Category Archives: Packaging Materials

The ‘wonder material’ graphene has many interesting characteristics, and researchers around the world are looking for new ways to utilise them. Graphene itself does not have the characteristics needed to switch electrical currents on and off and smart solutions must be found for this particular problem. “We can make graphene structures with atomic precision. By selecting certain precursor substances (molecules), we can code the structure of the electrical circuit with extreme accuracy,” explains Peter Liljeroth from Aalto University, who conceived the research project together with Ingmar Swart from Utrecht University.

Seamless integration

The electronic properties of graphene can be controlled by synthesizing it into very narrow strips (graphene nanoribbons). Previous research has shown that the ribbon’s electronic characteristics are dependent on its atomic width. A ribbon that is five atoms wide behaves similarly to a metallic wire with extremely good conduction characteristics, but adding two atoms makes the ribbon a semiconductor. “We are now able to seamlessly integrate five atom-wide ribbons with seven atom-wide ribbons. That gives you a metal-semiconductor junction, which is a basic building block of electronic components,” according to Ingmar Swart.

Chemistry on a surface

The researchers produced their electronic graphene structures through a chemical reaction. They evaporated the precursor molecules onto a gold crystal, where they react in a very controlled way to yield new chemical compounds. “This is a different method from that currently used to produce electrical nanostructures, such as those on computer chips. For graphene, it is so important that the structure is precise at the atomic level and it is likely that the chemical route is the only effective method,” Ingmar Swart concludes.

Electronic characteristics

The researchers used advanced microscopic techniques to also determine the electronic and transport characteristics of the resulting structures. It was possible to measure electrical current through a graphene nanoribbon device with an exactly known atomic structure. “This is the first time where we can create e.g. a tunnel barrier and really know its exact atomic structure. Simultaneous measurement of electrical current through the device allows us to compare theory and experiment on a very quantitative level,” says Peter Liljeroth.

An international team of physicists, materials scientists and string theoreticians have observed a phenomenon on Earth that was previously thought to only occur hundreds of light years away or at the time when the universe was born. This result could lead to a more evidence-based model for the understanding the universe and for improving the energy-conversion process in electronic devices.

Using a recently discovered material called a Weyl semimetal, similar to 3D graphene, scientists at IBM Research (NYSE: IBM) have mimicked a gravitational field in their test sample by imposing a temperature gradient. The study was supervised by Prof. Kornelius Nielsch, Director at the Leibniz Institute for Materials and Solid State Research Dresden (IFW) and Prof. Claudia Felser, Director at the Max Planck Institute for Chemical Physics of Solids in Dresden.

After conducting the experiment in a cryolab at the University of Hamburg with high magnetic fields, a team of theoreticians from TU Dresden, UC Berkeley and the Instituto de Fisica Teorica UAM/CSIC confirmed with detailed calculations that they observed a quantum effect known as an axial-gravitational anomaly, which breaks one of the classical conservation laws, such as charge, energy and momentum.

This law-breaking anomaly had previously been derived in purely theoretical reasoning with methods based on string theory. It was believed to exist only at extremely high temperatures of trillions of degrees, as an exotic form of matter, called a quark-gluon plasma, at the early stages of the universe deep within the cosmos or created using particle colliders. But to their surprise, the researchers discovered that it also exists on Earth in the properties of solid-state physics, on which much of the computing industry is based on, spanning from tiny transistors to cloud data centers. This discovery is appearing today in the peer-reviewed journal Nature.

“For the first time, we have experimentally observed this fundamental quantum anomaly on Earth which is extremely important towards our understanding of the universe,” said Dr. Johannes Gooth, an IBM Research scientist and lead author of the paper. “We can now build novel solid-state devices based on this anomaly that have never been considered before to potentially circumvent some of the problems inherent in classical electronic devices, such as transistors.”

“This is an incredibly exciting discovery. We can clearly conclude that the same breaking of symmetry can be observed in any physical system, whether it occurred at the beginning of the universe or is happening today, right here on Earth,” said Prof. Dr. Karl Landsteiner, a string theorist at the Instituto de Fisica Teorica UAM/CSIC and co-author of the paper.

