Category Archives: LEDs

(December 11, 2010) — Researchers from Queen Mary, University of London (UK) and the University of Fribourg (Switzerland) have shown that a magnetically polarized current can be manipulated by electric fields.

Published in the journal Nature Materials, this discovery opens up the prospect of simultaneously processing and storing data on electrons held in the molecular structure of computer chips — combining computer memory and processing power on the same chip.

"This discovery has been made with flexible organic semiconductors, which are set to be the new generation of displays for mobile devices, TVs and computer monitors, and could offer a step-change in power efficiency and reduced weight of these devices," said Dr. Alan Drew, from Queen Mary’s School of Physics, who led the research.

Spintronics — spin transport electronics — has rapidly become the universally used technology for computer hard disks. Designed in thin layers of magnetic and non-magnetic materials, giant magnetoresistive (GMR) spin valves use the magnetic properties, or spin, of electrons to detect computer data stored in magnetic bits. In contrast, computer processing relies on streams of electrically charged electrons flowing around a tiny circuit etched into a microchip.

Dr. Drew and his team have investigated how layers of lithium fluoride (LiF) — a material that has an intrinsic electric field — can modify the spin of electrons transported through these spin valves. He explains: "While in theory, devices that combine electron charge and spin are conceptually straightforward, this is the first time anybody has shown it is possible to proactively control spin with electric fields."

Professor Christian Bernhard, from the University of Fribourg Physics Department, describes their successful technique: "Using the direct spectroscopic technique Low Energy Muon Spin Rotation (LE-μSR), our experiments have visualised the extracted spin polarisation close to buried interfaces of a spin valve."

The experiments were performed at the Paul Scherrer Institute. The method employs the magnetic properties of muons – unstable subatomic particles. "In such an experiment the muons are shot into the material and when they decay, the decay products carry information about the magnetic processes inside the material," explains Professor Elvezio Morenzoni from PSI, where the technique has been developed. "The unique thing about low energy muons is that they can be placed specifically in a particular layer of a multi-layer system. Thus using this method one can study the magnetism in any single layer separately."

The paper "Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer" is authored by L. Schulz, L. Nuccio, M.Willis, P. Desai, P. Shakya, T. Kreouzis, V. K. Malik, C. Bernhard, F. L. Pratt, N. A. Morley, A. Suter, G. J. Nieuwenhuys, T. Prokscha, E. Morenzoni,W. P. Gillin and A. J. Drew.

 Read more about semiconductor device architectures

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(December 10, 2010) — Diodes Incorporated (Nasdaq: DIOD), high-quality application specific standard products manufacturer and supplier, released its first device in its unique PowerDI5060 package, the DMP3010LPS 30V rated p-channel enhancement mode MOSFET, offering designers of notebooks, netbooks and other consumer electronics improvements in reliability and reductions in PCB space requirements.

With a junction to case thermal resistance (Rthj-c) of 2.1°C/W, the PowerDI5060’s thermal resistance is 10 times lower than an SO8 alternative, improving on power dissipation performance, resulting in cooler running and more reliable product design. Its off-board height of 1.1mm is also 54% less than that of SO8, making it well suited for low profile applications.

With a large drain pad significantly reducing package inductance and resistance parameters, the PowerDI5060 package helps to significantly boost p-channel MOSFET performance. With the DMP3010LPS’s low typical on-resistance of 7.8mΩ at 10V VGS on-state losses are effectively minimized in load switching and battery charging duties.

Diodes Incorporated (Nasdaq: DIOD) manufactures and supplies high-quality application specific standard products within the broad discrete, logic, and analog semiconductor markets. Diodes serves the consumer electronics, computing, communications, industrial, and automotive markets. Diodes’ products include diodes, rectifiers, transistors, MOSFETs, protection devices, functional specific arrays, single gate logic, amplifiers and comparators, Hall-effect and temperature sensors; power management devices, including LED drivers, DC-DC switching and linear voltage regulators, and voltage references along with special function devices, such as USB power switches, load switches, voltage supervisors, and motor controllers. For further information, including SEC filings, visit http://www.diodes.com.

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(December 6, 2010 – PR Newswire) — Ultratech, Inc. (Nasdaq: UTEK), lithography and laser-processing systems supplier to semiconductor device and high-brightness LED (HB-LED) makers, opened an advanced manufacturing facility in Singapore. Ultratech plans to spend more than $125 million dollars over the next several years in support of its Singapore International Operations.

