Tag Archives: letter-pulse-tech

Making a magnet from a piece of iron and a coil or wire, or another magnet, is a simple experiment. An external electric or magnetic field can align groups of atoms in the iron over time so that they take on their own permanent magnetic field. A similar accelerated process stores information on computer hard disks. A special case of magnetism, known as ferrimagnetism, could enable even faster switching of magnetism, leading to massive improvements in the way computers handle information.

Now, an international research group, led by Osaka University physicists, has provided new insight into how the composition of ferrimagnetic materials can affect their interactions with light. They recently reported their findings in Applied Physics Express.

“We know that laser pulses can reverse the magnetization in certain ferrimagnetic alloys, but light also affects other properties of the material,” coauthor Hidenori Fujiwara says. “To learn more about the interactions of the magnetism with light, we studied the spin dynamics of ferrimagnetic thin films containing different proportions of gadolinium.”

Ferrimagnetic materials can be thought of as a mixture of electrons spinning at different sites in the material. Some of the spins might cancel each other out, but a certain residual magnetization will remain. Firing an ultra-fast laser pulse at the material may completely flip the spin direction, reversing the magnetism, or may disrupt the spins, causing a kind of wobbling known as spin precession. The type of behavior shown strongly depends on the material’s temperature and composition.

The researchers used an advanced synchrotron measurement setup developed in their previous studies to show that slightly varying the composition of an alloy dramatically changed its response to the laser pulse. Slightly more gadolinium in the films led to flipping of the magnetic spin; slightly less led to spin precession at room temperature.

The researchers’ setup could also visualize the wave-like nature of the spin precession over a few nanoseconds following the laser pulse. They showed that the angle of precision, or the angle of the spin wobble, was the largest reported to date.

“These are complex systems with many different interacting properties, but we have extracted some clear relationships between the composition of a ferrimagnetic alloy and its magnetic interactions with light,” coauthor Akira Sekiyama says. “Understanding these behaviors is important from a fundamental physics standpoint, and essential for applying these material systems in advanced electronic devices.”

Researchers from Finland and Taiwan have discovered how graphene, a single-atom-thin layer of carbon, can be forged into three-dimensional objects by using laser light. A striking illustration was provided when the researchers fabricated a pyramid with a height of 60nm, which is about 200 times larger than the thickness of a graphene sheet. The pyramid was so small that it would easily fit on a single strand of hair. The research was supported by the Academy of Finland and the Ministry of Science and Technology of the Republic of China.

A similar structure was made experimentally by using laser irradiation in a process called "optical forging." Credit: The University of Jyväskylä

A similar structure was made experimentally by using laser irradiation in a process called “optical forging.” Credit: The University of Jyväskylä

Graphene is a close relative to graphite, which consists of millions of layers of graphene and can be found in common pencil tips. After graphene was first isolated in 2004, researchers have learned to routinely produce and handle it. Graphene can be used to make electronic and optoelectronic devices, such as transistors, photodetectors and sensors. In future, we will probably see an increasing number of products containing graphene.

“We call this technique optical forging, since the process resembles forging metals into 3D shapes with a hammer. In our case, a laser beam is the hammer that forges graphene into 3D shapes,” explains Professor Mika Pettersson, who led the experimental team at the Nanoscience Center of the University of Jyväskylä, Finland. “The beauty of the technique is that it’s fast and easy to use; it doesn’t require any additional chemicals or processing. Despite the simplicity of the technique, we were very surprised initially when we observed that the laser beam induced such substantial changes on graphene. It took a while to understand what was happening.”

“At first, we were flabbergasted. The experimental data simply made no sense,” says Dr Pekka Koskinen, who was responsible for the theory. “But gradually, by close interplay between experiments and computer simulations, the actuality of 3D shapes and their formation mechanism started to become clear.”

“When we first examined the irradiated graphene, we were expecting to find traces of chemical species incorporated into the graphene, but we couldn’t find any. After some more careful inspections, we concluded that it must be purely structural defects, rather than chemical doping, that are responsible for such dramatic changes on graphene,” explains Associate Professor Wei Yen Woon from Taiwan, who led the experimental group that carried out X-ray photoelectron spectroscopy at the synchrotron facility.

