Transistor performance, enhanced

Symmetrical placement of the ion-selective membrane is typical for the conventional ISE. It helped us to define the operating principles of these sensors and most important, to highlight the importance of the interfaces. Although such electrodes are fundamentally sound and proven to be useful in practice, the future belongs to the miniaturized ion sensors. The reason for this is basic there is neither surface area nor size restriction implied in the Nernst or in the Nikolskij-Eisenman equations. Moreover, multivariate analysis (Chapter 10) enhances the information content in chemical sensing. It is predicated by the miniaturization of individual sensors. The miniaturization has led to the development of potentiometric sensors with solid internal contact. They include Coated Wire Electrodes (CWE), hybrid ion sensors, and ion-sensitive field-effect transistors. The internal contact can be a conductor, semiconductor, or even an insulator. The price to be paid for the convenience of these sensors is in the more restrictive design parameters. These must be followed in order to obtain sensors with performance comparable to the conventional symmetrical ion-selective electrodes. 

Even though the origin of the improvement in OFET device characteristic upon a thermal treatment seems unveiled it is still unclear what causes the enhancement due to electrical cyclic stress. Flowever, additional experiments have shown that a electrical cyclic conditioning of annealed transistors does not yield a significant additional improvement in the device performance. We therefore suggest that the observed OFET improvement for both device treatments, have the same consequence. This implies that the electrical cyclic conditioning also leads to a promoted oxidation of the metallic fraction in the Ca passivation, as discussed for the substrate aimealing. 

As with pentacenes, silylethynylated anthradithiophene derivatives (9e-9g) (Figure 3.1.4) with substituents on the central aromatic ring have also been synthesized. [92] OTFTs fabricated with the trimethyl (9e) and triisopropyl (9g) derivatives showed negligible transistor characteristics while those with triethyl derivative (9f) deposited by solution gave a mobility of 1.0 cm V- s" with on/off ratio of 10 . The excellent performance of 9f was attributed to the enhanced Jt-orbital overlap observed in its crystalline thin-film structure. 

To map temperatures with the active matrix, it is very important that the thermal sensors respond strongly to temperature, while the change of performance of switching transistors remains small. Indeed, as mentioned earlier, the organic diode-based sensors exhibit a current enhancement by a factor of 20 when the temperature is varied from 30 to 160°C under the same conditions, the current of the organic transistors changed only by a factor of three. 

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