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Developing optimal fuel cells


February 25, 2010

by Takehiko Yaza, Seika Machinery

Executive overview
In developing new fuel cells, there are many obstacles to overcome. For example, gas diffusion must be improved, the volume of catalysts must be reduced and recondensation must be prevented. Another major difficulty is managing water in the fuel cell so that the proton exchange membrane is moisturized and water is quickly discharged from the cathode. Failure to control the water discharge properly will cause flooding at the cathode and a reduction of voltage. There will be a considerable difference depending on the materials selected and the treatment and processing of the materials. Failure to understand the properties of each individual material will make it impossible to develop the optimal fuel cell (Figure 1).

February 25, 2010 – Key factors to consider when developing new fuel cells include: controlling the gas diffusion, permeation, condensation, the reactive area, as well as moisturizing and discharging water. All of these factors depend on the particle size, fiber diameter of the materials and the through-pore structures in them at the electrodes. This article introduces tools that enable better understanding of these properties.

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Figure 1. Current issues for developing fuel cells.

Milling

In North America, ball mills are the most common method for reducing the size of catalyst particles and micro-porous layers of slurry. In a ball mill, the pulverizing energy is generated by steel balls in a gravity-based process. Generally, the milling energy is 1G. By contrast, in a bead mill, the dispersing slurry contains carbon blacks, catalysts and beads, which are mixed together by an agitator inside the milling vessel where particle communion breaks them down into smaller particles. The high-speed of the stirring device generates 100-500G of centrifugal force, providing very high energy. The bead mill makes a large difference in the velocity between the beads and the milled particles. Occasionally, the beads and slurry rotate together and the slurry is not pulverized efficiently. To solve this problem, the AIMEX Alpha Mill (Figure 2) uses an orifice contractile flow vessel. In this configuration, even low-speed rotation generates a very large velocity difference between beads and the slurry. By applying this principle, the milling operation can be carried out very effectively using 30μm beads. Consequently, micrometer-sized carbon black and platinum catalyst particles can be transformed into particles with nm sizes.

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Figure 2. a) Alpha Mill generates high ΔV with small power; b) comparison with the existing model.

When evaluating the efficiency of the slurry pulverization by particle size distribution, we recommend using Horiba Partica LA-950V2. This instrument has the closest correlation to data for NIST traceable to particle size standards and it provides the widest measuring range in the industry.

When the average diameter of the particle to be pulverized is ~0.5μm, even if the materials are crushed, agglomeration is prone to happen. To prevent this phenomenon, a dispersant can be added to the slurry, but this method does have limitations. Therefore, maintaining a high degree of dispersion while coating catalyst and micro-porous layers becomes more important and the Ultrasonic System PRISM series meets this requirement. This coating system uses ultrasonic energy and a nozzleless feed system to eliminate nozzle-blocking problems. The result of these modifications is a 1mm uniform coating thickness. In screen printers and other typical coating systems, it is difficult to provide a thin and uniform thickness without using a pressing machine.

Understanding pore structure

It is necessary to fully understand the pore structure of the coated catalyst layer and the micro porous layer, and the properties relative to water. Although the traditional method of mercury porosimetory generally is used to measure the opened pore structure and volume, the high-pressure measurement method will destroy the pore structure and cannot pick up the functional pores on the application. In contrast, the PMI Capillary Flow Porometer series can measure pore size distribution to determine gas diffusion, water permeability, and the repellent characteristics of the gas diffusion and catalyst layers, without the use of mercury and liquid nitrogen. It realizes automatic and short duration measurements based on the ASTM, bubble point and half-dry methods.

Figure 3 compares measurements made by the Mercury Porosimeter and the Capillary Flow Porometer on a polymer membrane that has only through-pores. The former shows 1-4μm of pore size distribution (peak pore size: 3μm) while the latter shows 1-1.2μm peak pore size:1.1μm difference.

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Figure 3. a) Measurement pore size distribution by Mercury Porosimeter; b) Measurement pore size distribution by Capillary Flow Porometer.

Gas diffusion

Specifically, gas diffusion is the phenomenon in which high-concentration gas flows towards low concentration gas, and eventually the concentration becomes even in the differentiated space with a concentration gradient. Differential pressure results in permeation, but this cannot be called diffusion. There are several measuring instruments for the water vapor transmission rate in the market, however, these instruments can measure only membranes without pores. When fuel cells use high permeability samples, it is difficult to evenly control the pressure at the primary and secondary sides, and the measurement instruments that can measure diffusion at high accuracy are not available. The Seika Moisture Vapor Diffusion Permeameter (MVDP) is integrated using the technologies to maintain high humidity to some degree and prevent condensation by means of temperature control and pressure control. Instead of using batch methods in gas chromatography, MVDP uses real-time technologies to measure concentrations.

As shown in Figure 4, the equipment can measure water vapor diffusion of gas diffusion layers and a proton exchange membrane, as well as oxygen diffusion of moisturized gas. In addition, it can measure gas permeability of generated condensation in the inside of a sample by simulating the flooding phenomenon.

