MATERIALS FOR ELECTROLUMINESCENT DISPLAYS

The Kyyiv Scientific Research Institute for Microelectronics Technique and Materials in Kyyiv, Ukraine, has facilities for producing EL devices. The material used is ZnS:Mn (yellow color), which in the past was purchased from Zelenograd (Russia). Presently, in Ukraine the source of the pure materials is located in Odessa. The lifetime for the display with this phosphor is 2,000 hrs; the goal is to reach 10,000-15,000 hrs using pure materials. EL indicators operate in the temperature range of -50 degrees centigrade to 80 degrees centigrade. The basic technical parameters of the EL indicators are: integral luminance of >40 cd/m2, contrast of better than 2:1 with external illuminance of 30,000 lx and better than 10:1 with 500 lx, a viewing angle >120 degrees, and operating voltages of 5 V and 250 V.

In the Department of Optoelectronics, Institute of Semiconductors at the Ukraine Academy of Sciences, thin-film EL structures are based on materials such as ZnS, ZnSe, and ZnS:Mn with colors of yellow orange, red, green, and blue. Recently, a new type of EL indicator based on the integration of the thin-film luminescent structure and active layers of ferroelectric ceramics has been developed. Two- colored matrix screen on glass and ceramic substrates are manufactured.

The Moscow State Institute of Electronics and Mathematics has done considerable work in EL displays at brightness levels greater than 50,000 lx, and claims to have an EL comparable to a CRT in a 15 cm x 15 cm format. The color was reported as yellow green, and the lifetime was given as greater than 10,000 hrs. The institute has operated the device over a variety of temperature ranges.

In display technology, the Elorma Scientific Industrial Corporation has investigated a DC and AC EL display. The role of Elorma in making the display was to modify the interface to enhance electron mobility of the phosphors with use of a siloxane film. The company's interests are in using the siloxane material developed at Elorma as a sublayer for photodioxides and possible substrate coating for displays. The proposed advantage of this organic is that it can protect the phosphors from alkalis from soda-lime glass substrates and thus enhance reliability and stability. This EL display consisted of ZnO - ZnS p-n junction with an organic polymer dielectric. The display was a 4" x 5" matrix with a yellow green color and an integral brightness of 180-250 cd/cm2, which was visible in sunlight. The luminescent material was a modification of existing phosphor in which ZnS particles were oxidized, covered with patches of Cu islands, and coated with a siloxane film. Other phosphors were also used, such as rare earth oxides for blue. The siloxane used in the display was patented; the patent was to be released in February 1994. Possible future applications of this organic material were proposed, such as a substrate in an LCD and as a photodioxide screen in a LED with narrowband emission.


Published: December 1994; WTEC Hyper-Librarian