US20060105493A1

US20060105493A1 - Encapsulation of organic devices

Info

Publication number: US20060105493A1
Application number: US11/141,476
Authority: US
Inventors: Arvid Hunze; Debora Henseler; Karsten Heuser
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2004-11-15
Filing date: 2005-05-31
Publication date: 2006-05-18
Also published as: US20090066240A1; US8552644B2; US20120228644A1; US8154200B2

Abstract

A method for encapsulating devices, in particular organic devices such as OLED-devices, comprising the steps of depositing organic active material on an active region of a substrate; providing a cap to enclose said organic active material within a space defined by a cap periphery adapted to adhere to the substrate; applying a thermally curable bonding material to said cap periphery or to regions of the substrate adapted to adhere to said cap periphery; mounting said cap onto the substrate so that said bonding material is between said cap periphery and the substrate; and curing the bonding material with electromagnetic radiation in the near infrared range to encapsulate the device. Furthermore, a corresponding batch process is disclosed.

Description

RELATED APPLICATION

This patent application claims the priority of U.S. provisional patent application Ser. No. 60/627,905, filed Nov. 15, 2004, the disclosure content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the fabrication of organic electronic devices. In particular, the invention relates to a method for encapsulation of organic devices such as light-emitting diodes (OLEDs).

BACKGROUND OF THE INVENTION

Organic devices such as OLED-devices contain at least one active organic layer on a substrate sandwiched between two electrodes. To protect the active organic layer and other functional parts of the device, a cap is bonded to the substrate with the help of a bonding material. Usually the cap is bonded to the substrate using polymeric adhesives, for example epoxy adhesives, as bonding material. The bonding material fixes the cap on the substrate and acts as a barrier to harmful atmospheric gases such as oxygen and moisture. After mounting the cap on the substrate, the adhesive has to be cured. Many commonly used adhesives can be cured by heat treatment, for example on a hot plate or in an oven. However, heat treatment can damage the active organic layer or other functional parts of the device and can therefore adversely affect the performance of the device. To avoid damaging of the device during the heat treatment, the curing temperatures are generally adjusted to the temperature tolerance of the active organic layer or other functional parts of the device and not only to the curing properties of the bonding material. On the one hand, this can lead to enhanced permeation rates for harmful atmospheric gases of the cured bonding material and on the other hand, limits the number of bonding materials suited for sealing the device. Particularly, higher curing temperatures can allow the use of bonding materials with lower permeation rates for gases like oxygen and moisture.
In U.S. Pat. No. 6,692,610, a method of fabricating devices such as OLED-devices is disclosed. The method includes applying an adhesive on a cap or substrate. The adhesive is partially cured to initiate the cross-linking process while remaining in the liquid phase. The cap is then mounted onto the substrate and the adhesive is cured to encapsulate the device. By partially curing the adhesive prior to mounting the cap, the curing of the adhesive can be achieved without prolonged exposure to UV-radiation or high temperatures, which can adversely impact the device.
However, this method requires a further process step which makes the production of devices more complicated and expensive. Furthermore, the above-mentioned U.S. Pat. No. 6,692,610 does not disclose an alternative to the heat treatment which would allow the use of bonding material with improved barrier properties.

SUMMARY OF THE INVENTION

One object of the invention is to provide an improved method for encapsulation of a device.
Another object of the invention is to provide an alternative to the heat treatment of the device for the curing of the bonding material.
The invention relates to a method for encapsulating a device comprising the steps:

- depositing organic active material on an active region of a substrate;
- providing a cap to enclose said organic active material within a space defined by a cap periphery adapted to adhere to the substrate;
- applying a thermally curable bonding material to said cap periphery or to regions of the substrate adapted to adhere to said cap periphery;
- mounting said cap onto the substrate so that said bonding material is between said cap periphery and the substrate; and
- curing the bonding material with electromagnetic radiation in the near infrared range to encapsulate the device.

