Method of fabricating full-color OLED arrays on the basis of physisorption-based microcontact printing process wtih thickness control

Abstract

A direct and effective method of fabricating full-color OLED arrays on the basis of microcontact printing process is disclosed. The key of the method lies in a physisorption-based microcontact printing process capable of controlling thickness of the printed films. The organic EL materials involved can be of either small or large molecular weights, as long as they are suitable for solution process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate the structure of a standard OLED.

FIGS. 2A-2C illustrate alternative arrangements of the anode and cathode in standard OLED arrays with active matrix or passive matrix actuation.

FIGS. 3A-3D illustrate four schemes of single full-color pixel.

FIGS. 4A-4H illustrate conventional fabrication methods of full-color OLED except the thermal evaporation, spin coating, and inkjet printing.

FIGS. 5A-5E illustrate the new μCP process employed in the present invention.

FIGS. 6A-6C illustrate a preferred embodiment of fabrication of a full-color OLED array.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following preferred embodiment of the present invention depicts fabrication of a full-color OLED array in parallel design as illustrated in FIG. 3B. To avoid tautological recitation, each OLED in the array is assumed to include only the imperative layers, namely, the anode 104, the EL layer 126, and the cathode 108. Referring to FIGS. 6A-6C illustrating how each layer is made, the present invention includes three steps as follows.

A. Disposition of Patterned Anodes.

Create columns of anodes 104 on a substrate 102 by means of any available suitable method, as shown in FIG. 6A. The substrate 102 is a rigid one, like glass, or a flexible one, like transparent polymeric film. Materials that the anode can be made of are not limited to metals, but also include conductive polymers. In addition to conductivity, transparency is another requirement for the materials that the anode is made if the display is designed so that the light is emitted from the anode.

B. Disposition of Organic Light Emitters. (This Step Represents the Heart of the Present Invention.)

Create a plurality of multi-layered organic light emitters on the anodes 104, each of which includes an EL layer 126. Creation of the EL layers 126 is accomplished by employing a new μCP process, including the following two phases: (B1) an inking phase capable of controlling thickness of the ink film deposited on the printing stamp and (B2) a printing phase.

The phase B1 further has two steps, namely, surface wetting and thin-film growth. FIGS. 5A-5C illustrate the inking phase of the new μCP process. The surface-wetting step is optional, depending on the situation. When necessary, the surface-wetting step is aimed at creating a wetting layer on the printing stamp with low surface free energy in order to facilitate successful creation of desired thin film of ink molecules at the next thin-film growth step. FIG. 5A shows a pre-patterned stamp 502. As discussed in the prior art of the standard μCP, the stamp 502 has a characteristic of very low surface free energy. FIG. 5B shows that a wetting layer 503 is formed on the surface of the stamp 502 after the surface wetting step. The wetting layer can be composed of highly evaporative solvent such as toluene or highly reactive functional group generated after a proper treatment on the stamp surface, for example, the hydroxyl, carboxyl, or peroxide generated after the O₂ plasma treatment on the surface of a printing stamp made of PDMS.

FIG. 5C shows a layer of thin-film of ink molecules created on the stamp by a suitable thin-film growth approach, like spin coating as the simplest suitable candidate. Subject to the selected thin-film growth approach, the film of ink may be disposed not only on the raised surfaces of the stamp 502 but also at valleys 506 of the same. As long as the valleys 506 are deep enough, the film at the recessed portions 506 will not affect the transfer of the ink molecules on the raised surfaces during the next printing phase.

The phase B2, as shown in FIG 5D, starts with placing the inked stamp 502 onto a substrate 512, followed by the application of an external heat source 514 with a suitable printing pressure 516 to the stamp 502 and the substrate 512. Application of the external heat and printing pressure is optional. When utilized, the external heat source 514 raises the temperature of the substrate 512 or the stamp 502 and consequently, improves the wetting and adhesive condition between the ink molecules and the substrate. The raised temperature of the substrate 512 or the stamp 502 can be higher or lower than the glass transition temperature of the ink molecules. The externally applied printing pressure 516 increases the effective contact area between the substrate 512 and the film of the ink molecules on the stamp 502, effectively enhancing the transfer of the ink molecules to the substrate. The temperatures of the substrate and stamp and the printing pressure can be adjusted to achieve optimal performance in the transfer of the ink molecules during the printing phase.