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 Figure 4. a) Measurement in-plane gas permeability test for carbon papers by MVDP; b) oxygen diffusion test for carbon papers by MVDP.

Many fuel cell materials are treated with a waterproofing chemical on the surface to prevent condensation, or are hydrophilically processed to retain moisture. The characteristics of Teflon-coated samples change with immersion time and temperature. The Seika Liquid Intrusion Meter measures the changes in properties and helps optimize fuel cell performance (Figure 5). A liquid permeability test using ultra-low differential pressure can monitor permeated water from large through pores in order of pore size.

The Mesys USM-200 thickness gauge is effective for the management of thickness for the proton exchange membrane manufacturing process. This method emits no radiation, and does not come in contact with, or destroy the samples during measurement.

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 Figure 5. a) Hydrophobic sample measurement; b) Hydrophilic sample measurement.

Conclusion

Because it is difficult to visualize the inner operation of a fuel cell — it is covered by separators made of metal or carbon — it is necessary to use measurements (to get structural information) and simulations (to get process information). Using these direct approaches brings in new ideas and compensates simulation results on super computers. Furthermore, using the aforementioned instruments, we developed simulators for monitoring gas permeability in chronological order on blocking pores by condensation (flooding) at GDL, while also creating a gas visualization system for gas diffusion and the concentration at GDL. However, these are only one set of requirements that need to be addressed before high-volume manufacturing of high-efficiency, cost-effective fuel cells can be realized. Going forward, we would like to discuss additional research proposals with interested parties and propose new equipment necessary to develop optimal fuel cells.

Acknowledgment

Teflon is a registered trademark of DuPont.

Biography

Takehiko Yaza has a bachelor of arts in economics from Takasaki City U. of Economics. He is a senior sales manager at Seika Machinery Inc., 3528 Torrance Blvd., Suite 100, Torrance, CA 90503 USA; ph.: (+1) 310.540.7310; e-mail [email protected]; www.seikausa.com.

by Vincent T. Renard and Vincent Jousseaume, CEA-Leti

Executive overview
There is every reason to be optimistic about the future of information processing because solutions are emerging to add new functionalities, such as sensors, peripheral to the computing core of microprocessors. These new functionalities implemented above ICs in the interconnection levels, or even in the packaging, could allow information-processing systems to interact directly with the environment in absence of direct user input. Interestingly, the ability to vary silicon’s resistance by a large degree, combined with small device dimensions, may again be a key to this qualitative, rather than quantitative revolution.

February 17, 2010 – As a semiconducting material, silicon’s resistance can be varied significantly by increasing current-carrier density either permanently by doping, or temporarily by applying an electrostatic potential. Using this property and CMOS technology, the microelectronic industry has been able to produce binary information-processing integrated circuits. Miniaturization, which has driven the increase in performance of such ICs, may soon reach a limit as the size of constituting devices evolves toward atomic scale. In this context, rod-shaped silicon nanocrystals (silicon nanowires) have shown the potential needed to realize these new functionalities. A well-known example is the silicon nanowire-based pH sensor developed at Harvard [1]. The nanowire was chemically functionalized to provide a surface that can undergo protonation and deprotonation, inducing changes in surface charges depending on the pH of the surrounding solution. This functionalization modifies the nanowire resistance by changing the electrostatic potential. Because of the high surface-to-volume ratio of the nanowire, the conductance of the device is very sensitive to subtle change in surface charges, and therefore to the pH.

The ability to dope silicon could also be used in nanowire-based devices using nanoscale pn junctions, such as with solar cells [2]. Here again, the high surface-to-volume ratio is crucial because solar cells need large surfaces to collect light efficiently and small volume to avoid carrier recombination. Many other potential applications have already been identified; it is therefore surprising that they haven’t yet been developed as commercial products. As usual, the use of new material in devices involves trade-offs. In the "plus" column are the potential for low cost, ease of fabrication, and an incredible variety of potential applications of silicon nanowires from electronics to optics, chemistry, and NEMS. In the "minus" column is that the production of silicon nanowires has remained incompatible with CMOS technology and therefore, nanowires are impossible to integrate above ICs.

Silicon nanowire fabrication: bottleneck to industrial use

The synthesis of silicon nanowires is a 40-year-old subject. Despite the tremendous amount of work dedicated to this challenge, fabrication surprisingly still relies on the same original recipe. This recipe uses a liquid gold nano-droplet to catalyze the growth from a gaseous precursor of silicon (typically SiH4). However, gold is prohibited in CMOS microelectronic factories because it degrades electrical properties of silicon. This is why manufacturers have been reluctant to use nanowire-based technology.

There have been recent attempts to use other CMOS-compatible metal catalysts (for example, copper), but this metal forms a liquid alloy with silicon only above 800°C — too high to be compatible with CMOS processing (TCMOS <450°C). It was recently discovered that the copper-based catalyst may remain in the solid state during growth, generating hope for a low-temperature synthesis. Unfortunately, soon after this discovery, diffusion during incubation (catalyst preparation) was identified as setting a fundamentally lower limit on the growth temperature using copper (T>500°C) [3]. Among the community of researchers, the pessimists thought that silicon nanowires would never be transferable to industry due to the fabrication problem, and the rare optimists thought that a change in paradigm was necessary to achieve that goal. The industrial use of silicon nanowires seemed to be stuck in a dead-end until the concept of "chemically activated incubation" [4] was discovered at CEA-Leti.

