JP2001022298A - Display panel and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adopt a constant current drive system for a luminous display element and to reduce the costs of design and production. SOLUTION: Segments, such as organic EL elements, having the same light emission area are formed on a display panel 20 and a mask is formed on a substrate constituting the display surfaces of these segments in such a manner that the display, such as the segments (42a to 42g) constituting the seven segments 30 or display items 32 indicating a character string (TIME), is made visible. As a result, the display device 10 has only the one kind of constant current sources of the same characteristics in a display element drive circuit 50 for the respective segments, by which the simplification of circuitry is made possible even when the constant current drive system is adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display panel comprising an LED, an EL element, an organic EL element and other self-luminous display elements, and a display device equipped with the same. And a display device equipped with the same.

[0002]

2. Description of the Related Art As typical display systems of display devices currently in circulation, there are a cathode ray tube (CRT) system, a light emitting diode (LED) system, a liquid crystal system, and an electroluminescence (EL) system. Among them, the CRT method is a display method in which a phosphor applied on a display screen emits light by stimulation of an electron beam. The CRT is a display device that has become the most widespread display for televisions and other displays due to this display method, and its performance and production technology have been established. However, C
It is difficult to reduce the size of the RT because it is necessary to provide an electron gun at a relatively large distance from the display screen.
There is a drawback that the power consumption is large as compared with other display methods, and it has not satisfied the recent demand for light, thin and small devices.

In view of the above, one of the reasons that the semiconductor manufacturing technology can be used at present is that display devices adopting the above-mentioned LED system and liquid crystal system have emerged, and various portable devices such as watches and mobile phones have been developed. It has been installed in. Among these display methods, the liquid crystal method is a light receiving type display element, and in order to sufficiently recognize display information in a dark place, it is necessary to provide an LED, a filament type light bulb, or the like as a backlight. On the other hand, the LED and the EL element are self-luminous display elements, and emit light spontaneously when a DC or AC current is applied to each element.

Therefore, in a small-sized display device mounted on a portable device, how to efficiently arrange the above-mentioned self-luminous display elements in a limited space, and how to provide low luminance while having sufficient luminance. The issue is how to achieve light emission with power consumption.

With the recent development of blue light emitting diodes, the above-mentioned LEDs have been combined with conventionally used red and green LEDs to increase the realism of full-color display. This is a display element that is expected to be more widely used in the future, in combination with the simplicity of the driving circuit used.

The EL element has a structure in which a phosphor is sandwiched between two electrode plates, and emits light when a voltage (in most cases, an AC voltage) is applied thereto. In particular, in recent years, research and development of an organic EL device using the above-described phosphor as an organic light-emitting layer have been progressing, and low-voltage driving and high-luminance light emission have been realized. This organic EL element is an injection element in which electrons are injected from one electrode and holes are injected from the other electrode, and the electrons and holes are recombined in the above-described organic light emitting layer. They are similar and basically operate under DC bias.

A self-luminous display element such as an LED or an organic EL element driven under such a DC bias is generally driven by two types of a constant voltage driving method and a constant current driving method. The constant voltage driving method is usually achieved by providing a constant voltage driving circuit for intermittently supplying a constant voltage to the self-luminous display element. This constant voltage driving circuit is a circuit for applying a constant voltage to each self-luminous display element (dot, segment, etc.) at a constant duty cycle.

Further, since only one constant voltage driving circuit is usually provided for a display screen composed of a plurality of self-luminous display elements, the constant voltage driving method realized by the constant voltage driving circuit In addition, the display device can be simplified or downsized, and the cost can be reduced. here,
The self-luminous display element has a light emission luminance proportional to a current density to be supplied, but usually, a voltage-current (VI) characteristic changes with time due to deterioration. Therefore, in the above-described constant voltage driving method, it is necessary to adjust the constant voltage to be applied according to the VI characteristics that have changed over time in order to always obtain a constant light emission luminance in the self-luminous display element.

Therefore, by adopting the constant current driving method as the driving method of the self-luminous display element, it is possible to solve the above-described problem that requires adjustment of the applied voltage in the constant voltage driving method. This constant current driving method is a method achieved by providing a constant current driving circuit for supplying a constant current to the self-luminous display element, whereby a constant current is always supplied even if the VI characteristic deteriorates with time. That is, it is possible to maintain a constant light emission luminance.

