Category Archives: Packaging Materials

The bill of materials (BOM) for an iPhone 7 equipped with 32 gigabytes (GB) of NAND flash memory carries $219.80 in bill of materials costs, according to a preliminary estimate from IHS Markit (Nasdaq: INFO), a source in critical information, analytics and solutions.

After $5 in basic manufacturing costs are added, Apple’s total cost to manufacture the iPhone 7 rises to $224.80. The unsubsidized price for a 32GB iPhone 7 is $649. IHS Markit has not yet performed a teardown analysis on the larger iPhone 7 Plus. This preliminary estimated total is $36.89 higher than the final analysis of the iPhone 6S published by IHS in December 2015.

“Total BOM costs for the iPhone 7 are more in line with what we have seen in teardowns of recent flagship phones from Apple’s main competitor, Samsung, in that the costs are higher than in previous iPhone teardown analyses,” said Andrew Rassweiler, senior director of cost benchmarking services for IHS Markit. “All other things being equal, Apple still makes more margin from hardware than Samsung, but materials costs are higher than in the past.”

Same shape. No jack.

While the overall shape and physical design of the iPhone 7 is similar to the iPhone 6S that preceded it, the new display has wider color gamut, including DCI-P3 as well as traditional sRGB, which improves the rendering of photos and videos. The device’s haptic engine, which provides the “click” feel for users, has also been improved for longer-duty cycles and better dynamic response. The home button is now static and mimics the MacBook in terms of a solid-state button design.

Apple has also eliminated the 3.5 millimeter headphone jack, allowing a larger battery and haptic motor. “Where there was an audio jack in the previous design, Apple replaced it with a symmetrical grill — not for speakers, but for the waterproof microphone, leaving more room for the larger battery and Taptic Engine,” Rassweiler said.

Increased base-model storage

Apple has increased the iPhone 7’s storage density. For the first time, the base model starts at 32 gigabytes (GB) – which is only the second time Apple has upgraded the base storage in the iPhone. From a cost perspective, the shift from 16GB/64GB/128GB iPhones to 32GB/128GB/256GB is a big jump. “Despite significant cost erosion in NAND flash over the last year, this increase in the overall memory cost definitely puts pressure on the bill of materials costs — and therefore margins — from Apple’s perspective,” Rassweiler said.

Intel returns

The Intel design win, and six years of absence that Intel had from the iPhone, is important to note. Even so, Intel still shares the processor business with Qualcomm. “Whereas Apple strives to have ‘one iPhone model for all carriers and markets,’ there are a number of different hardware permutations supporting various countries and carriers,” Rassweiler said. “Apple will likely look for ways to simplify the design moving forward, which means one supplier – whether Intel or Qualcomm – will likely dominate, as part of supplier and SKU streamlining.”

According to Wayne Lam, principal analyst of smartphone electronics, IHS Markit, “Largely left behind in the 4G LTE market, Intel has finally worked itself back into the iPhone, which is a huge win, but not one that is going to be financially significant in the near term for Intel.”

RF paths

Apple has also eliminated segmented antenna bands, which means the company is pushing all radio-frequency (RF) paths to the very ends of the phone – both on the top and bottom. The aluminum uni-body construction and design forces all RF paths into those two locations. Whereas other smartphones use a glass back and RF components with antennas mounted on the ample back spaces, Apple is restricted to just two physical antennas.  “This design limitation may force Apple to go back to an all-glass design again so that they can fit in 4x4MIMO LTE antennas and more features like wireless charging in the next iPhone iteration,” Lam said.

Modem moved

The baseband thin modem has been moved next to the A10 processor. Prior to the iPhone 7, the thin modem was always on the other side of the SIM card receptacle. “This is a subtle change but likely shows us where Apple wants to take this,” Lam said, “eventually putting the thin modem right on the apps processor package or even integrating it into the A-series processor.”

Officially water resistant

iPhone 7 is now officially rated as water resistant. “We also saw evidence of this water proofing design evolution in the earlier iPhone 6S, which included additional gasketing around critical connectors, as well as the use of WiFi antenna at the end of the primary speaker box,”Lam said. “Doing so pushes the antennas near the only other opening, for better reception and transmission.”

Jet-black polished case

Jet black polish is a new option on 128GB and 256GB models. “This is a new feature that produces a whole new look for the iPhone,” Lam said. “It is a lower yielding, time-intensive manufacturing step that adds cost, as well as considerable value, pushing the retail price higher for those requesting this option.”

Antenna speaker design

The antenna speaker design on the iPhone 7 came from the WiFi antenna packed into the speakers of Apple’s MacBook.  “Apple likes to reuse these unique designs throughout their product lines,” Lam said. In a first for the iPhone series, the headset speaker now doubles as a stereo speaker.

Upgraded camera

While not as groundbreaking as the two optical paths in the iPhone 7 Plus, the iPhone 7 camera has now been upgraded to optical image stabilization (OIS), for better low light performance.

