Reference is made to commonly-assigned, U.S. patent application Ser. No. 11/609,375 filed concurrently herewith, entitled “LIQUID DROP EJECTOR HAVING IMPROVED LIQUID CHAMBER” in the name of John A. Lebens, the disclosure of which is incorporated herein by reference.
The present invention relates generally to monolithically formed liquid chambers and, more particularly, to liquid chambers used in ink jet devices and other liquid drop ejectors.
Drop-on-demand (DOD) liquid emission devices have been known as ink printing devices in ink jet printing systems for many years. Early devices were based on piezoelectric actuators such as are disclosed by Kyser et al., in U.S. Pat. No. 3,946,398 and Stemme in U.S. Pat. No. 3,747,120. A currently popular form of ink jet printing, thermal ink jet (or “bubble jet”), uses electrically resistive heaters to generate vapor bubbles which cause drop emission, as is discussed by Hara, et al., in U.S. Pat. No. 4,296,421. Although the majority of the market for drop ejection devices is for the printing of inks, other markets are emerging such as ejection of polymers, conductive inks, or drug delivery.
In the past, print head fabrication involved the lamination of a nozzle plate onto the printhead. With this method alignment of the nozzle to the heater is difficult. Also the thickness of the nozzle plate is limited to above a certain thickness. Recently monolithic print heads have been developed through print head manufacturing processes which use photo imaging techniques. The components are constructed on a substrate by selectively adding and subtracting layers of various materials.
Ohkuma et al., in U.S. Pat. No. 5,478,606 discloses a method of monolithically fabricating an ink flow path and chamber with a nozzle plate.
In this method of forming ink flow path and chamber; the adjoining of the substrate 1 containing the electrothermal elements 2 and the ink flow path-forming member relies on the adhesion force of the resin 5 constituting the flow path-forming member. In the ink jet head, the flow path and chamber is constantly filled with ink in the normal state of use so that the periphery of the adjoining portion between the substrate and the flow path-forming member is in constant contact with the ink. Therefore, if the adjoining is achieved by the adhesion force only of the resin material, constituting the flow path-forming member, this adhesion can be deteriorated by the influence of the ink. The adhesion is especially poor in alkaline inks.
In addition, in most thermal ink jet heads the resin material adheres to in different regions an inorganic layer such as silicon nitride or silicon oxide. In other regions the resin is adhering to a tantalum layer used for cavitation protection. Such tantalum layer has a lower adhesion force than the silicon nitride layer to the resinous material constituting the flow path-forming member. Therefore the resin may peel off of the tantalum layer. In order to prevent this from occurring, Yabe in U.S. Pat. No. 6,676,241 discloses forming an adhesion layer composed of polyetheramide resin between the substrate and the flow path-forming member. In this case improved adhesion can be maintained between silicon nitride or Tantalum layer and adjoining flow path member resin. However it is important that this adhesion layer be properly patterned so that no portion is in contact with the electrothermal element. Patterning of this layer includes extra steps in the fabrication, increasing expense and lowering yield. Also since the resin constituting the flow path member is still in contact with the ink it could swell causing stresses to develop between it and the adhesion layer again causing delamination of the flow path member.
Stout et al., in U.S. Pat. No. 6,739,519 also discloses a method of monolithically fabricating an ink flow path and chamber with a nozzle plate using photodefinable epoxy over a sacrificial resist layer or alternatively, with a double exposure of a photodefinable epoxy. The patent discusses the problem of continued adhesion between the epoxy nozzle plate and the substrate. Since the epoxy has a much larger thermal coefficient of expansion than the substrate thermal stresses can develop during firing of the heaters leading to delamination. The patent proposes the use of a primer layer between nozzle plate and substrate. However the epoxy interface is still in close proximity to the heater.
The nozzle plate formed from a resin material is gas permeable. Therefore the ink in the chamber below the nozzle plate is subjected to increased evaporation. As a result, properties of the ink, such as viscosity, in the chamber may change causing degradation of ejection characteristics. Also, air from the outside entering the chamber can cause bubble formation again degrading the ejection. Inoue et al., in U.S. Pat. No. 6,186,616 discloses adding a metal layer to the top of the nozzle plate resin to prevent air ingestion. However care must be taken that good adhesion is formed between the resin and metal layer. Also the metal must be compatible with the ink so that it does not corrode. Higher temperature deposited materials cannot be used due to the thermal restrictions of the resin material.
With the inside of a chamber formed with epoxy another issue is the wetting of the chamber walls with the ink. It is important that the inner chamber walls be wetting with the ink. Otherwise priming of the head will be difficult. Also, after a drop is ejected the chamber is depleted of ink and must completely refill before another drop can be fired. Non-wetting walls will impede the refill process. The contact angle of the epoxy wall can be lowered, for example, by exposure to oxygen plasma. However the surface returns to a non-wetting state over time. Also the oxygen plasma roughens the surface of the epoxy that again impedes refill.