In one embodiment, the active region comprises OLED cells. In accordance with the invention, the thermally curable bonding material is cured with the help of near infrared radiation, which replaces the heat treatment used according to the state of the art. The near infrared radiation stimulates specific vibrations within the bonding material (e.g. vibrations of C—H-bindings in polymeric materials, such as epoxy adhesives) and the energy of the radiation is almost completely transferred to the bonding material for curing in a direct way. Therefore, the curing of the bonding material occurs locally, and heating of other parts of the device, in particular of the active organic layer, can be avoided.
By using near infrared radiation instead of heat treatment on a hot plate or in an oven, reduced process times can be achieved. It could be shown, for example, that a heat treatment of organic polymers for 30 minutes at 180° C. in an oven can be replaced by an irradiation step of only a few seconds. As bonding materials, adhesives such as epoxy adhesives or adhesive foils, such as thermoplastic foils, suited particularly for flexible applications can be used. Furthermore, other bonding materials, which require a heat treatment at higher temperatures for curing, can also be used. One example for such a bonding material is solder glass.
Compared to polymeric adhesives, solder glass shows improved barrier properties against atmospheric gases like oxygen and moisture. In one embodiment, the active organic layer is protected against residual near infrared radiation by means of a shadow mask. In a further embodiment, the near infrared radiation is focussed to be locally applied in the regions where the bonding material is applied. This ensures that the organic active layer of the device is not affected by the near infrared radiation. Preferably, the near infrared radiation is focussed in at least one line with a width of 1 to 2 mm.
The use of line-focussed near infrared radiation for curing the bonding materials facilitates the integration of the encapsulation step in a batch process leading to improved process times.
A method for encapsulating devices in a batch process comprises the steps:

- depositing organic active material on a plurality of active regions of a substrate;
- providing a plurality of caps for said plurality of active regions to enclose said organic active material within a space respectively defined by each cap periphery adapted to adhere to the substrate;
- applying a thermally curable bonding material to each said cap periphery or to regions of the substrate adapted to adhere to each said cap periphery such that said bonding material defines rectangular areas each containing one said active region, wherein said rectangular areas form a grid in such a way that the bonding material is arranged in parallel vertical lines and parallel horizontal lines;
- mounting said plurality of caps onto the substrate so that said bonding material is between each said cap periphery and the substrate; and
- curing said bonding material with electromagnetic radiation in the near infrared range focused in at least one line and applied sequentially across the substrate to encapsulate the devices.

The caps can be separated or integrated on a cap substrate. The cap substrate can be a planar plate, comprising for example metal or glass. Furthermore, it is also possible that corresponding to the active regions of the substrate, the plate has cavities in order to protect the organic active material within the active region from damage due to direct contact with the cap. If the cap has a cavity bending over the active region of the device, getter material can be positioned inside the cavity of the cap, which binds oxygen and moisture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 show schematic sectional views of an OLED-device according to the invention at different fabrication steps;
FIGS. 4 to 6 show schematic sectional views of an OLED-device during curing of bonding material with the help of near infrared radiation; and
FIGS. 7A to 7E show schematic top views of OLED-devices according to the invention at different fabrication steps of a batch process.

