BACKGROUND OF THE INVENTION

[0001] Printed electronics devices are electrical devices or components that have been produced by a printing process using conductive inks. Examples include electrical contacts, thin film transistors, capacitors, resistors, diodes, antennas, sensors, inductive coils and organic light emitting diodes (OLEDs). Known printed electronics may not provide sufficient adhesion, such that the ink can be easily removed from the substrate.

[0002] One known conductive ink printing process utilizes silver nano ink having a glass frit. The ink is applied to a glass substrate by ink-jet printing, and annealed at high temperatures (400°C or greater). Although the addition of the glass frit may be beneficial to the overall adhesion of the film due to grain growth, the high temperature that is required for the annealing process may limit the usefulness of this process.

[0003] Accordingly, an improved ink and process for printing electronic devices would be beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is a schematic view of a printing process according to one aspect of the present invention;

[0005] FIG. 2 is a flow chart showing a printing process according to one aspect of the present invention;

[0006] FIG. 3 is a schematic view of a device fabricated utilizing the process of FIG. 2;

[0007] FIG. 4 is an enlarged schematic view of a portion of the device of FIG. 3;

[0008] FIG. 5 is a flow chart showing a method of fabricating an OLED device according to another aspect of the present invention;

[0009] FIG. 6 is a schematic view of a device fabricated utilizing the process of FIG. 5;

[0010] FIG. 7 is flow chart of a process for fabricating a radio-frequency identification

(RFID) device according to another aspect of the present invention; and

[0011] FIG. 8 is a schematic view of a device fabricated utilizing the process of FIG. 7. DETAILED DESCRIPTION

[0012] For purposes of description herein, the terms "upper," "lower," "right," "left,"

"rear," "front," "vertical," "horizontal," and derivatives thereof shall relate to the invention as oriented in FIG. 1. However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following

specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

[0013] One aspect of the present invention is an ink comprising a liquid solvent, a binder, solid particles comprising a conductive material, and a low melting temperature glass frit (LMTGF). The solvent and binder may be any substance that adequately suspends the conductive material and the LMTGF. A plurality of conductive metal particles (e.g. silver particles) are dispersed in the solvent. A low melting temperature glass frit material is also dispersed in the solvent. The glass frit is preferably in the form of spherical particles having a diameter of about 200 nanometers to 50 microns, or 1 micron to 3 microns. The mass percentage of the glass frit is preferably about 33% or less of the ink.

[0014] It will be understood that inks of the present disclosure are not limited to a

specific composition. For example, the conductive material may comprise gold, copper, silver or graphene. Also, the solvent may comprise water, a high-viscosity organic liquid such as terpineol, or a low viscosity organic liquid such as toluene.

[0015] The LMTGF utilized in the ink may comprise a low-melting temperature glass developed as a low temperature sealant by Hitachi, Ltd. and Hitachi Chemical Co. Ltd. This LMTGF material is available under the trade name VS1307, Available from Hitachi Chemical Co. America. The LMTGF preferably has a melting temperature of about 220- 300°C (or less).

[0016] As discussed in more detail below, an ink according to the present invention is printed on a substrate, and the printed ink is then sintered utilizing a photonic sintering process whereby a pulse of high intensity light from a Xenon bulb is directed onto the ink. This quickly heats the ink to sinter the LMTGF, without significantly heating the substrate upon which the ink is printed. Because photonic sintering occurs very quickly, high production rates can be achieved utilizing a roll-to-roll process.

[0017] With reference to FIG. 1, a printing process/device 1 according to the present invention may utilize a roll of sheet material 4. The sheet material 6 is unrolled from roll 4, and ink is applied by a printer 8. The printer 8 may comprise an ink jet printer or other suitable printing device. The ink 12 then passes under a light 10 to cure the ink 12. The light 10 may comprise a Xenon light source having a high intensity light or other suitable photonic bulb. For example, light source 10 may comprise one or more Xenon bulbs that are able to deliver 20,000 Watts/cm ² , wherein about 30% of the energy into the system goes to light. The light source 10 emits a brief pulse of high intensity light that rapidly heats and sinters the ink 12. The light source 10 may provide a light pulse lasting from about 100 to about 1000 milliseconds. The light source 10 is preferably positioned about 0.5 inches to about 4-8 (several) inches from the ink 12 on sheet 6. Because the light from light source 10 has high intensity, yet short duration, thermal equilibrium between the particles of ink 12 and substrate/sheet 6 is never achieved. The result is that the particles are sintered then cooled before any substantial heat transfer to the

substrate/sheet 6 occurs. Following sintering by light source 10, the sheet 6 with cured ink 12A is then rolled onto a reel 14. Alternatively, sheet 6 with cured ink 12A may continue through subsequent printing units (not shown) where additional ink is deposited onto sheet 6 and/or cured ink 12A and cured utilizing additional high intensity light sources (not shown) to form additional functional layers.

