JP7312697B2 - Displays and electronics - Google Patents

Description

The present disclosure relates to display devices and electronic devices.

In recent years, there has been an increasing demand for higher definition and lower power consumption in display devices for mobile use.

For example, a display device using an organic electro-luminescence diode (OLED) disclosed in Patent Document 1 below is self-luminous and consumes low power, and thus is expected to be applied to mobile applications.

However, in such an organic electroluminescence element, since the organic electroluminescence layer is provided in common for all the light emitting elements, leakage of drive current is likely to occur between adjacent light emitting elements.

Therefore, Patent Literature 1 discloses a technique of arranging a relief pattern between light-emitting elements to block electrodes and charge transport layers. In addition, Patent Document 2 discloses a technique for suppressing leakage current between pixels by surface-treating a portion of the hole transport layer other than the light-emitting region of each pixel with ultraviolet rays to increase the resistance value of the portion irradiated with ultraviolet rays. Furthermore, Patent Document 3 discloses a technique of periodically applying a driving voltage to a light emitting element to suppress leakage current.

Japanese Patent Publication No. 2003-530660 JP 2004-158436 A JP 2014-52617 A

By the way, in an organic electroluminescence (organic EL) display, display is generally performed by driving an organic electroluminescence element with a thin film transistor formed on a glass substrate. In applications such as displays for televisions and smartphones, amorphous silicon and polycrystalline silicon, for example, are used as channel materials for transistors.

On the other hand, for high-definition and small display devices with a pixel pitch of 10 μm or less and resolution exceeding 2500 ppi, MOS (Metal-Oxide-Semiconductor) transistors formed on Si may drive organic electroluminescent elements.

The techniques disclosed in Patent Documents 1 and 2 are difficult to apply to such a display device with a high-definition pixel pitch. In addition, the technique disclosed in Patent Document 3 requires extremely complicated control of the driving voltage.

Therefore, the present disclosure proposes a new and improved display device and electronic device capable of suppressing leakage current between pixels.

According to the present disclosure, a display device is provided that includes an organic electroluminescent layer, a first electrode that is arranged on one main surface side of the organic electroluminescent layer and is common to a plurality of pixels, a plurality of second electrodes that are individually arranged for each pixel on the other main surface side of the organic electroluminescent layer, and a plurality of third electrodes that are arranged on the other main surface side of the organic electroluminescent layer and between the plurality of second electrodes.

Further, according to the present disclosure, there is provided an electronic device including a display section having an organic electroluminescent layer, a first electrode arranged on one main surface side of the organic electroluminescent layer and common to a plurality of pixels, a plurality of second electrodes arranged individually corresponding to each pixel on the other main surface side of the organic electroluminescent layer, and a plurality of third electrodes arranged on the other main surface side of the organic electroluminescent layer and between the plurality of second electrodes.

According to the present disclosure, it is possible to provide a display device and an electronic device in which leakage current between pixels is suppressed. Therefore, it is possible to prevent unintended light emission of the pixels due to the leak current and the accompanying deterioration of the color gamut of the displayed image.

As described above, according to the present disclosure, it is possible to provide a display device and an electronic device in which leakage current between pixels is suppressed.
Note that the above effects are not necessarily limited, and any of the effects shown in the present specification or other effects that can be understood from the present specification may be achieved in addition to or in place of the above effects.

1 is a cross-sectional view schematically showing a display device according to an embodiment of the present disclosure; FIG. 2 is a schematic plan view for explaining the arrangement of individual electrodes and third electrodes of the display device shown in FIG. 1. FIG. FIG. 2 is a schematic cross-sectional view for explaining the configuration of individual electrodes of the display device shown in FIG. 1; 2 is a schematic circuit diagram of an organic electroluminescence element provided in the display device shown in FIG. 1. FIG. 4 is a graph showing the relationship between leakage current and light emission current in a display device; 4 is a graph showing the relationship between luminance, leakage current, and emission current in a display device. FIG. 11 is a plan view showing the shape and arrangement of individual electrodes and third electrodes in a modified example of the present disclosure; FIG. 11 is a plan view showing the shape and arrangement of individual electrodes and third electrodes in a modified example of the present disclosure; FIG. 11 is a plan view showing the shape and arrangement of individual electrodes and third electrodes in a modified example of the present disclosure; FIG. 10 is a schematic cross-sectional view illustrating an individual electrode and a third electrode in a modified example of the present disclosure; FIG. 10 is a schematic cross-sectional view illustrating an individual electrode and a third electrode in a modified example of the present disclosure; FIG. 10 is a schematic cross-sectional view illustrating an individual electrode and a third electrode in a modified example of the present disclosure; FIG. 10 is a cross-sectional view schematically showing a display device according to a modified example of the present disclosure; FIG. 10 is a schematic cross-sectional view for explaining the configuration of an individual electrode in a modified example of the present disclosure; FIG. 4 is a cross-sectional view schematically showing an example of a display device that does not have a third electrode; 16 is a plan view showing the arrangement of pixels included in the display device shown in FIG. 15; FIG. FIG. 4 is a schematic diagram for explaining leakage current between individual electrodes; FIG. 4 is a schematic diagram for explaining leakage current between individual electrodes; 4 is a graph schematically showing the relationship between voltage and current in an organic electroluminescent layer; 16 is a schematic arrangement diagram of individual electrodes included in the display device shown in FIG. 15. FIG.

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description. In addition, the size of each member in the drawings is appropriately emphasized for ease of explanation, and does not represent actual dimensions or ratios between members.

Note that the description will be given in the following order.
1. Background and overview of the present disclosure 1.1. Problem of Leakage Current in Display Device 1.2. Overview of leakage current suppression according to the present disclosure 2 . Configuration of display device 3. Verification of influence of leak current 4 . Modification 5. summary

<1. Background and overview of the present disclosure>

[1.1. Problem of leakage current in display device]
First, prior to detailed description of the present disclosure, the problem of leakage current in a display device using an organic electroluminescence element will be described. 15 is a cross-sectional view schematically showing an example of a display device having no third electrode, which will be described later, FIG. 16 is a plan view showing the arrangement of pixels included in the display device shown in FIG. 15, FIGS. 17 and 18 are schematic diagrams for explaining leakage currents between individual electrodes, FIG.

