating glass layer deposited, for example, by plasma enhanced chemical vapor deposition (PECVD) techniques. The capping layer forms an oxide underlayer for the thermal resistor layer302. Although not shown, a Field Effect transistor (FET) may be created in the substrate300and may be connected to the resistor306via conductive traces304, in which the FET is to turn the resistor306on and off according to data from the electronic controller104. Thermal/firing resistors may be formed by depositing (e.g., by sputter deposition) the thermal resistor layer302over the substrate300. The thermal resistor layer302may be on the order of about 0.1 to 0.75 microns thick, and may be formed of various suitable resistive materials including, for example, tantalum aluminum, tungsten silicon nitride, nickel chromium, carbide, platinum, titanium nitride, etc. Resistor layers having other thicknesses are also within the scope of this disclosure.

A conductive layer formed of the conductor traces304may be deposited (e.g., by sputter deposition techniques) on the thermal resistive layer302and may be patterned (e.g., by photolithography) and etched to form the conductor traces304and an individually formed resistor306from the underlying resistive layer302. The conductive traces304may be made of various materials including, for example, aluminum, aluminum/copper alloy, copper, gold, and so on. An overcoat layer308(or overcoat layers) may be formed over the resistor306to provide additional structural stability and electrical insulation from fluid in the firing chamber314. The overcoat layer(s)308may generally be considered to be part and parcel of the resistor306, and, as such, may provide a final layer to the resistor306. The overcoat layer(s)308may include an insulating passivation layer formed over the resistor306and the conductor traces304to prevent electrical charging of the fluid or corrosion of the device in the event that an electrically conductive fluid is used.

The passivation layer may have a thickness on the order of about 0.1 to 0.75 microns, but may have other thicknesses, and may be formed (e.g., by sputtering, evaporation, PECVD, etc.) of suitable materials such as silicon dioxide, aluminum oxide, silicon carbide, silicon nitride, glass, etc. The overcoat layer(s)308may also include a cavitation barrier layer over the passivation layer that helps dissipate the force of the collapsing drive bubble left in the wake of each ejected fluid drop. The cavitation layer may have a thickness on the order of about 0.1 to 0.75 microns but may also have a greater or lesser thickness, and may be formed of tantalum deposited by a sputter deposition technique.

The cavitation layer may generally be considered to be the final layer of the resistor306and may therefore make up the surface of the resistor306. Fluid may flow from a fluid source through a fluid slot310in the substrate300and the fluid may flow into the firing chamber314through another slot (not shown). The fluid slot310may be formed in the substrate300by processes that include, for example, a laser ablation step followed by a non-isotropic wet etch step using chemicals such as potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH). The laser ablation step may micromachine a deep trench in the substrate300, starting at the bottom of the substrate and proceeding up through the substrate to remove a bulk portion of the substrate. The wet etch step may generally complete formation of the laser deep trench by both removing the substrate300from the frontside where the thin film layers302,304and308have been previously removed and removing the substrate300proceeding from the backside of the deep laser trench. In addition, or alternatively, the fluid slot310may be formed through a laser ablation step, followed by a dry etch step, and by a wet etch step.

As also shown inFIG. 3, the fluid ejection device114may include a fluidics layer312, which may be a pattered SU8 layer or other polymeric compound such as IJ5000 formed onto the top of the substrate300as a dry film laminated by heat and pressure, for example, or as a wet film applied by spin coating. SU8 and IJ5000 are photoimageable negative acting compounds, and the firing chamber314(and other channels/passageways) may be formed in the fluidics layer312by photo imaging techniques. An orifice plate316including nozzles (orifices)116may be provided over respective firing chambers314such that each firing chamber316, associated nozzle116, and associated thermal resistor306are aligned. In some examples, the fluidics layer312and the orifice plate316are integrated as a single structure formed of SU8 or another appropriate material. In other examples, the orifice plate316is a separate element and is attached or adhered to the fluidics layer, as shown inFIG. 3.

The fluid ejection device114is further depicted as including a bond pad318, which may be formed of an electrically conductive material, such as gold, in electrical communication with the conductor traces304. The bond pad318is also depicted as being in electrical communication with an electrical interconnect320. The electrical interconnect320, which may be a flexible electrical interconnect320, may electrically connect the resistor306to the electrical contacts202(FIG. 2). In this regard, the resistor306may receive firing signals via the electrical interconnect320.

