JP5543889B2 - Wiring forming method and wiring - Google Patents

Description

  The present invention relates to wiring.

Conventional wiring techniques that use metal wiring or high-purity impurity regions formed on a semiconductor substrate rely on semiconductor-based electronic devices. Wiring by current photolithography technology is extremely fine. This makes the semiconductor-based electronic device very compact. The manufacturing process of such a wiring goes through many processes such as film formation, resist application, exposure, development, etching, and peeling. For example, metals such as Al and Cu are formed on a semiconductor substrate by a physical vapor deposition technique such as sputtering or vapor deposition. Impurity ions such as B and P are implanted into the semiconductor substrate by an ion implantation technique to form a conductive portion. Amorphous silicon formed on the substrate by the chemical vapor deposition technique is transformed into polysilicon by annealing to form a wiring layer. Many of the layers and coatings formed as described above are patterned by an etching process such as reactive ion etching using a resist having a pattern determined by a photolithography process as a mask. Some vacuum levels are required, for example, about 10 ⁻⁶ Torr. Regardless of the vacuum level, installation and maintenance of equipment and the like are expensive. The material formed by such a process lacks flexibility due to inorganic properties. And since it is a high-temperature process, it cannot be used for plastic films.

  Larger wiring circuits are manufactured by methods that do not require expensive equipment or maintenance of manufacturing equipment. A printed wiring board is manufactured by etching a copper clad thin plate simultaneously with a printing technique. Printed boards include hard epoxy / glass laminates and soft polyimide laminates. As another manufacturing method, there is a method in which a conductive paste such as silver is directly printed on a substrate. These pastes use screen printing technology. Depending on the resolution, inkjet technology is used.

  These manufacturing methods are not expensive. However, a compact device such as a semiconductor device cannot be manufactured using this method. Furthermore, the wiring produced by these methods is not transparent. Therefore, the wiring made by these methods cannot be applied to those requiring transparent conductivity such as an electroluminescent display and a liquid crystal display.

  ITO (Indium Tin Oxide) is generally used as the transparent conductive film. When forming an ITO film using a printing technique, a suspension of ITO particles using a binder (polymer) is used. However, the ITO film produced by the printing technique has a higher resistance than the ITO film produced by the physical vapor deposition technique. Recently, transparent conductive polymer materials have been developed. Generally, a conductive property is imparted using a dopant, and the conductive conductive polymer material is applied onto a substrate by screen printing or ink jet technology. However, this technique has not yet achieved the same conductivity as that of the ITO film. In addition, the presence of the dopant is considered to have an adverse effect on the control of the conductive properties.

  The carbon nanotube is a tubular material having a diameter of 1 μm or less. An ideal carbon nanotube forms a tube with a carbon hexagonal mesh plane parallel to the tube axis. This tube may be multiple. The carbon nanotubes are theoretically expected to exhibit metallic (conductive) or semiconducting properties depending on how the hexagonal network made of carbon is connected and the thickness of the tube. And it is expected as a future functional material. For these reasons, application as a transparent conductive film is also thriving. However, the thickness and direction are random depending on the structure and manufacturing method of the carbon nanotube. At the time of use, it is necessary to purify after the synthesis and to process according to the form of use.

  Patent Document 1 discloses a method of forming wiring using carbon nanotubes that are also expected as a transparent conductive film. For example, a carbon nanotube dispersion is applied to the entire surface of the substrate to form a carbon nanotube film, and a binder solution is applied to the carbon nanotube film in accordance with a predetermined pattern. Examples of the application method include screen printing, ink jet printing, and gravure printing. Then, by drying the solvent, the binder remains in the carbon nanotube film, strengthening the carbon nanotube network. Thereafter, washing is performed with a solvent that does not dissolve the binder. Thereby, the part which is not strengthened by the binder is easily removed from the substrate. The portion reinforced with the binder remains on the substrate, and the wiring is formed. Alternatively, a photoresist is applied over the carbon nanotube coating and the carbon nanotube network is impregnated with the photoresist. Thereafter, a photolithography technique is used to form a wiring. This technique using a photoresist can provide finer pattern wiring than the former method of patterning a binder. Moreover, it can be applied to a silicon-based device manufacturing method. As yet another method, a carbon nanotube film (wiring) patterned beforehand may be directly formed on the substrate by screen printing, ink jet printing, or gravure printing. The wiring may be formed by combining these two or more methods. For example, the gate lines and associated gate electrodes of the switching transistors of the electroluminescent display device may be formed by a photolithography process of a photoresist impregnated with carbon nanotubes. Thereafter, the anode electrode of the electroluminescent element of the display device may be formed by screen printing a carbon nanotube solution on the device intermediate having the gate line and the gate electrode formed thereon.

