Patent Application
20050225863
The present invention relates generally to display technologies and more particularly to relates to reduction of ambient light reflections off of displays.
Many display technologies are well known and such technologies are continuing to advance rapidly. For example, modem active matrix display technology can be incorporated into display devices that are relatively lightweight, thin, and which provide high resolution and richly coloured pictures for televisions, computer monitors, and more generally, for a wide variety of display devices that can be incorporated into appliances like personal digital assistants and cellular telephones. While current active matrix displays can be expensive, it is expected that further research will result in advances that will can reduce the costs of such displays and lead to overall greater usage of active matrix display devices.
Active matrix displays are proving to be superior in many ways to older display technologies such as cathode-ray tubes (“CRT”). However, the problem of “glare” off of active matrix displays is also a concern, just as with older CRTs. “Glare” can be defined as ambient light that is reflected off of the device and back towards the viewer, thereby reducing the contrast and overall performance of the display device.
Thus, it is also known to incorporate technology to reduce reflectance into displays and thereby improve their performance. In the case of active matrix displays (or indeed, any other type of pixellated display) it is known to use a black matrix of filtering material. The black matrix is mounted in a complementary fashion to the matrix of pixels in the display, such that the black matrix is a generally continuous filter that surrounds each pixel. Black matrices are described in a number of patents and patent applications, such as “Anti-reflector black matrix for use in display devices and method for preparation of same”, EP 716 334 to Steigerwald (“Steigerwald #1”); “Transmissive Display Device Having Two Reflection Metallic Layers of Differing Reflectances”, U.S. Pat. No. 6,067,131 to Sato (“Sato”); “Anti-reflector black matrix display devices comprising three layers of zinc oxide, molybdenum and zinc oxide”, U.S. Pat. No. 5,570,212 to Steigerwald (“Steigerwald #2”); “Anti-reflector Black Matrix Having Successively A Chromium Oxide Layer, a Molybdenum Layer And a Second Chromium Oxide Layer”, U.S. Pat. No. 5,566,011 to Steigerwald (“Steigerwald #3”); and, “Low Reflectance Shadow Mask”, U.S. Pat. No. 5,808,714 to Rowlands et al. (“Rowlands”). One particular disadvantage to Steigerwald #1, Steigerwald #2 Steigerwald #3 and Rowlands is that they are confined to black matrix structures having specific sets of materials. A more general discussion of applying a black matrix as applied to a display having colour filters is found in U.S. Pat. No. 5,587,818 to Lee (“Lee”).
However, such prior art black matrix structures are not always useful or practical to incorporate into display devices. For example, prior art black matrix structures are frequently formed as a separate unit from the display, thereby eventually requiring the assembly of the black matrix structure to the display structure, such as by mounting the black matrix structure to the front of the display.
It is also known to use optical interference to reduce reflectance in various thin film display technologies, such as electroluminescent devices (“ELD”s). For example, reducing reflectance of ambient light can be achieved by using additional thin film layers sandwiched between one or more layers of the ELD, which are configured to achieve destructive optical interference of the ambient light incident on the display, thereby substantially reducing reflected ambient light. Optical interference technology is discussed in detail in U.S. Pat. No. 5,049,780 to Dobrowolski et al., (“Dobrowolski”) and U.S. Pat. No. 6,411,019 to Hofstra et al. (“Hofstra”). In addition, certain inventors of the present invention have also contemplated the use of the optical interference technology taught in Hofstra and Dobrowolski in conjunction with the bus lines that form the matrix surrounding each pixel in an active matrix display. See Canadian Patent Application 2,364,201 filed Dec. 12, 2001.
More recently, U.S. Pat. No. 6,429,451 to Hung (“Hung”) has proposed another type of ambient light reducing layer also for incorporation into a pixel of the ELD.
However, notwithstanding the improvements provided by the prior art, it is now been discovered that the prior art does not provide ambient light reduction across all areas of the display, as is now offered by polarizers that are also used with prior art displays. Because polarizers can offer substantially uniform ambient light reduction across the entire viewable surface of the display, polarizers can be preferred over other prior art solutions that embed or otherwise incorporate the ambient light reduction means within the actual display structure. In order to obviate the need for polarizers and achieve the attendant advantages eliminating the post production costs associated with polarizers, it is desired to provide a means to substantially uniformly reduce ambient light reflection across the entire viewable surface of the display by means of embedding the contrast enhancement apparatus within the display.
It is therefore an object of the present invention to provide a display that obviates or mitigates at least one of the disadvantages of the prior art.
An aspect of the invention provides a display device comprising a plurality of emitting pixels and at least one switching electronic corresponding to each pixel for selectively activating or deactivating the pixel. The device also comprises at least one additional component for interconnecting the pixels and the switching electronics, and at least two ambient light reducing members each integrally embedded into at least one of: a) the pixels, b) the switching electronics and c) the at least one additional component. The ambient light reducing members are disposed in a plane that is visible to a viewer and are selected from materials and thicknesses such that the reduced ambient light reflections in the plane are substantially uniform.
