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Research Alert: January 26, 2015

Monday, January 26th, 2015

Solving an organic semiconductor mystery

Organic semiconductors are prized for light emitting diodes (LEDs), field effect transistors (FETs) and photovoltaic cells. As they can be printed from solution, they provide a highly scalable, cost-effective alternative to silicon-based devices. Uneven performances, however, have been a persistent problem. Scientists have known that the performance issues originate in the domain interfaces within organic semiconductor thin films, but have not known the cause. This mystery now appears to have been solved.

Naomi Ginsberg, a faculty chemist with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory and the University of California (UC) Berkeley, led a team that used a unique form of microscopy to study the domain interfaces within an especially high-performing solution-processed organic semiconductor called TIPS-pentacene. She and her team discovered a cluttered jumble of randomly oriented nanocrystallites that become kinetically trapped in the interfaces during solution casting. Like debris on a highway, these nanocrystallites impede the flow of charge-carriers.

“If the interfaces were neat and clean, they wouldn’t have such a large impact on performance, but the presence of the nanocrystallites reduces charge-carrier mobility,” Ginsberg says. “Our nanocrystallite model for the interface, which is consistent with observations, provides critical information that can be used to correlate solution-processing methods to optimal device performances.”

Ginsberg, who holds appointments with Berkeley Lab’s Physical Biosciences Division and its Materials Sciences Division, as well as UC Berkeley’s departments of chemistry and physics, is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Exciton dynamics reveals aggregates with intermolecular order at hidden interfaces in solution-cast organic semiconducting films.” Co-authors are Cathy Wong, Benjamin Cotts and Hao Wu.

Ginsberg and her group overcame the challenges by using transient absorption (TA) microscopy, a technique in which femtosecond laser pulses excite transient energy states and detectors measure the changes in the absorption spectra. The Berkeley researchers carried out TA microscopy on an optical microscope they constructed themselves that enabled them to generate focal volumes that are a thousand times smaller than is typical for conventional TA microscopes. They also deployed multiple different light polarizations that allowed them to isolate interface signals not seen in either of the adjacent domains.

“Instrumentation, including very good detectors, the painstaking collection of data to ensure good signal-to-noise ratios, and the way we crafted the experiment and analysis were all critical to our success,” Ginsberg says. “Our spatial resolution and light polarization sensitivity were also essential to be able to unequivocally see a signature of the interface that was not swamped by the bulk, which contributes much more to the raw signal by volume.”

The methology developed by Ginsberg and her team to uncover structural motifs at hidden interfaces in organic semiconductor thin films should add a predictive factor to scalable and affordable solution-processing of these materials. This predictive capability should help minimize discontinuities and maximize charge-carrier mobility. Currently, researchers use what is essentially a trial-and-error approach, in which different solution casting conditions are tested to see how well the resulting devices perform.

“Our methodology provides an important intermediary in the feedback loop of device optimization by characterizing the microscopic details of the films that go into the devices, and by inferring how the solution casting could have created the structures at the interfaces,” Ginsberg says. “As a result, we can suggest how to alter the delicate balance of solution casting parameters to make more functional films.”

Rice-sized laser, powered one electron at a time, bodes well for quantum computing

Princeton University researchers have built a rice grain-sized laser powered by single electrons tunneling through artificial atoms known as quantum dots. The tiny microwave laser, or “maser,” is a demonstration of the fundamental interactions between light and moving electrons.

The researchers built the device — which uses about one-billionth the electric current needed to power a hair dryer — while exploring how to use quantum dots, which are bits of semiconductor material that act like single atoms, as components for quantum computers.

“It is basically as small as you can go with these single-electron devices,” said Jason Petta, an associate professor of physics at Princeton who led the study, which was published in the journal Science.

The device demonstrates a major step forward for efforts to build quantum-computing systems out of semiconductor materials, according to co-author and collaborator Jacob Taylor, an adjunct assistant professor at the Joint Quantum Institute, University of Maryland-National Institute of Standards and Technology.

“I consider this to be a really important result for our long-term goal, which is entanglement between quantum bits in semiconductor-based devices,” Taylor said.

The original aim of the project was not to build a maser, but to explore how to use double quantum dots — which are two quantum dots joined together — as quantum bits, or qubits, the basic units of information in quantum computers.

“The goal was to get the double quantum dots to communicate with each other,” said Yinyu Liu, a physics graduate student in Petta’s lab. The team also included graduate student Jiri Stehlik and associate research scholar Christopher Eichler in Princeton’s Department of Physics, as well as postdoctoral researcher Michael Gullans of the Joint Quantum Institute.

