circuit with three capacitors in series, two from the insulators and one from the phosphor.

The voltage drop across each layer is proportional to the dielectric constant and the layer

thickness. The electrical threshold voltage is the voltage at which the phosphor layer

experiences a Zener breakdown as electrons are injected by tunneling into the phosphor

layer. Above threshold, the phosphor layer becomes two Zener diodes back to back.

 A typical trapezoidal waveform that is used to drive an ACTFEL device is shown

in Fig 2.6. The device is driven at 2.5 kHz with 5 [ts rise and fall times and a 30 [ts pulse

width [28].

2.4.1 Charge-Voltage (Q-V) Diagram

 Charge-Voltage data are very useful for electrical characterization of an ACTFEL

device. A typical Charge-Voltage diagram is shown in Fig 2.7 [29]. The description of

the diagram is as following:

1. Initially, at zero voltage there is zero charge.

2. As the voltage is ramped below threshold, the slope of Q-V is equal to the
 capacitance of the phosphor and insulators.

3. Above threshold, the slope is equal to the capacitance of the two insulators only
 since the phosphor layer breaks down.

4. As the voltage is reduced below threshold, the slope again becomes the capacitance
 of the phosphor and insulators. However, at zero voltage the charge is non-zero
 because of the trapped charge at the phosphor/insulator interface.

2.4.2 Brightness-Voltage (B-V) Curve

 Brightness-voltage data are the most important measurement used to evaluate an

ACTFEL device. A typical B-V curve is shown in Fig 2.8. From this curve, several

important ACTFEL parameters can be obtained.