Category Archives: MEMS

From lifesaving smart headsets for truck drivers to gliding electric skateboards, five companies using MEMS and sensors will compete for audience votes during the Technology Showcase at the SEMI | MSIG MEMS & Sensors Executive Congress on November 1-2 in Napa Valley, Calif. As a featured event at the MEMS & Sensors Industry Group (MSIG) annual professional forum for executives from MEMS/sensors manufacturing and their end-user customers, the Technology Showcase highlights the newest and most unique MEMS/sensors-enabled applications in the industry.

“This year’s Technology Showcase finalists at the MEMS & Sensors Executive Congress are as fascinating as they are diverse,” said Frank Shemansky, CTO of SEMI | MSIG. “Imagine, for example, a MEMS-based switching element the width of a human hair, enabling RF switching that is 1,000 times faster and lasts 1,000 times longer than traditional mechanical switches. That is the kind of MEMS technology that could dramatically improve wireless applications, and it is just one of our Tech Showcase finalists ─  the others are equally compelling. The Tech Showcase is always a big draw at the Executive Congress because it gives attendees the chance to personally interact with the finalists’ demos to decide their vote for the winner – one of whom will be ‘crowned’ at the close of the conference.”

Tech Showcase Finalists

The LEIF eSnowboard by LEIF Technologies is the world’s first light electric vehicle that moves just like a snowboard. The LEIF brings to the pavement the smooth, sliding moves only found on a mountain or a wave — up to 23 mph and 15 miles per battery pack.

The Maven Co-Pilot by Maven Machines is the first smart headset for truck drivers. Employing MEMS, sensor fusion, wearable technology, machine intelligence and mobile-cloud architecture, the Maven Co-Pilot monitors drivers’ fatigue and distraction levels 50 times per second to provide accurate instantaneous early warnings to both drivers and fleet managers.

Menlo Digital-Micro-Switch Technology by Menlo Micro demonstrates fundamental materials’ advancements that improve the size, speed, power handling and reliability of MEMS switches. Smaller than the width of a human hair, Menlo Micro’s switching elements are so small that hundreds of them fit in a space smaller than 10mm2. Menlo Micro switches operate 1,000x faster than traditional mechanical switches — in a few microseconds rather than milliseconds. Their scalable architecture allows the handling of 100s of volts and 10s of amps without arcing. Menlo Micro’s devices last 1,000x longer than traditional mechanical switches, supporting billions of cycles without performance degradation.

The Berries Smart Sensor series by eLichens are patented autonomous non-dispersive infrared (NDIR) gas sensors offered in a 2 x 2 x 1cm package. These sensors integrate a dual-channel feature for a calibration-free long-life cycle. The miniaturized optical gas sensor is a complete system in package (SIP) integrating a proprietary infrared MEMS emitter and detectors, a highly efficient patented optical sampling chamber, and signal processing. The Berries series address the demanding requirements of the gas-sensing industries, where accuracy, auto-calibration and low power consumption are essential for new generations of gas- and air-detection products.

Coupled Time Domain Simulation for MEMS Sensors and System Integration by PZFlex lets engineers model and simulate a wide range of physics in new MEMS areas such as piezoelectric micromachined ultrasonic transducers (PMUTs) for fingerprint sensing. Engineers can conduct large-scale time-domain finite element analysis (FEA) simulation using PZFlex to gain insights into discrete device performance, device array performance, and full system performance for a PMUT fingerprint sensor embedded within a smartphone touch-display stackup.

MEMS & Sensors Executive Congress 2017 will take place November 1-2 at the Silverado Resort and Spa in Napa Valley, Calif. For more information, please contact SEMI via email: [email protected] or visit: www.semi.org/en/mems-sensors-executive-congress-2017.

A team of University of Wisconsin–Madison engineers has created the most functional flexible transistor in the world — and with it, a fast, simple and inexpensive fabrication process that’s easily scalable to the commercial level.

It’s an advance that could open the door to an increasingly interconnected world, enabling manufacturers to add “smart,” wireless capabilities to any number of large or small products or objects — like wearable sensors and computers for people and animals — that curve, bend, stretch and move.

Literal flexibility may bring the power of a new transistor developed at UW–Madison to digital devices that bend and move. PHOTO COURTESY OF JUNG-HUN SEO, UNIVERSITY AT BUFFALO, STATE UNIVERSITY OF NEW YORK

Literal flexibility may bring the power of a new transistor developed at UW–Madison to digital devices that bend and move. PHOTO COURTESY OF JUNG-HUN SEO, UNIVERSITY AT BUFFALO, STATE UNIVERSITY OF NEW YORK

Transistors are ubiquitous building blocks of modern electronics. The UW–Madison group’s advance is a twist on a two-decade-old industry standard: a BiCMOS (bipolar complementary metal oxide semiconductor) thin-film transistor, which combines two very different technologies — and speed, high current and low power dissipation in the form of heat and wasted energy — all on one surface.

As a result, these “mixed-signal” devices (with both analog and digital capabilities) deliver both brains and brawn and are the chip of choice for many of today’s portable electronic devices, including cellphones.

“The industry standard is very good,” says Zhenqiang (Jack) Ma, the Lynn H. Matthias Professor and Vilas Distinguished Achievement Professor in electrical and computer engineering at UW–Madison. “Now we can do the same things with our transistor — but it can bend.”

Ma is a world leader in high-frequency flexible electronics. He and his collaborators described their advance in the inaugural issue of the journal npj Flexible Electronics, published Sept. 27.

Making traditional BiCMOS flexible electronics is difficult, in part because the process takes several months and requires a multitude of delicate, high-temperature steps. Even a minor variation in temperature at any point could ruin all of the previous steps.

Ma and his collaborators fabricated their flexible electronics on a single-crystal silicon nanomembrane on a single bendable piece of plastic. The secret to their success is their unique process, which eliminates many steps and slashes both the time and cost of fabricating the transistors.

“In industry, they need to finish these in three months,” he says. “We finished it in a week.”

He says his group’s much simpler high-temperature process can scale to industry-level production right away.

“The key is that parameters are important,” he says. “One high-temperature step fixes everything — like glue. Now, we have more powerful mixed-signal tools. Basically, the idea is for flexible electronics to expand with this. The platform is getting bigger.”

His collaborators include Jung-Hun Seo of the University at Buffalo, State University of New York; Kan Zhang of UW–Madison; and Weidong Zhou of the University of Texas at Arlington.

Providing deep insights and perspectives on the challenges and opportunities in automotive electronics, the second edition of “FUTURECAR: New Era of Automotive Electronics Workshop” will be held November 8-10 at Georgia Tech in Atlanta, Georgia. SEMI (http://www.semi.org) and Georgia Tech, collaborators for the event, see unprecedented technical challenges and opportunities in electrical, mechanical and thermal designs, and new digital, RF, radar, LiDAR, camera, millimeter wave, high-power and high-temp technologies. The workshop will highlight rapid advancements in automotive electronics technologies and applications, and explore technical and business barriers and opportunities that are best addressed collectively across the supply chain.

