# Patent

## Title
Miniature aerosol jet and aerosol jet array

## Abstract

A miniaturized aerosol jet, or an array of miniaturized aerosol jets for direct printing of various aerosolized materials. In the most commonly used embodiment, an aerosol stream is focused and deposited onto a planar or non-planar target, forming a pattern that is thermally or photochemically processed to achieve physical, optical, and/or electrical properties near that of the corresponding bulk material. The apparatus uses an aerosol jet deposition head to form an annularly propagating jet composed of an outer sheath flow and an inner aerosol-laden carrier flow. Miniaturization of the deposition head facilitates the fabrication and operation of arrayed deposition heads, enabling construction and operation of arrays of aerosol jets capable of independent motion and deposition. Arrayed aerosol jets provide an increased deposition rate, arrayed deposition, and multi-material deposition.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/635,847, entitled “Miniature Aerosol Jet and Aerosol Jet Array,” filed on Dec. 13, 2004, and U.S. Provisional Patent Application Ser. No. 60/669,748, entitled “Atomizer Chamber and Aerosol Jet Array,” filed on Apr. 8, 2005, and the specifications and claims thereof are incorporated herein by reference.


BACKGROUND OF THE INVENTION
Field of the Invention (Technical Field)
The present invention relates to direct printing of various aerosolized materials using a miniaturized aerosol jet, or an array of miniaturized aerosol jets. The invention more generally relates to maskless, non-contact printing onto planar or non-planar surfaces. The invention may also be used to print materials onto heat-sensitive targets, is performed under atmospheric conditions, and is capable of deposition of micron-size features.
SUMMARY OF THE INVENTION
The present invention is a deposition head assembly for depositing a material on a target, the deposition head assembly comprising a deposition head comprising a channel for transporting an aerosol comprising the material, one or more inlets for introducing a sheath gas into the deposition head; a first chamber connected to the inlets; a region proximate to an exit of the channel for combining the aerosol with the sheath gas, thereby forming an annular jet comprising an outer sheath flow surrounding an inner aerosol flow; and an extended nozzle. The deposition head assembly preferably has a diameter of less than approximately 1 cm. The inlets are preferably circumferentially arranged around the channel. The region optionally comprises a second chamber.
The first chamber is optionally external to the deposition head and develops a cylindrically symmetric distribution of sheath gas pressure about the channel before the sheath gas is combined with the aerosol. The first chamber is preferably sufficiently long enough to develop a cylindrically symmetric distribution of sheath gas pressure about the channel before the sheath gas is combined with the aerosol. The deposition head assembly optionally further comprises a third chamber for receiving sheath gas from the first chamber, the third chamber assisting the first chamber in developing a cylindrically symmetric distribution of sheath gas pressure about the channel before the sheath gas is combined with the aerosol. The third chamber is preferably connected to the first chamber by a plurality of passages which are parallel to and circumferentially arranged around the channel. The deposition head assembly preferably comprises one or more actuators for translating or tilting the deposition head relative to the target.
The invention is also an apparatus for depositing a material on a target, the apparatus comprising a plurality of channels for transporting an aerosol comprising the material, a sheath gas chamber surrounding the channels, a region proximate to an exit of each of the channels for combining the aerosol with sheath gas, thereby forming an annular jet for each channel, the jet comprising an outer sheath flow surrounding an inner aerosol flow, and an extended nozzle corresponding to each of the channels. The plurality of channels preferably form an array. The aerosol optionally enters each of the channels from a common chamber. The aerosol is preferably individually fed to at least one of the channels. A second aerosolized material is optionally fed to at least one of the channels. The aerosol mass flow rate in at least one of the channels is preferably individually controllable. The apparatus preferably comprises one or more actuators for translating or tilting one or more of the channels and extended nozzles relative to the target.
The apparatus preferably further comprises an atomizer comprising a cylindrical chamber for holding the material, a thin polymer film disposed on the bottom of the chamber, an ultrasonic bath for receiving the chamber and directing ultrasonic energy up through the film, a carrier tube for introducing carrier gas into the chamber, and one or more pickup tubes for delivering the aerosol to the plurality of channels. The carrier tube preferably comprises one or more openings. The apparatus preferably further comprises a funnel attached to the tube for recycling large droplets of the material. Additional material is optionally continuously provided to the atomizer to replace material which is delivered to the plurality of channels.
An object of the present invention is to provide a miniature deposition head for depositing materials on a target.
An advantage of the present invention is that miniaturized deposition heads are easily incorporated into compact arrays, which allow multiple depositions to be performed in parallel, thus greatly reducing deposition time.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.



A BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings:
FIG. 1a is a cross-section of a miniature deposition head of the present invention;
FIG. 1b displays isometric and cross-sectional views of an alternate miniature deposition head that introduces the sheath gas from six equally spaced channels;
FIG. 1c shows isometric and cross-sectional views of the deposition head of FIG. 1b with an accompanying external sheath plenum chamber;
FIG. 1d shows isometric and a cross-sectional views of a deposition head configuration that introduces the aerosol and sheath gases from tubing that runs along the axis of the head;
FIG. 1e shows isometric and a cross-sectional views of a deposition head configuration that uses internal plenum chambers and introduces the sheath air through a port that connects the head to a mounting assembly;
FIG. 1f shows isometric and cross-sectional views of a deposition head that uses no plenum chambers, providing for the largest degree of miniaturization;
FIG. 2 is a schematic of a single miniaturized deposition head mounted on a movable gantry;
FIG. 3 compares a miniature deposition head to a standard M3D® deposition head;
FIG. 4a is a schematic of the multiplexed head design;
FIG. 4b is a schematic of the multiplexed head design with individually fed nozzles;
FIG. 5a shows the miniature aerosol jet in a configuration that allows the head to be tilted about two orthogonal axes;
FIG. 5b shows an array of piezo-driven miniature aerosol jets; and
FIG. 6 shows perspective and cutaway views of the atomizer assembly used with miniature aerosol jet arrays.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Best Modes for Carrying Out the Invention
Introduction
The present invention generally relates to apparatuses and methods for high-resolution, maskless deposition of liquid and liquid-particle suspensions using aerodynamic focusing. In the most commonly used embodiment, an aerosol stream is focused and deposited onto a planar or non-planar target, forming a pattern that is thermally or photochemically processed to achieve physical, optical, and/or electrical properties near that of the corresponding bulk material. The process is called M3D®, Maskless Mesoscale Material Deposition, and is used to deposit aerosolized materials with linewidths that are an order of magnitude smaller than lines deposited with conventional thick film processes. Deposition is performed without the use of masks. The term mesoscale refers to sizes from approximately 1 micron to 1 millimeter, and covers the range between geometries deposited with conventional thin film and thick film processes. Furthermore, with post-processing laser treatment, the M3D® process is capable of defining lines having widths as small as 1 micron.
The M3D® apparatus preferably uses an aerosol jet deposition head to form an annularly propagating jet composed of an outer sheath flow and an inner aerosol-laden carrier flow. In the annular aerosol jetting process, the aerosol stream enters the deposition head, preferably either directly after the aerosolization process or after passing through the heater assembly, and is directed along the axis of the device towards the deposition head orifice. The mass throughput is preferably controlled by an aerosol carrier gas mass flow controller. Inside the deposition head, the aerosol stream is preferably initially collimated by passing through a millimeter-size orifice. The emergent particle stream is then preferably combined with an annular sheath gas. The carrier gas and the sheath gas most commonly comprise compressed air or an inert gas, where one or both may contain a modified solvent vapor content. For example, when the aerosol is formed from an aqueous solution, water vapor may be added to the carrier gas or the sheath gas to prevent droplet evaporation.
The sheath gas preferably enters through a sheath air inlet below the aerosol inlet and forms an annular flow with the aerosol stream. As with the aerosol carrier gas, the sheath gas flowrate is preferably controlled by a mass flow controller. The combined streams exit the extended nozzle through an orifice directed at a target. This annular flow focuses the aerosol stream onto the target and allows for deposition of features with dimensions as small as approximately 5 microns.
In the M3D® method, once the sheath gas is combined with the aerosol stream, the flow does not need to pass through more than one orifice in order to deposit sub-millimeter linewidths. In the deposition of a 10-micron line, the M3D® method typically achieves a flow diameter constriction of approximately 250, and may be capable of constrictions in excess of 1000, for this “single-stage” deposition. No axial constrictors are used, and the flows typically do not reach supersonic flow velocities, thus preventing the formation of turbulent flow, which could potentially lead to a complete constriction of the flow.
