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9 November 2006


HYPHEN program indicates GaN HEMTs on composite substrates more reliable than on silicon

At the 210th Meeting of The Electrochemical Society(ECS) in Cancun, Mexico last week, Picogiga International SAS of Les Ulis, France, a division of the Soitec Group and the leader of the European project HYPHEN (Hybrid Substrates for Competitive High Frequency Electronics), presented initial
material characterization results regarding gallium nitride (GaN) on compound engineered substrates ('Recent achievements of the GaN epitaxy by MBE on Silicon and Engineering Substrates' by P. Bove, H. Lahreche and J. Thuret).

The three-year project, which started in 2005, aims to develop and evaluate new types of composite substrates, based on silicon and silicon carbide materials, to provide cost-efficient solutions for advanced high-power devices used in wireless communication systems such as radar, satellite communications and base-stations.

HYPHEN's main objective is to bridge the gap between low-performance, low-cost single-crystal silicon and high-performance, high-cost single-crystal silicon carbide currently used as the starting substrates for GaN-based RF devices. The program expects to demonstrate that scalable composite substrates have dielectric and thermal properties far above those of silicon, while costing significantly less than semi-insulating SiC.

During the first year, the project has compared the two standard materials - GaN on bulk silicon and GaN on bulk SiC - with GaN grown on two composite engineered substrates: silicon on polycrystalline silicon carbide (SopSiC)
and SiC on polycrystalline SiC (SiCopSiC), engineered using Soitec's Smart Cut technology (the key technology behind its silicon-on-insulator wafers).

Picogiga says the results show that all the critical performance factors (crystal quality, mobility, surface morphology, etc) of GaN on composite substrate materials are equal to, or better, than the current industry-standard materials. These substrate comparisons were assessed using MOCVD and MBE.

Picogiga claims that the composite substrates also demonstrated superior results in terms of pilot production yield and repeatability. According to the preliminary results, epitaxy of GaN HEMTs on SopSiC composite substrates
is more reliable than on conventional silicon substrates. SopSiC, as a substrate for GaN growth, also has the advantage of being substantially cheaper and better suited to high volumes than bulk SiC substrates for a
frequency scale less than 10GHz.

"Until now, designers of GaN-based RF power devices have had to choose between the extremes of high-performance / high-cost SiC starting substrates and low-performance/low-cost silicon. The HYPHEN material characterization results indicate that composite materials like SopSiC provide a scalable, cost-effective substrate solution that can fill the chasm between the very high and the very low ends of the cost-performance trade-off," says Philippe Bove, Picogiga R&D director and HYPHEN project leader. "Composite substrates engineered with Smart Cut technology offer a high-added value for power devices, which will be assessed through the overall performance of GaN transistors."

The HYPHEN project is developing and characterizing the complete technology chain, from substrate to GaN HEMT device. The second phase, now underway, involves device processing.

* HYPHEN project partners include:

  • Picogiga (France), the III-V division of the Soitec Group
  • University of Padova (Italy) Information Engineering Department (DEI)
  • Alcatel-Thales III-V Lab (France)
  • The Research Institute for Technical Physics and Material Science (MFA)
  • Norstel (Sweden), supplier of HTCVD-grown high-purity SiC wafers
  • Institute of Electron Technology (IET) (Poland)
  • The IEMN research unit of the French national research organization, CNRS
  • The Thales-EADS joint venture United Monolithic Semiconductors (UMC).

The work is partly supported by the European Community, under the Innovation Society Technologies (IST) program of the 6th Framework Program.


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