IBM scientists predict this discovery will open up a rush of new developments around sensors, switches and thermoelectric coolers or energy-harvesting devices, for improved power consumption.

An international team of researchers has found a way to determine whether a crystal is a topological insulator — and to predict crystal structures and chemical compositions in which new ones can arise. The results, published July 20 in the journal Nature, show that topological insulators are much more common in nature than currently believed.

Topological materials, which hold promise for a wide range of technological applications due to their exotic electronic properties, have attracted a great deal of theoretical and experimental interest over the past decade, culminating in the 2016 Nobel Prize in physics. The materials’ electronic properties include the ability of current to flow without resistance and to respond in unconventional ways to electric and magnetic fields.

Until now, however, the discovery of new topological materials occurred mainly by trial and error. The new approach described this week allows researchers to identify a large series of potential new topological insulators. The research represents a fundamental advance in the physics of topological materials and changes the way topological properties are understood.

The team included: at Princeton University, Barry Bradlyn and Jennifer Cano, both associate research scholars at the Princeton Center for Theoretical Science, Zhijun Wang, a postdoctoral research associate, and B. Andrei Bernevig, professor of physics; professors Luis Elcoro and Mois Aroyo at the University of the Basque Country in Bilbao; assistant professor Maia Garcia Vergniory of University of the Basque Country and Donostia International Physics Center (DIPC) in Spain; and Claudia Felser, professor at the Max Planck Institute for Chemical Physics of Solids in Germany.

“Our approach allows for a much easier way to find topological materials, avoiding the need for detailed calculations,” Felser said. “For some special lattices, we can say that, regardless of whether a material is an insulator or a metal, something topological will be going on,” Bradlyn added.

Until now, of the roughly 200,000 materials catalogued in materials databases, only around a few hundred are known to host topological behavior, according to the researchers. “This raised the question for the team: Are topological materials really that scarce, or does this merely reflect an incomplete understanding of solids?” Cano said.

To find out, the researchers turned to the nearly century-old band theory of solids, considered one of the early landmark achievements of quantum mechanics. Pioneered by Swiss-born physicist Felix Bloch and others, the theory describes the electrons in crystals as residing in specific energy levels known as bands. If all the states in a group of bands are filled with electrons, then the electrons cannot move and the material is an insulator. If some of the states are unoccupied, then electrons can move from atom to atom and the material is capable of conducting an electrical current.

Because of the symmetry properties of crystals, however, the quantum states of electrons in solids have special properties. These states can be described as a set of interconnected bands characterized by their momentum, energy and shape. The connections between these bands, which on a graph resemble tangled spaghetti strands, give rise to topological behaviors such as those of electrons that can travel on surfaces or edges without resistance.

The team used a systematic search to identify many previously undiscovered families of candidate topological materials. The approach combined tools from such disparate fields as chemistry, mathematics, physics and materials science.

First, the team characterized all the possible electronic band structures arising from electronic orbitals at all the possible atomic positions for all possible crystal patterns, or symmetry groups, that exist in nature, with the exception of magnetic crystals. To search for topological bands, the team first found a way to enumerate all allowed non-topological bands, with the understanding that anything left out of the list must be topological. Using tools from group theory, the team organized into classes all the possible non-topological band structures that can arise in nature.

Next, by employing a branch of mathematics known as graph theory — the same approach used by search engines to determine links between websites — the team determined the allowed connectivity patterns for all of the band structures. The bands can either separate or connect together. The mathematical tools determine all the possible band structures in nature — both topological and non-topological. But having already enumerated the non-topological ones, the team was able to show which band structures are topological.

By looking at the symmetry and connectivity properties of different crystals, the team identified several crystal structures that, by virtue of their band connectivity, must host topological bands. The team has made all of the data about non-topological bands and band connectivity available to the public through the Bilbao Crystallographic Server. “Using these tools, along with our results, researchers from around the world can quickly determine if a material of interest can potentially be topological,” Elcoro said.

The research shows that symmetry, topology, chemistry and physics all have a fundamental role to play in our understanding of materials, Bernevig said. “The new theory embeds two previously missing ingredients, band topology and orbital hybridization, into Bloch’s theory and provides a prescriptive path for the discovery and characterization of metals and insulators with topological properties.”