After a predetermined printing duration passes, or while a predetermined temperature is reached, or while a predetermined printing pressure is reached, or while a combination of these conditions is met, the printing phase is switched to a demolding phase. In the demolding phase, the temperatures of the substrate and stamp and the downward printing pressure on the stamp are lowered in a coordinated manner according to the P-V-T (pressure-volume-temperature) rheological behavior of the ink molecules in order to effectively reduce the surface roughness and residual internal stress in the final printed film. FIG. 5E shows the final printed film 504 after the demolding phase.

Repeat the aforementioned steps B1 and B2 three times to discretely dispose the red, green, and blue EL layers 126 of a full-color OLED pixel. FIG. 6B shows that the EL layers 126 of vertically interleaved columns of red 126R, green 126G and blue 126B are disposed orthogonally on the columns of anodes 104 by the μCP method. The sequence of red, green, and blue EL columns is design dependent. In addition to the orthogonal arrangement, the EL layers 126 can alternatively be disposed directly on top of the columns of anodes 104.

For performance optimization, the organic light emitters 106 are most likely to include one or more of the ETL 128, EIL 130, HTL 124, and HIL 122 layers. Fabrication of these other layers can be completed by the aforementioned steps B1 and B2 or other available approaches. Except the EL layer 126, these other layers are optional subject to requirement.

C. Disposition of Cathodes.

Dispose the cathodes 108 on the patterned EL layer 126 indicated in step B through available suitable method. The materials that the cathode 108 is made include both metals and conducting polymers. Transparency is also a requirement on the cathode materials if the device is designed to have the light come out from the cathode. Thermal evaporation of the selected cathode material through a mask is the commonest disposition method of the cathodes 108. For solution-based conductive polymers, however, the μCP process of the aforementioned steps B1 and B2 as shown in FIGS. 5A-5E constitutes an effective fabrication method. FIG. 6C shows a sectional view of the full-color OLED array in which the cathodes 108 are disposed.

Furthermore, for the passive matrix OLED arrays, when insulating banks are placed between the EL layers 126 made in the aforementioned step B, the cathode 108 in the step C is not necessarily discretely deposited on top of each EL layer 126, thus allowing for non-directional methods of disposition, such as the direct thermal disposition approach. Placement of the insulating banks between the EL layers 126 can also be completed using the μCP described in the aforementioned steps B1 and B2.

While the present invention has been particularly described as stated above, it will be understood by those skilled in the art that changes to the foregoing in form and detail may be made without departing from the spirit and scope of the present invention. For example, although the aforementioned embodiment was merely concerned with three essential layers including the anode, the EL layer, and cathode, other optional layers such as HIL, HTL, ETL, and EIL can be incorporated into the present invention through any available deposition methods if necessary. It is also feasible to adopt the completely pixelated anodes/cathodes as shown in FIG. 2C in the above embodiment. Further, the preparation sequence of the anodes and the cathodes can be completely converse to that of the aforementioned embodiment. Furthermore, for the purpose of convenient illustration, the parallel design indicated in FIG. 3B is employed in the aforementioned embodiment for generation of full-color pixels. The disclosed invention can also be applied to other full-color pixel designs. While the stack design shown in FIG. 3A is applied for fabrication, the red, green, and blue EL layers can be stacked upon one another in multi-layered disposition in the step B of the aforementioned embodiment. While the second parallel design shown in FIG. 3C is applied, the step B can be adopted for creation of the color filter layers 342, 344, and 346 as well as the EL layer of the white illuminant source 350. While the third parallel design indicated in FIG. 3D is applied, the step B can be employed to create the light conversion layers 362, 364, and 366 and the EL layer of the light source 370.

It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the following claim.

Claims

1. A method of fabricating full-color OLED arrays on the basis of microcontact printing process, comprising steps of: A. creating a plurality of anodes or cathodes on a substrate;B. creating a plurality of multi-layered organic light emitters on the anodes or cathodes created in the step A, wherein each of the light emitters has an organic EL layer created by two phases of:B1. inking phase capable of controlling desired thickness andB2. printing phase; andC. creating a plurality of electrodes, which are cathodes while said anodes are created on said substrate or which are anodes while said cathodes are created on said substrate, on said organic light emitters created in the step B to accomplish fabrication of said OLED arrays.