The novel 3D graphene is stable and it has electronic and optical properties that differ from normal 2D graphene. Optically forged graphene can help in fabricating 3D architectures for graphene-based devices.

Understanding the impact of valve flow coefficient (Cv) in fluid systems for microelectronics manufacturing

BY STEPHANE DOMY, Saint-Gobain Performance Plastics,

When scaling up, or down, a high-purity liquid installation – many complex factors need to be considered from ensuring the integrity of the transported product to the cleanliness of the environment for both the safety of the process and the operator [1]. In my 15 years working in the semiconductor fluid handling component industry, I’ve learned that the Cv is a bit misunderstood. Given the Cv formula can be used for any flow component in a fluid line, most are familiar with it, yet few consider how it relates to their specific installation. Therefore, this article will focus on factors that pertain to achieving a specific flow performance and specifically the flow coefficient (Cv) as it relates to valves.

Cv empirical explanation and more

As we know, when working on a turbulent flow the Cv formula is: Cv= Q√(SG / ∆P) where Q is the flow going through the valve in gallons per minute (GPM), SG is the specific gravity of the fluid and ∆P is the pressure drop in PSI through the component. In the semiconductor industry, due to the low velocity of the transported fluid the high purity chemistry and slurries are mostly in a semi–turbulent state or a laminar state. Yet you’ll notice there is not a single link to the viscosity of the transported product in the Cv formula. This is significant given the viscosity directly impacts the Cv value when the flow is in a semi-turbulent or laminar mode. Consider that if you calculate the pressure drop in your system with the formula above you could end up with a result that is 4 to 5 times lower. No doubt this inaccuracy can cause significant issues in your installation.

To take this further, let’s analyze how pressure drop based on flow evolves through a valve by comparing a Saint-Gobain Furon® Q-Valve (1⁄2” inner flow path and 1⁄2” pipe connection) to a standard semiconductor industry valve of the same size. The Saint-Gobain valve, which meets the requirements of the semiconductor industry (metal free, 100% fluoropolymer flow path and so on), has a Cv of 3.5 – one of the best for its dimensions. To ease the calculation, we will use deionized (DI) water, which will free us of the specific gravity or impact of the viscosity if we are not in the right state.

As we can see on the graph in FIGURE 1, at a normal flow rate used in micro-e for 1⁄2” 5 to 10 lpm; the pressure drop difference between a standard valve and a Saint-Gobain valve is in the range of 0.1 to 0.3 PSI. At first glance, this does not appear to be much. However, let’s factor in a viscous product and that you have a number of these lines in your flow line — now the numbers start to accumulate. And by moving from a standard valve to a Saint-Gobain valve, as described above, you start to see a significant difference in pressure drop, which could occur across your installation. That being said, up to a certain limit (defined by another component in your installation, such as your pump pressure capability or some more delicate device) an “easy” counter is to increase the pressure through put of your pump but it is at the expense of wasting energy and adding the potential for additional shearing or particle generation in your critical fluid. Now that we have reviewed, the impact of the Cv on our flow and how this could impact our installation, let’s see what can potentially impact the Cv.

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Design impact on Cv and resulting trade-off

The first impact that may come to mind is a larger orifice – and it’s correct. The size of the orifice can benefit flow through and directly relates to the volume of your valve. However there are trade-offs for this improved Cv. The first is cost increase. A higher volume requires a larger valve, which can cost up to 50% more than the initial valve due to specific material and process requirements. Additionally, as highlighted in “Design Impact for Fluid Components” by increasing the size of the component (due to the specific micro-e material requirements), you could lose pressure rating performance [1]. Also when increasing the inner volume of your valve, you potentially increase volume retention as well as particle generation, given that using larger actuation systems results in more points of contact and creates a hub for generating particles. Another possible drawback is significant velocity loss, but that will have to be addressed in another article. The critical point to be taken here is the importance of choosing the right size orifice – too small and flow can be restricted too much and too big and you may end up paying for other problems.

Another potential impact to Cv is the difference in valve technology. Though there more, I’ll specifically cover stopcock/ball valves, weir style valves; and diaphragm valves. Other valve technologies, such as the butterfly valve, will not be discussed because their construction materials are generally not used for fluid handling components for the semiconductor industry.