The advanced manufacturing facility will be capable of producing over 100 lithography steppers annually for the advanced packaging and the HB-LED markets. Along with providing engineering support in Singapore, the new facility will also serve as headquarters for Ultratech’s global service operations and Asia Pacific sales organization. Ultratech plans to start manufacturing lithography systems at its Singapore facility beginning in late 2010 with the first tool shipments to customers scheduled for the first quarter of 2011.

Ultratech Chairman and CEO Arthur W. Zafiropoulo said, "After an extensive study in the Asia Pacific region, we selected Singapore for several business reasons including being conveniently located to Ultratech’s served markets. We expect 75% of our business to be located in the Pacific region, and with this new facility in Singapore Ultratech can better serve customers from Thailand to Taiwan." In related news, SAFC Hitech announced plans to build a facility in Taiwan for transfilling, technical service and production of chemical precursors used for high brightness LED and silicon semiconductor manufacturing.

Ultratech, Inc. (Nasdaq: UTEK) designs, manufactures and markets photolithography and laser processing equipment. Visit Ultratech online at www.ultratech.com.

(December 3, 2010) — The top makers of LEDs; how LED fab is changing, in technological scope and geographical size; and the driving applications for LED adoption are covered in two recent reports. IMS Research primarily covers LED suppliers and markets, while EPIC and Yole look mainly at the markets and fab equipment.

IMS Research believes the market for LEDs (including all types: Standard, AlInGaP and InGaN) has grown from $6.1 billion in 2009 to about $10.0 billion in 2010, driven by economic recovery, lighting and TV and monitor backlights. This means that suppliers have to grow by 64% this year just to maintain their market share. In Yole Développement and EPIC’s jointly published base scenario, packaged LED revenues will reach $8.9b in 2010 and grow to $25.7b in 2015 and approach $30b in 2020. Growth will be driven by large LCD backlight applications through 2013-2014.

In terms of volume, LED die surface will increase from 6.3b mm2 to 51b mm2 in 2015, a 41.6% CAGR.

This will drive substrate volumes to growth from 12.7M × two-inch-equivalent (TIE) in 2009 to 84.4M TIE in 2015, a 37.1% CAGR (smaller than the die surface increase due to significant expected manufacturing yield improvements).

LED suppliers

Nichia remains at the top of the LED sector, with Samsung LED, Seoul Semiconductor and Cree growing faster than average in 2010, according to IMS Research.

Nichia is still the number one supplier by total revenue in 2009 and 2010; however, it will be challenged strongly by Samsung LED in 2011.

Samsung LED now has the capacity to take the number one position, and increasing demand for LED TVs from Q2 2011 onwards should enable them to do so. In 2009, IMS Research ranked Samsung as 3rd and in 2010 as 2nd, changing places with Osram, which occupied second place for many years.

Lumileds, which was ranked 3rd by IMS Research in 2006, 2007 and 2008, has fallen to 4th position in 2009 and a provisional 6th in 2010. Lumileds’ market share has actually been fairly steady but they provisionally fall in rank in 2010 due to tremendous growth from Seoul Semiconductor and Cree. Along with Samsung, these suppliers are among those who have taken significant share in 2010.

2011 will be an interesting year for the LED industry, with Samsung and others further continuing to challenge Nichia’s leadership position.

There are already more than 60 companies involved in the epitaxy of GaN-based LEDs. This number will keep increasing in the next couple years, but we expect a significant amount of consolidation starting 2013 as many companies will not have reached the critical mass and technology necessary to survive and will disappear or be absorbed by larger players,” explains Dr Philippe Roussel, senior project manager at Yole.

LED manufacturing will be dominated by Asian countries, with already 90% of the epitaxy capacity located in Taiwan, Korea, China and Japan.

The packaged LED market is experiencing tremendous growth with an expected CAGR of 28.2% between 2009 and 2015, according to Yole Développement and EPIC.

LED applications

The 3 cycles toward $30 billion are mobile displays, LCD TV and general lighting, say Yole and EPIC. Although the LED TV backlighting boom has temporarily fallen in Q4 2010 due to supply chain corrections, 2010 was still a year of tremendous growth in the LED industry. For lighting, IMS Research believes Cree is ahead. For automotive, Osram is the market leader. Nichia is also strong in both these sectors as well as backlighting and signage/large displays.