2. The method as defined in claim 1, wherein in the step A, said anodes or cathodes are parallel or discretely arranged one by one.

3. The method as defined in claim 1, wherein in the step A, said substrate is made of a rigid material like glass or a flexible material like polymeric film.

4. The method as defined in claim 1, wherein in the step A, each of said anodes or cathodes is made of metal or conductive organic material.

5. The method as defined in claim 1, wherein in the phase B1, a film of ink molecules with desired thickness is disposed with a suitable film-growth approach on a pre-patterned or flat printing stamp made of low surface free energy material; while a flat stamp is applied, a further step of patterning must be done after the film of ink molecules grows on said stamp; while it is necessary, before disposing the film of ink molecules with the film-growth approach, a wetting layer having temporary surface wetting potency is disposed on said stamp, like a layer of highly evaporative solvent, to temporarily enhance affinity between the surface of said stamp and said ink molecules.

6. The method as defined in claim 5, wherein in the phase B2, a patterned film disposed on said stamp is transferred onto a substrate by printing; during the printing, while it is necessary, an external heat source or a printing pressure can be applied to said substrate or said stamp in order to enhance the chance of successful transfer of the patterned film.

7. The method as defined in claim 6, wherein in the phase B2, after the surface of the film being transferred is hardened, said stamp can be removed from said substrate; while it is necessary, before said stamp is removed from said substrate, a demolding phase can be additionally provided upon reaching a predetermined printing duration, a predetermined temperature, a predetermined pressure, or a combination of these conditions, during which the externally applied printing pressure and the temperature of the substrate or the stamp are reduced synchronously according to pressure-volume-temperature (P-V-T) rheological behavior of the ink molecules to maintain constant volume of said film while said film is cooled off, whereby after said stamp is removed, the transferred pattern of said film has good surface smoothness and evenness and reduced residual internal stress.

8. The method as defined in claim 1, wherein in the step B, said organic light emitters are composed of multi-layered materials, in which an organic EL layer is essential and, while it is necessary, a plurality of additional layers capable of enhancing performance of said EL layer are disposed on and beneath the EL layer.

9. The method as defined in claim 8, wherein said organic light emitters further comprise an electron transport layer (ETL) and/or an electron injection layer (EIL) disposed on said EL layer, or a hole transport layer (HTL) and/or a hole injection layer (HIL) disposed beneath said EL layer.

10. The method as defined in claim 9, wherein said additional layers can be made according to the step B.

11. The method as defined in claim 8, wherein said organic light emitters comprise parallel columns of red, green, and blue light emitters and easily share said additional layers during their creation.

12. The method as defined in claim 8, wherein said organic light emitters comprise red, green, and blue light emitters stacked upon one another, which sequence depends on design.

13. The method as defined in claim 8 or 11, wherein said organic light emitters are made of suitable color filter materials instead of the organic EL ones for filtering an incident white light into red, green, and blue lights, and a white illuminator made of a suitable EL material is created and disposed on said color filter materials.

14. The method as defined in claim 8 or 11, wherein said organic light emitters are made of light conversion materials instead of the organic EL ones for converting an incident light having a predetermined frequency into red, green, and blue lights, and an organic light emitter capable of emitting said predetermined frequency is created and disposed on said light conversion materials.

15. The method as defined in claim 1, wherein in the step C, said cathodes or anodes are located over said organic light emitters.

16. The method as defined in claim 1, wherein in the step C, said cathodes or anodes are made of metals and disposed by a suitable method like the thermal evaporation through a mask.

17. The method as defined in claim 1, wherein in the step C, said cathodes or anodes are made of conductive organic materials and disposed by a suitable method like the one according to the step B.

18. The method as defined in claim 1 or 15, wherein when said organic EL light emitters in the step B have insulated areas therebetween, said cathodes in the step C is not necessarily located over said light emitters and is disposed by a suitable non-directional method like direct thermal evaporation.