Improved battery life

The battery has been increased to 1960mAhr capacity from 1715mAh in the previous iPhone 6s.  This change is consistent with Apple’s claims of improved battery life.

Solid State Technology announced today that its premier semiconductor manufacturing conference and networking event, The ConFab, will be held at the iconic Hotel del Coronado in San Diego on May 14-17, 2017. A 30% increase in attendance in 2016 with a similar uplift expected in 2017, makes the venue an ideal meeting location as The ConFab continues to expand.

    

For more than 12 years, The ConFab, an invitation-only executive conference, has been the destination for key industry influencers and decision-makers to connect and collaborate on critical issues.

“The semiconductor industry is maturing, yet opportunities abound,” said Pete Singer, Editor-in-Chief of Solid State Technology and Conference Chair of The ConFab. “The Internet of Things (IoT) is exploding, which will result in a demand for “things” such as sensors and actuators, as well as cloud computing. 5G is also coming and will be the key technology for access to the cloud.”

The ConFab is the best place to seek a deeper understanding on these and other important issues, offering a unique blend of market insights, technology forecasts and strategic assessments of the challenges and opportunities facing semiconductor manufacturers. “In changing times, it’s critical for people to get together in a relaxed setting, learn what’s new, connect with old friends, make new acquaintances and find new business opportunities,” Singer added.

Dave Mount

David Mount

Solid State Technology is also pleased to announce the addition of David J. Mount to The ConFab team as marketing and business development manager. Mount has a rich history in the semiconductor manufacturing equipment business and will be instrumental in guiding continued growth, and expanding into new high growth areas.

Mainstream semiconductor technology will remain the central focus of The ConFab, and the conference will be expanded with additional speakers, panelists, and VIP attendees that will participate from other fast growing and emerging areas. These include biomedical, automotive, IoT, MEMS, LEDs, displays, thin film batteries, photonics and advanced packaging. From both the device maker and the equipment supplier perspective, The ConFab 2017 is a must-attend networking conference for business leaders.

The ConFab conference program is guided by a stellar Advisory Board, with high level representatives from GLOBALFOUNDRIES, Texas Instruments, TSMC, Cisco, Samsung, Intel, Lam Research, KLA-Tencor, ASE, NVIDIA, the Fab Owners Association and elsewhere.

Details on the invitation-only conference are at: www.theconfab.com. For sponsorship inquiries, contact Kerry Hoffman at [email protected]. For details on attending as a guest or qualifying as a VIP, contact Sally Bixby at [email protected].

Materials with large dielectric constants — aka “high-K materials” — have recently garnered attention for their potential use within future generations of reduced-dimension semiconductor devices.

Barium strontium titanate, one such material, possesses an inherently large dielectric constant that can be altered significantly by an applied electrical field — by as much as a factor of 10. While this property has been known to exist for more than half a century and many researchers have attempted to exploit it, the technology has been limited by the low quality of the material. By semiconductor industry standards, the material is considered to be defective.

But researchers at University of California, Santa Barbara, who began exploring thin-film tunable dielectrics using sputtered material nearly two decades ago, are now trying to leverage advanced and scalable materials deposition techniques like molecular beam epitaxy (MBE) to create tunable, high-frequency integrated circuits and devices with high-quality materials that are comparable to modern semiconductor technology.

As the group reports this week in Applied Physics Letters, from AIP Publishing, by using extremely high-quality epitaxial materials they were able to greatly reduce the dielectric loss in ferroelectric tunable radio-frequency (RF) capacitors. Advances at the fundamental level, such as this one, open the door to future RF materials and devices that can be electrically reconfigured or “tuned” to adapt to changing environments.

The catch is that the deposition of complex oxides, such as barium strontium titanate, is problematic because of the high temperatures and oxygen-rich environment involved.

“Our work was made possible by recent advances in a hybrid form of MBE at UCSB that uses metal organic precursors,” explained Susanne Stemmer, a professor at the Materials Research Laboratory at UCSB.

The material’s large dielectric constants “present fabrication challenges because the inherently high capacitance density of the films requires smaller electrode dimensions and finer lithography than many typical integrated capacitor structures,” said Robert York, a professor in the Electrical & Computer Engineering department at UCSB. “Low-loss reactive devices also pose significant measurement challenges at microwave frequencies. The close collaboration of materials scientists and electrical engineers, and years of experience in device processing, was integral to the success of our work.”

Significantly, the team’s work clarifies that early work within the field that reported disappointing performances of BST-based devices was limited primarily by deposition and processing methods — not by intrinsic limitations of the underlying material itself.

“Our work also demonstrates that with suitable modifications, MBE systems — a proven technology for large-scale manufacturing of compound semiconductor materials — can be used to deposit a wide variety of high-quality materials,” Stemmer noted.

