Organic Thin-Film Transistor Applications by Brajesh Kumar Kaushik Brijesh Kumar Sanjay Prajapati & Poornima Mittal

Author:Brajesh Kumar Kaushik, Brijesh Kumar, Sanjay Prajapati & Poornima Mittal
Language: eng
Format: epub
Publisher: CRC Press

FIGURE 6.5 (a) Device structure of an F16CuPc-based OTFT and (b) chemical structure of an F16CuPc.

FIGURE 6.6 (a) Ids–Vds and (b) √Ids–Vgs characteristics of an F16CuPc-based OTFT.

6.2.2.2 C60-BASED n-TYPE OTFT

Fullerene has been considered a promising n-type material due to its highest mobility among other OSCs. A high-quality thin film of fullerene organized under an ultra-high vacuum exhibits the electron mobility comparable to that of amorphous silicon. To obtain a C60 film from amorphous to highly crystalline structure, Faimen et al. reported the range of substrate temperature from room temperature to 250°C [11]. This material is well suited to being deposited on the plastic substrate, thereby preferring to obtain a high-performance, flexible, n-type OTFT. A number of high-performance soluble fullerene derivatives have been investigated during the last decade. Figure 6.7a shows the device structure of a C60-based n-type OTFT, and Figure 6.7b presents the chemical structure of a C60 semiconductor that consists of a soccer ball-like simple structure.

A titanium silicon-dioxide (TiSiO2) layer of 132 nm is sandwiched between 8 and 4 nm SiO2 dielectric layers. Upper and lower layers of SiO2 are employed to stabilize device performance by suppressing gate leakage. Furthermore, the thicknesses of silicon gate and C60 active material are 30 and 60 nm, respectively. The S/D top contacts made up of a bilayer of lithium fluoride (LiF) and aluminum are 1 and 100 nm thick, respectively.

The channel length and width are 100 and 1000 μm, respectively. In addition, the electron affinity for C60 active material is 3.7 eV. The electrical characteristics are illustrated in Figure 6.8. This device demonstrates a current of 5.2 μA at Vds = Vgs = 5 V, owing to the high dielectric constant of 15.7 for multilayers of dielectric that produce a capacitance of 96.5 nF/cm2. The device shows reasonably good performance in terms of mobility, threshold voltage and on/off current ratio, which are obtained as 0.92 cm2/Vs, 1.3 V, and 0.84 × 105, respectively.

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