Category Archives: LEDs

Problems frequently arise as a result of an incomplete or absent formal risk assessment when processes are modified or new materials introduced.

BY ALAN IFOULD and ANDREW CHAMBERS, Edwards, North Somerset, UK

The sub-fab is home to the many pumps and abatement systems that not only help to create the pristine environments required in the process chambers of the numerous tools in the cleanroom, but also handle the exhaust gases and by-products generated by the manufacturing process. In this respect, the efficiency and efficacy of sub-fab operations directly affect the availability, productivity, total operating cost and yield of the manufacturing fab above. Perhaps more importantly, in addition to supporting the process vacuum, equipment in the sub-fab is designed to render cleanroom process wastes harmless and ready for safe disposal or, if appropriate, release into the environment. As such, they are vital to protecting the safety of the people working in the fab as well as those living and working in the surrounding community, and ultimately, all of us who share that environment. The very nature of the process materials and reaction byproducts handled in the sub fab, which may be variously corrosive, toxic, pyrophoric, flammable or environmentally damaging, creates significant risks, especially for those who must operate and maintain the equipment located there. Moreover, as device manufacturing becomes more complex, with the introduction of new materials, new precursors and new processes, the risk of mistakes with potentially catastrophic consequences in both human and financial terms will only increase.

While ultimate responsibility for personnel safety in the sub-fab lies with the fab operator, equipment manufac- turers have a part to play by optimizing their products not only for efficient, effective and reliable operation, but also by ensuring any risks associated with operation, maintenance and repair are assessed and minimised to the greatest extent possible.

There is often a strong focus on technical performance and cost attributes when selecting sub-fab equipment. However, processes and procedures to ensure optimum operation and continuous mitigation of risks to service personnel are equally critical; these demand the devel- opment of clear and effective operating procedures and guidelines – in industry jargon “best known methods” or BKMs – to ensure the equipment achieves its full performance potential and safety integrity maintained. The manufacturers of sub-fab equipment are perhaps in the best position to define these guidelines since they will typically have acquired an understanding of the risks posed by hazardous materials on a case-by-case basis during the course of system optimization. Frequent development of BKMs is undertaken in collaboration with the process tool manufacturer or early adopters of the process. However, defining operating and maintenance methods and procedures that are truly the best known requires a commitment to doing so at the highest levels of corporate management, and a formal process of reporting, analysis, synthesis and dissemination throughout the equipment support community.

A key component of any BKM program is the active participation of the equipment manufacturer’s service personnel who are responsible for installing, commissioning and maintaining the equipment and are also likely to have first- hand knowledge and experience of the potential hazards. Since service personnel are invariably in the front-line when safety incidents occur, they are well motivated to contribute since they themselves are often at greatest risk, and it is essential that their contribution is incorporated into product development programs to complement the technical performance with assured safety and reliability.

Even a cursory search of the internet will quickly reveal numerous examples of fab and sub-fab incidents. Amongst the lessons that can be taken from these events is that the risk management process and the resulting controls have to cover every foreseeable circumstance across the equipment lifecycle: installation, commissioning, operation, servicing and maintenance. Notable recent serious accidents include:

– March 2014 – A fab worker dies after a carbon dioxide leak

– January 2013 – One worker dies and four others are hospitalized after a hydrofluoric acid leak at a manufacturing facility

– September 2013 – A fire at major memory fab results in the closure of the facility with losses estimated in the range of $1 billion and a measurable impact on global DRAM pricing

– August 2012 – A security guard and 3 firefighters are hospitalized when a fire occurs in the exhaust ducts of a photovoltaic manufacturing laboratory in Singapore. The entire facility is shut down for weeks and 35 workers are laid off

These were events with consequences visible and far-reaching enough to make the national and international news. However, experience indicates that smaller events, often with narrowly-averted disastrous consequences, occur on a much more frequent basis with adverse impacts on fab productivity. These events are typically not widely broadcast, thereby limiting the community learning that might otherwise take place.

