FIELD OF THE INVENTION

[0001] The present invention relates to devices and methods for electrospray devices.

BACKGROUND

BACKGROUND OF ELECTROSPRAY PROCESS

[0002] Electrostatic atomization, also known as electrospray, usually refers to the atomization of a liquid through the Coulombic interaction of charges and the applied electric field. Electrostatic atomization offers several advantages over alternative atomization techniques. Electrospray droplet streams are mainly due to the net charge on the surface of the droplets that is generated and the coulombic repulsion of the droplets. This net charge causes the droplets to disperse, preventing their coalescence. Also, the trajectory of a charged droplet can be guided by an electrostatic field. Another advantage of this type of atomization is the ability to control the size distribution of the spray and under specific electrodynamic operating conditions, obtain a monodispersed spray. Because of these advantages, a wide number of applications exist where electrodynamic atomization can be used.

[0003] Electrospray can be described by three different processes. The first process is the formation of the liquid meniscus at a capillary tip which results from a number of forces acting on the interface, including surface tension, gravitational, electrostatics, inertial, and viscous forces. Sir Geoffrey Taylor was the first to calculate analytically a conical shape for the meniscus through the balance of surface tension and electrical normal stress forces which we now know is called the 'Taylor cone' in electrospray and appears in the cone-jet mode. (See Fig. 2)

[0004] The cone -jet mode is one of the most widely studied and used modes of electrospray. In the cone-jet mode, liquid leaves the capillary in the form of an axisymmetric cone with a thin jet emitted from its apex. The small jet of liquid issuing out of the nozzle is electrostatically charged when subjected to an intense electric field at the tip of the capillary nozzle (Birmingham, et al., 2001). The droplets are approximately 10 micron in diameter. The charged droplets are propelled away from the nozzle by the Coulomb force and are dispersed out as a result of charge on the droplets.

DESCRIPTION OF RELATED ART

[0005] Controlled deposition has drawn enormous interest recently as a maskless, bottom-up fabrication technique for many novel functional structures such as solar cells [Deng 2010]. These applications require rapid and precise deposition of either pico liters (pi) of solutions/suspensions or their final particle product in predefined patterns. Currently, the dominant deposition technique is inkjet printing (UP), which has been successfully applied to dispense inorganic particles, polymers, and other inks. The UP print head uses a short pressure pulse generated either thermally or piezoelectrically to expel one or more 100 pi liquid droplets out of a nozzle whose typical orifice dimension is 30-60 microns (μιη). The working principle of UP may impose several restrictions on the type of suspension and solution it can handle. For example, the instantaneous pressure pulse introduces high shear rate of 10 ⁵ / s, which induces the production of wasted satellite droplets. The UP also limits the liquid viscosity to 20 centipoise (cP), [U. S. Schubert, 2004] which is below the viscosity of many polymer solutions of medium to high concentrations.

[0006] These UP limitations can be easily overcome by the electrospray (ES) because of its entirely different atomization mechanism that relies solely on electric charging. A typical ES system can be implemented by feeding a liquid with sufficient electric conductivity through a capillary that is charged at high potentials relative to a nearby ground electrode. Among many of the modes that ES can be operated in, the most remarkable one is the cone-jet mode. In this mode, the liquid meniscus takes a conical shape with a fine jet issuing from the cone tip. Clogging is generally not an issue for ES even with suspensions of high particulate concentrations because the ES capillary bore is typically two orders of magnitudes larger than the jet/droplet diameter. For the same reason, the ES can also easily handle high viscosity solutions without causing a substantial pressure drop. Additionally, the shear rate in an ES is generally more modest than in UP Another key feature of the ES is the quasi-monodispersity of the droplets. The ES capability of producing monodisperse droplets with relative ease is unmatched by any other droplet generation scheme, especially in the submicron range. Since, when the deposition device is mounted on a precision translational stage, as is typically the case in UP, the resolution is primarily determined by the droplet size, ES controlled deposition exhibits better spatial resolution as compared to UP. A line width of 10 nm and pattern resolution of Ιμιη using a single ES source have been demonstrated. To avoid spray expansion due to Coulombic repulsion among charged droplets, a few approaches have been implemented, including bringing the substrate very close (less than 100 μιη) to the ES source before the spray expands [Park 2007], refocusing the spray electrostatically using a sharp grounded electrode below the substrate [Lee 2007], or predefining the pattern on a semiconducting or nonconducting substrate via contact charging [Lenggoro 2006] or the inclusion of an aperture with integrated gas cleaning [Birmingham unpublished].

SUMMARY

[0007] A method and system is described herein for producing an electrospray of desired droplet size and monodispersity. The system comprises a pump for pumping a liquid to a capillary tube. A voltage source is configured for applying a voltage pulse to the tip of the capillary tube. The voltage pulse start time is set for a time when a first volume of the liquid has accumulated at the tip of the capillary tube. The first volume of the liquid is based on a desired first droplet size. The first voltage pulse amplitude is set at or above a minimum voltage required to atomize the first volume of the liquid.

[0008] The testing of the exemplary electrospray system generated uniform droplets without daughter or satellite droplets. Measurements of the uniform droplet diameters revealed a droplet size around 80 microns without daughter satellites. The selection of specific electrical conditions such as frequency, waveform, and intensity produced different droplet distributions at will.

[0009] The exemplary electrospray system, because of its entirely different atomization mechanism producing monodispersed droplets that relies solely on electric charging coupled with a liquid with sufficient applied electric fields through a capillary that is charged at high potentials relative to a nearby ground electrode. This exemplary electrospray system can be fabricated from a sheet architecture method. The exemplary electrospray system does not clog even with suspensions of high particulate concentrations, can also easily handle high viscosity solutions without causing a substantial pressure drop, and maintains a minimal shear rate. The key feature of the exemplary electrospray system is the quasi-monodispersity of the droplets. The exemplary electrospray system capability of producing monodisperse droplets with relative ease is unmatched by any other droplet generation scheme, especially in the submicron range. Since, when the deposition device is mounted on a precision translational stage, as is typically the case in piezoelectric-driven ink jet printers (UP), the resolution is primarily determined by the droplet size, therefore, exemplary electrospray system controlled deposition exhibits better spatial resolution as compared to UP. A line width of 10 nm and pattern resolution of Ιμιη using a single exemplary electrospray system source have been demonstrated.

[0010] The electrospray device can deposit conductors and dielectrics (insulators) for planarization applications or (flexible or nonflexible) electronic production on substrates. Solar cells can be printed on both sides of flexible substrates. Groups of these electrospray devices can be grouped to separate lithium-containing salts from water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention is described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:

[0012] The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the detailed description, serve to explain the principles and implementations of the invention.

[0013] Figure 1 shows the major components of an electrospray apparatus in accordance with an exemplary embodiment.

[0014] Figure 2 shows a capillary tube with an electrospray emanating from a Taylor cone at the tip of the capillary tube.

[0015] Figure 4 is a schematic that shows the forces acting on the volume meniscus.

[0016] Figure 5 is a chart that shows the synchronization of the voltage applied to the injector for atomization to occur.

[0017] Figure 6 is a photograph that shows a typical distribution of the droplet diameter measured on the spray axis for pulsed electrospray using a Phase Doppler Anemometer (PDA).

[0018] Figure 7 is a chart that illustrates Maximum Current Calculations Based on Rayleigh Limit.

[0019] Figure 8 is a chart that shows the relationship between the predicted droplet diameter as a function of the liquid flow rate.

[0020] Figure 9 is a chart illustrating Driving Pressures Required for Conventional Spray Atomizers versus E-Field Atomizer (Electrospray).