The emitting pixels can be bottom emitting or top emitting. The at least one additional component can be a set of bus lines for delivering electrical current to the pixels and the switching electronics.
The emitting pixels can be comprised of an OLED stack and wherein at least one of the ambient light reducing members is integrated with the OLED stack.
The at least one of the ambient light reducing members can be integrated with the switching electronics. The at least one ambient light reducing members can thus form part of the electronic circuitry of the switching electronics. The switching electronics can include at least one transistor and the ambient light reducing member can be a storage capacitor for the at least one transistor.
The ambient light reducing member can be an optical interference member. Where an optical interference member is used it can include a semi-absorbing layer for reflecting a portion of incident ambient light, a substantially transparent layer for phase shifting another portion of ambient light and a reflective layer for reflecting the phase shifted ambient light such that the two reflected portions of light are out-of-phase and thereby destructively interfere.
Another aspect of the invention provides a display device comprising a plurality of emitting pixels. The device also comprises at least one switching electronic corresponding to each pixel for selectively activating or deactivating the pixel. The device also comprises at least one additional component for interconnecting the pixels and the switching electronics. An ambient light reducing member is integrally embedded into the switching electronic to form part of an electronic circuitry of the switching electronics. The ambient light reducing member is disposed in a plane that is visible to a viewer and selected from materials and thicknesses to reduce ambient light reflections. The electronic switching components include at least one transistor and the ambient light reducing member is a storage capacitor for the at least one transistor.
Another aspect of the invention provides a computer implemented method of matching the reflectance between different ambient light reducing members in a display comprising the steps of:
The first set of components in the method can be light emitting pixels and the at least one additional set of components can be switching electronics corresponding to the light emitting pixels.
The present invention will now be described, by way of example only, with reference to certain embodiments shown in the attached Figures in which:
Referring now to
It should be noted that terms such as “above” and “below” are used herein for convenience and are to be read in conjunction with the drawings, and as such are not to be construed in a limiting manner.
As previously mentioned, optical interference members 26a, 40a and 48a can be based on known formulations of optical interference members, as taught in, for example Hofstra and/or according to other desired means of formulating an optical interference member. However, due to the virtually infinite number of formulations of optical interference members the potential can arise for variations between those different formulations such that while all formulations may appear “dark” and have acceptable performance on their own, when different formulations are placed side by side, contrasts between those formulations may be detectable in an undesired way, such that the overall “darkness” of the display is non-uniform.
Accordingly, referring now to
Next, at step 160, a complete model for a display is assembled using the results of steps 110-150. Such a model can be assembled by physically building a sample display and/or through computer modeling. At step 170, the uniformity of ambient light reflection reduction from optical interference members 26a, 40a and 48a is measured. Where a physical model has been built, then such measurements are effected using measurement equipment using various ambient light conditions, and in the case of a computer model then simulated measurements are taken based on simulated ambient light conditions. Sample ambient light conditions can include direct sunlight, room lighting, and so forth, depending on the expected operating environment for the display.
At step 180, a determination is made as to whether the measured uniformity is acceptable. If yes, the method advances to step 190 and full production of the display can be commenced. However, typically the uniformity will not be acceptable on the initial design and the method advances to step 200, where the greatest level of disparity in uniformity is determined. The method advances to steps 210, 220 or 230 depending on whether the greatest disparity is caused by the optical interference member 26a, 40a or 48a, respectively. At those steps 210, 220 or 230, modifications to the corresponding optical interference member 26a, 40a or 48a are effected (and/or effected to the associated component), at which point the method returns to step 160 where a new matrix display model is generated. The method then moves again through steps 170 and 180 and through the remaining steps as needed until an acceptable uniformity level is achieved.
Method 100 is preferably implemented in computer software that includes known material sets and thicknesses ranges for developing optical interference members, and associated design specification for associated pixels and switching electronics. In this manner, a substantially uniformly dark matrix display can be modeled and developed in a time efficient manner.
It is presently preferred that the difference between the reflectivities of each optical interference member (or other ambient light reducing member) be less than about ten percent. More preferably, the difference between the reflectivities is less than about three percent. More preferably, the difference between the reflectivities is less than about one percent. It is presently preferred that the difference between the reflectivities is less than about 0.5 percent.
