Patent Application
20080043065
The accompanying drawings illustrate various embodiments of the present system and method and are a part of the specification. The illustrated embodiments are merely examples of the present system and method and do not limit the scope thereof.
The present exemplary systems and methods provide for the creation and operation of a printing system to deliver fluids in research and development processes. In particular, according to one exemplary embodiment, a pico-fluidic inkjet is described herein that can be manufactured with a drop ejector able to dispense, but in no way limited to, difficult-to-eject, high-valued fluids at high velocities. According to one exemplary embodiment, the present pico-fluidic inkjet has a reservoir, a chamber, a chamber layer, an actuating member, an actuator layer, an insulating stack layer, an orifice layer and an orifice. Further details of the present pico-fluidic inkjet, as well as exemplary methods for using the inkjet to dispense fluids onto a desired substrate will be described in further detail below.
As used in the present specification, and in the appended claims, the term “pico-fluidic inkjet” is meant to be understood broadly as including any material dispensing apparatus that may be used for the deposition of ink and other fluids including, but in no way limited to, drop-on-demand, thermal, piezoelectric, or hybrid dye-sublimation inkjets, and the like.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods for forming a pico-fluidic inkjet system. It will be apparent, however, to one skilled in the art that the present systems and methods may be practiced without these specific details. Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearance of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
Many references will be made to numbered items in various figures. References to a common number used in different figures, may or may not necessarily be referring to the same component. The context of the reference part will be understood from the included writing.
For the purposes of the present detailed description and the appended claims, the term “drop ejector” is meant to be understood as including a chamber, a chamber layer, an actuator layer, an actuating member, an insulating stack, a orifice layer and an orifice. The components of a drop ejector need not be exactly the same in each drop ejector, e.g., when talking of two separate drop ejectors the chamber dimensions may vary in each.
Additionally, for the purposes of the present detailed description and the appended claims, the term “stack layer height” is meant to be understood as a sum of the thicknesses of the chamber layer and the orifice layer of any given drop ejector. The term “stack layer” refers the chamber and orifice layers deposited above the actuating member.
Note that the drop ejector (200) represented in
Traditional uses for a fluidic inkjet material dispenser include printing, labeling, imaging and the like. Each of these activities demands a certain amount of precision to minimize variations in aspects such as grain size, drop size, tail length, and dot shape to name a few. According to one exemplary embodiment, the present systems and methods may not have the same limitations when applied to non-imaging procedures. As used herein, non-imaging procedures can include, but are no way limited to the following, printing of reagents, enzymes or other proteins into well-plates, Petri dishes, or filters for the purpose of fluid mixing or initiating chemical reactions.
The present exemplary system has the same basic form and components as those referred to and discussed with reference to
Furthermore,
According to one exemplary embodiment, the present systems and methods differ from a traditional inkjet delivery system by including a printhead drop ejector that is not practical for a traditional imaging inkjet system. Specifically the present exemplary systems and methods use a combination of at least one or more of the following attributes, higher orifice diameter to stack layer height ratios (O/L ratio), higher resistor length to orifice diameter ratios (R/O ratio), larger actuating members (350), and thinner stack layers (380). Each of the previous attributes modifies the drop ejector (300) in such a way that a combination of at least one or more of the following benefits is obtained: high throw drops, higher ejection efficiency, improved decap performance, and improved coefficient of variation, i.e., the ratio of the standard deviation to the mean, herein referred to as CV. Further details of the above-mentioned attributes as well as the attribute modifications will be provided below.