The focus of the 2017 FUTURECAR workshop is on electronics in the car of the future. Autonomous driving, in-car smartphone-like infotainment, privacy and security, and all-electric cars will be among the topics presented, with particular emphasis on how these advancements impact devices and packaging with respect to materials, tools, processes, substrates, packages, components and integrated functions in R&D and in manufacturing. This event provides a unique opportunity for the semiconductor manufacturing and automotive supply chains to connect, collaborate and identify areas for new solutions.

The plenary session on November 8 will feature presentations from leading experts from Mercedes Benz, Porsche, Bosch, Qualcomm, SAE International and Yole Développement. The workshop sessions on November 9-10 include:

  • Power devices and packaging
  • High-temperature materials and reliability
  • Sensing electronics
  • Computing and communications
  • Student posters

FUTURECAR draws on the synergy between Georgia Tech in R&D and its industrial partners, as well as SEMI in global electronics manufacturing stewardship across the supply chain. Key to the depth of the workshop is support and expertise from the technical co-sponsors International Electronics Manufacturing Initiative (iNEMI), IEEE Electronics Packaging Society (IEEE EPS) and International Microelectronics Assembly and Packaging (IMAPS), as well as SAE International, the global association representing engineers and experts in the aerospace, automotive and commercial vehicle industries.

Workshop co-chairs are Prof. Rao Tummala, Georgia Tech; Bettina Weiss, SEMI; Grace O’Malley, iNEMI; Christian Hoffman (Qualcomm), IMAPS; and Patrick McCluskey, IEEE.

For more information on FUTURECAR 2017 and to register, please visit http://www.prc.gatech.edu/FUTURECAR

 

By Yoichiro Ando, SEMI Japan

Shinzo Abe, the prime minister of Japan, plans to stage a Robot Olympics in 2020 alongside the summer Olympic Games to be hosted in Tokyo. Abe said he wants to showcase the latest global robotics technology, an industry in which Japan has long been a pioneer. Japan’s Robot Strategy developed by the Robot Revolution Initiative Council plans to increase Japanese industrial robot sales to 1.2 trillion JPY by 2020. This article discusses how the robotics industry is not just a key pillar of Japan’s growing strategy but also a key application segment that may lead Japan’s semiconductor industry growth.

Japan leads robotics industry

According to International Federation of Robotics (IFR), the 2015 industrial robot sales increased by 15 percent to 253,748 units compared to the 2014 sales. Among the 2015 record sales, Japanese companies shipped 138,274 units that represent 54 percent of the total sales according to Japan Robot Association (JARA). The robotics companies in Japan include Yaskawa Electric, Fanuc, Kawasaki Heavy Industries, Fujikoshi and Epson.

Source: International Federation of Robotics (global sales) and Japan Robot Association (Japan shipment)

Source: International Federation of Robotics (global sales) and Japan Robot Association (Japan shipment)

The automotive industry was the most important customer of industrial robots in 2015 that purchased 97,500 units or 38 percent of the total units sold worldwide. The second largest customer was the electrical/electronics industry (including computers and equipment, radio, TV and communication devices, medical equipment, precision and optical instruments) that showed significant growth of 41 percent to 64,600 units.

Semiconductors devices used in robotics industry

Robotics needs semiconductor devices to improve both performance and functionality. As the number of chips used in a robot increases and more advanced chips are required, the growing robotics market is expected to generate significant semiconductor chip demands.

FEA-RO-IA-R2000-SpotWeld-3

Semiconductor devices in robots are used for collecting information; information processing and controlling motors and actuators; and networking with other systems.

  • Sensing Devices: Sensors are used to collect information including external information such as image sensors, sound sensors, ultrasonic sensors, infrared ray sensors, temperature sensors, moisture sensors and pressure sensors; and movement and posture of the robot itself such as acceleration sensors and gyro sensors.

    Enhancing these sensors’ sensitivity would improve the robot performance. However, for robot applications, smaller form factors, lighter weight, lower power consumption, and real-time sensing are also important. Defining all those sensor requirements for a specific robot application is necessary to find an optimal and cost-effective sensor solution.

    In addition, noise immunity is getting more important in selecting sensors as robot applications expand in various environments that include noises. Another new trend is active sensing technology that enhances sensors’ performance by actively changing the position and posture of the sensors in various environments.

  • Data Processing and Motor Control Devices: The information collected by the sensors is then processed by microprocessors (MPUs) or digital signal processors (DSPs) to generate control signals to the motors and actuators in the robot. Those processors must be capable of operating real-time to quickly control the robot movement based on processed and analyzed information. To further improve robot performance, new processors that incorporate artificial intelligence (AI) and ability to interact with the big data cloud database are needed.
  • As robotics is adapted to various industry areas as well as other services and consumer areas, the robotics industry will need to respond to multiple demands. It is expected that more field programmable gate arrays (FPGAs) will be used in the industry to manufacture robots to those demands.

    In the control of motors and actuators, power devices play important roles. For precise and lower-power operation of the robot, high performance power devices using high band gap materials such as Silicon Carbide and Gallium Nitride will likely used in the industrial applications.

  • Networking Devices: Multiple industrial robots used in a production line are connected with a network. Each robot has its internal network to connect its components. Thus every robot is equipped with networking capability as a dedicated IC, FPGA or a function incorporated in microcontrollers.

Ando--industrial-automation

Smart Manufacturing or Industry 4.0 requires all equipment in a factory to be connected to a network that enables the machine-to-machine (M2M) communication as well as connection to the external information (such as ordering information and logistics) to maximize factory productivity. To be a part of such Smart Factories, industrial robots must be equipped with high-performance and high-reliability network capability.

Opportunities for semiconductor industry in Japan

Japanese semiconductor companies are well-positioned in the key semiconductor product segments for robotics such as sensors, microcontrollers and power devices. These products do not require the latest process technology to manufacture and can be fabricated on 200mm or smaller wafers at a reasonable cost. Japan is the region that holds the largest 200mm and smaller wafer fab capacity in the world and the lines are quite versatile in these product categories.

The robotics market will likely be a large-variety and small-volume market. Japanese semiconductor companies will have an advantage over companies in other regions because they can collaborate with leading robotics companies in Japan from early stages of development. Also, Japan may lead the robotics International Standards development which would be another advantage to Japanese semiconductor companies.

For more information about the robotics and semiconductor, attend SEMICON Japan on December 13 to 15 in Tokyo. Event and program information will be available at www.semiconjapan.org soon.

TowerJazz, the global specialty foundry, and Crocus, a developer of TMR magnetic sensor technology and embedded MRAM, today announce volume manufacturing of Crocus TMR (Tunnel MagnetoResistance) sensors, using TowerJazz’s 0.13um CMOS process with a dedicated magnetic module in the Cu BEOL. With Crocus’ magnetic process, know-how and IP, and TowerJazz’s process technology and integration expertise, Crocus has successfully licensed the TMR technology to an automotive Tier 1 customer, bringing increased business to both companies.

