DISPLAY DEVICE AND METHOD FOR MANUFACTURING DISPLAY DEVICE

A display device includes a light-emitting element layer that emits light in a way that unit pixels each forming a pixel are respectively controlled in brightness, a sealing layer provided on the light-emitting element layer, an ultraviolet absorbing layer provided on the sealing layer, and a flattening layer provided on the ultraviolet absorbing layer and made of organic resin having ultraviolet curability.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2016-030161 filed on Feb. 19, 2016 the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and a method for manufacturing the display device.

2. Description of the Related Art

There have been known display devices including a light-emitting element layer that emits light by controlling brightness in each unit pixel forming an image and a sealing layer that covers the light-emitting element layer. The sealing layer is provided so as to prevent moisture from outside penetrating into the inside of the device. As disclosed in JP2013-105947A, for example, a display device including a sealing layer formed of an inorganic material, a flattening layer formed of organic resin and stacked on the sealing layer, and a sealing layer formed of an inorganic material and stacked on the flattening layer has been known as a display device including a sealing layer. The flattening layer is formed of acrylic resin having ultraviolet curability, for example, hardened by being irradiated with ultraviolet rays, and formed on the light-emitting element layer.

When the flattening layer is irradiated with ultraviolet rays, the light-emitting element layer below the flattening layer may be affected by the ultraviolet rays, thereby degrading light emitting characteristics.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a display device that prevents a light emitting characteristics from being degraded, and a method for manufacturing the display device.

A display device according to one aspect of the present Invention includes a substrate, a light-emitting element layer that is provided on the substrate and emits light by controlling brightness in each unit pixel forming an image, a sealing structure provided on the light-emitting element layer, and an ultraviolet absorbing layer provided on the light-emitting element layer, wherein the sealing structure includes a first flattening layer that is provided on the ultraviolet absorbing layer and made of organic resin having ultraviolet curability.

A method for manufacturing a display device according to another aspect of the present invention includes the steps of preparing a substrate, providing a light-emitting element layer on the substrate, providing a sealing layer made of an inorganic material on the light-emitting element layer, providing an ultraviolet absorbing layer on the sealing layer, providing an organic resin having ultraviolet curability on the ultraviolet absorbing layer, and irradiating the organic resin with a ultraviolet ray so as to cure the organic resin.

DETAILED DESCRIPTION OF THE INVENTION

In the embodiments of the present invention, when a manner in which a structure is disposed “on” another structure is described, it is understood, if not otherwise stated, that simply describing “on” includes both a case in which the structure is disposed directly on the another structure in contact with each other and a case in which the structure is disposed above or over the another structure with a third structure interposed therebetween.

Referring toFIGS. 1 and 2, the overall general configuration of the display device according to the first embodiment will be discussed.FIG. 1is an external perspective view of a display device according to the first embodiment.FIG. 2is a schematic sectional view illustrating a cross section of the display device according to the first embodiment. In the first embodiment, a so-called organic electro luminescence (EL) display device using an organic EL element will be discussed as the display device, although the display device is not limited to this but may be a display device including a layer that emits light in a way that unit pixels P each forming a pixel are respectively controlled in brightness.

As shown inFIG. 1, a display device100includes a TFT (Thin Film Transistor) substrate10having a thin film transistor, for example, and a counter substrate20. As shown inFIG. 2, the counter substrate20is provided to oppose the TFT substrate10via a filler30. The display device100includes a display area M for image display and a frame area N around the display area M. A plurality of unit pixels P are provided in the display area M. InFIG. 1, only one unit pixel P is shown, although in reality a plurality of unit pixels P are arranged on the display area M in a matrix.

As shown inFIG. 2, the TFT substrate10includes a substrate11, a light-emitting element layer12provided on the substrate11, a sealing layer13provided on the light-emitting element layer12and formed of an inorganic material, a ultraviolet absorbing layer14provided on the sealing layer13, a flattening layer15provided on the ultraviolet absorbing layer14and formed of organic resin, and a sealing layer16provided on the sealing layer15and formed of an inorganic material. In the following, details of each layer and substrate included in the TFT substrate10will be discussed.

The substrate11has at least a circuit layer including a wiring. The details of the wiring of the circuit layer will be discussed later. The substrate11may be a resin substrate made of flexible polyimide, for example, or a glass substrate.

The light-emitting element layer12is a layer that emits light in a way that the unit pixels P each forming a pixel are respectively controlled in brightness. The light-emitting element layer12is a layer that is at least provided on the display area M, and includes an organic EL layer12a,a lower electrode12bprovided in the lower part of the organic EL layer12a,and an upper electrode12cprovided in the upper part of the organic EL layer12a.Although not shown here in detail, the organic EL layer12aincludes a charge transport layer, a charge injection layer, and a light-emitting layer, for example.

