silicon chip ;- Electricity and Light in One Chip

Electricity and Light in One Chip

Today's computer chips are chunks of silicon that use electrical pulses to crunch data. But IBM researchers are now making chips for tomorrow: chunks of silicon that also contain pathways for light pulses.

These optical circuits can exchange information with the conventional, electronic circuits in the same chip. This could transport data inside a computer significantly faster, because light signals can transport larger quantities of data at higher speeds than conventional copper electrical wiring can. A chip could use its optical—photonic—circuits for high-speed input and output.

"We need faster ways to shuttle information around," says Solomon Assefa, a member of the research team at IBM's Watson Research Center in Yorktown, New York. "Our main motivation is to build, in five years or so, exascale systems that will be 1,000 times faster than what we have now."

Today's supercomputers are dubbed "petascale" because their power is measured in petaflops, or quadrillions of floating-point operations per second. The U.S. Department of Energy has urged the development of machines capable of exaflops—quintillions of operations per second—to enable more powerful simulation-based research into climate change and renewable and nuclear energy.

Over the past seven years, IBM's researchers have developed a chain of individual silicon components that together can convert a chip's electrical signals into light signals and back again. Now they've found a way to build all of those components on the same chip without inhibiting the transistors' performance, using the standard complementary metal-oxide semiconductor (CMOS) techniques used to build processors and other chips today.

Now that this goal has been achieved in the lab, says Assefa, "the next step is to transfer this to a commercial fab, like those making chips today." Although the technology is not expected to be market-ready for around five years, IBM is keen to test its techniques on the production equipment for which they are designed.

This is a significant advance, says Bahram Jalali, a professor of electrical engineering at the University of California, Los Angeles, who helped kick-start silicon photonics when he developed the first silicon laser in 2004. "Integration with CMOS is a very difficult thing that has been a vision of many in the field for some time," he says.

Other companies have been developing silicon photonics as well. Earlier this year, Intel unveiled a collection of dedicated photonic chips that can be used to carry data between conventional electronic chips. Caltech spinoff Luxtera puts photonic components on a silicon wafer after the electronic silicon components have been completed.

IBM's technology can be more compact than either of these, says Assefa. "We're integrating on the same chip as the electronics, using the same piece of silicon, for both transistors and photonics," he says. "That means we're able to make much finer features and build the much denser and power-efficient structures needed to target future high-end systems." IBM's technology can fit a photonic transceiver—able to send and receive optical signals—into a space 10 times smaller than has been demonstrated before.
That's possible using new designs of photonic components that can be made at the same stage in the CMOS process in which transistors are etched, when lithography techniques precise to just tens of nanometers can be used. But it required some creative thinking to allow optical and electronic components to be built side by side.
For example, to create the last component, IBM researchers had to reinvent their photodetector, which receives incoming optical signals. "We wanted to use a layer of germanium, which is already used in CMOS processing, but had to find a way not to use too thick a layer, which would inhibit the transistors," says Assefa. The team figured out that carefully spaced tungsten "plugs" in contact with a germanium layer thin enough not to harm nearby transistors gave it the desired electronic properties.
Finding ways to design very small photonic components is impressive, says Jalali, because they have typically been orders of magnitude larger than electrical ones, such as transistors. "They have done well to lower, if not remove, that particular barrier," he says. "IBM has emerged as the industry leader at this stage." However, he points out that further big leaps in miniaturization are unlikely. The light-carrying portions of IBM's components have been scaled down to near the diffraction limit, the fundamental limit physics places on the size of optical components for any given wavelength of light. "That is a more difficult barrier to get around," says Jalali.

 

ibm :- IBM Makes Photonics Breakthrough

It may not be quite as exciting as a photonic transistor, but IBM’s latest technology breakthrough still raises hopes of a tremendous increase in computing power owing to photonic technology. The company’s new technology, dubbed CMOS Integrated Silicon Nanophotonics, integrates electronic and photonic devices onto the same silicon chip, potentially allowing faster and higher-performance connections between racks, servers, chips, and even devices on the chip.

Although the new technology does not have any immediate implications for increasing the speed of a processor, it has tremendous promise in the area of supercomputing, as well as in more mundane computers and computer networks. According to PhysOrg.com (“IBM's breakthrough chip technology lights the path to exascale computing”), the technology uses “the front-end of a standard CMOS manufacturing line and requires no new or special tooling.” As a result, the technology has greater potential for commercial success right from the start.

The technology permits greater integration of photonic devices, allowing the use of light pulses for communication among servers, devices, or chips. This technology, if IBM is able to flesh it out into a viable device or product, could help the company meet its goal of constructing an “exascale” computer by 2020. An exascale computer would be able to perform on the level of exaflops: 1018 computations per second (that’s a million trillion—or a billion billion—computations per second). Current supercomputers operate in the petaflop (1015 computations per second) range. Thus, IBM is hoping that its new nanophotonics technology will yield a 1,000-fold increase in computing power.

Again, this technology doesn’t increase processor speed. But processor speed is certainly not the only factor when it comes to computing power. In large-scale computing especially, individual processors are limited in performance by delays in, for instance, retrieving data from storage or even caches. These delays drive the need for each device (processor, cache, storage device, or other device) to be in close proximity to other devices. Furthermore, the speed of light places a fundamental limit on how quickly information can be transmitted across a given distance. Optical interconnections among devices, however, are in many ways superior to copper interconnections. Fiber optics is a widely used method of transmitting large amounts of information over long distances in a relatively inexpensive and reliable manner.

Applying a similar principle on a smaller scale—in particular, on the scale of a single chip—has yet to be realized, however. IBM is hoping that its nanophotonics technology will be the key to unlocking this new realm of possibilities. By speeding communication between devices and components on a chip, some of the limitation placed on processors by the (lack of) proximity to partner devices is removed. Of course, the fundamental limit remains—transmitting data over one meter, for instance, will always take at least 3.33 nanoseconds (at least if you believe the theory of special relativity). But IBM’s new technology may help bring current interconnects closer to this limit.

Although IBM’s focus for its new technology is limited to interchip connections, it is not discounting the possibility of reaching an even finer level of communication. According to Computerworld (“IBM chip breakthrough may lead to exascale supercomputers”), IBM photonics research scientist Will Green expressed hopes for enhanced intrachip connections, but the technology is not yet developed to that point: “There is a vision for the chip level, but that is not what we are claiming today.”

For supercomputing, the implications of a successful application of IBM’s technology are clear: greatly expanded potential computing power. Data centers may also benefit, although the benefits may be less pronounced. Nevertheless, the integration of photonic devices directly on silicon chips—and with no special new tooling technology beyond standard CMOS—could yield improved computing power. Furthermore, such integration may also open up possibilities for other technologies as more devices of different kinds become able to coexist on individual chips. As the DCJ has noted with other newly announced technologies, the proof really is in the pudding. Although the new IBM photonics technology sounds great with its promises of greatly increasing computing power, it’s only as good as a working device that employs it. Although development of a new technology is admirable, application of that technology to produce a result that yields a real and measurable performance improvement is even more admirable. In the meantime, we can only wait and see what IBM is able to do with this technology.


Read more about chips by jeffrey clark