Because quantum dots can communicate through the entanglement of light particles, or photons, the researchers designed dots that emit photons when single electrons leap from a higher energy level to a lower energy level to cross the double dot.

Each double quantum dot can only transfer one electron at a time, Petta explained. “It is like a line of people crossing a wide stream by leaping onto a rock so small that it can only hold one person,” he said. “They are forced to cross the stream one at a time. These double quantum dots are zero-dimensional as far as the electrons are concerned — they are trapped in all three spatial dimensions.”

The researchers fabricated the double quantum dots from extremely thin nanowires (about 50 nanometers, or a billionth of a meter, in diameter) made of a semiconductor material called indium arsenide. They patterned the indium arsenide wires over other even smaller metal wires that act as gate electrodes, which control the energy levels in the dots.

To construct the maser, they placed the two double dots about 6 millimeters apart in a cavity made of a superconducting material, niobium, which requires a temperature near absolute zero, around minus 459 degrees Fahrenheit. “This is the first time that the team at Princeton has demonstrated that there is a connection between two double quantum dots separated by nearly a centimeter, a substantial distance,” Taylor said.

When the device was switched on, electrons flowed single-file through each double quantum dot, causing them to emit photons in the microwave region of the spectrum. These photons then bounced off mirrors at each end of the cavity to build into a coherent beam of microwave light.

One advantage of the new maser is that the energy levels inside the dots can be fine-tuned to produce light at other frequencies, which cannot be done with other semiconductor lasers in which the frequency is fixed during manufacturing, Petta said. The larger the energy difference between the two levels, the higher the frequency of light emitted.

Claire Gmachl, who was not involved in the research and is Princeton’s Eugene Higgins Professor of Electrical Engineering and a pioneer in the field of semiconductor lasers, said that because lasers, masers and other forms of coherent light sources are used in communications, sensing, medicine and many other aspects of modern life, the study is an important one.

“In this paper the researchers dig down deep into the fundamental interaction between light and the moving electron,” Gmachl said. “The double quantum dot allows them full control over the motion of even a single electron, and in return they show how the coherent microwave field is created and amplified. Learning to control these fundamental light-matter interaction processes will help in the future development of light sources.”

Carbon nanotube finding could lead to flexible electronics with longer battery life

University of Wisconsin-Madison materials engineers have made a significant leap toward creating higher-performance electronics with improved battery life — and the ability to flex and stretch.

Led by materials science Associate Professor Michael Arnold and Professor Padma Gopalan, the team has reported the highest-performing carbon nanotube transistors ever demonstrated. In addition to paving the way for improved consumer electronics, this technology could also have specific uses in industrial and military applications.

In a paper published recently in the journal ACS Nano, Arnold, Gopalan and their students reported transistors with an on-off ratio that’s 1,000 times better and a conductance that’s 100 times better than previous state-of-the-art carbon nanotube transistors.

“Carbon nanotubes are very strong and very flexible, so they could also be used to make flexible displays and electronics that can stretch and bend, allowing you to integrate electronics into new places like clothing,” says Arnold. “The advance enables new types of electronics that aren’t possible with the more brittle materials manufacturers are currently using.”

Carbon nanotubes are single atomic sheets of carbon rolled up into a tube. As some of the best electrical conductors ever discovered, carbon nanotubes have long been recognized as a promising material for next-generation transistors, which are semiconductor devices that can act like an on-off switch for current or amplify current. This forms the foundation of an electronic device.

However, researchers have struggled to isolate purely semiconducting carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and “short” the device. Researchers have also struggled to control the placement and alignment of nanotubes. Until now, these two challenges have limited the development of high-performance carbon nanotube transistors.

Building on more than two decades of carbon nanotube research in the field, the UW-Madison team drew on cutting-edge technologies that use polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

Previous techniques to align the nanotubes resulted in less-than-desirable packing density, or how close the nanotubes are to one another when they are assembled in a film. However, the UW-Madison researchers pioneered a new technique, called floating evaporative self-assembly, or FESA, which they described earlier in 2014 in the ACS journal Langmuir. In that technique, researchers exploited a self-assembly phenomenon triggered by rapidly evaporating a carbon nanotube solution.

The team’s most recent advance also brings the field closer to realizing carbon nanotube transistors as a feasible replacement for silicon transistors in computer chips and in high-frequency communication devices, which are rapidly approaching their physical scaling and performance limits.