The initial growth cycle driven by small display applications is essentially complete and the LED industry growth is now driven by backlighting for large LCD display applications.  This segment will mature by 2015 but by then, the third growth cycle driven by general lighting applications will have kicked in, therefore limiting the risk of any significant and industry-wide downcycle in the period.

The adoption of LEDs for general lighting applications is strongly dependent on technology and manufacturing improvements and standards needed to drive the cost of LED solutions to a trigger point where massive adoption can start.  The exact trigger point varies per application, and will depend on intelligent design and marketing to connect LED technology with consumer demand. As a result, LED will progress into the market from niche to niche and progressively spread into all application segments.  Ultimately, the long lifetime of solid state lighting technology will completely transform the business model of the lighting sector by dramatically increasing the length of the replacement cycles.

For consumers, the initial large exposure to LED for general lighting applications will come in the form of LED bulb replacement that can be used in existing sockets.  As the initial perception of the technology by consumers will come from this first exposure to bulb replacement, their quality and performance will be critical to the future of the industry.  Standards and regulations are needed.

Dedicated LED modules and luminaires will come in a second wave and deliver the full benefit of the technology.  Additional standardization effort is needed to ensure a minimum level of upgradability and interoperability.

LED fab

Growth in general lighting applications will be enabled by significant technology and manufacturing efficiency improvements that will allow the cost per lumen of packaged LED to be reduced 10-fold between 2010 and 2020:

  • Economy of scale
  • LED efficiency improvement, including at high power (droop effect)
  • Improved phosphors
  • Improved packaging technologies
  • Significant improvements in LED epitaxy cost of ownership through yield and throughput.

Organic LEDs (OLEDs) are already widely commercialized for active displays, while for lighting OLEDs are still in their infancy.  EPIC and Yole Développement expect AMOLED to capture a significant portion of the small-display market by 2015 and to start penetrating the large-display market by 2016. For the general lighting market, massive investment and significant technology developments are required. This technology will start being offered to consumers in large volumes in 2016.

The equipment market will experience a dramatic growth cycle with demand driving the installation of close to 1400 reactors in the 2010-2012 period.

Anticipation of future demand and generous subsidies in China will trigger the installation of another 700-1000 reactors in the same period, leading to a short period of oversupply starting in late 2011. However, since this extra capacity will be mostly in hand of newcomers with little LED manufacturing experience, oversupply will mostly affect the low end of the market.

Also read: LEDs ramp in 2015, MOCVD reaps benefit: Gartner forecast

Yole/EPIC reporting: Tom Pearsall is secretary general of EPIC. Dr. Eric Virey holds a Ph-D in Optoelectronics from the National Polytechnic Institute of Grenoble. Dr. Philippe Roussel holds a Ph.D in Integrated Electronics Systems from the National Institute of Applied Sciences (INSA) in LYON. He leads the Compound Semiconductors Techno-economical market analysis department at Yole.

IMS reporting: IMS Research is a supplier of market research and consultancy services on a wide range of global electronics markets. Learn more at www.imsresearch.com

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December 2, 2010 — SAFC Hitech announced plans to build a new, dedicated facility in Kaohsiung, Taiwan for transfilling, technical service and production of chemical precursors used for high brightness LED and silicon semiconductor manufacturing. The new facility is expected to be operational by late 2011. The announcement follows the March 2010 production expansion of trimethylgallium (TMG) at its Bromborough, UK manufacturing site.

SAFC Hitech already operates a facility in Kaohsiung, designed to handle and characterize highly-specialized laboratory-scale chemicals and features a dedicated customer support center. This existing site is ISO 9001 certified for quality and ISO 14001 certified for safety and environmental protocols. The facility was originally built to service the semiconductor industry demands for ultra-high quality precursors using proprietary technologies. The site also provides integrated inert atmosphere transfilling stations, analytical instrumentation for the detection of ultra-low metallic and oxygen containing contaminants and dedicated cylinder preparation and packaging areas.