Starting with the simplest design, the stopcock/ball valve provides by far the best Cv of the three technologies mentioned. Considering the premium Cv achieved, you would assume they are expensive. Instead they are generally the cheapest of the three values mentioned. One drawback in using stopcock valves is the need for a liquid oring on the fluid path which may create compatibility issues. The exception is the Furon® SCM Valve, a stopcock valve that employs a PFA on PTFE technology and allows for oring-free sealing. Additionally, stopcock valves can lower pressure/ temperature ratings and have a tendency to generate a great deal of particles when actuated. This occurs when the key or ball is rotating inside the valve body. Both drawbacks are related to the PTFE/PFA construction materials required for the flow path by the micro-e industry.

The weir style valve, if done properly, should provide a very good Cv – perhaps not as good as a stopcock/ball valve, but still very good. And although liquid orings are not an issue, these valves have other drawbacks. In a weir style valve the diaphragm is generally a sandwich structure consisting of a thin layer of PTFE that is backed by an elastomeric component in which a metal pin is embedded to connect the membrane to the valve actuating system. It is the sandwich materials that generate a number of potential issues when used on critical, high purity chemistry. Specifically, the delamination of the sandwich creates the possi- bility of multiple points of contamination to the liquid (metal & elastomer). In addition, the significant surface contact between the membrane and the valve seat, which is necessary to secure a full seal, generates a lot of particles – though significantly less than a stopcock/ball valve.

The diaphragm valve is the most commonly used valve in the semiconductor industry as it offers a great balance in terms of the issues previously identified: potential contami- nation, materials and particle generation. The trade-off is that the construction of these valves is more complex and as a result they are priced higher than the average cost of the other valves. Additionally, the Cv performance is well below a stopcock/ball valve and slightly below a weir style valve. However, by using Saint-Gobain’s patented rolling diaphragm technology this does not have to be an issue. In fact, with this technology, we can offer the equivalent Cv of a weir style valve in combination with premium pressure and temperature capabilities as well as the cleanest valve technology – all of which allows for a system design with the lowest impact possible on the transported fluid.

As demonstrated in this document, understanding the Cv rating and the impacts that could affect that rating as it relates to valves is critical when optimizing an installation for fluid and energy efficiency. Cost aside, there are a number of issues that are unique to the semiconductor industry that ultimately guide and often restrict installation choices, such as: dead volume, particle generation, cleanliness as well as the physical and mechanical properties of appropriate polymers. Additionally, choosing the appropriate valve for your installation goes far beyond the simple notion that if “I need more flow, I will get a larger valve.” Most likely the residual effect of that choice will affect the performance of the system, particularly regarding cleanliness. Instead critical adjustments to your valve actuation mechanism and valve flow path designs as well as to your valve technology may allow you to achieve the required results – even if the installation still uses the same 1⁄2” valve…but more on this point in another article.

References

1. www.processsystems.saint-gobain.com/sites/imdf.processsystems. com/files/2015-12-03-part-one-design-impact-for-fluid-components.pdf

A new system combines acoustic, optical and reflectometric techniques to enable measurement of metals, dielectrics, resists and critical dimensions on a single platform.

BY CHEOLKYU KIM, Director of Metrology Product Management, Rudolph Technologies, Inc.

Rapid growth in the mobile device market is generating demand for advanced packaging solutions with higher levels of system integration and increased I/Os and functionality. This demand is driving 2.5D/3D integration of IC devices, which in turn requires sophisticated packaging technologies. Among various approaches, fan-out is gaining traction as outsourced semiconductor assembly and test (OSAT) houses and wafer foundries roll out their own technologies. As illustrated in FIGURE 1, the adoption of fan-out technology accelerated significantly in 2016, and is projected to reach $2.5 billion by 2021, a more than 10X increase from 2015.

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First generation “core” fan-out was geared toward mobile applications and had RDL lines that were typically 10/10μm (line/space) and larger. Second generation HDFO processes, which were developed to integrate multiple chips in a single package, use more RDL lines at smaller width and tighter pitch, down to 2/2μm and smaller. Growth in HDFO accelerated with the entry of Apple and TSMC in 2016 and accounts for the bulk of the fan-out growth projected through 2021 [2-4].

