Thin film electroluminescent devices with memory

Abstract

Thin film electroluminescent devices made from ZnS:Mn can be designed to exhibit an inherent hysteresis in the luminance versus applied voltage characteristics. This memory behavior offers attractive advantages for efficient operation of displays with very large information content. Additionally, such memory devices can also be switched by light or electron beams, making possible such applications as image storage and a CRT with an active faceplate. In view of its importance, the hysteresis phenomenon will be reviewed from both an experimental and a theoretical point of view. The switching characteristics of memory devices and some of the empirical requirements for observing the hysteretic behavior will be described. This background will then be used to discuss the ac device operation in terms of a phenomenological model which accounts for the necessary negative resistance required for the bistability of a microscopic region termed a filament. The observed voltage range for hysteresis in the device can then be explained as an ensemble effect since most of the emitted light comes from a dense array of localized filaments. Finally, some technological difficulties associated with memory devices will be illustrated by choosing the recent electroluminescent storage CRT as an example of a particularly demanding implementation. © 1983 SPIE.