Chemically activated incubation

It is well documented that the presence of oxygen is detrimental to silicon nanowire growth when gold is used as a catalyst. In recent decades scientists have therefore been trying to eliminate oxygen from their growth chamber because the vast majority of experiments were performed using gold. Naively, researchers conducting the first experiments using non-gold catalysts at CMOS-compatible temperatures repeated this oxygen hunt applying the old empirical knowledge. Using the traditional method, the silicon precursor SiH4 was then decomposed on the metal particle and silicon incorporated into the particle. Here, everything was controlled by diffusion of silicon in a metal-rich particle, which can be quite slow at low temperature.

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Schematics and yield of the a) diffusion-based incubation vs. b) chemically-activated incubation methods at 400°C.

In the case of copper, the actual catalyst is a copper-silicide (Cu3Si) and even the formation of this catalyst (incubation) takes an extremely long time at CMOS-compatible temperatures and prevents nanowire growth (see figure). We found that oxidizing copper before growth is extremely positive for nanowire synthesis at temperatures as low as 400°C, which is exactly opposite the result obtained with gold. This is due to the very high reactivity of cuprous oxide, which chemically activates the formation of Cu3Si. This observation, therefore, demonstrates that the synthesis temperature of silicon nanowires is limited by catalyst preparation, rather than by the growth itself.

Conclusion

Chemically activated incubation solves the first prerequisite for industrial transfer of silicon nanowires. Notably, our research was performed in the CEA-Leti clean room with an industrial tool on 200mm wafers so that our processes can be transferred to industry. Nevertheless, achieving CMOS compatibility is not the single issue to be resolved for a complete industrial transfer. For example, some applications (e.g., vertical transistors in interconnection) need control of the growth direction. Until now, the only available solution to this problem has been transferring the crystalline information from the substrate to the nanowires using epitaxy. However, achieving growth perpendicular to the substrates using this method requires substrates oriented in a particular crystallographic direction, which can be particularly expensive (i.e., industry-incompatible). Here again, being able to grow nanowires in any direction and on any substrate will probably necessitate a conceptual leap to exit the apparent dead-end. Other, simpler applications such as solar cells don’t need precise control of the growth direction. Determining whether integration of those can be achieved clearly is the most promising next step.

Biographies

Vincent T. Renard received his PhD in nanosciences from Institut National des Sciences Appliquées in Toulouse (2005) and is a research associate at CEA-Leti, MINATEC, Grenoble, France.

Vincent Jousseaume received his PhD in materials science from the U. of Nantes, France (1998) on conducting polymers and a HDR (Habilitation à diriger des recherches) on thin films in microelectronic from the Polytechnics Institute of Grenoble, France (2006). He is a senior scientist at CEA-Leti, MINATEC, 17 rue des Martyrs, 38054 Grenoble, cedex 9 France; e-mail [email protected]; www.leti.fr.

References

[1]. Y. Cui, Q. Wei, H. Park C.M. Lieber, "Nanowire Nanosensors for Highly Sensitive and Selective Detection of Biological and Chemical Species," Science, 293,1289 (2001)
[2]. B. Tian, "Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources," et al., Nature, 449, 885 (2007).
[3]. B. Kalache et al., "Observation of Incubation Times in the Nucleation of Silicon Nanowires Obtained by the Vapor–Liquid–Solid Method," Jpn. J. Appl. Phys., Part 2 45, L190 (2006).
[4]. V.T. Renard, et al., "Catalyst Preparation for CMOS-compatible Silicon Nanowire Synthesis," Nature Nanotechnology, 4, 654 (2009).

by Jan Provoost, IMEC

Executive overview
A prototype headset, combining wireless and low-power electronics, was recently validated for sleep staging. The device is an R&D product of IMEC (Belgium) and Holst Centre (Netherlands). It shows the future direction for body monitoring for medical and recreational use: low cost, extremely low energy, very long autonomy, and comfortable to wear.

February 10, 2010 – Sleep monitoring is a medical technique to assess a person’s sleep quality and to uncover sleep disorders. Such disorders, if left untreated, are a major health risk. It is estimated that 10% of the U.S. population have sleep apnea, resulting in up to 38,000 deaths per year. Worldwide, 1 billion people suffer from chronic nasal congestion during their sleep, which lowers their quality of sleep and puts their health at risk.

The economic challenge

Sleep monitoring, as it is currently done, is expensive and cumbersome. The test — called polysomnography (PSG) — measures various body parameters, each requiring their own instrumentation. As a subset of the complete PSG test, sleep staging, for example, requires running an EEG (electroencephalogram) to monitor the brain activity, an EOG (electro-oculogram) to monitor the eye activity, and an EMG (electromyogram) to monitor the chin muscle activity. All these parameters must be obtained at the same time, and continuously during a night’s sleep. The entire PSG test requires measuring even more parameters.