According to a 2016 MarketsandMarkets report, the overall magnetic field sensors market was valued at USD $2.25 billion in 2015 and is expected to reach S4.16 billion by 2022, at a CAGR of 8.87% between 2016 and 2022. The growth of this market is driven by the rising demand for MEMS-based sensors across industry verticals, surge in the automotive industry, increasing demand for high-quality sensing devices, and continuous growth in consumer electronics applications.

Magnetic transducers which sense magnetic field strength are widely used in modern industry and electronics to measure current, position, motion, direction, and other physical parameters. Crocus’ TMR technology is a CMOS-based, robust technology capable of offering important advantages in sensitivity, performance, power consumption, size and full integration with CMOS to create monolithic single die ICs. Benefits to customers come in the form of low power, a robust design and high temperature performance. Crocus TMR solutions are ideally suited for many applications ranging from IoT to consumer, medical, automotive and industrial equipment.

“We selected TowerJazz because of their high flexibility and capabilities to adapt their TS13 platform to incorporate our TMR technology which includes magnetic materials that are typically not used in CMOS. TowerJazz’s vast manufacturing expertise is enabling us to successfully fulfill the needs of several market sectors combined with increased performance required in next-generation sensors. TowerJazz has been our development partner for many years and together we have achieved technology maturity leading to expanded business and successful licensing of Crocus IP,” said Michel Desbard, Crocus CEO.

“As the demand for IoT applications in our daily life is ever-increasing, there is an even greater need for intelligent sensing, low power and improved performance. Crocus’ successful licensing of their IP, along with TowerJazz’s manufacturing capability and know-how, enables us to deliver highly-advanced and competitive embedded-solutions to multiple customers in various markets. Through our partnership with Crocus, we are broadening our presence in the sensors’ market, complementing our MEMS and image sensing programs,” said Zmira Shternfeld-Lavie, VP of TOPS BU and R&D Process Engineering.”

Crocus’s TMR magnetic sensor is expected to displace existing sensor technologies in many applications. Crocus’ TMR magnetic sensor product family includes multiple architectures which are based on its Magnetic Logic Unit, a disruptive CMOS-based rugged magnetic technology.

IDTechEx predict that 2017 will be the first billion dollar year for wearable sensors. These critical components are central to the core value proposition in many wearable devices. The “Wearable Sensors 2018-2028: Technologies, Markets & Players” report includes IDTechEx’slatest research and forecasts on this topic, collating over 3 years of work to provide a thorough characterisation and outlook for each type of sensor used in wearable products today.

Despite sales volumes from wearable products continuing to grow, creeping commoditisation squeezes margins, with hardware sales being particularly vulnerable. This has led to some consolidation in the industry, with several prominent failures and exits, and challenging time even amongst market leaders in each sector. As hardware margins are squeezed, business models are changing to increasingly focus on the valuable data generated once a device is worn. Sensors are responsible for the collection and quality of that data, so understanding the capabilities and limitations of different sensor platforms is critical to understanding the progress of the industry as a whole.

In the report, IDTechEx address 21 different types of wearable sensor across 9 different categories as follows: Inertial Measurement Units (IMUs), optical sensors, electrodes, force/pressure/stretch sensors, temperature sensors, microphones, GPS, chemical & gas sensors & others. Hundreds of examples from throughout the report cover a breadth of technology readiness, ranging from long-established industries to early proof-of-concepts. The report contains information about the activities of over 115 different companies, with primary content (including interviews, exhibition or site visits by the authors) to more than 80 different companies, large and small.

IDTechEx describe wearable sensors in three waves. The first wave includes sensors that have been incorporated in wearable for many years, often being originally developed for wearable products decades ago, and existing as mature industries today. A second wave of wearable sensors came following huge technology investment in smartphones. Many of the sensors from smartphones could be easily adapted for use in wearable products; they could be made-wearable. Finally, as wearable technology hype and investment peaked, many organisations identified many sensor types that could be developed specifically with wearable products in mind. These made-for-wearablesensors often remain in the commercial evaluation or relatively early commercial sales today, but some examples are already becoming significant success stories.

WearableSensors_Large

Click to enlarge.

Billions of wearable electronic products are already sold each year today. Many have already experienced significant hardware commoditisation, with tough competition driving prices down. Even as wearable devices become more advanced, introducing more sensors and better components to enhance value propositions, lessons of history tell us that hardware will always be prone to commoditisation. As this happens the role of sensors only becomes more important; with hardware prices being constantly squeezed, increasing proportions of the value that companies can capture from products will be from the data that the products can generate.

The key hardware component for capturing this data is the sensors, so understanding the development and prospects of sensors today is critical to predicting the potential for this entire industry in the future. “Wearable Sensors 2018-2028: Technologies, Markets & Players” is written to address the needs of any company or individual looking to gain a clearer, independent perspective on the outlook for various types of wearable sensor. The report answers detailed questions about technology, markets and industry trends, and supported by years of primary research investment collated and distilled within.

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.

Screen Shot 2017-09-26 at 1.32.39 PM

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

BY ARABINDA DAS and JUN LU, TechInsights, Ottawa, ON

Last year was a great year for photovoltaic (PV) technology. According to Renewable Energy World magazine, since April 2016, 21 MW of solar PV mini-grids were announced in emerging markets [1]. The exact numbers of installed solar grids for 2016 has not been published yet but looking at the data for 2015, the PV industry is growing, helped by the $/watt for solar panels continuing to drop. The $/watt is obtained by taking the ratio of total cost of manufacturing and the number of watts generated. According to the Photovoltaic Magazine, the PV market continued to grow worldwide in 2015. The magazine also makes reference to the newly published report by the International Energy Agency Photovoltaic Power System (IEA PVPS) programme’s “Snapshot of Global Photovoltaic Markets 2015,” which also states that the total capacity around the globe has crossed the 200 GW benchmark and is continuing to grow [2]. This milestone of 200 GW in installed systems is a remarkable achievement and makes us think of the amazing journey of PV technology. The technology was born in Bell Labs, around 1954, with a solar cell efficiency of just 4% [3]. By the end of the 20th century, the overall solar cell efficiency was close to 11% and the worldwide installed capacity of PV was only 1 GW [3]. Today, seventeen years later, it has soared to 200 GW, with single junction cells having efficiencies around 20% [2].

Si-based solar cells

To celebrate this important milestone, we put TechInsights’ analysis and technical databases to work to investigate the structure of solar cells of two leading manufacturers and compare them to earlier technologies. We chose to analyze Si-based solar cells only, as they represent over 85% of the global market. According to the 2016 IHS Markit report, the top three PV module suppliers in the world are Trina Solar, SunPower, and First Solar [4]. We procured panels from Trina Solar, a Chinese based company, and SunPower, an American company, and carried out a structural analysis of these panels. These analyses helped us take a snapshot of current PV technology. We compared these two types of panels with an older panel from our database. This panel is about eight years old and was made by Kaneka (Japan). We will provide an overview of each panel and their underlying structure.

