Transistor source electrode

Fig. 125. Top. cross section of the transistor structure. The drain and source electrodes make ohmic contacts with the LB film. The carrier concentration and, therefore, the conductance of the LB film is controlled by the gate. Bottom schematic layout of the finger shaped drain and source electrodes [776]...

An OTFT comprises three electrodes (source, drain, and gate), a gate dielectric layer, and an organic or polymer semiconductor layer. In operation, an electric field is applied across the source-drain electrodes, and the transistor is turned on when a voltage (VG) is applied to the gate electrode, which induces a current flow (fD) from the source electrode to drain electrode. When VG = 0, the transistor is turned off, fD should in theory be 0, that is, no current is flowing. 

A plurality of thin film field effect transistors 11 are deposited onto a substrate 12. Each of the transistors has a source electrode 13, a drain electrode 14 and a gate electrode 15. Source lines 17 link the source electrodes in each row of the transistors and drain lines 18 link the drain electrodes in each column of the transistors. The source lines and drain lines are electrically isolated by a planarization layer 19. A mercury cadmium telluride layer 20 is deposited onto the planarization layer followed by a top electrode layer 23. The gate electrodes are connected with the mercury cadmium telluride layer by connectors 21. A cross-section of the imager is shown below. 

Using impedance spectroscopy we measured transistors with solution processed pentacene as the semiconductor. Fabrication details are discussed in Section 13.3.1. We have made use of a ring-type transistor, in which the source electrode forms a closed ring around the transistor channel and the drain electrode, at which the current is monitored. Using this geometry, the measurements are insensitive to parasitic currents that may flow outside the transistor area [29]. 

Illustrated in Figure 24.4 is the output characteristic of a pentacene OFET with Au drain-source electrodes and a 200 nm Si02 dielectric [32]. The OFET exhibits unipolar p-type behaviour with a hole mobility = 0.165 cmWs, a threshold of = -4.5 V as well as an On/Off ratio of >10. These parameters have been derived from the respective transfer characteristics. The absence of an s-shaped feature in the linear range of the characteristic indicates ohmic contacts between the Au electrodes and the pentacene active layer. This is attributed to the good matching of the ionisation potential of the organic semiconductor and the Au work frmction. However, employing a Ca drain-soirrce metallisation, with an otherwise identical OFET device structure, the transistor did not exhibit any current in the electron accumulation mode. This is unexpected, since the metal work frmction is well matched to the electron affinity of pentacene. 

For a poly(parabanic acid) resin as substrate, a6T as semiconductor, and cyanoethylpullulan, a highly flexible device could be obtained which shows no changes in the transistor characteristic after bending and twisting. However, the metallic gate and source electrodes sometimes disconnect. A really pure all-organic FET with a graphite-based polymer ink used to prepare the source and drain contacts does not even show this instability [305],... 

In 2002, David Nilsson reported an electrochemical transistor using poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT PSS) as the active layer [14]. In this system, both the electronically conducting system (PEDOT) and the dopant are polymers and therefore nonvolatile as the oxidation state of the PEDOT is altered. PEDOT is pristinely doped and is therefore in its high conducting state. This allows us to define the drain, source, and gate as well as the transistor channel in PEDOT PSS solely, see Fig. 9.1. As the gate is addressed positively, vs. the source electrode, PEDOT in the channel is reduced to its neutral state. 

Some applications for conducting polymers (like source, drain, gate, and coimector in organic field effect transistors, [transparent] electrode or raw material for highly conducting paints and lacquers with... 

Fig. 5. Metal-insulated semiconductor field effect transistor with n-channel (n-MISFET). (A) the state with uncharged G-I-Su capacitor, (B) open transistor with charged G-I-Su capacitor. Abbreviations S, source electrode D, drain electrode G, gate electrode Su, substrate Al, aluminium contact I, insulator (dielectric) n-Si, p-Si, n- or p-type of silicone...

A junction field-effect transistor or JFET is a type of transistor in which the current flow through the device between the drain and source electrodes is controlled by the voltage applied to the gate electrode. 

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