Abstract:
An OLED display and touch screen system includes a substrate; an OLED display including an array of individually addressable OLEDs formed on the substrate; and a touch screen including an OLED light emitter formed on the substrate the OLED light emitter defining an optical cavity for reducing the angle of emission of light from the OLED light emitter and a light sensor formed on the substrate across the display from the OLED light emitter, and optics located around the display above the OLED light emitter and the light sensor for directing light emitted from the OLED light emitter across the display to the light sensor.

Description:
This is a continuation-in-part of application U.S. Ser. No. 10/346,987 filed Jan. 17, 2003 now U.S. Pat. No. 7,042,444. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to organic light emitting diode (OLED) displays and, more particularly, to an OLED display with a touch screen. 
     BACKGROUND OF THE INVENTION 
     Modem electronic devices provide an increasing amount of functionality with a decreasing size. By continually integrating more and more capabilities within electronic devices, costs are reduced and reliability increased. Touch screens are frequently used in combination with conventional soft displays such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma displays and electroluminescent displays. The touch screens are manufactured as separate devices and mechanically mated to the viewing surfaces of the displays. 
     US 2002/0175900 A1 by Armstrong, published Nov. 28, 2002, describes a touch system for use with an information display system including a frame defining an opening corresponding in size and shape to an information display area of a display. On each side is positioned an array of light emitting devices with a light-transmissive prism positioned along each array of light emitting devices such that light emitted from the light emitting devices is directed across the touch input area. The system also includes light detection devices positioned at each corner of the frame. In a preferred embodiment, the light emitting devices are organic light emitting diodes. 
     When such a touch screen is used with a flat panel display, the touch screen is simply placed over the flat panel display and the two are held together by a mechanical mounting means such as an enclosure. These prior art arrangements combining touch screens and OLED displays suffer from a variety of drawbacks. The use of frames increases the parts count, weight, and cost of the device. The separation between the touch screen and display increases thickness. Redundant components found in the display and touch screen further increase cost and decrease performance as compared to more integrated solutions. Moreover, the need for separate cabling for the touch screen increases manufacturing costs 
     Thus, there remains a need for an improved touch screen, flat panel display system that minimizes device weight, removes redundant materials, decreases cost, eliminates special mechanical mounting designs, increases reliability, and minimizes the degradation in image quality. 
     SUMMARY OF THE INVENTION 
     The need is met according to the present invention by providing an OLED display and touch screen system that includes a substrate; an OLED display including an array of individually addressable OLEDs formed on the substrate; and a touch screen including an OLED light emitter formed on the substrate the OLED light emitter defining an optical cavity for reducing the angle of emission of light from the OLED light emitter and a light sensor formed on the substrate across the display from the OLED light emitter, and optics located around the display above the OLED light emitter and the light sensor for directing light emitted from the OLED light emitter across the display to the light sensor. 
     ADVANTAGES 
     The display according to the present invention is advantageous in that it provides a thin, light, easily manufacturable display having reduced weight, size, and cost and a greater reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view showing the basic structure of an integrated OLED display and touch screen according to the present invention; 
         FIG. 2  is a schematic top view of the integrated OLED display and touch screen; 
         FIGS. 3   a, b , and  c  are schematic top views of an integrated OLED display and touch screen showing alternate locations of the emitters and sensors; 
         FIG. 4  is a schematic side view of an integrated OLED display and touch screen wherein the optics located around the frame are mirrored surfaces of the frame according to one embodiment of the invention; 
         FIG. 5  is a schematic side view of an integrated OLED display and touch screen wherein the optics located around the frame are light pipes; and 
         FIG. 6  is a schematic side view of an integrated OLED display and touch screen wherein the OLED display is a bottom emitting display. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a top-emitting OLED display device with an integrated optical touch screen according to one embodiment of the present invention includes a rectangular substrate  42  with an encapsulating cover  44 . Located on the substrate is an OLED display  60  including electrodes and multiple layers of materials such as hole-injection layers and electron transport layers as is well known in the art (not shown). Light  49  emitted from the display passes through the encapsulating cover  44  or is reflected from the substrate  42  and is emitted through the encapsulating cover  44 . At one side of the rectangular substrate  42  is an array of infrared OLED light emitters  62 . Infrared OLED light emitters are known and can be made, for example, by doping OLED devices with rare-earth ions such as neodymium or erbium. At the opposite side of the rectangular substrate  42  is an array of infrared light sensors  64 . The sensors may include filters to improve their frequency response. 
