Patent Application
20090315457
This application is based on and claims priority of Japanese Patent Application No. 2008-164382 filed on Jun. 24, 2008, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a flexible organic EL display employing a plastic film as a substrate and a method of manufacturing the same.
2. Description of the Related Art
An organic EL (Electroluminescence) display is expanding rapidly its applications into an information equipment, and the like. Recently the flexible display employing a plastic film as a substrate attracts attention. Such flexible display can be utilized not only for the ultra-slim and lightweight mobile display, which can be rounded and housed and is convenient for carrying, but also for the large display.
However, the plastic film possesses weak stiffness and has a low heat distortion temperature. Therefore, heat distortion such as warp, expansion/contraction, or the like easily occurs in the manufacturing step accompanied by heat treatment. For this reason, in the manufacturing method of forming various elements directly on the plastic film, the conditions of the manufacturing step accompanied by heat treatment, etc. are restricted, and high-precision alignment becomes difficult. As a result, in some cases the element substrate having desired characteristics can not be manufactured.
In order to avoid such problem, there is the method of manufacturing the element substrate for the liquid crystal display device by aligning the amorphous silicon TFT element, the color filter, etc. on the heat resistant and stiff glass substrate with high precision under the unlimited manufacturing conditions, thereby to constitute the transfer layer, and then transferring the transfer layer onto the plastic film (Patent Literature 1 (Patent Application Publication (KOKAI) 2001-356370)).
Also, the flexible display needs the flexible TFT element that can follow the bending. It is feared that the amorphous silicon TFT or the low-temperature polysilicon TFT as the driving transistor in the prior art cannot obtain satisfactory reliability. Therefore, as the driving transistor for the flexible display, the TFT employing the organic semiconductor or the oxide semiconductor that is flexible and can follow the bending as the active layer attracts attention.
In Patent Literature 2 (Patent Application Publication (KOKAI) 2003-255857), it is set forth that the organic EL display is manufactured by forming sequentially the gate electrode, the gate insulating film, the organic semiconductor layer, and source/drain electrodes on the plastic substrate, or the like, and then forming the organic EL element on the anode which is connected to the drain electrode.
Also, in Patent Literature 3 (Patent Application Publication (KOKAI) 2007-96055), it is set forth that the semiconductor device including the thin film transistor using the oxide semiconductor such as the zinc oxide, or the like.
Meanwhile, the organic semiconductor layer and the organic EL layer have such a problem that performance is degraded by the photolithography or etching step accompanied by the process using organic solvent, water, plasma, electron beam, heat treatment, or the like, and in turn these layers hardly function.
Also, the technology to construct the flexible organic EL display by forming the TFT using the oxide semiconductor and the organic EL element on the plastic film has not been sufficiently established. A method of forming the desired TFT using the oxide semiconductor and the desired organic EL element stably on the plastic film with high yield is earnestly demanded.
It is an object of the present invention to provide a flexible organic EL display in which a desired oxide semiconductor TFT and an organic EL element are formed stably on a plastic film with high yield, and a method of manufacturing the same.
The present invention is concerned with a flexible organic EL display of active matrix type in which a TFT and an organic EL element are provided in every pixel, which includes a plastic film; an adhesive layer formed on the plastic film; a lower insulating layer formed on the adhesive layer; the organic EL element embedded in the lower insulating layer and constructed by forming an anode, an organic EL layer, and a cathode sequentially from a bottom; an upper insulating layer formed on the organic EL element; the TFT embedded in the upper insulating layer, and constructed by forming an oxide semiconductor layer, a source electrode and a drain electrode, a gate insulating layer, and a gate electrode sequentially from a bottom; and a via hole provided in the upper insulating layer and reaching the drain electrode of the TFT; wherein the cathode is connected electrically to the drain electrode of the TFT via the via hole.
The flexible organic EL display of the present invention is manufactured in such a way that the transfer layer including the TFT, the insulating layer for coating the TFT, the organic EL element, and the insulating layer for coating the element is formed in a peelable state on the temporary substrate (the glass substrate, or the like), and then the transfer layer is transferred/formed on the plastic film via the adhesive layer in a state that the top and bottom reverses. Therefore, the TFT and the organic EL element are transferred onto the plastic film in a state that the top and bottom reverses from the structure that is formed on the temporary substrate.