DETAILED DESCRIPTION OF THE DRAWINGS

In accordance with one embodiment of the invention, FIGS. 1, 2 and 3 show cross-sectional views of an OLED-device at different process steps. Referring to FIG. 1, the OLED-device comprises one or more active organic layers 1 with organic active material sandwiched between two electrodes 2, 3 formed on a substrate 4 in an active region 5. Electrical connections to the electrodes 2, 3 can be made by bond wires via bond pads 6. When an electrical current is applied to the OLED-device, electrons and holes are injected into the organic material of the active organic layer 1 by the electrodes 2, 3. The charge carriers recombine within the active organic layers 1 and the released energy is emitted as visible light.
To form a pixel matrix of a display, the upper and lower electrode 2, 3 can be patterned in strips perpendicular to each other. For the patterning of the upper electrode 3, pillars, preferably with an overhanging structure, can be used. The patterning of electrodes is described in U.S. Pat. Nos. 6,699,728, U.S. Pat. No. 6,696,312 and U.S. Pat. No. 6,784,009, which are incorporated by reference herein for all purposes.
Usually the lower electrode 2 adjacent to the substrate 4 acts as an anode forming an electrical contact with ohmic characteristics to the adjacent active organic material of the active organic layer 1 and injects holes into it. Preferably the anode 2 comprises a material with high work function for electrons and good transparency for the light emitted by the OLED-device. A suitable material for the anode 2 is, for example, Indium-Tin-Oxide (ITO).
As substrate 4, a glass plate or a plate based on polymeric plastic material can be used. In order to reduce the overall thickness of the OLED-device as far as possible, a thin substrate 4 is often used. Polymeric plastic materials, for example foil, are particularly useful for the fabrication of flexible OLED-devices. Examples for these materials are poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(enthylene naphthalate) (PEN), polycarbonate (PC), polyimides (PI), polysulfones (PSO), poly(p-phenylene ether sulfone) (PES), polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS) and poly(methyl methyleacrylate) (PMMA).
The active organic layers 1 can comprise one or more hole injection layers, preferably adjacent to the anode 2 with reduced injection barrier for holes. Furthermore, the active organic layers 1 can comprise one or more hole transportation layers, one or more electron transportation layers and at least one emission layer. As active organic material of the active organic layers 1, small molecules or polymeric material can be used. Materials based on small molecules are usually deposited by evaporation, while polymeric materials are usually deposited by solvent processes like doctor-blading, spin-coating, printing processes or other common solvent processes.
The upper electrode 3 opposite the lower electrode 2 usually serves as a cathode. To minimize the injection barrier for electrons, the cathode 3 is preferably comprises a metal or a compound material with a low work function for electrons. Such materials are generally sensitive to corrosion or other degenerating mechanisms. For OLED-devices with polymeric active organic material, metals like Ca or Ba are often used for the cathode 3. In order to protect these sensitive materials against external influences such as atmospheric gases and to guarantee a good electrical contact, a layer of Al or Ag (not shown) is placed on top of cathode 3.
Besides the cathode 3, the active organic layer 1 can also be impaired by external influences. Therefore, the active regions 5 comprising the electrode layers 2, 3 and the active organic layer 1 is encapsulated with a cap 7 as hermetically as possible. As cap 7, a glass plate or a metal part can be used. Furthermore, the cap 7 should be mounted without direct contact to the active organic layer 1 or electrodes 2, 3 to avoid causing any damage to these functional parts of the OLED-device. To a avoid direct contact between the active organic layer 1 and the cap 7, the cap has a cavity corresponding to the active region 5 of the OLED-device. Alternatively, it is also possible to use a plane plate as cap 7. The use of a plane plate as cap 7, which is in direct contact with the active organic layer 1 can improve the encapsulation of the device, since the active organic layer 1 is not in contact with air.
For the encapsulation of the OLED-device, a thermally curable bonding material 8 such as epoxy adhesive or solder glass is deposited on a sealing region 9 of the substrate 4 (FIG. 2) surrounding the active region 5 with the functional parts of the OLED-device. Further, the active region 5 can comprise support posts or spacer particles to avoid contact between the cap 7 and the functional parts in the active region 5. The use of spacer particles for the encapsulation of OLED-devices is described in documents WO 01/45140 and WO 01/44865, which are incorporated herein by reference for all purposes. If spacer particles or support posts are used, it can be helpful to deposit the bonding material 8 on the support posts or spacer particles as well. Alternatively or additionally, the bonding material 8 can be deposited on the regions of the cap 7 which will contact the substrate 4 after assembly. The bonding material 8 can be deposited by means of dispensing or printing methods, for example screen printing.
After depositing the bonding material 8, the cap 7 is mounted onto the substrate 4 as shown in FIG. 3. If epoxy adhesive is used as bonding material 8, an initial UV-irradiation step may be necessary to initiate the curing process.
Subsequently, the bonding material 8 is cured by applying a broadband near infrared radiation 10 with wavelengths centered in the range of 0.8 to 1.5 μm. This sort of near infrared radiation 10 is particularly suited to achieve a homogenous drying or curing of polymeric adhesives and avoids an overheating of the polymeric surface of the adhesive sometimes caused by other kinds of infrared radiation 10. A further characteristic of this process is that very high energy densities up to 1.5 MW/m³can be used, which considerably reduces the time required for curing the bonding material.
Since the bonding material 8 is sandwiched between the cap 7 and the substrate 4, it is necessary for the application of the near infrared radiation 10 that at least the cap 7 or the substrate 4 is made of a material transparent to near infrared radiation 10, such as glass, and a near infrared source 11 emitting the near infrared radiation 10 is positioned on the side of the transparent material in such a way that the infrared radiation 10 can reach the bonding material 8