It would therefore be advantageous to have an alternative choice for the inner chamber wall that is wetting with the ink, such as silicon oxide or silicon nitride. Such layers have excellent adhesion to the substrate layers used in the printhead. These layers are deposited at high temperatures and have other excellent properties for use in contact with the ink, such as material robustness, low thermal expansion, low moisture absorption and moisture permeability,
Ramaswami et al., in U.S. Pat. No. 6,482,574 discloses an all-inorganic chamber by depositing a thick 5-20 μm layer of oxide, patterning and etching to form the chamber, filling the chamber with a sacrificial layer that is then planarized, depositing a nozzle plate, and removing the sacrificial material. This procedure contains the difficult process of filling and planarizing the sacrificial material in the chamber region. Lack of planarization causes variation in chamber heights and loss of adhesion between chamber and nozzle plate. They also discuss the difficulty of depositing high quality dielectric material for the nozzle plate if the sacrificial material has temperature restrictions. It is also difficult to process such thick layers of oxide with long deposition and etch times. Such thick layers left on the substrate also have a tendency to crack due to stress build-up.
In commonly assigned U.S. Pat. No. 6,644,786 a chamber formation method is disclosed for a thermal actuator drop ejector. Non-photoimageable polyimide is patterned as the sacrificial layer allowing deposition of a high temperature inorganic structural layer such as silicon oxide or silicon nitride to form the chamber walls and nozzle plate. In this case only one deposition of the inorganic layer is needed to define both chamber walls and nozzle plate.
The above patent described formation of a chamber surrounding a single thermal actuator. No description is made of extending this process using thermal bubble jet heaters as drop ejectors. No description is made in extending the chamber formation to large arrays of ejectors with a corresponding large area ink feed port and how to provide structural support for this feed line. It is important for the structural design to be extensible. The chip containing the large array of drop ejectors also contains driver circuitry and logic on the chip that must be protected from the ink.
It is an object of the present invention to provide a liquid drop ejector comprising a plurality of liquid chambers where the chamber walls and nozzle plate are made from an inorganic material and formed using a sacrificial organic material.
It is also an object of the present invention to provide a region of organic material suspended of the liquid supply feed increasing the mechanical robustness of the liquid drop ejector.
It is also an object of the present invention to provide ribs in the liquid supply feed of the liquid drop ejector to further increase the mechanical robustness of the liquid drop ejector.
It is also an object of the present invention to provide gaps in the chamber walls to reduce the stress of the structure.
It is also an object of the present invention to provide an organic material layer over the circuitry of the liquid drop ejector for protection from the ink.
According to one aspect of the present invention, a liquid drop ejector includes a substrate and a plurality of liquid chambers. Portions of the substrate define a liquid supply. Each liquid chamber is positioned over the substrate and includes a nozzle plate and a chamber wall. The nozzle plate and the chamber wall include an inorganic material. The inorganic material of the nozzle plate and the chamber wall is contactable with liquid when liquid is present in each liquid chamber. A region of organic material is positioned over the substrate and located relative to the nozzle plate and the chamber wall such that the region of organic material is not contactable with liquid when liquid is present in each liquid chamber. The region of organic material is bounded by chamber walls of neighboring liquid chambers located on opposite sides of the liquid supply.
According to another aspect of the present invention, a liquid drop ejector includes a substrate and a plurality of liquid chambers. Portions of the substrate define a liquid supply. Each liquid chamber is positioned over the substrate and includes a nozzle plate and a chamber wall. The nozzle plate and the chamber wall include an inorganic material. The inorganic material of the nozzle plate and the chamber wall is contactable with liquid when liquid is present in each liquid chamber. A region of organic material is positioned over the substrate and located relative to the nozzle plate and the chamber wall such that the region of organic material is not contactable with liquid when liquid is present in each liquid chamber. No region of organic material is present between adjacent liquid chambers located on the same side of the liquid supply.
According to another aspect of the present invention, a liquid drop ejector includes a substrate and a liquid chamber for receiving a liquid. The liquid chamber is positioned over the substrate and includes a nozzle plate and a chamber wall. The nozzle plate and the chamber wall include an inorganic material. The inorganic material of the nozzle plate and the chamber wall is contactable with the liquid when the liquid is present in the chamber. The nozzle plate includes a top surface. The chamber wall includes two wall portions of inorganic material spaced apart from each other such that a gap exists between the two wall portions. The gap extends to the top surface of the nozzle plate. A region of organic material is positioned over the substrate and located relative to the nozzle plate and the chamber wall such that the region of organic material is not contactable with the liquid when the liquid is present in the chamber.
