Category Archives: Packaging Materials

A collaborative effort between research groups at the Technical University of Freiberg and the University of Siegen in Germany demonstrates that the physical properties of SrTiO3, or strontium titanate, in its single crystal form can be changed by a relatively simple electrical treatment. SrTi03 is a mineral often studied for its superconducting properties.

The treatment, described this week in Applied Physics Letters, from AIP Publishing, creates the effect known as piezoelectricity, where electricity results from mechanical stress, in the material which did not originally see piezoelectric effects. This could be extremely important as our technologically-oriented society makes ever-growing demands for new materials and unusual properties.

Crystalline materials are made of atoms and electrons, which arrange themselves in periodic patterns. The atomic structure of a crystal is similar to a piece of a cross-stitching pattern, but the scale is about ten million times smaller. While a cross-stitching technique might be tricky at first, once you learn the pattern, you just repeat the same stitches to fill the available space. Nature works much the same way in building crystals: it “learns” how to connect atoms with each other in a so-called unit cell and then repeats this building block to fill the space making a crystal lattice.

Looking at a crystal structure is somewhat like looking at fabric through a magnifying glass. Using a technique called X-ray diffraction, researchers apply external stimuli (e.g. stretch or an electric voltage) to a crystal and see how different connections (atomic “stitches”) respond.

“The idea for this work was born when I was giving a colloquium talk in TU Freiberg, presenting our new technique for time-resolved X-ray diffraction and investigating piezoelectric material. Our colleagues in Freiberg had been investigating artificially created near-surface volumes of SrTiO3 crystals, with properties different from the normal bulk SrTiO3,” said Semën Gorfman, a University of Siegen physicist.

The Siegen research team had developed unique experimental equipment to investigate crystal structures under a periodically varying field using X-ray diffraction that is mobile and can connect to any available instrument, such as a home-lab X-ray diffractometer or a synchrotron beamline.

“Since the measurements are non-routine, this experimental equipment makes our research truly unique and original,” Gorfman said. “It turned out that the technique developed at Siegen, was ideally matched to the research direction that the Freiberg team was working on, so we came up with the hypothesis to be tested (piezoelectricity in field-modified near surface phase of SrTiO3 crystal), and a suggested experimental method (stroboscopic time-resolved X-ray diffraction), performed the experiment and got results.”

This work shows that new physical properties can be created artificially, reporting the piezoelectric effect in the artificially designed new phase of SrTiO3, a material that is not piezoelectric under normal conditions.

“We believe that physical properties of migration field induced polar phase in SrTiO3 opens a new and interesting chapter for research, Gorfman said. “The challenge now is to make the effect practical so that it can be used for devices.”

The global market for nanotubes was valued at $1,250.00 million in 2015 and is expected to grow at a CAGR of 17.9% during the forecast period 2016-2025. According to a recent report by Research and Markets, “Global Carbon Nanotubes Market – Segmented by Type, Application and Geography – Trends and Forecasts (2016 – 2025)”, the single-walled carbon nanotubes (SWTs) are expected to reach 689.35 million by 2018 with a CAGR of 22.5%.

Carbon nanotubes have high thermal conductivity, elasticity, tensile strength, absorbency, etc. as a result of which they have been widely used in the fields of nanotechnology, semiconductors, optics, etc. At present the carbon nanotubes account for about 28% market share of the total nanomaterial market. The production capacity of the carbon nanotubes is highest in the Asia-pacific region, followed by the North America and Europe. This domination of the Asia-pacific region is expected to continue as the demand for the carbon nanotubes is growing in the Asia-pacific region.

The global Carbon Nanotubes market is dominated by a few large suppliers/producers operating in multiple industry segments. The number of companies producing carbon nanotubes is expected to double in the next five years. Moreover, there is a lot of research being done regarding these nanotubes to enhance its properties. The number of publications being published about them has increased a lot over the last decade.

Asia-Pacific has the largest installed capacity of carbon nanotubes, mainly due to the significant presence of the electrical & electronics market in Japan, South Korea, Taiwan, China, and Singapore. Moreover, due to the industrialization and urbanization in the developing countries, the demand for the electronic products is increasing resulting in increasing usage of the carbon nanotubes. Hence a number of developing nations notably China and India, which due to their higher population levels, will potentially be large and profitable markets for the carbon nanotubes.

