By a News Reporter-Staff News Editor at Life Science Weekly — A patent by the inventors Otsuki, Shigeyoshi (Koganei, JP); Eguchi, Toshimasa (Koganei, JP); Yamaguchi, Shinya (Koganei, JP); Okamoto, Mamoru (Koganei, JP), filed on March 4, 2010, was published online on July 1, 2014, according to news reporting originating from Alexandria, Virginia, by NewsRx correspondents (see also Sumitomo Chemical Company, Limited).
Patent number 8766273 is assigned to Sumitomo Chemical Company, Limited (Tokyo, JP).
The following quote was obtained by the news editors from the background information supplied by the inventors: “The present invention relates to an organic EL display which is formed by using, particularly, a plastic substrate and is driven by a thin film transistor including an active layer containing a non-metallic element and a method of manufacturing the organic EL display.
“Recently, as development of technologies for materials, manufacturing, driving circuits, and the like, a technology for electroluminescence (EL) has been put to practical use of an organic EL display as one of flat panel displays (FPDs).
“In 1997, a monochromatic organic EL display was put to practical use. After that, area colorization of the organic EL display is implemented, so that the use thereof is expended to displays such as a small-size audio apparatus or a mobile terminal. In 2001, the colorization was put to practical use by a passive-matrix-type color display for a mobile phone. After that, an active-matrix-type colorization has been made by using thin film transistors. In 2007, the organic EL display was adopted to 11-inch TVs. Recently, large-size TVs having 40 inches or more has been developed.
“In an organic EL device configuring an organic EL display, an electron injection layer, an electron transport layer, a light emitting layer, a hole transport layer, a hole injection layer, and the like are stacked between positive and negative electrodes, and a current is allowed to flow in the organic EL device by applying a voltage between the positive and negative electrodes, so that light is emitted. A plurality of display pixels constructed with the organic EL devices are two-dimensionally arranged and used as a display.
“For the colorization of an organic EL display, various methods such as a paint division method, a color conversion method, a micro-cavity method, or a color filter method have been proposed. Among these methods, the paint division method and the color filter method are representative methods.
“In the paint division method, a display pixel is divided into a plurality of pixels, which are called sub-pixels as devices for emitting light of red ®, green (G), and blue (B). Four colors including white (W) and the three colors of RGB may be used for the sub-pixels.
“In the color filter method, white light is emitted, and an RGB color filter is combined with the sub-pixels, so that the colorization is implemented. Similarly to the paint division method, the color filter for the sub-pixels may include four colors of white (W) and the RGB.
“The organic EL device is a surface-shaped self light-emitting device made of a totally solid state material. In comparison with a liquid crystal display, a plasma display, or the like, the organic EL display using the organic EL device is excellent in terms of thin device implementation, a high-speed responsibility, characteristics of viewing angle, and the like. Recently, a flexible display using a plastic substrate has been developed. As a driving method of the organic EL display, there are a passive matrix type and an active matrix type.
“In the passive matrix type, positive and negative electrodes of the organic EL device as interdigitated electrodes are disposed in the X and Y directions; the one electrode is used as a scan electrode; and the other electrode is used as a data electrode. Light is emitted by applying a voltage from an external constant current circuit to the pixels at the intersections. Since the thin film transistor for driving the organic EL device is unnecessary, the passive matrix type has an advantage in terms of production cost in comparison with the later-described active matrix type. However, since the number of scan electrodes is increased as the number of pixels in the display screen is increased, the duty ratio of driving the pixel is decreased. Therefore, there is a limitation in that high luminance may not be obtained.
“In the active matrix type, turning ON and OFF of the thin film transistor (TFT) is performed for each pixel, so that the lighting state is maintained by holding capacitance (condenser). Therefore, high luminance can be sustained although the number of pixels is increased. Accordingly, the active matrix type can be used for the applications such as TVs where the number of pixels is large.
