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EETE OCT 2013

Solid phase epitaxy enables tensilestrained GeSn MOSFET devices on Si By Julien Happich KULeuven, imec and AIST have announced a new solid phase epitaxy process developed to integrate GermaniumTin (GeSn) metal-oxide semiconductor field-effect transistor (MOSFET) devices on silicon. This was the first time that a depletionmode junction-less GeSn pMOSFET on silicon was demonstrated in operation, an important step toward achieving tensile strain in MOSFET devices and increasing their mobility. To improve performance in next-generation scaled complementary metal-oxide semiconductor (CMOS) devices, researchers are exploring the integration of novel materials with superior electron mobility. This includes GeSn, a promising semiconductor candidate as channel material, due to its superior physical properties. GeSn enables increased switching speed of MOSFET devices and can be used in fast optical communication, explain the researchers. While most prototype GeSn channel MOSFETs are fabricated on Ge substrates, silicon integration is preferred for CMOS compatibility. However, epitaxial growth of GeSn on silicon substrates poses several challenges, including limited solubility of Sn in Ge (0.5%), its compositional fluctuations, Sn segregation, and large lattice mismatch (>4%). Researchers from KULeuven, imec and AIST developed a solid phase epitaxy process, achieving single-crystalline GeSn layers as thin as 10μm on silicon substrates showing tensile strain, attractive for strain engineering TEM image of NiGeSn metal S/D MOSFET. TEM is observed along 11-2, the channel direction is -110 and the surface orientation is (111). of Ge channels. Furthermore, it reduces the difference between the direct and indirect band transition, resulting in acquisition of a direct band gap group IV material. Lastly, due to its nonequilibrium deposition conditions, the new method enables the development of GeSn with high Sn concentrations. By decreasing the channel thickness with reactive ion etching (RIE) from around 30 to about 10nm, the researchers improved the on/off ratio by more than one order of magnitude. Additionally, hole depletion in the ultrathin (10nm) GeSn layers on silicon resulted in good transfer characteristics with an on/off ratio of 84. In the future, research will focus on optimizing the GeSn MOSFET on silicon devices to further increase the channel mobility. LED packaging market will keep soaring for the next two years By Christoph Hammerschmidt In a LED market environment where packaging represents the largest single opportunity for cost reduction and dozens of different packaging styles resist any attempt for standardizing, packaging materials and equipment enjoy stable growth - at least for now, states a study from market researcher Yole Devéloppement. The good news amongst the hodgepodge of packaging types: LEDs are going mainstream, but they are not becoming a mature commodity soon. Nevertheless, packaging is a very critical factor for the commercial success of LED manufacturers. They need to tightly watch the developments in the areas of materials, substrates and processes. According to the report titled “LED Packaging”, the package substrate market will attain a CAGR of 20% over the period from 201o through 2017 - only that we are already halfway into this period and the growth will flatten around 2016 and even turn negative in 2017. While there is plenty of headroom for innovation, it remains paramount that these solutions offer LED manufacturers an overall reduction in terms of dollar per lumen, the report says. The LED packaging equipment market, which stagnated in 2012 due to oversupply, has returned to growth. But again, this market will peak out around 2016, predicts Yole. The current situation in this segment is characterized through the fact that LED packers are widely using retrofitted equipment from the IC industry, which means that they rely on existing materials and technologies. In this constellation, the LED manufacturers benefit from decades of R&D efforts in the general semiconductor industry, but it limits the LED industry somewhat since the manufacturing platforms it is utilizing is not really optimized for LED production. In the meantime, the LED industry has gained enough momentum to become attractive for equipment and materials providers to develop dedicated solutions for LED manufacturing. Based on this situation, the Yole report describes materials and equipment used in LED packaging, market size, volume, trends broken down to process steps, and key suppliers. Key features are, among others, a detailed technical analysis of LED packaging processes, LED market metrics, supply chain analysis and a technology roadmap. 16 Electronic Engineering Times Europe October 2013 www.electronics-eetimes.com


EETE OCT 2013
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