The growth of this market is mainly influenced by the development of the synthesis methods, advancement in the carbon nanotubes to enhance its properties and growing applications. The increasing demand for electronic & storage devices and in the energy sector, where carbon nanotubes find extensive applications, will drive the demand for the carbon nanotubes. The key challenge in this market is the high cost of production and purity of the carbon nanotubes. There is a baseline for the production of carbon nanotubes based on safety regulations, hence the productivity is less. Another challenge is with the difficulty in the acquirement of patents in nanotechnology.

Some of the key vendors of carbon nanotubes are CNano technology, Nanocyl, Covestro, Showa Denko, Arkema, carbon solutions, carbon NT&F, catalyx nanotech and CNT.

 

Controlling the flow of heat through semiconductor materials is an important challenge in developing smaller and faster computer chips, high-performance solar panels, and better lasers and biomedical devices.

For the first time, an international team of scientists led by a researcher at the University of California, Riverside has modified the energy spectrum of acoustic phonons– elemental excitations, also referred to as quasi-particles, that spread heat through crystalline materials like a wave–by confining them to nanometer-scale semiconductor structures. The results have important implications in the thermal management of electronic devices.

Led by Alexander Balandin, Distinguished Professor of Electrical and Computing Engineering and UC Presidential Chair Professor in UCR’s Bourns College of Engineering, the research is described in a paper published Thursday, Nov. 10, in the journal Nature Communications. The paper is titled “Direct observation of confined acoustic phonon polarization branches in free-standing nanowires.”

The team used semiconductor nanowires from Gallium Arsenide (GaAs), synthesized by researchers in Finland, and an imaging technique called Brillouin-Mandelstam light scattering spectroscopy (BMS) to study the movement of phonons through the crystalline nanostructures. By changing the size and the shape of the GaAs nanostructures, the researchers were able to alter the energy spectrum, or dispersion, of acoustic phonons. The BMS instrument used for this study was built at UCR’s Phonon Optimized Engineered Materials (POEM) Center, which is directed by Balandin.

Controlling phonon dispersion is crucial for improving heat removal from nanoscale electronic devices, which has become the major roadblock in allowing engineers to continue to reduce their size. It can also be used to improve the efficiency of thermoelectric energy generation, Balandin said. In that case, decreasing thermal conductivity by phonons is beneficial for thermoelectric devices that generate energy by applying a temperature gradient to semiconductors.

“For years, the only envisioned method of changing the thermal conductivity of nanostructures was via acoustic phonon scattering with nanostructure boundaries and interfaces. We demonstrated experimentally that by spatially confining acoustic phonons in nanowires one can change their velocity, and the way they interact with electrons, magnons, and how they carry heat. Our work creates new opportunities for tuning thermal and electronic properties of semiconductor materials,” Balandin said.

Researchers at the NYU Tandon School of Engineering have pioneered a method for growing an atomic scale electronic material at the highest quality ever reported. In a paper published in Applied Physics Letters, Assistant Professor of Electrical and Computer Engineering Davood Shahrjerdi and doctoral student Abdullah Alharbi detail a technique for synthesizing large sheets of high-performing monolayer tungsten disulfide, a synthetic material with a wide range of electronic and optoelectronic applications.

“We developed a custom reactor for growing this material using a routine technique called chemical vapor deposition. We made some subtle and yet critical changes to improve the design of the reactor and the growth process itself, and we were thrilled to discover that we could produce the highest quality monolayer tungsten disulfide reported in the literature,” said Shahrjerdi. “It’s a critical step toward enabling the kind of research necessary for developing next-generation transistors, wearable electronics, and even flexible biomedical devices.”

The promise of two-dimensional electronic materials has tantalized researchers for more than a decade, since the first such material — graphene — was experimentally discovered. Also called “monolayer” materials, graphene and similar two-dimensional materials are a mere one atom in thickness, several hundred thousand times thinner than a sheet of paper. These materials boast major advantages over silicon — namely unmatched flexibility, strength, and conductivity — but developing practical applications for their use has been challenging.