David Vanderbilt, a professor of physics and astronomy at Rutgers University who was not involved in the study, called the work remarkable. “Most of us thought it would be many years before the topological possibilities could be catalogued exhaustively in this enormous space of crystal classes,” Vanderbilt said. “This is why the work of Bradlyn and co-workers comes as such a surprise. They have developed a remarkable set of principles and algorithms that allow them to construct this catalogue at a single stroke. Moreover, they have combined their theoretical approach with materials database search methods to make concrete predictions of a wealth of new topological insulator materials.”

The theoretical underpinnings for these materials, called “topological” because they are described by properties that remain intact when an object is stretched, twisted or deformed, led to the awarding of the Nobel Prize in physics in 2016 to F. Duncan M. Haldane, Princeton University’s Sherman Fairchild University Professor of Physics, J. Michael Kosterlitz of Brown University, and David J. Thouless of the University of Washington.

Chemistry and physics take different approaches to describing crystalline materials, in which atoms occur in regularly ordered patterns or symmetries. Chemists tend to focus on the atoms and their surrounding clouds of electrons, known as orbitals. Physicists tend to focus on the electrons themselves, which can carry electric current when they hop from atom to atom and are described by their momentum.

“This simple fact — that the physics of electrons is usually described in terms of momentum, while the chemistry of electrons is usually described in terms of electronic orbitals — has left material discovery in this field at the mercy of chance,” Wang said.

“We initially set out to better understand the chemistry of topological materials — to understand why some materials have to be topological,” Vergniory said.

Aroyo added, “What came out was, however, much more interesting: a way to marry chemistry, physics and mathematics that adds the last missing ingredient in a century-old theory of electronics, and in the present-day search for topological materials.”

Taiwan is the world’s largest consumer of semiconductor materials for the seventh consecutive year, bringing new opportunities in this increasingly critical sector.  SEMICON Taiwan (13-15 September), held at Taipei’s Nangang Exhibition Center, will feature over 1,700 booths and 700 exhibitors, and more than 45,000 attendees from the global electronics manufacturing supply chain. This year, in addition to the much-anticipated Executive Summit, themed “Transformation: A Key to Solution,” 27 international forums will be held, exploring major issues. Speakers from TSMC, UMC, Powerchip, NVIDIA, Micron and Amkor will share their insights on trends and strategies of the next-generation electronics industry.

According to the SEMI Material Market Data Report, Taiwan’s semiconductor materials consumption was US$9.8 billion in 2016 − the world’s largest. Global semiconductor manufacturing equipment billings reached US$13.1 billion in Q1 2017, exceeding the record quarterly high set in Q3 2000. These figures signal that application drivers will continue to drive the development of a supply chain feeding their manufacturing processes, equipment and materials.

“As SEMICON Taiwan celebrates its 22nd year, the exhibition area will be expanded to closely align with the four major trends of applications in the market, which include Internet of Things (IoT), Smart Manufacturing, Smart Transportation, and Smart Medtech,” said Terry Tsao, president of SEMI Taiwan. “This year, SEMICON Taiwan aims to increasingly connect the entire manufacturing ecosystem vertically and horizontally. In addition, it will provide an overview of market trends and leading technologies in the industry, with forums and business matching activities which will enable collaboration and new opportunities.”

Theme Pavilions and Region Pavilions Focus on Opportunities

In addition to the eight customary theme pavilions, five new pavilions are featured this year, and to promote cross-border collaboration, eight regional pavilions are offered. The 21 pavilions include:

Theme Pavilions
  • Automated Optical Inspection (AOI)
  • Chemical Mechanical Planarization (CMP)
  • High-Tech Facility
  • Materials
  • Precision Machinery
  • Secondary Market
  • Smart Manufacturing & Automation
  • Taiwan Localization

 
New Theme Pavilions
  • Circular Economy
  • Compound Semiconductor
  • Flexible Hybrid Electronics/Micro-LED
  • Laser
  • Opto Semiconductor

 
Regional Pavilions
  • Cross-Strait
  • German
  • Holland High-Tech
  • Korean
  • Kyushu (Japan)
  • Okinawa (Japan)
  • Silicon Europe
  • Singapore

Co-located with SEMICON Taiwan 2017, the SiP Global Summit will discuss three key system-in-package topics:

  • Package Innovation in Automotive
  • 3D IC, 3D interconnection for AI and High-end Computing
  • Innovative Embedded Substrate and Fan-Out Technology to Enable 3D-SiP Devices

Participants will share trends on 2.5D/3D IC technologies, and the evolution and challenges of embedded technologies and wafer level packaging.

