CN1385053A - Encapsulation of organic electronic devices - Google Patents

Abstract

The present invention relates to an electronic device structure that prevents environmental moisture and oxygen from reacting with materials used to manufacture the device, thereby preventing environmental moisture and oxygen from detrimental to device performance by employing a hermetically sealed enclosure containing a porous desiccant effect.

Description

Encapsulation of organic electronic devices

field of invention

The present invention relates to organic polymer based electronic devices such as diodes, for example light emitting diodes and photodiodes. More specifically, the present invention relates to the fabrication process and structure of such devices, which results in high device efficiency and promotes a long lifetime acceptable to the market.

Background of the invention

Solid-state electronic devices fabricated from conjugated organic polymers have attracted attention. Diodes based on conjugated polymers, especially light-emitting diodes (LEDs) and photodiodes, are of particular interest due to their application possibilities in display and sensor technology. These related documents, as well as other papers, patents and patent applications, are incorporated herein by reference.

The structure of such devices includes coatings or films of electro-optically active conjugated organic polymers bonded opposite electrodes (anode and cathode) and supported on a solid substrate.

In general, materials useful as active layers in polymer diodes, especially LEDs, include semiconducting conjugated polymers, such as semiconducting conjugated polymers capable of photoluminescence. In certain preferred forms of assembly, the polymer is a semiconducting conjugated polymer that is photoluminescent and can be dissolved and processed from solution into a uniform thin film.

The anodes of such electronic devices based on organic polymers generally consist of higher work function metals and transparent non-stoichiometric semiconductors such as indium/tin-oxide. The function of this anode is to inject holes into the otherwise filled pi-bands of the semiconducting light-emitting polymer.

Lower work function metals such as barium and calcium are preferred as cathode materials in various configurations. Ultrathin layers of such low work function metals and their oxides are preferred. The function of this low work function cathode is to inject electrons into the otherwise empty pi*-band of the semiconducting light-emitting polymer. The holes injected from the anode and the electrons injected from the cathode recombine in a luminescent manner within the active layer and emit light.

Although low work function materials are required for efficient electron injection from the cathode and satisfactory device performance, unfortunately low work function metals such as calcium, barium, strontium and their oxides are typically chemically reactive species . They react readily with oxygen and water vapor at room temperature and more violently at elevated temperatures. Such reactions destroy their required low work function properties, degrading the critical interface between the cathode material and the light-emitting semiconducting polymer. This is a chronic problem that causes the efficiency (and light output) of the element to decrease rapidly during storage and during stress, especially at high temperatures.

Solid-state devices based on other organic polymers suffer from similar stability issues. The structure of the photosensitive device and the array of devices and the materials used are very similar to those found in polymer-based LEDs. The main difference between polymer-based LEDs and photosensors is that very reactive low work function electrodes do not need to be used, and the polarity of the electrodes is often reversed. However, moisture and oxygen react with the components of such devices, thereby degrading the performance of the devices over time.

One way to reduce the deleterious effects of atmospheric exposure is to enclose the device in a barrier that separates the active material from moisture. This approach has had some success, but it has not always been adequate to solve the problems caused by small amounts of moisture trapped inside the envelope or diffused in over time.

Kawami et al. in US Pat. No. 5,882,761 disclose a method of packaging a light-emitting device, which is fabricated using a thin film of light-emitting organic molecules as the active layer, with the aim of solving the problem of water contamination. This patent describes placing a water-reactive solid compound such as sodium oxide within the envelope of the element. This reactive compound covalently reacts with the water in the envelope and converts the water into a solid product. For example, as mentioned sodium oxide reacts with water to produce solid sodium hydroxide. This patent describes its use of these water-reactive compounds to remove water in order to retain moisture at elevated temperatures. Kawami et al. pointed out that materials that physically absorb moisture cannot be used because moisture will be released at high temperatures (eg, 85° C.).

The water-reactive solid compound in the Kawami patent is itself highly reactive, so that its reaction products are also highly reactive. Therefore there is a need for a method of encapsulating solid-state electronic devices based on organic polymers that is sufficiently protected from water vapor and Oxygen diffuses into the device, preventing a limited lifetime.

Furthermore, many known methods to achieve sealing of electronic devices require heating the device to temperatures above 300° C. during the packaging process. Most polymer-based light emitting devices cannot withstand such high temperatures.