[0010]

However, the conventional constant current drive circuit must be provided for each self-luminous display element in a display screen composed of a plurality of self-luminous display elements. However, there is a problem that the circuit configuration becomes large-scale or complicated, and the cost increases. In particular, when a segment designed by an arbitrary shape is used as a self-luminous display element, the area of each segment arranged on the display screen is usually different. In order to change the light emission luminance according to the display content to be displayed, an individual constant current drive circuit for supplying a current proportional to the area of each segment is required, which complicates the display device design process and circuit configuration. The problem becomes more pronounced.

Also, when a display screen is constructed by arranging a plurality of dots of the same area as self-luminous display elements and arranging them in a matrix, these dots are usually compared with the above-described segments. Since a large number is required, a large number of constant-current driving circuits for driving each dot are also required, which causes a problem that the circuit configuration of the display device is complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and employs a constant current driving method suitable for a characteristic of a luminance change with time of a self-luminous display element, and a design process and a configuration of a display device and a circuit. And a display device equipped with the display panel, in which the design and manufacturing costs are reduced.

[0013]

In order to achieve the above object, a display panel according to the present invention includes a plurality of self-luminous display elements having the same light-emitting area, and a light-emitting portion of each self-luminous display element, for example, a self-luminous display element. A mask is formed on a back surface or a front surface of a substrate (corresponding to a glass substrate described later) serving as a display surface of the light emitting display element so as to have a desired display shape.

According to the present invention, the display shape visually recognized by each self-luminous display element can be designed to be a desired one like a conventional display panel, and the light-emitting area where each self-luminous display element actually emits light is: Since the self-luminous display elements on the display panel are the same, only one type of constant current source is required to drive each of the self-luminous display elements at a constant current.

Further, the display device of the present invention includes a display panel having a plurality of self-luminous display elements having the same light-emitting area, wherein a mask is formed on a light-emitting portion of each self-luminous display element so as to have a desired display shape. A constant current source having the same characteristic is provided for each of the self-luminous display elements of the display panel, and a display element driving circuit for driving each of the self-luminous display elements with a constant current. As a result, it is possible to perform constant-current driving by a constant-current source having the same characteristics even for a plurality of self-luminous display elements having different display shapes.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a display panel and a display device according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited by the embodiment. In particular, in this embodiment,
A description will be given of a case where a self-luminous display element having a 7-segment configuration, which is commonly used when digitally displaying a numerical value, emits light.
An example in which an element is used will be described.

FIG. 1 is a block diagram showing a schematic configuration of a display panel and a display device according to the present invention. In FIG. 1, a display device 10 includes a display panel 20 in which a plurality of segments are arranged to form a display screen, a switch for turning on / off light emission of each segment arranged in the display panel 20, and a constant current source. Element driving circuit 50, CP
And a display control circuit 60 that appropriately decodes a display signal given from a control circuit (not shown) such as a U and selectively controls on / off of each switch of the display element driving circuit 50. .

In FIG. 1, the display panel 20 comprises
Segments 42a, 42b, 42c, 42d, 42e,
7 segment 30 composed of 42f and 42g
And an organic EL element capable of displaying a display item 32 indicating a character string “TIME”. In particular, FIG.
, The segments 42b, 42c and 42e
Indicates a driven state, that is, a light emitting state,
Thereby, the number “7” can be recognized.

Here, each of the segments 42a, 42b, 42c, 42d, 42 serving as components of the seven segments 30
e, 42f, and 42g generally do not all have the same area for design reasons and the like. Therefore, as described above, in order to drive them by the constant current driving method, a constant current source corresponding to the area of each segment is required. However, each segment shown in FIG. 1 can be visually recognized as being a component of a conventional seven-segment 30 whose area is not unified as in the past, but in fact, all the light-emitting areas are the same.