Also shown inFIG. 3is a thin film membrane322that covers most of the exposed surfaces of the fluid ejection device114shown in that figure. According to an example, the thin film membrane322may be a film that is to act as a barrier between the fluid (e.g., ink) contained in the firing chamber314and the fluidics layer312. In one regard, the thin film membrane may protect the fluidics layer312from decomposing upon exposure to certain types of fluids, e.g., fluids with aggressive chemistries, and may also protect the fluidics layer312from delaminating from the substrate300. The thin film membrane322may also provide additional protection to the resistor306. Moreover, the thin film membrane322may provide moisture protection on the electrical interconnect320, which may improve reliability of the electrical interconnect320.

The thin film membrane322may be formed of a dielectric material, such as a metal oxide. Examples of suitable materials may include hafnium oxide, titanium oxide, aluminum oxide, hafnium silicon nitride, silicon oxide, silicon nitride, or the like. In addition, the thin film membrane322may be formed through atomic layer deposition (ALD) of the thin film materials at a relatively low temperature, e.g., less than about 150° Celsius. By depositing the thin film materials at the relatively low temperature, damage caused by high heat to the fluidics layer312and other components of the fluid ejection device114may be avoided. ALD of the thin film materials may also be performed to make the thin film membrane322have a relatively small thickness, e.g., about 100 angstroms, and the thin film membrane322may be formed to be pinhole and crack free and to conformally coat the wall(s) of the fluidics layer312forming the firing chamber314.

Although the thin film membrane322has been depicted inFIG. 3as being formed onto the fluidics layer312, the orifice plate316, and the electrical interconnect320, in other examples, the thin film membrane322may be formed prior to the formation or placement of one or more of these components. For instance, the thin film membrane322may be formed prior to attachment of the electrical interconnect320onto the bond pad318and/or prior to the attachment of the orifice plate316onto the fluidics layer312. In an example in which the thin film membrane322is formed prior to attachment of the electrical interconnect320to the bond pad318, a portion of the thin film membrane322may be formed on top of the bond pad318. In one example, the electrical interconnect320may be positioned directly on top of that portion of the thin film membrane322as the thin film membrane322may be sufficiently thin to enable sufficient levels of electrical signals to pass therethrough. In another example, the portion of the thin film membrane322that is positioned directly on top of bond pad318may be removed prior to attachment of the electrical interconnect320to the bond pad318. In this example, the portion of the thin film membrane322on top of the bond pad318may be removed via etching or other suitable manner of removal. Various other examples regarding the formation of the thin film membrane322are described in detail herein below.

With reference now toFIG. 4, there is shown a flow diagram of a method400of fabricating a fluid ejection device, such as the fluid ejection device114depicted inFIGS. 1-3, according to an example of the present disclosure. Although the method400includes blocks listed in a particular order, it is to be understood that this does not necessarily limit the blocks to being performed in this or any other particular order. In general, in addition to the fabrication techniques specifically called out in the method400, the various operations in the method400may be performed using various precision microfabrication techniques such as electroforming, laser ablation, anisotropic etching, sputtering, dry etch, wet etch, photolithography, etc.

Various operations in the method500are also described with respect toFIGS. 5A-5F, which show various stages of fabrication of the fluid ejection device114.

As shown inFIG. 4, at block402, a resistor306may be formed on a substrate300. According to an example, the substrate300, which may be formed of silicon or other material such as, glass, a semiconductive material, a composite material, etc., may be obtained as shown inFIG. 5A. The substrate300may be formed with a fluid slot prior to or after formation of the resistor306on the substrate300. In addition, the resistor306may be formed on the substrate300, for instance, by sputter deposition, and may be formed of various materials and thicknesses as noted above. The formation of the resistor306may also include the formation of the thermal resistor layer302and the conductor traces304, as also discussed above and as shown inFIG. 5B.

At block404, an overcoat layer308or overcoat layers308may be formed on the resistor306. For instance, the overcoat layer(s)308may be deposited onto the conductor trace304and the resistor306through any suitable deposition process. An example of the deposited overcoat layer(s)308is shown inFIG. 5C. As shown therein, a portion of the conductor trace304may be removed prior to deposition of the overcoat layer(s)308. In addition, the deposition of the overcoat layer(s)308may form a final layer of the resistor306and may be referred to as a cavitation barrier layer. The overcoat layer(s)308made of tantalum, for example.