Enhanced deposition characteristics are obtained by attaching an extended nozzle to the deposition head. The nozzle is attached to the lower chamber of the deposition head preferably using pneumatic fittings and a tightening nut, and is preferably approximately 0.95 to 1.9 centimeters long. The nozzle reduces the diameter of the emergent stream and collimates the stream to a fraction of the nozzle orifice diameter at distances of approximately 3 to 5 millimeters beyond the nozzle exit. The size of the orifice diameter of the nozzle is chosen in accordance with the range of desired linewidths of the deposited material. The exit orifice may have a diameter ranging from approximately 50 to 500 microns. The deposited linewidth can be approximately as small as one-twentieth the size of the orifice diameter, or as large as the orifice diameter. The use of a detachable extended nozzle also enables the size of deposited structures to be varied from as small as a few microns to as large as a fraction of a millimeter, using the same deposition apparatus. The diameter of the emerging stream (and therefore the linewidth of the deposit) is controlled by the exit orifice size, the ratio of sheath gas flow rate to carrier gas flow rate, and the distance between the orifice and the target. Enhanced deposition can also be obtained using an extended nozzle that is machined into the body of the deposition head. A more detailed description of such an extended nozzle is contained in commonly-owned U.S. patent application Ser. No. 11/011,366, entitled “Annular Aerosol Jet Deposition Using An Extended Nozzle”, filed on Dec. 13, 2004, which is incorporated in its entirety herein by reference.
In many applications, it is advantageous to perform deposition from multiple deposition heads. The use of multiple deposition heads for direct printing applications may be facilitated by using miniaturized deposition heads to increase the number of nozzles per unit area. The miniature deposition head preferably comprises the same basic internal geometry as the standard head, in that an annular flow is formed between the aerosol and sheath gases in a configuration similar to that of the standard deposition head. Miniaturization of the deposition head also facilitates a direct write process in which the deposition head is mounted on a moving gantry, and deposits material on a stationary target.
Miniature Aerosol Jet Deposition Head and Jet Arrays
Miniaturization of the M3D® deposition head may reduce the weight of the device by more than an order of magnitude, thus facilitating mounting and translation on a movable gantry. Miniaturization also facilitates the fabrication and operation of arrayed deposition heads, enabling construction and operation of arrays of aerosol jets capable of independent motion and deposition. Arrayed aerosol jets provide an increased deposition rate, arrayed deposition, and multi-material deposition. Arrayed aerosol jets also provide for increased nozzle density for high-resolution direct write applications, and can be manufactured with customized jet spacing and configurations for specific deposition applications. Nozzle configurations include, but are not limited to, linear, rectangular, circular, polygonal, and various nonlinear arrangements.
The miniature deposition head functions similarly, if not identically, to the standard deposition head, but has a diameter that is approximately one-fifth the diameter of the larger unit. Thus the diameter or width of the miniature deposition head is preferably approximately 1 cm, but could be smaller or larger. The several embodiments detailed in this application disclose various methods of introducing and distributing the sheath gas within the deposition head, as well as methods of combining the sheath gas flow with the aerosol flow. Development of the sheath gas flow within the deposition head is critical to the deposition characteristics of the system, determines the final width of the jetted aerosol stream and the amount and the distribution of satellite droplets deposited beyond the boundaries of the primary deposit, and minimizes clogging of the exit orifice by forming a barrier between the wall of the orifice and the aerosol-laden carrier gas.
A cross-section of a miniature deposition head is shown in FIG. 1a. An aerosol-laden carrier gas enters the deposition head through aerosol port 102, and is directed along the axis of the device. An inert sheath gas enters the deposition head laterally through ports connected to upper plenum chamber 104. The plenum chamber creates a cylindrically symmetric distribution of sheath gas pressure about the axis of the deposition head. The sheath gas flows to conical lower plenum chamber 106, and is combined with the aerosol stream in a combination chamber 108, forming an annular flow consisting of an inner aerosol-laden carrier gas flow and an outer inert sheath gas flow. The annular flow is propagated through an extended nozzle 110, and exits at the nozzle orifice 112.
