Field-effect transistor transfer characteristics

Figure 17.3 Output and transfer characteristics of unipolar field-effect transistors with neat Cso (a, c) and neat CuPc (b, d) films. The substrates were treated with 02-plasma and the films evaporated at 375 K substrate temperature. The direction of the hysteresis is indicated by arrows. (Figure adopted from Ref. [27].)...

Flexible picene thin film field-effect transistors have been fabricated using a gate dielectric from poly(tetra-lluoro-/7-xylylene) on a poly(ethylene terephthalate) substrate [39]. These field-effect transistors show /I-channel output/transfer characteristics. A sensing effect for oxygen is observed. The hysteresis in the transfer curves is negligible. The parylene gate can eliminate a reduction in the drain current. 

Fig. 29 a Top contact and b bottom contact field-effect transistor structures for determination of charge-transport properties of organic semiconductors, c Typical output characteristics and d transfer characteristics of an organic field-effect transistor with Spiro-TAD 61 as active material (measurements by T.P.l. Saragi)... 

The field effect transistor method has also been applied for the determination of hole mobilities. For Spiro-TAD 56 in a top-contact structure field effect transistor (Fig. 29a), we measured an apparent mobility of 8 x 10 cm /Vs by evaluating the transfer characteristic in the saturation regime [112]. 

Cobalt-PPy-cobalt nanowire was electrochemically synthesized inside alumina membrane and the field-effect transistors were fabricated by patterning a gate on one side of the cobalt-PPy-cobalt nanowire [409]. The measiued output and transfer characteristics are as good as or better than PPy film field-effect transistors. The gain of the nanowire field-effect transistors could be controlled with successive electrochemical doping of the PPy segment. 

Figure 13.16 shows a SiNW 4 p.m in length and 9.5 nm in width. Figure 13.16a shows the silicon oxide mask. The thickness of the fabricated mask is about 3 nm. After etching, the SiNW is contacted to two platinum electrodes (Fig. 13.16b). The fabricated SiNW is the main element of a field-effect transistor formed by introducing a gate electrode. Here, the gate electrode is situated at the back of a silicon-on-insulator wafer. The output and transfer characteristics of the transistor formed with the SiNW described above are shown in Fig. 13.16d. The output curve (left panel) shows a clear dependence on the gate voltage. The off-state drain current leakage is about 10 A. The device shown above has an on/off current ratio of 10, and it can be used to develop very sensitive biomolecular sensors.

Fig. 2 (a) Output and (b) transfer characteristics of a near-ideal organic field-effect transistor in hole accumulation, (c) Extraction of mobility and threshold voltage from the square root plot of the saturation current... 

Fig. 16 Electron and hole field-effect mobilities of pentacene-based OEETs for different polymeric gate dielectrics depicted in Fig. 15. The respective mobilities have been extracted from transfer characteristics of either unipolar p-channel or unipolar n-channel transistors. For one gate dielectric gold or Ca source/drain metals have been used to define the polarity of the field-effect transistors...

Typical transfer and output characteristics of a solution-processed pentacene FET with channel length L = 20 pm and W = 1000 pm are shown in Fig. 13.7. The characteristics were obtained under ambient conditions. The field effect mobility of the FET is 0.01 cm2 V-1 s-1 at Vg = —20 V. On less typical wafers mobilities as high as 0.25 cm2 V-1 s 1 have been observed. The drain current modulation 1d(Vd = —1 V, Vg = -20 V)/ID(VD = —1 V, VG = 10 V) of 10s is routinely obtained. By improving the uniformity and by reducing the parameter spread the integration level could be increased to about 103 transistors. 

It is of crucial importance that the extracted field-effect mobility and threshold voltage obtained from transistor characteristics are therefore not exclusively channel properties but influenced by the contact formation at the source and drain electrodes. Commonly, the transfer line method (TLM) is used to extract the contact resistance from the OFET current/voltage dependence [69]. The method stems from a conventional technique to estimate contact resistances, and was developed for amorphous silicon TFTs. The prevailing contact resistance is determined by varying the channel length L of the transistor. Since the total resistance is the sum of the channel resistance Vd//d and the total contact resistance R =Ris, +I id), the total resistance 7 tot in the linear region can be written as... 

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