JP-T-2006-513557

  By the way, a method of patterning carbon nanotubes, for example, a method of forming various types of patterning after forming a carbon nanotube film on the entire surface of the substrate requires removal of unnecessary portions of the carbon nanotube film. Therefore, waste occurs. In addition, the process is complicated.

  Therefore, it is preferable to directly form a carbon nanotube film patterned beforehand by a coating method such as screen printing, inkjet printing, or gravure printing. However, in order to do so, it is necessary to adjust the carbon nanotube dispersion liquid to have ink properties suitable for the coating method used. In general, the carbon nanotube dispersion liquid is adjusted by a dispersant such as a surfactant. The carbon nanotube dispersion liquid has a relatively low viscosity. By the way, in order to match with the coating method, a viscosity adjusting agent and a surface tension adjusting agent are required. However, when these additives are used, the dispersibility of carbon nanotubes generally deteriorates. Therefore, it is actually not easy to directly form a carbon nanotube film that has been patterned in advance by a coating method such as screen printing, ink jet printing, or gravure printing. In other words, it is not easy to form wiring with carbon nanotubes.

  Therefore, the problem to be solved by the present invention is to provide a technique capable of easily forming a wiring made of carbon nanotubes. In particular, it is to provide a technology that can form high-definition wiring easily and with high productivity using carbon nanotubes.

The above issues are
A wiring formation method comprising:
The invention is solved by a wiring forming method comprising a step of forming a wiring by spraying a carbon nanotube-containing aerosol.

In particular, a wiring formation method,
The aerosol jet process includes an aerosol jet process in which the carbon nanotube-containing dispersion is sprayed on the substrate in a wiring pattern by an aerosol jet means,
The wiring is formed by the aerosol jet process, which is solved by the wiring forming method.

  Alternatively, in the wiring forming method, an aerosol jet process in which an aerosol containing a conductive substance other than carbon nanotubes is sprayed on a substrate in a wiring pattern by aerosol jet means together with or differently from the carbon nanotube-containing aerosol. It is solved by the wiring forming method characterized by comprising.

  Alternatively, the wiring forming method is characterized by comprising an aerosol jet process in which the binder-containing aerosol is sprayed onto the substrate together with or differently from the carbon nanotube-containing aerosol by aerosol jet means. Solved by.

  Alternatively, it is solved by the wiring forming method, wherein the aerosol jet process is controlled so that the carbon nanotube density is constant or fluctuates.

  The above-described problem is solved by a wiring formed by performing the above-described wiring forming method.

  According to the present invention, the wiring is formed by spraying the carbon nanotube dispersion liquid in a predetermined wiring pattern directly by the aerosol jet means. Therefore, the material utilization efficiency is high. That is, there is little waste.

  The ink (paint: aerosol constituting ink) used for the aerosol jet means has few restrictions on the physical properties. That is, there are few restrictions on the characteristics required for ink as compared with the ink (paint) required in the case of a coating method such as screen printing, ink jet printing, or gravure printing. This means that less additive is added to the carbon nanotube dispersion. Therefore, since there is little addition of an additive, there is little fear of a fall of physical properties, such as electroconductivity.

  When using an aerosol jet means, it is easy to aerosolize carbon nanotubes and materials other than carbon nanotubes separately and mix them in the aerosol state. Therefore, the combined use of carbon nanotubes and materials other than carbon nanotubes is easy. This is very advantageous for wiring formation.

  Drying speed is fast because it is sprayed with aerosol. It can be said that the film formation is almost completed at the time of deposition. This makes it easy to control the thickness of the wiring. For example, it is advantageous for forming electrodes and wirings. For example, continuous formation is possible.

  The obtained wiring is precise and has high resolution. And productivity is high.