[0021] Figure 10 is a schematic view of the exemplary electrospray system validation test set up.

[0022] Figures 11A and 11B are schematic representations of the topography of a non-uniform dielectric-coated silicon wafer (A) and desired uniform planarized silicon wafer (B).

[0023] Figures 12A and 12B are schematic representations of the topography of a coated silicon wafer (A) and the coating process as a function of silicon structure wall slope (B). [0024] Figure 13 is a schematic representation of the topography of the planarization problem.

[0025] Figures 14A and 14B are schematic representations of the topography of a non-uniform dielectric-coated silicon wafer with vias (A) and desired re-etched planarized silicon wafer (B).

[0026] Figures 15A and 15B are scanning electron micrographs of electrospray deposited of singular epoxy thin films for planarization.

[0027] Figure 16 is a scanning electron micrograph (SEM) of electrospray deposited smooth coating thin films for planarization.

[0028] Figure 17 is a scanning electron micrograph (SEM) of electrospray deposited coating thin films filling voids for planarization.

[0029] Figures 18A and 18B are schematics of Multiple Coaxial Needle Mixing including a side cross section view (A) and a bottom view (B).

[0030] Figure 19 is a scanning electron micrograph of electrospray deposited of multiple epoxy thin films for planarization.

[0031] Figure 20 is a scanning electron micrograph of an aperture through which electrospray droplets are passed.

[0032] Figure 21 is a scanning electron micrograph of thick film deposited after passing through aperture.

[0033] Figures 22A and 22B are scanning electron micrographs of Tetra Ethyl Ortho Silane (TEOS) deposited onto a substrate (A) a thickness measurement and (B) the rough surface is revealed. [0034] Figures 23A and 23B are scanning electron micrographs of Thermosetting Epoxy deposited onto a substrate (A) a thickness measurement and (B) the smooth surface is revealed.

[0035] Figure 24 is a scanning electron micrograph of Conductive Colloidal Carbon (Graphene) deposited onto a substrate.

[0036] Figures 25A and 25B are scanning electron micrographs of silver deposited onto a substrate (A) a thickness measurement and (B) the rough dendritic surface features are revealed.

[0037] Figure 26 is a photograph of a Ring Oscillator Printed Electronics on a Polymer Sheet that accommodates the Dielectrophoretic (DEP) Deposition of purified semiconductor carbon nanotubes to form a functional electronic circuit.

[0038] Figure 27 is a schematic of Ring Oscillator electronic circuit.

[0039] Figure 28 is a schematic of Multi- Junction Solar Cell.

[0040] Figure 29A is a scanning electron micrograph of an LED with incorporated catalyst and Figure 29B is a chart showing the spectra of the deposited materials of the LED.

[0041] Figure 30 is a schematic of a Microstructured Array Filter with Electrospray Enhanced Collection.

[0042] Figure 31 is a schematic showing separation of lithium from water satellites using Electrospray.

DETAILED DESCRIPTION

[0043] Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in different figures. The figures associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy.

[0044] In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of various implementations, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application and business related constraints, and that these specific goals vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a developments effort may be complex and time-consuming, but are nevertheless routine undertakings of engineering for those of ordinary skill in the art having the benefit of this disclosure.

[0045] Use of directional terms such as "upper," "lower," "above," "below", "in front of," "behind," etc. are intended to describe the positions and/or orientations of various components of the invention relative to one another as shown in the various Figures and are not intended to impose limitations on any position and/or orientation of any embodiment of the invention relative to any reference point external to the reference.

[0046] Those skilled in the art recognize that numerous modifications and changes may be made to the exemplary embodiments without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the preferred embodiment is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof.

EXEMPLARY ELECTROSPRAY SYSTEM

[0047] Fig. 1 shows an exemplary electrospray apparatus 100. The exemplary electrospray system 100 has a liquid reservoir 102 configured to hold a liquid 104. A pump 106 has an inlet connected to the liquid reservoir 102. A gas source 108 provides a gas to maintain a positive pressure on the liquid 104 in the liquid reservoir 102 to provide sufficient pressure and flow of the liquid 104 to the pump 106 inlet. In the exemplary embodiment, the pump 106 is a syringe pump driven by a linear motor, providing an accurate and steady flow rate from an output of the pump 106. However, in other embodiments, the pump 106 may be a different type of pump.

[0048] The outlet of the pump 106 connects to a capillary tube 110. The capillary tube 110 is conductive. In the exemplary embodiment, the capillary tube 110 comprises a dielectric material (such as glass) coated with a conducting material (such as metal), but in other embodiments may have other suitable construction, such as all metal construction. The capillary tube 110 has a capillary tube tip 112 which is open, allowing the liquid 104 to exit. In the exemplary embodiment, the capillary tube tip 112 is flat, but in other embodiments may be tapered or have some other suitable shape.

[0049] The exemplary electrospray system 100 includes a voltage source 114 connected to the capillary tube 110. The voltage source 114 is configured to generate a large potential difference between the capillary tube 110 and a ground electrode 120. When the pump 106 is providing liquid 104 to the capillary tube 110, an electric field generated by the potential difference between the capillary tube 110 and ground electrode 120 will cause the liquid 104 exiting the capillary tube tip 112 to form an electrospray 122. The electrospray 122 will comprise primary droplets 116 and satellite droplets 118.

[0050] The exemplary electrospray system 100 has a controller 124 connected to the voltage source 114 and the pump 106. The controller 124 is configured to control the flow rate of the pump 106 and configured to control the voltage source 114. In some embodiments, the controller 124 is absent and the pump 106 and voltage source 114 are controlled manually.

[0051] In some embodiments, the exemplary electrospray system 100 has an optical verification system 134. The optical verification system 134 measures the size and velocity of the particles in the electrospray 122.

PRINCIPLES OF OPERATION

[0052] The key innovations are based on the injection of the droplets and control of the atomization process with an electric field. The innovation was the specific approach to the use of ion liquid propulsion for injection of the droplets from the injection ports and dielectrophoretic (DEP) force acting on the liquid-gas interface for controlling the atomization and prevention of satellite droplets. Further, the electrostatically-charged droplets are maintained at the original size without coalescence for very efficient and controllable combustion. Both ion liquid propulsion and DEP control of the interface are accomplished using the same set of micromachined microinjectors and electrodes. The details of microinjector geometry and electrode orientation are provided in the following section and will be discussed in more depth later.

[0053] Ion drag pumping is not new and neither is the use of DEP force for manipulation of flow field and particle or droplet trajectories within the flow. The electric field induced pressure gradients for driving the flow can be written as seen in equation 1 : where ε is the dielectric permittivity of the fluid, p is the mass density, Q is the electric field space charge density, T is the temperature, and E is the applied electric field strength. The first term in the right hand side of equation (1) represents the force on the free charges present and gives rise to the so called Coulomb force, which is the primary driving force in most ion-drag pumps for pumping a liquid or gas in the single-phase mode. The second and third terms are the electrostrictive force and the dielectrophoretic (DEP) force and will be discussed in the following paragraph in more detail. The electrostrictive force does not play a significant role in the exemplary devices and methods discussed herein. In equation (1), Q is the space charge density and is defined as follows in equation 2:

Q = (2)

(u + μΈ)Α where, / is the current, ^u is the bulk fluid velocity, μ is the ion mobility, E is the field strength, and A is the flow cross-sectional area. In the simplest form for a laminar flow within a circular flow cross-section, one may derive a relationship between the pressure rise (Δρ) produced by the pump, the driving voltage and the pump geometrical parameters using the relationships suggested by Takashima et al. (1988) and Stuetzer (1960) for the bulk velocity dependence on the current and voltage as well as the relationship between voltage and current (see equation 3): where ^u is average droplet escape velocity in m/s, μ is the ion mobility in m ² /Volt-sec, and ε is the permittivity in C/volt-m. It turns out that to solve for velocity in terms of the applied electric field strength, the pressure gradient becomes almost similar to the famous equation for electrostatic precipitators.

