Hybrid race car of transistors debuts

Fast device requires very little energy

Combining the engines of a Ferrari and a Honda Civic would not lead to a fast, fuel-efficient car. Yet the simple trick of coupling a power-sipping transistor to a high-speed one has created a transistor that excels in both categories without any obvious weaknesses.

“This is a great advancement,” says Adrian Ionescu, a nanoelectronics engineer at the Swiss Federal Institute of Technology in Lausanne. “And we already have all the materials needed to build it, so I think they can very quickly implement it in industry.” The new transistor could soon find its way into the flash memory chips that store data in computers, tablets and smartphones, Ionescu says.

Transistors, particularly a variety called metal-oxide semiconductor field-effect transistors, or MOSFETs, are building blocks of the electronic age. They have gates that rapidly open and close to control the flow of electric current within microprocessors and memory chips.

For decades, engineers have shrunk transistors, providing increased computing muscle and data storage in the same space. But now transistors can’t get much smaller. The gates of current MOSFETs are so thin — just several atoms wide — that electrons can burrow through via a phenomenon called quantum tunneling. Scientists have successfully harnessed these tunneling electrons in flash memory chips, but the process requires a lot of energy, most of which goes to waste. “The main showstopper in consumer electronics is power consumption,” Ionescu says.

Electrical engineer Peng-Fei Wang at Fudan University in Shanghai was familiar with MOSFETs, but his expertise was another type of transistor called a tunneling field-effect transistor, or TFET. This relatively new technology cannot compete with MOSFETs for speed, but it can function on very small amounts of energy. Since 2001, Wang has worked to integrate TFETs into mainstream electronics.

In the Aug. 9 Science, Wang and colleagues describe how they built a modified MOSFET with an embedded TFET. Like other MOSFETs used in flash memory, the new transistor exploits quantum tunneling electrons, but the presence of the TFET allows it to run on very little energy. Low power consumption translates to high speed because it takes less time for the circuit to build up the energy threshold required for the transistor to work.

Wang says his hybrid transistors should seamlessly make their way into standard memory chips because the transistors don’t require new materials or manufacturing methods. That could allow mobile devices to have better battery life, quicker reading and writing times to the flash memory inside and greater longevity. Wang’s team says that the transistors remain reliable for a quadrillion operations, a billion times as efficient as existing technology.

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