Organic electroluminescence device and fabrication method thereof

Abstract

An organic electroluminescence device is disclosed which includes: a substrate; a thin film transistor formed on the substrate; a first electrode formed on the substrate provided with the thin film transistor; an organic light emission layer and a second electrode sequentially formed on the first electrode; and a first light absorption layer formed over the thin film transistor and configured to shield light emitted from the organic light emission layer. As such, the organic electroluminescence device employing the oxide thin film transistor can secure reliability against light.

Claims

1. An organic electroluminescence device comprising: a substrate having a plurality of pixel regions; a display element on the substrate in each of the pixel regions, the display element comprising: a thin film transistor on the substrate, the thin film transistor having a source electrode and a drain electrode; an insulation layer covering the thin film transistor; a first electrode connected to the thin film transistor through a contact hole in the insulation layer; an organic light emission layer formed on the first electrode; a second electrode formed on the organic light emission layer; a first light absorption layer formed directly on top of the insulation layer in between the thin film transistor and the organic light emission layer, the first light absorption layer configured to shield the thin film transistor from light emitted from the organic light emission layer; and a passivation layer formed directly on top of the first light absorption layer and at least a portion of the first electrode and formed directly below the organic light emission layer.

2. The organic electroluminescence device of claim 1, wherein the thin film transistor includes a semiconductor layer formed from an oxide.

3. The organic electroluminescence device of claim 2, wherein the oxide is a compound represented by the following chemical formula 1:
A.sub.wB.sub.xC.sub.yO.sub.z  [Chemical formula 1] wherein 1, “A”, “B” and “C” are one of indium In, gallium Ga, zinc Zn, aluminum Al and tin Sn, respectively, and “w”, “x”, “y” and “z” are natural numbers of not less than 1 but no more than 10.

4. The organic electroluminescence device of claim 1, further comprising a second light absorption layer formed under the thin film transistor and configured to shield the thin film transistor from external light.

5. The organic electroluminescence device of claim 1, further comprising a second light absorption layer formed on the first light absorption layer under the organic light emission layer.

6. The organic electroluminescence device of claim 1, wherein the first light absorption layer is formed from an organic material or a non-conductive inorganic material, the non-conductive inorganic material having a band gap energy of at most 2 eV.

7. The organic electroluminescence device of claim 6, wherein the non-conductive inorganic material is one of germanium Ge, copper oxide CuO and gallium arsenide GaAs.

8. The organic electroluminescence device of claim 6, wherein the organic material includes at least two color filters selected from a group which consists of red, green and blue color filters.

9. The organic electroluminescence device of claim 1, wherein the thin film transistor is one of a coplanar structure, an inverted coplanar structure, and an etch stopper structure.

10. An organic electroluminescence device comprising: a substrate having an active area divided into a plurality of pixel regions; a transistor array on the substrate including a plurality of thin film transistors in each of the pixel regions, each of the plurality of thin film transistors having a source electrode and a drain electrode; an insulation layer covering the plurality of thin film transistors; an organic light emitting diode array including a plurality of organic light emitting diodes in each of the pixel regions, each organic light emitting diode of the organic light emitting diode array having a first electrode coupled to a corresponding thin film transistor of the transistor array through a corresponding contact hole in the insulation layer, an organic light emission layer, and a second electrode; a plurality of first light absorption layers disposed directly on top of the insulation layer in between a corresponding thin film transistor in the transistor array and a corresponding organic light emitting diode in the organic light emitting diode array; and a passivation layer formed directly on top of the plurality of first light absorption layers and at least a portion of the first electrodes of the organic light emitting diode array, the passivation layer formed directly below the organic light emission layers of the organic light emitting diode array.

11. The organic electroluminescence device of claim 10, wherein the first light absorption layer is fabricated from a material that selectively absorbs light having a wavelength of less than 450 nanometers.

12. The organic electroluminescence device of claim 10, wherein the first light absorption layer is formed from a material having a band gap energy of at most 2 ev, the material being one of an organic material or a non-conductive inorganic material.

13. The organic electroluminescence device of claim 10, wherein the first light absorption layer is formed from one of a non-conductive inorganic material of silicon, germanium, copper oxide, and gallium arsenide.