That is, each segment 42 shown in FIG.
a, 42b, 42c, 42d, 42e, 42f and 4
2g is simply the light emitting segment portions 41a, 41b, 41
Only a part of the regions c, 41d, 41e, 41f, and 41g (hereinafter, referred to as light-emitting windows) is visually recognized. In other words, the light emitting segment portions 41a, 41b, 4
By masking a part of each of 1c, 41d, 41e, 41f and 41g, the element shape of the 7 segment 30 is apparently configured.

Similarly, the display item 32 is also used as the above-mentioned light-emitting window, so that the light-emitting window is a part of the light-emitting segment portion 31 which is an area where light is actually emitted so that the light emission of only the character string "TIME" can be visually recognized. Is masked.

This means that by providing the display element drive circuit 50 with a plurality of constant current sources having the same characteristics, it becomes possible to visually recognize the light emission of the segments having different display shapes on the display panel 20. It is not necessary to prepare constant current sources having different characteristics one by one according to the light emitting area of the segment as in the related art.

Next, the manufacturing process of the display panel shown in FIG. 1 will be described. FIG. 2 is an explanatory diagram for explaining a manufacturing process of the display panel 20 by using a cross-sectional view taken along the line AA ′ of FIG. FIG. 2 shows a process of manufacturing an organic EL element having a three-layer element structure when the substrate is made of glass.

In FIG. 2A, first, the glass substrate 1
A mask 102 is formed on screen 01 by screen printing using ink so as to form the segment 42b of FIG. 1 as a light emitting window. Then, taking into account the shape and size of the light emitting segment portion 41b of FIG.
1 and an ITO (Indium Tin Oxid
The transparent conductive film 103 such as e) is formed by a vacuum evaporation method (FIG. 2B).

Subsequently, a hole transport layer 104 is laminated on the transparent conductive film 103 (FIG. 2C), and an organic light emitting layer 105 is further laminated on the laminated hole transport layer 104 (FIG. 2C). 2 (d)). Here, in particular, the organic light emitting layer 105
The light emitting area of the other light emitting segment portions 31, 41a,
It is necessary to form the light emitting areas 41c, 41d, 41e, 41f, and 41g so as to have the same light emitting area. The organic light-emitting layer 105 can be formed by vacuum deposition when a low molecular weight dye is selected as the organic light-emitting layer 105, and cast when a polymer is selected as the organic light-emitting layer 105. (Spin coating or dip coating).

Then, the electron transport layer 106 is laminated on the organic light emitting layer 105 (FIG. 2E), and the laminated electron transport layer 1 is formed.
Further, a metal such as aluminum (Al) is laminated as a back electrode 107 by vacuum evaporation on the surface of the rear electrode 107 (FIG. 2).
(F)), a final element structure can be obtained.

In FIG. 2F, the glass substrate 101
In this case, the surface on the side where the above-mentioned lamination is not performed coincides with the surface of the display panel 20, and an appropriate voltage is applied between the transparent conductive film 103 and the back electrode 107 by the display element driving circuit 50. (Actual current drive in this embodiment), the organic light emitting layer 105 emits light.

At this time, light generated from the organic light emitting layer 105 reaches the user's eyes via the transparent conductive film 103 and the glass substrate 101, but the light is partially blocked by the mask 102. Therefore, the emission shape that is actually visually recognized is the shape formed by the mask 102, that is, the segment 42b.

Therefore, by applying the above-described manufacturing process to each segment on the display panel 20, the light-emitting segment portions 31, 41a, 41b, 41c, 41d, and 41, having the same light-emitting area on the display panel 20, 4
1e, 41f and 41g are formed, and the segments 42a, 42b, 4
2c, 42d, 42e, 42f and 42g and the display item 32 can be obtained.

In the manufacturing process shown in FIG. 2, a mask 10 is provided between the glass substrate 101 and the transparent conductive film 103.
2 was formed, but as shown in FIG.
An organic EL element is formed by a process excluding the printing process of the mask 102 in FIG.
As described above, the mask 102 may be printed on the surface of No. 01. Also in this example, similarly to the element structure shown in FIG. 2F, it is possible to obtain the same effect that the light emitting area is the same and the visible shape can be arbitrarily formed.

