Report:A Semi-Floating Gate Transistor for Low-Voltage Ultrafast Memory and Sensing Operation

Report:A Semi-Floating Gate Transistor for Low-Voltage Ultrafast Memory and Sensing Operation

  10:19:00 AM    Science Lover

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Researchers at Fudan University in China have discovered a way to speed up traditional computer transistors by embedding tunneling field-effect transistors (TFETs) in them. In their paper published in the journal Science, the team describes how embedding TFETs in such transistors allows for them to be run with less power, which in turn causes them to run faster.

Schematic view of an SFG memory cell. A pn junction diode between the FG and D makes the FG semi-floating. The device’s symbolic representation is also shown. Credit: Science 9 August 2013: Vol. 341 no. 6146 pp. 640-643 DOI: 10.1126/science.1240961

Most modern computers are run with either metal-oxide-semiconductor field-effect transistors (MOSFETs) or a variation of them called floating-gate (FG) MOSFETs. Such transistors are now reaching their physical limit as far as how thin they can be—just a few atoms thick. For that reason, researchers have been looking for other ways to get more bang for their buck. In this new effort, the researchers turned to TFETs, which use quantum tunneling to move electrons through very thin material.

TFETs have traditionally been used in very low power devices. In this endeavor, they researchers created a TFET that could be used to control the electrodes that monitor the flow of electricity into a MOSFET—in this case, the floating-gate variety (it has an additional electrode gate that allows a charge to be retained). The idea is that if the gate could be made to open and close faster, the transistor as a whole would operate faster. Current chips require a build-up of charge before the gate can be opened or closed—which requires time. TFETs, because they require less power, don't take as long to do their work, thus embedding one in a floating gate-MOSFET would alleviate the necessity of power buildup prior to gate changes, allowing for quicker opening and closing. That's exactly what the team in China has done. Testing thus far has shown MOSFETs with embedded TFETs have improved transistor speeds as well as reduced power requirements.

The team reports that because of the way their TFETs are constructed, embedding them in current model MOSFETs should not require reconfiguration or the use of any new materials. This means that the new TFET technology could be put into use almost immediately, bumping up the speed of computers and hand held devices while lessening the amount of energy used, resulting in longer battery life.

More information: A Semi-Floating Gate Transistor for Low-Voltage Ultrafast Memory and Sensing Operation, Science 9 August 2013: Vol. 341 no. 6146 pp. 640-643 DOI: 10.1126/science.1240961

ABSTRACT

As the semiconductor devices of integrated circuits approach the physical limitations of scaling, alternative transistor and memory designs are needed to achieve improvements in speed, density, and power consumption. We report on a transistor that uses an embedded tunneling field-effect transistor for charging and discharging the semi-floating gate. This transistor operates at low voltages (?2.0 volts), with a large threshold voltage window of 3.1 volts, and can achieve ultra–high-speed writing operations (on time scales of ~1 nanosecond). A linear dependence of drain current on light intensity was observed when the transistor was exposed to light, so possible applications include image sensing with high density and performance.

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Plastic Electronics Could Slash the Cost of Solar Panels

Plastic Electronics Could Slash the Cost of Solar Panels

  11:01:00 PM    Science Lover

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A new technique developed by Princeton University engineers for producing electricity-conducting plastics could dramatically lower the cost of manufacturing solar panels.

Plastic transistor Princeton researchers have developed a new way to manufacture electronic devices made of plastic, employing a process that allows the materials to be formed into useful shapes while maintaining their ability to conduct electricity. In the plastic transistor pictured here, the plastic is molded into interdigitated electrodes (orange) allowing current flow to and from the active channel (green). (Credit: Loo Research Group)

By overcoming technical hurdles to producing plastics that are translucent, malleable and able to conduct electricity, the researchers have opened the door to broader use of the materials in a wide range of electrical devices.

With mounting concerns about global warming and energy demand, plastics could represent a low-cost alternative to indium tin oxide (ITO), an expensive conducting material currently used in solar panels, according to the researchers.

"Conductive polymers [plastics] have been around for a long time, but processing them to make something useful degraded their ability to conduct electricity," said Yueh-Lin Loo, an associate professor of chemical engineering, who led the Princeton team. "We have figured out how to avoid this trade-off. We can shape the plastics into a useful form while maintaining high conductivity."

A multi-institutional team reported on its new technique in a paper published online March 8 in the Proceedings of the National Academy of Sciences.

The area of research, known as "organic electronics" because plastics are carbon-based like living creatures, holds promise for producing new types of electronic devices and new ways of manufacturing existing technologies, but has been hampered by the mysterious loss of conductivity associated with moldable plastics.

"People didn't understand what was happening," said Loo, who co-wrote the paper. "We discovered that in making the polymers moldable, their structures are trapped in a rigid form, which prevented electrical current from traveling through them."

Once they understood the underlying problem, Loo and her colleagues developed a way to relax the structure of the plastics by treating them with an acid after they were processed into the desired form.

Using the method, they were able to make a plastic transistor, a fundamental component of electronics that is used to amplify and switch electronic signals. They produced the electrodes of the transistor by printing the plastic onto a surface, a fast and cheap method similar to the way an ink-jet printer produces a pattern on a piece of paper.

Loo said the technique potentially could be scaled up for mass production presses akin to those used to print newspapers. "Being able to essentially paint on electronics is a big deal," Loo said. "You could distribute the plastics in cartridges the way printer ink is sold, and you wouldn't need exotic machines to print the patterns."

By allowing plastic solar cells to be manufactured using low-cost printing techniques and by replacing ITO as the primary conducting material, the plastics the team developed hold potential for lowering the cost of solar panels.

Currently, the electricity generated by plastic solar cells is collected by a transparent metal conductor made of ITO. The conductor must be transparent so that sunlight can pass through it to the materials in solar cells that absorb the light energy.

A rare and pricey byproduct of mining, ITO had come under increasing demand for use in flat-screen televisions, mobile phones and other devices with display screens. "The cost of indium tin oxide is skyrocketing," Loo said. "To bring down the costs of plastic solar cells, we need to find a replacement for ITO. Our conducting plastics allow sunlight to pass through them, making them a viable alternative."

The researchers anticipate that the plastics also could replace expensive metals used in other electronic devices, such as flexible displays. In addition, the scientists are beginning to explore the use of the plastics in biomedical sensors that would display a certain color if a person had an infection. For instance, the plastics turn from yellow to green when exposed to nitric oxide, a chemical compound produced during ear infections in children.

If the devices could be produced at a low cost, they might be useful in developing countries that lack advanced medical facilities. "You wouldn't need any fancy machines or lab equipment to diagnose an infection," Loo said, "all you would need is your eyes to see the color change in the plastics."

The co-authors of the paper were Joung Eun Yoo, who received her doctorate in chemical engineering from the University of Texas-Austin in 2009 with Loo as her adviser; Kimberly Baldwin, a high school student who spent a summer in Loo's lab; Jacob Tarver, a Princeton chemical engineering graduate student; Enrique Gomez of Pennsylvania State University; Kwang Seok Lee and Yangming Sun of the University of Texas-Austin; Andres Garcia and Thuc-Quyen Nguyen of the University of California-Santa Barbara; and Hong Meng of DuPont Central Research and Development.

The research was supported by the National Science Foundation, the W.M. Keck Foundation and the Arnold and Mabel Beckman Foundation.

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