METHOD TO PRINT ORGANIC ELECTRONICS WITHOUT CHANGING ITS PROPERTIES

Abstract

Method for high throughput, highly reproducible, direct write plasma jet deposition of organic electronic materials through nozzles containing non-concentric tubes with inner tube having higher dielectric constant and/or higher wall thickness than the outer tube, so that the inner tube containing the aerosol of organic electronic materials is shielded from the outer tube containing plasma and the organic electronics is focused at the outlet of the nozzle through the after-glow region of the atmospheric pressure plasma. Ensuring reproducibility of the method for printing organic electronic materials by removing the contaminants and residues in inner tube using reactive gas and generating a plasma discharge at a potential significantly higher than the operating potential for printing so that the plasma is generated in both the inner and outer tube for dielectric barrier discharge plasma jet based cleaning of the nozzle.

Claims

1. A plasma jet printer for high throughput direct write printing of conducting electronic materials without changing its material properties, comprising: a nozzle with two non-concentric tubes, with inner tube having different thickness and/or higher dielectric constant than then outer tube; a inner tube with higher thickness and/or higher dielectric constant for carrying aerosol of electronic materials and for shielding the aerosol from getting exposed to high energy plasma species surrounded in the outer tube; a outer tube with lower thickness and/or dielectric constant than the inner tube and that carries a gas for creating a plasma discharge inside the outer tube; a inner and outer tube having different axis along the length of the tube; a outer tube with the outer walls in conical shape to create a high pressure and turbulence at the outlet of the nozzle; a electrode assembly on the outer nozzle connected to a high voltage power supply for creating a plasma discharge to be confined between the outer wall of the inner tube and the inner wall of the outer tube; a nebulizer for generating the aerosol of organic electronic materials; a tube for transporting the aerosol containing organic electronic materials to the inner tube of the nozzle; a tube for carrying gas through the outer nozzle for generating plasma discharge; a nozzle outlet where the aerosol containing organic electronics enters the after-glow discharge of the plasma for directing the organic electronic materials to the substrate; wherein the after-glow region of the plasma discharge from the nozzle has the ability to direct and print the electronic materials without changing the chemical structure and bonding nature of the organic materials due to plasma; wherein the reproducibility of organic electronic materials printing is ensured by reactive plasma jet cleaning of the inner nozzle by passing reactive gases and generating a plasma at significantly higher potential than the operating potential for printing so that the dielectric barrier discharge plasma is generated both in the inner and outer tubes that remove the residues and contaminants formed during deposition.

2. A device according to claim 1, wherein the organic electronic materials used for deposition can be used any of the following cathode materials, anode materials, electron injection layer, electron transporting layer, exciton/hole blocking layer, emissive layer, exciton/electron blocking layer, hole transporting layer, hole injection layer and anode material.

3. A device according to claim 1, wherein the reproducibility of the organic electronic material printing can be sustained by cleaning of the inner tube and the nozzle using plasma jet cleaning wherein the reactive gases can be fed during cleaning process with significantly higher applied potential than that used for printing so that the plasma discharge is created both in the inner tube and in the outer tube that helps remove the contaminants and residues attached to the inner wall of the inner tube during printing.

4. A device according to claim 1, wherein the plasma jet printer nozzle can be used for printing organic electronics by exposing the aerosol containing organic materials only to the after-glow region outside the nozzle and shielding from the outer tube containing plasma species by operating at a lower applied potential and the cleaning of the nozzle is carried out by generating plasma in both the inner and outer tube by operating at a significantly higher potential.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows a schematic of the plasma jet printer nozzle according to an embodiment of the invention containing non-concentric tubes with inner tube having a higher dielectric constant or wall thickness higher than the outer tube and with the outer tube having a conical shaped wall focused towards the nozzle outlet such that the gas in the outer tube undergoes turbulence and creates high pressure at the nozzle that drives the gas with high pressure and increased after-glow region.

[0043] FIG. 2 shows a schematic of the plasma jet printer nozzle according to an embodiment of the invention containing two non-concentric tubes with the inner tube inclined at an angle above 0.1 degree and up to 45 degrees with provisions for the addition of various process gases through the sides of the outer nozzle. Various process gases including helium, argon, hydrogen, nitrogen, carbon dioxide, oxygen, methane, alkane, alkene, silane, carbon tetra fluoride, sulfur hexafluoride, etc., can be used on their own or with appropriate mixture to suit various requirements.

