During this research a silicon substrate was removed from a multi-cell GaN-HEMT that was fabricated with a silicon substrate; the back surface of the GaN-HEMT was then polished to make it thinner and flatter, after which it was bonded directly onto a diamond substrate using a nano adhesion layer. A multi-cell structure was used for the parallel alignment of eight transistor cells of a type found in actual products. This enabled the fabrication of a multi-cell GaN-on-Diamond HEMT using a single-crystal diamond as the substrate, with high heat dissipation (thermal conductivity of 1,900 W/mK).
This superior heat dissipation suppresses temperature degradation, decreasing the temperature rise of the GaN-HEMT from 211.1ºC to 35.7ºC during operation. This improves output per gate width from 2.8 W/mm to 3.1 W/mm as well as raising power efficiency from 55.6 percent to 65.2 percent, report the researchers, achieving significant energy savings.
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