Graphene (a single layer of carbon) has been explored for electronic switches (transistors), but its lack of an energy band gap poses difficulties for semiconductor applications. “You can’t turn off the graphene transistors,” explained Shahrjerdi. Unlike graphene, tungsten disulfide has a sizeable energy band gap. It also displays exciting new properties: When the number of atomic layers increases, the band gap becomes tunable, and at monolayer thickness it can strongly absorb and emit light, making it ideal for applications in optoelectronics, sensing, and flexible electronics.

Efforts to develop applications for monolayer materials are often plagued by imperfections in the material itself — impurities and structural disorders that can compromise the movement of charge carriers in the semiconductor (carrier mobility). Shahrjerdi and his student succeeded in reducing the structural disorders by omitting the growth promoters and using nitrogen as a carrier gas rather than a more common choice, argon.

Shahrjerdi noted that comprehensive testing of their material revealed the highest values recorded thus far for carrier mobility in monolayer tungsten disulfide. “It’s a very exciting development for those of us doing research in this field,” he said.

As Francis Crick, one of Britain’s great scientists, once said: “If you want to understand function, study structure.” Within the realm of chemical physics, a clear example of this is the two forms of carbon — diamond and graphite. While they differ only in the atomic arrangement of atoms of a single element, their properties are quite different.

Differences between the properties of seemingly similar elements of a “family” can be intriguing. Carbon, silicon, germanium, tin and lead are all part of a family that share the same structure of their outermost electrons, yet range from acting as insulators (carbon) to semiconductors (silicon and germanium) to metals (tin and lead).

Is it possible to understand these and other trends within element families? In an article this week in The Journal of Chemical Physics, from AIP Publishing, a group of researchers from Peter Grünberg Institute (PGI) in Germany, and Tampere University of Technology and Aalto University in Finland, describe their work probing the relationship between the structure (arrangement of atoms) and function (physical properties) of a liquid metal form of the element bismuth.

“There are relatively few — less than 100 — stable elements, which means that their trends are often easier to discern than for those of alloys and compounds of several elements,” said Robert O. Jones, a scientist at PGI.

The group’s present work was motivated largely by the availability of high-quality experimental data — inelastic x-ray scattering (IXS) and neutron diffraction — and the opportunity to compare it with results for other liquids of the Group 15 nitrogen family (phosphorus, arsenic, antimony and bismuth). Phosphorus seems to have two liquid phases, and the amorphous form of antimony obtained by cooling the liquid crystallizes spontaneously and explosively.

Their structural studies use extensive numerical simulations run on one of the world’s most powerful supercomputers, JUQUEEN, in Jülich, Germany.

“We’re studying the motion of more than 500 atoms at specified temperatures to determine the forces on each atom and the total energy using density functional calculations,” Jones explained. “This scheme, for which Walter Kohn was awarded the 1998 Nobel Prize in chemistry, doesn’t involve adjustable parameters and has given valuable predictions in many contexts.” While density functional theory is in principle exact, it is necessary to utilize an approximate functional.

The positions and velocities of each atom, for example, are “stored at each step of a ‘molecular dynamics’ simulation, and we use this information to determine quantities that can be compared with experiment,” he continued. “It’s important to note that some quantities that are given directly by the simulation, such as the positions of the atoms, can only be inferred indirectly from the experiment, so that the two aspects are truly complementary.”

One of their most surprising and pleasing results was “the excellent agreement with recent IXS results,” Jones said. “One of the experimentalists involved noted that the agreement of our results with the IXS ‘is really quite beautiful,’ so that even small differences could provide additional information. In our experience, it’s unusual to find such detailed agreement.”

In terms of applications, the group’s work “provides further confirmation that simulations and experiments complement each other and that the level of agreement can be remarkably good — even for ‘real’ materials,” Jones pointed out. “However, it also shows that extensive, expensive, and time-consuming simulations are essential if detailed agreement is to be achieved.”

Jones and his colleagues have extended their approach to even longer simulations in liquid antimony at eight different temperatures, with the goal of understanding the “explosive” nature of crystallization in amorphous antimony (Sb).

“We’ve also run simulations of the crystallization of amorphous phase change materials over the timescale — up to 8 nanoseconds — that is physically relevant for DWD-RW and other optical storage materials,” he added, emphasizing that these types of simulations on computers today typically require many months. “They show, however, just how valuable they can be, and the prospects with coming generations of computers — with even better optimized algorithms — are very bright.”