At block406, a fluidics layer312may be formed over the substrate300. As discussed above, the fluidics layer312may be a film, such as SU8 or IJ5000, that is applied over the substrate300and patterned using photo imaging techniques. In one regard, the fluidics layer312may be patterned to have surfaces that define a firing chamber314about the resistor306, among other features. An example of the fluidics layer312and the firing chamber314are shown inFIG. 5D. As also shown inFIG. 5D, a bond pad318may be formed to be in electrical contact with the conductor traces304such that electrical signals may be communicated to the resistor306through the bond pad318and the conductor traces304.

In addition, as shown inFIG. 5E, an orifice plate316may be positioned on the fluidics layer312such that a nozzle116of the orifice plate316is positioned over and in fluid communication with the firing chamber314. Moreover, as shown inFIG. 5F, an electrical interconnect320may be placed in electrical communication with the bond pad318. The electrical interconnect320may include contacts formed of electrically conductive materials, e.g., gold, one of which may be bonded to the bond pad318through any suitable bonding technique. According to an example, the electrical interconnect320is a flexible electrical interconnect320.

At block408, a thin film material may be deposited onto the surfaces of the fluidics layer312that define the firing chamber314and a portion of the overcoat layer(s)308that forms part of the firing chamber314to form a thin film membrane322that covers the surfaces of the fluidics layer that define the firing chamber and the portion of the overcoat layer that forms part of the firing chamber. The thin film material may be a material selected from the group of materials including hafnium oxide, titanium oxide, aluminum oxide, hafnium silicon nitride, silicon oxide, or the like. According to an example, and as shown inFIG. 5F, the thin film material324may be deposited through atomic layer deposition (ALD). Through performance of ALD, the thin film material324may be deposited over the nozzle116and may enter into the firing chamber314, covering the surfaces that form the firing chamber314.

In addition, ALD of the thin film material324may be performed at a relatively low temperature, e.g., less than about 150° Celsius, to thus prevent degradation of the fluidics layer312during the deposition process. Moreover, the thin film membrane322may be formed to have a substantially constant thickness of about 100 angstroms across the components of the fluid ejection device114and to be substantially pinhole and crack free. Following implementation of the method400, the fluid ejection device114may have a thin film membrane322as shown, for instance, inFIG. 3. As an alternative to ALD, the thin film material324may be deposited through plasma enhanced chemical vapor deposition (PECVD) at low temperature.

According to an example, a cover326, for instance, tape, may be provided on a top contact328of the electrical interconnect320prior to deposition of the thin film material324. In this example, the cover326may be removed following formation of the thin film membrane322to thus expose the top contact328of the electrical interconnect320.

In other examples, however, the thin film membrane322may be formed at another other stage of fluid ejection device114fabrication. In a first example, the thin film membrane322may be formed following placement of the orifice plate316on the fluidics layer312and prior to placement of the electrical interconnect320. In this first example, the thin film material324may be deposited onto the components as shown inFIG. 6A, which may result in a portion330of the thin film membrane322covering the bond pad318. According to an example, the portion330of the thin film material324covering the bond pad318may be removed, for instance, through etching, abrasive techniques, etc., prior to placement of the electrical interconnect320. In another example, a cover (not shown) may be provided on the bond pad318prior to deposition of the thin film material324and the cover may be removed following formation of the thin film material322and prior to placement of the electrical interconnect320. In a yet further example, the electrical interconnect320may be placed on the portion330of the thin film membrane322covering the bond pad318. As the thin film membrane322is relatively thin, e.g., around 100 angstroms, electrical signals may flow from the electrical interconnect320to the bond pad318through the portion330of the thin film material324.

In a second example, the thin film membrane322may be formed following formation of the fluidics layer312and the firing chamber314. In this second example, the thin film material324may be deposited onto the components as shown inFIG. 6B, which may result in a portion330of the thin film material324covering the bond pad318and other portions332,334of the thin film material324covering top surfaces of the fluidics layer312. The portion330of the thin film material324covering the bond pad318may be removed or may remain as discussed above with respect to the first example. In addition, the portions332,334of the thin film material324covering the top surfaces of the fluidics layer312upon which the orifice plate316is to be placed may also be removed in any of the manners discussed above with respect to the bond pad318, e.g., etching, abrasive techniques, use of a cover, etc., prior to placement of the orifice plate316on the fluidics layer312. Alternatively, the orifice plate316may be placed on top of the fluidics layer312with the portions332,334of the thin film membrane322positioned therebetween.