14. The organic electroluminescence device of claim 10, wherein the first light absorption layer is an organic material that includes at least two color filters selected from a group consisting of red, green and blue color filters.

15. The organic electroluminescence device of claim 10, further comprising a second light absorption layer formed under the thin film transistor array configured to shield the plurality of thin film transistors from external light.

16. The organic electroluminescence device of claim 10, further comprising a second light absorption layer formed on the first light absorption layer under an organic light emission layer of the organic light emitting diode array.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated herein and constitute a part of this application, illustrate embodiment(s) of the present disclosure and together with the description serve to explain the disclosure. In the drawings:

(2) FIG. 1A is a cross-sectional view showing an organic electroluminescence device of the related art;

(3) FIG. 1B is an enlarged view largely showing a region A in FIG. 1A;

(4) FIG. 2A is a cross-sectional view showing an organic electroluminescence device according to an embodiment of the present disclosure;

(5) FIG. 2B is an enlarged view largely showing a region A in FIG. 2A;

(6) FIG. 3 is a data sheet illustrating an optical band gap characteristic of a semiconductor layer of organic electroluminescence device according to an embodiment of the present disclosure;

(7) FIGS. 4A and 4B are planar views showing a formation region of a light absorption layer of an organic electroluminescence device according to an embodiment of the present disclosure;

(8) FIG. 5 is a data sheet illustrating expected transmittance of a light absorption layer of an organic electroluminescence device according to an embodiment of the present disclosure with respect to wavelength;

(9) FIG. 6 is a data sheet comparing characteristics of a thin film transistor when light absorption layers different from one another are applied to the organic electroluminescence device according to an embodiment of the present disclosure; and

(10) FIGS. 7A through 7F are cross-sectional views illustrating a method of fabricating an organic electroluminescence device according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) Reference will now be made in detail to an organic electroluminescence device and a fabrication method thereof in accordance with embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. These embodiments introduced hereinafter are provided as examples in order to convey their spirits to the ordinary skilled person in the art. Therefore, these embodiments might be embodied in a different shape, so are not limited to these embodiments described here. In the drawings, the size, thickness and so on of a device can be exaggerated for convenience of explanation. Wherever possible, the same reference numbers will be used throughout this disclosure including the drawings to refer to the same or like parts.

(12) FIG. 2A is a cross-sectional view showing an organic electroluminescence device according to an embodiment of the present disclosure. In detail, FIG. 2A is a cross-sectional view showing a white OLED device of a bottom emission mode according to an embodiment of the present disclosure. FIG. 2B is an enlarged view largely showing a region A in FIG. 2A.

(13) Referring to FIG. 2A, the organic electroluminescence device 100 according to an embodiment of the present disclosure is configured with a first substrate 111 and a second substrate (not shown). The first substrate 111 and the second substrate are separated from each other in such a manner as to face each other.

(14) The organic electroluminescence device 100 includes a thin film transistor array 114 formed on the first substrate 111, and a first electrodes 142 independently formed on the thin film transistor array 114 in every pixel. Also, the organic electroluminescence device 100 includes an organic light emission layer 144 formed on the first electrode 142, and a second electrode 145 formed on the entire surface of the organic light emission layer 144.

(15) The thin film transistor array 114 includes a driving thin film transistor T which can be formed in any one of an edge stopper structure and a coplanar structure. If the driving thin film transistor T is formed in the edge stopper structure, a bottom gate thin film transistor can be applied to the driving thin film transistor T. Moreover, an etch stopper for etch prevention can be formed on a channel layer opposite to the gate electrode. Meanwhile, the driving thin film transistor T of the coplanar structure allows a gate electrode and source and drain electrodes to be all formed on one surface of an active layer. Also, an inverted coplanar structure corresponding to a bottom gate structure can be applied to the driving thin film transistor T.

