Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Plural light emitting devices
Patent
1997-03-06
1999-09-14
Tran, Minh Loan
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Plural light emitting devices
257 89, 257103, H01L 3300
Patent
active
059526807
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to monolithic arrays of light emitting diodes for the generation of light at multiple wavelengths, and multicolor displays based on such arrays.
BACKGROUND OF THE INVENTION
In our technical world displays have an important function as human interfaces for making abstract information available through visualization. In the past, many applications for displays were identified and realized, each with its own specific requirements. Therefore, different display technologies have been developed, each having their own strengths and weaknesses with respect to the requirements of particular display applications, thus making a particular display technology best suited for a particular class of applications.
The most important display applications being pursued are based on cathode ray tubes (CRT), liquid crystal displays (LCD), or vacuum fluorescent, plasma, light emitting diode (LED), electroluminescent, and electromechanic displays. Among the most decisive criteria dictating an appropriate display technology are cost of fabrication, power efficiency, reliability, weight, size of screen, depth, brightness, gray-scale capabilities, dynamic range, resolution (i.e. the minimum size of an addressable picture element on the display), contrast, dependence of the contrast on the viewing angle, switching speed of a particular pixel (pixel element), sunlight readability, color range, chrominance and chrominance contrast. CRTs have a dominant position on the display market due to their low price and their multicolor, high resolution and gray-scale capabilities. However, they have disadvantages if low weight, low power, small depth and sunlight readability is desired, for example in applications for battery driven portable computers.
The other mentioned display technologies come into play in areas where CRTs show weaknesses, especially if the weight, the depth and/or the power consumption of CRTs are simply not acceptable. For example, in applications for wrist watches or portable computers--an important domain of flat panel displays--or, generally, in applications which require large and/or flat displays, alternate technologies are preferred.
Due to their advantages--low weight, low power consumption, low depth--LCDs became the dominant flat panel display technology. The LC-material is cheap and the fabrication processes are scalable although at considerable cost, so that displays of arbitrary size can be made. However, many applications such as high resolution graphics or full motion video require high resolution, often in combination with high pixel switching speed. In these cases, LCD technology has drawbacks. In LCDs, high resolution is achieved with x-y matrix addressing techniques, thus reducing the number of address lines. However, x-y matrix addressing, in combination with the fundamental physical properties of LC materials, lead to high resolution only at the expense of a poor contrast between adjacent pixels, a small maximum viewing angle and other effects further deteriorating image quality, for example cross talk between pixels. These drawbacks can be partly overcome with so called `active` x-y matrix addressing (see "A gray-scale addressing technique for thin-film-transistor/liquid crystal displays" by P. M. Alt et al., IBM Journal of Research and Development Vol. 36, No. 1, pp. 11-22, 1992). However, active matrix addressing requires a network of transistors of the same size as the display itself, each transistor controlling the charge stored in one capacitor, each capacitor influencing the orientation of the LC molecules between its electrodes and thus defining one pixel of the entire display. Today, the active matrix addressing makes possible brilliant full color displays capable of graphics with reasonable resolution or full motion video. However, large flat panel LCDs with active matrix addressing are expensive due to the costs of the fabrication of the transistor matrix array. In spite of the improvements due to the active matrix addressing, undesirable dra
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Dougherty Anne Vachon
International Business Machines - Corporation
Tran Minh Loan
LandOfFree
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