Small smaller

A new method to fabricate smallest transistors may revolutionise the chip industry

Published: Wednesday 31 December 1997

the number of transistors in a single chip has been growing steadily for many years. Simultaneously, the size of transistors has been shrinking at a faster rate. Most researchers believe that after a certain point, the shrinking of transistors size would stop as there is a lower limit for the transistors to work efficiently. The limit for the size of the transistor gate -- the part of the transistor responsible for switching on and off -- is normally considered to be about 30 nanometres. One nanometre is a billionth of a metre.

Researchers at nec s Fundamental Research Laboratories, Tsukuba, Japan, however, report that they have developed a transistor which has a gate of only 14 nanometres. If the device is produced commercially, it would have far reaching implications on the microelectronics industry ( Science , Vol 278, No 5337).

For fabricating the ultra-small gate, the researchers modified the design of a commonly used transistor known as metal-on-oxide semiconductor field effect transistor ( mosfet) . The device uses a central channel that lies between the source and drain regions of the electrons. The gate electrode is present above the channel that controls the channel's conductivity. Hence, electron flows between the source and the drain. The researchers at nec added another gate electrode on top of the lower gate.

This extra gate allows the formation of ultra-shallow drain and source regions, which allow much narrower gate to control it. Designing such a modified device is not easy with conventional lithographic techniques that are used for microelectronics fabrication. So the nec scientists used a sharply focused electron beam along with a new high resolution organic material to fabricate the device.

The demonstration of the ultra-small device does not mean that the commercial application of the transistor is around the corner. There are many hurdles yet to be crossed before the new technology could be applied in electronics. It is hard to pack these transistors closely onto a chip. Also the device uses a lot of power compared to conventional ones. But the researchers are hopeful of overcoming all these shortcomings and manufacture such transistor at commercial level.

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