[0054] DEP force exists when the following two conditions are simultaneously satisfied: (a) there is a gradient of the electric field strength, and (b) there is a change in the dielectric constant across the interface separating the two phases (Lee and McConnel, 1995; Andres, 1996). We have previously used this approach for separation of oil droplets from a refrigerant vapor (Birmingham, et al., 1999). The DEP force experienced by a droplet is calculated from the following equation 4:

VlEl ² (4)

k ₂ + _x where d is particle diameter, ε ₀ is dielectric constant in vacuum, k is the relative dielectric constant, and E is the electric field strength. K is 1 for air and approximately 2 for most other heavy liquid fuels. Therefore, there is a significant change in the dielectric constant giving rise to measurable force acting on the interfaces between these two fluids (i.e., air and liquid fuel). Previous investigators have examined the use of DEP force for spray atomization (Olumee et al., 1998; Chang et al, 1995). It is clear that if any external force is to be effectively used for formation of droplets, it should act near and on the liquid-air interface, at the point where the droplets are being formed. This process would prevent excessive pressure loss in the system as well as provides more local control on formation of droplets. The results indicate that using an E-field force for controlling atomization and suppression of satellite droplets by directly interacting with the liquid-gas interface converge.

[0055] Electrospraying has been shown to generate a very narrow size distribution of droplets. Based on the theory of electrohydrodynamics (EHD), the key to electrostatic spraying is the electric stress on the liquid interface. A strong enough electric field can produce instabilities in the interface resulting in breakup of the liquid jet issued out of the nozzle and emission of fine droplets from the jet. Hartman et al. (2000) has shown that the cone-jet mode can experience both kink and varicose instabilities very similar to a natural jet break-up or Rayleigh instability, depending on the ratio of the electric normal stress over the surface tension stress. As this ratio increases with increasing flow rate and electric stresses, the number of satellite droplets formed increases. In general, a bimodal distribution of the droplets is shown to exist while the satellite droplets are forced to the periphery of the spray (Hartman, et al., 1999).

[0056] The foundation of the exemplary devices and methods described herein is the precise control of electrospray using a tuned pulse voltage signal. There is a clear relationship between the volume of a drop available at the tip of an electrostatic injector and the minimum voltage required to spray the drop as shown in Fig. 3. Fig. 3 shows Threshold Voltage as a Function of the Volume of Fluid at the Tip of Capillary (Wittren, et al., 2003).

[0057] For a given amount of liquid accumulated at the tip of a capillary needle, the minimum voltage or threshold voltage corresponding to the breakup of the liquid meniscus was determined. For example, for a droplet of 0.4 μΐ, 4500 VDC is needed for atomization. For a given meniscus volume at the tip of the atomizer, the maximum voltage pulse amplitude has to exceed a critical amount for atomization to take place and for a given voltage, the drop volume cannot exceed a maximum volume for atomization to take place.

[0058] This phenomenon is easily explained through a force balance, where the surface tension force is the stabilizing force and the electric stresses are the destabilizing part of the equation. The forces acting on the volume meniscus are shown in Figure 4. As the volume of the droplet decreases, the surface tension acting on the liquid meniscus increases. Because of this increased surface tension, the electric field intensity acting on the drop has to be increased in order for atomization to occur. This approach to electrostatic atomization is very unique and the foundation of the current proposal. Our results and analysis show that by pulsing the electric field, spray-on-demand is possible.

[0059] This technique can also be easily applied for use in this application and one option for fluid delivery. Figure 5 shows the synchronization of the voltage applied to the injector (capillary tube) for atomization to occur. The voltage is first supplied to the capillary syringe (tube) which in turn forms a liquid meniscus at the tip of the injector (capillary tube). When the volume of liquid at the injector tip reaches the desired amount, a voltage pulse is sent to the injector (capillary tube) causing atomization. This timing circuit (controller 124) can be adjusted for various flow rates and/or various injection times for spray-on-demand applications.

[0060] Figure 5. Timing diagram showing that the voltage pulse supplied to injectors immediately follows the voltage pulse provided to the syringe (capillary tube).

[0061] The structure of pulsed electrospray has been explored to verify that pulsing the electric field does not affect the monodispersity of the electrospray. Figure 6 shows a typical distribution of the droplet diameter measured on the spray axis for pulsed electrospray using a Phase Doppler Anemometer (PDA) (Wittren et al., 2003). The spray can be considered monodispersed because of the narrowness of the size distribution. The droplet size was also measured as a function of radial coordinate with the origin at the capillary tip to determine size variance across the electrospray. Figure 6 shows the radial size distribution of the droplets across the jet measured in the near field of the cone-jet mode electrospray measured with a Phase Doppler Anemometer (Wittren et al., 2003). Note that the mean droplet diameter varies between 7.5 μιη to 9.0 μιη along the center of the jet for a continuous electrospray. This uniformity in droplet size is also a benefit to combustion because it increases the efficiency.

FABRICATION OF AN ELECTROSPRAY DEVICE

[0062] Fabricate an Electrospray System to Generate 5 nanometer and larger (around 150 micron) Diameter Monodispersed Droplets.

[0063] The electrospray capillary orifice or bore is typically two orders of magnitudes larger than the cone jet and the monodispersed droplet diameter. In order to establish the monodispersed submicron droplet generation, (glass, Teflon, or other dielectrics) capillaries were coated with a conductor. The tip of the capillary could be flat or an angle to produce the droplets. The capillary bore combined with the flow rate of fluid (head pressure) at the selected electrical conditions produced the desired droplet monodispersity and diameter.

[0064] Atomizer Design and Fabrication

[0065] Most of the atomization modeling, as discussed earlier is based on empirical correlations and results obtained by other investigators for electrospray. The critical parameters for design will be to evaluate the operating parameters that lead to the minimum amount of power for the given flow rates. [0066] For electrospray atomization to take place, the electrical relaxation time of the fluid has to be much shorter than the hydrodynamic transit time of the fluid flow. That is, the following inequality has to be satisfied (see equation 5):

(t _e ≡pe K) « (t _h ~ LIU) (5) where t _e is the electrical relaxation time of the fluid and th is the hydrodynamic time of the fluid flow, β, ε ₀ , and K are the relative permittivity, permittivity in vacuum, and electrical conductivity of the fluid, respectively, L is the axial characteristic length scale, and U is the characteristic jet velocity. Using this relationship, one is able to find the most appropriate combination of fluid property (conductivity), flow rate, and flow geometry. In fact, one of the outcomes of this relationship is that for a given fluid and nozzle, there is an upper limit to the flow rate of the liquid to ensure electrospray atomization. However, Equation 5 reveals that as the flow rate increases, the higher should the conductivity of the liquid be. For very low conductivity dielectrics such as hydrocarbon fuels, one can add trace amount of an additive such as Stadis 450 (DuPont) to increase the electrical conductivity without significant change in other properties. Further, the right choice of electrodes for spray may relax the criterion in Equation 5 to the point that even if the above criterion has not been met, electrospray can be obtained at high flow rates. This is essentially the thesis behind our research to identify the most practical engineering solution for application in gas turbines, diesel engines, and other heavy fuel operating engines, where the fuel flow rates are high. When using polar liquids with large dielectric constants (such as alcohol) or high viscosity non-polar liquids (such as liquid fuels), the current varies as shown below in equation 6: where / is the current (in Amperes), Q is the flow rate out of the nozzle (m /s), and γ is the surface tension of the fluid (in N/m). I ₀ is the dimensionless current and Q ₀ is the dimensionless flow rate as defined below in equation 7:

1 / 2

P (7)

[0067] The maximum charge on droplets, q _max , is set by the well-known Rayleigh Limit (RL) as described below in equation 8 (Rayleigh, 1882):

<7 _max = π(%ε ₀ γ<? (8)

The limit of the current leaving in form of charge on the droplets is then the product of the RL and the number density of droplets leaving the jet per unit time (flux) in equation 9:

Based on this equation, for spray of isopropanol into the air the following curve is expected, as shown in Figure 9. As it will become clear, the data that we obtained from experiments at 10 μΐ/s flow rate draws approximately 0.4 μΑ οί current, with droplets nearly 30 micron in diameter.

