This invention relates to organic light emitting diode (OLED) displays.
Organic light emitting diodes (OLEDS) are made from luminescent organic materials that generate light when a direct current is passed through the materials. Certain characteristics of OLEDs make them appealing to those skilled in the art of electronic display technology. For example, OLEDS have a low operational voltage, a relatively high brightness, and the ability to emit different colors of light. OLED displays may be used in many applications such as displays for portable electronic devices, flat screen computer displays, or automobile stereo displays.
A typical OLED display includes an array of OLEDs formed on a glass plate or other transparent substrate. A stack of organic layers, including an electroluminescent layer, is packed between a cathode layer and an anode layer. The cathode layer and the anode layer provide the electrical power to the OLEDs in order to emit light from the diodes. The cathode layer includes a series of cathode lines, which form the pixel rows of the display, and the anode layer includes a similar series of anode lines to form the pixel columns. Solder connections have been used to electrically connect cathode and anode lines to an external drive circuit, but only through connections at the edges of the display. Typically, a pixel in the OLED flat panel display comprises a group of three OLED sub-pixels of different colors.
In prior art OLED flat panel displays, active elements, such as the cathode lines, anode lines, and diodes, are packed between a front panel and a back panel. An epoxy adhesive covering the active elements couples the front panel and back panel together. The glass material of the front panel and the epoxy material covering the OLEDs are poor thermal conductors compared to the solder connections at the edge of the display. The thermal insulation of the epoxy and glass material surrounding the all or most of the OLEDs throughout the pixel array cause a high operating temperature of the OLEDs. Also, the OLEDs further from the edges of the display have a greater level of thermal insulation than the OLEDs on the edge of the display. Thus, the operating temperatures of OLEDs vary with the OLEDs further from the edges of the display having higher temperatures.
The power consumption of an OLED integrated into a flat panel display may be enough to significantly raise the operating temperature of the diode. Higher levels of brightness in OLED flat panel displays may result in a greater level of heat generation per diode. The operational life and the efficiency of the OLED display are two significant design issues that are impacted by operating temperature. For example, the aging effects of the OLEDs are accelerated by increased operating temperature and the efficiency of the OLEDs is decreased as the operating temperature is increased. The trend in OLED display technology is for higher levels of brightness and efficiency with longer life spans.