“In an active matrix type liquid crystal display, one transistor for selecting pixels is sufficient. However, in the case of an active matrix type organic EL display, at least two TFTs are needed. In other words, besides the transistor for selecting the pixels, a transistor for allowing a current to flow in the organic EL device of the selected pixel and allowing the organic EL device to emit light is needed. Therefore, if an aperture ratio of the display is considered, in the case of the organic EL display, the size of the TFT becomes an important problem in comparison with the case of a liquid crystal display. If the size of the TFT is small, the aperture ratio of the display can be increased.
“The TFT using an oxide thin film as the active layer is transparent with respect to visible light, so that it can be expected that the aperture ratio of the display is increased.
“As TFTs used to an active matrix type, an a-Si TFT using an amorphous silicon (a-SI) as the active layer and a low-temperature p-Si TFT using a low-temperature polysilicon (low-temperature p-Si) as the active layer are put to practical use and widely used as a liquid crystal display (refer to JP 2008-59824 A).
“In this manner, in order to implement a large-size, high-accuracy organic EL display using an organic EL device, an active matrix driving type needs to be selected as described above. In this case, if an a-Si TFT is used as the TFT, since the field effect mobility is about 0.5 cm.sup.2/Vs, in the case where the area of the pixel is large or the case where the number of scan electrodes is large, for example, 2,000 or more, there is a problem in terms of high-speed responsibility and high luminance. In other words, in the case where the size of the pixel of the organic EL device is large, in order to flow a sufficient current, the size of the TFT needs to be large. However, the aperture ratio of the pixel is decreased, so that high luminance may not be implemented. In addition, in the case where the number of scan electrodes is large due to high accuracy, as the number of scan electrodes is increased, the writing time is shortened. Therefore, a sufficient time for charging the holding capacitance may not be secured, so that turning on of the TFT may not be satisfactorily performed.
“In addition, in the a-Si TFT, a change in the reverse voltage Vt due to current stress is large, so that the occurrence of unbalance of the driving current is inevitable for a long time of the driving. In the organic EL device, the unbalance of the driving current leads to irregularity in luminance.
“On the other hand, in the case where a low-temperature p-Si TFT is used, the mobility is in a range from 50 cm.sup.2/Vs to 150 cm.sup.2/Vs, so that the TFT can be sufficiently adopted to the driving of a large-size, high-accuracy organic EL display. In addition, since a change in Vt due to the current driving is smaller by two digits or more than that of the a-Si, there is no problem.
“However, in the manufacturing of the low-temperature p-Si, in order to perform molten crystallization of a silicon film, excimer laser beams are needed; and in the case of a large-size display, an excimer laser beam having a length corresponding to a screen width is needed. In the current state, the maximum length of the laser beam is 465 mm, and thus, a display having a width more than the maximum length may not be manufactured by using a low-temperature p-Si.
“In addition, with respect to the low-temperature p-Si TFT, since the manufacturing process temperature is high, from 500.degree. C. to 600.degree. C., the plastic substrate may not be used. Therefore, it is difficult to implement a flexible display.”
In addition to the background information obtained for this patent, NewsRx journalists also obtained the inventors’ summary information for this patent: “The invention is to provide a large-size, high-accuracy organic EL display using a plastic substrate and a method of manufacturing an organic EL display using a roll-shaped long plastic substrate.
“In order to solve the aforementioned problems and achieve the objects, the invention is configured as follows.
“According to a first aspect of the present invention, there is provided an organic EL display which includes an organic EL device having at least a lower electrode, an organic layer including at least a light emitting layer, and an upper electrode and a thin film transistor on a transparent plastic substrate, wherein a source electrode or a drain electrode of the thin film transistor is connected to the lower electrode, wherein the plastic substrate has a gas barrier layer, wherein the thin film transistor is formed on the gas barrier layer, wherein the thin film transistor includes an active layer containing a non-metallic element which is a mixture of oxygen (O) and nitrogen (N) and has a ratio of N to O (N number density/O number density) from 0 to 2, and wherein the organic EL device is formed at least on the gas barrier layer or on the thin film transistor.
“A second aspect is the organic EL display according to the first aspect, wherein a short-side length of a display screen of the organic EL display is 465 mm or more.
“A third aspect is the organic EL display according to the first aspect, wherein the organic EL device includes layers of emitting at least three primary colors of red ®, green (G), and blue (B).