The prospects of applications within other areas of materials science are extremely good, but the group is now turning its attention to memory materials of a different type — for which the formation and disappearance of a conducting bridge (a metallic filament) in a solid electrolyte between two electrodes could be the basis of future storage materials.

“Details of the mechanism of bridge formation are the subject of speculation, and we hope to provide insight into what really happens,” Jones said.

Engineers at the University of California San Diego have fabricated the first semiconductor-free, optically-controlled microelectronic device. Using metamaterials, engineers were able to build a microscale device that shows a 1,000 percent increase in conductivity when activated by low voltage and a low power laser.

The discovery paves the way for microelectronic devices that are faster and capable of handling more power, and could also lead to more efficient solar panels. The work was published Nov. 4 in Nature Communications.

The capabilities of existing microelectronic devices, such as transistors, are ultimately limited by the properties of their constituent materials, such as their semiconductors, researchers said.

For example, semiconductors can impose limits on a device’s conductivity, or electron flow. Semiconductors have what’s called a band gap, meaning they require a boost of external energy to get electrons to flow through them. And electron velocity is limited, since electrons are constantly colliding with atoms as they flow through the semiconductor.

A team of researchers in the Applied Electromagnetics Group led by electrical engineering professor Dan Sievenpiper at UC San Diego sought to remove these roadblocks to conductivity by replacing semiconductors with free electrons in space. “And we wanted to do this at the microscale,” said Ebrahim Forati, a former postdoctoral researcher in Sievenpiper’s lab and first author of the study.

However, liberating electrons from materials is challenging. It either requires applying high voltages (at least 100 Volts), high power lasers or extremely high temperatures (more than 1,000 degrees Fahrenheit), which aren’t practical in micro- and nanoscale electronic devices.

To address this challenge, Sievenpiper’s team fabricated a microscale device that can release electrons from a material without such extreme requirements. The device consists of an engineered surface, called a metasurface, on top of a silicon wafer, with a layer of silicon dioxide in between. The metasurface consists of an array of gold mushroom-like nanostructures on an array of parallel gold strips.

The gold metasurface is designed such that when a low DC voltage (under 10 Volts) and a low power infrared laser are both applied, the metasurface generates “hot spots”–spots with a high intensity electric field–that provide enough energy to pull electrons out from the metal and liberate them into space.

Tests on the device showed a 1,000 percent change in conductivity. “That means more available electrons for manipulation,” Ebrahim said.

“This certainly won’t replace all semiconductor devices, but it may be the best approach for certain specialty applications, such as very high frequencies or high power devices,” Sievenpiper said.

According to researchers, this particular metasurface was designed as a proof-of-concept. Different metasurfaces will need to be designed and optimized for different types of microelectronic devices.

“Next we need to understand how far these devices can be scaled and the limits of their performance,” Sievenpiper said. The team is also exploring other applications for this technology besides electronics, such as photochemistry, photocatalysis, enabling new kinds of photovoltaic devices or environmental applications.

Worldwide silicon wafer area shipments increased during the third quarter 2016 when compared to second quarter 2016 area shipments according to the SEMI Silicon Manufacturers Group (SMG) in its quarterly analysis of the silicon wafer industry.

Total silicon wafer area shipments were 2,730 million square inches during the most recent quarter, a 0.9 percent increase from the 2,706 million square inches shipped during the previous quarter. New quarterly total area shipments are 5.4 percent higher than third quarter 2015 shipments and are at their highest recorded quarterly level.

“Global silicon wafer demand continued to grow during this quarter,” said Dr. Volker Braetsch, chairman SEMI SMG and senior vice president of Siltronic AG. “Year-to-date shipments are trending slightly above the same period as last year.”

Silicon* Area Shipment Trends

Millions of Square Inches

3Q 

2015

2Q 

2016

3Q 

2016

Q1 + Q2 + Q3 

2016

Q1 + Q2 + Q3 

2015
Total

 

2,591

2,706

2,730

7,973

7,930

 

Silicon wafers are the fundamental building material for semiconductors, which in turn, are vital components of virtually all electronics goods, including computers, telecommunications products, and consumer electronics. The highly engineered thin round disks are produced in various diameters (from one inch to 12 inches) and serve as the substrate material on which most semiconductor devices or “chips” are fabricated.