“This is not an incremental improvement in performance,” Arnold says. “With these results, we’ve really made a leap in carbon nanotube transistors. Our carbon nanotube transistors are an order of magnitude better in conductance than the best thin film transistor technologies currently being used commercially while still switching on and off like a transistor is supposed to function.”

The researchers have patented their technology through the Wisconsin Alumni Research Foundation and have begun working with companies to accelerate the technology transfer to industry.

Solid State Watch: January 16-22, 2015

Thursday, January 22nd, 2015
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Research Alert: May 20, 2014

Tuesday, May 20th, 2014

Lighting the way to graphene-based devices

Researchers with Berkeley Lab and the University of California (UC) Berkeley have demonstrated a technique whereby the electronic properties of GBN heterostructures can be modified with visible light. Feng Wang, a condensed matter physicist with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Physics Department, as well as an investigator for the Kavli Energy NanoSciences Institute at Berkeley, led a study in which photo-induced doping of GBN heterostructures was used to create p–n junctions and other useful doping profiles while preserving the material’s remarkably high electron mobility.

“We’ve demonstrated that visible light can induce a robust writing and erasing of charge-doping in GBN heterostructures without sacrificing high carrier mobility,” Wang says. “The use of visible light gives us incredible flexibility and, unlike electrostatic gating and chemical doping, does not require multi-step fabrication processes that reduce sample quality. Additionally, different patterns can be imparted and erased at will, which was not possible with doping techniques previously used on GBN heterostructures.”

“We’ve shown show that this photo-induced doping arises from microscopically coupled optical and electrical responses in the GBN heterostructures, including optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene,” Wang says. “This is analogous to the modulation doping first developed for high-quality semiconductors.”

While the photo-induced modulation doping of GBN heterostructures only lasted a few days if the sample was kept in darkness – further exposure to light erased the effect – this is not a concern as Wang explains.

“A few days of modulation doping are sufficient for many avenues of scientific inquiry, and for some device applications, the rewritability we can provide is needed more than long term stability,” he says. “For the moment, what we have is a simple technique for inhomogeneous doping in a high-mobility graphene material that opens the door to novel scientific studies and applications.”

SMIC and other groups collaborate to setup the “IC Advanced Technology Research Institute”

China’s largest and most advanced semiconductor foundry this week announced that SMIC, Wuhan Xinxin, Tsinghua University, Beijing University, Fudan University and the Chinese Academy of Sciences and Microelectronics have collaborated to setup the “IC Advanced Technology Research Institute” to create the most advanced IC technology research and development institution in China.

Currently, the research institute will focus on the mainstream 20nm and below technologies for research and development which includes advanced logic technology, advanced non-volatile memory technology, verification of domestic equipment and materials, and related IP qualifications etc. It will also follow up with the industry’s technology development and the actual needs of the customers, and will invite design, equipment, material companies, and upstream and downstream industries. They can join in as a member or in project collaboration. This institute will strengthen its international exchange and cooperation, to promote the establishment our IP infrastructure, to speed up the cultivation of patents and talent, in order to raise the core competitiveness of innovation in China’s IC industry.

On Solid State Technology: What to look for at IITC

Are you at IITC this week? Here’s a look at the key presentations being given and topics being covered all week at the 17th annual IITC/AMC conference in San Jose, California.

Research Alert: May 13, 2014

Tuesday, May 13th, 2014

SRC and UC Berkeley pursue a more cost effective approach to 3D integration

University of California, Berkeley researchers sponsored by Semiconductor Research Corporation (SRC) are pursuing a novel approach to 3D device integration that promises to lead to advanced mobile devices and wearable electronics featuring increased functionality in more low-profile packages.

The research focuses on integrating extra layers of transistors on a vertically integrated 3D monolithic chip using printing of semiconductor “inks” as compared to the current method of chip-stacking through 3D interconnect solutions.

The new process technology could help semiconductor manufacturers develop smaller and more versatile components that are less expensive and higher performing by enabling cost-effective integration of additional capabilities such as processing, memory, sensing and display. The low-temperature process is also compatible with polymer substrates, enabling potential new applications in wearable electronics and packaging.

To fabricate such devices, new material and process methodologies are needed for depositing nanoparticles for semiconductors, dielectrics and conductors. The research is particularly focused on solution-based processing due its low temperature compatibility with CMOS metallization as well as the potential for lower cost manufacturing.

“Initial results from the Berkeley team show that reasonably high performance can be obtained from ink-jet printed devices with process temperatures that are compatible with post-CMOS metallization, thus enabling a new route to monolithic 3D integration,” said Bob Havemann, Director of Nanomanufacturing Sciences at the SRC.