“A fourth aspect is the organic EL display according to the first aspect, wherein the organic EL device includes at least a white light emitting layer and a color filter layer.
“A fifth aspect is the organic EL display according to the first aspect, wherein the thin film transistor is transparent, wherein a portion of the organic EL device is two-dimensionally and continuously formed through a transparent insulating layer on the thin film transistor, and wherein the lower electrode of the organic EL device is transparent.
“A sixth aspect is the organic EL display according to the first aspect, wherein the upper electrode of the organic EL device is a light-reflective electrode.
“A seventh aspect is the organic EL display according to the first aspect, wherein the thin film transistor includes a cohesive layer or an adhesive layer at a side of the gas barrier layer.
“An eighth aspect is the organic EL display according to the seventh aspect, wherein the thin film transistor includes a glass substrate.
“A ninth aspect is the organic EL display according to the first aspect, wherein the thin film transistor is directly formed on the plastic substrate.
“According to a tenth aspect of the present invention, there is a method of manufacturing the organic EL display according to any one of the first to ninth aspects, including at least: forming an organic EL device portion by forming at least a lower electrode, an organic layer including at least a light emitting layer, and an upper electrode on a transparent plastic substrate; forming a gas barrier layer on the transparent plastic substrate which has a shape of a long roll; forming a thin film transistor by forming an active layer containing a non-metallic element which is a mixture of oxygen (O) and nitrogen (N) and has a ratio of N to O (N number density/O number density) from 0 to 2 on the gas barrier layer through a sputtering method; and forming the organic EL device at least on the gas barrier layer or on the thin film transistor.
“An eleventh aspect is the method according to the tenth aspect, wherein a short-side length of a display screen of the organic EL display is 465 mm or more.
“A twelfth aspect is the method according to the tenth aspect, further including a step of forming layers of emitting at least three primary colors of red ®, green (G), and blue (B) in the organic EL device.
“A thirtieth aspect is the method according to the tenth aspect, further including a step of forming at least a white light emitting layer and a color filter layer in the organic EL device.
“A fourteenth aspect is the method according to the tenth aspect, wherein the thin film transistor is transparent, wherein a portion of the organic EL device is two-dimensionally and continuously formed through a transparent insulating layer on the thin film transistor, and wherein the electrode of the organic EL device is transparent.
“A fifteenth aspect is the method according to the tenth aspect, wherein the thin film transistor is formed by being transferred to the plastic substrate through a cohesive layer or an adhesive layer, after the thin film transistor is formed on a glass substrate in advance and a portion or the entire of the glass substrate is removed.
“A sixteenth aspect is the method according to the tenth aspect, wherein the thin film transistor is directly formed on the plastic substrate.
“According the above configurations of the invention, the following effects can be obtained.
“In the invention disclosed in claim 1, even in the case where the thin film transistor including an active layer containing a non-metallic element which is a mixture of oxygen (O) and nitrogen (N) and has a ratio of N to O (N number density/O number density) from 0 to 2 is formed at a temperature of 200.degree. C. or less, the performance is equivalent to or higher than performance of a thin film transistor using amorphous silicon formed on a glass substrate at 200.degree. C. or more. The embodiment is very appropriate for the case where the thin film transistor is formed on a plastic substrate of which the heat resistant temperature is lower than that of a glass substrate. On the other hand, the organic EL device is a self light-emitting device made of a totally solid state material and has no dependency of a viewing angle, and the organic EL device is very appropriate for a device of a flexible display formed on a plastic substrate. In addition, it is possible to easily obtain a thin film transistor having a high field effect mobility, so that the thin film transistor is very appropriate for a large-screen, high-accuracy display using an organic EL device which is a current-driven device.
“In the invention disclosed in claim 2, a short-side length of a display screen of the organic EL display C is 465 mm or more. In a large-screen, high-accuracy organic EL display, low-temperature P-Si TFTs can be adopted. However, with respect to the size of a display screen using the low-temperature P-Si TFTs, a laser annealing apparatus which is an expensive manufacturing apparatus is needed, and due to the limitation of the size of the laser annealing apparatus, if the short-side length is not 465 mm or less, mass production may not be made. But, in the embodiment, due to the thin film transistors B, it is possible to manufacture a manufacturing apparatus for the display screen having a short-side length of 465 mm or more with a relatively low production cost.