All data cited in this release is inclusive of polished silicon wafers, including virgin test wafers and epitaxial silicon wafers, as well as non-polished silicon wafers shipped by the wafer manufacturers to the end-users.

The Silicon Manufacturers Group acts as an independent special interest group within the SEMI structure and is open to SEMI members involved in manufacturing polycrystalline silicon, monocrystalline silicon or silicon wafers (e.g., as cut, polished, epi, etc.). The purpose of the group is to facilitate collective efforts on issues related to the silicon industry including the development of market information and statistics about the silicon industry and the semiconductor market.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with the Austrian company EV Group (EVG) have successfully manufactured a silicon-based multi-junction solar cell with two contacts and an efficiency exceeding the theoretical limit of silicon solar cells. For this achievement, the researchers used a “direct wafer bonding” process to transfer a few micrometers of III-V semiconductor material to silicon, a well-known process in the microelectronics industry. After plasma activation, the subcell surfaces are bonded together in vacuum by applying pressure. The atoms on the surface of the III-V subcell form bonds with the silicon atoms, creating a monolithic device. The efficiency achieved by the researchers presents a first-time result for this type of fully integrated silicon-based multi-junction solar cell. The complexity of its inner structure is not evident from its outer appearance: the cell has a simple front and rear contact just as a conventional silicon solar cell and therefore can be integrated into photovoltaic modules in the same manner.

Wafer-bonded III-V / Si multi-junction solar cell with 30.2 percent efficiency ©Fraunhofer ISE/A. Wekkeli

Wafer-bonded III-V / Si multi-junction solar cell with 30.2 percent efficiency ©Fraunhofer ISE/A. Wekkeli

“We are working on methods to surpass the theoretical limits of silicon solar cells,” says Dr. Frank Dimroth, department head at Fraunhofer ISE. “It is our long-standing experience with silicon and III-V technologies that has enabled us to reach this milestone today.” A conversion efficiency of 30.2 percent for the III-V / Si multi-junction solar cell of 4 cm² was measured at Fraunhofer ISE’s calibration laboratory. In comparison, the highest efficiency measured to date for a pure silicon solar cell is 26.3 percent, and the theoretical efficiency limit is 29.4 percent.

The III-V / Si multi-junction solar cell consists of a sequence of subcells stacked on top of each other. So-called “tunnel diodes” internally connect the three subcells made of gallium-indium-phosphide (GaInP), gallium-arsenide (GaAs) and silicon (Si), which span the absorption range of the sun’s spectrum. The GaInP top cell absorbs radiation between 300 and 670 nm. The middle GaAs subcell absorbs radiation between 500 and 890 nm and the bottom Si subcell between 650 and 1180 nm, respectively. The III-V layers are first epitaxially deposited on a GaAs substrate and then bonded to a silicon solar cell structure. Subsequently the GaAs substrate is removed, and a front and rear contact as well as an antireflection coating are applied.

“Key to the success was to find a manufacturing process for silicon solar cells that produces a smooth and highly doped surface which is suitable for wafer bonding as well as accounts for the different needs of silicon and the applied III-V semiconductors,” explains Dr. Jan Benick, team leader at Fraunhofer ISE.

“In developing the process, we relied on our decades of research experience in the development of highest efficiency silicon solar cells.” Institute Director Prof. Eicke Weber expresses his delight: “I am pleased that Fraunhofer ISE has so convincingly succeeded in breaking through the glass ceiling of 30 percent efficiency with its fully integrated silicon-based solar cell with two contacts. With this achievement, we have opened the door for further efficiency improvements for cells based on the long-proven silicon material.”

“The III-V / Si multi-junction solar cell is an impressive demonstration of the possibilities of our ComBond® cluster for resistance-free bonding of different semiconductors without the use of adhesives,” says Markus Wimplinger, Corporate Technology Development and IP Director at EV Group. “Since 2012, we have been working closely with Fraunhofer ISE on this development and today are proud of our team’s excellent achievements.” The direct wafer-bonding process is already used in the microelectronics industry to manufacture computer chips.

