ECSEL-prosjekt OSIRIS, Optimal SiC substRates for Integrated Microwave and Power CircuitS

OSIRIS project, a Research and Innovation Action (RIA), started on 1st May 2015. It aimed at improving substantially the cost effectiveness and performance of gallium nitride (GaN) based millimetre wave devices. It proposed to elaborate innovative SiC materials using isotopic sources in order to offer thermal conductivity improvement of 30% which is important for SiC power electronics and microwave devices using GaN high electron mobility transistors (HEMT) grown on SiC semi-insulating substrates. The improved thermal SiC properties should be obtained by using single isotopic atoms for silicon and carbon, namely 28Si and 12C. The SiC wafer size was targeted to 100mm (4-inches) which is today widely used in industry. For microwave GaN/SiC HEMT, this isotopic approach should create a complete shift in the currently used SiC substrate/GaN epi-wafer technology by growing the high thermal conductivity (+30%) semi-insulating SiC on top of lower cost semiconducting SiC substrates. The project aimed at evaluating HEMT microwave power performance improvement at 30GHz thanks to better thermal environment. For power electronics, this innovation was essentially focused on thermal improvement not on price fall, i.e. better electron mobility at a given power dissipation as mobility and drift mobility decrease with temperature and also better carrier transport thanks to lower scattering rates. Schottky and p-i-n diodes were tested using this material. OSIRIS Partnership includes six companies and three public institutions from four European countries: France, Norway, Slovakia, and Sweden. ISOSILICON?s role in the consortium is to procure the requested isotopes and develop appropriate enrichment techniques at the industrial scale. An obvious difference between isotopes of a same element is their respective atomic mass. The tiny mass differences may induce likewise small variations in the physical and/or chemical behavior of molecules bearing those isotopes e.g. gas diffusion, deviation in a gravitational or/and centrifugal field, boiling and freezing points, electrochemical potentials, molecular vibrational energy levels etc. The small differences may under certain favorable conditions be exploited for enrichment or depletion of one isotope with respect to the other(s). The effect is however so tiny that just to observe or/and measure it most of the time poses a major challenge. Consequently, purification to a suitable degree always requires the enrichment step be repeated many times. Frequently cited enrichment methods include gas permeation through a membrane, distillation, electrolysis, electromagnetic deviation, centrifugation, nozzle separation, ion mobility, chemical exchange, chromatography, LASER induced molecular excitation. Within OSIRIS a feasibility study has confirmed that silicon isotopes were currently not industrially/commercially produced, but several methods could be envisaged for their purification. Our study looked closer at (i) Molecular Laser Induced Separation (MLIS), in which a fine tuned LASER may selectively excite a specific molecular energy level (ii) Aerodynamic Separation Process (ASP) combining centrifugal and nozzle separation (iii) Chemical Exchange of isotopes when weak chemical bonds (e.g. hydrogen bonding) are involved (iv) gas chromatography, in which a silicon bearing gas molecule (silane SiH4) moves through a packed column charged with a stationary phase. Light and heavy molecules may have different apparent velocities through the stationary phase, thus enabling isotope discrimination. In gas chromatography a combination of several phenomena such as gas permeation enhanced by a large specific area of the stationary phase can lead to effective isotopic segregation. The same four methods can also be developed and applied to carbon isotopes. Experimental results achieved within OSIRIS have shown evidence of isotopic separation with Isosilicon?s proprietary chromatographic systems. The enrichment factor was so promising that Isosilicon and OSIRIS partners decided to put all efforts on this process route. Our intermediate conclusion is that the method is capable of achieving 1000 kg/year 99% 28Si at a cost of 5 ?/g and that the barrier of 1 ?/g can be overcome with a production volume between 10 and 20 metric tons per year.

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Prosjektet er organisert som et europeisk forskningskonsortium med deltakere langs hele verdikjeden. Oppstrøms finner vi Isosilicon som er ansvarlig for anrikningsteknologier. I midten av verdikjeden har vi tre svenske universiteter og bedrifter som er ansvarlige for SiC-substratene, GaN belegging og noen halvlederkomponenter. Nedstrøms finner vi 4 franske og akademiske og industrielle grupper samt 1 slovakisk universitet som er ansvarlige for testing og karakterisering av systemene. Hensikten med hele prosjektet er å skaffe europeisk industri uavhengige og konkurransedyktige strategiske komponenter med høy ytelse. Se for øvrig vedlegg: Prosjektbeskrivelse.