A display device 200 shown in FIG. 15 is a display device using an active matrix type organic electroluminescent element. In the display device 200, an organic electroluminescent layer 210 is arranged on an interlayer insulating film 280, an individual electrode 220 as an anode is arranged on the side of the interlayer insulating film 280 of the organic electroluminescent layer 210, and a transparent common electrode 230 as a cathode is arranged on the opposite side of the organic electroluminescent layer 210. A protective insulating film 240 , a color filter layer 250 , a sealing resin 260 and a cover glass 270 are laminated in this order on the transparent common electrode 230 . On the other hand, in the interlayer insulating film 280, contacts 281 and wirings 283 are arranged for connecting the individual electrodes 220 to a pixel driving circuit (not shown).

The organic electroluminescent layer 210 can emit white light, for example, when a voltage is applied between the transparent common electrode 230 and the individual electrodes 220 . White light emitted from the organic electroluminescent layer 210 passes through the transparent common electrode 230 and the protective insulating film 240 and enters the color filter layer 250 . The color filter layer 250 has a red color filter 250R, a green color filter 250G, and a blue color filter 250B that are divided corresponding to each individual electrode 220 . The red color filter 250R, green color filter 250G, and blue color filter 250B convert incident light into red, green, and blue, respectively, and emit them toward the sealing resin side. The emitted light further passes through the sealing resin 260 and the cover glass 270 and is emitted to the outside.

An example of the pixel arrangement in the active matrix display device 200 is shown in plan view in FIG. As shown in FIG. 16, the individual electrode 220 and the corresponding red color filter 250R, green color filter 250G and blue color filter 250B form red pixel SP _R , green pixel SP _G and blue pixel SP _B as sub-pixels. Such a large number of red pixels SP _R , green pixels SP _G and blue pixels SP _B enable emission of three primary colors of red, green and blue, and constitute one pixel. By arranging such pixels in a matrix, a display panel for color-displaying an image corresponding to an input signal is configured.

Here, the leakage current between pixels will be considered. 17 and 18 are schematic diagrams for explaining the leakage current between the individual electrodes 220, and FIG. 19 is a graph schematically showing the relationship between the voltage and current of the individual electrode (anode) 220 when voltage is applied to the organic electroluminescent layer 210. As a result of the inventors' trial production of various display elements and examination, it was found that there are cases where the leakage current flowing between the individual electrodes 220 greatly raises the potential of the non-light-emitting individual electrodes 220, and that the main path of the leakage current is the lower layer portion of the organic electroluminescent layer 210 shown in FIG. A detailed description will be given below.

In the display device 200 described above, the organic electroluminescent layers 210 are not separated by color, and the individual electrodes 220 corresponding to the sub-pixels are connected under the organic electroluminescent layers 210 . The organic electroluminescent layer 210 is not a good insulator by its nature, and it is difficult to completely suppress leakage current between adjacent individual electrodes 220 . That is, on the side of the individual electrode 220 of the organic electroluminescent layer 210, an organic material layer into which charges such as holes can be easily injected is arranged. Therefore, current can leak through such an organic material layer as a leak path. Typically, the sheet resistance of the organic electroluminescent layer 210 is considered to be on the order of 10 ¹² Ω/□ or less.

Considering such a leakage path of the organic electroluminescent layer 210, the resistance RIE _-IE of the portion where the leakage current flows between the adjacent individual electrodes 220 is approximately represented by (sheet resistance Ω/□ of the organic electroluminescent layer 210)×(distance between the individual electrodes 220)/(length of one side of the individual electrode 220). The amount of leakage current is affected by the relationship between the resistance _RSP in the thickness direction of the organic electroluminescent layer 210 and the resistance RIE _-IE between the individual electrodes 220 when a voltage is applied.

On the other hand, considering the emission current characteristics shown in FIG. 19, the emission current of the organic electroluminescent layer 210 is extremely small when the voltage applied by the individual electrode 220 is relatively small. In other words, the current-voltage characteristic is not ohmic but rises sharply from around 3.5 V, and when the applied voltage is low, the resistance _RSP in the thickness direction of the organic electroluminescent layer 210 is large. Therefore, when it is desired to perform display by light emission of low luminance, the resistance _{R_SP} with respect to the resistance R_IE _-IE increases, and the influence of the leakage current increases.

Therefore, in the display device 200 as shown in FIG. 15, it is difficult to suppress the leakage current that unintentionally flows between the individual electrodes 220 that feed the organic electroluminescent layer 210 . In addition, it was considered that the influence of the leak current becomes more pronounced when a low voltage is applied to the organic electroluminescent layer 210 in order to perform low-luminance display.

The leak current flowing between the individual electrodes 220 described above can cause the color gamut of the display device 200 to deteriorate. If only the blue pixel _SPB is to emit light to display a pure blue color, for example, a voltage can be applied between the central individual electrode 220B and the transparent common electrode 230 in FIG. However, as indicated by the arrows in FIG. 20, leakage currents flow to the surrounding individual electrodes 220R and 220G corresponding to the adjacent red and green pixels SP _R and _SPG . As a result, the pixels SP _R and SP _G around the pixel SP _B glow in red and green, and the color purity of blue displayed in the pixel SP _B is reduced. A similar phenomenon occurs when other colors such as red and green are developed, so the displayable color gamut is narrowed.

Furthermore, in a display device having a fine pixel pitch _PP , deterioration in color reproducibility especially at low luminance caused by leakage current becomes remarkable. A specific description will be given below. When miniaturizing the inter-pixel pitch _PP , it is generally appropriate to miniaturize the arrangement of the individual electrodes 220 so as to maintain a similar shape. For example, when halving the size of the individual electrodes 220, it is realistic to approximately halve the distance between adjacent individual electrodes 220. This is because the dimensions of the individual electrodes 220 and the distance between the individual electrodes 220 are set based on the accuracy of photolithography during manufacturing.