In respect of process exhausts, three types of hazard recur repeatedly as manufacturing processes evolve and new process materials are introduced: condensation of reactive chemical precursors or reaction products, corrosion due to condensation of acidic materials, and pipe blockage due to accumulation of condensate in significant volume. The images in FIGURES 1-3 show a few examples.

FIGURE 1. (left) Condensed explosive polysiloxane material in an epitaxial deposition system process foreline, (middle and right) CVD exhaust pipe destroyed by explosion of condensed process by-product.

FIGURE 1. (left) Condensed explosive polysiloxane material in an epitaxial deposition system process foreline, (middle and right) CVD exhaust pipe destroyed by explosion of condensed process by-product.

FIGURE 2. (left) Acidic TEOS-based polymer with a pH of approximately 1, (middle) Condensed corrosive Br2-based liquid, (right) Exhaust pipe damaged by exposure to condensed acidic material.

FIGURE 2. (left) Acidic TEOS-based polymer with a pH of approximately 1, (middle) Condensed corrosive Br2-based liquid, (right) Exhaust pipe damaged by exposure to condensed acidic material.

FIGURE 3. Exhaust blockage caused by various materials (left) AlCl3 from a metal etch process, (middle) NH4Cl from an LPCVD process, (right) Unknown material deposited in the exhaust of a metal carbide CVD process.

FIGURE 3. Exhaust blockage caused by various materials (left) AlCl3 from a metal etch process, (middle) NH4Cl from an LPCVD process, (right) Unknown material deposited in the exhaust of a metal carbide CVD process.

In many cases, the cause of the risk is understood and solutions exist, but problems frequently arise as a result of an incomplete or absent formal risk assessment when processes are modified or new materials introduced. For example, condensation of potentially dangerous or explosive materials can usually be prevented by carefully controlling the temperature of the exhaust gas through the pipework and pumps. Pipe heating systems are widely available for forelines and exhaust pipes, and pumps can be designed with internal thermal management, but if the risk is not properly assessed, the appropriate controls will not be put in place. Furthermore, while a risk analysis may conclude that exhaust pipe heating is required in a specific case, it should also recognize that key to its effective implementation is the avoidance of cool spots, particularly at bends and junctions. Even a small local drop in temperature can create a hazardous situation despite the application of what is widely perceived as an effective protective measure – a subtle effect, but one with which field service personnel have become familiar through hard-won experience. At a practical level, if each process exhaust is designed in isolation, such considerations make their design and implementation a time-consuming and labor-intensive process. However, as noted in a previous publication [1] the ability to maintain effective thermal control throughout the exhaust stream can be enhanced by integrating the vacuum pumping and point- of-use abatement functions together with the interconnecting exhaust pipes into a single unified system. In this way the pipe routing can be standardized to permit optimization of the exhaust pipe heating installation for each specific process and to avoid the need for customization in the field. Integration and standardization also permits careful optimization of pump capacities and pipe diameters and routing to minimize power consumption and maximize destruction or removal efficiency (DRE). Finally, whether consid- ering an integrated system or not, secondary enclosures for pumps, abatement and exhaust pipes provide an additional layer of protection by permitting hazardous materials to be routed away from personnel in the event of an unintended release.

In some cases, it is not possible to prevent the accumu- lation of hazardous materials. It then becomes essential to monitor the deposition and remove it through periodic maintenance procedures. For example, blockage can be monitored by measuring the pressure drop over the length of the exhaust pipe – as material accumulates in the pipe the pressure drop increases. By monitoring for blockage, operators can ensure that the system is cleaned before its performance impacts production and at the same time avoid cleaning more frequently than required. Integrated vacuum and abatement systems often combine monitoring capabilities with automated software to alert operators of the need for maintenance.