SEMATECH reports higher dose sensitivity progress in novel photoresist platforms

SEMATECH announced today that researchers have reported progress which could significantly improve resist sensitivity by incorporating metal oxide nanoparticles for extreme ultraviolet (EUV) lithography, bringing the technology another step toward enabling the development of high performance resists required to enable EUV for high-volume manufacturing (HVM).

SEMATECH engineers, in association with scientists from Cornell University, have demonstrated significantly higher dose sensitivity by incorporating metal oxide nanoparticles, with a resolution dose that is less than one fifth of that normally used with EUV scanner throughput calculations. These significant advances are critical in moving forward the infrastructure that will prepare EUV lithography for HVM at 20nm half-pitch.

“These resist platforms have the potential to significantly relax the EUV source power requirements to enable high-throughput EUV lithography—which has been the most critical barrier to enabling EUV to enter high-volume manufacturing,” said Michael Lercel, SEMATECH’s senior director of Technology. “With these disruptive photoresist platforms, SEMATECH is working toward enabling breakthrough high performance resists that move forward the infrastructure that will prepare EUV for cost-effective manufacturing.”

Taking the lead out of a promising solar cell

Northwestern University researchers are the first to develop a new solar cell with good efficiency that uses tin instead of lead perovskite as the harvester of light. The low-cost, environmentally friendly solar cell can be made easily using “bench” chemistry — no fancy equipment or hazardous materials.

“This is a breakthrough in taking the lead out of a very promising type of solar cell, called a perovskite,” said Mercouri G. Kanatzidis, an inorganic chemist with expertise in dealing with tin. “Tin is a very viable material, and we have shown the material does work as an efficient solar cell.”

Kanatzidis, who led the research, is the Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences.

The new solar cell uses a structure called a perovskite but with tin instead of lead as the light-absorbing material. Lead perovskite has achieved 15 percent efficiency, and tin perovskite should be able to match — and possibly surpass — that. Perovskite solar cells are being touted as the “next big thing in photovoltaics” and have reenergized the field.

Kanatzidis developed, synthesized and analyzed the material. He then turned to Northwestern collaborator and nanoscientist Robert P. H. Chang to help him engineer a solar cell that worked well.

“Our tin-based perovskite layer acts as an efficient sunlight absorber that is sandwiched between two electric charge transport layers for conducting electricity to the outside world,” said Chang, a professor of materials science and engineering at the McCormick School of Engineering and Applied Science.

Their solid-state tin solar cell has an efficiency of just below 6 percent, which is a very good starting point, Kanatzidis said. Two things make the material special: it can absorb most of the visible light spectrum, and the perovskite salt can be dissolved, and it will reform upon solvent removal without heating.

“Other scientists will see what we have done and improve on our methods,” Kanatzidis said. “There is no reason this new material can’t reach an efficiency better than 15 percent, which is what the lead perovskite solar cell offers. Tin and lead are in the same group in the periodic table, so we expect similar results.”

Perovskite solar cells have only been around — and only in the lab — since 2008. In 2012, Kanatzidis and Chang reported the new tin perovskite solar cell with promises of higher efficiency and lower fabrication costs while being environmentally safe.

“Solar energy is free and is the only energy that is sustainable forever,” Kanatzidis said. “If we know how to harvest this energy in an efficient way we can raise our standard of living and help preserve the environment.”

The solid-state tin solar cell is a sandwich of five layers, with each layer contributing something important. Being inorganic chemists, Kanatzidis and his postdoctoral fellows Feng Hao and Constantinos Stoumpos knew how to handle troublesome tin, specifically methylammonium tin iodide, which oxidizes when in contact with air.

The first layer is electrically conducting glass, which allows sunlight to enter the cell. Titanium dioxide is the next layer, deposited onto the glass. Together the two act as the electric front contact of the solar cell.

Next, the tin perovskite — the light absorbing layer — is deposited. This is done in a nitrogen glove box — the bench chemistry is done in this protected environment to avoid oxidation.

On top of that is the hole transport layer, which is essential to close the electrical circuit and obtain a functional cell. This required Kanatzidis and his colleagues to find the right chemicals so as not to destroy the tin underneath. They determined what the best chemicals were — a substituted pyridine molecule — by understanding the reactivity of the perovskite structure. This layer also is deposited in the glove box. The solar cell is then sealed and can be taken out into the air.

A thin layer of gold caps off the solar-cell sandwich. This layer is the back contact electrode of the solar cell. The entire device, with all five layers, is about one to two microns thick.