Brief description of the invention

The present invention relates to an electronic device comprising a polymeric electronic device comprising a pair of electrodes disposed opposite to each other and an active polymer layer interposed between the electrodes; A surface and an opposite outer surface adjacent to the external atmosphere; a desiccant adjacent to the inner surface that has a pore structure and is capable of drawing water into its pore structure by physical absorption; wherein the hermetic encapsulation encloses the polymer electronic device Sealed to isolate the polymer electronics and desiccant from the outside atmosphere. The present invention also relates to a method of fabricating an increased lifetime polymer electronic device by encapsulating the polymer electronic device in a hermetic encapsulation with a solid desiccant.

In a preferred embodiment, the desiccant is incorporated into one or more layers of the substrate supporting the polymeric electronic device.

As used herein, the phrase "adjacent" does not necessarily mean that one layer is directly adjacent to another layer, but that it is close to a first surface location (for example, a desiccant is close to its inner surface), when the second surface opposite the first surface. (such as the outer surface) compared.

Brief description of the drawings

Fig. 1 represents the cross section of representative device of the present invention;

Figure 2 shows the impact of different drying materials on the lifetime of packaged devices under 85°C and ambient humidity conditions;

Figure 3 shows the comparison of the water removal efficiency of the present invention with the removal efficiency of materials and methods used in the current technology; and

Figure 4 shows the water removal stability of the method of the present invention compared to the method used in the current technology.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As best seen in FIG. 1, the electronic device 100 of the present invention comprises a polymer electronic device 110 consisting of an anode 112 and a cathode 114 with associated leads 116, 118, an electroactive organic polymer layer 120 and The substrate 122 in this embodiment. The device 110 also includes an encapsulation box 124, which seals the electronics from the atmosphere. The package consists of a substrate 122 as a base, with a cover or cover 126 secured to the base 122 by an adhesive 128 . The desiccant 130 is enclosed in the box 124 and is preferably secured to the inner surface 132 of the box by an adhesive 134 . Substrate

Substrate 122 is generally air and moisture impermeable. In a preferred embodiment, the substrate is glass. In a second preferred embodiment, the substrate is silicon. In a third preferred embodiment, the substrate is a flexible substrate such as a gas impermeable plastic or composite material comprising a combination of inorganic and plastic materials. Examples of effective flexible substrates include sheets or multilayer laminates of flexible materials such as impermeable flexible plastics such as polyester, for example polyethylene terephthalate, or made of plastic sheets and deposited A composite material composed of an optional metal or inorganic dielectric layer thereon. In a preferred embodiment, the substrate is transparent (or translucent), which allows light to enter the encapsulation area or allows light to be emitted to pass through the encapsulation area. Packaging box

Hermetic enclosure 126 seals polymer electronics 110 from the atmosphere. How the airtight box is composed is not critical as long as the process sequence does not have a detrimental effect on the components of the polymer electronics 110 . For example, the airtight box 126 may consist of multiple panels bonded together with an adhesive. In a preferred embodiment, the airtight box consists of a cover 126 bonded to a substrate. As best seen in FIG. 1 , the preferred substrate 122 is the substrate of the polymer electronic device 110 .

The material used to make up the airtight box 126 should be air and moisture impermeable. In one embodiment, the cover is made of metal. In another embodiment, the cover is made of glass or of ceramic material, air and water impermeable plastics can also be used.

The thickness of the cover 126 is not critical in the present invention as long as the cover is thick enough to form a continuous barrier (no voids and no pinholes). The thickness of the cover 126 is preferably between 10-1000 μm. In cases where the substrate is not a polymeric electronic device substrate (not shown), it is conceivable that the base could be made of the same material as the cover. As best seen in FIG. 1, cover 126 is sealed to substrate 122 by adhesive 128. As shown in FIG. The adhesive should be cured at a temperature lower than the decomposition temperature of the activation layer 120, such as below 75°C, preferably below 50°C, preferably at room temperature or at a moderate temperature. This is advantageous because it avoids the high temperatures common in the prior art, which often damage or degrade the electronic device 110 . Preferred adhesives include epoxies which cure under UV radiation or at the above-mentioned moderate temperatures (or both). As best seen in Figure 1, leads 116, 118 extend from the device. These wires should also be sealed with adhesive 128, but functionally equivalent wire structures can also be used. solid desiccant