Julien Penders, R&D program manager at IMEC sums up the complications as follows. "Typically, a polysomnography test is performed in sleep laboratories at hospitals, and the number of people that can be tested is limited by the availability of the equipment and qualified personnel." He further notes that, the current sleep studies are not representative of people’s normal sleep. Rather, they are done in a hospital, which is unnatural at best, and for some, even intimidating. Several companies have already introduced portable systems, allowing monitoring in the home environment. But these systems still have important issues, Penders observes, those being size, weight, and limited connectivity. "Moreover, the patients often misplace the electrodes. And for these portable solutions, as with standard PSG equipment, people have to try and sleep packed in sensors and wires, which is really uncomfortable."

Go miniature and wireless

The solution, says Penders, is to go micro-sized and wireless: "What you need is a small, low power, well-integrated system that can be set up by everyone, and that allows home monitoring. That would make sleep diagnosis accessible for a lot more people. And it would give better, more natural results."

To prove this point, IMEC has integrated the state-of-the-art of its sensor R&D into a comfortable sleep stage monitoring prototype. The monitor is a lightweight, wearable, miniaturized headset. On the headset are three sensor nodes measuring two EEG-channels, two EOG-channels, and one EMG-channel. These five signals provide the minimum required information for sleep staging according to the Rechtschaffen and Kales standard.

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Figure 1. Sleep monitoring headset.

Each sensor node measures only 20 × 60 × 8mm3. Each of them includes two ultra-low power biopotential read-out ASICs to amplify and filter the captured signals and a wireless radio to send the data to a recording computer. Unlike traditional systems, this monitor requires no additional wires from the head to the body or from the head to the recording device, making it comfortable to wear. The nodes consume only 5mA, allowing the 12 hours autonomy that are needed for sleep monitoring.

"These sensor nodes have several exceptional characteristics, but there is one that really stands out," explains Rudy Lauwereins, professor of electrical engineering at the University of Leuven (Belgium). "It’s the exceptional signal conditioning and amplification integrated into the biopotential read-out ASIC." He notes that, for the EEG, the monitor needs to pick up a brain signal of only 60μV. "But you somehow have to filter that 60μV signal from a 1V noise, caused by muscle movements." According to Lauwereins, this can be accomplished by ensuring that two electrodes see the muscle movement as a common signal and the brain signal as a differential signal. He says that, if the amplifier has a common mode rejection ratio (CMRR) of ~120dB, you can extract the much smaller brain signals. However, to obtain this high CMRR, instrumentation amplifiers are needed, and these are traditionally very bulky. "This ASIC integrates this functionality on one IC. A chip that is low-power, moreover, and can handle many channels in parallel."

The portable sleep monitoring system was recently validated in the sleep laboratory at the University Hospital Center in Charleroi, (Belgium), against a commercially available reference system. This validation proves, in general, that wireless headsets could replace current monitoring systems, for the purpose of monitoring sleep stages. It also shows that this particular prototype is mature and ready for product development.

The future of body monitoring

The portable and comfortable home-monitor for sleep is only one example of what will be possible with the next wave of electronics. Electronics combining powerful ICs and sensors in ultra-small packages, flexible or even stretchable, with wireless radios included, and using only ultralow amounts of power will be achievable.

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Figure 2. Flexible wireless monitoring node.

In healthcare, for example, it is thought that this kind of sensor will become widespread in the years to come. They will make healthcare cheaper, replacing often expensive and unwieldy instruments. Additionally, they will enable continuous home monitoring, a major demand for an ageing population, and they will add monitoring possibilities that are now near impossible.

Stephan Claes, professor of psychiatry at the Leuven University (Belgium) explains that researchers have a good understanding of the physiological reactions to stress, and they can measure them. "But we have to do this in the hospital, which is unnatural, and which allows us only to do one measurement, or a few at most," he observes. "That is simply not enough to get a good picture of how someone feels during the day." He explains that, with the sensors we’ll be able to follow patients for a longer time, say a few days. "And we will do that in their natural environment, with their family or colleagues, giving us access to their complete day and night stress rhythm, something we’re not able to measure today."

IMEC’s team at Holst Centre has long been working on the base technology to enable body area networks (BANs). Such BANs are networks of sensors that span the body and that communicate with each other and with the environment. "Our ambition is to create autonomous sensors that tap their energy from the sun or from the temperature gradients between the body and the sensors," says Penders. "So these electronics need to be extremely low-power, running on tens to hundreds of microwatts." IMEC is also working on scavengers that deliver that amount of energy. To demonstrate what is possible and what the future holds in store, IMEC has integrated sensors and scavengers in prototype products. Examples include a T-shirt with integrated ECG monitor that runs on solar cells integrated in the T-shirt’s fabric, and a two-channel EEG headband with integrated thermoelectric converter for human body heat and Si photovoltaic cells.