Another key discovery for the team was “exposing the susceptibility of the material to contamination by other organic materials commonly used in photolithography processes, which required some changes in the fabrication process that, in retrospect, may have factored into the low quality factors reported in the past,” York pointed out.

In terms of applications, materials capable of being altered electronically show enormous potential for adaptive or reconfigurable electronic systems — particularly high-frequency communications.

“For example, tunable capacitors using barium strontium titanate can be used to create tunable antennas for cellular communications, which allows a small antenna to be tuned over a wide frequency range or enables a phone to adapt to different surroundings for improved efficiency and battery life,” York said.

Barium strontium titanate devices can also be used to create low-cost phase-shifter devices for phased-array antennas in mobile satellite communication systems.

“In fact, some barium strontium titanate devices are already used for commercial RF electronics and the infrastructure for deposition and fabrication already exists within most semiconductor foundries, so the timeline for exploiting this advance could be relatively short compared to the typical timeline for a materials advance,” York added.

While numerous research avenues exist for further exploring the materials involved, and improving the processing and device design, one immediate next step for the team is to “demonstrate high-performance integrated circuits with films deposited directly on metal electrodes,” Stemmer said. “Integration with other commercially viable substrate materials is also of interest.”

It is the double helix, with its stable and flexible structure of genetic information, that made life on Earth possible in the first place. Now a team from the Technical University of Munich (TUM) has discovered a double helix structure in an inorganic material. The material comprising tin, iodine and phosphorus is a semiconductor with extraordinary optical and electronic properties, as well as extreme mechanical flexibility.

Flexible yet robust – this is one reason why nature codes genetic information in the form of a double helix. Scientists at TU Munich have now discovered an inorganic substance whose elements are arranged in the form of a double helix.

The substance called SnIP, comprising the elements tin (Sn), iodine (I) and phosphorus (P), is a semiconductor. However, unlike conventional inorganic semiconducting materials, it is highly flexible. The centimeter-long fibers can be arbitrarily bent without breaking.

“This property of SnIP is clearly attributable to the double helix,” says Daniela Pfister, who discovered the material and works as a researcher in the work group of Tom Nilges, Professor for Synthesis and Characterization of Innovative Materials at TU Munich. “SnIP can be easily produced on a gram scale and is, unlike gallium arsenide, which has similar electronic characteristics, far less toxic.”

Countless application possibilities

The semiconducting properties of SnIP promise a wide range of application opportunities, from energy conversion in solar cells and thermoelectric elements to photocatalysts, sensors and optoelectronic elements. By doping with other elements, the electronic characteristics of the new material can be adapted to a wide range of applications.

Due to the arrangement of atoms in the form of a double helix, the fibers, which are up to a centimeter in length can be easily split into thinner strands. The thinnest fibers to date comprise only five double helix strands and are only a few nanometers thick. That opens the door also to nanoelectronic applications.

“Especially the combination of interesting semiconductor properties and mechanical flexibility gives us great optimism regarding possible applications,” says Professor Nilges. “Compared to organic solar cells, we hope to achieve significantly higher stability from the inorganic materials. For example, SnIP remains stable up to around 500°C (930 °F).”

Just at the beginning

“Similar to carbon, where we have the three-dimensional (3D) diamond, the two dimensional graphene and the one dimensional nanotubes,” explains Professor Nilges, “we here have, alongside the 3D semiconducting material silicon and the 2D material phosphorene, for the first time a one dimensional material – with perspectives that are every bit as exciting as carbon nanotubes.”

Just as with carbon nanotubes and polymer-based printing inks, SnIP double helices can be suspended in solvents like toluene. In this way, thin layers can be produced easily and cost-effectively. “But we are only at the very beginning of the materials development stage,” says Daniela Pfister. “Every single process step still needs to be worked out.”

Since the double helix strands of SnIP come in left and right-handed variants, materials that comprise only one of the two should display special optical characteristics. This makes them highly interesting for optoelectronics applications. But, so far there is no technology available for separating the two variants.

Theoretical calculations by the researchers have shown that a whole range of further elements should form these kinds of inorganic double helices. Extensive patent protection is pending. The researchers are now working intensively on finding suitable production processes for further materials.

Interdisciplinary cooperation

An extensive interdisciplinary alliance is working on the characterization of the new material: Photoluminescence and conductivity measurements have been carried out at the Walter Schottky Institute of the TU Munich. Theoretical chemists from the University of Augsburg collaborated on the theoretical calculations. Researchers from the University of Kiel and the Max Planck Institute of Solid State Research in Stuttgart performed transmission electron microscope investigations. Mössbauer spectra and magnetic properties were measured at the University of Augsburg, while researchers of TU Cottbus contributed thermodynamics measurements.

