BC Au electrode OTFTs based on the process sequence of pentacene/OTS/AP plasma treatment/Au electrode (patterned)/APS/SiO2 was fabricated. The electrical characteristics of OTFTs with plasma treatment showed relatively high performances of devices with a low-contact resistance (Fig. 7). The current crowding effect seen in the output characteristics of the reference device can be responsible for the low performance of the device. [43,44]. In contrast, the fabricated device with 12 kV AP plasma treatment reveals the highest performance including a mobility, an on/off current ratio (Ion/Ioff), Vt, and low subthreshold slope (S) of 0.23 cm2 V-1 S-1, 9.8 × 105, −1.63 V, and of 0.16 mV dec-1 (Table 2).
To gain a better understanding of AP plasma treatment on APS affecting their electrical performance, the contact resistance at the BC electrodes for pentacene OTFTs were extracted using the transmission line method .
In the linear regime of the output curves, the total resistance (Ron), which is the sum of the channel resistance (RCh) and the contact resistance (RC), is expressed by
where W is the channel width, L the channel length, µ the linear mobility on the contact region, Cox the gate oxide capacitance per unit, and VT the threshold voltage. Table 2 shows the width of the normalized contact resistance RcW based on Eq. (1). The extracted RcW were 29 , 66, and 2630 kΩ-cm at VG = −20 V for OTS/AP plasma (12 kV)/APS, OTS/AP plasma (5 kV)/APS, and