According to another aspect of the present invention, a method of manufacturing a liquid ejector includes providing a substrate; and forming a plurality of liquid chambers over the substrate by: providing an organic material over the substrate; patterning the organic material to create a location for the chamber wall of each liquid chamber; forming a nozzle plate and a chamber wall for each liquid chamber by depositing an inorganic material over the patterned organic material such that the inorganic material of the nozzle plate and the chamber wall is contactable with liquid when liquid is present in each liquid chamber; and removing a portion of the patterned organic material such that a region of organic material remains and is bounded by chamber walls of neighboring liquid chambers, wherein the region of organic material is not contactable with liquid when liquid is present in each liquid chamber.
In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
As described below, the present invention provides a method for forming a nozzle plate and chamber for a liquid drop ejector. The most familiar of such devices are used as printheads in ink jet printing systems. Many other applications are emerging which make use of devices similar to ink jet printheads, however which emit liquids other than inks, that need to be finely metered and deposited with high spatial precision. The terms ink jet and liquid drop ejector will be used herein interchangeably. The invention described below also provides for an improved chamber and nozzle plate for a liquid drop ejector.
In
A thermal barrier layer 24 may be formed of a variety of materials such as deposited silicon dioxide, field oxide, glass (BPSG) and oxynitride. This layer provides thermal and electrical isolation between the electrothermal element 2 and substrate 1. On top of the thermal barrier layer 24 is an electrically resistive heater layer 26. This electrically resistive heater layer is in this embodiment formed with a ternary Tantalum Silicon Nitride material.
An electrically conductive layer 28 is deposited on top of the electrically resistive heater layer 26. The electrically conductive layer 28 is formed from a metal typically used in MOS fabrication such as aluminum, or an aluminum alloy containing copper and/or silicon. The electrically conductive layer 28 is patterned and etched to form conductive traces which connects to the control circuitry fabricated on the ink jet printhead 20 and also defines the electrothermal heaters 2.
As shown in
As shown in
In
The substrate 1 is optionally thinned to a thickness of 300-400 μm and patterned on the backside with resist. In
As illustrated in
The inorganic material layer also forms pillars 46. In this embodiment they extend and are attached to the substrate 1 through the protection and insulating passivation layers. In other embodiments the filter pillars 46 can be suspended from the top nozzle plate 44.
In
The presence of ribs along the ink feed ports can cause printing artifacts due to the lower feed capability of ink chambers located adjacent to the ribs. We have found that for ribs less than 40 μm in width there are no such artifacts. Alternatively for strength purposes and aspect ratio for etching the ribs we have found that the rib width should be greater than 10 μm and should be connected to the center support region. In a preferred embodiment the rib width is 15-25 μm. These widths are measured at the back side of the substrate. Since the etch through the substrate is not completely anisotropic, the width of the rib at the center support region will be less than this value.
Referring back to
Outside of the chamber over the rest of the device area is a thick polyimide passivation layer 40, and top liner layer 42. The deposited inorganic layer 34 forms both the nozzle plate 44 and the top liner layer 42. The combination of passivation layer 40 and top liner layer 42 protects the device circuitry on the ink jet printhead 20 from degrading due to environmental effects and contact with the ink.
In a particular embodiment, the inorganic layer 34 defines an ink chamber 36 where ink is heated by the corresponding electrothermal element 2 and defines a nozzle 18 through which the heated ink is ejected forming an ink drop 50. The operation of the device is as follows. An electrical pulse is applied to an electrothermal heater 2. The heat pulse causes nucleation of a bubble in the chamber that grows, expelling ink from the ink chamber 36 through the nozzle 18 in the form of a drop, and also pushing ink back toward the ink feed port emptying most of the ink chamber of ink. The ejection frequency of the device is limited by the time it takes to refill the ink chamber 36. A hydrophobic chamber wall will increase the refill time causing incomplete refill of the chamber before the next firing pulse. This in turn results in ejection of a smaller and misdirected drop or in the worst case, no drop. A hydrophobic chamber wall also has a larger tendency to trap bubbles during refill. Bubbles trapped in the chamber of ink feed port again degrade the drop ejection. Organic materials used in the prior art are more hydrophobic than the inorganic liner layer of the present invention. The present invention gives the freedom to adjust the chamber to be hydrophilic by the use of inorganic materials that have a higher surface energy for water-based inks.
We have also found that the high temperature, plasma deposited silicon nitride and silicon oxide forming the chamber walls 38 have better adhesion to the protection and passivation layers on the substrate than epoxy based materials. Thus the device is more robust for long term resistance to delamination.
From the foregoing, it will be seen that this invention is one well adapted to obtain all of the ends and objects. The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modification and variations are possible and will be recognized by one skilled in the art in light of the above teachings. For example, the present invention is not limited to chamber formation of thermal bubble jet devices but also includes chamber formation for other drop ejection methods such as thermal or electrostatic actuator or piezoelectric activated liquid devices. Such additional embodiments fall within the scope of the appended claims.
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Number | Date | Country | |
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20080136867 A1 | Jun 2008 | US |