This is the first year that the International Test Conference (ITC) will be co-located with SEMICON Taiwan 2017, also marking the first time that ITC is held in Asia. The conference will focus on the rapid growth of emerging applications like IoT and automotive electronics, and how testing technologies are challenged by rapid advancements of manufacturing processes, 3D stacking and SiP.

For more information about SEMICON Taiwan 2017, please visit www.semicontaiwan.org or follow us on Facebook.

TECHCET CA—the advisory service firm providing electronic materials information—today announced that specialty chemical precursor market for the deposition of dielectrics and metals in integrated circuit (IC) fabrication is forecasted to increase at ~10% CAGR through the year 2021. TECHCET’s proprietary Wafer Forecast Model (WFM) shows that 3D-NAND devices are expected to grow at a rapid pace from 2016 and become one of the top three market segments by 2020. Logic ICs will continue to evolve, from 3D finFET devices to Gate-All-Around Nano-Wires (GAA-NW), enabled by new critical materials and manufacturing processes as detailed in new reports from TECHCET, “Advanced Insulating Dielectric Precursors,” and “ALD/CVD High-k & Metal Precursors.”

Precursors tracked by TECHCET for ALD/CVD of metal and high-k dielectric films on IC wafers include sources of aluminum, cobalt, hafnium, tantalum, titanium, tungsten, and zirconium. The total market for 2017 is now estimated to be US$435M, growing to US$638M in 2021. The top-2 suppliers are estimated to hold more than half of the total available market, with many players competing to supply the next enabling molecule. In particular, cobalt precursor demand is forecasted to reach >$80M in 2021 as foundries transition to below 14nm-node processing. As a potential conflict mineral, TECHCET tracks the sub-suppliers of cobalt.

“Metal precursors have had double-digit growth over an extended period of time, and we expect that to continue as the IC industry transitions to 10nm- and 7nm-node logic and 3D-NAND fabrication, with an average long term CAGR of 11% over 2013 to 2021,” says Dr. Jonas Sundqvist, lead author of the report, senior technology analyst with TECHCET and researcher with Fraunhofer IKTS. “Dielectric precursors growth today is clearly driven by dielectric PEALD deposition in multiple patterning, and by dielectric CVD in 3D-NAND.”

Precursors tracked by TECHCET for ALD/CVD/SOD of advanced dielectric films on IC wafers include multiple sources of silicon. The total market for 2017 is now estimated to be just over US$400M, growing to US$560M in 2021. Current growth over 10% is expected to slow slightly to be in the 8-10% range over 2019-2021. Anticipated near-term developments include transitions from CVD to ALD for several IC fab modules.

By Pete Singer

Semiconductor manufacturers use a variety of high global warming potential (GWP) gases to process wafers and to rapidly clean chemical vapor deposition (CVD) tool chambers. Processes use high GWP fluorinated compounds including perfluorocarbons (e.g., CF4, C2F6 and C3F8), hydrofluorocarbons (CHF3, CH3F and CH2F2), nitrogen trifluoride (NF3) and sulfur hexafluoride (SF6). Semiconductor manufacturing processes also use fluorinated heat transfer fluids and nitrous oxide (N2O).

Of these, the semiconductor industry naturally tends to focus its attention on CF4 since it is one of the worst offenders, with an atmospheric half-life of 50,000 years. “CF4 the hardest to get rid of and it’s one of the worst global warming gases,” said Kate Wilson, VP Marketing, Subfab Solutions – Semiconductor Division of Edwards. “We tend to use that as an indicator of how much of the other global warming gases, as well, are being emitted by the industry. If we’re dealing with that (CF4) well, we tend to be managing the rest of the gases pretty effectively.”