Recreational monitoring

Next to the obvious medical applications, body sensors will also be applied recreationally. Think of e-learning, for example, where the learning program is adapted to the attention span of the students. Or gaming, where you could use brain waves measured by a portable EEG monitor to steer the game.

Recently, the recreational possibilities were visualized in a work of art. With ‘Steel Sky’ (Staalhemel), Christophe De Boeck, a Belgian artist, created an environment where you can listen to what is going on in your brain. The setting is a large room with steel plates attached to the ceiling. As people walk below the steel plates, their brainwaves are captured by a miniaturized, wireless 8-channel EEG monitor (Fig. 3). These signals activate hammers that tick on the steel plates above their head. It’s an artful rendering of an affective environment, with objects that react to the moods and thoughts of people. All this made possible with advanced, unobtrusive electronics.

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Figure 3. Participant at the Staalhemel exhibit.

Conclusion

Today’s developments in electronics enable fabricating comfortable monitor packages for medical and recreational use. ICs and sensors can be combined in small packages, flexible or even stretchable, with wireless radios included, and using only ultralow amounts of power. At IMEC, researchers are working to develop the necessary components and integrate them with matching embedded software to create invisible, comfortable body monitors. As a technology demonstrator, they have built a sleep monitor; and they have proven that it has an equivalent functionality of more bulky commercial systems used in hospitals.

Biography

Jan Provoost received his Master’s degree in Languages in 1989 and his Master’s degree in Information Sciences in 1993, both at the U. of Leuven Belgium. He is a science writer at IMEC, Kapeldreef 75, B-3001 Heverlee, Belgium; e-mail [email protected].

February 8, 2010 – Researchers at IBM say they have once again set the mark for graphene-based transistors, setting a new mark of 100GHz cutoff frequency (100 billion cycles/sec), the highest achieved so far for any graphene device.

Graphene, the single-atom-thick layer of hexagonally-arranged carbon atoms, possesses unique and intriguing electrical, optical, mechanical, and thermal properties. "A key advantage of graphene lies in the very high speeds in which electrons propagate," which scientists hope to leverage into vastly faster transistors, stated T.C. Chen, VP of science & technology at IBM Research. (In Dec. 2008 IBM set the previous mark of 26GHz cutoff frequency.)

The latest work, part of the DARPA-backed Carbon Electronics for RF Applications (CERA) program as part of efforts to develop next-generation of communication devices, was achieved using wafer-scale epitaxially grown graphene, with process technology "compatible" with those used in advanced silicon device fabrication. Uniform, high-quality graphene wafers were synthesized by thermal decomposition of a silicon carbide (SiC) substrate. The graphene transistor itself has a metal top-gate architecture, and a "novel" gate insulator stack (polyhydroxystyrene polymer spin-coated to 10nm thickness, and oxide deposited by ALD); the high dielectric constant layer has capacitance of about 195nF/cm2. Gate length was a "modest" 240nm, IBM says, with plenty of room for scaling and optimization (the goal is to get to ~50nm); maximum frequency could be increased by decreasing gate resistance with a thicker metal stack or multifinger gate layout, IBM says.
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SEM image of (A) a top-gated Hall bar device and (B) a top-gated field-effect transistor fabricated on the epitaxial graphene wafer. The scale bar in (B) is 2μm. (Source: Science)

IBM also notes that the frequency performance of this graphene transistor exceeds the cutoff frequency of silicon transistors of the same gate length (~40GHz). Also, devices based on graphene obtained from natural graphite showed similar performance, indicating that performance can be obtained from graphene with different origins. (The Dec. 2008 work used graphene flakes extracted from natural graphite.)

by Neha K. Choksi, SmallTech Consulting LLC

February 8, 2010 – Historically, the microfluidics industry has been challenged to achieve a strong return on investment. With the exception of inkjet printing, a key killer application has yet to be identified. This leaves many wondering whether the field has true potential or whether reality is masked in hype. Dr. Holger Becker, co-founder and CSO of microfluidic ChipShop GmbH, shared insights and perspective gained from his nearly 20 years in the industry with the Bay Area MEMS Journal Club on January 28, 2010. 

The interest in microfluidics gained steam in the early 1990s with the idea of microTas (micro total analysis systems). But by 2005, many investors became disenchanted with the field because much of their investment had not paid off. Thanks to a better understanding of what microfluidics can do, microfluidics is gaining back its popularity — but with wiser and more open eyes.

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Despite his optimism for the industry, Becker encourages realistic expectations for product development. Even with the advances in simulation capability, multiple design iterations should be anticipated. However, in the last few years alone, process know-how has increased significantly. The resistance to adoption is another huge, usually unanticipated hurdle. Microfluidics offers its advantages, but convincing users to switch from existing technologies can be challenging. One pathway to address their reluctance is to make microfluidic systems compatible with existing technology. For example, microfluidic ChipShop has created off-the-shelf items of the same form factor as lab slides, or that can be used with an adapter frame for a microtiter plate format, enabling users to interface with standard laboratory automation. 