As design rules for HDFO approach those of front-end processes, so too will requirements for process control and, in consequence, the need for more accurate and repeatable metrology. Until now, manufacturers have characterized metal films, such as RDL and under bump metallization (UBM), using semi-automated measurement tools, such as contact profilometers, which are easy to use and relatively inexpensive. However, these tools are not the best solution for measuring a variety of products with varying topographies in high volume production.

High Density Fan-Out process control

HDFO processes include one or more RDL, the number depending on the application. Like front-end processes, HDFO processes use additive and subtractive technol- ogies to create patterns of conductive metal lines isolated by dielectric materials. As RDL lines become smaller, controlling line resistance with appropriate dimensional control has become essential. For an RDL process, the most important parameters to monitor are dielectric thickness, Cu seed layer thickness, Cu thickness and line width (CD). In general, the process must operate inside a window that varies within 10% of the target value. This, in turn, requires measurement tools with a gauge capability (3σ repeatability + reproducibility) of 10% of the variability, or 1% of the target value. In addition to delivering accuracy and repeatability, the metrology system must be able to operate on product wafers and, therefore, 1) be able to measure test structures smaller than 50μm, 2) be non contact/non-destructive/ non-contaminating, 3) be fast enough to support high volume production and 4) be able to handle the significant surface topography and substrate/wafer warpage that are induced by the HDFO process.

As shown schematically in FIGURE 2, the metrology system described here (MetaPULSE® AP, Rudolph Technologies), combines picosecond ultrasonic laser sonar (PULSETM), automated optical microscopy and reflectometry to meet all the requirements for RDL process control in a single system. The acoustic technique, well proven and widely accepted for metal film metrology in front-end applications, is a first principle technology that provides accurate measurements of metal film thickness for UBM and RDL.

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Measurements of RDL thickness with this technique on dense line arrays, pads and bumps have shown excellent correlation to cross sectional scanning electron microscope (X-SEM) results. The precision and gage capability of the technology have been validated down to 2μm and meet OSAT and foundry RDL roadmap requirements.

The integration of a high-resolution reflectometer provides accurate measurements of dielectric and resist thickness, ranging from a few 1000Å to 60μm, on product wafers. The incorporation of an automated optical microscope/high-resolution camera provides gage-capable CD measurements. CD measurements can be made simultaneously with thickness measurements. The addition of optical CD measurements and reflectometer-based transparent film thickness measurements to the acoustic platform provides an efficient and comprehensive in-line RDL metrology solution that eliminates the need to route wafers to multiple measurement tools.

PULSE acoustic thickness measurements on opaque films

FIGURE 3 illustrates the principles of the PULSE acoustic measurement technology. An extremely short laser pulse is focused onto a small spot on the sample surface where the energy of the laser pulse is absorbed by the film surface. This causes a sudden increase of surface temperature, and rapid thermal expansion launches a sound wave on the surface that travels into the film. When the sound wave reaches an interface with an underlying film, it is partially reflected back to the surface as an echo. Upon arrival at the surface, the echo causes a change in optical reflectivity, which is detected to measure the round-trip travel time of the sound wave. Film thickness can be calculated from the travel time of the sound wave and the speed of sound in the material. Some of the energy from the original sound wave is transmitted through the interface. In a multi-layered stack, the progressing sound wave returns a distinct echo from each interface. An analysis of the round-trip travel time for each successive echo permits the calculation of the thickness of each layer. Typical data acquisition times vary from 1s to 4s per site. Repeatability is < 0.1% of target thickness, meeting the 10% GR&R requirement. FIGURE 4 shows the correlation between X-SEM and PULSE measurements for RDL in the 1.25μm-1.5μm thickness range. The excellent correlation clearly demonstrates the accuracy of PULSE thickness measurements.

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Reflectometer thickness measurements on transparent films

FIGURE 5 (left) demonstrates the strong correspondence between a measured reflectometer signal and a model fitted curve for 5μm polyimide on Si. The figure also shows the correlation between reflectometer measurements and a fab reference metrology tool. The excellent correlation with the reference tool confirms the accuracy of reflectometer measurements. Data collection time for reflectometer measurements is typically less than 1s. The reflectometer has excellent sensitivity with Å level resolution and gage-capable R&R.

