NER: Field Effect Transistor Using Long Conjugated Semiconducting Molecular Wires

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0210501GuoThis proposal was received in response to the Nanoscale Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NER category. The focus of this proposal is to study the electrical properties of a special class of molecules, namely, conjugated polymer wires, and to implement transistor structures based on the field effect. Devices based on organic materials have been identified as one alternative for future electronics. The attractive features of molecular electronics are that it provides an opportunity to study a new group of materials on the molecular level, while offering us a whole new micro- and nanoelectronics technology. Currently there are two areas of research in organic electronics, one is molecular electronics, and the other is organic thin film transistor. In the molecular electronics area, there have been several successful demonstrations of experimental working devices. One of the biggest challenges, however, in the application of molecular electronic device is the difficult in connecting individual molecules to form functional circuits. As a result, practical applications of molecular devices have been primarily aimed at memory circuits, where the circuit's layout is relatively simple. In another area, researches on organic thin film transistors (TFTs) based on conjugated polymers and oligomers have been conducted for over a decade, and have been envisioned as an alternative to the more traditional a-Si TFTs. However the extremely low mobility of these organic films has presented an immense challenge, and placed serious limitation to its practical application. Recognizing the technical difficulty in these two ends, we propose to use three types of conjugated macromolecules to implement transistor structures. These molecules are semiconducting conjugated polymers that are in the form of long rigid wires. The PIs will synthesize and fabricate the device such that the two ends of the molecule will covalently bond to the source/drain electrodes. Through a systematic study of this type of molecular transistor, they would like to address both the device performance issues such as whether these semiconducting wires can offer sufficient conductance and drive capability for practical applications, as well as their extendibility to implement simple molecular circuits based on the operation principle of field effect transistor. In comparison with conventional semiconductor devices, a remarkable aspect of molecular wires is that their response may be dominated by quantum coherence effect, possibly even at high temperature. So the proposed molecular wire transistor can also help to understand many outstanding questions on transport phenomenon in such structures. They believe that with advanced nanofabrication technologies and the organic synthesis expertise of this NER team, they are in a unique position to realize the proposed molecular wire transistor, and to study various transport properties in this new class of molecular electronics.