The Pros and Cons of Current OLED based Displays

Organic light emitting diodes (OLEDs) are solid-state semiconductor devices that convert electrical energy into light. Generally, OLEDs are fabricated by disposing one or more layers of organic thin films between two conductors or electrodes. When electrical current is applied to the electrodes, light is emitted from the organic layers.

On the positive side of the equation, OLED technology may be used to fabricate ultra-thin displays that could generally operate at lower voltages than traditional display technologies, such as liquid crystal display (LCD) technologies in which light is separately generated and the color of the light modulated by an LCD panel placed between the light and the viewer. In addition, an OLED display may provide better contrast ratios, frame rate, color and/or power efficiency than a comparable LCD display.

On the negative side of the equation, these advantages of an OLED display may be reduced or absent when the OLED display is used to generate large amounts of white display area. In particular, because an OLED display is a light emissive (as opposed to light transmissive) technology, to display a white area, the OLED panel typically has to energize and emit light from a range of the various color channels present at each pixel of the OLED display. As a result, the display of white areas on an OLED display may be power intensive and relatively inefficient.

OLED Displays are Weak in Productivity Applications

According to Apple, the relative power inefficiency in displaying white spaces using an OLED display may be particularly problematic in certain contexts. For example, certain applications, such as word processing, spreadsheet design and use, database design and use, e-mail, and other business or productivity applications, typically utilize dark or black alphanumeric characters on a white background, such as to simulate writing or printing on a sheet of paper. As a result, these applications may cause the display of large expanses of white background with relatively little area devoted to the non-white alphanumeric characters. Such applications, therefore, may make the use of traditional OLED displays unsuitable or undesirably power intensive for battery powered and/or portable electronic devices, such as handheld devices.

Apple's Proposed OLED Display Solution

Apple's invention describes the use of a display suitable for use in a battery-powered electronic device such as a notebook or handheld electronic devices (iPhone, iPad etc).

Implementing a Switchable Display Layer

In one embodiment, the disclosed display includes various layers including a transparent light emissive display panel (e.g., an OLED panel) and a solid (e.g., white) or printed background layer, such as a white transflective sheet. In addition, the display includes an opacity switchable layer, disposed between the transparent light emitting panel and the background layer. The switchable layer may be switched, in whole or in part, from an opaque or semi-opaque state to a transparent or semi-transparent state.

For example, in one embodiment, the switchable layer may be opaque, e.g., black, in the absence of a current. However, upon application of a current all or part of the switchable layer may become transparent so that the underlying background layer is visible.

In certain embodiments, an opacity switchable layer is provided between an OLED panel and the background layer. In one embodiment, all or portions of the switchable layer may be selectively switched between transparent and opaque states. In such an embodiment, when all or part of the switchable layer is transparent, the background layer is visible through the OLED layer and the transparent portions of the switchable layer. Conversely, when all or part of the switchable layer is opaque, the background is not visible through the OLED layer and the opaque portions of the switchable layer.

In one implementation, an OLED display employing a switchable layer and solid background, as discussed herein, may be 30% more power efficient than a comparably sized LCD screen, while still providing superior frame rates and/or contrast.

Apple's patent FIG. 5 noted above depicts an example of layers of a display panel with a switchable layer set to block transmission of light in accordance with aspects of the present disclosure; Patent FIG. 6 depicts an example of layers of a display panel with a switchable layer set to transmit light.

As depicted in Apple's patent FIG. 8, the various layers of the display may be joined or adhered by various intervening layers. For example, in the depicted embodiment, the OLED panel, the switchable layer and the background layer may be adhered or joined using respective layers of an optically clear adhesive (OCA). In one implementation, the layers of OCA may be between about 0.05 mm and 0.15 mm in thickness.

A Side Benefit: Apple's Backside Logo on the iPhone could be illuminated

Apple also states that the substrate layer may be a printed substrate, e.g., a corporate logo, emblem, name, or mark. In such an embodiment, the printed matter, such as a logo, may be visible when the OLED panel is not emitting light and when the switchable layer is in a transparent state. In such an embodiment, the switchable layer may be implemented or may utilize an approach that results in the switchable layer being transparent in the absence of an electrical field. In such an implementation, the printed matter, e.g., the logo or emblem, present on the substrate layer may be visible when the electrical device 8 is off, i.e., when the display is unpowered.

Apple's patent application was originally filed in Q2 2010 by inventors Rivera Alvarez, Jose Felix, Albert Golko and Daniel Jarvis.

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