While problems associated with accumulation of materials in process exhausts is arguably the most frequently encountered hazard faced by sub-fab maintenance personnel, another widely applied risk mitigation strategy, particularly for flammable process materials, is dilution below their lower flammability limit (LFL) with an inert gas such as nitrogen. However, it is important to understand the nature of the chemical processes occurring in the deposition chamber and to base the dilution calculation on the composition and volume of the effluent gas rather than the precursor. For example, TEOS is a precursor gas widely used in the chemical vapor deposition of silicon oxide films. The lower temperature needed for the CVD process and the absence of aggressive reaction products are the main advan- tages of using TEOS compared with traditional precursors such as silane and the mechanical and electrical properties of Si02 films deposited from TEOS are also very good. The decomposition products of TEOS in the gas phase in the absence of oxygen include organic fragments (ethanol, ethanal, ethene, methane, carbon monoxide), and in the presence of oxygen include water vapour, carbon dioxide, ethanal and methanol [2], many of which are flammable. A dilution calculation based on the amount of TEOS entering the chamber rather than the volume of decompo- sition products exiting the chamber could easily lead to an underestimate of the required volume of diluent and the presence of a flammable mixture in the exhaust pipe in some circumstances. Once again, a rigorous risk assessment is required to identify such potential hazards and put corrective measures in place where needed.

Risk assessment and communication

It should be clear from the preceding discussion that a detailed technical understanding of semiconductor manufacturing processes and materials and their impact on sub-fab equipment is a prerequisite for safe and efficient pumping and abatement of process exhaust. In particular, ensuring the safety of sub fab operations requires a formal process for risk assessment. Once determined, safe operating proce- dures must be codified and effectively communicated to field personnel, and a mechanism must exist to update procedures based on feed-back from the field. FIGURE 4 is taken from the Risk Assessment Procedure [3] used at Edwards (adapted from Semi S10) and illustrates the Risk Rating Table, a matrix by which risks are evaluated and appropriate responses determined.

Once risks are assessed the information must be effec- tively communicated to users and field service personnel. To ensure appropriate dissemination of required information, Edwards publishes Application Notes for equipment users and Safety Application Procedures (SAP) for service engineers.

Conclusion

The hazardous nature of many of the materials present in the semiconductor manufacturing process creates significant safety risks for fab personnel and others living or working near the fab, and financial risks for manufacturers and investors. Managing those risks takes more than good intentions and common sense precautions. It requires a detailed and continuously updated technical understanding of the processes and materials based on broad experience across many different types of applications, and ideally, partnership with process tool manufacturers during development and optimization of new processes. As in other high risk industries – nuclear, aviation, automotive, healthcare, oil, rail and military – best practice safety and risk management is heavily influ- enced by equipment manufacturers, who are in the best position to understand the capabil-
ities of their products across a wide range of applications.

Ultimately the fab management team own the responsibility for managing risk and safety with the highest levels of corporate respon- sibility. Semiconductor equipment manufacturers, and in particular, manufacturers of pumping and abatement systems that handle and safely dispose of hazardous materials, have an invaluable supporting role to play with their continuous accumulation of know-how and formal processes for risk assessment, including a mechanism for distributing safety information to, and incorporating feedback from, the field.

References

1. Andrew Chambers, Managing hazardous process exhausts in high volume manufacturing, Solid State Technology, 2016 Issue 2
2. Van der Vis, M.G.M., et al, The thermodynamic properties of tetrae- thoxysilane (TEOS) and an infrared study of its thermal decomposition, Colloque C3, supplement au Journal de Physique 11, Volume 3, aofit 1993, http://dx.doi.org/10.1051/jp4:1993309
3. Adapted from Semiconductor Equipment and Materials International (SEMI) standard S-10, http://www. semi.org

Pixelligent Technologies, a developer of high-index advanced materials for solid state lighting and display applications and producer of PixClear products, announced today that it closed $10.4 million in new funding. The round was led by The Abell Foundation, The Bunting Family Office, and David Testa, the former Chief Investment Officer of T. Rowe Price. Funds will be used to complete the installation of additional manufacturing capacity, open new offices in Asia, and continue to drive innovation in lighting, display and optical applications.