Table 1 consolidates some of the important param- eters of the three panels. The SunPower panel is based on monocrystalline silicon and the Trina solar panels are based on polycrystalline silicon. The older Kaneka panel is based on amorphous Si thin film technology. The panel from Kaneka is an earlier product; their recent products are made using hybrid technology, a combination of amorphous films and polycrystalline substrates, The Kaneka panel complements very well the other two products which are based on Si crystalline wafers. The technology to fabricate the solar cells (thin film, multi-crystalline or mono-crystalline) has a direct impact on the efficiency of the cells and on their electrical parameters like the open circuit voltage (Voc) and the short circuit current (Isc), as can be seen in Table 1. This table also shows that the Kaneka thin-film based panel has the lowest nominal power among the three. The ratio of nominal power to the light power that is received by the PV panel is indicative of its efficiency. It can be seen also that Kaneka’s thin film panel has the highest open circuit voltage which is the maximum voltage available from the solar cell without any load connected to it.

Screen Shot 2017-09-26 at 1.06.20 PM

Table 1 indicates that SunPower is the only one among the three that uses an n-type substrate and has the highest solar efficiency. SunPower has the lowest weight per meter-square of all the panels assessed (9.3kg).

Unlike SunPower panels, most installed Si solar panels employ a p-type substrate, even though the first silicon-based solar cells developed at Bell Labs were based on n-type Si substrates [3]. Researchers J. Libal and R. Kopecek posit that the industry transitioned to p-type substrates because the initial usage of solar cells was in space applications and p-type wafers demonstrated less degradation in the presence of cosmic rays. They suggest that for terrestrial applications there is growing evidence that n-type based solar panels are preferred over p-type based panels [5]. The reasons for choosing n-type Si substrates rather than p-type substrates are because the former are less sensitive to metallic impurities and thus are less expensive to fabricate. In general, the minority carrier diffusion lengths in n-type substrates are higher than p-type Si substrates. Also, n-type Si substrates can withstand higher processing temperatures than p-type substrates, which are prone to boron diffusion. According to the International Technology Roadmap for Photovoltaic (ITRPV), n-type based substrates will increase in prevalence and may eventually replace the p-type monocrystalline Si cells [6].

Thin film based solar panels are very different from monocrystalline Si cells. Thin film cells have the lowest efficiency and yet they too have a role to play in the PV industry. They are the most versatile; they can be coated on different substrates such as glass, plastic or even flexible substrates. The other big advantage of amorphous solar films is that they can be manufac- tured in a range of shapes, even non-polygonal shapes, thus they can be used in various applications. Also, thin film solar panels are not affected by high temper- atures, unlike crystalline solar panels. Thin film based panels made from amorphous Si are more effective for wavelengths between 400 nm to 700 nm, which is also the sensitive spectrum of the human eye; thus they can be used as light sensors [7]. Usually, thin film panels are almost half the price of monocrystalline panels. Amorphous silicon solar cells only require 1% of the silicon used in crystalline silicon solar cells [7].

Multi-crystalline (MC) solar panels are also cheaper than monocrystalline solar panels. MC panels are made by melting raw silicon and confining them into square molds, where they are cooled. This MC-Si process does not require the expensive Czochralski process. In the early days, the cost of fabrication of MC-Si panels was higher than thin film based panels. Now, due to the major advances in fabrication technologies, these panels often have the best $/ watt, which represent the ratio of cost to manufacture to energy output [8]. It is difficult to compare $/watt directly from different manufacturers and different types of solar panels as the technology is manufacturing is changing rapidly and often the most recent products of a manufacturer are not compared. A more sensible factor of comparison would be the ratio of total kilowatt-hours the system generates in its lifetime divided by the cost per square unit of the panel. To make a detailed estimation even the installation cost and tolerance to shade, overall reliability must be included in the calculations, which is beyond the scope of this article.

Solar panel overview

FIGURE 1 shows the panel from Kaneka. It indicates that the Kaneka solar panel cells are long strips that run across the whole length of the panel. The color of the panels is a shade of purple. The Kaneka Solar which is amorphous Si-based, has a very uniform color. The inherent structure of amorphous Si-films has many structural defects because they are not crystalline and thus are tolerant to other defects like impurities during manufacturing, unlike crystalline based panels [7]. The color of the thin film panels is strongly thickness dependent because thickness affects the light absorption. A solar cell’s outward appearance can range from blue to black and is dependent on the absorption and reflectivity of their surface. Ideally, if the cell absorbs all the light impinging on the surface it should be black. FIGURE 2 shows the panels from Trina solar and Sunpower. The Trina Solar panel has a blueish color and each cell is perfectly square. The SunPower SPR-X20- 250-BLK solar cell has a uniform blackish color. The spacing between the cells, the interconnect resis- tance, the top contacts and the materials used for the connections affect the overall performance of the panel. All three manufacturers connect their cells within a PV module and PV modules within an array in a series configuration.

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Table 2 summarizes the cell dimensions for the three manufacturers. Kaneka panels have the narrowest space (0.55mm) between the cells. The Trina solar panel has a 3 mm wide gap and a 5 mm gap, between two adjacent solar cells, in the horizontal and vertical direction respectively. These gaps are used for bus electrodes. In the SunPower solar panel, the metal grid is placed on the back surface eliminating metal finger width as a layout constraint. This design significantly reduces the finger resistance and improves the series resistance.

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For all panels, interconnects are made between the cells. The metallization and interconnects between the cells is a field of technology on its own. There are various techniques like lithography, laser grooving and printed contacts and these details are discussed more in detail elsewhere [9, 10, 11].

Solar panel cross-sections

In this section, we look into the layers deposited on the substrates. Cross-sectioning these big panels is not a trivial feat. These panels are covered with tempered glass and shatter during sawing and cross-sectioning. To extract a small rectangular piece requires patience and involves sawing and grinding processes. In most cases, the glass was removed before doing the cross-section. FIGURE 3 illustrates two SEM cross-sectional images and one schematic drawing. The SEM cross-sectional images show the top and bottom part of the Kaneka solar cell. In figure 3(a), the active layers comprise indium- tin- oxide, an amorphous silicon layer capped with zinc oxide, silver and a very thin layer of Ni-Al. On top of the Ni-Al film, solder is deposited. Ni-Al provides better adhesion to solder. Two electrical contacts are made between the cells, one to the indium-tin-oxide for the back contact and the other to the Ni-Al layer. Figure 3(b) exposes the layers under the glass substrate. The rear surface of the glass substrate is covered by a soft material such as EVA (ethyl-vinyl-acetate), which in turn is covered by a rear Polyvinyl Fluoride (PVF) layer called the backsheet (Tedlar or similar). EVA is also used on the top surface (figure 3(a)). The usage of these layers is standard practice in the PV industry. The main function of these layers is that they are impervious to moisture and are stable under prolonged exposure to sunlight. On the front side, EVA also helps to reduce reflection and provides good adhesion between the top glass and the solar panels. Figure 3(c) shows the complete stack in the Kaneka solar cell.

