Patent Application
20080231959
The present invention relates to an arrangement for display modules for use in electronic devices, such as portable radio communication terminals. In particular, the present invention is concerned with display modules having improved brightness and reflectance properties, and with increased suitability for use in small size electronic devices.
The first commercially attractive cellular telephones or terminals were introduced in the market at the end of the 1980's. Since then, a lot of effort has been made in making smaller terminals, with much help from the miniaturisation of electronic components and the development of more efficient batteries. Today, numerous manufacturers offer pocket-sized terminals with a wide variety of capabilities and services, such as packet-oriented transmission and multiple radio band coverage.
In mobile phones of today, a front window is typically used to protect the display unit, e.g. the liquid display module, from physical abuse, such as scratches, pressure and shocks, and from environmental strain. The front window is typically manufactured of a plastic material and between the display unit and the front window there is provided an air gap to make sure that the plastic window can bend or flex without touching the display unit. Usually a dust gasket is arranged to prevent dust from appearing between the display unit and the front window.
One problem with the prior art display modules is the luminance losses due to reflection of light in the interface between material layers in the display modules having different refraction indexes.
An aspect of the aforementioned problem is that roughly 12% of the backlight luminance, i.e. the light from the display unit to the viewer, will be lost before reaching the eye due to reflection in the interface between the display unit and the air gap, and in the interface between the air gap and the front window. If this 12% loss could be reduced it would be possible to lower the power consumption of the electronic device.
Another aspect of the aforementioned problem is that the outdoor performance of the display module is not optimal due to the low reflectance of light entering the display unit. In correspondence with the description regarding backlight, about 12% of the incident light will be lost and thus only 88% of the incident light will reach the display unit in the best case, i.e. when the angle of incidence is perpendicular to the display unit. A part of these 88% will then be reflected back from the display unit, e.g. a liquid crystal module (LCM). Commonly used liquid crystal modules normally reflect 3-5% of the incoming light. A rough calculation of the amount of reflected sunlight that carries the picture information from the display would be: 88%*5%*88%≈3.9%. In other words, approximately 4% of the incoming sunlight will be reflected and will contain the picture information. This value should be compared with the 12% of the incoming light that is reflected before reaching the display unit and thus does not contain any picture information. When comparing 4% containing picture information and 12% without picture information it is understood that it can be hard to view the picture information, e.g. hard to read the information on the display. Consequently, a user of e.g. a mobile phone having a prior art display module, often has to shield off the display in order to be able to read the information, especially if the sunlight is strong.
The ratio between the reflected light containing picture information and the reflected light without picture information can be improved by using anti-reflex (AR) treated surfaces. However, anti-reflex treatment suffers from some drawbacks such as an expensive process that is sensitive for bad handling. If for example, the surface is not perfectly clean, the anti-reflex treatment will encapsulate all dust, finger prints, etc., which will be visible to a viewer. Further, in the prior art display modules, three surfaces need to be anti-reflex treated in order to provide a good result, i.e. the both surfaces, top and bottom, of the front window and the top surface of the liquid crystal display (LCD) polarizer have to be treated.
Another drawback with the prior art display modules is the risk of getting dust in the air gap between the front window and the display unit which may substantially deteriorate the image quality experienced by a user, causing customers to complain.
An overall object of the present invention is to provide a display module having improved brightness and reflectance properties, and with increased suitability for use in small size electronic devices. More particular, an object of the invention is to overcome the above-mentioned problems and the aspects of the problems.
The objects of the invention are fulfilled by a display module for use in an electronic device, comprising a front window and a display unit. An intermediate layer of a transparent material is sandwiched between said front window and said display unit, said intermediate layer being formed by a material selected in dependence of the material of the front window in order to minimize reflection in the interface between said front window and said intermediate layer.
In one embodiment, said intermediate layer has a refraction index nil that matches the refraction index nfw of said front window.
In one embodiment, said display unit has a top portion having a refraction index matching the refraction index of the intermediate layer.
In one embodiment, said intermediate layer being constituted of sub-layers, wherein a top sub-layer has a refraction index that matches said front window, a bottom sub-layer has a refraction index that matches said display unit, and a possible intermediate sub-layer has a refraction index that matches both a sub-layer located above the intermediate sub-layer and a sub-layer located below the intermediate sub-layer.
In one embodiment, said intermediate layer is a transparent film.