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Automated optical CD measurements

Using the optical microscope/ high resolution camera system, users can define multiple regions of interest (ROI) for CD measurements, including single line and multi-line arrays. The built-in measurement algorithms can report individual or average values. Extension of the CD technique to also measure overlay has shown promising results and additional work is in progress to fully characterize the capability. FIGURE 6 shows images and signals from CD measurements on lines and arrays. The strong correlation between optical CD and X-SEM measurements (FIGURE 7) validates the accuracy of the technique. CD measurement with the optical microscope is limited by the micro- scope’s resolution, typically 1μm or larger. Since SEM resolution is typically on the scale of nanometers, the correlation requires proper calibration. The results shown in Fig. 7 are after calibration.

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Multi-layered stacks

Most of RDL plating requires prior deposition of a Cu seed layer, the thickness of which must also be tightly controlled. FIGURE 8 (left) shows examples of the acoustic signals acquired from three Cu/ Ti stacks of varying thickness. The first positive peak of each signal gives the round-trip travel time of the sound wave in the Cu film, while the spacing between first and second positive peaks gives the round-trip travel time through the Ti layer. The echo positions are used to calculate the thickness of Cu and Ti layers simultaneously. Figure 8 (right) shows the signal of an Au/Ni/Cu/Al stack measured on UBM. The echo from each layer is distinct. Knowing the arrival times of the echoes and the speed of sound in the materials, the system calculates the thickness of all four layers simultaneously, with 3σ repeatability less than 1% for each of the layers.

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Warped wafer handling

The thin wafers/substrates used in HDFO processes can be warped significantly at several different steps in the process, most significantly by the mismatch between thermal expansion coefficients of the molding compound and the die. Warpage of 2mm or more poses a major challenge to handling and measurement systems. A specially designed vacuum chuck has three concentric vacuum zones. Applying vacuum to the zones sequentially, starting with the innermost zone and working out, the chuck pulls and holds warped wafers flat against itself to allow accurate measurements.

Conclusions

High density fan-out packaging is essential for advancing growth in mobile and networking applica- tions. The integration of multi-chip modules in fan-out processes requires complex processing using tools and materials that are significantly more expensive than traditional packaging lines. We have described an automated metrology solution that combines acoustic measurements with high resolution reflectometry and optical microscopy to provide comprehensive, gage- capable measurements for characterizing critical process steps in high volume production applications. Simultaneous measurement of multiple parameters on a single platform eliminates the need to route product through several different tools, improving the speed and efficiency, and reducing the overall cost-of-ownership, of the metrology process.

References

1. “Fan-out technnologies and MarketTrends 2016 Report”,Yole Devel- oppement, July 2016
2. “What is driving advanced packaging platforms development?”, T. Buisson and S. Kumar, Chip Scale Review, pp. 32-36,May-June 2016 3. “Recent advances and trends in advanced packaging”, J. Lau, Chip
Scale Review, pp. 46-54, May-June 2017.
4. “Status of Advanced Packaging Report,” Yole Developpement, June 2017.

Over the past half-century, scientists have shaved silicon films down to just a wisp of atoms in pursuit of smaller, faster electronics. For the next set of breakthroughs, though, they’ll need novel ways to build even tinier and more powerful devices.

A study led by UChicago researchers, published Sept. 20 in Nature, describes an innovative method to make stacks of semiconductors just a few atoms thick. The technique offers scientists and engineers a simple, cost-effective method to make thin, uniform layers of these materials, which could expand capabilities for devices from solar cells to cell phones.

Stacking thin layers of materials offers a range of possibilities for making electronic devices with unique properties. But manufacturing such films is a delicate process, with little room for error.

“The scale of the problem we’re looking at is, imagine trying to lay down a flat sheet of plastic wrap the size of Chicago without getting any air bubbles in it,” said Jiwoong Park, a UChicago professor with the Department of Chemistry, the Institute for Molecular Engineering and the James Franck Institute, who led the study. “When the material itself is just atoms thick, every little stray atom is a problem.”

Today, these layers are “grown” instead of stacking them on top of one another. But that means the bottom layers have to be subjected to harsh growth conditions such as high temperatures while the new ones are added — a process that limits the materials with which to make them.