To date Pixelligent has raised over $36.0M in equity funding and has been awarded more than $12M in U.S. government grant programs to support the development of its proprietary PixClear products and PixClearProcess. The Pixelligent nanotechnology platform includes proprietary nanocrystal synthesis, capping technology, high volume manufacturing and application engineering that supports ink jet, slot die, UV curing, spray coating, and numerous other manufacturing processes.

“We have clearly established Pixelligent as the leading high-index materials manufacturer for demanding solid state lighting and OLED display applications throughout the world. Pixelligent is partnering with leading advanced materials suppliers to deliver breakthrough performance that currently spans applications in 12 discrete markets including: lighting, displays, printed and flexible electronics, AR/VR, optically clear adhesives, MEMS, gradient index lenses, and others with a combined total over $9B in market opportunities. We have numerous commercial applications currently in the market and expect additional product introductions before the end of 2016,” said Craig Bandes, President & CEO of Pixelligent Technologies.

“We started our partnership with Pixelligent in 2011 when the company relocated to Baltimore City and have seen the company achieve all of their critical technology and manufacturing milestones, while establishing a global brand and presence. Our investment objective is to support leading edge companies that deliver breakthrough technology and products and create jobs in our local community. Pixelligent is at the forefront in delivering on the promise of the nanotechnology revolution. We are proud of what the team at Pixelligent has accomplished to date and we look forward to their continued growth and success,” said Eileen O’Rourke, CFO of The Abell Foundation.

Veeco Instruments Inc. (NASDAQ: VECO) announced today that Epistar Corporation (TSE: 2448) has ordered multiple TurboDisc EPIK 700 Gallium Nitride (GaN) Metal Organic Chemical Vapor Deposition (MOCVD) Systems for the production of light emitting diodes (LEDs). The Veeco systems will be used to meet demand for various applications.

“The improved demand of solid state lighting combined with the need to compete in a competitive market dictates we choose the most productive and most cost-efficient MOCVD platform in the industry,” said Dr. MJ Jou, President, Epistar Corporation. “Veeco has been our supplier of choice dating back to their innovative K465i system. After adopting their latest EPIK platform, we have achieved superior yield results and lowered manufacturing costs. The addition of these new EPIK MOCVD systems will help advance our production goals and improve our product competitiveness.”

Based on Veeco’s proven TurboDisc technology and the proprietary Uniform FlowFlange, the award-winning EPIK 700 MOCVD system enables customers to achieve an improved cost per wafer savings compared to previous MOCVD systems through improved wafer uniformity, reduced operating expenses and increased productivity.

“We believe that a leader such as Epistar ramping production to meet demand of LEDs is a positive sign for the industry as a whole,” said James T. Jenson, Senior Vice President, Veeco MOCVD Operations. “Veeco’s superior MOCVD technology is the number one choice of manufacturers looking for a competitive edge in a market that seems to be turning upward again. We look forward to supporting Epistar’s future MOCVD requirements as they continue their growth plans.”

SEMI today announced that SEMICON Japan 2016, at Tokyo Big Sight on December 14-16, has increased exhibition and programming to keep pace with high-growth semiconductor segments in Japan. SEMICON Japan, celebrating its 40th anniversary, is the leading electronics event in Japan, with more than 700 exhibitors and 35,000 attendees.

