JP2002208485A - Organic el display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent drop of light emission efficiency without changing the driving voltage for RGB color mixing. SOLUTION: For the organic LED display, light emission layers 5-B, 5-G, 5-R of an organic LED, emitting blue, green, and red-colored light, are separated by separation walls 4, and the width of at least one color of the light emission layer of either 5-B, 5-G, or 5-R is formed so as to differ from the width of another light emission layers of 5-B, 5-G, and 5-R. By the above, a white color display is enabled to set into an appropriate chromaticity, while making the light emitting efficiency and brightness optimum, without bigly changing the driving voltages of respective pixels of blue, green, and red color.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting thin film such as an organic semiconductor film which emits light by passing a driving current through the light emitting thin film.
The present invention relates to an organic LED display using an L (electroluminescence) element or an LED (light emitting diode) element.

[0002]

2. Description of the Related Art In recent years, with the advent of a highly information-oriented society, the demand for personal computers, portable information terminals, information communication devices, or composite products thereof has been increasing. Thin and lightweight displays are suitable for these products.
Liquid crystal display or self-luminous EL element or LED
A display device using elements or the like is used. The latter self-luminous display device has features such as good visibility, wide viewing angle characteristics, and high-speed response suitable for displaying moving images. Is expected. In fact, in recent years, rapid improvement in luminous efficiency of organic EL elements or organic LED elements (hereinafter collectively referred to as OLEDs) using an organic substance as a light emitting layer, and progress in network technology enabling video communication have been made. Together, the expectations for OLED displays are only growing.

An example of a prior art OLED display is described in Pioneer R & D Vol. 8, No. 3, pp. 41-49. According to this, as shown in FIG. 7, n anodes 61 are arranged vertically and m cathodes 62 are arranged horizontally.
Are arranged at each intersection, and pixels P11,..., Pmn
Are provided, and each anode line is driven by a constant current source 63 for each cathode line, and time-division driving is performed to sequentially scan each cathode line.

In place of the above simple matrix, each pixel has T
Active matrix driving with an FT is also being studied. The technology for manufacturing and driving an OLED display as an active matrix structure is disclosed in, for example,
No. 41048 and US Pat. No. 5,555,0066, which is one of the priority applications of the present application, and International Patent Publication WO98, which describes driving voltage in more detail.
/ 36407 and the like. By these,
A typical pixel of an active matrix OLED display has at least two TFs as shown in FIG.
The light emission luminance of the OLED 76 is controlled by an active element driving circuit including a T switch transistor Tsw73, a driver transistor Tdr74, and one storage capacitor 75. Specifically, the voltage stored in the storage capacitor 75 via the switch transistor 73 defines the gate voltage of the driver transistor 74, and drives the OLED 76 with a current determined thereby.

In the above-mentioned conventional OLED display, OLEDs emitting blue, green and red light are provided at equal intervals regardless of the pixel addressing method, and therefore, the pixel widths of all colors are configured to be equal. I have. Here, the relationship between the emission luminance of each color and the input signal voltage becomes the maximum luminance when the input signal has the maximum value. The color image is displayed by controlling the emission luminances of blue, green, and red, respectively. When the blue, green, and red input signals have the maximum values, the maximum white light emission luminance is obtained. At this time, in order to set the chromaticity of the white display to coordinates such as point C, for example, the color mixture ratio is determined from the chromaticities of blue, green, and red emission. For example, shifting the chromaticity of white display in the blue direction is realized by reducing the levels of green and red input signals to lower the light emission level.

[0006]

However, if the input signal level of a certain color is reduced for adjusting the chromaticity of white display as described above, the effective number of display gradations will be reduced. That is, in the OLED display having the conventional configuration, there is a problem that the gradation display quality or luminance is deteriorated. Also, to increase the overall brightness,
A method of increasing the drive voltage to increase the current density flowing into the pixel is also conceivable. However, according to this method, there is a problem from the viewpoint of power consumption because the luminous efficiency decreases in inverse proportion to the drive voltage. . The present invention provides an element configuration that improves luminance without changing the drive voltage, that is, while maintaining good luminous efficiency, in order to solve such a problem.

[0007]

An OLED display according to the present invention has a plurality of electrode groups on a substrate, and has a plurality of pixels formed in a matrix form by the plurality of electrode groups. Each have a light emitting layer provided with a fluorescent dye that emits blue, green and red light.
An LED which emits blue, green and red light
The light emitting layer of the LED is separated by a partition, and the width of at least one color of the OLED light emitting layer provided with the fluorescent dye is different from the width of the light emitting layer of the other color OLED. .

As a result, it is possible to optimize the luminous efficiency and the luminance and to set the white display to an appropriate chromaticity without drastically changing the driving voltage of each of the blue, green and red light emitting pixels. .