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FIGURE 4 presents the stack of materials on the multi- crystalline substrate of the Trina Solar panel. The substrate is p-type and has a very thin phosphorous doped region near the top surface. This n-doped region forms the PN junction. A silicon nitride anti-reflective coating layer is deposited on top of the substrate and in designated areas the passivation is opened and silver is deposited to make electrical contact to the n-doped regions. At the bottom of the multi-crystalline substrate, there is also a thin region of high p-doping concentration and this forms the back surface field layer. This solar cell module is fabricated using passivated emitter and full metal back-surface-field (BSF) technology. BSF technology is implemented to mitigate rear surface recombination and this is done by doping heavily at the rear surface of the substrate. This high doping concentration keeps minority carriers (electrons) away from the rear contact because the interface between the high and low doped areas of same conductivity acts like a diode and restricts the flow of the minority carriers to the rear surface. Passivated emitters in the front side and BSF layer on the rear side improve the efficiency of the cells. Figure 3(b) is the schematic repre- sentation of the cell without the EVA and PVF layers.

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FIGURE 5 shows an optical cross-section of the SunPower cell. Figure 5(a) shows that SunPower employs a backside junction technology with interdigitated backside p-emitter and n-base metal. This means that both the contact’s n and p-electrodes are at the bottom of the substrate and are placed in in an alternating manner. Having all the metal contacts on the rear side has two big advantages:

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1. Metallic contacts are reflective and occupy space that can be used to collect more sunlight; transferring these contacts to the rear side improves the cell efficiency and also leaves the front surface with a uniformly black color, which is more aesthetic for the home users.

2. It reduces bulk recombination. The mono-crystalline substrate is only 120 μm thick. It is designed so that the carrier is generated close to the junction. The substrate is n-type and p-electrodes are formed by localized doping on the bottom part of the substrate.

Figure 5(b) illustrates the general structure of the cell.

FIGURE 6 depicts a SEM cross-section of the metal fingers that connect to the interdigitated electrodes. The pitch between the metal fingers is 920 um and repeats over the entire back surface of the panel.

All three manufacturers employ some sort of surface texturing along with anti-reflective coatings to reduce reflection but SunPower uses the most advanced technology for surface texturing. FIGURE 7 illustrates a SEM topographical image of the front surface texture of the monocrystalline substrate having pyramids, which are etched into the silicon surface. These faceted surfaces increase the probability of reflected light entering back to the surface of the substrate. A similar concept is also applied to the back surface.

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The future is sunny and bright

Of the three panels we analyzed, SunPower solar panels employ the most advanced technologies and they illustrate how the solar cell has evolved over the ages. It started from a simple PN junction, then passivated emitters were intro- duced along with local back-surface-field (BSF) technology, which came to be known as Passivated-Emitter with Rear Locally (PERL) diffused technology. In contrast, today the most advanced technology is interdigitated back contacts along with passivated contacts.

In addition to these advances, there is great progress in tandem cells and multi-junctions to capture the different wavelength regions of the sun’s rays. A recent article in IEEE spectrum magazine presented the state of art of record-breaking PV cells made with different techniques such as thin film, crystalline Si, single junction, multi-junction cells. PV cells especially the multi-junction cells, have now crossed the 50% efficiency barrier [12]. Similarly, a publication from the alterenergy.org has collected all the major advances made in PV technology and discusses concepts like colloidal quantum dots and GaAs for cell technology, along with new applications [13]. Today, we regularly read about new materials (like perovskites) and come across new techniques that improve solar panel efficiencies, including new manufacturing methods to reduce the overall cost of fabrication. Moreover, PV cells are used in an innovative manner. The installation of PV panels is no more restricted to isolated rooftops or solar farm. An article in the Guardian made a reference to a solar panel road in Normandy, France [14]. At TechInsights, we will continue to keep an eye on emerging solar cell technologies.

The efforts emerging from various organizations all over the world are very encouraging. There are indeed many challenges for renewable energy to overcome before fiscal parity with fossil fuels is achieved; particularly for PV energy. Nevertheless, there is an increased focus on climate change issues. This has resulted in a significant amount of resources being allotted to PV technology in many countries, especially in developing countries such as China, India, and Brazil [1, 2]. This optimistic scenario reminds us of the song “I Can See Clearly Now” by the 1970s American singer Johnny Nash, where the refrain runs optimistically, “It’s gonna be a bright, bright sun-shiny day.”

References

1. http://www.renewableenergyworld.com/articles/2017/01/21-mw- of-solar-pv-for-emerging-market-community-mini-grids-announced- since-april.html;
2. http://www.pv-magazine.com/news/details/beitrag/iea-pvps— installed-pv-capacity-at-227-gw-worldwide_100024068/#ixzz4MB1 a44hq
3. The history of solar: https://www1.eere.energy.gov/solar/pdfs/solar_ timeline.pdf
4. http://news.ihsmarkit.com/press-release/technology/ihs-markit- names-trina-solar-sunpower-first-solar-hanwha-q-cells-and-jinko-
5. www.pv-tech.org/guest…/n_type_silicon_solar_cell_technology_ ready_for_take_off
6. http://www.itrpv.net/; http://www.itrpv.net/Reports/Downloads/2016/ 7. http://www.solar-facts-and-advice.com/amorphous-silicon.html
8. http://energyinformative.org/solar-cell-comparison-chart-mono-
polycrystalline-thin-film/
9. RP_0706-14839-O-4CS-11Kaneka
10. RP_0616-41931-O-5SA-100_Trina
11. RP_0716-42662-O-5SA-100_SunPower
12. http://spectrum.ieee.org/green-tech/solar/what-makes-a-good-pv-
technology
13. http://www.altenergy.org/renewables/solar/latest-solar-technology.
html
14. https://www.theguardian.com/environment/2016/dec/22/solar-panel-
road-tourouvre-au-perche-normandy

Advancements in spintronics


September 25, 2017

Applications now include nanoscale Spintronics sensors that further enhance the areal density of hard disk drives, through MRAMs that are seriously being considered to replace embedded flash, static random access memories (SRAM) and at a later stage dynamic random access memories (DRAM).

BY HIDEO OHNO, MARK STILES, and BERNARD DIENY, IEEE

Spintronics is the concept of using the spin degree of freedom to control electrical current to expand the capabilities of electronic devices. Over the last 10 years’ considerable progress has been made. This progress has led to technologies ranging from some that are already commercially valuable, through promising ones currently in development, to very speculative possibilities.

Today, the most commercially important class of devices consists of magnetic sensors, which play a major role in a wide variety of applications, a particularly prominent example of which is magnetic recording. Nonvolatile memories called magnetic random access memories (MRAMs) based on magnetic tunnel junctions (MTJs), are commercial products and may develop into additional high impact applications either as standalone memories to replace other random access memories or embedded in complementary metal–oxide–semiconductor (CMOS) logic.

Some technologies have appealing capabilities that may improve sensors and magnetic memories or develop into other devices. These technologies include three- terminal devices based on different aspects of spin-transfer torques, spin-torque nano-oscillators, devices controlled by electric fields rather than currents, and devices based on magnetic skyrmions. Even further in the future are Spintronics-based applications in energy harvesting, bioinspired computing, and quantum technologies.

But before we get into detail about where Spintronics is today, we need to cover the history of Spintronics.