With the world’s largest installed fab capacity of over 4.1 million (200mm equivalent) wafers per month and its diverse product mix, Japan is well-positioned to meet the increasing demands of the new world of electronics – from innovations in mobile technologies to the growing “World of IoT” devices.  SEMICON Japan 2016 connects the players and companies across the electronics manufacturing supply chain by facilitating communications and partnerships. Highlights of the exhibition area include:

  • Themain exhibit zone includes a Front-end Process zone and a Back-end/Materials Process zone.
  • “World of IoT (Internet of Things)”, a “show-within-a-show,” is where semiconductor manufacturing intersects IoT applications including wearable, health care, medical, automotive, and more. The World of IoT this year newly expands its scope to include flexible hybrid electronics (FHE), an essential enabling technology for IoT applications. Exhibiting companies include Japanese flexible and printed electronics companies from key institutes and associations for the industry area.
  • The Sustainable Manufacturing Pavilion, features solutions for the expanding IoT market driving 200mm lines; exhibitors include used and refurbished equipment, cleanroom-related, environmental safety, and more.
  • The Manufacturing Innovation Pavilion showcases innovations for leading-edge lower-cost semiconductor devices; exhibitors include advanced lithography, 2.5D/3D-IC, innovative manufacturing systems, specialty materials, OLED/LED/PE manufacturing equipment and materials.
  • Innovation Village, an interactive exposition showcase arena. Exhibitors are early-stage startups seeking funding, partners, and media exposure in the domain of electronics, materials, IT, tele-communications, bio, med-tech, environment, security or hardware.

For complete information of exhibits and programs, visit www.semiconjapan.org/en.

 

The upconversion of photons allows for a more efficient use of light: Two photons are converted into a single photon having higher energy. Researchers at KIT now showed for the first time that the inner interfaces between surface-mounted metal-organic frameworks (SURMOFs) are suited perfectly for this purpose – they turned green light blue. The result, which is now being published in the Advanced Materialsjournal, opens up new opportunities for optoelectronic applications such as solar cells or LEDs. (DOI: 10.1002/adma.201601718)

Photon upconversion: energy transfer between the molecules is based on electron exchange (Dexter electron transfer). Credit: Illustration: Michael Oldenburg

Photon upconversion: energy transfer between the molecules is based on electron exchange (Dexter electron transfer). Credit: Illustration: Michael Oldenburg

Metal-organic frameworks (MOFs) are highly ordered molecular systems that consist of metallic clusters and organic ligands. At the Institute of Functional Interfaces (IFG) of KIT, researchers developed MOFs that grow epitaxially on the surfaces of substrates. These SURMOFs (surface-mounted metal-organic frameworks) can be produced from various materials and be customized using different pore sizes and chemical functionalities so that they are suited for a broad range of applications, e.g. for sensors, catalysts, diaphragms, in medical device technology or as intelligent storage elements.

Another field of application is optoelectronics, i.e. components that are capable of converting light into electrical energy or vice versa. Many of these components work on the basis of semiconductors. “The SURMOFs combine the advantages of organic and anorganic semiconductors,” Professor Christof Wöll, Director of IFG, explains. “They feature chemical diversity and crystallinity, allowing us to create ordered heterostructures.” In many optoelectronic components, a so-called heterojunction – this is an interfacing layer between two different semiconductor materials – controls the energy transfer between the various excited states. Researches of the KIT Institute of Microstructure Technology (IMT) now created a new piggyback SURMOF in which a second SURMOF grew epitaxially, i.e. layer by layer, on a first one. At this heterojunction, it was possible to achieve photon upconversion, transforming two low-energy photons into a single photon with higher energy, by virtually fusing them together. “This process turns green light blue. Blue light has a shorter wavelength and yields more energy. This is very important for photovoltaics applications,” explains Professor Bryce Richards, Director of IMT. The scientists are presenting their work in Advanced Materials, one of the leading journals for materials science.

The photon upconversion process shown by the Karlsruhe researchers is based on the so-called triplet-triplet annihilation. Two molecules are involved: a sensitizer molecule that absorbs photons and creates triplet excited states, and an emitter molecule that takes over the triplet excited states and, by using triplet-triplet annihilation, sends out a photon that yields a higher energy than the photons that were originally absorbed. “The challenge was to create this process as efficiently as possible,” explains Dr. Ian Howard, leader of a junior research group at IMT. “We matched the sensitizer and emitter layers in a way to obtain a low conversion threshold and a higher light efficiency at the same time.”

