Layers OFETs

Simulations for Thin-Layer OFETs and the Corresponding Capacitor... 

Fig. 4.1. A traditional four layer OFET design. When the device is biased so that a sheet of charge is formed between the source and drain, current can flow through the channel when a bias is applied between the source and drain, the details of which depend on the magnitude of the bias. When the device is biased in an operating region which eliminates the sheet charge in the channel, the device is insulating and little current flows, independent of the applied source/drain bias.

For the sake of consistency, the four basic OFET layers will be referred to as the gate layer, gate dielectric layer, source/drain layer, and active layer. OFETs with integrated devices may also re-use one of these four layers for hybrid device integration or introduce additional layers for connectivity or other active device formation. The position of these layers is shown in two idealized OFET cross sections in Fig. 4.12. 

Figure 14-12. Various types of OFETs. (a) Inverted coplanar on a highly doped Si wafer, (b) inverted coplanar on a neutral substrate, (c) inverted staggered oil a neutral substrate, (d) inverted staggered using the dielectric layer as the substrate.

When a third electrode is added to the structure shown in Fig. 8.12a, below the substrate, it creates an electric field in the insulating substrate, which is perpendicular to the path of the current between the two contacts to the selective layer. Such a structure became known as the Organic Field-Effect Transistor (OFET). It is discussed here and not in Chapter 6 because it belongs to the family of organic chemiresistors. 

OFETs with wet-deposited films of 48 as the active layer in bottom contact geometry were fabricated on highly doped n-type silicon wafers with the organic semiconductor layer (ca. 50 nm) deposited from chloroform solution [70], OFETs made from 48 exhibited negative amplification, which is typical of... 

Fig. 2 Molecular structures of some polymers used as insulator layer in the reported phthalocyanine-based OFET devices...

Figure 4 shows the molecular structures of the monomeric phthalocyanines used as the active layer of p-type OFET devices, and Table 1 organizes the performance of these phthalocyanine-based OFETs. As can be seen, unsubstituted metal-free phthalocyanine and its metal complexes, axial substituted metal phthalocyaines, and peripheral tetra-substituted phthalocyanines all can work as p-type semiconductors for OFET devices. Most of the semiconductors composed of peripheral unsubstituted and axial substituted phthalocyanine derivatives are prepared through vacuum deposition method with a few exceptions being made of corresponding single... 

CuPc thin films, and the enhanced physical connection between source-drain electrodes and semiconductor channel associated with the PMMA polymer layer, the OFET performance of this bottom-contact device was significantly improved with leakage current being reduced by roughly one order of magnitude and on-state current enhanced by almost one order of magnitude. The hole mobility of this bottom-contact OFET device reached 0.01 cm2 V-1 s 1, which is comparable with that of top-contact device but much higher than that of normal bottom-contact device without polymer layer [45],... 

By introducing Lewis-acid V2O5 thin film between semiconductor and insulator layers, Minagawa et al. fabricated CuPc-based OFETs that can be turned on by positive gate voltage, which showed improved hole mobility in comparison... 

The thickness dependence of mobility in CuPc-based OFETs on amorphous Si02 substrate was investigated by Gao et al. in 2007 [66], The results demonstrated that the mobility increased with increasing the thickness of CuPc layer and then was saturated at the thickness of 7.8 nm with mobility about 0.008 cm2 V-1 s-1. In 2008, Du and co-workers fabricated CuPc-based OFETs using PMMA and P(MMA-co-GMA) as gate insulators, and the difference between devices with different polymer gate insulators were explained with XRD, AFM, and SEM measuring... 

OFETs with spin coated film of H2TPP from a chloroform solution as active semiconductor layers, Al as gate electrode, and Cd as source-drain electrodes were fabricated by Checcoli and co-workers in 2003 [100]. This device exhibited zero-bias hole transfer mobility of 0.007 cm2 V-1 s-1 with a threshold of —7.5 V and field-dependent mobility, as high as 0.012 cm2 V-1 s-1. 

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