Park’s team instead made the films individually. Then they put them into a vacuum, peeled them off and stuck them to one another, like Post-It notes. This allowed the scientists to make films that were connected with weak bonds instead of stronger covalent bonds–interfering less with the perfect surfaces between the layers.

“The films, vertically controlled at the atomic-level, are exceptionally high-quality over entire wafers,” said Kibum Kang, a postdoctoral associate who was the first author of the study.

Kan-Heng Lee, a graduate student and co-first author of the study, then tested the films’ electrical properties by making them into devices and showed that their functions can be designed on the atomic scale, which could allow them to serve as the essential ingredient for future computer chips.

The method opens up a myriad of possibilities for such films. They can be made on top of water or plastics; they can be made to detach by dipping them into water; and they can be carved or patterned with an ion beam. Researchers are exploring the full range of what can be done with the method, which they said is simple and cost-effective.

“We expect this new method to accelerate the discovery of novel materials, as well as enabling large-scale manufacturing,” Park said.

A research group consisting of scientists from Tomsk Polytechnic University, Germany and Venezuela proved vulnerability of a two-dimensional semiconductor gallium selenide in air. This discovery will allow manufacturing superconducting nanoelectronics based on gallium selenide, which has never been previously achieved by any research team in the world.

The study was published in Semiconductor Science and Technology.

One of the promising areas of modern materials science is the study of two-dimensional (2D) materials, i.e. thin films consisting of one or several atomic layers. 2D materials due to their electrical superconductivity and strength could be a basis for modern nanoelectronics. Optic applications in nanoelectronics require advanced materials capable of ‘generating’ great electron fluxes upon light irradiation. Gallium selenide (GaSe) is one of the 2D semiconductors that can cope with this problem most efficiently.

‘Some research teams abroad tried to create electronic devices based on GaSe. However, despite extensive theoretical studies of this material, which were published in major scientific journals, the stability of the material in real devices remained unclear,’ says Prof. Raul Rodriguez, the Department of Lasers and Lighting Engineering.

The research team revealed the reasons behind this. They studied GaSe by means of Raman spectroscopy and x-ray photoelectron spectroscopy that allowed proving the existence of chemical bonds between gallium and oxygen. Photoluminescence in oxidized substance is absent that also proves the formation of oxides. It means that the scientists revealed that GaSe oxidizes quickly in air and loses its electrical conductivity necessary for creating nanoeletronic devices.

‘GaSe monolayers become oxidized almost immediately after being exposed to air. Further research of GASe stability in air will allow making proposals how to protect it and maintain its optoelectronic properties,’ emphasize the authors.

According to Prof. Rodriguez, for GaSe not to lose its unique properties it should be placed in a vacuum or inert environment. For example, it can be applied in encapsulated devices that are vacuum-manufactured and then covered with a protective layer eliminating air penetration.

This method can be used to produce next generation optoelectronics, detectors, light sources and solar batteries. Such devices of ultra-small sizes will have very high quantum efficiency, i.e. they will be able to generate large electron fluxes under small external exposure.

The labor-intensive, manual process of recording precise measurements across various wafer coordinates is now programmable for automated data collection and report generation.

ACU-THIK™ is an automated thickness measurement tool incorporating dual contact probes for high accuracy inspection of semiconductor wafers. Six Heidenhain measuring devices are integrated into the ACU-THIK™ system which can be configured to accommodate wafer diameters of 100mm – 400mm and larger. Acu-Gage customers can have a system customized for their precise needs to make differential gage measurement faster and easier.

Diagnosing as well as controlling thickness, bow and warp in semiconductor wafer production is now automated when using ACU-THIK™. Users can preprogram multiple pattern operations to fulfill planned production cycles. Additionally, the system supports robotics integration to further free up operators for other important tasks.

ACU-THIK’s automated measurements can improve quality-assured production yields by:

  • Calculating wafer thickness across X/Y points to resolution and repeatability of .00025mm/.00001 inch (10 millionths of an inch)
  • Determining the amount of bow deviation in an unclamped wafer established by three or more points at equidistant locations
  • Examining the entire wafer for warp by incorporating more comprehensive data points to provide a more useful measurement of the full wafer shape
  • Accelerating throughput with 15 data points of X/Y thickness measurements in under two minutes as well as increasing accuracy of wafer thickness and flatness definitions
  • Validating pre- and post-measurement integrity of data collection for each wafer inspection – ACU-THIK™ calculates the thickness of a certified gage block prior to as well as after the wafer inspection routine is complete.