[0068] The above calculations will be integrated into fluid dynamics modeling to predict the sizes and percentages of the droplets to be produced and the power requirements (see Figure 7). [0069] Figure 7. Maximum Current Calculations Based on Rayleigh Limit

[0070] If this equation is combined with equation (2), a relationship between the flow rate and droplet size can be developed in equation 10.

-2 / 3

d 0.365{K/ _£o ) ^{1 / 2} { - l)- ^{1 / 4} Q- (10)

[0071] The following Figure 8 shows the relationship between the predicted droplet diameter as a function of the liquid flow rate.

[0072] The atomizer produces extremely small droplets (<10 micron) using very low driving pressure, as shown in Figure 9. While conventional atomizers required a significant pressure to atomize the liquid, the electrospray or e-field atomizer does not. It turns out the power requirements for electrospraying are less than 0.5 W for 1 ml/s of isopropanol sprayed.

[0073] Figure 9. Driving Pressures Required for Conventional Spray Atomizers versus E-Field Atomizer (Electrospray).

[0074] Fabricate a Verification System to Monitor Electrospray System to Generate Nanometer and larger Diameter Monodispersed Droplets.

[0075] The demonstration that electrospray generation of monodispersed droplet can be precisely deposited upon a substrate is possible. The verification setup is shown in Figure 10, below.

[0076] We fabricated an optical verification system 134 to characterize the droplet diameters, velocity, and composition (with an infrared laser system (Birmingham, US Patent April 2010). This enables every droplet to be analyzed before deposition onto a substrate and discarded if the composition is not accepted.

BACKGROUND OF ELECTROSPRAY APPLICATIONS INCLUDING PRECISE MIXING,

REACTION, DEPOSITION, AND COLLECTION

[0077] Background of Precise Mixing of Liquids to using Electrospray Process

[0078] The charge and size of the droplets can be controlled to some extent by adjusting the liquid flow rate and the voltage applied to the nozzle. Charged droplets are self-dispersing in the space due to mutual Coulomb repulsion that results in the absence of droplet agglomeration.

[0079] Reduction in drop size is a major driver in the precision micro-fluidic markets for both printing and precision dispensing applications. Drop placement accuracy and overall jet-to-jet uniformity

[0080] requirements are also expected to grow more stringent to improve quality and to allow the technology to expand into electronic materials deposition applications such as integrated circuit (IC) interconnects and display printing, ultimately leading to transistor or backplane applications. At the same time, increased printing speeds call for higher firing rates and greater overall uniformity over that operating range. MEMS processes, a set of processes developed out of the IC industry to "sculpt" and assemble IC sized electromechanical structures, offer fabrication materials and processes with suitable flexibility and capability to form the platform for a product family to meet these evolving market needs. Silicon-based MEMS processing began at Bell Laboratories in the mid 1980's. Since their introduction, MEMS devices have become the standard in a variety of high volume fields including automotive sensors.

[0081] Paint-mixing is an emerging application for electrospray precise mixing. Home Depot receives millions of dollars of returned custom paint due to the slight color variation upon mixing. For example, the variation of color is around 1% or approximately 10,000 ppm. The electrospray precise mixing can achieve nanodroplet accuracy or O.Olppm. Color variations of this slight variation are not discernible with the human eye.

[0082] Electrospray processes can enhance semiconductor deposition for planarization coating approaches.

[0083] Several methods used for thin layer deposition on a substrate:

• casting of a solution or colloid suspension on a substrate, followed by solvent evaporation,

• cathode spraying, applicable for metal layers preparation,

• condensation of vapors of a material on the substrate,

• radio-frequency sputtering,

• laser ablation,

• chemical vapor deposition,

• physical vapor deposition,

• microwave plasma coating,

• flame-assisted vapor deposition,

• electrodeposition of the layer by electrolysis, used for metals deposition, and electrospraying. [0084] Using conventional methods, large amounts of material is lost to the chamber walls when cathode spraying, chemical vapor deposition, or vapor condensation is used. When a solution or suspension of a material to be deposited is sprayed by mechanical atomizers, or simply poured onto a substrate, the layer is not sufficiently homogeneous and of the same thickness on the entire surface.

[0085] Electrospraying utilizes electrical forces for liquid atomization. Droplets obtained by this method

[0086] are highly charged to a fraction of the Rayleigh limit. The advantage of electrospraying is the droplets can be extremely small, down to the order of 5 nanometers, and the charge and size of the droplets can be controlled to some extent by electrical means. Motion of the charged droplets can be controlled by an electric field. The deposition efficiency of the charged spray on an object is usually higher than that for uncharged droplets. The motion of the charged droplets can be easily controlled (including deflection or focusing) by an electric field. The deposition of a charged spray or solid particles on an object can be more effective than for uncharged ones [Jaworek, 2001]. Electrospray is, or potentially can be applied, to planarization processes for semiconductor manufacturing.

[0087] Chip-producers described the problems with planarization of the silicon wafers. Planarization is the uneven surface topography created during each step in multilevel metallization of silicon wafers. The need is for an optically transparent and viscous dielectric to follow the contours of the silicon structures as shown in Figure 11. To this end, the dental epoxy (Easy Glaze) serves as a mask for the ion milling processes and the desire to deposit 1-10 microns uniform thickness. Different sections (from 3 by 3 mm to 3 by 3 cm) of the 300 mm silicon wafers [C4] need to be repaired. The focused ion beam (FIB) sample coating is used to protect the region of interest from ion beam damage and the coating can conform to the surface geometry of the surface without worrying about planarization. The objective of this project is to use coatings to reduce FIB time. Currently, the repairs are accomplished by a Joel ion beam etcher (IBE) milling the nonfunctional parts of the silicon chip. The IBE sample coating is usually utilized to planarize the surface of the sample. These small sections are placed on Die Level wafers for regional coating.

[0088] Figure 11. Schematic representation of the topography of a non-uniform dielectric-coated silicon wafer (left) and desired uniform planarized silicon wafer (right). [0089] Chip-makers desire to run some tests on different epoxies and composites for the coating of silicon wafers. They are interested in applying a smooth and even epoxy coating on samples that are about 10 by 10mm. Our thickness specification will probably range from 10-40μιη since most of these samples will go into the broad ion beam system. The smaller geometry samples that are prepared on the FIB systems will require a thickness from 0.1-3μιη. These samples will probably range in size from 12 microns by 12microns to 20 microns by 34 microns.