Lomonosov MSU physicists found a way to “force” silicon nanoparticles to glow in response to radiation strongly enough to replace expensive semiconductors used in display business. According to Maxim Shcherbakov, researcher at the Department of Quantum Electronics of the Moscow State University and one of the authors of the study, the developed method considerably enhances the efficiency of nanoparticle photoluminescence.

The key term in the problem is photoluminescence — the process, when materials irradiated by visible or ultraviolet radiation start to respond with their own light, but in a different spectral range. In the study, the material glows red.

In some of the modern displays, semiconductor nanoparticles, or the so-called quantum dots, are used. In quantum dots, electrons behave completely unlike those in the bulk semiconductor, and it has long been known that quantum dots possess excellent luminescent properties. Today, for the purposes of quantum-dot based displays various semiconductors are used, i.e. CdSe, etc. These materials are toxic and expensive, and, therefore, researchers have long been scrutinizing the far cheaper and much more studied silicon. It is also suitable for such use in all respects except one — silicon nanoparticles vaguely respond to radiation, which is not appealing for optoelectronic industry.

Scientists all over the world were seeking to solve this problem since the beginning of the 1990’s, but until now no significant success has been achieved in this direction. The breakthrough idea about how to “tame” silicon originated in Sweden, at the Royal Institute of Technology, Kista. A post-doctoral researcher Sergey Dyakov (a graduate of the MSU Faculty of Physics and the first author of the paper) suggested placing an array of silicon nanoparticles in a matrix with a non-homogeneous dielectric medium and cover it with golden nanostripes.

‘The heterogeneity of the environment, as has been previously shown in other experiments, allows to increase the photoluminescence of silicon by several orders of magnitude due to the so-called quantum confinement,’ says Maxim Shcherbakov. ‘However, the efficiency of the light interaction with nanocrystals still remains insufficient. It has been proposed to enhance the efficiency by using plasmons (quasiparticle appearing from fluctuations of the electron gas in metals — ed). Plasmon lattice formed by golden nanostripes allow to “hold” light on the nanoscale, and allow a more effective interaction with nanoparticles located nearby, bringing its luminescence to an increase.’

The MSU experiments with samples of “gold-plated” matrix with silicon nanoparticles made in Sweden brilliantly confirmed the theoretical predictions – the UV irradiated silicon for the first time shone bright enough to be used it in practice.

The first author of the paper Sergey Dyakov will present the findings on The 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (September 17-22, Crete). The work was also published in the Physical Review B (“Optical properties of silicon nanocrystals covered by periodic array of gold nanowires”).

For decades, scientists have tried to harness the unique properties of carbon nanotubes to create high-performance electronics that are faster or consume less power — resulting in longer battery life, faster wireless communication and faster processing speeds for devices like smartphones and laptops.

But a number of challenges have impeded the development of high-performance transistors made of carbon nanotubes, tiny cylinders made of carbon just one atom thick. Consequently, their performance has lagged far behind semiconductors such as silicon and gallium arsenide used in computer chips and personal electronics.

Now, for the first time, University of Wisconsin-Madison materials engineers have created carbon nanotube transistors that outperform state-of-the-art silicon transistors.

The UW-Madison engineers use a solution process to deposit aligned arrays of carbon nanotubes onto 1 inch by 1 inch substrates. The researchers used their scalable and rapid deposition process to coat the entire surface of this substrate with aligned carbon nanotubes in less than 5 minutes. The team's breakthrough could pave the way for carbon nanotube transistors to replace silicon transistors, and is particularly promising for wireless communications technologies. Credit: Stephanie Precourt

The UW-Madison engineers use a solution process to deposit aligned arrays of carbon nanotubes onto 1 inch by 1 inch substrates. The researchers used their scalable and rapid deposition process to coat the entire surface of this substrate with aligned carbon nanotubes in less than 5 minutes. The team’s breakthrough could pave the way for carbon nanotube transistors to replace silicon transistors, and is particularly promising for wireless communications technologies. Credit: Stephanie Precourt

Led by Michael Arnold and Padma Gopalan, UW-Madison professors of materials science and engineering, the team’s carbon nanotube transistors achieved current that’s 1.9 times higher than silicon transistors. The researchers reported their advance in a paper published Friday (Sept. 2) in the journal Science Advances.

“This achievement has been a dream of nanotechnology for the last 20 years,” says Arnold. “Making carbon nanotube transistors that are better than silicon transistors is a big milestone. This breakthrough in carbon nanotube transistor performance is a critical advance toward exploiting carbon nanotubes in logic, high-speed communications, and other semiconductor electronics technologies.”

This advance could pave the way for carbon nanotube transistors to replace silicon transistors and continue delivering the performance gains the computer industry relies on and that consumers demand. The new transistors are particularly promising for wireless communications technologies that require a lot of current flowing across a relatively small area.

As some of the best electrical conductors ever discovered, carbon nanotubes have long been recognized as a promising material for next-generation transistors.

