New insulator strengthens future of Moore's Law

Computer manufacturers are in a constant battle to keep pace with Moore's Law -- which states that processing power will double every 18 months. Lately they've been pushing against the limits of the material with which they work, but some European researchers may have a solution that will sustain the growth of computing speed.

There is a limit to how small microelectronics devices can be made. As the parts get smaller, they reach a point where they no longer perform the function that they are intended to perform -- as the silicon dioxide (SiO2) insulation used in transistors is reduced to a few atomic layers, for example, electrons become able to tunnel straight through the insulation. This restriction results in a limit to how many transistors can be placed on one chip.

In a letter published in the 1 January issue of Nature, Clemens Foerst from the Clausthal University of Technology in Germany and colleagues described how to grow strontium titanate -- an oxide more suitable for the task -- on silicon. Strontium titanate is better suited to be an insulator in transistors because it has a higher dielectric constant (k), which leads to it having a higher capacitance, or the ability to store electric charges.

The upshot of this is that chip manufacturers will be able to keep cramming more transistors on a chip and to continue doubling processing power every 18 months.

"Transistors are switches for electrical current," Foerst told ZDNet Australia . "By applying a small voltage to the 'gate', a current between two contacts (that is, source and drain) can be switched on and off. The most important driver for the speedup of microelectronic devices has been the miniaturisation of transistors. The closer the two contacts are together, the faster the switching."

Until now, the problem has been finding a material with a high dielectric constant (high-k) that also displayed the other useful qualities of silicon dioxide, which include being hard, tough and dense, water and heat resistant, being deposited as a vapour and piled up nearly defect free.

Using computer simulations, Foerst and his colleagues have explained the process of forming the strontium titanate layer on silicon, and thus predict how the electrical properties can be controlled.

"We now understand the chemistry of the interface formation between the two building blocks (that is, silicon wafer and the strontium titanate) and the interplay of the atomic species involved," said Foerst. "This knowledge is crucial in order to focus research and to design and optimise deposition processes. Without understanding the basic chemical processes, the experimentalist has to rely on trial and error… [and] is virtually blind."

"If strontium titanate (or maybe in the end another high-k oxide?) is used in transistors, the industry will be able to follow Moore's law," said Foerst. He expects strontium titanate -- or a different crystalline high-k oxide -- will have to be used in transistors by 2010 keep up the pace of innovation.

"As there is roughly a four year gap between research and production, the development phase should be finished in 2006," said Foerst. "After the chemistry is understood now, engineers now have to design processors and build prototypes. New materials also require new production lines in the factories, which have to be designed after research is finished. It is getting tight."

Clausthal University of Technology has applied for a patent on the technology.