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Breakthrough in new materials could be the key to revolutionary transparent electronics

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Flexible, Transparent Electronics


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The optical transparency of the new materials can enable futuristic, flexible and transparent electronics. Credit: RMIT University.

Filling a critical gap in the material spectrum

A new study published this week could pave the way for the next generation of transparent electronics.

Such transparent devices could potentially be embedded in glass, flexible displays, and smart contact lenses to bring futuristic, sci-fi-like devices to life.

For several decades, researchers have been looking for a new class of electronics based on semiconductor oxides, the optical transparency of which could allow this fully transparent electronics to be used.

Oxide devices can also find applications in power electronics and communications technology, reducing the carbon footprint of our utilities.

A team led by RMIT has introduced ultrafine beta-tellurite in a family of two-dimensional (2D) semiconductor materials, providing an answer to this long-term search for a highly mobile p-type oxide.

“This new, highly mobile p-type oxide fills a critical gap in the material spectrum, enabling fast and transparent circuits,” says Team Leader Dr. Torben Daenecke, who led the collaborative work on the three FLEET nodes.

Other key advantages of long-sought oxide-based semiconductors are their stability in air, less stringent purity requirements, low cost, and ease of deposition.

“The missing link in our advance was finding the right, ‘positive’ approach,” says Torben.

Positivity was lacking

There are two types of semiconductor materials. “N-type” materials contain a large number of negatively charged electrons, while “p-type” semiconductors contain many positively charged holes.

It is the amalgamation of n-type and p-type complementary materials that allows electronic devices such as diodes, rectifiers, and logic circuits to be created.

Deposition of molten metal

The molten mixture of tellurium and selenium, rolled over the surface, precipitates an atomically thin sheet of beta-tellurite. Credit: FLEET

Modern life is critically dependent on these materials as they are the building blocks of every computer and smartphone.

An obstacle to oxide devices has been that although many high performance n-type oxides are known, there is a significant lack of high quality p-type oxides.

Theory prompts action

However, in 2018, a computational study found that beta tellurite (β-TeO2) could be an attractive candidate for p-type oxide, with tellurium’s special place on the periodic table means it can behave as a metal or non-metal, providing it oxide with unique beneficial properties.

“This prediction prompted our team at RMIT University to study its properties and applications,” says Dr. Torben Daenecke, FLEET associate researcher.

Liquid metal – the way to explore 2D materials

Dr. Daenecke’s team demonstrated the separation of beta-tellurite using a specially developed synthesis technology based on liquid metal chemistry.

“A molten mixture of tellurium (Te) and selenium (Se) is prepared and allowed to roll on the surface,” explains one of the authors of the article, Patjari Aukaraserinont.

“Due to the presence of oxygen in the ambient air, the melt drop naturally forms a thin surface oxide layer of beta-tellurite. When a drop of liquid rolls over the surface, this oxide layer sticks to it, depositing atomically thin sheets of oxide on its way. “

“The process is similar to drawing: you use a glass rod as a pen, and liquid metal is your ink,” explains Ms. Aucaraserenont, FLEET PhD student at RMIT.

Ali Zawabeti, Patjari Aukaraserinont and Torben Daeneke

RMIT Team (from left to right): Ali Zawabeti, Patjari Aukaraserinont and Torben Daeneke with transparent electronics. Credit: FLEET

While the desired β-phase of tellurite rises below 300 ° C, pure tellurium has a high melting point, above 500 ° C. Therefore, selenium was added to develop alloy which has a lower melting point, which makes synthesis possible.

“The ultra-thin sheets we got are only 1.5 nanometers thick, which equates to just a few atoms. The material was very transparent in the visible spectrum with a band gap of 3.7 eV, which means they are virtually invisible to the human eye, ”explains co-author Dr. Ali Zawabeti.

Beta Tellurite Evaluation: Up to 100X Faster

To evaluate the electronic properties of the developed materials, field effect transistors (FET) were manufactured.

“These devices showed characteristic p-type switching as well as high hole mobility (about 140 cm2V-1s-1), showing that beta-tellurite is ten to one hundred times faster than existing p-type oxide semiconductors. The excellent on / off ratio (over 106) also proves that this material is suitable for energy efficient and fast devices, ”said Ms. Patjari Aukaraserinont.

“The findings fill a major gap in the digital library of materials,” said Dr. Ali Zawabeti.

“Having a fast transparent p-type semiconductor at our disposal could revolutionize transparent electronics, as well as improve displays and improve energy efficient devices.”

The team plans to further explore the potential of this new semiconductor. “Our further research into this exciting material will focus on integration into existing and next generation consumer electronics,” says Dr. Torben Daenecke.

