WO2002006891A1

WO2002006891A1 - Display

Info

Publication number: WO2002006891A1
Application number: PCT/DE2001/002521
Authority: WO
Inventors: Stephan Windisch; Siegfried DOBRAWA
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-07-17
Filing date: 2001-07-06
Publication date: 2002-01-24

Abstract

The invention relates to a display with a light source for illuminating the display background, said light source comprising a two-dimensional organic light-emitting diode.

Description

DISPLAY

The invention relates to a display with a light source for illuminating the display background.

In addition, the invention relates to a device with a corresponding display.

Displays, in particular liquid crystal displays (LCDs), are usually illuminated by a light source in the form of an LED, incandescent lamp or CCFT (Cold Cathode Fluorescence Tube), the light of which is coupled into a light guide. This light guide is designed in such a way that the display is illuminated as homogeneously as possible. This is particularly important when using displays in small portable devices such. B. mobile devices, pagers or PDAs (Personal Digital Assistants) to ensure that the entire facility takes up as little space as possible. When reducing the thickness of the light guide, certain limits cannot be undershot without the efficiency of the light guide being impaired and the number of light sources required or the power of the light sources being increased. In particular, optimization of the light guide, with which the light emitted punctually from the individual light sources is distributed in the light guide so that the illumination is as homogeneous as possible, can only be achieved with difficulty under a certain light guide thickness. The use of individual point-shaped light sources therefore often leads to bright spots in the display backlight, the so-called “hot spots”.

Another alternative to illuminating displays are the so-called Elektrolu ineszens films. Such a film is mounted flat underneath the respective display and emits light over the entire surface with a very homo ^¬ genes luminance distribution. A disadvantage of this technology, however, is that the operation of an electroluminescent film usually requires AC voltages from 80 volts up to 200 volts, which have to be generated in a special control circuit - in the case of portable devices from the battery voltage. Activation by an alternating voltage stimulates the electroluminescent film to mechanical vibration. This can be perceived as a hum, which is particularly annoying when used in mobile devices.

It is an object of the present invention to provide an alternative to this prior art.

This object is achieved in that the light source comprises a flat organic light emitting diode.

Organic light-emitting diodes (OLEDs) usually consist of various organic compounds that are applied in layers to a carrier material. As a voltage e ^~ -hole pairs are generated in the known inorganic light emitting diodes (LED) by the application, which recombine at an interface, whereby light is emitted. This emitted light emerges from the OLED if the layers are thin enough. A distinction is made here between the actual OLEDs, which consist of short-chain organic compounds, and the so-called polymer light-emitting diodes (PLEDs), which are long-chain organic polymer compounds. For the purposes of this document, the term “organic light-emitting diodes *” means all forms of organic light-emitting diodes, in particular also the PLEDs.

The organic light-emitting diodes have only a small thickness of a few tenths of a millimeter and can in principle be arranged directly under the display over a large area, so that the light from the light-emitting diode is emitted directly through the display > ω tt h- ¹ π σ in o Üi O Oi tr Φ ^ p tr Hi N <cn tr tr ¹ <ω 3 SQ ≤ HPP CΛ H 3 <! Φ tr ^ N Ω PS

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Light guide before a uniform luminance distribution, which facilitates the uniform irradiation. The use of the organic light-emitting diode thus reliably avoids the occurrence of “hot spots” in the display lighting.

In each of the cases, the organic light-emitting diode can either be applied to a separate carrier, for example a glass plate or the like, or else to a circuit board, for example the main circuit board of the device or a separate display circuit board which carries the control electronics for the display. Alternatively, the organic light-emitting diode can also be applied directly to the back of the display or to the light entry surface. That is, in this case, the display or the light guide itself form the carrier for the light-emitting diode.

In a further variant, the organic light-emitting diode is integrated as a layer in the display or the light guide.

Due to the flat design and the low circuit complexity, combined with only low voltages for operating the OLEDs, such a display is particularly suitable for use in small mobile devices, for example mobile telephones, pagers, PDAs, pocket calculators, etc. In particular in the case of such small, portable devices The lighting of devices should be as homogeneous and bright as possible, whereby the power consumption must be kept low while reducing the volume or the thickness of the lighting module.

