cover story epigan
EpiGaN is currently offering state-of-the-art GaN epitaxial layers deposited crack-free, on Si up to 150 mm or, for specific applications, on SiC. Wafer diameters of 200mm are under development. The availability of large wafers to be processed in existing Si CMOS fabs explains how GaN-on-silicon technology excels at combining affordability with great performance.
The Promise of GaN With its superior properties, GaN promises to be a suitable material for power switching devices operating at significantly higher frequencies without suffering from major losses. This is due to the drastically lower on-state resistance of GaN power transistors, combined with considerably reduced in/output capacitances. The higher switching frequency substantially reduces the volume of accompanying passive components such as inductors, current transformers and capacitors.
Thus, in the future, the volume of power systems will be smaller and they will be more lightweight. In the long run, GaN power electronics will combine these significantly improved operational properties with lower costs. The efficiency of present systems is largely limited by the active components used.
To accelerate the progress on this future-oriented, energy-saving power technology, the EU has established a three-year research project, called “HiPoSwitch”. EpiGaN is substantially participating in the effort.
HiPoSwitch has a total budget of 5.6 million euros. To this, the EU is contributing about 3.6 million Euros. Eight European program partners are covering the complete value chain, from academic research and development (Ferdinand-Braun- Institute, Leibniz-Institute fuer
Hoechstfrequenztechnik, Slovak Academy of Sciences, Vienna University of Technology; University of Padua, to industrial application (AIXTRON SE, Artesyn Austria, EpiGaN, and Infineon Technologies Austria. The objective is to make GaN power transistors and 200mm GaN-on- silicon substrates commercially available and marketable world-wide. HiPoSwitch is coordinated by the Berlin-based Ferdinand-Braun-Institute.
The European Space Agency (ESA) has also invested significant levels of funding in establishing a European value chain of space worthy GaN- devices, in particular within the GREAT2 project. Today, they also support EpiGaN in the establishment of a European GaN material source through a three years contract, aiming at material production both either RF or High Voltage applications for space suppliers.
Fig 1: 150 mm and 4-inch GaN-on-silicon epiwafers
All these efforts cater to the promise that transistors based on GaN-on-silicon could grab a major share of the power device market. Converting their potential into success hinges on scaling production to the handling large wafer sizes and employing appropriate passivation techniques - according to EpiGaN founders Marianne Germain, Joff Derluyn and Stefan Degroote.
There is a tremendous opportunity, the EpiGan founders say, for realising substantial reductions in energy losses associated with AC/DC and DC/DC conversion. If a new generation of electronic devices can combine higher power levels with lower switching losses at higher operating frequencies, they will boost the efficiency of power systems, while trimming their size and weight.
EpiGaN: Making Nitrides Affordable
As wide band gap semiconductors GaN-on-silicon devices belong to a superior class of materials: One of their biggest advantages is their high breakdown voltage, which stems from a field strength that is an order of magnitude higher than that of silicon. Due to the high carrier mobility and concentration associated with the two-dimensional electron gas (2DEG) of the AIGaN/GaN heterostructure, nitride devices in switching applications also combine a low on-resistance with high switching speed. Their wide band gap properties enable them to operate at high temperatures.
Development of nitride power devices has been underway for more than a decade, and their progress has enabled today’s switching devices to outperform their silicon rivals. In the performance stakes at very high voltages (>1200V), SiC is a tougher opponent, but GaN more than holds its own. GaN-on-silicon is the most cost-efficient wide- band-gap technology. It has developed to a point where it is feasible to deposit advanced
The European Space Agency (ESA) has also invested
significant levels of funding in
establishing a European
value chain of space worthy GaN-devices, in particular within the GREAT2 project
Issue 2 2012
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