In the organic EL layer12a,an area in contact with the lower electrode12bcorresponds to respective unit pixels P, and light is emitted in this area. The unit pixels P are divided by a bank layer14, and an area where the organic EL layer12aand the lower electrode12bare separated by the bank layer14does not emit light. The upper electrode12cis disposed on the organic EL layer12aacross the unit pixels P. In the first embodiment, the lower electrode12band the upper electrode12care an anode and a cathode, respectively, but are not limited to these, and the polarity may be reversed. The upper electrode12c,through which light from the organic EL layer12apasses, may be formed as a transmission electrode using transparent conductive material, for example. Materials such as indium tin oxide (ITO) or indium zinc oxide (IZO) may be used as the transparent conductive material. Alternatively, the upper electrode12cmay be formed in a thin film using aluminum (Al), silver (Ag), or alloy of Ag and magnesium (Mg) in a thickness that allows light to pass therethrough, or formed in a laminated film of these metal thin films and the transparent conductive material.

The first embodiment may employ a color-separation method for splitting the organic EL layer12ato emit light of colors according to colors of pixels, or a color filter method in which all pixels emit light of the same color (e.g., white) and only light in a predetermined wavelength in each pixel transmits a color filter provided on the counter substrate20.

The sealing layers13and16are provided so as to prevent moisture ingress from outside penetrating into the display device100. The sealing layers13and16are made of silicon nitride (SiN), but not limited to this, and may be made of any inorganic material excellent in moisture resistance, such as silicon oxide. The flattening layer15is made of acrylic resin, but not limited to this, and may be made of any organic resin having ultraviolet curability, such as epoxy resin.

Referring toFIGS. 2 and 3, the principle of light emission of the light-emitting element layer will be discussed.FIG. 3is a circuit diagram illustrating a circuit formed on each unit pixel P. As shown inFIG. 3, a wiring of the circuit layer included in the substrate11has a scanning line Lg, a video signal line Ld orthogonal to the scanning line Lg, and a power source line Ls orthogonal to the scanning line Lg. A pixel control circuit Sc is provided on each unit pixel P of the circuit layer, and the pixel control circuit Sc is connected to the lower electrode12bthrough a contact hole (not shown). The pixel control circuit Sc includes a thin film transistor and a capacitor, and controls power supply to an organic light-emitting diode Od provided to each unit pixel P. The organic light-emitting diode Od is composed of the organic EL layer12a,the lower electrode12b,and the upper electrode12c,each described above referring toFIG. 2.

As shown inFIG. 3, the pixel control circuit Sc includes a drive TFT11a,a storage capacitor11b, and a switching TFT11c. The gate of the switching TFT11cis connected to the scanning line Lg, and the drain of the switching TFT11cis connected to the video signal line Ld. The source of the switching TFT11cis connected to the storage capacitor11band the gate of the drive TFT11a. The drain of the drive TFT11ais connected to the power source line Ls, and the source of the drive TFT11ais connected to the organic light-emitting diode Od. When a gate voltage is applied to the scanning line Lg, the switching TFT11cis ON state. At this time, when a video signal is supplied from the video signal line Ld, charges are stored in the storage capacitor11b. By the charges stored in the storage capacitor11b, the drive TFT11ais caused to be ON state. A current then flows from the power source line Ls to the organic light-emitting diode Od, and the organic light-emitting diode Od emits light.

The pixel control circuit Sc may be any circuit for controlling current supply to the organic light-emitting diode Od, and not to be limited to the one shown inFIG. 3. For example, the pixel control circuit Sc may further include an auxiliary capacitor other than the storage capacitor11bin order to increase the capacity. The polarity of the transistors constituting the circuit is also not limited to an example shown inFIG. 3.

In the first embodiment, the ultraviolet absorbing layer14is made Of titanium oxide (TiOx, x principally is 2) having transparency. The titanium oxide absorbs an ultraviolet ray at a wavelength of 365 nm, and has property of transmitting visible light. The ultraviolet absorbing layer14is provided to protect the light-emitting element layer12from an ultraviolet ray. The ultraviolet absorbing layer14is not limited to be made of titanium oxide, but may be a layer made of any material that absorbs an ultraviolet ray and transmits light from the light-emitting element layer12.

In the display device100according to the first embodiment, the ultraviolet absorbing layer14is disposed between the light-emitting element layer12and the flattening layer15, which is provided on the light-emitting element layer12and made of organic resin having ultraviolet curability, and thus the light-emitting element layer12is less likely to be affected by a ultraviolet ray even if the ultraviolet ray is irradiated to cure the flattening layer15. As such, it is possible to prevent deterioration of the light-emitting element layer12due to irradiation of ultraviolet rays, to thereby prevent shortening of the life of the device.

Next, referring toFIG. 4, a method for manufacturing the display device according to the first embodiment will be discussed.FIG. 4is a flow chart of the method for manufacturing the display device according to the first embodiment.

