The way to overcome this, Gargini explains, is to add thin layers of “buffer” materials on the silicon that have an atom spacing similar to it, then gradually adjust the chemical compositions of the buffer layers, until they have atom spacing similar to that of indium antimonide. Finding the ideal chemical ratios to provide the best buffer layers will be one of the major challenges to integrating indium antimonide on Intel’s existing silicon platform, he says.
In addition to finding the best buffer for the InSb “islands” on the silicon wafer, according to Jesus del Alamo, an electrical engineer at MIT who specializes in microelectronics, engineers must also consider the insulating layer, the “gate dielectric,” on top of the transistor, which is crucial to the electrical operations of the device. Currently, silicon transistors use a layer of silicon dioxide as the gate dielectric. For compound semiconductors, though, silicon dioxide does not work as an insulating material, says del Alamo. The interface quality between compound semiconductors and silicon dioxide is not good enough and the dielectric constant of silicon dioxide is too small. Therefore, a whole new class of high-quality gate dielectrics will need to be developed. “That will be a huge challenge,” he says.
Del Alamo still believes, however, that such hurdles will be overcome as the field matures. “I’m very optimistic that we’ll come up with these breakthroughs,” he says.
Intel’s Gargini expects that the technology, which Intel began researching about three years ago, will move toward manufacturing in about another decade. He also emphasizes that compound semiconductors are only one of a number of possibilities for future microprocessors. In fact, Intel has many ideas in the works, from extreme ultraviolet lithography, for making silicon transistors smaller, to developing silicon lasers, modulators, and detectors, in which beams of light instead of copper wires could be used to transmit data within a chip (see “Intel’s Breakthrough”). “Don’t expect [compound semiconductors] in a product tomorrow,” Gargini says. “But it’s in the pipeline.”
Home page image courtesy of Jesus del Alamo, electrical engineer, department of electrical engineering and computer science, MIT. Caption: Chip with transistors and test structures made of the compound semiconductor indium gallium arsenide (InGaAs). Chip is used to diagnose device operations.