thousand hours) and multiplexing capabilities, but failed to achieve acceptable reliability.

A milestone in thin film EL (TFEL) devices was achieved by Inoguchi et al (Sharp

Corporation) who introduced an ac thin-film approach in 1974 [6, 7]. The team of

researchers at Sharp fabricated a device modeled after a capacitor that consisted of

manganese-activated zinc sulfide as the phosphor and yttrium oxide for the sandwiching

insulators. This was the first high-brightness, long-lifetime device. Sharp succeeded in

developing this technology and introduced a monochrome television display in 1978 [8].

Planar systems introduced multicolor and full-color displays in 1982 [9] and 1994 [10],

respectively. Thus, today thin film electroluminescent displays are very active in the

market place. Major research interest will be focused on improving device brightness,

stability and efficiency.

 2.2 ACTFEL Device Structure

2.2.1 Monochrome Structure

 The most common structure used for alternating current thin film

electroluminescent (ACTFEL) devices is illustrated in Fig 2. l(a) [11]. It is also called a

MISIM (metal-insulator-semiconductor-insulator-metal) structure. This device usually

uses glass as a transparent substrate on which a transparent bottom electrode is deposited.

The following step is the deposition of a transparent insulator, the phosphor layer,

another insulator layer, and an opaque electrode. Because the substrate is transparent

glass, the light can be transmitted through the glass into the eyes of the viewer. Also,

glass is cheap and widely available in any size. In addition, it does not contain alkali

metals which have been found to diffuse into the semiconducting phosphor layer and

cause the devices to degrade over time [12].