First, a substrate11including a circuit layer is prepared (Step ST1). Subsequently, a bank layer14and a light-emitting element layer12are formed on the substrate11(Step ST2). Further, a sealing layer13composed of silicon nitride is formed on the light-emitting element layer12, using materials that includes silicon, ammonia gas, and nitrogen gas, by a chemical vapor deposition (CVD) method (Step ST3) . A plasma CVD method may be employed as the CVD method to turn source gas into plasma and initiate a chemical reaction. In this step, a reaction between silicon and ammonia gas generates silicon nitride, and nitrogen gas is used for adjusting pressure. The sealing layer13is formed along with a shape of the light-emitting element layer12.

Further, an ultraviolet absorbing layer14composed of titanium oxide having ultraviolet ray absorbency is formed on the sealing layer13(Step ST4). Subsequently, acrylic resin is provided on the ultraviolet absorbing layer14(Step ST5). Thereafter, the fluid acrylic resin is irradiated with ultraviolet rays so as to be cured (Step ST6). The acrylic resin irradiated with ultraviolet rays is cured, and with this, a flattening layer15is formed as a resin layer. Upon receiving ultraviolet rays, the ultraviolet absorbing layer14composed of titanium oxide exhibits a hydrophilic property. As such, wettability of the acrylic resin provided on the ultraviolet absorbing layer14is enhanced. For this reason, compared to a case where the flattening layer15is directly formed on the sealing layer13, the flattening layer15is evenly and uniformly formed on the ultraviolet absorbing layer14.

A sealing layer16composed of silicon nitride is then formed on the flattening layer15(Step ST7). The sealing layer16may be formed by the same method as the sealing layer13. The method for forming the sealing layers13and16each composed of an inorganic material is not limited to the CVD method, but other methods such as a sputtering method or an atomic layer deposition (ALD) method may also be used. The ultraviolet absorbing layer14may also be formed by the CVD method similarly to the sealing layers13and16, or by other methods such as a sputtering method or an ALD method. With the steps above, manufacturing of the TFT substrate10is completed.

After Step ST7is completed, a counter substrate20is provided to oppose to the TFT substrate10through a filler layer30(Step ST8). The display device100according to the first embodiment is manufactured through the steps described above.

Referring toFIG. 5, a display device200according to the second embodiment will be discussed.FIG. 5is a schematic sectional view illustrating a cross section of the display device according to the second embodiment. The display device200has the same structure as the display device100except having a flattening layer18and a sealing layer19. Specifically, the display device200includes a sealing layer13provided on a light-emitting element layer12, an ultraviolet absorbing layer14provided on the sealing layer13, a flattening layer15provided on the ultraviolet absorbing layer14, a sealing layer16provided on the flattening layer15, a flattening layer18provided on the sealing layer16, and a sealing layer19provided on the flattening layer18.

The flattening layer18may be formed using the same material and the same method as the flattening layer15. Further, the sealing layer19may be formed using the same material and the same method as the sealing layer16. In this way, the flattening layers composed of organic resin are provided doubly in the display device200, and thus it is possible to form a more flat and smooth layer than that of the display device100. Further, the triple sealing layers composed of an inorganic material are provided, and thus, compared to the display device100, it is possible to more readily prevent moisture ingress into the inside of the device. At the time the flattening layer15and the flattening layer18are formed, the layers respectively need to be irradiated with ultraviolet rays so that the organic resin is cured. In either case of ultraviolet-ray irradiation, the ultraviolet absorbing layer14absorbs ultraviolet rays, and serves to reduce an influence of the ultraviolet rays on the light-emitting element layer12.

Referring toFIG. 6, a display device300according to the third embodiment will be discussed.FIG. 6is a schematic sectional view illustrating a cross section of the display device according to the third embodiment. The display device300has the same structure as the display device100except that the sealing layer13and the ultraviolet absorbing layer14are laminated in a different order. Specifically, the display device300includes an ultraviolet absorbing layer14provided on a light-emitting element layer12, a sealing layer13provided on the ultraviolet absorbing layer14, a flattening layer15provided on the sealing layer13, and a sealing layer16provided on the flattening layer15. In this structure as well, similarly to the first embodiment, when the flattening layer15composed of organic resin having ultraviolet curability is irradiated with ultraviolet rays so as to be cured, the ultraviolet absorbing layer14absorbs the ultraviolet rays, and thus the light-emitting element layer12is less influenced by the ultraviolet rays.

The laminated structure of the sealing layers13and16and the flattening layer15as described in the first embodiment corresponds to the sealing structure of the present invention. Further, the laminated structure of the sealing layers13,16, and19, and the flattening layers15and18as described in the first to the third embodiments corresponds to the sealing structure of the present invention, the sealing layer13corresponds to the first sealing layer of the present invention, the sealing layer16corresponds to the second sealing layer of the present invention, the flattening layer15corresponds to the first flattening layer, and the flattening layer18corresponds to the second flattening layer. While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.