The Zero Defect Layout, or ZDL, corrects OLED pixel level manufacturing issues. The current yield rates for OLED displays are very low; estimates range from 60%-70% for simple panels to less than 1% for large, complex panels.
This leads to two problems:
- High manufacturing costs.
- Inability to produce both high resolution and large format displays.
The inability to produce large and high resolution displays limits the market share of OLEDs to small format, low resolution displays. Compounding this issue is the high manufacturing cost, which affects profitability and the ability to remain competitive. As a result, even with superior image quality, OLEDs cannot enter lucrative, revenue-generating spaces such as:
- Primary cell phone and PDA displays
- Televisions (standard, high definition, large and small format)
- Laptop displays
- Computer monitors
The ZDL lowers the manufacturing costs by raising the manufacturing yield. The increased yield then allows for the production of high resolution and large format displays. For smaller displays, the ZDL puts AMOLEDs into a similar price range as AMLCDs.
The manufacture of any display invariably results in a certain percentage of pixel level defects. In LCDs these pixel level defects are usually dead or stuck pixels — pixels that do not allow light to pass through or are always on, respectively. Pixel level defects in OLED displays generally result in a dead pixel.
While a set number of pixel defects is considered acceptable for a display, based on the manufacturing guidelines of the company, the current low resolution of OLEDs combined with a relatively high pixel defect rate leads to a low manufacturing yield. For OLEDs, pixel defects are the result of many possible factors. Both POLED and SMOLED are susceptible to dust and water contamination during the materials depositing process. There are also situations where a faulty backplane can cause a pixel defect.
The ZDL is able to compensate for pixel level defects with a varying degree of success based upon the type and severity of the defect. Imperfect compensation occurs when the amount of pixels per screen are very high. Using the ZDL, the pixels with imperfect compensation will not be black, but will be slightly dimmer than a standard “good” pixel.
Perfect compensation will occur with the right ZDL configuration and a low number of pixel defects. A ZDL pixel that uses perfect compensation will not be any different than a standard “good” pixel to the eye. The drop in brightness for a perfectly compensated pixel will be below the threshold of the human eye, although there will be a statistical difference.
The three figures on this page show the following:
- How pixel level defects may appear on a low resolution OLED screen. Each defective pixel is ‘dead’ and thus does not emit light.
- How that same display may look when a ZDL with imperfect compensation is used. The difference in pixel luminance will be based on ZDL configuration and the number of defects. Note that the darkened pixel effect is greatly exaggerated here for illustration purposes.
- How a display using the ZDL with perfect compensation may look. While there is a statistical difference in the brightness of the “good” and “bad” pixels, the difference is so slight that the human eye can not determine which pixels are “good” and which pixels are “bad”.