(16) As shown in FIG. 2B, the driving thin film transistor T can be formed in the coplanar structure. Referring to FIG. 2B, the driving thin film transistor T is completed by depositing a buffer layer 112 on the substrate 111 and sequentially forming a semiconductor layer 120, a gate insulation film 121, a gate electrode 122, a first insulation layer 123 and source and drain electrodes 124a and 124b. A second insulation layer 130, a first electrode 142, an organic light emission layer 144 and so on are sequentially formed on the substrate 111 provided with the source and drain electrodes 124a and 124b of the driving thin film transistor T.

(17) Referring to FIGS. 2A and 2B, electrons injected from the second electrode 145 and electric-holes injected from the first electrode 142 are drifted toward the organic light emission layer 144 when a voltage is applied between the first electrode 142 and the second electrode 145. As such, the electrons and the electric-holes applied into the organic light emission layer 144 collide and are recombined with each other within the organic light emission layer 144, thereby generating light. In this case, the first electrode 142 is used as an anode and the second electrode 145 is used as a cathode.

(18) If the organic electroluminescence device 100 is a white OLED device, the organic light emission layer 144 emits white light. As such, red, green and blue color filters 131, 132 and 133 are formed between the second insulation layer 130 and the first electrode 142 in red, green and blue pixel regions, respectively. Meanwhile, no color filter is formed in a white pixel region. In accordance therewith, the white pixel region allows white light W generated in the organic light emission layer to be output.

(19) Alternatively, if the organic electroluminescence device is fabricated in the bottom emission mode, light emitted from the organic light emission layer 144 is radiated to the exterior through the first electrode 142 and the first substrate 111. In this case, the second electrode also performs a function of a reflective plate.

(20) The first electrode 142 can be formed from a transparent conductive material such as ITO (indium-tin-oxide), IZO (indium-zinc-oxide) or others. The second electrode 145 can be formed from an opaque metal material with a reflective property. For example, the second electrode 145 can be formed from one selected from a metal group which includes aluminum Al, gallium Ga, calcium Ca, magnesium Mg and so on.

(21) The semiconductor layer 120 can be formed from an oxide semiconductor material such as IGZO. Preferably, the semiconductor layer 120 is formed from an oxide semiconductor material with mobility of at least 30 cm2/Vs. The oxide semiconductor material can be represented in the following chemical formula 1.
A.sub.wB.sub.xC.sub.yO.sub.z  [Chemical formula 1]

(22) In the chemical formula 1, “A”, “B” and “C” are one of indium In, gallium Ga, zinc Zn, aluminum Al and tin Sn, respectively. Also, “w”, “x”, “y” and “z” are natural numbers of not less than 1 but no more than 10.

(23) However, an oxide semiconductor layer with a high mobility is sensitive to light. To address this matter, the organic electroluminescence device 100 according to an embodiment of the present disclosure includes a light absorption layer 136 which is formed over the thin film transistor and used to shield light emitted from the organic light emission layer 144.

(24) Preferably, the light absorption layer 136 is formed from a material selectively absorbing wavelength light which can affect deterioration of the semiconductor layer 120. As such, the concentration of heat for the light absorption layer 136 can be prevented. The wavelength of light affecting the light deterioration of the semiconductor layer 120 can be obtained from an optical band gap characteristic of the semiconductor layer 120.

(25) FIG. 3 is a data sheet illustrating an optical band gap characteristic of a semiconductor layer of an organic electroluminescence device according to an embodiment of the present disclosure. In detail, FIG. 3 illustrates the optical band gap characteristic of the semiconductor layer which has a mobility of not less than 30 cm2/Vs and is formed from IGZO with a fixed composition ratio.

(26) Referring to FIG. 3, optical band gap energy of the IGZO semiconductor layer with the mobility of at least 30 cm2/Vs and a fixed composition ratio becomes a range of about 2.75˜2.8 eV. The optical band gap energy of about 2.75˜2.8 eV corresponds to energy of light with a wavelength range of 433 nm˜450 nm. As such, when light with wavelengths of no more than 450 nm is irradiated, the IGZO semiconductor layer is deteriorated by light.