The X/Y location for each thickness data point automatically outputs to Excel for further analysis. Programming software runs on Windows 7. Both hardware and software come delivered as a turnkey system including installation and training.

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Leti, a technology research institute of CEA Tech, announced today it has developed a methodology for testing high-speed wireless communications on airplanes that allows different system deployments in cabins, and assesses wireless devices before they are installed.

In a joint research project with Dassault Aviation, Leti demonstrated a channel-measurement campaign over Wi-Fi frequency in several airplanes, including Dassault’s Falcon business jet. Using a channel sounder and a spatial scanner, Leti teams determined a statistic model of the in-cabin radio channel, constructed from the antenna position and the configuration of the aircraft.

A radio-frequency channel emulator and the in-cabin channel model were used to test Wi-Fi designed for passenger communication and entertainment before installation in the aircraft. In that test, two different wireless access points and different antenna configurations for Wi-Fi networks deployed in an aircraft cabin were evaluated. Based on an extensive test campaign, mean values of performance parameters, together with the operating margin, were provided according to the device configuration, kind of traffic and channel conditions.

In addition, the technology gives aircraft designers key tools to define wireless communication systems that enhance passenger experience, without aircraft immobilization.

“This research collaboration with Dassault is a critical first step toward validating wireless connectivity systems before they are installed in aircraft,” said Lionel Rudant, Leti strategic marketing manager. “Wireless systems have multiple benefits, ranging from more efficient monitoring of aircraft comfort and safety to reducing the weight of planes.”

Leti’s roadmap also addresses goals for wireless sensor networks, which are part of an industry effort to replace the hundreds of miles of wiring required to connect thousands of sensors and other detectors located throughout aircraft to monitor safety and comfort factors. The factors range from ice detection, tire pressure and engine sensors to cabin pressure, smoke detection and temperature monitoring.

Rudant will present details of Leti’s proof of concept at the AeroTech Conference and Exhibition, Sept. 26-28 in Fort Worth, Texas. His talk, “Test of in-flight wireless connectivity with radio channel emulator”, will be on Sept. 27 at 8 a.m. in room 201B.

Scarce metals are found in a wide range of everyday objects around us. They are complicated to extract, difficult to recycle and so rare that several of them have become “conflict minerals” which can promote conflicts and oppression. A survey at Chalmers University of Technology now shows that there are potential technology-based solutions that can replace many of the metals with carbon nanomaterials, such as graphene.

They can be found in your computer, in your mobile phone, in almost all other electronic equipment and in many of the plastics around you. Society is highly dependent on scarce metals, and this dependence has many disadvantages.

Scarce metals such as tin, silver, tungsten and indium are both rare and difficult to extract since the workable concentrations are very small. This ensures the metals are highly sought after – and their extraction is a breeding ground for conflicts, such as in the Democratic Republic of the Congo where they fund armed conflicts.

In addition, they are difficult to recycle profitably since they are often present in small quantities in various components such as electronics.

Rickard Arvidsson and Björn Sandén, researchers in environmental systems analysis at Chalmers University of Technology, have now examined an alternative solution: substituting carbon nanomaterials for the scarce metals. These substances – the best known of which is graphene – are strong materials with good conductivity, like scarce metals.

“Now technology development has allowed us to make greater use of the common element carbon,” says Sandén. “Today there are many new carbon nanomaterials with similar properties to metals. It’s a welcome new track, and it’s important to invest in both the recycling and substitution of scarce metals from now on.”

The Chalmers researchers have studied the main applications of 14 different metals, and by reviewing patents and scientific literature have investigated the potential for replacing them by carbon nanomaterials. The results provide a unique overview of research and technology development in the field.

According to Arvidsson and Sandén the summary shows that a shift away from the use of scarce metals to carbon nanomaterials is already taking place.

“There are potential technology-based solutions for replacing 13 out of the 14 metals by carbon nanomaterials in their most common applications. The technology development is at different stages for different metals and applications, but in some cases such as indium and gallium, the results are very promising,” Arvidsson says.