By this matter, the TFT is composed of the oxide semiconductor layer, the source electrode and the drain electrode, the gate insulating layer, and the gate electrode sequentially from the bottom, and is embedded in the upper insulating layer. Also the organic EL element is composed of the anode, the organic EL layer, and the cathode sequentially from a bottom, and is embedded in the lower insulating layer.
Then, the via hole reaching the drain electrode of the TFT is provided in the upper insulating layer in which the TFT is embedded, and the cathode is connected electrically to the drain electrode of the TFT via the via hole.
In the present invention, since such transfer technology is employed, the organic EL element is formed under the TFT such that this element is protected by the lower insulating layer and the upper insulating layer and is embedded therein. As a result, such a situation can be prevented that steam from an outside air and moisture in the plastic film enter into the organic EL element, and thus reliability of the organic EL element can be improved.
Also, in the preferred mode of the present invention, the gate insulating layer of the TFT is formed of an insulating layer which contains no hydroxyl group and is obtained by polymerizing/cross-linking poly vinyl phenol, poly methyl silsesquioxane, or polyimide by applying a heat treatment (anneal). In the present invention, since the transfer technology is utilized, the insulating layer containing no hydroxyl group can be formed by heat-treating the coating film such as poly vinyl phenol, or the like at a temperature of 180° C. or more on the heat-resistant temporary substrate, in the formation of the gate insulating layer. Therefore, the gate insulating layer which has a sufficient dielectric breakdown electric field strength (1 MV/cm or more) and can follow a bending stress can be transferred/formed on the plastic film easily.
Further, the transfer technology is utilized in the present invention. Therefore, in the formation of the oxide semiconductor TFT, the oxide semiconductor layer can be thermally treated on the heat-resistant temporary substrate at a temperature of 200° C. or more. As a result, the oxide semiconductor layer acting as the active layer of the TFT having the desired electric characteristics (Vth, etc.) can be transferred easily onto the plastic film.
Also, the present invention is concerned with a method of manufacturing a flexible organic EL display of active matrix type in which a TFT and an organic EL element are provided in every pixel, which includes the steps of forming a transparent peelable layer on a temporary substrate; forming the TFT constructed by forming a gate electrode, a gate insulating layer, a source electrode and a drain electrode, and an oxide semiconductor layer over the transparent peelable layer sequentially from a bottom; forming a first insulating layer on the TFT; forming a via hole reaching the drain electrode of the TFT, by processing the first insulating layer; forming the organic EL element composed of a cathode connected to the drain electrode via the via hole, an organic EL layer formed on the cathode, and an anode formed on the organic EL layer, on the first insulating layer; forming a second insulating layer on the organic EL element; adhering a plastic film onto the second insulating layer via an adhesive layer; and transferring/forming the second insulating layer, the organic EL element, the first insulating layer, the TFT, and the transparent peelable layer onto the plastic film via the adhesive layer, by peeling the temporary substrate along a boundary between the temporary substrate and the transparent peelable layer.
By using the manufacturing method of the present invention, the foregoing flexible organic EL display of the present invention can be manufactured easily.
In the present invention, the transparent peelable layer is used as the separating layer at a time of the transfer operation. Thus, the transparent peelable layer exposed after the temporary substrate is peeled off can be utilized as the surface protection layer. Therefore, in the manufacturing method utilizing the transfer technology, there is no necessity to remove the peeling layer or to form particularly the surface protection layer. As a result, the manufacturing steps can be simplified and a cost reduction can be achieved.
As explained above, in the present invention, the desired oxide semiconductor TFT and the desired organic EL element can be formed stably on the plastic film with high yield.
An embodiment of the present invention will be explained with reference to the accompanying drawings hereinafter.
In the method of manufacturing the flexible organic EL display according to the present embodiment, as shown in
The transparent peelable layer 22 is formed of a polyimide layer that is obtained by condensing tetracarboxylic acid (anhydride) and diamine. As the tetracarboxylic acid (anhydride), benzophenone tetracarboxylic anhydride or pyromellitic acid anhydride is employed. Also, as the diamine, 3,3′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminobenzophenone, or 4,4′-diaminobenzophenone is employed.