In one embodiment of the invention, the near infrared radiation 10 is focussed to yield a radiation spot with a diameter of 5 mm or a line focus with a confinement of 1 to 2 mm. Preferably, the near infrared radiation 10 emitted by the near infrared radiation source 11 is focussed, for example by means of a reflector 12, in such a way that the maximum energy density is located inside the bonding material 8 as schematically shown in FIG. 4.
In another embodiment of the invention, non-focused near infrared radiation 10 is used to cure the bonding material 8 as schematically shown in FIG. 5.
To protect the active organic layer of the OLED-device against residual near infrared radiation 10, it can be helpful to use a shadow mask 13. It can be used in connection with unfocussed near infrared radiation 10, as schematically shown in FIG. 6, or focussed near infrared radiation 10 (not shown).
To avoid damage of the active organic layer or other functional parts of the OLED-device by permeating harmful atmospheric gases, the active region can comprise a getter material, for example Ba, which can bind them chemically or physically. The getter material can be arranged for example as a layer (not shown) on the surface of the cap arranged opposite the active region. The getter material can also be included in the bonding material 8. Getter materials for OLED-devices are described in more detail in U.S. published application Nos. 2004-0051449 and U.S. 2004-0048033, which are incorporated herein by reference for all purposes.
FIGS. 7A to 7E show different steps of a batch process using at least one line-focused near infrared source 11 for the encapsulation of several OLED-devices according to one embodiment of the invention.
As described above in more detail, the functional parts of several OLED-devices are processed on a substrate 4.
The bonding material 8 is dispensed or otherwise deposited in rims surrounding the active regions 5 of the OLED-devices, and a plurality of caps 7 are positioned above for encapsulation. Furthermore, the plurality of caps 7 can be integrated on a cap substrate, such as a metal or glass plate. The plate can be plane or provide cavities corresponding to the active regions 5 of the OLED-device on the substrate 4.
The bonding material 8 forms rims which are arranged along parallel vertical lines and parallel horizontal lines. The rims of the bonding material 8 are deposited in such a way that they define rectangular active regions 5 with width a* and height b* arranged in a regular grid such that adjacent active regions 5 are spaced from each other at a horizontal distance d_Hand at vertical distance d_V. In the following, the vertical lines are numbered from the left side to the right side by V1 to V8 and the horizontal lines from the bottom to the top by H1 to H6.
To cure the bonding material 8, a near infrared source 11 emitting line-focused radiation is positioned parallel to the outer vertical line V1 of the grid on the left side above the rims formed by the bonding material 8. By shifting the near infrared source 11 by the distance a* to the right, the next line V2 of bonding material 8 is cured. In a subsequent step, the radiation source 11 is shifted by the distance d_Hto the right to start curing the bonding material 8 surrounding the next array of OLED-devices with the vertical line V3. Instead of shifting the near infrared source 11 to the right, it is also possible to shift the substrate 4 to the left. In the same way as the rims of bonding material 8 limiting the vertical sides of the rectangular areas are cured, the rims of bonding material 8 limiting the horizontal sides of the rectangular areas can be cured in subsequent steps.
If the horizontal and vertical distances a=a*+d_Hand b=b*+d_Vare large enough to position two near infrared wire sources 11 a and 11 b parallel to each other within these distances, the number of irradiation steps can be reduced. For example, for near infrared wire sources of the Company Adphos, the minimum distance between two line-focussed wire sources is 50 mm. As shown in FIG. 7B, the vertical lines V1 and V3 limiting adjacent active regions can be cured in a single step by means of two vertical infrared wire sources 11 a and 11 b arranged parallel to each other. By shifting the near infrared wire sources 11 a, 11 b by the distance 2 a to the left (or the substrate to the right), the vertical lines V5 and V7 the bonding material 8 can be cured in a subsequent step (see FIG. 7B). In the next step the near infrared wire sources 11 a, 11 b are positioned in such a way that the infrared wire source 11 a is parallel above the vertical line V2 and that the infrared wire source 11 b is parallel to the vertical line V4 to cure them. The other vertical lines V6 and V8 of bonding material 8 are cured by shifting the infrared wire sources 11 a, 11 b to the right (or the substrate to the left) by the distance 2 a (see FIG. 7C). The distances a, a*, b and b* can have values of a few mm up to several cm.
The curing of the horizontally arranged rims of bonding material 8 forming the horizontal lines H1 to H6 by means of two horizontal wire sources 11 a and 11 b arranged parallel to each other at a distance b is shown in FIGS. 7D and 7E. As described for the vertical lines V1 to V8 of the bonding material 8, the horizontal lines H1 to H6 of bonding material 8 can be cured in subsequent steps by shifting the near infrared wire sources 11 a, 11 b or the substrate 4.
In a first step, the infrared wire sources 11 a, 11 b are positioned in such a way above the bonding material 8 that the wire source 11 a is positioned parallel above the horizontal line H1 and the wire source 11 b is positioned parallel above the horizontal line H3. After curing the horizontal lines H1 and H3, the near infrared wire sources 11 a, 11 b are shifted to the top by the distance 2 b and the horizontal line H5 is cured. Equivalently to the curing of the vertical lines V1 to V8, the near infrared wire sources 11 a, 11 b are then positioned in such a way that the wire source 11 a is positioned parallel above the horizontal line H2 and the wire source 11 b is positioned parallel above the horizontal line H4 (see FIG. 7D). By shifting the near infrared wire sources 11 a, 11 b to the top by the distance 2 b (or the substrate to the bottom) the remaining horizontal line H6 can be cured (see FIG. 7E).
After curing all rims of bonding material 8, the OLED-devices can be separated, for example by sawing.
The method for encapsulation is not limited to OLED-devices. Furthermore, it is particularly suited for the encapsulation of organic solar cells or organic photodetectors.
The scope of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which particularly includes any combination of the features which are described in the claims, even if this feature or this combination of features is not explicitly referred to in the claims or in the examples.