Link: “Highly mobile semiconductor two-dimensional β-TeO2 p-type” April 5, 2021, Nature Electronics
DOI: 10.1038 / s41928-021-00561-5

FLEET researchers from RMIT, ANU and UNSW collaborated with colleagues from Deakin University and the University of Melbourne. Matthias Wurdak of FLEET (ANU) conducted 2D nanosheets transfer experiments, and Kurosh Kalantarzade (UNSW) helped with material and device characteristics analysis.

This project was supported by the Australian Research Council (Center of Excellence and DECRA programs), the authors also acknowledge support from the RMIT University Microscopy and Microanalysis Foundation (RMMF), RMIT University Micronano-Nanotechnology Research Center (MNRF), and funding obtained through postdoctoral MacKenzie program. University of Melbourne Scholarship Program.





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A revolutionary technique designed to dramatically reduce scattered light in space telescopes

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A revolutionary technique designed to dramatically reduce scattered light in space telescopes


Scattered light decomposition using ultrafast time-of-flight imaging. Credit: Lionel Clermont / Liege Spatial Center / University of Liege.

A team of researchers from the Center for Spatial Spaces of Liege (CSL) of the University of Liege has just developed a method for determining the sources and origin of scattered light in space telescopes. This is a major breakthrough in space technology that will aid in the acquisition of ever more accurate space imagery and the development of ever more efficient space instruments. This research has just been published in the journal. Scientific reports

Space telescopes are becoming more powerful. Technological developments in recent years have made it possible, for example, to observe objects further and further in the Universe or to measure the composition of the Earth’s atmosphere with even greater accuracy. However, there is another factor limiting the performance of these telescopes: stray light. Long known phenomenon: stray light results in light reflections (ghostly reflections between lenses, scattering, etc.), which degrade image quality and often result in blurry images. Until now, the methods for testing and characterizing this scattered light during the telescope design phase have been very limited, making it easy to know if the instrument was sensitive to the phenomenon, forcing engineers to revise all their calculations. in positive cases, leading to significant delays in the commissioning of these advanced tools.


Over time, various sources of scattered light (ghosts) appear and disappear on the detector. The arrival time is related to the length of the optical path, we can identify each participant and compare them with the theoretical model. Credit: Lionel Clermont / Liege Spatial Center / University of Liege.

Researchers at the Center Spatial de Liège (CSL), in collaboration with the University of Strasbourg, have just developed a revolutionary method to solve this problem using a femtosecond pulsed laser to send light beams to illuminate the telescope. “The scattered light beams take (in a telescope) different optical paths from the beams that form the image,” explains Lionel Clermont, an expert in space optical systems and scattered light at CSL. Thanks to this and with the help of an ultra-fast detector (with a resolution of the order of 10-9 seconds, ie, one thousandth of a millionth of a second), we measure the image and various effects of scattered light at different times. In addition to this decomposition, we can identify each of the participants using their arrival time, which is directly related to the optical path, and thus know the source of the problem. “

CSL engineers demonstrated the effectiveness of this method in an article just published in the journal. Scientific reportsin which they present the first film showing ghostly reflections in a refractive telescope at different times. “We were also able to use these measurements to reverse engineer theoretical models,” says Lionel Clermont, “which will allow, for example, better imaging models in the future.”

By comparing these measurements with numerical models, scientists will now be able to pinpoint the origin of the scattered light and thus act accordingly to improve the system, both by improving equipment and developing correction algorithms.

This method, developed at CSL, is not just a scientific curiosity, it could lead to a small revolution in the field of high-performance space instruments. “We have already received a lot of interest from ESA (European Space Agency) and industrialists in the space sector,” says Marc Georges, metrology and laser expert at CSL and co-author of the study. This method solves an urgent problem that has not been solved until now. “

In the near future, CSL researchers intend to continue developing this method, raise its TRL (Technology Readiness Level) and bring it to an industrial level. Industrial applications are already planned for the FLEX (Fluorescence Explorer) Earth observation telescope, which is part of ESA’s Living Planet program. The researchers hope they can apply this to scientific instruments as well.

Ref: “Scattered Light Characterization Using Ultrafast Time-of-Flight Imaging” by L. Clermont, W. Uring and M. Georges, 12 May 2021, Scientific reports
DOI: 10.1038 / s41598-021-89324-y





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Engineers harvest energy from Wi-Fi signals to power small electronics

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Engineers harvest energy from Wi-Fi signals to power small electronics


The microcircuit contains about 50 torque oscillators. Credit: National University of Singapore.

Researchers have developed a method using torque oscillators to use wireless signals and convert them into energy to power small electronics.

