Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1998-04-27
2001-12-04
Wilczewski, Mary (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S027000, C438S099000, C438S070000
Reexamination Certificate
active
06326224
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to organic light emitting diodes and more specifically to methods for enhancing the power and/or color of the light output of organic light emitting diodes.
BACKGROUND OF THE INVENTION
Light emitting diode (LED) arrays are becoming more popular as an image source in both direct view and virtual image displays. One reason for this is the fact that LEDs are capable of generating relatively high amounts of light (high luminance), which means that displays incorporating LED arrays can be used in a greater variety of ambient conditions. For example, reflective LCDs can only be used in high ambient light conditions because they derive their light from the ambient light, i.e. the ambient light is reflected by the LCDs. Some transflective LCDs are designed to operate in a transmissive mode and incorporate a backlighting arrangement for use when ambient light is insufficient. In addition, transflective displays have a certain visual aspect and some users prefer a bright emissive display. However, these types of displays are generally too large for practical use in very small devices, such as portable electronic devices.
Organic electroluminescent device (OED) arrays are emerging as a potentially viable design choice for use in small products, especially small portable electronic devices, such as pagers, cellular and portable telephones, two-way radios, data banks, etc. OED arrays are capable of generating sufficient light for use in displays under a variety of ambient light conditions (from little or no ambient light to bright ambient light). Further, OEDs can be fabricated relatively cheaply and in a variety of sizes from very small (less than a tenth millimeter in diameter) to relatively large (greater than an inch) so that OED arrays can be fabricated in a variety of sizes. Also, OEDs have the added advantage that their emissive operation provides a very wide viewing angle.
In spite of all the advantages of OEDs there are still some draw backs to their use. One of the drawbacks is the fact that light emitted by OEDs is dependent upon the amount of current applied to the OED. Thus, to produce sufficient light for use in displays substantial amounts of current must be applied. As a typical example, with a 64×32 array of devices forming a four line by 11 character display the following devices will use approximately the listed amount of power to produce equal light out. If the devices are semiconductor light emitting diodes the display will require approximately 1 Watt (w) of power; organic light emitting diodes will require approximately 150 mw of power; LCDs with a backlight will require approximately 120 mw of power; and reflective LCDs will require approximately 20 mw of power.
One additional problem with the use of LCDs is the contrast ratio, or the difference between light and dark pixels. LCDs have a contrast ratio of 3-6 while OEDs and LEDs have a contrast ratio in excess of 150. Thus, while OEDs and LEDs produce sufficient light for operation under any ambient light conditions, they use a comparatively large amount of power.
An additional problem in the use of OEDs in displays is the generation of the colors necessary to achieve a full color display. Red, green and blue OEDs can be fabricated but they require different organic materials and, thus, each color must be fabricated separately. Furthermore, the colors achieved are not a pure primary color, but have a relatively broad spectrum. Even though red, green, and blue materials in OEDs are available, only green materials have stable and high brightness emission. There still exists problems associated with reliability and lifetime in blue and red materials.
Accordingly, it is highly desirable to provide a method of enhancing light output of an OED which uses less power.
It is a purpose of the present invention to provide a new and improved method of generating light with improved purity of color.
It is a further purpose of the present invention to provide a method of purifying the light output of an OED having substantially any wavelength.
SUMMARY OF THE INVENTION
The above problems and others are at least partially solved and the above purposes and others are realized in a method of purifying a primary color. The method includes providing an organic light emitting diode having a diode light output with a broad spectrum including a fraction of the primary color. A microcavity structure is formed in cooperation with the organic light emitting diode to define an optical length of the microcavity structure. The optical length of the microcavity structure is such that light emitted from the microcavity structure is the primary color, purified.
In a more specific embodiment, the formation of the microcavity structure includes the step of forming a first microcavity with an optical length such that light emitted from the first microcavity light is the primary color, purified. In yet another embodiment, the formation of the microcavity structure includes a step of forming a second microcavity in tandem with the first microcavity, and the optical length of the second microcavity being such that light emitted from the second microcavity is the primary color further purified. Formation of additional microcavities, in tandem, is also contemplated.
REFERENCES:
patent: 5405710 (1995-04-01), Dodabalapur
patent: 5469018 (1995-11-01), Jacobsen
patent: 5478658 (1995-12-01), Dodabalapur
patent: 5780174 (1998-07-01), Tokito
patent: 5932895 (1999-08-01), Shen
patent: 5949187 (1999-09-01), Xu et al.
Lee Hsing-Chung
So Franky
Xu Ji-Hai
Goodwin David
Koch William E.
Motorola Inc.
Wilczewski Mary
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