On-Off Current Ratio

Figure 9.7a shows an example of a-Si H TFT transfer characteristics in linear regime with different W/L ratios and an example of a-Si H TFT characteristics in saturation regime with W/L = 170 pm/6 kpm. A threshold voltage (Vth) of 10 = 11 V, a field-effect mobility (p) of 0.2 0.3 cm2/(V s), a subthreshold swing slope of 0.8 dec/V, and a current ON/OFF ratio of larger than 106 for VGS from —10 to 30 V were obtained from these curves for a-Si H TFTs. These devices were used in 4-a-Si H TFTs AM-PLEDs. The electrical properties of a-Si H TFTs used in 3-a-Si H TFTs AM-PLEDs are described in Ref. [18]. 

The transistor performance is generally characterized by field-effect transistor (FET) mobility (j i), current on/off ratio (f n/f0ff), and threshold voltage (Vj)-... 

It was found that 368 exhibits ambipolar activity with appreciable electron (0.12 cm2 V 1 s ) and hole (0.008 cm2 V 1 s-1) mobilities at the substrate growth temperature of 70°C, and 371 shows monopolar n-type activity with a high mobility of 0.32 cm2 V-1 s-1 for semiconducting films deposited at a substrate temperature of 25°C. 373 exhibits stable n-type activity even in the air although the observed electron mobility in the air (0.01 cm2 V-1 s ) is somewhat lower than that under vacuum (0.08 cm2 V-1 s-1). In the case of 368 films grown at 70°C, both n- and p-type mobilities as well as current on-off ratios are enhanced by orders of magnitude compared to films grown at 25°C. 369 exhibits only p-type activity, with no detectable n-type behavior. Hole mobility extracted from the transfer plot is 5 x 10-14 cm2 V-1 s 1 with... 

TFT devices based on 638, 637, and 636 have been fabricated. Mobilities (p), current on/off ratio (Ion/I0 ) and threshold voltages (Vt) are collected. The data clearly show that both n-type carrier mobility and Ion/Io(( ratios increase with decreasing re-core conjugation length (636 —> 638), approaching 0.05 cm2 V-1 s 1 and 105, respectively. The threshold voltage is 35-42 V for 636 and 637 and 25-30 V for 638. Remarkably similar trends in mobility and I0n/I0 ratio are found in the p-type series. A more detailed study on this type of compounds appeared (04JA13480). 

Dithienosilole-thiophene copolymers 21 (Fig. 10) can show excellent FET performances.38 With the copolymers as the active layer, remarkably high hole mobility from 0.02 to 0.06 cm2/(V s) can be achieved. Furthermore, the FET devices possess high current on/off ratios of 105—106. The FET devices also display impressive stabilities under repeated on/off cycles up to 2000 in air. 

Table 4.3 summarizes the FET mobility and current on/off ratio data for OTFTs prepared using vacuum deposited indolo[3,2-b]carbazoles (5) as the channel semi-... 

Using DHPT-SC as the semiconductor in OFETs, a field effect mobility of 0.012 cmWs and a current on/off ratio of >10 can be realised, which is among the highest OFET mobilities fabricated achieved with solution-processed oligothiophenes. 

X 10 cmWs and a current on/off ratio of 2.5x10 at F s=-80V. The device made from BT7 showed a reduced charge carrier mobility of... 

Figure 6.12 Field-effect mobilities and current on/off ratios of OFET devices annealed at 120 °C for different time intervals, using DHBTP-SC (circles) and DHPT-SC (rectangles) as the semiconductors. Open symbols depict the on/off current ratio whereas solid symbols the field-effect mobility.

Table 1. Spin-coated CPB thin film (<20 nm) deposition condition and pentacene-based TFT device performance (mobility and on/off ratio) - polymer/crosslinker concentration ratio (mg/ml mg/ml), solvent, film thickness (D, nm), RMS roughness (p, nm), leakage current density at an electric field of 2 MV/cm (J, A/cm2), mobility (ji, cm2/Vs), and Current On/off Ratio (/<, /< ) ...

A new class of semiconductors based on a tertiary diamine structure, 5,11-disub-stituted indolo[3,2-/ ]carbazole (15a-15d) (Figure 3.1.5) have been reported.[109,l 10] The derivatives are soluble in organic solvents such as toluene, chloroform, and chlorobenzene. OTFTs using these carbazole derivatives (15a-15d) exhibited p-chan-nel behavior with mobilities of up to 0.12 cm V s and a current on/off ratio of 10 . Recently dichloro derivatives (15e-15f) of these carbazoles gave improved device performance with mobility of 0.14 cm V s . [lll] 2,7-Carbazolevinylene-based conjugated oligomers, 15h-15j, have also been tested in OTFTs.[112,113] The higher mobility of 15h (0.30 cm V s with on/off ratio of 10 ) compared to 15J (10 cm V s with on/off ratio of 10 ) is attributed to the relative coplanar structure of the former and twisted biphenyl units in latter. 

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