Since the triplet transfer is based on the exchange of electrons, the photon upconversion process revealed by the researchers includes an electron transfer across the interface between the two SURMOFs. This suggests the assumption that SURMOF-SURMOF heterojunctions are suitable for many optoelectronic applications such as LEDs and solar cells. One of the limitations for the efficiency of today’s solar cells is due to the fact that they can only use photons with a certain minimum energy for electric power generation. By using upconversion, photovoltaic systems could become much more efficient.

ams AG (SIX: AMS), a provider of high performance sensors and analog ICs, has launched the smallest ever optical sensor module that delivers a combination of colour (RGB), ambient light and proximity sensing, providing OEMs with design flexibility and the ability to provide a better display viewing experience.

The TMD3700 footprint, at 4.00 x 1.75mm, is the smallest footprint available in the market, and with height of 1.00mm, its low-profile is ideal for next-generation mobile phones with extremely tight layout and mechanical design constraints. Its wide 45 degree field-of-view, ambient light sensing accuracy of +/-10% and operating range of 200mlux to 60Klux behind dark glass enable smartphones to measure the surrounding light environment and automatically adjust display colour and brightness for optimal viewing.

The TMD3700 colour sensor channels each have UV and IR blocking filters and a dedicated converter allowing simultaneous data capture necessary for accurate measurements. The combination of photopic colour and ambient light sensing enables smartphones to perform real-time adjustment of the display properties, such as white point, colour gamut and colour saturation, to achieve the best visual colour accuracy.

The TMD3700 features allow dynamic elimination of both electrical and optical crosstalk producing reliable proximity detection, a function used by smartphone manufacturers to disable the touchscreen display when it is held close to the user’s face. In addition, the module’s integrated IR LED is calibrated for maximum performance and consistent operation.

“Smartphone OEMs are continually condensing their product profiles while seeking ways to improve display performance for the best visual appeal. The availability of the TM3700 light sensing and proximity detection performance in a compact package enables innovative display management for today’s space-constrained smartphones,” said Darrell Benke, Strategic Program Director for Advanced Optical Solutions at ams.

The Semiconductor Industry Association (SIA), representing U.S. leadership in semiconductor manufacturing, design, and research, today announced worldwide sales of semiconductors reached $79.1 billion during the second quarter of 2016, an increase of 1.0 percent over the previous quarter and a decrease of 5.8 percent compared to the second quarter of 2015. Global sales for the month of June 2016 reached $26.4 billion, an uptick of 1.1 percent over last month’s total of $26.1 billion, but down 5.8 percent from the June 2015 total of $28.0 billion. Cumulatively, year-to-date sales during the first half of 2016 were 5.8 percent lower than they were at the same point in 2015. All monthly sales numbers are compiled by the World Semiconductor Trade Statistics (WSTS) organization and represent a three-month moving average.

“Global semiconductor sales increased slightly from Q1 to Q2 but remain behind the pace from last year, due largely to global economic uncertainty and sluggish demand,” said John Neuffer, president and CEO, Semiconductor Industry Association. “Sales into Japan and China have been a bright spot midway through 2016, and a modest rebound in sales is projected during the second half of the year.”