Carbon nanotube transistors should be able to perform five times faster or use five times less energy than silicon transistors, according to extrapolations from single nanotube measurements. The nanotube’s ultra-small dimension makes it possible to rapidly change a current signal traveling across it, which could lead to substantial gains in the bandwidth of wireless communications devices.

But researchers have struggled to isolate purely carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and disrupt their semiconducting properties — like a short in an electronic device.

The UW-Madison team used polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

“We’ve identified specific conditions in which you can get rid of nearly all metallic nanotubes, where we have less than 0.01 percent metallic nanotubes,” says Arnold.

Placement and alignment of the nanotubes is also difficult to control.

To make a good transistor, the nanotubes need to be aligned in just the right order, with just the right spacing, when assembled on a wafer. In 2014, the UW-Madison researchers overcame that challenge when they announced a technique, called “floating evaporative self-assembly,” that gives them this control.

The nanotubes must make good electrical contacts with the metal electrodes of the transistor. Because the polymer the UW-Madison researchers use to isolate the semiconducting nanotubes also acts like an insulating layer between the nanotubes and the electrodes, the team “baked” the nanotube arrays in a vacuum oven to remove the insulating layer. The result: excellent electrical contacts to the nanotubes.

The researchers also developed a treatment that removes residues from the nanotubes after they’re processed in solution.

“In our research, we’ve shown that we can simultaneously overcome all of these challenges of working with nanotubes, and that has allowed us to create these groundbreaking carbon nanotube transistors that surpass silicon and gallium arsenide transistors,” says Arnold.

The researchers benchmarked their carbon nanotube transistor against a silicon transistor of the same size, geometry and leakage current in order to make an apples-to-apples comparison.

They are continuing to work on adapting their device to match the geometry used in silicon transistors, which get smaller with each new generation. Work is also underway to develop high-performance radio frequency amplifiers that may be able to boost a cellphone signal. While the researchers have already scaled their alignment and deposition process to 1 inch by 1 inch wafers, they’re working on scaling the process up for commercial production.

Arnold says it’s exciting to finally reach the point where researchers can exploit the nanotubes to attain performance gains in actual technologies.

“There has been a lot of hype about carbon nanotubes that hasn’t been realized, and that has kind of soured many people’s outlook,” he says. “But we think the hype is deserved. It has just taken decades of work for the materials science to catch up and allow us to effectively harness these materials.”

The researchers have patented their technology through the Wisconsin Alumni Research Foundation.

The researchers in Jonathan Claussen’s lab at Iowa State University (who like to call themselves nanoengineers) have been looking for ways to use graphene and its amazing properties in their sensors and other technologies.

Iowa State engineers are developing real-world, low-cost applications for graphene. CREDIT: Photos by Christopher Gannon/Iowa State University.

Iowa State engineers are developing real-world, low-cost applications for graphene. Credit: Photos by Christopher Gannon/Iowa State University.

Graphene is a wonder material: The carbon honeycomb is just an atom thick. It’s great at conducting electricity and heat; it’s strong and stable. But researchers have struggled to move beyond tiny lab samples for studying its material properties to larger pieces for real-world applications.

Recent projects that used inkjet printers to print multi-layer graphene circuits and electrodes had the engineers thinking about using it for flexible, wearable and low-cost electronics. For example, “Could we make graphene at scales large enough for glucose sensors?” asked Suprem Das, an Iowa State postdoctoral research associate in mechanical engineering and an associate of the U.S. Department of Energy’s Ames Laboratory.

But there were problems with the existing technology. Once printed, the graphene had to be treated to improve electrical conductivity and device performance. That usually meant high temperatures or chemicals – both could degrade flexible or disposable printing surfaces such as plastic films or even paper.

Das and Claussen came up with the idea of using lasers to treat the graphene. Claussen, an Iowa State assistant professor of mechanical engineering and an Ames Laboratory associate, worked with Gary Cheng, an associate professor at Purdue University’s School of Industrial Engineering, to develop and test the idea.

And it worked: They found treating inkjet-printed, multi-layer graphene electric circuits and electrodes with a pulsed-laser process improves electrical conductivity without damaging paper, polymers or other fragile printing surfaces.

“This creates a way to commercialize and scale-up the manufacturing of graphene,” Claussen said.

The findings are featured on the front cover of the journal Nanoscale‘s issue 35. Claussen and Cheng are lead authors and Das is first author. Additional Iowa State co-authors are Allison Cargill, John Hondred and Shaowei Ding, graduate students in mechanical engineering. Additional Purdue co-authors are Qiong Nian and Mojib Saei, graduate students in industrial engineering.

Two major grants are supporting the project and related research: a three-year grant from the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 11901762 and a three-year grant from the Roy J. Carver Charitable Trust. Iowa State’s College of Engineering and department of mechanical engineering are also supporting the research.

