1. Field of the Disclosure
The present disclosure relates generally to fluid ejection devices, and more particularly, to a fluid ejection device adapted to prevent bulging of a nozzle plate over fluid vias of the fluid ejection device on an exposure to a fluid, such as ink.
2. Description of the Related Art
Presently, fluid ejection devices, such as inkjet printheads, are configured to have fluid vias constructed within a substrate, such as a silicon wafer, by various conventional methods. Such conventional methods include spinning of a positive resist material on an entire silicon wafer used for making the fluid ejection devices, and exposing areas corresponding to fluid vias while masking remaining areas of the silicon wafer with a photo reticle. Subsequently, the exposed positive resist material is developed away from the areas that correspond to the fluid vias. Thereafter, silicon material in the fluid vias is etched through the entire silicon wafer. Specifically, techniques such as Deep Reactive Ion Etching (DRIE) may be used to etch the silicon material in the fluid vias. Once the silicon material in the fluid vias is etched, a nozzle plate is laminated on top of a plurality of flow features spanning through the fluid vias. The silicon wafer may then be diced into individual chips, i.e., printheads. The printheads may then be attached to a tab circuit, and then bonded to a fluid bottle, such as a Noryl bottle to form the fluid ejection devices.
However, it is observed that over time, a Photo Imageable Nozzle Plate (PINP) based printhead suffers from bulging of the nozzle plate over fluid vias configured at end portions of the printhead, such as the outermost fluid vias for fluids including cyan ink and black ink, after exposure to the respective type of the fluids. Such a phenomenon is known as “via bulge”. Specifically, the bulging of the nozzle plate or the “via bulge” occurs because a silicon sliver deposited on the two outermost fluid vias is very thin (less than 800 micrometers) and may easily get distorted over a time period, while fluid is ejected (for example, during printing). Over time and during repeated usage of the printhead, a force is applied to the edges of the printhead. Such a force may squeeze the printhead and cause the nozzle plate over the outermost fluid vias to bulge. If the bulging of the nozzle plate is severe, then adhesion of the nozzle plate to plurality of flow features may be compromised, thereby, de-lamination of the nozzle plate may occur. Consequently, the de-lamination of the nozzle plate may lead to severe misdirected nozzles, thereby, compromising print quality.
To avert “via bulging”, it has been fairly suggested to introduce bridge structures within/across fluid vias of a fluid ejection device. FIG. 1 is one such embodiment. It depicts a fluid ejection device 100 that includes a substrate 10 and a fluid via 20 configured within the substrate 10. The fluid via 20 includes at least one bridge structure 30 spanning across the via 20 that assists in avoiding bulging of a nozzle plate 40 laminated over the substrate 10. Specifically, the at least one bridge structure 30 assists in preventing squeezing of the fluid ejection device 100, thereby, preventing bulging of the nozzle plate 40. Further, the at least one bridge structure 30 may be introduced within the fluid via 20 by placing the at least one bridge structure 30 imaged in a photo reticle used for fabricating the fluid ejection device 100. The at least one bridge structure 30 includes a top surface 32 aligned with a top surface (not shown) of the substrate 10. As depicted in FIG. 1, the nozzle plate 40 may have integrated flow features, such as a plurality of flow features 42, and built-in nozzles, such as a plurality of nozzles 44.
However, it has been thought that bridge structures of this type are typically very thin, and accordingly, are fragile. For example, a printhead without any bridge structure may withstand a drop height ranging from about nine inches to about fifteen inches without breaking. In contrast, a printhead with the foregoing bridge structures may withstand a drop height of only about two inches, thereby resulting in shattering that may prove detrimental to electronic circuitry of the printhead and may also lead to clogging of fluid passages within the printhead.
Further, bridges like FIG. 1 are suspected to affect the flow of fluid to a plurality of heaters (ejection elements) of a printhead, thereby, causing fluid starvation. Specifically, the bridge structures may act as a barrier to fluid flow and may also cause an increase in fluid cross-talk between adjacent ejection elements. For example, when an ejection element fires fluid, most of the fluid is ejected through a nozzle, but a significant amount of the fluid is blown back. The volume/amount of the fluid that is blown back may to enter an adjacent ejection element, if the bridge structure is close enough to the ejection element and is acting as a barrier. Furthermore, bridge structures with flat top surfaces can serve as a source for bubble formation.
Accordingly, there persists a need for an efficient fluid ejection device that is adapted to eliminate/prevent via bulge problem without resulting in additional problems, such as fluid starvation, fluid cross-talk and bubble formation.