Regionally, sales increased compared to June 2015 in China (1.7 percent), but fell in Asia Pacific/All Other (-11.0 percent), the Americas (-10.8 percent), Europe (-5.5 percent), and Japan (-1.3 percent). Sales were up slightly compared to last month in the Americas (3.0 percent), China (2.2 percent) and Europe (1.7 percent), but down somewhat in Japan (-1.0 percent) and Asia Pacific/All Other (-0.6 percent).

sales graph sales table

Ultratech, Inc. (Nasdaq: UTEK), a supplier of lithography, laser­ processing and inspection systems used to manufacture semiconductor devices and high-brightness LEDs (HBLEDs), as well as atomic layer deposition (ALD) systems, today announced that it has received an ‘Outstanding Supplier Award’ from SJ Semiconductor Corp. Based in China, SJ Semiconductor is a pure play Middle-End-Of-Line (MEOL) semiconductor foundry house specializing in advanced wafer-level packaging. The award was presented to Ultratech by SJ Semiconductor CEO Cui Dong on July 27, at the company’s ‘Phase-I Mass Production, Outstanding Supplier Event’ at their facility in China. This award is further validation of Ultratech’s market leadership position in the advanced packaging lithography segment.

Rezwan Lateef, Ultratech’s General Manager and Vice President of Lithography Products, stated, “Ultratech has maintained its market leadership in the advanced packaging lithography segment by offering superior on-wafer results with industry leading cost-of-ownership and reliability in high-volume manufacturing environments. In recent years, Ultratech has expanded its presence in China, both in personnel and infrastructure, to support the burgeoning Chinese OSAT market. Ultratech believes that the SJ Semiconductor ‘Outstanding Supplier Award’ is a validation of our efforts in this region. We look forward to our continued partnership and to working closely with this valued customer to meet their future production and technology requirements.”

Ultratech is a supplier of lithography steppers for advanced packaging applications that include traditional copper pillar and wafer-level packaging (WLP), as well as the more advanced fan-out WLP and 3D ICs. The AP300 family of lithography systems is built on Ultratech’s customizable Unity Platform, delivering superior overlay, resolution and side wall profile performance while enabling cost-effective manufacturing. These systems are particularly well suited for copper pillar, fan-out, through-silicon via (TSV) and silicon interposer applications. In addition, the platform has numerous application-specific product features to enable next-generation packaging techniques, such as Ultratech’s award winning dual-side alignment (DSA) system, utilized around the world in volume production.

Researchers at the University of Illinois at Urbana Champaign have developed a new method for making brighter and more efficient green light-emitting diodes (LEDs). Using an industry-standard semiconductor growth technique, they have created gallium nitride (GaN) cubic crystals grown on a silicon substrate that are capable of producing powerful green light for advanced solid-state lighting.

A new method of cubic phase synthesis: Hexagonal-to-cubic phase transformation. The scale bars represent 100 nm in all images. (a) Cross sectional and (b) Top-view SEM images of cubic GaN grown on U-grooved Si(100). (c) Cross sectional and (d) Top-view EBSD images of cubic GaN grown on U-grooved Si(100), showing cubic GaN in blue, and hexagonal GaN in red. Credit: University of Illinois

A new method of cubic phase synthesis: Hexagonal-to-cubic phase transformation. The scale bars represent 100 nm in all images. (a) Cross sectional and (b) Top-view SEM images of cubic GaN grown on U-grooved Si(100). (c) Cross sectional and (d) Top-view EBSD images of cubic GaN grown on U-grooved Si(100), showing cubic GaN in blue, and hexagonal GaN in red. Credit: University of Illinois

“This work is very revolutionary as it paves the way for novel green wavelength emitters that can target advanced solid-state lighting on a scalable CMOS-silicon platform by exploiting the new material, cubic gallium nitride,” said Can Bayram, an assistant professor of electrical and computer engineering at Illinois who first began investigating this material while at IBM T.J. Watson Research Center several years ago.

“The union of solid-state lighting with sensing (e.g. detection) and networking (e.g. communication) to enable smart (i.e. responsive and adaptive) visible lighting, is further poised to revolutionize how we utilize light. And CMOS-compatible LEDs can facilitate fast, efficient, low-power, and multi-functional technology solutions with less of a footprint and at an ever more affordable device price point for these applications.”