FIG. 1b shows an alternate embodiment in which the sheath gas is introduced from six equally spaced channels. This configuration does not incorporate the internal plenum chambers of the deposition head pictured in FIG. 1a. Sheath gas channels 114 are preferably equally spaced about the axis of the device. The design allows for a reduction in the size of the deposition head 124, and easier fabrication of the device. The sheath gas combines with the aerosol carrier gas in combination chamber 108 of the deposition head. As with the previous design, the combined flow then enters an extended nozzle 110 and exits from the nozzle orifice 112. Since this deposition head comprises no plenum chambers, a cylindrically symmetric distribution of sheath gas pressure is preferably established before the sheath gas is injected into the deposition head. FIG. 1c shows a configuration for developing the required sheath gas pressure distribution using external plenum chamber 116. In this configuration, the sheath gas enters the plenum chamber from ports 118 located on the side of the chamber, and flows upward to the sheath gas channels 114.
FIG. 1d shows isometric and cross-sectional views of a deposition head configuration that introduces the aerosol and sheath gases from tubing that runs along the axis of the head. In this configuration, a cylindrically symmetric pressure distribution is obtained by passing the sheath gas through preferably equally spaced holes 120 in disk 122 centered on the axis of the head. The sheath gas is then combined with the aerosol carrier gas in a combination chamber 108.
FIG. 1e shows isometric and cross-sectional views of a deposition head configuration of the present invention that uses internal plenum chambers, and introduces the sheath air through a port 118 that preferably connects the head to a mounting assembly. As in the configuration of FIG. 1a, the sheath gas enters an upper plenum chamber 104 and then flows to a lower plenum chamber 106 before flowing to a combination chamber 108. However in this case, the distance between the upper and lower plenum chambers is reduced to enable further miniaturization of the deposition head.
FIG. 1f shows isometric and cross-sectional views of a deposition head that uses no plenum chambers, providing for the largest degree of miniaturization. The aerosol enters sheath gas chamber 210 through an opening in the top of aerosol tube 102. The sheath gas enters the head through input port 118, which is optionally oriented perpendicularly to aerosol tube 102, and combines with the aerosol flow at the bottom of aerosol tube 102. Aerosol tube 102 may extend partially or fully to the bottom of sheath gas chamber 210. The length of sheath gas chamber 210 should be sufficiently long to ensure that the flow of the sheath gas is substantially parallel to the aerosol flow before the two combine, thereby generating a preferably cylindrically symmetric sheath gas pressure distribution. The sheath gas is then combined with the aerosol carrier gas at or near the bottom of sheath gas chamber 210 and the combined gas flows are directed into extended nozzle 230 by converging nozzle 220.
FIG. 2 shows a schematic of a single miniaturized deposition head 124 mounted on a movable gantry 126. The system preferably includes an alignment camera 128 and a processing laser 130. The processing laser can be a fiber-based laser. In this configuration, recognition and alignment, deposition, and laser processing are performed in a serial fashion. The configuration significantly reduces the weight of the deposition and processing modules of the M3D® system, and provides an inexpensive solution to the problem of maskless, non-contact printing of mesoscale structures.
FIG. 3 displays standard M3D® deposition head 132 side by side with miniature deposition head 124. Miniature deposition head 124 is approximately one-fifth the diameter of standard deposition head 132.
Miniaturization of the deposition head enables fabrication of a multiplexed head design. A schematic of such a device is shown in FIG. 4a. In this configuration, the device is monolithic, and the aerosol flow enters aerosol plenum chamber 103 through aerosol gas port 102 and then enters an array of ten heads, although any number of heads may be used. The sheath gas flow enters sheath plenum chamber 105 through at least one sheath gas port 118. In this monolithic configuration, the heads deposit one material simultaneously, in an arrayed fashion. The monolithic configuration can be mounted on a two-axis gantry with a stationary target, or the system can be mounted on a single axis gantry, with a target fed in a direction orthogonal to the motion of the gantry.
FIG. 4b shows a second configuration for a multiplexed head. The figure shows ten linearly-arrayed nozzles (although any number of nozzles may be arrayed in any one or two dimensional pattern), each being fed by individual aerosol port 134. The configuration allows for uniform mass flow between each nozzle. Given a spatially uniform atomization source, the amount of aerosol delivered to each nozzle is dependent on the mass flowrate of the flow controller or flow controllers, and is independent of the position of the nozzle in the array. The configuration of FIG. 4b also allows for deposition of more than one material from a single deposition head. These different materials may optionally be deposited simultaneously or sequentially in any desired pattern or sequence. In such an application, a different material may be delivered to each nozzle, with each material being atomized and delivered by the same atomization unit and controller, or by individual atomization units and controllers.