The history of spintronics

Spintronics dates to the 1960s and was discovered by a group at IBM headed by Leo Esaki, a Japanese physicist who would later go on to win a share of the Nobel Prize I 1973 for discovering the phenomenon of electronic tunneling. Esaki and his team conducted a study which showed an antiferromagnetic barrier of EuSe sandwiched between metal electrodes exhibits a large magnetoresistance.

Subsequent advances of semiconductor thin film deposition techniques such as molecular beam epitaxy led to the development of semiconductor quantum structures, which prompted studies of magnetic multilayers. Ensuing studies of magnetic multilayers resulted in the discovery of giant magne- toresistance (GMR) in 1988. This effect was used to make magnetic sensors, which boosted the areal density of information stored on hard disk drives and led to the 2007 Nobel Prize in Physics awarded to Albert Fert and Peter Grunberg.

Since then rapid progress has continued to enhance both the role and the potential of Spintronics. So, let’s take a look at where we are now.

Where we are now

Applications now include nanoscale Spintronics sensors that further enhance the areal density of hard disk drives, through MRAMs that are seriously being considered to replace embedded flash, static random access memories (SRAM) and at a later stage dynamic random access memories (DRAM). Applica- tions also include devices that utilize spin current and the resulting torque to make oscillators and to transmit information without current.

Now let’s look at those applications and more in-depth.

Modern Hard Disk Drives: Two breeds of Spintronics sensors have replaced traditional anisotropic magnetoresistance (AMR) sensors. Those sensors include giant magnetoresistance (GMR) sensors (used in hard disk drives between 1998 and 2004) and tunnel magnetoresistance (TMR) sensors (used since 2004).

Those sensors are part of the technology development that enabled the increase of storage density of hard disk drives by several orders of magnitude, laying the foundation of today’s information age in the form of data centers installed by the cloud computing industry.

Magnetoresistive Random Access Memory (MRAM): MRAM and particularly spin-transfer- torque MRAM (STT-MRAM) is a nonvolatile memory with very high endurance and scalability. The current STT-MRAM technology uses an array of MTJs with an easy axis of magnetization oriented out of the plane of the layers. These MTJs utilize interface perpendicular anisotropy at the CoFeB–MgO interface, along with the large TMR of the system, for reading the state of magnetization. The spin-transfer torque exerted by a spin polarized current is used to change the magneti- zation direction, offering an efficient way of rewriting the memory. FIGURE 1 show the main families of MRAM that have evolved since 1995.

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Three Terminal Magnetic Memory Devices: Recent physics developments raise the prospect of three- terminal spintronic memory devices. These devices have an advantage over the standard two-terminal devices used in memory applications such as MRAM in that separating the read and write functions poten- tially overcomes several future roadblocks in the devel- opment of MRAM. There are two writing schemes: one is based on spin currents generated by an electrical current running through a heavy metal adjacent to the free layer of the MTJ. The current causes a spin current both in the bulk of the heavy metal and at the interface; this spin current then exerts a torque, called the spin-orbit torque, on the magnetization. In this scheme, the write current does not pass through the MTJ, separating the write and read functions. The other scheme uses current-induced domain wall motion to move a domain wall in the free layer of the MTJ from one side of the fixed layer to the other. In this scheme, the current passes through the free layer, but not the tunnel barrier, again separating the read and write functions.

Standby-Power-Free Integrated Circuits Using MTJ-Based VLSI Computing: Spintronic-based nonvolatile embedded working memory used in conjunction with CMOS-based logic applications is a crucial first step toward standby-power-free logic circuits that are much needed for Internet of Things (IoT) applications. MRAM based logic-in-memory reduces the overhead of having memory and logic apart and gives both minimized interconnection delay and nonvolatility.

Security: These devices have shown great promise for logic and memory applications due to their energy efficiency, very high write endurance, and nonvolatility. Besides, these systems gather
many entropy sources which can be advantageously used for hardware security. The spatial and temporal randomness in the magnetic system associated with complex micromagnetic configurations, the nonlinearity of magnetization dynamics, cell-to-cell process variations, or thermally induced fluctuations of magnetization can be employed to realize novel hardware security primitives such as physical unclonable functions, encryption engines, and true random number generators.

Spin-Torque and Spin-Hall Nano-Oscillators: Spin-torque nano-oscillators (STNO) and spin-Hall effect nano-oscillators (SHNO) are in a class of miniaturized and ultra-broadband microwave signal generators that are based on magnetic resonances in single or coupled magnetic thin films. These oscil- lators are based on magnetic resonances in single or combined magnetic thin films where magnetic torques are used to both excite the resonances and subsequently tune them. The torques can be either spin-transfer torques due to spin-polarized currents (STNOs) or spin Hall torques due to pure spin currents (SHNOs). These devices are auto-oscillators and so do not require any active feedback circuitry with a positive gain for their operation. The auto-oscillatory state is strongly nonlinear, causing phase– amplitude coupling, which governs a wide range of properties, including frequency tunability, modulation, injection locking, mutual synchronization, but also causes significant phase noise. STNOs and SHNOs can, in principle, operate at any frequency supported by a magnetic mode, resulting in a potential frequency range of over six orders of magnitude, from below 100 MHz for magnetic vortex gyration modes to beyond 1 THz for exchange dominated modes. Since STNOs and SHNOs can also act as tunable detectors over this frequency range, there is significant potential for novel devices and applications.

Beyond the applications listed, the spin degree of freedom is also being used to convert heat to energy through the spin Seebeck effect, to manipulate quantum states in solids for information processing and communication, and to realize biologically inspired computing. These may lead to new develop- ments in information storage, computing, communication, energy harvesting, and highly sensitive sensors. Let’s take a look at these new developments.

Thermoelectric Generation Based on Spin Seebeck Effects: The study of combined heat and spin flow, called spin caloritronics, may be used to develop more efficient thermoelectric conversion. Much of the focus of research in spin caloritronics has been the longitudinal spin Seebeck effect, which refers to spin-current generation by temperature gradients across junctions between metallic layers and magnetic layers. The generated spin current in the metallic layer gets converted into a charge current by the inverse spin Hall effect, making a two-step conversion process from a thermal gradient perpen- dicular to the interface into a charge current in the plane of the interface. This process can be used for thermoelectric conversion. Device structures using the spin Seebeck effect differ significantly from those using conventional Seebeck effects due to the orthog- onality of the thermal gradient and resulting charge current, giving different strategies for applications of the two effects.

Electric-Field Control of Spin-Orbit Interaction for Low-Power Spintronics: Control of magnetic properties through electric fields rather than currents raises the possibility of low energy magnetization reversal, which is needed for low-power electronics and Spintronics. One specific way to accomplish this low energy switching is through electric-field control of electronic states leading to modification of the magnetic anisotropy. By applying a voltage to a device, it is possible to change the anisotropy such that the magnetization rotates into a new direction. While such demonstrations of switching alone are not sufficient to make a viable device, voltage controlled reversal is a promising pathway toward low-energy nonvolatile memory devices.