“In the invention disclosed in claim 3, in the case where full-color display is performed by an organic EL display, a configuration for emitting light of at least three primary colors of red ®, green (G), and blue (B) is needed. In this case, since the emitted light of the organic EL device A is directly used as it is, in the full-color display method, the highest light use efficiency is preferred, and a configuration for emitting light of four colors or six colors including white (W), yellow (Y), cyan (C), and the like in addition to RGB may be used.
“In the invention disclosed in claim 4, the organic EL device includes at least a white light emitting layer and a color filter layer. Instead of emitting light of three primary colors or light of four colors to six colors, full color display can be made by using a white light emitting layer and a color filter layer. In this case, since only a single white light emitting layer may be formed as the light emitting layer, there is no need to form separate light emitting layers for different colors of the emitted light. Therefore, the number of processes can be reduced, and the manufacturing apparatus is more simplified, so that it is possible to obtain the effective in that the manufacturing can be performed with a more inexpensive apparatus. Similarly to a color liquid crystal panel, the full color display is performed by allowing the light from the white light emitting layer to transmit through the color filter layer.
“In the invention disclosed in claim 5, since transparent materials are used for the thin film transistor, the insulating planarizing layer 300 as an insulating material, and the lower electrode of the organic EL device, although a large-size thin film transistor is used, the light emission of the organic EL device can be used for display without blocking thereof. Accordingly, an aperture ratio of the display can be increased, and light use efficiency can be improved, so that the embodiment is appropriate for saving energy.
“In the invention disclosed in claim 6, since the upper electrode of the organic EL device is configured with a light-reflective electrode, among the light generated from the organic EL device, the light propagating toward the upper side in the opposite direction of the display side is also reflected toward the display-side direction by the upper electrode, so that the light can be effectively used for display. Accordingly, there is an advantage in that the light use efficiency of the organic EL device A can be improved.
“In the invention disclosed in claim 7, a cohesive layer or an adhesive layer is provided to the side of the gas barrier layer of the plastic substrate, so that the separately-produced thin film transistor can be attached to be fixed on the plastic substrate by using the cohesive layer or the adhesive layer. In addition, a roll-to-roll method where taking out from the rolled state and winding to the rolled state are performed can be used during the manufacturing. Therefore, even in the case where there is no equipment for forming a thin film transistor B on a long substrate, there is an advantage in that a thin film transistor substrate manufactured separately in a sheet shape can be used.
“In the invention disclosed in claim 8, with respect to a thin film transistor which requires a high-temperature process so that the thin film transistor may not be directly formed on the plastic substrate, there is an advantage in that, after the thin film transistor is separately produced on the glass substrate, the thin film transistor can be used in the state where the thin film transistor is attached on the plastic substrate by using a cohesive layer or an adhesive layer. In this case, if the thickness of the glass substrate is reduced by etching using hydrogen fluoride water or the like or by polishing using a polishing agent, it is possible to effectively reduce the thickness of the device.
“In the invention disclosed in claim 9, if the thin film transistor is directly formed on the plastic substrate, since the substrate is flexible, the substrate is very appropriate for a flexible display. In addition, in the case where the display is an organic EL display, the organic EL device is a totally-solid-state device and has no dependency of a viewing angle. Therefore the organic EL device is very appropriate for a flexible display.
“In the invention disclosed in any one of claims 10 to 16, it is possible to manufacture the organic EL display according to any one of claims 1 to 9.”
URL and more information on this patent, see: Otsuki, Shigeyoshi; Eguchi, Toshimasa; Yamaguchi, Shinya; Okamoto, Mamoru. Organic EL Display and Method of Manufacturing Organic EL Display. U.S. Patent Number 8766273, filed March 4, 2010, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=\%2Fnetahtml\%2FPTO\%2Fsrchnum.htm&r=1&f=G&l=50&s1=8766273.PN.&OS=PN/8766273RS=PN/8766273
Keywords for this news article include: Sumitomo Chemical Company Limited.
Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC
