Machine Design

Plugging leaky nanocircuits

The gate dielectric in a transistor electrically insulates the gate from the channel in which current flows.

Silicon dioxide has been the dielectric of choice for over 40 years. But as transistors continue to shrink, gate dielectric gets thinner and that raises current leakage and heat build-up. Intel for its 65-nm process uses a silicon-dioxide gate dielectric just 1.2-nm thick, or roughly five atomic layers, for example.

The company's latest 45-nm transistors, however, replace the silicon dioxide with a slightly thicker hafnium-based high- gate dielectric. The material cuts leakage current more than tenfold, though it is not compatible with silicon, necessitating a special metal gate material. The novel dielectric/metal combination boosts drive current — a measure of transistor performance — by 20%, and cuts source-drain leakage more than fivefold. Moreover, the 45-nm process doubles transistor density compared with 65-nm circuits and chops active switching power nearly 30%.

"The implementation of high- and metal materials marks the biggest change in transistor technology since the introduction of polysilicon gate MOS transistors in the late 1960s," says Intel cofounder Gordon Moore.

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