     As shown in  FIG. 2 , a second pair of emitter and sensor arrays are arranged on the other two sides of the rectangular substrate  42 . According to the present invention, both the light emitters  62  and sensors  64  are integrated on the same substrate as the OLED display  60 . Optics, such as mirrors  66  are arranged over the encapsulating cover  44  directly above the emitter and sensor arrays for directing light emitted from the light emitters  62  across the display to the light sensors  64 . The mirrors  66  can be constructed using glass or plastic prisms with a reflective side arranged at approximately 45 degrees to the cover  44 . Alternatively, the mirrors can be supported at approximately 45 degree angles with respect to the cover  44 . A touch screen controller (not shown) is connected to the touch screen to operate the emitters  62  and sensors  64 . 
     Referring to  FIGS. 3   a, b  and  c , a top view of alternative arrangements of the light emitters  62  and sensors  64  are shown. In the arrangement shown in  FIG. 3   a , the light emitters  62  are located in two arrays adjacent two contiguous edges of the display  60  and the sensors  64  are located in two arrays adjacent the other two edges of the display  60 . In the arrangement shown in  FIG. 3   b , the light emitters  62  and sensors  64  are interdigitated in arrays surrounding the display  60 . In the arrangement shown in  FIG. 3   c , emitter arrays are located on all four sides of the display area  60  and sensors  64  are located at the corners of the display  60 , similar to the arrangement shown by Armstrong in published US Patent Application 2002/0175900. 
     In operation, the infrared OLED light emitters  62  emit light in every direction. The light is reflected from the 45 degree mirrors  66  located above the emitters and pass over the surface of the OLED display  60 . After passing over the surface of the OLED display, the light is reflected by the 45 degree mirrors located above the sensors  64  to the infrared sensors  64 . The sensors  64  detect the light and produce feedback signals that are supplied to the touch screen controller and interpreted in a conventional manner to locate the position of an object that interrupts the light from the emitters  62 . Because the touch screen elements are integrated on a common substrate with the display, a single connector may be used for both the touch screen and the display. Elements of the touch screen controller and/or the display controller may be integrated on the substrate. 
     Because each infrared OLED light emitter  62  emits light in every direction, a single emitter can be used in conjunction with multiple sensors  64  to detect a touch. Alternatively, multiple emitters can be used in conjunction with a single sensor to detect a touch. The emitters and sensors can be energized sequentially or in common to optimize the performance of the touch screen under a wide variety of conditions, including high ambient light, low-power operation, a noisy environment, or high performance mode. 
     Because OLED light emitting elements emit light equally in every direction, not all of which will strike the 45 degree mirrors, the performance of the present invention can be enhanced by increasing the amount of light that is emitted orthogonally to the substrate so that a greater percentage of the light will reflect from the mirrors. In conventional practice, up to 80% of the light emitted is lost because it is not transmitted through the cover or substrate of the display. Instead the light may be emitted in a direction parallel to the substrate and will waveguide through the light emissive layers. Therefore, reducing the amount of light emitted parallel to the substrate that propagates through the light emissive layers of organic materials by waveguiding action will increase the amount of light that is emitted usefully toward the mirrors. 