SAFC Hitech sees the LED manufacturing market growing rapidly, particularly HBLEDs that are used in applications such as backlighting in flat panel television sets and energy efficient lighting. “As mass manufacturing continues its rise, we are experiencing significant increases in customer and partnership activities in the Asia-Pacific region," said Philip Rose, SAFC Hitech President.

Strategies Unlimited, a market research firm, projects market growth for HBLEDs averaging 29.5% per year, reaching over $19 billion by 2014. The application with the highest forecast growth rate is signs/displays, with a CAGR of 60.6%.  Illumination has the next-highest growth rate, with a projected CAGR of 45.4%.

 

 

(December 2, 2010) —Soitec, supplier of engineered substrates, and Sumitomo Electric Industries, provider of compound semiconductor materials, are working together to develop engineered gallium nitride (GaN) substrates. The alliance will draw on Sumitomo Electric’s GaN wafer manufacturing technology and Soitec’s Smart Cut layer transfer technology by which ultra-thin GaN layers are transferred from a single GaN wafer to produce multiple, engineered GaN substrates. The engineered substrates retain the original, high crystalline quality of Sumitomo Electric’s GaN wafer at a lower cost, to facilitate widespread use of GaN substrates in applications like high-brightness LEDs (HB LEDs) as well as electric power devices for hybrid and full electric vehicles.

"We are delighted to work with Sumitomo Electric and excited about what we have been able to achieve together so far. We are partnering with the leader in GaN wafer manufacturing to offer engineered substrates that have the best crystal quality available today. This collaboration represents the first step of an important move in our strategy to address the need for dramatically improved efficiency in power conversion and lighting with innovative materials engineering solutions," said André-Jacques Auberton-Hervé, CEO of Soitec.

The Soitec Group provides engineered substrate solutions that serve as the foundation for today’s most advanced microelectronic products. The group leverages its proprietary Smart Cut technology to engineer new substrate solutions, such as silicon-on-insulator (SOI) wafers, which became the first high-volume application for this proprietary technology. Since then, SOI has emerged as the material platform of the future, enabling the production of higher-performing, faster chips that consume less power. Today, Soitec produces more than 80% of the world’s SOI wafers. Headquartered in Bernin, France, with two high-volume fabs on-site, Soitec has offices throughout the United States, Japan, and Taiwan, and a new production site in Singapore. Three other divisions, Picogiga International, Tracit Technologies, and Concentrix Solar, complete the Soitec Group. 

Learn more about Soitec at www.soitec.com

(November 30, 2010) — Driven by the rapid recovery in automotive production and inventory rebuilding among sensor component suppliers, the market for automotive microelectromechanical system (MEMS) sensors will expand to record size in 2010, according to market research firm iSuppli, now part of IHS Inc. (NYSE: IHS).

Marking a new high point for the industry, shipments of automotive MEMS sensors will reach 662.3 million units in 2010, up a robust 32.1% from 501.2 million units in 2009. The projected year-end levels — including replenishment of inventory pipelines that were depleted during the recession — will exceed even the pre-crisis high point in 2007 of 640 million sensors, iSuppli data research shows. iSuppli had initially expected automotive MEMS sensors to hit only 591 million units in 2010.

"The recovery in automotive MEMS shipments represents a happy turnaround from the depressed levels of 2009 when shipments cratered and reached a nadir, and the years ahead will provide additional room for expansion," said Richard Dixon, Ph.D., senior analyst for MEMS and sensors at iSuppli.

Nonetheless, growth will slow in 2011. Shipments will climb just 7.3% as the market normalizes following the exuberance in 2010. Production then will pick up again in 2012, and growth rates end up north of 13% by 2014.

New MEMS applications, markets in auto

One significant engine of automotive MEMS growth is the use of sensors in passenger cars supporting mandated safety technologies such as electronic stability control (ESC) and tire pressure monitoring systems (TPMS).

The United States and Europe have led the adoption of legislation on such safety systems, and other countries like Australia and Canada have quickly followed suit. Similar mandates are now being adopted in South Korea and are expected in Japan, accelerating overall adoption rates worldwide. The extra opportunity from both ESC and TPMS for automotive MEMS suppliers to Japan and Korea will correspond to additional revenue of some $120 million in those regions alone for the next five years, iSuppli has determined.