To create a successful product, Becker emphasizes the need to assemble the right development team. Because of the multidisciplinary nature of the field, the team must include expertise in microfluidics, materials, manufacturability, and a strong understanding of the application. A common mistake that developers make, according to Becker, is spending 80% of their focus on the front-end — when in reality, 80% of the production cost is often back-end processing. Including manufacturing conversations in early stages is critical to the product’s overall feasibility.

Another avoidable pitfall is changing the technology in the middle of production, deviating from that of the initial design. A change in technology, whether it is material, design, or processing, can have large implications on the performance of the device. To ensure that lessons learned during the initial design phase can be transferrable to production, Becker advises that the prototypes be made in a scalable, production-compatible technology.

The opportunities

By being cognizant of the potential pitfalls and acting accordingly, a product developer has many opportunities for success. Becker predicts that market entry is likely to be successful in high-end application niches such as cancer diagnostics. Other opportunities such as food and water diagnostics and veterinary medicine may have lower barriers for entry and the potential for large volume economics. Interest in microfluidics is emerging as a potential key enabler for other products in addition to possible end-user applications.

In addition to direct prospects in microfluidics, Becker sees opportunities to support the field. In many cases, the application does not require the large volumes that the automotive, mobile device, and printing applications offer. Therefore, there is a need for cost-effective, yet flexible manufacturing techniques. Choosing the optimal material is also difficult. A huge variety of polymers are available, but a consolidated standardized database that lists all the particular characteristics that a designer may need would be a very useful tool. Because the material selection is so vast, literature tends to focus on a few "favorite" materials with which the industry is already familiar or experienced, but may, or may not, be optimal for the application. Production worthy quality control process improvements are also necessary in order to reduce screening cycle time of the complex devices that microfluidics entail.

With the right multidisciplinary team, planning for manufacturability, and vigilance towards understanding the application and its barriers to entry, microfluidics has a bright future. In Becker’s words: "Microfluidics has, after following a typical high-tech market acceptance curve with ups and downs, emerged as a true enabler for a multitude of products in the analytical and life science industry. It has taken longer than anticipated, but the light we finally see at the end of the tunnel is definitely not that of an oncoming train."

Neha K. Choksi is a founding member of SmallTech Consulting, LLC, 325 Sharon Park Drive #632, Menlo Park, CA 94025, e-mail [email protected], www.SmallTechConsulting.com.

February 3, 2010 – Researchers at Rice U. have figured out a way to transfer patterns of carbon nanotubes from a substrate to any other surface in a single dry room-temperature step, and then reuse the substrate with intact catalyst particles to grow more.

The research, published in ACS Nano, started with first-year postgrad Cary Pint "playing around with water vapor" to clean up amorphous carbons on some single-walled carbon nanotubes (SWNT), and discovering that the nanotubes he was extracting stuck to the tweezers — this led to investigating how the process could transfer CNTs to other surfaces. In his work, CNTs are grown via chemical vapor deposition (CVD) and etched with a mix of hydrogen gas and water vapor to weaken the bonds formed with the metal catalyst. Once stamped, the CNTs lay down and adhere via van der Waals forces to the new surface, leaving all traces of the catalyst behind.


A potassium bromide window covered by a film of single-walled carbon nanotubes, transferred from the growth substrate, which serves as a template, at right. (Source: Rice U.)


Among the results of the work: a crisscross film of nanotubes made by stamping one set of lines onto a surface and then reusing the catalyst to grow more tubes and stamping them again over the first pattern at a 90-degree angle. The process took about 15 minutes.

Eventually Pint sees the technique, which he says can scaled up "easily," can be used to embed nanotube circuitry into electronic devices. Future steps for the process are to make highly efficient optical sensing devices, and look at doping techniques to enable more precise growth of metallic (conducting) or semiconducting SWNTs.

His own goal is to develop the process to make a range of highly efficient optical-sensing devices. He’s also investigating doping techniques that will take the guesswork out of growing metallic (conducting) or semiconducting SWNTs.

The paper also describes a process for quickly and easily termining the range of diameters in a batch of nanotubes grown through chemical vapor deposition, something many spectroscopic techniques can’t do for structures >2nm in diameter. "This is important since all of the properties of the nanotubes — electrical, thermal and mechanical — change with diameter," Pint said. The good news: the method involves a Fourier transform infrared (FTIR) spectrometer, which "nearly every university has …sitting around that can do these measurements," he added.

From the ACS Nano paper abstract:

Utilizing this transfer approach, anisotropic optical properties of the SWNT films are probed via polarized absorption, Raman, and photoluminescence spectroscopies. Using a simple model to describe optical transitions in the large SWNT species present in the aligned samples, polarized absorption data are demonstrated as an effective tool for accurate assignment of the diameter distribution from broad absorption features located in the infrared. This can be performed on either well-aligned samples or unaligned doped samples, allowing simple and rapid feedback of the SWNT diameter distribution that can be challenging and time-consuming to obtain in other optical methods. Furthermore, we discuss challenges in accurately characterizing alignment in structures of long versus short carbon nanotubes through optical techniques, where SWNT length makes a difference in the information obtained in such measurements. This work provides new insight to the efficient transfer and optical properties of an emerging class of long, large diameter SWNT species typically produced in the CVD process.