     A reduced angle of emission from the OLED light emitting elements can be achieved by forming an optical cavity between the electrodes providing current to the OLED light emitting elements. Electrodes can be made of highly reflective, thin layers of metal. By making the electrode opposite to the direction of emission completely reflective and the electrode though which light passes partially reflective, an optical cavity can be formed. The optical cavity must be tuned to the preferred frequency at which light is to be emitted by carefully depositing layers of the required thickness. The light within the cavity will form a standing wave pattern at the desired frequency and with a reduced angle of emission. Optical cavities of this type are known in the art, as are suitable metallic electrodes, for example silver. See for example published US US Patent application 20030184892 published 2003 Oct. 2, by Lu et al., which is incorporated herein by reference. It is also possible to use optical cavity designs that produce coherent laser light as described in published US patent application No. US20030161368 published 2003 Aug. 28 by Kahen et al. and US20020171088 published 2002 Nov. 21 by Kahen et al. which are incorporated herein by reference. Applicants have demonstrated both incoherent and coherent OLED light emission having a reduced angle of emission from the perpendicular that is suitable for the present invention. 
     In a bottom-emitting display, the electrode  18  must be partially reflective while the electrode  30  can be totally reflective. In a top-emitter configuration, the electrode  18  is reflective while the electrode  30  is partially reflective. 
     Applicants have demonstrated the use of an optical cavity for the enhancement of light emission from an OLED structure with both white-light emitting materials and for red, green, and blue light-emitting materials. In all cases, the use of a properly sized cavity with the use of a thin layer of silver or silver compounds as the partially reflective electrode and a thicker layer of either silver or aluminum or compounds of aluminum or silver as the reflective electrode results in greater light emission orthogonal to the electrodes and with a narrower spectrum. Partially transparent electrodes may also consist of a two-layer structure in which a first layer is a transparent conductor and a second layer is a partially reflective mirror. 
     In conventional practice, the use of an optical cavity in a display application has the significant drawback of a color change as the display is viewed at angles other than the orthogonal. In the present invention, no such disadvantage is seen since only light that is emitted toward the mirror is used and the emitted light is not intended for viewing. 
     The emitters may be energized sequentially to provide multiple signals thereby increasing the signal-to-noise ratio of the result and providing a more detailed map of any touching implement that inhibits the transmission of the infrared light. In yet another mode, the emitters are energized simultaneously and the relative amount of light sensed by the sensors  64  are used to detect a touch. In this arrangement, the emitters  62  can be a single long emitter with a single control signal. 
     The use of multiple emitters and sensors enables a very robust sensing apparatus. Single-point failures can be overcome and convex shapes can be detected. High-reliability operation is possible by combining signals from various emitters sensed by various sensors. The infrared signal itself may be modulated to overcome background noise or different frequencies of infrared light may be emitted and detected. 
     Referring to  FIG. 4 , the 45 degree mirrors  66  located above the emitters  62  and sensors  64  may be formed by a reflective surface on an enclosure  70  enclosing the integrated display and touchscreen. Referring to  FIG. 5 , the optics for directing light emitted from the light emitter  62  across the display to the light sensor  64  may comprise light pipes  72 . 
     Referring to  FIG. 6 , a bottom-emitting OLED display device with an integrated optical touch screen according to another embodiment of the present invention includes a rectangular substrate  42  with an encapsulating cover  44 . Located on the substrate is an OLED display  60  including electrodes and multiple layers of materials such as hole-injection layers and electron transport layers as is well known in the art (not shown). Light  49  emitted from the display passes directly through the substrate  42  or is reflected from the encapsulating cover  44  and passes through the substrate  42 . 
     Because the present invention does not require a separate frame or substrate for the touch screen, it reduces the weight, size (thickness), and cost of a combined touch screen and OLED display device. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           42  substrate 
           44  encapsulating cover 
           49  emitted light 
           60  OLED display 
           62  light emitter 
           64  light sensor 
           66  mirror 
           70  enclosure 
           72  light pipe