Sapphire chips linked by light

By Kimberly Patch, Technology Research News

One of the challenges of making computer chips is efficiently ferrying information into and out of them. This is usually done via metal wires. Researchers from Johns Hopkins University have worked out a way to speed information to and from chips using light rather than wire.

The method is a way of using the fiber optics technology that make high-speed networks fast to bring information directly onto a chip. The ones and zeros of digital information are transmitted through wires using the absence or presence of electrical current. The same type of information is transmitted through fiber optics using the absence or presence of a pulse of light. Fiber optics is much faster than electronics, because pulses of light can be sent through fiber much faster than an electrical switch can flip on and off.

To transmit information to a chip using light, the researchers had to change the structure of the chip. The new design could speed information transfer on and off chips by five times.

Computer chips are usually made up of thin slices of the semiconductor silicon. The researchers added layers of synthetic sapphire, an insulator that does not conduct electricity, but allows light to pass through.

They used microlasers to beam light perpendicular to the plane of the wafer, and bonded microdetectors onto the sapphire layer of the chip to pick up the light transmissions. "The light is transmitted through the plane of the electronics," said Alyssa Apsel, a graduate student at Johns Hopkins University.

Once the signal reaches its destination, it goes through an optical receiver that transforms the light signal back to an electrical signal that can be handled by the chip's electrical wiring.

The researchers' prototype is capable of shunting information on and off the chip at the rate of one gigabit per second, according to Apsel. Four minutes of full-motion video contain about one gigabit of information.

As the parts of the chip get smaller, chip communications get faster because information does not have as far to travel. The components of the researchers prototype are half a micron wide. The next generation of the researchers chip will have features as small as 0.1 microns, a size equivalent to today's production electronics, said Apsel. A micron is one thousandth of a millimeter.

At 0.1 microns, the researchers' design has the potential to run at 5 gigabits per second, said Apsel. Today's production computer chips have bus speeds that are generally below one gigabit per second. The design is also fairly power efficient, according to Apsel. The 0.5 micron prototype uses about 10 microwatts, and the next generation may use less, she said.

The new chip design could be used to improve the internal rates of data transfer among chips in a computer. It could also be used to improve the speed of information transfer in future Local Area Networks, said Apsel. There is also a biological application, she added. "There are uses in biological sensory systems... which require a higher level of circuit-to-circuit connectivity than current systems are capable of," she said.

The researchers are working on improving the efficiency of their design, and producing larger arrays of opto-electronic links. "We would like to ultimately build very high-performance systems using optical interconnects," said Apsel.

It will be a few years before the technology can be made practical, Apsel said.

Apsel's research colleague is Andreas Andreou. They published the research in the third quarter, 2001 issue of the IEEE Circuits and Systems magazine. The research was funded by the Army Research Laboratory (ARL) and the Defense Advanced Research Projects Agency (DARPA).

Timeline:   3-5 years
Funding:   Government
TRN Categories:  Optical Computing, Optoelectronics and Photonics; Integrated Circuits
Story Type:   News
Related Elements:  Technical paper, "Silicon on Sapphire CMOS for Optoelectronic Microsystems," IEEE Circuits and Systems magazine, third quarter, 2001.


March 13, 2002

Page One

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Sapphire chips linked by light

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