Before the cover 126 is sealed to the substrate 122 and the electronic device 110 is packaged, a solid desiccant (drying material) 130 is inserted. The shape of the desiccant is not critical. For example, the desiccant can be in the form of a porous packed powder, a compressed tablet, a solid contained in a gel, a solid encapsulated in a cross-linked polymer, and/or a film. The desiccant can be placed in the enclosure 124 in various ways. For example, the desiccant 130 can be added to the coating of the substrate or the inner surface of the cover (not shown), or, as is apparent in FIG. on the inner surface 132 . Additionally (not shown) a desiccant may be added to the flexible substrate of the electronic device or to one or more layers of a multilayer or laminated substrate.

The nature of the solid desiccant is important. It is a porous solid, most commonly an inorganic solid with a controllable pore structure, water molecules can enter the pore structure, but in this structure the water molecules are physically absorbed and seem to be trapped and not released into the environment of the packaging box middle. Molecular sieves are one such material. In a preferred embodiment, the desiccant enclosed in the sealed package is a zeolite. Zeolites are well known materials and are commercially available. In general, any type of zeolite can be used to trap water. Zeolites are known to consist of almost equal amounts of oxides of aluminum and silicon with sodium as the counterion. Zeolite materials absorb moisture through physical absorption rather than through chemical reaction. Physical absorption is preferred.

In a more preferred version, the desiccant 130 packaged into the capsule is a desiccant known as Tri-Sorb (sold from Süd-Chemie Development Packaging Company, a member of the Süd-Chemie Group, Division of United Catalysts, Belen , New Mexico) zeolite material. The structure of Tri-Sorb consists of nearly equal amounts of oxides of aluminum and silicon with sodium as a counterion. Tri-Sorb physically absorbs moisture. When encapsulated by the method described in the present invention, the remarkable improvement in the stability and lifespan of the polymer LED can be seen from the examples. Specifically, the desiccant loaded with physically absorbed zeolite material is significantly better than barium oxide, which chemically absorbs moisture.

The amount of desiccant to be added should provide sufficient capacity to absorb moisture trapped inside the enclosure when it is sealed. The water absorption capacity of a desiccant is a known property. The internal volume of the device and the air humidity inside the enclosure are easily determined. After these factors are taken into account, a sufficient weight of desiccant can be determined and added.

In a preferred embodiment, desiccant may be added in excess of the calculated amount to counteract the amount of residual water vapor entering the active device region through imperfect edge seals and/or residual permeability through the substrate. active layer

Promising materials for the active layer 120 in electronic devices protected by the present invention, such as polymer LEDs, are poly(phenylene vinylene), PPV, and soluble derivatives of PPV such as poly(2-methoxy-5 -(2'-Ethyl-hexyloxy)-1,4-phenylenevinylene) ie MEH-PPV, a semiconducting polymer with eg energy gap >2.1 eV. US Patent No. 5,189,136 describes this material in more detail. Another material described as useful in the present invention is poly(2,5-bis(cholestalkoxy)-1,4-phenylenevinylene), BCHA-PPV, an energy gap > 2.2 eV semiconducting polymers. Such materials are described in more detail in US Patent Application Serial No. 07/800,555. Other suitable polymers include, for example, the poly(3-alkanes) reported by D. Braun, G. Gustafsson, D. Mc Branch and A. J. Heeger in J. Appl. Phys. (Journal of Applied Physics) 72, 564 (1992) thiophene) and related derivatives reported by M.Berggren, O.Inganas, G.Gustafsson, J.Rasmusson, M.R.Anderson, T.Hjertberg and O.Wennerstrom; G.Grem, G.Leditzkg, B.Ullrich and G Poly(p-phenylene) reported by Lerising in Adv.Mater, (Modern Materials) 4,36 (1992), and Z.Yang, I.Sokolik, F.E, Karasz in Macromolecules (Macromolecules), 26, 1188 ( 1993), polyquinolines reported by I.D. Parker in J. Appl. Phys. Appl. Phys. Lett. (Applied Physics, Applied Physics Communications) 65, 1272 (1994). Blends of conjugated semiconducting polymers in non-conjugated host polymers can also be used as active layers for polymer LEDs, as reported by C. Zhang, H. von Seggem, K. Pakbaz, B. Kraabel, Synth. Met. by H.W. Schmidt and A.J. Heeger, (Synthetic Materials) 62, 35 (1994). Also available are blends comprising two or more conjugated polymers, as reported in Synth. Met. (Synthetic Materials), 48 243 ( 1995). In general, materials used as active layers in polymer LEDs include semiconducting conjugated polymers, more specifically semiconducting conjugated polymers exhibiting photoluminescence, and still more specifically exhibiting photoluminescence and being soluble Semiconducting conjugated polymers that can be converted from solution to uniform thin films. High work function anode

