AC electroluminescent structures and displays

L. Yourukova, K. Kolentsov, A. Rachkova

       The hybrid technology is one of the alternatives of plasma, liquid crystal and LED technologies for the fabrication of displays. This technology is the result of scientific investigations, inventions and know-how of the group. The wide application of these displays is due to the easy design, up-to date technological and operation characteristics as well as to significant advantages in the economical consumption of electrical energy and also helps the protection of the environment.
        The electroluminescent displays are multilayer sandwich-like structures which, upon application of voltage with fixed amplitude and frequency, emit light with various colors. The active electroluminescent layer of the structures, prepared on the basis of II-VI compounds, is a heterogeneous matrix. Light emission of this layer is based on the principles of the pre-breakdown electroluminescence. The basic novelty of this technology is the inclusion in this structure of a protective layer from a wide-band gap semiconductor or silicon-containing polymer thin film. In addition to the protective functions this films increase the brightness (about 20 times in comparison with conventional electroluminescent structures) life-time and stability of the structures. This brightness is sufficiently high for practical application. This improvement is due to processes taking part at the interface "active layer - protective layer".

       The hybrid electroluminescent displays, prepared on the basis of these structures, have following advantages:

flat construction and possibility for creation of displays, having various sizes, forms, configurations, high density of the pixels on small area;

       these displays can be used for representation of static and dynamic information;

       high reliability (to 1.10^-6 1/h);

       large viewing angle, ensuring observation from a wide range of angles without distortions and substantial loss of brightness;

       possibility for multi-color light emission in one and the same structure;

       relatively cheap technology.

       The hybrid electroluminescent displays can be employed for presentation of various light information in metro stations, airports, hotels, technological and production lines, for various indicators in cars, lifts, cinema- and theater halls and houses, scales in metallurgical production, advertisement boards etc.

       Three-color (R, G, B) matrix element with the width and the interval between the tracks above 50 micrometers is developed on a laboratory level.

Display samples of letters and digits, prepared by the developed hybrid technology were presented at World Exhibitions of Innovations and Inventions (1996-2000) and have been awarded by the authoritative International Jury with:
   two silver medals, (Sofia, 1996, 1998),
   four Gold medals (Sofia, Bulgaria 1997, Manila, Philippines 1998, Sofia, Bulgaria 2004, 2005),
   a honorary cup, (Pittsburgh, USA, 1999)
   and
   two diplomas (Tokyo, Japan, 2000 and Brussels, Belgium, 2000) – International Exhibitions of Invention, Research, Innovation and New Product.