The Iowa State Research Foundation Inc. has filed for a patent on the technology.

“The breakthrough of this project is transforming the inkjet-printed graphene into a conductive material capable of being used in new applications,” Claussen said.

Those applications could include sensors with biological applications, energy storage systems, electrical conducting components and even paper-based electronics.

To make all that possible, the engineers developed computer-controlled laser technology that selectively irradiates inkjet-printed graphene oxide. The treatment removes ink binders and reduces graphene oxide to graphene – physically stitching together millions of tiny graphene flakes. The process makes electrical conductivity more than a thousand times better.

“The laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate,” Das said. “They heat locally. They bombard locally. They process locally.”

That localized, laser processing also changes the shape and structure of the printed graphene from a flat surface to one with raised, 3-D nanostructures. The engineers say the 3-D structures are like tiny petals rising from the surface. The rough and ridged structure increases the electrochemical reactivity of the graphene, making it useful for chemical and biological sensors.

All of that, according to Claussen’s team of nanoengineers, could move graphene to commercial applications.

“This work paves the way for not only paper-based electronics with graphene circuits,” the researchers wrote in their paper, “it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells and (medical) devices.”

Two scientists at the University of Central Florida have discovered how to get a solid material to act like a liquid without actually turning it into liquid, potentially opening a new world of possibilities for the electronic, optics and computing industries.

When chemistry graduate student Demetrius A. Vazquez-Molina took COF-5, a nano sponge-like, non-flammable manmade material and pressed it into pellets the size of a pinkie nail, he noticed something odd when he looked at its X-ray diffraction pattern. The material’s internal crystal structure arranged in a strange pattern. He took the lab results to his chemistry professor Fernando Uribe-Romo, who suggested he turn the pellets on their side and run the X-ray analysis again.

The result: The crystal structures within the material fell into precise patterns that allow for lithium ions to flow easily – like in a liquid.

The findings, published in the Journal of the American Chemical Society earlier this summer, are significant because a liquid is necessary for some electronics and other energy uses. But using current liquid materials sometimes is problematic.

For example, take lithium-ion batteries. They are among the best batteries on the market, charging everything from phones to hover boards. But they tend to be big and bulky because a liquid must be used within the battery to transfer lithium ions from one side of the battery to the other. This process stores and disperses energy. That reaction creates heat, which has resulted in cell phones exploding, hover boards bursting into flames, and even the grounding of some airplanes a few years ago that relied on lithium batteries for some of its functions.

But if a nontoxic solid could be used instead of a flammable liquid, industries could really change, Uribe-Romo said.

“We need to do a lot more testing, but this has a lot of promise,” he said. “If we could eliminate the need for liquid and use another material that was not flammable, would require less space and less packaging, that could really change things. That would mean less weight and potentially smaller batteries.”

Smaller, nontoxic and nonflammable materials could also mean smaller electronics and the ability to speed up the transfer of information via optics. And that could mean innovations to communication devices, computing power and even energy storage.

“This is really exciting for me,” said Vazquez-Molina who was a pre-med student before taking one of Uribe-Romo’s classes. “I liked chemistry, but until Professor Romo’s class I was getting bored. In his class I learned how to break all the (chemistry) rules. I really fell in love with chemistry then, because it is so intellectually stimulating.”

Uribe-Romo has his high school teacher in Mexico to thank for his passion for chemistry. After finishing his bachelor’s degree at Instituto Tecnológico y de Estudios Superiores de Monterrey in Mexico, Uribe-Romo earned a Ph.D. at the University of California at Los Angeles. He was a postdoctoral associate at Cornell University before joining UCF as an assistant professor in 2013.

The findings were pursued by a team lead by Uribe-Romo in collaboration with scientists at UCLA’s Department of Chemistry and Biochemistry. It’s a partnership the team is pursuing to see if COF-5 is indeed the material that could revolutionize battery and mobile device industries.

One of the most critical issues the United States faces today is preventing terrorists from smuggling nuclear weapons into its ports. To this end, the U.S. Security and Accountability for Every Port Act mandates that all overseas cargo containers be scanned for possible nuclear materials or weapons.

Detecting neutron signals is an effective method to identify nuclear weapons and special nuclear materials. Helium-3 gas is used within detectors deployed in ports for this purpose.

The catch? While helium-3 gas works well for neutron detection, it’s extremely rare on Earth. Intense demand for helium-3 gas detectors has nearly depleted the supply, most of which was generated during the period of nuclear weapons production during the past 50 years. It isn’t easy to reproduce, and the scarcity of helium-3 gas has caused its cost to skyrocket recently — making it impossible to deploy enough neutron detectors to fulfill the requirement to scan all incoming overseas cargo containers.

Helium-4 is a more abundant form of helium gas, which is much less expensive, but can’t be used for neutron detection because it doesn’t interact with neutrons.