According to the Environmental Protection Agency (EPA), estimating fluorinated GHG emissions from semiconductor manufacture is complicated and has required a significant and coordinated effort by the industry and governments. It was historically assumed that the majority of these chemicals were consumed or transformed in the manufacturing process. It is now known that under normal operating conditions, anywhere between 10 to 80 percent of the fluorinated GHGs pass through the manufacturing tool chambers unreacted and are released into the air.

In addition, fluorinated GHG emissions vary depending on a number of factors, including gas used, type/brand of equipment used, company-specific process parameters, number of fluorinated GHG-using steps in a production process, generation of fluorinated GHG by-product chemicals, and whether appropriate abatement equipment has been installed. Companies’ product types, manufacturing processes and emissions also vary widely across semiconductor fabs.

The good news is that many companies in the semiconductor manufacturing industry have successfully identified, evaluated and implemented a variety of technologies that protect the climate and improved production efficiencies. Solutions have been investigated and successfully implemented in the following key technological areas:

  • Process improvements/source reduction
  • Alternative chemicals
  • Capture and beneficial reuse
  • Destruction technologies (known as abatement)

In 2011 the industry set new targets for 2020, which it summarizes as:

  • The implementation of best practices for new semiconductor fabs. The industry expects that the implementation of best practices will result in a normalized emission rate (NER) in 2020 of 0.22 kgCO2e/cm2, which is a 30 percent NER reduction from the 2010 aggregated baseline.
  • The addition of “Rest of World” fabs (fabs located outside the World Semiconductor Council (WSC) regions that are operated by a company from a WSC association) in reporting of emissions and the implementation of best practices for new fabs.
  • NER based measurement in kilograms of carbon equivalents per area of silicon wafers processed (kgCO2e/cm2), which will be the single WSC goal at the global level.

“We’re finding as we get down to the lower levels and different things come up as the highest priority in the fab where we’re moving into more and more lower usage processes, which are requiring abatement now in order to get those levels down to meet the targets of 2020 in the industry,” Wilson explained.

The main area for potential improvement now is etch, especially in older 200mm fabs where etch processes may not have been fitted with PFC abatement devices. This is particularly true for etch processes making extensive use of CF4. “The area where we still have the most gaps is clearly etch,” Wilson said. In CVD processes, most of the benefit was done by material shifts rather than actual abatement, although we clearly do need to abate the other gases in those processes. For the etch side, there are still quite a few customers that really only do the toxic emission abatement rather than the global warming gas emission abatement. But we do see, across almost all of our customer base, people have either fairly recently moved to fully abating all the PFC type gases or will be shortly.”

Wilson said some other gases have been coming up more recently in terms of things like N2O, which people are putting more focus on now as it’s becoming a larger part of the fab footprint of global warming materials.

For PFC abatement, Edwards offers the Atlas range of products, which destroys PFCs by burning them. This is followed by a wet scrub of the byproducts. This works quite well, but Wilson cautions that in can be tricky for some processes, such as chamber cleans with NF3. “If the burn is not correct and you get too hot, there’s actually the potential to create PFC’s. And so, it is quite critical to have well-controlled burn technology to make sure that you don’t actually cause issues where we didn’t have them before.”

Wilson said another area where they have seen some issues with PFCs being created is with processing of carbon-doped materials, such as low-k dielectrics. “When they do the chamber clean, they’re cleaning off predominately silicon dioxide but there’s carbon in there so that can create PFCs and CF4 as well so there’s a requirement to look at abatement in those areas,” she said.

Another piece of good news is that no company in the supply chain is waiting for legislation to be enacted before they act themselves. “Right from consumers to the consumer manufacturers, the car manufacturers, consumer electric manufacturers, our direct customers, the equipment manufacturers plus the major players within semiconductor and flat panel display, it seems that at every level there’s a commitment that this is the right thing to do,” Wilson said. “At every level people are pushing to get the requirements more stringent and it’s almost not about legislation anymore, it’s about everybody actually thinks it’s a good idea and they want to do it.”

Across all process areas in the fab effective abatement technologies reduce the GHG emissions significantly. The reductions per process area are shown in the diagram.

Across all process areas in the fab effective abatement technologies reduce the GHG emissions significantly. The reductions per process area are shown in the diagram.