In one embodiment, said intermediate layer is an immersion oil.
In one embodiment, said intermediate layer is a transparent glue.
In one embodiment, said display unit has a refraction index nd substantially equal to the refraction index nfw of said front window, said refraction indexes nd, nfw being approximately 1.5.
In one embodiment, said display unit and said intermediate layer are arranged air-tight.
In one embodiment, the top surface of said front window has an anti-reflex coating.
In one embodiment, said front window is attachable to a housing portion of said electronic device.
In one embodiment, said display module being attachable and detachable from an electronic device.
In one embodiment, said electronic device is a mobile radio terminal.
In one embodiment, said electronic device is a mobile phone.
The present invention also relates to an electronic device comprising the inventive display module.
The present invention has, among others, the following advantages:
In a typical embodiment, the luminance loss in reflections from the back light will only be 4% in the best case, i.e. when the angle of incidence is perpendicular and the material of the intermediate layer is selected in such a way that the refraction index of the intermediate layer matches the refraction indexes of the material of the front window and the display unit. Consequently, 96% of the backlight luminance, containing the picture information, will reach the viewer. In correspondence, only 4% of the incoming light will be reflected without reaching the display unit and thus does not contain any picture information. Thus 96% of the incoming light will reach the display unit, and 96%*5%*96%≈4.6% of the incoming light will be reflected from the display unit and contain the picture information. Consequently, the ratio between the reflected light containing picture information and the reflected light without picture information is improved.
When the transmitted light from back lighting is reduced, the power consumption of the display module can be reduced, and when the reflection of incoming light is reduced, the contrast in the image can be improved. Further, there will be no need for shielding or shadowing the display in order to be able to read the information on it.
a) The display module can be manufactured thinner since the air gap is removed, and consequently the electronic devices comprising the display module can also be made thinner.
b) The dust problem with the prior art display units can be removed by mounting the front window together with the display unit in e.g. a clean room to ensure good optical connection between the display unit and the front window.
c) If anti-reflex treatment is to be used in order to further improve the ratio between the reflected light containing picture information and the reflected light without picture information, only one surface, i.e. the top surface of the front window, has to be treated.
The features and advantages of the present invention will be more apparent from the following description of the preferred embodiments with reference to the accompanying drawings, on which
a illustrates schematically a cross-section of an embodiment of the inventive display module;
The present description relates to the field of display modules for use in electronic devices, and in particular radio communication terminals. The term radio terminal or communication terminal, also denoted terminal in short in this disclosure, includes all mobile equipment devised for radio communication with a radio station, which radio station also may be mobile terminal or e.g. a stationary base station. Consequently, the term radio terminal includes mobile telephones, pagers, communicators, electronic organisers, smart phones, PDA:s (Personal Digital Assistants), laptop computers, and DECT terminals (Digital Enhanced Cordless Telephony). Hence, although the structure and characteristics of the invention are mainly described herein, by way of example, in the implementation in a mobile phone, this is not to be interpreted as excluding the embodiment and implementation of the invention in other types of electronic devices. In particular, the invention is suitable for use, though not restricted thereto, in any electronic devices where the brightness and reflectance properties of the display module, and small dimension are important. Further, the present invention is equally applicable to stationary devices and for radio transmission to and from stationary devices. Such stationary devices include e.g. desktop computers. Furthermore, it should be emphasised that the term comprising or comprises, when used in this description and in the appended claims is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. The term match, matches or matching when used in this description text is taken to specify that the refraction indexes of two layers of material correspond to each other in such a way that reflection in the interface between the two layers is eliminated or at least minimised. In embodiments of the invention, the refraction indexes of two layers of material match each other if the difference in refraction index between the two layers is less than 0.3, preferably less than 0.1, and more preferably less than 0.05. It should also be emphasised that the term substantially equal, when used in expressions such as “the refraction index of a first layer of material is substantially equal to the refraction index of a second layer of material” is used to specify that the difference in refraction indexes between the two layers is less than 0.3, preferably less than 0.1, and more preferably less than 0.05.
Prior art and exemplary embodiments of the invention will now be described with references made to the accompanying drawing. In the figures, the same reference numerals are used for the same or corresponding components or parts.
The display module 10 is provided with an air gap G between the front window 12 and the top polarizer 16 to make sure that the plastic window 12 can flex without touching the polarizer 16.
