Electrical and Thermal Performance of AlGaN/GaN HEMTs on Diamond Wafer for RF Applications

AlGaN/GaN high electron mobility transistors (HEMTs) on SiC substrates have been reported with extremely high RF power densities reaching 40 W/mm . Such capabilities of AlGaN/GaN heterostructure, however, cannot be exploited for real applications without developing aggressive and novel thermal management techniques to control the channel temperatures so that the devices can operate reliably. Although the SiC substrate with its good thermal conductivity (350-400 W/m-K) is an attractive choice for high power GaN HEMTs, it is not good enough to take the full advantage of GaN. 

Further, the epitaxial growth defects at the interface of GaN and SiC make it worse for thermal performance . Consequently, today’s discrete HEMTs in production are typically limited to the power densities of around 5-7 W/mm, while same devices are further restricted below 5 W/mm when used in high power MMIC amplifiers . 

To address the above problem and make use of untapped RF power of GaN, we have been investigating AlGaN/GaN HEMTs on high thermal conductivity polycrystalline diamond substrates. Using this approach, we have recently reported a record of over 7 W/mm RF power for GaN-on-diamond HEMTs at 10 GHz .

We have presented a detailed electrical and thermal performance evaluation of GaN-on-diamond HEMTs. Device wafers have been developed by removing the host Si (111) substrate and transitions layers of GaN-on-Si wafer and subsequently depositing 50 nm dielectric and 100 µm thick CVD diamond layer. Very promising DC characteristics are achieved for HEMTs with maximum current densities in excess of 1 A/mm and operation up to 40 V. Further development is needed to improve the gate leakage current. These devices achieve a record RF power for GaN-on-diamond HEMTs at 10 GHz. Significant improvement of PAE is expected with reduction of  leakage current. Further, thermal measurements confirmed over 25 % lower channel temperature rise for GaN-ondiamond HEMTs compared to a standard GaN-on-SiC HEMTs at a fixed power dissipation condition. This significant improvement shows the promise that GaN-ondiamond approach holds for advancing the GaN technology to significantly higher power levels.

CSMH has been committed to the research and development and production of diamond materials. Now it has products such as diamond heat sink ,diamond wafer, diamond window to provide customers with a comprehensive thermal management solution.