Field-effect transistor stability

Figure 15-29 Operation of a chemicalsensing field effect transistor. The transistor is coated with an insulating Si02 layer and a second layer of Si3N4 (silicon nitride), which is impervious to ions and improves electrical stability. The circuit at the lower left adjusts the potential difference between the reference electrode and the source in response to changes in the analyte solution such that a constant drain-source current is maintained.

Functionalization of pentacene with the specific aim of improving performance in devices is a recent endeavor - the first use of a functionalized pentacene in a field-effect transistor was reported only recently (2003) [26], Functionalization of pentacene has led to the ability to engineer the solid-state arrangement, electronic, and solubility properties of this important semiconductor and to improve its stability and film-forming ability. Recent functionalized pentacene materials have yielded devices with properties comparable with those of the parent acene, have enabled the formation of devices from solution-deposited films, and have even changed the semiconductor behavior of this organic molecule from p-type to n-type. As functionalization strategies are refined, materials with all of the properties necessary for commercial device applications should soon be developed. 

The first section of the book is devoted to industrial applications. In two articles written by two of the major companies active in this field, PolylC and Evonik, the applications that presently attract the most interest fi om a commercial point of view are described. At the same time, the key problems related to the manufacturing of cheap electronics through a printing process are addressed. These two chapters provide an excellent introduction to the more applied aspects of the field and also define the Ifamework for the following chapters in the book, which all address problems that in one way or the other are related to producing organic field effect transistors and to improving their performance and stability. 

Accordingly, in this contribution we will address the transport properties of selected materials, tetracene, diindeno[l,2,3-cd l, 2, 3 -lm]perylene (DIP), etc. (see Figure 25.1), which show different chemical stabilities and susceptibilities on (photo-)oxidation due to their respective aromaticity [11]. The temperature dependent charge carrier mobility proves to be an indicator of high sensitivity for chemical and structural irregularities and can be accessed by injection-free Time-Of-Flight (TOF) and injection-based Field-Effect Transistor (FET) and Space-Charge-Limited-Current (SCLC) studies. 

Novel oligomers based on P-substituted thiophene derivatives were synthesised with the aim to build-up a small molecule organic field-effect transistor (OFET). The developed material, a,o)-dicyano-P,P -dibutylquaterthiophene (DCNDBQT), exhibits exeellent thermal, optical and electrochemical stability. 

Chua, L.L., Ho, P.K.H., Sirringhaus, H. and Friend, R.H., High-stability nltrathin spin-on benzocyclobntene gate dielectric for polymer field-effect transistors, Appl. Phys. Lett, 84, 3400-3402, 2004. 

Ong, B. et al.. Polythiophene-based field-effect transistors with enhanced air stability,... 

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