Multi-cell GaN-HEMT on single-crystal diamond

September 02, 2019 //By Julien Happich
In collaboration with the National Institute of Advanced Industrial Science and Technology (AIST), Mitsubishi Electric has developed a gallium nitride-high electron mobility transistor (GaN-HEMT) in a multi-cell structure (multiple transistors cells arranged in parallel) bonded directly to a single-crystal diamond heat-dissipating substrate.

The company claims the direct bonding of a multi-cell GaN-HEMT to a single-crystal diamond substrate is a world’s first, improving the power efficiency of high-power amplifiers in mobile communication base stations and satellite communications systems.

GaN-on-Diamond HEMT view from above and cell structure.

Mitsubishi Electric aims to refine the GaN-on-Diamond HEMT prior to its commercial launch sometime around 2025. The company handled the design, manufacture, evaluation and analysis of the GaN-on-Diamond HEMT and AIST developed the direct bonding technology. A part of this achievement is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Today, most existing GaN-HEMTs that use a diamond substrate for heat dissipation are created using a GaN epitaxial layer foil from which silicon substrate has been removed and onto which diamond is deposited at high temperature.

HEMTs are then fabricated on the diamond substrate of the flattened GaN wafer. However, because the thermal expansion coefficients of GaN and diamond are different, the wafer can warp during the manufacturing process, making it difficult to fabricate large multi-cell GaN-HEMTs.

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