By Pete Singer

In order to increase device performance, the semiconductor industry has slowly been implementing many new materials. From the 1960s through the 1990s, only a handful of materials were used, most notably silicon, silicon oxide, silicon nitride and aluminum. Soon, by 2020, more than 40 different materials will be in high-volume production, including more “exotic” materials such as hafnium, ruthenium, zirconium, strontium, complex III-Vs (such as InGaAs), cobalt and SiC.

These new materials create a variety of challenges with regard to process integration (understanding material interface issues, adhesion, stress, cross-contamination, etc.). But they also create new challenges when it comes to material handling.

“As we go through technology node advancements, people are looking at the potential of different materials on the wafer,” notes Clint Haris, Senior Vice President and General Manager of the Microcontamination Control Division at Entegris (Billerica, MA). “They’re looking at different chemicals that are required to clean those materials to reduce defects and improve their operational yield, and what we’re increasingly seeing is that fabs are concerned with the fact that contamination can be introduced in the fluid stream anywhere in that long process flow.”

Haris said that part of their mission at Entegris is to make sure that the entire supply chain – from the development of a chemistry at the supplier to its use on a wafer in a fab – is working in harmony, particularly with regard to any materials that might “touch” the chemicals. “Not only do you want to filter and purify things throughout the whole fluid flow,” he said, “but you want to have that last filtration right before the fluid touches the surface of the wafer.”

The goal of filtration is, of course, to remove contaminants and particles before they reach the wafer, but the exact purity required can be a moving target. “Today we’re seeing a lot of these materials and liquids, which have a parts per trillion purity level, but there’s a desire to move to parts per quadrillion,” Haris said. That’s the equivalent of one drop in all the water that flows over Niagra Falls in one day.

In addition to the filtration challenge of achieving that level, there’s the question of do the analytical tools exist to actually measure contaminants at that level. The answer – not yet. “It’s actually a real issue where some of the metrology tools cannot meet our customers’ needs at those levels, and so one of the things that we’ve done is we’ve developed some techniques internally to enhance the capability of metrology,” Haris said. “We also work on how we prepare our samples so you can detect contamination at those levels.” Because that level of detection is so difficult — in some cases impossible – Haris said fabs are increasingly putting additional filters at the process tool and at the dispense nozzle to “protect against the unknown.”

Earlier this year, Entegris introduced Purasol™, a first-of-its-kind solvent purifier that removes a wide variety of metal microcontaminants found in organic solvents used in ultraclean chemical manufacturing processes. Using tailored membrane technology, the purifier can efficiently remove both dissolved and colloidal metal contaminants from a wide variety of ultra-pure, polar and non-polar solvents. “One of the main things that our customers are seeing is a concern with metal contamination in the photo process that can result in particular defects (see Figure), such as bridge defects,” Haris explained. Increasingly, fabs are moving from just filtration (removing particles) to purification (removing ions and metals), he added.

Illustration of metal contamination inducing defects on lithography process.

Illustration of metal contamination inducing defects on lithography process.

Entegris also recently acquired W. L. Gore & Associates’ water and chemical filtration product line for microelectronics applications. “This is a Teflon-based product line, which is used in ultrapure water filtration for semiconductor fabs, but it’s also a product that we’re selling into some of the fine chemical purification markets for some of the chemistries that are brought into the fabs,” Haris said. “We are focused on new product development and M&A to enhance our capability to support our customers as they overcome these contamination challenges..”

A new low-temperature solution printing technique allows fabrication of high-efficiency perovskite solar cells with large crystals intended to minimize current-robbing grain boundaries. The meniscus-assisted solution printing (MASP) technique boosts power conversion efficiencies to nearly 20 percent by controlling crystal size and orientation.

The process, which uses parallel plates to create a meniscus of ink containing the metal halide perovskite precursors, could be scaled up to rapidly generate large areas of dense crystalline film on a variety of substrates, including flexible polymers. Operating parameters for the fabrication process were chosen by using a detailed kinetics study of perovskite crystals observed throughout their formation and growth cycle.

“We used a meniscus-assisted solution printing technique at low temperature to craft high quality perovskite films with much improved optoelectronic performance,” said Zhiqun Lin, a professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “We began by developing a detailed understanding of crystal growth kinetics that allowed us to know how the preparative parameters should be tuned to optimize fabrication of the films.”