FIG. 5a shows a miniature aerosol jet in a configuration that allows the head to be tilted about two orthogonal axes. FIG. 5b is a representation of an array of piezo-driven miniature aerosol jets. The array is capable of translational motion along one axis. The aerosol jets are preferably attached to a bracket by flexure mountings. The heads are tilted by applying a lateral force using a piezoelectric actuator, or alternatively by actuating one or more (preferably two) galvanometers. The aerosol plenum can be replaced with a bundle of tubes each feeding an individual depositing head. In this configuration, the aerosol jets are capable of independent deposition.
Atomizer Chamber for Aerosol Jet Array
An aerosol jet array requires an atomizer that is significantly different from the atomizer used in a standard M3D® system. FIG. 6 shows a cutaway view of an atomizer that has a capacity sufficient to feed aerosolized mist to ten or more arrayed or non-arrayed nozzles. The atomizer assembly comprises an atomizer chamber 136, preferably a glass cylinder, on the bottom of which is preferably disposed a thin polymer film which preferably comprises Kapton®. The atomizer assembly is preferably set inside an ultrasonic atomizer bath with the ultrasonic energy directed up through the film. This film transmits the ultrasonic energy to the functional ink, which is then atomized to generate an aerosol.
Containment funnel 138 is preferably centered within atomizer chamber 136 and is connected to carrier gas port 140, which preferably comprises a hollow tube that extends out of the top of the atomizer chamber 136. Port 140 preferably comprises one or more slots or notches 200 located just above funnel 138, which allow the carrier gas to enter chamber 136. Funnel 138 contains the large droplets that are formed during atomization and allows them to downward along the tube to the bath to be recycled. Smaller droplets are entrained in the carrier gas, and delivered as an aerosol or mist from the atomizer assembly via one or more pickup tubes 142 which are preferably mounted around funnel 138.
The number of aerosol outputs for the atomizer assembly is preferably variable and depends on the size of the multi-nozzle array. Gasket material is preferably positioned on the top of the atomizer chamber 136 as a seal and is preferably sandwiched between two pieces of metal. The gasket material creates a seal around pickup tubes 142 and carrier gas port 140. Although a desired quantity of material to be atomized may be placed in the atomization assembly for batch operation, the material may be continuously fed into the atomizer assembly, preferably by a device such as a syringe pump, through one or more material inlets which are preferably disposed through one or more holes in the gasket material. The feed rate is preferably the same as the rate at which material is being removed from the atomizer assembly, thus maintaining a constant volume of ink or other material in the atomization chamber.
Shuttering and Aerosol Output Balancing
Shuttering of the miniature jet or miniature jet arrays can be accomplished by using a pinch valve positioned on the aerosol gas input tubing. When actuated, the pinch valve constricts the tubing, and stops the flow of aerosol to the deposition head. When the valve is opened, the aerosol flow to the head is resumed. The pinch valve shuttering scheme allows the nozzle to be lowered into recessed features and enables deposition into such features, while maintaining a shuttering capability.
In addition, in the operation of a multinozzle array, balancing of the aerosol output from individual nozzles may be necessary. Aerosol output balancing may be accomplished by constricting the aerosol input tubes leading to the individual nozzles, so that corrections to the relative aerosol output of the nozzles can be made, resulting in a uniform mass flux from each nozzle.
Applications involving a miniature aerosol jet or aerosol jet array include, but are not limited to, large area printing, arrayed deposition, multi-material deposition, and conformal printing onto 3-dimensional objects using 4⁄5 axis motion.
Although the present invention has been described in detail with reference to particular preferred and alternative embodiments, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the Claims that follow, and that other embodiments can achieve the same results. The various configurations that have been disclosed above are intended to educate the reader about preferred and alternative embodiments, and are not intended to constrain the limits of the invention or the scope of the Claims. Variations and modifications of the present invention will be obvious to those skilled in the art, and it is intended to cover all such modifications and equivalents. The entire disclosures of all patents and publications cited above are hereby incorporated by reference.