Wiring diagram using carbon nanotubes Schematic structure diagram of carbon nanotube in wiring Schematic structure diagram of (carbon nanotube + conductive material) in wiring Schematic structure diagram of (carbon nanotube + binder) in wiring

  The first invention is a wiring forming method. In particular, it is a wiring formation method using carbon nanotubes utilizing an aerosol jet method. In the present invention, the wiring is, for example, a line connecting electrodes (or terminals). Or it may be an electrode (or terminal). It may include both. Either is fine. The method includes a step of forming wiring by spraying an aerosol containing carbon nanotubes. In particular, an aerosol jet process is provided in which the carbon nanotube-containing dispersion liquid is sprayed on the substrate in an aerosol state with a wiring pattern by an aerosol jet means. Wiring is formed by this aerosol jet process. That is, the wiring of the target pattern is formed by spraying the carbon nanotube-containing dispersion liquid on the substrate in the aerosol state by the aerosol jet means. As the aerosol jet means, for example, Maskless Mesoscale Material Deposition M3D (trademark) apparatus manufactured by Optomec can be used. The basic technical idea of this apparatus is also disclosed in, for example, US Pat. No. 7,045,015.

  In some cases, there is provided an aerosol jet process in which an aerosol containing a conductive substance other than carbon nanotubes is sprayed onto the substrate in a wiring pattern by aerosol jet means together with or differently from the carbon nanotube-containing aerosol. For example, when a conductive material such as Ag or Cu is used together with a carbon nanotube to form a wiring, first, each aerosol is formed. Then, the carbon nanotube aerosol and a conductive substance aerosol such as Ag and Cu formed separately from the carbon nanotube aerosol are mixed in an aerosol state. If this mixed aerosol is sprayed, there is no need to prepare a mixed dispersion of carbon nanotubes and conductive materials such as Ag and Cu. The mixed dispersion is difficult to adjust as much as the amount of components is increased, whereas the single component dispersion is easy to adjust the components and is simpler. That is, there are few restrictions for adjusting each dispersion liquid for forming each aerosol, and it is easy. As the conductive material, in addition to Ag and Cu, for example, Al, Sb, Be, Cd, Cr, Co, Au, Ti, Zn, iron, steel, or alloys thereof, doped metal oxides, PEDOT / PSS, carbon black, etc. are mentioned. Of course, it is not limited to these.

  The above method is also applied to a binder used for enhancing the durability of the wiring. That is, it preferably includes an aerosol jet process in which the binder-containing aerosol is sprayed onto the substrate together with or differently from the carbon nanotube-containing aerosol by aerosol jet means. For example, each of the aerosols is formed. Then, the carbon nanotube aerosol and the binder aerosol are mixed in an aerosol state. Spray this mixed aerosol. This eliminates the need to prepare a mixed dispersion of carbon nanotubes and binder. This is very convenient.

  In the aerosol jet process, the carbon nanotube density is controlled to be constant or variable depending on the case. For example, the aerosol jet process is controlled so that the carbon nanotube density in the electrode portion and the carbon nanotube density in the wiring portion are different. Incidentally, if the carbon nanotube density in the wiring portion is controlled so as to be low, the semiconductor characteristics are exhibited at this point.

  A second invention is a wiring formed by carrying out the wiring forming method.

  Hereinafter, description will be given with reference to the drawings.

  FIG. 1 is a wiring diagram of carbon nanotubes produced by carrying out the method of the present invention. The wiring structure includes an electrode 1, a wiring 2 made of carbon nanotubes, and a substrate 3.

  The electrode 1 serves to pass a current through the wiring 2 and to interconnect with another wiring 2. This electrode may be a transparent electrode or an opaque electrode. The constituent material is a metal material. Alternatively, a conductive polymer material or a carbon material may be used. Note that the metal material generally has high electrical conductivity. Therefore, it is preferable to be comprised with a metal material. Examples thereof include Li, Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Ag, Au, Cu, Ni, Pr, Pt, Cr, Mo, W, Mn, Ni, and Co. These alloys are also mentioned. Of course, it is not limited to these. In addition, Au, Ag, and Cu are particularly preferable from the viewpoint of high conductivity and chemical inertness. Alternatively, carbon nanotubes can be used. When using carbon nanotubes, the method of the present invention is preferably employed.