Therefore, the display panel 20 according to the embodiment
According to the method, since the mask 102 is formed on the glass substrate 101, even if a plurality of organic EL elements, which are self-luminous display elements, are formed so as to have the same light emitting area, a display shape that can be visually recognized finally. Are the segments 42a, 4
A desired display shape such as 2b, 42c, 42d, 42e, 42f, and 42g and the display item 32 can be obtained. Therefore, in the display device 10 according to the present embodiment in which the display panel 20 is mounted, when the constant current driving method is adopted, the display element driving circuit 50 of the display device 10 has a self-luminous display having the above-described light emitting area. A power supply for supplying a constant current required to drive (emit) the element can be provided by only one type of constant current source. In other words, even for segments and display items having different display shapes, there is no need for a constant current source having different characteristics for each segment as in the related art. As a result, in the display device and the display element driving circuit, the design process can be simplified, the circuit layout thereof can be efficiently realized, and the size and the manufacturing cost can be further reduced.

[0032]

As described above, according to the display panel of the present invention, a plurality of self-luminous display elements having the same light-emitting area are provided, and the light-emitting portion of each self-luminous display element has a desired display shape. Since the mask is formed as described above, it is possible to design a display shape visually recognized by each self-luminous display element as desired, as in a conventional display panel. In addition, since each light emitting display element has the same light emitting area where light is actually emitted, only one kind of constant current source may be prepared to drive each of these light emitting display elements at a constant current. In addition to simplifying the circuit configuration of the display element driving circuit for driving the display device, it is possible to further reduce the size and the manufacturing cost of the display device including the display panel and the display element driving circuit. Becomes

Second, according to the display panel of the present invention, an organic electroluminescent element can be used as a self-luminous display element, so that a display with low power consumption and high luminance emission can be realized.

Third, according to the display device of the present invention,
Equipped with a plurality of self-luminous display elements having the same light emitting area,
A display panel in which a mask is formed in a light emitting portion of each self-luminous display element so as to have a desired display shape, and a constant current source having the same characteristics are provided for each of the self-luminous display elements of the display panel. Since the display device includes a display element driving circuit that drives the elements at a constant current, the light emission luminance can be unified without requiring a constant current source having different characteristics for each self-luminous display element as in the related art. Further, the design process can be simplified, the circuit layout can be efficiently realized, and the display element drive circuit and the display device can be further reduced in size and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a display panel and a display device according to the present invention.

FIG. 2 is an explanatory diagram for explaining a manufacturing process of the display panel according to the present invention.

FIG. 3 is an explanatory diagram for explaining another example of the display panel according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Display apparatus 20 Display panel 30, 42a-42g Segment 31, 41a-41g Light emitting segment part 32 Display item 50 Display element drive circuit 60 Display control circuit 101 Glass substrate 102 Mask 103 Transparent conductive film 104 Hole transport layer 105 Organic light emitting layer 106 electron transport layer 107 back electrode

Continued on the front page (72) Inventor Susumu Fujita 1-8-1, Nakase, Mihama-ku, Chiba City, Chiba Prefecture Inside SIIR D Center Co., Ltd. (72) Masafumi Hoshino 1-8-1, Nakase, Mihama-ku, Chiba City, Chiba Prefecture (II) Inventor Atsuya Akase 1-8 Nakase, Mihama-ku, Chiba-shi, Chiba F-term (reference) 5C080 AA06 BB01 DD03 EE05 EE25 FF01 FF03 FF09 GG02 JJ01 JJ02 JJ06 5C094 AA44 BA23 BA29 CA15 ED15 GA10 HA10 5C096 AA27 BA04 BC19 CA26 CA32 CB07 CC06 CC07 CC23 CJ01 CJ03 FA12

Claims (4)

[Claims] 1. A display panel comprising a plurality of self-luminous display elements having the same light-emitting area, wherein a mask is formed on a light-emitting portion of each self-luminous display element so as to have a desired display shape. 2. The display panel according to claim 1, wherein the mask is formed directly on a front surface or a back surface of a substrate serving as a display surface of the self-luminous display element. 3. The display panel according to claim 1, wherein the self-luminous display element is an organic electroluminescence element. 4. The display panel according to claim 1, wherein a constant current source having the same characteristic is provided for each of the self-luminous display elements of the display panel. A display device, comprising: a display element driving circuit that performs constant current driving.