Tag Archives: silicon

Atom-Thin Processor

An international team of researchers has reported a breakthrough in fabricating atom-thin processors — a discovery that could have far-reaching impacts on nanoscale chip production and in labs across the globe where scientists are exploring 2D materials for ever-smaller and –faster semiconductors.

The team, headed by New York University Tandon School of Engineering Professor of Chemical and Biomolecular Engineering Elisa Riedo, outlined the research results in the latest issue of Nature Electronics.They demonstrate that lithography using a probe heated above 100 degrees Celsius outperformed standard methods for fabricating metal electrodes on 2D semiconductors such as molybdenum disulfide (MoS₂). Such transitional metals are among the materials that scientists believe may supplant silicon for atomically small chips.

The team’s new fabrication method — called thermal scanning probe lithography (t-SPL) — offers a number of advantages over today’s electron beam lithography (EBL). First, thermal lithography significantly improves the quality of the 2D transistors, offsetting the Schottky barrier, which hampers the flow of electrons at the intersection of metal and the 2D substrate. Also, unlike EBL, the thermal lithography allows chip designers to easily image the 2D semiconductor and then pattern the electrodes where desired. Also, t-SPL fabrication systems promise significant initial savings as well as operational costs: They dramatically reduce power consumption by operating in ambient conditions, eliminating the need to produce high-energy electrons and to generate an ultra-high vacuum. Finally, this thermal fabrication method can be easily scaled up for industrial production by using parallel thermal probes.

Source: https://engineering.nyu.edu/

High Power Generator Utilizes Thermal Difference Of Only 5ºC

Objects in our daily lives, such as speakers, refrigerators, and even cars, are becoming “smarter” day by day as they connect to the internet and exchange data, creating the Internet of Things (IoT), a network among the objects themselves. Toward an IoT-based society, a miniaturized thermoelectric generator is anticipated to charge these objects, especially for those that are portable and wearable.

Due to advantages such as its relatively low thermal conductance but high electric conductance, silicon nanowires have emerged as a promising thermoelectric material. Silicon-based thermoelectric generators conventionally employed long, silicon nanowires of about 10-100 nanometers, which were suspended on a cavity to cutoff the bypass of the heat current and secure the temperature difference across the silicon nanowires. However, the cavity structure weakened the mechanical strength of the devices and increased the fabrication cost. To address these problems, a team of Japanese researchers from Waseda University, Osaka University, and Shizuoka University designed and successfully developed a novel silicon-nanowire thermoelectric generator, which experimentally demonstrated a high power density of 12 microwatts per 1cm2, enough to drive sensors or realize intermittent wireless communication, at a small thermal difference of only 5ºC.

Because our generator uses the same technology to manufacture semiconductor integrated circuits, its processing cost could be largely cut through mass production,” says Professor Takanobu Watanabe of Waseda University, the leading researcher of this study. “Also, it could open up a pathway to various, autonomously-driven IoT devices utilizing environmental and body heats. For instance, it may be possible to charge your smartwatch during your morning jog someday.”

The newly developed thermoelectric generator lost the cavity structure but instead shortened the silicon nanowires to 0.25 nanometers, since simulations showed that the thermoelectric performance improved by minimizing the device. Professor Watanabe explains that despite its new structure, the new thermoelectric generator demonstrated the same power density as the conventional devices. More surprisingly, thermal resistance was suppressed, and the power density multiplied by ten times by thinning the generator’s silicon substrate from the conventional 750 nanometers to 50 nanometers with backside grinding.

Source: https://www.waseda.jp/

Harvesting Clean Hydrogen Fuel Through Artificial Photosynthesis

A new, stable artificial photosynthesis device doubles the efficiency of harnessing sunlight to break apart both fresh and salt water, generating hydrogen that can then be used in fuel cells.

The device could also be reconfigured to turn carbon dioxide back into fuel.

Hydrogen is the cleanest-burning fuel, with water as its only emission. But hydrogen production is not always environmentally friendly. Conventional methods require natural gas or electrical power. The method advanced by the new device, called direct solar water splitting, only uses water and light from the sun.

If we can directly store solar energy as a chemical fuel, like what nature does with photosynthesis, we could solve a fundamental challenge of renewable energy,” said Zetian Mi, a professor of electrical and computer engineering at the University of Michigan who led the research while at McGill University in Montreal.

Faqrul Alam Chowdhury, a doctoral student in electrical and computer engineering at McGill, said the problem with solar cells is that they cannot store electricity without batteries, which have a high overall cost and limited life.

The device is made from the same widely used materials as solar cells and other electronics, including silicon and gallium nitride (often found in LEDs). With an industry-ready design that operates with just sunlight and seawater, the device paves the way for large-scale production of clean hydrogen fuel.

Previous direct solar water splitters have achieved a little more than 1 percent stable solar-to-hydrogen efficiency in fresh or saltwater. Other approaches suffer from the use of costly, inefficient or unstable materials, such as titanium dioxide, that also might involve adding highly acidic solutions to reach higher efficiencies. Mi and his team, however, achieved more than 3 percent solar-to-hydrogen efficiency.

Source: https://news.umich.edu/