Figure 3 (a) shows the characteristics of IZO TFTs, the fabrication process of which can be seen in Ref. [
12]. It is shown that the mobility and threshold voltage are 13.3 cm
2/(V·s) and 0.3 V, respectively. Note that, the TFTs have excellent turn-off performance with the leakage current as about 50 fA. The OLED device structure is ITO(170 nm)/MeO-TBD:F4-TCNQ(150 nm, 4 wt%)/NPB(20 nm)/Bebq2(30 nm)/LiF(1 nm)/Al(200 nm), which emits red light. The characteristics of OLED are shown in Fig. 3(b). The current efficiency
h = 21 cd/A and its area is 4900 mm
2. The
W/
L of the driving TFT (T4) is designed as 20 mm /10 mm based on the characteristics of TFTs and OLED to make the target luminance of OLED up to 800 cd/cm
2. T1, T2 and T3 are the common switching TFTs, the
W/
L of which is chosen as 10 mm/10 mm. The capacitance of C1 and C2 can be set as a small value to ensure timely charging in the data input period since the leakage current of TFTs is low enough, such as 0.4 pF. The value of
VDD should be large enough to make the driving TFT (T4) working at the saturation region in the whole range of data voltage. The high/low voltage of control signals (V1, V2, V3) is set to turn on/off TFT completely. The design parameters of the proposed pixel circuit are all indicated in Table 1.