“This offers hope,” says Sandén. “In the debate on resource constraints, circular economy and society’s handling of materials, the focus has long been on recycling and reuse. Substitution is a potential alternative that has not been explored to the same extent and as the resource issues become more pressing, we now have more tools to work with.”

The research findings were recently published in the Journal of Cleaner Production. Arvidsson and Sandén stress that there are significant potential benefits from reducing the use of scarce metals, and they hope to be able to strengthen the case for more research and development in the field.

“Imagine being able to replace scarce metals with carbon,” Sandén says. “Extracting the carbon from biomass would create a natural cycle.”

“Since carbon is such a common and readily available material, it would also be possible to reduce the conflicts and geopolitical problems associated with these metals,” Arvidsson says.

At the same time they point out that more research is needed in the field in order to deal with any new problems that may arise if the scarce metals are replaced.

“Carbon nanomaterials are only a relatively recent discovery, and so far knowledge is limited about their environmental impact from a life-cycle perspective. But generally there seems to be a potential for a low environmental impact,” Arvidsson says.

Facts:

Carbon nanomaterials consist solely or mainly of carbon, and are strong materials with good conductivity. Several scarce metals have similar properties. The metals are found, for example, in cables, thin screens, flame-retardants, corrosion protection and capacitors.

Rickard Arvidsson and Björn Sandén at Chalmers University of Technology have investigated whether the carbon nanomaterials graphene, fullerenes and carbon nanotubes have the potential to replace 14 scarce metals in their main areas of application (see table in attached image). They found potential technology-based solutions to replace the metals with carbon nanomaterials for all applications except for gold in jewellery. The metals which we are closest to being able to substitute are indium, gallium, beryllium and silver.

Decades ago, the Moore’s law predicted that the number of transistors in a dense integrated circuit doubles approximately every two years. This prediction was proved to be right in the past few decades, and the quest for ever smaller and more efficient semiconductor devices have been a driving force in breakthroughs in the technology.

With an enduring and increasing need for miniaturization and large-scale integration of photonic components on the silicon platform for data communication and emerging applications in mind, a group of researchers from the Hong Kong University of Science and Technology and University of California, Santa Barbara, successfully demonstrated record-small electrically pumped micro-lasers epitaxially grown on industry standard (001) silicon substrates in a recent study. A submilliamp threshold of 0.6 mA, emitting at the near-infrared (1.3?m) was achieved for a micro-laser with a radius of 5 μm. The thresholds and footprints are orders of magnitude smaller than those previously reported lasers epitaxially grown on Si.

Their findings were published in the prestigious journal Optica on August 4, 2017 (doi: 10.1364/OPTICA.4.000940).

“We demonstrated the smallest current injection QD lasers directly grown on industry-standard (001) silicon with low power consumption and high temperature stability,” said Kei May Lau, Fang Professor of Engineering and Chair Professor of the Department of Electronic & Computer Engineering at HKUST.

“The realization of high-performance micron-sized lasers directly grown on Si represents a major step toward utilization of direct III-V/Si epitaxy as an alternate option to wafer-bonding techniques as on-chip silicon light sources with dense integration and low power consumption.”

The two groups have been collaborating and has previously developed continuous-wave (CW) optically-pumped micro-lasers operating at room temperature that were epitaxially grown on silicon with no germanium buffer layer or substrate miscut. This time, they demonstrated record-small electrically pumped QD lasers epitaxially grown on silicon. “Electrical injection of micro-lasers is a much more challenging and daunting task: first, electrode metallization is limited by the micro size cavity, which may increase the device resistance and thermal impedance; second, the whispering gallery mode (WGM) is sensitive to any process imperfection, which may increase the optical loss,” said Yating Wan, a HKUST PhD graduate and now postdoctoral fellow at the Optoelectronics Research Group of UCSB.

“As a promising integration platform, silicon photonics need on-chip laser sources that dramatically improve capability, while trimming size and power dissipation in a cost-effective way for volume manufacturability. The realization of high-performance micron-sized lasers directly grown on Si represents a major step toward utilization of direct III-V/Si epitaxy as an alternate option to wafer-bonding techniques,” said John Bowers, Deputy Chief Executive Officer of AIM Photonics.