The new technique is reported July 7 in the journal Nature Communications. The research has been supported by the Air Force Office of Scientific Research (AFOSR) and the National Science Foundation (NSF).

Georgia Tech Research Scientist Ming He adjusts the equipment for the meniscus-assisted solution printing (MASP) technique used to fabricate perovskite films for solar cells. (Credit: Rob Felt, Georgia Tech)

Georgia Tech Research Scientist Ming He adjusts the equipment for the meniscus-assisted solution printing (MASP) technique used to fabricate perovskite films for solar cells. (Credit: Rob Felt, Georgia Tech)

Perovskites offer an attractive alternative to traditional materials for capturing electricity from light, but existing fabrication techniques typically produce small crystalline grains whose boundaries can trap the electrons produced when photons strike the materials. Existing production techniques for preparing large-grained perovskite films typically require higher temperatures, which is not favorable for polymer materials used as substrates – which could help lower the fabrication costs and enable flexible perovskite solar cells.

So Lin, Research Scientist Ming He and colleagues decided to try a new approach that relies on capillary action to draw perovskite ink into a meniscus formed between two nearly parallel plates approximately 300 microns apart. The bottom plate moves continuously, allowing solvent to evaporate at the meniscus edge to form crystalline perovskite. As the crystals form, fresh ink is drawn into the meniscus using the same physical process that forms a coffee ring on an absorbent surface such as paper.

“Because solvent evaporation triggers the transport of precursors from the inside to the outside, perovskite precursors accumulate at the edge of the meniscus and form a saturated phase,” Lin explained. “This saturated phase leads to the nucleation and growth of crystals. Over a large area, we see a flat and uniform film having high crystallinity and dense growth of large crystals.”

To establish the optimal rate for moving the plates, the distance between plates and the temperature applied to the lower plate, the researchers studied the growth of perovskite crystals during MASP. Using movies taken through an optical microscope to monitor the grains, they discovered that the crystals first grow at a quadratic rate, but slow to a linear rate when they began to impinge on their neighbors.

“When the crystals run into their neighbors, that affects their growth,” noted He. “We found that all of the grains we studied followed similar growth dynamics and grew into a continuous film on the substrate.”

The MASP process generates relatively large crystals – 20 to 80 microns in diameter – that cover the substrate surface. Having a dense structure with fewer crystals minimizes the gaps that can interrupt the current flow, and reduces the number of boundaries that can trap electrons and holes and allow them to recombine.

Using films produced with the MASP process, the researchers have built solar cells that have power conversion efficiencies averaging 18 percent – with some as high as 20 percent. The cells have been tested with more than 100 hours of operation without encapsulation. “The stability of our MASP film is improved because of the high quality of the crystals,” Lin said.

Doctor-blading is one of the conventional perovskite fabrication techniques in which higher temperatures are used to evaporate the solvent. Lin and his colleagues heated their substrate to only about 60 degrees Celsius, which would be potentially compatible with polymer substrate materials.

So far, the researchers have produced centimeter-scale samples, but they believe the process could be scaled up and applied to flexible substrates, potentially facilitating roll-to-roll continuous processing of the perovskite materials. That could help lower the cost of producing solar cells and other optoelectronic devices.

“The meniscus-assisted solution printing technique would have advantages for flexible solar cells and other applications requiring a low-temperature continuous fabrication process,” Lin added. “We expect the process could be scaled up to produce high throughput, large-scale perovskite films.”

Among the next steps are fabricating the films on polymer substrates, and evaluating other unique properties (e.g., thermal and piezotronic) of the material.

Umicore’s business unit Precious Metals Chemistry today inaugurated its production unit for advanced metal organic precursor technologies used in the semiconductor and LED markets, respectively TMGa (Trimethylgallium) and TEGa (Triethylgallium). The event was attended by European and overseas customers as well as local and regional politicians. The guest of honor was Dr. Barbara Hendricks, Germany’s Federal Minister for the Environment, Nature Conservation, Building and Nuclear Safety.

Umicore’s TMGa manufacturing process is innovative and unique. It offers a more sustainable and ecological production method by minimizing hazardous side streams and material losses and optimizing yield to nearly 100%.