China will also account for a large portion of the automotive MEMS action. Compared to U.S. or European vehicles, the electronics content of low- and mid-range vehicles in China is about 50% or less, but sensor penetration will steadily increase — first in powertrain applications to reduce carbon emissions and afterward as safety sensors for additional airbags and ESC systems.

Among the new applications providing suppliers greater production opportunities for automotive MEMS sensors, the most prominent include usage of gas sensors to control air quality in the cabin; infrared thermopiles to monitor temperature; microbolometers to aid night-vision systems and MEMS oscillators to boost rear-view cameras.

Sensor fusion — using existing sensor signals with additional algorithms to satisfy new applications — will be a contentious issue, however, Dixon said. While the sales of accelerometers used to measure inclination as part of an electronic parking brake (EPB) will accelerate in Europe in the next five years, EPB prospects are also dampened by ESC systems, which already contain the 2-axis accelerometers capable of delivering the required inclination signal for parking brakes.

Other applications that will propagate the use of sensors include passenger protection systems that detect impacts by means of either accelerometers or pressure sensors located in the front bumper; as well as stop-start systems that need pressure, and other non-MEMS based measurements to supply critical data when a vehicle’s engine is turned off at a junction, Dixon said.

Consumer-oriented MEMS suppliers

iSuppli also notes that some consumer-oriented MEMS sensor suppliers are making inroads into the automotive market, widening the pool of players participating in the space.

In particular STMicroelectronics, MEMS supplier for consumer and mobile applications, so far has targeted non-safety critical applications in automotive such as car alarms and navigation. STMicro has now entered the airbag market with a high-g accelerometer. STM is expected to leverage its significant manufacturing economies of scale, which likely will lead to additional price pressures and new cost structures in the industry.

Read More in "Auto Production Recovery and Rebuilding of Inventory to Drive Record MEMS Revenue in 2010" at http://www.isuppli.com/MEMS-and-Sensors/Pages/Auto-Production-Recovery-and-Rebuilding-of-Inventory-to-Drive-Record-MEMS-Revenue-in-2010.aspx?PRX

iSuppli’s market research reports help deliver information on the status of the entire electronics value chain. iSuppli’s MEMS & Sensors market research provides up-to-date, insightful coverage of the consumer, automotive, and high-value markets for MEMS, or microelectromechanical sensors. Visit http://www.isuppli.com/Pages/Home.aspx for more information.

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(November 29, 2010) — Electrical engineers generate short, powerful light pulses on a chip — an important step toward the optical interconnects that will likely replace the copper wires that carry information between chips within today’s computers. University of California, San Diego (UC San Diego) engineers developed the first ultra compact, low power pulse compressor on a silicon chip to be described in the scientific literature. Details appeared online in the journal Nature Communications on November 16.

 
Scanning electron micrograph of dispersive grating before deposition of SiO2 overcladding. (Decorative red filter added to image.)

This miniaturized short pulse generator eliminates a roadblock on the way to optical interconnects for use in PCs, data centers, imaging applications and beyond. These optical interconnects, which will aggregate slower data channels with pulse compression, will have far higher data rates and generate less heat than the copper wires they will replace. Such aggregation devices will be critical for future optical connections within and between high speed digital electronic processors in future digital information systems.

"Our pulse compressor is implemented on a chip, so we can easily integrate it with computer processors," said Dawn Tan, the Ph.D. candidate in the Department of Electrical and Computer Engineering at UC San Diego Jacobs School of Engineering. Tan led development of the pulse compressor.

"Next-generation computer networks and computer architectures will likely replace copper interconnects with their optical counterparts, and these have to be complementary metal oxide semiconductor (CMOS) compatible. This is why we created our pulse compressor on silicon," said Tan, an electrical engineering graduate student researcher at UC San Diego, and part of the National Science Foundation funded Center for Integrated Access Networks.

The pulse compressor will also provide a cost effective method to derive short pulses for a variety of imaging technologies such as time resolved spectroscopy – which can be used to study lasers and electron behavior, and optical coherence tomography – which can capture biological tissues in three dimensions.

In addition to increasing data transfer rates, switching from copper wires to optical interconnects will reduce power consumption caused by heat dissipation, switching and transmission of electrical signals.