An optical interference member (such as optical interference members 26a, 40a or 48a) can be based on a three layer structure of: i) a semi-absorbing layer that is partially reflective, partially absorbing and partially transmissive of ambient light, ii) a substantially transparent layer that phase shifts the incoming ambient light, and iii) followed by a reflective rear layer (which may be electrically part of the pixel or other component with which the optical interference member is associated, or not, as desired). Where the optical interference member is based on this structure, then the software will be optimized to choose materials and thicknesses based on the appropriate functionalities of those layers. Thus, the software package will look for materials and thicknesses of the semi-absorbing layer such that a portion of ambient light incident on the member is partially reflected off of the member, while a remaining portion passes into the partially transmissive layer therebehind. The software will then choose thicknesses and materials for the partially transmissive layer such that a phase shift of about one-hundred-and eighty-degrees occurs in the ambient light passing through partially transmissive layer. The final reflective rear layer is chosen to provide sufficient reflection, and/or have appropriate electrical properties. The overall optical interference member may be work function matched for an OLED pixel, and/or may be otherwise electrically matched with its surrounding materials. The software will thus include a database of possible materials for a semi-absorbing layer that includes Cr, Al, Mg:Ag, inconel or Ni, Cu, Au, Mo, Ni, Pt, Rh, Ag, W, Co, Fe, Ge, Hf, Nb, Pd, Re, V, Si, Se, Ta, Y, Zr. The software will thus include a database of possible materials for a partially reflecting material that includes Aluminum Silicon Monoxide, Chromium Silicon Monoxide, Al2O3, SiO2, ZrO2, HfO2, Sc2O3, TiO2, La2O3, MgO, Ta2 O5, ThO2, Y2O3, CeO2, AlF3, CeF3, Na3 AlF6, LaF3, MgF2, ThF4, ZnS, Sb2O3, Bi2O3, PbF2, NdF3, Nd2O3, Pr6O11, SiO, NaF, ZnO, LiF, GdO3.
The software can also include databases of other types of optical interference members based on other types of structures (i.e. the type of structure in PCT/CA02/00844, or PCT/CA03/00498, incorporated herein by reference), so that a plurality of different types of optical interference members can be selected in order to achieve the desired uniformity.
The embodiments in
As another example,
In general, it should be understood that the structures in
Of particular note, optical interference member 40d acts as a storage capacitor to hold the charge that is used to activate the transistor that ultimately provides current to pixel 24d in order to cause pixel 24d to emit light. Concurrently, optical interference member 40d acts to mask the switching electronics used to activate pixel 24d.
Switching electronics also includes a drive TFT 212d, that itself includes a semi-conductor 204d, which can be made from CdSe, or a-Si or poly-Si. Drive TFT 212d also includes a source 202d, a drain 206d, a channel 208d, and a substrate 200d.
It is to be noted that optical interference members 40d and 48d are of the above-described three-layer format, but other optical interference member configurations are contemplated. The composition of the optical interference member may depend on the particular application. The initial, semi-absorbing layer 48d1 can be Cr, Al, Ag, Mg, Cs, Pt, Au, Li, and their alloys. They can be deposited using thermal evaporation, e-beam, or sputtering techniques. The subsequent substantially transparent phase shifting layer 48d2 (which is also conducting in this embodiment) can be made of AlSiO, CrSiO, chrome oxide, zinc oxide, indium tin oxide, indium oxide, and other transparent conducting oxides.
(In other embodiments, an insulating phase shifting layer can be made of SiO, SiO2, Si3N4, SiON, ZnO, and other dielectric materials.)
The semiconductor component of thin-film transistors may utilize amorphous silicon, poly-silicon, continuous-grain silicon, cadmium selenide, and/or other suitable semiconducting materials. An exemplary technological method to fabricate the display in
As another example,
It should now be apparent that other configurations of top emitting display configurations, other than those in
While only specific combinations of the various features and components of the present invention have been discussed herein, it will be apparent to those of skill in the art that desired subsets of the disclosed features and components and/or alternative combinations of these features and components can be utilized, as desired. For example, other display technologies can be used instead of OLED light-emitting pixels—such as inorganic or TFEL light emitting pixels. As another example, each pixel could be a shutter means that passes light emitted from a back light when the pixel is activated.
Furthermore, for each OLED pixel 24, the optical interference member 26 embedded therein can be made of materials that directly work function matches with the emitting organic material of the optical interference member 26, or, a work function matching layer of LiO, LiF or the like can be inserted between the optical interference member 26 and the emitting layer of the pixel 24 in order to provide work function matching.
It is to be further understood that the examples of
Furthermore, while the embodiments herein discuss ambient light reducing layers based on optical interference, it is contemplated that other types of ambient light reducing layers that can be integrally incorporated into the various layers of a display can also be used in the method of
The present application claims priority from U.S. Patent Application No. 60/387,414 filed Jun. 11, 2002, the contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA03/00904 | 6/11/2003 | WO | 12/10/2004 |
| Number | Date | Country | |
|---|---|---|---|
| 60387414 | Jun 2002 | US |
