On May 8, 2014, the US Patent & Trademark Office published a patent application regarding methods for improving AMOLED displays. Today's patent pending invention covers new methods for greatly improving gray level controls that improves overall color. While some may not take Apple's work on AMOLED too seriously because of disparaging comments that Apple executives have made over time, think again. While Apple's CEO was talking at the Goldman Sachs conference held on February 12, 2013 he stated that "If you buy things online, you should think twice before you depend on the color of the OLED display. The Retina display is twice as bright as an OLED display. Some people use OLED displays, but the color saturation is awful." Yet while Apple's CEO was downplaying OLED publicly, the fact is that Apple had just recruited a former senior researcher at LG Display to work on OLED display technology a week earlier. Apple's executives downplay current OLED displays available from competitors, but that doesn't mean that Apple can't vastly improve upon it for future products that use flexible displays that are primarily OLED based.
Apple's Patent Background
Flat panel displays, such as AMOLED displays, are commonly used in a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., cellular telephones, audio and video players, gaming systems, and so forth). Such display panels typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, such devices may use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage.
AMOLED displays typically include picture elements (e.g. pixels) arranged in a matrix to display an image that may be viewed by a user. Individual pixels of an AMOLED display may generate light as a voltage is applied to each pixel. The voltage applied to a pixel of an AMOLED display may be regulated by two thin film transistors (TFTs). For example, a circuit switching TFT may be used to regulate current flowing into a storage capacitor, and a driving TFT may be used to regulate the voltage being provided to the OLED of an individual pixel. Connections between the TFTs in an AMOLED display may extend through an area of the pixel that may otherwise be used for displaying image data. In certain configurations, a pixel aperture ratio is a ratio between a transparent area of the pixel that can be used to display image data and a total area of the pixel. Thus, connections between the TFTs may decrease the area of a pixel that can be used to display image data and thereby lower the aperture ratio of pixels of the AMOLED display.
In electronic displays, the gray level of each pixel may determine the intensity of the output of the pixel. In certain displays, the intensity of each pixel's output may vary from black at the lowest intensity to white at the highest intensity.
As mentioned above, one of the TFTs of an AMOLED display may regulate a voltage being provided to the OLED of an individual pixel. The range of voltages that is applied to a gate electrode of the driving TFT may determine the amount of current flowing to the OLED and thus, the gray scale level of a pixel. An increased range of voltages that may be applied to the gate of the driving TFT may give more precise control over the gray level in an AMOLED display.
Apple Invention Covers Methods for Improving AMOLED Displays
Apple's invention generally relates to electronic displays and, more particularly, to devices and methods for achieving more precise gray level control and an increased aperture ratio in active matrix organic light emitting diode (AMOLED) electronic displays.
Embodiments of the present disclosure relate to devices and methods for increasing the aperture ratio and the gray level control of pixels of an AMOLED display. For example, a display for an electronic device may include a driving thin film transistor (TFT) having a first source, a first drain, a first channel, and a first gate electrode.
Additionally, a circuit switching TFT may include a second source, a second drain, a second channel, and a second gate electrode. A gate insulator layer may be disposed over the first source, the first drain, and the first channel of the driving TFT, and the second source, the second drain, and the second channel of the circuit switching TFT. The second gate electrode of the circuit switching TFT may be disposed over the gate insulating layer.
An interlayer dielectric (ILD) may be disposed over the gate insulating layer and the second gate electrode of the circuit switching TFT. The first gate electrode of the driving TFT may be disposed over the ILD. Disposing the first gate electrode over the ILD may allow a direct electrical connection to the second source of the circuit switching TFT. This direct connection may decrease an area occupied by the connection circuitry mentioned above. Moreover, because the area of the direct connection is reduced, the pixel aperture ratio of pixels of the display may be increased.
Apple's patent FIG. 6 noted below is a cross-sectional view of a portion of an AMOLED display having a driving TFT. It also points to where the interlayer dielectric (ILD) is located in the display makeup.
Apple additionally illustrates disposing the gate electrode over the ILD rather than over the gate insulator layer produces a larger separation between the gate electrode and the channel of the driving TFT. The larger separation may increase the voltage range applied to the gate electrode and improve the gray level control.
Apple's current patent notes that the displays may apply to both Macs and iDevices. In respect to our opening summary pointing to "flexible displays" for future devices, Apple's cool futuristic iPhone patent application pointed to OLED as a possible display candidate. Here's another flex display patent covering OLED with unique functionality.
Apple credits Shih Chang and Yu Cheng Chen as the inventors of patent application 20140125565 which was originally filed in Q4 2012. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
A Few Other Notable OLED Patents from Apple
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