Claims

1. A method for encapsulating a device comprising the steps of:

depositing organic active material on an active region of a substrate;

providing a cap to enclose said organic active material within a space defined by a cap periphery adapted to adhere to the substrate;

applying a thermally curable bonding material to said cap periphery or to regions of the substrate adapted to adhere to said cap periphery;

mounting said cap onto the substrate so that said bonding material is between said cap periphery and the substrate; and

curing the bonding material with electromagnetic radiation in the near infrared range to encapsulate the device.

2. The method of claim 1, wherein the bonding material is selected from the group consisting of epoxy adhesive, adhesive foils and solder glass.

3. The method of claim 1, further comprising:

providing a shadow mask to protect the active material against the near infrared electromagnetic radiation.

4. The method of claim 1, wherein the curing step comprises:

focusing the near infrared radiation to be locally applied in the regions where the bonding material is applied.

5. The method of claim 4, wherein the focusing step comprises:

focusing the near infrared electromagnetic radiation in at least one line with a width of 1 to 2 mm.

6. The method of claim 1, wherein the active region comprises OLED cells (organic light emitting cells).

7. A method for encapsulating devices in a batch process comprising the steps of:

depositing organic active material on a plurality of active regions of a substrate;

providing a plurality of caps for said plurality of active regions to enclose said organic active material within a space respectively defined by each cap periphery adapted to adhere to the substrate;

applying a thermally curable bonding material to each said cap periphery or to regions of the substrate adapted to adhere to each said cap periphery such that said bonding material defines rectangular areas each containing one said active region, wherein said rectangular areas form a grid in such a way that the bonding material is arranged in parallel vertical lines and parallel horizontal lines;

mounting said plurality of caps onto the substrate so that said bonding material is between each said cap periphery and the substrate; and

curing said bonding material with electromagnetic radiation in the near infrared range focused in at least one line and applied sequentially across the substrate to encapsulate the devices.

8. The method of claim 7, wherein the bonding material is selected from the group consisting of epoxy adhesive, adhesive foils and solder glass.

9. The method of claim 7, further comprising:

10. The method of claim 7, wherein the curing step comprises:

11. The method of claim 10, wherein the focusing step comprises:

12. The method of claim 7, wherein each of said plurality of active regions comprises OLED cells (organic light emitting cells).

13. The method of claim 7, wherein the step of providing said plurality of caps comprises:

providing a cap substrate and forming said plurality of caps in said cap substrate.