The researchers then tested the device under simulated full sunlight and recorded a power conversion efficiency of 5.73 percent.

Solid State Watch: May 2-8, 2014

Friday, May 9th, 2014
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The Week in Review: May 9, 2014

Friday, May 9th, 2014

SEMATECH announced this week that researchers have reached a significant milestone in reducing tool-generated defects from the multi-layer deposition of mask blanks used for extreme ultraviolet lithography, pushing the technology another significant step toward readiness for high-volume manufacturing.

University of California, Berkeley researchers sponsored by Semiconductor Research Corporation (SRC) are pursuing a novel approach to 3D device integration that promises to lead to advanced mobile devices and wearable electronics featuring increased functionality in more low-profile packages.

GlobalFoundries this week introduced an optimized semiconductor manufacturing platform aimed specifically at meeting the stringent and evolving needs of the automotive industry.

Peregrine Semiconductor announced shipment of the first RF switches built on the UltraCMOS 10 technology platform.

BASF inaugurated a new Electronic Materials Sampling and Development facility in Hillsboro, Oregon. The new facility is a strategic step towards establishing a North American footprint to supply materials for semiconductor manufacturing applications related to the electronics industry.

Veeco Instruments Inc. has appointed Shubham Maheshwari, 42, as its new Executive Vice President, Finance and Chief Financial Officer (CFO). Mr. Maheshwari replaces David D. Glass, who announced his retirement from Veeco last December.

Avago Technologies Limited and LSI Corporation announced Avago has completed its acquisition of LSI Corporation for $11.15 per share in an all-cash transaction valued at approximately $6.6 billion.

Microchip Technology Inc., a provider of microcontroller, mixed-signal, analog and Flash-IP solutions, this week introduced a new parallel Flash memory device.

The Semiconductor Industry Association announced that worldwide sales of semiconductors reached $78.47 billion during the first quarter of 2014, marking the industry’s highest-ever first quarter sales.

Qualcomm elected Harish Manwani to board of directors. Manwani brings more than 35 years of consumer product and global management experience, and currently serves as the Chief Operating Officer at Unilever PLC.

The Week in Review: March 21, 2014

Friday, March 21st, 2014

Research from University of California, Berkeley scientists sponsored by Semiconductor Research Corporation (SRC) promises to revolutionize portable radio frequency (RF) electronics and communication systems via advancements in on-chip inductors by leveraging embedded nanomagnets. The UC Berkeley research focuses on using insulated nano-composite magnetic materials as the filling material to shrink the size and improve the performance of high frequency on-chip inductors, thereby enabling a new wave of miniaturized electronics and wireless communications devices.

North America-based manufacturers of semiconductor equipment posted $1.29 billion in orders worldwide in February 2014 (three-month average basis) and a book-to-bill ratio of 1.00, according to the February EMDS Book-to-Bill Report published today by SEMI.   A book-to-bill of 1.00 means that $100 worth of orders were received for every $100 of product billed for the month.

Dr. Tzu-Yin Chiu, Chief Executive Officer & Executive Director of SMIC presented the SEMICON China 2014 opening keynote yesterday and was given a SEMI Outstanding EHS Achievement Award.

EV Group (EVG), a supplier of wafer bonding and lithography equipment for the MEMS, nanotechnology and semiconductor markets, today announced that it has opened a new, wholly owned subsidiary in Shanghai, called EV Group China Ltd., which will serve as regional headquarters for all of EVG’s operations in China.  The new subsidiary, which houses a local service center and spare parts management facility, will further strengthen EVG’s presence in the region and support the company’s ongoing efforts to improve service and response times to local customers.

ChaoLogix, Inc., a semiconductor technology provider focused on developing embedded security and low-power design intellectual property, today introduced ChaoSecure technology that deters side channel attacks on semiconductor chips and contributes a superior layer of security compared to existing solutions. ChaoLogix’s ChaoSecure technology is a hardware-based solution designed to provide optimal performance at the nexus of security and power. Proven in silicon and validated by an independent security lab, ChaoSecure is a secure standard cell library that can be easily integrated into an existing integrated circuit (IC) — making it the ideal security solution in terms of cost and performance for designing complex applications ranging from smart cards to smart phones.

Applied Materials, Inc. this week announced that it was named a 2014 World’s Most Ethical Company by the Ethisphere Institute, an independent center of research promoting best practices in corporate ethics and governance. This is the third consecutive year Applied Materials has received the annual award, which recognizes organizations that continue to demonstrate ethical leadership and corporate behavior.


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