Another structure that has been developed is known as the "inverted" structure

which is shown in Fig 2.1(b). In this case, the substrate is opaque (e.g., silicon) and

therefore a transparent electrode is required on the top of the ACTFEL structure [13]

through which light leaves the device toward the viewer. Because there is no requirement

for the substrate to be transparent in the inverted structure, ceramics can be used for the

substrate materials, which allows higher temperature processing.

 The two kinds of devices mentioned above are "full-stack" devices. However, there

is another type of device which is known as a "half-stack" device. This type of device is

similar to either a standard or inverted device, but lacks one of the two insulating layers.

It's shown in Fig 2.2. Because it lacks the top insulator, the device processing will be

simpler. This type of device is normally used for research purposes due to lower

reliability.

2.2.2 Full-color Structure

 There are several approaches to the development of full color EL displays. Two

common approaches will be discussed here, which are patterned-phosphor structure and

"color-by-white" filtered structure.

 For patterned-phosphor structure, also called a red-green-blue display, the red,

green, and blue phosphor layers are patterned so that each pixel is divided up into four

sub-pixels that contain a red, green and two blue phosphor regions (Fig 2.3(a)). The

advantages of this structure are a simpler drive structure, being identical to that of a

monochrome panel and the use of aluminum electrodes for self-healing breakdown [12].

However, because it will require masking and etching, the processing is more

complicated.