Patent Application
20110018938
Printing devices, such as liquid jet printers, may feed liquid ink through a substrate to a firing port. While the liquid ink is fed through the substrate, such as through a channel that extends through the substrate, the liquid ink will come into contact with the channel walls. In an example wherein the substrate is manufactured of silicon and the liquid ink is a pigmented ink including charged dispersants, the liquid ink may etch the channel wall of the substrate such that silicon leaches into the pigmented ink. The presence of silicon in the ink may cause a blockage or partial blockage of the firing port. It may be desirable to reduce such blockage or partial blockage of the firing port to improve the print quality of the printing device.
Strengthening structures 28 may be referred to as ribs and may be formed in a variety of shapes and sizes. In one example embodiment, structures 28 may be recessed from the front side 68 and the backside 64 of substrate 22. The structures 28 may have a width 28a (
In one example embodiment, substrate 22 is formed from a starting substrate of a [100] silicon wafer that may be 150 or 200 millimeters (mm) in diameter and 675 or 725 micrometers (um) in thickness. The starting silicon wafer may have a concentration of 10̂14 to 10̂19 atoms/cm3 of impurities such as boron, phosphorous, arsenic, or antimony, for desirable device performance. The starting silicon wafer may also have a low level of interstitial oxygen.
Still referring to
Ink 42 may be contained in an ink supply (not shown) and may be flowed through supply structure 26, through aperture 20 in substrate 22, through firing channel 34 of firing chamber 24, and out of firing orifice 36 to print an image on a sheet of print media 18 (
Charged dispersants 44 in a pigmented ink 42 or high pH solvent may etch a silicon material, such as an exposed wall 46 of aperture 20 of silicon substrate 22, which may result in silicon particles 48 leaching into ink 42. The presence of silicon particles 48 in ink 42, above a known part per million (ppm) threshold, such as above ten (10) ppm, may result in the precipitation of silicon at firing orifice 36, so that the firing orifice 36 may become blocked or partially blocked, thereby reducing the accuracy and printing capability of nozzle plate 16 of printing device 10.
The printing device 10 of the present invention, therefore, includes a protective coating 50 formed on exposed walls 46 of apertures 20 of substrate 22 so that the silicon material of substrate 22 is out of contact of ink 42. Protective coating 50 may also completely coat the backside 64 of substrate 22. Protective coating 50 may also completely coat strengthening structures 28, and interior wall surfaces 52 of firing chamber 24. Protective coating 50 may also coat the interior surface of supply structure 26, such as a fluidic manifold. Protective coating 50 may be formed of an ink impervious material such as silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3), hafnium oxide (HaO2), a conformal polymer formed from a gas phase monomer such as polyxylene, an organic polymer, a plated metal such as nickel, gold or palladium, and other materials such as silicon carbide, or any other ink impervious material or combination of materials. The ink impervious coating 50 will prevent, or will substantially reduce, etching of the silicon substrate 22 material by ink 42 such that silicon particles 48 are not (or a very low number are) present in ink 42 so that firing orifices 36 do not become blocked or partially blocked by silicon precipitation at firing orifices 36.
This example process as described immediately above allows for low temperature deposition of protective coating 50 over the substrate 22 and over the interior walls 52 of the firing chamber 34, which may be manufactured of photo imagable epoxy. In the example embodiment mentioned above, where the application is performed from both the backside 64 and the front side 68, coating 50 may encapsulate the firing chamber 35 entirely, preventing chemical attack from the ink. The deposition temperature of chamber 60 may be maintained at 170 degrees Celsius or less so that the photo imagable epoxy material is not damaged.
