Manufacturing Bits: Oct. 7

Europe’s TFET project; next-gen imprint; valleytronics.

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Europe’s TFET project
A new European project has revealed more details about its plans to develop a next-generation chip technology called tunnel field-effect transistors (TFETs).

EPFL is coordinating this new European research project, dubbed E2SWITCH. The project also includes IBM, Forschungszentrum Jülich, the University of Lund, ETHZ, Imec, CCS, SCIPROM and IUNET. The project has been funded for up to 4.3 million euros over 42 months.

The mission of the project is to develop TFETs at voltages below 0.25V. The devices will make use of SiGe/Ge and III-V materials and other technologies. For example, the project plans to explore new device concepts, such as a density-of-state (DOS) switch exploiting the effects of dimensionality. The DOS switch could deliver a sub-threshold swing less than 10mV/decade.

European project aims to develop the TFET. (Source: EPFL)

European project aims to develop the TFET. (Source: EPFL)

Mobile devices, such as smartphones or smartwatches, could be the first applications for TFETs. “Our objective is to make the next generation of transistors, which can still operate at voltages below 0.3 Volts and even as low as 0.1V,” said Adrian Ionescu, an EPFL professor and the coordinator of E2SWITCH, on the university’s Web site. “Between 125 and 150 degrees, digital circuits begin to lose their functionality. However, our new technology will not only consume less energy, but will be more stable over a wider temperature range, opening the possibility for more robust applications in the automotive and aerospace fields.”

Heike Riel, a fellow at IBM Research in Zurich, added: “Power dissipation is a fundamental challenge for nanoelectronic circuits. Within E2SWITCH we aim to significantly reduce the power consumption of electronics by researching TFETs based on III-V heterostructure nanowires with wrap-around gate and directly integrated on standard silicon substrates.”

Next-gen imprint
The University of Twente has developed a next-generation nanoimprint technology. The process creates nanostructures using tiny stamps.

It combines soft lithography with pulsed laser deposition (PLD), which enables the development of heteroepitaxial patterns of perovskite oxide materials.

The mold used for creating patterns consists of polymer material called polydimethylsiloxane (PDMS). Using PDMS as a mold, a pattern of zinc oxide can be placed on the perovskite. Then, a sandwich of different materials can be made using PLD. Zinc oxide is used because of its compatibility with the high temperatures reached during the PLD process. PLD, or laser ablation, can be used to deposit complex materials on substrates.

Making nanostructures using tiny stamps. (Source: University of Twente)

Making nanostructures using tiny stamps. (Source: University of Twente)

PLD is different than other physical vapor deposition techniques. In PLD, a high power laser is used. The laser evaporates material from a target. The vaporized material, in turn, condenses on a substrate.

Using PLD, the University of Twente MESA+ Research Institute and SolMateS recently put a new twist on the finFET. A piezoelectric stressor layer has been deposited around the finFET, thereby enabling what researchers call the PiezoFET. The PiezoFET could enable steep sub-threshold slope devices. In the lab, this device was also able to reduce the leakage by a factor of five.

Valleytronics
Electronic components store information using the electrical charge of an electron. This requires moving electrons from one point to another, which create unwanted energy consumption.

To harness the properties of electrons, researchers have been exploring the field of spintronics. This, in turn, could one day enable new devices that consume less power.

Riken, the University of Tokyo and Hiroshima University have put a new spin on spintronics. Researchers have devised ultrathin films of a semiconducting material, which forms the basis of a technology called valleytronics.

Valleytronics is based on the behavior of electrons and its band structure. The idea behind valleytronics is to encode information without moving the electrons “Semiconductors and insulators derive their electrical properties from a gap between the highest band occupied by electrons, known as the valence band, and the lowest unoccupied band or conduction band in the band structure,” said Yoshihiro Iwasa of Riken, on the organization’s Web site. “If there are two or more dips in the conduction band or peaks in the valence band, we say that the band structure contains valleys.”

Researchers used spectroscopy techniques to identify valleys in the band structure of an ultrathin layer of molybdenum disulfide. Molybdenum disulfide is a member of a family of 2D materials known as transition metal dichalcogenides.

Researchers created films consisting of one to four atomic layers of molybdenum disulfide. The atoms in the layers were slightly shifted from those in the level beneath, meaning researchers were also to harness the spin of electrons. “We uncovered strong coupling between the valley and spin degrees of freedom,” said Iwasa.


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