"At UC San Diego, we recognized the enabling power of nanophotonics for integration of information systems close to 20 years ago when we first started to use nano-scale lithographic tools to create new optical functionalities of materials and devices — and most importantly, to enable their integration with electronics on a chip. This Nature Communications paper demonstrates such integration of a few optical signal processing device functionalities on a CMOS compatible silicon-on-insulator material platform," said Yeshaiahu Fainman, a professor in the Department of Electrical and Computer Engineering in the UC San Diego Jacobs School of Engineering. Fainman acknowledged DARPA support in developing silicon photonics technologies which helped to enable this work, through programs such as Silicon-based Photonic Analog Signal Processing Engines with Reconfigurability (Si-PhASER) and Ultraperformance Nanophotonic Intrachip Communications (UNIC).

Pulse compression for on-chip optical interconnects

The compressed pulses are seven times shorter than the original — the largest compression demonstrated to date on a chip.

Until now, pulse compression featuring such high compression factors was only possible using bulk optics or fiber-based systems, both of which are bulky and not practical for optical interconnects for computers and other electronics.

The combination of high compression and miniaturization are possible due to a nanoscale, light-guiding tool called an “integrated dispersive element” developed and designed primarily by electrical engineering Ph.D. candidate Dawn Tan. The new dispersive element offers a much needed component to the on-chip nanophotonics tool kit.

Dawn Tan, the Ph.D. candidate in the Department of Electrical and Computer Engineering at UC San Diego Jacobs School of Engineering who led development of the pulse compressor.

The pulse compressor works in two steps. In step one, the spectrum of incoming laser light is broadened. For example, if green laser light were the input, the output would be red, green and blue laser light. In step two, the new integrated dispersive element developed by the electrical engineers manipulates the light so each spectrum in the pulse is travelling at the same speed. This speed synchronization is where pulse compression occurs.

Imagine the laser light as a series of cars. Looking down from above, the cars are initially in a long caravan. This is analogous to a long pulse of laser light.

After stage one of pulse compression, the cars are no longer in a single line and they are moving at different speeds. Next, the cars move through the new dispersive grating where some cars are sped up and others are slowed down until each car is moving at the same speed. Viewed from above, the cars are all lined up and pass the finish line at the same moment.

This example illustrates how the on-chip pulse compressor transforms a long pulse of light into a spectrally broader and temporally shorter pulse of light. This temporally compressed pulse will enable multiplexing of data to achieve much higher data speeds.

“In communications, there is this technique called optical time division multiplexing or OTDM, where different signals are interleaved in time to produce a single data stream with higher data rates, on the order of terabytes per second. We’ve created a compression component that is essential for OTDM,” said Tan.

The UC San Diego electrical engineers say they are the first to report a pulse compressor on a CMOS-compatible integrated platform that is strong enough for OTDM.

“In the future, this work will enable integrating multiple ‘slow’ bandwidth channels with pulse compression into a single ultra-high-bandwidth OTDM channel on a chip. Such aggregation devices will be critical for future inter- and intra-high speed digital electronic processors interconnections for numerous applications such as data centers, field-programmable gate arrays, high performance computing and more,” said Fainman, holder of the Cymer Inc. Endowed Chair in Advanced Optical Technologies at the UC San Diego Jacobs School of Engineering and Deputy Director of the NSF-funded Center for Integrated Access Networks.

Learn more at http://www.ucsd.edu/

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Energy storage research – specifically high performance cathodes made of low-cost nanocarbons — will be part of the focus on a new collaborative effort between The Dow Chemical Company and University of Queenland’s Australian Institute for Bioengineering Nanotechnology (AIBN). Dow will contribute approximately $AU1.74million ($UDS1.7million) in the three-year alliance. In addition to improved energy storage systems, AIBN will conduct research on sustainable sources for chemicals and new-generation circuitry.

The research into high performance cathode materials based on low-cost nanocarbons will involve the research group led by Professor Max Lu and Dr. Denisa Jurcakova. The objective of the project is to develop improved cathode materials with high energy and power densities for applications in hybrid vehicles and renewable energy storage systems.

Caption: PhD student Sean Muir, AIBN’s Dr Denisa Jurcakova, Dow chairman and CEO Andrew Liveris and Professor Max Lu.

Research in the project will involve novel material design, synthesis, electrochemistry and fundamental chemistry. The improved nanoparticles developed will find use in batteries with potential use not only in portable devices, but for hybrid vehicles and energy storage for renewable resources such as sun and wind.