The invention is explained in more detail below with reference to the accompanying drawings using two exemplary embodiments. The features shown there and the features already described above can be essential to the invention not only in the combinations mentioned, but also individually or in other combinations. They represent: co U> I \ 3 to F-> F- ¹ no üi o cn O

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Alternatively, the organic light emitting diode 6 may selbstver ^¬ understandable on a separate support, for example on a glass plate to be applied, then the organic light emitting diode is glued together with the carrier, for example, under the glass substrate 3 of the display unit 1 to the rear side. 4

In the version shown in FIG. 2, a conventional LCD 1 is also used, the LCD controller 14 being applied directly to the lower glass carrier 3 as an ^{exemplary embodiment} and thus representing the above-mentioned “Chip On Glass ^Xλ structure (COG). The connection of the display 1 to the main circuit board 11 of the mobile radio device again takes place via a conductor track film 12.

In contrast to the exemplary embodiment according to FIG. 1, however, the organic light-emitting diode 7 is not applied directly to the rear side 4 of the glass carrier 3. Instead, there is a bridge-like light guide 8 with two foot surfaces under the glass carrier 3 directly adjacent to the rear side 4. These two foot surfaces form the light entry surfaces 9 of the light guide 8. A flat, strip-shaped organic light-emitting diode adjoins the foot surfaces, which illuminate the foot surfaces uniformly. In the case shown, these are individual organic light-emitting diode segments 7, which are each assembled to form a strip-shaped light-emitting diode, so that the foot surfaces are covered over the entire area. In principle, however, it can of course also be two continuous, elongated individual light-emitting diodes.

The individual organic light-emitting diodes 7 are here applied directly to the main circuit board 11, which thus serves as a carrier for the organic light-emitting diodes 7. During installation, the light guide 8 is simply placed with the foot surfaces in a suitable position on the strips consisting of the organic light-emitting diodes 7. The bridge-like light guide 8 is designed such that the light is guided from the foot surfaces to the bridge surface adjoining the rear side 4 of the display 1, which serves as the light exit surface 10 in this light guide 8. The dimensions of the light guide 8 are selected such that the light exit surface 10 irradiates the entire active surface of the display

The appropriate redirection of the incident light within the light guide 8 from the light exit surface 10 can be done by suitable positioning of integrated prisms in the light guide 8. These prisms are e.g. B. in the underside of the light guide 8 opposite the light exit surface 10 and have different sizes distributed over the surface, so that the less light is deflected upwards out of the light exit surface 10, the smaller the distance from the foot surfaces, so that overall a uniform luminance is achieved.

In principle, of course, a light guide with a different shape can also be used instead of the bridge-like light guide. For example, it can be an L-shaped light guide with only one light entry surface, or a flat, block-shaped light guide is used in which the light is radiated into the side edge surfaces.

Due to the use of the flat organic light-emitting diodes, which are applied in strips, from which the light is evenly coupled into the light guide 8, no “hot spots” occur at the light exit surface. This embodiment has the advantage over the exemplary embodiment according to FIG. 1 that it is also possible to use OLEDs which are not available in very large areas or are too expensive for the production of simple, inexpensive devices. In addition, the optimization of the cn

Claims

claims

1. Display (1) with a light source (6, 7) for illuminating the display background, characterized in that the light source (6, 7) comprises a flat organic light emitting diode (6, 7).

2. Display according to claim 1, characterized in that the organic light-emitting diode (6) is arranged over a large area under the display (1) and the light from the light-emitting diode (6) is emitted directly through the display (1).

3. Display according to claim 1, characterized by a light guide (8) with a light entry surface (9) which is illuminated by the organic light-emitting diode (7), the light being guided through the light guide (8) to the display (1) and from there a light exit surface (10) is emitted from uniformly spatially distributed.

4. Display according to claim 3, characterized in that the light entry surface (9) of the light guide (8) is smaller than the light exit surface (10).

5. Display according to claim 3 or 4, characterized in that the light guide (8) has a plurality of light entry surfaces

(9).

6. Display according to claim 5, characterized in that the light guide (8) has a bridge-like shape with two foot surfaces, the foot surfaces forming the light entry surfaces (9) and adjoining a flat organic light-emitting diode (7), and the bridge-like light guide ( 8) is designed such that the light is guided from the foot surfaces to a bridge surface adjacent to the rear (4) of the display (1), which forms the light exit surface (10) and from which the light passes through the display (1) is emitted.

7. Display according to one of claims 1 to 6, characterized in that the organic light-emitting diode (7) is applied to a separate carrier (11).

8. Display according to one of claims 1 to 6, characterized in that the organic light-emitting diode (6) on the back (4) of the display (1) or on the light entry surface is applied.

9. Display according to one of claims 1 to 6, characterized in that the organic light-emitting diode is integrated as a layer in the display or the light guide.

10. Device with a display (1) according to one of claims 1 to 9.

11. The device according to claim 10, characterized in that the device is a mobile terminal.