February 3, 2010 – Researchers at the U. of Michigan have developed a new biosensor that uses carbon nanotubes (CNT) and paper to quickly and inexpensively detect algae in drinking water.

Their research, published in Nano Letters, centers on microcystin-LR (MC-LR), a chemical compound produced by blue-green algae cyanobacteria, found in nutrient-rich waters and a leading biological water pollutant, and suspected of causing liver damage and possibly liver cancer. Safe drinking water is a crucial issue in both developing and developed countries — water treatment plans can neither completely remove or even test often enough for a toxin like MC-LR, according to Nicholas Kotov, project leader and U. Michigan professor in of chemical engineering, biomedical engineering and materials science and engineering.

So the team set to develop a simple, inexpensive technology to detect multiple toxins. Their work mixed carbon nanotubes with antibodies for MC-LR and impregnated them in a strip of paper. When the paper comes into contact with water contaminated with MC-LR, the antibodies spread apart the CNTs in order to reach and bond with the MC-LR, and that spreading changes the CNTs‘ electrical conductivity, which is measured by an external monitor.

From the Nano Letters paper abstract:

An antibody to the microcystin-LR (MC-LR), one of the common culprits in mass poisonings, was dispersed together with SWNTs. This dispersion was used to dip-coat the paper rendering it conductive. The change in conductivity of the paper was used to sense the MC-LR in the water rapidly and accurately. The method has the linear detection range up to 10 nmol/L and nonlinear detection up to 40 nmol/L. The limit of detection was found to be 0.6 nmol/L (0.6 ng/mL), which satisfies the strictest World Health Organization standard for MC-LR content in drinking water (1 ng/mL) and is comparable to the detection limit of the traditional ELISA method of MC-LR detection, while drastically reducing the time of analysis by more than an order of magnitude.


The device generates results in about 12 minutes, and it’s about the size of a home pregnancy test, so it’s easily portable. And by simply swapping in different antibodies, it can be adapted to detect other harmful chemicals or toxins in water or food, the researchers say.

The research was done in collaboration with China’s Wuxi University, funded by the National Science Foundation, the Air Force Office of Scientific Research, and the National Institutes of Health, as well as the National Science Foundation of China and the 11th Five Years Key Programs for Science and Technology Development of China. U. of Michigan is pursuing patent protection for the IP and is seeking partners to help commercialize the technology.


SEM images of (a) the face and (b) the edge of the 13 deposition 10 cycles paper electrode. (Source: Nano Letters)

February 1, 2010 – Like sister electronics/device industries, MEMS suffered through a lousy early 2009 but managed to make it somewhat respectable for the full year — thanks to a handful of key applications that are pushing into "major commoditization" for high-volume markets, according to an overview by iSuppli.

Like the overall semiconductor industry (and most others), the first quarter of 2009 was lousy for sales of MEMS devices, and despite an improving climate through the rest of the year, sales finished the year down about 8.6% from the prior year, to about $600M. Taken with a decline in 2008 as well, the MEMS industry shed about $1.2B in revenue.

Hardest hit among MEMS sectors is, as has been tracked, the auto sector, which saw shipments plummet 20% in 2009. Cars were among the worst-hit industries in the economic meltdown, and since each car incorporates multiple sensors, this was magnified to the MEMS auto sensor sector as well. Other end-use sectors took a beating, from consumer applications (printers and projectors) to industrial applications (instrumentation, oil/gas exploration, health usage monitoring).

While MEMS shipments sales declined, shipments actually rose by about 10% in 2009, which reflects "major commoditization" for the technology in areas such as consumer electronics and particularly mobile phones, according to iSuppli’s Richard Dixon, in a statement. Among the brighter spots for MEMS in 2009:

  • Accelerometers. Cell phones are now "recognized as the primary driver of MEMS sensor sales," noted Dixon. Of the 1000 new phones iSuppli examined in 2009, 27% of them had an accelerometer on board (vs. 11% in 2008). Accelerometer prices fell much faster than anticipated, which helped widen their consumption, he noted (and even too much, oversaturating the market for Nintendo Wii controllers). Big winners here include suppliers STMicroelectronics and Bosch Sensortec. (Another MEMS technology that broke into use for cell phones: Microvision’s MEMS scanning laser technology, offered through Vodaphone’s Nokia N97, for the Spanish market, Dixon points out.)
  • MEMS microphones. Commoditization is also the story with MEMS microphones, which compete on price with incumbent and inexpensive microphone technology, Dixon notes. MEMS microphone technology was "disproportionally" hurt by the rapid decline of Motorola, an early adopter of the technology, but it’s also been helped by incorporation into Apple’s new fifth-generation iPod nano. Knowles is still "the 1000 lb. gorilla" in MEMS microphones, but ST and Bosch are making plays into this market, seeking ways to bring new work into their 200mm MEMS fabs — Bosch through its acquisition of Akustica, and ST by partnering with Omron.
  • DLP. Another bright spot in 2009 for MEMS devices was the pico projector, which can operate either piggybacked on a cell phone or as a compact standalone unit. Samsung offered the first of these devices domestically in early 2009, with LG joining the game in late 2009. Both of them use Texas Instruments’ digital light processing (DLP) technology.
  • Gyroscopes. These made big leaps in 2009, with gaming in the Nintendo Wii MotionPlus plug-in addition to its controller offering advanced motion gaming. Beneficiary of this was InvenSense, though STMicro also is laying out a range of consumer gyroscopes in 2010, "which is sure to speed adoption for gaming in mobile platforms in future," Dixon notes.