Control of Spin Defects in Wide-Bandgap Semiconductors for Quantum Technologies: The spins in deep level defects found in diamond (nitrogen- vacancy center) and in silicon carbide (divacancy) have a quantum nature that manifests itself even at room temperature. These can be used as extremely sensitive nanoscale temperature, magnetic-field, and electric-field sensors. In the future, microwave, photonic, electrical, and mechanical control of these spins may lead to quantum networks and quantum transducers.

Spintronic Nanodevices for Bioinspired Computing: Bioinspired computing devices promises low-power, high-performance computing but will likely depend on devices beyond CMOS. Low-power, high performance bioinspired hardware relies on ultrahigh- density networks built out of complex processing units interlinked by tunable connections (synapses). There are several ways in which spin-torque-driven MTJs, with their multiple, tunable functionalities and CMOS compatibility, are very well adapted for this purpose. Some groups have recently proposed a variety of bioin- spired architectures that include one or several types of spin-torque nanodevices.

Skyrmion-Electronics: An Overview and Outlook: The concept of skyrmions derives from high energy physics. In magnetic systems, skyrmions are magnetic textures that can be viewed as topological objects. Theory suggests that they have properties that might make them useful objects in which to store and manip- ulate information. Many of the ideas are similar to ideas that were developed decades ago for bubble memory or, more recently, racetrack memory. There are several possible advantages for skyrmion devices as compared to other related devices. They are potentially higher density and lower energy, although the arguments for these remain to be experimentally verified.

So, what does the future of spintronics have in store?

The future

Spintronics will continue to have increasing impact, but the future is somewhat uncertain. The importance of magnetic sensors is likely to remain important while the importance of the magnetic sensors in hard disk drives appears to depend on the economics of mass storage in the cloud.

MRAM seems likely to play an increasing role both as standalone memory and embedded in CMOS. The degree of adoption still depends on a few technical and many economic considerations. The acceleration, over the past few months, of announcements and demonstrations related to STT-MRAM produced by major microelectronics companies, seems to indicate that large volume production of STT-MRAM is getting quite close. If the adoption of this technology by microelectronics industry becomes a reality, the whole field will be strongly boosted.

In the future, Spintronics can play a critical role in areas such as IoT, ultralow-power electronics, high-performance computing (HPC). Besides, in the next 10 to 15 years, we are likely to see a much greater role played by alternative forms of computing. The role that Spintronics plays in those technologies is likely to be strongly influenced by the success of MRAM. If MRAM is successful, we will have developed the ability to manufacture it making it easier to import into other technologies.

Some of the recent technical developments that have significant virtues for applications will likely play a role in technology 10 to 15 years from now but many will not. Research on many of these ideas will continue and will spawn related areas. Material research is key along this road.

Innovative materials allowing efficient charge to spin and spin to charge current conversion, or good control of magnetic properties by voltage, or efficient injection/manipulation/detection of spins in semicon- ductors can play major roles. Along with this idea, the use of oxide materials in spintronic devices can become quite important. Oxides share crystal- linity with semiconductors in distinction to metallic magnetic devices. Will the greater control that comes with crystallinity give advantages to oxides in future devices? These are some of the many topics that are likely to be addressed in the coming years.

The basics of laser marking are reviewed, as well as current and emerging laser technologies.

BY DIETRICH TÖNNIES, Ph.D. and DIRK MÜLLER, Ph.D., Coherent Inc., Santa Clara, CA

Laser marking is established at multiple points in semiconductor production and applications continue to diversify. There are several laser technologies servicing the application space. This article reviews the basics of laser marking and the current and emerging laser technologies they utilize. It is intended to give a clear sense of what applications parameters drive the choice of laser (speed, cost, resolution, etc.), and provide those developing a new application some guidance on how to select the optimum technology.

Laser marking basics

Laser marking usually entails inducing a visible color or texture change on a surface. Alternatively, although less commonly, marking sometimes involves producing a macroscopic change in surface relief (e.g.engraving). To understand what laser type is best for a specific marking application, it is useful to examine the different laser/ material interactions that are generated by commonly used laser types.

Most frequently, lasers produce high contrast marks through a thermal interaction with the work piece. That is, material is heated until it undergoes a chemical reaction (e.g. oxidation) or change of crystalline structure that produces the desired color or texture change. However, the particulars of this process vary significantly between different materials and laser types.

CO2 lasers have been employed extensively for PCB marking because they provide a fast method of producing high contrast features. However, they are rarely selected when marking at the die or package level. This is because the focused spot size scales with wavelength due to diffraction. CO2 lasers emit the longest infrared (IR) output of any marking laser. Additionally, IR penetrates far into many materials, which can cause a substantial thermal impact on surrounding structures. Consequently, CO2 laser marking is limited to producing relatively large features where a significant heat affected zone (HAZ) can be tolerated.

Fiber lasers, which offer high power output in the near IR, have emerged over the past few years as one of the most cost effective tools for high-speed marking. Furthermore, the internal construction of fiber lasers renders a compact footprint, facilitating their integration into marking and test handlers. Cost and space savings are further enhanced when the output of a single, high power fiber laser is split, feeding two scanner systems.

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But fiber lasers have disadvantages, too. One reason for the low cost of many fiber lasers is that they are produced in high volumes with designs meant for general-purpose applications. For example, they usually produce a high quality beam with a Gaussian intensity profile. This is advantageous for many material processing applications, but not always for laser marking. In fact, a more uniform beam intensity distribution, called a flat-top profile, is sometimes more useful since it produces marks with a sharper, more abrupt edge (rather than a smooth transition from the marked to the unmarked region). Coherent recently introduced a new type of fiber (NuBEAM Flat-Top fiber technology) which enables efficient conversion of single-mode laser beams into flat-top beam profiles, specifically to address this issue.

Other quality criteria, such as high-purity linear polarization, and stability of pulse energy and pulse width, are difficult to achieve with low-cost fiber lasers. This limits their use in more stringent or sensitive marking applications. From a practical standpoint, most fiber lasers cannot be repaired in the field, but are replaced as a whole. This leads to longer equipment downtime and increased maintenance efforts as compared to traditional marking lasers based on diode-pumped, solid-state (DPSS) technology (specifically, DPSS is used here to refer to lasers with crystal resonators).

DPSS lasers also emit in the near infrared. Generally, these lasers are more expensive than a fiber laser of the same output power level. So, infrared DPSS lasers are most commonly used in applications having technical requirements that cannot be met by fiber lasers,such as high volume production of more advanced and expensive semiconductor devices.

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One advantage of DPSS laser technology is that it can be configured to directly produce a multi-mode beam profile which is essentially flat-top. The Coherent ❘ Rofin PowerLine E Air 30-1064 IC is an example which has found extensive use in semiconductor marking, since it provides an efficient way to rapidly produce very high contrast marks.

