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Tiny Transistor: Step Toward Molecular-Scale Electronics
CELIA HENRY
The company that invented the first transistor more than 50 years ago has now developed what it claims is the first truly molecular-scale transistor. The critical dimension of the new transistor--which affects output current and switching speed and is known as the channel length--is the length of just one molecule, only 1–2 nm.
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| MINIATURIZERS Schön (right) and coworker Zhenan Bao devised first molecular-scale transistor. |
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| COURTESY OF BELL LABS |
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A Bell Labs team led by physicist Hendrik Schön has created field-effect transistors made with monolayers of conjugated organic molecules built on top of doped silicon, which is structured with vertical steps [Nature, 413, 713 (2001)].
One of the challenges in constructing such small transistors is making the electrical contacts. Schön and his colleagues let self-assembly do the work. The organic molecules--4,4´-biphenyldithiol, for example--self-assemble on a thin layer of gold that serves as one electrode; a second gold layer deposited on top of the organic molecules serves as the other electrode.
Using this device, the researchers were able to demonstrate gain of more than five orders of magnitude. In addition, two of these transistors were used to build an inverter circuit, which switches a "0" input to a "1," or vice versa. In the present device, about 1,000 molecules--the ones closest to the vertical portion of the step, which serves as a third, or "gate," electrode--are actively involved. Future work will explore whether such amplification and switching can be achieved with single molecules.
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