16 December 2002 -- Agere Systems researchers have unveiled a breakthrough discovery that proves silicon-based integrated circuits (ICs) will still perform reliably even as their transistors continue to shrink. The discovery significantly extends the performance limits of silicon as a semiconductor material beyond current expectations.
The implications of this research - published in the scientific journal Nature - for the electronics industry are far-reaching. With IC companies able to use silicon for many years to come, a move to a more costly and unproven technology for high performance circuitry, in the near term, is unnecessary.
This will allow companies to continue to develop new, innovative electronic products that are higher performing and cost effective for end-users.
There are many challenges to stretching the performance of an IC by squeezing more and more transistors onto individual chips to increase overall performance. However, the most fundamental challenge involves a thin layer of insulation, or dielectric film, that is an integral part of each transistor.
Scientists have been anticipating the limitations of silicon as a semiconductor material for years and are investing heavily in the search for an alternative to silicon as the base material.
"Our discovery shows that silicon has more steam left in it and gives everyone a little breathing room while we try to discover new ways to continue to shrink transistor structures," said M. Ashraf Alam, distinguished member of technical staff at Agere.
Until recently, semiconductor researchers believed silicon dioxide (SiO2) as a thin-film dielectric would not be usable at a thickness of less than 20 angstroms. Historically, silicon field effect transistors used thicker films as gate insulators.
Any small breakdown across this insulator would quickly lead to other defects nearby, resulting in a dramatic increase in leakage, causing failure of the entire chip. Researchers thought that a similar dielectric breakdown in thinner films would also cause chip failure.
Recently, Agere scientists Alam, Kent Smith, Bonnie Weir and Paul Silverman made a major advance in understanding how thinner films behave. Breakdowns in thinner insulators were found to be independent of one another, so they do not "snowball" into the kind of sudden failure seen in devices with thicker films. Alam explained, "As transistors get smaller, this film gets thinner and the time to breakdown becomes shorter.
Researchers had previously found that the breakdown in thin films was not as catastrophic as breakdowns in thicker films, but this work shows how fundamentally different a breakdown in a thin film is.
This allows engineers to calculate the slight increase in leakage current which occurs with time, and demonstrates that, in general, the increase in leakage will not affect the performance of a circuit. This is good news for the communications semiconductor industry, but also for the scientific community at large."
By proving the reliability of the thin dielectric films, researchers essentially extended the limits of silicon as a semiconductor material.
"The work is fundamental to our industry in terms of being able to understand the limits of integrated circuit reliability and how we can continue to stretch the performance of IC devices as we shrink them," said Mark Pinto, vice president, Processing, Aggregation and Switching Division of Agere Systems.
"Without this breakthrough, IC technology at the 130nm node could not be proven to meet standard reliability assurance, and 90nm technology would not offer much performance advantage. Previous-generation IC process technologies could never offer the level of performance that's being required by customers today."
The paper concludes "our results imply that most modern ICs may have been unintentionally over-designed for reliability, and it is possible to design faster ICs with higher operating voltage without sacrificing reliability. While difficult issues do remain, our work effectively removes oxide breakdown as a fundamental roadblock to continued scaling of silicon ICs."
The team will present a related paper providing the details of this work and its implications to various generations of technology at the IEEE International Electron Devices Meeting in December.
More information can be found on Agere's website www.agere.com