## Claims

1. An apparatus for depositing a material on a target, said apparatus comprising:
a plurality of channels for transporting an aerosol comprising the material;
a sheath gas chamber surrounding two or more of said channels;
a region proximate to an exit of each of said channels for combining the aerosol with sheath gas, thereby forming an annular jet for each channel, said annular jet comprising an outer sheath flow surrounding an inner aerosol flow; and
a plurality of separate extended nozzles extending from said region, one of said separate extended nozzles corresponding to each one of said channels and reducing the diameter of each said annular jet.

2. The apparatus of claim 1 wherein said plurality of channels form an array.

3. The apparatus of claim 1 wherein the aerosol enters each of said channels from a common chamber.

4. The apparatus of claim 1 wherein the aerosol is individually fed to at least one of said channels.

5. The apparatus of claim 4 wherein a second aerosolized material is fed to at least one of said channels.

6. The apparatus of claim 1 wherein an aerosol mass flow rate in at least one of said channels is individually controllable.

7. The apparatus of claim 1 comprising one or more actuators for translating or tilting one or more of said channels and extended nozzles relative to the target.

8. The apparatus of claim 1 further comprising an atomizer comprising:
a cylindrical chamber for holding the material;
a thin polymer film disposed on the bottom of said chamber;
an ultrasonic bath for receiving said chamber and directing ultrasonic energy up through said film;
a carrier tube for introducing carrier gas into said chamber; and
one or more pickup tubes for delivering the aerosol to said plurality of channels.

9. The apparatus of claim 8 further comprising a funnel attached to said tube for recycling large droplets of the material.

10. The apparatus of claim 8 wherein additional material is continuously provided to the atomizer to replace the material which is delivered to said plurality of channels.

11. The apparatus of claim 8 wherein said carrier tube comprises one or more openings.