The following processes may be utilized to form protective coatings 50: plasma enhanced chemical vapor deposition (PECVD) of silicon dioxide; atomic layer deposition (ALD) of aluminum oxide; atomic layer deposition of hafnium oxide; inductively coupled plasma chemical vapor deposition (ICP CVD) of silicon dioxide; inductively coupled plasma chemical vapor deposition (ICP CVD) of silicon nitride; microwave plasma assisted chemical vapor deposition (CVD) of silicon dioxide; chemical vapor deposition of a conformal polymer formed from a gas phase monomer (such as polyxylene); deposition of an organic polymer with a plasma assist process; and electro less plating of a metal (such as nickel); and electroplating a metal (such as nickel, gold or palladium). The following high temperature coating processes can be used on print head architectures that are fabricated from materials that do not degrade at high temperatures. For example, the firing chamber may be fabricated from an electroplated metal, a silicon oxide or a polyimide: plasma enhanced chemical vapor deposition (PECVD) of silicon carbide; and plasma enhanced chemical vapor deposition (PECVD) of silicon nitride. Each of these processes may be utilized to form coating 50 in apertures 20 of substrate 22 of a printhead formed in many different configurations. For example, the printhead may have a nozzle plate made from an electroformed metal, a photo imageable polymer, a polyimide, or a polymer nozzle plate where the nozzles are formed by laser ablation. The apertures 20, or slots, in substrate 22 may be formed by techniques such as wet etch, reactive ion etch, abrasion jet machining, laser ablation, and a combination of these techniques.
In another example process, a sacrificial resist may be applied to areas where coating 50 is not be applied, such as to bond pads, for example. After deposition of coating 50, the sacrificial resist may be removed by a liftoff process to provide the finished device 10.
Coating 50 of the present invention may reduce etching of silicon from substrate 22 into ink 42 such that the part per million (ppm) content of silicon in an ink 42 may be reduced, such as to less than 10 ppm, and approximately 5 ppm silicon, for example, which may reduce or eliminate the formation of silicate rings at firing orifice 36. Substrate 22 and aperture 20 without coating 50 have been determined to have a much higher silicon ppm content, such as approximately 23 ppm silicon. Testing to determine the above listed outcomes was performed wherein a substrate was submersed in 10 ml of ink 42 for two days at 70 degrees Celsius. The sawn edges of the substrate were coated with a silicon epoxy to prevent etching of the die edge. The ink sample in both cases (the coating substrate and the uncoated substrate) were then evaluated for silicon concentration using inductively coupled plasma spectrometry (ICP) analysis. It is noted that silicon epoxy, which was utilized to seal the die edges, typically yields a silicon content of 3.5 ppm. Accordingly, the coated substrate 22 and aperture 20, which was measured to produce an ink 42 having a silicon content of 5 ppm, may have contributed only 1.5 ppm of silicon from the coated substrate. In contrast, the uncoated substrate 22 and aperture 20 which was measured to produce an ink 42 having a silicon content of 23 ppm, may have contributed as much as 19.5 ppm of silicon from the coated substrate 22 and aperture 20, well above the threshold of 10 ppm which may be though to produce silicate rings at firing orifices 36.
In another ink soak test, coated and uncoated substrate 22 and aperture 20 were assembled in pens, filled with ink 42, and stored for seven days at 60 degrees Celsius. Subsequently a small sample of ink was expelled through the nozzles and evaluated for silicon concentration using ICP analysis. The pens with coated substrate 22 and aperture 20 were measured to produce an ink 42 having a silicon concentration of 7.4 ppm. In contrast, pens with uncoated substrate 22 and aperture 20 were measured to produce an ink 42 having a silicon concentration of 53 ppm, well above the threshold of 10 ppm which may be thought to produce silicate rings at firing orifices 36.
In both test samples, ink 42 was fired through firing orifice 36 including both the coated and uncoated substrate 22 and it was found that print reliability and directionality was not compromised by inclusion of coating 50.
The process of applying protective coating 50, as described herein, allows the use of corrosive inks with readily formable and patternable substrates, such as silicon. Accordingly, use of coating 50 on readily available substrates may reduce the use of highly robust substrates, such as stainless steel substrates, that may not be readily formable or patternable using known technologies. Accordingly, the use of protective coating 50 increases the class of inks with which well known substrates, such as silicon, may be utilized, without encountering silicon precipitation or leaching into the inks 42.
In other embodiments, other substrates may be utilized such as glass, for example.
Other variations and modifications of the concepts described herein may be utilized and fall within the scope of the claims below.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/05663 | 4/29/2008 | WO | 00 | 9/17/2010 |