A suitable higher work function metal for use as anode material 112 is a transparent conductive film of indium/tin-oxide [H. Burroughs, D.D.C. Bradley, A.R. Brown, R.N. Marks, K. Mackay, R.H. Friend, P.L. Burns, and A.B Holmes, Nature 347, 539 (1990); D. Braun and A.J. Heeger, Appl. Phys. Lett. 58, 1982 (1991)]. In addition, thin films of conductive polymers can also be used, such as by G.Gustafsson, Y.Cao, G.M.Treacy, F.Klavetter, N.Colaneri and A.J.Heeger, Nature (natural), 357, 477 (1992); Y.Yang and A.J.Heeger, Appl.Phys.Lett. (Applied Physics Communications) 64, 1245 (1994) and U.S. Patent Application Serial No. 08/205,519; Y.Yang, E.Westerweele, C.Zhang, P.Smith and A.J. Heeger, J.Appl.Phys. (Journal of Applied Physics) 77,694(1995); J.Cao, A.J.Heeger, J.Y.Lee and C.Y.Kim, Synth.Met.(Synthetic Materials) 82,221(1996) and Y. Confirmed by Cao, G. Yu, C. Zhang, R. Menon and A. J. Heeger, Appl. Phys. Lett, (Applied Physics Letters) 70, 3191 (1997). A bilayer anode comprising an indium/tin-oxide film and a polyaniline film in the form of an emeraldine salt is preferred because, as a transparent electrode, both materials enable the light emitted from the LED to radiate from the device at an efficient level. low work function cathode

Lower work function metals suitable for cathode material 114 are alkaline earth metals such as calcium, barium, strontium and rare earth metals such as ytterbium. Alloys of low work function metals, such as alloys of magnesium in silver and lithium in aluminum are also well known in the art (US Patent Nos. 5,047,687; 5,059,862 and 5,408,109). The thickness of the electron injection cathode layer is in the range of 200-5000 Å, as demonstrated in the prior art (U.S. Pat. , 67(1995) 2281). The lower limit of 200-500 Angstroms (Å) is required to form a continuous film (full coverage) of the cathode layer (U.S. Patent 5,512,654; J.C.Scott, J.H.Kaufman, P.J.Brock, R.DiPietro, J.Salem and J.A.Goitia, J.Appl. Phys. (Journal of Applied Physics), 79 (1996) 2745; I.D. Parker, H.H. Kim, Appl. Phys. Lett. (Communications of Applied Physics, 64 (1994) 1774). In addition to good coverage, the thicker cathode layer is believed to provide self-encapsulation to isolate oxygen and water vapor from the active components of the device.

Electron-injecting cathodes containing ultrathin layers of the alkaline earth metals calcium, strontium, and barium have been reported in high-brightness and high-efficiency polymer light-emitting diodes. Compared with conventional cathodes made of the same metal (and other low-efficiency metals) with film thicknesses greater than 200 Å, ultra-thin alkaline-earth metal cathodes with a thickness of less than 100 Å are more luminescent than polymers in terms of stability and lifetime Diodes have been significantly improved (Y. Cao and G. Yu, US Patent Application 08/872,657).

For polymer light-emitting diodes with high brightness and high efficiency, it has also been reported that the electron injection cathode containing oxides of ultra-thin alkaline earth metal calcium, strontium and barium (PCT application No.US99/23775 such as Y.Cao, 1999 10 Submitted on 12 March).

The structures and materials used for photosensitive devices and device arrays are very similar to the fabrication of polymer-based LEDs. The main difference between polymer-based LEDs and photosensors is that reactive low work function electrodes are not used and the polarity of the electrodes is reversed. But long-lived photosensitive devices made of conductive polymers require airtight packaging. Therefore, the packaging box of the present invention is also useful for these devices, the packaging is sufficient to prevent the diffusion of water vapor and oxygen into the device, and does not limit its lifetime.