[0009]

(Embodiment) Referring to FIG.
An embodiment of the present invention will be described. FIG. 1 according to the invention
1 schematically shows a cross-sectional view of an OLED display. According to this, in the OLED display according to the present invention,
A thin film transistor pixel circuit 2 for driving an organic LED is formed on a glass substrate 1, and an interlayer film 3 is formed on the thin film transistor pixel circuit 2.
Partition walls 4 that define pixels are provided at a plurality of intervals. Light-emitting cells RGB are provided in a region partitioned from the substrate by a plurality of spaces.
Groups 5-R, 5-G, 5-B are formed. Partition wall 4
Is installed above the thin film transistor circuit 2.
The light emitting cell includes at least an organic layer, and is provided with fluorescent dyes that emit red, green, and blue light corresponding to the RGB groups, and is sandwiched between the anode 6 and the cathode 7. The contact 6 is connected between the anode 6 and the thin film transistor circuit 2.

In the present embodiment, the spacing Wr of the partition walls forming the light emitting cells having a fluorescent dye group emitting red light (hereinafter referred to as a red light emitting cell) group, and then the light emitting cells having the fluorescent dye group emitting blue light ( Hereinafter, the spacing Wb between the partition walls forming the blue light emitting cell group and the spacing W between the partition walls forming the light emitting cell group (hereinafter, green light emitting cell) having the fluorescent dye group emitting green light will be described.
It is configured to become narrower in the order of g. In the present embodiment, a display panel having an image resolution of about 100 color pixels / inch is configured, so that the pitch of one color pixel is Wr + Wg + Wb = 252 μm, and Wr = 10
0 μm, Wg = 52 μm, and Wb = 100 μm. This is clear in the conventional example because Wr = Wg = Wb = 84 μm.

FIG. 2 is a plan view of a color pixel including a red light emitting cell, a blue light emitting cell, and a green light emitting cell of the OLED display according to the present invention. Although the width of each cell is different as described above, the length L of the other side is common. The light emitting area decreases as the width of the cell decreases, but the relationship is not proportional. This is because it is necessary to provide a wiring, a capacitance and a circuit for driving in each cell, and these cells have a fixed value and a predetermined area without being proportional to the width. Part A in FIG. 2 shows that partition walls are provided on these circuit elements. In the cell area (W ×
If the ratio of the light emitting area S in L) is defined as the aperture ratio, in the present embodiment, 30% when W = 50 μm and 4% when W = 80 μm.
At 5%, W = 100 μm, 60% was obtained. Using this, the emission area ratio for each color in the conventional example is S
While r: Sg: Sb = 1: 1: 1, in the present embodiment, Sr: Sg: Sb = 4: 1: 4. Further, when compared between Sr, the light emitting area of the red light emitting cell according to the present invention was about 1.7 times as large as that of the conventional one, and 0.42 times that of the green light emitting area.

As described above, when the light emitting area of the cell is changed, the total amount of current can be increased by the area ratio when the driving voltage is kept the same. This effect will be described. FIG.
Shows an outline of the dependence of the luminous efficiency η (lm / W) of light emission on the forward applied voltage (Vf) in the OLED.
As the forward applied voltage Vf increases, light emission turns on at Vf = Vt. At the point of the forward voltage V0 that is higher than the voltage Vt by about 1 to 2 V, η reaches the maximum, and thereafter, η decreases in a relationship inversely proportional to Vf−Vt. V0
Is somewhat different depending on the OLED material, but the above luminous efficiency behavior is almost the same. The input power is the product of the forward voltage Vf (V) applied to the diode and the forward current If (A) flowing through the diode. The magnitude of the forward current If is determined by the light emitting area S (cm ² ) and the current. It is the product of the density i (A / cm ² ). The current density i is uniquely determined depending on the forward voltage.

For example, R having V0 near Vf = 5V,
The luminous efficiency of the G and B OLEDs is 2 lm /
W, 20 lm / W and 2 lm / W. The color mixture ratio for realizing white at point C from the chromaticity of each color is 1: 2: 1. Using this combination of RGB OLEDs, a color image is constituted by cells of Sr: Sg: Sb = 1: 1: 1 according to the prior art. As an example, consider the case where G is driven with maximum efficiency. In this case, assuming that the total power consumption in the G portion of the panel is 1 W, the luminous flux is 20 lm. In consideration of the color mixture ratio, the luminous flux from the R and B portions of the panel needs to be 10 lm. It is erroneous to estimate that 5 W is required for both R and B at 10 lm / (2 lm / W) to achieve this. Because, in order to obtain a large current, the current density must be increased, and for that purpose, the forward voltage must be increased, and driving must be performed at a point where the luminous efficiency is reduced as shown in FIG. For example, the luminous efficiency becomes 1.5 lm / W, and the required power increases to about 7 W for both R and B. As a result, the total white luminous flux from the panel was 40 lm, and the total power consumption was 15 W (white luminous efficiency was 2.7 lm /
W).