[0090] The objective is to create a monodispersed 1-5 micron and 10 nanometer diameter drops and place the drops uniformly onto a wafer surface. Several companies have asked to produce monodispersed droplets of various sizes using the technology. We have generated 4 nanometer to 150 micron diameter droplets using electrospray. As shown in Figure 12, the problem to be solved is the large aspect ratios of the silicon structures create steep sidewalls that are being coated instead of filling voids for satisfying conventional planarization approaches.

[0091] Figure 12. Schematic representation of the topography of a coated silicon wafer (top) and the coating process as a function of silicon structure wall slope (bottom).

[0092] The quality of thin film formed on a substrate strongly depends on the size of particles or droplets forming the layer, their monodispersity, and their uniform distribution on the surface. Smaller particles, of narrow size distribution, should be generated in order to reduce the number and size of voids, flaws and cracks in the film. The droplets need to be uniformly dispersed over the substrate ensuring the layer to be uniform and of the same thickness. The electrospray is a promising tool for production of high quality layers and films because it fulfills all these requirements (see Figure 13). The desirable characteristic of a planarization process is to fill the gaps while maintaining a uniform film thickness. This is only possible with a fluid seeping into the cracks without forming voids.

[0093] Figure 13. Schematic representation of the topography of the planarization problem.

[0094] Filling in vias (holes) or filling between copper bump pillars is another semiconductor manufacturing problem. Besides the silicon wafer repair for ion milling, the vias (or electrical feed-throughs as shown in Figure 14) need to be coated and uniformly re-etched. Currently, Intel is using copper (Cu) bumps and titanium (Ti) for their electronic metals. (Many chip- manufacturers have abandoned chemical-mechanical-polishing (CMP)).

[0095] Figure 14. Schematic representation of the topography of a non-uniform dielectric-coated silicon wafer with vias (left) and desired re-etched planarized silicon wafer (right).

SUMMARY OF RESULTS

[0096] By taking advantage of the electrospray monodispersed droplet production, finer film features such as line widths and patterns have been achieved. The planarization of electronics has been successfully demonstrated with targeted thin films. Flexible electronics production has been accomplished.

[0097] Results for Electrospray Processes can Enhance Semiconductor Deposition for Planarization Coating

[0098] For a given liquid, stable and monodisperse electrosprays can be established within certain ranges of liquid flow rates and applied voltages for a given cone-jet domain. The droplet size is found to be dependent on the liquid flow rate and the applied voltage. The electrostatic technique allows generating fine droplets in micro- and nanometer size range, with narrow size distribution. Electrostatic forces disperse the droplets homogeneously in the space between the nozzle and the substrate. Our electrospray process is also easy to control by adjusting liquid flow rate and the voltage applied to the nozzle, and it is less expensive in production of thin films than chemical or physical vapor deposition, or plasma spraying requiring high vacuum installations. The film thickness can be simply controlled by varying the concentration and flow rate of the precursor solution (see Figure 15).

[0099] Figure 15. Scanning electron micrograph of electrospray deposited of singular epoxy thin films for planarization.

[00100] The uniform film thickness produces the ideal planarization structure. However, the surface of the film should also be smooth without any peaks or valleys. These excellent coating results are found in Figure 16.

[00101] Figure 16. Scanning electron micrograph (SEM) of electrospray deposited smooth coating thin films for planarization.

[00102] The ability of the electrosprayed-dental epoxy to fill the voids of typical semiconductors is shown in Figure 17. The ability to deposit these films enables "chip editing" to design around defects.

[00103] Figure 17. Scanning electron micrograph (SEM) of electrospray deposited coating thin films filling voids for planarization.

[00104] Perhaps the most straightforward implication is drop sizes can be substantially reduced. This has implications within the printing market, but also has implications for the precision dispensing of electronic materials. Given the strength of the relationship between drop size and dimensions, drop sizes on the order of 10 femto-liters and corresponding line widths on the order of <15 nm should be possible through dimensional scaling. These line widths or larger features are appropriate for IC packaging application and printed circuit applications.

[00105] It should be noted that as the nozzle dimension decreases and the drop mass is reduced, the drop velocity will increase substantially. This combination is indeed a fortunate combination when viewed from the perspective of drop placement accuracy. Note that as drop velocity decreases, all other things being equal, the accuracy of drop placement goes down. Therefore it is desirable to maintain drop velocity. At small drop masses, the drop speed decreases more quickly as the drop moves away from the nozzle due to aerodynamic drag. Hence, without an attendant increase in velocity, a decrease in drop size leads either to small printing stand-off distances or to a less accurate jet. Here, we see that for uniform scaling, the increase in speed at lower drop mass is needed.

BACKGROUND OF COAXIAL MIXING ELECTROSPRAY PROCESS

[00106] The need for coaxial electrospray processes to produce rapid mixing of two epoxy components for deposition has been pioneered by our effort. Many researchers [Loscertales, 2002, Larsen, G.;2003, Man ^' n, A ^' . G.; 2007, Chen, X.; 2005,] have used coaxial electrosprays for encapsulation. However, by achieving nanoscale monodispersed droplet generation, the reaction rates for the "on-the-fly" production of mixed epoxies have produced uniform films for deposition on semiconductors. One would expect that the final morphologies of products are mainly affected by electrohydrodynamic parameters (electric field strength, flow rate) and properties of the jetting liquids (concentration, viscosity, conductivity, surface tension, et al), and all of parameters can be controlled with relative ease. These parameters also play similar roles in our experimental system. Besides these, however, the rational design of the compound nozzle is the key point for the successful fabrication of epoxy mixing with the novel planarization structure. To do this job, the outer shell liquid must surround and interact with each inner core fluid completely to form a mixed epoxy liquid. Therefore, each inner capillary should not contact with other inner capillaries. By this way, shell fluid flows through the gaps between inner capillaries and outer needle, ensuring a complete mixing of core fluids due to the enhanced mixing of nanoscale materials. If the inner capillaries made contact with each other, multiple inner fluids would get mixed, resulting in the premature mixing, causing a polymerization and blocking of the flow.

[00107] We have demonstrated a very facile and effective compound-fluidic electrospray technique to produce multi-component epoxies with a novel nanostructure in a single coaxial electrospray step (see Figure 18). Such nanoscale epoxies can promise not only to enlarge the functionality of a single entity by loading multiple ingredients simultaneously, but also can protect each of the ingredients from each other and from the environment, which is critical for the effective planarization of semiconductor material active ingredients, such as sensitive and reactive materials. The general technique could be readily extended to produce diverse mixed materials with many other functional materials. This multifunction, high efficiency technique may establish an avenue for a wide range of applications, such as a microreactor.

[00108] Figure 18. Schematic of Multiple Coaxial Needle Mixing including a Top View of Coaxial alignment of Electrospray ed Materials.

[00109] In an ideal method of preparation of semiconductor nanoparticles one should be able: 1) to control the average size of the particles; 2) to obtain a very narrow distribution of sizes; 3) to passivate the surface and eliminate surface states; and 4) to control the shape of the particles. One of the possible ways to solve these problems simultaneously is to restrict the reaction volume in which the particles are created. This has been done by using the multiple shell electrospray system for the deposition of reacting epoxy materials.

[00110] As shown in Figure 19, the mixing of epoxies (such as Futurabond) involved the comingling of two epoxies to produce a mixed epoxy deposition. The deposition of the mixed epoxy enabled better adhesion of the deposited film to the semiconductor surface. One of the two components mixed was an acid etch epoxy that provides a better surface for attachment. The objective was to deposit a film with a thickness around one micron.