The invention will be further elucidated with reference to the following examples. These examples are just to illustrate different implementation modes of the present invention, and should not be regarded as limiting the present invention.

Example 1

A zeolite-based desiccant (Tri-Sorb) was used as desiccant. A polymer light emitting diode (LED) array is taken as an example of a polymer based electronic device.

An air- and water-tight enclosure made of glass containing sheets composed of zeolites (obtained from Süd-Chemie Development Packaging, a member of the Süd-Chemie Group, a division of United Catalysts, located in Belen, New Mexico), It encapsulates the LED array so that it is sealed from the atmosphere.

The desiccant is sealed in the package, and the desiccant is fixed on the inner surface of the impervious cover with a heat-curing epoxy resin (Araldite 2014, Ciba Specialty Chemicals Inc., East Lansing, Michigan) as an adhesive,

The desiccant is in powder pellet form. The impermeable cover is attached to the substrate with an adhesive. The overall device structure 100 is shown in FIG. 1 . The cover is sealed on the glass substrate with Araldite 2014 as adhesive.

Immediately after the package is sealed, the size of the luminescent pixel is measured. The packaged devices were then placed in an oven at 85°C with ambient humidity for an extended period of time. At intervals of 50 hours, the device was taken out of the furnace, and the luminescent pixel size was measured again. The deterioration of polymer electronic devices due to the action of moisture and oxygen is quantified by the loss of active area. In this particular example, the loss of light emitting area of a pixelated LED display was measured. As shown in Figure 2, Tri-Sorb resulted in less than 2% loss of luminescent area after storage at 85°C for 300 hours.

Also, as shown in Figure 2, a zeolite-based desiccant (in this particular example under the trade name Tri-Sorb) clearly outperformed other examples such as BaO and _CaSO4 (which were effective desiccants previously used in this technical field Materials) (USA 5,882,761). This example shows that zeolite-based desiccants can be very effective desiccants even at high temperatures.

Example 2

This example repeats the experiment of Example 1, except that the storage conditions are changed, including high humidity, ie 85°C/85% relative humidity. As shown in Figure 3, the polymer device lost 5% of the emissive area after 300 hours.

It can also be seen from Figure 3 that the zeolite system outperforms many other desiccants including BaO and CaO (which were effective desiccant materials in a prior patent, US Pat. No. 5,882,761).

This example shows that zeolite-based desiccants are effective desiccants even in high temperature, high humidity environments.

Example 3

This example repeats the experiment of Example 1, except that the desiccant is packed in a porous bag in powder form and fixed to the inner surface of the impermeable cover with an adhesive. The loss and comparison of the emission area are shown in Fig. 2 and Fig. 3.

This example shows that the specific physical shape of the desiccant is not important.

Example 4

In this example, a thermogravimetric weight loss study was performed on Tri-Sorb and BaO to compare their performance in persistent water removal from electronic device packaging boxes. Standard calibrated thermogravimetric analysis equipment was used. Tri-Sorb and BaO tablets were heated in dry air (from room temperature to 400 °C) while continuously monitoring the quality of the tablets, no hysteresis was found.

The results are shown in Figure 4. Both samples absorbed moisture at room temperature. When heated, both release water due to thermodynamic processes, thereby reducing the sample weight. However, it can be seen that the Tri-Sorb releases less water. At 85°C, the Tri-Sorb sample released three times less water than the BaO sample.

This example shows that the water retention properties of Tri-Sorb are better than BaO (it is a special agent applied by Pioneer as a good desiccant at 85°C) at high temperature.

As can be seen from the above description, the present invention provides a technique for encapsulating polymer light emitting devices at the lowest possible process temperature. This packaging method advantageously provides a seal between the device and the ambient air of harmful moisture and oxygen. In addition, the packaging method does not significantly increase the total thickness of the device brought about by the packaging of the device. Again, the present packaging method requires fewer individual steps than methods currently known in the art.