Another useful feature of DPSS lasers, which produce pulsewidths in the nanosecond regime, is that their output is much more stable than that of fiber lasers. This makes it much easier to reliably frequency double or triple their infrared light within the laser head, giving a choice of output in the green or ultraviolet (UV). Output at these wavelengths provides two significant benefits. First, they offer additional options in matching the absorption of the material to the laser wavelength. Stronger absorption generally yields higher marking efficiency and reduced HAZ, since the laser light doesn’t penetrate as far into the material. The second benefit of shorter wavelengths is the ability to focus to smaller spot sizes (because of their lower diffraction) and produce smaller, finer marks.

However, frequency multiplied DPSS lasers are generally more costly and voluminous than either fiber lasers or infrared DPSS lasers with comparable output power. Lower power translates into reduced marking speed.

Therefore, green and UV DPSS lasers are typically employed when they offer a significant advantage due to the particular absorption characteristics of the material(s) being marked.

Another emerging and important class of marking lasers has pulsewidths in the sub-nanosecond range. Due to the nature of the laser/material interaction at short pulsewidths, these lasers tend to produce the smallest possible HAZ with excellent depth control.

There are just a few products currently on the market that exploit this property. One example is the PowerLine Pico 10 from Coherent ❘ Rofin which generates 0.5 ns laser pulses in either the near IR (8 W total power) or green (3 W total power), at pulse repetition rates between 300 kHz and 800 kHz. This combination of output characteristics makes it capable of high speed marking of a wide range of materials where mark penetration depth must neces- sarily be shallow because of low material thickness, or to minimize HAZ.

Laser marking today

Typically, the first consideration in choosing a laser for a specific application is matching the absorption characteristics of the material with the laser wavelength. Similarly, desired feature size is also driven by laser wavelength, as well as by the precision of the beam scanning system. Next, HAZ constraints usually determine the maximum pulsewidth which can be used (although this choice is again highly material dependent). To see how these parameters interact in practice, it’s useful to review some real world applications.

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Epoxy-based molding compounds

The most commonly used molding compounds absorb very well in the near IR. Specifically, the near IR laser transforms the usually black molding compound into a gray/white powder, yielding high contrast marks. Plus, many IC packages have mold compound caps thick enough to easily tolerate a marking depth of 30 μm to 50 μm. As a result, many marking systems based on near IR lasers, both fiber and DPSS, are currently in use.

However, some semiconductor devices with small form factor have only thin mold compound caps to protect wire bonded silicon dies, and a marking depth of only 10 μm or less is required. Increasingly, green lasers are used for this type of shallow marking because of a stronger absorption at this wavelength by the epoxy matrix.

Ceramics

The process window when marking ceramics, such as used in packaging power semiconductors, high-brightness LEDs, RF devices, saw filters or MEMS sensors, is relatively narrow. Accurate focus and high pulse energy are critical to ensure reliable marking results, and ideally, the laser marker should have the capability to adjust the focus of the laser beam onto the ceramic surface in real time, in order to compensate for package height variations. Because of their more reliable interaction with ceramic materials, DPSS lasers based on Nd:YAG, which offer high pulse energies and relatively long pulses, are often still used for marking ceramic lids and substrates. Coherent ❘ Rofin has also developed a special fiber laser (the PowerLine F 20 Varia IC), which offers adjustable pulse widths up to 200 ns, specifically to improve process windows for marking applications of this type.

The ceramic substrates used with high-power LEDs often require tiny marks to identify individual devices. IR lasers are the preferred lasers for marking these ceramic substrates, providing their spot size is not too big for the layout to be marked. For very small marking features a green laser or UV laser is often required.

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Organic substrates

IC substrates or interposers are marked during production with traceable data matrix codes. The thin green solder resist layer on top of the substrate has to carry the mark, and care has to be taken that the copper underneath the solder resist is not exposed. Moreover, data matrix codes can be quite small, with cell sizes of only 125 μm or even less. Since the spot size of the focused laser beam must thus be much smaller than the cell size, the final spot diameter must be significantly less than 100 μm.

Defective IC substrates often are identified by marking large features (e.g., a cross) into the solder resist layer. Although the part is defective, the properties of the mark are still important. This is because it has to be reliably recognized by subsequent processing tools, and also, because any delamination of the solder resist layer might cause problems during succeeding processes.

IC strips have gold pads along their periphery which are used to identify parts found to be defective after die attach and wire bonding. For defective parts, the gold pad is marked by converting its color from gold to black or to dark grey.

Ideally, it is desirable to have one laser marker that can accomplish all three of these marking applications tasks. The green DPSS laser has become the standard laser marker for these applications, with UV lasers occasionally employed for high-end substrates.

Semiconductors

The growing demand for flip-chip devices, wafer-level packaging and defective die identification drives the need for direct marking of silicon, GaAs, GaN/sapphire or other semiconductors. Silicon is partially trans- parent in the near IR, and lasers at this wavelength are used whenever deep marks into silicon are required, such as placing wafer IDs near the wafer edge. Near IR laser markers are also selected for marking molded fan-out wafer level packaging wafers.

However, for marking either flip-chips or the backside of wafers, green lasers are preferred because of the strong absorption of this wavelength in silicon. Wafer backside marking requires only very shallow marks and the shallow laser penetration avoids potential damage to the circuitry on the reverse side of the flip-chip or wafer. The need for shallow marking also minimizes the laser power requirement. For example, Coherent ❘ Rofin provides a 6 W green laser (the PowerLine E 12 SHG IC) that is well suited for wafer backside marking, and can also mark the wafer through the tape whenever the wafer is mounted on a film frame.

Metals

Near IR lasers are widely used for marking the metal lids used with microprocessors and other high power consumption ICs.

Leadframes, which are plated with tin, silver or gold, are marked either before or after plating. Since leadframes are used for cost sensitive devices, capital investment is critical, and economical fiber lasers are often chosen for this reason.

Laser marking tomorrow

As packages get thinner and smaller, they will require shallower, higher resolution marks. Sub-nanosecond lasers are the most promising method for producing these types of marks, and are compatible with a wide range of materials. The diverse capabilities of this technology are shown in Figure 5, which depicts marking results on four different materials using a sub-nanosecond laser (Coherent ❘ Rofin PowerLine Pico 10-532 IC).

The first image is a flexible IC substrate; very thin solder resist layers and metal coatings make it important that the laser does not cause delamination. Here, the circular gold pad has been converted to black without delamination. In the next image, an IC substrate has been given a white mark, again without delaminating the solder resist.

The third image shows very small characters (< 150 μm) marked on the backside of a silicon wafer containing hundred thousands of tiny discrete semiconductor devices. Producing marks of this resolution through the film would be difficult to accomplish with a nanosecond pulsewidth laser.

The final image is a copper leadframe coated with thin silver film. Here, the goal is to produce a shallow mark with high contrast without engraving the under- lying material, which has been accomplished with the sub-nanosecond laser.

Conclusion

Semiconductor fabrication and packaging represent challenging marking applications, often requiring small, fine marks produced without a significant effect on surrounding material. An overall trend towards smaller and thinner device geometries will drive increased use of higher precision laser tools, such as those utilizing green and UV nanosecond lasers, and even sub-nanosecond lasers, while cost-sensitive applications will continue to utilize inexpensive fiber lasers.