April 2002

Motorola's Superchip

Silicon is cheap; "compound semiconductors" are fast. Combining the two could yield cheaper cell phones and DVD players.

By Ivan Amato

While lying on the beach during a vacation on the Spanish coast in 1999, physicist Jamal Ramdani had an epiphany. As the sand complied to the contours of his body, Ramdani, a researcher at Motorola Labs in Tempe, AZ, suddenly envisioned a solution to a puzzle that had perplexed the semiconductor industry for 30 years: how to combine cheap silicon with high-speed, light-emitting but far more expensive semiconducting materials like gallium arsenide, all on a single wafer.

Because the materials are physically mismatched, layering one on top of the other to produce a chip with optimal electronic and optical properties has been virtually impossible. It may have been the sand on that Spanish beach, which is made of the same mineral from which silicon wafers are derived, that provided Ramdani with the pivotal hint. In any case, Ramdani recalls, "I came back to Phoenix, borrowed a machine for growing compound semiconductors, and in two or three shots, we had gallium arsenide sitting on silicon."

The benefits of having the functionality of gallium arsenide-particularly its abilities to handle wireless communications and emit light-on an inexpensive silicon chip were not lost on Motorola executives. High-performance chips made out of gallium arsenide and other so-called compound semiconductors are widely used in everything from cell phones to switches in optical communications networks. At the very least, Ramdani's invention could mean replacing these costly chips with far less expensive gallium-arsenide-on-silicon ones. In the two years since Ramdani's breakthrough, Motorola has filed over 300 patents on the technology; last fall, the company used Ramdani's method to build prototype chips for boosting signals in cell phones. To commercialize the new material, Motorola has started up a wholly owned subsidiary-Thoughtbeam, in Austin, TX-promising the new materials will find their way into electronic and optical devices within the next two years.

The impact of Motorola's chip technology could go far beyond cheaper cell phones or optical devices. Today, if you want a fast, inexpensive microprocessor, you need a silicon chip; if you want a chip to handle optical functions or high-frequency radio signals, you need compound semiconductors like gallium arsenide or indium phosphide. As a result, equipment like cell phones and communications network switches requires multiple semiconductor devices. Eventually, predict some experts, the Motorola technology could make it possible to integrate the functions of gallium arsenide and silicon on a single chip, using each of the materials for what it does best. The result would be a superchip. Instead of having multiple chips in a DVD player doing different tasks-generating light to read the disc, fielding input from viewers, decoding digital data into images and sound-a single chip could handle it all.

The semiconductor industry has been dreaming of such a superchip for decades-and a number of researchers are actively pursuing that dream. For instance, Eugene Fitzgerald, a materials scientist at MIT, has been working on the problem for over a decade and has published descriptions of his own technique for growing gallium arsenide on silicon. He and many other skeptics question whether the Motorola technology will prove to be a grand slam. "Every few years, there is a so-called solution, but upon closer examination, you see that it isn't one at all," says Fitzgerald.

Others, however, are so impressed with the potential of Ramdani's breakthrough that they believe the technology could fundamentally change the dynamics of the chip-making business, finally bridging the materials divide between silicon and compound semiconductors that has become a fundamental fact in the industry. According to Steve Cullen, director and principal analyst of semiconductor research services at Cahners In-Stat Group, the Motorola advance could "go down in history as a major turning point for the semiconductor industry."