Such polyimide layer is transparent until its film thickness is about 5 μm. However, when its film thickness is increased up to a thickness of about 20 μm that functions as a complete film, this polyimide layer is tinged with yellowish. This coloring is caused due to the basicity of amine, and thus this yellow coloring can be weakened by reducing the basicity of amine. That is, when a film thickness of the transparent peelable layer 22 is set thick, this coloring can be weakened by using the diamine that is coupled with substituent having electron-suction property.
In this case, when the coloring does not become an issue, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, or the like may be employed as the amine.
Then, as shown in
The gate electrodes 32a, 32b are formed by forming an aluminum (Al) layer, chrome (Cr) layer, a gold (Au) layer, an ITO (Indium Tin Oxide) layer, an IZO (Indium Zinc Oxide) layer, or the like by using the sputter method, or the like, and then patterning the layer by using the photolithography and the etching.
Then, as shown in
In the present embodiment, because the flexible display is manufactured by utilizing the transfer technology, the gate insulating layer 34 is formed on the heat-resistant glass substrate 10. Therefore, the coating film can be heat-treated at a desired temperature. As a result, the gate insulating layer 34 not containing a hydroxyl group can be obtained easily from the above coating material.
In the gate insulating layer 34 obtained by such method and not containing a hydroxyl group, dielectric breakdown electric field strength of 1 MV/cm or more can be obtained and a flexible insulating layer which follows a bending stress is constituted. Thus, this flexible insulating layer can be employed preferably as the TFT gate insulating layer of the flexible display.
Otherwise, an inorganic insulating layer such as a silicon oxide layer (SiOx), a silicon nitride layer (SiN), a tantalum oxide layer (Ta2O5), or the like may be employed as the gate insulating layer 34.
Then, the gate insulating layer 34 is processed by the photolithography and the etching. Thus, a first via hole VH1 reaching the gate electrode 32b of the Dr-TFT is formed.
Then, as shown in
At this time, the drain electrode 36b of the Sw-TFT is connected electrically to the gate electrode 32b of the Dr-TFT via the first via hole VH1. The source electrodes 36a, 36x and the drain electrodes 36b, 36y are formed by patterning the conductive layer made of the same material as the gate electrodes 32a, 32b by using the photolithography and the etching.
Then, as shown in
As the oxide semiconductor layers 38a, 38b, a transparent amorphous oxide semiconductor made of indium (In)-zinc (Zn)-oxygen (O) series, indium (In)-Zinc (Zn)-gallium (Ga)-oxygen (O) series, or the like is employed.
As the method of forming the oxide semiconductor layers 38a, 38b, first, an oxide semiconductor layer made of the above material (film thickness: 50 to 100 nm) is formed like a blanket on the source electrodes 36a, 36x and the drain electrodes 36b, 36y, and the gate insulating layer 34 by the sputter method.
Then, the oxide semiconductor layer is heat-treated (annealed) in a temperature atmosphere of 200° C. or more (200° C. to 300° C. (preferably 250° C. or more)). Then, the oxide semiconductor layer is patterned by the photolithography and the etching. The oxide semiconductor layer formed by the sputter method functions as the active layer of the TFT with the desired electric characteristics (Vth, etc.) by applying the heat treatment at about 200° C. In the present embodiment, the oxide semiconductor layers 38a, 38b is an n-type semiconductor.
In the present embodiment, as described later, the oxide semiconductor layers 38a, 38b is formed on the heat-resistant glass substrate 10, and then transferred onto the plastic film. Therefore, in forming the oxide semiconductor layers 38a, 38b, the heat treatment can be applied at a desired temperature. On the contrary, in the case that the oxide semiconductor layer is directly formed on the plastic film, the heat treatment in excess of 200° C. cannot be applied because the expansion/contraction of the plastic film is caused. Therefore, it is difficult to form the oxide semiconductor layer with the desired electric characteristics.
Accordingly, a Sw-TFT 5 composed of the gate electrode 32a, the gate insulating layer 34, the source electrode 36a, the drain electrode 36b, and the oxide semiconductor layer 38a connected electrically to the source electrode 36a and the drain electrode 36b, is obtained. Also, a Dr-TFT 6 composed of the gate electrode 32b, the gate insulating layer 34, the source electrode 36x, the drain electrode 36y, and the oxide semiconductor layer 38b connected electrically to the source electrode 36x and the drain electrode 36y, is obtained. Then, the drain electrode 36b of the Sw-TFT 5 is connected electrically to the gate electrode 32b of the Dr-TFT 6 via the first via hole VH.