 

January 27, 2010 – Researchers at IBM in Zurich have achieved a world record in areal data density on linear magnetic tape, updating what is still a reliable long-term storage technology despite the rise of digital and optical storage media.

In work with Japan’s Fujifilm, the researchers recorded data on a prototype tape at a density of 29.5 billion bits/in2, about 39× the areal data density of today’s industry-standard magnetic tapes. Key to the work was development of "several new critical technologies," including:

 

  • A new dual-coat magnetic tape based on barium ferrite (BaFe) particles, developed by Fujifilm "in close collaboration" with IBM. The tape uses ultrafine perpendicularly-oriented BaFe magnetic medium without using expensive metal sputtering- or evaporation-coating methods. (Fujitsu separately described its contribution: A new dispersion material was used to control agglomeration of micrified particles; microparticulation of BaFe particles to 1600nm3 (about one-third the size of current metal particles), with uniform dispersion and uniform coating of super smooth thin magnetic layer, were achieved.)

  • Three new servo control technologies that increase by 25-fold the number of data tracks on a half-inch-wide tape: a new servo pattern to enable high-bandwidth nanometer-scale position information, a new method for detecting and decoding position information in the servo pattern, and state-space-based control concepts. Together these enable track-follow performance of <24nm standard deviation, and reduce track width to <0.45nm.

  • Signal-processing algorithms for the data channel — an advanced data read channel based on a new data-dependent noise-predictive, maximum-likelihood (DD-NPML) detection scheme, to enable accurate detection of data despite reduced signal-to-noise ratio (from using an ultranarrow 0.2μm data reader head). Linear density increase of <50% relative to today’s IBM LTO Gen4 cartridge was achieved.

  • Two new low-friction giant magnetoresistive (GMR) read/write head assemblies — a reduced-friction head assembly enabling smoother magnetic tapes, and a GMR head module incorporating optimized servo readers.

 

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The read-write machine where IBM scientists in Zurich demonstrated the new record in magnetic tape data density of 29.5 billion bits per square inch, about 39× the areal data density of today’s most popular industry-standard magnetic tape product. (Photo courtesy of IBM Research – Zurich)

"This exciting achievement shows that tape storage is alive and strong and will continue to provide users reliable data protection, while maintaining a cost advantage over other storage technologies, including hard disk drives and flash," said Cindy Grossman, VP of IBM’s tape and archive storage systems unit, in a statement. The demo also "represents a step towards developing technologies to achieve tape areal recording densities of 100 billion bits per square inch and beyond. Such technologies will be necessary to keep up with the rapid increase in digital information," added IBM Fellow Evangelos Eleftheriou.

End goal of the technology is for cartridges that can store up to 35 terabytes of uncompressed data, about 44× the capacity of IBM’s LTO Gen4 cartridge — enough to store 35 million books. (In real-world measurements that’d require nearly 250 miles of library bookshelves.) Ultimately the goal is 100 billion bits/in2, to keep up with the endless and rising tide of digital information.

The companies note that tape-based storage is used to store up to petabytes of information, at as little as 1/10th the cost of hard disk drive (HDD) storage systems, and is far more energy efficient. Many corporations (especially older ones) still use plenty of tape backup for their systems.

Click to Enlarge
Evangelos Eleftheriou, IBM Fellow, holds the BaFe particle-based dual-coat magnetic tape used in the data storage demo. (Photo courtesy of IBM Research – Zurich)

 

 

 

 

January 21, 2010 – Unidym Inc. says it has completed three agreements to nonexclusively license out its intellectual property related to carbon nanotubes (CNT) for use in applications including aerospace and military.

The three deals are as follows:

– A unidentified large Japanese materials company, for technology (US Patent #6,852,410) covering use of CNTs to make high-performance carbon fibers for structural composites

– Torrey Pines Technologies, a San Diego-based maker of RF, microelectronics, and automated equipment, for a suite of patents related to using vertically aligned nanotubes and nanofibers as thermal interface materials.

– Nano Lab, a Boston-based manufacturer of vertically aligned CNTs, for technology (US Patent #6,863,942) covering growth of vertically aligned carbon nanotubes on certain substrates.

"Licensing our IP outside of our core market in printable electronic materials, illustrates the breadth of Unidym’s patent portfolio," said Mark Tilley, CEO of Unidym, in a statement. "In-line with our strategy to monetize the value of our IP, we will continue to seek revenue generating licensing opportunities beyond the markets in which we intend to sell our high-margin electronic inks and films."