With the advent of the digital age, the number of Wi-Fi sources for wirelessly transferring information between devices has grown exponentially. This leads to widespread use of the 2.4 GHz radio frequency that WiFi uses, with redundant signals available for alternative use.

To harness this underutilized energy source, a research team from the National University of Singapore (NUS) and Japan’s Tohoku University (TU) have developed technology that uses tiny smart devices known as torque oscillators (STOs) to collect and convert wireless radio frequencies into energy. to power small electronics. In their study, the researchers successfully harvested energy using Wi-Fi band signals to wirelessly power a light emitting diode (LED) without using any kind of battery.

“We are surrounded by Wi-Fi signals, but when we are not using them to access the Internet, they are inactive and this is a huge waste. Our latest result is a step towards converting the available 2.4 GHz radio waves into a clean energy source, which reduces the need for batteries to power the electronics we regularly use. Thus, small electrical devices and sensors can be powered wirelessly using radio frequency waves as part of the Internet of Things. With the advent of smart homes and cities, our work could lead to energy efficient applications in communications, computing and neuromorphic systems, ”said Professor Yang Hyunsoo of NUS’s Electrical and Computer Engineering Department, who led the project.

Yang Hyunsoo and Raghav Sharma

The research breakthrough was made by a team led by Professor Yang Hyunsoo (left). Dr. Raghav Sharma (right), the first author of the article, holds a microcircuit in which about 50 torque oscillators are built. Credit: National University of Singapore.

The study was carried out in collaboration with the research team of Professor Guo Yong Xin, who also works with the Department of Electrical and Computer Engineering at NUS, and Professor Shunsuke Fukami and his team from the Technical University. Results published in Nature Communications May 18, 2021

Converting Wi-Fi Signals into Usable Energy

Torque generators are a class of new devices that generate microwaves and are used in wireless communication systems. However, the application of STO is difficult due to the low power output and wide line width.

While cross-synchronization of multiple STOs is a way to overcome this problem, existing circuits, such as short-range magnetic coupling between multiple STOs, have spatial limitations. On the other hand, long distance electrical synchronization using vortex generators is limited to frequency characteristics of only a few hundred MHz. Dedicated current sources are also required for individual STOs, which can complicate overall on-chip implementation.

To overcome spatial and low frequency limitations, the research team developed an array in which eight STOs are connected in series. Using this array, the 2.4 GHz electromagnetic radio waves that WiFi uses were converted into a constant voltage signal, which was then transmitted to a capacitor to light up a 1.6V LED. When the capacitor charged for five seconds, it could light up alone and with the same LED for one minute after turning off the wireless power.

In their study, the researchers also highlighted the importance of electrical topology for the design of STO systems on a chip and compared series versus parallel design. They found that the parallel configuration is more useful for wireless transmission due to better time domain stability, spectral noise characteristics, and impedance mismatch control. On the other hand, series connections have the advantage of collecting energy due to the additive effect of diode voltage from STO.

Commenting on the importance of their results, Dr. Raghav Sharma, the first author of the paper, shared: “In addition to creating an STO array for wireless transmission and energy collection, our work also demonstrated control over the timing state of coupled STOs. using injection blocking from an external RF source. These results are important for promising synchronized STO applications such as high-speed neuromorphic computing. “

Next steps

To enhance their technology’s ability to harvest energy, researchers are looking to increase the amount of STO in their array. In addition, they plan to test their energy harvesters to wirelessly charge other useful electronic devices and sensors.

The research team also hopes to work with industry partners to explore the development of embedded STOs for autonomous smart systems that could open up possibilities for wireless charging and wireless signal detection systems.

Reference: “An array of electrically coupled spin-torsion oscillators for 2.4 GHz data transmission and energy harvesting” Raghav Sharma, Rahul Mishra, Tung Ngo, Yong-Sin Guo, Shunsuke Fukami, Hideo Sato, Hideo Ono and Hyunsu Yang, 18 May 2021 Nature Communications
DOI: 10.1038 / s41467-021-23181-1





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Advances in nanotechnology allow for thinner transistors with exceptional performance

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Interface Between Semimetal and 2D Semiconductor


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At the interface between a semimetal (bismuth) and a two-dimensional semiconductor (MoS2), there is no energy barrier for the passage of electrons, which leads to an ultra-low contact resistance between them. Credit: Courtesy of the researchers

Atomically thin materials are a promising alternative to silicon transistors; researchers can now more efficiently connect them to other elements of the microcircuit.

Moore’s Law, the famous prediction that the number of transistors that can be placed on a microchip doubles every couple of years, runs into basic physical constraints. These constraints could stunt decades of progress unless new approaches are found.

One new area of ​​research is using atomically thin materials instead of silicon as the basis for new transistors, but connecting these “2D” materials to other traditional electronic components has proven difficult.