Here, if the current-voltage characteristics of the organic electroluminescent layer 210 are approximated by a simple resistance, the resistance of the organic electroluminescent layer 210 is inversely proportional to the area of the individual electrodes 220 . For example, when the pixel pitch _PP is set to 1/2, the resistance _RSP of the portion of the organic electroluminescent layer 210 corresponding to the individual electrode 220 increases four times.
On the other hand, the resistance RIE _-IE between the individual electrodes 220 is considered to be unchanged in view of the above equation because the ratio of the distance between the individual electrodes 220 and the length of one side of the individual electrode 220 does not change even if the pixel pitch _PP is changed. Therefore, as the pixel pitch _PP becomes smaller, the resistance _RSP of the portion of the organic electroluminescent layer 210 with respect to the resistance _RIE-IE between the individual electrodes 220 increases in inverse proportion to the square of the pixel pitch _PP , and the influence of the leak current between the individual electrodes 220 increases. As a result, the color reproducibility of the display device 200 tends to deteriorate at low luminance.

[1.2. Overview of suppression of leakage current according to the present disclosure]
As described above, the present inventors have identified that the leak current between the individual electrodes 220 is generated via the organic electroluminescent layer 210 . Furthermore, the present inventors have found that the leak current affects the color reproducibility of the display device 200, especially at low luminance, and that the smaller the pixel pitch _PP , the greater the effect of the leak current.

For the purpose of suppressing the influence of such a leak current, the present inventors considered placing an additional electrode (third electrode described later) 90 between the individual electrodes 20 (20B, 20G, 20R) as shown in FIGS. The present inventors have found that by setting the potential of the third electrode 90 closer to the potential of the transparent common electrode 30 than the potential of the individual electrode 20, the leakage current generated in the individual electrode 20 can be absorbed by the third electrode 90. The present disclosure will now be described in more detail.

<2. Configuration of Display Device>
Next, the display device according to this embodiment will be described in detail. FIG. 1 is a cross-sectional view schematically showing an example of the display device according to the present embodiment, FIG. 2 is a schematic plan view for explaining the arrangement of the individual electrodes and the third electrode of the display device shown in FIG. 1, FIG. 3 is a schematic cross-sectional view for explaining the configuration of the individual electrodes of the display device shown in FIG. 1, and FIG.

The display device 100 shown in FIGS. 1 to 4 is a top-emission display device including active matrix organic electroluminescence elements. In the display device 100, an organic electroluminescent layer 10 is arranged on an interlayer insulating film 80. An individual electrode (second electrode) 20 as an anode is arranged on the main surface of the organic electroluminescent layer 10 on the interlayer insulating film 80 side, and a transparent common electrode (first electrode) 30 as a cathode is arranged on the opposite main surface. Further, a third electrode 90 is arranged between the individual electrodes 20 on the main surface of the organic electroluminescent layer 10 on the interlayer insulating film 80 side. A protective insulating film 40 , a color filter layer 50 , a sealing resin 60 and a cover glass 70 are laminated in this order on the transparent common electrode 30 . In the interlayer insulating film 80, contacts 81 and wirings 83 for connecting the individual electrodes 20 to the pixel drive circuit, and contacts 85 and wirings 87 for connecting the third electrodes 90 are arranged. A circuit for driving the organic electroluminescence element OLED as shown in FIG. 4 is appropriately arranged in the interlayer insulating film 80 and on the semiconductor substrate (not shown) below it.

In the present embodiment, in the display device 100, like the _display device 200, the red pixel SP _R , the green pixel SP _G , and the _blue pixel _{SP B as} shown in FIG. An image can be displayed by arranging these pixels in a matrix.

The organic electroluminescent layer 10 contains an organic luminescent material and is provided on the individual electrodes 20 and the interlayer insulating film 80 as a continuous film common to all organic electroluminescent elements OLED. Also, the organic electroluminescent layer 10 emits light when an electric field is applied between the individual electrode 20 and the transparent common electrode 30 .

Specifically, when an electric field is applied, holes are injected into the organic electroluminescent layer 10 from the individual electrodes 20 and electrons are injected from the transparent common electrode 30 . The injected holes and electrons recombine in the organic electroluminescent layer 10 to form excitons, and the energy of the excitons excites the organic light-emitting material, causing the organic light-emitting material to emit fluorescence or phosphorescence.

Here, the organic electroluminescent layer 10 may be formed with a multilayer structure in which a plurality of functional layers are laminated. For example, the organic electroluminescent layer 10 may have a structure in which a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are stacked in order from the individual electrode 20 side. Also, the organic electroluminescent layer 10 may be formed in a so-called tandem structure in which a plurality of light emitting layers are connected via a charge generating layer or an intermediate electrode.

The organic electroluminescent layer 10 is composed of a hole-transporting material, an electron-transporting material, an electric charge-transporting material, an organic light-emitting material, or the like, depending on its layer structure. Each of such materials is not limited, and it is possible to adopt a suitable combination of known materials.
Further, the wavelength of the light emitted by the organic electroluminescent layer 10 can be appropriately set according to the application, and in the display device 100 according to this embodiment, the emission wavelength is set so that the emission color is white.

Further, as described above, the organic electroluminescent layer 10 is a continuous film common to the organic electroluminescent elements OLED, and is formed continuously over a plurality of pixels in plan view. Here, in the case of an organic electroluminescent display with a pixel pitch of several tens of microns or more, organic electroluminescent layers that emit red, green, and blue light may be formed separately for each color by mask vapor deposition or the like. However, in the case of a high-definition small display using Si-MOS with a pixel pitch of 10 μm or less, it is difficult to divide the organic electroluminescent layer for each color. Therefore, when manufacturing a display device 100 with a small pixel pitch, it is suitable to form the organic electroluminescent layer 10 that emits white light so as to cover the entire effective pixel area, and to disperse the light into red, green, and blue colors by means of the color filter layer 50 disposed thereon.

On the other hand, since the organic electroluminescent layer 10 has no layer discontinuity, it is considered that leakage current tends to easily flow between pixels. However, in the display device 100 according to the present embodiment, leakage current flows through the third electrode 90, which will be described later, so movement of the leakage current between pixels is suppressed.