DETAILED DESCRIPTION OF THE INVENTION

[0044] FIG. 1 shows the schematic of the plasma jet printer nozzle for high throughput direct write printing of organic electronic materials using the after-glow region of the atmospheric pressure plasma and shielding of the aerosol containing organic electronics from the high energy plasma species generated in the dielectric barrier discharge. Various process gases including helium, argon, hydrogen, nitrogen, carbon dioxide, oxygen, methane, alkane, alkene, silane, carbon tetra fluoride, sulfur hexafluoride, etc., can be used on their own or with appropriate mixture to suit the need and depending on the suspension of the organic electronic material.

[0045] FIG. 1 shows the following elements:

[0046] Non concentric conical shaped outer tube 1 with a specific dielectric constant and a specific wall thickness, with a narrow end at the outlet of the nozzle;

[0047] Inner tube 2 with a dielectric constant and/or wall thickness higher than that of tube one;

[0048] Inner region 3 of the inner tube where the aerosol containing organic electronic materials will be transported towards the substrate by a feed gas and also the region that will be shielded from plasma in the outer region by the inner tube;

[0049] Plasma region 4 of the outer tube where a gas for creating discharge is fed and undergo high pressure constriction at the narrow region, and also the region rich in high energy plasma species including electrons, ions, free radicals, excited species, metastable species with high electron and ion density; this region corresponds to the area inside the outer tube and between the electrodes;

[0050] After glow region 5 outside the nozzle where the electrons and ions are at very low energy and contain mainly deexcited species, with low electron and ion density than the plasma region 4 existing between the electrodes 6 in outer tube;

[0051] Electrodes 6 placed in the outer side of the outer tube and connected to the high voltage power supply for generating plasma in the region 4;

[0052] Inlet 7 for gas that generates a plasma discharge in the region 4 and an after glow in the region 5;

[0053] Inlet 8 for aerosol containing the organic electronic materials and other electronic materials to be printed. This is also the inlet for passing reactive gases for plasma cleaning of the inner nozzle to retain the reproducibility of the printing process.

[0054] FIG. 2 shows the following elements:

[0055] Non concentric conical shaped outer tube 1 with a specific dielectric constant and a specific wall thickness, with a narrow end at the outlet of the nozzle;

[0056] Inner tube 2 with a dielectric constant and/or wall thickness higher than that of tube one;

[0057] Inner region 3 of the inner tube where the aerosol containing organic electronic materials will be transported towards the substrate by a feed gas and also the region that will be shielded from plasma in the outer region by the inner tube;

[0058] Plasma region 4 of the outer tube where a gas for creating discharge is fed and undergo high pressure constriction at the narrow region, and also the region rich in high energy plasma species including electrons, ions, free radicals, excited species, metastable species with high electron and ion density; this region corresponds to the area inside the outer tube and between the electrodes;

[0059] After glow region 5 outside the nozzle where the electrons and ions are at very low energy and contain mainly deexcited species, with low electron and ion density than the plasma region 4 existing between the electrodes 6 in outer tube;

[0060] Electrodes 6 placed in the outer side of the outer tube and connected to the high voltage power supply for generating plasma in the region 4;

[0061] Inlet 7 for gas that generates a plasma discharge in the region 4 and an after glow in the region 5;

[0062] Inlet 8 for aerosol containing the organic electronic materials and other electronic materials to be printed; this is also the inlet for passing reactive gases for plasma cleaning of the inner nozzle to retain the reproducibility of the printing process; the axis of the outer tube being 9;

[0063] The axis of the inner tube in 10 and different from 9 with angle between 0.1 degree to 45 degrees;

[0064] organic electronic materials 11 being directed by the after-glow region 5 on to the substrate 12;

[0065] According to one embodiment of the invention; the plasma jet printer nozzle preferably consists of non-concentric outer and inner tubes 1 and 2 made of any one or more of the following: silicon, silicon wafer, quartz, glass, ceramic, plastic, machinable ceramic, glass reinforced epoxy, polyimide, polyetheretherketone, fluoropolymer, aluminum, or any other dielectric material. The outer tube also may contain two metal electrodes 6 connected to high voltage power supply for creating a plasma discharge in the plasma jet chamber. The high voltage power supply can be any one of the following AC, DC, radio frequency, pulsed power supply. The after-glow region 5, through which the material to be deposited is focused to the substrate.