  The wiring 2 is composed of carbon nanotubes. In particular, it is constituted by the implementation of the method of the invention. The specific structure of the wiring 2 formed in this way is shown in FIGS. The carbon nanotubes constructed by carrying out this method have a structure intertwined in a network. In this network structure, since the carbon nanotube-containing dispersion is sprayed by the aerosol jet means, the entanglement reliability is very high. Because of this network structure, the conductivity is reliable and high. Whether the carbon nanotubes are intertwined can be confirmed by observing with a scanning electron microscope.

  The wiring 2 is composed of carbon nanotubes. Any carbon nanotube can be used as long as it is a carbon nanotube. However, at least 50% or more is preferably a single-wall carbon nanotube (SWCNT) carbon nanotube. The carbon nanotubes are preferably those in which carbon nanotubes are intertwined from the viewpoint of conductivity. That is, if the carbon nanotubes are intertwined, the conductivity is improved. In the present invention, since the aerosol jet means is employed, the entanglement between the carbon nanotubes is promoted due to the spraying by the aerosol jet means.

  The manufacturing method of the SWCNT is not limited. For example, it can be produced using a production method such as an arc discharge method, a chemical vapor phase method, or a laser evaporation method. However, SWCNT obtained by the arc discharge method is preferable from the viewpoint of crystallinity. This is easily available.

  The carbon nanotube is preferably a carbon nanotube subjected to acid treatment. Acid treatment is to bring an acidic liquid into contact with carbon nanotubes. For example, it is the process which immerses SWCNT in an acidic liquid. Or it is the process which sprays acidic liquid on SWCNT. There are no particular restrictions on the acidic liquid used. An inorganic acid or an organic acid can be used as appropriate. Specific examples include nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and mixtures thereof. Nitric acid or a mixed solution of nitric acid and sulfuric acid is preferable. And as for the conditions of an acid treatment, it is preferable that temperature is 80 to 100 degreeC, and it is preferable that time is 1 day-7 days. When SWCNT and carbon fine particles are physically bonded via amorphous carbon by such acid treatment, they are separated by decomposition of amorphous carbon. In addition, the fine particles of the metal catalyst used at the time of SWCNT preparation are decomposed. As a result, the conductivity is improved. That is, when the acid treatment is compared with the case where the acid treatment is not performed, the former has improved conductivity.

  The carbon nanotubes are preferably filtered. That is, the impurities are removed by filtration, the purity is improved, and the decrease in conductivity and the decrease in light transmittance can be prevented. There is no particular limitation on the filtration method. For example, suction filtration, pressure filtration, cross flow filtration, or the like can be used. However, cross-flow filtration using a hollow fiber membrane is preferable from the viewpoint of scale-up.

  The carbon nanotube dispersion used in this method preferably also contains fullerenes (including fullerene analogues). This is because the durability is improved as compared with the conductive film containing no fullerene. Any fullerene may be used. For example, C60, C70, C76, C78, C82, C84, C90, C96 etc. are mentioned. Of course, a mixture of these fullerenes may be used. C60 is particularly preferable from the viewpoint of dispersion performance. Furthermore, C60 is easy to obtain. Further, not only C60 but also a mixture of C60 and another kind of fullerene (for example, C70) may be used. Further, metal atoms may be appropriately included in the fullerene. The analogs include those having a known functional group such as hydroxyl group, epoxy group, ester group, amide group, sulfonyl group, ether group, phenyl-C61-propyl acid alkyl ester, phenyl-C61-butyric acid alkyl ester. And hydrogenated fullerene. Among these, those having an OH group (hydroxyl group) are particularly preferable. This is because the dispersibility is high. In addition, when there is little quantity of a hydroxyl group, a dispersibility improvement degree will fall. On the other hand, if too much, synthesis is difficult. Accordingly, the amount of hydroxyl groups is preferably 5 to 30 per molecule of fullerene. In particular, 8 to 15 is preferable. If the amount of fullerene added is too large, the conductivity is lowered. On the other hand, if the amount is too small, the effect is difficult to occur. Therefore, the amount of fullerene is preferably 10 to 1000 parts by mass with respect to 100 parts by mass of the carbon nanotubes. In particular, the amount is preferably 20 to 500 parts by mass with respect to 100 parts by mass of the carbon nanotube.