The transparent common electrode 30 functions as a cathode of the organic electroluminescence element OLED. Therefore, when a voltage is applied to the organic electroluminescent layer 10, the potential of the transparent common electrode 30 becomes lower than the potential of the individual electrodes 20, which will be described later. Also, the transparent common electrode 30 is provided on the organic electroluminescent layer 10 as a continuous film common to all the light emitting elements. The transparent common electrode 30 may be formed as a light transmissive electrode using a material with high light transmittance and a small work function. For example, the transparent common electrode 30 may be formed of a transparent conductive material such as indium tin oxide, indium zinc oxide, zinc oxide, aluminum-doped zinc oxide, or gallium-doped zinc oxide, or may be formed as a light-transmitting thin film (e.g., 30 nm or less) using a metal alloy such as aluminum (Al), magnesium (Mg), silver (Ag), calcium (Ca), or sodium (Na). Also, the transparent common electrode 30 may be formed by stacking a plurality of films made of the above metals or alloys.

The individual electrode 20 is provided on the interlayer insulating film 80 for each pixel and functions as an anode of the organic electroluminescence element OLED. As shown in FIG. 2, in plan view, the individual electrodes 20 are arranged at regular intervals based on a predetermined pixel pitch _PP corresponding to the arrangement and shape of the pixels. Specifically, an individual electrode 20R corresponding to a red pixel, an individual electrode 20G corresponding to a green pixel, and an individual electrode 20B corresponding to a blue pixel are repeatedly arranged with a predetermined interval of boundary regions interposed therebetween. Also, in the present embodiment, the individual electrodes 20 each have a hexagonal shape in plan view.

The individual electrode 20 may be formed as a light reflecting electrode with a material having a high light reflectance and a large work function. For example, the individual electrode 20 may be formed of a single substance or an alloy of a metal such as Cr, Au, Pt, Ni, Cu, Mo, W, Ti, Ta, Al, Fe, or Ag, or may be formed by laminating a plurality of these metal films. Among them, Al has a high reflectance of 90% or more for visible light, and can have functions as a power feeder and a reflector at the same time. When Al is used as the individual electrode 20, a small amount of Cu may be added.

Further, as shown in FIG. 3, the individual electrode 20 may be formed by laminating an electrode 201 and a conductive light reflecting layer 202 . In this case, the electrode 201 can also use a material suitable for injecting holes into the organic electroluminescent layer 10 . Alternatively, the electrode 201 may be formed as a transparent electrode using a transparent conductive material such as indium zinc oxide or indium tin oxide. The light reflective layer 202 can be composed of a single metal or alloy such as Cr, Au, Pt, Ni, Cu, Mo, W, Ti, Ta, Al, Fe, or Ag.

Further, as shown in FIG. 1 , a plurality of third electrodes 90 are arranged in boundary regions between the plurality of individual electrodes 20 so as to be in contact with the main surface of the organic electroluminescent layer 10 . Also, as shown in FIG. 2, in the present embodiment, the plurality of third electrodes 90 are regularly arranged so as to be equally spaced from the adjacent individual electrodes 20R, 20G, and 20B in plan view. From another point of view, the plurality of third electrodes 90 are arranged so as to surround each of the individual electrodes 20R, 20G, and 20B at a predetermined distance in plan view.

The plurality of third electrodes 90 are connected to the internal circuit of the display device 100 via contacts 85 and wirings 87, and are commonly set to a constant potential. Specifically, when a voltage is applied to the organic electroluminescent layer 10, the potential of the third electrode 90 is set to be smaller than the sum of the potential of the transparent common electrode 30 and the threshold voltage for the organic electroluminescent layer 10.

As a result, even when a voltage is applied to the organic electroluminescent layer 10 by the transparent common electrode 30 and the individual electrodes 20, and a leakage current is generated from the individual electrodes 20 to which the voltage is applied, the leakage current can preferentially flow through the third electrode 90. Therefore, leakage current is prevented from flowing from the individual electrode 20 to which the voltage is applied to the adjacent individual electrode 20 . As a result, it is possible to prevent the organic electroluminescent layer 10 from emitting light due to the voltage generated by the leakage current between the individual electrode 20 and the transparent common electrode 30 which is not intended.

Specifically, for example, as shown in FIG. 2, when a voltage is applied to the organic electroluminescent layer 10 between the central individual electrode 20B and the transparent common electrode 30, the leakage current generated in the individual electrode 20B preferentially flows through the surrounding third electrode 90 (arrows in the figure). As a result, leak current is prevented from flowing through the surrounding individual electrodes 20B and 20G, and surrounding green and red pixels are prevented from emitting light. As a result, deterioration of the color purity of the blue pixels corresponding to the individual electrodes 20B is prevented, and the display device 100 can display an image in a wide color gamut.

The potential of the third electrode 90 as described above is preferably lower than the potential of the transparent common electrode 30 . Thereby, the leakage current generated in the individual electrode 20 can preferentially flow to the surrounding third electrode 90 more reliably. Further, in this embodiment, the individual electrode 20 is an anode and can have a positive potential when a voltage is applied. Therefore, the potential of the third electrode 90 can be, for example, 0 V or less in such a case.

Furthermore, the potential of the third electrode 90 is preferably the same as the potential of the transparent common electrode 30 . Thereby, the setting of the potential of the third electrode 90 described above can be achieved more easily, and the configuration of the display device 100 can be simplified. That is, the third electrode 90 and the transparent common electrode 30 can be connected by wiring or the like, and the potential can be managed by the same wiring. For example, when the potential of the transparent common electrode 30 as a cathode is set to 0V, the potential of the third electrode 90 can also be set to 0V. Further, for example, when the transparent common electrode 30 is set to a negative potential to increase the potential difference with the anode to increase the luminance of the organic electroluminescence element OLED, the potential of the third electrode 90 can also be set to a negative potential.

The lower limit of the potential of the third electrode 90 is not particularly limited as long as it is within a range in which a reverse current does not substantially flow through the organic electroluminescent layer 10 . For example, the potential of the third electrode 90 may be about 10 V lower than the potential of the transparent common electrode 30 . However, even if the potential of the third electrode 90 is set to a potential significantly lower than that of the transparent common electrode 30, for example, a potential lower than 5 V or more, the effect of suppressing the leakage current described above is not significantly improved. The effect of suppressing the leak current described above can be sufficiently obtained by setting the potential of the third electrode 90 to be lower than the potential of the transparent common electrode 30 by 2V.

