2.5.2 Electrodes

 Top and bottom electrodes, one of which must be transparent, are required for

ACTFEL device. For the standard device, the first layer deposited on the glass substrate

is the transparent electrode. The requirements of the electrode are that they are

conductive so that it will not affect the RC time constant of the device and transparent so

that it can minimize the absorption. Additionally, it must withstand the thermal

processing of subsequent layers. The most common transparent electrode is indium tin

oxide (ITO), whose resistivity is about 50/o for thickness that range from 300-500 nm.

The high conductivity comes from the high concentration of shallow donors located only

few meV below the conduction band. These donors can be thermally activated into the

conduction band at room temperature. Sn+4 sitting substitutionally on an In+3 site and

oxygen vacancies [32] plus intentionally doped F ions are the primary sources of these

donors. Other candidates for transparent electrodes are ZnO and ZnO:( Al, In, Ga) [33].

 The top electrode is the last layer that is deposited for the standard ACTFEL

device. The main requirement for it is that it has low resistivity and can be resistant to

electromigration under high electric fields [34]. The most common top electrode is

aluminum due to its good conductivity, resistance to ion migration and good

processibility. In addition, because aluminum is highly reflective, it enhances brightness

but reduces the contrast in a display.

2.5.3 Insulators

 The main purpose of the insulator layer in ACTFEL device is to prevent current

flow through the device and protect the phosphor layer from electric breakdown from

fields of up to 2 MV/cm. Because of the important role of the insulators, the requirements