  The ink used in this method contains a solvent in addition to the carbon nanotubes. There are no particular restrictions on the solvent. However, a solvent having a boiling point of 200 ° C. or lower (preferably lower limit is 25 ° C., further 30 ° C.) is preferable. The low boiling point solvent is preferable because it is easy to dry after coating. Specifically, water, alcohol compounds such as methanol, ethanol, normal propanol, and isopropanol (particularly alcohols having 7 or less carbon atoms, especially aliphatic alcohols), or a mixture thereof are preferable. This is because the hydroxyl group-containing fullerene has high solubility, and a carbon nanotube dispersion with a higher concentration can be obtained. And in the case of water, since the solvent (volatile component) process after application | coating is unnecessary, it is especially preferable. In addition, for example, ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ester compounds such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, methoxyethyl acetate, diethyl ether, ethylene glycol dimethyl ether, Ethyl cellosolve, butyl cellosolve, phenyl cellosolve, ether compounds such as dioxane, aromatic compounds such as toluene and xylene, aliphatic compounds such as pentane and hexane, halogenated hydrocarbons such as methylene chloride, chlorobenzene and chloroform, and mixtures thereof Can also be used. When the dispersibility of the carbon nanotube is inferior, it is preferable to perform ultrasonic irradiation because the dispersibility increases.

FIG. 2 shows a case where the wiring is composed of carbon nanotubes, whereas FIG. 3 shows a case where the wiring is composed of carbon nanotubes and a conductive material. In FIG.
The conductive material is indicated by reference numeral 4. This is formed as follows. First, a carbon nanotube aerosol is produced from a dispersion of carbon nanotubes. Also, a conductive substance aerosol is produced from the dispersion liquid of the conductive substance. After each aerosol is made, both are mixed. This mixed aerosol is ejected from the nozzle. Thereby, the wiring as shown in FIG. 3 is formed.

  2 and 3 do not use a binder for fixing and protecting the wiring, while FIG. 4 shows a case where the binder 5 is used. This is formed as follows. First, a carbon nanotube aerosol is produced from a dispersion of carbon nanotubes. If necessary, a conductive substance aerosol is prepared from a dispersion of the conductive substance. Furthermore, a binder aerosol is produced from the binder solution. After each aerosol is made, the carbon nanotube aerosol and the binder aerosol are mixed. In some cases, a conductive substance aerosol is also mixed. This mixed aerosol is ejected from the nozzle. As a result, a wiring as shown in FIG. 4 is formed. Resin is used as the binder. For example, a thermoplastic resin, a thermosetting resin, an elastomer, etc. are mentioned. Specific examples include polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, polyimide, polycarbonate, polyethylene terephthalate, cellulose, gelatin, chitin, polypeptide, polysaccharide, and polynucleotide. In addition, silicon-based resins are also included. A mixture of these may also be used. Furthermore, ceramic hybrid polymers, phosphine oxides and chalcogenides may be used. Of course, it is not limited to these.

  If an aerosol jet device is used, the ink is first aerosolized by an atomizer, and the nozzle is sprayed to make it go out spirally. Even a line-like wiring can be easily formed with high resolution. it can. If an aerosol jet device of a type in which two or more atomizers are connected is used, separately aerosolized materials are mixed in the nozzle, and the mixed aerosol is ejected from the nozzle. Therefore, the wiring of the type shown in FIGS. 3 and 4 can be easily formed. Since separately prepared inks can be used, that is, mixing is not in the ink state but in the aerosol state, so that inconvenience such as agglomeration during ink hardly occurs. Moreover, even if the composition is such that it is cross-linked over time when mixed during ink, there is no need to worry about pot life. In addition, generally the distance between the nozzle of an aerosol jet apparatus and a board | substrate is about 1-5 mm. The nozzle diameter is not particularly limited. In the case of forming fine wiring, it is about 100 to 300 μm, for example.