[00111] Figure 19. Scanning electron micrograph of electrospray deposited of multiple epoxy thin films for planarization.

[00112] Results for Electrospray Through an Aperture to Deposit Films

[00113] One method for limiting the area where an electrospray film was deposited is to use an aperture to limit the area of the deposited film. An aperture off-set from the semiconductor surface can be used to pass the electrospray droplets through to create the deposited film on the semiconductor surface. An aperture of approximately 15 microns in diameter that was used for the successful deposition is shown in Figure 20. A pulse of gas is used to clear the aperture between electrospray uses.

[00114] Figure 20. Scanning electron micrograph of aperture through which electrospray droplets passed.

[00115] Any desired film thickness of insulator such as epoxy can be electrosprayed through the off-set aperture as shown in Figure 21.

[00116] Figure 21. Scanning electron micrograph of thick film deposited after passing through aperture.

[00117] Similarly, the demonstrations of the electrospraying of thin films including silane-bearing materials and thermosetting epoxies are shown in Figures 22 and 23 respectively. The bumpy surface can be made more uniform by electrospraying the TEOS directly onto the substrate. Also, epoxies that are cured by thermal processing can produce thin uniform films.

[00118] Figure 22. Tetra Ethyl Ortho Silane (TEOS) deposited onto a substrate (left) a thickness measurement and (right) the rough surface is revealed.

[00119] Figure 23. Thermosetting Epoxy deposited onto a substrate (left) a thickness measurement and (right) the smooth surface is revealed.

[00120] Approach for the Deposition of Insulators or Conductors for Planarization Coating

[00121] The production of flexible circuits composed of conductive and dielectric components is an electrohydrodynamic process. In the case of electrospray-driven or electrohydrodynamic (EHD) pumping and acceleration of the droplets, the fluids with higher dielectric constant will yield higher pumping power. The ions and dipoles movement under an electrical field resulting in liquid pumping has been investigated by many researchers (see Seyed-Yagoobi, et al., 1989a,b; Sato, 1991; Choi, 1995; Shekarriz, et al, 1999; and Ahn et al, 1997).

[00122] To create a versatile planarization coating that is also conductive, one could electrospray carbon to create an interconnecting matrix within the film deposited on the semiconductor surface. The addition of conductive carbon nanotubes [CNT] (SWeNT Inc.) or colloidal carbon Graphene enables the change of a dielectric insulator into a conductive material as shown in Figure 24. The carbon forms a conductive matrix that enables large voltages (as experienced with a Transmission Electron Microscope [TEM]) to be dispersed without creating micrograph luminescence points that obscure the desired image.

[00123] Figure 24. Conductive Colloidal Carbon (Graphene) deposited onto a substrate.

[00124] Conventional approaches to TEM involve the deposition of a silver film to enable a micrograph to be obtained. Silver solutions or colloids can be deposited upon a substrate to enable the obtaining of a TEM with the same luminescence-limiting property as shown in Figure 25. Therefore, dielectrics and conductors can be precisely placed with the desired thickness using the electrospray technique to not only provide planarization coatings, but consequently produce flexible printed circuits.

[00125] Figure 25. Silver deposited onto a substrate (left) a thickness measurement and (right) the rough dendritic surface features are revealed.

[00126] Approach for the Deposition of Insulators or Conductors to Produce Flexible Electronics Circuits.

[00127] We combined a dielectrophoretic (DEP) alignment in an electrospray process for carbon nanotube (CNT) deposition with printable electronics to create a ring oscillator as shown in Figure 26. A ring oscillator is an integrated circuit made up of transistors that together produce defined periodical electrical signals (e.g. blinking). In more complex circuits, these ring oscillators are often used as clock generators. The ring oscillator shown in Figure 26 was printed with silver nanoparticles and CNT in a solution and the device can print with segregated CNT according to function (e.g. conductive, n-type and p-type semiconductors) inks. With this printed ring oscillator prototype photographed below, coupled with the DEP purified, deposited, and aligned carbon nanotube (CNT), we are able to confirm that its integrated circuit is fully- functional.

[00128] The circuit itself (shown in Figure 26) is for a ring oscillator. The conductive traces were made from silver nanoparticle and CNT ink. Ink was deposited on the plastic substrate (HP LaserJet overhead transparency, similar to type C2934A) using an HP printer cartridge mounted on a precision XY-stage.

[00129] Figure 26. Photograph of Ring Oscillator Printed Electronics on a Polymer Sheet that accommodates the Dielectrophoretic (DEP) Deposition of purified semiconductor carbon nanotubes to form a functional electronic circuit.

[00130] A ring oscillator is a device composed of an odd number of gates whose output oscillates between two voltage levels as shown in Figure 27. The gates, or inverters, are attached in a chain; the output of the last inverter is fed back into the first. The feedback of this last output to the input causes oscillation.

[00131] Figure 27. Schematic of Ring Oscillator electronic circuit.

[00132] The significance of the ring oscillator fabricated on a printed integrated circuit (PIC) with functionally-segregated, purified, and DEP-deposited carbon nanotubes (CNT) demonstrates a complete electronic circuit made functional by the combined techniques. This breakthrough represents the first step to demonstrate the possibility of incorporating nanotubes into nanoelectronics and conventional printed circuit architectures. It also enables the detailed study of the performance-limiting aspects in carbon nanotubes and offers a way to evaluate their potential as a platform for future nanoelectronics technology.

PRINTABLE INTEGRATED CIRCUITS (PIC) FLEXIBLE ELECTRONICS

[00133] The term "printable electronics" refers to circuitry created out of polymer and conductive nanomaterial inks using printing technologies. Printable integrated circuit (PIC) electronics offers compelling advantages over more conventional ways of producing electronic circuits. These include the ability to cost effectively mass produce products that could never be created using the old semiconductor large cost paradigm. Ink-jet printing offers the potential to create specialized circuits in very small runs which will reduce prototyping costs. Lastly, printable electronics will also enable us to create new forms of PIC filter products embedded with intelligence (e.g. sensors) or other features that will enhance revenue possibilities. Using modest upfront investments, a smaller company can manufacture these PIC products. The electrospray printing of electronics, for example, may be the precursor of some of the digital manufacturing trends that will enable desktop manufacturing of various kinds. It is possible to imagine that having designed circuitry, it will be possible for an engineer to feed information from a file to the printer and have it print out a prototype as shown in Figure 28.

[00134] Production of an Electrosprayed Efficient Multi-junction Solar Cell

[00135] The advantage of this printed electronics approach is directly applicable to solar cells. The deposition of precisely mixed fluids (optically-interrogated and verified), along with the precise deposition onto flexible moving substrate surfaces has been demonstrated. Carbon nanotubes [CNT], Graphene, or other suitable conductive material can be deposited as transparent electrodes, combined with any n- or p-doped photovoltaic nanoparticles such as silicon, gallium arsenide (GaAs), copper indium gallium (di)selenide (CIGS), and especially (tailored quantum dots) mixed in a conducting matrix that can be optically interrogated for composition and precisely placed on a substrate surface. Quantum dots with tailored band gaps for capture of certain part of the solar spectrum is formulated in inks that can be precisely placed on a moving substrate surface that on the reverse side has printed rectifying antennas. This multi- junction solar cell (see Figure 29) with thermal recovery (rectennas and nanoparticle thermowells) can be printed, with an upper limit of efficiencies of this combination system of around 88%.

[00136] Figure 28. Schematic of Multi- Junction Solar Cell.