(27) In view of this point, the light absorption layer 136 shown in FIG. 3 is designed to absorb larger energies than 2.8 eV, i.e. shorter wavelength light than 450 nm. As such, the light absorption layer 136 shown in FIG. 3 can be formed from a material with smaller band gap energy than 2.8 eV. For example, the light absorption layer 136 can be formed from one non-conductive inorganic material of silicon Si (1.1 eV), germanium Ge (0.67 eV), copper oxide CuO (1.2 eV), gallium arsenide GaAs (1.43 eV) and so on. Alternatively, the light absorption layer 136 can be formed to have a double layer structure of red and green color filters which are formed from organic materials.

(28) Such a light absorption layer 136 formed from one of the organic and inorganic materials is preferably disposed over the thin film transistor as shown in FIGS. 2A and 2B, in order to shield light emitted from the organic light emission layer 144. Alternatively, the light absorption layer 136 can be disposed under the thin film transistor, in order to shield external light.

(29) If the light absorption layer 136 is disposed under the thin film transistor, the light absorption layer 136 is preferably formed between the substrate 111 and the buffer layer 112. In this case, the light absorption layer 136 is preferably formed from a non-conductive inorganic material such as silicon Si (1.1 eV), germanium Ge (0.67 eV), copper oxide CuO (1.2 eV), gallium arsenide GaAs (1.43 eV) and so on.

(30) When the light absorption layer 136 is formed in the double layer structure of the red and green color filters 131 and 132, the light absorption layer 136 is preferably formed in the same layer as red, green and blue color filters which are formed in red, green and blue pixel regions.

(31) FIGS. 4A and 4B are planar views showing a formation region of a light absorption layer of an organic electroluminescence device according to an embodiment of the present disclosure.

(32) Referring to FIG. 4A, the light absorption layer 136 (shown in FIG. 2A) of the organic electroluminescence device of the according to an embodiment of the present disclosure may be locally formed only over the thin film transistors.

(33) Alternatively, the light absorption layer 136 (shown in FIG. 2A) of the organic electroluminescence device may be formed in the entire area with exception of openings, as shown in FIG. 4B.

(34) More specifically, the organic electroluminescence device according to an embodiment of the present disclosure includes the red, green and blue pixel regions. The red, green and blue pixel regions are defined by crossing gate lines GL, data lines DL and power lines PL.

(35) A switching thin film transistor TS, a driving thin film transistor TD connected to the switching thin film transistor TS, the first electrode 142 (shown in FIG. 2A) or other, and a storage capacitor C are formed in each of the red green and blue pixel regions.

(36) The switching thin film transistor TS includes a gate electrode connected to one of gate lines GL, a source electrode connected to one of the data lines DL, and a drain electrode connected to a gate electrode 122 (shown in FIG. 2B) of the driving thin film transistor TD and the storage capacitor C. The driving thin film transistor TD includes the gate electrode 122 connected to the drain electrode of the switching thin film transistor TS and the storage capacitor C, a source electrode 124a (shown in FIG. 2B) connected to one of the power lines PL, and a drain electrode 124b (shown in FIG. 2B) connected to the first electrode 142 (shown in FIG. 2A).

(37) The switching thin film transistor TS is turned-on and transfers a data signal on the respective the data line DL to the storage capacitor C and the gate electrode 122 (shown in FIG. 2B) of the driving thin film transistor TD, when a scan pulse is applied to the respective gate line GL. The driving thin film transistor TD replies to the data signal applied to its gate electrode 122 (shown in FIG. 2B) and controls a current I flowing from the respective power line PL toward an organic electroluminescence element (not shown). In accordance therewith, a light quantity emitted from the organic electroluminescence element is adjusted.

(38) The light absorption layer 136 (shown in FIG. 2A) is formed not only over the driving thin film transistor TD but also over the switching thin film transistor TS. As described above, the light absorption layer 136 can be locally formed only over the thin film transistors. Alternatively, the light absorption layer 136 can be formed on the entire area with exception of the openings.

(39) FIG. 5 is a data sheet illustrating expected transmittance of a light absorption layer of the organic electroluminescence device according to an embodiment of the present disclosure with respect to wavelength. In detail, FIG. 5 is a graphic diagram showing expected transmittance with respect to wavelength when the light absorption layer 136 (shown in FIG. 2A) is formed in the double layer structure of the red and green color filters.