[0018] Because the light source 10 cures and sinters the ink very rapidly, the sheet

material 6 can be fed at a relatively high speed. For example, a process according to one aspect of the present invention may utilize a feed rate of 5 to 20 (or more) feet per second. The sheet 6 may be fed at a constant velocity (rate), or the sheet 6 may be fed at a variable rate whereby the sheet 6 slows or stops during the printing and/or sintering steps. Print speeds can be significantly greater than 20 feet per second if a sufficient number and intensity of photonic bulbs are provided to heat and sinter the ink. Thus, the process of the present disclosure can be utilized in roll-to-roll printing/sintering processes having extremely high feed rates. [0019] Testing has shown that a photonic curing process utilizing LMTGF according to the present invention results in significant inter-granular dispersion of the glass between conductive particles (e.g. silver) contained within the ink. This densifies the film, resulting in greater adhesion to the substrate, and lower electrical resistance in the cured ink 12A. Testing has also shown that the photonically sintered ink provides greater adhesion to the substrate relative to conventional sintering processes utilizing high melting temperature glass. Furthermore, testing has shown that the addition of glass frit to the ink reduces the electrical resistance of the ink relative to ink that does not include a glass frit.

[0020] In a preferred embodiment, the sheet or substrate 6 may comprise a thin glass material. However, the substrate or sheet 6 may also comprise plastic, coated paper or other materials. For example, the sheet 6 may comprise a soda lime glass material having a thickness of about 0.125 inches. Alternatively, the substrate 6 may comprise a paper material such as an uncoated free sheet material.

[0021] With further reference to FIGS. 2-4, a device 20 (FIGS. 3 and 4) may be fabricated utilizing a process 22 shown in FIG. 2. Process 22 includes a first step 24 in which conductive material (e.g. ink) including an LMTGF adhesion promoter is printed onto substrates 26A and 26B (FIG. 3). The ink 12 is then photonically sintered/cured as shown at step 28. Electrical conductors 30A and 30B are then attached to the ink 12 by soldering to thereby create a circuit. In the illustrated example, the device 20 includes an electrochromic center layer 32, and the substrates/layers 26A and 26B comprise ITO (Indium Tin Oxide) glass that is adhered to electrochromic center layer 32. The device 20 can therefore form electrochromic glass that changes with respect to light

absorption/reflection when electrical power is applied from a power supply 34.

[0022] The LMTGF utilized in the ink 12 to produce device 20 provides increased

adhesion and maintains the integrity of the electrical contacts during annealing processes such as soldering the ink 12 to the conductors 30A and 30B.

[0023] With further reference to FIG. 5, a process 42 according to another aspect of the present invention includes a first step 44 in which a transport layer 46 (FIG. 6) is printed on a cathode 48. The transport layer 46 may be formed by printing ink comprising LMTGF according to the present invention that is cured at step 50 utilizing photonic curing. At step 52, additional layers of ink comprising LMTGF are printed and cured. The additional layers may comprise an emitting layer 54 and a second transport layer 56. An anode 58 may then formed utilizing the printing and curing steps 44 and 50. The layers may then be adhered to a glass sheet 60, and an electrical power source 62 may be connected to cathode 48 and anode 58 utilizing conductors 64 and 66, respectively. The resulting device 40 comprises an OLED display that emits light 68.

[0024] Photonic curing to produce the OLED display 40 provides for fast curing times

(increased throughput). Furthermore, the increased adhesion from the LMTGF maintains the integrity of the film layers during subsequent printing processes to thereby improved durability.

[0025] With further reference to FIG. 7, a process 72 according to another aspect of the present invention includes a first step 74 in which ink including LMTGF is printed on a substrate 76 to form an RFID 78 (FIG. 8). At step 80, the ink that forms RFID 78 is cured/sintered utilizing photonic curing according to the present invention. The substrate 76 may comprise paper, glass, polymer, or other suitable material. Photonic curing provides for rapid curing, thereby providing an increased throughput.

Furthermore, the LMTGF provides increased adhesion, and maintains the integrity of the RFID. This, in turn, provides for increased durability when handling a device 70, and also provides for longer functionality of RFID 78 and increased production ratio.

[0026] It is to be understood that variations and modifications can be made on the

aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.