In addition, in the present embodiment, the plurality of third electrodes 90 is an island-shaped electrode group having a smaller area than the individual electrodes 20 . Thus, by arranging a plurality of third electrodes 90 in the form of dots, the area required for installing the third electrodes 90 can be reduced, and the area of the individual electrodes 20 can be made relatively large. As a result, the area used for light emission of the organic electroluminescent layer 10 can be increased, and even when the organic electroluminescent layer 10 emits light with the same luminance and the same current, the current density in the organic electroluminescent layer 10 can be made relatively small. In this case, deterioration of the organic electroluminescent layer 10 can be suppressed, and the life of the display device 100 can be extended.

The area of each third electrode 90 is not particularly limited as long as the connection with the contact 85 is ensured, and can be reduced according to the accuracy of the manufacturing process of the display device 100 . For example, the area of each third electrode 90 can be 5% or less, preferably 3% or less, of the area of each individual electrode 20 .

Also, the distance between each third electrode 90 and the adjacent individual electrode 20 is not particularly limited, and the third electrode 90 and the individual electrode 20 are spaced apart to the extent that a short circuit does not occur.

Also, the third electrode 90 is arranged in the same layer as the individual electrode 20 . That is, the third electrode 90 is formed simultaneously in the same process during manufacturing. Thereby, the third electrode 90 can be easily and reliably arranged between the individual electrodes 20 , and the third electrode 90 can be reliably arranged so as to be in contact with the organic electroluminescent layer 10 .

Further, the material and layer structure of the third electrode 90 can be the same as the material and layer structure of the individual electrode 20 .

The protective insulating film 40 is provided on the transparent common electrode 30 to protect the organic electroluminescence element OLED from the external environment, especially to prevent moisture and oxygen from entering the organic electroluminescence layer 10 . The protective insulating film 40 may be made of a material with high optical transparency and low water permeability, such as silicon oxide (SiO _x ), silicon nitride (SiN _x ), aluminum oxide (AlO _x ), or titanium oxide (TiO _x ).

The color filter layer 50 is provided on the protective insulating film 40 and color-divides the light generated by the organic electroluminescence element OLED for each pixel. Specifically, the color filter layer 50 has a red color filter 50R, a green color filter 50G, and a blue color filter 50B that are divided corresponding to each individual electrode 20 . The red color filter 50R, the green color filter 50G, and the blue color filter 50B convert incident light from the organic electroluminescent layer 10 side into red, green, and blue, respectively, and emit the converted light toward the sealing resin 60 side. Also, the color filter layer 50 may be a resin layer that selectively transmits light in the visible light wavelength band corresponding to red light, green light, or blue light.

The sealing resin 60 is placed on the color filter layer 50 and seals each member below the color filter layer 50 . Also, the cover glass 70 is arranged on the sealing resin 60 to protect the display portion of the display device 100 .

The interlayer insulating film 80 is arranged under the organic electroluminescent layer 10 and carries the individual electrodes 20 and the third electrodes 90 . At the same time, the interlayer insulating film 80 accommodates contacts 81 and wirings 83 that connect the individual electrodes 20 to a pixel driving circuit (not shown), and contacts 85 and wirings 87 that connect the third electrodes 90 to an external circuit. Note that the interlayer insulating film 80 can accommodate other wirings, elements, and the like, if necessary. The interlayer insulating film 80 is made of insulating silicon oxynitride, for example. The wirings 83 and 87 are made of a conductor such as copper (Cu) or aluminum (Al), and connect the individual electrode 20 and the third electrode 90 to an external circuit.

As described above, the display device 100 has a drive circuit for driving the organic electroluminescence elements of the display device 100 on a semiconductor substrate or the like (not shown). The drive circuit is usually divided into pixels by a MOS process. Here, an example of a circuit forming one pixel of the display device 100 will be described. FIG. 4 is a circuit diagram illustrating an example of a circuit forming one pixel of the display device 100. As shown in FIG.

As shown in FIG. 4, a circuit forming one pixel of the display device 100 includes an organic electroluminescence element OLED, a driving transistor DTr, a capacitive element C, and a selection transistor STr.

As described above, the organic electroluminescent element OLED is a self-luminous light emitting element in which the individual electrode 20, the organic electroluminescent layer 10, and the transparent common electrode 30 are laminated. The individual electrode 20 of the organic electroluminescence element OLED is connected to the power supply line PL via the drive transistor DTr, and the transparent common electrode 30 of the organic electroluminescence element OLED is connected to the ground line at ground potential. The organic electroluminescence element OLED functions as one pixel of the display device 100 .

The drive transistor DTr is, for example, a field effect transistor. One of the source and the drain of the drive transistor DTr is connected to the power supply line PL, and the other of the source and the drain is connected to the individual electrode 20 of the organic electroluminescence element OLED. Also, the gate of the drive transistor DTr is connected to either the source or the drain of the selection transistor STr. The drive transistor DTr is connected in series with the organic electroluminescence element OLED, and drives the organic electroluminescence element OLED by controlling the current flowing through the organic electroluminescence element OLED according to the magnitude of the gate voltage applied from the selection transistor STr.

The selection transistor STr is, for example, a field effect transistor. One of the source and drain of the select transistor STr is connected to the gate of the drive transistor DTr, and the other of the source and drain is connected to the signal line DL. Also, the gate of the selection transistor STr is connected to the scanning line SL. The select transistor STr samples the voltage of the signal line DL and then applies it to the gate of the drive transistor DTr, thereby controlling the signal voltage applied to the gate of the drive transistor DTr.

Capacitive element C is, for example, a capacitor. One end of the capacitive element C is connected to the gate of the drive transistor DTr, and the other end of the capacitive element C is connected to the power supply line PL. The capacitive element C maintains the gate-source voltage of the drive transistor DTr at a predetermined voltage.

In the display device 100 according to the present embodiment described above, the third electrode 90 is arranged between the individual electrodes 20, and the potential of the third electrode 90 is lower than the potential of the transparent common electrode 30 plus the threshold voltage for the organic electroluminescent layer 10. As a result, even when a voltage is applied to the organic electroluminescent layer 10 by the transparent common electrode 30 and the individual electrodes 20, and a leakage current is generated from the individual electrodes 20 to which the voltage is applied, the leakage current can preferentially flow through the third electrode 90. Therefore, leakage current is prevented from flowing from the individual electrode 20 to which the voltage is applied to the adjacent individual electrode 20 . As a result, it is possible to prevent the organic electroluminescent layer 10 from emitting light due to the voltage generated by the leakage current between the individual electrode 20 and the transparent common electrode 30 which is not intended. In addition, surrounding pixels corresponding to other colors are prevented from unintentionally emitting light, and the display device 100 can display an image in a wide color gamut.