Now researchers in Massachusetts Institute of Technology, The University of California at Berkeley, a Taiwan semiconductor company, and others have found a new way to create these electrical connections that can help unlock the potential of 2D materials and promote miniaturization of components – perhaps enough to expand Moore’s Law. at least in the near future, the researchers say.

The results are described in the journal. Nature, in an article by recent MIT alumni Ping-Chun Shen, Ph.D. ’20 and Kong Su, Ph.D. ’20, postdoc Yusuan Lin, Ph.D. ’19, MIT professors Jing Kong, Thomas Palacios and Joo Li, and 17 others employees of the Massachusetts Institute of Technology, the University of California at Berkeley, and other institutions.

Single layer semiconductor transistor

Single layer semiconductor transistor illustration. Credit: Courtesy of the researchers

“We’ve solved one of the biggest challenges of miniaturizing semiconductor devices — the contact resistance between a metal electrode and a single-layer semiconductor material,” says Su, who now works at the University of California, Berkeley. The solution turned out to be simple: using a semimetal, an element of bismuth, to replace conventional metals to bond with a single layer material.

Such ultra-thin single-layer materials, in this case molybdenum disulfide, are seen as a major contender for breaking the miniaturization limits currently faced by silicon transistor technology. But creating an efficient, highly conductive interface between such materials and metal conductors to connect them to each other, as well as to other devices and power supplies, has been a challenge holding back progress towards such solutions, Su says.

At the interface between metals and semiconductor materials (including these single-layer semiconductors), a phenomenon called a metal-induced gap state occurs, which results in the formation of a Schottky barrier, a phenomenon that prevents the flow of charge carriers. The use of a semi-metal whose electronic properties are between metals and semiconductors, combined with proper energy equalization between the two materials, solved the problem.

Lin explains that the rapid pace of miniaturization of transistors that make up computer processors and memory chips stalled earlier, around 2000, until a new development that allowed 3D semiconductor-on-chip architecture broke the congestion in 2007. and rapid progress resumed. But now, he said, “we think we are on the edge of another bottleneck.”

Miniature transistors with exceptional performance

With this technology, miniature transistors with exceptional performance are demonstrated to meet the requirements of the technology roadmap for future transistors and microchips. Credit: Courtesy of the researchers

The so-called two-dimensional materials, thin sheets only one or a few atoms thick, meet all the requirements for a further leap in the miniaturization of transistors, potentially reducing several times the key parameter called channel length – from about 5 to 10 nanometers in modern chips with subnanometer scale. Many such materials are under extensive research, including a whole family of compounds known as transition metal dichalcogenides. The molybdenum disulfide used in the new experiments belongs to this family.

The problem of achieving metal-to-metal contact with such low resistance materials has also impeded fundamental research into the physics of these new single-layer materials. Because existing connection methods have such high resistance, the tiny signals needed to track the behavior of electrons in a material are too weak to pass through. “There are many examples from physics that require low contact resistance between metal and semiconductor. So this is a huge problem for the world of physics as well, ”says Su.

It can take some time and further development to understand how to scale and integrate such systems commercially. But for such applications of physics, the researchers say, the impact of new discoveries can be felt quickly. “I think that in physics, many experiments can immediately benefit from this technology,” says Su.

Meanwhile, the researchers continue their research as they continue to shrink their devices and look for other pairs of materials that could improve electrical contacts with another type of charge carrier known as holes. They solved the problem for the so-called N-type transistor, but if they can find a combination of channel material and electrical contact to create an efficient single-layer P-type transistor, it will open up many new possibilities for the next generation. They say chips.

Reference: “Ultra-low contact resistance between semi-metal and single-layer semiconductors” Ping-Chun Sheng, Kong Su, Yuxuan Lin, Ang-Sheng Chou, Chao-Ching Cheng, Ji-Hong Park, Min-Hui Chiu, Ang-Yu Lu, Hao. -Ling Tan, Mohammad Mahdi Tavakoli, Gregory Pitner, Xiang Ji, Zhengyang Kai, Nannan Mao, Jiangtao Wang, Vincent Tung, Joo Lee, Jeffrey Bokor, Alex Zettl, Chi-Yi Wu, Thomas Palacios, Line-Jong Li and Jing May 12, 2021 Nature
DOI: 10.1038 / s41586-021-03472-9

In addition to the Massachusetts Institute of Technology and UC Berkeley, the team included researchers from Lawrence Berkeley National Laboratory, Taiwan Semiconductor Manufacturing Company, National Taiwan University and King Abdullah University of Science and Technology in Saudi Arabia. This work was supported by the National Science Foundation, the US Army Research Office, the Office of Naval Research, and the US Department of Energy.





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