MURRAY HILL, N.J. -- Silicon chips may reach their performance limits several years later than previous predictions, according to researchers at Lucent Technologies' Bell Labs.

A limiting factor in producing increasingly smaller and faster silicon-based transistors is the transistor's insulating layer. Made of silicon dioxide, the insulating layer on today's chips averages 12 atoms thick.

While other research groups have said that nine to 10 atoms would be the thinnest insulating layer for reliable, practical silicon chips, Ashraful Alam and his Bell Labs colleagues have shown that the intrinsic reliability limit is fewer than six atoms, or 1.5 nanometers.

As a result, the Bell Labs researchers concluded that the "doomsday" scenario for the conventional silicon chip might be delayed until after 2005, instead of the next couple of years as the other research groups had predicted.

"Achieving such thin dimensions with the required intrinsic reliability was previously thought to be impossible," Alam said.

The insulating layer, also known as the gate oxide, is the device's smallest feature. It lies between the transistor's gate electrode, which turns current flow on and off, and the channel through which this current flows. The gate oxide acts as an insulator by protecting the channel from the gate electrode, thus preventing a short circuit.

By continually reducing both the gate oxide thickness and the length of the gate electrode, the semiconductor industry has doubled the transistor's switching speed every 18 to 24 months, following what is known as Moore's Law.

Because the projected intrinsic lifetime of silicon dioxide as an insulating layer has been extended, the semiconductor industry will have more time to develop alternative insulating layers, which will be needed to continue making transistors smaller and smaller. Alternatively, if other insulating materials are not found, totally new semiconductor technologies will be needed.

"These results will help us direct our process development efforts to continue advancing integrated circuit performance for demanding wireless and networking applications," said Gregg Higashi, a technical manager at Lucent's Microelectronics Group.

To obtain their reliability results, the Bell Labs researchers first studied how thicker gate oxide layers withstood high voltages over many days and developed sophisticated computer models to simulate those results. They then used the same physics-based models to show that a transistor with a 1.5-nanometer gate oxide operating at three volts for several hours would be comparable to a similar transistor operating at one volt for 10 years - a very strong reliability indicator.

This theoretical work by Alam, Jeff Bude and Andrea Ghetti is confirmed by experimental work on ultra-thin gate oxides. Using conventional manufacturing techniques, Bell Labs researchers Yi Ma and Melissa Brown made the ultra-thin gate oxides by growing atomic layers that were exceptionally uniform and smooth. Bonnie Weir and Paul Silverman then tested the reliability of the transistors to show that the previous experimental work on ultra-thin oxides from other research groups had yielded unduly pessimistic results.

The Bell Labs researchers presented their research results about gate oxide reliability last week at the International Reliability Physics Symposium in San Jose, Calif.

Bell Labs is celebrating its 75th anniversary this year. One of the most innovative R&D entities in the world, Bell labs has generated more than 40,000 inventions since 1925. It has played a pivotal role in inventing and perfecting key communications technologies for most of the 20th century, including transistors, digital networking and signal processing, lasers and fiber-optic communications systems, communications satellites, cellular telephony, electronic switching of calls, touch-tone dialing, and modems. Today, Bell Labs continues to be a haven for some of the best scientific minds. With more than 30,000 employees located in 25 countries, it is the largest R&D organization in the world dedicated to communications and the world's leading source of new communications technologies. For more information on Bell Labs, visit http://www.bell-labs.com.

Lucent Technologies, headquartered in Murray Hill, N.J., USA, designs and delivers the systems, software, silicon and services for next-generation communications networks for service providers and enterprises. Backed by the research and development of Bell Labs, Lucent focuses on high-growth areas such as optical and wireless networks; Internet infrastructure; communications software; communications semiconductors and optoelectronics; Web-based enterprise solutions that link private and public networks; and professional network design and consulting services. For more information on Lucent Technologies, visit its Web site at http://www.lucent.com.

Steve Eisenberg
Lucent Technologies
908-582-7474 (work)
Email:seisenberg@lucent.com

Michael Jacobs
Lucent Technologies
908-582-5330 (work)
Email:mejacobs@lucent.com