Also, as described above, the smaller the pixel pitch, the greater the influence of the leakage current. In addition, when a fine pixel pitch of 10 μm or less is to be realized, it is suitable to arrange a continuous white organic electroluminescent layer and perform color conversion by a color filter layer. The display device 100 according to the present embodiment described above can sufficiently suppress the influence of leakage current between pixels even when such a fine pixel pitch is employed.

<3. Verification of Influence of Leakage Current>
Next, the display device 100 and the display device 200 are compared to verify the influence of leakage current due to the presence or absence of the third electrode 90 . Here, the power supply line for light emission of the display device 100 and the display device 200 is set to a positive voltage, for example, 8 V, and the potential of the anode (individual electrodes 20, 220) can be used up to about 6 V by turning on the driving transistor DTr. This design is such that a maximum potential drop of about 2 V occurs between the source and drain of the driving transistor DTr. On the other hand, the potential of the cathode (transparent common electrodes 30, 230) was set to ground potential (0 V).

First, based on the current-voltage characteristics of the organic electroluminescent layer 210 shown in FIG. 19, FIG. 5 shows the result of estimating the emission current and the leak current that flows to the adjacent individual electrode 220 when the third electrode 90 does not exist. In addition, FIG. 5 shows the measurement results of the light emission current in the display device 100 and the leakage current that flows to the adjacent individual electrodes 20 . Numerical values in the graph of FIG. 5 indicate voltage values of the individual electrodes 20 and 220 when emitting light.

When the light emission current shown on the horizontal axis, that is, the current flowing through the organic electroluminescent layer 210 is 10 ⁻¹² A or less, the leakage current reaches 1/10 or more of the light emission current, and when it is 10 ⁻¹³ A or less, it becomes almost the same as the light emission current. On the other hand, in the display device 100 in which the third electrode 90 is set to 0 V, the leak current is suppressed to about 1/10 of that in the display device 200, and the effect of suppressing the leak current is particularly remarkable on the low voltage side of 3 V or less. Furthermore, in the display device 100 in which the third electrode 90 is set to −2 V, the leak current can be suppressed to 1/100 or less of that in the display device 200. FIG.

Further, FIG. 6 shows values obtained by subtracting the value obtained by dividing the leakage current flowing through the adjacent individual electrode 20, 220 by the light emission current when various voltages are applied to one individual electrode 20, 220, from 1. FIG. The value on the vertical axis in this graph indicates the relationship between the light emission current and the leak current, and therefore serves as a measure of the width of the color gamut of the display devices 100 and 200. FIG. The horizontal axis of FIG. 6 indicates the luminance, and more specifically, the luminance when the individual electrodes 20 and 220 of all sub-pixels of the organic electroluminescence element OLED, that is, all sub-pixels of red, green, and blue belonging to all pixels, are illuminated with a predetermined voltage.

As shown in FIG. 6, in the display device 200 that does not have the third electrode 90, at 1 nit, which is sufficiently visible luminance, the color gamut deterioration due to the leakage current between the individual electrodes 220 cannot be ignored.

On the other hand, in the display device 100 having the third electrode 90, the leak current that causes color mixture is 1/10 or less of the light emission current even at an imperceptibly low luminance of 0.001 nit, and the decrease in color gamut can be kept to about 10%. However, as shown in FIG. 6, in view of the wide color gamut, the effect of setting the potential of the third electrode 90 to a lower voltage (-2V) than the potential of the transparent common electrode 30 of 0V was not dramatic. On the other hand, if the potential of the third electrode 90 is made lower than the potential of the transparent common electrode 30, the power consumption of the display device 100 as a whole may increase. Therefore, when it is necessary to suppress the leakage current between the individual electrodes 20 to the utmost limit, it has been considered to make the potential of the third electrode 90 even lower than the potential of the transparent common electrode 30 .

In addition, in the display device 100, the third electrode 90 was arranged as a dot with a small area, but it was possible to sufficiently suppress the leak current as described above. The area of the individual electrode 20 in such a display device 100 is only about 12% smaller than the area of the individual electrode 220 in the display device 200 shown in FIG.

<4. Variation>
An embodiment of the present disclosure has been described above. Several variations of the above embodiments of the present disclosure are described below. In addition, each modification described below may be applied to the above embodiment of the present disclosure independently, or may be applied in combination to the above embodiment of the present disclosure. Further, each modification may be applied instead of the configuration described in the above embodiment of the present disclosure, or may be additionally applied to the configuration described in the above embodiment of the present disclosure.

First, in the above-described embodiment, the transparent common electrode 30 is the cathode and the individual electrode 20 is the anode, but the present disclosure is not limited to this. The transparent common electrode 30 may be the anode and the individual electrodes 20 may be the cathode. In this case, the potential of the transparent common electrode 30 is higher than the potential of the individual electrodes 20 when a voltage is applied to the organic electroluminescent layer 10 . The potential of the third electrode 90 is greater than the potential of the transparent common electrode 30 minus the threshold voltage for the organic electroluminescent layer 10 . Thereby, the effect of suppressing the leak current between the individual electrodes 20 can be obtained.

In the above case, the potential of the third electrode 90 is preferably equal to or higher than the potential of the transparent common electrode 30 , and more preferably the same as the potential of the transparent common electrode 30 . Furthermore, the upper limit of the potential of the third electrode 90 is not particularly limited, and may be within a range in which a reverse current does not substantially flow through the organic electroluminescent layer 10 . However, the effect of suppressing the leak current described above can be sufficiently obtained by setting the potential of the third electrode 90 to be 2 V higher than the potential of the transparent common electrode 30 .

Further, in the above-described embodiment, the pixels and the individual electrodes 20 have hexagonal shapes, but the present disclosure is not limited to this. Also, the arrangement of the third electrode around the individual electrode may be appropriately changed according to the shape of the individual electrode and its application.