Then, as shown in
Then, the first protection insulating layer 46 is processed by the photolithography and the etching. Thus, a second via hole VH2 reaching the drain electrode 36y of the Dr-TFT 6 is formed.
Then, as shown in
Then, as shown in
Then, as also shown in
As the light emitting layer 54 of low polymer-series, the material in which the doping material is mixed into the host material is employed, and the doping material (molecules) emits a light. As the host material, there are Alq3 and a distyrylarylene derivative (DPVBi), for example, while as the doping material, there are a coumalin 6 for the emission of green light and DCJTB for the emission of red light, for example.
When a full color display is implemented by respective light emitting layers 54 for the three primary colors, a red light emitting layer, a green light emitting layer, and a blue light emitting layer are formed on the electron transporting layers 52 of the pixel portions (not shown) for three primary colors (red (R), green (G), and blue (B)) respectively. Otherwise, when a white light emitting layer is employed as the light emitting layer 54, the full color display can be implemented by combining the white light emitting layer with color filters.
Then, as shown in
Otherwise, the electron transporting layer 52, the light emitting layer 54, and the hole transporting layer 56 are formed by the ink jet system as a pattern respectively.
Accordingly, an organic EL layer 50 composed of the electron transporting layer 52, the light emitting layer 54, and the hole transporting layer 56 is obtained.
In this case, a mode in which only either of the electron transporting layer 52 and the hole transporting layer 56 is formed may be employed, or such a mode in which both the electron transporting layer 52 and the hole transporting layer 56 are omitted may be employed.
Then, as also shown in
As described later, the cathode 26 and the anode 58 are composed as a combination in which one is the transparent conductive layer and the other is the opaque conductive layer. A combination of the transparent and opaque in them is selected depending on whether the light emitted from the organic EL layer 50 is passed through the anode 58 or the cathode 26.
Accordingly, an organic EL element 2 composed of the cathode 26, the organic EL layer 50, and the anode 58 is obtained.
Then, as also shown in
Then, as shown in
Then, as also shown in
In
With the above, a flexible organic EL display 1 of the present embodiment is obtained.
As shown in
The organic EL element 2 is constructed by stacking the anode 58, the organic EL layer 50, and the cathode 26 sequentially from the bottom. The organic EL layer 50 is constructed by stacking the hole transporting layer 56, the light emitting layer 54, and the electron transporting layer 52 sequentially from the bottom. Then, the organic EL element 2 is embedded in the second protection insulating layer 59 such that an upper surface of the cathode 26 and an upper surface of the second protection insulating layer 59 constitute the identical surface.
Also, the first protection insulating layer 46 is formed on the organic EL element 2. The Sw-TFT 5 and the Dr-TFT 6 are embedded side by side in the lateral direction in the first protection insulating layer 46. Like the organic EL element 2, the Sw-TFT 5 and the Dr-TFT 6 formed on the glass substrate 10 are arranged in a state that the top and bottom reverses.
The Sw-TFT 5 is constructed by forming the oxide semiconductor layer 38a, the source electrode 36a and the drain electrode 36b, the gate insulating layer 34, and the gate electrode 32a sequentially from the bottom. Similarly, the Dr-TFT 6 is constructed by forming the oxide semiconductor layer 38b, the source electrode 36x and the drain electrode 36y, the gate insulating layer 34, and the gate electrode 32b sequentially from the bottom.
The respective source electrodes 36a, 36x and the respective drain electrodes 36b, 36y are arranged to extend from the inner areas of the gate electrodes 32a, 32b to the outer side. The oxide semiconductor layers 38a, 38b arranged in the opposing areas located between them constitute the channel portions of respective TFTs.
Also, the buffer layer 24 and the transparent peelable layer 22 are formed in order on the Sw-TFT 5 and the Dr-TFT 6. The transparent peelable layer 22 functions as the surface protection layer 23.
In the Sw-TFT 5 and the Dr-TFT 6 in
In the method of manufacturing the flexible organic EL display of the present embodiment, on the glass substrate 10, the oxide semiconductor TFT (the Sw-TFT 5 and the Dr-TFT 6) is formed between the buffer layer 24 and the first protection insulating layer 46, the organic EL element 2 is formed between the first protection insulating layer 46 and the second protection insulating layer 59, and these elements are transferred onto the plastic film 20.
By employing such approach, the organic EL element 2 is formed under the oxide semiconductor TFT (the Sw-TFT 5 and the Dr-TFT 6) such that this element is protected with the first and second protection insulating layers 46, 59 and embedded therein. As a result, such a situation can be prevented that steam from an outside air and moisture in the plastic film 20 enter into the organic EL element 2, and thus reliability of the organic EL element 2 can be improved.
Also, as content should be mentioned specially, the organic EL element 2 is protected with the multi-layered gas barrier layer composed of the buffer layer 24, the gate insulating layer 34, and the first protection insulating layer 46,and which is provided to the surface on the TFTs 5, 6 side, thereby higher reliability can be obtained.
Further, in the present embodiment, since the transfer technology is utilized, in the formation of the gate insulating layer 34, the insulating layer not containing the hydroxyl group can be formed by heat-treating the coating film such as poly(vinyl phenol), or the like at a temperature of 180° C. or more on the glass substrate 10. Therefore, the gate insulating layer 34 that has a sufficient dielectric breakdown electric field strength (1 MV/cm or more) and can follow a bending stress can be transferred/formed on the plastic film 20.
Also, in the present embodiment, since the transfer technology is utilized, the oxide semiconductor layers 38a, 38b can be thermally treated on the glass substrate 10 at a temperature of 200° C. or more upon forming the oxide semiconductor layers 38a, 38b. Accordingly, the oxide semiconductor layers 38a, 38b function as the active layer of the TFT with the desired electric characteristics (Vth, etc.), and the TFT which has stable electric characteristics and whose reliability is high can be constructed.
Also, the transparent peelable layer 22 is used as the separating layer at a time of the transfer operation. Thus, the transparent peelable layer 22 exposed after the glass substrate 10 is peeled off can be utilized as the surface protection layer 23. Therefore, in the manufacturing method utilizing the transfer technology, there is no necessity to remove the peeling layer or to form particularly the surface protection layer. As a result, the manufacturing steps can be simplified and a cost reduction can be achieved.
An equivalent circuit in
Also, a holding capacitor Cs is formed between the gate electrode 32b of the Dr-TFT 6 and the power supply (Vdd) line 60. Also, the drain electrode 36b of the Sw-TFT 5 is connected to the gate electrode 32b of the Dr-TFT 6, and the source electrode 36a of the Sw-TFT 5 is connected to a data line 62. Further, the gate electrode 32a of the Sw-TFT 5 is connected to a scanning line 64.
The equivalent circuit in
Then, a current flowing to the Dr-TFT 6 and the organic EL element 2 has a value that responds to a gate-source voltage of the Dr-TFT 6. Thus, the organic EL element 2 continues to emit a light at a luminance that responds to the current value.
A pixel having such constitutions are aligned plurally in a matrix fashion and the writing is repeated through the data line 62 while sequentially selecting the scanning line 64, thereby an active-matrix type organic EL display can be composed. In this manner, the light is emitted from the light emitting layers 54 of respective pixel portions to the outside, and the image can be obtained.
The flexible organic EL display 1 in
In
In particular, in the flexible organic EL display la in
In
In this manner, in the flexible organic EL displays 1, la of the present embodiment, the light can be emitted from the plastic film 20 side or the opposite side to the plastic film 20, by controlling the transparent/opaque combination between the cathode 26 and the anode 58.
Next, an external connection area of the flexible organic EL display of the present embodiment will be explained hereunder.
In the gate external connection area A, a large number of gate connection electrodes 70 connected to the scanning line (64 in
The transparent peelable layer 22 is left in the main portion of the flexible organic EL displays 1 as the surface protection layer 23. But the stacked films containing the surface protection layer 23 are removed collectively in the gate external connection area A and the source external connection area B, and the gate connection electrode 70 and the source connection electrode 72 are exposed.
That is, by reference to
Also, by reference to
In order to expose the gate connection electrodes 70 and the source connection electrodes 72, a mask for protecting the display area but exposing collectively the external connection areas A, B may be arranged, and then the stacked film containing the surface protection layer 23 may be etched via the mask by the plasma etching, or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-164382 | Jun 2008 | JP | national |