(40) As seen from FIG. 5, it is evident that the light absorption layer 136 (shown in FIG. 2A) formed in the double layer structure of the red and green color filters 131 and 132 (shown in FIG. 2A) almost completely absorbs light with wavelength of below 600 nm. As such, the IGZO semiconductor layer with mobility of 30 cm2/Vs can be almost completely protected from deterioration which is caused by light.

(41) FIG. 6 is a data sheet comparing characteristics of a thin film transistor when light absorption layers different from one another are applied to an organic electroluminescence device according to an embodiment of the present disclosure. In detail, a first graphic diagram illustrates a characteristic of the thin film transistor when a light absorption layer including only a red color filter is applied. A second graphic diagram illustrates another characteristic of the thin film transistor when a light absorption layer including only a green color filter is applied. A third graphic diagram illustrates still another characteristic of the thin film transistor when the light absorption layer 136 (shown in FIG. 2A) formed in the double layer structure of the red and green color filters 131 and 132 (shown in FIG. 2A) according to an according to an embodiment of the present disclosure is applied.

(42) As seen from FIG. 6, it is evident that the light absorption layer 136 (shown in FIG. 2A) formed in the double layer structure of the red and green color filters 131 and 132 (shown in FIG. 2A) according to an embodiment of the present disclosure largely enhances a characteristic of the thin film transistor, compared to other light absorption layers including only one of the red and green color filters. In detail, when the light absorption layer 136 (shown in FIG. 2A) formed in the double layer structure of the red and green color filters 131 and 132 (shown in FIG. 2A) according to an embodiment of the present disclosure is applied, the threshold voltage Vth of the thin film transistor decreases by 0.2V (i.e., ΔVth=−0.2V). Meanwhile, the threshold voltage Vth of the thin film transistor decreases by 13V (i.e., ΔVth=−13V) when the light absorption layer including only the red color filter is applied. Also, the threshold voltage Vth of the thin film transistor decreases by 12V (i.e., ΔVth=−12V) when the light absorption layer including only the green color filter is applied. In other words, it is evident that the thin film transistor deteriorates when the light absorption layer including only one of the red and green color filters is applied.

(43) FIGS. 7A through 7F are cross-sectional views illustrating a method of fabricating an organic electroluminescence device according to an embodiment of the present disclosure.

(44) Referring to FIG. 7A, the method of fabricating an organic electroluminescence device according to an embodiment of the present disclosure allows a thin film transistor array 114 including driving thin film transistors T to be firstly formed on a substrate 111.

(45) In order to form the driving thin film transistors T, a buffer layer 112 is firstly formed on the entire surface of the substrate 111 and active layers 120′ are formed on the buffer layer 112. The active layers 120′ are formed from an oxide with a high mobility. Also, the active layers 120′ can be formed using one of a vapor deposition method and a photolithography method. For example, the active layers 120′ are prepared by forming an oxide film of IGZO or others using the vapor deposition method and patterning the oxide film. The formation of a film is performed in order to form a polycrystalline oxide semiconductor sintered compound which is formed from IGZO or others. One of a sputtering method and a pulse laser deposition (PLD) method can be used in the formation of the film. Preferably, the sputtering method is used for mass production.

(46) The process of patterning the oxide film can be performed by forming photoresist patterns on the oxide film of IGZO or others corresponding to portions, which the active layers 120′ will be formed, and then etching the oxide film using an acid solution such as an mixed liquid of hydrochloric acid, nitric acid and dilute sulfuric acid, another mixed liquid of phosphoric acid, nitric acid and acetic acid, or others. The aqueous solution including phosphoric acid, nitric acid and acetic acid can remove exposed portion of an IGZO film during a short time.

(47) A gate insulation film 121 and a gate electrode 122 are sequentially formed in the central region of each active layer 120′. Subsequently, a first insulation layer 123 and source and drain electrodes 124a and 124b are sequentially formed, thereby completing the driving thin film transistor T.

(48) As shown in FIG. 7B, a second insulation layer 130 is formed on the entire surface of the substrate 111 provided with the source and drain electrodes 124a and 124b of the driving thin film transistors T. The second insulation layer 130 can be prepared by coating an insulation material on the entire surface of the substrate 111. As an example of the insulation material, one of an organic insulation material and an inorganic insulation material can be used. The organic insulation material can become an acryl based organic compound or others. The inorganic insulation material can become silicon oxide SiOx, silicon nitride SiNx or others.

