Organic Field-Effect Transistors OFETs

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. 

The first devices of this type appeared in the early 1970s (Barbe and Westgate, 1970). The field of OFETs literally exploded in the mid-1980s when the first claims of flexible polymer electronics were made (Kozeuka et al., 1987). The subject was first reviewed by Horowitz (1998) and hundreds of OFET-related papers have been published since. 

It has been known that operation of OFET is affected by the chemical ambient, namely by the presence of oxygen and humidity. This problem has been conveniently turned into an advantage by promoting OFET as new type of chemical sensor for gases and vapors (Torsi et al., 2000). They lack an explicit quantitative relationship between the concentration of the detected species and the device output. The results are invariably given as change of current or relative change of current.  

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As a class of n-type organic semiconductors, PBI derivatives have received considerable attention for a variety of applications [312, 313], for example, for organic or polymer light-emitting diodes (OLEDs and PLEDs) [314, 315], thin-film organic field-effect transistors (OFETs) [316, 317], solar cells [318, 319], and liquid crystals [320]. They are also interesting candidates for single-molecule device applications, such as sensors [321], molecular wires [322], or transistors [141]. 

The meso-functionalized bis(thien-2-yl)methanes 267 (X=S) and bis(furan-2-yl)methanes 267 (X=0) were used for synthesizing the first neutral meso-functionalized tetrathia[22]annulene derivatives 271 (X=S) and tetraoxa[22]annulene derivatives 271 (X=0) (Scheme 105). The compounds were tested for organic field effect transistor (OFET) studies and have shown good mobilities with p-type semiconductor behavior (11JCS(CC)905,12JCS(CC)121). 

The field known as organic or plastic electronics is centered on field effect transistor (FET)-based circuits mounted on large-area and/or flexible substrates. When the semiconductor is organic, the device is referred to as an organic field-effect transistor (OFET). Work on OFET has been extensively reviewed, most notably and comprehensively in Chemistry of Materials and Journal of Materials Research special issues, to which the one of us has contributed three articles [1-3]. 

In the past decade, the research on organic field-effect transistors (OFETs) has experienced remarkable progress mainly because of the development of novel OFET materials, which have allowed to reach carrier mobility values good enough to compete with amorphous silicon. 

Basics of Organic Field Effect Transistors (OFETs). 278... 

Figure 2. (a) Schematic cross section of an organic field-effect transistor (OFET). (b) Schematic cross section of an organic electrochemical transistor (OECT). The applied source-drain voltage Vd and gate voltage Vg are also shown. 

In the context of organic field-effect transistors (OFETs), two novel 1,4-dithiins, 43-ry and 7>-anti, have been prepared as pentacene analogues <2004JOC2197, 2003JOC9813>, consisting of the parent 1,4-dithiin with a benzo[7]thiophene on both sides <2004TL7943>. 

Fig. 16 Structures of crystalline fluorene co-oligomers used in organic field effect transistors (OFETs)...

Presently there exists a strong research interest in the understanding, development, and optimisation of organic field effect transistors (OFETs) [1, 2]. Two classes of semiconducting organic materials are considered, namely molecular materials which are processed into thin films by vacuum sublimation [1, 2], and polymers which are deposited onto substrates in the form of solutions, for instance by spin coating [3]. In this chapter we report on OFETs based on thin polycrystalline films of the molecular material pentacene (Pc) as the semiconducting material. 

In recent years great effort has been devoted to conjugated polymers as organic field-effect transistor (OFET) active layers [1]. An important parameter relevant to the operation of an OFET is the charge carrier mobility which determines the overall performance of any polymer-based devices. 

Hysteresis effects usually occur in organic field-effect transistors (OFET) or MIS capacitors [1-4], A detailed literature survey will be given in Section 16.2. In spite of the large number of publications, systematic investigations of the hysteresis effects are rare. Examples are discussed e.g. in Ref [5]. 

Assembly, Structure, and Performance of an Ultra-Thin Film Organic Field-Effect Transistor (OFET) Based on Substituted Oligothiophenes... 

DCNDBQT organic field effect transistors (OFETs) were fabricated on a highly doped n-Si wafer with 30 nm silicon dioxide. Firstly, the silicon surface was rinsed with Dl-water, acetone and iso-propanol in order to remove small particles and organic impurities. Secondly, the substrate was treated with oxygen plasma and silanised for 26 hours at 60 °C by hexamethyldisilazane (HMDS) in order to improve the OFET performance [21]. As source-drain contacts of the bottom contact transistors (BOC) gold was used, which was evaporated through a shadow mask on the silieon dioxide (see Figure 5.2). 

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