A dust gasket 20 arranged to prevent dust from entering in the gap between the display unit and the front window 12, also acts as a spacer between the front window 12 and the polarizer 16.
When light passes through different layers of medium there will be a luminance loss due to reflection in each junction between a first medium and a second medium when the refraction index differs between the two media. This is for example the case for light in the interface between air and plastic. Depending on the angle of incidence, the reflection of the light will differ. In a perpendicular angle of incidence, the loss will be minimized. The reflection in the interface between air and glass or plastic is typically about 4%, when the angle of incidence is perpendicular.
The present invention overcomes the above-mentioned problems with the prior art by minimizing the reflection of light between different material layers of the display module. This is achieved by minimizing the difference in refraction index between adjacent layers of material, whereby the reflected light R will be minimized according to the formula: R=[(n2−n1)/(n2+n1)]2, where n1 is the refraction index of the first layer of material and n2 is he refraction index of the second layer of material.
In one embodiment of the invention, the front window is manufactured of polymethyl methacrylate, such as PMMA SH 200, having a refraction index of approximately 1.5. PMMA SH 200 has typically a refraction index in the range of 1.49-1.52. Other suitable materials are Plexiglass® or Plexiglass-based materials having a refraction index matching the refraction index of the display unit.
The intermediate layer 24 is preferably selected from a material such that it has a refraction index nil that matches the refraction index nfw of said front window 12. Thus, the intermediate layer 24 is preferably configured of a transparent material having substantially the same refraction index as the front window 12. The intermediate layer 24 is for example constituted of a transparent film, an immersion oil, a transparent glue or another suitable material having a refraction index matching the refraction index of the display unit. As is well known, such an oil or glue can be tailor-made to obtain a certain refraction index.
According to one embodiment of the invention, the front window, the intermediate layer and the display unit have a refraction index of approximately 1.5.
The display unit 13 and the intermediate layer 24 can be arranged air-tight.
In one embodiment of the invention, the top surface of the front window 12 has anti-reflex coating in order to further improve the ratio between the reflected light containing picture information and the reflected light without picture information. The display unit 13 can further be configured for attachment at a carrier frame 18 such as a Printed Wiring Board PWB.
The front window 12 is preferably attachable to a housing portion 22 of said electronic device. The electronic device can for example be realised as a mobile radio terminal or a mobile phone.
In a special case, the glass plates 14, 14′ are configured to have a refraction index nd substantially equal to the refraction index nfw of the front window 12. The refraction indexes nd, nfw being approximately 1.5.
The display unit 13 can further comprise a bottom polarizer 16′, which is arranged between the rear plate 14′ and a carrier frame 18.
The present invention has been described above with the reference to a display unit realised in the form of a liquid crystal display or a liquid crystal module. However, the display unit can also be realized as any kind of a Flat Panel Display FPD, e.g. Thin Film Transistor TFT, Twisted Nematic TN display, Super Twisted Nematic STN display, Color STN CSTN display, Organic Light Emitting Diode OLED, or plasma display. In an alternative embodiment the display unit is realized as a Cathode Ray Tube CRT.
At least one of the electrodes 102, 104 is transparent to the emitted light, in general the anode 102. In one typical embodiment, anode 102 is a substrate of transparent indium-tin-oxide (ITO), whereas the cathode 104 may be a layer of aluminium. In various types of PLEDs described in the prior art, additional layers of material may be included between the electrodes 102, 104, e.g. for enhancing the electron or the hole injection efficiency. It has for instance been proposed to insert a thin layer of LiF, Al2O3 or Ca between polymer layer 103 and cathode 104 to enhance the electron injection efficiency. A transparent protective layer 101 is preferably applied over the anode 102. In reality, the protective layer 101 is often a glass substrate, whereas the ITO substrate is used as a base on which the other layers are applied by spinning and evaporation deposition, in a manner well known to the skilled person.
The present invention has been exemplified using a LCD, a PLED, or an OLED. However, it should be understood that the invention is applicable in other kinds of display units suitable for use in electronic devices.
The principles of the present invention have been described in the foregoing by examples of embodiments or modes of operations. However, the invention should not be construed as being limited to the particular embodiments discussed above, which should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present inventions, as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP 05104918.7 | Jun 2005 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP06/62970 | 6/7/2006 | WO | 00 | 5/9/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60692213 | Jun 2005 | US |