[00137] The objective of this design was to develop and demonstrate a novel solar cell design and manufacturing processes consistent with production of very low cost solar cells (<$0.08 per watt) that are lightweight, flexible, rugged, with greater than 60% power conversion efficiency and a 20-year lifetime, while keeping the nanocluster domains uniform in the proper atomic ratios, especially over large areas. In the photovoltaic [PV] sector, there is a need for high throughput low-cost processes because other common production methods (evaporation of the elements in vacuum; sputtering of the metals) suffer from relatively slow throughput, poor material utilization, and relatively high vacuum. Current solar cell technology is expensive, but for the home or business owner, the approximately $1 per watt cost is too high to compete with conventional grid power. Real energy costs can be substantially higher for the military, but high acquisition costs and difficult form factors still limit the adoption of solar technologies.

[00138] Organic solar cell technology, on the research level, has improved to the point where simple printed cells can have a power conversion efficiency of 6 percent, close to that of commercial amorphous silicon cells and at a level where there is commercial viability. The organic cells could potentially cost 80 percent less than cells with similar efficiency. To reach this production cost, manufacturing processes and cell designs need to be developed consistent both with large scale manufacturing and with the precision, cleanliness, and control necessary to obtain optimal cell performance. The challenges here push the state-of-the-art not only in demanding high performance from the active materials, but also in light trapping, electrode design, and barrier strategies, all of which must be consistent with low cost manufacturing on flexible substrates.

[00139] Production of an Electrosprayed Ultracapacitor

[00140] One objective of this technology is to fabricate nanometer thick films on a substrate. If this approach is successful, the paradigm of using microtechnology-established techniques to fabricate nanotechnology devices will be established. The ability to fabricate nanometer-size structures using microtechnology techniques was the initial focus of this electronics fabrication approach. The use of electrosprayed nanodroplets to form a uniform film thickness of only 2-3 Angstroms takes advantage of the repulsive forces imbedded in the aerogel layer design to maintain uniformity of the layers deposited while excluding the CNT. (Obviously, surfactants are not added to the formulation and the solution is not sonicated).

[00141] Example: Tetra-ethyl-ortho-silane (TEOS) was diluted into alcohol (either anhydrous ethanol or isopropanol) at a concentration in the range of 10-20%, and the reaction was acid catalyzed. The acid (dilute HC1, 1M) was added drop-wise to stirring TEOS/alcohol solution, and then was allowed to sit for a period of time to allow the polymerization of the silcates, between 24-48 hours. The sol-gel was then further diluted with alcohol and stored under refrigeration to slow any further polymerization. Before use, the sol-gel solution was diluted as necessary for the application method and coating thickness desired.

[00142] The curing temperature affects pore size. The sol-gels were cured around an upper limit of -200C. For the stainless steel micropillars, acid and base washes were used to prep the surface. An important nitric acid wash was followed by a hydroxide wash for surface preparation.

[00143] The placement of a single atom layer of conductor materials such as CNT followed by a single layer of electrosprayed dielectric materials on a substrate to form ultracapacitors is a novel approach. An ultracapacitor with high energy capacity and power density are needed for energy storage applications in electric vehicles and other electrical devices. Ultracapacitors lie between a battery and capacitor. Conventional batteries provide stored energy for extended periods of time, but have peak-power and cycling limitations. Because ultracapacitors move electrical charges between conducting materials, instead of chemical reactions, they maintain an ability to cycle far longer than batteries. The fabrication of a solid capacitor with electrosprayed angstrom- thick dielectric layers and conductor plates produces a capacitance that is hundreds of times greater than current capacitor technology.

[00144] In a manner similar to the printed circuit fabrication, electrosprayed dielectrics will be deposited to create CNT -thick metal layers separated by a dielectric layer. The advantages of the construction of a solid capacitor can be seen in equation 1 : a where C is the capacitance, k is the dielectric constant of 1000 for high dielectric strength insulator, So is the permittivity constant 8.9 xlO ¹² C ² /Nm ² , A is the area of the capacitor conductors of 0.01 m ² , and d is separation distance between conductors estimated to be 3 x 10 ^{" 10} m. The capacitance of the ultracapacitor is estimated to be 326,330 μΡ or 0.3 Farads [F]. Obviously, this ultracapacitor represents a major breakthrough in electronic components.

[00145] The energy stored is related to the charge at each interface, q (Coulombs), and potential difference, V (Volts), between the electrodes. The energy, E (Joules), stored in a capacitor with capacitance C (Farads) is given by the following equation 2.

(2)

2 2

[00146] Supercapacitors are simply capacitors employing plates with extremely high surface areas providing a high storage capacity. Maximizing the surface area of the electrodes within the available space means the thickness of the dielectric must be minimized. This in turn limits the maximum working voltage of the capacitor. For this reason, the planarization approach to repairing semiconductors is used to fill the voids of the high surface area electrodes with a high dielectric material that allows the high working voltage combined with a large capacitance. For supercapacitors with a capacitance of over 1000 Farads or more with a working voltage of over 10,000 volts establishes a new energy storage device.

[00147] Benefits of Proposed Printed Electronics Technology

[00148] The proposed system offers a number of advantages over the current and state-of-the-art technologies: The successful platform technology uses the development of printed integrated circuits (PIC) on flexible or durable substrates with DEP-deposition of functionally-segregated and purified carbon nanotubes (CNT) to form electronic circuits.

This electronics platform can be extended to include sensing elements to form biophysical sensors to monitor heart conditions and other opportunities in medical diagnostics, health monitoring, and rapid prototyping of printable integrated circuits (IC). Additional applications also include penetration of existing PIC markets (displays, miniature sensors, and RFIDs).

The printable electronics platform could be extended to air and other fluid media and create "smart" sampling/filters that reveal what hazards exist in the environment in rapid fashion. The opportunities in sensors (e.g. chemical, optical, RF, IR, acoustic) and integrated/embedded electronics (e.g. small UAVs, helmets, physiological status monitoring, blast dosimetry) are environmentally hardened and can be implemented on flexible and curved surfaces.

Printable solar cells enable high-efficiency low cost solar cells to be mass-produced.

[00149] Background of Electrospray Anodizing-like Process

[00150] Anodizing is an electrolytic passivation used to increase the thickness of the oxide layer on the surface of metal parts. The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than does bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light. Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic devices. Anodic films are most commonly applied to protect aluminum alloys, although processes also exist for titanium, zinc, magnesium, niobium, and tantalum. Iron or carbon steel metal exfoliates when oxidized under neutral or alkaline microelectrolytic conditions, (i.e., the iron oxide or rust) by anoxic anodic pits and large cathodic surface, these pits concentrate anions, such as sulfate and chloride, accelerating the underlying metal to corrosion. Anodization changes the microscopic texture of the surface and changes the crystal structure of the metal near the surface. Thick coatings are normally porous, so a sealing process is often needed to achieve corrosion resistance. Anodized aluminum surfaces, for example, are harder than aluminum but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle.

[00151] Due to the precise patterning, electrospray stiction "anodizing" is possible. Photo quality images and graphics in vivid color may be printed onto the unsealed porous oxide layer using color dyes via electrospray printing. Line art quality graphics can be achieved by use of a printer. Color graphics may also be directly applied. Printed anodizing is sealed to prevent or reduce dye bleed out and uses include baseball bats, signs, furniture, surgical trays, motorcycle components, military camouflage, and architectural molding.

[00152] Background of Electrospray Light-Emitting Diode (LED) with Band-Modified Catalyst for Air Treatment - Replace Phosphors [00153] When a light-emitting diode (LED) is switched on, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. LED's present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, and faster switching.