(49) Also, red, green and blue color filters 131, 132 and 133 are formed on the second insulation layer 130 corresponding to respective pixel regions, respectively. At the same time, a light absorption layer 136 is also formed in a stacked structure of the red and green color filters 131 and 132.

(50) The light absorption layer 136 is formed over not only the driving thin film transistors T but also switching thin film transistors even though it not shown in the drawings. The formation range of the light absorption layer 136 can be limited to the upper portions of the thin film transistors, but can be expanded into the entire area with exception of openings.

(51) The procedure of forming the red, green and blue color filters 131, 132 and 133 and the light absorption layer 136 will now be described in detail. First, the red color filter 131 is formed on the second insulation layer 130 corresponding to the red pixel region and the thin film transistors by coating a red color resist including a red dye on the second insulation layer 130 and patterning the red color resist through a photolithography procedure and an etching process. The green color filter 132 is formed on the second insulation layer 130 corresponding the green pixel region and on the red color filter 131 which is disposed over the thin film transistors, by coating a green color resist including a green dye on the second insulation layer 130 provided with the red color filter 131 and patterning the green color resist through another photolithography procedure and another etching process. The blue color filter 133 is formed on the second insulation layer 130 corresponding to the blue pixel region, by coating a blue color resist including a blue dye on the insulation layer 130 provided with the red and green color filters 131 and 132 and patterning the blue color resist through still another photolithography procedure and still another etching process.

(52) In this way, the red, green and blue color filters 131, 132 and 133 are formed in the red, green and blue pixel regions, respectively, and the light absorption layer 136 including the stacked red and green color filters 131 and 132 are formed over the thin film transistors. Although it is explained that the light absorption layer 136 is formed in a double layer structure of the red and green color filters 131 and 132, the light absorption layer 136 can be formed in a triple layer structure of the red, green and blue color filters 131, 132 and 133. In the stacking order of the color filters, it is explained herein that the red color filter 131 is first formed, but the green color filter 132 can be first formed. However, the stacking order of the color filters is preferably set in consideration of the degree of deterioration caused by a developer.

(53) Referring to FIG. 7C, drain contact holes 141 are formed in the second insulation layer provided with the red, green and blue color filters 131, 132 and 133 and the light absorption layer 136. Also, first electrodes 142 are formed on the second insulation layer 130 provided with the drain contact holes 141. Each of the first electrodes 142 is connected to the respective drain electrode 124b through the respective drain contact hole 141. The first electrodes 142 are formed by depositing a transparent conductive material on the entire surface of the second insulation layer 130 provided with the drain contact holes 141 and patterning the deposited transparent conductive material through a photolithography procedure and an etching process.

(54) As shown in FIG. 7D, a passivation layer 143 is formed by depositing an insulation material on the entire surface of the substrate 111. The passivation layer 143 is partially removed through a photolithography procedure and an etching process and partially exposes each of the first electrodes 142. Such a passivation layer 143 is used to protect the thin film transistors from moisture and alien substances.

(55) Referring to FIG. 7E, an organic light emission layer 144 and a second electrode 145 are sequentially formed on the partially exposed first electrodes 142.

(56) Referring to FIG. 7F, the first substrate, 111 which is provided with the second electrode 145 and faces a second substrate 211, is combined with the second substrate 211 by means of a sealant 301. In accordance therewith, the organic electroluminescence device according to an embodiment of the present disclosure is completed.

(57) As described above, the present disclosure can allow the light absorption layers to be disposed over and under the thin film transistor. In accordance therewith, the deterioration of the thin film transistor caused by light can be prevented. As a result, the organic electroluminescence device can enhance reliability against light.

(58) Although the present disclosure has been limitedly explained regarding only the embodiments described above, it should be understood by the ordinary skilled person in the art that the present disclosure is not limited to these embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the present disclosure. Accordingly, the scope of the present disclosure shall be determined only by the appended claims and their equivalents without being limited to the detailed description.