Next, a color image is constituted by the pixels according to the present invention using the same OLED as described above. Assuming that the driving voltage in the G portion is the same as that of the above-described conventional technology, the area can be increased by 0.42 times, so that the total current that can flow is also 0.42 times, the power consumption is 0.42 W, and the luminous flux is 8.4 lm. Becomes From the color mixing ratio, the luminous flux from the R and B portions of the panel is 4.
2lm is indispensable. On the other hand, since the areas of R and B are four times as large as G, the driving voltage is not shifted from the optimum point,
It can be charged up to 0.42 × 4 = 1.7W. That is, a desired luminous flux can be achieved while maintaining the optimum efficiency. As a result, the total white luminous flux from the panel is 16.8 lm, the total power consumption is 5 W (the luminous efficiency of white is
3.4 lm / W). The present invention has advantages over the prior art in that the drive voltage does not need to be changed and the luminous efficiency is optimal.

As described above, in the present invention, the patterning of the color pixels is performed.
A method suitable for a large screen was used. Hereinafter, this will be described. FIG. 4 to FIG. 6 are process flows for producing the organic LED shown in FIG. These figures show the cross section of the thin film transistor in more detail. After the pattern of the anode 6 is formed on the surface of the substrate, the partition 4 is formed (FIG. 4).
(A)). It can be formed using ordinary photolithography. As the material, an acrylic or polyimide photosensitive material can be used. In order to make the surface of the partition wall water-repellent, a plasma treatment using CF ₄ gas is performed after the partition wall formation, or a material having a fluorine atom in advance for the partition wall material may be used (FIG. 4 ( b)).
Thereafter, a solution containing a charge transport material is applied on the same substrate, and the solution is dried to form a charge transport layer 24 (FIG. 4C). Next, a transfer substrate is pressed against this substrate. The transfer substrate 21 is provided with a light-to-heat conversion layer 19 and a transfer layer 20 containing a red, green or blue dye (FIG. 5D). In this state, the laser beam 2 for transfer is
2 is irradiated to a desired position (FIG. 5E). By performing this operation on the material for each of the red, green, and blue sub-pixels,
The light emitting layers 23 of each color can be formed only on the charge transport layer (FIG. 6F). Thereafter, the cathode 6 is formed (FIG. 6G). According to this forming method, high-definition pixels can be formed regardless of the shape of the laser beam. At that time, since the partition is located at a position lower than the surface of the dye transfer, color mixing of the dye is hard to occur.

The present invention is not limited to the above embodiment. For example, although the case where the partition wall is a straight line is mainly described, an essential requirement is that the light emitting area differs depending on the color.

[0017]

As described above, according to the present invention,
In an organic LED display, it becomes possible to optimize luminous efficiency and luminance and to set white display to an appropriate chromaticity without drastically changing the driving voltage of each of blue, green and red light emitting pixels. effective.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an organic LED display according to the present invention.

FIG. 2 is a plan view of a color pixel of an organic LED display according to the present invention.

FIG. 3 is a diagram for explaining luminous efficiency.

FIG. 4 is a diagram for explaining a process flow for creating the structure of FIG. 1;

FIG. 5 is a diagram for explaining a process flow for creating the structure of FIG. 1;

FIG. 6 is a diagram for explaining a process flow for creating the structure of FIG. 1;

FIG. 7 is a diagram for explaining a conventional technique.

FIG. 8 is a diagram for explaining a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Thin film transistor circuit, 3 ... Interlayer film, 4 ... Partition, 5 ... Light emitting cell, 6 ... Anode, 7 ... Cathode.

Claims (5)

[Claims] A plurality of electrodes formed on the substrate and a plurality of pixels formed in a matrix form by the plurality of electrode groups, and each of the plurality of pixels emits blue, green and red fluorescent light; Organic LED having light emitting layer provided with dye
And the organic LE emitting blue, green and red light
The light emitting layer of D is an organic LED display separated by a partition, and the organic light emitting layer provided with the fluorescent dye.
An organic LED display, wherein the width of at least one color of the light emitting layer of the ED is different from the width of the light emitting layer of the organic LED of another color. 2. The partition walls are provided at unequal intervals, and the width of at least one color of the light emitting layer of the organic LED in each pixel is equal to the width of the light emitting layer of the organic LED of another color. 2. The organic LED display according to claim 1, wherein the display is different. 3. The organic LED display according to claim 1, wherein the height of the light emitting layer is the same as or higher than a partition wall formed between adjacent pixels. 4. The organic LED display according to claim 1, wherein control of a current flowing through a light emitting layer of the organic LED provided in the pixel is controlled by a thin film transistor provided in the pixel. 5. A semiconductor device comprising: a plurality of electrode groups on a substrate; and a plurality of pixels formed in a matrix form by the plurality of electrode groups. Each of the plurality of pixels emits blue, green, and red light. An organic LED display comprising an organic LED having a light emitting layer provided with a fluorescent dye, wherein the light emitting areas of the blue, green, and red light emitting organic LEDs differ depending on the color.