Research into new-generation circuitry for electronics will be completed by Professor Andrew Whittaker’s and Dr. Idriss Blakey’s research group. Researchers will use organic synthesis, physical chemistry and electrical engineering to craft functional plastics and polymers for the manufacture of integrated circuits. The new generation of circuits will increase performance, decrease size and cost and have potential uses in computers, cameras, smart phones, hand-held gadgets and even fridges.

Escalating oil costs and concerns about carbon dioxide emissions make it imperative to develop new manufacturing processes based on renewable substrates rather than diminishing fossil fuels. Research carried out in the third project will be led by Professor Lars Nielsen and Dr. Jens Kromer, and will use scientific advances in the biosciences to genetically reprogram bacteria to produce the chemical building blocks of the future.

 

by Laura Peters, contributing editor

IEDM Previews:
Intel fabs highest mobility pFET with Ge channel
University of Tokyo first to demo III-V self-aligned source/drain
IBM, Macronix identify phase-change memory failure mode
Record photodiode quantum efficiency from Taiwan lab
How strain can protect devices from ESD
SEMATECH tipping III-V MOSFET, FinFET, and resistive RAM
TSMC anneal for gate-last HKMG process
Imec IEDM presentations to cover More than Moore, ITRS
When do TSV stresses affect device operation?
Multi-threshold-voltage flexibility in FDSOI
CMOS imager works from light to night
Carbon nanotube vias approach production densities
IBM Alliance simplifies pFET HKMG
IM Flash details 25nm NAND

November 19, 2010 – Phase-change memory (PCM) devices require high current density (5-20MA/cm2) to melt the phase-change material and change its state. During an investigation of the impact of current density and current polarity on cycling endurance, researchers from the IBM/Macronix PCRAM Joint Project discovered electromigration-induced failures when PCM cells are reverse-stressed. The team will report on this finding at the upcoming International Electron Devices Meeting (IEDM, 12/6-8 in San Francisco, CA).

Most PCM cell designs are asymmetrical, such as the mushroom cell design used in the IBM/Macronix cycling experiments. The structure consists of a TiN, cup-shaped bottom electrode contact (BEC) with interconnect, germanium-antimony-telluride (Ge2Sb2Te5 or GST) phase-change layer, TiN top electrode contact and copper back-end-of-line. Two cell connections (Figure 1), allowed either conventional bit-line-at-TEC (top electrode contact) cell operation or bit-line-at-BEC (bottom electrode contact) cell operation. By controlling the DC bias on the bit line and source line, current travels through the cell in either forward (TEC-to-BEC) or reverse (BEC-to-TEC) direction using positive pulses on the word line.

Cycling in forward-reset/forward-set mode, devices operated reasonably up to 108 cycles, while failures occurred in the reverse-reset/reverse-set testing after only 104 cycles. The impact of stressing at low current (40μA) also led to early failures when reverse-stressed cells became stuck open after 3 × 104 seconds. The high resistance of the stuck cells remained after several hours of baking at 165°C, indicating a failure similar to electromigration. The effect of varying pulse current (Figure 2) indicates endurance is more strongly affected by pulse current in the reverse-stressed cells.

Click to Enlarge
Figure 1: Two operating modes of the bit-line at top electrode contact (BL at TEC) forward array (top) and bit-line at bottom electrode contact (BL at BEC). With the bit line positively biased at VBL and VSL=0V, current through the phase-change element is controlled by the gate pulse.

TEM and EDX analysis of failed samples showed that for forward-stressed cells, there is significant depletion of Sb, Ge and Te, and Sb especially migrates toward the GST/BEC interface. In the reverse-stressed cells, Sb, Ge and Te depletion occurs, but located in a region on top of the bottom electrode contact. Since GST is a p-type semiconductor, in the reverse-stressed condition, holes flow from the BEC into the GST, causing potential voids.

The IBM/Macronix team suggests that PCM designs follow an asymmetric design and PCM operation should ensure current crowding only occurs in the direction of electron flow.

Click to Enlarge Click to Enlarge
Figure 2: In forward-stressing operation, endurance is reduced with higher pulse current, and the effect saturates when current is increased further (left). In reverse-stressed devices, endurance is much more susceptible to pulse current. High hole current may cause voids that cannot be repaired by the next melting (right).