Dr. Lothar Mussmann, Vice-President of Umicore Precious Metals Chemistry said, “I am proud that this patented innovation has now become a world-class and industrial scale manufacturing plant. It will provide benefits for our customers and the environment and underlines Umicore’s position as a pioneer in sustainable technologies.”

Umicore Precious Metals Chemistry is the only European manufacturer of TMGa and TEGa and supplies customers across the world from its Hanau manufacturing base. Umicore Precious Metals Chemistry helps to reduce cost of ownership through its innovative approach to process chemistry and its collaborative approach with customers and end users.

About Trimethylgallium and Umicore’s manufacturing process

Trimethylgallium (TMGa) is a colorless liquid with very high vapor pressure, which boils at low temperatures. Umicore’s new production process increases the yield of TMGa in comparison with current production technologies. In this way, organic solvents can be completely dispensed with. The TMGa is prepared by chemically reacting gallium trichloride with a more efficient methylating agent in molten salt. This reduces the amount of waste per kilogram of TMGa by more than 50%, with the resulting intermediates being recycled in the process. The finished product is then used in the semiconductor industry, where it evaporates in closed systems onto a substrate. This creates, for example, environmentally friendly LED lamps.

Today SEMI announced that the two-day Strategic Materials Conference (SMC) − devoted to materials technology and business drivers in the electronics supply chain − is slated for September 19-20 at San Jose’s Doubletree by Hilton Hotel. For over a decade, SMC has been the leading conference dedicated to electronic materials. The 2017 conference theme, Materials Accelerating Innovation, will delve into the demand drivers for new materials. A full conference agenda and registration details can be found here.

Electronic materials and processes will continue to enable the extension of semiconductor device development for the foreseeable future. SMC provides a comprehensive review of the economic and environmental influences, strategic and technical challenges, and regional trends. The conference also highlights opportunities in adjacent markets and basic research activities feeding the supply chain. Presentations by industry thought leaders, academics, and analysts will analyze technologies and trends enabling extension of innovative solutions in wafer processing. SMC 2017 sessions include:

  • Keynotes:
    • Mark Papermaster, CTO and senior VP, AMD
    • Dave Hemker, CTO and senior VP, Lam Research
    • Sunny Hui, senior VP, Semiconductor Manufacturing International Corp (SMIC)
  • Economic/Market Trends: The Consolidation Game (M&A), China, 200mm & More: Experts weigh in on trends in materials and semiconductor equipment growth, demand, and applications, as well as the impact of the global economy on the semiconductor market.
  • Process Challenges at 5nm & Beyond: Leading-edge transistor development is focused on scaling and connecting vertical structures for advanced designs bringing new process and material challenges, requiring collaboration across the semiconductor supply chain.
  • Universities − Innovation Drivers: University research has been key to enabling the industry’s exponential growth. As the industry faces daunting challenges, the role of university research in materials is more critical than ever.
  • The Future of Materials Market in China: Speakers from government, suppliers, and multi-nationals will discuss China’s semiconductor materials industry, government policies, growth opportunities, and best practices for operating in this expanding environment.
  • Materials Supply Chain Challenges in Adjacent Industries: Electronic devices take many forms beyond silicon. Flexible electronics, embedded memory, medical devices, automotive electronics, Flat Panel Displays, and OLEDs have unique challenges.
  • Heterogeneous Integration – Implications on Materials & Packaging: With 10nm fab budgets estimated at up to $10 billion, “sticker shock” has set in. Enter Heterogeneous Integration — integrating separately manufactured components into higher-level assemblies to enable expanded functionality at a lower cost than traditional scaling.
  • Panel Discussion – Business Strategy and Collaboration Model:  Panelists will address current and emerging material challenges through focused R&D Investment, collaboration throughout the vertical supply chain, and application of innovative business strategy to ensure win-win for all participating companies.

The Strategic Materials Conference attracts the key players from every segment of the semiconductor manufacturing industry. The conference provides comprehensive, in-depth content and exceptional networking opportunities for professionals who share strategic objectives for the electronics manufacturing ecosystem. To learn more and to register, visit www.semi.org/SMC.