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.