A group of Texas Tech University researchers led by Professors Hongxing Jiang and Jingyu Lin report this week in Applied Physics Letters, from AIP Publishing, that they have developed an alternative material — hexagonal boron nitride semiconductors — for neutron detection. This material fulfills many key requirements for helium gas detector replacements and can serve as a low-cost alternative in the future.

The group’s concept was first proposed to the Department of Homeland Security’s Domestic Nuclear Detection Office and received funding from its Academic Research Initiative program six years ago.

By using a 43-micron-thick hexagonal boron-10 enriched nitride layer, the group created a thermal neutron detector with 51.4 percent detection efficiency, which is a record high for semiconductor thermal neutron detectors.

“Higher detection efficiency is anticipated by further increasing the material thickness and improving materials quality,” explained Professor Jiang, Nanophotonics Center and Electrical & Computer Engineering, Whitacre College of Engineering, Texas Tech University.

“Our approach of using hexagonal boron nitride semiconductors for neutron detection centers on the fact that its boron-10 isotope has a very large interaction probability with thermal neutrons,” Jiang continued. “This makes it possible to create high-efficiency neutron detectors with relatively thin hexagonal boron nitride layers. And the very large energy bandgap of this semiconductor — 6.5 eV — gives these detectors inherently low leakage current densities.”

The key significance of the group’s work? This is a completely new material and technology that offers many advantages.

“Compared to helium gas detectors, boron nitride technology improves the performance of neutron detectors in terms of efficiency, sensitivity, ruggedness, versatile form factor, compactness, lightweight, no pressurization … and it’s inexpensive,” Jiang said.

This means that the material has the potential to revolutionize neutron detector technologies.

“Beyond special nuclear materials and weapons detection, solid-state neutron detectors also have medical, health, military, environment, and industrial applications,” he added. “The material also has applications in deep ultraviolet photonics and two-dimensional heterostructures. With the successful demonstration of high-efficiency neutron detectors, we expect it to perform well for other future applications.”

The main innovation behind this new type of neutron detector was developing hexagonal boron nitride with epitaxial layers of sufficient thickness — which previously didn’t exist.

“It took our group six years to find ways to produce this new material with a sufficient thickness and crystalline quality for neutron detection,” Jiang noted.

Based on their experience working with III-nitride wide bandgap semiconductors, the group knew at the outset that producing a material with high crystalline quality would be difficult.

“It’s surprising to us that the detector performs so well, despite the fact that there’s still a little room for improvement in terms of material quality,” he said.

One of the most important impacts of the group’s work is that “this new material and its potential should begin to be recognized by the semiconductor materials and radiation detection communities,” Jiang added.

Now that the group has solved the problem of producing hexagonal boron nitride with sufficient thickness, as well as crystalline quality to enable the demonstration of neutron detectors with high efficiency, the next step is to demonstrate high-sensitivity of large-size detectors.

“These devices must be capable of detecting nuclear weapons from distances tens of meters away, which requires large-size detectors,” Jiang added. “There are technical challenges to overcome, but we’re working toward this goal.”

Recent breakthroughs in materials engineering of low-resistance W barriers/liners and bulk fill are making it possible to extend W use to next-generation devices.

BY JONATHAN BAKKE, Applied Materials, Santa Clara, CA

Tungsten (W), with its low resistivity and minimal electro-migration, has long been used for a variety of applications in fabricating semiconductor devices. For instance, it is used for logic contact, local interconnect (LIC), and metal gate (MG) fill as well as DRAM buried word line and contact and 3D NAND MG and contact. Sustained scaling, however, is posing challenges to its continued use with conventional process flows. Interconnect dimensions have shrunk to the point at which contact resistance is becoming an obstacle to realizing optimum transistor performance; fill integrity degrades as aspect ratios and the degree of re-entrance increase, making it difficult to ensure high-quality metallization.

At earlier nodes, larger dimensions made W fill possible using conformal CVD deposition. Now, overhang around the tops of ultra-small openings or bowing from the interconnect etch open preclude the conformal process from completely filling features without voids, while center seams are an inevitable result of conformal deposition, even in the absence of voids. These attributes render extremely small features vulnerable to breach during CMP, causing high resistance or complete failure of an inter- connect. High feature densities and lack of via redundancy in advanced chip designs mean that a single void can cause complete device failure and significant yield loss.

Fortunately, recent breakthroughs in materials engineering of low-resistance W barriers/liners and bulk fill are overcoming these limitations and making it possible to extend W use to next-generation devices. The former lower resistance by simplifying fill film requirements and enlarging the volume available for W fill; the latter eliminates undesirable seams to create more robust structures.