On the way to the industrial manufacturing of III-V / Si multi-junction solar cells, the costs of the III-V epitaxy and the connecting technology with silicon must be reduced. There are still great challenges to overcome in this area, which the Fraunhofer ISE researchers intend to solve through future investigations. Fraunhofer ISE’s new Center for High Efficiency Solar Cells, presently being constructed in Freiburg, will provide them with the perfect setting for developing next-generation III-V and silicon solar cell technologies. The ultimate objective is to make high efficiency solar PV modules with efficiencies of over 30 percent possible in the future.

The young researcher Dr. Romain Cariou carried out research on this project at Fraunhofer ISE with the support of a Marie Curie Postdoctoral Fellowship. Funding was provided by the EU project HISTORIC. The work at EVG was supported by the Austrian Ministry for Technology.

SunEdison Semiconductor Limited (NASDAQ:SEMI) (“SunEdison Semiconductor”) announced today that it has received notice that the Investment Committee of the Ministry of the Economic Affairs of the Republic of China has approved the proposed acquisition of SunEdison Semiconductor by GlobalWafers Co., Ltd. (“GlobalWafers”), and that the Austrian antitrust authority has concluded its review.  As a result, all pre-closing antitrust requirements have been completed.

As previously announced on August 17, 2016, GlobalWafers and SunEdison Semiconductor entered into a definitive agreement for the acquisition by GlobalWafers, through a wholly owned subsidiary, of all of the outstanding ordinary shares of SunEdison Semiconductor in an all-cash transaction valued at US$683 million, including SunEdison Semiconductor outstanding net indebtedness, pursuant to a scheme of arrangement under Singapore law.  Under the terms of the agreement, SunEdison Semiconductor shareholders will receive, upon consummation of the scheme of arrangement, US$12.00 per share in cash for each ordinary share.

Researchers from the Moscow Institute of Physics and Technology (MIPT), Technological Institute for Superhard and Novel Carbon Materials (TISNCM), Lomonosov Moscow State University (MSU), and the National University of Science and Technology MISiS have shown that an ultrastrong material can be produced by “fusing” multiwall carbon nanotubes together. The research findings have been published in Applied Physics Letters.

According to the scientists, a material of that kind is strong enough to endure very harsh conditions, making it useful for applications in the aerospace industry, among others.

The authors of the paper performed a series of experiments to study the effect of high pressure on multiwall carbon nanotubes (MWCNTs). In addition, they simulated nanotube behavior in high pressure cells, finding that the shear stress strain in the outer walls of the MWCNTs causes them to connect to each other as a result of the structural rearrangements on their outer surfaces. The inner concentric nanotubes, however, retain their structure completely: they simply shrink under pressure and restore their shape once the pressure is released.

The main feature of this study is that it demonstrates the possibility of covalent intertube bonding giving rise to interconnected (polymerized) multiwall nanotubes; these nanotubes being cheaper to produce than their single-wall counterparts.

“These connections between the nanotubes only affect the structure of the outer walls, whereas the inner layers remain intact. This allows us to retain the remarkable durability of the original nanotubes,” comments Prof. Mikhail Y. Popov of the Department of Molecular and Chemical Physics at MIPT, who heads the Laboratory of Functional Nanomaterials at TISNCM.

A shear diamond anvil cell (SDAC) was used for the pressure treatment of the nanotubes. The experiments were performed at pressures of up to 55 GPa, which is 500 times the water pressure at the bottom of the Mariana Trench. The cell consists of two diamonds, between which samples of a material can be compressed. The SDAC is different from other cell types in that it can apply a controlled shear deformation to the material by rotating one of the anvils. The sample in an SDAC is thus subjected to pressure that has both a hydrostatic and a shear component, i.e., the stress is applied both at a normal and parallel to its surface. Using computer simulations, the scientists found that these two types of stress affect the structure of the tubes in different ways. The hydrostatic pressure component alters the geometry of the nanotube walls in a complex manner, whereas the shear stress component induces the formation of sp³-hybridized amorphized regions on the outer walls, connecting them to the neighboring carbon tubes by means of covalent bonding. When the stress is removed, the shape of the inner layers of the connected multiwall tubes is restored.

Carbon nanotubes have a wide range of commercial applications by virtue of their unique mechanical, thermal and conduction properties. They are used in batteries and accumulators, tablet and smartphone touch screens, solar cells, antistatic coatings, and composite frames in electronics.