Examples in which the shape of the individual electrode and the arrangement of the third electrode are changed are shown in FIGS. In FIG. 7, the individual electrodes 21R, 21G, and 21B corresponding to red, green, and blue are rectangular according to the shape of the pixel and arranged in stripes. In addition, the third electrode 90A is arranged on an extension line of the corners of the individual electrodes 21R, 21G, and 21B so as to be separated from the individual electrodes 21R, 21G, and 21B to such an extent that a short circuit does not occur.

In FIG. 8, the individual electrodes 22R, 22G, and 22B corresponding to red, green, and blue are square according to the shape of the pixel. In addition, the third electrode 90B is arranged on the extended line of the corners of the individual electrodes 22R, 22G, and 22B so as to be separated from the individual electrodes 22R, 22G, and 22B to such an extent that a short circuit does not occur. However, the third electrode 90B is not arranged on extension lines of corners of the individual electrodes 22R, 22G, and 22B. In this way, the third electrodes 90B are arranged regularly, and part of them may not be arranged as necessary. In addition, it is possible to dispose the third electrode around individual electrodes that are likely to be affected by leak current, while not arranging third electrodes around other individual electrodes.

FIG. 9 also shows the arrangement of the individual electrodes 23R, 23G, 23B, and 23W when the color filter layer has white pixels that do not use a color conversion member. The individual electrodes 23R, 23G, 23B, and 23W corresponding to red, green, blue, and white have a square shape according to the shape of the pixel. Also, the third electrode 90C is arranged on the extended line of the corners of the individual electrodes 23R, 23G, 23B and 23W and is spaced apart from the individual electrodes 23R, 23G, 23B and 23W to the extent that short-circuiting does not occur. Employing such white pixels is advantageous in improving the maximum luminance.

In addition, in the embodiment and the modification described above, the third electrode is described as being point-shaped, but the present disclosure is not limited to this. For example, the third electrode can take various shapes, for example, it can be a linear electrode extending between individual electrodes. Also, the third electrode may have a mesh shape extending between the individual electrodes.

Also, the arrangement of the individual electrodes and the third electrode on the interlayer insulating film can be appropriately changed according to the method of forming them. In FIG. 10, the interlayer insulating film 80A has a convex portion 803 on which the individual electrode 24 and the third electrode 90D are arranged. Such interlayer insulating film 80A, individual electrode 24 and third electrode 90D can be obtained by forming an anode and a new common electrode on an interlayer insulating film such as those used in wiring of a general LSI (large-scale integrated circuit), and processing them using known photolithography and dry etching.

In FIG. 11, an interlayer insulating film 80B is further embedded in the gap region between the individual electrode 25 and the third electrode 90E. In such a case, since the plane formed by the individual electrode 25, the third electrode 90E, and the interlayer insulating film 80B is relatively smooth, it is possible to prevent the formation of locally thin portions when the organic electroluminescent layer is formed. As a result, uniform light emission is possible regardless of the part. Such a structure can also be realized using a known general LSI manufacturing process or TFT (thin-film-transistor) manufacturing process.

In FIG. 12, the interlayer insulating film 80C has a convex portion 803A, and the individual electrode 26 and the third electrode 90F are arranged on the convex portion 803A. An insulating film 805 is formed on the individual electrode 26 and the third electrode 90F. In this case, the organic electroluminescent layer in the opening region of the insulating film 805 emits light, and the effective area of the individual electrode 26 is the area of the opening surrounded by the insulating film 805 . Such a structure can be formed by further forming an insulating film on the electrode and then removing a part of the insulating film so as to form an opening in addition to the structure in FIG.

As a wiring for supplying power to the third electrode, for example, as shown in FIG. 13, a light shielding layer 88 made of metal may be used instead. The light shielding layer 88 is arranged in the interlayer insulating film 80 to block the light emitted from the organic electroluminescent layer 10 and protect the pixel driving MOS transistors and TFTs in the lower layer. The light shielding layer 88 is formed continuously over the entire display portion of the display device 100, and can be formed of a metal layer having low reflectance and transmittance, such as titanium nitride or tungsten. The potential of the third electrode 90 can be set by connecting the light shielding layer 88 and the third electrode 90 with a contact 87A and connecting the light shielding layer 88 to an external circuit.

Further, in the above-described embodiment, the individual electrode 20 is assumed to have a function as a reflector, but the present disclosure is not limited to this. For example, as shown in FIG. 14, the individual electrode 27 is formed as a transparent electrode using a transparent conductive material such as indium zinc oxide or indium tin oxide. On the other hand, a reflector 89 such as a metal film is arranged below the individual electrodes 26 in the interlayer insulating film 80D.

Also, the display device according to the present disclosure may be of a bottom emission type. In this case, the individual electrodes are transparent electrodes, and the reflector in the interlayer insulating film is omitted.

Furthermore, in the above-described embodiment, the organic electroluminescent layer is formed continuously over a plurality of pixels, but the present invention is not limited to this, and organic electroluminescent layers that emit red, green, and blue light may be formed separately for each color by mask vapor deposition or the like. When the pixel pitch is relatively large, such as several tens of microns or more, the method of dividing the organic electroluminescent layer by color is suitable. Such a configuration is also possible when the display device is driven by a thin film transistor made of amorphous silicon, polycrystalline silicon, oxide semiconductor, or the like. In the case where the organic electroluminescent layer is divided for each color in this way, the display device according to the present disclosure having the third electrode can suitably suppress leakage current between pixels.

The circuit configuration used for driving light emission of the display device is not limited to that shown in FIG. 4, and various known circuits can be employed. In addition, various pixel driving methods having correction operations for improving the uniformity of image quality within the panel have been devised, but the technology of the present disclosure can be widely applied regardless of these detailed pixel driving methods. However, in some cases, instead of keeping the voltage applied to the third electrode at a constant value, a control such as turning off a switch such as a transistor installed between the constant potential line and the third electrode during a period in which the contribution to light emission is small, such as a correction operation, may be adopted.

<5. Summary>
As described above, according to the present disclosure, it is possible to suppress the influence of leakage current between individual electrodes in a display device having an organic electroluminescent element. Therefore, surrounding pixels corresponding to other colors are prevented from emitting light unintentionally, and the display device can display an image in a wide color gamut.