  The substrate 3 may be made of any material as long as the electrode 1 and the wiring 2 can be formed. Specifically, it is made of resin. Examples of the resin include polystyrene (PS), polymethyl methacrylate (PMMA), styrene-methyl methacrylate copolymer (MS), polycarbonate (PC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET). ), Polyethylene naphthalate (PEN). Of course, it is not limited to these. You may comprise with insulating materials, such as glass and a ceramic. When forming the wiring according to the present invention, it is not necessary to use a high temperature atmosphere. Therefore, the application of the present invention is advantageous in the case of a resin substrate having low heat resistance.

  Hereinafter, the present invention will be described with specific examples. However, the present invention is not limited by the following examples. The conductivity was relatively evaluated using a tester.

[Example 1]
Commercially available single wall carbon nanotubes (SWCNT) were purified. That is, purification was performed by steps such as acid treatment, water washing, centrifugation, and filtration. A 0.02% surfactant (TritonX-100 (manufactured by GE Healthcare)) aqueous solution was added to the purified carbon nanotube solution. And the ultrasonic wave was irradiated with the chip | tip type | mold ultrasonic device. As a result, a 1000 ppm carbon nanotube dispersion was obtained.
This carbon nanotube dispersion was supplied to an aerosol jet device manufactured by Optomec, USA, and the carbon nanotube aerosol was jetted from a nozzle. As a result, a 2 mm square electrode part and a 20 μm wide wiring connected thereto were formed on PET film A4100 (manufactured by Toyobo) (see FIG. 1).
Thereafter, in order to remove the surfactant, washing with methanol was performed. Then, drying at 100 ° C. was performed.
When the conductivity of the obtained wiring was examined, it was good.

[Example 2]
The same operation as in Example 1 was performed except that a 2.5 mM silver nitrate aqueous solution was supplied to the aerosol jet apparatus of Example 1. That is, the carbon nanotube aerosol and the silver nitrate aerosol were separately produced, and the separately produced aerosols were mixed and ejected from a nozzle to form a wiring.
As a result of investigating the conductivity of the obtained wiring, the wiring had Ag, and thus the conductivity of Example 1 or higher was shown.

[Example 3]
The same procedure as in Example 1 was performed except that 3.8 wt% of Aerocera (a binder manufactured by Panasonic Electric Works: a silicon resin containing hollow silica) was supplied to the aerosol jet apparatus of Example 1. That is, the carbon nanotube aerosol and the binder aerosol were separately produced, and the separately produced aerosols were mixed and ejected from a nozzle to form a wiring.
When the conductivity of the obtained wiring was examined, the conductivity equivalent to that of the carbon nanotube of Example 1 was shown.

[Example 4]
The carbon nanotube dispersion liquid of Example 1 was supplied to an aerosol jet apparatus manufactured by Optomec, USA, and the carbon nanotube aerosol was sprayed onto a silicon substrate with a 300 nm thermal oxide film. The aerosol was sprayed at a location corresponding to the 200 μm square electrode so that the carbon nanotubes had a high density. Aerosol was sprayed at a location corresponding to a location (20 μm wide wiring portion) connected to the electrode portion so that the carbon nanotubes had a low density.
Thereafter, in order to remove the surfactant, washing with methanol was performed. Then, drying at 100 ° C. was performed.
When the transistor characteristics of the obtained wiring were evaluated, good semiconductor characteristics were shown at wiring locations where the carbon nanotubes were low density.

1 Electrode 2 Wiring 3 Substrate 4 Conductive substance 5 Binder

Claims (4)

A method of forming a wiring composed of carbon nanotubes ,
The aerosol jet means, an aerosol of the carbon nanotube-containing dispersion, without a mask, on a substrate, comprising the aerosol jet process blown in a pattern of lines,
A wiring forming method, wherein the wiring is formed by the aerosol jet process. It is characterized by comprising an aerosol jet process in which an aerosol containing conductive material other than carbon nanotubes is sprayed on a substrate in a pattern of wiring with or different from the aerosol containing carbon nanotubes by an aerosol jet means without a mask. The wiring forming method according to claim 1. The wiring according to claim 1 or 2 , further comprising an aerosol jet process in which the binder-containing aerosol is sprayed onto the substrate without a mask by aerosol jet means, together with or different from the carbon nanotube-containing aerosol. Forming method. It claims 1 to 3 or of a wiring forming method characterized by carbon nanotube density aerosol jet process to constant or variations are controlled.

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