Using a combination of the following attributes: higher O/L ratio, higher R/O ratio, larger actuating member (350), and thinner stack layer (380), an increased drop volume and velocity can be obtained. By having higher drop volume and velocity, higher momentum can be achieved which in turn leads to high throw, a characteristic that while not well suited to forming inkjet images is often desired for dispensing difficult-to-eject, high-valued fluids at high velocities onto a desired substrate. The present exemplary system illustrated in
The formation of a printhead uses many technologies associated with semiconductor processing and integrated circuit design. According to one exemplary embodiment, a printhead can be integrally manufactured using a photolithography process. A substrate of a predetermined thickness is typically prepared as the actuator layer of the drop ejector (300). Vias and circuitry are then created on the surface of the wafer using photolithographic and metal deposition processes. The vias and circuitry are connected to an actuating member, which is formed on the substrate. An insulating stack layer is then grown or deposited on the surface of the actuating member to provided protection from the chemical contents to be dispensed and possible cavitations. A chamber layer is created using a negative photoresist. A sacrificial layer is then deposited on the surface of the wafer, upon which the orifice layer of the drop ejector is formed. Using a positive photoresist and an etchant, a orifice can be formed into the orifice layer of the drop ejector. The sacrificial layer is then removed via an etchant or acid bath. A method for fabricating printheads with the present exemplary configuration will now be described below.
According to one exemplary embodiment, a thermal driving type inkjet printhead having the structure described in reference to
Once the actuating member is formed, an insulating stack layer is formed over the actuating member to protect the actuating member (420). The formation of the insulating stack layer over the actuating member could be done in many ways including, but not limited to, spinning on an insulating layer, and patterning it to sufficiently cover said actuating member. According to the present exemplary system and method, the insulating stack is formed to be sufficiently thin to meet the predetermined criteria of the present system.
After the forming of the actuating member and insulating stack, a negative photoresist is coated on the entire surface of the substrate to a predetermined thickness. Coated photoresist is then patterned using a photolithography process so as to surround the material chamber and create the chamber layer (430). With the patterned photoresist forming the chamber layer (430), a sacrificial layer is then formed by filling the space that is surrounded by the chamber layer with a positive photoresist. Over this sacrificial layer a negative photoresist is then deposited and patterned creating the orifice layer of the drop ejector (440). Specifically, the sum of the thicknesses of the chamber and orifice layer is sufficiently thin to achieve higher O/L ratios and higher velocities with lower drop weights with higher efficiencies, as compared to traditional TIJ material dispensers.
Using a last photolithography process, a orifice is formed in the orifice layer of the drop ejector (450). As previously mentioned, the orifice is formed with dimensions configured to generate high O/L, and R/O ratios, high throw design, and improved decap times, as described above. The sacrificial layer is also removed opening up the chamber of the drop ejector.
A number of DMDs were formed using the methodologies illustrated in
Table 1 below illustrates a comparison of the kinetic energy of three traditional thermal inkjets and three DMDs incorporating the present system and method.
As shown in Table 1 above, the drops of material ejected by high throw designs 1 through 3 have more energy than all but the largest drops used in traditional imaging inkjets. While high velocity drops can be generated by incorporating larger actuating members (350), high R/O ratio by itself generally creates more waste heat. Rather, the present exemplary drop ejector (300) illustrated in
Table 2 below illustrates a number of exemplary dimensions of the tested material dispensers as well as their respective orifice diameter to stack layer height ratios (O/L) and R/O ratios.
As can be seen in Table 2, the O/L ratios of the DMDs using the present system range from 1.00-1.45, which is significantly larger than the O/L ratio of traditional TIJ material dispensers, which range from 0.35-0.65. Table 2 also illustrates that the R/O ratios of the DMDs using the present exemplary configuration illustrated in
Table 3 shows the throw distance of ejected drops, where the distance traveled is defined to be the location relative to the orifice where the velocity has decreased to 1% of the initial value. While current imaging printheads use approximately 5 pL volumes and 12 m/s velocity, and consequently have a travel distance of about 11 mm, the DMDs using the present exemplary system have drop volumes in the 100-250 pL range and velocities in the 15-20 m/s range, and consequently have travel distances between 70 and 120 mm.