The display device described above can also be used as a display unit of various electronic devices that displays an input image signal or an internally generated image signal as a still image or a moving image. Examples of such electronic devices include music players equipped with storage media such as semiconductor memories, imaging devices such as digital cameras and video cameras, notebook personal computers, game devices, and mobile information terminals such as mobile phones and smartphones.

Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field of the present disclosure can conceive of various modifications or modifications within the scope of the technical idea described in the claims, and these are naturally understood to belong to the technical scope of the present disclosure.

Also, the effects described herein are merely illustrative or exemplary, and are not limiting. In other words, the technology according to the present disclosure can produce other effects that are obvious to those skilled in the art from the description of this specification in addition to or instead of the above effects.

Note that the following configuration also belongs to the technical scope of the present disclosure.
(1)
an organic electroluminescent layer;
a first electrode disposed on one main surface side of the organic electroluminescent layer and common to a plurality of pixels;
a plurality of second electrodes arranged individually for each pixel on the other main surface side of the organic electroluminescent layer;
and a plurality of third electrodes disposed between the plurality of second electrodes on the other main surface side of the organic electroluminescent layer.
(2)
The display device according to (1), wherein when a voltage is applied to the organic electroluminescent layer, the potential of the first electrode is lower than the potential of the second electrode, and the potential of the third electrode is lower than the potential of the first electrode plus a threshold voltage for the organic electroluminescent layer.
(3)
The display device according to (2), wherein the potential of the third electrode is equal to or lower than the potential of the first electrode.
(4)
The display device according to (1), wherein when a voltage is applied to the organic electroluminescent layer, the potential of the first electrode is higher than the potential of the second electrode, and the potential of the third electrode is higher than the potential of the first electrode minus the threshold voltage for the organic electroluminescent layer.
(5)
The display device according to any one of (2) to (4), wherein the potential of the third electrode and the potential of the first electrode are the same.
(6)
The display device according to any one of (1) to (5), wherein the third electrode is arranged in an island shape in plan view.
(7)
The display device according to any one of (1) to (6), wherein the third electrodes are arranged at regular intervals from the plurality of second electrodes adjacent to each other in plan view.
(8)
The display device according to any one of (1) to (7), wherein the second electrode and the third electrode are arranged in the same layer.
(9)
The display device according to any one of (1) to (8), wherein the organic electroluminescent layer is formed continuously over the plurality of pixels in plan view.
(10)
an organic electroluminescent layer;
a first electrode disposed on one main surface side of the organic electroluminescent layer and common to a plurality of pixels;
a plurality of second electrodes arranged on the other main surface side of the organic electroluminescent layer and individually corresponding to each pixel;
and a plurality of third electrodes disposed between the plurality of second electrodes on the other main surface side of the organic electroluminescent layer.

10, 210 organic electroluminescent layer 20, 20B, 20G, 20R, 21B, 21G, 21R, 22B, 22G, 22R, 23B, 23G, 23R, 23W, 24, 25, 26, 27, 220, 220B, 220G, 220R individual electrode 201 electrode 202 light reflecting layer 30, 230 Transparent common electrode 40, 240 Protective insulating film 50, 250 Color filter layer 50R, 250R Red color filter 50G, 250G Green color filter 50B, 250B Blue color filter 60, 260 Sealing resin 70, 270 Cover glass 80, 80A, 80B, 80C, 80D, 280 Interlayer insulating film 81, 85, 87A, 28 1 contact 83, 87, 283 wiring 88 light shielding layer 89 reflector 90, 90A, 90B, 90C, 90D, 90E, 90F third electrode 100, 200 display device

Claims (9)

an organic electroluminescent layer;
a first electrode disposed in contact with one main surface of the organic electroluminescent layer and common to a plurality of pixels;
a plurality of second electrodes individually arranged for each pixel so as to be in contact with the other main surface of the organic electroluminescent layer;
a plurality of third electrodes arranged so as to be in contact with the other main surface of the organic electroluminescent layer and between the plurality of second electrodes so as not to be in contact with the plurality of second electrodes;
The third electrode is arranged in an island shape in plan view and has a smaller area than the second electrode,
The plurality of second electrodes and the plurality of third electrodes are both hexagonal in plan view,
the second electrodes adjacent to each other are positioned so that their vertices face each other in a plan view,
The second electrode and the third electrode that are adjacent to each other are positioned so that one sides face each other in a plan view.
display device. 2. The display device according to claim 1, wherein when a voltage is applied to the organic electroluminescent layer, the potential of the first electrode is lower than the potential of the second electrode, and the potential of the third electrode is lower than the potential of the first electrode plus the threshold voltage for the organic electroluminescent layer. 3. The display device according to claim 2, wherein the potential of said third electrode is equal to or lower than the potential of said first electrode. 3. The display device according to claim 2, wherein the potential of said third electrode and the potential of said first electrode are the same. 2. The display device according to claim 1, wherein said third electrode is arranged at equal intervals from said plurality of second electrodes adjacent to each other in plan view. 2. The display device according to claim 1, wherein said second electrode and said third electrode are arranged in the same layer. 2. The display device according to claim 1, wherein said organic electroluminescent layer is formed continuously over said plurality of pixels in plan view. 2. The display device according to claim 1, wherein when a voltage is applied to the organic electroluminescent layer, the potential of the first electrode is higher than the potential of the second electrode, and the potential of the third electrode is higher than the potential of the first electrode minus the threshold voltage for the organic electroluminescent layer. an organic electroluminescent layer;
a first electrode disposed in contact with one main surface of the organic electroluminescent layer and common to a plurality of pixels;
a plurality of second electrodes arranged in contact with the other main surface of the organic electroluminescent layer and individually corresponding to each pixel;
a plurality of third electrodes arranged so as to be in contact with the other main surface of the organic electroluminescent layer and between the plurality of second electrodes so as not to be in contact with the plurality of second electrodes;
The third electrode is arranged in an island shape in plan view and has a smaller area than the second electrode,
The plurality of second electrodes and the plurality of third electrodes are both hexagonal in plan view,
the second electrodes adjacent to each other are positioned so that their vertices face each other in a plan view,
The second electrode and the third electrode that are adjacent to each other are positioned so that one sides face each other in a plan view.
Electronics.

Images