Typically, GaN forms in one of two crystal structures: hexagonal or cubic. Hexagonal GaN is thermodynamically stable and is by far the more conventional form of the semiconductor. However, hexagonal GaN is prone to a phenomenon known as polarization, where an internal electric field separates the negatively charged electrons and positively charged holes, preventing them from combining, which, in turn, diminishes the light output efficiency.

Until now, the only way researchers were able to make cubic GaN was to use molecular beam epitaxy, a very expensive and slow crystal growth method when compared to the widely used metal-organic chemical vapor deposition (MOCVD) method that Bayram used.

Bayram and his graduate student Richard Liu made the cubic GaN by using lithography and isotropic etching to create a U-shaped groove on Si (100). This non-conducting layer essentially served as a boundary that shapes the hexagonal material into cubic form.

“Our cubic GaN does not have an internal electric field that separates the charge carriers–the holes and electrons,” explained Liu. “So, they can overlap and when that happens, the electrons and holes combine faster to produce light.”

Ultimately, Bayram and Liu believe their cubic GaN method may lead to LEDs free from the “droop” phenomenon that has plagued the LED industry for years. For green, blue, or ultra-violet LEDs, their light-emission efficiency declines as more current is injected, which is characterized as “droop.”

“Our work suggests polarization plays an important role in the droop, pushing the electrons and holes away from each other, particularly under low-injection current densities,” said Liu, who was the first author of the paper, “”Maximizing Cubic Phase Gallium Nitride Surface Coverage on Nano-patterned Silicon (100)”, appearing Applied Physics Letters.

Having better performing green LEDs will open up new avenues for LEDs in general solid-state lighting. For example, these LEDs will provide energy savings by generating white light through a color mixing approach. Other advanced applications include ultra-parallel LED connectivity through phosphor-free green LEDs, underwater communications, and biotechnology such as optogenetics and migraine treatment.

Enhanced green LEDs aren’t the only application for Bayram’s cubic GaN, which could someday replace silicon to make power electronic devices found in laptop power adapters and electronic substations, and it could replace mercury lamps to make ultra-violet LEDs that disinfect water.

Today SEMI announced registration opened for Europe’s largest electronics manufacturing exhibition, SEMICON Europa (25-26 October) in Grenoble. Featuring over 100 hours of technical sessions and presentations, SEMICON Europa includes semiconductor equipment and materials as well as additional topics, such as Imaging, Power Electronics, and Advanced Packaging. Newly restructured Fab Management Forum and a new flexible hybrid electronics conference, 2016FLEX.  Innovation Village returns, focused on startups and emerging technologies. Register now to take advantage of early-bird pricing for conferences, forums, and select sessions.

SEMICON Europa’s Fab Manager Forum has expanded to become the Fab Management Forum, to address a wider audience – with best practices for management, organization, and manufacturing in new wafer fabs.  SEMICON Europa’s Advanced Packaging Forum is more important than ever in the industry’s efforts to shrink devices to smaller form factors, lower power consumption, and flexible designs.

The new flexible hybrid electronics conference 2016FLEX Europe will debut at SEMICON Europa, replacing the Plastics Electronics Conference.  Program topics focus on the integration of silicon electronics onto flexible and printed substrates in a wide range of applications including: automotive, medical, wearables, IoT and others.

SEMICON Europa rotates between Grenoble (France) and Dresden (Germany), two of Europe’s largest electronic clusters. With the support of public and private stakeholders across Europe, the new SEMICON Europa enables exhibitors to reach new audiences and business partners and take full advantage of the strong microelectronic clusters in Europe. Over 400 exhibitors at SEMICON Europa represent the suppliers of Europe’s leading electronics companies. Learn more about exhibiting at SEMICON Europa.

To learn more about SEMICON Europa (exhibition or registration), please visit: www.semiconeuropa.org/en. Register now to secure your space and take advantage of SEMICON Europa’s early-bird pricing and exhibition opportunities.