On May 22, 2014, the US Patent & Trademark Office published a patent application from Apple that reveals their ongoing work on future flexible OLED displays. Apple's invention covers the implementation of bendable metal traces that won't break or crack under conditions of the display that require bending or curvature. This supports Apple's patent application regarding hollow structures that include a possible future iPhone. Bendable metal traces represent a key attribute to assist the design of durable flexible displays for future devices.
Apple's Patent Background
To fabricate a flexible display, many display components have been developed to use organic materials, such as organic light emitting layer, organic passivation layer and polymer substrate as a flexible substrate. However, it is difficult to replace metal traces of the display with an organic material, because electrical conductivity of the organic material is not as high as the metal traces. The metal traces may be broken or disconnected when a display panel is bent, because the metal traces have a fracture strain limit of about 1%. Some other components still use silicon nitride, which may also be cracking. Therefore, it is desirable to have display components to be bendable or flexible.
Apple's Invention Covers Flexible Displays with Bendable Metal Traces
Apple's invention generally relates to flexible displays for computing devices, and more particularly to implementing a flexible display with metal traces that may bend as the display flexes, without breaking or cracking.
According to Apple, the display may be an organic light emitting diode (OLED) display. The display includes a flexible substrate that supports an array of pixels or sub-pixels and thin film transistors that drive each pixel or sub-pixel. The display may be flexible about one or more axes. For example, the display may be rolled to form a cylinder or bent into a non-planar shape. By providing such flexibility, portability and certain operations of the display may be enhanced.
Broadly, a sample flexible display may be constructed from a polymer substrate, an organic light-emitting layer (e.g., an OLED layer) upon the substrate, and an organic passivation layer encapsulating or overlying the light-emitting layer. The substrate may be formed from any suitable material; a polymer is but one example. As a more specific example, the substrate may be formed from polyimide. It should be appreciated that additional layers may be present in a sample flexible display.
Generally, and as shown in Apple's patent FIG. 1 below, a flexible display 100 includes flexible substrate that supports subpixels 102A-C. A metal line #104 may connect the various subpixels 102A-C and also the pixels. Such lines may be, for example, be gate and/or data lines that may carry other information and/or signals.
Conventional metal signal lines or traces are straight, and may be subject to cracking or breaking when the flexible display is bent. That is, the bending motion may strain the metal lines, which may result in cracking or breaking. Accordingly, certain embodiments disclosed herein employ serpentine metal traces, as shown in FIG. 1.
These serpentine traces may have several properties making them suitable for use with flexible displays. For example, when the flexible display is bent, rolled or otherwise deformed, the serpentine metal lines may stretch along their circular portions, rather than break.
In Apple's patent FIG. 3 noted above we generally see a depiction of a gate line overlapping a series of data lines #302. As shown, the gate line #304 may be straight for a first portion (304A) of its length and then serpentine for a second portion (304B) of its length.
In such an arrangement, it is contemplated that the section of the panel having the straight data line would not bend, while the section having the serpentine line would be capable of bending. It should be appreciated that some embodiments may permit bending of the display even if the gate (or other) lines are all straight.
The line labeled "bending edge" illustrates one possible line along which the flexible display may bend. It should be appreciated that the location of the bending edge is arbitrary and used for illustrative purposes; the display may bend at many other points or along many other lines that are not labeled. Likewise, the display may bend along a complex curve or in multiple dimensions. Some embodiments may even permit the folding of a display.
In the first design 700A shown in Apple's patent FIG. 7 above, we see that it employs a pair of sine wave-shaped metal traces #702 and #704. The two metal traces overlap only at certain points #706. Essentially, the first and second metal traces are approximately 180 degrees out of phase with one another, such that the upper part of the second metal trace is linearly aligned with the lower part of the first metal trace. This can be seen along the line marked "bending edge" in first redundancy design 700A of FIG. 7. It should be appreciated that the offset between the two traces may be as large or as small as desired.
Apple credits Byung Yang, John Zhong, Shih Chang, Vasudha Gupta and Young Park as the inventors of patent application 20140138637 which was originally filed in Q1 2013. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
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