Low-resistance liners

To date, high-resistivity TiN has been predominantly used as an adhesion layer for CVD W and to block fluorine penetration during the bulk fill process. W does not grow directly on TiN; thus, it requires deposition of a nucleation layer before the fill step. As logic devices scale through the 10 nm node and beyond, the maximum critical dimension (CD) of the LIC willbe

Metal-organic deposition of thin W-based films offers an ideal solution, because it can eliminate high-resistance liners and nucle- ation layers while maintaining adhesion and fluorine-barrier properties equiv- alent to those of the current process flow. A new W liner has been developed that lowers line resistance for further device scaling: plasma-enhanced (PE) CVD W that nucleates on metal and oxides.

The PECVD W film is produced using a specialized chemical in the presence of reactive plasma that breaks down the ligands. The film composition is primarily W, and the atoms from the decomposed ligands are bonded to the W. The amorphous character of the film and the dopants in it from the ligand lead to good adhesion to dielec- trics and fluorine barrier properties in the 20-30Å range.

FIGURE 1 shows a simulation of a contact plug in the 4-30nm range. The model contains parallel and series resistors for the plug and through resistance. Features are assumed to be straight wall trenches. Resistance of 12 μΩ*cm is used for W at all thicknesses, which under-estimates the benefit of PECVD W. Scattering at film interfaces is not taken into account. The inflections in the curves (from right to left) occur when a film is removed due to volume constraints. It is clear that the benefit of PECVD W increases exponentially as CDs decrease, especially without the nucleation layer.

FIGURE 1. Plug resistance simulation demonstrates the significant benefit of PECVD W without a nucleation layer.

FIGURE 1. Plug resistance simulation demonstrates the significant benefit of PECVD W without a nucleation layer.

SiO2 trench structures with CDs ranging from 10nm to 150nm and a depth of 100nm were used to investigate W line resistance and evaluate gap-fill performance. As shown in FIGURE 2, line resistance in a ~10 nm CD dropped by nearly 90% compared with the conventional stack.

FIGURE 2. PECVD W plus gap fill reduces line resistance by nearly 90% over the conventional stack. The inset TEM shows conformal gap fill and CMP integration for PECVD W.

FIGURE 2. PECVD W plus gap fill reduces line resistance by nearly 90% over the conventional stack. The inset TEM shows conformal gap fill and CMP integration for PECVD W.

Seam-suppressed gap fill

Until now, feature dimensions have made W fill integration possible using nucleation followed by conformal CVD deposition – which always leaves a seam in features. At CDs

A new approach employs a unique, “selective” suppression mechanism that results in a bottom-up fill free of seams or voids. Pre-treating the nucleation layer creates preferred W growth from the bottom of the structure upwards and less on the field, minimizing the likelihood of void-creating pinch-off and seams (FIGURE 3). Experiments showed the process to be successful on structures with CDs ranging from 10nm to 150nm.

FIGURE 3. a.Cross-sectional TEM image of SSW partial fill of 30nm CD,100nm deep trench pattern with overhang created byAr sputter and PVD Ti. (b) TEM image of seamless SSW fill of the same structure. (c) TEM image of standard CVD W gap fill with seam.

FIGURE 3. a.Cross-sectional TEM image of SSW partial fill of 30nm CD,100nm deep trench pattern with overhang created byAr sputter and PVD Ti. (b) TEM image of seamless SSW fill of the same structure. (c) TEM image of standard CVD W gap fill with seam.

Electrical tests confirmed that SSW lowered line resistance compared to that of conventional CVD W (FIGURE 4). Post-CMP defect analysis by top-down view SEM revealed a narrow seam in conventional CVD W after W CMP (FIGURE 5a), while none is visible after SSW fill (FIGURE 5b).

FIGURE 4. Line resistance comparison of SSW and conventional CVD W on 10nm trench.

FIGURE 4. Line resistance comparison of SSW and conventional CVD W on 10nm trench.

Tungsten 5-1

FIGURE 5. Top-down SEM image of a) conventional CVD W process with visible seam in the center of the trench and b) SSW fill on the same structure.

FIGURE 5. Top-down SEM image of a) conventional CVD W process with visible seam in the center of the trench and b) SSW fill on the same structure.

Conclusion

For the next several nodes of logic and memory fabrication, W will remain an important material in interconnect and gate metallization. However, as scaling continues, transi- tions in process flows will be necessary to achieve low contact and line resistance while maintaining gap-fill integrity. A new W-based barrier/liner has been produced through precision materials engineering that improves device performance and integration while simplifying process flows. Similarly, a new SSW gap-fill process increases the volume of W (potentially lowering resistance), creates more robust features for post-fill integration, and relaxes requirements on CMP and dielectric etch steps, thus delivering performance, device design, and yield benefits.

For further detail on the processes presented in this article, see Bakke, J., et al., “Fluorine-Free Tungsten Films as Low Resistance liners for Tungsten Fill Applications” and Kai,W.,etal.,“ImprovingTungstenGap-FillforAdvance Contact Metallization,” presented at the 2016 IEEE Inter- national Interconnect Technology Conference.