[00154] Our approach is to print LED's that emit UV and higher energy frequencies that can be directly coupled into band-modified titanium oxide to create an air purification device that can be placed inside refrigerators to control odors and delay ripening (see Figure 29).

[00155] Figure 29. (Left) SEM of LED with incorporated catalyst and (right) Spectra of deposited materials of LED.

BACKGROUND OF ELECTROSPRAY CHARGING OF LIQUIDS TO CAPTURE SUBMICRON

AND LARGER AEROSOLS

[00156] Charging process is an important step influencing the collection efficiency of dust. The well-known two important charging processes are field charging and diffusion charging. The field charging is known to be effective for the large particles. On the other hand, diffusion charging becomes dominant as the particle size decreases. The valley area where the two charging mechanism are weak is usually found around the particle size of 0.2 μιη. Several methods have been proposed and demonstrated to increase the collection efficiency of submicron particles. These methods include precharging, particle agglomeration and combination with other technology such as a bag filter, a cyclone and a scrubber. For the agglomeration of submicron particles into larger ones, alternating current (AC) corona or a dielectric-barrier discharge (DBD) has been implemented in front of an electrostatic precipitator (ESP) [Byeon 2006, Koizumi, 2000]. The application of electrically charged water droplets for the collection of aerosol particles charged to the opposite polarity has been proposed in the early 1940's [Penny, 1944]. Researchers investigated the use of electrospray in wet scrubber for dioctyl phthalate (DOP) aerosol and reported a collection efficiency increase from 68.8 % to 93.6 % [Pilat, 1975]. A very similar system, charged droplet scrubbing, was also reported for the removal of fine particles [Lear, 1975]. One of the important parameters in particulate scrubbers is the liquid/gas (QL QG) ratio. Typical QL QG ratio in the conventional scrubber ranges from 1 L/m ³ to 5 L/m ³ [Cooper, 2002]. On the other hand, the electrically assisted wet-scrubber is usually operated with the QL QG ratios of about 0.1 L/m ³ ~ 0.01 L/m ³ , which is one or two orders of magnitude less than the conventional scrubbing process [Lear, 1075]. An electrospray scrubber using a twin- fluid nozzle, being large in the QL/QG ratios at 1.8 L/m ³ , has also tested for the removal of oppositely charged particles [Schmidt, 1992]. Recently, the electrospray-based air purifier using water- ethanol mixture was successfully tested [Tepper, 2007].

[00157] The microstructured array platform can be adapted for a wide range of sampling and treatment applications from contaminated air and surfaces. The proposed approach is to use a recently patented invention (US Patent #6,110,247 Micromachined Impactor Pillars transferred to the inventor) described as micropillars that are electrospray-coated to capture particulate and adsorb the vapors. In this configuration, the coated microstructures are uniformly arranged impaction surfaces for efficient collection of particles without a large pressure drop. The micropillars are arranged in rows and are spaced apart from each other to form well-defined air passageways that retain the 1-10 micron diameter particles. (Electric fields are added to collect submicron (nanometer) particles due to their enhanced electrical mobility). When a particle- laden fluid stream flows through the micropillars, particles diffuse or impact and become deposited on the surfaces of the micropillars. The gas stream is deflected aside and flows around the micropillars leaving adsorbed vapors on specialized micropillar coatings. We have produced a microstructured array filter with electrospray enhanced collection to efficiently concentrate nanometer size diameter droplets and larger aerosols as shown in Figure 30.

[00158] Figure 30. Schematic of Microstructured Array Filter with Electrospray Enhanced Collection.

[00159] An electrospray has been used in conjunction with a microstructured array filter with electrostatic fields applied to enhance the collection efficiency of nanometer sized particles.

[00160] The major advantages can be summarized as follows:

Despite the small liquid/gas ratio, a visible influence of the electrospray on the particle collection was observed. The particle collection with the electrospray increased as the particle size decreases. On the other hand, collection efficiencies in the microstructured array filter increased with the particle size at higher applied voltages, but their difference was very small.

The electrospray of the deionized water produced nanometer or micrometer sized monodispersed droplets in a spray mode. The combined effect of nanometer droplet accumulation on the particles to enhance the collection efficiency became clearer as the particle size increased to 0.1 nm.

The possibility of reduction in energy consumption was also demonstrated by the combined system. Further enhancement may be possible by optimizing the operational parameters such as liquid/gas ratio, spray mode, polarity and the proper configuration.

THE SIMULTANEOUS EXTRACTION OF LITHIUM AND WATER FROM BRINE

[00161] Lithium production is critical for projected economic development in countries around the world. The uses of Lithium extend beyond batteries, and include both industrial and medical applications. Lithium sources can be found in various mined minerals around the world as well as brines that are the remnants of evaporated seas. This describes a novel process to simultaneously separate lithium and water from brine. The current and most wide spread process to produce lithium from brines is sun-driven evaporation. The proposed process uses electrospray to simultaneously separate lithium and water. This concurrent separation solves two problems endemic to the geographic production area:

1. Lithium Production is a valuable economic resource.

2. Water is a scarce resource in the brine lake areas.

[00162] The principal investigator has significant experience in the development of electrospray injectors and in innovative filtration technologies. This effort is an extension of our work in electrospray of low conductivity dielectric as well as high conductivity fluids. We discovered the electro-inertial separation (EIS) in our laboratory purely by accident when we observed separation of larger molecules and particles from the remainder of the seawater stream when the fluid was electrosprayed. While we consider this development as low risk, we believe that this is an enabling technology and the success in its development will offer a tremendous potential in commercialization of processes and products into a growing worldwide market, including third- world countries with tremendous economic burdens. We are very confident that this effort will yield high return on investments.

[00163] As seen in Figure 31, the separation of lithium and water is readily accomplished with the brine proceeding into the center and the water satellite droplets collected. Figure 31 is a schematic drawing that demonstrates how a simple electrically-driven device can separate lithium and water from brine. To make the process very efficient, multistage electrospray separation is combined with a microstructured array working in parallel to provide high separation efficiency at low pressure drops (high throughput). The production of clean water and lithium from seawater (brine) is an important advance:

1. The segregated droplet size can be selected to avoid drift (due to rapid Stokes Settling) and prevent lithium migration to (or contamination) of adjacent areas.

2. The separation continues as long as power is applied and stops when the power is terminated.

3. The charged lithium droplets immediately proceed to ground (in a fashion similar to charged paint deposition to a grounded object).

4. The satellite droplets produce clean water.

[00164] Figure 31. Separation of lithium from water satellites using Electrospray.

[00165] In conventional designs, the close placement into tight-fitting configurations of electrospray needles requires the placement of a suppressing electromagnetic field (extractor electrode) to enable the large scale processing of fluids to be accommodated by these devices. We have eliminated the extractor electrode by the selection of electrical conditions. For example, the electrospray processing of brine requires 1 kW of electrical power to produce 74 liters of water with approximately 0.07 kg of Lithium-bearing salts. As shown in Figure 31, the extractor electrode is eliminated.

[00166] Overall Design of the Water Production Device:

[00167] The overall design of the water production device (30 cm by 30 cm by 10 cm tall) has the following characteristics:

1. Can process water directly (electrospray brine separation) while extracting water.

2. Microstructured Array plates extract water.

3. These filters are regenerable and shown in Figure 32.

[00168] Figure 32. A large collection of Electrospray Devices can be integrated to Accommodate Large Industrially-Significant Fluid Flows with Electromagnetic suppression Field

[00169] This electrospray device can be integrated into architectural structures where the separation of brine can be combined with the production of clean water for buildings.