Claims (26)

1. an electronic device (100) comprising:

Polymer-electronics device (110), it comprises pair of electrodes (112,114) opposite one another and places active polymer (120) between two electrodes;

Airtight envelope box (124), it has inner surface (132) adjacent with the polymer-electronics device and the opposed outer surface adjacent with outside atmosphere;

Drier (130), adjacent with inner surface, this drier has a kind of loose structure, and can capture water by Physical Absorption, makes it enter loose structure;

Wherein the level Hermetic Package box is with this polymer-electronics device package, so that this polymer-electronics device and drier and outside atmosphere are separated.

2. method of making long-life electronic device based on organic polymer comprises:

Purchase polymerization electronic device (110), the mutual pair of electrodes facing of this device tool (112,114) and place active polymer (120) between the electrode;

This polymer-electronics device is encapsulated in the level Hermetic Package box (124) with solid drier (130), this drier has loose structure, can capture water by Physical Absorption, and make it enter loose structure, this enclosure separates device and drier and outside atmosphere.

3. the method for the electronic device of claim 1 and/or claim 2, wherein this polymer-electronics device comprises the substrate with at least one substrate layer, solid drier is incorporated among one or more layers of this at least one substrate layer.

4. the method for the electronic device of claim 1 and/or claim 2, wherein drier is a molecular sieve.

5. the method for the electronic device of claim 1 and/or claim 2, wherein drier comprises zeolite.

6. the method for the electronic device of claim 1 and/or claim 2, wherein drier comprises Trisorb.

7. the method for the electronic device of claim 1 and/or claim 2, it is free isolated wherein being present in drier in the enclosure and electrode and polymeric layer.

8. the method for the electronic device of claim 1 and/or claim 2, wherein drier is present on the surface in this level Hermetic Package box.

9. the method for the electronic device of claim 1 and/or claim 2, wherein the polymer-electronics device also comprises the substrate of support polymer layer and electrode, drier is present on the surface of this substrate in the base.

10. the method for the electronic device of claim 1 and/or claim 2, wherein drier is attached on the surface in this level Hermetic Package box

11. the electronic device of claim 1 and/or the method for claim 2, wherein drier is bonded on the interior surface of this level Hermetic Package box.

12. the electronic device of claim 1 and/or the method for claim 2, wherein drier exists with the pelleting form.

13. the electronic device of claim 1 and/or the method for claim 2, wherein drier exists with the powder type that is contained in the porous bag.

14. the electronic device of claim 1 and/or the method for claim 2, wherein drier exists with the solid form that is contained in the porous gel.

15. the electronic device of claim 1 and/or the method for claim 2, wherein drier exists with the solid form that is contained in the film.

16. the electronic device of claim 1 and/or the method for claim 2, wherein drier exists with the solid form that is contained in the bonding agent.

17. the electronic device of claim 1 and/or the method for claim 2, wherein this comprises anode and negative electrode to electrode, and this negative electrode comprises the metal or the metal oxide of the low work function of water reaction.

18. the electronic device of claim 1 and/or the method for claim 2, wherein this comprises anode and negative electrode to electrode, and this negative electrode comprises the alkaline-earth metal or the metal oxide of the low work function of water reaction.

19. the electronic device of claim 1 and/or the method for claim 2, wherein this comprises anode and negative electrode to electrode, and this negative electrode comprises the water reactive explosive that is selected from calcium, barium, strontium, calcium oxide, barium monoxide and strontium oxide strontia.

20. the electronic device of claim 1 and/or the method for claim 2, wherein this polymer-electronics device is a light-emitting diode.

21. the electronic device of claim 1 and/or the method for claim 2, wherein this polymer-electronics device is a light-sensitive detector.

22. the electronic device of claim 1 and/or the method for claim 2, wherein this level Hermetic Package box is made up of the polylith assembly with adhesive bonds.

23. the electronic device of claim 1 and/or the method for claim 2, wherein this bonding agent is a low temperature adhesive.

24. the electronic device of claim 1 and/or the method for claim 2, wherein this low temperature adhesive is an epoxy resin.

25. the electronic device of claim 1 and/or the method for claim 2, wherein this level Hermetic Package box comprises the substrate bonding with cover.

26. the electronic device of claim 1 and/or the method for claim 2, wherein the polymer-electronics device also comprises, the substrate of support polymer layer and electrode, wherein this level Hermetic Package box comprises and the bonding substrate of cover, and with substrate as substrate.

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