Two chips in one: Researchers combine microprocessor materials

Sep 16, 2009 by David L. Chandler
Graduate student Will Chung displays a hybrid chip being developed in Professor Tomas Palacios' lab. The machine in the background is used to combine the semiconductor materials into one chip. Photo - Patrick Gillooly

(PhysOrg.com) -- An MIT team led by Tomás Palacios, assistant professor in the Department of Electrical Engineering and Computer Science, has succeeded in combining two semiconductor materials, silicon and gallium nitride, that have different and potentially complementary characteristics, into a single hybrid microchip. This is something researchers have been attempting to do for decades.

For decades, researchers have been trying to combine semiconductor materials that have different and potentially complementary characteristics into a single microchip. Now, an MIT team has finally succeeded in this effort, an advance that could point to a way of overcoming fundamental barriers of size and speed facing today's silicon chips.

The standard semiconductor material for most of today's computer chips is silicon, and the main way engineers have improved the speed of silicon chips so far is to keep making them smaller. But silicon chips are now approaching their fundamental size limits, says Tomas Palacios, assistant professor in the Department of Electrical Engineering and Computer Science. "We won't be able to continue improving silicon by scaling it down for long," he says. "It's very difficult to make them a lot smaller."

One way around the size limitation is to use new advanced materials for the . "There are several semiconductor materials that offer better performance than silicon," Palacios says. "The problem is, even though they allow for very fast transistors, they cannot compete with silicon in terms of integration and scalability."

A present-day silicon chip may contain more than a billion identical transistors, but researchers run into problems when they try to make similar large numbers of transistors using new materials. "They can make one, 10 or even a few hundred that are really fast," Palacios says, but find it very difficult to make them in larger quantities. Companies have spent decades and billions of dollars building up the technology for making silicon chips efficiently and reliably. Given that long and expensive development process, it's hard for any new material to catch up and be competitive, Palacios says.

Two materials, one chip

But it turns out that most of those transistors on a chip — for example, ones used to store information in the chip memory — don't really need to perform at maximum speed. Only a much smaller number, 5 to 10 percent of the total, are actually carrying out the computations and need to be as fast as possible, he says.

The solution that Palacios and his graduate student, Will Chung, developed is one that many other researchers have tried unsuccessfully to achieve: Combining two different kinds of materials on a single, hybrid chip. Conventional silicon would provide the vast majority of the transistors, while a different semiconductor material with better performance would be used for the transistors that need to work faster.

Palacios and Chung created a chip that combines silicon transistors on the same wafer with ones made from , a semiconductor material that has a much better performance than silicon. The results were initially presented in June at the Device Research Conference in Pennsylvania, and are being published in the October issue of the IEEE journal Electron Device Letters.

Instead of trying to grow the high-performance semiconductor material on top of a silicon chip as others have attempted, Palacios and Chung made the new hybrid chip by embedding a gallium nitride layer into the same type of silicon substrate that is used by the silicon electronics industry. This not only produces a faster chip, but one that is highly efficient (having most of the transistors operate at slower speeds means that the chips do not consume too much energy). Moreover, the chips can be manufactured using the standard technology currently used for commercial silicon chips.

Advantages and challenges

Thomas Kazior, technical director of Advanced Microelectronics Technology at Raytheon Integrated Defense Systems, says the new advance addresses some of the present limitations of both silicon and gallium nitride technology. This could "enable a new class of high-performance mixed-signal and digitally controlled RF [radio frequency] circuits for use in a wide range of Department of Defense and commercial applications," he says.

Besides microprocessor chips, the new integrated technology can be used for other applications such as hybrid chips that combine lasers and electronic components on a single chip, and energy-harvesting devices that can harness the pressure and vibrations from the environment to produce enough power to run the components.

Such hybrid chips could also lead to much more efficient cell phone manufacturing, Palacios says. Present-day cell phones generally use at least four or five separate chips made from different semiconductor materials, "With this technology, you could potentially integrate all these functions on a single chip."

Raytheon's Kazior agrees, saying this technology "provides a path to RF 'systems on a chip.'"

At present, the new technique has been used to make chips that are about one square inch in size. Conventional manufacturing processes typically use larger wafers, 8 or 12 inches in diameter, so the research now is focused on overcoming the difficulties of scaling up the process to produce these larger chips, without sacrificing quality. "We have several ideas in that direction," Palacios says. "We are already discussing with several companies how to commercialize this technology and fabricate more complex circuits." However, it could take a couple of years to get to the point where it could be commercialized, he says.

Kazior says "To be truly usable this technology needs to be scaled to larger-wafer diameters. In addition, challenges of device reliability and thermal management of the high-power [gallium nitride] transistors need to be addressed."

More information: “Seamless On-Wafer Integration of Si(100) MOSFETs and GaN HEMTs” Jinwook W. Chung, Tomás Palacios, et al. IEEE Electron Device Letters, October 2009

Provided by Massachusetts Institute of Technology (news : web)

Explore further: X-ray detector on plastic delivers medical imaging performance

add to favorites email to friend print save as pdf

Related Stories

Graphene could lead to faster chips

Mar 19, 2009

(PhysOrg.com) -- New research findings at MIT could lead to microchips that operate at much higher speeds than is possible with today's standard silicon chips, leading to cell phones and other communications ...

Rensselaer student invents alternative to silicon chip

May 13, 2008

Even before Weixiao Huang received his doctorate from Rensselaer Polytechnic Institute, his new transistor captured the attention of some of the biggest American and Japanese automobile companies. The 2008 ...

Engineers show nanotube circuits can be made en masse

Jul 04, 2008

Most innovations don't go far unless there is a way to turn them into products that are manufacturable on a mass scale. That's why new research on carbon nanotubes, presented June 19 by a group of Stanford electrical engineers, ...

Researchers develop hybrid silicon evanescent laser

Nov 15, 2005

In what promises to be an important advance, researchers at the University of California, Santa Barbara have developed a novel laser by bonding optical gain layers directly to a silicon laser cavity. This hybrid laser offers ...

Recommended for you

Android gains in US, basic phones almost extinct

9 hours ago

The Google Android platform grabbed the majority of mobile phones in the US market in early 2014, as consumers all but abandoned non-smartphone handsets, a survey showed Friday.

Five features an Amazon phone might offer (Update)

10 hours ago

A report this week in The Wall Street Journal that Amazon is planning to release a smartphone has prompted industry analysts and technology blogs to muse about what the device might offer.

LinkedIn membership hits 300 million

11 hours ago

The career-focused social network LinkedIn announced Friday it has 300 million members, with more than half the total outside the United States.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

sender
not rated yet Sep 17, 2009
Softradio technology just took a topological leap. Waiting for when this hits nematic liquid crystals and optronics.

More news stories

LinkedIn membership hits 300 million

The career-focused social network LinkedIn announced Friday it has 300 million members, with more than half the total outside the United States.

Researchers uncover likely creator of Bitcoin

The primary author of the celebrated Bitcoin paper, and therefore probable creator of Bitcoin, is most likely Nick Szabo, a blogger and former George Washington University law professor, according to students ...

Impact glass stores biodata for millions of years

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...