Generally higher velocities mean higher throw drops. High throw drops are especially advantageous when applied to non-imaging procedures such as enzyme implantation or chemical mixing. For example, a DMD as detailed in Tables 1 and 2 can be used to dispense an enzyme into a well-plate. The high throw of the dispenser is not only inexpensive in comparison to CIJ material dispensers, but also uses less fluid than a CIJ or an operator using a micro-pipette. Further, where as traditional TIJ material dispensers are limited by the distance that they can eject a drop, the DMDs having a volume of about 100 pL and a initial velocity of 19.9 m/s can travel 88 mm before velocity is reduced to 1% of initial velocity. Having the extra latitude in firing distance, allows the DMDs to jet onto non-flat topography, such as indentations in coating applications or well-plates, where the interference between the material dispensers itself and the topography prevents moving the orifices close to the substrate of interest. Particularly, in well-plate applications such as the current example, high throw minimizes the amount of fluid that sticks to the side walls of a well and maximizes the amount of the fluid that reaches the bottom of the well. Thus, high throw improves the efficiency of the jetting event and allows effective mixing and deposition onto the surface of interest.
As mentioned previously, a DMD incorporating the present exemplary system and method also exhibits improved decap performance and CVs. As used herein, decap is meant to be understood as the length of time that a fluid remains a liquid while being exposed to the atmosphere in the orifice. Short decap times are due to increasingly small orifices and rapidly evaporating solutions Due to the nature of the fluids used by the present exemplary system, decap time is a very relevant consideration. Many functional materials (sol gels, pre-cursors, nano-particle suspensions, monomers, to name a few) are diluted or based in highly-evaporative solvents. Consequently, decap performance when jetting functional materials is much worse than typically seen with the aqueous colorant fluids dispensed by traditional inkjet material dispensers. The present system overcomes such obstacles by incorporating higher O/L and R/O ratios, larger actuating members (350), and thinner stack layers (380). A DMD drop ejector exhibiting the above mentioned attributes is particularly suited for the selective deposition of a number of functional materials. A DMD drop ejector using the present system (300) evacuates a higher percentage of the total volume available (thereby improving CVs) and improves drop velocity, which translates to improved decap times.
Further, Table 4 illustrates the corresponding volumes of the orifice, chamber and their sum to determine the ejection efficiency (total volume ejected vs. volume available in chamber and orifice) of the inkjet material dispenser.
As can be seen in Table 4, the ejection efficiency of traditional TIJ material dispensers ranges from approximately 35-42%. In contrast, the DMDs incorporating the present system and method exhibit an increased ejection efficiency of between 50 and 63%.
Moreover, Table 5 illustrates an overall comparison of traditional TIJ material dispensers to DMDs that incorporate the present exemplary system and method. More specifically, Table 5 includes a comparison between the ratios of nucleation pressure to viscous loss (ReXEu, Re being the Reynolds number and Eu being Euler's number).
As can be seen in Table 5, the traditional TIJ material dispensers exhibit a ReXEu ratio that ranges from 30-60. In contrast, the ReXEu ratios exhibited by the DMDs using the present exemplary system and method range from 100-200. As previously mentioned, the DMDs incorporating the present exemplary system and method have a higher O/L and R/O ratio, larger actuating members (350), and a thinner stack layer (380). These attributes also resulted in improved decap times when compared to traditional TIJ material dispensers.
The improved decap times exhibited by the present DMDs result in many advantages including, but in no way limited to, eliminating printing defects associated with startup/decap, crisp startup edges, high printhead utilization, the ability to use traditionally difficult-to-eject fluids, and improved directionality via closer media spacing.
In conclusion, the present exemplary system and method provide a simple printhead with a modified drop ejector that is inexpensive, versatile and designed for non-imaging processes. More specifically, according to one exemplary embodiment, the present drop ejector includes a chamber, a chamber layer, an orifice layer, an orifice, an actuator layer, an actuating member, and insulating stack configured to achieve high throw drops, higher O/L and R/O ratios, higher ejection efficiency, improved decap performance, and improved C.Vs.
The preceding description has been presented only to illustrate and describe the present system and method. It is not intended to be exhaustive or to limit the disclosure to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the disclosure be defined by the following claims.