[0066] The outer and inner tubes 1 and 2 can either be made of same dielectric materials but with different wall thickness, with 2 preferably being thicker than 1, or the outer and inner tubes can be made of two different materials with varying dielectric constant with inner tube 2 having a higher dielectric constant than the outer tube 1.

[0067] Nonreactive, noble gases like helium, argon etc., can be used to create the discharge as well as for printing. In order to retain the chemical characteristics, electronic properties and optical properties of the materials, any of the non reactive gases including helium, argon, nitrogen could be used or gases which are compatible and non reactive with the solution of the organic electronic material. Reactive gases including nitrogen, oxygen, hydrogen, carbon dioxide, alkane, alkene, carbon tetra fluoride, sulfur hexafluoride etc., can be used for cleaning of the nozzle. The reactive and non-reactive gases can either be used on their own or with appropriate mixture of gases to obtain the required plasma processing condition.

[0068] The material to be coated may either taken as a colloid or as a solution and the colloid/solution is aerosolized and carried by a carrier gas into the non-concentric plasma jet tube where a plasma discharge is generated in the outer region 4 and the aerosol in region 3 is shielded from the high energy plasma species by the dielectric 2. Depending on the nature and type of nanomaterial/micromaterial/solution used, nature and type of coating required, concentration of the material in colloid/solution, and the nature and type of substrate used, the plasma process parameters may be tailored using appropriate gas mixtures, gas flow ratios and electrical energy input for generating the plasma.

[0069] In order to get an after-glow region that stays outside the nozzle and help print the organic electronic materials without changing its material properties, appropriate mixture of gases, gas flow ratios, concentration and electrical energy input are optimized to obtain desired film characteristics.

[0070] The electronic properties, optical properties, electro luminescent properties of the printed material will be maintained and optimized by appropriate choice of gas mixture and plasma process parameters.

[0071] Among the significant advantages of the present invention is the ability to print organic electronic materials in a high throughput fashion using the after-glow region of the atmospheric pressure plasma discharge and shielding the aerosol containing organic electronics from the high energy species of the plasma region between the electrodes using higher dielectric constant inner tube or inner tube with thicker wall to prevent plasma species surrounding the inner tube from interacting with the aerosol.

[0072] Display devices, touch panels, organic light emitting diodes, photovoltaic devices and similar such devices that use organic electronic materials required to be printed using multiple techniques with pre and/or post processing and longer processing time can now be accomplished with direct write plasma jet printing of the present invention. The after-glow-based direct write plasma jet printing allows chemical structure, electronic properties and optical properties to be maintained and preserved during the printing process by appropriate choice of gas and plasma process parameters.

[0073] The electron density of the plasma depends on various process conditions, and one prominent feature deciding the electron density of the plasma is the nature of gas used to generate the discharge. The electron densities in argon and helium are different. Argon plasma has higher electron density than the helium plasma for the same process parameters and for atmospheric pressure plasmas the electron density in argon is 2.5 times higher than helium. The thermal conductivity of gases also varies. As a result, the energy of the plasma varies depending on the nature and type of gases used to generate the discharge. When the aerosol containing organic electronic material enters the plasma, it will be subjected to electrons, ions and radical bombardment from the plasma species resulting in serious chemical structure change and modification of electronic and optical properties which will deteriorate the device performance. In order to avoid this the inner tune of the nozzle is designed in such a way that the plasma generated by dielectric barrier discharge will only be present in the outer tube and the inner tube will remain inert to the plasma species. The aerosol containing the organic electronic materials will only interact with the after-glow region of the plasma present outside the nozzle which will have much lesser ion and electron density as well as less energetic deexciting species that will not alter the material properties if properly controlled.

[0074] Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. It should be understood, therefore, that the invention may be practiced otherwise than as specifically set forth herein.